How to ensure fasteners remain tightly sealed in applications that are prone to vibration is a question engineers frequently attempt to solve. Eventually, vibration loosens fasteners by creating relative motion between the threads. Loose fasteners are certainly a maintenance nuisance but also a hazard in several applications, including in power generation, transportation, manufacturing, and others.
According to J.W. Winco, a manufacturer and distributor of standard machine parts, adequate torque is an obvious first step to ensuring fasteners are properly installed. The use of washers to lengthen the ratio of clamped length is another option for certain applications. The washer may add extra friction to the joint and maintain the clamping force
Threadlockers, used to seal or lock fastener assemblies together, and vibration-proof fasteners are two other alternatives.
Threadlockers Safety wire (or lockwire). These are chemical adhesives applied to a fastener, such as Loctite. However, Loctite acts like a lubricant when wet and can affect torque so it is ineffective in certain applications. It’s also not made for high-temperature conditions.
Safety wiring is a locking device that prevents fasteners from loosening. The correct technique is critical for proper installation and the work can be time-consuming. Additionally, it’s important to think twice before drilling holes into fasteners, which can significantly reduce their reliability over time.
Vibration-proof fasteners. Some fasteners are better designed to cope with vibration than others. For example, consider bolts and screws with pre-installed nylon patches, which typically hold up for about five cycles of removal and reuse.
There are also vibration-proof fasteners that are engineered to prevent self-loosening due to vibration. These include hex nuts with nylon inserts, jam nuts, lock nuts, slotted hex nuts, tooth lock washers, lock washers, and spring washers. Such fasteners may have a unique thread design that distributes stressed more evenly or an extra clamping system that reduces rotation.
Unfortunately, there is no failsafe solution. The efficacy of vibration-proof fasteners will depend on the application, so maintenance checks are essential.