ii

GEAR PUMP

ii

DESIGN AND FABRICATION OF GEAR PUMP

Course Code:

Course Title:

Submitted By:

Muhammad Saqib Anwar

Muhammad Nouman

Mudassir Hussain

Hamza Ahmed

32-Mechanical (B)

Date: May 29th, 2012

Submitted to:

Engr Akhtar Khurshid

Assistant Professor

Department of Mechanical

Engineering, College of

E&ME, NUST

M E 251

M anufacturing Processes

A Project Report on

iii

Table of Contents Abstract .............................................................................................................................. 1

Project Overview .............................................................................................................. 1

External Gear Pump ........................................................................................................ 1

Theory of Operation .......................................................................................................... 2

Literature Review ............................................................................................................. 3

Technical Details ............................................................................................................... 4

Gears ............................................................................................................................. 4

Bearings ......................................................................................................................... 6

Shafts ............................................................................................................................. 7

Housing .......................................................................................................................... 8

M anufacturing Processes Involved ................................................................................ 9

Gear Hobbing ................................................................................................................ 10

Sand Casting ................................................................................................................. 11

Machining ..................................................................................................................... 11

Grinding........................................................................................................................ 12

Press Fitting ................................................................................................................. 13

Calculations for Discharge Rate of a Gear Pump ..................................................... 14

Advantages and Applications of an External Gear Pump ..................................... 15

Conclusion ........................................................................................................................ 17

References ........................................................................................................................ 17

1

DESIGN AND FABRICATION OF GEAR PUMP

Abstract

Gear pump is a mechanical device which is used in numerous industrial applications.

It uses the meshing of gears to pump fluid by displacement. Since the gear pump

requires high dimensional accuracy and precise machining, one has to be very adept

while manufacturing it. The main impetus for this project is to get familiarized with

various fabrication techniques and to enhance our manufacturing skills.

Project Overview

A gear pump uses the meshing of gears to pump fluid by displacement. They are one

of the most common types of pumps for hydraulic fluid power applications. Gear

pumps are also widely used in chemical installations to pump fluid with a certain

viscosity. There are two main variations; external gear pumps which use two

external spur gears, and internal gear pumps which use an external and an internal

spur gear. Gear pumps are positive displacement (or fixed displacement), meaning

they pump a constant amount of fluid for each revolution. The motive of this project

is to design and fabricate an external gear pump.

External Gear Pumps

External gear pumps are a popular pumping principle and are often used as

lubrication pumps in machine tools, in fluid power transfer units, and as oil pumps

in engines.

External gear pumps can come in single or double (two sets of gears) pump

configurations with spur (shown), helical, and herringbone gears. Helical and

herringbone gears typically offer a smoother flow than spur gears, although all gear

types are relatively smooth. Large-capacity external gear pumps typically use helical

or herringbone gears. Small external gear pumps usually operate at 1750 or 3450 rpm

and larger models operate at speeds up to 640 rpm. External gear pumps have close

tolerances and shaft support on both sides of the gears. This allows them to run to

pressures beyond 3,000 psi / 200 bar, making them well suited for use in

hydraulics. With four bearings in the liquid and tight tolerances, they are not well

suited to handling abrasive or extreme high temperature applications.

Tighter internal clearances provide for a more reliable measure of liquid passing

through a pump and for greater flow control. Because of this, external gear pumps

2

are popular for precise transfer and metering applications involving polymers, fuels,

and chemical additives.

Figure 1. Exploded View of an External Gear Pump

Theory of Operation

External gear pumps are similar in pumping action to internal gear pumps in that

two gears come into and out of mesh to produce flow. However, the external gear

pump uses two identical gears rotating against each other -- one gear is driven by a

motor and it in turn drives the other gear. Each gear is supported by a shaft with

bearings on both sides of the gear.

1. As the gears come out of mesh, they create expanding volume on the inlet side of

the pump. Liquid flows into the cavity and is trapped by the gear teeth as they

rotate.

