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September 29, 1998

4 Min Read
Mold temperature control takes simplified approach


Here the WatchDog solves the common heating problem of multiple temperature zones on a single mold.

Like most molders, Trend Plastics has its fair share of mold temperature controllers lying around the plant. And like most molders, from time to time a mold temperature controller up and dies. On one such occasion recently, operations manager Mike Phillips was awakened at midnight by the nightshift supervisor who was in a panic because the remaining available mold temperature controller had just broken on him. "I told him," says Phillips, "on my desk you will find a WatchDog. He installed it, I went back to sleep, and it did the trick."

The WatchDog is not of the four-legged, barking variety, but of the mold temperature control variety. And unlike mold temperature controllers, it requires no power to operate, relying instead on the tried and true laws of physics to modulate the temperature of molds.

Trend, based in Olathe, KS, operates 37 presses ranging from 15 to 300 tons, molding everything from electrical and electronic parts to consumer products. The company employs 80 people who work in three shifts, seven days a week. Phillips says he gave the WatchDog a try because of his "problem children." Says Phillips, "We had to be able to zone out certain parts of the mold to get the results we needed." Specifically, he had an ABS thin-wall part with one mold zone that he needed to hold at 135F. Multiple zones in one mold means multiple mold temperature controllers. At about $2000 for a 9-kW mold temperature controller, this strategy is a pricey one.

In mid-1997 Phillips bought six WatchDogs to see if they could perform as his mold temperature controllers did, but for a fraction of the cost. He put a WatchDog on the mold running the ABS part and ran it for 10 hours with a digital thermometer to monitor the zone temperature. The result-it never varied more than 1 deg F from the setpoint. "It made the big man very happy," says Phillips.

The simplicity that makes the WatchDog so effective is the kind that makes you wonder why no one thought of it sooner. Manufactured by Burger Engineering, also based in Olathe, the WatchDog indirectly controls mold temperature by modulating the rate of flow of coolant through the mold. It installs, power-free, right on the coolant line exiting the mold. On a basic level, it's really just a fancy thermostat-faster flow removes more heat, cooling the mold; slower flow removes less heat, heating the mold.

On a more technical level, the WatchDog uses thermal expansion with a proprietary heat exchange fluid. The user picks a setpoint with a dial on the WatchDog; a conical valve moves toward or away from the seat to modulate flow, depending upon the setpoint. And the device is designed with controlled flow, so that some fluid is always flowing through the WatchDog-that is, you can't shut off coolant flow with the WatchDog. The temperature dial on the current WatchDog allows water temperature setpoints from 80F to 120F. This allows Phillips to hold mold temperatures as high as 135F and 175F. Burger is currently developing a new WatchDog with water setpoint ranges from 100F to 180F.

Burger's sales and marketing manager Russ Longley says that for multiple-zone control you can attach different WatchDogs, each with a different setpoint, to coolant lines. By attaching a manifold, you can pass all of the coolant lines through one WatchDog with one setpoint. As easy to install and set up as the WatchDog is, the real attraction may be the price. Phillips says smaller molders particularly should be pleased by the $384 price tag (with manifold) a unit carries. For the benefit of molders who don't use temperature controllers often, Phillips also points out that the WatchDog installs in 5 minutes, is easily adjustable, and can be quickly disassembled for cleaning and maintenance-especially handy if your water is dirty or hard.

Savings at Trend Plastics have come in two areas. The first, says Phillips, is energy savings, which he estimates will be in the hundreds of dollars for 1997. The second is in repair. "We're also talking here about the repair costs of mold temperature controllers themselves," he says. Phillips estimates that every two to three years he spends "several hundred dollars" to repair worn and broken parts on a mold temperature controller.

Thanks to the success of the WatchDog, Phillips says he is buying only two more mold temperature controllers this year, as opposed to the six for which he originally budgeted. And every supervisor on the shop floor now has a WatchDog in his toolbox, if it's not already on a mold. Although Phillips swears by the WatchDog, he does not see the end of the mold temperature controller in sight. "I think there will always be a niche for them," he says, particularly for high-heat, quick-response applications. "But like everything else, there's always a place where low-cost alternatives are great."

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