CN107764659B - Coal rock mechanical testing device and method under low-temperature liquid nitrogen impact - Google Patents
Coal rock mechanical testing device and method under low-temperature liquid nitrogen impact Download PDFInfo
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- CN107764659B CN107764659B CN201711190457.3A CN201711190457A CN107764659B CN 107764659 B CN107764659 B CN 107764659B CN 201711190457 A CN201711190457 A CN 201711190457A CN 107764659 B CN107764659 B CN 107764659B
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 198
- 239000007788 liquid Substances 0.000 title claims abstract description 113
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 99
- 239000003245 coal Substances 0.000 title claims abstract description 95
- 239000011435 rock Substances 0.000 title claims abstract description 22
- 238000012360 testing method Methods 0.000 title claims abstract description 19
- 238000000034 method Methods 0.000 title claims description 17
- 239000006260 foam Substances 0.000 claims abstract description 31
- 238000007789 sealing Methods 0.000 claims abstract description 31
- 238000002591 computed tomography Methods 0.000 claims abstract description 8
- 238000002474 experimental method Methods 0.000 claims abstract description 8
- 230000009471 action Effects 0.000 claims abstract description 7
- 238000009413 insulation Methods 0.000 claims description 57
- 229910052755 nonmetal Inorganic materials 0.000 claims description 28
- 238000003384 imaging method Methods 0.000 claims description 6
- 238000003825 pressing Methods 0.000 claims description 5
- 230000008569 process Effects 0.000 claims description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000005520 cutting process Methods 0.000 claims description 3
- 238000005553 drilling Methods 0.000 claims description 3
- 239000000741 silica gel Substances 0.000 claims description 3
- 229910002027 silica gel Inorganic materials 0.000 claims description 3
- 230000001360 synchronised effect Effects 0.000 claims description 3
- 238000005516 engineering process Methods 0.000 abstract description 4
- 230000006835 compression Effects 0.000 abstract description 2
- 238000007906 compression Methods 0.000 abstract description 2
- 238000007654 immersion Methods 0.000 abstract 1
- 230000008859 change Effects 0.000 description 5
- 230000035699 permeability Effects 0.000 description 5
- 238000011160 research Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 4
- 238000011161 development Methods 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 241000863480 Vinca Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000010257 thawing Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/003—Generation of the force
- G01N2203/0042—Pneumatic or hydraulic means
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- Analysing Materials By The Use Of Radiation (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
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Abstract
The invention relates to a coal rock mechanical testing device under low-temperature liquid nitrogen impact, which mainly comprises a liquid nitrogen sealing device, a loading device, a liquid level device, an infrared control device, a liquid nitrogen supply device and an industrial CT scanning device. The liquid nitrogen sealing device mainly comprises a sleeve and a base to form a closed environment, so that liquid nitrogen dissipation is reduced. The liquid level elevation device consists of a foam plate and a baffle plate, the infrared control device consists of two infrared emitters and sensors, and the heights of the foam plate and the baffle plate are changed along with the liquid level height of liquid nitrogen due to the action of buoyancy. The baffle cooperates with the infrared emitter, and the sensor receives signals and then indicates the motor to work through the PLC controller. Through automatic liquid nitrogen supply system, the device can realize that the uniaxial compression experiment is carried out under the condition of liquid nitrogen immersion, can study the mechanical properties of coal and rock under the ultralow temperature condition, further cooperates with CT scanning technology, can explore the fracturing mechanism of the coal body under the simultaneous action of stress field and ultralow temperature field.
Description
Technical Field
The invention belongs to an experimental testing device, and particularly relates to a coal rock mechanical testing device and method under low-temperature liquid nitrogen impact.
Background
Coal is an important strategic resource in China, and the occupied ratio of the coal is the largest in the energy sources in China. The permeability of the coal seam is a key parameter for gas extraction and coal seam development. The coalbed methane reserves of China are huge, but most coalbeds of China belong to low permeability coalbeds, gas is not easy to extract, and environmental pollution and resource waste are caused. Therefore, the research on the permeability-increasing method of the low-permeability coal bed is a key problem of high-efficiency extraction of coal bed gas and gas control. The liquid nitrogen and other low-temperature fluids are injected into the coal bed to influence the micro pore structure of the coal bed, and change the permeability and mechanical properties of the coal bed, so that the method is an effective way for coal anti-reflection and fracturing.
