CN111025208B

CN111025208B - Magnetic material orientation testing method

Info

Publication number: CN111025208B
Application number: CN201911387958.XA
Authority: CN
Inventors: 侯德鑫; 叶树亮
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2019-12-30
Filing date: 2019-12-30
Publication date: 2022-04-26
Anticipated expiration: 2039-12-30
Also published as: CN111025208A

Abstract

The invention discloses a rapid test method for determining the orientation of a magnetic material. The anisotropy of the magnetic property is reflected by utilizing the anisotropy of the heat transfer property, the pulse point heating is carried out on the test surface of the sample by using laser during the test, the temperature field change of the heated sample surface in the thermal diffusion process is recorded by using a thermal imager, and the orientation of the anisotropic magnetic material is judged according to the thermal diffusion speed difference in different directions. In the testing process, the laser heating and the thermal imager observation are carried out in a non-contact mode, so that the method is more convenient to apply and is suitable for scenes such as online detection and the like; in the test process, laser heating is pulse excitation, and the observation time is generally only tens to hundreds of milliseconds, so the test speed is very high; and in the test process, electromagnetic excitation is not required to be applied to the sample, so that the problem of magnetizing the sample is solved.

Description

Magnetic material orientation testing method

Technical Field

The invention relates to the field of magnetic materials, in particular to a rapid test method for determining the orientation of a magnetic material.

Background

Many magnetic materials are oriented during production, and need to be magnetized before use, and the orientation needs to be determined before magnetization; some magnetic material products can judge orientation through shape and size, but some products cannot judge orientation through appearance and need detection. Methods for detecting the orientation of anisotropic magnetic materials generally use electromagnetic principles, such as magnets, eddy current sensors, eddy current coils, etc., but these methods tend to magnetize the magnetic material, are complicated to operate, and take a long time.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: how to simply and rapidly judge whether the magnetic material is isotropic or anisotropic, and detect the orientation of the anisotropic magnetic material.

The technical scheme adopted by the invention for solving the technical problem is as follows:

the invention uses spot laser to heat the surface of the sample, uses thermal imager to observe and record the temperature field change of the surface of the sample, and detects the orientation of the magnetic material according to the difference of thermal diffusion speed in different directions, which comprises the following steps: selecting a temperature field at a certain moment after pulse heating, performing Gaussian fitting on the temperature of an area near the laser heating, calculating the ratio R of the fitting radiuses in two spindle directions which are perpendicular to each other on the plane where the area is located, and then judging the anisotropy condition according to the ratio R: if the ratio R is close to 1, namely |1-R | < Thresh, the properties of the two directions are consistent, and the laser heating surface is an orientation surface or the sample is an isotropic material; if |1-R | ≧ Thresh, the two-direction properties are different, the sample is an anisotropic material, the laser heating surface is not an orientation surface, and Thresh is a threshold value.

Further, at least two surfaces of the sample in different directions are tested, and if the radius ratio R is close to 1, the sample is an isotropic sample and is not oriented.

Furthermore, the area of the hot spot is the largest when the temperature in the temperature field at a certain moment after the pulse heating is selected and is higher than the set temperature threshold.

The invention has the beneficial effects that: in the test process, laser heating and thermal imager observation are carried out in a non-contact mode, so that the application is more convenient, and the method is suitable for scenes such as online detection and the like; in the test process, laser heating is pulse excitation, and the observation time is generally only tens to hundreds of milliseconds, so the test speed is very high; and in the test process, electromagnetic excitation is not required to be applied to the sample, so that the problem of magnetizing the sample is solved.

Drawings

Fig. 1 is a schematic structural diagram of a test system according to embodiment 1 of the present invention.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present invention clear, the present invention will be further described with reference to the accompanying drawings, in which:

examples

The basic structure of the test system is shown in FIG. 1: the square magnetic material sample 1 is positioned below the laser 2 and the thermal imager 3, and data output by the thermal imager 3 is recorded and analyzed by the measurement and control software 4; the thermal imager 3 is mounted and the sample 1 is arranged such that the direction of the principal axis of the sample coincides with the direction of the rows and columns of the thermal image. During testing, the laser 2 projects laser 5 to the surface of the sample 1, and laser spots are round points with small sizes and the diameters of the round points are smaller than 0.2 mm; during testing, the laser 2 performs pulse type heating on the central position of the sample 1, and the pulse width is less than 50 ms; the thermal imager 3 records the surface temperature data of the sample 1 starting from the moment of heating, denoted T (τ, x, y), where τ denotes time and x and y denote spatial coordinates.

