Thanks for the response Jack. I am in the middle of putting all this stuff together and it is giving me fits.
I started off with a general question and I was going to work from there based on your answer. For the purposes of this question the PVT is a custom tool that has two almen blocks that simulate the two peened diameters on the piston. Off the top of my head the diameters are 1.11 and 2.11 for the head. The overall length of the PVT is the same as the piston and uses the same tooling to drive it under the shot stream. Not a scrap part, but an accurate stand in.
This piston requires .004-.007A intensity and 200% coverage. Using the static almen stand I settled in comfortable at about .0050A at 2 passes for the shaft and .0054A for the piston head. It is a little closer to the nozzle. Since we rotated the part so slowly we were able to peen the entire surface under a single program.I felt that this was an accurate intensity rating and was very repeatable.
I am now rotating the PVT under the same conditions as the part. The same settings on pressure, shot flow, stand off, and angle of impingement are now producing intensity ratings for the shaft at about .0064A at 8 passes and .0061A at the head at 16 passes. I am still trying to nail down why the intensity rating would increase with the rotation of the PVT. The shot stream has not increased in intensity in any way. The shot is still coming in at the same velocity and at the same angle. I understand the difference in exposure time for the two surfaces, the head has almost twice the surface velocity as the shaft at the same RPM. In both cases the traverse rate of the nozzle is the same, I cannot change that on the machine at all.
It appears to me that spinning the PVT has changed the dynamic of the strip coverage. Which is the more accurate intensity? That is what is bothering me. If would like to see some numbers I should have some in the next day or two and perhaps I am missing something that you will pick up.
