Injection molding machine & some common polymer

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Injection Molding Machine & Some Common Polymer Khondoker Shafiqul Islam Ullash Assistant Manager (Operation) RFL-RPL (Shine-Bathware) Email : [email protected] Mobile : 01924-601330,01788- 56759

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Injection Molding Machine & Some Common Polymer Khondoker Shafiqul Islam UllashAssistant Manager (Operation)RFL-RPL (Shine-Bathware)Email: [email protected]: 01924-601330,01788-56759

TopicPlasticProcessing of PlasticsMoldingInjection MoldingBasic working Principle of injection molding MachineInjection Mold LayoutScrew Type Injection PressesPress ParametersClamping MechanismsMold TypeInjection Molding DefectsDefects & causeSafety of IMMCommon Problem & Important Fact & IMMSome Common Polymers Abbreviations

PlasticsThere are two types of plastics:Thermosets and Thermoplastics

Thermosets are NOT recyclable because they undergo a permanent chemical change when heated. This is known as heat hardening.

Thermoplastics are Recyclable because they only undergo temporary physical change when heated. When the heat is removed, they return to their original state. This is known as heat softening.In Our Bathroom Fittings Item We Use Thermoplastic.

Processing of PlasticsThere are a wide variety of manufacturing processes that exist for plastic production. A wide variety of plastic manufacturing processes existThe two different materials are used for the different processes. For example, Thermosets are usually used in Compression Molding, High Pressure Lamination, and Reaction Injection MoldingWhereas, Thermoplastics are usually used in Injection Molding, Extrusion, Blow Molding, Calendering.ExtrusionLamination (Calendaring) Thermoforming CastingMoldingExpansionFoamingSpinningSolid-Phase Forming

MoldingMolding is the most common plastic forming or finishing method. There are many different methods in plastic molding. Methods for molding include:Compression MoldingTransfer MoldingRotational MoldingReaction Injection MoldingBlow Molding Injection MoldingHere we use Injection Molding process for Bathroom & PVC fittings Manufacturing

Injection MoldingInjection molding is most popular process. This process is used to form complex plastic parts. By using this process we produces typical injection molded parts are fittings, Up Down stick, Up Down Block, Tap Body, Satu pan, Etc.Here is a pictorial of a typical injection molding machine and part. It is the most common of the plastic forming processes today, accounting for approximately 30% of all plastics produced.

BaseElectrical Control UnitInjection UnitClamping UnitBasic Part of Injection Molding Machine:

AlarmTie BarEjector Hydraulic CylinderFixed PartMonitor & Key boardMove ablePartEjector Plate & PinBaseToggleToggle BodyClamping & Hydraulic CylinderBasic Part of Injection Molding Machine: Clamping Unit

HopperMain BarrelHydraulic CylinderAuto LoaderHopper MagnateHopper DryerBasic Part of Injection Molding Machine: Injection Unit

Basic working Principle of injection molding Machine

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Basic working principle of injection molding machine is as follows-Plastic material is heated to the glass transition point (or beyond) and pressurized. The mold is closed.Pressurized plastic melt is forced into the mold.The mold remains closed while part hardness.Upon cooling, the mold opens, the part is removed and the process repeats.

The key points to this are getting the plastic to fill the mold and keeping it there, and then ejecting the part after it has solidified. To help ensure good fill, it must employ good fluid flow principles when designing the cavity.

Basic working Principle of injection molding Machine

Basic working Principle of injection molding Machine

one should try to avoid sharp corners in the runner system. In addition, after the part is filled, the packing pressure is maintained so the part will not shrink away from the wall during solidification. Another key design consideration is the process of ejecting the part. The part should hang on the moving side as it retracts pulling free of the fixed side. Then ejector pins push the part out of the moving side mold. To allow for ejection, one must include some taper or draft in the part. Typically, this is between 0.5o to 3o.We have 114 Injection Molding Machine for Plastic & PVC Manufacturing.Maximum is Horizontal type with different clamping force.

Injection Mold Layout: The plastic melt flows from the injection nozzles and enters the mold at the sprue. From the sprue the plastic flows into the runners and ultimately through the gates into the part. Gate and runner design is an important part of the mold design. To help ensure that the mold fills completely, one should balance the mold so that all cavities fill at the same time. When the cavities are the same, a symmetric layout is used. If the cavities are all markedly different, often the gates and runners must be sized/shaped differently in order to allow all cavities to fill in the same amount of time.

