Galling occurs when two metals or metal surfaces are subjected to sliding friction that generates heat and plastically deforms the surfaces. It causes the surface oxide layers to fuse together, forming a weld between the materials that can lead to significant mechanical failure. Galling tends to occur in applications involving high loads and large apparent areas of contact. However, the use of dissimilar materials, lubrication, and rougher surfaces can reduce the tendency for galling to occur.
Stainless steel hardware is especially susceptible to galling because it is relatively soft compared to other common metals. In addition, it has a natural passive chromium oxide layer that is easily rubbed off by rubbing and pressure. When this happens, the metal is exposed to more frictional force, which in turn can cause it to deform and interfere with the mating material. This starts a snowball effect that leads to more frictional force, more deformation, and ultimately more galling.
The key to preventing galling is to avoid situations that create frictional stresses between different metals. It is also important to lubricate the fastener during assembly, and use the right lubricant for each situation. There are many different types of lubricants available, and some are better at preventing galling than others. For example, some lubricants contain molybdenum compounds that can be used to prevent galling. In addition, tightening bolts at a slower speed can help to reduce the risk of galling by reducing the amount of heat generated during tightening.
In addition, avoiding using shot peened metals in applications that are susceptible to galling can also be effective. These metals are typically rougher than cold rolled metals, which increases the likelihood of frictional wear.
Finally, educating employees on the early signs of galling can be effective. If a mechanic recognizes that a threaded surface is beginning to seize, he or she can stop the tightening process before it becomes too late. This can help to prevent damage to the threaded surface and save time, money, and equipment.
Galling is a serious problem that can lead to a variety of mechanical problems, including failure of fasteners and other components. In order to minimize the chances of galling, manufacturers should take all steps necessary to prevent it. This can include using different metals, thread designs, and lubrication. In addition, they should consider using premium stainless steel fasteners that are designed to be less prone to galling. This will ensure that the equipment is safe and reliable and prevent costly downtime.