Nippon Paint Compnay, Ltd.

Katsuhiro Takeshita

Tamotsu Sobata

A treatment solution which is stored in a treatment vessel is supplied to a mixing vessel and a simple fluoride solution is supplied into the mixing vessel from a simple fluoride supply vessel to convert aluminum salt of complex hydrofluoric acid which is contained in the treatment solution to complex hydrofluoric acid. Concentration of HF remaining in the mixed solution is measured with a metal silicon electrode meter provided in an HF concentration measuring part, so that a control signal is transmitted from a control unit to a pump and a flow control part on the basis of the data as obtained. The simple fluoride solution is supplied from the simple fluoride supply vessel to the treatment solution which is stored in the treatment vessel to return the activity of the treatment solution stored in the treatment vessel and to control the same in a prescribed range.

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Hirakata, Japan

Katsuhiro Takeshita