Injection Molding: Get the Right Machine

Getting the correct machine size is critical in injection molding, but many sites don’t realize that selecting a machine that’s too large for the job has very definite implications for energy use. Last month (May’s E-Saving Tip #64) we talked about the base load for hydraulic machines; for older hydraulic machines, this is an average of 75% of the total load.

Choosing a machine that’s too large for the molding can have a dramatic effect on the base load. If the machine is too large, then the base load rises as a proportion of the total load. For example, in the worst case that we have measured, the base load was 93% of the average load. This means that 93% of the energy was being used simply to operate the machine and only 7% was being used to produce the part—this is a recipe for disaster.

If you must use a larger machine than necessary (because of scheduling issues) then it’s even more important to get the main motor switched off as soon as possible.

Actions:

Get the right machine for the job. Choosing a large machine (with a high base load) can increase energy costs so much that the job actually becomes uneconomical.
Measure the base load for all old hydraulic machines and calculate the idling costs of these machines. The financials will act as an incentive for further action.

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.