IMM Plant Tour: Molding above and beyondIMM Plant Tour: Molding above and beyond

Perhaps you think you’ve seen or heard it all in the IM industry . . . until you happen upon a custom molder producing parts considered impossible for this process. Would you believe a part with walls 5 inches thick weighing 400 lb could emerge from an injection molding press? At EnviroTech Molded Products, these are among the kinds of parts they make. Every day.

Of course, to radically diverge from accepted guidelines, adjustments must be made to the molding machine. EnviroTech, a privately held company, devised a way to modify existing molding equipment and processes using a custom-designed accumulator that stores the huge amounts of melted resin needed for each shot. According to Forrest Day, director of technology and product development, the two-stage process uses an extruder to fill the accumulator and a company-designed injection unit to fill the mold.

Called bulk injection molding, the proprietary process was invented in 1963 by Steve Davis, a member of EnviroTech’s earliest incarnation as an operating unit of Eimco Corp. At the time, Davis was looking for a way to make large, heavy-wall (150-lb, 1-inch-thick) parts for big rotary drum vacuum filters for the chemical processing industry. After seeing the bulk IM process succeed, the group spun  off from Eimco as a stand-alone company. It is now the world leader in large, heavy-wall IM parts, and was recently acquired by the Klinkau Group (Germany), a global supplier of molded filter plates.

Living Large
In going where most molders have never gone before, EnviroTech works with a unique set of challenges. Its products compete not only with metal castings, but also with plastics machined or fabricated from sheet stock. Cycle times are longer than conventional injection molding processes (the company declines to say how long), and mold temperature and process control are critical to success.

On the flip side, molding large, thick parts does have its benefits. Because of the thickness, polymer chains have a greater freedom and, thus, a more random orientation. This, in turn, provides more uniform material properties throughout. Low injection pressures (about 10,000 psi) contribute to lower molded-in stress and greater dimensional stability. Controlled and continuous packing phases ensure that voids, sinks, and porosity are eliminated or reduced to specified levels.

Bulk IM accommodates parts up to 400 lb with wall sections up to 5 inches thick on a routine basis. “Resin suppliers tell us we can’t do the things we’re doing,” says Day, “but we consistently prove them wrong. We’ve made wall sections up to 13 inches thick, but only on special occasions.”

Because of its specialty, EnviroTech is the single-source supplier for many of its OEM customers. “We provide technical expertise, quality parts, reliable delivery, and responsible pricing,” says Day, “and our customers tell us that no one else can mold the size and quality of parts that we do.”

In addition to its custom molding operations, which account for 70 percent of sales, the company also produces a line of proprietary recess and membrane filter plates. These are sold under the EnviroTech name, and are also made for OEMs to be sold under each one’s brand name. “This is a product that we manufacture, market, and sell for end users and OEMs,” he says, “in which we own the tooling.”

To control the bulk IM process, a custom process controller had to be built for the machines with special software packages programmed to monitor and control equipment parameters. Other quality equipment, including ultrasonic inspection to uncover voids, needed modification so that it would work with thick parts.

Size and Substance
During a recent IMM tour of the Salt Lake City operation (a second facility is located near Milan, Italy), Day pointed out the reasons why large molded parts are in such great demand by customers in industrial and even aerospace markets. “Plastics offer better chemical and corrosion resistance than stainless steel or cast metals at 20 percent of the weight and usually a significant reduction in cost.”

The process can also handle complex configurations and molded-in inserts. Parts can be produced in minutes rather than days or weeks. Molded-in, flanged inserts rather than post-installed inserts improve pullout and torque resistance for industrial applications. “Even when the price of a molded part exceeds that of a casting or machined plastic part, customers often prefer the molding for its ability to withstand operating conditions without failure,” he says.

Production quantities tend to be on the low to medium side, typically from 50 to 50,000 pieces per year, although EnviroTech is capable of high-quantity production when required. “One high-speed, thin-wall part that we are molding represents an unusual volume for us,” says Day. The OEM customer makes exercise equipment, and the part is being produced in HIPS (.150-inch wall) at a rate of several hundred thousand per year.

