Home Forums General Discussion Shot Peening Process, Intensity, Coverage Meaning of A2 intensity unit

I understand what an intensity specification followed by A, C, or N means.

I have been reviewing 40-year old drawings and specifications and have been coming across callouts like:
"Intensity 0.008-0.012 A2"

What does the "2" in "A2" mean? Is it officially defined anywhere? I suspect it is obsolete, but I still need to know.

Thanks.

Jim Andrus

The original gage, invented by J. O. Almen and patented in 1944 was superceded by General Motors in November of 1943 and referred to as #2 Almen gage. For a while specifications were careful to identify which gage was to be used for measuring intenisty and the 2 in A2 is used to identify the #2 gage. This is explained in SAE documents J442 and J443. The terminology was later dropped when it was unlikely that anyone would still use the original gage.
By the way, the original gage designed by Almen used two knife edges for strip support whereas the General Motors design used the 4-ball platform support. This took into consideration the compound curvature nature of the strip.