Testing HARDLOCK Nut for Reusability

Are Locknuts reusable? Most locknuts can be reused several times. But the majority of locknuts are Prevailing Type which degrade from multiple usages. The prevailing torque will lessen over many usages reducing the ability for the nut to grip the bolt. However, HARLDOCK does not have prevailing torque and grips onto the bolt after being seated. The HARDLOCK Nut does not degrade/ plastically deform like Prevailing Type Locknuts do.In order to prove that HARDLOCK Nut can be reused we have used the same HARDLOCK nut over 50 repeated Vibration tests (Junker test). Resultingly we find that there is no change in the remaining preload for the first and last vibration tests.

Test samples

HARDLOCK Nut → M12 Class 4, Zinc plated (Trivalent Chromate Coating)
Hexagon bolt → M12 × 70 mm, Class 4.8, Zinc plated

Test Method

test schematics
  • (1) Tighten the HLN and commence the tightening test.
  • (2) Subject the fastener to a Junker test to confirm the loosening prevention effect.
  • (3) Next conduct the tightening test.
  • (4) Attach and detach the HLN eight times and then conduct a re-tightening test.
  • (5) Repeat steps 1 to 4 until the nut has been tightened 51 times in step 4.

HARDLOCK Nut installation
Convex nut (First nut): Torqued to approximately 70% of the bolts yield point 20kN.
Concave nut (Second nut): Installed with the one-sided contact method. Torqued until there is no gap between the two nuts on one side.

Test Results

Junker Test #1

results after first tightening

Junker Test #2

results after 51st tightening