CN116678305A - Coating thickness measuring method based on sweep frequency eddy current - Google Patents
Coating thickness measuring method based on sweep frequency eddy current Download PDFInfo
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- CN116678305A CN116678305A CN202310741533.4A CN202310741533A CN116678305A CN 116678305 A CN116678305 A CN 116678305A CN 202310741533 A CN202310741533 A CN 202310741533A CN 116678305 A CN116678305 A CN 116678305A
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- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000011248 coating agent Substances 0.000 title claims abstract description 16
- 238000000576 coating method Methods 0.000 title claims abstract description 16
- 239000011247 coating layer Substances 0.000 claims abstract description 34
- 239000002985 plastic film Substances 0.000 claims abstract description 27
- 239000000758 substrate Substances 0.000 claims abstract description 21
- 229910052751 metal Inorganic materials 0.000 claims abstract description 16
- 239000002184 metal Substances 0.000 claims abstract description 16
- 238000004519 manufacturing process Methods 0.000 claims abstract description 4
- 239000011159 matrix material Substances 0.000 claims description 12
- 238000012360 testing method Methods 0.000 claims description 7
- 239000000523 sample Substances 0.000 claims description 6
- 230000005284 excitation Effects 0.000 claims description 4
- 230000035699 permeability Effects 0.000 claims description 2
- 230000008859 change Effects 0.000 abstract description 6
- 238000001514 detection method Methods 0.000 description 14
- 238000005516 engineering process Methods 0.000 description 10
- 238000005259 measurement Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 2
- 238000011527 multiparameter analysis Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000010963 304 stainless steel Substances 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 1
- 229910001069 Ti alloy Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009675 coating thickness measurement Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
- G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
- G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
The invention discloses a coating thickness measuring method based on sweep frequency eddy currents, which comprises the steps of firstly manufacturing a plurality of plastic sheets with different standard thicknesses to replace a non-conductive coating layer, then sequentially placing the plastic sheets on a metal substrate, then collecting enough eddy current data in a specific frequency band based on a sweep frequency eddy current thickness detecting platform, fitting the eddy current data through matlab to obtain a relation between the coating thickness and the minimum value of the change quantity of an impedance imaginary part, and finally measuring the eddy current data of a tested piece only by a detecting platform when the coating thickness is actually measured, so as to calculate the minimum value of the change quantity of the impedance imaginary part, and converting the coating thickness through the relation.
Description
Technical Field
The invention belongs to the technical field of nondestructive thickness measurement of eddy currents, and particularly relates to a coating thickness measurement method based on sweep frequency eddy currents.
Background
After the metal surface is corroded or worn, equipment damage, pipeline leakage and product pollution can be caused, so that serious accidents such as combustion or explosion and the like are caused, resources and energy are seriously wasted, and the national economy is greatly lost.
The coating technology is a technology for endowing the material and the surface specific performance of the parts thereof, improving the use value of the material and prolonging the service life of the parts, the uniform thickness of the coating is one of the preconditions that the material has specific protection function, and the life cycle, the bonding strength, the stress condition, the material consumption, the matrix temperature distribution and the like of the coating are directly influenced by the thickness of the coating and the uniformity of the coating. Therefore, the detection and evaluation of the coating layer thickness is of great importance.
The conventional single-frequency eddy current technology is difficult to eliminate interference factors such as conductivity, shape and the like of a substrate in the detection of the thickness of a coating layer. The sweep frequency eddy current detection technology is a method for detecting a conductive test piece by collecting enough eddy current data in a specific frequency band, and the performance of the method is superior to that of the conventional eddy current detection technology in the aspect of analyzing a plurality of parameters. The method is based on the sweep frequency eddy current detection technology, and aims to develop a set of thickness detection modules aiming at a non-conductive coating layer on a conductive substrate. The influence of the conductivity and the thickness of the matrix material in the thickness detection process is eliminated by utilizing the advantages of the multi-parameter analysis of the sweep frequency eddy current technology, so that the measurement accuracy is improved, and the environmental adaptability is improved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a coating thickness measuring method based on sweep frequency eddy current, which is used for measuring the thickness of coating layers on different matrixes.
