JPH0543989B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a shot flaw detection device for detecting shot flaws that occur due to the shooting of both poles during electroplating, and in particular to a shot flaw detection device that continuously forms the surface of a steel plate. The present invention relates to a shoot 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 electric plating lines, and as the distance between the electrode and the steel plate continues to shorten, the problem of shot flaws caused by contact between the electrode and the steel plate has become a more serious problem. I'm getting used to it. The present invention refers to a shoot flaw detection device that automatically detects the occurrence of such shoot flaws.

[Conventional technology]

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, and is connected to an energizing roll 12 and a back-up roll 1.
6, and is sent to the right in the figure through a large number of cells. The upper electrode 141 and the lower electrode 142 are made of steel plate 1
They are placed above and below the steel plate 10 to form a plating layer on both sides of the steel plate. AC power supply (single phase or 3 phase)
One end of the plating tank 162 is connected to the energizing roll 12 of each cell, and the other end is connected to the upper and lower electrodes 141, 142 of each cell via a rectifier circuit 161 provided for each upper and lower electrode 141, 142 of each plating tank.
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 such a configuration, a layer of precipitated zinc is formed on the upper and lower surfaces of the steel sheet 10 that is continuously supplied from the left side of the figure, and the thickness of the plating layer increases as it goes to the right side of the figure.

In general, in addition to the power consumed in the plating reaction itself, a considerable proportion of the power consumed in an electric plating line is consumed as heat generated by electric resistance between the electrodes 141, 142 and the steel plate 10. ing. 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 it has become about 8 to 12 mm.

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, or the shape of the welded part connecting the steel plates is defective. The frequency of occurrence of shortening between the electrode and the steel plate tends to increase year by year. When the electrode and the steel plate shoot, a large amount of current temporarily flows, melting the contact area and causing shot flaws on the surface of the steel plate.
These shot flaws include those that occur singly and those that occur continuously due to hunting of the steel plate, and as a result, there are cracks that occur periodically due to metal fragments adhering to the rollers 12 and 16. . Conventionally, the only way to detect the occurrence of such shoot defects was to visually inspect the plated product.

[Problems to be Solved by the Invention] Visual inspection not only tends to delay discovery, but also makes it difficult to find the cells that are the cause of shot defects. As a result, a large amount of products with shot defects are produced, resulting in a problem that the yield is significantly reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to propose a shoot flaw detection device that can quickly detect the occurrence of shoot flaws in an electric plating line and immediately identify which plating cell is the cause.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of a shot flaw detection device in an electroplating line according to the present invention. In the figure,
An electroplating line for electroplating the surface of the steel plate 10 has an electrode 14 connected to one pole of the DC current source 16 and an electrode 14 connected to the other pole of the steel plate 1.
0, and an energizing roll 12 that contacts 0.

The feature of the shot flaw detection device of the present invention is that the electrode 1
a current transformer that detects the amount of current flowing between 4 and the current-carrying roll 12 and outputs a signal according to the amount of current;
A current detecting means 50 such as a shunt, a differentiating means 52 that differentiates a signal and outputs a differential value, and a comparing means 54 that determines whether the differential value is within a predetermined range.
and a state holding means 56 for holding the comparison result of the comparing means 54 and outputting a shot flaw detection signal.

[Effect]

When a shot flaw occurs, the flowing current changes rapidly. If this current is detected by the current detection means 50, differentiated by the differentiation means 52, and compared with a predetermined value by the comparison means 54, this sudden change can be detected, and this state can be maintained by the state holding means 56. For example, a shoot flaw detection signal indicating that a shoot flaw has occurred is obtained. If this shot flaw detection device is provided for each line that supplies current to each electrode of each cell, the location causing the shoot flaw can be immediately determined.

〔Example〕

FIG. 2 is a diagram showing a method of installing a current transformer as an example of the current detection means 50 (FIG. 1), and shows the configuration of a transformer rectifier circuit in a conventional mesh line except for the current transformer 501. This diagram is a single-line diagram (skeleton) that uses one line regardless of the number of phases. For example, a three-phase alternating current of 3,300 volts is reduced to 45 volts in a three-phase transformer 163 to enable a large current (approximately 20,000 amperes) to be taken out, and a thyristor 164 whose ignition is controlled by a controller (not shown) is used. Therefore, it is converted into direct current, and the + side is supplied to the upper or lower electrode, and the - side is supplied to the current-carrying roll.

