Device and method for measuring thermal expansion coefficient of rock at high temperature and high heating rate

Abstract

The invention provides a device and a method for measuring the thermal expansion coefficient of rock at high temperature and high temperature rise rate. The device comprises a graphite crucible, an induction heating device, a temperature monitoring device, an image acquisition device and a processing device, the induction heating device is used for performing induction heating on the graphite crucible, and the graphite crucible is used for bearing a rock sample and heating the rock sample; the temperature monitoring device is used for monitoring the temperature when the rock sample is heated in a non-contact manner, and the image acquisition device is used for acquiring an image when the rock sample is heated; and the temperature monitoring device and the image acquisition device are connected to the processing device. According to the invention, the temperature monitoring device and the image acquisition device are adopted to carry out non-contact observation on the strain condition of the rock surface, so that the thermal expansion coefficient of the rock under the conditions of high temperature and high heating rate can be accurately obtained, and reliable data support is provided for research and application of a microwave-assisted rock breaking technology.

Description

Technical Field

[0001] The invention relates to the field of rock mechanics analysis, in particular to a device and method for measuring the thermal expansion coefficient of rock at high temperature and high heating rate. Background Art

[0002] With the acceleration of industrialization, hard rock breaking technology plays an increasingly important role in mining, geological exploration and other fields. In recent years, microwave-assisted rock breaking, as a new hard rock pretreatment method, has attracted widespread attention because it can significantly reduce the mechanical strength of rocks. This technology induces the deterioration of the internal structure of rocks through microwave heating and assists mechanical crushing, thereby effectively improving the efficiency of hard rock processing.

[0003] However, in the research and application of microwave-assisted rock breaking technology, a key scientific issue is how to accurately obtain the thermophysical parameters of rocks under high heating rate conditions, especially the thermal expansion coefficient. In existing studies, due to the lack of thermophysical parameters at high heating rates, researchers usually use parameters at low heating rates for numerical simulation, which undoubtedly weakens the correlation between numerical simulation and actual rock behavior. Therefore, the development of a measurement device and method for rock thermophysical parameters at high heating rates is of great significance for microwave-assisted rock breaking.

[0004] There are currently two main technical difficulties in measuring the thermal expansion coefficient of rocks under high temperatures and high heating rates: one is the heating method of the rocks, and the other is the observation method of the thermal expansion of the rocks.

[0005] Resistance wire heating, infrared heating, laser irradiation heating and induction heating are several common heating methods, but the heating rate of resistance wire heating is slow and the maximum heating temperature is limited, which cannot meet the high temperature requirements of microwave heating of rocks. Although infrared heating has a faster heating rate, it often relies on a reflective surface to focus infrared rays on the sample, so the size of the heated sample is generally small. These limitations also restrict its application in this scenario; although laser irradiation heating has great advantages in heating capacity and heating rate, the laser can only achieve local heating (spot heating). Even if the laser movement path can be controlled, its heating uniformity is still difficult to guarantee; induction heating is a heating method with high energy utilization efficiency, but this method is mostly used in the field of heating metal materials and cannot directly meet the temperature uniformity requirements in the measurement of thermal expansion coefficient.

[0006] High temperature strain gauge method, interference method and digital image correlation (DIC) are currently the commonly used methods for high temperature strain measurement. As a contact measurement method, the high temperature strain gauge method is affected by temperature and needs to take temperature compensation measures. The quality of the adhesion between the strain gauge and the material surface will also affect the accuracy of the measurement. In addition, the high temperature strain gauge can only obtain single-point one-dimensional deformation data, and the amount of measurement data is also limited by the number of strain gauges pasted, which also limits the application of the strain gauge method. Non-contact interference methods, such as laser interferometry, can achieve high-precision measurement (sub-micron level), but they require precise laser interferometry systems and complex calibration procedures. Therefore, they have strict environmental requirements, especially vibration isolation requirements. In addition, the high cost of the interference system also limits its application.