In order to achieve the above purpose, the invention provides a coating thickness measuring method based on sweep frequency eddy current, which is characterized by comprising the following steps:
(1) Manufacturing a metal matrix; making different standard thickness d 1 ,d 2 ,…,d n N plastic sheets replace the non-conductive coating layer;
(2) Sequentially placing plastic sheets with different standard thicknesses on a metal matrix, and then placing the metal matrix on a horizontal tabletop;
(3) Vertically attaching an eddy current coil at the front end of the eddy current probe to the plastic sheet;
(4) Setting a signal generator to be in a sweep frequency mode, and setting a scanning frequency band and a scanning step length as lambda;
(5) The signal generator is used for generating a signal in a scanning frequency range by using a step length lambda to align the plastic sheet d on the substrate i Scanning, and recording the corresponding impedance imaginary part of the eddy current coil under each frequency;
(6) The corresponding impedance imaginary part sizes under two adjacent frequencies are differenced to obtain the impedance imaginary part variation, and then the minimum value of the impedance imaginary part variation is found out and recorded as delta l i ；
(7) Changing the plastic sheet, repeating the steps (5) and (6), finding out the minimum value of the impedance imaginary part variation corresponding to the plastic sheets with different standard thicknesses, and recording as Deltal 1 ,Δl 2 ,…,Δl i ,…,Δl n ；
(8) Thickness value d of plastic sheet to be different standard thickness 1 ,d 2 ,…,d n And the corresponding minimum value Deltal of the impedance imaginary part variation 1 ,Δl 2 ,…,Δl i ,…,Δl n Inputting the measured value into a fitting tool matlab, and fitting a fourth-order polynomial of the thickness D of the coating layer and the minimum value l of the variation of the imaginary part of the impedance through the matlab;
D＝p 1 l 4 +p 2 l 3 +p 3 l 2 +p 4 l+p 5
wherein p is 1 ～p 5 Fitting coefficients;
(9) Placing the tested piece with the coating layer on a substrate, and then finding out the minimum value delta l of the impedance imaginary part variation according to the steps (3) - (6);
(10) Let al=l, substituting the fitting formula in step (8) to calculate the coating layer thickness D of the test piece.
The invention aims at realizing the following steps:
according to the method for measuring the thickness of the coating layer based on the sweep frequency eddy current, a plurality of plastic sheets with different standard thicknesses are firstly manufactured to replace a non-conductive coating layer, then the plastic sheets are sequentially placed on a metal substrate, then enough eddy current data in a specific frequency band is collected based on a sweep frequency eddy current thickness detection platform, the eddy current data is fitted through matlab to obtain a relation between the thickness of the coating layer and the minimum value of the change quantity of the imaginary part of impedance, and finally when the thickness of the coating layer is actually measured, only the detection platform is required to measure the eddy current data of a tested piece, so that the minimum value of the change quantity of the imaginary part of impedance is calculated, and the thickness of the coating layer is converted through the relation.
Meanwhile, the sweep-frequency eddy-current-based coating thickness measuring method has the following beneficial effects:
(1) The minimum change of the impedance of the imaginary part of the eddy current coil is used as the electromagnetic insensitivity of the thickness measurement of the coating layer, so that the influence of the conductivity and the thickness of the substrate material in the thickness detection process is eliminated, and the main curve of the thickness measurement of the coating layer irrelevant to the substrate is obtained, thereby improving the measurement precision and the environmental adaptability.
(2) Compared with the conventional single-frequency eddy current technology, the method for detecting the conductive test piece by collecting enough eddy current data in a specific frequency band can eliminate interference factors such as conductivity and shape of a matrix by utilizing the advantage of multi-parameter analysis of the sweep frequency eddy current technology.
(3) The method for detecting the conductive test piece by collecting enough eddy current data in the specific frequency band is adopted, the sweep frequency signal has rich frequency spectrum information, and the performance of the method is superior to that of the conventional eddy current detection technology in the aspect of analyzing a plurality of parameters.
(4) The method and the device have the advantages that the characteristic information of the to-be-measured piece is obtained by acquiring the impedance information of the eddy current coil at different sweep frequency points to perform parameter analysis on the to-be-measured piece, and finally, the lowest point in the impedance change response curve can be used as an electromagnetic insensitive characteristic point to eliminate interference of the substrate, so that the thickness of coating layers on different substrates can be measured.
Drawings
FIG. 1 is a flow chart of a method for measuring the thickness of a coating layer based on sweep frequency eddy current;
FIG. 2 is a schematic diagram of a swept-frequency-based eddy current thickness detection platform;
FIG. 3 is a schematic view of a metal substrate and plastic sheet;
fig. 4 is a coating layer thickness measurement curve.
