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May 1, 2002

4 Min Read
Small shop takes big chance on gas assist


Figure 1. Durden Enterprises' design for this medical device features a hollow channel molded in with gas assist, eliminating secondary ops.

I am Bill Durden of Durden Enterprises Inc. We are a job shop injection molding and tooling house doing $5 million in sales a year. This is important, so that you can appreciate the scale that we are using to manage this gas-assist project."

With these words Durden, vp and gm, opened his presentation at Molding 2002 in March and took conference attendees through the trials and tribulations of what it takes for a small shop to get going with one of the high-tech systems we love to report on in the trade press. Durden and company had no prior experience with gas assist. Still, his story has a happy ending.

The company's saga began after Durden read an article on a Molding 2001 presentation by Carl M. Olson of Hi-Tech Mold & Tool Inc. (Pittsfield, MA). Olson had discussed Hi-Tech's application of gas-assist technology in molding a complex PVC P-trap used in the HVAC industry (see April 2001 IMM, pp. 86-87 for the Molding 2001 report, and April 2002 IMM, pp. 62-66 for a High-Tech plant tour).

Durden thought gas assist could be used to produce a PP medical airway with a molded-in hollow channel air tube (see Figure 1). Airways are used by emergency medical teams to wedge a patient's mouth open and ensure that he or she can breathe.

He explained that his customer's part had originally been marketed 15 years earlier, but that it cost three times more than competitive models, and was pulled. Durden presented his new concept to the customer, did a rough tool design, and quoted the job. That's when the fun started.


Figure 2. By varying the size of the overflow wells in this four-cavity family mold, Durden Enterprises was able to use volume balancing and less-costly nozzle gas injection.

Sticker Shock
Durden says he thought gas-assist equipment would be priced in the $20,000 to $25,000 range. Once shopping started he found prices ran more like $50,000 to $80,000.

"This is the same price I would pay for a 70-ton molding machine that would run 85 to 95 percent of the time, seven to 10 years, 24 hours a day, six days a week," he says. "It's not the kind of money that we spend on a job shop project for a customer that has little sales history and possible sales of $0." Durden would be forced to look outside for gas-assist services. In the meantime, the project continued.

Next came the final tool design. Durden wanted to produce four different-sized airways per shot in an aluminum mold. He says everyone insisted on balancing the cavities and on using expensive multiple gas control features in the mold (Figure 2). "Well," he says, "balancing cavities means different things to different folks. One wanted to control flow by runner size and length, the next by gate size, and the next wanted to do both."

It was decided to use volume to balance things out by varying the size of the overflow pockets for each airway size. Each part would fill to about 90 percent of capacity using equally sized gates and runners. The gas could be shot through the injection nozzle instead of the mold and there still would be equal distribution into each cavity.

The Story's Moral
"It took a long, long time to convince our toolroom that it doesn't have to run perfectly the first time . . . that it's just an R&D tool," says Durden. Anyway, after sampling parts on his J-85 EL II all-electric JSW, Durden had one more problem to solve—namely, financing.

"The financial side of the puzzle was to find a friendly competitor that could produce parts until the volume justified our purchasing our own equipment, or when we had another project that would make it economically feasible." Such a competitor (unnamed) was found in Tennessee.

He concludes, saying, "The moral to this story is that it might never have been completed if all the cost factors were known up front. But, by proceeding in ignorance, a will found a way."

Sales of the airway have started. At Molding 2002, Durden said it was too early to tell whether or not the product would be a market success. Regardless, he thanked his customer, Henry Wall; gas-assist suppliers Alliance, Gain, and NitroJection; and Delta Tooling for their assistance.

Contact information
Durden Enterprises Inc., Auburn, GA
Bill Durden; (770) 963-0637
[email protected]

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