Are you experiencing chromate rub off on your zinc-plated parts?
As we continue to see a rise in the use of trivalent chemistries and less of the “ambient” running hexavalent chromates, the simple fix of raising the temperature may not be the solution to the rub-off headache during these cold days of winter.
Here are four quick tips to help.
Temperature: As the rinse water temperature is colder during the winter months, particularly in northern climates, the rinsability of many of the processes is diminished. Therefore, longer rinse times increase flow rates, and if possible, warming of the rinse waters is highly recommended. Read more.
pH and product concentration: Typically pH is controlled by the addition of product; however over time, too much product can be added to maintain the pH. When the pH is checked, the range may call for the pH to be lowered, however, Read more.
Zinc thickness: Sometimes it isn’t the chromate at all. The chromate may have a few parameters nearing the upper or lower control limits, and the first thought is to start adjusting the chromate in order to achieve the desired finish. Before reacting, assess the entire process. Read more.
Streaks and patterns not detected until chromate is dry: Many times streaks, patterns, and stains are exposed after the chromate is dried. Check for clean rinsing, Zn brightener levels, nitric sour dip concentrations, and part cleanliness prior to plating. All of these things could be sources of patterns magically appearing after the chromate is dry. The chromate is just highlighting the issue, not causing it.