Many expert scholars have made a great deal of intensive research on the anti-reflection of liquid nitrogen impact coal and have obtained a certain research result. The published patent document WO2017/016168 A1 discloses a coal rock sample liquid nitrogen circulation freeze thawing anti-reflection simulation test system and method, guo Xiaokang and the like of Hebei university of science and technology are used for carrying out liquid nitrogen semi-leaching coal fracturing anti-reflection test research by utilizing self-designed experimental devices, and the experimental devices can be used for researching the permeability and mechanical properties of coal rock after liquid nitrogen impact, but cannot be used for researching the change of coal rock properties when an ultralow temperature field and a stress field generated by liquid nitrogen act simultaneously, and have a certain gap with engineering practice. The microscopic structural change of the coal rock is observed by using a CT technology, and the method has certain limitation.
Disclosure of Invention
The invention aims to provide an automatic, visual and convenient-to-operate coal rock mechanical testing device under low-temperature liquid nitrogen impact. The device can simulate the state of loaded coal under the impact of liquid nitrogen, further research the change of the mechanical property and the permeability of the coal rock under the ultralow temperature and the uniaxial compression state, and explore the microstructure change of the coal rock in the process by combining with a CT technology.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
the coal rock mechanical testing device under the impact of low-temperature liquid nitrogen comprises a liquid nitrogen sealing device, a loading device, a liquid level elevation device, an infrared control device, a liquid nitrogen replenishing device and an industrial CT scanning device;
the liquid nitrogen sealing device comprises a nonmetallic heat insulation sleeve, a heat insulation base and a sealing cover; the nonmetallic heat insulation sleeve is arranged in a base groove of the heat insulation base, the sealing cover is positioned at the top end of the nonmetallic heat insulation sleeve, and a sleeve groove is formed in the inner side wall of the nonmetallic heat insulation sleeve;
the loading device comprises a servo loading instrument, a pressure head and a gasket; the pressure head passes through the sealing cover and is pressed on the gasket, the gasket is positioned inside the nonmetal heat insulation sleeve and positioned at the top end of the coal sample which is also positioned inside the nonmetal heat insulation sleeve, and the servo loader applies axial pressure to the pressure head;
the liquid level elevation device is positioned in the nonmetal heat insulation sleeve and comprises a foam plate and a baffle plate; the baffle plate is fixedly arranged on the foam plate;
the infrared control device comprises an infrared emission device, an infrared sensor, a PLC controller and a wire; the infrared sensor and the infrared emission device are oppositely arranged in parallel, and are both arranged on the sealing cover, the upper end of the baffle plate penetrates through the sealing cover and floats between the infrared sensor and the infrared emission device, and the infrared sensor is connected with the PLC controller through a lead;
the liquid nitrogen replenishing device comprises a motor, a gear, a rack bar, a piston, a liquid nitrogen tank, a replenishing pipeline and a valve, wherein the motor is connected with the PLC through a wire; the motor drives a piston in the liquid nitrogen tank to move, so that liquid nitrogen is conveyed to the interior of the nonmetallic heat-insulating sleeve through a supply pipeline;
the industrial CT scanning device comprises an X-ray source, a receiver and a computer; wherein the X-ray source and the receiver are fixedly arranged at two sides of the outer part of the nonmetallic heat insulation sleeve, and a space is arranged between the nonmetallic heat insulation sleeve and the nonmetallic heat insulation sleeve respectively; the imaging plane center of the receiver, the coal sample center and the X-ray source center are positioned on the same horizontal straight line, the imaging plane of the receiver is vertical to the straight line, and the image received by the receiver is stored in a computer.
Further, in the liquid level elevation device, the main body structure of the foam plate is a circular arc-shaped block body and protrudes to form a tail part at the middle part of the outer edge of the main body structure, the tail part of the foam plate is inserted into a sleeve groove of the nonmetal heat insulation sleeve to be connected in a sliding mode, and the foam plate drives the baffle plate to lift under the buoyancy effect.
Further, in the infrared control device, the frame structure of the infrared emission device is a groove plate with scales, and two slidable infrared emitters, namely a first infrared emitter and a second infrared emitter, are arranged on the groove plate, and the positions of the first infrared emitter and the second infrared emitter can be selected through the height of a coal sample and the height of the liquid nitrogen liquid level.
