Calculating Concentrations of Elemental Additions
How do you calculate the concentration of elemental additions?
Knowing the concentration of elemental additions in a zinc bath has many applications for a galvanizer. These values are very important in the quality control process. Presented below, are methods for calculating concentrations of elemental additions in the zinc bath and the weight of additions needed to reach the desired concentration. The most common method for reporting these values is by weight concentration. Therefore, this method is presented first with the less common method of volume concentration following.
Weight Concentration
The concentrations of additives in the zinc kettle are usually reported in units of weight percentage. This is certainly the easiest method for tracking these quantities. The only information needed is the initial concentration, the weight of the addition, and the total weight of the zinc kettle. The weight of the zinc in the kettle can be found simply by multiplying the volume of the kettle by the liquid density of zinc. Below is the formula for calculating the weight of a zinc bath in pounds if the dimensions are measured in feet.
Bath Weight = Length x Width x Depth x 410
After the bath weight is obtained, the current weight of an element in the kettle can be determined. This is done by multiplying the known concentration by the total weight of the zinc bath.
Weight of Element in Kettle = Bath Weight x Concentration
However, the concentrations in the formula above must be converted into a decimal number before using them. For example, if the nickel concentration of a bath is reported as 0.02%, this number must be converted 0.0002 in the formula above. Now, the concentration of an element in the kettle can be determined after a known amount is added to the kettle.
Final Concentration = Weight of Addition + Weight of Element in Kettle / Bath Weight
Once again, this concentration will be reported in decimal form but can be converted to the more standard form of a percentage. Working from the other direction, the needed weight of an addition can be calculated to raise the concentration of an element to the desired value.
Needed Weight of Addition = (Desired Concentration x Bath Weight) - Weight of Element in Kettle
Volume Concentration While rare, there may be a need for reporting the quantities of elemental additions in the zinc bath in terms of volume percentages. The guide below acts as a reference for this method in case the need ever arises.
If your concentrations are already known in weight percentages but need to be converted to volume percentages, the weight percentage can be multiplied by the ratio of the liquid density of zinc (410 lbs/ft3) over the liquid density of the element in question. The liquid densities of some common elemental additions are provided in the table below.
Volume Concentration = Weight Concentration x (410/Liquid Density of Element)
| Addition | Liquid Density (lbs/ft3) | Liquid Density (kg/m3) |
|---|---|---|
| Zinc | 410 | 6,570 |
| Nickel | 488 | 7,810 |
| Lead | 665 | 10,660 |
| Magnesium | 99 | 1,584 |
| Antimony | 408 | 6.530 |
| Bismuth | 627 | 10,050 |
| Aluminum | 148 | 2,375 |
To calculate a new volume concentration after an addition, volume concentration must first be re-converted back into weight values as this is the method for measuring additions.
Initial Weight of Element in Bath = Volume Percentage x Volume of Bath x Liquid Density of Element
With the initial weight of the element in the bath known and the weight of the addition known, the volume concentration of the element after an addition can be calculated.
Final Volume Concentration = Initial Weight of Element in Bath + Addition Weight / Liquid Density of Element x Volume in Bath
Similar to before, this formula can be rearranged to find the weight of an addition needed to reach the desired concentration.
Needed Addition Weight = (Desired Volume Concentration x Liquid Density of Element x Volume of Bath) - Initial Weight of Element in Bath
© 2023 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.