阅读说明：本技术 一种基于温差的裂纹磁粉检测方法 (Crack magnetic powder detection method based on temperature difference ) 是由 康宜华 陈彦廷 于 2021-08-17 设计创作，主要内容包括：本发明属于铁磁材料无损探伤相关技术领域,其公开了一种基于温差的裂纹磁粉检测方法,所述检测方法包括以下步骤：首先,在磁化场内,将与被测试件存在温差的磁粉喷洒在被测试件上,并实时获取被测试件的热像图；接着,对获取的热像图进行处理以获得被测试件的温度变化,继而依据得到的温度变化结果对被测试件进行裂纹识别；其中,当被测试件内存在裂纹时,裂纹处产生的漏磁场将吸引磁粉聚集而形成磁痕,磁痕处的温度与被测试件其他区域的温度不同,且磁痕处的温度与被测试件温度之间的差别由于磁粉聚集而被放大。本方法避免了在人工去除非相关磁痕时影响裂纹磁痕的信息,使用的是普通干磁粉,易于去除与回收,对试件的污染较低,对环境无污染。(The invention belongs to the related technical field of nondestructive inspection of ferromagnetic materials, and discloses a crack magnetic powder detection method based on temperature difference, which comprises the following steps: firstly, spraying magnetic powder with temperature difference with a tested piece on the tested piece in a magnetization field, and acquiring a thermograph of the tested piece in real time; then, processing the obtained thermal image to obtain the temperature change of the tested piece, and then carrying out crack identification on the tested piece according to the obtained temperature change result; when a crack exists in the tested piece, magnetic powder is attracted to gather by a leakage magnetic field generated at the crack to form a magnetic trace, the temperature of the magnetic trace is different from the temperature of other areas of the tested piece, and the difference between the temperature of the magnetic trace and the temperature of the tested piece is amplified due to the gathering of the magnetic powder. The method avoids influencing the information of the crack magnetic traces when the non-related magnetic traces are manually removed, uses common dry magnetic powder, is easy to remove and recycle, has low pollution to a test piece, and has no pollution to the environment.)

1. The crack magnetic powder detection method based on the temperature difference is characterized by comprising the following steps:

firstly, spraying magnetic powder with temperature difference with a tested piece on the tested piece in a magnetization field, and acquiring a thermograph of the tested piece in real time; then, processing the obtained thermal image to obtain the temperature change of the tested piece, and then carrying out crack identification on the tested piece according to the obtained temperature change result;

when a crack exists in the tested piece, magnetic powder is attracted to gather by a leakage magnetic field generated at the crack to form a magnetic trace, the temperature of the magnetic trace is different from the temperature of other areas of the tested piece, and the difference between the temperature of the magnetic trace and the temperature of the tested piece is amplified due to the gathering of the magnetic powder.

2. The method for testing magnetic powder for cracks based on temperature difference as claimed in claim 1, wherein: the spraying time of the magnetic powder is less than or equal to 3 seconds; the acquisition frequency of the thermal image is more than or equal to 100 Hz.

3. The method for testing magnetic powder for cracks based on temperature difference as claimed in claim 1, wherein: when the tested piece is a normal-temperature test piece, the temperature of the magnetic powder is set to be more than or equal to 100 ℃ and less than or equal to the Curie temperature.

4. The method for testing magnetic powder for cracks based on temperature difference as claimed in claim 1, wherein: and when the tested piece is a test piece subjected to heat treatment, the temperature of the magnetic powder is set to be normal temperature.

5. The method for testing magnetic powder for cracks based on temperature difference according to any one of claims 1 to 4, wherein: the magnetic powder is ferroferric oxide, and the particle size of the magnetic powder is less than 100 mu m.

6. The method for testing magnetic powder for cracks based on temperature difference according to any one of claims 1 to 4, wherein: and acquiring a thermal image by adopting a thermal imager, wherein the shooting visual angle of the thermal imager is vertical to the surface of the tested piece.

