Preventing Thread Galling

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Thread galling is an unsightly and frustrating fastener problem that causes mated components to stick together or “lock-up.” This process occurs between materials such as stainless steel, aluminum, and titanium where microscopic high points of the thread surfaces rub against each other during tightening or installation. As the friction between these materials builds they can rub through the protective oxide layer and expose the raw material beneath, increasing the chances of a weld or galling that can cause damage to the threads and make it difficult or impossible to remove the components. In severe cases of galling the metals will even fuse together causing them to become permanently locked in place. This condition is referred to as cold welding and it is the reason why preventing thread galling is so important in any assembly.

There are several ways to reduce the risk of thread galling during fastener assembly and installation. One of the simplest is to lubricate the threads before tightening. There are many lubricants available but it is important to consider the end use of the assembly when selecting a lubricant as some may not be appropriate for certain applications for safety reasons. Consult a fastener representative to find lubricants that will provide good lubrication for the application while not negatively impacting the performance of the assembly or compromising its integrity.

Another simple way to avoid thread galling is to slow down the nut or bolt tightening speed. Faster speeds generate more heat on the thread flanks, creating more friction and increasing the chance of galling. When working with lock nuts or prevailing torque locknuts that require high levels of tightening pressure this is especially important.

Cleaning the threads of a fastener before use can also greatly decrease its chances for galling as well. Debris and grit in the threads can increase friction between mating surfaces and contribute to galling. It is also a good idea to inspect the threads for signs of damage like nicks and dents that could also contribute to galling.

It is also a good idea to apply an anti-seize compound on the threads of a fastener prior to installation. This type of lubricant is designed specifically to prevent galling by providing a barrier between the fastener and the material it contacts, allowing them to slide past each other with minimal friction or heat. Most hardware stores carry anti-seize compounds in a variety of different formulations that are designed for the environment where they will be used.

In addition to lubricating and slowing down the installation process, the most effective way to prevent galling is to choose the right combination of fasteners for an assembly. For instance, choosing a softer metal such as aluminum or titanium can help reduce the risk of galling since they have lower hardness ratings than harder materials such as stainless steel. If this is not possible consulting a fastener representative can help select materials with a comparable hardness rating that are less likely to gall with each other.

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