Refractory material internal structure defect nondestructive detection method based on radar scanning

Abstract

The invention belongs to the technical field of non-destructive detection of refractory material products, and discloses a non-destructive detection method for internal structure defects of a refractory material based on radar scanning, which aims at special refractory material products such as cast products with higher density, sintered products with higher volume density and the like, and detects the internal structure defects of the refractory material through linear scanning or regional scanning. The method comprises the following steps: forming a time slice view of which the observation thickness can be randomly adjusted by combining a linear waveform, a two-dimensional map and a migration view, and identifying and judging the types, sizes and positions of defects in the refractory material product by integrating all imaging characteristics and data to form a multi-dimensional data analysis system; quantitative analysis on internal defects such as shrinkage porosity and closed pores of the refractory material is realized; the method is non-destructive, compared with conventional detection means such as infrared rays and X-rays, the method is simpler, more convenient and safer, the accuracy and comprehensiveness of internal structure defect recognition are improved, a reliable non-destructive detection means is provided for quality control of refractory material products, and the method has definite industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology for refractory materials, and particularly relates to a non-destructive testing method for internal structural defects in refractory materials based on radar scanning. Background Technology

[0002] Conventional methods for detecting the internal structure of refractory materials include X-ray detection, industrial CT, and ultrasonic detection. These methods have significant limitations, including limited penetration, sample size restrictions, and low accuracy. This is particularly true for certain special materials, such as high-density cast products and high-bulk-density sintered products. For example, X-rays can only penetrate some conventional brick blanks with low bulk density; due to attenuation, they cannot penetrate high-density blanks. When detecting electrofused cast chromium corundum refractory bricks, X-rays cannot penetrate the blank thickness, resulting in no image for reference. Industrial CT, as the most accurate conventional detection method, requires sample preparation and has strict limitations on the size of the sample, allowing only the detection of small samples. Ultrasonic detection has strong penetration but low accuracy. Infrared detection is only for qualitative judgment and has poor accuracy. Under certain harsh service conditions, there are extremely high requirements for the internal structure of special refractory products, and the above conventional detection methods cannot provide effective judgment.

[0003] Ground penetrating radar (GPR) technology is widely used in geological exploration. It utilizes the principle of electromagnetic wave reflection. When a wave propagates in a medium, it will be partially reflected when the dielectric constant changes, forming a unique hyperbolic structure. By analyzing the travel time, amplitude, and waveform characteristics of the reflected wave, the location, shape, and nature of the target can be inferred. It is a non-destructive detection method.

[0004] In the existing technology, although GPR technology has been applied to many fields such as civil engineering, geotechnical engineering, and road non-destructive testing, its application in the field of refractory materials is relatively limited. The patent document "Non-destructive testing method for refractory components" (EP3194940B1) involves radar (electromagnetic wave) detection methods, which only propose a detection method for cast refractory bricks of specific materials. However, the recognition and processing of images are not perfect, and there is a lack of systematic application and imaging analysis methods.

[0005] Refractory materials exhibit a variety of internal defects, including shrinkage cavities and isolated closed pores. The size and location of these defects significantly impact product quality. Furthermore, the imaging process is complex, relying primarily on manual analysis and identification of the images, which is highly subjective. Differences in technician experience contribute to misjudgments and errors in image analysis, reducing the accuracy and efficiency of ground-penetrating radar (GPR) detection. Therefore, a non-destructive analysis and verification method is urgently needed for refractory materials where conventional detection methods are insufficient. This method should be able to quantitatively analyze and determine the type, size, and location of internal defects to ensure the reliability and service life of refractory products under specific working conditions. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a non-destructive testing method for internal structural defects in refractory materials based on radar scanning. By combining linear waveforms, two-dimensional spectra, and migration views in the non-destructive testing of internal structural defects in refractory products using radar linear scanning or area scanning, a time-slice view with arbitrarily adjustable observation thickness is formed. By integrating all imaging features and data, the type, size, and location of defects inside the refractory product are identified and judged, forming a multi-dimensional data analysis system that improves the accuracy and comprehensiveness of defect identification.

