Anti-Seize Compounds Can Prevent Galling

Failing to lubricate threaded fasteners can contribute to galling. Using anti-seize compounds and properly applying them can actively reduce the likelihood of galling.

The phenomenon is more likely to occur under conditions with high loads and large apparent areas of contact. Using hard, dissimilar materials with low ductility and rougher surfaces typically reduces galling behavior.
What is Galling?

Galling is a form of abrasive wear that can occur when two materials in sliding contact rub together with poor lubrication. This rubbing causes heat and friction, which eventually results in the material transfer between the two metals on an atomic level. This causes the surfaces to fuse together, in a process that is sometimes called cold welding.

Most often, this occurs in metal fasteners like aluminum and stainless steel that are exposed to high amounts of friction force as they’re being torqued. However, galling can also affect any type of metal machinery that becomes subjected to excessive friction.

To develop galling, the metals must be both hard and ductile with a crystal structure that promotes cohesive attraction. It’s important to select alloys with these characteristics for applications that may be susceptible to galling. Other methods of reducing galling include the use of a lubricant, selecting coarse threads and avoiding overtightening. The occurrence of galling can also be reduced by using a self-lubricating alloy such as free machining martensite or Hiduron, or by incorporating surface treatments like molybdenum disulfide or titanium nitride.
What Causes Galling?

Galling can be at large or microscopic levels, and it affects both stainless steel and non-stainless steel materials. This adhesive wear typically occurs in areas of high contact-force sliding and low lubrication. It can cause failure of components with tight tolerances or seized fasteners.

The main cause of galling is friction between the contacting surfaces, resulting in excessive heat generation and a lack of sufficient ductility to dissipate that heat. Certain metals are more prone to galling, such as aluminum or austenitic stainless steel, whereas others resist it more readily, like brass and bronze.

Preventing galling requires proper assembly procedures, use of a commercial anti-seize, and keeping the fastener threads clean and free of debris. Slowing down the speed of installation during tightening also helps reduce galling because it allows the surface to cool down more and prevents excess frictional heating. Using coarse threads rather than fine ones is also beneficial since they have a larger contact area that spreads out the force and dissipates the heat.
What Metals Are Prone to Galling?

Metals that are prone to galling tend to do so because of the high amount of friction they undergo when being tightened. The galling process also requires ductile material and a crystal structure that supports cohesive performance. This combination often impacts softer metals such as aluminum and stainless steel fasteners.

Typically, stainless steel hardware will have a zinc coating that acts as a buffer between the thread materials, however, this can be stripped by excessive force or poor installation. This can lead to more friction which leads to deformation and then galling.

For this reason, it is important to use a proper torque wrench and install hardware with care to prevent galling. Additionally, choosing a harder grade stainless steel is also important to reduce the risk of galling. For example, duplex stainless steels are less prone to galling than austenitic grades. Alternatively, selecting a coarse thread and/or using a locking mechanism can help reduce the amount of heat and friction generated during installation.
How to Prevent Galling

Thankfully, most cases of galling are preventable. Mechanics should take steps to avoid or identify galling early on and stop it from happening. This not only prevents costly damage to fasteners and equipment but also keeps materials in the correct position for assembly or actuation, which is vital in machinery and production equipment.

Using lubricants can help reduce the friction that leads to galling. There are several lubricants on the market designed specifically for this purpose, such as anti-seize compounds. In addition, choosing the right material for fasteners can also minimize galling. For example, selecting stainless steel with a higher work-hardening rate, such as duplex stainless steel, can reduce the likelihood of galling.

Additionally, utilizing plated materials rather than raw, untreated stainless steel can minimize the risk of galling. Plating helps to maintain the protective oxide layer and resist galling, as well as offers additional corrosion resistance. Lastly, selecting coarse threads rather than fine ones can reduce the likelihood of galling as well.