How to Prevent Thread Galling During Assembly, Tightening and Installation
During tightening or installation, fasteners generate heat from friction between their threaded surfaces. This heat can cause materials to bond together or weld, a process called galling. Severe galling can even make the two parts unremovable, a problem commonly known as “cold welding.” It’s easy to prevent thread galling with simple actions during assembly, tightening and installation.
Stainless steel hardware is particularly susceptible to galling because of its relatively soft nature. The protective oxide coating that enables these soft metals to slide over one another during fastening is easily rubbed off under the pressure and movement of the bolt being tightened. Without this barrier, the metals come into direct contact with each other and friction builds leading to a snowball effect. Each new layer of material that adheres to a mating metal surface creates additional friction and more heat which essentially welds the materials together. The result is the two pieces can’t be separated or removed, a major hassle and disruption that causes a delay in operations.
The best way to avoid thread galling is to lubricate the fastener and the mating hardware. A good lubricant will allow the fasteners to move smoothly over each other without creating friction or heat buildup. A wide variety of dry film lubricants and antiseize compounds are available. Some common choices include USP-grade castor oil and a nickel-based grease, although antiseize compounds are more commonly used on stainless threads. If your fasteners come with a lubricant already applied, it’s a good idea to use it.
Other triggers for galling are debris caught in the threads, overtightening of hardware, and handling of the hardware or fasteners during shipping and storage. Poor packaging and haphazard tossing of heavy equipment in a bag can also nick or dent threaded hardware causing them to bang against each other during handling.
High-speed tightening can generate high levels of heat on the thread flanks before they can dissipate from the rest of the fastener body. Slowing down the tightening RPM speed will greatly reduce or, in some cases, eliminate this issue.
It’s also helpful to choose materials that are as similar as possible to one another. Using different types of material may not be practical for your application, but selecting a softer grade metal than the hardened metal that’s being installed or removed will reduce or eliminate the possibility of galling.
Lastly, to prevent thread galling it’s essential to inspect all of your hardware for damage and dirt prior to installation. If a fastener appears to be binding or sticking before you add tightening pressure, it’s best to stop and allow the threads to cool down for a minute or two. This will give any bonded materials time to break apart and the opportunity for the original lubrication to be restored. These simple steps will significantly reduce your chances of thread galling and can help you be more productive and ensure your projects go as planned. Contact Norwood Screw Machine Parts for more information about thread galling and prevention or to learn more about the performance oriented fasteners we offer that are enhanced with anti-galling defense mechanisms.
