JPH10288590A - Method for inspecting defect of resin coated steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a defect such as air void or adhesion defective point generated in a coated steel material by pretreating and heating the coated steel material, and inspecting it in the manufacturing process of applying a coating material. SOLUTION: A coated steel material A is pretreated and then passed through a heating furnace 1 to heat the coated steel material. A, and a coating material 2 is stuck thereto and pressure-adhered by a pressure roller 3. Thereafter, the coated steel material A is forcedly cooled with a cooling water discharged from a cooler 8, the coating material 2 is heated by a heating source 4, and the surface is photographed by an infrared detector 5 to observe the surface temperature distribution of the coated steel material 2. The thermal image signal of the infrared detector 5 is inputted to an image processing device 9, and image-processed to measure the temperature distribution of the coated steel material 2. Since the part having a high temperature in the surface temperature distribution of the coating material 2 is regarded as a defective part such as air void or adhesion defective point, the position of this defective part is displayed on a display device 9a. Thus, a resin-coated steel material highly reliable to anticorrosion is manufactured through such a manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a resin-coated steel material for defects. And a defect inspection method for inspecting a defect.

[0002]

2. Description of the Related Art In general, steel sheet piles and coated steel pipes coated with a coating are coated with:
50 μm to 10 mm thick for corrosion protection or design
A coating material made of resin is coated. In a resin-coated steel material coated with such a coating material, floating or swelling (hereinafter, referred to as an air void) between the steel material and the coating material or a peeling portion (poor adhesion) of the coating material end portion occurs. If there is a large number, the reliability of the corrosion prevention of the steel material decreases.

[0003] Conventionally, in the work process of the coating and covering process, an inspection is performed to determine whether or not the coating and covering material is properly covered in order to maintain reliability. The inspection method is usually performed by visually inspecting or touching a defect such as an air void. Further, as another inspection method, there is a method of peeling a part of the coating material and inspecting for the occurrence of air voids or poor adhesion. Furthermore, there is a method of inspecting the occurrence of air voids and poor adhesion by peeling a part of the coating material. In the method of inspecting the occurrence of air voids and poor adhesion by peeling such a coating material, it is necessary to repair the portion after peeling.

Incidentally, a method for detecting a water-containing portion of a covered pipe is disclosed in Japanese Patent Application Laid-Open No. Hei 6-118040. In this inspection method, a thermal image is taken of a pipe, and an air layer and a water-containing portion are detected from the surface temperature distribution. Since the heat transfer coefficient between the air layer and the water-containing portion is largely different, the temperature generated by the difference is large. A water-containing part is detected based on the distribution. However, this inspection method is not a method of detecting a water-containing portion by specially heating a pipe in order to raise a defective portion.

Further, Japanese Patent Application Laid-Open Nos. 61-132848, 62-198708, and 2-1
No. 2045, JP-A-3-188363, etc.
There is a method of inspecting the peeling portion of the coating, and a method of inspecting the peeling of the coating film by far infrared rays, induction heating, and heating light and a method of providing a temperature difference by forced cooling are disclosed.

[0006]

In the conventional coating and coating of coated steel pipes and steel sheet piles, the coating and coating material itself is heated and melted and brought into close contact with the coated steel material to perform coating and coating processing. Alternatively, the coating and covering treatment is performed by bringing the adhesive layer of the coating and covering material into close contact with a heated steel pipe or steel sheet pile. In such a coating-coating process, if a large number of air voids or poor adhesion occurs between the coating material and the steel material, the reliability of the anticorrosion due to the coating decreases.

Conventionally, a method of inspecting a defect such as an air void or a portion having poor adhesion by visual observation or finger touch can be detected if it is relatively large. However, there is a disadvantage that it is very difficult to confirm the existence of a small defect.
In addition, the method of inspecting the entire covering portion by finger eclipse has a drawback that the operation is extremely complicated and severe for the operator. If the number of defects, such as air voids and poor adhesion, is large, a part of the coating is peeled off and inspected. Was peeled off and inspected. Such a peeled portion needs to be repaired, and there is a disadvantage that the repair and repair take time, resulting in an increase in cost.

