TODAY TOPIC Chain Drivers

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Transcript TODAY TOPIC Chain Drivers

Chain Drivers
Why we need chain drivers?
On belt and rope drives that slipping may
occur. In order to avoid slipping, steel
chains are used.
The chains are made up of number of rigid
links which are hinged together by pin joints in
order to provide the necessary flexibility for
wrapping round the driving and driven wheels.
These wheels have projecting teeth of special
profile and fit into the corresponding recesses
in the links of the chain as shown in Fig. The
toothed wheels are known as *sprocket
wheels or simply sprockets.
Explanation through diagram
Practical applications of
chain drives
The chains are mostly used to transmit motion
and power from one shaft to another, when the
centre distance between their shafts is short
such as in bicycles, motor cycles, agricultural
machinery, conveyors, rolling mills, road rollers
The chains may also be used for long centre
distance of upto 8 metres.
The chains are used for velocities up to 25 m / s
and for power upto 110 kW. In some cases,
higher power transmission is also possible.
Advantages and Disadvantages of
Chain Drive over Belt or Rope Drive
As no slip takes place during chain drive, hence perfect velocity ratio is obtained.
Since the chains are made of metal, therefore they occupy less space in width than a
belt or rope drive
It may be used for both long as well as short distances
It gives a high transmission efficiency (upto 98 percent).
It gives less load on the shafts.
It has the ability to transmit motion to several shafts by one
chain only.
It transmits more power than belts.
It permits high speed ratio of 8 to 10 in one step.
It can be operated under adverse temperature and
atmospheric conditions.
The production cost of chains is relatively high.
The chain drive needs accurate mounting and
careful maintenance, particularly lubrication
and slack adjustment.
The chain drive has velocity fluctuations
especially when unduly stretched.
Terms Used in Chain Drive
Pitch of chain
It is the distance between the hinge centre of a link and the corresponding hinge centre
of the adjacent link, as shown in Fig. It is usually denoted by p.
Pitch circle diameter of chain sprocket.
It is the diameter of the circle on which the hinge centres of
the chain lie, when the chain is wrapped round a
sprocket as shown in above Fig. The points A, B, C, and
D are the hinge centres of the chain and the circle
drawn through these centres is called pitch circle and its
diameter (D) is known as pitch circle diameter.
Relation Between “Pitch” and “Pitch
Circle Diameter (p and d)
Relation Between “Pitch” and “Pitch
Circle Diameter (p and d)
A chain wrapped round
the sprocket is shown in
Fig.. Since the links of
the chain are rigid,
therefore pitch of the
chain does not lie on
the arc of the pitch
The pitch length
becomes a chord.
Consider one pitch
length AB of the chain
subtending an angle Ө
at the centre of
sprocket (or pitch
D = Diameter of the pitch circle, and
T = Number of teeth on the sprocket.
From Fig. we find that pitch of the chain
We can observe that:
AC = OA sinθ = OA sin(180/T ).
As AC = p/2 and OA = d/2,
p/2 = (d/2)sin(180/T )
p = d sin (180/T )
Or d = p cosec (180/T )
Kinematics of Chain Drive
Let us consider two sprockets, in which driven sprocket
is larger than the driver sprocket. AC is the pitch of
driving sprocket, and BB2 is the pitch of driven sprocket.
We want to compare the angular velocities of two
Kinematics of Chain Drive
Initially when the driving sprocket was at A, the driven
was at B, with the centers O1 and O2 respectively. To
find the instantaneous centre, we produce O1O2 and AB
to meet an point I.
Kinematics of Chain Drive
If ω1 and ω2 are the angular velocities of
driver and driven sprockets respectively,
ω1 * O1I = ω2 * O2I
ω1/ ω2 = O2I/ O1I
= (O2O1+ O1I)/ O1I
ω1/ ω2 = 1+(O2O1/ O1I).
So, ω1/ ω2 is inversely proportional to “O1I”.
Kinematics of Chain Drive
The instantaneous centre of rotation changes along with
the rotation.
The relation ω1/ ω2 = 1+(O2O1/ O1I) represents the
minimum velocity ratio, as B is the lowest point of pitch
and I is at the greatest distance from the driving
Kinematics of Chain Drive
When A moves to A1, B moves to point B1.
So the instantaneous centre of rotation
will be I1.which as compared to I, is
nearer from the driven sprocket. So
velocity ratio will be maximum.
Kinematics of Chain Drive
In actual practice, the smaller sprocket
must have a minimum of 18 teeth and
hence the variation of velocity ratio from
the mean value is very small.
Classification of Chains
The Chains, on the
basis of their use,
are classified into
the following three
Hoisting or hauling
(or crane) chains.
Conveyer (or
tractive) chains.
Power transmitting
Hoisting or hauling (or crane)
These chains are used for hoisting and
hauling purposes. These are of two
Chains with oval links.
Chains with square links.
Hoisting or hauling (or crane)
Chains with oval
The links are
of oval shape. The
joint of each link is
welded. Such type
of chains are used
only at low speeds
such as chain hoists
and in anchors of
marine work.
Hoisting or hauling (or crane)
Chains with square links:
The links are of square
shape. Such type of chains are used in
hoists, cranes, dredges. These are
cheaper than oval link chains, but the
kinking occurs easily on overloading.
Conveyer Chains
These chains are
used for elevating
and conveying the
continuously. These
are of two types:
Detachable or hook
joint type chain.
Closed joint type
Conveyer Chains
Usually manufactured by cast iron.
Do not have smooth running qualities.
Run at low speeds of about 3 to 12
Power transmittin chains
of power when the distance between the shafts is short
•Have provision for efficient lubrication
Three types
1.Block chain
2.Bush roller chain
3.Inverted tooth or silent chain
Power transmittin chains
Block chain
it is also known as bush chain
Produce noise because of rubbing between teeth and links
Power transmittin chains
Bush Roller chain
it consist of
1. Outer plate or pin link plate
2. Inner plate or roller link plate
3. Pins
4. Bushes
5. Rollers
Advantages of bush chain
•Simple in construction
•It gives good service under sever
•Can be used with little lubrication
•Produce little noise
•Rollers resist wear
inverted tooth or silent chain
•Noiseless running
•Eliminates the effects on chain
and sprocket caused by stretching
Length of chain
L=∏(r1 + r2)+2x+ (r1 -
Numerical Examples
A chain drive is used for reduction
of speed from 320rpm to 128rpm. The
number of teeth on driven sprocket is 50,
(a)Find the number of teeth on driving
(b)If the pitch circle diameter of driving
sprocket is 300mm, find out the pitch of
chain drive.
Numerical Examples
A chain drive having a speed of driving
sprocket 220rpm, and the number of teeth
on the driving and driven sprocket are 24
and 48 respectively.
(a) Find out the driven speed of sprocket.
(b) If p=25mm, find out the circle
diameter of driven sprocket.
(c) If k=33, find out the length of chain.
Numerical Examples
A chain drive is used for reduction of
speed from 240rpm to 120 rpm. The
number of teeth on the driving sprocket is
20. Find the number of teeth on the
driven sprocket. If the pitch circle
diameter of the driven sprocket is 800mm,
determine the pitch and length of chain.
Numerical Problem
A chain drive is used for increase in speed
from 180rpm to 360rpm. The number of
teeth on the driven sprocket is 30. If the
pitch circle diameter of the driving
sprocket is 900 mm and center to center
distance between two sprockets is
Determine the length and the pitch of the