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Zinc Plating Cosmetics

September 17, 2008

I'm getting killed because of scratches to a zinc plate finish on cold rolled steel .036" thick. The spec on the print reads "zinc plated, clear (Crill) chromate conversion". We time save the flat, form the sides, send part out for plating, then silk screening. Every operation is very aware of the scratching problem, handles with care and inspects.

After we receive the part from screening we wrap the part in low tac plastic. This is done in good lighting (100 Candles) and the Operator looks closely at each part with the Supervisor and QC spot checking. The part is then wrapped in a foam sheet and vertically stacked in the shipping box so the part bears no weight in shipping. A piece of cardboard is placed between each part and each box is "snugged" with paper to ensure minimal lateral movement in transit. Still the customer finds scratches and sends them back - currently 25%. The part is roughly 17" x 15" x 1 5/8". The scratches are light, often hard to see and often the part has to be rotated to see it. Once you see it it sticks out like a sore thumb.

Am I, or my customer expecting too much from zinc plating, or am I missing something? This is a big customer and jobs could be lost over this so please comment.

Richard Webb
Sheet Metal Job Shop - Quality Engineer - Bloomingdale, Illinois, USA

Hi, Richard. In many (if not most) cases, zinc is considered a functional finish, not a decorative finish, so you won't find as many parallels to your situation as you might like. You and your customer must agree on the inspection criteria so that if it passes your inspection, and is not marred in transit, it will pass theirs. Considering the stakes, this may mean installing identical inspection booths in both locations, since discovery of defects is so tightly linked to lighting. Sorry I could not put my finger on it immediately, but there are articles (I believe by Safranek) on the design and lighting of plating inspection booths.

If the problem was some kind of scuffing, or brightness or lack of brightness in an area, I might blame the packaging, but I don't think you would get actual scratches on separately wrapped components.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 22, 2008