From such a viewpoint, as a method for detecting a defect such as an air void or a poor adhesion portion generated between the steel material of the coated and coated steel material and the coated material, a method of detecting by a nondestructive inspection method is desirable. In a conventional nondestructive inspection, there is a method of detecting a water-containing portion from a surface temperature distribution using an infrared camera. However, no external heating of the pipe is performed to detect the water-containing portion in the pipe covered with the heat insulating material. Therefore, there is a disadvantage that it is difficult to inspect a defective portion such as a very small air void or a poor adhesion portion. Further, far infrared or induction heating, a method of performing a peeling inspection of the coating film by heating light or a method of providing a temperature difference by forced cooling is disclosed,
Providing a new heating / cooling process in the production process of the coated steel material requires new capital investment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in consideration of the above-described problems, such as the occurrence of air voids and poor adhesion between a coating material of a coating steel material and a coating steel material such as a steel pipe or a steel sheet pile. It is an object of the present invention to provide a method for inspecting a defect of a resin-coated material for detecting a defect.

[0010]

Means for Solving the Problems The present invention has been made to achieve the above object, and the invention of claim 1 has the following features.
The coating and covering material is coated by applying pressure to the coated steel material such as steel sheet piles and steel pipes. After coating and coating, the coating is heated and melted and bonded. And a defect inspection method for a resin-coated steel material characterized by detecting the presence of a portion having a poor adhesion. In the present invention,
By pre-treating and heating the coated steel material and performing an inspection during the manufacturing process of applying the coating and covering material, the presence of air voids and poor adhesion portions can be detected without providing a new heating process.

Further, in the invention of claim 2, after coating and covering the coated steel material such as a steel sheet pile and a steel pipe by pressure bonding and coating, the coated steel is heated and melted and bonded. This is a defect inspection method for a resin-coated steel material, which comprises forcibly cooling and detecting the presence of an air void or a poor adhesion portion based on a difference in temperature drop. According to the present invention, the coated steel material is pre-treated, heated, coated with a coating material, and then inspected in a manufacturing process of cooling, so that air voids and poor adhesion portions can be obtained without providing a new cooling process. Can be detected.

According to a third aspect of the present invention, in the defect inspection method for a resin-coated steel material according to the first or second aspect, infrared rays emitted from the coating material are reflected by a mirror and observed by infrared detecting means. And a method for inspecting the defect of the resin-coated steel material, wherein a temperature distribution of the coating material is detected. In the present invention, by using a mirror for the defect inspection method of the resin-coated steel material, it is possible to inspect the entire inspection target in which the coated steel material of the steel pipe or the flat steel plate is coated with the resin without increasing the number of infrared cameras installed. .

According to a fourth aspect of the present invention, in the method for inspecting defects of a resin-coated steel material, the temperature distribution of the coating material is temporally or spatially differentiated, and the size of an air void or a poor adhesion portion is determined from the temperature distribution. The defect inspection method for a resin-coated steel material according to claim 1, wherein the defect is detected. According to the present invention, a defective portion can be numerically inspected by using the calculating means of the image processing means based on a thermal image signal by infrared rays.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is a method for detecting a defect in a resin-coated steel material.

FIG. 1 shows an outline of an apparatus for producing a resin-coated steel material. In the figure, reference numeral 1 denotes a coated steel material A such as a steel plate, a steel sheet pile, or the like.
2 is a resin coating material such as a polyethylene sheet provided with an adhesive layer in which various additives are mixed in a mixture of asphalt and rubber in a polyethylene sheet, etc. 3 is coated with a polyethylene sheet A pressure roller 4 for pressing against the steel material 2 to firmly pressurize and bond the steel material 2
A heating source such as an infrared lamp, a laser beam, a gas burner, or an electric heater for heating the steel plate; 5, an infrared detector by an infrared camera or the like for detecting the surface temperature of the coated steel material 2; A cable connecting the processing apparatus, 7 a transport roller for transporting the coated steel A, 8 a cooler for spraying water or the like to cool the heated coated steel A, 9 an image processing by a computer or the like Device, 9a is a CT for displaying a processing result by the image processing device
R and other display devices.

