JPH02134553A - Short-circuit flaw detecting apparatus in electric plating line - Google Patents

Abstract

PURPOSE:To make it possible to detect the occurrence of short-circuit flaws quickly by providing a current detecting means which detects the amount of the current flowing between an electrode and a current conducting roll and outputs the signal corresponding to the amount of the current. CONSTITUTION:An electric plating line is composed of the following parts: an electrode 14 which is connected to one electrode of a DC source 16; and a current conducting roll 12 in contact with a steel plate 10 which is connected to the other electrode. A current detecting means 50 detects the amount of a current flowing between the electrode 14 and the roll 12 and outputs the signal corresponding to said amount. A differential means 52 differentiates the signal and outputs the differentiated amount. A state holding means 56 holds the result of comparison of a comparing means 54 which judges whether the differentiated value is within a specified range or not and outputs the detected signal of a short-circuit flaw. When the detecting device is provided for every line which supplies current to the electrode of each cell, the place which is the cause of the short-circuit flaw can be immediately judged.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a short-circuit detection device for detecting short-circuit defects caused by short-circuiting of both electrodes during electroplating, and particularly to a short-circuit detection device for detecting short-circuit defects that occur when both electrodes are short-circuited during electroplating. The present invention relates to a short flaw detection device suitable for electroplating lines that perform electroplating processes such as zinc plating and alloy plating.

In recent years, various energy-saving technologies have been developed for electroplating lines, and as the distance between the electrode and the steel plate continues to shorten, the problem of short-circuit defects caused by contact between the electrode and the steel plate has become a more serious problem. It is becoming. The present invention refers to a short flaw detection device that automatically detects the occurrence of such short flaws.

(Prior Art) FIG. 6 is a diagram showing a typical electrogalvanizing line.

The steel plate 10 before plating is continuously supplied from the left side of the figure,
It is narrowed between the energizing roll 12 and the backup roll 16 and sent to the right in the figure through a large number of cells. The upper electrode 141 and the lower electrode 142 are arranged above and below the steel plate 10 to form a plating layer on both sides of the steel plate 10. AC electrode II
! One end of the
, 142 are connected to the upper and lower electrodes 141 and 142 of each cell, respectively, through a rectifier circuit 161 provided for each cell. Although the plating solution containing zinc ions is not shown, it is jetted toward the surface of the steel plate 10 from the vicinity of the upper and lower electrodes 141 and 142, and is circulated by a pump.

With this configuration, a layer of precipitated zinc is formed on the upper and lower surfaces of the steel plate 10 that is continuously supplied from the left side of the figure, and the thickness of the plated layer increases toward the right side of the figure.

In general, the power consumed in an electroplating line includes, in addition to the power consumed by the plating reaction itself, the power consumed by the electrode 141,
A considerable proportion of the power is consumed as Joule heat due to the electrical resistance between the steel plate 142 and the steel plate 10. The best way to reduce this is to reduce the electrical resistance by minimizing the distance between the electrode and the steel plate, so as mentioned above, various techniques have been developed to shorten this distance. Recently, there have been about 8 to 12 theories.

Therefore, the steel plate 10 may hunt vertically due to an imbalance in the pressure of the plating liquid jets from the upper and lower electrodes 141 and 142 sides, or the shape of the welded part connecting the steel plates is defective. The frequency of short circuits between electrodes and steel plates tends to increase year by year. When the electrode and the steel plate are short-circuited, a large amount of current temporarily flows, melting the contact area and causing short-circuit flaws on the surface of the steel plate.

These short-circuit flaws include those that occur singly and those that occur continuously due to hunting of the steel plate, and as a result, there are dents that occur periodically due to metal fragments adhering to the rollers 12 and 16. . Conventionally, the only way to detect the occurrence of such short-circuit defects was to visually inspect the plated product.

[Problem to be solved by the invention]

Visual inspection not only tends to delay discovery, but also makes it difficult to identify the cell that caused the short circuit. As a result, a large amount of products with short-circuit defects are produced, resulting in a problem that the yield is significantly reduced.

Therefore, it is an object of the present invention to provide a short-circuit detection device that can quickly detect the occurrence of short-circuit defects in an electroplating line and immediately determine which plating cell is the cause of the short-circuit defects.

[Means to solve the problem]

FIG. 1 is a principle diagram of a short flaw detection device in an electroplating line according to the present invention. In the figure, an electroplating line for electroplating the surface of a steel plate 10 includes an electrode 14 connected to one pole of a DC current source 16 and a current-carrying roll 12 connected to the other pole and in contact with the steel plate 10. Equipped with:

The short flaw detection device of the present invention is characterized by a current detection means 50 such as a current transformer or a shunt that detects the amount of current flowing between the electrode 14 and the current-carrying roll 12 and outputs a signal according to the amount of current. , a differentiating means 52 that differentiates the signal and outputs a differential value, a comparing means 54 that determines whether the differential value is within a predetermined range, and a comparison result of the comparing means 54 is held to detect short flaws. The present invention also includes a state holding means 56 for outputting a signal.

[For production]

When a short circuit occurs, the flowing current changes rapidly. This current is detected by the current detection means 50, and the differentiating means 5
This rapid change can be detected by differentiating by 2 and comparing it with a predetermined value by the comparing means 54. If this state is maintained by the state holding means 56, a short flaw detection signal indicating that a short flaw has occurred can be generated. is obtained. If this short-circuit detection device is provided for each line that supplies current to each electrode of each cell, it is possible to immediately determine the location where the short-circuit has occurred.

