Hello, new guy, question about surface discontinuities in fasteners 1

[Methos1979]

Hello,

I'm a QC Material Specialist for large underwater communications systems manufacturer. I've run into an issue with regard to some surface features in small stainless steel screws and as to whether they are conforming to the ASTM specs we use. Particularly I'd like some direction on opinions on what the differences are between bursts, seams, quench cracks or forge cracks. I am using primarily ASTM F788 to inspect to. I have photos I can upload if that is allowed and would help. I believe that what we are seeing in the heads of these very small screws (.086-56 UNC 2A)is likely conforming but I'm getting push back.

Any help is appreciated.

Scott

 

[Methos1979]

Here's a better photo of a similar screw. The 'crack' is no so much a crack under high magnification but rather a 'separation' where I can clearly see the bottom which would seem to indicate it's not likely an actual crack. Is this a burst?

 

[swall]

You are dealing with bursts in this particular instance. Bursts arise in headed fasteners due to either raw material issues or die design issues.

 

[metengr]

This may help

http://www.indfast.org/info/free-te...rsts_ Prevention and Detection - Brahimi.pdf

 

[Methos1979]

Excellent - thank you so much. That was very helpful and exactly what I needed to confirm my suspicions.

 

[Methos1979]

I'm still getting some push back on my interpretations of the two specifications. ASTM F879 has verbiage and drawings that show head discontinuities are not permissible when the burst runs from the socket to the edge of the head. The same basic verbiage and drawing is in ASTM F788 but F788 has verbiage in the beginning of the document that states the content therein only applies to fasteners .125" or larger. This would seem to indicated that these specifications do not apply to screws smaller than .125", which is the case we are dealing with. But does that mean that the ASTM F879 specs still do apply even though the F788's do not or does it mean that the F879 specs also do not apply due to the small size.

It seems to hinge on the statement in F879 that says, "10.2.1 The surface discontinuities for these products shall conform to Specification F788 and the additional limitations specified herein."

F788 makes it clear that it's specifications that are similar to F879 with regard to head discontinuities only apply to screws greater than .125". So does this mean that any screw smaller than .125" is exempt from F879's call outs or to do they apply. At this point we are erring on the side of caution and just discarding anything with a head discontinuity that runs from the socket to the edge just to be sure. But for future reference I'd like to know what the experts think.

 

[CoryPad]

ASTM F879 section 10.2.1.1 does not allow forging defects connecting the socket to the head periphery, so that is clear. For the F788 issue, I think you would have to get mutual agreement between supplier and purchaser to have F788 apply to smaller sizes.

 

[Screwman1]

That is a heading burst.