Summary for chromate flaking on zinc Discussion
Flaking of chromate on zinc plated crimped ferrules is described by Paul Morris, who says a ferrule with heavy zinc plating and dichromate coating had worked fine for years but recently the dichromate started flaking during crimping. He notes that the bright parts flake while the dull ones do not, and asks whether too much brightener in the dichromate could be the cause. In the reply, the answerer says Paul is “dead right” if the observation is that the bright finish is the problem, but adds an important distinction: if the zinc itself is peeling, the issue is too much brightener in the plating tank, not the dichromate. If only the dichromate is peeling and the zinc remains intact, the likely cause is residual brightener film left on the parts because the dichromate process is not properly neutralizing it. The discussion points to process chemistry and surface condition, not just the topcoat.
February 27, 2012
Q. We have a product that is a ferrule 1.947″ -1.927″ long .065 – .058 Thick and 2.445″ – 2.420″ dia. They are zinc plated to a minimum of .003 thickness with dichromate coating over entire part. We have noticed of late that the dichromate finish flakes of when crimping we have not had this problem for well over ten years but has started again. Do you have any suggestion as to why this might be happening. We have noticed that the bright ones flake and the dull one do not. Could it be to much brightener in the dichromate.
Paul Morris
buyer – Steubenville, Ohio, USA
March 12, 2012
If that’s your observation, you are dead right; however, if it’s the zinc peeling off then it’s too much brightener in the plating tank, not the dichromate.
If it’s the dichromate peeling off and not the base zinc metal then it’s the residual film of the brightener on the parts that has not been neutralized by an ineffective dichromate process.
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
