How to Prevent Galling Between Fasteners

Galling occurs when two metal surfaces come into contact and fuse together, creating a solid mass of material that cannot be separated or removed. This process is accelerated by high compressive forces such as those created during fastener tightening. Stainless steel and aluminum fasteners are particularly susceptible to galling due to the fact that these materials form an oxide layer that is broken under normal use, exposing the underlying metal to friction and other damaging conditions. In most cases, galling can be prevented by using a special anti-seize lubricant to reduce the amount of heat and friction generated during installation.

The most common cause of galling is excessive friction between mating threaded components during fastener assembly or removal. The friction between the threads can create high levels of heat that lead to localized surface heating and melting, resulting in a weld between the components and the formation of a “galled” region. In extreme cases, the welded area can be difficult to remove without the aid of a cutting tool, and in some situations may require destroying or grinding away the entire component.

Fortunately, there are several ways to prevent galling between fasteners, including the use of a lubricant and reducing the speed of tightening. A lubricant can significantly reduce the amount of heat and friction that is produced during installation, while a specialized anti-seize formula can provide protection against galling by slowing down the rate at which the bolt is tightened.

Another important factor to consider is the type of fastener and material used in the application. Stainless steel and aluminum fasteners tend to be more prone to galling, while harder materials can resist galling more readily. Likewise, a cold rolled thread will generally be less prone to galling than a cut thread.

To determine a material’s ability to resist galling, engineers can perform a button and block test. A small button specimen and a large block specimen are deadweight loaded in a Brinell hardness tester to create parallel contacting surfaces. The button is then rotated against the block at varying speeds and stress levels until the point of unlubricated galling stress is reached. This is an excellent method for evaluating the galling resistance of different materials.

The best way to avoid galling is to apply a lubricant to the bolt threads and nut inner threads before installation. A lubricant can be applied with a brush or mop, or through systems that automatically apply a chemical lubricant to the bolt during installation. It is also a good idea to tighten bolts by hand rather than using power tools, as this will decrease the amount of heat and friction generated during installation. Finally, using coarse threads will help reduce the chance of galling due to increased clearance between the threads. Lastly, it is critical to follow the torque specification for a specific fastener to avoid galling. For additional questions or assistance, please feel free to reach out to our team of engineering experts.galling