Machine Screw with Yield Stress Rating

[kcme2005]

Does anyone know a good supplier where I can purchase machine screws with a certificate giving the yield stress rating?

We are working on an ATEX listing and the agency is requesting the yield stress rating for a screw we are using. The cert we recieved from our vendor only gives the tensile rating. The agency will not accept this. Our vendor is a distributor, who recieves the screws from another distributor, and another, and so on. They couldn't get any yield information for us.

We tried to have the screws tested, but they are too small.(#10 x 1" Phillips Pan Head Screw, Self-Tapping, Type A)

We have been unable to find any other vendors that can supply us with screws including a cert with the yield rating. Any ideas?

 

[Carburize]

I would use a value of 75% of the UTS and describe it in vague terms like "typical expected minimum".

 

[kcme2005]

Thanks for the idea - it was a good one!! But sadly, I already tried that.

The agency won't accept anything other than a cert from the manufacturer with the yield rating, or a test report from a certified lab.

 

[Carburize]

Do you know why they are asking for this data?
We supply ATEX certified equipment where fasteners might have some significance in the evaluation and we have never been requested to supply this level of information.

 

[TVP]

Standards such as ISO 898-1 indicate that small fasteners (both diameter and length) that cannot be tensile tested should be torsion tested instead, according to ISO 898-7. Was a similar standard, perhaps ASTM or SAE, specified for this product?

 

[Kenneth]

ASME B18.6.4 (

http://members.asme.org/catalog/ItemView.cfm?ItemNumber=N02198)

lists a number of tests that are appropriate for these Type "A" thread self-tapping fasteners, including Drive, Ductility, Hydrogen Embrittlement and (as TVP sugessted) Torsional Strength Tests. Maybe one or more of these tests would satify your customer? I've (personally) never heard of a "yield stress rating"...

 

[metman]

It is not uncommon to specify torqueing fasteners to 60%-75% of yield and in some cases specifying exceeding yield strength for maximum preload. If the application is critical, I can understand their desire to know the the tested yield.

 

[yates]

The only snag is - there is no way of accurately measuring yield (.02 percent yield stress for example) in threaded fasteners. A yield point can be measured on a test-piece of the raw material but (particularly if they are stainless screws) the yield of the screws will depend on cold work (were the threads rolled ?)
As TVP says, small size screws are usually tested in torsion rather than in tension. Even though the final user is asking for the yield strength of the screws, he is not going to be able to use these values in any kind of meaningful analysis of the screw's performance.