Coupling

It is the mechanical element used to connect two shaft of a transmission system and transmit the torque from one shaft to another

Coupling

COUPLING

It is the mechanical element used to connect two shafts of a transmission system and transmit the torque from one shaft to another.

Functions of coupling: It connects the shafts of two different units such as an electric motor and

machine.

It introduces mechanical flexibility between two connected units and tolerates small misalignment between the connecting shafts.

It reduces the transmission of vibrations and shocks between two connected units.

Requirements of good coupling

• It should transmit the full power from one shaft to another.

• It should keep the shafts in perfect alignment.

• It should absorb the slight misalignment that may be present between the driver and drive shaft.

• It should be easy to connect and disconnect.

• It should have no projecting parts.

Types of Coupling

• Rigid couplings– Muff and sleeve coupling– Split muff or compression coupling– Flanged coupling

• Flexible Couplings– Bushed-pin type flexible coupling– Oldham coupling– Universal coupling

Rigid Couplings

• Rigid couplings are used to connect two shafts which are perfectly aligned.• These couplings are not capable of tolerating any misalignment between

two shafts.• These couplings are not capable of absorbing shocks and vibrations.• These are simple and inexpensive.

.

Rigid Flanged coupling

Rigid couplings

• Rigid couplings do not allow any misalignment of connecting members.

• Not of absorbing shocks and vibration.

Muff and sleeve coupling

Use to connect two line shafts

• Muff and sleeve coupling• Split muff or compression coupling• Flanged coupling

A protected type rigid flange coupling

It consists of two flanges : one keyed to the driving shaft and other to the driven shaft. One of the flange has projected portion and other has a corresponding recess. This helps to bring two shafts in line and maintain the alignment.The two flanges are coupled together by means of bolts and nuts. The number of bolts used are generally three, four or six. The two keys are staggered at right angles along the circumference of the shafts.• The flanges are made of cast iron, cast steel, or steel.

The torque is transmitted from the driving shaft to the left side flange through the key. It is then transmitted from the left side flange to the right side flange through the bolts. Finally, it is transmitted from the right side flange to the driven shaft through the key.

Advantages 1. The flange coupling is easy to assemble and

disassemble.2. It has high torque transmitting capacity.Disadvantages 3. The flange coupling cannot tolerate misalignment

between driving and driven shafts.4. It requires more radial space.Applications

The flange coupling is used for connecting electric motor to pump or compressor.

Split muff or compression coupling

Flexible couplings

• It is used to connect shafts having small amount of lateral or/and angular misalignment.

• These coupling are capable of absorbing shocks and vibration.

• Bushed-pin type flexible coupling• Oldham coupling• Universal coupling

Bushed-pin type flexible coupling

Used to connect diesel engine to generator

Oldham coupling

Use to connect Two eccentric shafts

Universal coupling

Sr. No. Comparison Parameters Rigid Coupling Flexible Coupling

1 Purpose To connect two shafts which are perfectly aligned

To connect two shafts having small misalignment

2 Alignment Cannot tolerate any misalignment

Can tolerate any misalignment

3 Shock and vibration Cannot absorb Shock and vibration

Can absorb Shock and vibration

4 Deflection Deflection is less Deflection is more

5 Cost Less expensive More expensive

BearingsIntroduction• Bearing is a mechanical element, which supports the

rotating element. Thus it permits the relative rotating motion between two parts.

• Due to relative motion, a moving part comes in contact causing friction with the stationary part, resulting wear of mating surface. To reduce the frictional resistance and wear, a lubricant is provided between the mating surface.

• A lubricant is a substance placed between the two surfaces which reduces friction, wear and takes away heat is known as lubricant.

• Generally mineral oil, vegetable oil or grease are used as lubricant in bearings.

Types of Bearings

a) Sliding Contact Bearingsb) Rolling Contact Bearings

Sliding Contact Bearings

• In sliding contact bearings, the motion between the shaft and the bearing is purely sliding. Because of the surface contact, the friction between the rotating shaft and bearing surface is high and hence lubrication is necessary.

• They are used for crankshaft in I.C. engine, ball mills, centrifugal machines in sugar industry, turbo-generators centrifugal pumps. etc.

Rolling Contact Bearing

• Rolling motion takes place along the surfaces of contact between the parts. Steel balls or rollers are interposed between the moving and fixed elements, which offer rolling friction. They are also known as antifriction bearings. They have point or line contact with moving element.

Ball bearing

Single Row Double Row

The Ball Bearing

• It is as shown in Fig.• It also consists of four major

parts.(i) Outer race (ii) Inner race (iii) Balls and (iv) Cage

• It consist of number of balls placed between the races. The balls are placed properly by the cage, which acts like a separator. All balls are free to rotate within the cage and are able to roll inside the outer race and inner race.

• A position clearance is kept between the races to accomplish slight misalignment of balls due to load.

• Ball bearings are able to take only radial loads. It is used in high speed applications like grinders, cutters etc.

• Deep groove ball bearings are able to sustain radial load as well as axial (thrust) load.

Deep Groove Ball Bearing

Cylindrical Roller Bearing

Angular Contact Bearing

Taper Roller Bearing

Self-Aligning Bearing

Thrust Ball Bearing

Sr. No. Comparison parameter Ball bearing Roller Bearing

1 Rolling bearing Spherical ball Cylindrical roller

2 Nature of contact Point contact Surface contact

3 Load carrying capacity low High

4 Radial dimensions More Less, use for compactness

5 Axial dimensions less more

Sr. No. Comparison parameter Sliding contact bearing Rolling contact bearing

1 Nature of relative motion sliding rolling2 Starting friction high low3 Running friction low High4 Load carrying capacity More Less, use for compactness5 Nature of load Can take shock load Poor in taking shock load6 Type of load Either radial or axial Can take combine radial & axial

7 speed Suitable for high speed application Not suitable for high speed

8 Life More Less9 Positional accuracy Poor Good10 Lubrication Required continuous supply Not Required continuous supply

11 Noise Noise less More noise12 Initial cost High Low13 Maintenance More less14 Application Steam and gas engine, crankshaft

bearing, marine, conveyors, centrifugal pumps

Automotive gear box, m/c spindle, automobile