A device for detecting defects of insulating coating of metal workpiece

Abstract

A metal workpiece insulating coating defect detection device mainly includes a liquid tank, a reference workpiece, a workpiece to be tested, a capacitance measurement module of the workpiece to be tested, a reference workpiece capacitance measurement module, a liquid level ruler, and a reference limit ring and a measurement limit ring. The present invention can quickly obtain the coating thickness data of the workpiece to be tested along the measurement height direction by comparing the workpiece to be tested with the reference workpiece, without requiring information such as the dielectric constant of the coating. The present invention does not damage the workpiece to be tested, is simple and convenient to implement, and has a wide prospect of promotion and application.

Description

Technical field:

[0001] The invention belongs to the field of workpiece detection technology, and in particular relates to a metal workpiece insulating coating defect detection device. Background technology:

[0002] Metal components are widely used in the industrial field. In order to prevent corrosion, an insulating coating is usually applied on the surface of the metal component to isolate the corrosive environment from the base metal and extend the service life of the component. The quality of the insulating coating is crucial to the metal protection effect. The coating quality usually needs to be tested before it is put into use or during service.

[0003] The main coating detection methods include spark detection and ultrasonic detection. The principle of spark detection is that when the insulating anti-corrosion layer on the metal surface is too thin or defective, applying high voltage will form an air gap breakdown and generate spark discharge, generating a pulse signal for the alarm circuit. The spark detector scans along the workpiece to determine the location of the defect. The disadvantage of this method is that it needs to scan along the entire workpiece, and can only locate coating defects, but cannot make quantitative measurements of coating thickness parameters. Ultrasonic detection methods are widely used in coating detection. Ultrasonic coating detection methods can measure the thickness of the coating, as well as detect defects such as coating peeling and bubbling. However, coupling agents are usually required during the measurement process, the measurement procedure is complicated, and the accuracy is low. If the thickness of the inner coating is less than 350 microns, which is much smaller than the half-wavelength of the ultrasonic wave in actual applications, it is difficult to detect coating defects by directly measuring the thickness of the inner coating.

[0004] In view of the defects of the existing coating measurement methods and devices, the present invention proposes a non-intrusive measurement method suitable for ultra-thin coatings, which can realize the rapid measurement of the coating thickness of the workpiece. Summary of the invention:

[0005] A defect detection device for insulating coating of metal workpiece, characterized in that it mainly includes a liquid tank, a reference workpiece, a workpiece to be tested, a liquid electrode terminal, a capacitance measurement module of the workpiece to be tested, a capacitance measurement module of the reference workpiece, a liquid level gauge, a measurement stopper, a reference stopper, and a drain valve. The liquid tank is a trough-shaped container made of transparent organic glass, and the bottom is supported by supporting legs. A liquid level gauge is arranged on the side wall of the liquid tank, and a drain valve is installed on the side wall of the liquid tank near the bottom. A reference stopper and a measurement stopper are arranged on the outer bottom plate of the liquid tank. The end of the reference workpiece is installed on the reference stopper through an opening in the bottom plate of the liquid tank and is connected to the reference stopper. The end of the workpiece to be measured is installed on the measuring stopper through the opening of the bottom plate of the liquid tank, and maintains electrical contact with the contact electrode of the measuring stopper. The liquid electrode terminal is installed on the inner bottom plate of the liquid tank and immersed in the conductive liquid. One end of the capacitance measuring module of the workpiece to be measured is connected to the contact electrode of the measuring stopper through a metal wire, and the other end of the capacitance measuring module of the workpiece to be measured is connected to the liquid electrode terminal through a metal wire. One end of the capacitance measuring module of the reference workpiece is connected to the contact electrode of the reference stopper through a metal wire, and the other end of the capacitance measuring module of the reference workpiece is connected to the liquid electrode terminal.

[0006] The reference workpiece is a standard workpiece with a uniform coating on its surface, the base metal inside it is completely the same as the base metal of the workpiece to be measured, and the coating materials used by the reference workpiece and the workpiece to be measured are also completely the same.

