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Watch this page for case studies and topics concerning metal finishing. If you have a topic that you would like to discuss, please send your inquiry via email to Ron Kaehr. Topics of general interest may be posted here.

Case #1: Electroless nickel plating of heat treated steel.

Problem: A customer sent some parts requiring electroless nickel that had been heat treated. The parts had then been ground exposing bare steel, while the un-ground surfaces had heat treat scale. Masking the machined areas, if not impossible, would have been extremely time consuming. Since pickling the scale for removal could have damaging effects on the ground surfaces, the parts had to be removed from the acid frequently to have the scale smut removed, using a high pressure water blast. Excessive time in the acid could result in hydrogen embrittlement to the part while at the same time damaging the ground surfaces dimensionally. Post plating hydrogen embrittlement baking could possibly affect the hardness of the material.

Solution: It would have been better if the parts had been mechanically cleaned after heat treat by the means such as abrasive blasting (ie. glass bead blasting) prior to the final grinding operation. In that way, the plater can minimize the damaging effects of the pickling operation. A better looking part is then produced for less overall cost, since the plating cycle can be shortened. This solution would be valid for any electroplating sequence.

Case #2: Paint, Powder or Plating?

Case #3: Silkscreening on anodized aluminum.

Problem: A customer called concerning some anodized parts that were subsequently silkscreened. The silkscreened letters could be scraped off with his fingernail. Since the silkscreen used was supposed to be an epoxy type, he assumed that there should be better adhesion. His question was whether anodized surfaces could be silkscreened, or was it just a bad job.

Solution: This was fortunately an easy one to spot. During the anodize cycle, the temperature of the electrolyte was allowed to rise above acceptable levels. I was glad to tell him that this was not our work! If the temperature gets to above 80F, the electrolyte starts to chemically attack the anodic coating causing it to become non-adherent or powdery, primarily at the surface. The parts were dyed black and sealed conventionally in a nickel acetate bath. The film was dull and very unattractive, so the operator gave them a good coat of oil and wiped off the excess. The same effect can be noted when a stone is wetted with water or oil. Some of the oil is absorbed into the porous aluminum oxide coating. Wiping with solvent only removes the surface oil, not that which is trapped in the pores. The solution to this was to strip and re-anodize under the correct operating conditions.
Oil, parafin and other petroleum based compounds are occasionally used to improve the chemical resistance of the coating, or is used to increase the dielectric properties of the coating. These are exceptions though, used only for special applications.