The data T (τ, x, y) is analytically calculated as follows:

1) converting the temperature data into temperature rise data: Δ T (τ, x, y) ═ T (τ, x, y) -T (0, x, y); where τ is 0 is defined as the time at which the pulsed heating is started, and T (0, x, y) represents the initial temperature of the sample.

2) Calculating a temperature rise threshold min _ dT: calculating a temperature rise threshold value according to a noise equivalent temperature difference performance index (NETD) of the thermal imager, wherein min _ dT is C multiplied by NETD; the coefficient C is 4-10, for example, if the NETD index is 0.05 ℃, the coefficient C can be a threshold value at 0.4 ℃.

3) Determination of the analysis instant τ a: comparing the data of delta T (tau, x, y) at any time with a temperature rise threshold value min _ dT, regarding the area of which the temperature rise exceeds min _ dT as the thermal diffusion hot spot at the corresponding time, and selecting the time with the largest hot spot area as the analysis time tau a.

4) Extracting the temperature distribution curve data in the main shaft direction: and establishing a rectangular coordinate system by taking the center of the light spot as an origin and the row and column directions (namely the main shaft directions) of the thermal imager as x and y axes, and extracting temperature rise data of the time tau a on the x and y axes, wherein the temperature rise data are respectively recorded as delta Tx (x) and delta Ty (y).

5) And (3) curve fitting: gauss curve fitting was performed for Δ Tx (x) and Δ Ty (y), and radius parameters obtained by fitting were recorded as Rx and Ry, respectively.

6) The difference of the thermal diffusion speeds in the two main shaft directions is calculated by adopting the following formula:

where the min and max functions represent taking a smaller value and a larger value, respectively.

7) Determination of the anisotropy case: if the calculation results all meet the condition that epsilon is less than Thresh, the directions of the x main shaft and the y main shaft are different, and the test surface is not an orientation surface; otherwise, the directions of the two main axes x and y are considered to be the same, so that the test surface is an orientation surface, or the sample is an isotropic sample. The threshold epsilon can be taken from 0.1-0.2 by experience, or a large number of samples of the type are tested in advance, the average value of epsilon values tested by an oriented surface and a non-oriented surface is counted and is marked as epsilon 1 and epsilon 2, and the threshold is set as follows:

Thresh＝(ε1+ε2)/2。

if the test result shows that the directions of the x main shaft and the y main shaft are the same, the adjacent surface of the previous test surface can be selected for retesting; if the new test result has two different main axis directions, the sample is an anisotropic sample, and the first test surface is an orientation surface; otherwise the sample is isotropic material.

The embodiments described in this specification are merely illustrative of implementations of the inventive concept and the scope of the present invention should not be considered limited to the specific forms set forth in the embodiments but rather by the equivalents thereof as may occur to those skilled in the art upon consideration of the present inventive concept.

Claims

1. A magnetic material orientation test method is characterized in that: the method comprises the following steps of performing pulse type point heating on the surface of a sample by using spot light spot laser, observing and recording the surface temperature field change of the sample by using a thermal imager, and detecting the orientation of a magnetic material according to the difference of thermal diffusion speeds in different directions, wherein the method specifically comprises the following steps:

selecting a temperature field at a certain moment after pulse heating, performing Gaussian fitting on the temperature of an area near the laser heating, calculating the ratio R of the fitting radiuses in two spindle directions which are perpendicular to each other on the plane where the area is located, and then judging the anisotropy condition according to the ratio R: if the ratio R is close to 1, namely |1-R | < Thresh, the properties of the two directions are consistent, and the laser heating surface is an orientation surface or the sample is an isotropic material; if |1-R | > or more than Thresh, the properties of the two directions are different, the sample is an anisotropic material, the laser heating surface is not an orientation surface, and Thresh is a threshold value; and the Gaussian fitting is performed on the temperature rise data in the main shaft direction at the moment when the temperature rise exceeds a set value and the hot spot area is maximum.

2. The test method of claim 1, wherein: at least two surfaces of the sample in different directions are tested, and if the radius ratio R is close to 1, the sample is an isotropic sample and is not oriented.

3. The test method according to claim 1 or 2, characterized in that: and selecting the temperature field at a certain moment after pulse heating, wherein the area of the hot spot of which the temperature is higher than the set temperature threshold value in the temperature field at the moment is the largest.