Gary,
After reading your post, it sounds like a problem related to the size control of your shot. I don't think it's a "cast shot" problem. Most intensity problems can be traced back to shot size control.
You stated, after two hours the intensity increases in some of the machines? The physics of impacting shot particles is a continous reduction of size and mass (intensity). The increase you describe is counter to the known endurance of the shot particle's size.
Preconditioning of shot is a best practice for removing oxide and fugative particles, however I don't think it will assist in solving your problem.
You mentioned shooting shot against a hard steel surface for two hours and noticed the intensity increasing. How many passes is two hours of blasting?
Some machines are having this problem and not others? (This would indicate possibly a size control or velocity issue.)
Don't rule out Almen strips....are they all from the same manufacturer?
Do you do screen analysis of the shot mix and have new shot additions highly controlled.
What controls are there on pressure and shot flow?
Cast Shot does not work harden more than 1.5 Rockwell points, so it would be difficult to to have a measurable intensity gain.
As you know, nozzle wear can change velocities as well.
I hope this is helpful,
Joe