Detailed Description
The following description of the embodiments of the invention is presented in conjunction with the accompanying drawings to provide a better understanding of the invention to those skilled in the art. It is to be expressly noted that in the description below, detailed descriptions of known functions and designs are omitted here as perhaps obscuring the present invention.
Examples
FIG. 1 is a flow chart of a method for measuring the thickness of a coating layer based on sweep frequency eddy current.
In this embodiment, we first describe a platform for measuring thickness based on swept eddy current, as shown in fig. 2, and the main instruments used for the test in the figure are an IM3570 impedance analyzer, a signal generator, a dc power supply, and an oscilloscope of the japanese (HIOKI) company. The direct current power supply is set to be 12V and is connected into the sweep frequency eddy current thickness detection hardware module; the signal generator is set to be a sweep frequency signal, the frequency is from 10khz to 510khz, and the step length is set to be 50khz; and the impedance analyzer is connected with the eddy current coil to measure the impedance imaginary part.
The following describes a method for measuring the thickness of a coating layer based on sweep frequency eddy current in detail by combining a test platform, as shown in fig. 1, specifically comprising the following steps:
s1, manufacturing a metal matrix;
in this embodiment, the shape of the metal substrate is rectangular, and the metal substrate may be made of conductive metal with any conductivity, as shown in fig. 3 (a), for example, aluminum, copper, 304 stainless steel, titanium alloy, and the like; in this example, an aluminum substrate having a conductivity of 27MS/m was selected for the experiment.
As shown in fig. 3 (b), 6 plastic sheets of different standard thicknesses, which are six types of thicknesses of 250 μm, 798 μm, 1473 μm, 2002 μm, 2518 μm and 3032 μm, respectively, were fabricated instead of the non-conductive coating layer;
s2, sequentially placing plastic sheets with different standard thicknesses on a metal matrix, and then placing the metal matrix on a horizontal tabletop;
s3, vertically attaching an eddy current coil at the front end of the eddy current probe to the plastic sheet, as shown in FIG 2;
in this embodiment, the larger the outer diameter of the eddy current coil, the larger the linear section of the eddy current probe. In view of the subsequent inner diameter design and inductance value size limitations, an eddy current coil of 12mm outer diameter is selected here. In the inner diameter design, the ratio s of the inner diameter and the outer diameter is considered to influence the Q value of the electric eddy current coil, so that the Q value satisfies the following conditions when the electric eddy current coil is manufactured:
wherein f is the frequency of the current flowing through the coil, sigma is the conductivity of the coil, mu 0 Is vacuum magnetic permeability, phi is the outer diameter of the coil, d w The coil diameter s is the ratio of the inner diameter to the outer diameter of the electric eddy current coil, and C(s) is the Q factor of the coil.
In order to obtain as large a Q value as possible, s is here ensured to be between 0 and 0.3, so that the inner diameter is selected in the range from 3 to 5 mm.
In addition, in order to maximize the energy utilization of the eddy current probe and ensure the eddy current probe to work at higher efficiency, the ratio of the thickness to the outer diameter of the eddy current coil should be smaller than 0.1 when the thickness of the eddy current coil is designed.
S4, setting a signal generator to be in a sweep frequency mode, and setting a sweep frequency band and a sweep step length as lambda;
s5, after an excitation signal generated by an excitation signal source is input into the eddy current coil, the signal generator scans the plastic sheet d on the substrate in a frequency band with a step length lambda i Scanning, and recording the corresponding impedance imaginary part of the eddy current coil under each frequency;
s6, taking the difference of the corresponding impedance imaginary parts under two adjacent frequencies to obtain the impedance imaginary part variation, then finding out the minimum value of the impedance imaginary part variation,and recorded as Deltal i ；
S7, replacing the plastic sheet, repeating the steps S5 and S6, finding out the minimum value (namely electromagnetic insensitivity) of the impedance imaginary part variation corresponding to the plastic sheets with different standard thicknesses, and recording as Deltal 1 ，Δl 2 ，…，Δl i ，…，Δl 6 As shown in table 1;
table 1 is the electromagnetic insensitivity corresponding to different coating layer thicknesses on aluminum substrates;
| thickness of coating layer | 0 | 250 | 798 | 1473 | 2002 | 2518 | 3032 |
| Electromagnetic insensitivity | 196.21 | 209.94 | 231.78 | 253.79 | 259.78 | 263.48 | 266.56 |
TABLE 1
S8, thickness value d of plastic sheets with different standard thicknesses 1 ，d 2 ，…，d 6 And the corresponding minimum value Deltal of the impedance imaginary part variation 1 ，Δl 2 ，…，Δl i ，…，Δl 6 Inputting the measured value into a fitting tool matlab, and fitting a fourth-order polynomial of the thickness D of the coating layer and the minimum value l of the variation of the imaginary part of the impedance through the matlab;
D＝p 1 l 4 +p 2 l 3 +p 3 l 2 +p 4 l+p 5
wherein p is 1 ～p 5 For the fitting coefficient, the values are shown in table 2;
table 2 is the fitting coefficient values;
| parameter name | p 1 | p 2 | p 3 | p 4 | p 5 |
| Parameter value | 6.48e-4 | -0.5795 | 193.7 | -2.868e+4 | 1.587e+6 |
TABLE 2
In this embodiment, by fitting the measured data of the plastic sheets with different standard thicknesses, a thickness measurement curve of the coating layer irrelevant to the substrate is obtained, as shown in fig. 4, and the thickness of the coating layer can be obtained according to the curve under the condition that electromagnetic insensitivity is measured, so as to realize the thickness detection of the coating layer under the condition that the influence of the substrate is eliminated.