GateRunner

Sprue

MoldCavity

Screw Type Injection Presses: A reciprocating screw forces material into the mold. This screw action ensures that the same amount of material is always metered in, and it is equally dense along the length of the screw. Additionally the material will be much better mixed by the screw action which helps to maintain better consistency from shot to shot. Since the screw action generally helps to pack the material in better, a given plunger travel will push more material into the cavity. Finally the action of the screw, as it rotates and mixes, adds energy to the melt. However, band heaters are still needed to fully heat the melt. Screw meters plastic, plunger provides pressure

Band HeatersShooting Pot

NozzleHopperReciprocating Screw

Injection Molding Screws: The injection molding screw plunges forward to provide holding and packing pressure. The screw rotates as it retracts to meter and plasticize the melt. The screw is broken up into 3 regions. The Feed Section draws material from the hopper & starts movement into the shooting pot. In this section, channels between the flights are deep and the depth is constant. The next section, called the Transition Section, compresses and melts the plastic pellets. Most plasticization occurs in this section. The root diameter tapers, causing the channel depth to decrease. In the last section, the Metering Section, the correct fill is precisely measured out. This section has a constant channel depth.

Press Parameters: Generally, there are three common parameters used to describe the injection molding press capacity: Clamping forceShot size andInjection pressure. Clamping force is usually the most common method to refer to the injection molding press capacity. Thus, presses are talked about as being 90 ton, 250 ton, etc. The clamping force is the force available to hold the platens together. The platens contains the mold cavities. Clamping can be achieved using in-line hydraulic cylinders, mechanical toggle clamps, or a combination of the two (called hydro-mechanical).

Shot size is the amount of material that can be transferred into the mold in one shot. Shot sizes are usually specified in cubic centimeters or ounces.

Injection pressure is the pressure at the sprue that forces or injects the plastic melt into the mold. Specification by this parameter refers to the maximum injection pressure.

Clamping Mechanisms: There are a few different ways to provide the clamping force for the mold. The in-line hydraulic cylinder provides good force control, but requires large hydraulics that tend to be slow. The toggle clamps move quickly but provide poor force control. The hydro-mechanical clamping system is a combination of the two clamps. It uses a toggle mechanism for most of the travel and then uses the hydraulic cylinder for the locking force.

In line hydraulic cylinderToggle ClampIn our production floor we used Hydro mechanical Clamping System

1. Cold Runner Type

2. Hot Runner Type

Mold TypeIn The Basis of Runner Type

1.Single Plate Runner2.Three Plate Runner

Mold TypeIn The Basis of Plate Type

2.Cavity/Runner or Female Part1.Core/Mantel or Male PartMold Part:

Mold have two different parts

Injection Molding DefectsInjection molding can create defects on the finished product. Some of the more common Injection molding defects are Short ShotFlashingWeld LinesJettingEjector Pin MarksSink MarksWarpage/Residual Stresses

Designing for a part and the associated mold, its too important to keep these defects in mind as well as the fundamental objectives of filling, holding, packing and removing the part.

Short Shot: Short shot occurs when there is insufficient material to fill the mold cavity and/or the material solidifies too soon. It has several causes, including insufficient injection pressure, or insufficient time allowed during the injection process. Sometimes the material will freeze in a given section before it can reach the edges of the mold.

Flashing: Flashing occurs when there is too much material and it pushes its way out of the die; basically, the material overflows the cavity. This can be caused by too much injection pressure, too much injection time, or insufficient clamping force. It also can be caused by a poorly machined die that does not properly seal off the cavity.

Part Moderate-Heavy Flash

Weld Lines: Weld lines occur when flow fronts meet in the mold. In addition to being aesthetically unappealing, weld lines decrease the strength of the part. The cooler the fronts are when they meet, the less the plastic will be able to meld together; thus, the weld lines are more pronounced and the part is much weaker at this point.

Jetting: Jetting is generally caused when one gates a part in such a way that the material flow enters an open section with much space between the gate and the opposite wall. When the flow area is squeezed through the gate, the velocity increases, and the plastic melt shoots into the empty cavity mold. If there is nothing to break its path, it will shoot all the way through to the opposite wall, where it will quickly solidify. JettingAlternate gating eliminates jetting

Ejector Pin Marks: Once the part is sufficiently cooled, the cavity opens and ejector pins push the part out. The pins usually leave marks in the area where the ejector pins pushed the part. There are four different possible causes of the pin marks: One tries to eject the part before it solidifies and pins push through the part.1) Pin above flush2) Pin below flush3) Clearance around pin

Sink Marks: Sink marks are also common injection molding flaws. They are caused by excessively thick sections or abrupt changes in thickness.

