Loosening Torque is 30% Lower Than Tightening Torque
Loosening Torque is 30% Lower Than Tightening Torque
(OP)
Hi Guys,
we're testing some tightening/loosening torques on a diesel fuel filter we designed here at my work. the can is 6061 billet aluminum and the head that it threads into is cast 6060 aluminum. they have stub ACME threads. when tightening the can onto the head it seats on an O-ring which is compressed axially between the head and the can. i'm wondering what would be the reason that the loosening torque that much lower than the tightening torque. we torqued the heads on up to 237Nm which is the customers specs. on average the loosening torque is about 205-210Nm. Any thoughts guys? Thanks!
we're testing some tightening/loosening torques on a diesel fuel filter we designed here at my work. the can is 6061 billet aluminum and the head that it threads into is cast 6060 aluminum. they have stub ACME threads. when tightening the can onto the head it seats on an O-ring which is compressed axially between the head and the can. i'm wondering what would be the reason that the loosening torque that much lower than the tightening torque. we torqued the heads on up to 237Nm which is the customers specs. on average the loosening torque is about 205-210Nm. Any thoughts guys? Thanks!





RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
What happens when you repeat the process?
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FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
Is there metal-to-metal contact between the filter can and head faces after the thread connection is torqued? Or is there a gap between them, with contact only at the o-ring?
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
In this case, I believe that a good analogy is that it takes more force to drive a wedge into a crack than it does to drive one out of a crack. In fact, without friction, threads and wedges would always self loosen instantly.
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
RE: Loosening Torque is 30% Lower Than Tightening Torque
What is the operating pressure?
Is it truly an o-ring? The previous design that could be accidentally (or by design!) overtorqued and damage the o-ring sounds kind of risky. Note conventional oil filters use an unrestrained flat elastomeric seal, and the tightening spec is some fraction of a turn after first contact. As there is no pressure balancing effect the physical strength of the elastomer and the initial compression must do all the work.
Under significant pressure o-rings achieve a deform and create a considerable amount of pressure balancing, so an 0-ring in a well finished, correctly dimensioned "gland" can seal 1000 psi+ pressures "automatically" with quite modest initial compression.
When under pressure I would expect an 0-ring to exert a bunch more force on the can and filter head and also provide a bunch of additional resistance to loosening for free.
RE: Loosening Torque is 30% Lower Than Tightening Torque
This is only true if the tightening process is in one continues motion.