2. Liquid travels around the interior of the casing in the pockets between the teeth

and the casing -- it does not pass between the gears.

3. Finally, the meshing of the gears forces liquid through the outlet port under

pressure.

3

Because the gears are supported on both sides, external gear pumps are quiet-

running and are routinely used for high-pressure applications such as hydraulic

applications. With no overhung bearing loads, the rotor shaft can't deflect and cause

premature wear.

Figure 2. Pumping Action of an External Gear Pump

Literature Review

Gear pumps are among the oldest and most commonly used pumps within the

industry. Though the gear pump is extremely simple in its operating principle, the

fundamental understanding of the instantaneous pump flow has been a subject of

considerable interest for many years. The complexity of this subject arises due to the

nature of the geometry involved, which has typically required numerical analysis to

solve the governing equations. Much of the recent research that is most germane to

gear pump technology is briefly summarized in the following paragraph.

Research pertaining to the average flow rate of the gear pump has been conducted

by Frith and Scott [1]. In their work, the authors have related the degradation of the

average flow rate to the online generation of wear debris. In other research, authors

have emphasized a prediction in the fluid film thickness between the gear end-face

and the end wear-plate [2]. In this work, the authors were primarily concerned with

volumetric leakage and pump efficiency. For predicting the cyclic moments and

forces on the pump shaft, Foster, Taylor, and Bidhendi [5] conducted an in depth

analysis of the gear pump using a computer program for generating solutions. This

work considered the trapped volume of fluid between meshing teeth and the results

were shown to compare nicely with actual test data. Still, others have focused on

various tooth geometries in an effort to reduce and/or compare the discharge flow

amplitude of the pump [7]. Though all of this work has been valuable in and of itself,

none of this work has considered a comparison of same-size external gear pumps,

which use different numbers of teeth for the driving and driven gears. The question

related to tooth number is significant since other positive-displacement pump types

1 2 3

4

tend to exhibit different flow characteristics depending upon the number of discrete

pumping elements that are used. For instance, axial piston pumps have been shown

to exhibit significantly different pulse shapes for pumps that use an even versus an

odd number of pistons [8]. This present study is aimed at design and fabrication of

an external gear pump.

Technical Details

From an engineering perspective, Product design is a critical activity because it has

been estimated that, generally, 70 to 80% of the cost of product development and

manufacture is determined at the initial design stages. So, designing a product

meeting the international standards (ANSI, ASME, ASTM, ISO, SAE etc.) is a

prerequisite to machine functionality and design viability. Keeping in view the above

scenario, we devised a Gear Pump optimized for industrial applications. The

specifications of various components of an External Gear Pump are enlisted below.

i. Gears

A gear is a rotating machine part having cut teeth, or

cogs, which mesh with another toothed part in order

to transmit torque. Two or more gears working in

tandem are called a transmission and can produce

a mechanical advantage through a gear ratio and

thus may be considered a simple machine. Geared

devices can change the speed, torque, and direction

of a power source. The most common situation is for

a gear to mesh with another gear, however a gear can

also mesh a non-rotating toothed part, called a rack,

thereby producing translation instead of rotation.

The gears in a transmission are analogous to the wheels in a pulley. An advantage of

gears is that the teeth of a gear prevent slipping. In transmissions which offer

multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers

to a gear ratio rather than an actual physical gear. The term is used to describe

similar devices even when gear ratio is continuous rather than discrete, or when the

device does not actually contain any gears, as in a continuously variable

transmission. The gear used in our project was a spur gear.

5

Figure 3. Gear Nomenclature

Gear Specifications

The specifications of gear used in our project are enlisted in the table given in the

proceeding page. Below is a diagram representing the nomenclature of a spur gear.

Figure 4. Nomenclature of a Spur Gear

6

M aterial

Diametral

Pitch (P)

(in.)