In the example of FIG. 2, a current transformer 5 for current detection
01 is inserted into the primary side of the 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) using a shunt 502. The components other than 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 detection means shown in FIG. 2 or 3 is removed from an embodiment of the shot flaw detection device according to the present invention.

Operational amplifier IC1, capacitor C1, resistor R
1 is the differentiating means 52 in FIG.
A high-pass filter simply composed of C and R may be used, but since it is difficult to set appropriate constants, a circuit using such an operational amplifier is preferable. A circuit composed of an operational amplifier IC2, resistors R2 and R3, and a diode D1 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 used as a detector, this circuit is unnecessary. Operational amplifier IC3, IC4, resistor R4~8,
The circuit composed of the diodes D2 and D3 outputs the absolute value of the differential value in order to detect both the + side and the - side of the differential value by comparing them with one comparator. operational amplifier ic
5 outputs a logic " ₀ " signal when the output voltage of the absolute value circuit exceeds a predetermined value V0. Therefore, the comparison means 54 in FIG. 1 is realized by the absolute value circuit mainly composed of IC3 and IC4 and the comparator formed by IC5. Comparison means 54
As the configuration, a configuration that does not pass the absolute value circuit may be used. That is, two stages of comparators are provided, one for comparison with a predetermined value V ₀ and the other for comparison with a predetermined value −V ₀ ′, and when the differential value exceeds V ₀ or falls below −V ₀ ′, the logic It may also be configured to output a "0" signal. A flip-flop composed of NAND gates IC6 and IC7 realizes the state holding means 50 shown in FIG. "1" appears, and even if the input returns to "1", that value is held and becomes a flaw detection signal. SW1 is a switch for resetting the output of IC6 to "0" as an initial state. In addition to being constructed from a flip-flop as described above, the state holding means 50 may be constructed from a monostable multivibrator which outputs a signal only for a predetermined period of 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) are A to D in Figure 4, respectively.
represents the signal observed at a point.

The signal in column (A) is the signal from the detector. In addition,
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 Since it is stopped, it rapidly drops to 0. The signal in column (B) is the output of IC1 in FIG. 4, but 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 sharp signal appears at the position indicated by the X in column (A). (D)
The signal in the column is the output of IC6, which changes from L level to H level at the same time as shot flaw detection, and is held there.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to detect a cell in which a shot defect has occurred at an early stage. As a result, it is possible to minimize the amount of shot defects, and at the same time, it is possible to prevent electrode deterioration and roll scratch wear to a minimum, which is 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 shot flaw detection device according to the present invention, and Fig. 3 is a diagram showing current detection in the shoot flaw detection device according to the present invention. FIG. 4 is a diagram showing an embodiment of the shot flaw detection device according to the present invention; FIG. 5 is a diagram showing the operation of the circuit shown in FIG. 4; FIG. 6 is a typical diagram. This is a diagram showing the electric hook line. In the figure, 10... steel plate, 12... energized roll,
14... Electrode, 50... Current detection means, 54... Comparison means, 501... Current transformer, 502... Shunt.

Claims (1)

[Claims] 1. An electroplating line for electroplating the surface of a steel plate 10, which includes an electrode 14 connected to one pole of a DC current source 16 and an electrode 14 connected to the other pole of the steel plate 10. A shoot flaw detection device for detecting the occurrence of shoot flaws in an electroplating line that includes an energizing roll 12 in contact with the electrode 14 detects the amount of current flowing between the electrode 14 and the energizing roll 12; current detection means 50 that outputs a signal according to the current value, and differentiation means 5 that differentiates the signal and outputs a differential value.
2, a comparison means 54 for determining whether the differential value is within a predetermined range, and a state holding means 56 for holding the comparison result of the comparison means 54 and outputting a flaw detection signal. A shot flaw detection device in an electric plating line, which is characterized by: