Seals

Mechanical Seals Operating Principles

Essential elements of a mechanical seal

These are the three essential elements of a mechanical seal:

Seal faces: one rotating with the shaft and one stationary in the pump casing, cover or flange.

Secondary seals: one to seal the rotating face to the shaft and one to seal the stationary face to the pump cover or flange.

Metal parts: to transmit torque and to provide an axial mechanical force to load the faces.

Essential requirements for proper operation of a mechanical seal

These are the essential requirements:

Seal faces must be flat and polished.

Seal faces must be installed perpendicular to the shaft.

Spring force must be sufficient to maintain contact of the faces.

The fluid in the pump and seal area

Key Point: the fluid contacts the seal faces and other parts in wide open areas, in very small gaps and at the exit of the seal faces. Pressure and temperature of the fluid will depend on its location and determine its respective state, i.e. liquid, gaseous, solid or a mixture.

A few facts about the leakage (and wear) behavior of contacting mechanical seals:

It is essential for proper lubrication and wear of the faces. Normal leak rates range between immeasurably small to steady drips or

temporary to even small steams. Some seals leak some of the time, some seals never leak (measurably), and some leak all the time. Leakage patterns can be constant, progressive or erratic in nature.

It can be in liquid, gaseous and/or solid state. Successful contacting seals tend to have very low wear rates and low leakage

rates. Some forms of contact is necessary for low leakage rates. Non-contacting or

“full lift off” seals (hydrostatic or hydrodynamic tend to have visible, sizeably larger leakage rates.

The large majority of mechanical seals never wear out and are removed from service for some other reason.

Seal failures occur for a wide range of reasons. Some failures occur as aninteraction with the tribology of the interface.

Effective forces in a Mechanical Seal

These are the forces operating in mechanical seals:

Axial and radial forces

Closing and opening forces

Hydrostatic and hydrodynamic forces

Leakage of a liquid lubricated mechanical seal

Key point: leakage rate Q strongly depends on the gap height h

The gap height is determinate by several factors: materials, manufacturing quality, lubrication regime, face distortions.

The leak rate of a contacting seal is also influenced by other pump related factors such as run outs and vibration levels.

Power Consumption of a liquid lubricated mechanical seal

Important Points:

Face friction, churning and soak in heat.

Flush to dissipate the heat in order to control the gap temperature.

Coefficient of friction can swing considerably during operational transients.

The key is to maintain the gap profile as parallel as possible, i.e.minimize distortions.

Lubrication regimes of liquid lubricated mechanical seals

Mechanical Seals Operating Principles

Seal Balance

To reduce the axial face contact force which allows to seal high pressures, i.e. up to 3000 psig with one set of faces.

It is the ratio (k) of 2 geometric areas: the closing (Ah) and opening area (Ac)

For unbalanced seals k = 1

For balanced seals k = 1

Classification of Mechanical Seals

Mechanical seals are classified by arrangement and configuration

Mechanical seals are classified by arrangement and configuration.

The wide variety of seal types is due to the diversity of applications each utilizing different machinery, fluids and processes.

Selection of the best type is not always easy and straight forward as there is usually a compromise between economical and technical factors.

Classification of Mechanical Seals

Mechanical seal classification by arrangement:Single seals

Inside mounted = pressure on outside diameter of parts

Outside mounted = pressure on inside diameter of parts

The inside mounted mechanical seal is most popular type of single mechanical seal.

Most seals are designed to leak so that the liquid or gas will lubricate the seal faces. Applications that do not utilize substances that must be contained, such as hazardous gases, dangerous chemicals or flammable liquids, will generally use single seals.

Mechanical seal classification by arrangement:Dual seals

Pressure between seals is higher than seal chamber pressure (typically min. 30 psig).

External fluid lubricates both sets of faces.

Leakage to the atmosphere is external fluid.

Is also called a "Double seal".

Pressure between seals is lower than seal chamber pressure (typically atmospheric).

External fluid only lubricates the most outside set of faces. The most inside faces are lubricated with the pumped fluid. The most outside seal serves as a safety seal or containment device.

Leakage to the atmosphere is external fluid, possibly mixed with small amounts of pumped fluid.

Is also called a "Tandem seal".

Faces can be configured in several ways: face to back, face to face and back to back.

Mechanical seal classification by arrangement, i.e.design

Classification by pusher vs. non-pusher and balanced vs. non-balanced

Pusher vs. Non-pusher

Pusher seals utilize a dynamic secondary seal which moves axially with the major seal face. Non-pusher seals have a static secondary seal which stays stationary against the shaft or sleeve.

Defined by the secondary seal type: o-ring or polymer wedge versus bellow, rubber or metal.

Application fields of each type overlap.

Most apparent distinction is the pressure limit.

Acquisition cost can vary widely.

Balanced vs. Unbalanced

Reduced closing forces

Reduced power consumption

For pressure up to 3000 psig

Always recommended for volatile liquids

High closing forces

Low leakage

For pressure up to 200 psig

Not recommended for volatile liquids

Classification by Face Pattern

Examples are hydro-grooves, wavy faces, tapered faces.

Intended to increase opening forces in order to improve lubrication.

Friction is reduced at the expense of a higher leak rate.

Stationery rotating seals and rotating spring seals

Stationary spring seals are recommended by high speeds > 5000 ft/min.

Stationary spring seals are more suitable for machinery with inherently larger tolerances such a heavy duty slurry pumps and older pumps which have looser tolerances.

Cartridge seals and split seals

Cartridge seals

Seal are pre-assembled with sleeve and flange in one unit.

Easy to install.

No measurements during installation.

Spring load is preset.

May be factory tested with air, water or oil.

More costly as compared to component seal.

Split seals

Seat is axially split.

Does not require disassembly of thepump to install = reduce down time.

Leaks more than a conventional seal.

More costly as compared toconventional seal.

Classification by containment devices

Mechanical Seal Application Limits

Many factors need to be considered in the application of a mechanical seal

Here are some of the factors that need to be considered:

Pressure & speed (PV limit = Pressure x Velocity).

Temperature.

Fluid properties or characteristics.

Run out of the shaft.

Seal chamber type, available space radial and axial.

Flushing/cooling arrangements, utilities in the plant.

Mode of operation of the pump in the plant: continuous, cyclic, multi-purpose.

Static versus dynamic pressure.

Test requirements.

* Photograph Agency: picturestation.net

General application guide per seal type

* Copyright for photograph

Seal Type Applications

Non-pusher elastomeric bellows seal A - B - D - E - L

Non-pusher metal bellows seal A - D - E - F - I - J - L

Pusher o-ring secondary seal A - B - G - H - K

Pusher polymer seal A - B - G - K

Pusher stationary slurry seal A - B - C - D - E - F - M

Pusher split seal A - B - K

Pusher dual gas seal A - B - E - F - G - H - L

Fluid - CharacteristicsA - Clean LubricatingB - Clean Non-lubricatingC - ViscousD - Clogging / Scaling / Polymerizing / FibrousE - CrystallizingF - Molten LiquidG - Corrosive - AcidsH - High Vapor PressureI - CryogenicJ - High Temperature (> 260 ºC / 500 ºF)K - Solids (< 0.1% by volume and less than 10 micrometers (394 micro inches) in size.L - Solids (< 2% by volume and less than 10 micrometers (394 micro inches) in sizeM - Solids (> 2% by volume).

Typical dynamic pressure and temperature limits of common seal types

Seal Type Pusher Non-pusher Balanced Unbalanced Max. Pressure(kPag/psig)

Temperature Range(ºC / ºF)

Elastomeric bellows

x x 2070 / 300 -40 to 205 / -40 to 400

Elastomeric bellows

x x 6900 / 1000 -40 to 205 / -40 to 400

Metal bellows

x x 2070 / 300 -75 to 425 / -100 to 800

O-ring secondary seal

x x1380 / 200 -40 to 260 / -40 to

500

O-ring secondary seal

x x 6900 / 1000 -40 to 260 / -40 to

500

Polymer secondary seal

x x1380 / 200 -75 to 260 / -100

to 500

Polymer secondary seal

x x 5070 / 500 -75 to 260 / -100

to 500

Stationary slurry

x x 2670 / 400 -40 to 205 / -40 to 400

Split seal x x 1380 / 200 -40 to 205 / -40 to 400

Dual gas seal x x 2070 / 300 -40 to 260 / -40 to 500

Dual gas seal x 1725 / 250 -40 to 260 / -40 to 500

Typical PV – Limits of face material combinations in non-lubricating fluids, i.e. watery substances

PV = face pressure x velocity

Is an indicator for the severity of an application

Is limited in usefulness

For lubricating fluids multiply number by 1.5

Primary Ring Mating Ring PV Limit(MPa x m/s)

PV Limit(psi x ft/min)

Glass-Filled PTFE Ceramic / Silicon Carbide

6.13 25,000

Carbon Cast Iron 24.52 100,000

Carbon Ceramic 24.52 100,000

Carbon Tungsten Carbide 122.59 500,000

Carbon Silicon Carbide 147.11 600,000

Tungsten Carbide Tungsten Carbide 24.92 120,000

Silicon Carbide Silicon Carbide 85.81 350,000

Typical angular misalignment limits

Shaft Speed(rpm)

Pusher & MetalBellows(mm)

Pusher & MetalBellows

(in)

ElastomerBellows(mm)

ElastomerBellows

(in)

500 0.152 0.006 0.279 0.011

1000 0.127 0.005 0.254 0.010

2000 0.089 0.0035 0.191 0.0075

3000 0.064 0.0025 0.152 0.006

4000 0.051 0.002 0.127 0.005

5000 0.038 0.0015 0.089 0.0035

6000 0.025 0.001 0.151 0.002

Overview of mechanical seal drive mechanisms

Wide variety of methods which will depend on the component: drive collar, seal face and sleeve.

Drive mechanisms transmits torque from the shaft to the rotating face, keep the stationary seal face from spinning in the pump flange and fix the drive collar to the shaft.

In cartridge seals the sleeve will have an axial force from the hydraulic piston effect. Its drive mechanisms is used to keep the sleeve from moving axially.

Space in the pump may be an important factor.

Shaft material hardness may be critical.

Drive mechanisms can wear out prematurely if excessive run out occurs in the seal area of the pump.

Drive Mechanisms for drive collars and seal faces

Drive mechanisms for seals sleeves of cartridge type seals

Description of seal faces loading devices

Wide variety of types but they can be categorized as either a spring or a bellows of some kind.

Seal face loading devices impart an axial load to maintain contact when there is no hydraulic pressure from the pumped medium.

At higher pressures the spring force is only a small fraction of the overall face pressure.

At face speeds above 5000 ft/min the spring element is installed stationary because of the centrifugal effects.

Mechanical seal mating ring types

Wide variety of shapes.

Its function is to provide a flat surface for the other face to run against.

Be aware of clamped designs since bolt forces can create waviness.

Support surfaces for mating rings may require a high degree of flatness to avoid waviness.

Mechanical Seal Mating Ring Types

Mechanical Seal Gland Design

Functions of mechanical seal glands

Support stationary components.

Contain throttle bushing.

Allow for seal setting.

Provide centering of seal components.

Provide port location for flushes.

Bushing types

The purpose of bushings are the following:

They direct leakage from seal.

Bushings minimize leakage under seal failure.

They provide isolation for quench.

They protect seal from radial sleeve motion.

Cartridge Seal With Fixed Bushing

Cartridge Seal With Floating Bushing

Shaft-centered glands

Gland is centered by the shaft through setting clips.

Concentricity of seal chamber bore not critical.

Concern for weight of gland assembly.

Popular with lower duty pumps.

Gland-piloted glands

Gland is centered by internal or external pilot fit between gland and seal chamber.

Setting plate provide axial positioning.

Common of heavier duty pumps.

Flush arrangements

Purpose of Flush:

Introduce fluid into seal chamber to improve the environment.

Work to support the piping plan.

Removal of seal generated heat.

Removal of vapor bubbles.

Protect against erosion.

Lantern Ring Connection

Stuffing box using lantern ring connection

flush arrangements

Single Point Injection

Large Bore Seal Chamber Point Flush

Annulus Flush

Annulus Flush

Multiport Flush

Multiport Flush

Glossary - A's

Abrasion (r) the surface loss of a material due to frictional forces.

Absorption the penetration of matter in bulk into other matter, as in dissolving of a gas by a liquid.

Accelerator (r) a compounding material used in small amounts with a vulcanizing agent to increase the speed of vulcanization.

Accelerator, delayed action (r) an accelerator that, in conjunction with other curing agent(s), produces, at vulcanizing temperatures, a period of no significant cross-linking, followed by a period of rapid cross-link formation.

Accuracy a concept of exactness. When applied to a test method, it denotes the extent to which bias is absent; when applied to a measured value, it denotes the extent to which both bias and random error are absent.

Activator (r) compounding material used in small proportions to increase the effectiveness of an accelerator.

Adhesion failure (r) the loss of structural integrity due to the separation of two bonded surfaces at the bond interface.

Adsorption the surface retention of matter by other matter.

Agglomerate, latex (r) a cluster of rubber particles in a colloidal aqueous suspension of such particles.

Agglomerates (r) clusters of particles of compounding materials contained in a continuous rubber phase.

Aging (act of) (r) exposure of materials to a deteriorating environment for a specified time interval.

Aging (r) the irreversible change of material properties during exposure to a deteriorating environment for a specified time interval.

Aliphatic straight-chain hydrocarbons. Three sub-groups are alkanes, alkenes, and alkynes.

Alloy (r) a unique composition of two or more polymers that has one or more of the polymers treated or processed in a special way to confer enhanced performance characteristics on the resulting material.

Alpha particle a positively charged particle consisting of two protons and two neutrons.

Amorphous materials with no definite arrangement of atoms.

Ampere or Amp a unit of current—the rate at which electrons move past a reference point.

Angstrom (Å) a unit of length, an angstrom is one ten-thousandth of a micron (10-4 µm) or 100,000,000 Å=1 cm.

Anisotropic (sc) an etch process that exhibits little or no undercutting.

Anneal (sc) a high-temperature processing step, designed to minimize stress in the crystal structure of the wafer.

Anticoagulant (r) a substance added to field latex to retard bacterial action which would otherwise cause rapid coagulation of the latex.

Antidegradant (r) a compounding material used to retard deterioration caused by oxidation, ozone, light and combinations of these.

Anti-extrusion ring (r) a thin ring installed on the lowpressure side of a seal to prevent elastomer extrusion into the clearance gap.

Antiflex cracking agent (r) a compounding material used to retard cracking caused by cyclic deformations.

Antioxidant (r) compounding material used to retard deterioration caused by oxidation.

Antiozonant (r) compounding material used to retard deterioration caused by ozone.

Antistatic agent (r) a material which reduces the tendency for accumulation of electric charge on the surface of an article.

Aromatic oil a hydrocarbon process oil containing at least 35%, by mass, of aromatic hydrocarbons.

Ash (r) the residue from incineration of a material under specified conditions.

Ashing (sc) the process of removing photoresist with oxygen plasma.

Atmospheric-pressure chemical vapor deposition (APCVD) (sc) a method for depositing layers at atmospheric pressure.

Attenuation a reduction in intensity of energy traveling through a medium or space.

Autoclave (r) a vessel used for vulcanizing rubber compounds by means of steam pressure.

(sc) This term is generally associated with the semiconductor industry. (r) This term is generally associated with the rubber industry.

Glossary - B's

Backrinding (r) a molding defect in which the rubber adjacent to the flash line shrinks below the surface of the molded product, with the flash line often being ragged and torn.

Bake-out (r) secondary post-curing operation designed to remove residual volatile materials.

Batch (r) the product of one mixing operation.

Beta particle an electron or positron emitted from a nucleus.

Bipolar transistor (sc) a transistor (consisting of an emitter, base and collector) whose action depends on the injection of minority carriers from the base by the collector.

Blank (r) a portion of a rubber compound of suitable volume to fill the cavity of a mold.

Bleeding (r) the exuding of a liquid compounding material from the surface of a vulcanized or unvulcanized rubber.

Blister (r) a cavity or sack that deforms the surface of a material.

Bloom (r) a liquid or solid material that has migrated to the surface of a rubber and generally changes the surface appearance.

Blowing agent (r) a compounding material used to produce gas by chemical or physical action, or both, in the manufacture of hollow or cellular articles.

Borophosphosilicate glass (BPSG) (sc) a compound of boron, phosphorus, silicon and oxygen.

Bound monomer (r) monomer that is combined or reacted with itself or other types of monomers in a polymerization reaction to form a polymer.

Breakaway friction (r) the force required to overcome friction to start a body in motion over a surface.

Brittle point (r) the temperature at which elastomers break when subjected to an impact.

Bulk modulus of elasticity (r) also known as compression modulus, the ratio of compressive force applied to a surface per unit surface area to the change in volume of the substance per unit volume.

Bumping, molding process (r) the application, release, and reapplication of pressure prior to the start of vulcanization to vent entrapped gases, thereby facilitating complete filling of the mold.

Butt joint (r) a connection made with two ends cut at right angles.

(sc) This term is generally associated with the semiconductor industry.(r) This term is generally associated with the rubber industry.

Glossary - C's

Calender (r) a machine with two or more parallel, counterrotating rolls with a controllable, roll-to-roll spacing, rotating at selected surface speeds and controlled temperatures, used for sheeting, laminating, skim coating (topping) and friction coating, to a controlled thickness and/or surface condition.

