Assignmnt Tribo Dev

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MAHARISHI MARKANDESHWAR UNIVERSITY

Assignment of Tribology on types of bearing materials and wearing resistant materials

Submitted to: Submitted by:

Mr. Arun Kumar Sir Devender Singh

Section: Eb2 (sem. 6th

)

Date: 4 May, 2012


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BEARING MATERIALS

For successful operation of bearing system, it is necessary to select proper material for particular operatio

Following are important bearing materials which are commonly used.

METALLIC GROUP

1. Babbitt metal (or white metal)a. Lead-based babbittb. Tin-based Babbitt

2. Bronze3. Copper lead alloys4. Tin-aluminium alloys5. Silver6. Porous metals7. Hard materials

Figure 1: metallic bearings


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NON-METALLIC MATERIALS

1. Carbon graphite2. Plastics3. Rubber4. Wood

Figure 2: non-metallic bearing

These non-metallic bearings are made of various composite materials like polymers, petroleum products and hav

vast application.


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BABBITT METAL BEARINGS

Figure 3: BABBITT BEARING

Babbitt metal is an antifriction metal alloy first produced by Isaac Babbitt in 1839. These are most important alloyas bearing materials. These alloys consists relatively hard crystals embedded in softer matrix. They are composeprimarily of tin, copper and antimony, with traces of other metals added in some cases and lead substituted for t

in others. Theses have silver appearance and hence the can be sometimes called as White metals.

There are general two classes of babbit :

a. Lead-based alloys.b. Tin-based alloys.

Tin-based white metal is an alloy with minimum 88% tin (Sn) , the rest of alloy composition is Antimony (Sb

copper, cadmium and small amounts of other elements that are added to improve the fineness of grain structure anhomogeneity during the solidification process. This is important for load carrying and sliding properties of th

alloy. Lead content in this alloy composition is an impurity, as the fatigue strength deteriorates with increasing lea

content, which should not exceed 0.2% of cast alloy composition.


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ADVANTAGES

1. Excellent bond ability2. Good conformability3. High score resistance4. Non-corrosive5. Ability to embed dirt6. Low coefficient of friction

DISADVANTAGE

1. Low compressive strength2. Low fatigue strength3. Low-load carrying capacity

BRONZE BEARINGS

Figure 4 : BRONZE BEARINGS

These are common type of bearing materials which are generally used in those working conditions where loadspeeds and temperature are moderate (medium level). These are widely used as bearing material for aircraft an

railways and other heavy machines.

ADVANTAGES

1. Great strength2. Helpful in moderate load, speed, temp.3. Excellent cast ability


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4. Good machining characteristics They can be made as a single solid unit and hence have max reliability

DISADVANTAGES

1.

Adhere to shaft surfaces at higher temperatures2. As the rubbing speed increases due poor lubrication steel journals get heated and bronze score to thsurface

3. Poor conformability4. Poor embeddability5. Used in case when alignment b/w shaft and frame supporting bearing is good

Figure 5: bronze heavy bearings


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COPPER-LEAD ALLOYS

These are generally made of mixture of copper and lead and small amount of other elements like nickel, ti

zinc , etc . These can carry more load (high carrying capacity) as compared to babbitts . Also, these are basical

bonded in thin layers to a backing or steel. These are prepared by casting or by sintering powders which result in

phase of continous phase of copper and unalloyed lead dispersion.

ADVANTAGES1. High compressive strength2. High fatigue strength3. They can be used in load carrying4. Work in high temperatures

DISADVANTAGES

1. Poor conformability as compared to babbitts2. Low embeddability3. These are basically used in the case of rigid shafts where deflection and end rubbing are not encountered


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TIN-ALUMINIUM ALLOYS

Figure 6: tin aluminium alloy

Tin-aluminum bearings were developed to provide bearings that carry high loads. As a bearing material, unalloye

aluminium has a tendency to seize to steel mating surfaces . it was found that 20% of tin added to aluminiu

improves seizure resistance, cold working and annealing helps to prevent brittleness. These are generally used tractors, and diesel engines.

ADVANTAGES

1. Good resistance to corrosion2. High thermal conductivity which helps in removing the heat away from the bearing surface.3. High fatigue strength4. High ductility5. High load carrying capacity6. Excellent service life in engine bearings with loas upto 27.5 MPa7. These bearings have comparatively cooler operations8. These are not expensive

DISADVANTAGES

1.

Moderate embedding properties2. Poor compatibility3. High coefficient of thermal expansion4. If used as a solid un-backed bearings, these alloys are weak to maintain an interference fit5. On cooling theses may shrink and may cause cracks6. Have limited range of working temperatures


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SILVER

Figure 7: silver bearings

Pure silver has many disadvantages. So, silver bearings with overlay have found extensive use in highly loade

aircraft engine bearings with overlay have found extensive use in highly loaded aircraft engines bearings and othheavy duty applications.

