Closed Molding: Old and New
A plastics consultant since 1973, Bill D. Snow established E.M.C. Co. in Ft. Worth, Texas in 1960 and, in 1962, designed and built a fully automated thermoforming machine for his own use that, by 1965, was being sold to other plastics manufacturers through E.M.C.'s Machinery Division. In 1967, E.M.C. Co., renamed
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In recent years, I have read accounts of "new" composite manufacturing methods that look a lot like some processes that were actually first developed at my Ft. Worth, Texas-based thermoforming company, E.M.C. Plastics. One method in particular is the comolding of a thermoformed thermoplastic exterior "shell" and thermoset composite in a closed molding process. Back in the late 1960s, we developed something very similar, called "Press Reinforcing."
It all started because every time I entered an acrylic bathware factory, I got a migraine headache from the styrene odor. At that time, we supplied aluminum molds and thermoforming machines used to form thin-gauge acrylic bathtub and lavatory shells. The shells were reinforced with chopped fiberglass in a sprayup process. It was a mystery to me how people could work in such an environment. I kept thinking there had to be a better way and began to look into closed molding. At that time, however, E.M.C. knew a lot about thermoforming sheet plastics but very little about the thermoset resins used for reinforcing. What we did know was these were dissimilar materials, so we knew we had to learn something about thermosets. It was not long before we found that other people — people who really knew what they were doing — had similar ideas and had attempted solutions for quite a while. Owens Corning Fiberglass, for instance, had been working on something called Comoforming.
One of the first things that we recognized in our work with polyester resins in closed molds was that there was a need to maintain a consistent mold temperature for repeatable results. Others who had experimented with closed molding tried to use epoxy or even polyester molds. About that time, however, we acquired a pattern shop with a furnace, which we renamed Southwest Pattern & Casting Co. We expanded the furnace capacity and developed a process method to cast-to-size aluminum molds, some weighing as much as 1,134 kg/2,500 lb. We were among the first to cast aluminum molds for bathtubs. It cost more than $70,000 (USD) to finally understand what we were doing, develop the process and make it repeatable. Then we designed and built our own pressure platen press that cost about $125,000. To control mold temperature, we cast stainless steel waterlines within the mold walls. Our thermoformed acrylic shape was generally seated on the male mold, continuous strand fiberglass mat was applied and fitted to the male mold and then a pre-measured amount of low-profile polyester was dispensed directly onto the mat. The platens were evenly closed, applying pressure at approximately 1.38 bar/20 psi. Mold temperature was controlled in both male and female molds.
When we announced, finally, that we had a temperature-controlled closed molding process that could produce a composite-reinforced acrylic bathtub in three minutes closed press time, people found this hard to believe — keep in mind, this was 1970. The word got around, however, and soon it was an unusual day if there wasn't at least one group in for a day's visit to discuss requirements for applications that ranged from automobile parts to fire extinguisher boxes.
One of the most successful ventures began with a phone call in 1973 from Ken Valoir, owner of Montreal-based Val-Mar Swimming Pool Co., the largest pool manufacturer in Canada. Most were of the "above ground" type and used a vinyl liner as the water container, affixed to the inside of a circular structure. To withstand the tremendous weight and pressure of the water in his 6.1m/20-ft diameter pools, Valoir used very stout, arc-shaped, 1.62m by 22.13m (5 ft by 7 ft), fiberglass panels, made with a gel-coat-and-spray-up process and bolted to each other using a specially designed aluminum extrusion that added strength to each joint.
