JPH09264875A - Measuring method for plate sticking quantity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and easily calculate plate sticking quantity from a current value flowed so far, by differentiating a measured electric potential value two times, and taking the middle paint of two points, at zero, before and after minimum differentiation value as the time consumed from the beginning till pealing of a sticking substance. SOLUTION: A test piece picked from a plating board is constant-current- electrolyzed in an electrolytic solution, as an anode, and change with lapse of time in electric potential is measured. The time corresponding to specified electric potential is decided as the time period from starting of electrolysis which was required for peeling of a test piece sticking matter. And Faraday's law is applied to the current value which had flown by that time, and the plate sticking quantity of the test piece is calculated. At this time, the measured potential value is differentiated two times in respect of time, and the middle point of two paints, at zero, before and after minimum differentiation value is taken as the time corresponding to the specified electric potential. In this manner, the sticking quantity which is equivalent to that obtained by the method with a tangent line is rapidly and easily obtained with automatic calculation of a computer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the amount of plating deposits, and more specifically, the inflection point position of the potential-time curve measured when determining the amount of plating deposits on a tin plate, etc., by the electrolytic stripping method. It is related to the technology to judge more accurately than the law

[0002]

2. Description of the Related Art In order to produce a high quality plated steel sheet, the plating amount is accurately measured and the plating conditions are adjusted.
It is necessary to control so that the plating thickness is always appropriate.
For that purpose, it is necessary to quickly and accurately measure the coating weight, and various methods for measuring the coating weight are conventionally known. For example, the amount of tin deposited on the tin plate and the amount of metallic chromium deposited on the tin-free steel plate can be determined according to JIS-G.
-3303 (Appendix 1) and JIS-G-3315 (Appendix 1), a so-called electrolytic stripping method and a test method called a fluorescent X-ray method are often used.

Among them, in the electrolytic stripping method, a carbon rod electrode (cathode), a test piece holder and a silver reference electrode are attached in an electrolytic cell, and constant current electrolysis is performed in a predetermined electrolytic solution using the test piece as an anode. It is something to do. Then, during electrolysis, the potential of the test piece was continuously drawn on the recording paper with a potentiometer, and the potential-time curve (v
-T curve) is calculated, and the amount of electricity flowing from the curve to a certain specific potential value is calculated, and converted into the amount of adhesion according to Faraday's law.

By the way, in the electrolytic stripping method, when specifically determining the plating deposition amount from the potential-time curve, electrolysis proceeds and the dissolution of the sample shifts from the plating layer such as the tin layer (chromium layer) to the base steel. Since an inflection point A as shown in FIG. 4 sometimes appears on the potential-time curve 1, the inflection point A is used. That is, it is general that the inflection point A is set to the “certain specific potential” and the amount of adhesion is calculated using the amount of current flowing from the start of electrolysis to that point (commonly known as inflection point). Called the law). However, in the case where the sample is a tin plate, this inflection point A often does not appear clearly, so that there is a problem for a person to judge the inflection point A. Therefore, as shown in FIG. 4, a tangent line d ₁ is tentatively drawn at a position considered to be an inflection point A of the potential-time curve 1, and a horizontal line d ₂ is drawn at a portion where the potential of the curve 1 is constant. A method for obtaining the amount of adhesion based on the amount of current flowing in the time t ₁ to the intersection B between the tangent line d ₁ and the horizontal line d ₂ has been proposed and has been widely used (hereinafter referred to as “tangent method”). .

[0005]

However, even if the tangent method is used, when the tangent d ₁ is manually drawn from the recording paper on which the potential-time curve is drawn, the tangent d is set by the operator.
There is a problem that the reliability of the measurement data is lacking because ₁ is different. Further, there is a method of automatically performing this tangent method by a device without manual operation, and by this method, the tangent line d ₁ and the horizontal line d
_{When 2} is subtracted, infinite numbers of horizontal lines d ₂ on the ground iron side appear, which causes another problem that makes it difficult to specify. This is because the change in the inclination at each instant is small in the part of constant potential, and therefore the device cannot clearly determine where it becomes constant. If this is done accurately, it is necessary to catch minute changes in the voltage, and it is almost impossible to do with current equipment.

