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

distance

Force

Torque calculation

• Kellermann & Klein

Torque = ( p/2π + 0,583 d μf + D/2 μt) *F• F= clamp Force• P= pitch

• Rotzler

Tightening energy ratio

Source : Cetim

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Thread friction ~ 40%

Underhead friction ~ 50%

Tension ~ 10%

A high friction in the thread adds

high torsion

TOTAL ENERGY SUPPLIED BY

THE TIGHTENING

TORQUE

Tightening energy ratio

Source : Grupo Aztec

Tightening energy ratio

12%

32%

56%

Source : Bolt Science

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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.

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Specific friction with wedge lock effect components

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

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• µa > µi

Specific friction with wedge lock effect components

consequence

• 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

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Clamp load increase when untightening②

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).

• Different product could have :– different α– different cam height

Þ the clamp load increase could be a bit different

Þ the wedge effect requires α>β. We cannot deduct any better or worse effect.

Þ Only the residual clamp load prooves the efficiency.

Consequence ②

Consequence

• 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

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Consequence

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.

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THANK YOU FOR YOUR ATTENTION