Capacitor (sc) a discrete device which stores electrical charge on two conductors separated by a dielectric.

Cell (r) a single small cavity surrounded partially or completely by walls.

Chalking (r) the formation of a powdery residue on the surface of a rubber, commonly resulting from surface degradation.

Chamber clean (sc) typically, a gas or plasma cleaning of the chamber to prevent the buildup of polymer or contamination on the chamber walls.

Chemical vapor deposition (CVD) (sc) a method for depositing some of the layers which function as dielectrics, conductors or semiconductors. A chemical containing atoms of the material to be deposited reacts with another chemical, liberating the desired material, which deposits on the wafer while by-products of the reaction are removed from the reaction chamber.

Chemisorption (r) a chemical adsorption process in which weak chemical bonds are formed between gas or liquid molecules and a solid surface.

Chip (sc) die or device, one of the individual integrated circuits or discrete devices on a wafer.

Coagent (r) a compounding ingredient used in small amounts to increase the cross-linking efficiency of certain no-sulfur vulcanizing systems or to modify the properties given by such systems.

Coefficient of friction (r) the force in the direction of motion required to move one surface with respect to another, divided by the force normal to the two surfaces.

Coefficient of thermal expansion (r) the increment in volume of a unit volume of material for a rise of one degree temperature at constant pressure.

Cohesive failure (r) a rupture occurring entirely within any single uniform layer of the assembly.

Cold flow (r) slow deformation, under gravitational force, at or below room temperature.

Comonomer (r) one of the two or more monomer species that polymerize to form a copolymer.

Complimentary metal oxide semiconductor (CMOS) (sc) N- and P-channel MOS transistors on the same chip.

Composite seal (r) a seal composed of two or more dissimilar materials.

Compound (r) an intimate admixture of a polymer(s) with all the materials necessary for the finished article.

Compression (r) the amount of deformation on a seal, often calculated by dividing the deformation by the original seal cross-sectional diameter.

Compression molding (r) molding process in which the material is placed directly in the mold cavity and compressed to shape by closure of the mold.

Compression set (r) the residual deformation of a material after removal of the compressive stress.

Conditioning (environmental) (r) the storage of a rubber, under specified conditions (time, temperature, humidity) prior to testing.

Conditioning (mechanical) (r) the prescribed program of deformation of a specimen prior to testing.

Conductive rubber (r) an elastomer having high conductivity. Conductor (sc) a material which is easily able to conduct electricity.

Copolymer (r) a polymer formed from two different monomers. Covalent bonding chemical bonding whereby each atom of a bound pair contributes one electron to form a pair of electrons.

Crack(s), atmospheric (r) fissure(s) originating in the surface of a rubber vulcanizate or product as a result of natural weathering.

Crack(s), ozone (r) fissure(s) originating in the surface of a rubber vulcanizate, caused by exposure to an ozone-containing environment; the fissure(s) are perpendicular to the direction of strain.

Crack(s), flex (r) fissure(s) originating in the surface of a rubber vulcanizate, resulting from cyclic deformation (usually bending).

Creep the time-dependent part of a strain resulting from stress.

Cross-link (r) chemical bond bridging one polymer chain to another.

Cross-linking agent (r) compounding material that produces cross-linking in rubber.

Crystallization, polymer (r) arrangement of previously disordered polymer segments of repeating patterns into geometric symmetry.

Cure (r) see vulcanization, the preferred term.


Glossary - D's

Decibel (dB) an expression of the ratio of two values of power or voltage in logarithmic terms.

Density the mass-per-unit volume of a material.

Deposition (sc) process in which layers are formed as the result of a chemical reaction in which the desired layer material is formed and coats the wafer surface.

Desiccant (r) compounding material used to irreversibly absorb moisture present (in a rubber mix) particularly for the purpose of minimizing risk of porosity during vulcanization.

Developer (sc) chemical used to remove areas defined in the masking and exposure step of wafer fabrication.

Die swell (r) difference between the dimensions of the cross section of an extrudate and the corresponding dimensions of the die orifice by which the extrudate is formed.

Dielectric (sc) a material that conducts no current when it has voltage across it.

Diene polymer (r) a polymer formed from one or more monomer species, at least one of which is a diolefin.

Diffusion the spontaneous mixing of one substance with another when in contact with, or separated by, a permeable membrane or microporous barrier.

Diffusion (sc) a process used in semiconductor fabrication which introduces minute amounts of impurities (dopants) into a substrate material and permits the impurity to spread into the substrate. The process is very dependent on temperature and time.

Dipole a molecule with positive and negative charge centers.

Dispersing agent (latex) (r) a surface-active substance used to facilitate the suspension of solid compounding materials in a liquid medium and to stabilize the dispersion thereby produced.

Dispersion (the act of) (r) application of shearing forces to distribute one or more compounding materials uniformly throughout the mass of a continuum material.

Dopant (sc) an element that alters the conductivity of a semiconductor by contributing either a hole or electron to the conduction process. For silicon, the dopants are found in Groups III and V of the periodic table.

Doping (sc) the introduction of impurity atoms (dopants) into the crystal lattice of a semiconductor.

Dry etching (sc) a process resulting in the selective removal of material, achieved by the use of gas or plasma.

Dry-ox (sc) the growth of silicon dioxide using oxygen and hydrogen, which forms water vapor at process temperatures, rather than using water vapor directly.

Dumbbell specimen (r) a flat specimen having a narrow, straight central portion of essentially uniform cross section.

Durometer (r) an instrument for measuring the indentation hardness of rubber.

Dynamic random access memory (DRAM) (sc) memory device for the storage of digital information. The information is stored in a “volatile” state.

Dynamic seal (r) a seal designed to prevent leakage between surfaces which move relative to each other.


Glossary - E's

Elastic limit (r) the greatest stress that a material is capable of sustaining without any permanent strain remaining upon complete release of the stress.

Elastomer (r) a viscoelastic macromolecular material that can respond to large deformations.

Electronegativity (sc) a material that has a tendency to attract electrons to itself.

Elongation (r) the extension of a uniform section of a specimen expressed as percentage of the original length.

Elongation, ultimate the elongation at the time of rupture.

Emulsifying agent (latex) (r) a surface-active substance used to facilitate the dispersion of an immiscible liquid compounding material in another liquid and to stabilize the emulsion thereby produced.

Epitaxial (sc) (Greek for “arranged upon”) the growth of a single-crystal semiconductor film upon a single-crystal substrate.

Erasable programmable read-only memory (EPROM) (sc) device that allows stored information to be erased; erasing is typically accomplished with ultraviolet light. Esters a compound formed by the elimination of water and the bonding of an alcohol and an organic acid. Characterized by “–C=C-O-“ bonding.

Etch (sc) a process for removing material in a specified area through a wet or dry chemical reaction or by physical removal, such as a sputter etch.

Ethers a compound characterized by “-O-“ bonding

Evaporation (sc) a process step that uses heat to change a material (metal or metal alloy) from its solid state to a gaseous state with a result of the source being deposited on wafers. Both electron beam and filament evaporation are common in semiconductor fabrication.

Exposure (sc) method of defining patterns by the interaction of light or other form of energy with photoresist that is sensitive to the energy source.

Extender (r) an organic material used to augment the polymer in a compound.

Extensometer (r) a device for determining elongation of a specimen as it is strained.

Extrudate (r) the material that issues from an extruder.

Extruder machine designed to force a rubber or rubber mix through an orifice, which is often shaped to the geometry of the desired product.

Extrusion (r) 1) the continuous shaping of a material during plastic passage through a die. 2) the displacement of a part of the seal into the clearance gap under action of fluid pressure or thermal expansion.


Next F's

Glossary - F's

Face seal, flange seal (r) an axial contact seal.

Fatigue life (dynamic) (r) the number of deformations required to produce a specified state of fatigue breakdown in a test piece or product that is deformed under a prescribed set of conditions.

Field oxide (sc) the region on an electrical device where the oxide serves the function of a dielectric.

Field-effect transistor (FET) (sc) a transistor consisting of a source, gate and drain, whose action depends on the flow of majority carriers past the gate from the source to the drain. The flow is controlled by the transverse electric field under the gate.

Filler (r) a solid compounding material, usually in finely divided form, which may be added in relatively large proportions to a polymer for technical or economic reasons.

Fissure (r) a surface split or crack.

Flash (r) the excess material protruding from the surface of a molded article at the mold junctions.

Flex life (r) the number of cycles required to produce a specified state of failure in a specimen that is flexed in a prescribed method.

Flow (sc) a process step in which the wafer temperature is elevated so that the deposited PSG or BPSG surface layer’s topography smoothes out due to the film’s low viscosity at elevated temperatures. The flow temperature is primarily dependent on incorporation of the dopant.

Flow marks (r) marks or lines on a molded product, caused by imperfect fusion or “knitting”of material.

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Fluorocarbon elastomer (r) also known as fluoroelastomer.

Fluorosilicone (r) a fluorinated silicone elastomer.

Foam stabilizer (latex) (r) a substance used in the preparation of latex foam to help stabilize the foam latex before gelation, drying and vulcanization.

Formula (r) a list of the materials and their amounts used in the preparation of a compound.

Frequency the number of periodic oscillations, vibrations or waves per unit of time.

Furnace (sc) a piece of equipment containing a resistanceheated element and a temperature controller. It is used to maintain a region of constant temperature with a controlled atmosphere for the processing of semiconductor devices.

Furnace carbon black (r) type of carbon black produced by the decomposition reaction of hydrocarbons when injected into a high-velocity stream of combustion gases under controlled conditions.


Next G's

Glossary - G's

Gallium arsenide (GaAs) (sc) a semiconductor material with the advantage of producing radiation-resistant and higherspeed devices than those produced using silicon as a substrate.

Gamma radiation (sc) the emission of high-energy photons.

Gasket (r) a deformable material clamped between essentially stationary faces to prevent the passage of matter through an opening or joint.

Gate oxide (sc) a thin, high-quality silicon dioxide film that causes the induction of charge, creating a channel between source and drain regions of an MOS transistor.

Gel, dry rubber (r) the portion of unvulcanized rubber insoluble in a chosen solvent.

Gland (r) a cavity into which a seal is installed.

Grain (r) anisotropy introduced into rubber during processing operations.

Gum compound (r) a rubber compound containing only those ingredients necessary for vulcanization and small amounts of other ingredients for processing, coloring and improving the resistance to aging.


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Glossary - H's

Hardness (r) a material’s ability to resist a distorting force (indentor point).

Heat buildup (r) the accumulation of thermal energy generated within a material as a result of hysteresis, evidenced by an increase in temperature.

Hertz (Hz) an international unit for frequency—the number of cycles per second.

Hole (sc) the absence of a valence electron in a semiconductor crystal. Motion of a hole is equivalent to motion of a positive charge.

Homogeneous having uniform composition or structure.

Homogenization (r) repeated passage of raw rubber through a mill or other mixing device, under specified conditions, to ensure uniformity.

Homopolymer (r) a polymer formed from a single monomer species.

Hybrid integrated circuit (sc) a structure consisting of an assembly of one or more semiconductor devices and a thin-film integrated circuit on a single substrate, usually ceramic.

Hydrogen bonding unusually strong dipole-dipole attractions that occur among molecules in which hydrogen is bonded to a highly electronegative atom.

Hydrophilic affinity toward water (water-loving); a hydrophilic surface is one that will allow water to spread across it in large puddles.

Hydrophobic aversion to water; a hydrophobic surface will not allow large puddles of water, but rather will form droplets. These surfaces are often termed “de-wetted.”

Hydroscopic attracts and absorbs water.

Hysteresis the lagging of strain behind stress during deformation.


Glossary - I's

Impact resistance (r) resistance to fracture under shock force. Impedance the total opposition offered by an electric circuit to the flow of an alternating current. It is the combination of resistance and reactance.

In situ (sc) Refers to the sequential process steps that can be completed without removing the wafers from one process environment to another.

Inhibitor (r) a material used to suppress a chemical reaction.

Integrated circuit (IC) (sc) a circuit in which many elements are fabricated and interconnected on a single chip of semiconductor material.

Interlayer dielectric (ILD) (sc) films that insulate between the wafer surface and the first metal layer. They are typically some form of doped silicon dioxide, formed by reaction between a silicon source gas (silane or TEOS), an oxidizing gas (O2, N2) and dopant source gases.

Intermetal dielectric (IMD) (sc) films that insulate between two layers of conductive metal.

Ion an atom that has either gained or lost electrons, making it a charged particle.

Ion implantation (sc) introduction of selected impurities (dopants) by means of high-voltage ion bombardment to achieve desired electronic properties in defined areas.

Ionic bonding the electrostatic attraction between oppositely charged ions—characterized by electron transfer.

Isotactic (r) a polymeric molecular structure containing a sequence of regularly spaced asymmetric atoms arranged in like configuration in the polymer chain.

Isotropic (sc) having the same properties in all directions.

(sc) This term is generally associated with the semiconductor industry. (r) This term is generally associated with the rubber industry. Next J's

Glossary - K's

Ketone an organic compound containing the carbonyl group “-C=O.”

Kinetic friction (r) the minimum force required to maintain a body in motion over a surface.


Glossary - L's

Latex (r) colloidal aqueous dispersion of rubber.

Light-emitting diode (LED) (sc) a semiconductor device in which the energy of minority carriers in combining with holes is converted to light.

Lip seal (r) a custom seal, static or dynamic, that seals on a flexible extension.

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Lithography (sc) process of pattern transfer; when light is utilized, it is termed “photolithography,” and when patterns are small enough to be measured in microns, it is referred to as “microlithography.”

Lot (r) a mass of material or collection of articles of similar composition and characteristics.

Low-pressure chemical vapor deposition (LPCVD) (sc) system with the deposition environment less than atmospheric pressure. Most LPCVD systems use a quartz “boat” (wafer holder) placed in a furnace which is brought up to deposition temperature.


Glossary - M's

Mask (sc) a glass plate covered with an array of patterns used in the photomasking process. Mask patterns may be formed in emulsion, chrome, iron oxide, silicon or a number of other opaque materials.

Masterbatch (r) a homogeneous mixture of rubber and one or more materials in known proportions for use as a raw material in the preparation of the final compounds.

Mastication (r) a breakdown or softening of raw rubber, or a mix, by the combined action of mechanical work (shear) and atmospheric oxygen, sometimes accelerated by the use of a peptizer and frequently at elevated temperatures.

Metalization (sc) 1) the deposition of a thin film pattern of conductive material onto a substrate to provide interconnection of electronic components or to provide conductive contacts. 2) the layer of high-conductivity metal used to interconnect devices on a chip. Aluminum is commonly used.

Microhardness (r) hardness measured with an instrument having a smaller indentor and applying a lower force than the standard instrument, permitting measurements on smaller specimens or thinner sheets that are not amenable to measurement by normal instruments.

Micron (µm) a unit of length, one millionth of a meter.

Mill (r) a machine used for rubber mastication, mixing or sheeting, having two counter-rotating rolls with adjustable longitudinal axis separation that usually rotate at different speeds.

Mismatch (r) a defect resulting from differing cross-section dimensions in adjacent mold halves.

Mixer (r) a machine that incorporates and disperses compounding ingredients into rubber to form a mix or a compound through the action of mechanical work (shear).

Mixer, internal (r) a machine with a closed cavity in which a specially shaped rotor (or rotors) masticates the rubber or incorporates and disperses compounding materials into the rubber, or both.

Modulus, tensile (r) See tensile stress, at given elongation the preferred term.

Modulus, Young’s the ratio of normal stress to corresponding strain for tensile or compressive stresses below the proportional limit of the material.

Mold cavity (r) hollow space in the mold designed to impart the desired form to the product being made.

Mold marks (r) surface imperfection transferred to a molded product from corresponding marks on a mold.

Mold release (r) see release agent (mold).

Molding shrinkage (r) the difference in dimensions between a molded product and the mold cavity in which it was molded, both the mold and product being at normal room temperature when measured.

Molding, compression (r) the process of forming a material to a desired shape by flow induced by a force applied after a material is placed in the mold cavity.

Molding, injection (r) the process of forming a material by forcing it from an external heated chamber through a sprue (runner, gate) into the cavity of a closed mold by means of a pressure gradient that is independent of the mold clamping force.

Molding, transfer (r) the process of forming a material by forcing it from an auxiliary heated chamber through a sprue (runner, gate) into the cavity of a closed mold by means of a pressure gradient that is dependent on the mold clamping force.

Molecule smallest quantity of a substance that retains the properties of that substance.

Monomer (r) a low-molecular-weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.

Mooney viscosity (r) the measurement of the plasticity of compounded or uncompounded elastomeric seal material.


Glossary - N's

Necking the localized reduction in cross section that may occur in a material under tensile stress.

Negative resist (sc) photoresist that remains in areas that were not protected from exposure by the opaque regions of a mask while being removed by the developer in regions that were protected. A negative image of the mask remains following the development process.

Network (r) a three-dimensional structure formed by interchain or intrachain bonding of polymer molecules in combination with chain entanglements.

Nip (r) the radial clearance between rolls of a mill or calender on a line of centers.

Nitrile (Buna-N) (r) a common hydrocarbon elastomer.

Non-fill (r) defect resulting from the failure of the rubber to fill out all the mold pattern detail.

Non-polar pertaining to an element or compound which has no permanent dipole moment.


Glossary - O's

Occlusion (r) process by which materials are entrapped within the folds of a given substance during manufacture.

