IMM 10/00

I was pleased to see the two articles, "Water Basics for Molds" by Bill Tobin (pp. 72-75) and "The Troubleshooter" by Bob Hatch (pp.88-92), in the July 2000 issue of Injection Molding Magazine. For almost 20 years I have been worrying about how water flows through holes in molds. Friends tell me I should get a life and maybe they're right.

Since developing and patenting our Pulsed Heating and Pulsed Cooling Mold Temperature Control Systems, we have identified two main problems with mold cooling, and have spent the last 10 years preaching the message in the wilderness.

1. Coolant flow is king! The more water the better.

2. Don't restrict the water flow with small water fittings and mold pipe looping.

I was inspired by Bill Tobin's article, "Mold Cooling" (January 1994, Injection Molding Magazine), which included a chart showing guidelines for water flow for different-sized cooling channels.

Through experimental work and the cooling of hundreds of production molds, I found that Bill was a little light on his required minimum flow rate in the 1994 chart. It's good to see that in the 2000 article, he has increased his minimum flow ("7/16 inch in diameter requires 1.5 gal/min of flow"). This is a very complex set of calculations and when you apply theory to practice there are always some discrepancies. Our own results show that somewhere greater than 4 gal/mm gives optimum results with this size cooling channel.

In Bob Hatch's article he has independently demonstrated these two key messages: Don't loop it, manifold it; and don't restrict the coolant flow, make the mold the restriction to flow, not the fittings. By manifolding the mold and changing the water fittings from 1/8 to 3/8 inch, he increased the possible water flow (for a given water pressure) from 10 to 60 percent through this cooling channel. Increasing the thread size in the cooling channel from ¼ to 3/8 inch, using longer hoses and piping to maximize water flow, makes the mold the restriction and therefore a more effective heat exchanger.
-Rowland Evans, R.E. Promotional Services Ltd.