[0007] At present, the testing device and method for the thermal expansion coefficient have the following deficiencies: The resistance wire heating method has the disadvantages of low heating rate and maximum heating temperature limitation, while infrared heating and laser heating have obvious local heating problems for heating larger samples. In addition, the existing induction heating methods are mostly used in the field of metal heating, and the temperature uniformity problem during the heating process is not considered.

[0008] Rock is an anisotropic material composed of minerals. Its overall thermal expansion during heating is affected by the thermal expansion of multiple minerals. Existing strain measurement methods mostly measure one-dimensional deformation data, and optical interferometry places extremely high demands on the measurement system. Summary of the invention

[0009] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate, including a graphite crucible, an induction heating device, a temperature monitoring device, an image acquisition device and a processing device.

[0010] The induction heating device is used to induction heat the graphite crucible, which is used to carry the rock sample and conduct the heat to the rock sample after being heated by the induction heating device, thereby heating the rock sample. The temperature monitoring device is used to non-contactly monitor the temperature of the rock sample when it is heated, and the image acquisition device is used to acquire images of the rock sample when it is heated. The temperature monitoring device and the image acquisition device are connected to the processing device. The temperature information and image information acquired by the temperature monitoring device and the image acquisition device can be observed in real time by the processing device and can be stored in the processing device.

[0011] When in use, the rock sample is placed in a graphite crucible, and the graphite crucible is inductively heated by an induction heating device, thereby heating the rock sample. Induction heating can quickly raise the temperature of the rock sample. During the heating process, a temperature monitoring device and an image acquisition device are used to collect the temperature and image of the rock sample, which is convenient for subsequent analysis of the thermophysical parameters of the rock sample under high temperature and high heating rate conditions.

[0012] Furthermore, it also includes a quartz cover, which is used to close the opening of the graphite crucible, block the air flow inside and outside the graphite crucible, reduce the influence of the air flow on the imaging, and play a role of heat preservation.

[0013] Furthermore, a heat plate is provided at the bottom of the graphite crucible for placing the rock sample. Of course, in order to achieve a high heating rate, the heat plate needs to be made of a material with a high thermal conductivity coefficient, such as copper, and can be made of a plurality of copper discs stacked together or a single complete copper column block.

[0014] Furthermore, it also includes an auxiliary light source for illuminating rock samples to facilitate the collection of rock images.

[0015] Furthermore, the wavelength range of the auxiliary light source is 400-500 nm. It has been found through experiments that these wavelengths are not easily distorted by the change of refractive index caused by temperature.

[0016] Furthermore, a filter is included, the wavelength of light passing through the filter is adapted to the auxiliary light source, and the filter is arranged between the image acquisition device and the rock sample. The wavelength of 400-500nm light waves is obviously different from the wavelength of thermal radiation, and thermal radiation can be more easily blocked by the filter.

[0017] Furthermore, the image acquisition device is a CCD camera, preferably a high-resolution grayscale camera. The grayscale camera has a stronger sensitivity to light and does not require color information. It only captures light intensity data, can provide better contrast, and helps to improve the quality of image acquisition.

[0018] Furthermore, the temperature monitoring device is an infrared camera.

[0019] Furthermore, the induction heating device includes an induction coil, and a coolant is provided in the induction coil.

[0020] The present invention also provides a method for measuring the thermal expansion coefficient of rock at high temperature and high heating rate, which is used in the above-mentioned device and comprises the following steps: S1. Install a temperature monitoring device and place a graphite crucible without a rock sample at the induction heating device.

[0021] S2. Start the temperature monitoring device, start collecting temperature information, start the induction heating device; conduct a trial run of heating the graphite crucible, and use the processing device to observe and store data.

[0022] S3. Turn off the induction heating device, remove the graphite crucible, and wait for it to cool naturally.

[0023] S4. Place the rock sample into a graphite crucible, install the image acquisition device, and connect the processing device to adjust the image size.

[0024] S5, start the temperature monitoring device and the image acquisition device, start collecting temperature and image information, and start the induction heating device.

