Recommended Torque for Steel- Brass Combo 1

[gdodd]

At our company, we have a standard listing of recommended torque for steel to steel, zinc plate steel and friction modified steel fasteners but nothing on bimetal combination fastener systems.

I have been asked to determine the grade of steel bolt required to assemble a plastic part with threaded brass inserts to a steel flange.

The bolts are 6 and 8 mm diameter and the maximum torque applied will be 15Nm for the 6mm bolt and 35Nm for the 8mm bolt.

If the inserts were steel my references suggest a 10.9 bolt for both. Is this also a suitable bolt grade for brass inserts?

Thanks in advance
GD

 

[CoryPad]

GD,

You seem to have this a little backward. The required property class for a screw is based on what clamping force is required. The applied torque is calculated based on this clampign force. The axial thread engagement (insert length/height) is calculated to resist the maximum possible pretension. In my experience, a plastic component cannot resist the localized stresses (at bearing locations and along the plastic/brass interface) created by a 10.9 property class screw. For a 10.9 to work, the insert length and screw head outer contact diameter need to be enormous.

Regards,

Cory

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