4 Chromate Tips for Zinc Plating in the Winter

When the weather grows colder, simply raising the temperature of your plant may not be enough to save you from the headache of chromate rub off on zinc plated parts.

In zinc plating, chromate is a protective conversion coating and is applied over a zinc-plating surface. Doing this improves the surface’s resistance to corrosion and leaves behind a clear yellow-gold or blue finish. When you run into chromate issues, you should first turn towards these four simple tips for the cold season.

1. Temperature: The rinse water temperature is colder in winter months, especially in northern climates. Because of this. The rinsability of many processes, particularly alkaline zinc, is diminished. Therefore, longer rinse times with increased flow rates, and if possible, warming of the rinse waters is highly recommended.

The temperature of the chromate must be within the manufacturer’s recommended ranges. There are some varying definitions of ambient throughout manufacturing. Some understand it to correlate temperatures as low as 70 to 75 degrees Fahrenheit. Ensure that understandings are consistent before proceeding.

Although chromates can work well enough in the winter months at around 60° F, a more consistent chromate film can be achieved if the chill is removed from the bath via an over-the-side electric heater. Temperature is still a critical parameter of the chromate film reaction and shouldn’t be overlooked.

1. pH and Product Concentration: Typically, pH is controlled by the addition of product. However, over time, there can be so much product present that the pH cannot be maintained. When the pH is checked, the range may call for it to be lowered. However, the product might already be out of range or near the control parameter. Here, consult your vendor on the specific acid to use to lower the pH without increasing the product concentration. Be careful, using the wrong acid could significantly affect the reaction and color of the chromate film.
2. Zinc Thickness: Sometimes it isn’t the chromate at all. The chromate may have a few parameters nearing the upper or lower control limits. You might first think about adjusting the chromate to get the desired finish.

Before reacting, assess the entire process. Often, change in the part configuration will lead to a thinner Zn deposit in the low current density (LCD) areas. The chromate film needs a particular thickness of Zn deposit to properly form. In the LCD areas of the work, it may look as if the chromate film is not working. But the true reasons is that there isn’t enough Zn present for it to work on. The Zn bath may need an increase in amperage or an adjustment of chemistry to help with distribution and burning.

1. Streaks and Patterns: Oftentimes streaks, patterns, and stains are seen suddenly after the chromate is dried. Check for clean rinsing, Zn brightener levels, nitric sour dip concentrations, and part cleanliness prior to plating. These could be sources of patterns magically appearing after the chromate is dry. The chromate is just highlighting the issue, not causing it.

Conclusion

Don’t let the cold weather affect your zinc plating operations. Follow these four easy-to-implement suggestions for applying chromate when the temperatures get low.