[0007] The technical solution adopted in this invention is: a non-destructive detection method for internal structural defects in refractory materials based on radar scanning, comprising the following steps:

[0008] Step 1: Setting up the survey line

[0009] The radar measurement area and measurement line of the refractory product blank are determined according to the type and size of the refractory product blank;

[0010] Step 2: Detection Preparation

[0011] Set the key parameters of the radar system and match refractory material products with different sizes and materials;

[0012] The formula for calculating the step frequency is:

[0013]

[0014] Where Rmax is the target distance, which is generally the thickness of the blank to be measured.

[0015] c: Speed ​​of light in a vacuum, taken as 3e 8 ;

[0016] ε r Dielectric constant;

[0017] △f: Step frequency;

[0018] Use this formula to calculate the appropriate step frequency to avoid missed or incorrect judgments due to inappropriate frequency.

[0019] Step 3: Perform linear or area scans and acquire data.

[0020] Linear or regional scanning is performed on the refractory product blank. Electromagnetic waves are emitted into the radar measurement area and measurement line using a step-frequency continuous wave radar, and the electromagnetic wave echo signals reflected from the radar measurement area and measurement line of the refractory product blank are collected.

[0021] Linear scan data is obtained by performing a single scan along any direction of the refractory material blank to be tested;

[0022] Multiple scans are performed along any surface of the blank to be tested in the horizontal and vertical directions at fixed intervals to obtain regional scan data.

[0023] Step 4: Obtain linear waveforms, 2D spectra, and migration views.

[0024] The radar A-scan image is synthesized based on the electromagnetic wave echo signal; that is, the transmitter and receiver antennas generate the original hyperbola, i.e., the A-scan signal, based on the trajectory of electromagnetic waves reflected in different media.

[0025] As the receiver antenna moves, multiple A-scan signals are collected along the scanning path, and the A-scan signals are superimposed along the direction of travel to generate a two-dimensional map.

[0026] Collect A-scan signals and two-dimensional spectra. Based on the amplitude of the A-scan signals and the movement logic in the two-dimensional spectra, add color enhancement to the structural features to generate a migration view.

[0027] Step 5: Spectrum Processing

[0028] After all the data from the measuring lines are collected, the migration views are combined and superimposed according to the measuring line sequence, i.e., the corresponding positions on the refractory product blank, to obtain a general view of the internal structure of the blank. The time slice view is formed by observing the different thickness slices of the blank corresponding to the propagation time.

[0029] Step Six: Map Recognition, Multi-View Comprehensive Analysis and Defect Identification

[0030] After the area scan is completed, the time slice view is reviewed to confirm that there is no interference from cluttered signals. The location of the billet with abnormal signals in some areas is further determined. By combining the linear waveform, two-dimensional spectrum, migration view and time slice view, the type, location and size of defects inside the billet are determined.

[0031] The main internal structural defects of refractory products are shrinkage porosity and closed pores. Shrinkage porosity defects are identified by the presence of discontinuous, broken and dense strong reflection signals of the same phase axis in the two-dimensional spectrum. Closed pore defects are identified by the presence of regular crescent-shaped hyperbolic waveforms with obvious three-phase vibration in the two-dimensional spectrum.

[0032] Step 7: Data processing and quantitative calculation of defects.

[0033] After the linear scan is completed, the position of a certain abnormal signal in the billet is first determined by combining the two-dimensional spectrum and the migration view. Then, the abnormal signal is analyzed and calculated by combining the peak intensity of the linear waveform of the abnormal signal, the hyperbola period of the interface signal in the two-dimensional spectrum, and the coordinates of the imaging boundary of the abnormal signal in the migration view.

