How to Prevent Galling

Galling is the seizing or abrading of threads due to rubbing over time. Often different kinds of fasteners, such as those made of stainless steel, aluminum and titanium are most likely to be subject to galling when tightened. While it is important to know how to recognize and stop galling once it occurs, what is even more important during the manufacturing process is the initial prevention. If the correct steps are taken from the beginning, you may lower the risk of galling from the get go.

One type of galling can happen during the manufacturing process due to an improper rolling die setting. To prevent galling in the dies during the manufacturing process, the wire may be coated with copper for lubricity. This copper coating is removed after thread rolling by pickling the finished fasteners.

Another way to minimize or prevent galling is through the use of a top coat by limiting metal-to-metal contact of engaging threads. There are different types of top coats that can be used, each with different ideal conditions.

•   Lubrication with “Molylub”
Molybdenum disulphide particles in this “Molylub” prevent metallic contact, minimizing abrading. This type of lubricant can be used when normal oil or lubricants may not be enough to prevent galling.
•   Film lubricants containing silver, aluminum or copper
These types of lubricants assist in decreasing the coefficient of friction. Most anti-seize compounds applied at the assembly line contain these metal particles.
•   TEFLON sealing tape
This option is most useful for large threaded components such as pipes and valves when threads of these parts could be wrapped with a thin TEFLON-sealing tape.

Tribological coating is another option when analyzing what type of galling prevention will work best. These Fluoropolymer coats are a blend of resins and fluoropolymer lubricants that provide low friction, chemical and corrosion resistance as well as non-wetting and release or non-stick properties up to
550° F.

Bossard offers an ecosyn®-lubric coating that is a tribological dry coating system for mechanically stressed fastening elements and their components. This coating is applied as a thin layer non-electrolytically. It also offers built-in lubricating properties and additional corrosion protection.
Stainless steel fasteners are frequently prone to galling when assembled. It is important to consider how galling can be prevented from the beginning to avoid further problems, cost and labor later on.