7. The crack magnetic powder inspection method based on temperature difference as claimed in claim 6, wherein: and averaging the temperature values of each pixel point recorded by the thermal imager along the time sequence, wherein if the difference value between the temperature average value of the local pixel point and the temperature average values of the rest of the pixel points is within a preset range, the position of the local pixel point corresponding to the tested piece is a crack area.

8. The method for testing magnetic powder for cracks based on temperature difference according to any one of claims 1 to 4, wherein: and magnetizing the tested piece by using a coil, a magnetic yoke or a conducting wire.

9. The method for testing magnetic powder for cracks based on temperature difference according to any one of claims 1 to 4, wherein: and after crack identification, the method also comprises the steps of carrying out demagnetization treatment on the tested piece and recycling magnetic powder.

10. The crack magnetic powder inspection method based on temperature difference according to claim 9, wherein: the residual magnetism of the tested piece is eliminated by adopting an alternating current demagnetizing method, and then the removal and the recycling of the magnetic powder are completed in a vibration or wind power mode.

Technical Field

The invention belongs to the related technical field of nondestructive testing of ferromagnetic materials, and particularly relates to a crack magnetic powder testing method based on temperature difference.

Background

With the demand of social production and development, the demand of ferromagnetic members in various industrial fields is greatly increased, and the surface quality of ferromagnetic members is increasingly required. The nondestructive testing mainly comprises five methods: the method comprises the following steps of ultrasonic detection, ray detection, eddy current detection, magnetic particle detection and penetration detection, wherein the magnetic particle detection is an important nondestructive detection technology with large and wide range, and over 70 percent of steel members in aviation, aerospace, military industry, railways and petroleum industry and over 80 percent of steel safety members in automobiles need of magnetic particle detection.

According to different configurations of the used magnetic powder, the conventional magnetic powder inspection can be classified into dry inspection and wet inspection in which the magnetic powder is configured in a water-based or oil-based form to form a magnetic suspension. The magnetic powder particles in the magnetic suspension have good fluidity, so the weak leakage magnetic field can also attract the magnetic powder particles in the suspension to be stacked to form magnetic traces. For the convenience of identification, the magnetic powder particles are also coated with fluorescent agent, which can obviously improve the contrast of the stacked magnetic traces. Therefore, wet magnetic powder detection has high sensitivity, but wet detection can pollute the detected test piece, often needs complicated procedure to clear away the result of use on test piece surface, and the use of fluorescent agent can pollute the environment. The dry detection directly uses dry magnetic powder to detect a test piece, and the magnetic powder is usually automatically dropped after demagnetization because of no attachment of suspension. Therefore, the pollution of the dry detection to the test piece is low, and the test piece is easy to recycle. However, dry magnetic powder has poor fluidity in air, and in industry, the magnetic powder is usually added to the surface of a test piece and then blow off irrelevant magnetic powder, so that magnetic traces at crack positions are reserved. This operation also inevitably blows away the magnetic powder on the part of the crack magnetic traces. Therefore, when the crack size is small, the detection capability of the dry detection is poor, the influence of manual operation is large, and the requirement on an operator is high.

In addition, high temperature test pieces are also one of the difficulties in magnetic particle testing, and many test pieces are in a high temperature state after a heat treatment process, such as annealing, normalizing, quenching, tempering, and the like. The magnetic suspension is easy to evaporate and lose efficacy at a high temperature. Some manual auxiliary operations in the traditional magnetic particle testing are difficult to carry out, how to guarantee the precision of the magnetic particle testing replaces the fussy manual operation, and the problem that the magnetic particle testing needs to be solved emphatically in the automatic development is solved.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a crack magnetic powder detection method based on temperature difference, wherein the detection method adopts magnetic powder with a certain temperature difference with a tested piece for detection, then uses a thermal imager to record the temperature, and then calculates the position of the crack through thermal image data. The detection method can extract the crack information from the temperature abnormity in the accumulation process of the magnetic powder, avoids influencing the crack magnetic trace information when the irrelevant magnetic traces are removed manually, can detect the test piece in a high-temperature state by adopting the normal-temperature magnetic powder, is easy to remove and recycle the magnetic powder, has low pollution to the test piece and has no pollution to the environment because the common dry magnetic powder is used.