Off-register (r) misalignment of mold halves causing out-of round O-ring cross section.

Olefins a family of hydrocarbons with one carbon-carbon double bond.

Oligomer (r) a polymer consisting of only a few monomer units, such as a dimer, trimer, tetramer, etc., or their mixtures.

O-ring (r) see seal, 0-ring.

Outgassing the release of adsorbed or occluded gases or water vapor, usually by heating.

Oxidation a chemical reaction in which a compound loses electrons.

Oxidation (sc) the growth of oxide on silicon when exposed to oxygen. This process is highly temperature-dependent.


Glossary - P's

Paraffins saturated straight-chain hydrocarbons of the methane series.

Passivation (sc) the final layer in a semiconductor device, forming a hermetic seal over the circuit elements. Plasma nitride and silicon dioxide are materials primarily used for passivation.

Pellicle (sc) a thin film of an optical-grade polymer that is stretched on a frame and secured to a mask or reticle. This solves the problem of airborne contamination forming on the mask. The pellicle keeps the dirt out of the focal plane.

Perfluoroelastomer (r) a fully fluorinated fluoroelastomer.

Permanent set (r) the permanent distortion of an elastomer after being strained.

Permeability the permeation rate divided by the pressure gradient of the gas or vapor. For a homogeneous material that obeys Fick’s law, the permeability is equal to the product of the diffusion coefficient and the solubility coefficient of the gas or vapor.

Permeance the permeation rate divided by the pressure differential of a gas or vapor between opposite faces of a solid body.

Permeation rate the flow rate of a gas or vapor, under specified conditions, through a prescribed area of a solid body, divided by that area.

Physiosorption (r) a physical adsorption process in which there are van der Waals forces of interaction between gas or liquid molecules and a solid surface.

Phosphosilicate glass (PSG) (sc) a material commonly used for dielectrics before metalization, also for passivation. These films are composed of phosphorous-doped silicon dioxide.

Photoresist (sc) the light-sensitive organic polymer film spun onto wafers and “exposed” using high-intensity light through a mask. The exposed photoresist is dissolved with developers, leaving a pattern of photoresist which allows etching to take place in some areas while preventing it in others.

Physical vapor deposition (PVD) (sc) the layering of a vapor, usually by means of evaporation or “sputtering.”

Pigment (r) an insoluble compounding material used to impart color.

Plasma high-energy gas made up of ionized particles.

Plasma etching (PE) (sc) the use of energized gases to chemically remove a surface.

Plasma nitride (sc) a silicon-nitrogen film deposited using

PECVD, most often as a final passivation layer.

Plasma-enhanced chemical vapor deposition (PECVD) (sc) a deposition system primarily used for deposition of silicon oxide and silicon nitride films. A plasma is

used in addition to a heat source which allows for lower temperature processing (200°–400°C).

Plasticizer (r) a compounding material used to enhance the deformability of a polymeric compound.

Polar describing a molecule or radical that has, or is capable of developing, electrical charges. Polar molecules ionize in solution and impart conductivity.

Polymer (r) a substance consisting of macromolecules characterized by the repetition (neglecting ends, branch junctions and other minor irregularities) of one or more types of monomeric units.

Polymer network (r) a three-dimensional reticulate structure formed by chemical or physical linking of polymer chains.

Polysilicon (Poly) (sc) polycrystalline silicon, extensively used as conductor or gate material in a highly doped state.

Porosity (r) the presence of numerous small cavities.

Post-cure (r) heat or radiation treatment, or both, to which a cured or partially cured thermosetting plastic or rubber composition is subjected to enhance the level of one or more properties.

Pot life (r) the period of time during which a reacting thermosetting plastic or rubber composition remains suitable for its intended use after mixing with a reaction-initiating agent.

Precision a concept of uniformity based on the magnitude of the random errors. The smaller the random errors, the higher the precision.

Primary accelerator (r) the principal, highest concentration accelerator used in a vulcanizing system.

Processability (r) the relative ease with which raw or compounded rubber can be handled in rubber machinery.

Processing aid (r) a compounding material that improves the processability of a polymeric compound.


Glossary - R's

Radial clearance (r) the difference in the radial dimensions between the sealing surfaces of a radial seal.

Radicals atoms or polyatomic molecules with at least one unpaired electron.

RCA Clean (sc) a multi-step wet chemical process to clean wafers before oxidation; named after RCA, the company that invented the procedure.

Reactive ion etching (RIE) (sc) an etching process that combines plasma and ion beam removal of the surface layer. The etchant gas enters the reaction chamber and is ionized. The individual molecules accelerate to the wafer surface. At the surface, the top layer removal is achieved by the physical and chemical removal of the material.

Recipe (r) a formula, mixing procedure and any other instructions needed for the preparation of a product.

Recovery (r) the degree to which a rubber product returns to its normal dimensions after being distorted.

Reinforcement (r) the act of increasing the mechanical performance capability of a rubber by the incorporation of materials that do not participate significantly in the vulcanization process.

Release agent (mold) (r) a substance applied to the inside surfaces of a mold or added to a material to be molded, to facilitate removal of the product from the mold.

Resilience (r) the ratio of energy output to energy input in a rapid (or instantaneous) full recovery of a deformed specimen.

Resilience, impact (r) the ratio of output to input mechanical energy in a rapid deformation and recovery cycle of a rubber specimen.

Resistivity, volume the ratio of the electric potential gradient to the current density when the gradient is parallel to the current in the material.

Retarder (r) a material used to reduce the tendency of a rubber compound to vulcanize prematurely.

Reticle (sc) a reproduction of the pattern to be imaged on the wafer (or mask) by a step-and-repeat process. The actual size of the pattern on the reticle is usually several times the final size of the pattern on the wafer.

Reversion (vulcanization) (r) deterioration of vulcanizate properties that may occur when vulcanization time is extended beyond the optimum.

Rubber (r) a material that is capable of recovering from large deformations quickly and forcibly, and can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in a boiling solvent such as benzene, methyl ethyl ketone or ethanol toluene azeotrope.

Rubber hardness degree, international (IRHD) (r) a measure of hardness, the magnitude of which is derived from the depth of penetration of a specified indentor into a specimen under specified conditions. The scale is so chosen that zero would represent a material showing no measurable resistance to indentation, and 100 would represent a material showing no measurable indentation.

Runner (r) the secondary feed channel for transferring material under pressure from the inner end of the sprue to the cavity gate.


Glossary - S's

Scanning electron microscope (SEM) (sc) microscope used to magnify images as much as 50,000 times by means of scanning with an electron beam. The impinging electrons cause electrons on the surface to be ejected. The ejected electrons are collected and translated into a picture of the surface.

Scarf joint (r) a connection made with two ends cut at an angle and overlapping.

Scorch (r) premature vulcanization of a rubber compound.

Scorch, Mooney (r) the time to incipient cure of a compound when tested in the Mooney shearing disk viscometer under specific conditions.

Seal (r) any material or device that prevents or controls the passage of matter across the separable members of a mechanical assembly.

Seal, 0-ring (r) a product of precise dimensions molded in one piece to the configuration of a torus with circular cross section, suitable for use in a machined groove for static or dynamic service.

Secondary accelerator (r) accelerator used in smaller concentrations, compared to the primary accelerator, to achieve a faster rate of vulcanization.

Semiconductor (sc) a material whose electrical resistivity is intermediate between that of conductors and insulators, in which conduction takes place by means of holes and electrons.

Set (r) strain remaining after complete release of the force producing the deformation.

Shelf life (r) see storage life, shelf.

Shock load (r) the sudden application of an external force.

Shrinkage (r) 1) decrease in volume of a seal in service due to extraction of fillers. 2) decrease in volume of an elastomeric compound during molding.

Silicide (sc) a compound of silicon with a refractory metal. Common silicide semiconductor films (used as interconnects) include titanium, tungsten, tantalum and molybdenum.

Silicon dioxide (SiO2) (sc) a non-conducting layer that can be thermally grown or deposited on silicon wafers. Thermal silicon dioxide is commonly grown using either oxygen or water vapor at temperatures above 900°C.

Silicon nitride (Si3N4) (sc) a nonconductive layer chemically deposited on wafers at temperatures between 600° and 900°C.

Silicone rubber (r) poly dimethyl siloxane elastomer.

Solubility the ability or tendency of one substance to blend uniformly with another.

Sorption the term used to denote the combination of absorption and adsorption processes in the same substance.

Specific gravity the ratio of the weight of a given substance to the weight of an equal volume of water at a specified temperature.

Spew line (r) line on the surface of a molded product at the junction of the mold parts.

Spin-on-glass (SOG) (sc) a dielectric suspended in a liquid solvent at room temperature, allowing the material to be “spun” onto a wafer. Most SOG films are siloxane polymers dissolved in alcohol-ketone solvents. After being “spun” on the wafer, the wafers must be baked to drive off the solvent.

Sputtering (sc) a method of depositing a thin film of material on wafer surfaces. A target of the desired material is bombarded with radio frequency-excited ions which knock atoms from the target; the dislodged target material deposits on the wafer surface.

Squeeze (r) the compression of a seal, usually expressed as a percentage calculated by dividing the deformation by the original seal cross-sectional diameter.

Standard clean one (SC1) (sc) a mixture of ammonium hydroxide, hydrogen peroxide and UPDI. The first step in the RCA Cleaning process, which is designed to remove organic material.

Standard clean two (SC2) (sc) a mixture of hydrochloric acid, hydrogen peroxide and UPDI. The second step in the RCA Cleaning process, which is designed to remove metals and other inorganic material.

Static seal (r) a seal in which the sealing surfaces do not move relative to each other.

Steam oxide (sc) thermal silicon dioxide grown by bubbling a gas (usually oxygen or nitrogen) through water at 100°C.

Stepper (sc) a machine which steps a reticle directly onto the wafer. A reticle can be produced at lower defect level and with tighter dimensional control than an entire mask, resulting in wafer images having fewer defects. Alignment of reticle to wafer is accomplished by reflecting a laser beam through a special reticle pattern (alignment target) and off a corresponding pattern on the wafer.

Stiction (r) the increase in static friction resulting from prolonged seal compression.

Stiffness, bending (r) the force required to produce a bent configuration under specified conditions.

Stock (r) see compound.

Storage life, shelf (r) the period of time after production during which a material or product that is stored under specified conditions retains its intended performance capabilities.

Strain the unit change, due to force, in the size or shape of a body referred to its original size or shape.

Stress the intensity, at a point in a body, of the internal forces (or components of force) that act on a given plane through the point.

Stress relaxation (r) the decrease in stress after a given time at constant strain.

Stripping (sc) removal process; usually refers to photoresist.

Susceptor (sc) a component of many equipment systems on which the wafer is placed. Frequently made of high-purity graphite.

Swelling (r) the increase in volume of a specimen immersed in a liquid or exposed to a vapor.


Glossary - T's

Target (sc) the material to be sputtered during the sputtering process.

Tear (r) mechanical rupture initiated and propagated at a site of high stress concentration caused by a cut, defect or localized deformation.

Tear strength (r) the maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen.

Tensile set (r) the extension remaining after a specimen has been stretched and allowed to retract in a specified manner expressed as a percentage of the original length.

Tensile strength the maximum tensile stress applied during stretching a specimen to rupture.

Tensile stress a stress applied to stretch a test piece (specimen).

Tension fatigue (r) fracture, through crack growth, of a component or test specimen subjected to a repeated tensile deformation.

Tension set (r) the strain remaining after a test piece or product has been stretched and allowed to retract.

Terpolymer (r) a polymer formed from three monomer species.

Thermal carbon black (r) type of carbon black produced under controlled conditions by the thermal decomposition of hydrocarbon gases in the absence of air or flames.

Thermal degradation (r) irreversible and undesirable change in the properties of a material due to exposure to heat.

Thermal diffusion (sc) a process by which dopant atoms diffuse into the wafer surface by heating the wafer in the range of 1,000°C and exposing it to vapors containing the desired dopant.

Thermoplastic elastomer (TPE) (r) a diverse family of rubberlike materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials.

Topography the characteristic of a surface referring to its degree of flatness and smoothness.

Torr pressure unit; international standard unit replacing the English measure, millimeters of mercury (mm-Hg).

TR-10 (r) a test method for approximating the low-temperature capabilities of an elastomer.

Transistor (sc) a semiconductor device that uses a stream of charge carriers to produce active electronic effects. The name originated from the electrical characteristic of “transfer resistance.”

Transition, first order (r) a reversible change in phase of a material; in the case of polymers, usually crystallization or melting.

Transition, glass (Tg ) (r) the reversible physical change in a material from a viscous or rubbery state to a brittle, glassy state.


Glossary - U's

Ultrapure deionized water (UPDI) (sc) a highly purified water in which all charged species of ionizable organic and inorganic salts have been removed.

Ultraviolet (UV) electromagnetic radiation in the wavelength 4– 400 nanometers.

UV stabilizer (r) a compounding material that, through its ability to absorb ultraviolet radiation and render it harmless, retards the deterioration caused by sunlight and other UV light sources.


Glossary - V's

Vacuum evaporation (sc) a deposition technique whereby the deposited gas results from an evaporation process.

Van der Waals force an attractive force between two atoms due to a fluctuating dipole moment in one molecule inducing a dipole moment in the other molecule which then interact.

Vapor pressure the pressure of the vapor in equilibrium with its liquid or solid phase.

Virtual leak (sc) an “apparent” leak in a vacuum system that is often traceable to some internal release of occluded and/or sorbed gases.

Viscoelasticity (r) a combination of viscous and elastic properties in a material with the relative contribution of each being dependent on time, temperature, stress and strain rate. Viscosity the resistance of a material to flow under stress.

Viscosity, Mooney (r) a measure of the viscosity of a rubber or rubber compound determined in a Mooney shearing disk viscometer.

Void, cellular material (r) a cavity unintentionally formed in a cellular material and substantially larger than the characteristic individual cells.

Volatilization also known as vaporization, the conversion of a chemical substance from a liquid or solid state to a gaseous or vapor state.

Volt a unit of electromotive force or difference in electric potential.

Volume swell (r) the increase in dimension caused by the absorption of a fluid.

Vulcanizate (r) the product of vulcanization, a cross-linked rubber.

Vulcanization (r) an irreversible process during which a rubber compound, through a change in its chemical structure (for example, cross-linking), becomes less plastic and more resistant to swelling by organic liquids, while elastic properties are conferred, improved, or extended over a greater range of temperature.

Vulcanizing agent (r) compounding material that produces cross-linking in rubber.

Vulcanizing system (r) the combination of a vulcanizing agent and, as required, accelerators, activators and retarders used to produce the desired vulcanization characteristics or vulcanizate characteristics.


Glossary - W's

Wafer flat (sc) flat area(s) ground onto the wafer’s edges to indicate the crystal orientation of the wafer structure and the dopant type.

Warm-up (r) the reduction in viscosity of a rubber or rubber mix, by mechanical work and heat, to render it suitable for further processing.

Wavelength the length of the wave to complete one cycle.

Wicking (r) transmission of a gas or liquid, due to a pressure differential or capillary action, along fibers incorporated in a rubber product.

Wiper ring (r) a device designed to keep out foreign material.


Glossary - Y's

Yield point that point on the stress-strain curve, short of ultimate failure, where the rate of stress with respect to strain goes through a zero value and may become negative.

Yield strain the level of strain at the yield point.

Yield stress the level of stress at the yield point.


Glossary - Z's

NOTE: Many definitions in the above Glossary are from ASTM D1566. Additional terminology relating to rubber can be found there.

(sc) This term is generally associated with the semiconductor industry. (r) This term is generally associated with the rubber industry

O-ring and Seal Design Theory

The use of an o-ring as a seal is mainly to prevent the transfer of fluid (liquid, solid or gas) between two or more regions. The components of the seal are the o-ring itself and the contact surfaces. The elastomeric o-ring relies on a compressive force acting on the o-ring

to prevent the transfer of fluid between regions. Successful seal design ensures adequate seal compressive force while optimizing the destructive stress acting on the o-ring as a result of the compression or of the environment.

Three Models for Characterizing Viscoelastic Behavior Are:

1. Maxwell Model (dashpot and spring in series) 2. Kelvin (Voigt) Model (dashpot and spring in parallel) 3. Standard Linear Solid (dashpot and spring in series with a

spring in parallel).*

O-ring and Seal Design Topics

Incompressibility, Viscoelasticity and Thermomechanical Considerations

Nonlinear Finite Element Analysis (FEA)

Static Seal Gland Design

Static Gland Dimensions - Axial-Static Glands

Static Gland Dimensions - Axial Vacuum - Static Glands

Static Gland Dimensions - Trapezoidal Vacuum

Static Gland Dimensions - Conical

Static Gland Dimensions - Tube Fitting Boss Seals

Static Gland Dimensions - Radial

Dynamic Seal Gland Design

Dynamic Gland Dimensions - Rotary Seals

Dynamic Gland Dimensions - Reciprocating Seals

Gland Design 1 - Special Considerations, Part 1

Gland 2 - Special Considerations, Part 2

Gland 3 - Special Considerations, Part 3

Elastomers for Semiconductor Plasma Environments

O-Rings and Seals in Vacuum Environments

Permeation

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Outgassing and Vacuum Weight Loss

Trapped Gas

Three Considerations

Incompressibility

A material is incompressible if it exhibits zero volumetric change (isochoric) under hydrostatic pressure. Theoretically, Poisson's ratio is exactly one-half (0.5) and the bulk modulus is infinite (and det f = 1).

