Report Main

8/8/2019 Report Main

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wear and anti-scuff properties of oil or an additive, in oil. The operating conditions can

be made to simulate, as far as possible, those in a practical machine. Pin-on-disc

tribometers are not suitable for the wear behaviours of conventionally used sliding

bearings. For this purpose a new wear testing machine for sliding bearings is needed. The

main goal of this project is to measure the wear behaviour of conventionally used sliding

bearings. For this purpose a new wear testing machine is designed and fabricated for

sliding bearings.

1.1 OBJECTIVES OF THE PROJECT

The main objectives of this work are as follows.

Study about bearings

Design and fabrication of the sliding bearing wear testing machine.

To investigate the wear behaviour ofconventionally used sliding

bearing material such as bronze by using the fabricated sliding bearing wear

testing machine.

1.2 SCOPE OF THE PROJECT

In the design of bearings it is required that the wear of the engaging components be

minimum. Material selection is very important for reducing the wear. For this purpose

different materials are to be studied, tested and their wear rate needs to be estimated. Pin

on disc tribometers are widely used to obtain the wear rate of metals, but they are not that

accurate in predicting the wear rate of sliding bearings. So in the present work a new

wear testing machine was designed and fabricated to find the wear behaviour of sliding

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bearings. The finding from the experiments can be used to design sliding bearings and the

designs will be more accurate when compared to designs made on the basis of results

from pin on disc tribometer.

1.3 STRUCTURE OF THE REPORT

A detailed literature survey is made in chapter (2). In the next chapter a detailed study

about bearing is also given. Chapter (4) discusses the design and fabrication of the wear

testing machine. A detailed description of wear testing is given in chapter (5). In Chapter

(6), presents the results obtained from the testing machine is given. In the final chapter

conclusion to the work is given.

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CHAPTER 2

LITERATURE SURVEY

Sliding wear behaviour of bronzes under varying material composition, microstructure

and test conditions [1] has been discussed by B K Prasad. In this paper sliding wear

behaviour of some leaded-tin and aluminium bronzes has been studied over a wide range

of applied pressures and speeds using a pin-on-disc machine. Wear rate, frictional heating

and surface roughness of the samples were monitored during the tests. The wear response

of specimens has been correlated with the features of their wear surfaces, subsurface

regions and debris particles and explained in terms of varying elemental concentrations

and specific characteristics of various micro constituents in terms of thermal stability,

cracking and lubricating tendency and load bearing capability. Wear rate of leaded-tin

bronzes decreased with increasing sliding speed while the aluminium bronze exhibited an

opposite trend. High wear rates corresponded to more severe microcracking tendency on

and in the regions below the wear surfaces and coarser debris formation. Improved wear

performance of the leaded-tin bronzes with increasing sliding speed could be attributed to

the suppressed microcracking tendency favouring effective smearing of the lubricating

phase (lead) leading to lubrication. Deteriorating wear behaviour of the aluminium

bronze with speed/pressure could be due to the occurrence of more severe wear

conditions leading ultimately to specimen seizure.

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Unlubricated rolling-sliding wear mechanisms of complex aluminium bronze against

steel [3] has been discussed by Shi Z et al. In this paper, unlubricated rolling-sliding wear

tests of as-received and electron beam surface melted complex aluminium bronze,

CA104, against hardened En19 steel have been carried out. Test samples have been

examined using optical microscopy, scanning electron microscopy and microhardness

measurements. It is found that both adhesive wear and delamination wear occur in the

wear process and the wear debris forms in two ways. Two types of structures exist in the

wear debris, which are related to a deformed and a highly deformed subsurface structure

in the tested samples. Electron beam surface melting improves the wear resistance of the

material but the wear mechanisms involved have not been fundamentally changed.

Electron beam surface melting produces a martensitic layer on the surface of complex

aluminium bronze and increases the hardness.

Mechanical, friction and wear behaviours of a novel high-strength wear-resisting

aluminum bronze [4] has been discussed by Li Y et al. In this paper, the microstructural

effects on mechanical and tribological behaviors of aluminium bronze, a novel high-

strength wear resisting aluminium bronze(KK) has been developed by optimizing

microstructures, modifying, adding special elements and controlling the casting process.

In aluminium bronze adding the anti friction component Pb, modifying components Ti

and B and controlling the melting and solidification process can effectively improve the

microstructures and mechanical friction and wear properties of aluminium bronze.

