Electroplating: Black Spots in Chrome Plating?

you probably have either contamination in the tank or your plating with too much current. Its most likely that you have some contamination.

If your getting balling and a thicker plate at the corners as well then your current is too high. It is also possible that your plating solution is too strong which would allow more current (because of less resistance to the solution).

Even less likely is that your final clean and rinse solutions are contaminated which is leaving smut on the parts being plated and causing the plate to be poor. This you would expect to cause problems all over the parts not just in the corners.

Are you using a buffered solution?

Scooter

Thanks Snewkirk, Thank you vary much for suggetions, we will go through for analysis of plating solution to check the contamination.

Hi,

We have an EPL (Electro-Plating-Line) - Black spot at the conductor entry is a problem, spots and streaks every where is a problem.

Chemistry of the dipping tanks and stirring are some answers.

Temp and current controls ................... more issues.

Enjoy a long, hard project to get a handle on Black Spot.

Regards,

Macker

I only have a little experience in depositing, and that from washcoating, not plating. If I may ask a question just for knowledges sake? I'd expect contamination left from a wash solution, or thicker plating in the corners to be a surface tension/wetting issue.

Why would electroplated material build up in corners of a flat sheet?

Thanks,

Rick

I don't remember the physics but you always get more current at the edges, corners have 2 edges so they are even more susceptible.

Scooter

Why would electroplated material build up in corners of a flat sheet?

The corners of the sheets have a greater kinetic exposure to the bulk plating solution (edges have less, and the centers of the sheet faces have the least). As known in the field of heterogeneous catalysis (chemistry at solid/liquid interfaces), extended flat metal surfaces essentially behave like 2-dimensional objects and therefore have less access to species dissolved in solution than do surfaces with a more 3-dimensional shape (i.e., greater surface curvature and/or point-like regions). To remedy this, try more vigorous stirring of the plating solution.

Your actual problem seems to be metallic contamination of either Copper or Zinc and in some cases lead if the color of spot is greyish. Remedy for this is to reduce the pH of the abth to below 3.0 and perform Low current dummy electrolysis with a corrogated sheet and observe the sheet at regular intervals after a certain period of time your dummy will be normal this indicates the absence of contamination. Then increase the pH to the normal range and start working. this will definetely solve the problem.

Praveen

Mumbai