[0034] The area S of the shrinkage is calculated through the following steps: Identify the boundary range of the abnormal reflection area in the migration view; determine the range of the abnormal area in the X-axis direction [x1, x2] and the range in the Y-axis direction [y1, y2]; import the migration view into image processing software and draw a closed contour along the boundary of the abnormal area; calculate the area enclosed by the closed contour and convert it into the actual area according to the image scale.

[0035] The formula for calculating the area S of shrinkage is as follows:

[0036]

[0037] Where I(i,j) is the binarized defect indication function, and Δx and Δy are the actual sizes of the pixels.

[0038] Closed pores: The diameter is estimated by comparing the peak intensity of a linear waveform with that of a standard sample, combined with the hyperbolic period. In the defect quantification step, the diameter D of the closed pore is calculated using the following formula:

[0039]

[0040] Where v is the propagation speed of electromagnetic waves in refractory materials, and ΔT is the period of the hyperbola.

[0041] The propagation speed v of electromagnetic waves is calculated using the following formula:

[0042]

[0043] Where c is the speed of light in a vacuum, and ε is the relative permittivity of the refractory material.

[0044] Electromagnetic waves travel different trajectories after reflection in different media, depending on the material properties—dielectric constant. The amplitude of the A-scan signal indicates the material changes.

[0045] The generated migration view is more intuitive for image recognition.

[0046] When probing large-volume billets, a system is established on the width and height surfaces of the billet. Generally, the billet is the thinnest, resulting in the highest detection accuracy. Sampling intervals of 50mm or 100mm are set in both the x and y axes for the arrangement of measurement lines. After data collection for all measurement lines is completed, the migration views are combined and superimposed according to the measurement line sequence and the corresponding positions on the billet to obtain a general view of the internal structure of the billet. This view can be observed by cutting slices of the billet at different thicknesses corresponding to the propagation time, and is called a time-slice view.

[0047] The radar system has a modulation frequency range of 400~6000MHz, which can be adjusted according to the thickness and accuracy requirements of the refractory material blank to be tested; the antenna type is a stepped frequency continuous wave radar antenna, a shielded dipole antenna, and a transceiver integrated or separate design; the sampling interval is 50mm or 100mm, which can be adjusted according to the detection accuracy requirements; the scanning method is linear scanning or area scanning: linear scanning is a single straight line scan along the X-axis or Y-axis, and area scanning is a two-dimensional planar scan according to a preset grid of 50mm×50mm or 100mm×100mm.

[0048] The main internal structural defects in refractory products are shrinkage porosity and closed pores. Shrinkage porosity refers to the insufficient shrinkage compensation caused by the solidification shrinkage of some metal oxides during the cooling and solidification process of refractory products, forming in the last solidified area of ​​the green body. It generally presents as dense, small, scattered, and irregularly shaped pores. Therefore, under radar detection, electromagnetic waves from this type of defect structure are continuously reflected in the green body-air-green body-air… pattern, resulting in a discontinuous, dense hyperbola in the two-dimensional image. The concept of a phase axis means that under conditions with only air and green body as media, the change in dielectric constant is stable, and the image will show the same phase. However, in the concrete industry, the media include concrete-steel structure-PVC pipe. The dielectric constant of PVC pipe < the dielectric constant of concrete < the dielectric constant of steel structure. Therefore, when encountering materials with large fluctuations in dielectric constant, the image will show different phases.

[0049] The identification criteria for closed-pore defects are the appearance of a regular crescent-shaped hyperbolic waveform in the two-dimensional waveform, with obvious three-phase vibration. The three-phase vibration characteristic refers to the three consecutive phase changes generated by the electromagnetic wave at the billet-air-billet interface, which are represented as a sequence of positive peak-negative peak-positive peak on the waveform diagram.

[0050] Ground-penetrating radar (GPR) is an electromagnetic technology for locating invisible targets or interfaces within a medium. Its working principle involves high-frequency electromagnetic waves, transmitted in broadband pulse form, through a transmitting antenna into the measured medium. These waves are reflected back by the target object or interface with electrical differences and received by a receiving antenna. The sensor receives the reflected waves from the target medium interface. When electromagnetic waves propagate in a medium, their wave speed, reflection, and transmission intensity are all related to the electromagnetic properties and geometry of the medium. Their path, electromagnetic field distribution, and waveform change depending on the electrical properties and geometry of the penetrating medium. Therefore, by analyzing the two-way travel time, amplitude, and waveform data of the received waves, the structure of the medium can be inferred. Analysis of the echo signals can determine the shape and structure of the target. Currently, radar image processing mainly relies on manual analysis and identification, which is inefficient. Furthermore, due to the influence of human subjectivity, misjudgments and incorrect assessments often occur. This invention studies the radar wave attenuation characteristics of refractory materials and the propagation characteristics of radar waves in lossy media, and for the first time proposes a method for judging and quantitatively analyzing the internal defects of refractory materials.

[0051] The beneficial effects of this invention are as follows: This invention's non-destructive testing method for internal defects in refractory materials based on radar scanning is non-destructive and, compared to conventional detection methods such as infrared and X-rays, is simpler and safer. For special refractory materials such as high-density cast products and high-bulk-density sintered products, linear or area scanning, combined with linear waveforms, two-dimensional spectra, and migration views, forms a time-slice view with adjustable observation thickness. By integrating all imaging features and data, the type, size, and location of internal defects in the refractory material are identified and judged, forming a multi-dimensional data analysis system. This enables quantitative analysis of internal defects such as shrinkage porosity and closed pores in refractory materials, with the smallest detectable independent closed pore diameter being 4 mm. In the non-destructive testing of internal structural defects in refractory materials, the integration of multiple image information improves the accuracy and comprehensiveness of defect identification, providing a reliable non-destructive testing method for the quality control of refractory materials, and has clear industrial application value. Attached Figure Description

[0052] Figure 1 This is an example diagram of the linear waveform of the present invention;

[0053] Figure 2 This is an example diagram of a two-dimensional atlas of the present invention;

[0054] Figure 3 This is an example diagram of the migration view of the present invention;

[0055] Figure 4 This is an example diagram of the time slice view of the present invention;

[0056] Figure 5 This is a flowchart of the method of the present invention;

[0057] Figure 6 This is a comparison diagram of typical defects in radar signal characteristics of the present invention;

[0058] Figure 7 This is a two-dimensional atlas, a time slice view, and a corresponding partial cross-sectional photograph of Embodiment 1 of the present invention;

[0059] Figure 8 This is a two-dimensional atlas and a corresponding partial cross-sectional photograph of Embodiment 2 of the present invention;

[0060] Figure 9 The images shown are two-dimensional maps, time slice views, and corresponding partial cross-sectional photographs of Embodiment 3 of the present invention. Detailed Implementation

[0061] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] The radar-based non-destructive testing method of this invention is applicable to the non-destructive testing of internal defects in refractory materials such as electrofused cast chromium corundum, electrofused cast zirconium corundum, sintered chromium zirconium corundum, magnesia-carbon bricks, and aluminosilicates. However, it is not applicable to highly conductive and high dielectric loss materials such as silicon carbide. The specific implementation of this invention will be further described in detail below with reference to examples.

[0063] Example 1:

[0064] like Figure 1-6 , Figure 7As shown, non-destructive testing of internal defects in an electrofused chromium corundum product was performed. The product dimensions were 560mm × 450mm × 200mm. A region scanning method was used. A rectangular coordinate system was established on the surface of the product, with the X-axis horizontal and the Y-axis vertical. A scanning start point, end point, and sampling interval of 50mm were set in both the X and Y directions. The Y-coordinate was fixed, and a linear scan was performed along the X-axis. The process was repeated until the entire rectangular area was covered, and the complete radar signal data for each grid point was recorded. After all the scanning lines were completed, a corresponding two-dimensional map, migration view, and time slice view were generated using inverse Fourier transform. The location of the abnormal signal appearing in the migration view corresponding to the location in the two-dimensional map was analyzed. A strong interface reflection signal (black-white-black) appeared in the two-dimensional map, characterized by discontinuities, breaks, and dense clusters of phase axes. This defect was determined to be shrinkage porosity within the product. The area of ​​contraction was calculated by combining the x and y axis positions corresponding to the abnormal signal boundary. The area of ​​contraction was calculated to be approximately 3cm × 3.8cm = 11.4cm². The cross-section showed accurate imaging and positioning, and the calculation results were reliable.

[0065] Example 2:

[0066] like Figure 1-6 , Figure 8 As shown, non-destructive testing of internal defects in an electrofused chromium corundum product was performed. The product dimensions were 450mm × 400mm × 130mm. A radar antenna was coupled to the surface of the product and moved at a constant speed (≤0.2m / s) along a predetermined length. The A-scan signal (amplitude-time curve) at each sampling point was recorded, and the scan length covered the entire test area. After linear scanning, the location of the abnormal signal appearing in the migration view corresponding to the position in the two-dimensional spectrum was analyzed. The strong interface reflection signal in the two-dimensional spectrum exhibited typical isolated body characteristics, showing a regular crescent-shaped hyperbolic waveform with obvious three phases. This defect was determined to be an independent closed pore inside the product. By comparing the peak intensity at the corresponding position of the linear waveform with previously accumulated standard samples of the corresponding material and defects, the hyperbolic period corresponding to the interface signal, and the x and y axis positions corresponding to the imaging boundary of the abnormal signal in the migration view, the diameter of the independent closed pore could be easily calculated; the calculated pore diameter was 5mm.

[0067] Example 3:

[0068] like Figure 1-6 , Figure 9As shown, non-destructive testing of internal defects in a sintered chromium-zirconium corundum product was performed. The product dimensions were 600mm × 400mm × 250mm. A rectangular coordinate system (X-axis horizontal, Y-axis vertical) was established on the surface of the blank. A scanning start point, end point, and sampling interval (typically 50mm) were set in the X and Y directions, respectively. With the Y coordinate fixed, a linear scan was performed along the X direction, moving to the next Y coordinate, repeating the above steps until the entire rectangular area was covered. Complete radar signal data for each grid point was recorded. After the area scan, the structural features of the entire product's interior were assessed using time slice views of different thicknesses. The radar imaging showed almost no abnormal signals, therefore it was determined that the internal structure of the blank was dense and essentially defect-free.

[0069] Comparative verification: Comparison of the detection results of Examples 1-3 of this invention with the cross-sectioned actual objects shows that the abnormal structure types identified by radar detection are accurate, the abnormal structure positioning is relatively accurate (within ±3mm of the detection equipment error range), and the size of the abnormal structures is accurately judged: the diameter error of independent closed pores is less than 0.5mm, and the shrinkage area error is less than 5%. Compared with industrial CT, this method can detect larger volume products; compared with X-rays, this method can penetrate high-density blanks and provide clear imaging.