No. of

teeth

(N )

Pitch

Dia. (d)

(in.)

Bore

(B)

(in.)

Outside

Dia. (D)

(in.)

Face

(l)

(in.)

Steel

NK11B

5 11 2.4 1.0625 2.8 1.750

A bearing is any of various machine elements that constrain the relative motion

between two or more parts to only the desired type of motion. This is typically to

allow and promote free rotation around a fixed axis or free linear movement; it may

also be to prevent any motion, such as by controlling the vectors of normal forces.

Bearings may be classified broadly according to the motions they allow and

according to their principle of operation, as well as by the directions of applied loads

they can handle.

Figure 5. Cross Sectional Views of a Ball Bearing

Bearing Specifications

ii. Bearings

Part No.

Boundary dimensions

(mm)

Basic load ratings

(N )

Weight

(lb)

Bore

(A)

Outer

diameter

(B)

Width

(C)

Dynamic

(Cr)

Static

(Cor)

6205 25 52 15 14000 7900 0.810

7

Bearing M aterial Specifications

Material Used: CS6208XXPKWS

Shaft is a mechanical component for transmitting torque and rotation, usually used

to connect other components of a drive train that cannot be connected directly

because of distance or the need to allow for relative movement between them. Shafts

are carriers of torque: they are subject to torsion and shear stress, equivalent to the

difference between the input torque and the load. They must therefore be strong

enough to bear the stress, whilst avoiding too much additional weight as that would

in turn increase their inertia.

M aterial Used: Mild Steel

Front View of a shaft driving the gear

Figure 6. Single view Orthographic Projections of Shafts

C S XX PK WS

Ball material:

C=Ceramic

(Si3N4)

No symbol =

Chrome Steel

Ring Material:

No symbol =

Chrome steel

S=Stainless

Steel (440C)

Closure:

XX=Open

(Standard

bearing width,

no seal)

No Symbol =

Open (Narrow

bearing width,

no seal)

Retainer

material:

PK=PEEK

No Symbol =

Metal

Lubrication:

Dry film

lubrication/

Coating

WS=Tungsten

Disulfide

iii. Shaft

Front View of a shaft connected to

the driven gear.

8

Housing is an important component of gear pump, which is used in order to prevent

leakage. This factor is quite significant while designing a gear pump. Below are the

2-D sketches of various components used in housing of gear pump. The Material used

was aluminum.

Figure 7. This figure represents the lower portion of housing. The upper portion was the replica of

lower portion. The bearings are fitted in the holes shown in the figure.

Figure 8. This figure represents the central portion of housing. The gears are fitted in this portion.

iv. Housing

9

M anufacturing Processes Involved

If we take few moments to inspect various objects around us (such as pencil, paper

clip, table, light bulb, door knob, and cell phone), we shall soon realize that these

objects have been transformed from various raw materials into individual parts and

assembled into specific products. Some objects, such as nails, bolts, and paper clips,

are made of one material; the vast majority of objects (such as toasters, bicycles,

computers, washers and dryers, automobiles, and farm tractors) are, however, made

of numerous parts from a wide variety of materials. A ballpoint pen, for example,

consists of about a dozen parts, a lawn mower about 300 parts, a grand piano

12,000 parts, a typical automobile 15,000 parts, a C-5A transport plane more

than 4 million parts, and a Boeing 747-400 about 6 million parts. All are

produced by a combination of various processes called manufacturing.

Figure 9. Classification of Manufacturing Processes

The significant processes used in our project include Gear Hobbing, Wood Working,

Sand Casting, Machining, Grinding and Press Fitting.

10

There are different processes by which gears can be generated such as Form Milling,

Gear Hobbing, Gear Shaping, Gear Broaching etc.; however we used the hobbing

process.