[0007] The reference limiter and the measuring limiter are exactly the same in structure, both of which are cylindrical structures with closed ends. A cylindrical contact electrode is provided at the closed end. The ends of the workpiece to be measured and the reference workpiece extend into the bottom of their respective limiters and maintain electrical connection with the contact electrode. Elastic sealing rings are provided inside the reference limiter and the measuring limiter. The inner diameter of the sealing ring is 1-2mm smaller than the diameter of the workpiece, and can form an effective seal on the side wall of the workpiece, so that the conductive liquid will not penetrate into the interior of the limiter.

[0008] Compared with the prior art, the present invention has the following beneficial effects:

[0009] (1) Fast response speed, which can realize the rapid measurement of the thickness distribution of the insulation layer of the workpiece to be measured along the line;

[0010] (2) The thinner the insulation layer, the higher the measurement accuracy, and the thickness of the insulation layer can be measured at the micron level;

[0011] (3) The measurement results are not affected by changes in parameters such as the salt content and temperature of the conductive liquid, and have a wide range of applications. Description of the drawings:

[0012] Figure 1 A schematic diagram of the structure of the present invention;

[0013] Figure 2Reference limiter structure diagram;

[0014] Figure 3 Reference stopper cross-section;

[0015] Figure 4 Reference workpiece structure diagram;

[0016] Figure 5 Reference workpiece cross-section diagram;

[0017] Figure 6 Schematic diagram of the structure of the workpiece to be tested;

[0018] Figure 7 Capacitance-level relationship diagram.

[0019] 1. Liquid tank; 2. Reference workpiece; 3. Workpiece to be measured; 4. Liquid electrode terminal; 5. Capacitance measurement module of workpiece to be measured; 6. Capacitance measurement module of reference workpiece; 7. Liquid level gauge; 8. Reference limiter; 9. Measuring limiter; 10. Drain valve; 11. Support leg; 12. Contact electrode; 13. Sealing ring; 14. Base metal; 15. Insulating coating. Specific implementation method:

[0020] like Figure 1 The figure is a schematic diagram of the structure of the present invention. A defect detection device for insulating coating of metal workpieces, characterized in that it mainly includes a liquid tank 1, a reference workpiece 2, a workpiece to be tested 3, a liquid electrode terminal 4, a capacitance measurement module 5 for the workpiece to be tested, a capacitance measurement module 6 for the reference workpiece, a liquid level gauge 7, a reference stopper 8, a measurement stopper 9, and a drain valve 10. The liquid tank 1 is a trough-shaped container made of transparent organic glass, and the bottom is supported by a supporting leg 11. A liquid level gauge 7 is provided on the side wall of the liquid tank 1, and a drain valve 10 is installed on the side wall of the liquid tank 1 near the bottom. A reference stopper 8 and a measurement stopper 9 are provided on the outer bottom plate of the liquid tank 1. The end of the reference workpiece 2 is installed on the reference stopper 8 through an opening on the bottom plate of the liquid tank 1 and is in contact with the reference stopper 9. The contact electrode 12 of the stopper 8 maintains electrical contact, the end of the workpiece 3 to be measured is installed on the measuring stopper 9 through the opening of the bottom plate of the liquid tank 1, and maintains electrical contact with the contact electrode 12 of the measuring stopper 9, the liquid electrode terminal 4 is installed on the inner bottom plate of the liquid tank 1 and immersed in the conductive liquid, one end of the capacitance measuring module 5 of the workpiece to be measured is connected to the contact electrode 12 of the measuring stopper 9 through a metal wire, and the other end of the capacitance measuring module 5 of the workpiece to be measured is connected to the liquid electrode terminal 4 through a metal wire, one end of the capacitance measuring module 6 of the reference workpiece is connected to the contact electrode 12 of the reference stopper 8 through a metal wire, and the other end of the capacitance measuring module 6 of the reference workpiece is connected to the liquid electrode terminal 4.

[0021] The reference stopper 8 and the measuring stopper 9 have the same structure. Figure 2 The figure shows the schematic diagram of the limiter structure. Figure 3 It is a schematic cross-sectional view of the position limiter. Both the reference position limiter 8 and the measurement position limiter 9 are cylindrical structures with closed ends, and cylindrical contact electrodes 12 are provided at the closed ends. As Figure 1 shown, the ends of the workpiece to be measured 3 and the reference workpiece 2 respectively extend to the bottom of the position limiter and are in electrical connection with the contact electrode 12; elastic sealing rings 13 are provided in the reference position limiter 8 and the measurement position limiter 9. The inner diameter of the sealing ring 13 is 1-2 mm smaller than the diameter of the workpiece, which can effectively seal the side walls of the workpiece to be measured 3 and the reference workpiece 2, and the conductive liquid will not penetrate into the interior of the position limiter.