Claims

1. A non-destructive testing method for internal structural defects in refractory materials based on radar scanning, characterized in that, Includes the following steps: Step 1: Setting up the survey line The radar measurement area and measurement line of the refractory product blank are determined according to the type and size of the refractory product blank; Step 2: Detection Preparation Set the key parameters of the radar system and match refractory material products with different sizes and materials; Step 3: Perform linear or area scans and acquire data. Linear or regional scanning is performed on the refractory product blank. Electromagnetic waves are emitted into the radar measurement area and measurement line using a step-frequency continuous wave radar, and the electromagnetic wave echo signals reflected from the radar measurement area and measurement line of the refractory product blank are collected. Step 4: Obtain linear waveforms, 2D spectra, and migration views. The radar A-scan image is synthesized based on the electromagnetic wave echo signal; that is, the transmitter and receiver antennas generate the original hyperbola, i.e., the A-scan signal, based on the trajectory of electromagnetic waves reflected in different media. As the receiver antenna moves, multiple A-scan signals are collected along the scanning path, and the A-scan signals are superimposed along the direction of travel to generate a two-dimensional map. Collect A-scan signals and two-dimensional spectra. Based on the amplitude of the A-scan signals and the movement logic in the two-dimensional spectra, add color enhancement to the structural features to generate a migration view. Step 5: Spectrum Processing After all the data from the measuring lines are collected, the migration views are combined and superimposed according to the measuring line sequence, i.e., the corresponding positions on the refractory product blank, to obtain a general view of the internal structure of the blank. The time slice view is formed by observing the different thickness slices of the blank corresponding to the propagation time. Step Six: Map Recognition, Multi-View Comprehensive Analysis and Defect Identification After the area scan is completed, the time slice view is reviewed to confirm that there is no interference from cluttered signals. The location of the billet with abnormal signals in some areas is further determined. By combining the linear waveform, two-dimensional spectrum, migration view and time slice view, the type, location and size of defects inside the billet are determined. Step 7: Data processing and quantitative calculation of defects. After the linear scan is completed, the position of a certain abnormal signal in the billet is first determined by combining the two-dimensional spectrum and the migration view. Then, the abnormal signal is analyzed and calculated by combining the peak intensity of the linear waveform of the abnormal signal, the hyperbola period of the interface signal in the two-dimensional spectrum, and the coordinates of the imaging boundary of the abnormal signal in the migration view.

2. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step two, the modulation frequency range of the radar system is 400~6000MHz, which is adjusted according to the thickness and accuracy requirements of the refractory material blank to be tested.

3. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step two, the radar system uses a stepped-frequency continuous-wave radar antenna; the formula for calculating the stepped frequency is as follows: Where Rmax is the target distance, which is generally the thickness of the blank to be measured. c: Speed ​​of light in a vacuum, taken as 3e 8 ; ε r Dielectric constant; △f: Step frequency; Use this formula to calculate the appropriate step frequency to avoid missed or incorrect judgments due to inappropriate frequency.

4. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step two, the sampling interval of the radar system is to scan the surface of the blank to be tested every 50 mm or 100 mm.

5. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step three, linear scanning involves performing a single scan along any direction of the refractory material blank to be tested, i.e., along the X-axis or Y-axis, to obtain linear scan data.

6. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step three, the area scanning involves multiple scans along the horizontal and vertical directions of the refractory product blank to be tested, using a two-dimensional plane scan at preset fixed intervals of 50mm×50mm or 100mm×100mm to obtain area scanning data.

7. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step six, the main internal structural defects of refractory products are shrinkage porosity and closed pores. The identification criteria for shrinkage porosity defects are the presence of discontinuous, broken and dense strong reflection signals of the same phase axis in the two-dimensional spectrum. The identification criteria for closed pore defects are the presence of regular crescent-shaped hyperbolic waveforms with obvious three-phase vibration in the two-dimensional spectrum.

8. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step seven, the shrinkage area S is calculated through the following steps: Identify the boundary range of the abnormal reflection area in the migration view; determine the range of the abnormal area in the X-axis direction [x1, x2] and the range in the Y-axis direction [y1, y2]; import the migration view into image processing software and draw a closed contour along the boundary of the abnormal area; calculate the area enclosed by the closed contour and convert it into the actual area according to the image scale. The formula for calculating the area S of shrinkage is as follows: Where I(i,j) is the binarized defect indication function, and Δx and Δy are the actual sizes of the pixels.

9. The non-destructive testing method for internal structural defects of refractory materials based on radar scanning according to claim 1, characterized in that: In step seven, the diameter of the closed vent is estimated by comparing the peak intensity of the linear waveform with that of the standard sample and combining this with the hyperbolic period. The diameter D of the closed vent is calculated using the following formula: Where v is the propagation speed of electromagnetic waves in refractory materials, and ΔT is the period of the hyperbola. The propagation speed v of electromagnetic waves is calculated using the following formula: Where c is the speed of light in a vacuum, and ε is the relative permittivity of the refractory material.

Images