Fastener Selection Criteria by Material

Hello,

I am trying to locate reference document(s) that will help me specify torque requirements for fasteners (screws, etc) that are based on the material used.

The product is an avionics electronics enclosure, which uses small screws and bolts to hold it together. I would like to specify the required torque based on the fastener and mating surface material, i.e. stainless steel vs plated steel vs plastic vs alumninum, etc.

This is a new FAA guideline we must follow yet they themselves cannot provide the references (typical).

I have browsed the ANSI & NIST sites with no luck.

Help! And thanks,

Harry

hsynovetz@uasc.com

 

[swertel]

Typically, you torque to 80-90% of proof strength of the bolt (ultimate tensile strength). Based on the bolt size, you can determine the torque to get the axial preload (90% proof).

MIL-HDBK-5 has some threaded fastener proof strengths in it. Section 8.1.5.

If you don't have a copy, MIL-HDBK-5 can be downloaded from

http://assist.daps.mil.

The handbook is a large pdf file, so best download it late in the evening when network traffic is lower. I know that I had to try to download it several times before my connection was not timed out and I could get the whole thing.

 

Thanks, I have various references regarding torque values for different fastener material (and the Hdbk was a bear to download).

I still need to know how to determine what the max torque should be to fasten (for example) using a steel screw to fastemn a circuit card to a plastic standoff, vs using the same fastener to secure aluminum frames together. I would imagine the "same" torque value used for athe aluminum example would shear the plastic.

Any ideas or leads?

Thanks!

 

[zengineerboy]

Hello,

In regards to plastic fastening, I always found that the manufacturer was very good with fabrication info, including fastening. I don't know if you have already tried this avenue of thought. I'll poke around and see what turns up.

Good Luck,

Steve