Home Forums General Discussion Specifications AMS-S-13165A is out!

I think this post is really important in getting the next revision of AMS 2430, and all shot peening specifications for that matter, on the right track. The only misleading part is that complete coverage not always leads to complete removal of the tracer. The way to evaluate complete coverage itself is quite difficult to state. I think the tracers should be used only as an aid to evaluate coverage, as it will give a more obvious indication of surfaces where coverage may be insufficient. It is true that tracers can be removed by ricochets that doesn't produce an actual dent in the surface, becausee of the shallow angle of impingement or other reasons. Surfaces showing traces of remaining tracers shall be subjected to visual inspection (10X - 20X) to confirm or not the presence of "real" dimples.

If I understand well the way fluorescent tracer works (I've never tested those myself), you have to produce a "master" part once the proper exposure time has been determined. This master should be prepared with the fluorescent tracer, so that the operator can compare the production parts (previously coated with tracer before shot peening) with the master and compare the amount of remaining fluorescence. If the level of fluerescence is the same, the amount of coverage of the master part has been reached on the production part. From my understanding, this method still relies on visual inspection for preparation of the master part.

I think the main problems with visual inspection are:

1 - subjectivity of the inspector, as a person can evaluate 60% and an other inspector 80% for the same observed area. This leads to complications when performing coverage mapping.

2 - Inspection of coverage on hard materials that leave really small and shallow dimples. I remember that a Boeing specifications give guidelines for use of the saturation time of the Almen strip and a correlation with the area being peened to determine the exposure time of the part. As concerned as I am about not confusing the Almen saturation time with the required exposure time, I think some guidelines should be provided for coverage evaluation on hard materials. I have however no idea at the moment of what those guidelines could be.

Anybody every used that correlation method for high hardness / high strength materials?