huangyhg

titanium bolt torque
hello,
i am going to use titanium bolts to assemble two parts of an space equipment and l have the next doubt when l use self-locking nut:
if the applicable torque for the bolt is 11 n.m for m6 metric, should l increase this torque in order to take into account the running torque from friction in the thread due to the self-locking characteristic of the nut?
and if l have to increase that torque, how much?
thank you very much and best regards,
esteban
yes, you need to increase the torque to overcome the running torque. the increase should be equal to the running torque. if you don't know this value, you should perform testing to obtain it.
regards,
cory
thank you corypad,
but l wonder if there is another way to know the running torque applicable fopr and titanium bolt m*6, and not by testing.
thank you very much and best regards,
esteban
the torque is a function of the force you want to induce in the bolt:
m=kdp
where:
m - torque
k - a constant (ususlly 0.15 for lubricated, 0.2 for dry)
d - the nominal bolt diameter i.e 6 mm in your case
p - the force tou want to induce in the bolt
this torque should be added to the running torque just before the nut or the bolt head touches the bolted furfaces.
the k value may be different for titanium. unless you know the k value for the bolts you have, test few bolts until they break and then calculate the actual k. from now on you can use the formula for any force you desire.
celemin,
the prevailing torque (running torque) of a joint is a function of many variables and not easily calculable. you can ask the fastener supplier to provide an estimate, or ask them to perform the testing - many are willing to do this as a customer service.
regards,
cory
esteban
to calculate the running torque (class 11 torque) mentioned above you take a dial or blade type torque wrench and measure the torque needed to turn bolt just before bolt contacts the surface to which it will be tightened. the torque wrench must be calibrated and the reading, if possible, should be in the middle of the scale on the wrench. after taking a few readings you can average them and add this value to the value from the chart, and then torque the rest of the bolts to that value. as titanium should be lubricated with a moly type lubricant, it should be added before taking readings for running torque. titanium is suspectable to galling when tightening and should be tightened with hand tools only, no automotive type air tools etc. should be used, because you can be at the required torque but the bolt is not tight. it is best to tighten a bolt a few turns and then go to one diametrically oposite it (if round pattern) and then tighten it, continuing this until bolts are snug. similiarly when torquing it is best to torque in stages, for instance torque half the total value first time, then a value about half the remaining value, and finally the full value.
for information on errors in torque wrenches see website.

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