BOLTED

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bolt securing

The Experts: Preventing galling and seizing

10 August 2017
2 comments

Text: Lena Kalmykova

photo: Jason Milburn

First published in Bolted #2 2013.

Q: When and why does galling and seizing appear?
A: Galling is caused by a combination of friction and adhesion between metallic surfaces during sliding. When galling occurs material is adhesively pulled from one surface leaving it stuck on the other in the form of a lump. This process spreads rapidly as the built up lumps induce more galling.

The tendency of material to gall is affected by the material’s ductility. Typically, softer materials are more prone to galling while harder materials are more resistant.

In bolting, thread galling appears during fastener tightening as pressure builds up between the contacting and sliding thread surfaces. Thread galling commonly occurs with fasteners made of stainless steel, aluminium, titanium, and other alloys.

In extreme cases galling leads to seizing – the actual freezing together of the threads and bolt lock-up. Continued tightening may lead to the breakage of the fastener or result in torn off threads.

Solution:

  1. Lubrication of the internal and/or external threads.
  2. Reduction of the installation RPM speed.
  3. Selecting different stainless alloy grades for the bolt and the nut reduces galling resulting from different degrees of hardness. However, the strength of the nut always needs to be greater than the strength of the bolt.

 

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  • Dear sir
    please what is the reason of stud bolt stuck for high pressure and temperature operation
    of bolt material is 1.7218

    • Frida (Nord-Lock)

      21 December 2015

      Dear sir,

      Thank you for your question. The materials mentioned in the article, such as stainless steel, have a tendency to gall very easily, also at “cold temperatures”. I general galling and seizing increase with temperature and pressure for all metallic materials. The best thing you can do is to lubricate the joints.