Appliance Design - August 2008 - (Page 20)

PLASTICS Water Works 1. 2. Injection phase 1. 2. 3. 4. Injection phase Water injection Water holding time An 3. example of a short-shot, water-assist molding process. 4. Water injection Water reverse flow New molding method uses water to reduce cycle times and improve Water holding time surfaces. by larry adams 20 applianceDESIGN August 2008 njection molding is a tried-and-true production technology that for years has been used to make millions of parts, large and small. Injection molding does have some drawbacks, however, especially with larger parts, such as visible sink marks and other Water reverse flow surface defects. To resolve those issues, the basic technology is being augmented with new equipment, materials, and processes. Since the early 1990s, a molding method that used nitrogen gas has been used in the U.S. and Europe. Using the gas-assist method, parts can be made on a molding machine that typically couldn’t be made with traditional injection molding such as very thick parts. And, as compared to traditional injection molding, gas assist can minimize sink marks and other surface defects that could be created as large parts cool. Gas-assist also proved effective in reducing part weight and moldedin stresses. But, a new technology has been developed that even improves on gas-assist’s impressive results. Today, the newest injection molding technology to hit the market is waterassist injection molding (WAIM). With this I method, water is used in place of gas to hollow out a part and it does so quicker than gas-assist, and improves wall thickness and wall uniformity across a part. The technology is used most efficiently to make hollow molded parts, which fall into two general categories: components that move fluids through them, and structural components such as oven and refrigerator handles, chain saw handles, office furniture chair arms, and other structural components that need to be sturdy, lightweight, and attractive on the outside. Research at BASF, a resin supplier based Florham Park, N.J., has developed WAIM resins, has also been done on molded part housings that would have an integrated tube coiling through the part, according to Randy Fleck, senior process engineer for BASF. One of the first applications for the waterassist technology was in the automotive industry making fluid-handling parts, but WAIM’s uses are evolving and may soon include any application that requires a hollow part, or could be redesigned to incorporate one to consolidate parts and reduce part weight. Resin suppliers such as BASF and DuPont www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - August 2008 Contents Editorial Shipments/Forecasts News Watch Plastics Switches Noise & Vibration Control Joining New Products Design Marts Association Report: CEA Advertiser’s Index

Appliance Design - August 2008

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