Compared with other aluminium bronze alloys of the same class, the novel KK bronze

has the best performance especially with regard to its friction and wears properties.

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Reproducibility of friction and wear results is ball-on-disc unidirectional sliding tests of

TiN-alumina pairings [5] has been discussed by M.Z. Huq. In this paper, validation test

methods for thin hard coatings, friction and wear characteristics of TiN coatings were

investigated. Ball-on-disc sliding tests were performed in ambient air of 50% FW at

various applied loads under a fixed sliding speed. The coefficient of friction was

measured on-line whereas the worn-off volume was determined by laser stylus

profilometry and mass loss measurements. The two wear loss methods were compared. It

was confirmed that the profilometry measured wear volume is linearly dependent on the

total dissipated energy as long as the coating is not worn through. From this study, the

effect of normal load on the friction and wear behaviour of TiN coatings and the

reproducibility of the tribotests are discussed. The coefficient of friction decreases as the

normal load increases, in contradiction to Amontons law. The characteristic friction

behaviour of TiN sliding against alumina is reproducible at different loads as long as the

wear is confined within the TiN coating. The reproducibility decreases with increasing

normal load and the maximum standard deviation in the co-efficient of friction is noticed

at a load of 15.82 N.

Reciprocal sliding wear of SIC particle-reinforced Al-Cu aluminium matrix composites

against stainless steel, high speed tool steel and ceramics contact [6] has been discussed

by Mingwu Bai. In this paper, the friction and wear of AI-Cu-SiC aluminium matrix

composite pins dry sliding against 4Cr13, W18Cr4V and Si3N4( SN) ceramic blocks were

investigated in a reciprocal friction test machine under applied loads of 20-175 N and

reciprocal speeds of 0.075-1.2 m/s. Five wear regimes, adhesion wear (mild,

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intermediate), abrasion wear, mild melt wear and severe abrasion wear are identified for

Al-Cu-SiC/4Crl3 tribopairs. Abrasion wear is the most severe wear mode of aluminium-

Sic composites. The selection of counterpart material is very critical in reducing dry

sliding wear of aluminium-SiC composites. The counterpart materials of high hardness

and high properties of iron oxide formation in situ are recommended.

Abrasive wear of aluminium composites--a review [7] has been discussed by R.L. Deuis.

In this paper, aluminium-silicon alloys and aluminium-based metal-matrix composites

(MMCs) containing hard particles offer superior operating performance and resistance to

wear. Composites characterized by a hardness greater than the abrasive particles and a

reinforcement phase of high fracture toughness and low mean free path, compared to the

abrasive grit dimension, exhibit high abrasive wear resistance. The abrasive wear of a

fibre-reinforced composite by small abrasive particles decreases as the fibre volume

fraction increases. For ductile materials subjected to abrasive wear, microploughing is the

most favoured mechanism, resulting in a low wear rate; Brittle materials usually exhibit

one of the following wear mechanisms: micro-cutting; micro fatigue or microcracking.

Wear behaviour results using AI-Si as the matrix is already masked by the fact that this

composition is an in situ composite in its own right, with Si as the second phase. Using

aluminium as the matrix material would enhance our understanding of reinforcement

particle-matrix interaction during the wear process. The composite coating formed

exhibits microstructutal and tribological properties characteristic of a bulk composite

material, but independent of substrate effects.

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Energy and wear analysis in lubricated sliding contact [8] has been discussed by Asuman

Alp. In this paper, lubricants are used to control friction and minimize wear in a variety

of tribological applications. When lubricants are used at the contact interface of two

sliding surfaces the material loss due to wear and the energy consumption due to friction

are reduced by several orders of magnitude. In railroad applications, lubricants are

routinely applied to the side of the rails to reduce friction and wear that occur between the

flange part of the wheel and the gauge side of the rail on curved tracks. Lubricated tests

were conducted in boundary lubrication regime to develop a standard testing method for

the measurement of railroad gauge side lubricant performance in sliding contact, on a

modified pin-on-disk system using AISI 1040 steel samples. Both friction and wear can

be reduced between the gauge of the rail and the flange of the wheel using the lubricants

tested Ranking of the lubricant performance for railroad gauge side application can be

based on: (a) amount of energy saved, (b) amount of sliding distances before the lubricant

breakdown took place, and (c) lubricant breakdown duration, and (d) extent of

acceleration monitored during steady-state and towards the end of the sliding

experiments. For the rail gauge side lubrication, the longer the lubricant breakdown

duration the less the number of lubricant applications needed. Lower friction and wear

values and less amount of wear debris were obtained in lubricated tests, when compared

with unlubricated tests.

