Injection molding — variable speed drives
For larger hydraulic machines with high operational hours one of the best methods to reduce energy use is the variable speed drive (also called variable frequency drive or inverter). As with pumps and fans, slowing the motor with a VSD will reduce energy use significantly but the savings are not generally as high as can be achieved with pumps and fans.
VSDs get the best savings during hold or packing when the pump does not deliver much hydraulic fluid and is simply holding the pressure and slightly packing the plastic. The VSD slows the motor down to keep the required pressure but not the constant volume that is normally supplied. In other phases of the cycle, a VSD will match the supply of fluid to the demand but the savings are not as great.
This technology is excellent for machines with variable displacement vane or gear pumps and very good for machines with variable volume pumps (although the savings may not be as great).
Actions:
- If the supplier offers the option of a pre-fitted VSD then this is a worthwhile option for new machines with large motors that are going to be operational for more than 6,000 hours/year.
- For existing hydraulic machines with large motors that are operational for more than 6,000 hours/year, it is worth looking at retrofitting a VSD. This is a specialist task and it is not as simple as fitting a VSD to a pump or fan. Take care in choosing you supplier and make sure they have experience in this area.
Dr. Robin Kent — ©Tangram Technology Ltd.
Note: Dr. Robin Kent is the author of Energy Management in Plastics Processing, published by Plastics Information Direct, and managing director of Tangram Technology Ltd., consulting engineers specializing in energy management in plastics processing. rkent@tangram.co.uk.