[0025] S6. Import the image information into the processing software to obtain the surface displacement and strain data of the rock sample, and combine it with the temperature information to obtain the thermal expansion data.

[0026] The present invention uses induction heating to rapidly heat up the graphite crucible, thereby rapidly heating up the rock sample, ensuring high temperature and high heating rate. In addition, the present invention uses a temperature monitoring device and an image acquisition device to perform non-contact observation of the strain condition on the rock surface, which can accurately obtain the thermal expansion coefficient of the rock under high temperature and high heating rate conditions, providing reliable data support for the research and application of microwave-assisted rock breaking technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the present invention.

[0029] In the figure: 1. graphite crucible; 2. heat sink; 3. rock sample; 4. quartz cover; 5. induction coil; 6. coolant; 7. auxiliary light source; 8. image acquisition device; 9. temperature monitoring device; 10. processing device; 11. filter. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Embodiment 1:

[0032] See also Figure 1 The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate of this embodiment includes a graphite crucible 1, an induction heating device, a temperature monitoring device 9, an image acquisition device 8 and a processing device 10. The graphite crucible 1 has the characteristics of high temperature resistance, strong thermal conductivity, good corrosion resistance, long service life, etc., a small thermal expansion coefficient, and a certain resistance to strain against rapid cooling and rapid heating.

[0033] The induction heating device is used to perform induction heating on the graphite crucible 1. The specific parameters of the induction coil 5 in the induction heating device need to be optimized to ensure that it can efficiently heat the graphite crucible 1 and ensure the heating uniformity of the rock sample 3. In addition, the inductance of the induction coil 5 needs to be calculated to confirm that its inductance matches the inductance of the induction heating device to ensure the normal operation of the induction heating system.

[0034] The induction coil 5 in this embodiment is a copper round tube coil. The coil is hollow and provided with a coolant 6, such as water, which is used in conjunction with a water pump and a water tank to circulate the coolant 6 to dissipate heat.

[0035] The graphite crucible 1 is used to carry the rock sample 3, and after being heated by the induction heating device, the heat is transferred to the rock sample 3, thereby heating the rock sample 3. A crucible working platform can also be provided to place the graphite crucible 1, and support lifting and rotation to adjust the position of the graphite crucible 1. A quartz cover 4 can also be configured to close the opening of the graphite crucible 1, block the air flow inside and outside the graphite crucible 1, reduce the influence of the air flow on the imaging, and play a role of heat preservation.

[0036] This embodiment also includes a heat plate 2, which is arranged at the bottom of the graphite crucible 1 and is used to place the rock sample 3. Of course, in order to achieve a high heating rate, the heat plate 2 needs to be made of a material with a high thermal conductivity coefficient, such as copper, and can be made of a plurality of copper discs stacked together or a single complete copper column block. The use of the heat plate 2 can make the rock sample 3 heated more evenly.

[0037] The temperature monitoring device 9 is used for non-contact monitoring of the temperature of the rock sample 3 when it is heated, and the image acquisition device 8 is used for acquiring images of the rock sample 3 when it is heated. The temperature monitoring device 9 and the image acquisition device 8 are connected to the processing device 10. The temperature information and image information acquired by the temperature monitoring device 9 and the image acquisition device 8 can be observed in real time by the processing device 10 and can be stored in the processing device 10.

[0038] A sealed working chamber can also be selected to achieve vacuum or inject low-pressure inert gas to protect the equipment from high-temperature oxidation. In addition, it can also reduce the impact of gas flow on the sample surface temperature and reduce the interference of gas flow on image acquisition. When the rock sample 3 is likely to oxidize at high temperature, a sealed working chamber should be configured to isolate oxygen.

[0039] This embodiment also includes an auxiliary light source 7 for irradiating the rock sample 3 to increase the brightness and facilitate the collection of rock images. Preferably, the wavelength range of the auxiliary light source 7 is 400-500nm. It has been found through experiments that these wavelengths are not easily distorted in the refractive index changes caused by temperature. Further, it also includes a filter 11, the wavelength of the light passing through the filter 11 is adapted to the auxiliary light source 7, and the filter 11 is arranged between the image acquisition device 8 and the rock sample 3. The light waves of 400-500nm are obviously different from the wavelengths of thermal radiation, and thermal radiation can be more easily blocked by the filter 11.

