Steel Bolts into Aluminum Torque Specs 1

[barrnich]

Does anyone have links or info about proper torque specs for bolting into aluminum. Preferably, metric, grade 8.8. Or would one recommend a lower grade for such applications? If someone could give an explanation on how to calculate it it would be appreciated also. Would it be different for different thread engagements?
Also I heard that metric bolts are designed to twist apart before the threads shear in the hole. (assuming the same material) This would not be the case for aluminum holes with short lengths, but would there be a theoretical thread engagement that will allow the bolt to break first?
Thanks
Barry

 

[diamondjim]

Machineries Handbook does have a
calculation for determining the
length of internal thread needed
to ensure that the internal threads
do not strip out and have the bolt
fail instead when the materials have
different mechanical properties.
If your application is strictly static
you could probably go with a very
low grade of bolt.
Heli-coil inserts are also designed
to overcome the weaknesses of
aluminum if you have the room to
use a heli-coil.

 

[CoryPad]

faq725-536 provides the details for you to calculate an appropriate torque specification.

Property class 8.8 is appropriate to use with threaded aluminium parts. A rule of thumb is axial thread engagement = 2d, where d = nominal thread diameter. Bolt fracture is the preferred mode, and you can design for this using the procedure shown in thread725-35222.

Regards,

Cory

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