Determination of friction coefficient in journal bearings [9] has been discussed by Bekir

Sadk Unlu. In this paper, friction coefficient knowing is important for the determination

of wear loss conditions at journal bearings. Tribological events that influence wear and its

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variations effect experimental results. In experiments, friction effects of bearings have

been examined at dry and lubricated conditions and at different loads and velocities. At

the beginning of the motion because of the dry friction, friction coefficient increases and

later decreases. As the load increases, friction coefficient decreases at dry condition. But

at lubricated condition, friction coefficient increases by increasing load because of

decreasing oil film thickness. Finally, bearing temperature increases by increasing load

and velocity.

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CHAPTER 3

BEARINGS

3.1 INTRODUCTION

A bearing is a machine element which supports another moving machine element known

as journal. It permits a relative motion between the contact surfaces of the members while

carrying the load. Due to the relative motion between the contact surfaces, a certain

amount of power is lost in overcoming frictional resistance and if the rubbing surfaces are

in contact, there will be rapid wear. In order to reduce frictional resistance and wear and

in some cases to carry away the heat generated, a layer of fluid (known as lubricant) may

be provided. The lubricant used to reduce the friction between the journal and bearing.

3. 2 CLASSIFICATION OF BEARINGS

Bearings may be classified in to different ways

3.2.1 Depending upon the direction of load to be applied

Radial bearings

Thrust bearings

3.2.1.1 Radial bearings

In radial bearings the load acts perpendicular to the direction of the motion of the moving

element.

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3.2.1.2 Thrust bearing

A thrust bearing is a particular type of rotary bearing. Like other rotary bearings they

permit rotation between parts, but they are designed to support a high axial load while

doing this.

3.2.2 Depending upon the nature of contact

Sliding contact bearings

Rolling contact bearings

3.2.2.1 Sliding contact bearings

In sliding contact bearings, the sliding takes place along the surface of the contact

between the moving element and the fixed element. Sliding contact bearings are also

known as plain bearings. Sliding bearings (plain bearings) are designed to transmit load

between two surfaces that are in relative motion. The simplest forms of sliding bearings

are used unlubricated and thus suffer from the penalty of high friction and wear.

Providing lubricant under favorable conditions separates the surfaces and reduces the

coefficient of friction by a factor of 100 and reduces the rate of wear by many orders of

magnitude. A bearing may be an integral part of the equipment but it is usually a separate

component either in the form of a round bushing, a half bearing, a thrust washer, a

flanged bearing (which can accommodate both radial and axial loads) or a wear plate.

Sliding bearing performance is substantially affected by the lubrication regime.

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3.2.2.2 Rolling contact bearings

In rolling contact bearings, the steel balls or rollers are interposed between the moving

and fixed elements. The balls offer rolling friction at two points for each ball or roller.

Rolling-contact bearings use special-grade steels designated as "bearing steels". For high

temperature applications, stainless steels, tool steels, cemented carbides, super alloys and

ceramics are useful in sliding or rolling contacts. If corrosion resistance is required,

stainless steels, hardfacing alloys, super alloys, titanium-base alloys, ceramics, carbon-

graphite and polymers should be considered. Journal bearing materials which require

conformability, embeddibility, softening under frictional heating and fail-safe properties.

3.3 MATERIALS USED FOR SLIDING BEARINGS

The materials commonly used for sliding contact bearings are Babbitt metal, bearing

bronzes, cast iron, silver, zinc-base alloys and aluminum-base alloys; some polymers also

fall under this classification. For sliding bearings operating in water, carbon-graphite is

an excellent selection; some polymers are appropriate for these applications as well. Self-

lubricating materials for use under dry sliding conditions include various polymers,

carbon graphite materials and metal-matrix composites.