[0022] The reference workpiece 2 is a standard workpiece with a uniform surface coating. The metal inside it is exactly the same as that of the workpiece to be measured 3, and the coating materials used for the reference workpiece 2 and the workpiece to be measured 3 are also exactly the same;

[0023] The working principle of the present invention is as follows:

[0024] As Figure 4 shown is a schematic diagram of the reference workpiece, Figure 5 which is a schematic cross-sectional view of the reference workpiece. The reference workpiece 2 is composed of a base metal 14 inside and an insulating coating 15. The insulating coating 15 covers the outer wall of the base metal 14 to form a double-layer structure. For the cylindrical workpiece shown in this embodiment, when immersed in water, a cylindrical capacitor is formed between the conductive liquid and the base metal 14, and the insulating coating 15 acts as the dielectric of the capacitor. The capacitance of this cylindrical capacitor can be calculated by formula (1):

[0025]

[0026] In the formula: L is the height of the conductive liquid in contact with the workpiece; d is the diameter of the conductive cylinder; δ is the thickness of the insulating coating 15; ε is the dielectric constant of the insulating coating 15.

[0027] It can be seen from the formula that since d, δ, and ε are all constants, the coating thickness and the liquid level height are linearly related. In addition, since the thickness of the insulating coating 15 is much smaller than the diameter d of the conductive core, that is, δ << d, so ln((d + 2δ) / d) is very small, and thus the capacitance change per unit length is very large, indicating that this method has high sensitivity. The thinner the insulating coating 15, the smaller δ, the higher the measurement accuracy. In addition, since ε is the dielectric constant of the insulating coating 15, its value only depends on the material of the insulating coating 15 and has nothing to do with the properties of the fluid itself. Therefore, the measured value only depends on the height of the conductive liquid phase in contact with the workpiece and is not affected by fluctuations in parameters such as the ion content, temperature, and pressure of the fluid itself.

[0028] Figure 6Schematic diagram of the workpiece to be tested. For the workpiece 3 to be tested, if the coating is uneven and the coating thickness suddenly increases at a certain liquid level, the measured capacitance value will change suddenly at this liquid level and no longer show a linear relationship. The capacitance increase is positively correlated with the coating thickness. For the cylindrical workpiece shown in this embodiment, the current coating thickness can be estimated by measuring the capacitance using the following formula:

[0029]

[0030] Formula (2) shows that by measuring the capacitance values ​​of the reference workpiece 2 and the workpiece to be measured 3, the relationship between the coating thickness of the workpiece to be measured 3 and the corresponding thickness of the reference workpiece 2 at the liquid level height can be obtained. The coating thickness of the reference workpiece 2 is a known value, so the coating thickness of the workpiece to be measured 3 at the current height can be calculated by formula (2). It can be seen that the present invention does not need to measure the dielectric constant of the coating, and the coating thickness at the same height can be obtained by measuring the capacitance values ​​of the reference workpiece 2 and the workpiece to be measured 3.

[0031] like Figure 7 As shown in the figure, for reference workpiece 2, since its coating is uniform, its capacitance value is linearly related to the liquid level height, while for workpiece 3 to be tested, since the coating thickness increases at a certain position, the corresponding capacitance value decreases. The coating defect position can be obtained according to the capacitance-height curve, and the corresponding coating thickness at this position can be calculated by formula (2).

[0032] The present invention works as follows:

[0033] (1) Installing the reference workpiece 2 in the reference stopper 8 through the bottom opening of the liquid tank 1, keeping the end of the reference workpiece 2 in electrical contact with the contact electrode 12 of the reference stopper 8; installing the workpiece 3 to be measured in the measurement stopper 9 through the bottom opening of the liquid tank 1, keeping the end of the workpiece 3 to be measured in electrical contact with the contact electrode 12 of the measurement stopper 9;

[0034] (2) Pour a conductive liquid such as water into the liquid tank 1, and the liquid level should not exceed the top of the reference workpiece 2 and the workpiece to be measured 3;