Near incompressibility means that Poisson's ratio is slightly less than 0.5.

Viscoelasticity

Rubber exhibits a rate-dependent behavior that can be modeled as a viscoelastic material whose properties change with temperature and time. Features of viscoelastic materials are:

Under constant stress leads to creep Under constant strain leads to stress relaxation During loading/unloading leads to hysteresis

1. Internal friction-rearrangement of molecular structure under load. 2. Strain-induced crystallization-formation and melting of crystallized

regions. 3. Stress softening (Mullin's effect). 4. Structural breakdown-the breakdown of reinforcing filler/ polymer

bonds. 5. Domain deformation-dispersed inclusions contribute to hysteresis.

Thermomechanical

Temperature change causes thermal strains. Material properties change. Heat flow may occur.

Nonlinear Finite Element Analysis (FEA)

Rubber is a unique material. In its polymer form during processing, it behaves like a highly viscous liquid. After cross-linking (curing), rubber can undergo large reversible deformations.

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The unique properties of rubber that require treatment different from traditional metal nonlinear finite element analysis are:

Large deformations (over 100%). Load-extension (stress-strain) characteristics are definitely nonlinear. Viscoelastic (spring and dampener) characteristics and timeand temperature-

dependence. Nearly incompressible (volume does not change appreciably under stress).

The finite element method is a technique for obtaining approximate numerical solutions to boundary value problems which predict the response of physical systems when subjected to external loads. The system or structure is characterized by many small individual pieces or elements which are connected at nodes. The solution of thousands of simultaneous equations for unknowns of displacements, rotations, or the hydrostatic pressure is obtained through a computer.

Nonlinear finite element analysis should be an integral part of the design and manufacturing processes. The advantages are numerous, including improved performance, faster time-to-market, optimal use of materials and verification of integrity before prototyping.

Static Seal Gland Design

There are three types of static seals:

Face (Flange) static seal Radial (Piston) static seal Crush static seal

A static seal is characterized by the absence of relative motion between sealing surfaces, or between the seal surface and a mating surface.

Static face seal applications: chamber lid seal, slit valve.

Static radial (piston) seal applications: ISO KF flange, filters.

Static crush seal applications: gas feed through, quartz tank.

Static Seal Gland Dimensions

Axial-Static Glands

Measurements in inchesMeasurements in

millimeters

Size W Dep Com Wid Fill Radi Radi Wid Dep W Siz

th p. th us us th th e

AS 568

0.070

0.048 31% 0.095 109%

0.010 0.25 2.41 1.22 1.78

AS 568

-000 ± .003

± .002

± 6% ± .005

± 19%

± .005 ± .13 ± .13 ± .05 ± .08

-000

AS 568

0.103

0.076 26% 0.145 97% 0.010 0.25 3.68 1.93 2.62

AS 568

-100 ± .003

± .004

± 6% ± .005

± 14%

± .005 ± .13 ± .13 ± .10 ± .08

-100

AS 568

0.139

0.105 24% 0.185 100%

0.018 0.46 4.70 2.67 3.53

AS 568

-200 ± .004

± .005

± 6% ± .005

± 13%

± .008 ± .20 ± .13 ± .13 ± .10

-200

AS 568

0.210

0.170 19% 0.285 91% 0.028 0.71 7.24 4.32 5.33

AS 568

-300 ± .005

± .005

± 4% ± .005

± 9%

± .008 ± .20 ± .13 ± .13 ± .13

-300

AS 568

0.275

0.225 18% 0.375 90% 0.028 0.71 9.53 5.72 6.99

AS 568

-400 ± .006

± .005

± 4% ± .005

± 7%

± .008 ± .20 ± .13 ± .13 ± .15

-400

B2401

0.122

0.093 24% 0.162 80% 0.018 0.46 4.12 2.36 3.10

B2401

G- ± .004

± .005

± 7% ± .005

± 12%

± .008 ± .20 ± .13 ± .13 ± .10

G-

GB2401

0.224

0.181 19% 0.304 72% 0.028 0.71 7.72 4.61 5.70

B2401

G- ± .006

± .005

± 4% ± .005

± 7%

± .008 ± .20 ± .13 ± .13 ± .15

G-

Note: Gland diameter should provide for no greater than 3% to 5% stretch (based on nominal O-ring ID).


Axial Vacuum-Static Glands

Measurements in inches Measurements in

millimeters

Size

WDepth

Comp.

Width

FillRadius

Radius

Width

Depth

WSize

AS 568

0.070

0.048 31% 0.095 109%

0.010 0.25 2.41 1.22 1.78 AS 568

-000 ± .003

± .002

± 6% ± .005

± 19%

± .005 ± .13 ± .13 ± .05 ± .08

-000

AS 568

0.103

0.076 26% 0.145 97% 0.010 0.25 3.68 1.93 2.62 AS 568

-100 ± .003

± .004

± 6% ± .005

± 14%

± .005 ± .13 ± .13 ± .10 ± .08

-100

AS 568

0.139

0.105 24% 0.185 100%

0.018 0.46 4.70 2.67 3.53 AS 568

-200 ± .004

± .005

± 6% ± .005

± 13%

± .008 ± .20 ± .13 ± .13 ± .10

-200

AS 568

0.210

0.170 19% 0.285 91% 0.028 0.71 7.24 4.32 5.33 AS 568

-300 ± .005

± .005

± 4% ± .005

± 9%

± .008 ± .20 ± .13 ± .13 ± .13

-300

AS 568

0.275

0.225 18% 0.375 90% 0.028 0.71 9.53 5.72 6.99 AS 568

-400 ± .006

± .005

± 4% ± .005

± 7%

± .008 ± .20 ± .13 ± .13 ± .15

-400

B2401

0.157

0.126 20% 0.212 74% 0.018 0.46 5.38 3.20 4.00 B2401

V- ± .004

± .005

± 5% ± .005

± 9%

± .008 ± .20 ± .13 ± .13 ± .10

V-

B2401

0.236

0.194 18% 0.319 71% 0.018 0.46 8.09 4.93 6.00 B2401

V- ± .006

± .005

± 4% ± .005

± 7%

± .008 ± .20 ± .13 ± .13 ± .15

V-

B2401

0.394

0.335 15% 0.536 68% 0.028 0.71 13.61 8.51 10.00

B2401

V- ± .012

± .005

± 4% ± .005

± 6%

± .008 ± .20 ± .13 ± .13 ± .30

V-

Note: Gland diameter should provide for no greater than 3% to 5% stretch (based on nominal o-ring ID).


Trapezoidal Vacuum-Static Glands


millimeters

Size

WDepth

Comp.

Width

FillRadius

Radius

Width

Depth

WSize

AS 568

0.070

1.78

AS 568

-000 ± .003

± .08

-000

AS 568

0.103

0.080 22% 0.090 107%

0.005- 0.13- 2.29 2.03 2.62

AS 568

-100 ± .003

± .003

± 6% ± .003

± 16%

0.015 0.38 ± .08 ± .10 ± .08

-100

AS 568

0.139

0.110 21% 0.125 102%

0.010- 0.25- 3.18 2.79 3.53

AS 568

-200 ± .004

± .004

± 5% ± .004

± 13%

0.031 0.79 ± .10 ± .10 ± .10

-200

AS 568

0.210

0.170 19% 0.180 102%

0.015- 0.38- 4.57 4.32 5.33

AS 568

-300 ± .005

± .005

± 4% ± .005

11% 0.031 0.79 ± .13 ± .13 ± .13

-300

AS 568

0.275

0.225 18% 0.240 99% 0.015- 0.38- 6.10 5.72 6.99

AS 568

-400 ± .006

± .005

± 4% ± .005

± 9% 0.063 1.60 ± .13 ± .13 ± .15

-400

B2401

0.157

0.126 20% 0.135 103%

0.010- 0.25- 3.43 3.20 3.10

B2401

G- ± .004

± .004

± 5% ± .003

± 11%

0.031 0.79 ± .08 ± .10 ± .10

G-

B2401

0.236

0.192 19% 0.203 101%

0.015- 0.38- 5.16 4.88 5.70

B2401

G- ± .006

± .006

± 4% ± .004

± 9% 0.063 1.60 ± .10 ± .10 ± .15

G-

B2401

0.157

0.126 20% 0.135 103%

0.010- 0.25- 3.43 3.20 4.00

B2401

V- ± .004

± .004

± 5% ± .003

± 11%

0.031 0.79 ± .08 ± .10 ± .10

V-

B2401

0.236

0.192 19% 0.203 101%

0.015- 0.38- 5.16 4.88 6.00

B2401

V- ± .006

± .006

± 4% ± .004

± 9% 0.063 1.60 ± .10 ± .10 ± .15

V-



Conical-Static Glands

Measurements in inches Measurements in millimeters

Size WDept

hComp

.Widt

hFill

Radius

Radius

Width

Depth

W Size

AS 568

0.070

0.095 0.095 0.008 0.20 2.41 2.41 1.78 AS 568

-000 ± .003

± .003 ± .003 ± .08 ± .08 ± .08 -000

AS 568

0.103

0.137 0.137 0.008 0.20 3.48 3.48 2.62 AS 568

-100 ± .003

± .005 ± .005 ± .13 ± .13 ± .08 -100

AS 568

0.139

0.186 0.186 0.008 0.20 4.72 4.72 3.53 AS 568

-200 ± .004

± .007 ± .007 ± .18 ± .18 ± .10 -200

AS 568

0.210

0.279 0.279 0.008 0.20 7.09 7.09 5.33 AS 568

-300 ± .005

± .010 ± .010 ± .25 ± .25 ± .13 -300

AS 568

0.275

0.371 0.371 0.012 0.31 9.42 9.42 6.99 AS 568

-400 ± .006

± .015 ± .015 ± .38 ± .38 ± .15 -400

B2401

0.157

0.210 0.210 0.008 0.20 5.33 5.33 3.10 B2401

G- ± .004

± .008 ± .008 ± .20 ± .20 ± .10 G-

B2401

0.236

0.316 0.316 0.008 0.20 8.03 8.03 5.70 B2401

G- ± .006

± .015 ± .015 ± .38 ± .38 ± .15 G-


Tube Fitting Boss Seals

Size

ID Tube

Dash

Tube

OD

ThreadMIL-S-8879

ADiam.+.015- .000

BMin. Full

Thread

Depth

CDiam

.

DDiam.+.015- .000

E

+.015- .000

Diam

Min.

-902

0.064

± .003

0.239± .005

2 0.125 .3125-24UNJF-3B 0.438 0.482 0.062 0.328 0.063 0.602

-903 0.06 0.301 3 0.188 .3750-24UNJF-3B 0.500 0.538 0.125 0.390 0.063 0.665

4± .00

3± .005

-904

0.072

± .003

0.351± .005

4 0.250 .4375-20UNJF-3B 0.562 0.568 0.172 0.454 0.075 0.728

-905

0.072

± .003

0.414± .005

5 0.312 .5000-20UNJF-3B 0.625 0.568 0.234 0.517 0.075 0.790

-906

0.078

± .003

0.468± .005

6 0.375 .5625-18UNJF-3B 0.688 0.598 0.297 0.580 0.083 0.852

-907

0.082

± .003

0.530± .007

7 0.438 .6250-18UNJF-3B 0.750 0.614 0.360 0.643 0.094 0.915

-908

0.087

± .003

0.644± .009

8 0.500 .7500-16UNJF-3B 0.875 0.714 0.391 0.769 0.094 1.040

-909

0.097

± .003

0.706± .009

9 0.562 .8125-16UNJ-3B 0.938 0.730 0.438 0.832 0.107 1.102

-910

0.097

± .003

0.755± .009

10 0.625 .8750-14UNJF-3B 1.000 0.802 0.484 0.896 0.107 1.165

-911

0.116

± .004

0.863± .009

11 0.688 1.0000-12UNJF-3B

1.156 0.877 0.547 1.023 0.125 1.352

-912

0.116

± .004

0.924± .009

12 0.750 1.0625-12UNJ-3B 1.234 0.877 0.609 1.086 0.125 1.415

-914

0.116

± .004

1.047± .010

14 0.875 1.1875-12UNJ-3B 1.362 0.877 0.734 1.211 0.125 1.540

-916

0.116

± .004

1.171± .010

16 1.000 1.3125-UNJ-3B 1.487 0.877 0.844 1.336 0.125 1.665

-918 0.11 1.355 18 1.125 1.5000-12UNJF- 1.675 0.877 0.953 1.524 0.125 1.790

6± .00

4± .012 3B

-920

0.118

± .004

1.475± .014

20 1.250 1.6250-12UNJ-3B 1.800 0.877 1.078 1.648 0.125 1.978

-924

0.118

± .004

1.720± .014

24 1.500 1.8750-12UNJ-3B 2.050 0.877 1.312 1.898 0.125 2.228

-928

0.118

± .004

2.090± .018

28 1.750 2.2500-12UNJ-3B 2.425 0.877 1.547 2.273 0.125 2.602

-932

0.118

± .004

2.337± .018

32 2.000 2.5000-12UNJ-3B 2.675 0.907 1.781 2.524 0.125 2.852


Radial-Static Glands

Measurements in ± .005 inches Measurements in

millimeters

Size

WDepth

Comp.

Width

FillRadius

Clear.

Radius

Width

Depth

WSize

AS 568

0.070

0.052 25% 0.095

94% 0.010 0.004

0.25 2.41 1.32 1.78

AS 568

-000 ± .003

± .003

± 7% ± .005

± 20%

± .005

± .002

± .13 ± .13 ± .08 ± .08

-000

AS 568

0.103

0.083 19% 0.145

89% 0.010 0.004

0.25 3.68 2.11 2.62

AS 568

-100 ± .003

± .003

± 5% ± .005

± 11%

± .005

± .002

± .13 ± .13 ± .08 ± .08

-100

AS 568

0.139

0.115 17% 0.185

91% 0.018 0.005

0.46 4.70 2.92 2.92

AS 568

-200 ± .004

± .003

± 5% ± .005

± 10%

± .008

± .002

± .20 ± .13 ± .08 ± .08

-200

AS 568

0.210

0.180 14% 0.285

86% 0.028 0.005

0.71 7.24 4.57 5.33

AS 568

-300 ± .005

± .004

± 4% ± .005

± 8%

± .008

± .002

± .20 ± .13 ± .10 ± .13

-300

AS 568

0.275

0.230 16% 0.375

88% 0.028 0.006

0.71 9.53 5.84 6.99

AS 568

-400 ± .006

± .005

± 4% ± .005

± 7%

± .008

± .002

± .20 ± .13 ± .13 ± .15

-400

B2401

0.075

0.055 26% 0.102

83% 0.010 0.004

0.25 2.59 1.40 1.90

B2401

P- ± .003

± .005

± 10%

± .005

± 19%

± .005

± .002

± .13 ± .13 ± .13 ± .07

P-

B2401

0.094

0.075 20% 0.129

74% 0.010 0.004

0.25 3.28 1.91 2.40

B2401

P- ± .003

± .005

± 8% ± .005

± 13%

± .005

± .002

± .13 ± .13 ± .13 ± .07

P-

B2401

0.122

0.098 19% 0.167

73% 0.018 0.004

0.46 4.24 2.49 3.10

B2401

G- ± .004

± .005

± 7% ± .005

± 11%

± .008

± .002

± .20 ± .13 ± .13 ± .10

G-

B2401

0.138

0.111 19% 0.189

73% 0.018 0.005

0.46 4.80 2.82 3.50

B2401

P- ± .004

± .005

± 6% ± .005

± 10%

± .008

± .002

± .20 ± .13 ± .13 ± .10

P-

B2401

0.224

0.183 18% 0.303

72% 0.028 0.005

0.71 7.70 4.65 5.70

B2401

P-, G-

± .006

± .005

± 4% ± .005

± 7%

± .008

± .002

± .20 ± .13 ± .13 ± .15

P-, G-

B2401

0.331

0.275 17% 0.455

69% 0.028 0.006

0.71 11.56

6.99 8.40

B2401

P- ± .006

± .005

± 3% ± .005

± 5%

± .008

± .002

± .20 ± .13 ± .13 ± .15

P-


Dynamic Seal Gland Design

Types of Dynamic Seals

Dynamic Seals: Reciprocal, Rotary Characterized by relative motion between the sealing surfaces. Reciprocal motion is most common in hydraulic cylinders or actuators, as well as in some types of valves. Rotary motion is common in many pump and valve applications.

Dynamic rotary seal applications:throttle valve

Dynamic Cycling Seals: Open-Close

A hybrid dynamic static application where the relative motion occurs when the sealing surfaces are separated and then rejoined.

Cycling (open-close) seal applications:slit valve, other valves

Dynamic Seal Gland Dimensions

Dynamic Glands - Rotary Seals


millimeters

Size

WDepth

Comp.

Width

Fill

Radius

Clear.

