Friday, March 13, 2009

Vibration-Proof Fasteners

Diane reporting, and today I’m quite intrigued by the issue of fasteners and vibration. On its face it seems like a simple question: How do you insure the fasteners won’t loosen in an application that is prone to vibration? In actuality, it seems if you put several engineers in a room to discuss the question, you may need a vibration-proof room to handle all the discussion that ensues.

Along with proper torque, common possible solutions boil down to these:
* Use of washers to lengthen the ratio of clamped length
* Threadlockers
* Safety wire (aka lockwire)
* Vibration-proof fasteners

There doesn’t seem to be too much controversy regarding threadlockers. These are chemical adhesives applied to the fastener, most notably Loctite. Keep in mind however that Loctite acts like a lubricant when wet and can affect torque. It also is not appropriate for high temperature situations.

Safety wiring, according to my reading, can be anything from completely useless to the ideal solution. This page offers a nice set of illustrated instructions on how to safety wire bolts on a motorcycle, by way of example. Obviously one “con” of this approach is the time it takes to do. Also, proper technique or lack thereof are huge factors. And adding holes to your fasteners will reduce their integrity.

Fasteners themselves can be designed to cope with vibration. For one thing, you can look for bolts and screws with nylon-patches pre-installed. These will hold up for approximately five cycles of removal and reuse. J.W. Winco offers a number of spring and ball plungers with locking nylon patches, so I include one here by way of illustration.

Our technical section includes some excellent information on the polyamide locking patch (PFB) as well as the micro encapsulation precoat 80 patch (MVK), designed for thread locking.

Fasteners designed specifically to cope with vibration include hex nuts with nylon inserts, jam nuts, lock nuts, slotted hex nuts, tooth lock washers, lock washers and spring washers. Again, there is some debate as to the efficacy of these depending upon the application. J.W. Winco sells a broad array of vibration proof fasteners in metric sizes, viewable in our catalog Section 19.

For an animated and “vibrating” debate on this topic, see this thread on http://www.eng-tips.com/. Which, by the way, is an excellent source of forums on all aspects of engineering,

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