Appliance Design - August 2008 - (Page 34)

Lock & Unlock JOINING A selection of Spiralock locking fasteners. Screw thread is both self-locking and reusable. by kevin peacock Kevin Peacock is an application engineer for Spiralock Corp., Madison Hts., Mich. 34 applianceDESIGN August 2008 EM product designers and fastener application engineers have struggled to provide a self-locking screw-thread system that is reusable and cost effective. Over the years, several locking systems for threaded fasteners have been developed and implemented in a wide range of commercial products. Most of these locking fasteners depend on some type of interference fit between the male and female thread. This interference is most commonly accomplished by deforming a few threads in the fastener, which is referred to in the fastener industry as an all-metal, prevailing-torque fastener. Another common approach to thread interference is the use of hard nylon or plastic to slightly impede the movement of the mating thread during assembly and tightening. The impediment can be in the form of a nylon ring on the top of the nut or a plastic plug that is inserted into the threaded region of the bolt. Although both of these prevailingtorque type fasteners initially appear to be simple and cost-effective solutions to fastener loosening, they have hidden costs, specifically when the issue of reusability is O addressed. It is widely accepted by engineers, assemblers, and service technicians that these fasteners are one-time-use locking fasteners. Most service manuals and assembly line procedures require that a new locking fastener be installed if disassembly has occurred for any reason. While this one-time use may be financially beneficial for fastener distributors and manufacturers, it is an extremely costly problem for OEMs. To the manufacturing engineer and assembly line personnel it may not seem like a significant cost to grab a new fastener out of the bin and reassemble the components, but there can be other logistical problems. With just-in-time bin replenishment by the fastener distributor, chronic reassembly can prematurely deplete the fasteners onhand and shut down the assembly line. Initial reassembly costs in the plant can be expensive, but do not compare to the profitdraining costs of warranty and service work performed in the field. Besides the exponential costs of field repairs for service and warranty, the process of getting replacement fasteners to remote corners of the world can 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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