Injection Molding: Base Loads

Modern injection molding machines are much more energy-efficient than older hydraulic machines, but there are a lot of older machines in use, and these use a lot of energy.

The biggest energy user in an older hydraulic machine is the hydraulic motor itself. One of the main reasons for this is the base load of these machines. In many machines, the base load from energy losses in the hydraulics is far higher than the actual energy used for the process. In fact, for all but the most recent machines, the base load is an average of 75% of the total load. This means that 75% of the energy goes in operating the machine and only 25% of the energy is used in producing the part.

It’s essential that you make sure that the machine is not using energy when it is not producing parts. This means switching the main motor(s) off as soon as the machine stops productive work.

Actions:

Check the base load for older hydraulic machines by monitoring the energy used with the main motor running but with the platens not moving—and be prepared for a big surprise.
For older hydraulic machines, turning off the hydraulic motor the moment the platens stop moving is one of the effective things you can do.
Fit controls to turn off the motor (e.g., the Eaton Easy Series). Do not try to change the people; they will always forget and cost you money.
Fit controls to turn off the downstream equipment (e.g., conveyors, granulators, and blowers) as soon as the main machine stops producing product

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.