ECN Forum Forums General Topics of the Trade General Discussion Area Torque Frequency

>there are aluminum heads for cars.
When I said copper and aluminum, I meant, of course, wiring. Engine heads are obviously cast, not extruded. I don't know whether they are really aluminum alloys. It would be bad news if an engine part squashed out or twisted as easily as an aluminum wire does!

The torque requirement in some cases is actually the force to stretch the bolt a certain amount. Some refer to this as pre-load. For the head bolts on nuclear reactor vessels they screw on the nut, then use a hydraulic powered nut on the end of the bolt that stretches the bolt so the permanent nut can be run down manually. Some of the other torquing is done without a torque wrench. Run the nut to hand tight(which is good contact and no bolt stretch) then, based on the bolt type and size, turn the nut a certain number of degrees or quarter turns. The thread angle and the number of turns will determine the amount the bolt will stretch. I do not know how to figure this with copper lugs which will have to compress to give the pre-load instead of the bolt stretching. Maybe there are tables or tables could be derived based on the malleability of copper. That may be how the manufacturers determine the torque requirements. It would be simpler for them to tell us how far to turn the bolt or nut after contact, but it is easier to prove an electrician did not torque properly than that he did not make the required turns. The lawyer just has to ask for a receipt for the purchse of the wrench. If he has one then ask for the calibration info. If he has that make him prove he or an employee never dropped it.