
12
Typical Torque/Slip Curves
Figure 2-3
Each clutch frame size has a thermal dissipation
capability based on the motor speed or the air volume
available. Smaller size clutches can generally dissipate
full load slip losses. However, as frame size increases,
the maximum airflow cannot completely cool the unit over
the full speed range. Because of this, a thermal limit is
established for each clutch frame size with different motor
speeds. The nameplate of each unit is stamped to show
the minimum operating speed at full load. The minimum
speed can be reduced when the load is also reduced.
Tables found elsewhere in this section list the horsepower
capacities and speed ranges of standard drives. For other
ratings, consult the factory. The formula shown below is
used to calculate the minimum continuous operating
speed for a given load torque and horsepower dissipation
capacity.
RPM min. = RPM mtr. - (HPd x 5250)
T
Where:
RPM min. = Minimum operating speed
RPM mtr. = Full load speed of the AC motor
HPd
= HP dissipation of the specific unit
T
= Maximum load torque at which RPM
min. is required, in lbs. ft.