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June 3, 1998

6 Min Read
Market Focus:  Industrial-Strength Products

There aren't many environments tougher than those faced by parts used in industrial products. These products have to work all day, every day, in harsh and corrosive conditions, reliably and faithfully. Here are some of the challenges faced by designers looking for toughness, lubricity, tolerances, and other demands.

Sorting conveyors replace machined parts with acetal

Engineers have reduced wear, operating expenses, and part costs of a high-speed sorting conveyor by redesigning the diverters in DuPont Delrin P acetal resin. The parts had been machined from UHMWPE, an ultrahigh molecular weight polyethylene; it offers low wear and friction, but doesn't have the potential for cost-effective design available with injection moldable Delrin.

On the Model QS-1 sorting conveyors built by Hytrol Conveyor, diverters move swiftly across the conveyor tubes, pushing products into takeaway lines. The diverter body, now injection molded in Delrin 100P, slides between steel tubes that are fastened at each end to roller chains to form a continuous belt. "Delrin gives us low friction in unlubricated operation," says Boyce Bonham, an engineer at Hytrol, "plus wear resistance, strength, and toughness for long-term durability."

The blocks move across the conveyor belt at speeds as high as 465 ft/minute. Hytrol engineers, working with designers at Molded Materials, eliminated three heavy metal plates that were required with the earlier design. Instead, an insert-molded bearing shaft and other features were integrally molded into the Delrin component. The new design, half the weight (1.1 lb) of the old design, reduces power costs and stress on block-moving mechanisms. It has a cross-ribbed structure to maximize strength and stiffness while minimizing weight. Eliminating three metal plates substantially reduces the total cost.

Delrin 100P is the toughest unmodified acetal resin available, according to DuPont's Mike Cole. It is one of the new generation of performance resins with a wide processing window, low mold deposit, and outstanding regrind stability.

Reliable neon signs depend on TPVs

Masters Technology Inc. (Glendale, AZ), a leading manufacturer of one- and two-piece insulator boots, housing caps, and GTO cable sleeving, critical to the operation of neon signs, needed a new and better suited material capable of meeting the strict demands of neon signage for its new Water-Tite Neon Products line.

Two of the material selection criteria included a UL 94 5V flame rating, the highest rating obtainable for a polymeric material, and excellent weather resistance to completely seal out contaminants, eliminating potential arcing that can pose serious safety concerns, such as fires. More important to Masters was the reduction of service calls required to maintain most neon signs. "All of our products are designed and manufactured to increase product safety and reduce lighting failures," says Masters president Herb Moulton. "The stringent testing requirement by UL, the Canadian Standards Assn., and the New York Bureau of Control Standards to receive listing and certifications presented a formidable challenge," he adds.

Together with materials supplier DSM Thermoplastic Elastomers, Masters engineers developed proprietary blends based on Sarlink thermoplastic vulcanizates (TPVs) that met all of the Water-Tite needs." These included good processibility as well as end-product performance required to meet and exceed the listing standards, testing criteria, and on-site rigors," says Moulton.

Acetal keeps regulator costs in line

A new plastic pneumatic pressure regulator is one-third the size and one-sixth the weight of comparable metal units. Thirty-six precision injection-molded parts are assembled by hand in about five minutes without gluing or ultrasonic welding; 19 of the parts, including the diaphragm plate, supply stem, body, dovetail slides, and vented pressure housing, are made with various grades of Celcon acetal copolymer from Hoechst Celanese. The subminiature regulators (just 31/2 inches high) are produced by the Air Logic Div. of Fred Knapp Engraving. One of the critical parts was the adjusting screw, which had to carry loads from the 200-lb spring. The screw is made of carbon-filled nylon 6/6. But this material was too expensive to use for most of the regulator parts.

Air Logic designer John Boticki explains: "This is a low-cost precision regulator. To do all the machining necessary to manufacture a metal regulator this small would probably double the price. It's a precision regulator, so it has to be hand-assembled. All the tolerances were specified for hand assembly."

Dimensional stability and lubricity were critical so the parts would go together with a leak-tight seal. Parts are molded to .003-inch tolerances, and hold those tolerances in service from 40 to 150F. "I believe the dimensional stability of Celcon over a wide temperature range is the leading advantage of this engineering material in pneumatic components." Another important criterion, Boticki added, was its chemical resistance, "far better than polysulfone or polycarbonate in its ability to resist various chemicals." And you don't have to dry it.

Four grades of Celcon are used. General purpose M90 handles the diaphragm and pressure plates, and other parts. The extra-low melt viscosity of M270 was needed for the regulator supply stem, because of walls .014 inch thick, feathering to .003 inch. Glass-coupled GC25A added additional strength and stiffness for the body, side ports, and other parts. A 25 percent glass-bead-filled GB25 molded the very flat, thin-walled dovetail slides. Cost of the materials used is $1.80 to $2.50/lb.

Eye surgery, auto engine diagnostics, semiconductor manufacturing, and bar coding are some of the regulator's application areas.

Fluoropolymers protect against contamination

The UltraPure fluid regulators and valves made by Furon use fluoropolymer resins from DuPont for all wetted parts. The innovative design, using Teflon and Tefzel resins, is engineered especially for semiconductor manufacturing and other operations with demanding requirements for purity. Nonwetted parts of the upper housing are polypropylene.

Kenji Kingsford, research and engineering manager at Furon, says that making all wetted parts from Teflon PFA or PTFE provides "a high level of protection against contamination and chemical attack." The body components are injection molded from Teflon PFA 440 HP, with internal flow passages radiused and fully swept to guard against particulate buildup. The diaphragms are made of Teflon PTFE; pneumonic regulators have four internal PTFE parts: poppet, bottom retainer, and two diaphragms; the manual version has one diaphragm. A positioning ring and two flare nuts are molded from Tefzel ETFE; critical exterior components offer strength and stiffness as well as chemical resistance.

UltraPure valves are similar to the regulators in design; however, in this case the poppets and diaphragms of PTFE are made in one piece, with top and bottom caps in Tefzel. There are several versions in the family, in both manual and pneumatic units.

A second Furon application of these materials is a new flare fitting that is injection molded from Teflon PFA. It's used for primary fluid-handling tubing and secondary containment tubing in chemical processing environments. The design is modular, allowing for stand-alone and bulkhead applications. This fitting was cited in the 1995 DuPont Plunkett awards for innovation with Teflon.

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