What is Thread Galling?
Thread galling occurs when the friction and pressure applied during installation, causes the male and female threads to seize together. Thread Galling has also been referred to as “Cold Welding”, because the bond formed once the threads have seized, is a strong as the bonds formed when welding. Once this Thread Galling has occurred, it is close to impossible to separate them without splitting the nut or cutting the bolt.
What Type of Bolts Can Experience Thread Galling?
Thread Galling is prevalent in bolts made of stainless steel, aluminium and titanium. Threads that have been damaged in the past, or have fine threads are also more susceptible to thread galling.
How do I Prevent Thread Galling?
Keep Installation Speed Slow!
The heat and friction generated by power tools during installation can contribute to galling. Slower speeds means less heat created, and therefore less risk of galling occurring.
Lubricate the Threads!
Using a lubricant on the external and or internal threads can reduce the friction that causes galling. The lubricant you use should contain large amounts of molybdenum disulfide.
Avoid Damaged or Dirty Threads!
Dirty and damaged threads are prone to galling. Try putting the nut on the bolt by hand. You should be able to thread it without a power tool. If you cannot thread it, it is most likely damaged.
Use different alloy grades!
Using a different alloy grade for the nut to the bolt can reduce galling. For example, 400 series stainless nuts work well with 316 stainless bolts.
If binding starts to occur: Stop!
If fasteners appear to be binding before you add tightening pressure, STOP and allow the elements to cool down for a few minutes before assessing the thread and starting again with a new nut.