Further, in the liquid nitrogen replenishing device, the rack bar is in close contact with the upper gear of the motor, and the lower end of the rack bar is connected with the piston, so that the piston is synchronous with the working state of the motor.
Further, the liquid nitrogen tank has good tightness and heat insulation, the lower side wall of the liquid nitrogen tank is communicated with one end of a supply pipeline, the other end of the supply pipeline is communicated with the lower side wall of the nonmetallic heat insulation sleeve, and a valve is arranged on the supply pipeline.
The testing method of the coal rock mechanical testing device under the impact of low-temperature liquid nitrogen comprises the following steps:
step one, preparing an experiment, namely taking out coal blocks from the mine, and drilling and cutting the coal blocks into standard coal samples;
step two, installing equipment, namely placing a coal sample in the center of the heat insulation base, and placing a gasket on the upper part of the coal sample; placing the foam board and the baffle plate into a nonmetallic heat insulation sleeve, and embedding the tail part of the foam board into a sleeve groove of the nonmetallic heat insulation sleeve; inserting the bottom of the non-metal heat insulation sleeve into a base groove, and coating silica gel on the contact part of the non-metal heat insulation sleeve and the heat insulation base to prevent liquid nitrogen from escaping; the sealing cover is covered, the infrared emission device on the sealing cover is parallel and opposite to the infrared sensor on the nonmetallic heat insulation sleeve, and the baffle is arranged between the infrared emission device and the nonmetallic heat insulation sleeve; then placing the gasket into a pressure head, and pressing the gasket at the bottom of the pressure head;
step three, connecting an infrared sensor, a PLC controller and a motor through wires; the first infrared emitter is adjusted to the scale position with the same height as the coal sample, and the second infrared emitter is adjusted to the scale position with the highest height of the set liquid nitrogen surface; opening the first infrared emitter and the second infrared emitter, switching on a power supply of the motor, and opening a valve;
step four, starting a servo loading instrument to apply axial pressure in the liquid nitrogen immersing process of the coal sample, so that the coal sample is simultaneously in an ultralow temperature field and an axial stress field; simultaneously, an X-ray source is turned on to emit X-rays, and a receiver is utilized to collect an internal structure image of the coal sample;
turning off the X-ray source after the experiment is finished, and unloading axial pressure by using a servo loader; closing the infrared emission device and closing the motor; taking down the pressure head, the nonmetal heat insulation sleeve and the gasket, and taking down the coal sample and storing; closing the valve, and keeping the residual liquid nitrogen in the liquid nitrogen tank in a sealed and heat-insulating manner.
Further, in the first step, the coal sample isΦStandard coal sample of 50×100 mm.
In the third step, the infrared sensor, the PLC and the motor are connected through wires; the first infrared emitter is adjusted to the position with the same scale as the height of the coal sample by 100mm, and the second infrared emitter is adjusted to the position with the same scale by 150mm, namely the scale with the 100mm of the first infrared emitter is the height of the coal sample, and the highest height of the liquid nitrogen surface exceeding the coal sample is set to be 50mm; opening the first infrared emitter and the second infrared emitter, switching on a power supply of the motor, and opening a valve;
and can realize the automatic supply of liquid nitrogen through infrared control device, the infrared control device working procedure is as follows: (1) the initial baffle is below 100mm in scale, the infrared sensor receives two infrared signals, and the motor rotates to drive the rack rod and the piston to be pressed into liquid nitrogen; the baffle is continuously raised along with the addition of the liquid nitrogen; (2) when the baffle plate is lifted to the position of 100mm of the scale to cover the infrared first infrared emitter, the infrared sensor receives an infrared signal, the original command is kept, the motor continues to work, and liquid nitrogen continues to be added; (3) when the baffle plate is lifted to the position of 150mm of the scale to cover the second infrared emitter, the infrared sensor cannot receive infrared signals, the motor is controlled to stop working, liquid nitrogen is not added any more, and the liquid nitrogen surface is lowered; (4) when the baffle just falls below the scale of 150mm, the second infrared emitter leaks, the infrared sensor receives an infrared signal, the original command is kept, the motor does not work, and the liquid nitrogen surface continues to descend; (5) and (4) automatically repeating the actions of (1) - (4) when the baffle plate is lowered below the scale of 100 mm.
