The centrifuge is used to separate liquids from solids and this requirement exists in many industries especially in chemical processes. The horizontal centrifuge consists from a main barrel (bowl) which rotates at high speed and inner screw conveyor (scroll) which rotates in the same direction but at lower speed. Wide ranges of slurries can be treated by varying the relative speed of the barrel and the screw.
Material is fed in at one end the scroll moves it along to other end at a rate, which extracts the required amount of liquid. Dry material is ejected at the other end. Usually the material in the barrel tends to drag the screw round at the barrel speed. The screw must therefore be braked in order to maintain its set speed. The amount of moisture extracted is set by the differential speed centrifuge and scroll, controlled by the Torspec eddy current brake (ECB) or back drive.
The braking action must be a non friction type to avoid maintenance problems and the brake must be capable of providing the maximum required braking torque continuously without overheating. Torspec Eddy Current Brake (ECB) perfectly matches these braking criteria and is utilized on decanter centrifuge applications, especially on Alfa Laval Decanter Centrifuges worldwide. They are referred as back drives. This back drive system utilizes Torspec ECB and Controller S5702TCP.
When the load drives the ECB (back drive) beyond set speed, it is detected by this controller and d.c. current is applied to the ECB (back drive) to bring the brake to the set speed (differential speed setting).If the reference voltage is used to select a desired screw speed, the ECB (back drive) will remain switched off until the screw is dragged round beyond the set speed . At this point, the feedback voltage and frequency will be bigger than reference, the Torspec ECB (back drive) unit will be switched on and the screw will be braked until the correct speed is reached.