JPH0894553A - Method of measuring coating weight - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a tangential line drawn on a potential-time curve and a horizontal line drawn at a constant potential portion of the curve when determining the plating deposition amount by the so-called tangential method of the electrolytic stripping method. It is an object of the present invention to provide a method for measuring the amount of plating adhered so that the intersection point position can be easily and quickly determined without human intervention. [Structure] In the method of calculating the plating adhesion amount of a plated plate by the JIS electrolytic stripping method, after measuring the change with time of the potential, the potential value is differentiated twice with respect to time and until the time when the differential value becomes a minimum. Calculate the amount of plating adhered from the value of the current applied to the.

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, when determining the amount of deposits of plating on a tin plate or the like by the electrolytic stripping method, the inflection point position of the measured potential-time curve is measured. It relates to a more accurate determination method than in the past.

[0002]

2. Description of the Related Art In order to manufacture a high-quality plated steel sheet, it is necessary to accurately measure the amount of the adhered plating, adjust the plating conditions, and control the plating thickness so that it 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 have been conventionally known. For example, the amount of tin deposited on a tin plate and the amount of metallic chromium deposited on a tin-free steel plate are
S-G-3303 (Annex 1), JIS-G3315
So-called electrolytic stripping method, fluorescent X specified in (Appendix 1)
A test method called a line method is often used.

By the way, 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 carried out in an electrolytic solution using the test piece as an anode. Continuously draw the potential of on the recording paper with a potentiometer,
The potential-time curve (vt curve) is obtained, the amount of electricity flowing from the curve to a certain specific potential value is calculated, and the amount of adhesion is obtained by Faraday's law.

As a method for specifically determining the plating adhesion amount from this potential-time curve, when the electrolysis progresses and the dissolution phenomenon shifts from the plating layer such as the tin layer (chromium layer) to the base iron, the curve shows Since an inflection point such as that shown in FIG. 4 appears, it is general that the inflection point A is set to the above-mentioned specific potential and the amount of adhesion is calculated from the amount of current passed during the electrolysis start (commonly known as the inflection point). Called the inflection method).

However, in the case of a tin plate, the inflection point A is often not clearly shown, and there is a problem for a person to make the judgment. Therefore, as shown in FIG. 4, a tangent line d ₁ is temporarily placed at a position considered to be the inflection point A of the potential-time curve _1.
And a horizontal line d ₂ is drawn on the portion of the curve 1 where the electric potential is constant, and the amount of adhesion is determined based on the amount of current flowing during the time to the intersection B between the tangent line d ₁ and the horizontal line d _2. Proposed and heavily used. (Hereafter referred to as the'tangent method ').

[0006]

However, even with this tangent method, when the tangent d ₁ is manually drawn from the recording paper on which the potential-time curve is drawn, the tangent d ₁ differs depending on the operator and the reliability of the measured data is improved. There was a problem of lack of sex. Further, there is also a method of automatically performing this tangent method by a device without manual operation. When the tangent line d ₁ and the horizontal line d ₂ are drawn by the method, countless horizontal lines d ₂ on the ground iron side appear and it becomes difficult to specify. There is another problem. 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 situation, the present invention considers the tangential line d ₁ drawn on the potential-time curve ₁ and the constant potential portion of the curve when determining the plating adhesion amount by the so-called tangential method of the electrolytic stripping method. It is an object of the present invention to provide a method for measuring the amount of plating adhered, which allows the position of the intersection with the drawn horizontal line d ₂ to be determined easily and quickly without human intervention.

[0008]

In order to achieve the above-mentioned object, the 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, and uses it. The present invention was devised on the basis that the above-mentioned intersection would be uniquely determined. 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 It is a method of measuring the amount of plating adhered, characterized in that the time at which the differential value becomes minimum is the time corresponding to the above-mentioned certain potential.

