Dry or Wet fasteners (re:thread404-173061)
Dry or Wet fasteners (re:thread404-173061)
(OP)
I am trying to resolve a dispute within our company in regards to wet vs. dry torque values. The dispute is over the condition of black-oxide cap screws when they come out of the box with a visible coating of "light oil". Our most experienced model builders beleive that these are still considered dry and I tend to agree with them. Our customer is convinced that these must be torqued to the corresponding "wet" values. Do we really need to wash all of our fasteners with acetone before assembly begins or can somebody on this forum provide a response that would convince our customer that we are right. (re:thread404-173061: Torque specs-dry vs oil)





RE: Dry or Wet fasteners (re:thread404-173061)
I would agree with you that a light coating of oil for shipping would not likely contribute greatly to lubrication of the fastener for tightening purposes.
RE: Dry or Wet fasteners (re:thread404-173061)
Well I think I agree with your customer that the wet values should be used but is it possible you can do some tests and measure the tension in the the bolts using the dry torque values you have and compare practical results with theory.
My belief that wet values should be used is from an experience I had many years ago, I was called to investigate some tapped brass inserts that were failing at the recommended dry torque, it turned out the fitters contaminated the screws accidently with a grease residue they had on their hands as they picked the screws up, this got onto the threads, reduced the friction coefficient and the increased preload was sufficient to strip the brass threads. After I got them to clean up themselves and their spanners and stated not to go near any grease till after they had tightened all contacts onto the inserts we never had another failure.
regards
desertfox
RE: Dry or Wet fasteners (re:thread404-173061)
Hopefully after a couple days a consensus will form...
RE: Dry or Wet fasteners (re:thread404-173061)
Have a look at table 2 in the link posted below:-
http:/
regards
desertfox
RE: Dry or Wet fasteners (re:thread404-173061)
If the clamp load is that critical the only way to truly determine the correct torque is to test it, as mentioned above.
I have investigated this for my current company and found two camps. One camp just uses the default SAE "K" factors. The second camp presumably has done internal testing and generated their own chart (and everyone's is different!). I used to have quite a bit of information on the subject but unfortunately my hard drive get erased by my IT department. :(
ISZ
RE: Dry or Wet fasteners (re:thread404-173061)
I was looking for some more sites which may throw up some more comparisons of wet and dry figures for torque or friction factors, you can see from table 2 in the first link that there is an overlap of the figures for both wet and dry.I found this other link that says that the torque factor for screws blackend and lightly oiled is 1 as the published data is for screws as supplied in this condition.
(see page 2 of the link)
www.alb
I have no idea what your torque figures are that you are looking at however I still think your best bet is some practical testing on the fasteners in question.
desertfox
RE: Dry or Wet fasteners (re:thread404-173061)
RE: Dry or Wet fasteners (re:thread404-173061)
Tremendous variation.
Tremendous overlap.
Do not rely on handbook values.
If your use is sufficiently critical that you need to "know" that the preload is what it is supposed to be, and for some reason you are using torque control to achieve that preload, then you need to test your specific materials in your specific application.
RE: Dry or Wet fasteners (re:thread404-173061)
RE: Dry or Wet fasteners (re:thread404-173061)
They did not accept "out of the box" cleanliness of the threads - because they required the threads be lubricated; nor default grease/oil/nothing as a proper lubricant for torquing. If large bolts were re-used, they had to be thread chased, and have new nuts and washers. Preferably, new bolts were used on re-assembly.
RE: Dry or Wet fasteners (re:thread404-173061)
Here's the tool to use:
ht
Good luck.
Terry
RE: Dry or Wet fasteners (re:thread404-173061)