Home Forums General Discussion Media, Shot, Beads, etc. optimal operating mix sieve testing results

Hello everyone,

what did your rule for operating mix sieve results look like?
here for peening with tunnel/turbine with 1mm CW we have the following rule: mini 80% of the mix above 0,8mm sieve.
It look alike the ams 2430 or MIL-S-13165.
Sometimes it's hard to reach this target (we have high intensity and use air separator not sieve).
What you rules look alike? did you specify max for fines, and from wich diameter would you consider it armful for the machines components?

here peening time is fixed (tunnel speed is not adjustable) and we are already above 100% coverage.
Sieve test allow us to check operating mix, operating mix allow us to reach correct intensity.
If when my historic operating mix rules is not respected, I still found conform almen arch, should I interprete that the rule is too strict, or than the almen plate is too saturated to give good results?

Have a nice day

Hello,

First, I would avoid using the term “operating mix” when discussing shot peening media. That term is generally associated with abrasive blast-cleaning operations, where a broad mixture of new, worn, and broken particles may be intentionally maintained to support cleaning efficiency.

Shot peening is a controlled special process. The media-size distribution must be tightly controlled in accordance with AMS2430 and the applicable AMS2431 media specification. A general rule such as “a minimum of 80% above a 0.8 mm sieve” may be appropriate for a cleaning operation, but it does not adequately control shot peening media. Both oversized and undersized particles must be controlled because changes in the size distribution can affect intensity, coverage, surface condition, and the resulting residual-stress profile.

I would also consider using only an air-wash separator to be a poor choice for controlling media in a shot peening application. An air-wash system can remove dust and some lighter particles, but it does not provide precise control of particle size and cannot reliably remove all broken, elongated, or otherwise non-round particles.

You stated that the process operates at a high intensity. High-intensity peening generally causes more rapid media breakdown, increasing the rate at which undersized and non-round particles enter the media supply. Without adequate screening and shape separation, these degraded particles can accumulate even though an Almen verification reading remains within the required range.

At a minimum, I recommend adding a mechanical sieve-screening system to the machine to continuously or routinely remove undersized and oversized particles. I would also consider adding a spiral separator, either integrated into the machine’s media-recovery system or used offline at established intervals, to remove non-round and damaged particles. The inspection frequency should be based on the demonstrated media-breakdown rate and the volume of media circulated.

Before concluding that the established sieve requirement is too restrictive or that the Almen strip is “too saturated,” I would need clarification on the following:

1. After performing the sieve test, are the unacceptable particles determined from the original representative sample or from a particular fraction separated during sieving? Sieve analysis determines particle-size distribution by weight, while particle-shape inspection is a separate evaluation performed on the appropriate sample or sieve fraction.
2. What original intensity value or values were established from the saturation curve?
3. What intensity range is specified on the engineering drawing?
4. When performing the production intensity verification, is the resulting arc height both:
* Within the engineering drawing’s specified intensity range; and
* Within ±0.0015 inch of the original intensity established from the saturation curve?
5. How long has it been since a complete saturation curve was performed using the current equipment configuration, process parameters, and media-size distribution?

A conforming verification arc height does not establish that a nonconforming media-size distribution is acceptable. Sieve analysis, particle-shape inspection, and Almen intensity verification control different characteristics of the process. An acceptable Almen reading confirms the energy delivered at the strip location under that particular test condition, but it does not demonstrate that the media distribution, coverage rate, surface effects, or residual-stress results remain equivalent to those obtained during the original process qualification.

An Almen strip also should not normally be described as “too saturated.” Saturation refers to the behavior of the complete saturation curve and is used to determine process intensity and saturation time. A single verification strip cannot establish whether the saturation curve or the process response has changed.

If the historical media-size limits cannot be maintained, the first step should be to investigate the media-reclamation system, separator performance, media-addition practices, and inspection frequency. If a different size distribution is proposed, it should be validated by performing a new saturation curve, confirming coverage, and demonstrating continued compliance with AMS2430, the applicable media specification, and the engineering drawing before revising the established limits.

Hello, thank you for your answer Walter!

I fully agree air separator only is a poor choice, but it's the way it is, and investment for sieve have been refused, every years.
I have never seen shape separator used for cut wire, only for cast shot, is that common in the US? If sieves are used, exploded shot with bad shapes should be eliminate by the sieves, isn'it?

We control over 8 sieves, but our rule is the sum of the last 3 ones, 80% of superior to 0,8mm. We don't have media bigger than the nominal (controled at reception) so we don't have an 1,4mm sieves as in AMS2430.

1. After performing the sieve test, are the unacceptable particles determined from the original representative sample or from a particular fraction separated during sieving? Sieve analysis determines particle-size distribution by weight, while particle-shape inspection is a separate evaluation performed on the appropriate sample or sieve fraction
Cut wire become rounder and rounder, then explode in bad shape, but only when small, this is clearly in the fraction we try to separate. Shape observation is not in the control routine

2. What original intensity value or values were established from the saturation curve?
0.23mm (0,0086inch) with almen C
0.95mm with almen A (0,037 inches) (out of range for A plate)



3. What intensity range is specified on the engineering drawing?
No intensity specified, only product lifetime

4. When performing the production intensity verification, is the resulting arc height both:
* Within the engineering drawing’s specified intensity range; and
* Within ±0.0015 inch of the original intensity established from the saturation curve?
In production, arc height is controlled with A plate, and we are within the ±0.0015 inch

5. How long has it been since a complete saturation curve was performed using the current equipment configuration, process parameters, and media-size distribution?
1 year

BR