Date Updated:May. 16. 2025
Vol.1 What is Seizing (Galling)?
Hey there!
I'm thrilled to kick off my lecture series, "What is a Screw?". If you have any problems, I will be happy to help.
Today, I would like to talk to you about "Seizing and Galling".
Do you have any experience with screw threads seizing?
If you try to drag a seized screw out by force, you will end up wasting tremendous time and effort on a broken screw.
But fear not! I'm here to share the secrets for preventing and solving this problem. Let's dive in!
What is thread galling?
Galling is a phenomenon in which a screw becomes unable to rotate. This is also commonly known as seizing.Related articles : Galling and Seizing
Why does thread galling occur?
There are two main reasons:(1) friction and adhesion (cold welding)
(2) external factors such as foreign matter
Friction and adhesion (cold welding)
Friction-generated thermal expansion during screw tightening leads to thread adhesion (cold welding), causing galling and seizing. Stainless steel screws are particularly prone to thread seizure for the following reasons:・Higher coefficient of friction (twice that of steel) generates heat more easily
・Lower thermal conductivity (1/3 of steel) makes it difficult for heat to dissipate
・Higher thermal expansion coefficient (twice that of steel) increases thread adhesion between male and female threads
Since seizing and galling are more likely to occur in high-temperature environments, steel screws are not entirely safe as well.
External factors such as foreign matters
Steel screw galling and seizing can also be caused by:・Screws tightened with burrs, etc.
・Excessive tightening torque
・Rough or dented thread surfaces
How to prevent seizing (galling)
First, regarding external factors, seizing and galling can be prevented by inspecting the thread condition prior to tightening and by applying appropriate torque.
Reducing the coefficient of friction prevents thread galling and seizing caused by friction (cold welding) through the following measures:
・ lubricant application
・ surface treatments specialized in Anti-Galling and Anti-Seize
While a lower friction coefficient eases screw tightening, applying the same torque can still damage threads.
Therefore, it is essential to prevent galling and seizure from external factors and to adjust the tightening torque.
Refer to the section on axial force variation due to surface treatment.
Comparison of axial force with regard to different surface-treatments
For applications where lubricants are unsuitable or plating delamination is a concern, consider using SNSL-PN surface-hardened screws to prevent seizing in clean environments.
That's it for today.
Thank you!