3.3.1: Babbitt metal

The tin base and lead base babbits are widely used as a bearing material, because they

satisfy most requirements for general applications. The babbits are recommended where

the maximum bearing pressure is not over 7 to 14 N/mm 2. Babbitt is commonly used in

Automobiles. They have an ability to embed dirt and have excellent compatibility

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properties under boundary lubrication. Compared with other bearing materials, babbitts

generally have lower load-carrying capacity and fatigue strength, are slightly more costly

and require a more complicated design. Also, their strength decreases rapidly with

increasing temperature. These shortcomings can often be avoided by using an

intermediate layer of high-strength, fatigue-resisting materials between the steel backing

and the thin babbitt surface layer. Such composite bearings frequently eliminate any need

for alternative materials with poorer compatibility characteristics.Common compositionsfor Babbitt alloys:

90% tin 10% copper

89% tin 7% antimony 4% copper

80% lead 15% antimony 5% tin

3.3.1.1 Tin Babbitt:

These materials are composed of 80 to 90% tin, with about 3 to 8% copper and 4 to

14% antimony added. An increase in the copper or antimony increases hardness and

tensile strength and decreases ductility. Increasing the percentage of these hardening

alloys above this range decreases both cracking resistance and fatigue strength.

3.3.1.2 Lead Babbitt:

Generally, these compositions range from 10 to 15% antimony plus up to 10% tin.

Lead babbitts based on lead-antimony-tin alloys have a structure consisting of hard

antimony-tin crystals in a relatively soft high-lead matrix. Compared to tin babbitts,

lead-base materials are less costly and have less tendency to score a shaft. With quick

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chilling to give a fine microstructure, thin surface layers for improved fatigue strength

and careful attention to bonding, lead babbitt gives excellent service and is used in

much greater volumes than tin Babbitt.

3.3.2 Bronzes

The bronzes are generally used in the form of machined bushes pressed in to the shell.

Bronze is the alloy of copper, tin and zinc. The bush may be in one or two pieces. The

bronzes commonly used bearing materials are gun metal and phosphor bronze.

3.3.2.1 Gunmetal

Gunmetal is a type ofbronze an alloy ofcopper, tin and zinc. Originally used chiefly

for making guns, gunmetal was superseded by steel. Gunmetal composed of 88% copper,

10% tin and 2% zinc. Gunmetal has good casting characteristics, particularly as a sand

casting and so is often employed in the production of pump casings and for similar

components where comparatively high strength, coupled with pressure tightness and

corrosion resistance are important requirements. Gunmetal is used for valve guides,

bearings and bushes, particularly in the gas and oil engine field and where bearing/shaft

alignments can be ensured and lubrication is good. Gunmetal has a low coefficient of

friction; very good corrosion resisting properties make its use common place in marine

engine ring.

3.3.2.2 Phosphor bronze

Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a significant

phosphorus content of up to 1%. The phosphorus is added as deoxidizing agent during

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melting. These alloys are notable for theirtoughness,strength, low coefficient of friction

and fine grain. The phosphorus also improves the fluidity of the molten metal and thereby

improves the castability and improves mechanical properties by cleaning up the grain

boundaries. Further increasing the phosphorus content leads to formation of a very hard

compound Cu3P (copper phosphide), resulting in a brittle form of phosphor bronze,

which has a narrow range of applications.

3.4 BEARING FAILURES

Plain or sliding bearings are lubricated by the formation of a hydrodynamic film of

lubricant, where the wedge formed lifts the shaft or journal off the bearing. Since

pressure in the wedge increases to a maximum near the point of minimum oil film

thickness and then completely disappears as the bearing clearance increases, the resultant

force, FR, both lifts the journal and displaces it slightly away from the wedge.

To prevent contact between a journal and its bearing, the minimum oil film thickness

must at all times be greater than the combined mean surface roughness of the journal and

bearing. This film thickness depends on the following four factors:

The lubricant viscosity.

Speed of journal rotation.

Load on the journal.

Operating temperature.

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Slight changes in load, lubricant flow to the bearing or temperature will alter the oil film

thickness, the most common of these being load changes due to some vibration or

harmonic in the system. A vibrating load alternately will decrease the film thickness and

increase the bearing offset; thus the journal center will follow an elliptical path within the

bearing if the vibration is a constant or may follow a complex path, as in the case of an

engine main bearing.

Abnormal wear and failures occur as the oil film thickness decreases to less than the

combined mean surface roughness. This may occur due to a lack of lubricant, an

abnormal load, excessive temperature or a combination of any of these factors.

