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When molds run hot and cold…

November 29, 2016

You water your lawn, you put water in your radiator and you drink water (probably not enough!) Did you know you should water your plastic injection mold, too?

Yep, that’s right.  If you want to establish true process control in plastic injection, “watering the tool” should be as important a step as coming up with a repeatable process in the first place.  Why?  In a word, consistency: if you don’t plan on watering, you could be setting yourself up for a whole lot of lost process control. Unfortunately, however, watering is often something that is overlooked by engineers.

Depending on your process, you could be watering to cool the tool, or heat it.  Both are equally as important.  Here are some things to consider:

Under Pressure
As you are undoubtedly aware, maintaining the proper pressure is a vital aspect of any plastic injection molding process.  But did you know that maintaining  an adequate amount of water pressure to the mold watering circuits is also vital?  The gallons per minute (GPM) rate should be calculated across each individual circuit before the first process run. Bear in mind that this measurement should be taken from both the supply and return of the circuit to assure that the drop in pressure is not too great.

Each circuit should be given a unique identifying number, and the numbers for both the supply and return of the circuit should be recorded. This lets you track a tool’s water capacity, and also helps to identify circuits that are affecting a mold’s process control.  In other words, when part defects can be traced back to swings in a mold’s cooling or heating consistency, the circuitry’s GPM rate can be measured and compared with the original data.

Go with the (turbulent) flow
Just like air turbulence, water turbulence is a key factor in mold temperature consistency.  Often described as the rolling and swirling motion of the water as it passes through the mold’s water circuitry, turbulent flow could lead to either to mold face temperatures which are either too low or too high. Simply put, mold face temperatures which are more uniform vastly improve process control.

More could be said about watering in regards to plastic injection molding, but that will be the subject of a later post.


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