If you work with metal machinery, it’s important to know what galling is and how to prevent it. The phenomenon is one that’s often overlooked by many industrial workers, but should not be ignored as it can have significant impacts on quality, safety and the functionality of expensive equipment.
Galling is the unintentional adhesion of a hard metal to a soft, softer metal surface. The most common examples of this are seen when threaded materials come into contact with each other under high amounts of friction. These forces cause the frictional heat energy to be concentrated in a very small area, which then causes material transfer between the two surfaces. The adhesion between the metals then continues to increase, eventually resulting in the formation of an adhesive lump between the two surfaces. This material then starts to erode, which can lead to serious failures for the components involved in the galling process.
The metals that are most likely to show galling effects are aluminum and stainless steel austenitic grade fasteners, but any type of metal machinery could be susceptible to this issue. The most common causes of galling in these instances are power tools, wrenches and hand tightening of fasteners that result in a large amount of sliding friction between the two materials under pressure.
While the exact reason for galling is unclear, it is thought to happen when a layer of protective oxide that normally exists between the surfaces of the materials becomes broken during the frictional force applied. This can occur if the surface of the material is rough, which may lead to the removal of the oxide coating, or it can happen as a result of chemical reactions between the different metals that are in contact with each other.
Whenever possible, it is best to use proper anti-seize compounds to help protect against this damaging effect on threaded components. These coatings are designed to be able to resist the formation of galling, as well as provide additional corrosion resistance and lubricity between mating surfaces.
When using anti-seize coatings, it is also a good idea to apply the correct application techniques. For example, it is recommended to allow for the coating to fully saturate into the threads of the bolt before starting any assembly or disassembly. Similarly, using lower wrench speeds during installation or removal will help to reduce the amount of frictional heating that is generated by the fastener as it is being tightened or removed.
A few other tips to prevent galling in the workplace include avoiding over tightening or loosening fasteners, making sure that the bolt is clean and free of debris before installing it and using the right tools for the job. It’s also a good idea to have the surfaces of any parts that might come into contact with each other undergo electropolishing to smooth any rough edges and help minimize the risk of galling. what is galling