Assembly Planbook - July 2008 - (Page 45)

in a resin. When the fastener is installed, the beads break, releasing the adhesive and initiating the curing process. Mechanical thread-lockers don’t bond to a fastener so much as increase friction between the mating threads. This makes it more difficult for the fastener to move. Nylon is the most common material for mechanical thread-locking. Nylon cannot be applied to fasteners in-house, but must be preapplied in a processing plant. The process requires the fastener to be heated to at least 425 F to fuse the nylon to the threads. Fasteners treated with a mechanical thread-locker normally require a higher installation torque, because they rely on thread jamming for their thread-locking properties. On the other hand, chemical thread-lockers have lubricating properties that reduce installation torque but, once cured, result in much higher locking strengths than mechanical thread-lockers. Indeed, mechanical thread-lockers have less For optimum locking, the thread-locker should be applied in a band at least then half the strength of adhesives. as wide as the diameter of the fastener. DIY or Preapply? If an assembler only treats a small number of fasteners with thread-lockers, it may not be a cost advantage to outsource the fasteners for preapplication of an adhesive or sealant. However, depending on the thread size, it’s usually most costeffective to outsource an entire yearly quantity at one time. There are many advantages to outsourcing the application of thread-lockers to fasteners, including eliminating the possibility of running out of adhesive during production. If application of thread-lockers is not your primary business, your labor force will be better employed assembling your product, not applying adhesives. Perhaps the biggest advantage of preapplying threadlockers is simply that engineers can be certain the adhesive will actually be on the fastener, in the correct amount and in the correct location. When line personnel apply liquid adhesives during assembly, the process is prone to error. Nuts, as well as bolts, can be treated with a thread-locker. The adhesive may not get dispensed on some fasteners, or it might not be applied in the right spot. Similarly, with preapplied thread-lockers, engineers can be sure their torque specifications will be met, because the amount of adhesive applied to each fastener will be carefully controlled. In fact, applicators typically provide test data indicating the tightening torque and breakaway torque for the material. Another advantage is that engineers need not worry about housekeeping or contamination issues. There is no liquid mess or sloppy run-off. Excess liquid thread-locker can be problematic, because some adhesives attack plastics. If a liquid adhesive is applied to a screw for plastic components, the runoff can harm the product. Preapplied threadlockers will not harm plastics, which is why a growing number of electronics assemblers are using these materials in their products. Lastly, preapplying a thread-locker saves assemblers time and money. Liquid adhesives often need a primer to stick to the metal surface of a fastener. The preapplication process Water-based thread-lockers are ideal for fasteners 0.25 inch in diameter eliminates this step. Moreover, every drop of liquid adhesive and larger. www.assemblymag.com July 2008 / ASSE M B LY 45 http://www.assemblymag.com

Table of Contents Feed for the Digital Edition of Assembly Planbook - July 2008

Assembly Planbook - July 2008 Contents Editorial Quality in Assembly Station to Station Assembly Lines Assembly in Action Surviving the Roller Coaster The Human Side of Manufacturing Do Your Fasteners Need a Preapplied Thread-Locker? Manufacturing Innovation A Century of Progress Trendsetting Plants Pulse Tools Get Smart Plastics: Design for X Product Reviews Products Advertisers Index Classified Leading Lean

Assembly Planbook - July 2008

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