Next, a method for detecting a defect in a resin-coated steel material performed in a manufacturing process of the resin-coated steel material according to an embodiment of the present invention will be described with reference to FIG. First, a coated steel material A such as a steel plate is coated with a polyethylene sheet having a thickness of 3 mm as a coating material 2. Prior to the coating process, coated steel material A
Is subjected to a blast treatment, a chromate treatment is performed, and a primer treatment is performed thereon. After performing such pretreatment on the coated steel material A, the coated steel material A is passed through the heating furnace 1 to be coated with the coated steel material A.
Heat. The coating material 2 is adhered to the heated coating steel material A, and the coated steel material A and the coating material 2
To adhere. Thereafter, the cooler 8 sprays water on the back surface of the coated steel material A to cool the coated steel material A.
The coated steel material A is transported by the transport roller 7 at a constant speed, and proceeds to a defect inspection step for inspecting the occurrence of air voids and the like.

In the defect inspection step of the resin-coated steel material, after the coated steel material A is forcibly cooled by cooling water or the like discharged from the cooler 8, the coating material 2 is heated by the heating source 4, and In the cooling process, the surface of the coating material 2 is
The surface temperature distribution of the coated steel material 2 is observed. If the cooling by the cooler 8 is set to a temperature suitable for the defect inspection, the heating by the heating source 4 is not necessary. After photographing by the infrared detector 5, the coating material A is naturally cooled or forcibly cooled. On the other hand, the thermal image signal from the infrared detector 5 is input to an image processing device 9 such as a computer and performs image processing,
The temperature distribution of the coated steel 2 is measured. The surface temperature distribution of the coating material 2 is observed, and a portion where the temperature of the surface temperature distribution is high is regarded as a defective portion such as an air void or a poor adhesion portion, and the position of the defective portion is stored in the image processing device 9. It is stored in the device and displayed on the display device 9a. If there is a defective portion such as an air void or a poor adhesion portion, the manufacturing conditions such as the pressing conditions of the pressing roller 3 and the heating temperature of the heating furnace 1 are changed, and partial defects are repaired, depending on the size and number of the defective portions. A process is performed. Through such a manufacturing process, a resin-coated steel material having high corrosion resistance is manufactured.

Next, the effectiveness of the defect inspection method in the manufacturing process of the above embodiment will be described with reference to FIGS. In this experiment, a steel sheet pile is used as the coated steel material A, and the steel sheet pile is coated with a polyethylene resin provided with an adhesive layer as the coating material 2. At that time, artificially 6m in diameter
Air voids of m and 20 mm were formed and the detection rate was verified. In this defect inspection method, as described with reference to FIG. 1, the coating material 2 is attached to the heated coated steel material A, and is press-fused by the pressure roller 3, and then the surface temperature distribution is measured.
Air void detection was performed.

The experimental results shown in FIG. 2 were obtained. The horizontal axis in the figure indicates the heating temperature from the initial surface temperature (room temperature), and the vertical axis indicates the number of defect determinations. The broken line (a) in the figure indicates the number of detected air voids having a diameter of 6 mm for each surface temperature, and the solid line (b) indicates the detected number of air voids having a diameter of 20 mm for each surface temperature. As is clear from the figure, in the range of about 3 ° C. to 35 ° C., the air voids indicated by the broken line (a) and the solid line (b) are both 100% (10 pieces / l).
0), and in the case of the broken line (a), 70% (7/10) is detected even when the heating temperature is about 1 ° C. In the case of the broken line (a), the temperature is about 35 ° C. to 1
80% (8/10) air voids are detected in the range up to 30 ° C., and the detection rate decreases stepwise in the range from 130 ° C. to 200 ° C. On the other hand, in the case of the solid line (b), 80% (8/10) is detected in the range of about 1 ° C.
90% in the range from about 35 ° C to 160 ° C (9 pieces / 1
0) air voids are detected, and 160 ° C to 200 ° C
In the range, the detection rate gradually decreases because the surface is deteriorated by heating.

