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Oversize bores after pickling

March 11, 2008

Hi friends,

I am Boopathy from India and I am facing a peculiar problem.I do seven-tank pretreatment for a MS pressed component in which the tolerance of the bore is 27 microns.
I am doing acid pickling with 30% concentrated HCl acid. Now the problem is I am receiving 8 to 12 components out of tolerance in 500 for bore oversize by 22 to 62 microns. The reason is

1. whether the raw material itself problematic?
2. whether the acid pickling timing is incorrect? (now the dip time is 5 minutes)
3. whether the tolerance is nonprocessable?
4. is it possible to corrode 62 microns in 5 minutes?
5. in any way the acid inhibitors will help?

can any one help me in this regard?

Boopathy Packirisamy
industrialist powder coating - Pondicherry, India

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Dear Bhoopathy,

8 - 12 components for 500 nos. Are these 500 nos your batch qty? Did it occur only once? repeatability should help you in this problem..

It doesn't seem to be a chemical process problem. Your jigs/dipping method may be incorrect. Or you may have to make your incoming inspection, more stringent, a few of your components may be out of tolerance. You may be doing random inspection...

Acid inhibitor shall help in inhibiting the whole reaction which may not help for 8 to 12 components out of 500..

regards

Keshava Prasad M
- Chennai, India
April 6, 2008

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Sir:

You need a good HCl inhibitor which will reduce acid attack of bare steel by about 1/2. Check my article published in Metal Finishing (the magazine) titled "Selection and Use of Acid Pickling Inhibitors."

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA
April 8, 2008