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#1211 05/19/16 08:42 PM
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Just a quick question regarding calculating the coverage runtime for difference id’s. On the od we ran passes with known intensity settings, to be able to determine the point at which >95% coverage was reached, from that we used the surface area & runtime to calculate the runtime for difference od’s, ie:

175mm dia @ 25mm/sec (coverage Check data) =

150mm dia @ 25 / 0.74 = 33mm / second.
200mm dia @ 25 / 1.30 = 19mm / second

My question is, would we be able to apply this philosophy to the id or would we use a different calculation? Would the formula differ if we were using 1, 2 and/or 3 orifice nozzles to achieve the said coverage?

tec #1212 05/20/16 12:50 PM
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Establishing time to achieve coverage (should be 98%, not 95%) and then using calculations for different parts is not only dangerous, it probably does not meet the requirements. You must demonstrate that you have achieved 98% coverage. From there you can do peening to "complete coverage" and in this case it would be just 98%. If you must do 150% coverage you would increase the exposure time by 50%. However, if you use a formula to calculate your exposure time for different size parts you may, or may not, have the correct (98% coverage). You should always perform trials to demonstrate you actually achieve the coverage required.
The coverage on the ID is another story. It will act a lot different then OD peeing due to ricochet (bouncing) media performing multiple impacts. You must also verify that you can achieve the required intensity within the ID.
I would not recommend that you rely upon formulas or calculations. Actual coverage inspection is always expected. You must be able to "Prove" you are correct with direct evidence.

tec #1213 05/20/16 05:23 PM
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It is always difficult to advise if one does not have all the facts. On the basis of the few available facts I must, for the very first time, disagree largely with Jack's analysis. 95% coverage could well be the optimum for the part concerned. 95% has the advantage of being measurable! Even if you were required to reach 98% then adding 50% to the measured times for 95% would achieve that objective in a controllable manner.

Your estimates on peening time versus OD are mathematically correct - surface area of a cylindrical surface being proportional to square of its diameter.

Estimates for ID peening times depend to a large extent on the ID value. Jack is correct to point out the ricochet effect.This is particularly important for small-diameter holes.If, however, you are dealing with large-diameter thin-walled tubes then predictions based on diameter/peening time ratios would be a reasonable guide.

One thing we do agree upon is that predictions must be tested by actual measurements.

tec #1214 05/23/16 01:38 PM
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Socrates: I agree with your disagreements. I jumped to a conclusion about degree of coverage desired. Usually people just ask for full coverage or complete coverage and this refers to the 98% rule. We have many examples of 80% coverage being completed in 20% of the time needed for 98% coverage and the results are quite satisfactory. Thanks for the correction.


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