As apparent from the results, the most suitable temperature range for detecting air voids is a temperature that is higher by 3 to 35 ° C. than the initial surface temperature. However, a detection rate of 50
%, It depends on the diameter of the air void, but when the diameter is 20 mm, it is possible to detect the surface temperature up to 1 to 180 ° C. higher. On the other hand, it shows that an air void having a large diameter can be detected up to 200 ° C. As described above, the defect detection rate depends on the diameter of the air void. However, the detection of the air void can be generally performed when the surface temperature of the coating material is in the range of 1 ° C. or more and 200 ° C. or less. It is clear that the detection rate also depends on the thickness of the coating material. When the heating temperature of the coating material is set to 1 ° C., the detection rate decreases because the temperature difference between the healthy part and the defective part becomes small. In the embodiment shown in FIG. 1, the coating material 2 is heated by the heating source 4 after being cooled by the cooler 8. However, the coated steel material A is cooled by the cooler 8 to, for example, 150 ° C.
After cooling to a predetermined degree and a predetermined time has elapsed, the coating material 2
By observing the surface temperature, defects such as air voids generated between the coating material of the resin-coated steel material and the coated steel material can be detected without performing the heating step by the heating source 4. In such a case, the heating source 4 can be used as a heating source for auxiliary temperature correction.

Next, regarding the defect detection rate of the present embodiment,
This will be described with reference to Tables 1 to 3. The conventional examples in Tables 1 to 3 are defect inspection methods based on visual inspection, finger touch, and the like. Examples are according to the present embodiment. Comparative examples are defect inspection methods similar to the present embodiment. In Examples of Table 1, after the coating material was fused to a steel plate, the coating material was cooled with water and cooled to room temperature, and then the heating temperature of the coating material was set at 2 from the initial surface temperature.
The defect is inspected by setting the temperature to 0 ° C. higher. The comparative examples in Table 2 show the results of detection by heating and fusing the coating material during the coating and coating process, and then allowing the coating material to cool naturally. In the comparative example of Table 3, after the coating and covering material was cooled to room temperature, the heating temperature of the coating and covering material was set at 2 times the initial surface temperature.
This is a result of detecting a defective portion by setting the temperature to 0 ° C. higher. The conventional example is a defect detecting method disclosed in Japanese Patent Application Laid-Open No. HEI 6-118040. The figure shows the result of detecting a defect without heating for detecting the defect.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

In the conventional detection method by visual observation or finger touch, in the experimental results in Table 1, an air void having a diameter of 6 mm could not be detected, but in Example 1, 100% detection was possible. In the case of an air void having a diameter of 10 mm, the detection rate of the conventional detection method was 20% (2/10), but in Example 1, 100% was detected. Also,
According to the experimental results shown in Table 2, the diameter of the air void was 10 m.
The detection rates at m and 20 mm were compared between the detection method by visual observation and finger touch and the method according to the example.

According to the experimental results in Table 2, when the diameter of the air void was 10 mm, the detection rate by the conventional method was 0%, but in the method of the comparative example, the detection rate was 90% (9/10). Met. When the diameter of the air void is 20 mm, the detection rate of the conventional method is 20% (2/10). The position of the air void was confirmed by a peeling test.

According to the experimental results shown in Table 3, it was impossible to detect air voids of 6 mm and 10 mm by the conventional method of performing a defect inspection without heating. However, in the example according to the present embodiment, 100% detection was possible.

Next, measurement conditions for detecting a defect such as an air void will be described with reference to FIG. In the figure, the vertical axis indicates the surface temperature of the coating material, the horizontal axis indicates the cooling time, the dotted line a indicates the initial surface temperature of the coating material, and b indicates the measured temperature range after heating. . In the figure, (a) is a temperature cooling curve of a portion which is soundly adhered, and (b) is a temperature cooling curve of a portion having poor adhesion such as an air void.