〔Example〕

FIG. 2 is a diagram showing how to install the current detection means 50 (FIG. 1) using a current transformer as an example, and except for the current transformer 501, the configuration is similar to that of a transformer rectifier circuit in a conventional plating line. represents. This figure is represented by a single line diagram (skeleton) that shows one line regardless of the number of phases. For example, a three-phase alternating current of 3,300 volts is stepped down to 45 volts at the three-phase transformer 163 to enable extraction of a large current (about 20,000 amperes), and ignition is controlled by a controller (not shown). The positive current is converted into direct current by a thyristor 164, and the positive side is supplied to the upper or lower electrode, and the positive side is supplied to the current-carrying roll.

In the example of FIG. 2, a current transformer 501 for current detection is inserted on the primary side of a three-phase transformer 163. In this case, since even the excitation current of the transformer 163 is detected, the detection sensitivity is correspondingly inferior.

FIG. 3 shows a second example of the current detection means 50 (FIG. 1) in which a shunt 502 is used.

The components other than the shunt 502 are the same as in FIG.

In the example of FIG. 3, current detection by shunt 502 is performed after being converted to direct current by thyristor 164. In this case, unlike the example shown in FIG. 2, the contribution of the excitation current of the transformer 163 is not included, so the detection sensitivity is high.

FIG. 4 is a circuit diagram in which a portion corresponding to the current detecting means shown in FIG. 2 or 3 is removed from an embodiment of the short circuit flaw detection device according to the present invention.

The differentiating circuit composed of the operational amplifier ICI, the capacitor C1, and the resistor R1 realizes the differentiating means 52 in FIG. Therefore, a circuit using such an operational amplifier is desirable. A circuit composed of an operational amplifier IC2, a resistor R2°R3, and a diode DI is used to invert and amplify the signal and to remove the influence of pulsation of the signal from the detector using the diode D1. Therefore, if a shunt provided on the secondary side of a transformer as shown in FIG. 3 is employed as a detector, this circuit is unnecessary.

The circuit consisting of operational amplifiers IC3 and IC4, resistors R4 to R8, and diodes D2 and D3 detects both the + and - sides of the differential value by comparing them with one comparator. It outputs the absolute value of . The output voltage of the absolute value circuit of the comparator constituted by the operational amplifier IC5 is a predetermined value ■.

When it exceeds 0, it outputs a logic “0” signal. Therefore, the comparison means 54 in FIG. 1 is realized by the absolute value circuit mainly composed of IC3 and IC4 and the comparator made of IC5. The comparison means 54 may have a structure that does not pass through the absolute value circuit. That is, the predetermined value ■. A comparator that performs a comparison with a predetermined value -■.

Two stages of comparators are provided to compare the differential value with ■.

or more than one ■. It is also possible to have a configuration that outputs a logic "0" signal when the voltage falls below 0.NAND gate C
6 and IC7 realizes the state holding means 50 shown in Fig. 1. When the output of IC4 becomes "0°" even for a moment, the input on one side of IC6 becomes "0" and its output becomes "0". "1" appears, and even if the input returns to "°1", that value is held and becomes a flaw detection signal. SWl is a switch for resetting the output of IC6 to "0" as the initial state. .

In addition to being constituted by a flip-flop as described above, the state holding means 50 may be constituted by a monostable multi-by-break, which outputs a signal only for a predetermined time.

FIG. 5 shows waveforms of signals at various parts observed in the circuit shown in FIG. 4, and represents the operation results of the circuit shown in FIG. (
Columns A) to (D) represent signals observed at points A to D in FIG. 4, respectively.

The signal in column (A) is the signal from the detector. Note that this signal is a signal from a current transformer provided on the primary side of the transformer as shown in FIG. Up to the point indicated by X in the diagram, there is only regular pulsation in the output of the current transformer, but a short circuit occurs at point X, so the current increases rapidly, and after that, the current flow to the cell is stopped. Since it is stopped, it suddenly drops to 0. (B) The 4M signal is the ICI in Figure 4.
In this output, a signal obtained by differentiating the signal in column (A) and inverting the sign appears. The signal in column (C) is the output of IC4. (A) A sharp signal appears at the position indicated by X in 4rJ. (D) The signal of l is the output of IC6,
Simultaneously with the detection of a short flaw, the level changes from L level to H level, and this level is maintained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to detect a cell in which a short circuit has occurred at an early stage. It is possible to minimize the amount of short-circuit defects, and at the same time, it is possible to prevent deterioration of the electrode or wear of the roll due to defects, which can be expected to make a significant contribution to reducing maintenance costs.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle of the present invention, Fig. 2 is a diagram showing a first example of current detection means in the short flaw detection device according to the present invention, and Fig. 3 is a diagram showing current detection in the short flaw detection device according to the present invention. FIG. 4 is a diagram representing an embodiment of the short circuit flaw detection device according to the present invention; FIG. 5 is a diagram representing the operation of the circuit shown in FIG. 4; FIG. 6 is a representative diagram. A diagram showing a typical electroplating line. In the figure, 10... steel plate, 12... energizing roll,
14... Electrode, 50... Current detection means,
54... Comparison means, 501... Current transformer, 50
2...Shunt. Zheng

Claims (1)

[Claims] 1. An electroplating line for electroplating the surface of a steel plate (10), comprising an electrode (14) connected to one pole of a direct current source (16), and the other A short flaw detection device for detecting the occurrence of short flaws in an electroplating line, which includes an energizing roll (12) connected to a pole of the electrode (14) and in contact with the steel plate (10). ), and a current detection means (50) that detects the amount of current flowing between the two and outputs a signal corresponding to the amount of current; and a differentiator (52) that differentiates the signal and outputs a differential value. Comparing means (54) for determining whether the differential value is within a predetermined range; and state holding means (56) for holding the comparison result of the comparing means (54) and outputting a flaw detection signal. A short flaw detection device in an electroplating line, comprising: