How to Avoid Chromium Problems in Chromium Plating

May 12, 2022

How to Avoid Chromium Problems in Chromium Plating

"Chrome Blows" and "Misplates". A common problem with chromium plating is poor coverage of the chromium, particularly around holes (although it may also be experienced in recesses and rough areas). This is generally due to the formation of hydrogen gas pockets and the upward sweep or "blow" of the gas from these areas. The problem can be overcome by suspending the articles in such a manner that gas pockets are avoided. It is often also necessary to plug all holes and seams. The chromium coverage into difficult areas can sometimes be improved by briefly "striking" the work at a higher voltage, before reducing to the normal voltage for the balance of the plating time.

"Whitewashing" and "False Burns". These terms refer to irregular white patches or streaks, which are sometimes experienced when plating bright chromium over nickel. The problem is caused by passivity in the nickel. The passivity can result from various conditions but is most frequently the result of a portion of the nickel surface becoming anodic even for an extremely short period. This can occur if the component or rack becomes bi-polar. A typical situation, in a conveyor type automatic machine, is where a section of the rack load becomes briefly bi-polar, either as the work exits the nickel or enters the chromium bath. The false burn may appear on the lower trailing corner of the rack when the bi-polarity occurs during exit from the nickel and on the lower leading corner of the rack if the bi-polarity is happening on entry to the chromium. Where this is the problem, live leads on exit and/or entry should be fitted. Passivity can also arise due to excessive dwell time in the chromium solution before the current is applied. Not surprisingly, any condition which makes the nickel more prone to passivity can contribute to the problem, for example, high brightener concentration or high pH.