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Problems with the removal of residual iron after shot peening



(-----) January 17, 2008

Hello,

I'm working in a aeronautic company, in the quality department. For some time we have a problem when we have to remove residual iron left on the surface of the aluminum piece after we made shot peening process. Our sequence decontamination of shot peening is to introduce the pieces in a bath of HNO3 50% with agitation for 15 minutes. This sequence, in principle, should be sufficient to eliminate the iron but is not the case. We don't know which may be the causes, contamination of shot, concentration of inadequate decontamination bath, whether we should have some intermediate step ... In addition we are unable to make any treatment as in the case of aeronautic many restrictions. What are the solutions for our problem ? And where it may be our fault? PLEASE

THANK YOU VERY MUCH

(EXCUSE MY ENGLISH)

SHEILA C.
QUALITY ENGINEER - ITALY
^


First of two simultaneous responses -- January 25, 2008

Cut down your blast pressure and replace the shot more often. You are probably driving iron fines - tiny partials- into the aluminum.

James Watts
- Navarre, Florida
^


Second of two simultaneous responses -- January 26, 2008

Contamination is always a problem when shot peening. Boeing company use to dedicate a specific blast cabinet for this purpose, but even they use to have to purge it periodically to clean up problems and prevent contamination.

tony kenton
AF Kenton
retired business owner - Hatboro, Pennsylvania
^


January 28, 2008

Sheila,

50% Nitric acid should be sufficient to decontaminate parts after shot peening. If 15 minutes is not sufficient time then simply extend the immersion time if it is practical to do so.

You may need to look at the analysis of the solution. If the solution is low in nitric acid that will explain why the process has slowed. You may also want to check the level of dissolved iron in the bath. If the bath is too heavily loaded this will prevent further iron from being dissolved. If this is the case the solution is to dump the tank and make up a fresh one.

Finally, check with your shot peeners about what sort of shot they are using and whether nitric acid is a suitable material to use for decontamination.

Brian Terry
Aerospace - Yeovil, Somerset, UK
^


February 5, 2008

Another option would be to use a ceramic media like glass beads instead of steel. This would obviously entail different shot velocity, duration, etc. There is a lot of information available on shot peening in general, and glass bead peening of aluminum in specific.

Toby Padfield
Automotive module supplier - Michigan
^


First of two simultaneous responses -- February 11, 2008

If you cannot switch to a non-ferrous shot, citric acid based passivation solutions will remove the surface iron contamination. Let us know if we can help.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner
^


Second of two simultaneous responses -- February 12, 2008

Shelia,

AK Kenton is right on as he recommends dedicating a blast cabinet for aluminum alloys to be shot peened. A commonly used media ( by Boeing and others) is Stainless Steel conditioned cut wire shot. This media will achieve the required Mil spec peening intensity "depth" and not leave free iron on the work piece. In fact, Stainless cut wire media will last 20-30X longer than cast steel shot. Be sure not to blast steel or iron alloys or use steel shot in this cabinet, as residual iron will be left on the next batch of aluminum alloy parts peened in it.

Tim Deakin
North Tonawanda, New York
^


February 18, 2008

CHANGE your sandblast media. Use plastic or glass particles to blast. With your actual sandblasting system use only 3 sec blasting.

Good luck

Jose Castellanos
- Minneapolis, Minnesota, USA
^


September 20, 2010

I am not quite sure. But I think grit blasting can be used for decontamination.

Alan King
- Kuala Lumpur
^

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