Syllabus

Part A: Mechanical Elements

Function, sketch, description and uses of shaft, axle, key (parallel key), coupling, (rigid flange), bearing (ball), clutch (single plate clutch), brake

Part B: Power transmission devices

Construction, working, comparison and applications of: Belt drive (flat and V-belt), chain drive and spur gear drive arranged with simple gear train.

Part A Mechanical Elements

Syllabus

Function, sketch, description and uses of shaft, axle, key (parallel key), coupling, (rigid flange), bearing (ball), clutch (single plate clutch), brake

Introduction to machine

Device consisting of various elements arranged together so as to perform the prescribed task to satisfy human needs.

Examples- pump set, I.C. engine, turbine, screw jack, C-clamp etc.

Machine (arrangement of elements)

Input (source of

energy)

Output (prescribed

task)

Introduction to machine elements It is individual part or component of a machine which performs

specific task.

Functions of machine elements are holding, supporting, transforming.

Types of machine elements 1. Holding- Axles, nuts and bolts, cotters, rivets, clamps

2. Supporting- Axle, bearing, brackets, body or frame

3. Power transmitting- shafts, pulleys, belts, sprocket, chains, gears etc.

Machine

E1 E2 E3 E4

Shafts Rotating member usually of circular C/S used to

transmit power or motion.

For this purpose, various rotating members such as gears, pulleys, sprockets etc. are mounted on it.

Fig. Shaft

Types of shafts

1. Transmission shaft

2. Machine shaft

Types of shafts 1. Transmission shaft

Fig. Transmission shaft

Used to transmit power between the source and the machines absorbing power.

They carry machine elements like pulleys, gears, flywheels, etc.

These shafts are subjected to bending and torsional moment.

M F G

G Machine

2. Machine shafts

Fig. machine shaft (drilling machine spindle)

They form an integral part of the machine itself.

They are also subjected to bending and torsional moment.

For example: Cam-shaft, crankshaft, machine spindle, etc.

Types of shafts

Spindle

Drill

Axle

An axle is a non-rotating or stationary machine element which carries no torque.

It is used to support the rotating machine elements like pulleys, brake drum, wheels, etc.

Though it is similar to shaft, it does not transmit torque; but it is subjected to bending moment only.

Whee l

Axle

Comparison between shaft and axle

Sr. No. Shaft Axle

1. Rotating element of a machine

Non-rotating or stationary element

2. Subjected to bending and torsional moment

Subjected to only bending moment

3. Used to transmit torque and support rotating elements.

Used to support rotating elements.

4. for. example: Machine shaft, transmission shaft

For example: front axle in 4-wheelers, 2- wheelers.

KEYS A key is the piece inserted in a axial direction between a shaft and hub to prevent

relative rotation but allow sliding movement along the shaft if required. Keys are temporary fastening and are always made of mild steel because they are

subjected to shearing and compressive stresses caused by the torque they transmit.

a keyway is the groove cut in the shaft or hub to accommodate a key. Key ways can be milled horizontally or vertically .

Functions: To prevent the relative motion between the shaft and the hub of rotating

element like : gear, pulley, or sprocket.

To transmit the torque from the shaft to the rotating element or vice-versa.

Keyway is a slot in a shaft and a hub of the rotating element to accommodate a

key.

It is inserted between the shaft and the hub of the rotating element so as to

prevent the relative motion between them.

Materials for key: Plain carbon steels

Alloy steels.

KEYS

Types of keys Saddle keys

Hollow saddle key Flat saddle key

Sunk keys Taper sunk keys Parallel sunk keys Father keys

Woodruff key (adjustable key)

Round keys Parallel pin Taper pin

Tangent keys Splines

Gib-headed key

Woodruff key

Taper sunk key

Taper sunk key

Kennedy keys consist of two tapered square keys placed 90 apart. Applications : Kennedy keys are used in heavy duty industrial applications.

A round key is a straight pin of circular cross-section, fitted into a common hole drilled at the interface of shaft and hub Applications : Round keys and taper pins are commonly used for low power drives.

A taper pin is a pin of circular cross-section, fitted into a common hole drilled through the hub and shaft, which is perpendicular to the axis of the shaft.

COUPLING

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

Shaft 1 (driving) Shaft 2 (driven)

Fig. Coupling

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 Couplings Rigid coupling

Muff or sleeve coupling

Split muff or clamp coupling

Flange coupling

Flexible Coupling

Bushed-pin type

Universal or Hooke's

Oldhams coupling

Bushed-pin type

Types of couplings Oldham's 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.

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 1. The flange coupling cannot tolerate

misalignment between driving and driven shafts.

2. It requires more radial space. Applications The flange coupling is used for connecting

electric motor to pump or compressor.

Protected type rigid flange coupling

Protected type rigid flange coupling

Bearings Bearing is a machine element which supports another

moving machine element called as journal.

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

Due to relative motion between the contact surfaces, there is friction and wear hence lubricant is required.

The commonly used lubricants are vegetable oil, silicon oil, grease, etc.

Bearing

Function of a Bearing

The main function of a rotating shaft is to transmit power

from one end of the line to the other.

