Reducing the required dip time for black chromate

A. The alternative that I am more familiar with is black chromating of zinc-iron alloy. Once the iron is in there in the plating, silver-free black chromating becomes easier and more practical.

A. You can have a workable dip time of 45 seconds with a silver hexavalent black chromate. Have plenty of silver nearby for additions. It will also require regular checking of pH. That means hourly. Temperature should be maintained at 80-85 degrees. Being done routinely. 30 seconds creates headaches, inconsistent results. It could be done. In my experience it is not worth the aggravation.

There is a working production non-silver black available? Maybe tri-valent? That equals color & corrosion protection? Meets automotive specs? LET US KNOW, PLEASE.

A. Using olive drab and black dye can give more reliability and better corrosion resistance than the silver blacks.

To keep dip times fast with silver based chromates you must introduce strict controls and the thing that effects speed most is pH, keep as low as practicable and check at least twice daily. Also warm bath and maintain at a constant temperature as this also keeps more silver in solution

A. Just a thought. When measuring immersion time (or cycle time) you need to include transfer time. This is the time necessary to remove the part from the chromate, drain and immerse in the first rinse. Often, this is forgotten leading to a variety of chromate problems or use of over-concentrated solutions. When you figure in transfer time, I bet you do have 45 seconds in your chromate. BTW On the subject of trivalent blacks for zinc plate (not alloy plate) the ones that I am aware of only work on alkaline zinc.