In order to achieve the above object, according to one aspect of the present invention, there is provided a crack magnetic powder inspection method based on temperature difference, the inspection method mainly comprising the steps of:

firstly, spraying magnetic powder with temperature difference with a tested piece on the tested piece in a magnetization field, and acquiring a thermograph of the tested piece in real time; then, processing the obtained thermal image to obtain the temperature change of the tested piece, and then carrying out crack identification on the tested piece according to the obtained temperature change result;

when a crack exists in the tested piece, magnetic powder is attracted to gather by a leakage magnetic field generated at the crack to form a magnetic trace, the temperature of the magnetic trace is different from the temperature of other areas of the tested piece, and the difference between the temperature of the magnetic trace and the temperature of the tested piece is amplified due to the gathering of the magnetic powder.

Further, the spraying time of the magnetic powder is less than or equal to 3 seconds; the acquisition frequency of the thermal image is more than or equal to 100 Hz.

Further, when the tested piece is a normal-temperature test piece, the temperature of the magnetic powder is set to be greater than or equal to 100 ℃ and less than or equal to the Curie temperature.

Further, when the test piece is a heat-treated test piece, the temperature of the magnetic powder is set to be normal temperature.

Furthermore, the magnetic powder is ferroferric oxide, and the particle size of the magnetic powder is below 100 mu m.

And further, acquiring a thermal image by adopting a thermal imager, wherein the shooting visual angle of the thermal imager is vertical to the surface of the tested piece.

Further, averaging the temperature values of each pixel point recorded by the thermal imager along the time sequence, and if the difference value between the temperature average value of the local pixel point and the temperature average values of the rest of the pixel points is within a preset range, determining that the position of the local pixel point corresponding to the tested piece is a crack area.

Further, a coil, a yoke or a conductive wire is used to magnetize the tested piece.

Further, the method also comprises the steps of carrying out demagnetization treatment on the tested piece and recycling magnetic powder after crack identification.

Further, the residual magnetism of the tested piece is eliminated by adopting an alternating current demagnetizing method, and then the removal and the recycling of the magnetic powder are completed in a vibration or wind power mode.

Generally, compared with the prior art, the crack magnetic powder detection method based on the temperature difference has the following beneficial effects:

1. in the magnetizing field, the magnetic powder with the temperature difference with the tested piece is sprayed on the tested piece, the thermal image of the tested piece is obtained in real time, the visible temperature data acquisition process is completed in the stage of applying the magnetic powder, irrelevant magnetic powder does not need to be removed, the influence of manual removal of the irrelevant magnetic powder on crack magnetic marks is avoided, the process flow of magnetic powder detection is simplified, and the automation degree is improved.

2. The method can extract crack information from temperature abnormity in the process of stacking magnetic powder, can detect the test piece in a high-temperature state, and has a wide application range.

3. The magnetic powder adopted by the invention is common dry magnetic powder, has no fluorescent agent, has less pollution to a test piece, has lower cost, is environment-friendly and is easy to remove and recycle the magnetic powder.

4. When being the normal atmospheric temperature test piece, the temperature of magnetic sets for more than or equal to 100 ℃ and less than or equal to curie temperature, guarantees from this that there is reasonable difference in temperature between being tested piece and the magnetic, has guaranteed better detectivity.

5. And the shooting visual angle of the thermal imager is perpendicular to the surface of the tested piece so as to reduce the attenuation of infrared energy.

