When a fastener becomes loose, it is due to a reduction in the tightening force (the bolt preload), which has two causes: non-rotational loosening (slackening) and rotational looseness (spontaneous loosening).
• Initial wear
Cause: Fatigue due to uneven wear in the connecting partsMain countermeasure: A conical spring washer having a spring counterforce
• Micro-embedding on seating surface
Cause: Localized Plastic deformation across all seating surfaces (nut face and bolt face).
Main countermeasure: A strong, rigid flat seating that does not sink
• Looseness from micro-movement wear and external forces such as excessive tightening
Cause: Wear accompanying horizontal displacement of the contact parts
Main countermeasure: A design incorporating high-strength materials, surface treatment such as carburization or nitriding, and the limiting pressure of the lubricant material
• Looseness due to heat
Cause: Relaxation caused by a difference in thermal deformation
Main countermeasure: A design taking into consideration the linear coefficient of expansion of the materials
Cause: Cyclic loads in the bolt axial direction, bolt transverse direction and bolt axial rotation direction
Main countermeasure: Parts that prevent looseness
When the bolt preload is low or drops, the number of cycles until bolt failure is reduced, creating a dangerous situation.
1. Reduced preload
The bolt bears most external forces, leading to a higher risk of bolt breakage or damage
2. Adequate preload
Because the fastened assembly as a whole bears most external forces, the bolt is not impacted and does not weaken
Incorporating countermeasures against non-rotational loosening, the Hardlock Nut operates on the wedge principle for a powerful anti-loosening effect.
The Hardlock Nut can therefore be used safely without concern about the tightening force dropping.
To learn more about the anti-loosening effects of the Hardlock Nut, read “Why the Hardlock Nut Does Not Loosen.”