Home Forums General Discussion Ask Dr. Peener Ceramic Bead Peening in Suction Blast Machine

Hi, can someone help me with a coverage question on suction blast machines.
We are trying to peen a part on a suction blast machine using ZIR shot 300 ceramic beads to an intensity of 15 to 20N @ 200% coverage. We estimate it will take 10 passes to obtain 100% coverage (using SAE J2277) 20 passes to get 200%. How can I reduce the time to 100% coverage?
We are running 5/16 medium venturi nozzles with 5/32 air orifice @ 160mm standoff. To get 15N we are running at 80PSI. I have reduced the amount of shot flowing as when we increased the pressure the shot flow started to pulse. I suspected that the increase in air caused a back pressure in the shot hose stopping the shot flow, or that too much shot was sitting in the line blocking the suction effect. We fixed this by reducing the amount of shot coming out of the hopper. Thus achieving intensity but reducing the coverage rate.
Would a larger Nozzle size give us intensity and reduced coverage time by increasing the rate of shot flow?
Lots to learn as we have never run a suction blast machine before.
Thanks Roy.
Christchurch NZ

Just two comments (but there must be many readers more qualified to comment than myself):
(1) re "shot sitting in the line blocking the suction effect" - you must keep running air for a few seconds after switching off the shot feed in order to clear the line. If this does not work then you appear to have supply pipe problems (such as air-intake blockage).
(2) Increasing the nozzle diameter is the obvious answer to your coverage problem provided that your air supply (compressor, ballast tank and pipe diameters) can cope. Doubling the diameter would then reduce coverage times by approximately a factor of four.