3.4.1 Lack of lubricant

An unfortunately common cause of engine failure occurs as an engine runs dry of oil,

resulting in a diminished flow of lubricant to the bearings. Because the big end bearings

rotate about the main bearings and are lubricated via the main bearings, the crank-shaft

becomes a centrifugal pump and the available lubricant supply preferentially feeds the

big end bearings.

3.4.2 Material failures

Under a continuous normal operation, a bearing should have infinite life because it is

protected by the oil wedge, and no metal-to-metal contact occurs. Bearing life is only

limited by the fatigue life of the bearing material. In reality, bearings must stop and

restart at regular intervals. An oil wedge can only be formed in a rotating bearing; hence,

it is when a bearing stops and restarts that wear occurs.

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Bearings also must absorb particles in the lubricant that otherwise would lead to

abnormal wear and failure. This property is called embedability. Although the bearing

surface is marked, this is not a failure and the bearing could have been expected to

continue in service for a normal life. Bearing erosion may occur from either cavitation or

corrosion.

3.4.3 Cavitation

Changes in the pressure wedge from grooves cut across the bearing caused entrained air

to be released at a micro level causing the cavitation. Cavitation initially erodes the

bearing overlay material but over a period of time will progress into the bearing material,

causing eventual failure if the bearing material has a poor resistance to fatigue.

3.4.4 Corrosion

Oxidation occurs during the service life of a lubricant, which produces acids. In engines

strong acids are produced from combustion. Acids attack the intergranular matrix. In

addition, further corrosion will break out larger grains of material resulting in bearing

failure.

3.4.5 Bearing melting

Heat is generated in bearings by friction in the lubricant as it forms an oil wedge. By

definition viscosity is the lubricant's resistance to shear; thus, higher viscosity lubricants

and bearings operating under higher loads stabilize at higher operating temperatures. The

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bearing material chosen for any operation must have a melting point higher than the

operating temperature.

The extra friction in a section of the load zone from a high spot in the bearing will cause

a localized failure. Since bearings are generally precision components, high spots are

caused by a solid object lodged behind the bearing shell.

3.5 WEAR MEASURING TECHNIQUES

Many different approaches have been used to determine amounts of wear, both

qualitatively and quantitatively. If material is actually lost during wear, then a commonly

used method of measurement is to determine the amount of removed material, perhaps by

weight loss, as is also done in the field of corrosion. Alternatively, if the wear process

leads to surface distress on some component, then surface roughening or cracking may be

measured. Other forms of surface and subsurface wear damage can be encountered, as

well, and can be measured by other direct and indirect methods. The amount of wear will

also influence the selection of measurement method. If large amounts of wear are

experienced, then relatively simple, inexpensive measurement approaches, such as

volume change or mass change determination, are usually conducted successfully.

Alternatively, if very small wear amounts are experienced, then more sensitive and costly

techniques are necessary to detect minute changes of mass or volume. The approach of

measuring mass change in this test method is usually quick and inexpensive, and

specimen costs can be low. Weld-overlay materials, coatings, ceramics, composites, and

many other types of materials can be studied using this method.

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3.5.1 Mass loss measures of wear

Wear loss can be determined by measuring either mass change or dimensional change.

The mass loss method is straightforward. It is necessary that an original part or specimen

(or equivalent) be weighed, and that the weight of the object after wear exposure is

determined and subtracted from the original to determine the difference in weight (that is,

mass change). As the parts involved become smaller and lighter or the wear loss becomes

smaller, it will be necessary to use increasingly sensitive weighing equipment. At some

point, the mass change will be too small for the method to be feasible. Other problems

with this approach include the need to clean the specimen carefully to avoid having

extraneous matter on the surface contribute to any weight difference. Of course, any

fluids or solids used in cleaning must be thoroughly removed or dried. Another

consideration is that material that was plastically displaced by the wear process but not

actually removed from the part will not be included in the weight difference. The amount

of wear can be described by the absolute amount of mass loss (in grams), or by the rate of

mass loss per unit of usage (grams per day), or by a fractional change in the mass of the

part involved (1% change per 100 hours of operation).

3.5.2 Linear measures of wear

A common alternative to the weight loss measure of wear is to measure dimensional

change. In many situations, the design of a component that is subject to wear will only

allow up to a certain loss of dimension before either the integrity or function of the

system is lost. In such cases, monitoring the dimensions of a part is a natural approach to

assessing the amount of wear encountered. Frequently, such studies lead to the

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establishment of criteria for servicing or for part replacement. Examples include the wear

of bushings or shafts, ball-bearing retainers, sliding actuator parts, and piston cylinder

wall contacts. Although this approach to wear measurement is frequently used, very small

amounts of wear are difficult to measure, much as in the case of wear measurement by

mass loss. Therefore, a natural approach was to measure the shape changes of those

components that were due to wear.

