Bearing

Topic Name Bearing

Name Muddassar Awan

THE UNIVERSITY OF LAHORE

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A Bearing is a device that support load and reduces the friction of motion between moving machine parts.

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Plain or slider bearing

Rolling or anti-friction bearing

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Plain or slider bearing : - In which the rotating shaft has a sliding

contact with the bearing which is held stationary. Due to large contact area friction between mating parts is high requiring greater lubrication.

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A linear table with four linear bearings

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Metals and Alloys

(1) Bronze

(2) Cast iron

(3) Steel (4) Silver (5) Copper based alloys (6)Aluminum Based materials

Non- Metal

(1)Wood

(2) Rubber

(3) Plastics

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Collar bearing

Footstep bearing Journal bearing

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Journal bearing – in this the bearing pressure is exerted at right angles to the axis of the shaft. This journal bearing is used for supporting a radial load. Shaft are generally made of mild steel.

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Foot step bearing – in this bearing the bearing pressure is exerted parallel to the shaft whose axis is vertical. Note that in this case the end of the shaft rests within the bearing.

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Collar bearing – Collar bearing mainly used on horizontal which carry a large axial force. Thrust bearing are used in bevel mountings, propeller drives, turbines, etc. Collar bearing also known as “Thrust bearings ”.

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Advantages Plain bearing are cheap to produce and have noiseless operation. They can be easily machined, and have vibration damping properties.

Disadvantages are they require large supply of lubricating oil, they are suitable only for relative low temperature and speed.

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Used rolling element between moving parts.

Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.

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Load on the Bearings

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Ball bearing

Roller bearing

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Ball bearing:

A bearing is type of rolling element bearing which uses balls to maintain the separation between the moving parts of the bearing. The purpose of a ball bearing is to reduce rotational friction and support axial and radial loads.

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Roller bearing:

Roller bearing use cylinder of greater length than diameter. It is typically have higher radial load capacity than ball bearing, but in low axial capacity and higher friction.

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Races and balls are high carbon chrome steel (to provide resistance to wear) machined and highly polished and hardened.

The cages are made of low-carbon steel.

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Deep Groove Ball Bearings

Primarily radial load carrying

Deep groove radial Bearing is one in which the race dimensions are close to the dimensions of the ball that run in it.

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Double row deep Groove

Increases radial load

Single row deep groove ball bearings

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Angular contact ball bearing

Angular contact bearing better support combined loads. The angle of contact on inner race is the same as that on the outer race.

Contact angle 10 to 45

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Dingle row angular contact ball bearings

Double row angular contact ball bearings

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Thrust ball Bearings

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.

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Needle Bearings

Use long and thin cylinder

The greater the contact area the greater the load

Support radial load

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Tapered Roller Bearing

Support high combine loads (wheel bearing)

Wheel rotates with little resistance/friction

Noiseless

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Cylindrical roller bearing :

Use thick and long cylinder.

Roller bearings typically have higher load capacity than ball bearings. If the inner and outer races are misaligned, the bearing capacity often drops quickly compared to either a ball bearing.

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Tapered roller bearing (TRB): TRB can take both radial and axial loads and used for gear

boxes for heavy trucks, bevel-gear transmission, lathe spindles, etc.

Thrust ball bearing: Thrust ball bearing are used for heavy axial loads and low

speeds.

Needle roller bearing: It use small diameter of rollers. They are used for radial load

at slow speed. They have the advantage of light weight and occupy small space.

They are used in aircraft industry, bench-drill spindles, etc.

APPLICATIONS OF ROLLER BEARINGS

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Around 16% of all premature bearing failures are a result of poor fitting or using incorrect mounting techniques. Individual applications may require mechanical, heat or hydraulic mounting methods for correct and efficient bearing mounting. Selecting the mounting technique appropriate for your application will help you extend your bearing’s service life and reduce costs resulting from premature bearing failure.

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Mounting bearings in a cold condition

Mounting bearings using heat

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Small and medium size bearings are generally cold mounted. Traditionally the bearing is mounted using a hammer and a length of old pipe. This practice can cause forces to be transmitted through the rolling elements, causing damage to the raceways. Proper fitting tools help prevent bearing damage by applying the forces to the bearing ring with the interference fit.

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Oil baths are often used for heating bearings prior to mounting. However, this method can contaminate the bearing, resulting in premature bearing failure. Today, induction heating is the most common technique for heating bearings since it allows a high degree of controllability, efficiency and safety.

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When dismounting bearings, care must be taken not to damage other machine components, such as the shaft or housing, as damage can result in compromising the machine’s efficiency and lifetime. Bearings are sometimes dismounted to maintain or replace other components of the machine. These bearings are often re–used. Individual applications may require mechanical, heat or hydraulic dismounting methods and tools to allow safe, correct and efficient bearing dismounting.

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Mechanical dismounting

Dismounting using heat

Hydraulic Techniques

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Bearing life

Bearing speed (rpm)

Accuracy

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• Bearing load – radial, thrust (axial) or both

Radial load Radial load

Thrust load

Bearings are selected from catalogs, before referring to catalogs you should know the followings:

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Life – number of revolution or hours of operation, at constant speed, required for the failure criterion to develop.

L10 = 500 (hours) x 33.33 (rpm) x 60 = 106 = 1 million revolutions

For ball bearings and spherical bearings:

For tapered bearings manufactured by Timken:

L10 = 3000 (hours) x 500 (rpm) x 60 = 90 x 106 = 90 million revolutions

– defines the number of revolution or hours of operation, at constant speed, in such a way that of the bearings tested (from the same group) will complete or exceed before the first evidence of failure develops. This is known as life.

Rating Life

L10

90%

– constant radial load that a group of bearings can carry for L10 life. Basic Dynamic Load Rating, C

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L10 = (C / F)a , a = 3 for ball bearings and a = 10/3 for roller bearings

F = applied radial load

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Select a deep groove ball bearing for a desired life of 5000 hours at 1725 rpm with 90% reliability. The bearing radial load is 400 lb.

Improper Lubrication - 43%

Improper Mounting - 27%

Other Lubrication Causes - 21% Separation in Storage

Temperature Limit Exceeded

Moisture Contamination

Fatigue - 9% Ultimate L10 Life Expectancy

64% of Bearing Failures are Lubrication Related IS Not The Whole Story

In the Industry We Serve, Most Bearings Fail Due To Some Form of CORROSION

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