Untightening torque Can we use the untightening / tightenigng torque ratio to estimate the efficiency of HEICO-LOCK ?

Action in the bolt

What is the tightening torque T= Force x distance Force distance

Torque calculation Kellermann & Klein Rotzler Torque = ( p/2π + 0,583 d μf + D/2 μt) *F F= clamp Force P= pitch Rotzler

Tightening energy ratio Underhead friction ~ 50% Source : Cetim TOTAL ENERGY SUPPLIED BY THE TIGHTENING TORQUE Tension ~ 10% ② A high friction in the thread adds high torsion Thread friction ~ 40%

Tightening energy ratio Source : Grupo Aztec

Tightening energy ratio 12% 32% 56% Source : Bolt Science ②

Tightening enegergy Ratio summary : 50% underhead of the bolt / nut friction 40% thread friction 10% generate tension /clamp load Only the clamp load serves the join. ① ②

Specific friction with wedge lock effect components ① TIGHTENING : Friction under the bolthead: The bolt/nut slides on the serrated surface of the HL washer UNTIGHTENING : Friction : The upper washer slides on the lower, at the cam side. Cam surface could be considered to flat surface

Specific friction with wedge lock effect components µa > µi

consequence ① The torque, taken by the friction between the cams when untightening is much lower than the torque taken by the friction under the bolt head on the serrated side. The Untightening / Tightening ratio, depends on friction coefficients on 2 differents surfaces

Clamp load increase when untightening ②

Clamp load increase when untightening Tension / clamp load increase

Clamp load increase when untightening Depending on: Cam angle α Cam height

Clamp load increase when untightening Depending on: Clamp length Case A Case B The elongation of the bolt when passing the cam peak is equal in value (few 1/10mm), but the % is much higher on short clamp length (case B) than long bolt (case A).

Consequence Different product could have : different α ② Different product could have : different α different cam height the clamp load increase could be a bit different the wedge effect requires α>β. We cannot deduct any better or worse effect. Only the residual clamp load prooves the efficiency.

Consequence ① ② Underhead frictions, are different Tightening / Untightening The torque need to beat the friction varies Clamp load increase could vary due the geometry of the washers The torque need to increase the clamp load and pass the peak varies

Consequence ① ② Untightening / Tightening ratio doesn’t give any information on the wedge effect efficiency. Tests available: Occular : tighten and then untighten. when turning left, it should slide between the cams. When passing the cam peak, a « click » should be feelt or heard. Junker test by simulating your joint. Real life montage and test.

THANK YOU FOR YOUR ATTENTION