To reduce and in some cases eliminate sink marks, one should try to minimize or remove material from excessively thick sections. These principles also help to eliminate residual stresses as well.

Warpage/Residual Stresses:Warpage is the out of plane distortion of an injection molded part, generated by constraining the part while cooling. Warpage is typically caused by anisotropic shrinkage. Several causes for anisotropic shrinkage are: Variations in thickness, Differing shrink rates due to melt orientation, Uneven cooling, Differences in the mold cavity pressure.

Suggested design changes to minimize distortion

Defect & CausesDefectCausesFlash:Injection pressure too highClamp forcetoo low

Warping:Non-uniform cooling rate

Bubbles:Injection temperature is too highToo much Moisture in materialNon-uniform cooling rate

Unfilled sections:InsufficientshotvolumeFlow rate of material too low

Sink marks:Injection pressure too lowNon-uniform cooling rate

Ejector marks:Cooling time too shortEjection force too high

Safety of IMMMold Size & Machine Size SelectionI-Bolt Joining & Clamping the Mold with D-clamp Water Line Connection Must be ok in moldAir line must be ok in Hopper NeckOil line should be checked properlyFor Core or thread mold; hydraulic system or motor should be CheckedBarrel Pre-Heating Raw materials Pre Heating (Need Basis)Limit switch of IMM door must be checkedEmergency Switch should work properlyPressure & Temperature setting appropriately for appropriate materials Hand Gloves wearing during operationAfter Unload the Mold it must be lubricated & eject water from water line of the mold with air pressure

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Problem & Important Fact in Injection Molding MachineCommon ProblemScrew BrokenClamping ProblemValve ProblemOil Filter jam Oil Leakage or oil Short ProblemLimit Switch ProblemMold Ejector Pin BrokenThermocouple DamageFire in Hopper

Important FactsNozzle & Mold CenteringElectrical Connection CheckMold Clamping ProperlyTemperature & PressureHydraulic Line CheckHopper temperature Check

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ABS (Acrylanitrile Butadiene Styrene): PA757Excellent impact resistanceGood MachinabilityExcellent aesthetic qualitiesEasy to paint and glueGood strength and stiffnessRelatively low cost

Density:1.060-1.080 gcm3Specific Gravity : 0.93

ABS isamorphousand therefore has no true melting point.

We set-up 190C to 240C in our Injection Molding Machine for ABS Production.Some Common Polymers:

POM (Polyoxymethylene): F20-03 high mechanical strength and rigidityHigh resistance to repeated impactsExcellent aesthetic qualitiesEasy to paint and gluehigh stiffnesslow friction and excellent dimensional stability

Density:1.411.42 g/cm3Specific Gravity : 1.41-1.43

POM homopolymer is a semi-crystalline polymer (7585% crystalline) with a melting point of 175C (347F).We set-up 160C to 190C in our Injection Molding Machine for POM.Some Common Polymers:

PP (Polypropylene): PP products can be sterilized in an autoclave.Good chemical resistanceToughGood fatigue resistanceIntegral hinge propertyGood heat resistance

Density:0.855 g/cm3( amorphous), 0.946 g/cm3(crystalline)Specific Gravity : 1.41-1.43

Perfectly isotactic PP has a melting point of 171C (340F).We set-up 220C-240C in our Injection Molding Machine for PP Material.Some Common Polymers:

GPPS (General Purpose Polystyrene): Excellent transparencyExcellent electric characteristicswater resistance and color abilityAppropriate for food packing containersEnables various product production due to excellent workability

Density:1.05g/cm3Specific Gravity :1.06

We set-up 200C to 240C in our Injection Molding Machine for GPPS Material.Some Common Polymers:

MB= Master bassHP=Homo polymerGPPS= General Purpose PolymerPE=Poly EthyleneLDPE=Low Density poly EthyleneHDPE=High Density Poly EthyleneHIPS=High Impact Poly StyreneSAN=Styrene acrylonitrile copolymerCP= Cellulose PropionatePA=Poly amide Cellular polymerPVC= Polyvinyl Chloride

Some Common Polymers Abbreviations:

Thank

you !