Drawings

FIG. 1 is a schematic diagram illustrating the principle of a magnetic particle inspection method for cracks based on temperature difference according to the present invention;

FIG. 2 is a schematic diagram of coil-type magnetization detection related to a crack magnetic powder detection method based on temperature difference provided by the invention;

FIG. 3 is a schematic diagram of a magnetic yoke type magnetization detection method related to the crack magnetic powder detection method based on temperature difference provided by the invention;

fig. 4 (a), (b), (c), and (d) are schematic diagrams of the test results of the magnetic powder test piece and the conventional magnetic powder test method for the magnetic powder card without removing the related magnetic powder, respectively;

fig. 5 (a) and (b) are schematic diagrams illustrating the detection results of two magnetic powder test pieces by using the temperature difference-based crack magnetic powder detection method provided by the present invention.

The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein: 1-a tested piece, 2-a magnetic induction line, 3-a crack, 4-a magnetic trace, 5-magnetic powder, 6-a non-crack area, 7-a first magnetizing coil, 8-a second magnetizing coil, 9-a thermal imager, 10-a magnetic powder spray gun and 11-an upper computer.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention provides a crack magnetic powder detection method based on temperature difference, which mainly comprises the following steps:

magnetizing the tested piece, and heating or cooling the magnetic powder to make the temperature of the magnetic powder different from that of the tested piece.

Specifically, before the magnetic powder is sprayed, the test piece needs to be magnetized to a saturated state, and the magnetization process needs to be maintained until the end of the inspection. Generally, the magnetization direction needs to be perpendicular to the direction of the crack to be tested to ensure that a maximum leakage field can be generated to attract the magnetic powder particles. When the tested piece is at normal temperature, the magnetic powder is heated by adopting a vortex heating or conduction heating method, the temperature of the heated magnetic powder cannot be higher than the Curie temperature, otherwise, the magnetic powder loses the ability of being attracted by a leakage magnetic field, and is preferably higher than 100 ℃ and less than or equal to the Curie temperature. For the detection of a high-temperature test piece after hot rolling or heat treatment processing, normal-temperature magnetic powder is directly used for detection, and the temperature of the test piece needs to be ensured to be higher than 60 ℃ so as to ensure good imaging effect.

Wherein, the magnetization can be carried out by selecting magnetic field sources such as coils, magnetic yokes, electrified leads and the like; the magnetic powder is dry powder without fluorescent agent, and mainly comprises ferroferric oxide, and the particle size of the magnetic powder is controlled below 100 μm.

And the magnetic powder is sent to the surface of the tested piece by adopting a negative pressure spray gun or a fan device, and the wind power cannot be too large when the magnetic powder is blown so as to avoid blowing away the magnetic powder above the cracks. Generally, the magnetic powder particles can be uniformly distributed in the space, in order to ensure a good imaging effect, the temperature difference between the magnetic powder and a tested piece can be large, so that the temperature gradient is large when the magnetic powder reaches the surface of the test piece, the heat transfer is fast, the temperature difference signal can disappear fast, the speed is fast as much as possible when the magnetic powder is sprayed, the accumulation of magnetic marks is completed within 3 seconds as much as possible, and the thermal imager is favorable for capturing the temperature signal.

And secondly, spraying magnetic powder on the magnetized tested piece in the magnetization field, acquiring a thermal image of the tested piece in real time, processing the acquired thermal image to acquire the temperature change of the tested piece, and further performing crack identification on the tested piece according to the acquired temperature change data.

Specifically, a thermal imager is adopted to collect the temperature of the detected area of the tested piece in real time, and thermal data is stored in a video mode. The sampling frequency of the thermal imager is above 100Hz, so that rapid temperature change can be captured. After the completion is sprayed to the magnetic, the host computer is handled the hot data of gathering, specifically is: compressing the video into a picture, averaging the temperature of each pixel point in each video on each frame, and arranging the average values according to the positions of the original pixel points to reconstruct a new image. Wherein the aggregation of the magnetic powder above the crack may result in an abnormally high or low temperature, and the identification of the crack may then be accomplished from the reconstructed image.