It needs a good support to ensure stability and

frictionless rotation. The support for the shaft is

known as bearing.

The shaft has a running fit in a bearing. All bearing are

provided some lubrication arrangement to reduced friction

between shaft and bearing.

It also sustains the forces acting on the shaft or axle and

transmits them to the frame of the machine.

Bearings are classified under two main categories:

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.

Rolling or anti-friction bearing : - Due to less contact area rolling friction is

much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.

Rolling contact bearing- Ball bearing

Major parts: Outer race Inner race Rolling element Separator or retainer

Types of ball bearings 1. Single row deep-groove ball bearings

2. Double row deep-groove ball bearings

3. Angular contact bearings

4. Self-aligning bearings

Roller bearing

Clutches Clutch is a mechanism to transmit rotary motion from one

shaft (driving shaft) to another coincident shaft, (driven shaft), as and when required, without stopping the driver shaft.

Clutches are also required to disengage the drive from engine to gearbox for changing the gears.

During slowing of vehicle or stopping, the clutch is used to disengage engine from drive wheels and enable smooth stopping of vehicle.

Since clutch is of friction material, it also takes care of speed and torque variation from engine crankshaft to gearbox input shaft.

Functions of the clutch

When clutch is engaged (clutch pedal position-up), the clutch transmits maximum power from engine crankshaft to gearbox input shaft.

When clutch is engaging (clutch pedal position-moving up), the clutch accommodates for minor slippages and hence provides smooth drive transmission without jerks.

When clutch is disengaged (clutch pedal position-down), the clutch allows driver to shift the transmission in various gear positions (first, second, third, etc.)

When clutch is disengaged (clutch pedal position-down), the engine can be cranked freely without transmitting the drive to wheels.

Types of Clutches 1. Friction clutches

These clutches work on the friction principle that when two independent disc have relative motion between them, friction is caused.

Friction clutches are the most commonly used clutches.

2. Positive clutches These clutches are used when positive drive is

required.

These type of clutches are used in sprocket wheels, gears, pulleys, etc.

Single Plate Clutch

Single plate is the most commonly used type of clutch on automobiles.

It provides quicker disengagement.

It consists of clutch disc, pressure plate, and a cover assembly which are bolted to the engine flywheel.

Single plate clutch

Major components Flywheel Friction plate Pressure plate Thrust spring Release lever Clutch cover Clutch shaft Thrust bearing

Advantages & Disadvantages

Advantages : Simple design of construction and working.

Better heat dissipation from single plate.

Gear changing with single plate clutch is easier.

It has better torsional vibration absorbing capacity.

Disadvantages : For higher power transmission, the surface area of

clutch plate increases and thereby increasing the overall size of clutch.

Clutch pedal force required is higher.

Brakes Brake is a device with the help of which artificial

frictional resistance is applied to a moving machine member, in order to stop or retard the motion of a machine.

While performing this function, the brake absorbs either kinetic energy of the moving member or potential energy given by objects being lowered by cranes, elevators, etc.

The energy absorbed by the brake is dissipated in the form of heat in the surrounding air, so that excessive heating of the brake lining does not take place.

Brakes

Mechanical brakes

Electric brakes

Magnetic brakes

Hydraulic

brakes

Types of brakes

1. Block brakes 2. Disc brakes 3. Band brakes 4. Internal or

external shoe brake

Disc Brake Disc brakes are more efficient and now-a-days

being adopted on large scale in the automotive segment.

It consists of a rotating brake disc mounted on the wheel and two friction pads positioned on either side of the disc.

The pressing of the stationary brake pads on the revolving disc causes friction, resulting in braking.

Advantages & Disadvantages Advantages : The operation and assembly of disc brake is much

simpler.

As the friction pads are flat, the wear and tear is uniform.

Heat dissipation is faster.

Disadvantages : The overall system cost is higher due to hydraulic

caliper and fluid lines.

The frictional area of pads is less, thereby requiring high pressure intensity fluid.

Part B Power transmission devices

Syllabus

Construction, working, comparison and applications of: Belt drive (flat and V-belt), chain drive and spur gear drive arranged with simple gear train.

Introduction

Usually power is transmitted by means of belts, ropes, chains and gears.

For large distances, belt, ropes and chains are used and for smaller distances, gears are used.

Belts, ropes and chains are flexible type of connectors.

Owing to slipping and straining action, belts and ropes are not positive drive.

On the other hand, chains and gears are positive drives (rigid).

Belt drives

Belt drive

It consists of 3 elements: Driving or head pulley Driven or tail pulley Endless belt

Power is transmitted because of frictional grip.

Speed ratio of belt drive: speed ratio = speed of driving pulley/speed of driven pulley = n/N = D/d = (D+t)/(d+t) Where, n and N = speed of driving and driven pulley in RPM d and D = diameters of driving and driven pulleys in mm t = thickness of belt in mm.

