More than ever, we are looking for ways to reuse and recycle in all parts of our daily life. But is it safe and effective to reuse screws that have already been used for other projects or functions?
How to Tell If a Screw Can Be Reused
Generally, fasteners may be reused if the bolt never exceeded its yield point. This sounds simple enough, but it may be hard to tell if a bolt has experienced a tensile load past its yield point. A bolt’s yield point represents the point at which it does not return to its original length when the load is removed. Like a spring, a bolt can take a permanent altered form if it is yielded and will remain longer after the load is removed.
What Else Contributes to the Reusability of Fasteners?
There are many factors that can contribute to fastener joint wear and tear and tensile forces. External loads that can affect the fastener include tension, shear, cyclic, prying and others. External forces can be the result of numerous different situations such as vibration, changes in a pipeline or impact from a hydraulic ram. Heat is another external factor that can lower the yield value of a screw.
Initial fastener instillation can also contribute to the reusability of a screw. It is important to use extreme caution when installing fasteners. Especially if an indirect method of tensioning is used, it is important to monitor over tightening to avoid a fastener yielding during the installation or service.
Is There an Easy Way to Check If I Can Reuse a Screw?
The simplest way to determine if a bolt has yielded is by screwing a nut on the previously used bolt. If the nut will not screw on the entire bolt thread length, then the screw is not safe to be reused since the bolt has yielded.
Repurposing Reused Screws
If it is determined that a fastener can be reused, it is important to then consider the use of the fastener. In critical applications, fasteners should never be re-used. The criticality of the application is up to the user, but if no one can be sure what forces were applied to the fastener, new fasteners should be used in re-assembly. Replacing a fastener with a new fastener is more cost effective in the long run than paying for significant damage if the joint fails upon using a repurposed fastener.
After careful consideration, if a fastener is reused, special attention must be paid to installation tools and practices. If the scatter or “K” factor is not controlled then the screw will not act as a spring in tension. Precise tightening methods will insure effective reusability. Most often upon reinstallation, a nut and bolt will require increased torque to achieve the desired clamp load.
Ultimately, there are many factors that need to be taken into consideration to determine if fasteners can be reused. Be sure that all measures have been taken to determine if it is safe to reuse a fastener before it is repurposed and installed.
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What have YOU reused screws for?
To learn more about rules for fastener reuse, contact us at ProvenProductivity@bossard.com.
Can Screws be Reused? by Bossard