Radius

Width

Depth

WSize

AS 568

0.070

0.066 5% 0.077 97%

0.010 0.014

0.25 1.96 1.68 1.78

AS 568

-000± .003

± .001 ± 5%

± .002

± 12%

± .005

± .002 ± .13 ± .05 ± .03

± .08 -000

AS 568

0.103

0.098 5% 0.110 99%

0.010 0.014

0.25 2.79 2.49 2.62

AS 568

-100 ± .003

± .001

± 4% ± .002

± 9%

± .005

± .002

± .13 ± .05 ± .03 ± .08

-100

AS 568

0.139

0.134 3% 0.146 99%

0.018 0.018

0.46 3.71 3.40 3.53

AS 568

-200 ± .004

± .002

± 4% ± .002

± 9%

± .008

± .002

± .20 ± .05 ± .05 ± .10

-200

B2401

0.075

0.073 2% 0.083 93%

0.010 0.014

0.25 2.11 1.85 1.90

B2401

P-± .003

± .001 ± 5%

± .002

± 11%

± .005

± .002 ± .13 ± .05 ± .03

± .08 P-

B2401

0.094

0.091 3% 0.102 96%

0.010 0.014

0.25 2.59 2.31 2.40

B2401

P- ± .003

± .001

± 4% ± .002

± 9%

± .005

± .002

± .13 ± .05 ± .03 ± .08

P-

B2401

0.138

0.135 2% 0.145 98%

0.018 0.018

0.46 3.68 3.43 3.50

B2401

P- ± .004

± .002

± 4% ± .002

± 8%

± .008

± .002

± .33 ± .05 ± .05 ± .10

P-


Dynamic Seal Gland Dimensions

Dynamic Glands - Reciprocating Seals


millimeters

Size

WDepth

Comp.

Width

Fill

Radius

Clear.

Radius

Width

Depth

WSize

AS 568

0.070

0.056 20% 0.095 93%

0.010 0.004 0.25 2.41 1.42 1.78

AS 568

-000± .003

± .001 ± 5%

± .005

± 14%

± .005

± .002 ± .13 ± .13 ± .03

± .08 -000

AS 568

0.103

0.089 13% 0.145 83%

0.013 0.004 0.33 3.68 2.26 2.62

AS 568

-100 ± .003

± .001

± 3% ± .005

± 9%

± .008

± .002

± .20 ± .13 ± .03 ± .08

-100

AS 568

0.139

0.121 13% 0.185 87%

0.018 0.005 0.46 4.70 3.07 3.53

AS 568

-200 ± .004

± .002

± 4% ± .005

± 9%

± .013

± .002

± .33 ± .13 ± .05 ± .10

-200

AS 568

0.210

0.186 11% 0.285 83%

0.028 0.005 0.71 7.24 4.72 5.33

AS 568

-300 ± .005

± .002

± 4% ± .005

± 7%

± .023

± .002

± .58 ± .13 ± .08 ± .13

-300

AS 568

0.275

0.237 14% 0.375 85%

0.033 0.006 0.84 9.53 6.02 6.99

AS 568

-400 ± .006

± .003

± 3% ± .005

± 6%

± .028

± .002

± .71 ± .13 ± .08 ± .15

-400

B2401

0.075

0.060 20% 0.102 93%

0.010 0.004 0.25 2.57 1.52 1.90

B2401

P-± .003

± .001 ± 5%

± .005

± 13%

± .005

± .002 ± .13 ± .05 ± .03

± .07 P-

B2401

0.094

0.080 15% 0.130 86%

0.010 0.004 0.25 3.35 1.98 2.40

B2401

P-± .003

± .001 ± 4%

± .005

± 10%

± .005

± .002 ± .13 ± .05 ± .03

± .07 P-

B2401

0.138

0.120 13% 0.185 86%

0.018 0.005 0.46 4.70 3.10 3.50

B2401

P- ± .004

± .002

± 4% ± .005

± 9%

± .008

± .002

± .20 ± .05 ± .03 ± .10

P-

2401

0.224

0.199 11% 0.304 83%

0.028 0.005 0.71 7.65 5.05 5.70

B2401

P- ± .006

± .003

± 3% ± .005

± 6%

± .008

± .002

± .20 ± .05 ± .03 ± .15

P-, G-

B2401

0.331

0.288 13% 0.450 85%

0.028 0.006 0.71 11.28 7.49 8.40

B2401

P- ± .006

± .003

±2% ± .005

± 5%

± .008

± .002

± .20 ± .05 ± .03 ± .15

P-


Gland Design

Special Considerations, Part 1

In many situations, it is very important to understand the anticipated response of an elastomer under a given compressive load. The compression/deflection curves for various elastomers are functions of the hardness (and bulk modulus) as well as the cross-sectional diameter. High-pressure applications may present unique challenges to elastomeric seals. Elastomers are essentially high-viscosity liquids-and as such will flow under extreme pressure conditions. In applications where the clearance gap is larger than that recommended for a traditional o-ring seal, the user

should consider backup rings. These flat or contoured rigid rings are inserted on the lowpressure side of the gland to prevent extrusion. Consideration of backup rings requires additional gland width to allow for elastomer expansion. In addition, chemical compatibility and ease of installation are other considerations when using backup rings.

Irregular, noncircular glands may present challenges for seal design. The chart at the right illustrates the minimum recommended bend radius for irregular glands. Smaller, sharper radii may result in excessive stress and seal damage.

Gland Design


In addition to compression, the stretch applied to o-rings in service (either to keep the o-ring in the gland during assembly or service, or to aid in the installation) can have an impact on the sealing performance. These effects can include:

Reduction in cross section As a seal is stretched, the cross section is reduced.

Gow-Joule effect (elevated temperatures) When an elastomer is stretched and the temperature elevated, the molecular chains will attempt to reduce the imposed stress. Excessive stretch can lead to premature cracking or seal failure.

Gland Design


High-pressure applications may present unique challenges to elastomeric seals. Elastomers are essentially high-viscosity liquids - and as such will flow under extreme pressure conditions. In applications where the clearance gap is larger than that recommended for a traditional o-ring seal, the user should consider backup rings. These flat or contoured rigid rings are inserted on the low pressure side of the gland to prevent extrusion. Consideration of backup rings requires additional gland width to allow for elastomer expansion. In addition, chemical compatibility and ease of installation are other considerations when using backup rings. The surface finish of the gland can have a significant impact on the vacuum performance of seals. The following charts highlight terminology and processing techniques for specific surface finishes. Special care should be taken when sealing quartz components - not only due to the potentially irregular surface finish, but also to "light piping" effects on clear components in the sealing contact areas. Polymeric glands offer unique challenges if plastic deformation and creep of the sealing components are not taken into account.

Surface Finish Processes

Semiconductor Plasma Environments and Elastomer Seals

Semiconductor plasma environments offer significant challenges for elastomer seals. Specific chemistries for metal, oxide, poly etch and photoresist stripping equipment include the use of fluorine-, oxygen-, and chlorine-partially-ionized plasmas.

The plasmas typically used are called "glow-discharge," and they operate in the range of 10-4 to 10 Torr, with electron densities of 109 to 1012 cm-3, and ion temperatures of 0.03 to 0.04eV (100-200°C).

The function of a plasma is determined by: 1) the ability to deliver a uniform flux of energetic (+) ions to a surface with controllable energy and flux, and 2) the ability to deliver spatially uniform, relatively large fluxes of atoms and/or molecular radicals to surfaces. Three plasma properties that affect performance are:

Chemical Reactivity-The partially ionized gas exhibits greater chemical reactivity.

Ion Bombardment-Collision of ions and solid surfaces can generate vertical profiles and sputtering of material. Ion energies (100 -1000eV) transferred to the lattice atoms create a very short-lived cascade of moving atoms. If some of these atoms have enough energy to overcome the binding energy with the right path (trajectory) they form sputtered particles (atoms). (One atom/~500eV.) These moving lattice atoms can cause chemical reactions to occur.

Electron Bombardment-Less important than the effects of energetic ions and chemically active radicals. Major effects are substrate heating and degradation of radiation-sensitive materials, e.g., plastics.

Traditional measures of elastomer compatibility cover volume swell and physical property degradation as a result of exposure to the gas. Plasma environments offer many additional challenges for compatibility and contamination performance of the elastomer.

Measures of elastomer compatibility in plasma environments should include weight loss (including elastomer physical properties), and surface structural and chemical changes as measured by SEM/EDS and ESCA. With all the variables involved, testing of the elastomer in the actual application is recommended. CF4 O2 1.00E+0 9.

Sealing in a Vacuum

Approximately 25% of the process steps in semiconductor fabrication require vacuum processes. A vacuum is a space from which all air and other gases have been removed. It is not possible to remove all the gases. The importance of vacuum lies mainly on the molecular level. Higher vacuums allow longer paths for molecules to take without colliding or reacting with other molecules or other surfaces.

Vacuum Level Torr

Rough 760 to 1

Medium 1 to 10-3

High 10-3 to 10-6

Very High 10-6 to 10-9

Ultra-High 10-9

Low vacuum is from atmospheric pressure (105 Pa) to 0.1 Pa (1 mTorr). The gas dynamics are characterized by viscous flow-the collisions between gas molecules. This pressure range is used for processes such as sputtering that depend on gas-phase chemical reactions and momentum transfer between molecules.

High vacuum is characterized by molecular flow-minimal collisions between gas molecules, and some collisions with chamber walls. The lowest pressure that can be reached with an unbaked system is 10-6 Pa (10-8 Torr). Ultra-high vacuum is again characterized by molecular flow. Elastomers are virtually non-existent with the lower pressure limit determined by hydrogen diffusing through metal walls.

Achieving Vacuum Levels

Rotary vane, piston and sorption pumps have a low-pressure limit of 10-1 to 10-3 Pa. They can discharge to atmospheric pressure. To achieve higher vacuum levels, diffusion or turbomolecular pumps are required. These pumps cannot discharge to atmospheric pressure. Instead, the discharge pressure range is 0.5-50 Pa. Therefore a second pump often called a "backing" or "fore" pump is used together with the diffusion or turbomolecular pumps. A third class of pumps, which are used to remove gas from chambers at high vacuum, are called "capture" pumps. The three main types of capture pumps are cryogenic pumps-freezing molecules on a wall; getter pumps-chemically reacting with the gas molecules; and ion pumps-accelerating the molecules to a high speed and burying them in a metal wall.

Typical Process Equipment Cross Section

Residual Gas Contaminants

Residual gas contaminants can be released from solid components in a chamber, and can lengthen the time it takes to evacuate a chamber and reduce ultimate level of

vacuum reached. It is often very difficult to distinguish between the sources of residual gas contaminants.

The "rate-of-rise" test or "leak back" test is a measure of the gas load the pump is removing. The pressure P (Torr) at any given time is equal to the ratio of the gas load Z (leaks and outgassing in Torr-liters/second) divided by the pumping speed S (liters/second).

Three primary sources of residual gas contaminants from elastomer seals are:

Permeation

Outgassing and Vacuum Weight Loss

Trapped Gas

Vacuum Permeation

The solubility and diffusion of a gas through an elastomer affects the pump-down time as well as the ultimate vacuum achieved in a vacuum seal. The gas permeation coefficient of a polymeric material is the volumetric flow rate of a gas under steady-state conditions through a unit surface area of unit thickness at unit pressure difference.

Q = K A (P1 - P2) d

Q is the permeation rate (cm3/sec)

K is the permeation coefficient (cm3 cm/sec cm2 atm)

A is the area (cm2)

P1 - P2 is the pressure gradient (atm)

d is the thickness (cm)

http://www.pspglobal.com/trapped-gas.html

http://www.pspglobal.com/outgassing-elastomers.html

http://www.pspglobal.com/vacuum-permeation.html

Permeability is a fundamental property of an elastomer. It is often desired to measure the rate of transmission of a vapor or liquid through the elastomer. This is called "transmission." In general:

Swelling decreases permeation rate

High pressures decrease permeation rate (reduction of free volume)

Higher temperatures increase diffusion rate and permeation rate

Inorganic fillers eliminate diffusive passages and lower permeability

Larger molecules of gas lower diffusion rate

Material He O2 H2O N2 CO2

Nitrile 8 2.5 760 0.1 25

EPDM 25-30 16-18 - 6-7 85

VMQ 250 75-450 8,000 200 2,000

FVMQ 140 80 - 40 400

FKM 9-22 1-2 40 0.05-0.7 5

FKM* 30 3 - 2 -

FFKM (PFE) 60-80 6-8 90-100 8-12 -

KEL-F - 0.1 - 0.1 0.5

PTFE - 0.04 - 0.14 0.12

Polyimide 1.9 0.1 - 0.03 0.2

Permeation Data for Various Polymers(units expressed in 10-8 sccm-cm/sec-cm2-atm)*Highly fluorinated compound

Outgassing and Weight Loss of Elastomers

Outgassing in elastomers is the release of volatile materials when the elastomers are heated. Outgassing affects vacuum performance. Outgassed components may include water vapor from the reaction of acid scavengers (i.e., MgO) and acid

during the curing process of elastomers. Also, low-molecular-weight species of antioxidants and UV stabilizers, unreacted polymer residues and degraded products may appear as outgassed components. Many traditional seal materials contain small amounts of low-molecular-weight plasticizers, or process aids, that can volatilize under vacuum conditions. Water vapor and carbon dioxide are also absorbed into seal elastomers exposed to air.

Weight loss measurements are often used as an indicator of outgassing in elastomers. Specific values for vacuum weight loss are dependent on the elastomer and sample conditioning.

Heating an o-ring seal for several hours at 100°C has been shown to reduce outgassing significantly. This "bake-out" procedure is less important for seals made from modern fluorocarbon and perfluorocarbon elastomers as the manufacturing process includes a several-hour post-curing step at temperatures above 200°C. Vacuum baking can provide even less outgassing.

Outgassing Rates of Elastomers and Various Materials

MaterialRATE*

(10-9 mbar/sec-cm2)

RATE**(10-8

Torr-liter/sec)

Stainless Steel 13.5

Steel, Chrome Plated 7.1

Stainless Steel,Electropolished

4.3

Aluminum 6.3

Nitrile 3,500 300

KEL-F 40 4

Silicone 18,000 2,000

Fluoroelastomer 1,140 2,000

Fluoroelastomer, baked 4 0.2

Perfluoroelastomer 0.3

PTFE 300 400

Polyimide 900 80

Pyrex glass 7.4

* Leybold Inficon, Inc.-"Vacuum" 1997** Peacock, R.N., J. Vac. Sci. Technol., Jan./Feb. 1980

Trapped Gas in O-Rings and Seals

The release of gas trapped by the elastomer in the groove (especially dovetail grooves) can slowly leak over time.

Comparisons of sealing materials and design alternatives are often made by charting the pump-down curve. Recording of temperature and pressure (vacuum) levels over time can provide useful information to equipment manufacturers.

Recent testing by a major vacuum components manufacturer confirmed that there were "no appreciable difference[s] in the permeation rates (increase in helium partial pressure) for brown or black Viton."*

Vacuum grease may not provide a significant reduction in permeation, but may improve the seal installation and repeated sealing performance.*

* Nor-Cal Products, Permeation of Various O-Rings, 1998

O-ring and Seal Failure Analysis

The failure of an o-ring or seal can cost the customer time and money as well as possibly endangering personnel. The analysis of a premature or unexpected o-ring or seal failure includes many factors, including the environment, the o-ring or seal design and the elastomer itself. The appearance of the defective o-ring or seal can provide significant insight into potential causes of failure.

O-ring and Seal Failure

In the semiconductor industry, the failure of a single o-ring or seal can result in millions of dollars in damaged production, downtime and maintenance costs. In many environments, an o-ring or seal failure can result in the complete evacuation of a facility-or worse, the exposure of personnel to toxic chemicals.

Prevention of o-ring and seal failures through proper design, material selection and maintenance certainly minimizes the risk of failure. Attention to the condition of replaced o-rings and seals, as well as the equipment performance over time, will result in improved process reliability, reduced operating costs and a safer work environment.

O-rings and seals often fail prematurely in applications because of improper design or compound selection. This section is designed to provide the viewer with examples of common failure modes. By correctly identifying the failure mode, changes in the design or sealing material can lead to improved o-ring and seal performance.

From the end-user's point of view, an o-ring or seal can fail in three (3) general ways:

Leaking Contamination Change in Appearance

It is useful to analyze the envionment, o-ring or seal design and elastomer when there is an o-ring or seal failure.

Topics:

Environment Analysis

O-ring and Seal Design Analysis

Elastomer Analysis

General Factors: Leaking, Contamination and Appearance Change

O-ring and Seal Failure Part 1: Extrusion, Over-Compression and Spiral Failure

O-ring and Seal Failure Part 2: Chemical Degradation, Thermal Degradation and Explosive Decompression

O-ring and Seal Failure Part 3: Plasma Degradation, Contamination and Abrasion

O-ring and Seal Failure Part 4: Compression Set, Outgassing/Extraction and Installation Damage

Environment Analysis

One major factor in possible o-ring or seal failure is the extreme and harsh environment in which o-rings and seals are expected to perform. In the semiconductor industry, the sealing environment can consist of virtually anything from inert gases at room temperatures to aggressive chemicals at very high temperatures. The sealing environment may result in chemical degradation or swelling of the sealing components. Elevated temperatures may cause seal degradation, swelling or outgassing. And the pressure - or more often, the vacuum environments - can cause outgassing and weight loss.

Contributing factors to o-ring and seal failure in the sealing environment include:

Chemical - the type of chemical(s) in service

Thermal - the operating ranges of the seal (also any thermal cycling)

Pressure/Vacuum - the range of pressures or vacuum levels in the process

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O-ring and Seal Design Analysis

Analysis of the o-ring or seal application is crucial to the understanding of possible failure. Most o-ring and seal design is performed by component suppliers and equipment manufacturers. The design is refined as experience is gained. As quickly as process technology changes, however, the experience gained with the o-ring or seal design may not be relevant to the latest process technology. Vacuum applications have historically relied on high levels of compression and gland fill to reduce permeation and trapped gases. These techniques, when applied to new materials, or at higher operating temperatures, can result in premature o-ring or seal failure.