Relatively smaller parts (up to 35 lb and 3-inch wall thickness) can be produced economically using conventional molding machines modified to produce large, heavy-wall parts, including what EnviroTech calls “intrusion” molding. Here, the machine injects and extrudes material simultaneously. Again, a proprietary arrangement prevents full details, but the process is similar to bulk injection.

With such unique processes, the company realizes, it must provide customers with the benefit of its expertise in design, materials, and secondary operations. “We’ve been designing for this process for 40 years, so no one knows it better. As a result, we offer single-source supply, including part design, design for manufacturability, material selection, and post-molding operations,” Day says.

EnviroTech has three mold designers on staff who specify much of the tool and part design and work with moldmakers in Salt Lake City, Chicago, and elsewhere. Sales engineers are also experienced product designers. “Often, we’re converting metal to plastic, so our experience in molding, design, and materials makes the conversion easier.”

Above-average Applications
While OEMs from industrial markets such as filtration, pump and valve, electrochemical, pulp and paper, pipe fittings, and equipment components are the majority of EnviroTech’s customer base, it also serves high-end aerospace applications. Recently, the company finished a developmental project for the F-22 and Joint Strike Fighter, both jet fighter programs for the U.S. Air Force.

Clear canopies used on jet fighters are traditionally made by drape-forming a thick sheet of acrylic. This process takes up to six weeks and has a 20 to 30 percent reject rate, in part because the forming method produces variations in thickness that make it impossible to polish the canopy so that it is optically correct.

EnviroTech began working on a monolithic PC canopy molded in one shot. With the Air Force, it designed the mold for a canopy that duplicated the front section of the F-16 fighter. Dow Plastics supplied the material. The scaled-down prototypes also included aluminum or titanium attachment devices that were insert molded at the edges of the canopy. These 78-lb, 2-inch-thick parts were produced in minutes vs. weeks for drape forming, and did not require polishing for optical correctness.

The objectives of the Lockheed/Air Force development program were to determine moldability and produce a small quantity of bulk injection canopies to verify optical characteristics, impact properties, and the improved attaching method for the frameless transparency program. Parts were tested for light transmittance, optical clarity, and bird strike impact strength. In all categories, the PC canopies met or exceeded requirements.

The molded-in attaching hardware was designed to improve the stealth characteristics of the fighter and allows technicians to replace damaged canopies in hours vs. days using the traditional method, one that requires bolting. This would save time and equipment in combat situations. Currently, the project is on hold while suppliers determine if a full-size mold (three times larger than the prototype) that is also optically correct can, in fact, be produced.

On the other end of the spectrum, a high level of engineering goes into industrial pumps as well. In fact, Day considers the company to be one of the premier molders of large pumps, both centrifugal and double diaphragm. “There are 13 different pump manufacturers among our customers, and we have been molding and designing these products since 1963.”

In papermaking, the molded-part applications range from cyclone cleaners to distribution manifolds. For instance, EnviroTech produces a nylon cyclone cleaner that replaces a cast-iron version at a 70 percent weight savings and 50 percent cost savings. In electrochemical applications, glass-filled PP copolymer replaces wood frames in nickel production plants because the wood absorbs chemicals and disintegrates over time.

Shop-floor Specifics
Due to the proprietary nature of this process, several equipment and plant layout details were omitted in this article at the molder’s request. However, the process of bulk injection is relatively straightforward, with most large, flat parts being produced in horizontal mold units. Because of the size, most parts are removed manually, and then stored in cooling racks prior to shipping.

Large areas of the shop floor are set aside to hold the current day’s production before it is sent to a finishing or shipping area. Relatively small parts, such as pumps and valves, are boxed up at the press. Material usage is high at several million lb/year, so the plant has several PP silos and a pneumatic materials handling system, custom-built with Conair components.

For smaller (2- to 30-lb) pump parts, the plant uses four JSW machines modified to do heavy-wall parts up to 3 inches thick. These presses were selected for superior platen stiffness, and run mostly multicavity molds for thick-wall parts with molded-in inserts.

Another area of the plant is set aside for assembly of EnviroTech’s first product—rotary drum vacuum filters for the chemical processing industry. Here, molded plates are bonded together to form large drum filters ranging in size from 3 to 10 inches in diameter and up to 16 inches long.