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topic 8590

Phosphating Process Audit


I want to audit supplier's facilities set up for phosphating treatment as a pre treatment to painting auto parts. Please give me audit checklist to perform process audit, and see whether the installed facilities are adequate.

Inamdar Satish Ramchandra
- Pune, Maharashtra, India


To start out auditing, get technical data sheets for all the chemicals they use from the supplier's chemical vendors. These sheets will at least give you the basics for what their process looks like, and the tech sheets will give proper parameters that should be under control. For example, ranges for pH, temperature, concentration, additive levels, contamination levels. The supplier should have reliable systems in place to monitor and control the critical variables.

You will also want to ask questions about the company, about the qualifications of the people there, and the company's practices. For example, what kind of quality control lab do they have, and is it staffed by trained/qualified technicians? Is the equipment automated or on manual control? Does the supplier use quality systems like ISO or QS? Is the shop unionized? Are there managers who have college degrees? How much does the company rely on their chemical vendors for technical support?

This should give you a good place to start. Your ability to audit would be greater if you gain expertise in the processes that you are auditing.

tim neveau
Tim Neveau
Rochester Hills, Michigan


First I would expect to see a minimum 7 stage system; cleaner, water rinse with conditioner added or applied on last halo, phosphating, rinse, sealer rinse (most likely chrome), water rinse, DI rinse. Check sprays for plugging with emphasis on first rinse. This is the source of most adhesion problems. Crystals like to form on the alkaline surface if the rinsing is poor. Do they have records of bath parameters, best in statistical form. Are they capable of meeting specs. Ideally a capability analysis would be nice as objective evidence.

Is there salt spray & humidity resistance results available to examine. Blistering under humidity may show problems with last rinses. Ask lots of questions mainly directed at the process operators.

Ron Zeeman
Continuous Colour Coat - Brampton, ON, CAN

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