JPH0480655A - Pinhole detector for insulation film - Google Patents

Abstract

PURPOSE:To enable detection to be free from effect of a change in charged current of an insulation film by arranging an insulation film charging electrode in front of an electrode which applies a voltage to an insulation film steel plate to be inspected to charge the insulation film with a potential the same in polarity as the electrode. CONSTITUTION:A power source 5 is connected electrically to an electrode 4 and a conveying roll 3 and the electrode 4 applies a voltage to an insulation film steel plate 1 to be inspected with the power source 5. A discharge current detector 6 detects a discharge current as caused by a pinhole existing in the insulation film 2 of the film steel plate 1 when the film steel plate 1 is conveyed below the electrode 4. The insulation film charging electrode 7 applies to the film 2 a potential the same in polarity as the electrode 4 from a power source 8. Then, the voltage is applied to the film 2 with the electrode 7 to charge and then, when the voltage is applied to the film steel plate 1 with the electrode 4 set therebehind 7, no current flows as the film 2 is already charged. Thus, a discharge current alone as generated when the pinhole exists in the film steel plate 1 is enhanced to be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an insulating coating pinhole detection device for a metal plate with an insulating coating.

[Prior Art] In recent years, in order to increase the added value of steel plates, composite materials have been commercialized by combining steel plates with other materials and having a composite effect. One of them is to coat the steel plate surface with a film, organic agent coating, inorganic agent coating, etc.
There are insulating coated steel sheets with improved corrosion resistance, appearance, insulation, etc.

By the way, if there is a break in the insulating film, such as a pinhole, the steel plate will be exposed, which will hinder the improvement of the above-mentioned characteristics.

For pinhole inspection, a device is known that projects light onto the material to be inspected and detects the transmitted light (for example, Japanese Patent Application Laid-Open No. 73757/1983). It is almost impossible to detect pinholes in the insulating film of this type because they do not penetrate through the steel plate underneath.

Furthermore, as a similar insulation coating inspection technique, an insulation coating pinhole detection device for coated steel pipes is known.

For example, as in Japanese Utility Model Application Publication No. 58-132864, a detection electrode connected to a high voltage source is inserted into a coated steel pipe, and pinholes are detected from the current flowing between the high voltage detection electrode and the coated steel pipe. It is something to do. If detection by this device is applied to a steel plate with an insulating coating, the electrode will come into contact with the insulating coating, and the high voltage load will cause the insulation coating to be damaged during this inspection process on a steel plate with an insulating coating that has a coating thickness of several tens of micrometers. is large.

Furthermore, when a voltage is applied to the steel plate to be coated with insulation to detect pinholes in the insulation coating, a current flows from the electrode to the insulation coating because the insulation coating is charged. The current depends on the type of insulation film and charging status.

Although the current varies depending on the sheet passing speed, etc., if the second change is larger than the current discharged into the pinhole, it cannot be determined whether the current is a pinhole or a current flowing to the insulating film.

In order to perform this discrimination detection, it is possible to divide the electrodes and detect each current separately, but it is costly to divide the electrodes and power supply and install them individually.

This results in increased complexity of the device. It is also possible to suppress the charging current of the insulating film, but if the insulating film is locally charged with charges in the opposite direction, pinholes cannot be identified and detected.

[Problems to be Solved by the Invention] The present invention prevents the electrical charging current of the insulation coating from being affected by various changes when a voltage is applied to the steel plate to be coated with the insulation coating, and prevents the pinholes from being reliably removed. The objective is to provide a device that can detect with high accuracy.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a voltage is applied to a steel plate with an insulation coating to be tested via an electrode, a discharge current from the insulation coating to be tested is detected, and the insulation coating is In an apparatus for detecting pinholes, an insulating coating charging electrode is provided in front of an electrode that applies a voltage to the insulating coating steel plate to be tested, which charges the insulating coating with a potential of the same polarity as the electrode.

[Function] According to the present invention, by pre-charging the insulating film with the insulating film charging electrode, the detection electrode and the insulating film have the same potential when voltage is applied to the detection electrode, so that both No current flows between them, and only the current passing through the pinholes in the insulating film can be detected.

[Example code] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the drawings, reference numeral 1 denotes a steel plate with an insulating coating to be tested, the surface of which is coated with an insulating coating 2 made of, for example, a film. A transport roll 3 is made of a conductor in this embodiment, and transports the insulating coated steel plate 1 to be tested in the direction of the arrow. Reference numeral 4 denotes an electrode, which is provided above the insulating coated steel plate 1 to be tested, facing the transport roll 3 and at a small interval, and applies a voltage to the insulating coated steel plate 1 to be tested. Reference numeral 5 denotes a power source, which is electrically connected to the electrode 4 and the transport roll 3. Reference numeral 6 denotes a discharge current detector, which detects the discharge that occurs when a pinhole exists in the insulation coating 2 of the insulation coating steel plate 1 to be tested and the pinhole comes under the electrode 4 while the insulation coating steel plate 1 to be tested is transported. It detects current.

By the way, it has been found that when a voltage is applied to the insulating coated steel plate 1 to be tested, the insulating coat 2 is charged, and a current flows from the electrode 4 to the insulating coat 2. Since this current is generated, it becomes difficult to distinguish it from a discharge current from a pinhole, resulting in a pinhole detection error.

In particular, detection errors of small pinholes and errors in detection of steel plates 1 coated with an insulating film 2 having a relatively large amount of charge increase. To solve this, I am doing the following.

An insulating coating charging electrode 7 that charges the insulating coating 2 is provided in front of the electrode 4 that applies a voltage to the insulating coating steel plate 1 to be tested. The insulating film charging electrode 7 applies a potential of the same polarity as the electrode 4 to the insulating film. 8 is its power source.

Then, a voltage was applied to the insulation coating 2 of the insulation coating steel plate 1 to be tested using the insulation coating charging electrode 7 to charge it, and then a voltage was applied to the insulation coating steel plate 1 to be tested using the electrode 4 installed at the rear. In this case, since the insulating coating 2 is already charged, no current flows, and only the discharge current generated when a pinhole exists in the insulating coating steel plate 1 to be tested is drawn out and detected.

[Effects of the Invention] As described above, according to the present invention, by pre-charging the insulating film with the insulating film charging electrode, the detecting electrode and the insulating film are at the same potential when a voltage is applied to the detecting electrode. Therefore, no current flows between the two, and only the current passing through the pinhole in the insulating film can be detected.

Therefore, pinholes can be reliably detected even in the case of minute pinholes and even in the case of an insulating film with a large amount of charge.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an apparatus according to an embodiment. 1 Insulating coating steel plate to be tested 2: Insulating coating 3゛Transport roll 4: Electrode 5 Power supply 6゛Discharge current pressure detector 7゛Insulating coating charged electrode 1. Power supply diagram

Claims (1)

[Scope of Claims] In an apparatus for applying a voltage to a steel plate with an insulating coating to be tested via an electrode, detecting a discharge current from the insulating coating to be tested and detecting a pinhole in the insulating coating, the voltage applied to the steel plate with an insulating coating to be tested is 1. An insulating film pinhole detection device, characterized in that an insulating film charging electrode for charging an insulating film with a potential of the same polarity as that of the electrode is provided in front of an electrode that applies a voltage.