Thread galling is the result of friction and adhesion between metallic surfaces that are meant to slide over each other. In this process, material from one surface gets attached to the other and causes damage. This can be extremely detrimental to the performance of a fastener, nut or screw. Luckily, there are preventative measures to take in order to avoid thread galling and keep your fasteners operating efficiently.
Metals that are resistant to galling, such as stainless steel, aluminum and Inconel, have a passivated oxide layer on their exposed surfaces that prevents corrosion and reduces direct metal-to-metal contact during fastening. However, this protective film can be rubbed off during installation pressures, which brings the softer metals into direct contact and creates friction that generates heat and eventually fuses them together into a solid mass.
Many different factors can contribute to thread galling, including the type of fastener, its materials and the way it is installed. For instance, high-quality fasteners can be manufactured with fine threads that are more prone to galling than coarse threaded options due to the smaller amount of turns they require. Threads that are not perpendicular to the bearing surface of the nut can also be more prone to galling, as can loosely installed threads. In addition, using tools that produce excessive friction and heat can increase the likelihood of galling.
All fasteners have some degree of roughness on their thread surfaces, and this can also increase the chance for galling. This is especially true of lathe cut bolts as they have rougher thread surfaces than those rolled between dies. However, the use of special anti-seizing and/or anti-galling lubricants can dramatically decrease the likelihood of galling.
These specialized lubricants typically contain additives such as molybdenum disulfide, graphite, mica, talc and extreme pressure waxes that are highly effective at reducing friction. In addition to these specialty lubricants, standard lubricants such as WD-40 can also be effective for reducing the chances of galling.
Another way to reduce the chance of thread galling is to install fasteners at a slower speed. This will reduce the amount of heat generated during tightening and allow time for that heat to dissipate.
Lastly, it is important to keep the fasteners clean during assembly and removal. This will help to reduce the friction between components and will prevent the accumulation of grit, dirt and other debris that can cause increased friction and lead to galling.
If you follow the tips discussed above, you can greatly reduce the occurrence of thread galling in your assemblies and prevent expensive repairs and downtime. For more information on thread galling or to obtain a product with anti-galling protection, contact the team at Norwood Screw Machine Parts. We provide a variety of performance-oriented fasteners enhanced with anti-galling defense mechanisms to ensure the longevity and efficiency of your assemblies.