Gear hobbing is also a milling operation, but the cutter, called a hob, is much more

complex and therefore much more expensive than a form milling cutter. In addition,

special milling machines (called hobbing machines) are required to accomplish the

relative speed and feed motions between the cutter and the gear blank. Gear hobbing

is illustrated in Figure 10. As shown in the figure, the hob has a slight helix and its

rotation must be coordinated with the much slower rotation of the gear blank in

order for the hob’s cutting teeth to mesh with the blank’s teeth as they are being

cut. This is accomplished for a spur gear by offsetting the axis of rotation of the hob

by an amount equal to 90 less the helix angle relative to the axis of the gear blank.

In addition to these rotary motions of the hob and the workpiece, a straight-line

motion is also required to feed the hob relative to the gear blank throughout its

thickness. Several teeth are cut simultaneously in hobbing, which allows for higher

production rates than form milling. Accordingly, it is a widely used gear making

process for medium and high production quantities.

Figure 10. Gear Hobbing Process

I. Gear Hobbing

11

Sand casting is the most widely used casting process, accounting for a significant

majority of the total tonnage cast. Nearly all casting alloys can be sand cast; indeed,

it is one of the few processes that can be used for metals with high melting

temperatures, such as steels, nickels, and titaniums. Its versatility permits the

casting of parts ranging in size from small to very large and in production quantities

from one to millions. Sand casting, also known as sand-mold casting, consists of

pouring molten metal into a sand mold, allowing the metal to solidify, and then

breaking up the mold to remove the casting. The casting must then be cleaned and

inspected, and heat treatment is sometimes required to improve metallurgical proper-

ties. The cavity in the sand mold is formed by packing sand around a pattern (an

approximate duplicate of the part to be cast), and then removing the pattern by

separating the mold into two halves. The mold also contains the gating and riser

system. In addition, if the casting is to have internal surfaces (e.g., hollow parts or

parts with holes), a core must be included in the mold. Since the mold is sacrificed to

remove the casting, a new sand mold must be made for each part that is produced.

The patterns used in the casting process were made of wood.

Figure 11. Steps in the production sequence in sand casting. The steps include not only the casting

operation but also pattern making and mold making.

Machining is the most widely used manufacturing processes, because most of the

industrial products have to be machined in order to bring them to net shape. For

example, bar stock is the initial shape, but the final geometry after a series of

machining operations is a shaft. Innumerable machining operations are performed in

II. Sand Casting

III. M achining

12

industries to achieve dimensional accuracies and other purposes, but we shall enlist

few of those used in our project.

Facing: The tool is fed radially into the rotating work on one end to create a flat

surface on the end.

Threading: A pointed tool is fed linearly across the outside surface of the rotating

workpart in a direction parallel to the axis of rotation at a large effective feed rate,

thus creating threads in the cylinder.

Boring: A single-point tool is fed linearly, parallel to the axis of rotation, on the

inside diameter of an existing hole in the part.

Drilling: Drilling can be performed on a lathe by feeding the drill into the rotating

work along its axis. Reaming can be performed in a similar way.

These machining operations are illustrated in Figure given below.

Facing Threading Boring

Drilling

Figure 12. Different Machining Operations

Grinding is a material removal process accomplished by abrasive particles that are

contained in a bonded grinding wheel rotating at very high surface speeds. The

grinding wheel is usually disk-shaped, and is precisely balanced for high rotational

IV. Grinding

13

speeds. Grinding can be likened to the milling process. Cutting occurs on either the

periphery or the face of the grinding wheel, similar to peripheral and face milling.

Peripheral grinding is much more common than face grinding. The rotating grinding

wheel consists of many cutting teeth (the abrasive particles), and the work is fed

relative to the wheel to accomplish material removal. Despite these similarities, there

are significant differences between grinding and milling: (1) the abrasive grains in the

wheel are much smaller and more numerous than the teeth on a milling cutter; (2)

cutting speeds in grinding are much higher than in milling; (3) the abrasive grits in a

grinding wheel are randomly oriented and possess on average a very high negative

rake angle; and (4) a grinding wheel is self-sharpening—as the wheel wears, the

abrasive particles become dull and either fracture to create fresh cutting edges or are

pulled out of the surface of the wheel to expose new grains.

