Tuesday, May 12, 2015

Galling

Stainless Steel Fasteners locking up? It’s not the quality of the parts but the common problem of using stainless steel fasteners. 

The beneficial nature of using stainless steel is that it is corrosion resistant. This property is due to the fact that stainless steel, among other alloys, generate a protective oxide surface film. Though this may be beneficial, it can sometimes lead to problems with installation.

Thread Galling occurs during fastener tightening and installation. When pressure builds between the contacting surfaces of the male and female threads, the protective oxides or coatings begin to shear, causing high points, or imperfections in the raw material of the two pieces to become locked together. The increase in friction causes the two parts to seize or “lock-up”. In serious cases, this difficultly understood problem is even referred to as “cold welding”, which illustrates the severity of the issue. Often, galling can cause damage to the thread of the fastener, but it can still be removed. In severe cases, the two materials completely weld together preventing loosening of the parts, and adding the difficult step of a forced removal and new parts to the process. The frustrating aspect of this is that both the nut and bolt can clear inspection individually, but fail to function effectively as a mechanical unit. 

Though this problem may be frustrating, it is avoidable. The main issue to address is to decrease the friction between the adjoining parts. This can be done in several ways including a slower installation process (RPMs). The idea behind this method is to reduce the friction (and thus heat), between the parts preventing the “welding” process. Our recommended method, due to its ease of implementation, is lubrication. Common methods include specially designed lubricants and waxes, however due to its safety and ease of availability, we recommend dipping the bolt in Maalox. 

Yes, that’s right, Maalox.  

Though this product may be designed to relieve upset stomachs, this liquid antacid has excellent lubricating qualities when it comes to installing fasteners, as well as qualities which help to protect the surface film of the fastener. As an added bonus, it is a product designed for human consumption, meaning that it is completely safe to use on food service and processing equipment, where stainless steel has become the standard. 

Other precautionary measures include using coarse threaded fasteners, using different grades of stainless steel for adjoining parts (take the corrosion resistance differences into consideration), and understanding the proper use of lock nuts. Because they are designed to add resistance to the existing threads of the bolt, it is best practice to make sure that a minimal amount of threads extend beyond the nut.

Reducing friction is the preemptive strike against this problem. That is why we recommend lubrication, and Maalox specifically, due to many of its properties beneficial to both sore stomachs and stainless steel. Galling can be a frustrating problem, but it can be prevented.     

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