FIG. 3 shows that the surface temperature of the coating material covering the steel sheet pile for the defect inspection is 10 ° C. to 20 ° C. from the initial surface temperature a.
Heat to high temperature. After that, it is a temperature cooling curve obtained by measuring the temperature every predetermined elapsed time after natural cooling. The measurement temperature is measured when the surface temperature of the healthy part is lowered by 5 ° C. to 15 ° C. This is because it takes time for the heat transmitted through the coating material to reach the air void and sufficiently heat it. The temperature cooling curves (a) and (b) shown in FIG.
Varies with the specific heat, thickness, and heating temperature of the material in order to affect the material and thickness of the coating material. In the present embodiment, as shown in the temperature cooling curves (a) and (b) of FIG. 3, the temperature distribution is inspected by paying attention to the fact that the cooling speed of the air in the air voids and the places of poor adhesion is low. And a defective portion such as an air void.

Next, another embodiment of the present invention will be described with reference to FIG. The figure shows a manufacturing process in which a polyethylene-lined steel pipe, which is a kind of coated steel pipe, is coated with a coating material 2 provided with an adhesive layer in which various additives are mixed into a mixture of asphalt and rubber on a polyethylene sheet or the like. As a part of this manufacturing process, a defect inspection of a resin-coated steel material is performed. In the same figure, the coated steel pipe B is blasted, chromate-treated, and then subjected to a primer treatment in the same manner as the steel sheet pile is coated on the coated material of the above embodiment, and then the coated steel pipe B is heated in the heating furnace 1. The coating process is performed by fusing the coating material 3. After the temperature of the fused coating material 2 is cooled by water cooling by a cooler 8, the coating material is heated using a heating source 4 such as an infrared heater (or a panel heater). After that, the coated steel pipe covered with the coated material 2 is detected by the infrared detectors 5 and 6 of the infrared camera after a predetermined time obtained from the cooling curve after natural cooling (or forced cooling). Then, these thermal image signals are input to image processing devices 9 to 12 such as a computer through cables, and image processing is performed to detect a defective portion such as an air void or a poor adhesion portion. Reference numeral 15 denotes a T die for pulling out the coating material 2, and 16 denotes an extruder. The infrared detectors 5 and 6 are arranged at positions where the entire outer periphery of the coated steel pipe can be thermally imaged. In addition, in the case of the coating-coated steel material by the resin-coated steel material manufacturing apparatus, the detection rate of a defective portion such as an air void or a poor adhesion portion is as described above. As described above, the heating source 4 may not be used.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining a defect inspection method for a coating material of a polyethylene-lined steel pipe, which is a kind of a coating-coated steel pipe. In the same figure, the present embodiment is implemented by the same configuration as that of the embodiment of FIG. 4 except for the infrared detection device and its image processing device, and is fused to a coated steel pipe B which is a heated coated steel pipe, and coated and coated. Perform processing.
Subsequently, the coated and coated steel pipe is once cooled by the cooler 8,
The coating material 2 is heated again by the heating source 4, the temperature distribution of the surface portion is directly photographed by an infrared detector 6 such as an infrared camera, and the reflected infrared rays are photographed through the mirrors 13 and 14 on the back side to cover the entire circumference. The surface temperature distribution of is detected. The measurement of the temperature distribution of the portion not in the field of view of the camera in this way is performed by mirrors 13 and 14.
Through the camera, the number of infrared detectors 6 installed,
It can be observed even in a narrow part. Alternatively, the image may be taken by rotating the infrared detection device 6 in the circumferential direction with reference to the center axis of the coated steel pipe B.

Next, the defect detection rate of the embodiment shown in FIGS. 4 and 5 will be described by comparing each example with the conventional example. Table 4 shows a comparison result between the embodiment of FIG. 4 and the conventional example, and Table 5 shows a comparison between the embodiment of FIG. 5 and the conventional example.

