Tension Testing: The Effect of Lubrication on K Factor
- Ray Wiltgen
- Apr 26, 2021
- 1 min read
Updated: Nov 28, 2023
Surprise results testing bolt tension with different lubricants.
Test Setup
Bolt and Nut Used for the Tests
Predicted Results Before Testing
Actual Results
Thread Conditions | Measured Clamp Force (lbs) | Calculated K Factor | Link to Video |
Dry  | 30,000 | 0.18 | https://youtu.be/8OwkjjqXGDE |
Anti-seize paste  | 32,000 | 0.17 | https://youtu.be/_V5ZhGfZZEg |
Anti-seize spray  | 35,000 | 0.15 | https://youtu.be/fKgE_KrrPYo |
WD-40 spray oil  | 28,000 | 0.20 | https://youtu.be/I3sNZw6L1L0 |
Oil  | 32,000 | 0.17 | |
Dirt  | 44,000 | 0.13 | https://youtu.be/C8cf5ZYIZ_c |
0.13 is very low!
Surprise Results – This is astonishingly low and very much unexpected. The dirt used for this test was gathered from the hole on a SAG mill in a gold mining operation. Normally we’d expect dirt to increase the K value, but this material created the opposite effect. For an actual installation, if this dirt is left on the thread, the bolt could be stretched beyond it’s yield point as shown in the experiment.
The Takeaways
It’s important to achieve the correct clamp force, as we’ve shown in previous posts (clamp force blog post link).
It’s difficult to predict the bolt clamp force as we’ve shown with these results.
For optimal results, tests that match as closely as possible to actual conditions should be done to determine the torque required to achieve the desired clamp load.
It’s difficult to get it right every time. Use a Security Locknut to protect your assembly when you don’t.
Having problems with bolted joints? Give us a call. We can help.
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