The o-ring and seal design and application can provide information about the cause of failure:

Static O-ring and Seals -axial and radial, confined or unconfined

Dynamic O-rings and Seals -axial (open-close) or radial (reciprocating or rotary)

Sealing Gland Dimensions - shape (square, trapezoidal, etc.)compressionglandfillstretch

Installation Procedures -stretch

Elastomer Analysis

Analytical techniques are used to identify the specific polymer type and compound. They can also be used to identify contamination sources on the surface, or surface properties which may have contributed to the failure. Traditional elastomer test methods can determine chemical compatibility, changes in dimension, hardness or physical properties. In vacuum systems, the analysis of outgassing components may lead to the identification

O-ring and Seal FailureGeneral Factors

Leaking, Contamination and Appearance Change

Seal Failure - Leaking

Seal Failure - Contamination

Seal Failure - Appearance Change

O-ring and Seal Failure Part 1

Extrusion, Over-Compression and Spiral Failure

Extrusion (and/or Nibbling)

Description: The o-ring or seal develops ragged edges (generally on the low-pressure side) which appear tattered.

Contributing Factors: Excessive clearances. Excessive pressure. Low-modulus/hardness elastomer. Excessive gland fill. Irregular clearance gaps. Sharp gland edges. Improper sizing.

Suggested Solutions: Decrease clearances. Higher-modulus/hardness elastomer. Proper gland design. Use of polymer backup rings.

Over-Compression

Description: The o-ring or seal exhibits parallel flat surfaces (corresponding to the contact areas) and may develop circumferential splits within the flattened surfaces.

Contributing Factors: Improper design-failure to account for thermal or chemical volume changes, or excessive compression.

Suggested Solutions: Gland design should take into account material responses to chemical and thermal environments.

Spiral Failure

Description: The o-ring or seal exhibits cuts or marks which spiral around its circumference.

Contributing Factors: Difficult or tight installation (static). Slow reciprocating speed. Low-modulus/hardness elastomer. Irregular O-ring surface finish (including excessive parting line). Excessive gland width. Irregular or rough gland surface finish. Inadequate lubrication.

Suggested Solutions: Correct installation procedures. Highermodulus elastomer. Internally-lubed elastomers. Proper gland design. Gland surface finish of 8-16 microinch RMS. Possible use of polymer backup rings.


Chemical Degradation, Thermal Degradation and Explosive Decompression

Chemical Degradation

Description: The o-ring or seal may exhibit many signs of degradation including blisters, cracks, voids or discoloration. In some cases, the degradation is observable only by measurement of physical properties.

Contributing Factors: Incompatibility with the chemical and/or thermal environment.

Suggested Solutions: Selection of more chemically resistant elastomer.

Thermal Degradation

Description: The o-ring or seal may exhibit radial cracks located on the highest temperature surfaces. In addition, certain elastomers may exhibit signs of softening-a shiny surface as a result of excessive temperatures.

Contributing Factors: Elastomer thermal properties. Excessive temperature excursions or cycling.

Suggested Solutions: Selection of an elastomer with improved thermal stability. Evaluation of the possibility of cooling sealing surfaces.

Explosive Decompression

Description: The o-ring or seal exhibits blisters, pits or pocks on its surface. Absorption of gas at high pressure and the subsequent rapid decrease in pressure. The absorbed gas blisters and ruptures the elastomer surface as the pressure is rapidly removed.

Contributing Factors: Rapid pressure changes. Low-modulus/ hardness elastomer.

Suggested Solutions: Higher-modulus/hardness elastomer. Slower decompression (release of pressure).


Plasma Degradation, Contamination and Abrasion

Plasma Degradation

Description: The o-ring or seal often exhibits discoloration, as well as powdered residue on the surface and possible erosion of elastomer in the exposed areas.

Contributing Factors: Chemical reactivity of the plasma. Ion bombardment (sputtering). Electron bombardment (heating). Improper gland design. Incompatible seal material.

Suggested Solutions: Plasma-compatible elastomer and compound. Minimize exposed area. Examine gland design.

Contamination

Description: The o-ring or seal exhibits foreign material on the surface within the cross section.

Contributing Factors: Process environment deposition. Reactions or degradation of the elastomer. Non-semiconductorgrade elastomer.

Suggested Solutions: Specify contamination level including manufacturing and packaging of the seals.

Abrasion

Description: The o-ring or seal or parts of it exhibit a flat surface parallel to the direction or motion. Loose particles and scrapes may be found on the o-ring or seal surface.

Contributing Factors: Rough sealing surfaces. Excessive temperature. Process environment containing abrasive particles. Dynamic motion. Poor elastomer surface

finish.

Suggested Solutions: Use recommended gland surface finishes. Consider internally lubed elastomers. Eliminate abrasive components.


Compression Set, Outgassing/Extraction and Installation Damage

Compression Set

Description: The o-ring or seal exhibits a flat-sided cross-section, the flat sides corresponding to the mating seal surfaces.

Contributing Factors: Excessive compression. Excessive temperature. Incompletely cured elastomer. Elastomer with high compression set. Excessive volume swell in chemical.

Suggested Solutions: Low compression set elastomer. Proper gland design for the specific elastomer. Confirm material compatibility.

Outgassing/Extraction

Description: This failure is often very difficult to detect from examination of the o-ring or seal. The o-ring or seal may exhibit a decrease in crosssectional size.

Contributing Factors: Improper or improperly cured elastomer. High vacuum levels. Low hardness/plasticized elastomer.

Suggested Solutions: Avoid plasticized elastomers. Ensure all seals are properly post-cured to minimize outgassing.

Installation Damage

Description: The o-ring or seal or parts of it may exhibit small cuts, nicks or gashes.

Contributing Factors: Sharp edges on glands or components. Improper sizing of elastomer. Low-modulus/hardness elastomer. Elastomer surface contamination.

Suggested Solutions: Remove all sharp edges. Proper gland design. Proper elastomer sizing. Higher-modulus/hardness elastomer.

Aerospace Standard AS568AO-ring Sizing Chart

These o-ring sizes are standard throughout the o-ring industry and also in most military applications. The SAE published the original document that established these o-ring sizes. The AS in AS568A stands for Aerospace Standard.

We are publishing the entire Aerospace O-ring Standard AS568A sizing chart for your convenience.

There are no standard o-ring sizes for metric o-rings. We have many sizes of metric o-rings in

stock and can easily manufacture what you need if we have already have a tool for that particular o-ring size. If not, we will be able to have your o-ring size manufactured but a tooling charge may apply.

If you have any questions or problems with o-ring sizes or this sizing chart, please contact us.

Product InformationO-Rings and Seals

Product Description

'AN' Style Wipers Snap in rod wipers

Back-ups Anti-extrusion devices

Buffer Rings Rod buffer rings

Caps & Plugs Polyethylene & vinyl protectors

Cat Lock Nuts Lock nuts

Cord Static & dynamic seals

* Copyright for photograph

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Crown Seals Double acting rod & piston seals

'D' Style Wipers Snap in rod wipers

'D' Style Wipers Stepped Stepped snap-in rod wipers

Disogrin U-Cups Single acting rod & piston; RO, PI, SY

Double Acting Fluid Seals Double acting piston ring with anti-extrusion rings

Double Acting P-Cups Piston head assembly double acting

'H' Style Wipers Snap in rod wipers

Homo U-Cups Rubber rod & piston seals

K-Seals Single acting rod & piston seals for pneumatic applications

'K' Style Wipers Snap in rod wipers

Lathe Cut Rings Static & dynamic seals

Metal Encased Wipers Metal clad rod wipers

Modular Bearings Anti-extrusion bearing rings

Oil Seals Rotary shaft seals with single and double lips

O-ring Kits O-ring kits to your exact specifications including printed descriptions

O-Rings Static & dynamic seals

Piston Cups Single and double acting piston seals

Piston Rings Square section double acting

Piston Rings, cont. Rectangular section double acting

Piston Rings, cont. Agricultural double acting

Piston Rings, cont. Chem-cast double acting

Piston Rings, cont. Cast iron double acting

Piston Rings, cont. CAT style 2-piece double acting

Poly Seals Single acting rod & piston

X-Rings Four lobed o-rings

Rubber O-rings Rubber o-rings and seals

Single Acting Fluid Seals Single acting rod & piston seals

Sleeve Mesh Protective netting

Spectra Seals Spring energized teflon seals

Thread Fitting Plugs Polyethylene threaded protectors

T-Seals Double acting rod & piston seals

T-Seals, cont. Capped T-seals 4-piece double acting

Uni-Rings Double acting rod & piston seals

Valve Seals Teflon seat rings and stem packing

Vee Packing Rod & piston seals and single & double acting










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V-Seals Rotary shaft seal types: VA, VE, VL, VS

Wear Rings Bearing rings of rods & pistons

Z-Seals Single acting rod & piston

O-Rings and SealsProducts Page 3

Product Description

Metal Encased Wipers

Metal clad rod wiper. An excellent heavy duty rod scraper, with a metal case to enable press-in applications. Used where dirt and ice conditions are severe, such as found on bulldozers, graders, and backhoes. Back

'D' Style Wipers

Snap-in rod wiper. Used in applications where conditions are abrasive and severe. This simple design snap-in wiper is commonly used in most hydraulic and downhole applications. Back

'AN' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are not severe. Commonly used in machine tool cylinders, such as valve operators and positioning cylinders. Back

'H' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are not severe. The double lip can also act as a rod seal in low pressure pneumatic cylinders. Back

'K' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are considered moderate. Commonly used on telescopic cylinders, dump trucks, lift trucks, and tailgate cylinders. Back

'D' Style Wipers

Stepped

Stepped snap-in rod wiper. A medium duty rod wiper that fits into a stepped groove. This wiper has the similar characteristics to the D-style wiper. Back

Double Acting

Fluid Seal

Double acting piston ring with anti-extrusion rings. This seal consists of a composite NBR 80 Shore and NBR impregnated cotton seal element. Complete with anti-extrusion wear rings for higher pressure capabilities. Back

Single Acting

Fluid Seal

Single acting rod & piston seal. This seal is similar to the polyseal. A good seal for lower pressure gland applications and for piston head applications where an adequate bearing is provided. Back

Uni-Rings Double acting rod & piston seal. The uniring consists of two bonded laminae. A hard 60 duro 'D', abrasion

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resistant seal, and a softer resilient activating lamina, which functions as an expander. Therefore radial preload and appropriate pressure activation are assured. Back


Product Description

O-RingsBackCordBack

Lathe Cut RingsBack

Static & dynamic seal. The O-ring is the simplest, most ingenious and effective sealing device. Because of its simple construction, the O-ring is readily adaptable to applications with limited space. It will effect a dependable dynamic and static seal through wide ranges of pressures and temperatures. Cord stock is also available in a full range of cross sections.

Back-Ups Anti-extrusion device. Back-ups are recommended for all O-ring applications with pressures over 1000 P.S.I. Available in contoured Nitrile; solid, split and spiral Teflon. Back

X- Rings Four-lobed O-ring. The X-Ring actually provides twice the number of sealing surfaces as an O-ring. The four-lobe design offers lower fiction than an O-ring, and due to the square cross section it resists spiral twist. Back

Poly Seals Single acting rod & piston seal. A pre-loaded elastomeric spring insures positive lip-contact at low pressure and vacuum conditions. The hydrostatic transfer of pressure through the elastomeric spring to the sealing lips provide a positive seal at high pressures. Excellent rod & piston seal for pressures to 5000 P.S.I. Back

Disogrin U-Cups

Single acting rod & piston seal. RO, PI & SY. An unloaded u-cup which provides lower friction in heavy duty rod and piston applications. Engineered for close tolerance and high pressure applications. Back

Z-Seals Single acting rod & piston seal. This seal is a squeeze type seal, combining the excellent sealability of an elastomeric seal element with the anti-extrusion characteristics of a hard thermoplastic base. Back

Modular Bearing

Anti-extrusion bearing ring. Modular bearings are incorporated with rod seals to prevent extrusion and compensate for side loading. Generally made of a hard thermoplastic material. Back











Spectra Seals

Spring energized Teflon seal. This seal consists of a U-shaped jacket made from various PTFE's, and is energized by a V-spring element. It's exceptional operating temperature range, chemical resistance, low-friction, and no-freeze characteristics allows for a wide range of uses. Back

K-Seals Single acting rod & piston seals for pneumatic applications. A light action seal designed primarily for nonlubricated pneumatic systems. Its unique design offers low friction, positive sealing, and long life generally expected from polyurethane. Back


Product Description

Piston Cups Single & double acting piston seal. Available in a composite rubber impregnated cotton, duck, homogeneous rubber, and urethane materials. Piston cups require a follower plate to hold the cup to the piston. Back

Double Acting P-Cups

Piston head assembly double acting seal. Made of homogeneous rubber bonded to a steel insert. This seal is designed to be bolted directly to the rod, thus making a simple, dependable, and cost effective piston seal. Back

Cat Lock Nuts

Lock nut. Manufactured from the finest quality steel, and heat treated to offer the proper strength for critical locking applications. Back

Buffer Rings Rod buffer ring. The buffer ring acts as a cushion seal in applications where shock loading is severe. The use of a buffer will increase rod seal life. Back

Wear Rings Bearing rings of rods & pistons. Wear rings are non-metallic bearings that support, guide and reduce friction between the fixed and reciprocating parts of hydraulic and pneumatic cylinders. Back

Vee Packing Rod & piston seal single & double acting seal. A multi-lip seal set consisting of top and bottom adaptors, and a number of Vee rings to provide the sealing surfaces. Generally used as valve stem packing, downhole applications, and multi-stage telescopic cylinders. Back

V-Seals Rotary shaft seal Types: VA, VE, VL, VS. The V-ring is made entirely of rubber. It is mounted on and rotates with the shaft. The lip seals against the housing, and the body of the seal holds the lip in position as well as seals against the shaft. Back

Caps & Plugs Polyethylene & viny protectors. Inexpensive and versatile, tapered caps and plugs are used to protect tubing, threaded and machined parts from moisture, dust, and impact damage. Back











Thread Fitting Plugs

Polyethylene threaded protectors. Plastic threaded protectors designed to fit flared and flareless hydraulic fittings, SAE O-rings ports, NPT pipe fittings, tube ends, and E.U.E. Back

Sleeve Mesh Protective netting. A stretchable plastic webbing material that protects smooth, threaded, machined, painted, or plated cylindrical parts. Available in mini or maxi coils. Back

Valve Seal Teflon seat rings & stem packing. Teflon seat rings available for various types of valves. U-packers, fabric vee sets, and fabric/Teflon vee sets available as stem packing for OEM replacement. Back


Product Description

Piston Rings

Square section double acting. A low cost, but effective seal for hydraulic and pneumatic cylinders. An excellent low friction, highly pressure sensitive sealing product in high frequency cylinders. Back

Rectangular section double acting. An effective and low cost piston ring. The rectangular shape has added stability to contend with shock loading. These seals also offer low friction and are highly pressure sensitive. Back

Agricultural double acting. This piston ring offer the same characteristics as the Rectangular Section Piston Ring. Commonly found on J.I. Case, John Deere, and White equipment. Back

Chem-Cast double acting. This piston ring consists of a reinforced thermoplastic OD sealing ring and an oval elastomeric expander ring. The Chem-Cast piston ring is an excellent seal at pressures to 50,000 P.S.I. Back

Cast Iron double acting. This ring is specially alloyed to provide an excellent combination of wear characteristics, temperature stability and impact strength for most standard hydraulic and pneumatic applications. Back

CAT Style 2-piece double acting. This rectangular section piston ring incorporates a Moly PTFE seal element for lower friction characteristics, with a rectangular Nitrile expander. The most common piston ring on Caterpillar. Back

T-Seals Double acting rod & piston seal. For use in long stroke hydraulic applications when spiral failure due to rolling in the seal groove has occurred. The T-Seal has hard nylon back-up rings to prevent extrusion at high pressures. Back

Capped T-Seal 4-piece double acting. This seal is a high pressure, high performance seal. It has excellent











extrusion resistance and low friction and wear characteristics. Found on Caterpillar, Hitachi, & John Deere equipment. Back

Homo U-

CupsRubber rod & piston seal. A low cost compact seal for pneumatic and low pressure hydraulic cylinders. An effective rod and piston seal on actuating cylinders. Back

Crown Seals

Double acting rod & piston seal. The crown seal is double acting, requiring one groove for a piston application. This seal will directly interchange in the grooves designed for T-Seals, O-Rings, & X-Rings. Back

Oil Seals

Note: We have many types of standard oil seals and specialty oil seals, so please call so we can help you pick out exactly what you need.

In terms of overall seal design, the following will give a brief explanation of some of the broad oil seal categories we commonly work with. Oil seals are classified according to the sealing element and the structure. The classification by sealing element corresponds to the first letter in the oil seals P/N style. The classification by structure corresponds to the second letter.

