nylon lock on nut vs loss of preload when torquing 1

[ddace]

"ADMINISTRATION KILLS ENGINEERING"

I am rigidly mounting a diesel engine with a through hole/slot that is connected to a rigid solid skid base.I am using 1 inch grade 8, coarse tread, zink plated shoulder bolts,washers at both ends and nuts have a nylon lock to help prevent loosening because of vibrations.

I am limited to a maximum clamp force of approx 80KN

Now the basic equation for relationship between torque and preload is

Fc=5T/D
Where
T = 80 000 N * 0.0254 m /5 = 406 N m

I would like to know:

1. should I account for losses by friction in the nylon ?and if so by how much ?

2. Will the pre-load obtained with this torque be appropriate for this joint (considering the harware used)?

Now i intend to torque dry at the head of the bolt and would like to know if anyone has comments or observations.

thanks to all

 

[CoryPad]

1) Yes you should account for the extra thread friction caused by the insert (polyamide/nylon). An accurate numerical answer is difficult to provide - the nut manufacturer should be able to help. In fact, they probably can test the entire joint for you and help determine proper assembly specifications.

2) The preload does not seem appropriate for this application. Typically, the minimum bolt preload is ~ 50% time the proof force. Your fastener size and strength mean 50% of proof is much higher than 80 kN. Therefore you should choose a smaller fastener or a weaker material.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[israelkk]

You could measure the friction torque between the nut and the bolt just before the nut touches the washer (in the lastthread before the clamping occur). Then add this value to the calculated torque. This is the recommended procedure in the MIL-STANDARDS, at least it used to be.