3.5.3 Area measures of wear

Certain wear contact geometries produce material loss over a localized area on the two

surfaces. In many cases, those areas of wear loss can be measured and are proportional to

the amount of wear. Examples would include worn areas on gear teeth, on bearing

retainers, and on sliding pads with contoured surfaces. If the curvature of the surface is

known, then the amount of wear can be quantified on the basis of the area worn. Because

many tribological components involve area contacts, as contrasted to point or line

contacts, area measures of wear are important. One frequently used laboratory test system

comprises a stationary block and a rotating ring. Several ASTM standards, that are

concerned with lubricants and material wear, utilize this type of system. Although the

initial contact between the two specimens is nominally a line (there is actually a small

lateral width associated with elastic deformation along the contact line), the resulting scar

on the block becomes a curved rectangular surface as the two components wear. The

volume worn from the block can be calculated from the two scar dimensions and the ring

(or scar) curvature, but it is also common to find the projected scar area reported. The

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ASTM standards involves scar width measurement only because it specifies the specific

block size, and hence, scar length and ring diameter.

3.5.4 Volume measures of wear

In a large proportion of reports that contain wear measurements, one finds the wear

amount reported in volume units, for example, mm3. This better enables a comparison of

wear among materials having different densities, and also permits easy calculation of

linear wear amounts or wear allowances. In some cases, it is actually necessary to directly

measure wear volume. This generally occurs when the worn region is very irregular or

unsymmetric in shape, or when high accuracy in the result is needed. Unfortunately, such

measurements are quite time-consuming. Two examples of direct volume determinations

associated with laboratory wear testing are given next to illustrate the methods involved.

The worn surface of interest was neither flat nor smooth enough to permit accurate use of

the usual geometric formulae. Therefore, the surface was traced on an X-Y stylus

profiling system, and the resulting data were digitized to facilitate further calculation.

With such data, it is straightforward to calculate the volume difference between the worn

specimen and the unworn original, which in this case was a sphere. This approach should

be possible for most worn contacts, as long as they can be cleaned of extraneous matter,

such as wear debris particles, and as long as sufficient lateral and vertical resolution are

offered by the stylus tip and system.

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CHAPTER 4

DESIGN AND FABRICATION OF WEAR TESTING

MACHINE

4.1 DESIGN

The design of wear testing machine includes the design of various components like shaft,

pulley, belt and ball bearing.

4.1.1 Motor selection

The motor selection is done on the basis of the total load acting on the motor. The power

of the motor is obtained from the equation 4.1 given below,

2 N T

P =60

(4.1)

Where,

P Power of the motor in KW

T Torque of the motor in Nm

N Speed of the motor in rpm

4.1.2 Pulley Design

In the wear testing machine two pulleys are needed, one to hold the bearing specimen and

the other is used to apply load on the specimen. The internal dimension of the pulley used

to hold the specimen should be such as to form a tight fit with the testing specimen. The

outer diameter of the pulley is selected based on the motor power. The volume of the

pulley is found using the equation 4.2.

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( )2 22 1- - 2V r r t A= (4.2)

Where r1 and r2 are inner and outer radius of the pulley, t is the thickness of the pulley

The mass of the pulley is found by equation 4.3 given below

M=V (4.3)

Where is the density of the cast iron pulley 7800kg/m3

4.1.3 Shaft design

Shaft is used to transmit the torque and the bending moment. The diameter of the shaft is

obtained using the equation 4.4.

316T

d =

(4.4)

Where,

d Diameter of the shaft in mm

T Torque of the motor in Nm

Shear stress of the shaft material in N/m2

4.1.4 Ball bearing

The ball bearing is used to support the shaft, to prevent it from bending. The ball bearing

is selected based on the outer diameter of the shaft and the load to be supported.

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4.1.5 Belt design

Velocity of the belt is obtained using the equation 4.5.

