Appliance Design - August 2007 - (Page 42)

JOINING SPEEDIER SILICONES A slow conveyor moves assembled glass stovetops from the robot that applies the sealant (right) to the next operation in the manufacturing process. Stovetops are not racked and are ready to be handled in the next manufacturing step. Two-part adhesives simplify stovetop assembly. by edward a.y. fisher, brian p. noonan, and john a. lafond Edward A.Y. Fisher is senior application chemist, Brian P. Noonan is application engineer, and John A. Lafond is market development manager, Loctite Industrial Adhesives, Henkel Corp., Rocky Hill, Conn. 42 applianceDESIGN August 2007 lexible, heat-resistant, one-part RTV silicones have traditionally been used to bond smooth glass or porcelain stovetops to metal stove frames. As a stove heats and cools, its components expand and contract at different rates, causing stress on adhesive joints. Silicones inherently exhibit very high elongation, which allows them to absorb this stress without failing cohesively or cracking the glass. Because silicones are based on the inorganic bond of silicon-to-oxygen, they can withstand much higher temperatures than epoxy or urethane adhesives that are based on organic carbon-to-carbon bonds. Throughout the life of a stove, adhesives must survive thousands of hours at elevated temperatures without degrading, a demand easily achieved by silicones. Although one-part RTV silicone adhesives offer superior flexibility and heat resistance, their curing mechanism has long constrained manufacturers of smoothtop or glass/ceramic cooking ranges, negatively affecting both the cost and efficiency of F the manufacturing process. RTV silicones require ambient moisture and significant cure time to develop the strength required to manipulate stovetops to apply the burners to the assembly. During the curing process, stovetops are typically racked from four to 24 hours in high humidity environments, a requirement that results in large quantities of work in process (WIP). This build up of WIP to allow sufficient curing extends the manufacturing cycle and prevents the next assembly process from beginning. To meet the moisture requirements of RTV silicones, manufacturers invest in costly humidity chambers and devote substantial floor space for stove top racking. Lower ambient humidity due to seasonal variations can compound manufacturing complexity further by extending required racking times. There are several other drawbacks to RTV silicones. These adhesives emit strong acetic acid (vinegar) vapors that corrode electronics and can be offensive to line workers. The maximum UL temperature rating of these www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - August 2007

Contents Editorial Shipments/Forecasts News Watch A Reed Switch is Simople, yet Versatile, and Designers are Finding New Uses for this Time-Tested Technology A Novel Actuation and Sensing Technology can Register a Light Touch, but Resist Blows from a Hammer Tracing the Source of Noise is Made Easier with Noise Source Identification Methods Appliance Noise can be Annoying, but Designers have Many Material Choices to Help Rein in the Racket Nanocomposites are No Longer a Technology for the Future. These Plastic Materials are Already on the Job A New High-Strength, Low-Density Glass-Microsphere Additive can Improve Plastic Part and Molding Performance A New Electromagnetic Weld/Bonding Process Helps Ensure Long-Term Integrity of Joints in Plastic Parts Snap-Based Technology Eases Installation and Makes Products More Serviceable Two-Part Silicone Adhesives Provide a Rapid-Cure Alternative to Traditional One-Part Silicones Classified DesignMart Advertiser’s Index Association Report: GAMA

Appliance Design - August 2007

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