Controlling the concentration of chemicals in the plating line is important. In most cases, such control is achieved using chemical analysis, which is difficult to perform rapidly because of the large amounts of manual work involved. To resolve this difficulty, a calculation method for concentration estimation was evaluated for this study.

Estimation was performed by adding or subtracting changes in concentration caused by solution transfer, rinsing, and evaporation from the initial concentration. After determining the equations for calculating each concentration change, a concentration estimation program was created by combining these equations.

Verification of the program using a simulated process revealed that the estimated values capture changes in the measured values, but some discrepancy exists between the estimated values and the measured values. This discrepancy might be attributable to the fact that the concentration calculations do not incorporate diffusion effects. Moreover, the drag-in solution might not be mixed sufficiently with the destination solution. Therefore, the experiment was conducted using a barrel, which was more likely to achieve sufficient mixing. The concentrations in all processes were then estimated correctly.

These findings indicate that chemical concentrations during plating and rinsing processes can be estimated by calculation. This inexpensive method, which is applicable to widely diverse processes and chemicals, can facilitate control of concentrations during plating processes.

To clarify factors causing hydrogen embrittlement from zinc plating on high-strength steel, high-strength steel sheets with zinc plating were loaded within the elastic limit for assessment by three-point bending. They were then unloaded. Crack initiation sources leading to rupture were visualized for the loaded part. Thereby, pre-cracks became observable before rupture.