Classification by Element:

S: Standard oil seals with a single sealing lip design. They are used to seal against internal media.Limitations: Peripheral Speed: 12 m/secTemperature: 120°C (250°F)Pressure: 0.3 Kg/cm2 (5-10 psi)

T: Oil seals with a double sealing lip design. The main lip seals against internal media, while the auxiliary lip (dust lip) provides protection against external dirt and dust.Limitations: Peripheral Speed: 10 m/secTemperature: 120°C (250°F)Pressure: 0.3 Kg/cm2 (5-10 psi)

V: An oil seal design where no spring is loaded. The flexible sealing element is used to seal internal media. It is suitable for sealing grease and protecting against dirt and dust. It can also be used along with other types of seals.Limitations: Peripheral Speed: 8 m/secTemperature: 120°C (250°F)Pressure: 0 Kg/cm2 (3 psi)




K: Oil seals where no spring is loaded. The flexible sealing element is used to seal against both internal and outer media and provides protection against dirt and dust.Limitations: Peripheral Speed: 5 m/secTemperature: 120°C (250°F)Pressure: 0 Kg/cm2 (3 psi)

D: This oil seal style is intended for sealing against both internal and external media. It is usually used to separate two liquids. The area between the two lips must be lubricated with grease, etc.Limitations: Peripheral Speed: 5 m/secTemperature: 120°C (250°F)Pressure: 0.3 Kg/cm2 (5-10 psi)

TX4: This design for oil seals is intended for reciprocating motion (not for rotary), especially for pressurized media.Limitations: Reciprocating Speed: 0.3m/secTemperature: 120°C (250°F)Pressure: 7Kg/cm2 (100 psi)

Classification by Structure:

Code Characteristics

C A rubber covered case - can be used on any shaft size. It prevents the metal case from rusting, corrosion, and prevents damage to the housing bore during assembly. Also, it is the most effective structure design to prevent bore leakage in oil seals.

B/BX2 A metal case - mainly used on shafts for which the diameters are below 150 mm.

A/AX2 A reinforced case - mainly used on shafts larger than 150 mm, or smaller shafts that require extra strength in the metal case.

BC Rubber covered "end-cap" plug - solid caps and no center hole. For sealing additional shaft location holes (shaft added later). For multiple hole housings requiring seal plug for unused shaft holes.

O-Ring Kits

Need to provide your customers with o-ring kits to install or repair your products? We specialize in making o-ring kits that are to your exact specifications. You choose the exact o-rings sizes you want and the materials for each o-ring. You tell us exactly

what you want printed on the description that goes with the kit. We take care of the rest.

Because we work with you to provide "just in time inventory," you can just give us a blanket order for your yearly usage. We will make them up and keep them in stock for you until you need them. You can have us send you as many o-ring kits as you want exactly when you need them.

We are completely flexible in providing our customers with exactly what they need. For example, we have one customer that orders hundreds of kits at a time. The flyer they use includes company information and directions on how to use the o-rings. Another customer orders a much smaller quantity of o-ring kits and they may have us ship them as few as ten at a time. Their flyer gives cautions on the types of chemicals that are not compatible with the elastomer.

If you are looking for an o-ring kit we recommend you call and talk to one of our engineers about designing exactly what you need. Too often people buy standardized o-ring kits only to find that some of the sizes they need are not there and they end up using a very small percentage of the o-rings in it.

Absolutely any size can go into the o-ring kit:

AS568A Standard sizes Metric sizes (you may need to purchase a tool to make metric sizes if we do

not have them in stock)

Absolutely any materials can be used for the o-rings:

Viton® Kalrez® Chemraz® Viton® Extreme™ ETP Simriz® Nitrile (buna-n) Neoprene Rubber Silicone Polyurethane Teflon encapsulated elastomers


Product Description

Piston Rings









Capped T-Seal 4-piece double acting. This seal is a high pressure, high performance seal. It has excellent extrusion resistance and low friction and wear characteristics. Found on Caterpillar, Hitachi, & John Deere equipment. Back

Homo U-


Crown Seals



Product Description










Piston Rings








Capped T-Seal 4-piece double acting. This seal is a high pressure, high performance seal. It has excellent extrusion resistance and low friction and wear characteristics. Found on Caterpillar, Hitachi, & John Deere equipment. Back

Homo U-


Crown Seals


Rubber O-rings











When we talk about "rubber" o-rings, we are using the term "rubber" to describe a whole host of o-rings that are made from a synthetic rubber-like material called an elastomer. We are not talking about o-rings made from natural rubber. Even though today the properties of natural rubber can be enhanced during the manufacturing process through a combination of adding ingredients to the liquid rubber mixture and then vulcanization or heating the mixture, the synthetic elastomers have superior properties over the natural rubber ones.

We offer all types of rubber o-rings from many compounds. We have rubber o-rings in a wide range of standard and non-standard sizes, everything needed for almost all sealing applications. One measures o-ring sizes by the inside diameter (ID) and the cross section (W). We carry all the standard sizes in the Aerospace Standard AS568A specifications. In addition, we have many non-standard sizes in both inches and metric measurements. If we do not have the size you need, we can custom design and make anything you need.

We also provide rubber o-rings in many types of elastomers including Viton®, Viton® Extreme™ ETP, Kalrez®, Chemraz®, Simriz®, nitrile (Buna-N), hydrogenated nitrile (HNBR), silicone, fluorosilicone, ethylene-propylene (EPR, EPDM), neoprene, polyurethane, Ethylene Propylene, and teflon encapsulated elastomers. We are certified by DuPont Dow Elastomers to sell Viton®, Viton® Extreme™ ETP and Kalrez®. These rubber o-ring compounds can be manufactured by molding or extrusion as well as rubber to metal bonding. We can provide you with standard rubber products or customized molded rubber products.

Here are a few tips for rubber o-rings:

The more extreme the temperature of your application, the shorter the life of your seal.

Rubber o-rings for static applications are more forgiving and will work with a wider range of materials than dynamic applications.

The higher the temperature, the more vulnerable your rubber o-rings are to harsh chemicals.

When installing, do not stretch the seal more than 5% because you can lose seal compression.

The maximum volume of the o-ring should never be more than the minimum volume of the gland.

The groove depth must be less than the o-ring cross-section and the groove width must be larger than the o-ring cross-section.

A general rule is to compress static o-ring cross-sections about 10% to 40% and dynamic ones about 10% to 30%.

Coat the rubber seals with an o-ring lubricant before you install them. Use o-ring lubricants that are compatible with all the fluids in your application

and do not use a lubricant that is made from the same material as the seal. You will not know for sure if your seals are right until you test them in your

actual application.

By the way, if you were interested in buying rubber o-rings, here are some specifications that might be interesting to you:

http://www.pspglobal.com/o-ring-sizes.html

http://www.pspglobal.com/o-ring-sizes.html

http://www.pspglobal.com/rubber-o-ring.html

Natural rubber is a manufactured product from the juice of the Hevea rubber tree (which is actually latex). The manufacturing process includes adding other ingredients and vulcanization (heating the liquid rubber).

The main use for natural rubber is for seals in automotive brakes plus food and beverage applications. It does not work well in hydraulic sealing applications.

The temperature range for most compounds is -60° to +220°F, dry heat only. The hardness range is from 40 to 90 durometers.

Metric O-rings and Seals

If you need metric o-rings or seals, please talk to us. We have some metric sizes in stock and can ship immediately. If you have an unusual size we do not stock, we can manufacture the part for you (there may be a tooling charge however).

In general, when you are thinking of o-rings for a product from the U.S., you are looking for o-rings measured in inches and when looking for a product manufactured in the rest of the world, you will want metric o-rings. However, the metric system is being used more and more in the U.S. for o-rings. The United States Metric Association says, "Just as English has become the global language of commerce, the metric system has become the global language of measurement."

BACKGROUND

The metric system was started way back in 1670 in France by Gabriel Mouton. He proposed a decimal system of measurement based on several physical measurements that will not vary. Over the years his work was improved on by a number of French scientists. Actually the metric system took quite a long time to become official in France (from 1670 to 1795) and went through periods of favor and disfavor during that time.

Eventually the metric system was adopted by almost all countries in the world, the U.S. being the notable exception. Because of the standardization of the measurements and the fact that math calculations are easy with the decimal system which is utilized by the metric system, it is well suited for all scientific and engineering work as well as for sizing o-rings.

Of course, metric o-rings are popular in a world which is rapidly developing technology. In the U.S. a law was passed in 1866 that said it is "lawful throughout the United States of America to employ the weight and measures of the metric system in all contracts, dealings or court proceedings." No law has been passed making the inch-pound system legal. The units of the inch-pound system were not officially defined in the courts until 1893 and then they were defined in terms of the metric standards.

A FEW CATEGORIES OF METRIC O-RINGS AND SEALS

Metric O-rings: These are seals that are shaped like a doughnut. They can be made from any elastomer such as Viton, Kalrez, Chemraz, Simriz, nitrile, silicone, neoprene, polyurethane, teflon encapsulated elastomers, and more.

Dynamic O-rings and Seals: These are seals that are in an application where there are moving parts.

Static O-rings and Seals: Metric o-rings or seals in an application where nothing is moving.

Oil and Grease Seals: They are designed with a lip that fits tightly against a shaft or housing that prevents fluids from moving from one side of the seal to the other.

Wipers and V-ring Seals: These are called exclusion seals because they prevent fluids from moving from one side of the seal to the other.

Hydraulic and Pneumatic Seals: A class of seals that include piston seals, rod seals, u-cups, vee-packing and flange packings; hydraulic seals work in an application with fluids and pneumatic seals work with air.

Metric O-ring Belts: These are power transmission belts.


Product Description

Metal Encased Wipers

Metal clad rod wiper. An excellent heavy duty rod scraper, with a metal case to enable press-in applications. Used where dirt and ice conditions are severe, such as found on bulldozers, graders, and backhoes. Back

'D' Style Wipers

Snap-in rod wiper. Used in applications where conditions are abrasive and severe. This simple design snap-in wiper is commonly used in most hydraulic and downhole applications. Back

'AN' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are not severe. Commonly used in machine tool cylinders, such as valve operators and positioning cylinders. Back

'H' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are not severe. The double lip can also act as a rod seal in low pressure pneumatic cylinders. Back

'K' Style Wipers

Snap-in rod wiper. A light duty wiper for use on pneumatic and hydraulic cylinders where conditions are considered moderate. Commonly used on telescopic cylinders, dump trucks, lift trucks, and tailgate cylinders. Back

'D' Style Wipers

Stepped

Stepped snap-in rod wiper. A medium duty rod wiper that fits into a stepped groove. This wiper has the similar characteristics to the D-style wiper. Back

Double Double acting piston ring with anti-extrusion rings.







Acting Fluid Seal

This seal consists of a composite NBR 80 Shore and NBR impregnated cotton seal element. Complete with anti-extrusion wear rings for higher pressure capabilities. Back

Single Acting

Fluid Seal

Single acting rod & piston seal. This seal is similar to the polyseal. A good seal for lower pressure gland applications and for piston head applications where an adequate bearing is provided. Back

Uni-Rings Double acting rod & piston seal. The uniring consists of two bonded laminae. A hard 60 duro 'D', abrasion resistant seal, and a softer resilient activating lamina, which functions as an expander. Therefore radial preload and appropriate pressure activation are assured. Back


Product Description

Piston Cups Single & double acting piston seal. Available in a composite rubber impregnated cotton, duck, homogeneous rubber, and urethane materials. Piston cups require a follower plate to hold the cup to the piston. Back

Double Acting P-Cups

Piston head assembly double acting seal. Made of homogeneous rubber bonded to a steel insert. This seal is designed to be bolted directly to the rod, thus making a simple, dependable, and cost effective piston seal. Back

Cat Lock Nuts

Lock nut. Manufactured from the finest quality steel, and heat treated to offer the proper strength for critical locking applications. Back

Buffer Rings Rod buffer ring. The buffer ring acts as a cushion seal in applications where shock loading is severe. The use of a buffer will increase rod seal life. Back

Wear Rings Bearing rings of rods & pistons. Wear rings are non-metallic bearings that support, guide and reduce friction between the fixed and reciprocating parts of hydraulic and pneumatic cylinders. Back

Vee Packing Rod & piston seal single & double acting seal. A multi-lip seal set consisting of top and bottom adaptors, and a number of Vee rings to provide the sealing surfaces. Generally used as valve stem packing, downhole applications, and multi-stage telescopic cylinders. Back

V-Seals Rotary shaft seal Types: VA, VE, VL, VS. The V-ring is made entirely of rubber. It is mounted on and rotates with the shaft. The










lip seals against the housing, and the body of the seal holds the lip in position as well as seals against the shaft. Back

Caps & Plugs Polyethylene & viny protectors. Inexpensive and versatile, tapered caps and plugs are used to protect tubing, threaded and machined parts from moisture, dust, and impact damage. Back

Thread Fitting Plugs

Polyethylene threaded protectors. Plastic threaded protectors designed to fit flared and flareless hydraulic fittings, SAE O-rings ports, NPT pipe fittings, tube ends, and E.U.E. Back

Sleeve Mesh Protective netting. A stretchable plastic webbing material that protects smooth, threaded, machined, painted, or plated cylindrical parts. Available in mini or maxi coils. Back

Valve Seal Teflon seat rings & stem packing. Teflon seat rings available for various types of valves. U-packers, fabric vee sets, and fabric/Teflon vee sets available as stem packing for OEM replacement. Back

Elastomers

Polymer chemistry is the backbone of our business. By carefully matching the customer's needs with our polymer technology, the optimum sealing solution for both performance and economy can be chosen.

Selecting A Sealing Elastomer

Types of Polymers

O-ring and Seal Materials

Common Polymers in Semiconductor Process Equipment

Nitrile (Buna-n) O-rings

Teflon Encapsulated O-rings

History of Polymers

Elastomer Processing - Part 1




Material Specifications - Part 1, ASTM D 2000

Material Specifications - Part 2, Japanese Industrial Standard (JIS) B 2401 O-rings

http://www.pspglobal.com/material-specifications-2.html




http://www.pspglobal.com/polymer-processing-4.html




http://www.pspglobal.com/polymers.html

http://www.pspglobal.com/teflon-encapsulated-o-rings.html

http://www.pspglobal.com/nitrile-buna-n.html

http://www.pspglobal.com/polymer-chart.html

http://www.pspglobal.com/polymers-elastomers.html

http://www.pspglobal.com/polymers-types.html

http://www.pspglobal.com/polymer-selection.html






Material Specifications - Part 3, Other Specifications

Selecting A Sealing Elastomer

The selection of a sealing elastomer may seem daunting. By first understanding the basic chemical alternatives and properties, however, the selection process is simplified. Knowledge of an elastomer's properties is useful in predicting seal performance. The proper combination of chemical compatibility, thermal stability, contamination potential and physical properties will provide the user with the optimum seal.

The seal industry uses many tests to determine an elastomer's chemical and thermal compatibility as well as physical properties which can have a great influence on the performance in high-pressure or vacuum environments. These properties can provide an insight into the mode of degradation or the retention of sealing properties-all useful information in predicting seal life or comparing economic alternatives.

Another difference in elastomer compounds is the compounding (or mixing) of ingredients. These factors can provide unique pigmentation, improved specific chemical or thermal properties, improved dynamic performance, reduced cost, improved electrical properties, reduced friction or sticking, and many other aspects of seal performance.

Types of Polymers

1. Thermoplastics (can be melted with the application of heat). Crystalline

crystallize when cooled

Amorphousno crystallization when cooled

Semicrystallinpolymers which contain both crystalline and amorphous segments


2. Thermosets (degrade rather than melt with the application of heat)

3. Elastomers (cross-linked)

Plastics are rigid long-chain polymers which are not usually connected or cross-linked. Plastics can either be thermoplastic-meaning they can be heated and cooled without changing propertiesor - thermoset, where an increase in temperature changes the chemical structure and properties. As a class, plastics have low elongation and high elongation set.

Elastomers are flexible long-chain polymers which are capable of cross-linking. Cross-linking chemically bonds polymer chains which can prevent reversion to a non-cross-linked polymer at elevated temperatures. The cross-link is the key to the elastic, or rubbery, properties of these materials. The elasticity provides resiliency in sealing applications.

Thermoplastic elastomers (TPEs) often combine the properties of elastomers with the ease of processability of thermoplastics. They are the result of a physical combination of soft, elastic polymer segments and hard, crystalline segments which are capable of cross-linking. Thermoplastic elastomers are generally classified by their structure rather than their chemical makeup.