60

NDV

= (4.5)

Where,

V Velocity of the belt in m/s

D Diameter of the cast iron pulley in mm

Power transmitted by the belt is obtained from the equation 4.6

P T V = (4.6)

Where

P Power transmitted by the belt in KW

T is the tension in the belt in Newton

Belt dimensions are obtained from the equation 4.7 as given below

tbT = (4.7)

Where the allowable stress, b is the width of the belt, t is the thickness of the belt

The center to center distance between the two pulleys is in meter and is obtained from

the equation 4.7

2

L DC

= (4.8)

Where L is the length of the belt, D is the diameter of the pulley

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4.2 FABRICATION

The newly designed and fabricated wear testing machine is shown in the figure 4.1.

Figure 4.1 Wear testing machine

The main structure of the testing machine is made with rectangular rail of mild steel. The

rectangular rails were welded together to form a rigid base to support the motor

vibrations and test loads. The motor is fixed in the structural support with bolts and

hexagonal nuts. The mile (hardened material) is connected to the motor shaft through

coupling arrangement. A ball bearing is then inserted into the mile and fixed at a suitable

location using a collar. A cast iron pulley is made by doing machining in a lathe. The

specimen to be tested are then inserted into the cast iron pulley as shown in figure 4.2

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Figure 4.2 cast iron pulley with bearing specimen

These specimens were formed into ring shape by means of a lathe and their inner surfaces

were made to ground finish. The specimen is shown in figure 4.3 and its specifications

are shown in table 4.1. Bearing Specimen is Gunmetal with a composition of 88%

Copper, 10 % tin and 2% Zinc.

TABLE 4.1 SPECIFICATIONOFBEARINGMATERIAL

Inner Diameter of thebearing

30 mm

Outer Diameter of thebearing

41 mm

Width of the bearingspecimen 10 mm

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Figure 4.3 Specimen

The pulley and specimen assembly is then inserted into the mile and is kept in a fixed

location using another ball bearing, which is inserted into the shaft after the pulley and

specimen assembly. The whole arrangement is then tightened with a hexagonal nut as

shown in the figure 4.4

Figure 4.4 Cast iron pulley tightened with hexagonal nut.

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The load on the test specimen is applied using a pulley and shaft arrangement. For this a

cast iron pulley is used and a ball bearing is inserted into it and is held stationary in the

shaft using collars. The whole assembly is then connected to the pulley carrying the test

specimen using a V belt as shown in the figure 4.5

Figure 4.5 Loading mechanism

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A plate is attached to the cast-iron pulley as shown in figure 4.6 in order to measure the

deflection due to the frictional force.A load cell is also connected to the plate to convert

the deflection into electrical signals.

Figure 4.6 Plate and load cell arrangement to measure frictional force

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CHAPTER 5

WEAR TESTING

The wear testing of the gun metal is carried out using the newly designed and fabricated

wear testing machine.

5.1 EXPERIMENTAL SETUP

The experimental set up is shown in figure 5.1

Figure 5.1 Experimental set up

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5.2 EXPERIMETAL PROCEDURE

At first the specimen to be tested is fitted in the cast-iron pulley. It is then inserted on the

shaft and placed between two ball bearings and the whole assembly is tightened with a

hexagonal nut. Now wear test of sliding bearing specimen were performed for 10 minutes

under two different wear loads as 20N and 30N.

When we start the experiment the mile turns and a force occur to put up with the friction

occurred between the mile and the specimen interface. This force creates a moment along

the mile axis and tries to turn the specimen. Due to this moment a deflection is obtained

on the angle plate attached to the cast-iron pulley. This deflection is recorded by means of

a transducer as voltage (v). This voltage is used to evaluate the frictional force and the

coefficient of friction value of bearing material is found.

The specimen is tested under both wet and dry condition. The weight of the specimen is

measured before and after each experiment using a precise electronic weighing machine

having an accuracy of 0.0001g. Now using the mass loss technique, wear rate can be

calculated.

masslosswear rate=

sliding distance5.1

Sliding distance (S) is obtained from the equation 5.2

tNrS 2=

5.2

Where r is the radius of the shaft, N is the speed of the motor,t is the time for wear

test.

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CHAPTER 6

RESULTS AND DISCUSSION

The motor selected is a three phase induction motor with a capacity of 1.1 KW at a speed

of 1445 rpm using the equation 4.1. Mass of the pulley is taken 1.4kg as obtained from

equation 4.3. Diameter of the shaft is calculated as 30 mm using equation 4.4. The

selected ball bearings are SKF 6204 and SKF 6206. A 33 grade V belt is selected using

equation 4.7.