[0035] (3) The current liquid level height L is measured by the liquid level ruler 7, and the reference workpiece 2 capacitance C is measured by the reference workpiece capacitance measurement module 6 r , the capacitance C of the workpiece 3 to be measured is obtained by the workpiece capacitance measurement module 5 to be measured m ;

[0036] (4) Drain a portion of the conductive liquid through the drain valve and record the capacitance C of the reference workpiece 2 at the new liquid level. r and the capacitance C of the workpiece 3 to be tested m ;

[0037] (5) Continuously lower the liquid level to obtain a series of reference workpiece 2 capacitances C corresponding to the liquid level heights r and the capacitance C of the workpiece 3 to be tested m ;

[0038] (6) Draw Figure 7 The curve shown is compared with the reference workpiece 2 capacitance C r and the capacitance C of the workpiece 3 to be tested m , use formula (2) to calculate the thickness distribution of the coating of the workpiece 3 to be measured.

[0039] The embodiment of the present invention uses a cylindrical workpiece for illustration, and the quality of the insulating coating of workpieces of other shapes can also be measured by this principle, and all belong to the protection scope of the present invention. The present invention compares the workpiece 3 to be measured and the reference workpiece 2 to quickly obtain the coating thickness data of the coating of the workpiece 3 to be measured along the height direction, without measuring the dielectric constant of the coating and other information. The present invention does not damage the workpiece 3 to be measured, is simple and convenient to implement, and has a wide prospect of promotion and application.

Claims

1. A device for detecting defects in insulating coatings of metal workpieces, characterized in that: The invention mainly comprises a liquid tank (1), a reference workpiece (2), a workpiece to be measured (3), a liquid electrode terminal (4), a capacitance measurement module of the workpiece to be measured (5), a capacitance measurement module of the reference workpiece (6), a liquid level gauge (7), a reference stopper (8), a measurement stopper (9), and a liquid discharge valve (10); the liquid tank (1) is a trough-shaped container, made of transparent organic glass, the bottom of which is supported by supporting legs (11); a liquid level gauge (7) is arranged on the side wall of the liquid tank (1), and a liquid discharge valve (10) is installed on the side wall of the liquid tank (1) near the bottom; a reference stopper (8) and a measurement stopper (9) are arranged on the outer bottom plate of the liquid tank (1); The reference stopper (8) and the measuring stopper (9) are identical in structure, both being cylindrical structures with closed ends, and a cylindrical contact electrode (12) is provided at the closed end; The reference workpiece (2) is a standard workpiece with a uniform surface coating, the metal inside it is completely the same as that of the workpiece to be measured (3), and the coating material used is completely the same as that of the workpiece to be measured (3); the end of the reference workpiece (2) is installed on the reference stopper (8) through the opening of the bottom plate of the liquid tank (1), and maintains electrical contact with the contact electrode (12) of the reference stopper (8); the end of the workpiece to be measured (3) is installed on the measuring stopper (9) through the opening of the bottom plate of the liquid tank (1), and maintains electrical contact with the contact electrode (12) of the measuring stopper (9); The liquid electrode terminal (4) is mounted on the inner bottom plate of the liquid tank (1) and immersed in the conductive liquid; one end of the capacitance measurement module (5) of the workpiece to be measured is connected to the contact electrode (12) of the measuring stopper (9) through a metal wire, and the other end of the capacitance measurement module (5) of the workpiece to be measured is connected to the liquid electrode terminal (4) through a metal wire; one end of the capacitance measurement module (6) of the reference workpiece is connected to the contact electrode (12) of the reference stopper (8) through a metal wire, and the other end of the capacitance measurement module (6) of the reference workpiece is connected to the liquid electrode terminal (4).

2. A metal workpiece insulating coating defect detection device according to claim 1, characterized in that: The ends of the workpiece to be measured (3) and the reference workpiece (2) respectively penetrate into the bottom of the reference stopper (8) and the measuring stopper (9), and maintain electrical connection with the contact electrode (12); the reference stopper (8) and the measuring stopper (9) are provided with elastic sealing rings (13), the inner diameter of the sealing ring (13) is 1-2 mm smaller than the diameter of the workpiece, and can form an effective seal on the side wall of the workpiece, so that the conductive liquid will not penetrate into the interior of the stopper.

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