The shooting visual angle of the thermal imager is perpendicular to the surface of the tested piece so as to reduce the attenuation of infrared energy, and the temperature resolution of the thermal imager is better than 0.1 ℃; the magnetic powder particles are attracted to be aggregated by the leakage magnetic field generated by the cracks. The temperature difference between the magnetic powder particles and the test piece can be amplified due to the aggregation of the magnetic powder particles and the test piece, and the position of the crack can be judged by identifying the abnormal temperature difference.

And step three, demagnetizing the tested piece and recycling the magnetic powder.

Specifically, after detection is completed, the magnetizing power supply is turned off, the residual magnetism of the tested piece is eliminated by using an alternating-current demagnetization method, magnetic powder is not adsorbed on the surface of the tested piece after the magnetic powder loses the attraction of a leakage magnetic field, and the removal of the magnetic powder can be conveniently completed by means of vibration or wind power. Because the magnetic powder particles are not sensitive to impurities, the removed magnetic powder can be recycled for multiple times.

As shown in fig. 1, the test piece 1 is made of ferromagnetic material, the magnetic induction lines 2 are generated by a magnetizing device, when the test piece 1 has no crack, the magnetic induction lines 2 uniformly pass through, when the test piece 1 has a crack 3, the magnetic induction lines 2 reach the air from the test piece 1 to form a leakage magnetic field, and the corresponding magnetic powder 5 is magnetized and then attracted to gather above the crack to form a magnetic trace 4. The magnetic powder density at the crack position is higher than that of the non-crack area 6, so that the crack position and other parts of the tested piece 1 generate larger temperature difference, and the thermal contrast can be found at the crack position in the visual field of the thermal imager 9, so that the crack can be identified.

Referring to fig. 2, when the coil-type magnetization detection is adopted, the first magnetizing coil 7 and the second magnetizing coil 8 which are oppositely arranged at intervals can generate a relatively uniform magnetic field to magnetize the tested piece 1 integrally. The direction of the magnetic induction lines is consistent with the arrangement direction of the tested piece 1, and the magnetic powder spray gun 10 can spray uniform thermal magnetic powder to the surface of the tested piece 1 in space. When cracks exist on the tested piece 1, magnetic powder particles are attracted by the leakage magnetic field to be accumulated to form magnetic traces 4, and the thermal imager 9 records the whole process of forming the magnetic traces. After the magnetic powder spraying is finished, the upper computer 11 processes and analyzes the thermal image data.

Referring to fig. 3, when the magnetic yoke type magnetization detection is adopted, the magnetic yoke is adopted to locally magnetize the tested piece, the direction of the magnetic force line is along the placing direction of the magnetic yoke, the magnetic powder spray gun 10 is also suitable for spraying hot magnetic powder, and magnetic marks are formed above the cracks. Due to the accumulation of the magnetic powder, the temperature of the magnetic marks is higher than that of the non-crack area, and the thermal comparison can be found through the thermal imager 9, so that the cracks can be identified.

Referring to fig. 4 and 5, a standard test piece 30/50 and 60/100 of a1 type standard magnetic powder is tested. And (3) adopting a traditional magnetic powder detection method, and blowing off redundant non-related magnetic powder if not manually. The magnetic traces of the groove are completely buried and cracks cannot be identified.

The magnetic powder test pieces 30/50 and 60/100 are detected by the detection method provided by the embodiment, and the selected mode of heating the magnetic powder particles is detected. The defect on the notch of the test piece can be clearly seen from the detection result, which shows that the sensitivity of the conventional dry magnetic powder detection can be achieved while the magnetic powder detection process is optimized. Meanwhile, the method has little pollution to the tested piece, reduces the requirement of an operator, can adapt to the detection working condition of the high-temperature test piece, and has higher detection capability on the tiny cracks.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.