Appliance Design - January 2008 - (Page 40)

PLASTICS Gas Shows Before and after photos of the Triton ATM panel. The sink marks or indentations on the panel on the right indicate the structural rib pattern on the underside of the part. On the panel on the left, however, where external gas-assist molding was used, the gas squeezed out the sinks, resulting in a smooth, highly cosmetic part. New Side External gas molding technique offers aesthetic and economic benefits. njection molding machines represent an established, reliable, effective means of making plastic parts, but use of the process becomes more challenging as the size of the part increases. The larger the part, the more tonnage required to clamp the part. In addition, common internal plastic part features such as reinforcing ribs, fastener bosses, component mounting placements, all become more problematic with larger parts because these features can create visible sink marks on the exterior side where aesthetics matter most. But now, an emerging technique is attracting attention because it can create a large plastic part that is ribbed for strength, yet is thinwalled and free of sink marks, ejection pin marks, warping and other part distortions. The technique, called external gas molding, uses pressurized nitrogen gas that is injected into the mold cavity that has been nearly filled with plastic resins. The gas forms a micro-thin layer between the plastic and the adjacent mold surface and uniformly presses the plastic against the opposite mold surface, smoothing out sink marks that could form as the plastic cools and begins to solidify and shrink. The technology has been licensed to three custom, injection-molding companies in I by larry adams 40 applianceDESIGN January 2008 the U.S. by Cinpres, a UK-based company that has exclusive rights to market the technology in North America and most of the world. In Japan, the Asahi Kasei Corp. has marketing rights. To date, the technology has been licensed to Bemis Manufacturing of Sheboygan Falls, Wis., Consolidated Metco of Portland, Ore., and Mack Molding of Arlington, Vt. Steve Ham, a retired plastics consultant with more than 30 years of experience using plastic materials, has worked with Cinpres since 2002 to help develop the technology. He says the benefits of EGM range beyond just removing sink marks. The technique helps reduce molded-in stress, improve dimensional stability, shrink the amount of material used, and reduce the tonnage required to clamp the material and produce the part. EGM is similar to the more familiar internal gas-assist technology in that it uses nitrogen gas and is injected into a mold cavity to press the plastic material and remove sink marks and other flaws. Like EGM, internal gas-assist is a low pressure molding technology. Unlike EGM, however, with internal gas assist, the gas is injected inside the melted resin creating a gas pocket inside the part, which makes it especially useful for www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - January 2008

Appliance Design - January 2008 Contents Editorial Shipments/Forecasts News Watch Makers of Commercial Refrigeration Equipment Turn to Variable-Speed Motors to Improve Energy Efficiency. New Motor Design and Control Scheme Makes Brushless Motors More Economically Feasible for a Wider Range of Applications. External Gas Molding, a Relatively New Technique, Solves Many of the Challenges Associated with the Injection Molding of Large Plastic Parts. Plastic Housings Offer Many Benefits: EMI Protection Isn't One of Them. But, New Materials and Techniques are Solving that Problem. Choosing the Optimal Strategy for Effective EMI Shielding Depends on Both Mechanical and Electrical Requirements Ethernet-Enabled Microcontroller Makes Networking Schemes Easier and More Cost Effective to Implement The Ever-Changing Array of Microcontroller Memory Options Makes it Imperative to Keep Abreast of What's Available to Determine the Optimal Choice for an Application. A Vast Range of Components and Finished Products will be Exhibited at the Country's Preeminent HVAC/R Show, AHR Expo, which is Scheduled for Jan. 22-24 in New York. Advertiser's Index Association Report: PRBA

Appliance Design - January 2008

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