Figure 13. A Grinding Machine with horizontal spindle and reciprocating worktable.

A press fit assembly is one in which the two components have an interference fit

between them. The typical case is where a pin (e.g., a straight cylindrical pin) of a

certain diameter is pressed into a hole of a slightly smaller diameter. Standard pin

sizes are commercially available to accomplish a variety of functions, such as (1)

locating and locking the components—used to augment threaded fasteners by

V. Press Fitting

14

holding two (or more) parts in fixed alignment with each other; (2) pivot points, to

permit rotation of one component about the other; and (3) shear pins. Except for (3),

the pins are normally hardened. Shear pins are made of softer metals so as to break

under a sudden or severe shearing load to save the rest of the assembly. Other

applications of press fitting include assembly of collars, gears, pulleys, and similar

components onto shafts.

Figure 14. Cross section of a solid pin or shaft assembled to a collar by interference fit.

Calculations for Discharge Rate of a Gear Pump

The empirical formula for calculating discharge rate is given as

Q = 0.95πC(D – C )lN

Where Q = discharge rate in lpm (liters per minute)

C = center to center distance between axis of gears (Center Distance)

D = outside diameter of gears

l = axial length of teeth (Face)

N = speed in rpm

Center Distance

(C)

(in.)

Outside

Diameter (D)

(in.)

Face

(l)

(in.)

Speed

(N )

(rpm)

2.4 2.8 1.750 1500

15

Center Distance = 2.4 in. = 0.6096 dm

Outside Diameter = 2.8 in. = 0.7112 dm

Face = 1.750 in. = 0.4445 dm

Speed = 1500 rpm

Q = 0.95πC(D – C )lN

Q = (0.95)(3.14)(0.6096)(0.7112 – 0.6096)(0.4445)(1500)

Q = 123.25 lpm

The external gear pump is a positive displacement (PD) type of pump generally used

for the transfer and metering of liquids. The pump is so named because it has two

gears that are side-by-side or external to each other. (This nomenclature

differentiates it from an internal gear pump, which has one gear positioned inside the

other.) The gear pump is a precision machine with extremely tight fits and

tolerances, and is capable of working against high differential pressures.

Another important advantage of the gear pump is its self-priming capability. Gear

pumps are capable of self-priming because the rotating gears evacuate air in the

suction line. This produces a partial vacuum that allows the atmospheric pressure to

force the liquid into the inlet side of the pump. This ability of the gear pump makes

it an ideal choice when the application requires that the pump be located above the

liquid level, and the liquid must be lifted to the pump. Because a gear pump cannot

create a perfect vacuum, the total lift (including pipe friction losses) should not

exceed about 7.5 PSI, or about one-half of the atmospheric pressure.

The tight clearances of the working parts inside a gear pump are what enable it to

effectively pump liquids against high pressure. Low viscosity fluids such as alcohols

and other solvents have more of a tendency to “slip” thru these tight spaces from the

higher-pressure discharge side of the pump back to the lower-pressure suction side of

the pump. The phenomenon of slip causes a reduction in flow rate and pump

Conversions

Advantages and Applications of an External Gear

Pump

16

efficiency. Slip depends on the magnitude of the differential pressure (i.e., the

difference between the discharge and suction pressures), the viscosity of the liquid

pumped and the working clearances inside the particular pump that is used. Slip

increases with decreasing viscosity, increasing differential pressure and increasing

gear-housing clearances, and is usually measured as a percent decrease from ideal

flow (i.e., flow with zero slip). For fluid viscosities greater than about 50-100 cP

(depending on the particular pump), the slip is minor, but it still depends on the

differential pressure. This behavior is shown in Figure 15, which compares a typical

gear pump’s performance curve for a thin fluid (such as water with a viscosity of

about 1 cP at room temperature) with that of a moderately viscous fluid (such as a

particular oil with a viscosity of 100 cP).

