Clutches are used to transfer torque while brakes are used to stop a load, typically a rotating load. While there are many different types of clutches and brakes, the focus here will be on some basic tips for selecting the proper clutch and/or brake for your application.
Clutch and/or Brake
At the most basic level, determine if the application calls for a clutch, a brake or a combination clutch and brake.
A clutch would be used in applications where it’s desirable to engage or disengage a load and motor while leaving the motor to run all of the time. When a clutch is used the load will be allowed to coast to a stop.
A brake would be used in applications where accurate stopping of the load is needed and the motor will stop as well.
A clutch and brake combination would be used where the load will be started and stopped while the motor continues to rotate.
The next choice is unit mounting. Both clutches and clutch brakes can mount to the motor shaft or be base-mounted and have input via a belt drive, chain drive or coupling.
Motor Horsepower and Frame Size
Next, define the motor horsepower and motor frame size. In the case of base-mounted units, it may be necessary to define the RPM at that location. Manufacturers provide quick selection charts where unit size is determined by finding the intersection of motor horsepower and speed at the clutch shaft. The charts are commonly created using the dynamic torque capacity for the product and the torque capacity for the motor plus an overload factor of some value. Using this method presumes that you’ve selected a motor that’s sized appropriately to the application. In applications where cycle rates are considered aggressive for the inertia of the load, it’s a good idea to consult with the application support staff of the manufacturer regarding the heat dissipation capacity.
In some cases, a given motor horsepower may have more than one frame size choice. For instance, 1 hp motors can be either a 56C frame or a 143TC frame and because this impacts the shaft size, it’s a critical piece of information to know. As with hp/RPM selection, manufacturers will provide charts where unit size and frame size are shown. Since frame size determines unit shaft size, that factor would be pre-determined.
The last remaining variable is coil voltage. The most common options are 6, 24 and 90V DC with 90V being widely preferred in North American markets, while 24V is more common in Europe. In both cases, clutch/brake manufacturers can provide power supplies to convert AC to DC if required.
Filed Under: Motion Control Tips, Brakes • clutches