Home Forums General Discussion Shot Peening Process, Intensity, Coverage Compare cast steel and cut wire media

Jack,
Do you know the comparable wear rates of Cast steel shot versus Cut Wire shot? We use S-70 M and we reject all shot that passes a #60 Mesh Sieve-(.0098”). Since we cull so much of our shot- the initial wear-in of the cut wire shot would be a concern. We currently purchase a special size distribution of S-70M cast steel shot which comes new to us as:
all pass -#40 sieve
98% stays above a #60 Sieve

New: -We usually see 2% on a #45 sieve and 48%- 58% on a #50 sieve and similar on a #60 sieve.

This has shortened the time to Saturation from SAE spec S-70 M shot which allows so much low mass shot.

Name and Company Withheld

Generally speaking, cut wire shot durability is in the range of 5-8 times that of cast steel shot, depending upon the peening intensity. I'm curious about you comment about the specially selected media giving you a reduced time to reach saturation. Do you conduct a saturation curve according to SAE J443 by subjecting a minimum of four strips for various exposure times? Smaller media will achieve saturation faster than large media since you have more "dent makers" per pound of the smaller media. For each pound of media projected you get more dents and hence have a shorter time to achieve saturation. I'd like to see your data for saturation curves.

Jack

Jack,
When I say “a larger shot size distribution reaches saturation faster” – this is not based on a new saturation curve for the new shot size but on the time to reach the “old- smaller” shots saturation. Could the size S-70M be so small that the finer particles have so little impact on the Almen "A" strip and therefore have less effect on arc height? We certainly see the differences in Compressive stress. The special shot gives us .002" higher than the bottom of the SAE Spec shot.

So would you expect the Special shot to need a longer time to saturate and yield a higher arc height?

I'm not sure what you mean by "time to reach saturation" if you aren't referring to a complete saturation curve. Time to reach saturation is influenced by several factors with shot size being one of the most important. For example, if you compare S-110 and S-230 shot you'll find that you have about 8 times as many particles per pound of S-110 compared to S-230. If you could reach saturation in one minute with the S-110 then it would take you about 8 minutes using S-230 (assuming you adjust air pressure or wheel speed to achieve the same intensity).

I suspect that you are actually referring to arc height readings, not saturation curves, and therefore possibly misinterpreting actual intensity. You might run a complete saturation curve and send me the data points so I can see the shape of the curve etc.