[0033]

[Table 4]

[0034]

[Table 5]

Table 4 shows the results obtained by artificially forming ten air voids and inspecting them by the method according to the embodiment and the conventional example. Compared with the conventional visual inspection or finger touch defect inspection, detection was not possible when the diameter of the air void was 6 mm, but according to the embodiment of FIG. 4, 90% detection was possible. In the case where the diameter is 20 mm, 100% is detected by the inspection method of the embodiment of FIG. 4, whereas 20% is detected by the conventional inspection method.

On the other hand, Table 5 shows a comparison result between the embodiment shown in FIG. 5 and a conventional example. The conventional example is a defect detection method based on direct visual observation or finger touch. In the embodiment of FIG.
In the method of detecting by reflecting infrared rays, the detection rate of a defective portion is slightly lower than that in the case of directly detecting the surface temperature of the anticorrosion coating covering material. However, by using a mirror to detect a defective portion, inspection is easy even in a narrow portion where measurement is difficult, and the number of cameras can be reduced.

Next, another embodiment of the method for inspecting a coating covering material for defects according to the present invention will be described. Note that, in the present embodiment, the arrangement of the inspection object, the measuring device, and the like are shown in FIGS.
The same device as described in the above is used. In these resin-coated steel manufacturing equipment, the defect detection is performed in the manufacturing process.The coating of the resin-coated steel pipe is heated and cooled, and the temperature of the coated material is detected by an infrared detector. The thermal image signal is input to an image processing apparatus and subjected to signal processing to detect air voids and floating. In this image processing, a temperature distribution of the coating material is created based on a thermal image signal obtained by time-differentiating a thermal image signal from the infrared detector, and a defective portion such as an air void is formed from a low temperature portion. It is to detect.

As shown in the above embodiment, after an air void having a diameter of 10 mm or 20 mm is artificially formed in the anticorrosion coating material, the coating material is heated and a thermal image obtained from the cooling process is obtained. Defects are detected by time differentiating the signal.
The image obtained by time differentiation is a thermal image in which the outline of the defective portion is more clear, and the size of the air void becomes clear. Therefore, after detecting the temperature distribution of the anticorrosion coating covering material using a mirror,
Even if the detection efficiency is slightly reduced by performing the time differentiation, the detection efficiency can be increased because the boundary portion becomes clearer. Further, by performing the time differentiation processing on the thermal image signal, a better detection result can be obtained than the above detection result. In the embodiment of FIG. 1, a case where the time differentiation processing is performed is set as an example, and a case where the time differentiation processing is not performed is set as a comparative example.

Similarly, the thermal image signal can be spatially differentiated by an image processing device to similarly provide a thermal image in which the outline of the defective portion is clearer. The size of the air void can be clarified. In the embodiment of FIG.
Table 7 shows the measurement error of the case where the spatial differentiation processing was performed as an example, and the case where the comparative example was not performed as a comparative example.

[0040]

[Table 6]

[0041]

[Table 7]

As is apparent from the results, it has been shown that the image processing for temporally or spatially differentiating the thermal image signal in the embodiment of FIGS. I have. Therefore, by performing time differentiation or spatial differentiation of the thermal image signal, measurement conditions are relaxed, and the detection rate can be further increased. In addition, since the outline of the defective portion is clear and the position can be easily specified,
Repair of defective parts can be done in a short time.

Further, in the embodiment shown in FIGS. 4 and 5, the steel material is heated to coat and cover the coating material, and after cooling, the material is heated again, and then the defect is detected. Without heating, the coating material is heated and wound and coated, and then the coating material is cooled naturally or uniformly forcibly, and the temperature distribution is observed to detect defects such as air voids. It is also possible.

In the above embodiment, a flat steel sheet pile or the like may be used to detect defects such as air voids by moving the infrared detector in the width direction of the coating material and photographing. Also,
In the case of a steel pipe, the measurement may be performed by rotating the infrared detector in the circumferential direction about the axis of the steel pipe.

