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Spot formation on printing rollers

2006

We are based in India, manufacturing CK45 or Mild Steel grade printing rollers. We have an in-house hard chrome plating facility. One problem that we are facing frequently is that of spots formation. In spite of the surface being very smooth before plating, there is spot formation after plating indicating that these white spots have been formed during plating. What could be the reason for it? Please recommend some solution, as I am upcoming entrepreneur and this problem is adding to my teething problems.

Also, we have a problem in plating 12mm rods of 3.6 meters length. Plating deposition on the lower end is nil. Plating variation is high i.e. as we go down plating deposition decreases. Plating thickness that we are looking at is 25 microns. We want a uniform deposition of 25 microns. Is it necessary to give current from below as well. Please advice.

Regards

N Pandya
- India

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First of three simultaneous responses --

Without seeing it, it is a guess at best. My guess is that the part is not uniformly clean, probably a polishing residue.
You are never going to get a perfectly uniform deposition over the entire rod, but you can come close with a conforming anode that you modify as required to get the plate that you need. Several guesses, you are using tank anodes that do not extend to near the bottom of the part. Next, the outgassing of gas formed on the part sweeps the "barrier layer" away as the gas proceeds upward, with the most sweep at the top. Next might be temperature stratification, but that does not really fit your description.

James Watts
- Navarre, Florida
2006

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Second of three simultaneous responses --

I will not comment about the spots. They may come from many different causes but the thickness variation sounds like temperature gradient, chemical homogeneity and electric resistance problems adding up. Your parts are very long. Maybe it's time to think of a horizontal tank.

Guillermo Marrufo
Monterrey, NL, Mexico
2006

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Third of three simultaneous responses --

Dear Mr Pandya;

I would recommend you to read a book entitled "Handbook of Hard Chromium Plating" first if you cannot consider outsourcing your Plating work to a contract shop. Your problems are simple and could be resolved by understanding a few plating fundamentals.

Regards,

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2006