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topic 10282

Acid tin plating staining/milkiness

adv. Tin Plating pointer     


We run a bright acid tin line(Stannous Sulphate). We have followed all advice from the supplier but at times we are getting a milky film built up on the parts. We currently use a caustic rinse in our final rinsing stages and this does not always work. The finish required is a bright even tin plate 5-7.5 microns thick. After plate we water rinse, caustic rinse (2-4 oz/gal) and then final rinse. We also have gone to the extent of rinsing even further and acidifying it again to get rid of possible alkaline residue as well but the milkiness still appears. The parts do look good but the milkiness does not sit well with the customer at times.

I would appreciate if any one has any ideas on this matter.

Lee Moss
- Calgary, Alberta, Canada


We too have experienced the milky appearance from time to time on our automated line and have a troubleshooting guide just for these occasions.

1. Are all mechanical processes in good working condition ie. agitation, regular filtration and maintenance!, chillers working at correct temp?

2. Are the rinse water tanks clean, have good circulation and exit flow?

3. Have you tested for stannic tin buildup or organic (brighteners, etc.) overload?

4. Have you hull celled to determine if bath efficiency has actually increased?.....I discover this gem occasionally and increase production while eliminating the milk.

5. Has the alkaline rinse solution outlasted it's useful life? Are the parts being left in long enough to work?

Remember that a non-heated alkaline cleaner will take longer for the same particle removal effect.

Regards and good luck,

G.W. Harding
- Chicago, Illinois, United States

July 24, 2009

Dear sir,
I like to answer to this question.If the brighteners, i.e., make up and maintenance are imbalanced we may get this milky shade, and caustic soda dip in not advisable even though it contains sulphuric acid, we can use proprietary chemical for final rinsing after tin plating and water rinse.
Check the metal content of tin and the thickness can also be increased. the base material is not known, please try to maintain the base material to be plated with tin plating.

- Bangalore, Karnataka, India

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