He wanted to increase his production, minimize spoilage and improve quality, and wondered if our process was practical for making acrylic-faced panels at least as strong as his fiberglass panels. He sent detailed drawings which I studied for a few days and determined that a thermoformed acrylic face backed with continuous strand fiberglass mat/polyester resin, should be stronger than his panel, even though ours, molded to 6.35-mm/0.25-inch total thickness, would be thinner. As was our custom with unusual projects, I got our group into the conference room for a brainstorming session, explained the objective, then asked our department heads to check my thinking and come up with ideas of their own. We returned to the conference room two days later and these were the findings: The thin (1.02-mm/0.040-inch) acrylic skin could be thermoformed in only 32 seconds. Cost estimates were in not only for patterns, thermoforming molds and Press Reinforcing matched molds but for an auto-loading/unloading thermoforming machine as well. Further, one engineer suggested an automatic trim-and-drill machine and had already ballparked its cost. E.M.C. Machinery, a sister-division we had formed to sell our thermoforming and Press Reinforcing equipment, provided a cost estimate for the press. Finally, there was consensus that 1 oz. fiberglass mat would be used and the desired 0.25-inch thickness would dictate use of exactly 3 gal of polyester resin to make each panel. By setting mold temperature at 57°C/135°F, we estimated the closed press time to be three minutes. Not bad at all for two days of thinking.
When I told Valoir that I thought we could complete a panel in an elapsed time of 5 minutes, 32 seconds, he nearly dropped his teeth, and by day four he was in Ft. Worth. We learned that he had been producing 60 panels per 10-hour day (the equivalent of three 20-ft pools) with 40 people. Our system would produce 86 or more panels per eight-hour day (four 20-ft pools) with only five people. A three-shift operation would produce 13 pools per day, requiring a maximum of 20 persons. The additional cost of materials wasn't a factor because of the huge improvement in productivity. Valoir told me that he had dreamed of something like this for years and immediately placed an order for the full system.
|We spent the following three months assembling and testing system components. The molds, thermoformer and reinforcing press were no problem. We had built many like them in the past. But we had never built anything like the trim-and-drill machine, so we had to do a lot of digging. Ultimately, we came up with a machine equipped with explosion-proof motors and diamond saw blades that could trim the four panel sides in one minute while, simultaneously, 12 holes were drilled at each end. It featured a vacuum holding fixture and a cyclone blower exhaust that extracted all cutting dust, letting none escape to the shop (another development considered "new" these days). It required a little more time than originally estimated, and I have to admit that my heart was in my stomach until I saw the first composite panel demolded, because we had never made a matched mold set as large as 3.25m2/35 ft2.|
After we had checked out everything and were sure there were no problems, we made a full set of panels and set up a pool out in our plant's front yard. The panels had a smooth inside surface to protect the liner and an attractively textured outer surface. When we installed the liner and filled it with water, it was the final test that proved the panel's strength and, to my great satisfaction, silenced all the doubters (we had quite a few of those).
After the equipment was installed in the Val-Mar facility, our technicians remained for a week or so to train Valoir's people (an uncommon practice among other equipment manufacturers at that time). Val-Mar added a dispensing unit, which made the process much like the resin transfer molding done today. With this new pool panel, Val-Mar expanded its markets and profits in both Canada and the U.S. beyond Valoir's fondest expectations.
In those days, there was such a lack of manufacturing know-how, particularly in our niche, that almost anyone with any imagination at all could be an innovator. We literally built our company around this type of problem solving. By 1973, nine major plumbingware manufacturers around the world were seriously considering Press Reinforcing for their plants. We thought we had discovered the secret of the ages, but the Oil Embargo of 1973 and subsequent worldwide feed stock shortage literally destroyed our dreams. Overnight, the world supply of sheet acrylic vanished — only two suppliers managed to weather that period — and all of our plumbingware prospects dropped their plans. During that time, we also provided the prototype parts and then made the machines and developed the process for closed molding of the 22 complex exterior body panels for the Bricklin sportscar, but only 2,854 were manufactured (1974-1976) before the mismanaged enterprise went bankrupt.
Our experience, however, helped to forge my firm belief at that time that sprayup and roll out in composites manufacturing would be outlawed in the U.S. within three years. Now, 30 years later, composite publications in Europe and the U.S. report closed molding of fiberglass as a recent development, and governments still threaten environmental restraints on the many "bucket, brush and roller" fiberglass manufacturers still stuck in time.