Torque Wrench Spring Storage 1

[Sanguilocks]

We are thinking of asking our techs to store torque wrenches on the lowest torque setting. The manufacturer recommends this because they say it makes the spring last longer. Isn't this trade off though? There will be more load cycles if we keep destressing and then restressing the tool internal springs for daily use. Is keeping the spring under stress worse for the fatigue life than the extra cycles it will cause? Should we only do this for wrenches that go unused for long periods?

 

[dgallup]

I think the manufacture must be concerned with creep, certainly not fatigue just sitting there. My torque wrenches recommend the same thing. I always do it because they sit for weeks or months between uses. If you use the torque wrenches daily I would see little benefit. In that case you should be checking their calibration on a regular basis.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[israelkk]

To my opinion the issue is not fatigue, it is relaxation of a spring under constant deflection and possible incorrect reading of the torque and deviations between calibrations. What kind of torque wrenches?

 

[Sanguilocks]

The wrenches are Utica brand and are calibrated yearly.

 

[israelkk]

As I wrote the spring is constantly loaded to some deflection if you leave it at some rated torque and may (probably) relax if the manufacturer bothered to warn to lower the torque. I am not familiar with the internal design (spring and volume available) but this points to my opinion to a bad design of the tool. A good design should not relax and loose force no matter how much the spring is deflected. How to do it is another issue and will probably result in a more expensive tool due to secondary operations on the spring and probably a more optimized spring design (design and material).

 

[israelkk]

dgallup

Creep is caused by constant force on the spring but in this case the spring is deflecetd to constant length therefore, the spring relaxes and loose force.

 

[dgallup]

Same result

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[israelkk]

dgallup

When the spring is compressed to a specified length the force of the spring is reduced with time due to relaxation. In creep test the force is constant. In the wrench the condition are of relaxation.

 

[dgallup]

Same result, the material moves, only the loading condition is different.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[israelkk]

The difference is in how much it moves (decrease). In relaxation it moves less because the force decreases all the time. Therefore, if under a creep test of constant force "F" the spring length decreases by some permanent amount, then if you press the same spring (in the wrench) to the same initial load "F" and leaves it for a long period of time the spring length will decrease less than in the creep test.