Using the above details a wear testing machine was fabricated. This newly designed and

fabricated wear testing machine is used to conduct the wear test of gunmetal at wet and

dry condition and the result obtained are as given below.

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Figure 6.1 shows the result obtained when the bearing is tested for 20 and 30N under dry

condition.

Figure 6.1. Wear rate for the bearing specimen (Dry condition)

From figure 6.1 it can be seen that wear rate is high at the beginning of the test and as the

time increases it can be seen that the wear rate gets reduced. The initial increase in wear

rate is due to the high frictional force at the start of the test. Later on it can be seen that

the wear rate decreases as the coefficient of friction decreases. The result obtained is

given in the table 6.1 and table 6.2.

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Table 6.1. Applied load 20 N under Dry condition

Time in minutes Volume loss in m3 Wear rate mg/km

10 3.82E-10 2.5

20 2.02E-10 1.322

30 1.80E-10 1.175

40 1.57E-10 1.03

50 1.35E-10 0.88

60 1.34E-10 0.88

Table 6.2. Applied load 30 N under Dry condition


10 7.42E-10 4.85

20 2.35E-10 1.54

30 2.02E-10 1.32

40 1.79E-10 1.17

50 1.68E-10 1.10

60 1.57E-10 1.03

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Figure 6.2 shows the result obtained when the bearing is tested for 20 and 30N under wet

condition.

Figure 6.2. Wear rate for the bearing specimen (wet condition)

From figure 6.2 it can be seen that wear rate is high at the beginning of the test and as the

time increases it can be seen that the wear rate gets reduced. From the result obtained for

the wet condition, it can be seen that the wear rate of the bearing material is about three

times less compared to the dry condition. The result obtained is given in the table 6.3 and

table 6.4.

Table 6.3. Applied load 20 N under wet condition

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Time in minutes Volume loss in m3 Wear rate mg/kg

10 1.46E-10 0.95

20 0.449E-10 0.294

30 0.337E-10 0.220

40 0.225E-10 0.147

50 0.225E-10 0.147

60 0.112E-10 0.07

Table 6.4. Applied load 30N under wet condition


10 1.69E-10 1.10

20 0.67E-10 0.441

30 0.56E-10 0.368

40 0.449E-10 0.294

50 0.337E-10 0.221

60 0.225E-10 0.147

The cumulative volume loss for the material under the dry and wet conditions are given

in the figures 6.3 and 6.4 respectively. From the figures it can be infered that the

cumulative volume loss increases as the time increases.It can also be found that the

cumulative volume loss is high under the dry condition.

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Figure 6.3. Cumulative volume loss of bearing at dry condition

Figure 6.4. Cumulative volume loss of bearing at wet condition

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Figure 6.5 shows that the wear rate of the specimen for both dry and wet conditions,

when loads of 20 N and 30N are applied. For the dry condition we can see that the wear

rate increases as the applied load is increased. In the wet condition also we can see an

increasing trend in the wear rate as the applied load is increased. This is because for the

lubricated case, as the load is incrased, the coefficient of friction increases due to

decrease in the oil film thickness.

Wear Rate Vs Applied Load

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.82

0 10 20 30 40 50

A lied Load in Newton

WearRateinmg/km

Dry Conditio

Wet Conditio

Fig. 6.5. Wear rates of bearing speciman at different conditions

CONCLUSIONS

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In this project a new sliding bearing wear testing machine was designed and fabricated.

Using the newly designed machine the wear rate of Gun metal was found both at wet and

dry condition with applied loads of 20 N and 30 N .The plots for wear rate Vs time for

the bearing specimen under wet and dry condition were obtained, from the result it is

inferred that the wear rates were initially high and later decreases as the time increases. It

is also found that the wear rate for wet condition is much less than that obtained for the

dry condition. The cumulative loss for the bearing material is also found. The results for

wear rate Vs applied load is also found for both wet and dry condition. For the dry

condition we can see that the wear rate increases as the applied load is increased. In the

wet condition also we can see an increasing trend in the wear rate as the applied load is

increased. This is because for the lubricated case, as the load is increased, the coefficient

of friction increases due to the decrease in oil film thickness.

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REFERENCES

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[7] A. Alp,A. Erdemir. Energy and wear analysis in lubricated sliding, Science direct,

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