Applications with constant torque are applications for which the load is typically not significantly altered by the speed. This includes conveyor belts, hoists and mixers.
If, for example, an engine block is positioned on a horizontal conveyor belt, the weight of that engine block will not change, regardless of the conveyor belt speed. The torque required to move this engine block is always the same. Of course, the friction and acceleration torque would change according to the operating conditions, but the torque needed to move the load still remains constant.
The energy required by such a system is proportional to the required torque and the speed of the motor.
P ~ T x n
If the speed can be reduced with a constant load as is the case in refrigeration cycles, one of the direct results will be energy savings. In other constant load applications, reduced speed will not have a huge impact. If, for example, the speed of a conveyor belt is reduced, the energy required to transport the goods from A to B stays approximately the same as the distance stays the same. Small savings are achieved through such factors as reduced frictional loss or optimised acceleration.
Nevertheless the use of speed control in constant torque applications is continuously increasing because of the benefits to the process itself, like:
- improving the efficiency of a process
- matching motor speed to the process requirements
- matching torque or power to the process requirements
- improving safety and the working environment
- reducing mechanical stress on machines
- reducing wear and tear
- lower noise levels
From Danfoss’ Facts Worth Knowing About Frequency Converters – free download here