S9, placing the tested piece with the coating layer on a substrate, and then finding out the minimum value Deltal of the impedance imaginary part variation according to the steps (3) - (6);
and S10, substituting Deltal=l into a fitting formula in the step S8, so as to calculate the coating thickness D of the tested piece.
While the foregoing describes illustrative embodiments of the present invention to facilitate an understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but is to be construed as protected by the accompanying claims insofar as various changes are within the spirit and scope of the present invention as defined and defined by the appended claims.
Claims (2)
1. The method for measuring the thickness of the coating layer based on the sweep frequency vortex is characterized by comprising the following steps of:
(1) Manufacturing a metal matrix; making different standard thickness d 1 ,d 2 ,…,d n N plastic sheets replace the non-conductive coating layer;
(2) Sequentially placing plastic sheets with different standard thicknesses on a metal matrix, and then placing the metal matrix on a horizontal tabletop;
(3) Vertically attaching an eddy current coil at the front end of the eddy current probe to the plastic sheet;
(4) Setting a signal generator to be in a sweep frequency mode, and setting a scanning frequency band and a scanning step length as lambda;
(5) After the excitation signal generated by the excitation signal source is input into the eddy current coil, the signal generator scans the plastic sheet d on the substrate in the frequency range with the step lambda i Scanning, and recording the corresponding impedance imaginary part of the eddy current coil under each frequency;
(6) The corresponding impedance imaginary part sizes under two adjacent frequencies are differenced to obtain the impedance imaginary part variation, and then the minimum value of the impedance imaginary part variation is found out and recorded as delta l i ；
(7) Changing the plastic sheet, repeating the steps (5) and (6), finding out the minimum value of the impedance imaginary part variation corresponding to the plastic sheets with different standard thicknesses, and recording as Deltal 1 ,Δl 2 ,…,Δl i ,…,Δl n ；
(8) Thickness value d of plastic sheet to be different standard thickness 1 ,d 2 ,…,d n And the corresponding minimum value Deltal of the impedance imaginary part variation 1 ,Δl 2 ,…,Δl i ,…,Δl n Inputting the measured value into a fitting tool matlab, and fitting a fourth-order polynomial of the thickness D of the coating layer and the minimum value l of the variation of the imaginary part of the impedance through the matlab;
D＝p 1 l 4 +p 2 l 3 +p 3 l 2 +p 4 l+p 5
wherein p is 1 ～p 5 Fitting coefficients;
(9) Placing the tested piece with the coating layer on a substrate, and then finding out the minimum value delta l of the impedance imaginary part variation according to the steps (3) - (6);
(10) Let al=l, substituting the fitting formula in step (8) to calculate the coating layer thickness D of the test piece.
2. The coating thickness measuring method based on the sweep frequency eddy is characterized in that the quality factor value of the eddy current coil meets the following conditions:
wherein, the method comprises the following steps of. f is the frequency of the current flowing through the coil, sigma is the conductivity of the coil, mu 0 Is vacuum magnetic permeability, phi is the outer diameter of the coil, d w The coil diameter s is the ratio of the inner diameter to the outer diameter of the electric eddy current coil, and C(s) is the Q factor of the coil.
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| CN202310741533.4A CN116678305A (en) | 2023-06-20 | 2023-06-20 | Coating thickness measuring method based on sweep frequency eddy current |
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