Custom Design Clutches and Brakes
Selection
Torque Calculations
Based on Motor HP of Drive
Based on Load Inertia and Time The formula to use when calculatingclutch torque requirement based onmotor HP is:5,250 x HP x 2.75*T = N What is the average torque required todecelerate a total load of 1.0 lb.ft. Example Based on Inertia and Time =308t WR
2 NT
av Where: WR
2 = inertial load in terms of lb.ft.
2 referred to at the unit location.N = RPM
t= time allowed for the engagement
Tav = Average Torque (lb.ft.)
This formula gives us the torque (T) andis the average amount of torque
required to accelerate a part from rest
to a rotation of N revolutions per minute,about its axis, in t seconds, or deceler-
ate a part from a rotation of N
revolutions per minute about its axis to
rest in t seconds.
Where:
HP = name plate HP of the motor*K = motor overload factor = 2.75N = RPM at the shaft where theclutch is locatedAll
electric motors can exceed theirrated torque for short periods of timeduring overload conditions. For a
industrial clutch to work properly in a system,
therefore, the clutch must be designedto handle this overload torque without
slipping. A K factor of 2.75 is based
on an average motor overload
capability of common electric motors.
Failure to include motor overload in
clutch designs can lead to premature
clutch failures as the clutch will have
too little torque capacity to handle the
overload output torque of the motor.The K factor is only used when
calculating clutch torque. When
selecting a brake, the K factor can be
ignored since the brake is not stopping
a driving motor. Therefore, the brakecalculation for torque will be:5,250 x HPT = N
2 from1750 rpm in .2 seconds?
WR
1750 RPMBrakeMotor 2 total == WR
Where:
2 load + WR
2 clutch+ componentsWR HP = name plate HP of the motorN = RPM must indicate the speed atthe shaft where the brake will be
mounted. This will account for
torque changes as the result of
speed reductions or increases.
2 = 1 lb.ft.
2 === 28.4 lb.ft.308t308(.2) WR
2 N1(1750)T
av Based on average torque,
A size 500 brake should be used. (T
av = 32 lb.ft.)
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