Hobson technical document
Nord-Lock Vibration Test Results: Clamp Load vs Nyloc Nut and Split Ring
A one-page Nord-Lock test chart, distributed by Hobson, showing bolt clamp load during a vibration test on an M8 class 8.8 bolt with a 25mm clamp length. It compares Nord-Lock washers with a regular nut, a nylon insert nut and a split ring washer, then shows what happens when the Nord-Lock joint is undone.
What this covers
- Vibration test chart
- Locking methods compared
- Untightening
Applies to Flat Washer, Mudguard / Penny Washer and Safety / Vibration-Lock Washer.
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Test bolt: M8 class 8.8, clamp length 25mm. The Nord-Lock joint was tightened to 70% of the bolt's yield point.
- With Nord-Lock washers the clamp load dropped a little at the start from normal settling, then held at about 15kN for the full 400 load cycles.
- The other fasteners lost most of their clamp load well before 400 cycles. A regular nut with a longer 50mm clamp length lasted longer but was close to zero by 400 cycles, and the nylon insert nut levelled out at a low clamp load rather than at zero.
- When the Nord-Lock joint is undone with a spanner, the tension first rises before it releases. Nord-Lock says this shows the locking function working.
Who it helps: Anyone choosing a locking method for bolts exposed to vibration.
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