What is Cold Welding?

Cold welding also known as Thread Galling is a phenomenon that can occur during the tightening - mainly at high speed - of threaded connections.

It is caused by a combination of pressure and friction (high friction value in stainless steel). You notice it when, while tightening a bolt, the threads get stuck in a nut or tapped hole. And, once the bolt is stuck you usually can't remove it the normal way. Then it becomes grinding, drilling or tapping.

How does cold welding occur?

During the tightening of fasteners, the pressure between the contact surfaces increases. This creates friction and damages the thread surface of both the external and internal threads.

These damaged surfaces then adhere to each other. The threaded connection seizes and, in extreme cases, the bolt or screw even breaks off.

Soft materials are often more sensitive than harder materials. Cold welding usually occurs with fasteners made of stainless steel, aluminum and titanium.

Cold welding also known as Thread Galling

How to prevent cold welding?

  • Tightening threaded connections at too high a speed is a common cause of cold welding. The higher the RPM, the more friction and thus a greater chance of thread deposition. So tighten the joint at a lower speed. This often reduces the problem or even solves it completely
  • Use lubricants (anti-seize)
  • In the case of stainless steel fasteners, choose a different quality for the nut than the bolt. However, the strength of the nut should always be greater than that of the bolt. In this case, bolts of stainless steel A2-70 quality are used in combination with nuts of stainless steel A4-80
  • Avoid using fasteners whose threads are damaged. The presence of dirt can also increase the risk of cold welding
  • Do not use a bolt to pull or push parts together. If you do, it will create additional pressure on the thread surface. It is better to bring the parts together in advance using clamps or adhesive pliers
  • Use pre-coated bolts

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