Calculating Bath Drag Out

Let’s say you are performing a cost of operations study and need to know what your solution loss is due to drag out over the course of time. You could put something under a rack or barrel as it comes out of the process solution to catch what drains off and measure. However, this method is impractical, inaccurate, and unsafe.

The best way to calculate drag out over time is to pick a component of the process that is not consumed in any other way except by drag out. A good example is sodium hydroxide in an alkaline zinc plating bath.


Example: Let’s say that you check your records and see that you have added 1000 lbs of sodium hydroxide over a month’s period of time, and you are running the sodium hydroxide level in the bath at 20 oz/gal.

1000 lbs X 16oz/lb = 16,000 ounces

16,000 oz divided by 20 oz/gal = 800 gallons solution loss

Now this would be your drag out for one month unless you have lost solution in some other manner like a tank leak or bail out.

Some other components that can be used to calculate solution loss are:

·  Potassium Chloride in a potassium acid chloride zinc bath.

·  Sulfuric Acid in an acid copper or acid sulfate tin bath.

·  Boric Acid in a nickel plating bath.