[0040] In this embodiment, the temperature monitoring device 9 is preferably an infrared camera, and the image acquisition device 8 is a CCD camera, and is further preferably a high-resolution grayscale camera. The grayscale camera has a stronger sensitivity to light and does not require color information. It only captures light intensity data, can provide better contrast, and helps to improve the quality of image acquisition.

[0041] The device uses the rock surface texture as the feature point for image processing, without the need for additional surface processing, such as the production of speckles.

[0042] Embodiment 2:

[0043] This embodiment is a method for measuring the thermal expansion coefficient of rock at high temperature and high heating rate, which is used in the device in the above embodiment and includes the following steps: The rock sample 3 is set as a circular sheet, and the plane size is equivalent to or slightly smaller than the soaking plate 2. According to the inductance matching range of the induction heating device, the number of turns and size of the induction coil 5 are preliminarily selected. According to the size and number of turns of the induction coil 5, the following parameters are determined: the size of the graphite crucible 1, the size of the soaking plate 2, and the size of the rock sample 3.

[0044] Verify the heating capacity of the induction coil 5 on the graphite crucible 1 within the physical parameter range of the induction heating device, and determine the appropriate physical parameter range, mainly the current size, according to the heating requirements (temperature increase size, heating rate).

[0045] On this basis, the spacing between the induction coils 5, the distance between the induction coils 5 and the graphite crucible 1, and the thickness of the heat spreader 2 are adjusted, the uniformity of the surface temperature of the rock sample 3 is used as the optimization criterion, and the standard deviation and range of the surface temperature of the rock sample 3 and the standard deviation and range of the temperature on the side of the rock sample 3 are used as optimization control indicators to optimize the temperature uniformity.

[0046] After the optimization is completed, if the temperature uniformity still does not meet the requirements, it is necessary to reduce the size of the graphite crucible 1, the heat plate 2, and the rock sample 3, and then verify the temperature uniformity of the upper surface and the side of the rock sample 3.

[0047] Based on the design method of the aforementioned induction coil 5, graphite crucible 1, heat sink 2, and rock sample 3, an instrument or sample that meets the requirements is customized, and a suitable heating current is confirmed.

[0048] Connect the induction coil 5, water pump, water tank and water pipe in place, turn on the water pump, and after stable operation for 1-3 minutes, confirm whether there is obvious water leakage. After checking that there is no problem, turn off the water pump and connect the relevant power cord of the induction heating device.

[0049] Install the temperature monitoring device 9 in place, and aim the lens at the heating position as vertically as possible.

[0050] Put a graphite crucible 1 for testing without a sample in it, start the water pump, wait for it to run stably, start the temperature monitoring device 9, start recording, and then start the induction heating device, adjust the current to the current range determined above, generally above 250A, for example, 300A. At this time, only the graphite crucible 1 is heated for trial operation, and at this current, it is heated for one minute, and the data of the temperature monitoring device 9 is observed to confirm the heating effect and record the information.

[0051] Turn off the induction heating device, but keep the water pump running for 1-3 minutes. Remove the graphite crucible 1 used for testing and wait for it to cool naturally.

[0052] Place the soaking plate 2 and the rock sample 3 into the graphite crucible 1 in sequence and adjust their positions. Install the image acquisition device 8 after it is ready, connect the computer to adjust the camera to a suitable frame size, install the auxiliary light source 7, and install the narrow-band filter 11.

[0053] The water pump power supply is turned on, and after the water pump runs stably, the image acquisition device 8 and the temperature monitoring device 9 are turned on, and the induction heating device is turned on to acquire the surface image of the rock sample 3 and record the surface temperature.