An overlay is thin galvanic coating of mainly lead and tin , which is applied directly on bearing material .

The over-layer is soft and ductile coating, its main objective is to ensure good embeddability and conformi

between the bearing sliding surface and the pin surface geometry.

ADVANTAGES

1. Improved embeddability2. More reliable3. High fatigue4. High thermal conductivity5. High load carrying capacity


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DISADVANTAGES

1. Low conformability2. Low embeddability3. Poor score resistance4. High cost of silver5. Low availability of raw material6. They are expensive to manufacture7. Expensive to buy

POROUS METALS (SINTERED METALS)

Figure 8: porous bearing

These are prepared as follows:

Two fine metal powders are mixed together and pressed in dies. After compression, they are sintered by heating high temperature. The temperature used for this process is between the melting points of two metals.

Bearing are submerged in oil for impregnation before use. A bearing of this kind is self-lubricating supplying o

through the interconnected pores and providing an oil film on bearing surface.

ADVANTAGES

1. These are used when there is lack of space2. The sintering operation causes powdered metal bearings to fuse into a strong compact.


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3. These bearings are suitable for light loads and moderate speeds

DISADVANTAGES

1. These can be applicable for low pressure2. Low heat3. No lubrication so life is less


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CARBON-GRAPHITE

Figure 9: carbon-graphite

These bearings are available in simple or complex type housing and can be pressed fitted or mechanically fitted tshaft housing. These are self-lubricating bearings which can operate within wide range of temperatures in air

well as in inert atmospheres. They themselves are also chemically inert.

These bearings find application in water pumps, pistons, piston rings, seal valve, valve parts, pump blades, oven

driers, mixers and filters.


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PLASTICS

Figure 10: plastic bearings

These are most important non metallic bearing material found in daily use. It find use in industrial machinery. Thplastic bearings provide better overall performances.

ADVANTAGES

1. Low value of coefficient of friction2. Less wear3. Good resistor of shocks4. Low cost5. Water can be used as lubricant

DISADVANTAGES

1. Poor thermal conductivity2. Cant operate in high temperatures3. Not strong mechanically


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RUBBER

Figure 11: rubber bearings

These bearings work well in circumstances where abrasive materials are present as lubricants. These bearings ar

used in ships , centrifugal pumps, deep-well pumps, etc.

It has number of parallel faces to support shaft in symmetry with axis of shaft.

ADVANTAGES

1. Resistant to dust and sand2. Low coefficient Of friction3. Works well above 500 rpm4. High conformability5. High embeddabilty


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WOOD

Figure 12: wood bearing

They find their application in light machinery as well as heavy machinery. They provide high resistance to wear.

They are non-contaminating and hence cab be used in food industry.

They are also self-lubricating.


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WEAR RESISTANT MATERIALS

MATERIAL SELECTION

Very generally speaking the property required of a wear-resistant material is the right combination of hardness an

toughness. Since these are often conflicting requirements ,

the selection of the best material will always be a compromise. Apart from the two properties mentioned abovthere are few general properties. Usually the right material for a given wear-resistant application can only b

selected after taking into consideration other factors that determine the rate of wear. Of these the most importan

are: Ambient temperature , or temperature of material in contact with the wear surface .Size distribution

particles flowing over the wear Abrasiveness of these particles. Type of wear to which wear surface subjected (i.e. gouging, sliding, impact, etc.)


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Velocity of flow of material in contact with wear surface moisture content or level of corrosive conditions. Gener

conditions (e.g. design of equipment, head room available, accessibility, acceptable periods of non-availability equipment). Some general guidance on material selection and methods of attaching replaceable components. givexamples of actual wear rates of various materials when handling abrasive materials. The subsequent tables giv

more detailed information on the various wear resistant materials.


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VARIOUS TYPE OF WEARING MATERIALS

In daily life we deal with many type of wearing resistant materials. They are called composite materials. Ma

wearing resistant materials are:

CERAMICS

These are one of the most prominent type of wear-resistant materials now days. We can find use of ceramics

industry as well as in house hold use.

These are used in industry in various machining applications now days these have a vast use. These are more chea

and easy to manufacture and reliable.

Main advantages of ceramics are:1. Easy to manufacture2. Causes no pollution3. Low cost4. Non-reactive with chemicals

Main disadvantages of ceramics are:


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1. They are very brittle2. Cant be used in places were heavy loads are applied3. They cannot be used where there is more fatigue and stress

METALS

Various metals are used in composite materials. Metals with good properties can used in composite materialMetals like hard steel , tungsten, tin are used in composite materials.

Metals are combined to manufacture composites which have vast application in heavy insustries.


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POLYMERS

Various petrochemical by-products can be used to make wear resistant composite materials. They have va

application in todays world.

Some of its application sectors are:

1. Automobile industry2. Space technology3. Aircraft industry4. Defence research5. In interior designing6. Sports goods

Editor: DEVENDER


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