MECHANICAL TRANSMISSION

Prepared by

Md. Shaha Jalal

ROTARY MACHINERY

Driver Connector Driven

Driver

•Turbine

•Electric Motor

etc.

ROTARY MACHINERY

Connector

•Coupling

•Modifiers

Driven

•Centrifugal

•Reciprocating

•Electrical

•Others

Couplings

•Spring

•Rubber Tyre

•Pin and Bush

•Gear

•Universal Joint

•Rigid

•Spider

Modifiers

•Belts

•Chains

•Fluid Coupling

•Gearbox

CONNECTORS

WHY COUPLING????

Couplings are used to connect two shafts end to

end in the same line to transmit torque or rotary

motion in unison at same RPM.

Some Drives transmit power but not at same

RPM and also not with shaft in same line.

Eg: Belt, Chain,Gear and Clutch drives

• Compensates for angular and parallel

misalignment( Only flexible coupling )

• To restrict the axial movement of

connecting shafts.

• To reduce transmission of shock load

from one shaft to another.

PURPOSE OF COUPLING

BASIC TERMINOLOGY

A measure of the angle between the center lines of

driving & driven shafts, where those center lines

would intersect approximately halfway between the

shaft ends.

Angular Misalignment:

Parallel Misalignment:

A measure of the offset distance between the center

lines of driving and driven shafts.

BASIC TERMINOLOGY

Distance Between Shaft Ends (DBSE) :

Distance between the faces of driving and driven

shafts.

Driving shaft Driven Shaft

DBSE

BASIC TERMINOLOGY

Backlash: Properly functioning mechanical systems need to have a

certain “clearance” (gap or play) between the components

transmitting motion under load.

Clearance is necessary to avoid interference, wear, and

excessive heat generation, ensure proper lubrication,

compensate for manufacturing tolerances, etc. Clearance

in the gear mesh means that the gap between the teeth of

one gear is by a small amount larger than the tooth width

of the mating gear. We also find a certain clearance in the

rolling bearings, namely a small clearance between the

inner race, rolling body (ball, roller) and outer race of the

bearing. The key and keyway of a shaft or hub usually

have clearance also.

BASIC TERMINOLOGY

Bore:

Central hole that becomes the mounting surface for

the coupling on the shaft.

Keyway:

Rectangular slot cut axially along the coupling bore.

Torsional Stiffness:

Resistance to twisting moment between driving and

driven halves of the coupling.

BASIC TERMINOLOGY

RIGID COUPLING

• High torque capacity

• Low Cost

• Easy Assembly

• Balancing design

•It requires same sizes of shaft

•Rigid coupling do not

accommodate for misalignment.

JAW COUPLING

Spider

• Large torque capacity

• Replaceable Spider

• Balancing design

BELLOW COUPLING

Bellow

• High torque capacity

• Balanced for high RPM

• Low Inertia

• No maintenance

• High torsional stiffness

• Constant Velocity

• Long Life

• Zero backlash

DISC COUPLING

Disc

• High torque capacity

• Balanced for high RPM

• Low Inertia

• No maintenance

• High torsional stiffness

• Constant Velocity

• Long Life

• Zero backlash

GEAR COUPLING

Transmitting higher

torques at low and high

speeds

Sleeve halves are bolted

to rigid flanges to form

two single flexing

coupling

Requires Lubrication

*

*

*

GRID FLEX COUPLING

• Simplicity

• Lubrication

• Simple/Ease maintenance

• Low Operational Cost

• Smooth Quieter Operation

RUBBER BLOCK

Low Intial & Operational

Cost

Smooth Power Transmission

Compact Size *

* *

*

Effective damping of

vibrations

TYRE FLEX COUPLING

Accommodate angular, parallel

and axial misalignment

Protects against vibration,

Impact loads and Heavy shocks

Ease of Assembly/Disassembly.

Ease of Alignment *

*

*

*

Bush

PIN BUSH COUPLING

• Simplicity in construction

• Varying stiffness characteristics

• No lubrication

• Simple/Ease maintenance

• Low operational cost

• Smooth and Quieter

Operation

a) Type of driving and driven equipments

b) Torque characteristics:?

c) Maximum and Minimum torque:?

d) Normal and maximum rotational speeds

e) Shaft sizes

f) Span or distance b/w the shafts

COUPLING-SELECTION

g) Changes in span due to thermal growth, racking of

bases or axial movement of connected shafts during

operation

h) Equipment position(horizontal,vertical and inclined)

i) Ambient conditions(dry,wet,corrosive,dust etc.,)

j) Bearing locations:?

k) Cost (initial coupling price, installation, maintenance

or replacement).

