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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
Time in minutes Volume loss in m3 Wear rate mg/km
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
Time in minutes Volume loss in m3 Wear rate mg/km
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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[2] Shi Z et al. Unlubricated rolling-sliding wear mechanisms of complex aluminium
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[3] Li Y et al. Mechanical, friction and wear behaviors of a novel high-strength wear-
resisting aluminum bronze against steel, Science direct , Wear197(1996), pp. 130-
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[4] Huq MZ. Reproducibility of friction and wear results inball-on-disc unidirectional
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[5] Mingwu Bai. Reciprocal sliding wear of SIC particle-reinforced Al-Cu aluminium
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[6] Zhenfang Zhang. Modeling steady wear of steel/Al2O3Al particle reinforced
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[7] A. Alp,A. Erdemir. Energy and wear analysis in lubricated sliding, Science direct,
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