O-Ring and SealMaterials

Elastomer & Temperatur

e

Applications Use With

These Fluids

Do Not Use With

These Fluids

Simriz®-10 C to +305 C

Compound Specific

Simriz® orings are molded of an elastomer that has the broadest chemical resistance of any elastomer. They combine the resilience and sealing force of an elastomer with chemical resistance approaching that of Teflon.

most chemicals

---

Aflas®-10 C to +204 C

Compound Specific

Aflas® is a unique fluoroelastomer resistant to petroleum oils, steam, hydrogen sulfide and amine corrosion inhibitors. This compound is generally used for sour gas oil field services.

petroleum oils, H2S,

steam

acetone, lacquers

Carboxilated Nitrile

-54 C to +135 C

A nitrile elastomer with low temperature and excellent abrasion resistance. Commonly used in Downhole applications.

petroleum oils, water

brake fluid,

phosphate esters

DuPont Performance Elastomers

Viton®-40 C to +204 C

Compound Specific

Featuring excellent resistance to petroleum products and solvents, with good high temperature and low compression set characteristics. For use with wide chemical exposure situations, and with low gas permeability, it is also suited for hard vacuum service.

petroleum oils,

gasoline, transmission

fluid

acetone, H2S, hot water, amines

Ethylene Propylene

-54 C to +150 C

Ethylene Propylene has excellent ozone and chemical resistance characteristics. Generally used in automotive brake systems.

brake fluids, refrigerants,

steam

petroleum oils,

diester lubricants

Fluorosilicone-56 C to +204 C

Fluorosilicone combines the good high and low temperature stability of silicone with the fuel, oil, and solvent resistance of fluorocarbon.

petroleum oils,

gasoline

acetone, ethyl

acetate

Highly Saturated

Nitrile (HSN, HNBR)

-26 C to +160 C

A nitrile elastomer with excellent resistance to petroleum oils, and sour gas. With the extended temperature range, HSN is becoming a preferred compound in the oil patch.

petroleum oils, H2S,

CO2

brake fluid

Neoprene-40 C to +135 C

Due to its excellent resistance to freon and ammonia, Neoprene is widely accepted as a preferred elastomer for refrigeration seals.

refrigerants, alcohol, ozone

petroleum oils,

Toluene

Nitrile (Buna-N)

-40 C to +135 CNitrile (Low-

Temp)-65 C to +120 C

Presently the seal industry's most widely used elastomer. Nitrile combines excellent resistance to petroleum based oils and fuels, silicone greases, hydraulic fluids, water and alcohols. It has a good balance of working properties such as low compression set, high tensile strength, high abrasion resistance, combined with a low cost.

petroleum oils,

water, hydraulic

oils

brake fluid,

ketones, phosphate esters,

H2S

Polyurethane-40 C to +105 C

An excellent elastomer with high abrasion resistance characteristics and high tensile strength. Used in high pressure hydraulic systems where highly stressed parts are subject to wear.

petroleum oils,

hydraulic oils

brake fluid

Silicone-65 C to +260 C

Silicone elastomer is resistant to high, dry heat, in primarily static applications. It has low compression set characteristics and a wide temperature range.

dry heat, alcohol,

vegetable oil

petroleum oils & fuels

Teflon-20 C to +204 C

Teflon is a tough, chemically inert elastomer possessing an incredible working range. For static and slow intermittent dynamic situations. Teflon

most chemicals

---

is hampered only by it's poor memory at low temperature.

Data is presented for use only as a general guide and should not be the basis for design decisions. If you need help choosing the right material for your application, just give us a call at 303-758-2728.

Common Polymers in SemiconductorProcess Equipment

ASTM

Polymer Trade Names Monomers

PLASTICS

Polyamideimide (PAI) TORLON®

Polybenzimidazole (PBI)

CELAZOLE® -(C7H6N2)-

Polycarbonate (PC) -COOC6H5C(CH3)2C6H5O-

Polyethylene (PE) -CH2CH2-

Polyetheretherketone (PEEK)

KETRON® -C6H5-CO-C6H5-O-C6H5-

Polyetherimide (PEI) ULTEM®

Polyimide (PI) DURATRON® N(C2O2)C6H5(C2O2)N-R-

Polypropylene (PP) CH2CH(CH3)-

Polyphenylenesulfide (PPS)

TECHTRON®

Polyvinylidine Fluoride (PVDF)

-CH2CF2-

Fluorinated Ethylene-Propylene (FEP)

TEFLON® FEP -CF2CF2-CF2CF(CF3)-

Perfluoroalkoxy (PFA) TEFLON® PFA -CF2CF2-CF2CF(OCF3)-

Polytetrafluoroethylene (PTFE)

TEFLON® PTFE -CF2CF2-

ELASTOMERS

NBR Nitrile (Buna-N) PARACRIL®, CHEMIGUM®

-CH2CH=CH(CH2)2CHCH(CN)-

EPDM Ethylene-Propylene Diene

VISTALON®, NORDEL®

-CH2CH2-CH2CH(CH3)-

VMQ Silicone SILASTIC®, SILPLUS®

-OSi(CH3)2-OSi(CH3)(CH=CH2)-

FVMQ Fluorosilicone SILASTIC® LS, FSE® -OSi(CH3)(CH=CH2)-OSi(CH3)(CH2CH2CF3)-

FKM Fluoroelastomer A VITON®, FLUOREL®

-CH2CF2-CF2CF(CF3)-

Fluoroelastomer B -CH2CF2-CF2CF(CF3)-CF2CF2-

Fluoroelastomer GF -CH2CF2-CF2CF(OCF3)-CF2CF2-

Fluoroelastomer ETP VITON®, ETP® -CF2CF2-CF2CF(OCF3)-CH2CH2-

Fluoroelastomer TFE/P AFLAS® -CF2CF2-CH2CH(CH3)-

FFKM Perfluoroelastomer (PFE)

AEGIS® CHEMRAZ® -CF2CF2-CF2CF(OCFnCF3)-

OTHER

VF2/CTFE KEL-F® -CH2CF2-CF2CFCl-

Compounds for Nitrile O-Rings (Buna n)

Nitrile (buna n) is a copolymer of butadiene and acrylonitrile, a compound that is commonly used in o-rings. It is the acrylonitrile that brings the strong resistant to petroleum products to the combination. As more acrylonitrile is put into the mixture of the two components, the resistance of the nitrile o-rings to petroleum products increases. Unfortunately, at the same time, the low temperature flexibility of the nitrile o-rings decreases with more acrylonitrile. Thus, compounding nitrile (buna n) becomes a balancing act. If one wants good flexibility at low temperatures, some hydrocarbon fuel and petroleum oil resistance at high temperatures will have to be sacrificed.

Because of the resistance to fuel and oil, and the reasonable cost, more o-rings are made from nitrile (buna n) than any other elastomer. In addition to use with petroleum oils and fluids, nitrile o-rings are used for cold water, silicone greases and oils, Di-ester base lubricants and ethylene glycol base fluids. They do not do well with ozone, sunlight and exposure to weather.

Sometimes knowing exactly which compound should go into the nitrile o-rings for your application is difficult. We are happy to talk about your situation and help you solve sealing problems.

Teflon Encapsulated O-Rings

Teflon is actually not an elastomer, it is a plastic. Our teflon encapsulated o-rings consist of a seamless teflon jacket over an elastomer core made from Viton® or silicone. (Actually several options for the core material and shape are possible.) The combination of a chemically resistant polymer jacket over a low-compression set elastomer provides unique properties. In general, teflon encapsulated o-rings are

chemically resistant and used to prevent the passage of corrosive fluids or gases in an application. While the outer teflon is resistive and hard, the core elastomer provides the memory of the o-rings when they are put under a compressive force.

Since teflon is practically chemically inert it means that the o-rings are able to resist almost all chemicals and keep the corrosive fluids and gases from getting through to the elastomer.

The extremely low coefficient of friction of teflon makes encapsulated o-rings an ideal choice when you are worried about surface wear.

Teflon exhibits a useful service life over a wide range of temperatures, from below -100° F, to temperatures of over 500° F. Its resistance to solvents remains excellent throughout a wide range of temperatures also. In addition, the low dielectric constant and electrical resistance also remain intact throughout this range.

Advantages of teflon encapsulated o-rings:

Chemically resistant Thermal stability from -76° to 500° Fahrenheit Low surface coefficient of friction (0.1 to 0.2) Low permeability Low compression set Economical, sometimes they replace o-rings or more expensive

materials such as Kalrez® Non-stick surface for easy clean-up Eliminates contamination of fluids by elastomers Complies with FDA regulations Nonflammable Reusable High impact strength Easy to lubricate Smooth surface No swelling Low cold flow Wide range of sizes

Our teflon encapsulated o-rings consist of teflon FEP and teflon PFA encapsulated over a Viton® core or silicone core. They are manufactured in a variety of shapes and cross-sections to meet various applications.

Shapes of teflon encapsulated o-rings:

Circle Square Rectangle Oval Half-circle

In addition, custom cross-sections such as solid Viton or silicone square or rectangular cores are available. These are often used as gaskets in cam-action type couplings or as an alternative to PTFE or envelope gaskets in flange sealing applications.

History of Polymers

As far back as 1839, Charles Goodyear first improved the elastic properties of natural rubber by heating with sulfur (vulcanization). It was not until the 1930s that the macromolecule model of rubber was understood. After World War II and through the 1950s rapid developments in synthetic polymers were made. Most commercial high-performance elastomers trace their origins to the 1960s and 1970s.

Polymers are long chains of repeating chemical units, or monomers. The chemical skeletal structures may be linear, cyclic or branched. When one monomer is polymerized, the resultant polymer is called a homopolymer. Examples include polyethylene, polystyrene and polytetrafluoroethylene (PTFE). Copolymers (or dipolymers) are derived from the polymerization of more than one type of monomer. The distribution of monomers in these copolymers can be statistical, random or alternating. Examples include ethylene-propylene and fluorocarbon elastomers (vinylidene fluoride and hexafluoropropylene). Terpolymers are three-monomer-unit polymers, such as ethylene-propylene-diene (EPDM) and specialty fluorocarbon grades.

Elastomer ProcessingPart 1

Polymerization

The beginning step for elastomers is the polymerization of the backbone and cure-site monomers. This is typically done by large chemical companies such as Du Pont, Dow, GE, Ausimont, Daikin and Dyneon. Common techniques are emulsion, microemulsion, and suspension polymerization. Polymerization combines two or more process gases

(monomers) into an aqueous environment and under specific temperature and pressure conditions connects the individual monomers into the desired polymer. Initiating agents, buffers and other chemicals may be added to the polymer reactor to achieve the desired chemical properties and polymerization dynamics.

Isolation

The backbone polymers are isolated (brought out of the emulsion), cleaned and dried.

Chemical agents may be added at this step to isolate the polymer "latex" into a more usable form. Once the polymer is cleaned and dried, the "crumb" polymer is shipped to compounders (or O-ring molders) for mixing.

Compounding (mixing)

The "crumb" polymer is mixed with a cross-linking agent and other functional fillers. The cross-linking agent allows chemical bonds to form between the polymer backbones, thus providing resiliency to the material. Functional fillers include reinforcing fillers, pigments, anti-degradants, acid scavengers and process aids. These ingredients are typically mixed together on a 2-roll mill or other custom mixing machinery.


Types of Polymerization Reactions

1. Condensation Polymerization-yields polymers with repeating units having fewer atoms than the monomers from which they are formed. This reaction generally involves the elimination of small molecules such as H2O or HCl.

2. Addition Polymerization

3. Chain Polymerization/Free Radical Polymerization- o A. Initiation: formation of free radicals by scission of a single bond

(homolysis), or by the transfer of a single electron to or from an ion or molecule (redox).

o B. Propagation: growth of macromolecular structure. o C. Chain Transfer and Termination: completing the polymerization

step.

Types of Chain Polymerization Methods

Bulk Polymerization-involves only the monomer and a monomer-soluble initiator.

Solution Polymerization-a solvent lowers the viscosity, assisting heat transfer and reducing the likelihood of auto-acceleration.

Suspension Polymerization-reaction mixture is suspended as droplets in an inert medium. Polymer particles are produced in the form of beads in the range of 0.1 to 2 mm in diameter.

Emulsion Polymerization-the initiator is not soluble in the monomer but soluble only in the aqueous dispersion medium. Polymer is produced in the form of a latex with particles in the range of 0.05 to 1 micron.


Once the material is compounded, it is shaped into sheets and then molded.

Extrusion

The sheet compound is extruded into a configuration similar to the desired finished part.

Clean Extrusion

Molding

Most of the elastomeric O-rings used in the semiconductor industry are compression molded. A preshaped form is inserted into a multi-section mold and transferred to a heated press. Under heat and pressure, the elastomer flows into the mold cavities and chemical cross-linking takes place (or begins to take place, depending on the specific elastomer compound). After a period of time ranging from several seconds to several minutes, the parts are removed from the hot molds. Depending on the compound, mold releases are often used. These diluted spray coatings are often a derivative of fluoropolymers, or silicone-based polymers.

Compression Molding

Flash Removal

After the parts are removed from the molds, they contain thin "flash" as a result of the elastomer flowing in the multi-section mold. This "flash" is typically removed by exposing the parts to a cryogenic tumbling process. The elastomer is cooled and tumbled, causing the thinner "flash" section to become brittle and break away from the main part. Additional tumbling or handdeflashing may be required on some part designs or compounds.

Cryo-deflash Unit

Curing

Some high-performance elastomers are subjected to a post-curing operation. Elastomer parts are exposed to high temperatures in carefully controlled environments for several hours to complete the curing process. Additionally, this post-curing step removes excess water vapor and volatile process additives, thereby improving vacuum and contamination performance.

Post-cure Ovens


Finishing and Inspection

After the parts are removed from the curing ovens, the parts are again cleaned and inspected to ensure the parts meet the material and dimensional specifications.

Automatic Inspection Machine

Cleaning

After the parts are inspected, acceptable parts are delivered to the Class 100 clean room for cleaning and packaging. An ultrapure deionized water (UPDI) rinsing cycle removes surface contamination from the parts.

Clean Room

Packaging

Acceptable parts are then counted and packaged, either individually or in bulk, in a heat-sealed clean inner bag. The parts are then packaged in an outer bag, with a complete description of the parts, lot number, the batch and cure date.

Material SpecificationsPart 1

ASTM D 2000

Specifications for physical properties of elastomeric seals can be very general or extremely specific in nature. Probably the most common general classification

system is ASTM D 2000 “Standard Classification System for Rubber Products in Automotive Applications.” The purpose of this classification system is to aid in the selection of practical rubber products for specific environments. It also provides a “line call-out” designation for the specification of materials.

Rubber materials are designated by type (heat resistance) and class (oil resistance). The heat resistance of an elastomer is based on changes in tensile strength of not more than ± 30%, elongation of not more than –50%, and hardness of not more than ±15 points after 70 hours of aging at the specified temperature. The oil resistance is based on the volume swell of an elastomer after a 70-hour immersion in ASTM Oil No. 3.

An example of the general classification positioning of different elastomers is shown in the chart below.

The line call-out, or specification, contains appropriate information for testing and designation for a sealing elastomer. The example shown illustrates a typical line call-out:


Japanese Industrial Standard (JIS) B 2401 O-rings

Another general material specification standard is the Japanese Industrial Standard (JIS) B 2401 “O-rings.” The classification system recommended by this standard is twofold, by material and by size and use. The material classification is as follows:

Class Remarks

Duro TensileStrengt

h

Elongation

Compression Set

Marking

1 ANon-mineral oil use

70 > 8.0 200%40% (70hr@120°C) 1 Blue Dot

1 BNon-mineral oil use

90 > 12.0 80%40% (70hr@120°C)

2 Blue Dots

2Non-gasoline use

70 > 8.0 160%25% (70hr@100°C) 1 Red Dot

3

Non-animal or -vegetable oil use

70 > 8.0 120% 25% (70hr@100°C)

1 Yellow Dot

4 C Heat resistant

70 > 3.5 50% 30% (22hr@175°C)

None

4 D Heat resistant

70 > 8.0 160% 40% (22hr@175°C)

1 Green Dot


Other Specifications

Other standards exist for the purpose of classifying and specifying elastomers for specific applications or environments. Among these standards are the Society of Automotive Engineers (SAE), and many governmental agencies, including the military. SAE J120a “Rubber Rings for Automotive Applications” is a recommended practice for the design and specification for static and dynamic, 70 Shore A hardness seals. Materials are classified and may be marked as:

Class I— Oil-resistant service (yellow-colored stripe), or, Class II— Gasoline-resistant service (red-colored stripe)

The following table highlights several key Aerospace Material Specifications (AMS), Military (MIL), and National Sanitation Foundation (NSF) standards. These standards cover a wide range of sealing applications and materials. Many of these standards require independent or accredited laboratory certification of the materials. In some instances, Underwriter’s Laboratory (UL) approval is required.

Specification Duro Polymer Thermal (°F)

Description ISC Cpd

AMS 3301 40 Silicone –85 to 400° General Purpose S40





AMS 3307 70 Silicone Low Compression Set, Non-Oil Resistant

S70

AMS 3326 60 Fluorosilicone

Fuel & Oil Resistant F60

AMS 3357 70 Silicone Lubricating Oil & Compression Set Resistant

S70

AMS 7257 75 Perfluoro High Temperature Z7257

AMS 7259 90 Fluorocarbon V90

AMS 7268 70 Silicone High Temperature & Low Compression Set

S310

AMS 7276 75 Fluorocarbon High Temp. Fluid, Very Low Compression Set

V75

MIL-R-25988Class 1, Grade 60

60 Fluorosilicone

–90 to 350° Oil & Fuel Resistant F60


70 Fluorosilicone



80 Fluorosilicone


MIL-R-83248Type 1, Class 1

75 Fluorocarbon –20 to 400° High Temperature, Fluid & Compression Set

V75

MIL-R-83248Type 1, Class 2

90 Fluorocarbon –20 to 400° High Temperature, Fluid & Compression Set

V90

ZZ-R-765Class 2A & 2B Grade 40

40 Silicone –80 to 437° High Temperature & Low Compression Set

S40


50 Silicone –103 to 437°

Low Temperature & Low Compression Set

S314


50 Silicone –80 to 437° High & Low Temp. & Low Compression Set

S50


60 Silicone –80 to 437° Low Temperature & Low Compression Set

S60




S313



S70




S80



S80

Certain semiconductor equipment manufacturers and wafer fabrication companies have begun to express an interest in developing relevant specifications for the semiconductor industry. A possible forum for this effort may come through the Standards Committee of the Semiconductor and Equipment Materials International (SEMI).

Seals

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