I’ve tried to determine where the specifications for ro-taps listed in J-444 and AMS 2430 originated. I can add the following. MIL-S-851C which was revised from the B revision in May of 1972 had the same wording as the current J-444.
We currently have four WS Tyler RX 29 models which meet these requirements and WS Tyler published specifications are 278 oscillations and 150 taps per minute. The four are running around 280 – 285 oscillations per minute which meet the SAE J-444 and AMS 2430.
I would suggest we look at couple of things before we make any changes in these specifications and please keep in mind that there are other private company peening specifications that also list this type information.
1. Round Robin testing of samples to see if any differences cased by oscillations differences exist. The problem with this is, test sieves openings will vary enough to make this small oscillations difference undetectable if any. The only way you could determine is to have the same test sieves and samples sent within this round robin. I would suggest this to be impracticable.
2. Request the manufactures tells us what the standard is. They are designing these machines, what standards are they designing too? Can we then assume that any difference in design will create insignificant differences in results? Maybe they would like to determine if any differences are created between the different machine oscillations.
My personnel opinion is there is no difference between 250 and 280 oscillations. This is what I would suggest. If I had a Ro-Tap that ran at 250 oscillations (opm) I would increase the 10 minute time to 11 minutes meeting the requirement of 2750 opm in ten minutes. The intent of this specification is not opms but to assure the material is screened with a mechanical machine and certain work is completed. In this case the work is defined as minimum Taps, Oscillations, in a given time. If an auditor will not accept that then you have a much bigger problem.
ASTM STP 447 Guidelines for Establishing Sieve Analysis Procedures discuss satisfactory sieving end points. It defines ultimate accuracy as not more than .5 percent change when increasing the time by 5 minutes.
You will find much more variation using two different test sieves then you will ever in two Ro-Taps.
Dennis Scharer
Technical Services Manager
Ervin Amasteel