Types of belts

Sr. No. Type Characteristics

1. Flat belt Rectangular C/S Moderate amount of power Used when pulleys are not more than 8 m apart Crowned pulleys are used

2. V-Belt Trapezoidal C/S Large amount of power and pulleys are nearer Pulleys are provided with groove

3. Circular belt

Circular C/S Large amount of power Pulleys are more than 8 m apart Pulleys are provided with groove

Materials used for belts Leather Cotton Rubber Balata

Comparison between flat and V-belt Sr. No.

Parameter Flat belt V-belt

1. Cost Low Higher

2. Maintenance Low Higher

3. Multiple speed ratio Can be used Cannot be used

4. Simplicity of design Simple to design Complex

5. Efficiency Higher Lower

6. Long center distance Can be used Short distances

7. Working environment Dusty and abrasive atmosphere

Dust free environment

8. Power trans. Capacity Lower High

9. High speed reduction Upto 4:1 Upto 7:1

10. Overall size of drive Bigger size Compact size

11. Use of multiple belts Restricted for single belt Multiple belts can be used

12. Smoothness of drive More noisy at higher speeds

Relatively smooth

Types of flat belt drives

Open belt drive

Crossed belt drive

Open belt with idler pulley drive

Compound belt drive

Advantages and disadvantages of belt drive Advantages Can be used for long Centre distances

Absorb shocks and vibrations

Lubrication is not required

Not affected due to dirt and dust

Do not require precise alignment of shaft and pulley

Disadvantages Low power transmitting capacity

Can not be used at extremely high speeds

Shorter life and more space as compared to gear drive

Not positive drive

Chain drive

To avoid slipping, chain drives are used Chain drive consists of chain and sprocket Chains are made up of no of rigid links hinged together Sprockets have projecting teeth of special profile and fit into the

corresponding recesses in the chain links. This drive is commonly used to transmit motion from shafts having

shorter centre distances. Used in bicycles, motor cycles, conveyors, road rollers, rolling mill,

agricultural machinery, etc.

Types of chain drive 1. Hoisting and hauling (crane) chains

2. Conveyor (tractive)chains

Used for hoisting purposes Operate at maximum velocity Links may be of oval or

square shape Oval shape is commonly used

Used for elevating and conveying materials

Operate at moderate speed Chains are made of CI Links may be of hook joint or closed

joint type

Advantages and disadvantages of chain drive over belt drive

Advantages No slip hence perfect speed ratio

Less space in width than belt drive

More transmission efficiency

Offers/provides less loads on the shafts

Can be operated under low/high temperatures

More power transmitting capacity

Disadvantages More cost

Needs accurate mounting and careful maintenance

Noisy operation

Comparison between chain and belt drive Sr. No.

Parameter Chain drive Belt drive

1. Drive elements Chain and sprockets Belt and pulleys

2. Type of drive Positive Non-positive

3. Power transmitting capacity

High Low

4. Transmission efficiency High Low

5. Space requirement Less More

6. Operating conditions Can operate in adverse conditions

Can not be operated in adverse conditions

7. Lubrication Required Not required

8. Operating noise More Less

9. Precise alignment Required Not required

10. Manufacturing cost More less

Gear drive Gears are defined as toothed wheels

which can transmit power and motion from one shaft to another shaft by means of successive engagement of teeth.

It is a positive drive and used for smaller centre distances.

Spur gear drive

Smaller gear is called as pinion and larger gear is called as gear. Speed ratio = speed of pinion/speed of gear = np /ng = dg /dp = Zg /Zp Where , np ,ng = pinion and gear speed in RPM dg and dp = diameters of gear and pinion Zg and Zp = no of teeth on gear and pinion

Spur gear drive Spur gears are used to transmit motion

between two parallel shafts. Simplest of all gears and easiest in

production Teeth of spur gear are cut along the

periphery and parallel to the axis of gear. They are made of steel, brass, other

metals and plastics. Advantages

Spur gears are easy to manufacture They are made in variety of sizes from less than 25 mm to several cm in

diameter. Less expensive High efficiency (upto 98 %)

Disadvantages Not used for high speed applications Noisy operation.

Applications : commonly used in machine tool gear box, watches, etc.

Gear train A gear train is a combination of two or more gears

which is used for power transmission.

It is used to obtain large speed reduction within a small space.

The nature of gear train used depends upon the required velocity ratio and the relative positions of the axes of the shafts.

They are commonly used in various machines, automobiles, clocks, ships, watches, etc.

Different types of gear trains are simple gear train, compound gear train, reverted gear train and epicyclic gear train.

Simple gear train

Simple gear train

If only one gear is mounted on each shaft and there is no relative motion between their axes then it is called as simple gear train.

If the distance between the two gears is large, then the intermediate gears are used.

If number of intermediate gears are odd then the motion of driver and driven gear is same.

Similarly, if the number of intermediate gears are even then the motion of driver and driven gear is opposite.

Comparison between gear drive and belt drive

Sr. No.

Parameter Gear drive Belt drive

1. Drive elements Gear and pinion

Belt and pulleys

2. Power transmitting capacity High Low

3. Space requirement Less More

4. Lubrication Required Not required

5. Operating noise Moderate Less

6. Precise alignment Required Not required

7. Manufacturing cost More Less

8. Type of drive Positive Non-positive