JP2001242148A - Concentration measuring apparatus for chromium plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concentration measuring apparatus for a chromium plating solution, which removes noises which are generated due to the influence of bubbles. SOLUTION: A naturally defoamed layer of an open system with a return passage is used in a concentration measuring apparatus, for a chromium plating solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the component concentration of a plating solution useful for bath management of chromium plating, and more particularly to a simple method for measuring the speed of sound suitable for in-line measurement.

[0002]

2. Description of the Related Art Chrome plating is widely used as decorative plating utilizing luster and industrial plating utilizing physical properties such as corrosion resistance and abrasion resistance. The plating solution is generally controlled by specific gravity measurement, and a component quantification method by titration is also performed as necessary.

In particular, in industrial plating, it is indispensable to maintain the composition of a bath within a certain range in order to maintain the quality of a plating film, but all of the conventional methods have some industrial disadvantages. The method based on specific gravity measurement is a method of measuring the specific gravity of a liquid using a float scale called a Baume meter, and basically utilizes the fact that the density of a chromic anhydride solution changes depending on the concentration. This method is a simple method of floating a scale in a liquid and is widely used,
From the viewpoint of accuracy, it is difficult to remove the influence of components other than chromic anhydride, and it is also difficult to control the measurement result by electrically feeding it back.

The component measurement by titration is a method of measuring each component of chromic anhydride concentration, trivalent chromium concentration and sulfuric acid concentration by titration, and has an advantage that each component can be quantitatively evaluated. It was difficult to perform constant monitoring because it was performed off-line and the time and labor required for the titration work.

As a method which can be used for in-line control by solving these problems, a method of obtaining a concentration from sound velocity measurement using the relationship between the sound velocity in a liquid and the density of the liquid has been put to practical use in some fields. However, when applied to a chromium plating solution, it is expected that a very complicated algorithm and a lot of correlation data will be required due to the complexity of the temperature dependence of the speed of sound in the solution. In addition, it was difficult to put it to practical use, because it needed to be used in combination with other analytical methods.

[0006] The composition of the chromium plating solution of interest here is generally the composition used for hard chromium plating, and specifically ranges from 250 ± 100 g / L chromic anhydride to 2 to 10 ml / L sulfuric acid.

The present inventor has previously studied in detail the relationship between the concentration of the aqueous solution and the sound velocity in the solution of chromic anhydride as the main component among the components in the solution used for chromium plating. It has been found that it is possible to measure by sound speed. (Japanese Patent Application No. 11-178704)
issue)

[0008]

However, when this is applied to in-line measurement, noise is superimposed on the measured value due to the influence of bubbles generated during the process, and it has been difficult to accurately measure the sound speed. (See Figures 3 and 4)

As a method for removing bubbles, a method using pressure has been conventionally proposed, and a means for assisting the method may be used together. This method is structurally complex because it applies pressure with the flow path closed, and is generally used, including safety measures, especially in the process of handling highly oxidizing dangerous liquids such as chromic acid. Is difficult.

Although air bubbles can be removed by standing in the air, it takes a long time to remove bubbles, so that continuous in-line measurement is not possible, resulting in intermittent measurement. In such a case, the drop in the liquid temperature is large and often exceeds the linear range of the temperature dependence of the sound speed, and accurate measurement is difficult. The present invention seeks to solve the above problems.

[0011]

To solve this problem, the degree of defoaming in the continuous flow path was experimentally evaluated. As a result, the combination of the low flow rate pump and the long flow path does not affect the sound velocity measurement. The inventors have found that such bubbles can be removed, and have reached the present invention.

That is, the apparatus of the present invention comprises a mechanism for removing bubbles in a chromic anhydride solution in a method for determining the chromic acid concentration in a chromic anhydride solution from the speed of sound in the solution. An apparatus for measuring the concentration of a chromium plating solution, comprising a removal tank provided with a return channel at normal pressure as a mechanism for removing bubbles.

An air bubble removing device is an open system natural defoaming tank having a return flow path illustrated in FIG. 1 and is used in the configuration of FIG. The flow path length and the flow velocity are experimentally obtained as conditions for reducing the noise of the sound velocity data to a necessary degree.

According to a first aspect of the present invention, there is provided a chromium plating solution comprising a mechanism for removing bubbles in a chromic anhydride solution in a method for determining a chromic acid concentration in a chromic anhydride solution from a sound velocity in the solution. Is a concentration measuring device.

According to a second aspect of the present invention, there is provided an apparatus for measuring the concentration of a chromium plating solution according to claim 1, further comprising a removing tank provided with a return flow path at normal pressure as a mechanism for removing bubbles. It is.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. Take a bypass flow from a liquid tank containing chromic anhydride as a main component with a pipe, supply it to a degassing tank with a pump, guide it to a measuring tank with a siphon, measure the sound speed in the liquid with a sound speed sensor, and make a temperature correction created in advance Calculate the concentration of chromic anhydride from the completed sound velocity-concentration table. The composition of the chromium plating solution targeted here is a composition generally used for hard chromium plating, and specifically ranges from chromic anhydride 250 ± 100 g / L sulfuric acid 2 to 10 ml / L.

[0017]

EXAMPLE An example of this method will be described. A bypass flow is taken from a chromium plating bath containing chromic anhydride as a main component at a temperature of 65 ° C. with a pipe, supplied to a defoaming tank by a pump (flow rate: 0.6 l / min), further guided to a measuring tank by a siphon, and 2 MHz ultrasonic The sound velocity in the liquid is measured by a sound speed meter comprising an oscillator and a sensor, and the concentration of chromic anhydride is calculated from a temperature-corrected sound velocity-concentration table prepared in advance. The sound velocity in the liquid when the defoaming tank is not used in this apparatus is as shown in FIG. 3, and the sound velocity in the liquid is stabilized as shown in FIG. 4 by using the defoaming tank to obtain accurate sound velocity data. I was able to. (The size of the plan view in FIG. 1 is 155 m
mx 255 mm. ) The concentration of chromic anhydride measured by this method was ± 0.3% as a result of a test with a solution of known concentration, and had the precision and reproducibility necessary for management.

[0018]

According to the present invention, it is a simple method of measuring the component concentration from only one physical quantity of the sound speed by a maintenance-free method of measuring the sound speed in-line, and continuously measuring and monitoring without a complicated pressurizing mechanism. Is possible.

It is not necessary to use in combination with other methods, for example, it is not necessary to maintain or replace the measuring electrode, which is a problem when used in combination with conductivity measurement. For example, the time required for the sampling operation and the human measurement operation required in the titration method is required. Can be omitted.

Since the physical quantity of the data can be automatically collected and simultaneously sent directly from the measuring instrument, it is optimal for feedback control.

[Brief description of the drawings]

Fig. 1 Folded channel water tank (with partition wall)

FIG. 2 Configuration of concentration measuring device

Fig. 3 Sound velocity in liquid (before defoaming)

FIG. 4 Sound velocity in liquid (after defoaming)

Claims (2)

[Claims] An apparatus for measuring the concentration of a chromium plating solution, comprising a mechanism for removing bubbles in the solution in a method for determining the concentration of chromic acid in a chromic anhydride solution from the speed of sound in the solution. 2. The chromium plating solution concentration measuring apparatus according to claim 1, further comprising a removing tank provided with a return channel at normal pressure as a mechanism for removing bubbles.