Chain Drive
Click here to download Chain Drive Selection Procedure and Sample Problem Presentation
One of the most power transmitting component in transportation machines like motor-cycles, bicycles, automobiles, conveyors, agriculture machinery and machine tools. Chain drives are flexible and made of number of links and its a intermediate between belts and gears drives. Chains can only be used to transmit power between parallel shafts. Unlike belt drives, chain drives uses special toothed wheels called sprockets.
Classification of chains
Load lifting chains
Hauling chains
Power transmission chains (roller chains)
Roller Chains
The roller chains has the following parts
Pin
Bushing
Roller
Inner link plate
Outer link plate
Polygonal effect
The chain passes around the sprocket as a series of chordal-links. This action is similar to a non-slipping belt wrapped around a rotating polygon.
For smooth operation of chain drives higher number of teeth 19 or 21 gives better life expectancy to the chain with less noise during operation.
It is preferable to use an odd number of teeth for the driving sprocket in combination with an even number of chain links for uniform wear and tear on the teeth and rollers. (In this case, a particular tooth of the sprocket wheel does not come in contact with a particular link of the chain for every rotation.)
Backsliding of chains
The wear of chain results in the elongation of the chain. In other words the pitch length is increased . this makes the chain to ride out on the sprocket teeth resulting in faulty chain sprocket engagement.
Galling
Galling is stick slip phenomenon between the pin and bushing. When the load is heavy and the speed is high , the highspots(joints) of the contacting surfaces are welded together .
Need for Lubrication
Chain drive requires lubrication for six purposes.
To resist wear of the pin-bushing joint
To cushion impact loads.
To dissipate any heat generated.
To flush away foreign materials
To lubricate chain-sprocket contact surfaces
To retard rust or corrosion
Types of lubrication
Manual Lubrication
Drip lubrication
Splash Lubrication
Spay Lubrication
Chain drive Selection - Using PSG Design Data Book
Step:1
Type of Chain
Roller Chain is selected for the application
Step:2
Determination of Transmission Ratio
Calculate transmission ratio (i) from PSG Design Data Book P. No: 7.74
Select the Preferred transmission ratio from PSG Design Data Book P. No: 7.74 based on the calculated (i) value
Pinion : small sprocket
Wheel : large sprocket
Step:3
Choose odd number of teeth
Choose even number of teeth
Select a random value between 30 to 50 or take average value for calculating "p"
if "a" value is not given assume a value(say 500 mm or 1000 mm)
w - select it based on the chain selected from PSG Design Data Book P. No: 7.71 to 7.73
k (coefficient of sag) - select it from PSG Design Data Book P. No: 7.78
A - select it based on the chain selected from PSG Design Data Book P. No: 7.71 to 7.73
lp - calculate it using the formula in PSG Design Data Book P. No: 7.75
ap - calculate it using the formula in PSG Design Data Book P. No: 7.75
e - calculate it using the formula in PSG Design Data Book P. No: 7.75
m- calculate it using the formula in PSG Design Data Book P. No: 7.75
Standard Number of Teeth on Pinion Sprocket (Z1)
For the preferred transmission ratio (i) from PSG Design Data Book P. No: 7.74 select recommend number of teeth on sprocket (Z1)
Step:4
Standard Number of Teeth on Wheel Sprocket (Z2)
From the preferred transmission ratio (i) and recommend number of teeth on sprocket (Z1) calculate number of teeth on wheel (Z2) using the formula in PSG. Design Data Bool P. No. 7.74
Step:5
Selection of standard pitch (p)
Using the formula of optimum centre distance in PSG. Design Data Book P. No. 7.74 and calculate pitch value (p)
After calculating pitch value, from PSG Design Data Book P. No: 7.74 select standard pitch value
Step:6
Calculation of Breaking Load (Q)
Rearrange the formula for Power Transmitted in PSG Design Data Book P. No: 7.77 and calculate breaking load in kgf
For calculating ks - use formula in page no. 7.76 & 7.77
Calculate speed "v" using formula
v
Select minimum factor of safety "n" based on the values of pitch and speed of small sprocket in PSG Design Data Book P. No: 7.77
Step:7
Selection of Chain
Based on the calculated breaking load and pitch value select the Roller chain from PSG Design Data Book P. No: 7.71 to 7.73
Step:8
Check for factor of safety
Using the formula in PSG Design Data Book P. No: 7.78 actual factor of safety
If the calculated actual factor of safety is greater than minimum factor of safety, then the design is safe
Step:9
Check for bearing stress
Using the formula of power transmitted in PSG Design Data Book P. No: 7.77 calculate bearing stress
Select the allowable bearing stress from PSG Design Data Book P. No: 7.77 based on speed of small sprocket and pitch value
If the calculated bearing stress is less than allowable bearing stress, then the design is safe
Step:10
Calculation of actual length of chain
Using the formula in PSG Design Data Book P. No: 7.75 calculate actual length of chain
Step:11
Calculation of exact centre distance
Using the formula in PSG Design Data Book P. No: 7.75 calculate exact center distance
Step:12
Calculation of pitch diameter of sprockets
Using the formula in PSG Design Data Book P. No: 7.78 calculate pitch diameter of sprockets