Recreation

Plastics provide structurally sound, durability, and safe equipment for sports and recreation facilities. The broad range of properties available from plastics has made them part of all types of sports and recreational equipment worldwide for land, water, and airborne activities. Rollerskate wheels have become abrasion- and wear-resistant polyurethane, tennis rackets are molded from specially reinforced plastics (using glass, aramid, graphite, and/or hybrid fibers), skis are laminated with RPs, RP pole-vaults extensively used to go "higher", and many more.

Appliance

By far most appliances use plastics to take advantage of the properties they inherendy provide ranging from aesthetics to structural integrated (corrosion resistance, tough, etc.) to insuladon. When examining the plasdcs in an appliance in addidon too different plastics being used, there are the many different fabricadng methods used to produce simple to complex parts.

Many success stories exit that include the benefits gained in the household and other places. In the past washing, drying, and ironing clothes was a rigorous, two-day affair involving the filling of metal tubs, scrubbing by hand, hanging clothes to dry, and headng cast-iron flat irons on a stove. With new technology and "plasdcs" laundry rooms and kitchens worldwide are operating in relatively a few minutes and looking better than ever before.

As one of many thousands of success examples, Milwaukee Electric Tool Corp. in the past found itself on the short end of the age-old supply-and-demand equation. That is, it was unable to keep up with demand for its heavy-duty electric power tools. Problem was that their machining operations could not turn out enough aluminum die-cast motor housings to keep up with market demand. The firm briefly considered what would have been a long-term solution; a state-of-the-art machining center. But a feasibility study showed that capital costs for such a facility would run into hundreds of thousands of dollars, while resulting savings would amount to a few cents per part.

Fortunately, there was the other option of using plastic motor housings. Du Pont agreed to produce plastic prototypes of the housing in Zytel nylon 82G plastic. Prototypes were quickly assembled; then they passed demanding drop tests and other field tests that are standard for Milwaukee Electric tools. When the housings of impact-resistant Zytel passed the tests with no problem, the firm had a new, lower-cost solution to its machining problem: a plastic housing, produced from a production mold that required no machining.

Redesign presented several additional opportunities. Initial target was to replace aluminum die-casting, and thereby eliminate machining as well as deflashing, trimming, and spadoning (a surface treatment that imparts a matte finish). But they also wanted to eliminate as many parts as possible, simplify the assembly, and use a product that worked as well or better than aluminum. Achieving these goals produced some spectacular benefits; parts costs dropped by two-thirds while manufacturing throughput rates increased. Savings in labor, machining, and assembly operations were augmented by lower capital and maintenance costs. As many as one million plastic housings were injection molded without major tool repair or replacement, vs. 100,000 parts for the die-casting operation.

Six parts in the housing were eliminated. Because plastic used is not conductive, designers were able to do away with insulating parts, such as a coil shield that separated the electric brush holder area from the aluminum, and the cardboard insulating sleeve that went between the copper wiring of the field core and the housing. Removing the sleeve had the added benefit of creating better airflow inside the housing, so the motor ran cooler under load. Press-fitting a rear ball bearing into the housing and keeping the bearing securely in place proved to be a major obstacle. The solution was to use eight small ribs inside the rear-bearing pocket. The ribs increase the amount of interference that can be overcome when press-fitting the ball bearing, and keep the bearing in its pocket with a strong, uniform force.

Another concern was achieving overall perpendicularity of the housing face where it fitted with a mating gear case. A molder solved this problem by repeatedly adjusting molded housing dimensions by a few thousands of an inch. Key to this fine-tuning was to establish three adjustment spots; one at each screw hole location. Thus it was much easier to design mating parts so that they sat on the lands, specific points, rather than trying to align a complete surface. Accurately repeating such minute dimensions required batch-to-batch plastic consistency and process control.

This example has been repeated many times over in many electrical devices. Many different electric appliance devices have been design and put in long production runs worldwide.

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