(At the risk of leading you down a rabbit hole): consider that most torque specs are for dry torque, but in many instances, anti-corrosion measures and anti-seize compounds are quite fine to use, but the torque values have to be adjusted waaaay lower to avoid over-torquing.
Consider, by way of example, the oil pan bleed screw. It and its threads are well lubed, and while granted, it is not holding much of a clamping load, it is still subject to heat cycles, vibration, etc, and yet it stays happily in.
(Not an Mechanical Engineer, just a fellow occasional wrench-spinner who has battled rust) When a clamping load is involved, it starts to matter if there is an expectation of vibration, at which point something like Nord-Lock is called for.
I am sure my much more knowledgeable peers here will point out the glaring mistakes and omissions I have made, causing learning to have occurred. :)
This is something I’ve seen several times. often in aerospace the threads are supposed to be lubricated but if you get lubricant under the head you can get way more preload than you expect. Same for changing the washer material for a thermal or other reason and not realizing it has much lower friction.
For unique applications in aerospace, it’s common to do testing to determine a non-standard torque-preload curve.
In some industries, preload is measured more directly using hollow bolts (so you can measure the before and after length therefore determine preload), ultrasonic measuring devices (same reason) or preload sensing/indicating washers (there are many types).
Consider, by way of example, the oil pan bleed screw. It and its threads are well lubed, and while granted, it is not holding much of a clamping load, it is still subject to heat cycles, vibration, etc, and yet it stays happily in.
(Not an Mechanical Engineer, just a fellow occasional wrench-spinner who has battled rust) When a clamping load is involved, it starts to matter if there is an expectation of vibration, at which point something like Nord-Lock is called for.
I am sure my much more knowledgeable peers here will point out the glaring mistakes and omissions I have made, causing learning to have occurred. :)
reply