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Cleaner Etching

We are a zinc plater and routinely electroclean steel parts for plating. Very often we experience small, round, permanent etch patterns in the base metal after electrocleaning (these are the size of a pencil eraser or smaller in diameter, typically they are consistently round in shape). I have only seen them on our acid zinc rack lines. They will typically occur after an addition has been made to the electrocleaner (we use a 2 part liquid electrocleaner). We drag the tank and find no parts that would cause a direct electrical short. Any experience with this type of problem and possible solutions?

Terry Windham
industrial finishing - Tucker, Georgia
2000

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First of three simultaneous responses--

Terry, there is a bunch of things to try.

Some are: Is the temperature within the guidelines of your cleaner vendor? Are chemical additions being poured directly on the work in the tank? Is the rectifier carrying the correct amperage? Is this pattern on all the parts at the top or bottom of the rack? I assume it is rack zinc. Recommend you contact your cleaner vendor-they sell it and should help you find the problem. If this etching is occurring prior to acid zinc plate, it has nothing to do with the plating bath.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan
2000

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Second of three simultaneous responses--

Terry:

I am sure there are other possible causes, but one could be particulate matter imbedded in the surface that is removed by the anodic effect on the steel part. I have seen this on steel from the mill that has had dirt, scale and other particulate matter rolled into the surface. Except from your statement that the etch pattern is round, I have seen mature rust on steel that left craters after electrocleaning. I am not knowledgeable of any out-of-control chemical causes in electrocleaning that produce round etch hole patterns on steel.

Good luck.

Bill Boatright
- Raleigh, North Carolina
2000

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Third of three simultaneous responses--

Terry, it sounds like you may have a problem with excess alkalinity. Are you doing analysis on the cleaner before additions are made. Dropping the temperature is a step in the right direction, but you might want to try making smaller more frequent additions.

Phil Pace
- Tulsa, Oklahoma
2000