Here is an in depth look at our problem.For example when setting air pressure at 80 psi we acheive about a .009A.we can run another strip at the same psi and acheive an .011A also.All of this is done with the same nozzles.the only difference is the amount of shot that is being pushed through the nozzle.
My question is how do we maintain shot flow consistency, so that the same amount of shot is being pushed through no matter what the psi.
hope this is enough info

thanx

[email protected]

You can install a MagnaValve made by Electronics Incorporated (www.magnavalve.com). It will regulate the media flow and send alarm signal in event there is fault condition.

(I'm curious, how do you know there is different amount of shot being pushed through the nozzle?)

Be sure that your media is within required specification and that your Almen holders are flat. If in doubt about the holders have them re-ground, preferably by blanchard grinding. Be sure the Almen gage is calibrated and the zero block is flat. Be sure your saturation curve is developed properly. You can request a FREE Almen saturation solver from our web site www.shotpeener.com.

I agree with Jack's comments but there is, for me, a residual problem. IF the only variable is shot flow rate then there should be no variation in Almen intensity. Higher shot flow rates will reduce the time required to attain a given Almen arc height but should not affect INTENSITY.

Actually, shot flow rate does affect intensity for air blast applications. A lean flow rate will allow higher air velocity and media velocity. Conversley, as the media flow rate increases there is increased turbulance and pressure drop at the nozzle thus lower velocity and peening intensity.
Since the peening is applied to Almen strips we have a complex problem: namely, more dents are being created with higher flow rate and thus shorter time to saturation. But, with lower flow rate the intensity will increase but the rate of coverage is reduced and therefore the time to reach Almen strip saturation will take longer.
The moral of the story is that flow rate needs to be monitored and also controlled in order to maintain a consistent process.

Try this a sample process.

1) Set the air pressure to achieve specified intensity.
2)Establish saturation by keeping the nozzle positioned perpendicular to the surface to be peened while using an approximate eight inch (8”) brush or stroke of the gun at ½” to 1 ½” per second. Use two (2) passes to peen the first strip, four (4) to peen a second, and continue as needed. Saturation is reached when doubling the number of passes results in no more than a 10% increase in arc height. A minimum of four (4) readings is required.

A couple of questions
1)Are you 100% sure the air pressure is constant?
2) Is the variation between operators or the same person?
3) How are you controlling media flow now?