In view of the above circumstances, the present invention has taken into account the above-mentioned circumstances, and when determining the amount of plating adhered by the so-called "tangential method" of the electrolytic stripping method, the tangent line d ₁ drawn on the potential-time curve ₁ and the constant potential of the curve. It is an object of the present invention to provide a method for measuring the amount of deposited plating that allows the position of the intersection B and the horizontal line d ₂ drawn on a part to be determined easily and quickly without the need for human intervention.

[0007]

In order to achieve the above object, the present inventor has noticed that the acceleration of the potential change rate obtained by differentiating the potential-time curve twice with respect to time has a minimum value,
The present invention was devised on the basis that the above-mentioned intersection is uniquely determined by utilizing it. That is, the present invention, a test piece collected from the plating plate is subjected to constant current electrolysis in an electrolytic solution to measure the change in potential with time, and a time corresponding to a certain specific potential is required for peeling the test piece adhered from the start of electrolysis. In the method of calculating the plating adhesion amount of the test piece by applying Faraday's law to the current value flowing up to that time, the measured potential value is differentiated twice with respect to time, and A method for measuring the amount of plating adhered, characterized in that the midpoint between the two points at which E ″ = 0 before and after the time when the differential value (E ″) becomes the minimum is set to the time corresponding to the above-mentioned specific potential. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a test piece taken from a plated plate is used as an anode to carry out constant current electrolysis in an electrolytic solution to measure a change in potential with time, and a time corresponding to a certain specific potential is tested from the start of electrolysis. Determined as the time required for peeling of the one-sided deposit, and applying the Faraday's law to the current value flowing up to that time, in the method of calculating the plating amount of the test piece, the measured potential value is the time Is differentiated twice, and the midpoint between the two points at which E ″ = 0 before and after the time when the differential value becomes a minimum is set as the time corresponding to the above-mentioned specific potential. This is the time when the acceleration becomes the minimum, that is, it corresponds to the position of the intersection B of the tangent line drawn on the potential-time curve and the horizontal line drawn at the portion of constant potential, and the position is easy, accurate and unique. Will be required by Position - even without recording the time curve Incorporating the potential values were measured with time and the automatic logic computer, so the value equivalent to the conventional tangent method is obtained quickly and easily.

A specific differential value is a first time value obtained by dividing a difference in potential value changing within that time, assuming a minute time (second) on the potential-time curve. ,
The second differential value is obtained by performing the same calculation on the potential change rate-time curve obtained above.
The contents of the present invention will be described below with reference to FIGS.

[0010]

EXAMPLE FIG. 3 shows the target amount of 2.80 g / m on the Fe substrate.
² shows a potential-time curve obtained with a tin plate plated with Sn. In obtaining the curve, first, a test piece having a size of 90 mmφ was sampled from the tin plate and used as an anode. Then, constant current electrolysis was carried out at a voltage of 5 mV and a current of 250 mA using a 1 N hydrochloric acid aqueous solution as the electrolytic solution and a carbon rod as the cathode. The result is the potential-time curve 1 in FIG.