[0054] The image data is imported into the DIC processing software to obtain the surface displacement and strain data of the rock sample 3, and the thermal expansion data is obtained by combining the data processing of the temperature monitoring device 9.

[0055] The present invention adopts induction heating, regulates the current size, optimizes the coil spacing, the thickness of the heat plate 2, and the size of the graphite crucible 1, and can heat to the target high temperature (above 500°C), and the heating rate meets the requirement (500°C / min).

[0056] The present invention utilizes the heat spreader 2 with excellent thermal conductivity to quickly transfer the temperature to the rock sample 3. The introduction of the heat spreader 2 can make the rock temperature rise more uniformly. The thickness of the heat spreader 2 can be adjusted by increasing or decreasing the number of the heat spreaders 2 or replacing the heat spreaders 2 with different thicknesses. In addition, the diameter size of the graphite crucible 1 and the diameter size of the rock sample 3 can also be changed to achieve a more stringent temperature uniformity effect.

[0057] The present invention utilizes an infrared camera to accurately grasp the temperature rise state of the rock sample 3 and determine the temperature uniformity of the surface of the rock sample 3 .

[0058] The present invention supports the configuration of a sealed cabin, which can prevent the equipment from high-temperature oxidation on the one hand, and on the other hand reduce the impact of gas convection on the surface temperature of the rock sample 3 and reduce the interference of air flow on image acquisition.

[0059] The present invention adopts a shorter wavelength light source in combination with a narrow bandpass filter 11 to reduce the influence of surface thermal radiation of the graphite crucible 1 and the rock sample 3 on image acquisition under high temperature conditions, thereby achieving clear image acquisition.

[0060] The present invention can utilize the texture of the rock surface as high-temperature speckle, thereby ensuring the stability of the speckle, and at the same time being able to observe richer real-time information on the surface, such as grain deformation, crack generation and development, etc.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate, characterized in that: It includes a graphite crucible, an induction heating device, a temperature monitoring device, an image acquisition device and a processing device; the induction heating device is used to induction heat the graphite crucible, and the graphite crucible is used to carry and heat the rock sample; the temperature monitoring device is used to non-contact monitor the temperature of the rock sample when it is heated, and the image acquisition device is used to acquire images of the rock sample when it is heated; the temperature monitoring device and the image acquisition device are connected to the processing device.

2. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: A quartz cover is also included, which is used to close the opening of the graphite crucible to block air flow and keep the temperature.

3. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: It also includes a heat soaking plate, which is arranged at the bottom of the graphite crucible and is used for placing the rock sample.

4. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: An auxiliary light source is also included for illuminating rock samples.

5. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 4, characterized in that: The wavelength range of the auxiliary light source is 400-500nm.

6. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 5, characterized in that: It also includes a filter, the wavelength of light passing through the filter is adapted to the auxiliary light source, and the filter is arranged between the image acquisition device and the rock sample.

7. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: The image acquisition device is a CCD camera.

8. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: The temperature monitoring device is an infrared camera.

9. The device for measuring the thermal expansion coefficient of rock at high temperature and high heating rate according to claim 1, characterized in that: The induction heating device comprises an induction coil, in which a cooling liquid is arranged.

10. A method for measuring the thermal expansion coefficient of rock at high temperature and high heating rate, used in the device as claimed in claim 1, characterized in that: The following steps are involved: S1. Install a temperature monitoring device and place a graphite crucible without a rock sample at the induction heating device; S2, start the temperature monitoring device, start collecting temperature information, and start the induction heating device; Graphite crucible heating test run, using processing equipment to observe and store data; S3, turn off the induction heating device, remove the graphite crucible, and wait for it to cool naturally; S4, placing the rock sample into a graphite crucible, installing an image acquisition device, and connecting the processing device to adjust the image size; S5, start the temperature monitoring device and the image acquisition device, start collecting temperature and image information, and start the induction heating device; S6. Import the image information into the processing software to obtain the surface displacement and strain data of the rock sample, and combine it with the temperature information to obtain the thermal expansion data.

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