KAMAL AKHTAR F.(120450119156)

MACHINE DESIGN - 1MECHANICAL-5CS.V.M.I.T.-BHARUCH

Prepared By…

Topic’s….

BELT TENSIONING METHODS

Chain drive introduction

Power transmitted by chain

Polygon effect in chain

BELT TENSIONING

METHODS

In order to transmit the power, the belt must be

provided with the sufficient initial tension.

In addition to the other parameters, the power

transmitting capacity of the belt drive also depends

upon the initial tension.

When a new belt is mounted on pulleys under tension;

it loses its initial tension due to elongation during its

service.

Hence, it is necessary to make a provision to adjust

the belt tension from time to time.

When the belts are hinged, as in case of flat belts, a

small length of belt can be cut to remove the slack .

However, this is not possible with endless belts.

Manual adjustment

In this method, as shown in the fig. the motor

can slide in the guidways provided in the base

plate.

The position of motor, and hence the initial

tensing can be adjusted manually with the help

of the screw and nut arrangement.

Once the desired tension is achieved, then the

bolts are tightened to fix the motor to the base

plate.

There are the weight of the motor is used to maintain the belts tension.

The motor is bolted to the base plate which is mounted on the pivoted support.

The belt tension is due to product of the weight W of the motor and the moment arm ‘e’.

By shifting the motor along the pivoted support, the moments arm ‘e’ can be adjusted so that the belt tension can be adjusted according to the power recruitments. This arrangement is popularly known as ROCKWOOD BELT DRIVE.

𝒆 =(𝑭𝒕𝟏× 𝒂) + (𝑭𝒕𝟐× 𝒃)

𝑾

There are idler pulley is held against the belts

by is own weight and the adjustable weight.

By changing the position of the adjustable

weight, the required belts tension can be

achieved.

In addition to adjusting the belt tension, the

idler pulley arranging also increases the arc of

contact.

Hence, this method’s advantage is as in drives

with short center distance and having a high

speed ratios.

Thank you

CHAIN DRIVES

What is chain Drive?

Chain drive is a way of transmitting

mechanical power from one place to another.

Construction

Chain drives consists of endless chain i.e rigid

links hinged together by pin joints running

around two sprocket (toothed) wheels.

ADVANTAGES.

Chain drives do not slip

Is a positive drive..so can be used in

application where constant speed

ratio is required.

Can be used for short as well as

long centre distances

Transmits large power over long distance

Compact compared to belt drives

Chains requires no tension on slack side, so bearing loads are reduced

Less expensive than gear drives.

Can operate at higher

temperatures than belts

No. of shafts can be driven by single

driving shaft using chain drive

Has high transmission efficiency as

much as 98%.

LIMITATIONS

High production cost of chains.

Due to polygon effect,it is not suitable

where precise motion is required.

Operates with noise.

Require proper maintenance.

Periodic lubrications & slack

adjustment are required.

Applications

Used for speed ratios upto 10:1

,velocities upto 25m/s & power

ratings upto 150kw.

Used in bicycles,motor

cycles,rolling mills,conveyors etc.

Thank you

Power Transmitting Chains

These chains are used for transmission of

power, when the distance between the centers

of shafts is short. These chains have provision

for efficient lubrication.

The power transmitting chains are of the

following three types….

Block chain

Bush roller chain

Inverted tooth or silent chain.

Block chain

A block chain, as shown in Fig11.31. is also known as

bush chain. This type of chain was used in the early

stages of development in the power transmission.

It produces noise when approaching or leaving the teeth

of the sprocket because of rubbing between the teeth

and the links.

Such type of chains are used to some extent as

conveyor chain at small speed.

Bush roller chain

A bush roller chain, as shown in Fig. 11.32, consists of outer plates or pin link plates,

inner plates or roller link plates, pins, bushes and rollers.

A pin passes through the bush which is secured in the holes of the roller between the

two sides of the chain.

The rollers are free to rotate on the bush which protect the sprocket wheel teeth

against wear.

A bush roller chain is extremely strong and simple in construction.

It gives good service under severe conditions. There is a little noise with this chain

which is due to impact of the rollers on the sprocket wheel teeth.

This chain may be used where there is a little lubrication.

The rollers then fit unequally into the cavities of the wheel.

The result is that the total load falls on one teeth or on a few teeth.

Inverted tooth or silent chain.

An inverted tooth or silent chain is shown in Fig. 11.33. It is designed to

eliminate the evil effects caused by stretching and to produce noiseless

running.

When the chain stretches and the pitch of the chain increases, the links ride

on the teeth of the sprocket wheel at a slightly increased radius.

This automatically corrects the small change in the pitch.

There is no relative sliding between the teeth of the inverted tooth chain

and the sprocket wheel teeth.

When properly lubricated, this chain gives durable service and runs very

smoothly and quietly.

Thank you

𝐷 =𝑝

sin(180𝑧 )

𝛾 =360

𝑧

Thank you