Installing an ABB machinery drive to control conveyor speed has eliminated grinder breakdowns at an animal feed mill. Markedly, it uses simple motor current feedback from the animal feed grinder to control the conveyor speed. The VSD regulates the speed of a screw conveyor. This avoids overloading the the grinding mill with raw material. Using the new controls, changes of ingredient are automatically compensated.

The system has also increased the amount of soft ingredients the grinder is able to process, and improved productivity. Burniston Mill in Scarborough, produces animal feed by grinding grains such as wheat and barley. The finished product is in the pellet form.

ABB machinery drive

The original installation employed a vibrating table which fed the grain into the grinding mill. However, because of its age the table was unreliable and often over-fed the mill. The motor had to work harder, resulting in current overloads that tripped the motor and stopped production. This was happening every two weeks on average. On each occasion the grain had to be dug out by hand, stopping production for at least an hour. Steve Barker, Mill Manager at Burniston Mill, asked electrical systems specialist MP Electric for a solution.

With the local ABB provider, they developed a solution using a 2.2 kW ABB machinery drive. Output from a current transformer on one of the phase conductors of the grinder motor supply cable controls the feeder speed. It does this using the 4-20 mA signal feeding into the analogue input of the VSD controlling a screw conveyor.

The speed of the conveyor changes up or down in inverse proportion to the current drawn by the grinder motor. The harder the grinder works, the lower the feed rate of the conveyor. The less hard it works, the higher the feed rate. This ensures that hard grains are not fed into the grinder too quickly, whereas soft grains feed in at a higher rate.

This has improved productivity by increasing the amount of soft ingredients the process is able to handle in any given period. Ian Robinson, director of MP Electric, says: “Burniston Mill is now making better use of its capacity, as the grinder is not idling at a low speed when grinding soft products.”