COUPLING-SELECTION

BELT

Flat Belts

V-belts

Synchronous Belt

FLAT BELT

• Used for general

purpose, low speed

applications.

FLAT BELT

A- Protective Cover

B-Tension Members

C-Cushion Compound

D-Compression Rubber

• High capacity belts are used to substantially

reduce the drive cost.

V-BELT

SYNCHRONOUS BELT

Also called timing belts and used when driven shaft

speed must be synchronized with the rotation of drive

shaft.

• Reduced vibration

• Reduced noise level

• increased power

• 100% tracking in both running directions without

flanges

• continuous tooth engagement

• Smooth interaction with idler and tensioners running

on the toothed side of the timing belt eliminating tooth

jumping, based on the overlapping tooth arrangement

SYNCHRONOUS BELT-

ADVANTAGES

* Has the advantage

of high flexibility of

flat belt and power

transmission rate of

V-belt.

V-RIBBED BELT

Belt cross

section

Load

KW

Belt top

width

(mm)

Belt

thickness

(mm)

A 0.75-5 13 8

B 2.0-15 17 11

C 7.5-75 22 14

D 22-149 32 19

BELT CLASSIFICATION

Belt width in mm

No. of Plys

Top & Botttom Rubber cover thickness

Belt confirming to code

Carcase Material ..e.g. Cotton,Nylon,Rayon

Carcase material density in OZ I.e. Weight of

carcase material per Sq yard/ply in OZ

Rubber grade..e.g. OR/HR/SHR

HOW TO SPECIFY A BELT?

GEARS

GEAR CLASSIFICATION

GEAR TERMINOLOGY

ADVANTAGES:

•Eliminates end thrust

• Ease of assembly

• Minimum maintenance

• High strength

• Efficient

• Economical

SPUR GEAR

DISADVANTAGES:

Cannot be used when axial

direction change is required.

Can’t use for high load.

HELICAL GEAR

•Greater Tooth strength

•Carry more load than spur gear

•Used to mesh two non-parallel

shafts.

•Less efficient

•Expensive

ADVANTAGES:

LIMITATIONS

STRAIGHT BEVEL GEAR

•Transfer power between

intersecting shaft

•Limited availability

•Not used for parallel shafts

•Become noisy at high speeds.

ADVANTAGE:

LIMITATIONS

SPIRAL BEVEL GEAR

•Teeths are cut in curved

manner

•Smooth and Quieter

Operation

To be used for high

transmission torque.

WORM GEAR

•Tolerate large loads and higher

speed ratios

•Meshes are self-locking

•Low efficiency

•Higher Friction losses.

ADVANTAGE:

LIMITATIONS

HERRING BONE GEAR

• Side by side opposite

hand helical gears

• Eliminates thrust load

• Alignment is very critical

to ensure proper teeth

engagement.

CROSSED HELICAL GEAR

* Crossed gear mesh in

which two shafts are

perpendicular to each

other

RACK AND PINION GEAR

•Only gearing component that

converts rotational motion to

translational motion

•Highly efficient

•Limited usefulness.

ADVANTAGE:

LIMITATION

CHAIN

DRIVES

Three types of chain drives

1, Roller chains

2, Inverted tooth

3, Leaf chains

CHAIN DRIVE-TYPES

• Simplicity of design and selection of components.

• Relatively inexpensive

• Virtually any length of chain can be obtained by

splicing

• Bearing loads are generally lower than for belts.

• Chain drives are 95-99% efficient.

CHAIN DRIVE-ADVANTAGES

CHAIN DRIVE-LIMITATIONS

• Lubrication is critical- non lubricated drives can wear

300 times faster than lubricated drives.

• Lubrication attracts dirt which leads to wear problems

• Life is usually low since an estimated 90-95% of chain

drives are improperly lubricated.

• Alignment is important as it affects life and stability.

• Chain drives are noisy due to metal to metal contact.

• Jerky motion.

ROLLER CHAINS

INVERTED TOOTH

* Transmits higher torques

These chains are used

for lifting loads and do

not involve tooth

sprockets or gear

wheels.

They are used on fork

lift trucks an machine

tools

LEAF CHAINS

FLUID COUPLING

FLUID COUPLING

FLUID COUPLING-INTERNALS