Next, using this potential-time curve, (1) the inflection point method (the inflection point is a), (2) the tangent method (the intersection point is b), and (3) twice according to the present invention. By the differential method (midpoint c), the amount of deposited plating corresponding to each case was obtained.
At that time, from the electrolysis time and the current value for each case,
The attached amount was converted by the following formula described in the JIS regulation. Tin plating amount, g / m ² = 0.61557 × (1 / S) × F × D (A) Here, S is the area (mm ² ) of the test piece, and D is each intersection point from the start of electrolysis ( a, b) and the time to the midpoint (c) (se
c) and F are current values (mA) between them, and are calculated by

Therefore, the plating adhesion amount by the inflection point method is
The time t _a to the point a in FIG. 3 is substituted into the above equation (A), and the value by the tangent method is obtained by substituting the time t _b to the point _b in FIG. On the other hand, the value in the second differentiation method according to the present invention is obtained as follows. First, the potential change rate-time curve 2 obtained by differentiating the potential-time curve 1 of FIG. 3 once with time
Get. The result is shown in FIG. Subsequently, the potential change speed in FIG. 2 is further differentiated with respect to time to obtain a potential change acceleration (E ″)-time curve 3. The result is shown in FIG.

In FIG. 1, before and after the point (b) at which E ″ shows a minimum value, the points corresponding to E ″ = 0 are a and d.
Therefore, in the present invention, the midpoint c between a and d is defined as the time “t _c corresponding to a certain specific potential, and the plating adhesion amount is obtained by substituting this t _c into the formula (A). 1 to 3, it can be seen that the points a and b are obviously different times, but there is almost no time difference between the points b and c. In order to determine whether the amount is appropriate, an electrolytic test was performed with the number of test pieces n = 10, and a significant difference test for the above three methods was performed.

The results are shown collectively in Tables 1 and 2, but t is different between the inflection point method (1) and the tangent method (2).
₀ = −2.4277 (≧ t ₀ (9005) = 2.2
6), and a significant difference was recognized between the two. That is, different amounts of adhesion were obtained for both.

[0015]

[Table 1]

[0016]

[Table 2]

On the other hand, in the second derivative method (3) according to the present invention, t ₀ = 0.3078 as compared with the tangential method of the above (2).
No significant difference was observed (≦ t ₀ (9.005) = 2.26) (risk rate 5%). That is, it was confirmed that the plating adhesion amount obtained by the second differentiation method according to the present invention is not different from that obtained by the tangent method of (2). The tangent method of (2) has a drawback in that the tangents do not match with each other depending on the operator or the automatic machine. However, in the second differentiation method according to the present invention, the time corresponding to a certain specific potential is uniquely determined, and the computer By using, there is an advantage that the amount of coating adhesion can be measured easily and quickly. Therefore, it is clear that the second derivative method according to the present invention is superior to the conventional tangent method.

[0018]

As described above, in the present invention, in the electrolytic stripping method, the potential-time curve is differentiated twice with respect to time, and the adhered amount is obtained in the time up to the intersection of two points E ″ = 0 around the minimum value. It is possible to quickly obtain the amount of adhesion equivalent to the tangential method because the calculation is made clear. Became.

[Brief description of drawings]

FIG. 1 is a diagram showing a curve relating to an acceleration of a potential change obtained by further differentiating the curve of FIG. 2 with respect to time.

FIG. 2 is a diagram showing a potential change rate curve obtained by differentiating the curve of FIG. 3 with respect to time.

FIG. 3 is a potential-time curve actually measured for a tin plate sample.

[Fig. 4] Potential by inflection point method and tangent method according to JIS-
It is a figure which shows the measurement result of a time curve.

[Explanation of symbols]

 1 Potential-Time curve 2 Potential change speed-Time curve 3 Potential change acceleration-Time curve

Claims (1)

[Claims] 1. A test piece taken from a plated plate is subjected to constant current electrolysis in an electrolytic solution to measure a change in electric potential with time, and a time corresponding to a certain specific electric potential is required for peeling a test piece adhered from the start of electrolysis. In the method of calculating the plating adhesion amount of the test piece by applying Faraday's law to the current value that has flowed up to that time, the measured potential value (E) is measured twice with respect to time (t). Differentiate and E ″ before and after the time when the differential value (E ″) becomes the minimum
A method for measuring the amount of plating adhered, wherein the midpoint between the two points where = 0 is set to the time corresponding to the above-mentioned specific potential.