[0009]

In the present invention, a test piece taken from a plated plate is subjected to 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 measured from the start of electrolysis to peeling of a test piece deposit. In the method of determining the required time and applying the Faraday's law to the current value flowing until that time to calculate the plating adhesion amount of the test piece, the measured potential value is differentiated twice with respect to time, Since the time at which the differential value becomes a minimum is set to the time corresponding to the certain specific potential, the intersection of the tangent line drawn on the potential-time curve and the horizontal line drawn at the constant potential portion is easy, and You will be asked exactly. Further, even if the potential-time curve is not recorded, by incorporating the measured potential value and time into the automatic logic of the computer, a value equivalent to that of the conventional tangent method can be obtained quickly and easily.

A specific differential value is obtained by assuming a minute time (second) on the potential-time curve and dividing the difference of the potential value changing within that time by the time to obtain the first value. Two
The differential value for the second time 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.

[0011]

1 to 3 show one embodiment of the present invention in which a target amount of Sn plating on a Fe substrate is 2.80 g /
An example of a tin plate attached as m ² is shown. First, a 90 mmφ test piece was sampled from the tin plate and subjected to constant current electrolysis at a voltage of 5 mV and a current of 250 mA using an anode, a carbon rod as a cathode, and an electrolytic solution as a 1N hydrochloric acid aqueous solution. As a result, the potential-time curve 1 shown in FIG. 1 was obtained.

Next, using this potential-time curve, the above-mentioned (1) inflection point method (inflection point is a point), (2) tangent method (intersection point is b point) and (3) the present invention The two-time differential method (minimum value is point c) according to the above method was used to determine the plating adhesion amount corresponding to each case. 2 and 3 show the potential-time curve 1 of FIG.
Of the potential change rate-time curve 2 obtained by differentiating once with respect to time and the potential change acceleration-time curve 3 obtained by further differentiating FIG. 2 with respect to time
Is.

As is apparent from FIGS. 1 to 3, points a and b
Although the points are at different times, there is almost no difference in time between points b and c. Therefore, the adhesion amount was converted from the electrolysis time and the current value for each case by the following formula described in the JIS standard. Tin plating amount, g / m ² = 0.61557 × 1 / S
× F × D Here, S is the area (mm ² ) of the test piece, D is the time (sec) from the start of electrolysis to the intersection point c, and F is the current value (mA) during that time. In order to confirm quantitatively what is shown in FIG. 3, 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 collectively shown in Tables 1 and 2, but between the (1) inflection point method and (2) tangent method, t ₀ = −2.4277 (≧ t
₀ (9.005) = 2.26), showing a significant difference between the two.

That is, different amounts of adhesion were obtained for both. On the other hand, in the (3) double differentiation method of the present invention, t ₀ = 0.3078 (≦ t ₀ (9.00) compared with the (2) tangent method.
5) = 2262), no significant difference was observed (risk rate 5%). That is, the measurement method according to the present invention is simpler and quicker than (2), but results in no difference in the measured value of the adhered amount.

Although this embodiment has been described with reference to a tin plate, it goes without saying that the present invention can be applied to all plating plates other than the tin plate that use the electrolytic stripping method.

[0016]

[Table 1]

[0017]

[Table 2]

[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 adhesion amount is calculated within the time up to the minimum value.
The amount of adhesion equivalent to that of the tangential method can be quickly obtained.
In addition, the measurement points were clarified even during automatic measurement without human intervention, and it became possible to easily determine the plating adhesion amount.

[Brief description of drawings]

FIG. 1 is a potential-time curve actually measured for a tin plate sample.

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

FIG. 3 is a diagram showing a curve relating to acceleration of potential change obtained by further differentiating the curve of FIG. 3 with respect to time.

FIG. 4 is a diagram showing measurement results of potential-time curves by an inflection point method and a tangent method according to JIS.

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuto Kawamura 1 Kawasaki-cho, Chuo-ku, Chiba City Inside the Kawasaki Steel Co., Ltd. (72) Inventor Shigeyuki Matsushima 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Chiba Inside the steel mill

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 potential with time, and a time corresponding to a certain specific potential is required from the start of electrolysis to peeling of a deposit on the test piece. In the method of calculating the plating adhesion amount of the test piece by applying Faraday's law to the current value flowing until that time, the measured potential value is differentiated twice with respect to time, and the derivative A method for measuring the amount of deposited plating, characterized in that the time at which the value becomes minimum is the time corresponding to the above-mentioned specific potential.