Figure 15. Performance curves for a typical external gear pump showing slip as a function of

viscosity and differential pressure.

Gear pumps – properly designed and engineered – can offer many advantages. These

include compactness, simplicity of design, easy serviceability, bi-directional flow

capability, ability to self-prime, pulseless flow, low NPSHR (net positive suction

head required), high MTBM (mean time between maintenance), high-pressure and

high-temperature capability, precise and accurate metering, and availability in

multiple seal configurations or sealless mag-drives. External gear pumps are used in

17

industrial and mobile (e.g. log splitters, lifts) hydraulic applications. Typical

applications include:

Lubrication pumps in machine tools

Fluid power transfer units

Oil pumps in engines

Circulation

Injection

Drum transfer

Chemical additive and polymer metering

Chemical mixing and blending (double pump)

Acids and caustic (stainless steel or composite construction)

In short, Gear Pumps are used in many industrial applications and manufacturing

processes are a key element in the designing and functionality of gear pump. All we

need to do is to apply these manufacturing processes effectively, so that we can

upheave our industry.

[1]. Frith, R. H., and Scott, W., 1996, ‘‘Comparison of an external gear pump wear

model with test data,’’ Wear,196, pp. 64 –71.

[2]. Koc, E., and Hooke, C. J., 1997, ‘‘An experimental investigation into the design

and performance of hydrostatically loaded floating wear plates in gear pumps,’’

Wear,209, pp. 184 –192.

[3]. Koc, E., 1994, ‘‘Bearing misalignment effects on the hydrostatic and hydro

dynamic behaviour of gears in fixed clearance end plates,’’ Wear,173, pp. 199–206.

[4]. Koc, E., 1991, ‘‘An investigation into the performance of hydrostatically loaded

end-plates in high pressure pumps and motors: Movable plate design,’’ Wear,141, pp.

249–265.

Conclusion

References

18

[5]. Foster, K., Taylor, R., and Bidhendi, I. M., 1985, ‘‘Computer prediction of cyclic

excitation sources for an external gear pump,’’ Proc. Inst. Mech. Eng., Part C: Mech.

Eng. Sci.,199, No. B3, pp. 175–180.

[6]. Chen, C. K., and Yang, S. C., 2000, ‘‘Geometric modeling for cylindrical and

helical gear pumps with circular arc teeth,’’ Proc. Inst. Mech. Eng., Part C: J. Mech.

Eng. Sci.,214, pp. 599– 607.

[7]. Mitome, K., and Seki, K., 1983, ‘‘A new continuous contact low-noise gear

pump,’’ Journal of Mechanisms, Transmission and Automation in Design,105, pp.

736 –741.

[8]. Manring, N. D., 2000, ‘‘The discharge flow ripple of an axial-piston swash-plate

type hydrostatic pump,’’ ASME J. Dyn. Syst., Meas., Control,122, pp. 263–268.

[9]. Kalpakjian S. and Schmid, S.R. (2008). Manufacturing Processes for

Engineering Materials. (5th ed., p. 1). NJ , USA: Pearson Education, Inc.

[10]. Groover M.P. (2010). Fundamentals of Modern Manufacturing (Materials,

Processes and Systems). (4th ed., pp. 225-227, 510-513, 604-605, 618, 541-542). USA:

John Wiley and Sons, Inc.

[11]. Yadav, S. K. (2010). To design, fabrication and testing of gear pump test rig.

Project Report, Galgotias College of Engineering and Technology, Mechanical

Engineering.

[12]. Gear Pump, Bearings, Gears, Drive Shaft. (May 22nd, 2012 .). Retrieved from

Wikipedia: http://www.wikipedia.com.