[0045]

As described above, according to the present invention, it is possible to easily detect the presence and location of a defect such as an air void, and the conventional visual or finger detection lacks reliability for anticorrosion. However, according to the inspection method of the present invention, almost 100% of defects such as small air voids can be detected, and the position can be easily specified.
There is an advantage that the defective portion can be easily repaired without requiring any time for the repair, and there is an advantage that the reliability of the steel sheet pile and the coated and coated steel pipe for corrosion prevention is further enhanced.

Further, in the defect inspection method for a resin-coated steel material of the present invention, the reflected infrared rays are detected by an infrared detector using a mirror, and the temperature distribution on the surface of the coating material is observed, so that the defect of the defective portion is detected. There is an advantage that a portion that is difficult to detect can be easily detected. Further, in the case where defects such as air voids occur frequently in the manufacturing process, it is possible to change the manufacturing conditions in pursuit of the cause immediately, and there is an advantage that it is possible to manufacture a corrosion-resistant product with stable quality.

Further, according to the present invention, there is an advantage that the detection rate can be further increased by performing time differentiation processing or spatial differentiation of the thermal image signal by the image processing apparatus.

Further, according to the present invention, since the work process of the coating and covering process includes a heating and fusing process, after the heating process, the coating and covering material is naturally cooled or forcibly cooled. By measuring the temperature distribution, it is not necessary to add a new heating step for inspection. For this reason, the cost for providing a new heating step is unnecessary. When an air void or poor adhesion is detected, it is necessary to heat again to fuse the coating, but when the air void or poor adhesion is detected, the temperature of the steel material is high, and the energy required for reheating is high. Has the effect of requiring less.

In addition, a cooling process such as water cooling or air cooling may be added to the work process of the coating and covering process in order to shorten the line. When the inspection is performed in this step, the cost for providing a new forced cooling step is unnecessary.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for manufacturing a resin-coated steel material for explaining an embodiment of a defect inspection method for a resin-coated steel material according to the present invention.

FIG. 2 is a diagram showing a defect detection rate with respect to a heating temperature in a defect inspection of a resin-coated steel material.

FIG. 3 is a diagram showing a temperature cooling curve of a coating material of a healthy part and a defective part.

FIG. 4 is a schematic view of an apparatus for manufacturing a resin-coated steel material for explaining another embodiment of the defect inspection method for the resin-coated steel material according to the present invention.

FIG. 5 is a schematic view of an apparatus for manufacturing a resin-coated steel material for explaining another embodiment of the defect inspection method for the resin-coated steel material according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Coating covering material 3 Pressure roller 4 Heat source 5, 6 Infrared detector 5a Cable 7 Transport roller 8 Cooler 9 Image processing device 9a Display device 10-12 Image processing device 13, 14 Mirror 15 T die 16 Extruder A, B Coated steel

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Fujita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Tadashi Kawamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Honko Co., Ltd.

Claims (4)

[Claims] 1. A coating and covering material, such as a steel sheet pile or a steel pipe, is heated and melted and bonded at the time of a coating and coating process for coating by applying a pressure to a coated steel material such as a steel sheet pile or a steel pipe, and then naturally cooled to lower its temperature. A defect inspection method for a resin-coated steel material, wherein the presence of an air void or a poor adhesion portion is detected based on the difference between the two. 2. A coating and covering material, such as a steel sheet pile or a steel pipe, which is heated and melted and bonded at the time of a coating and covering process for coating by applying a pressure to a coated steel material such as a steel sheet pile or a steel pipe, and then forcedly cooled to lower its temperature. A defect inspection method for a resin-coated steel material, wherein the presence of an air void or a poor adhesion portion is detected based on the difference between the two. 3. The temperature distribution of the coating material is detected by reflecting infrared light emitted from the coating material with a mirror and observing the infrared light with an infrared detecting means.
3. The method for inspecting a resin-coated steel material according to claim 1. 4. The method according to claim 1, wherein the temperature distribution of the coating material is time-differentiated or space-differentiated, and the size of an air void or a portion having poor adhesion is detected from the distribution.
Or the defect inspection method of the resin-coated steel material according to 3.