Compared with the prior art, the invention has the following beneficial effects: the invention puts the coal sample on the heat insulation base, the sleeve is inserted into the base groove for fixing, the upper part of the coal sample is put with a gasket, then the sleeve is covered with a sealing cover for sealing, and the sleeve is put into the pressure head; the foam plate drives the baffle to rise along with the rise of the liquid level, and controls the motor through the infrared sensor so as to automatically supply the liquid nitrogen; and meanwhile, a certain pressure is applied to the axial direction of the pressure head, a simulation experiment is carried out on the coal sample under the simultaneous action of a stress field and an ultralow temperature field, and the crack distribution and development condition of the internal structure of the coal sample are obtained by combining a CT scanning device, so that the operation is simple and convenient.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a side view of an infrared emitting device of the present invention.
Fig. 3 is a top view of a foam deck in accordance with the present invention.
The technical features represented by the numbers in the figures are as follows:
1-an insulating base; 2-a non-metallic insulating sleeve; 3-foam board; 4-coal sample; 5-a gasket; 6-pressing head; a 7-X-ray source; 8-an infrared emission device; 9-an infrared sensor; 10-baffle plates; 11-a base groove; 12-sleeve grooves; 13-X rays; 14-an electric motor; 15-a liquid nitrogen tank; 16-a piston; 17-axial pressure of the servo loader; 18-sealing the cover; a 19-X-ray receiver; 20-conducting wires; 21-a rack bar; 22-a first infrared emitter; 23-a second infrared emitter; 24-a supply line; 25-valve; 26-a PLC controller; 27-a computer; 28-gear.
Detailed Description
The present invention will be described in further detail with reference to examples, but embodiments of the present invention are not limited thereto.
As shown in fig. 1-3, a coal rock mechanical testing device under low-temperature liquid nitrogen impact mainly comprises: the electric equipment involved in the device is powered by the prior art, and the specific structure and specific power supply mode of the electric equipment are not repeated.
The liquid nitrogen sealing device comprises a nonmetallic heat insulation sleeve 2, a heat insulation base 1 and a sealing cover 18; the heat insulation base 1 is a stepped cylinder, a round base groove 11 is formed in the uppermost round table, the nonmetal heat insulation sleeve 2 can be inserted into the base groove 11 in a matched mode to be fixed, the inside of the sleeve is sealed, and the sealing cover 8 is arranged at the top end of the nonmetal heat insulation sleeve 2; the side wall of the non-metal heat insulation sleeve 2 is provided with a sleeve groove 12, and the tail part of the foam board 3 can be accommodated and fixed in the sleeve groove in a sliding way.
The loading device comprises a servo loading instrument (not shown in the figure), a pressure head 6 and a gasket 5; the lower part of the pressure head 6 is positioned in the nonmetal insulating nonmetal heat insulating sleeve 2, the lower end of the pressure head is pressed in a groove of the gasket 5, the lower part of the gasket 5 is a coal sample 4, the upper part of the pressure head 6 penetrates out of the sealing cover 8 and is positioned outside the nonmetal insulating nonmetal heat insulating sleeve 2, the axial pressure 17 can be precisely controlled and applied to the pressure head 6 through a servo loader, and the gasket 5 can uniformly stress the coal sample, and the servo loader is an RLW-500G tester of the company of Shannon laboratory instruments, inc. of vinca.
The liquid level elevation device comprises a foam plate 3 and a baffle plate 10; the foam board 3 is a circular arc-shaped block body and protrudes to form a tail part at the middle part of the outer edge of the foam board, as shown in fig. 3, wherein the tail part of the foam board 3 is inserted into the sleeve groove 12 for sliding connection so as to prevent the foam board 3 from swinging along with uneven buoyancy when liquid nitrogen rises or falls to influence the experiment; meanwhile, due to the buoyancy of the liquid nitrogen, the foam board 3 can drive the baffle 10 to lift.
The infrared control device comprises an infrared emission device 8, an infrared sensor 9, a wire 20 and a PLC (programmable logic controller) 26; the frame structure of the infrared emission device 8 is a groove plate with scales, and two slidable infrared emitters, namely a first infrared emitter 22 and a second infrared emitter 23, are arranged on the groove plate, and the positions of the first infrared emitter 22 and the second infrared emitter 23 can be selected through the height of a coal sample and the liquid nitrogen liquid level; the infrared sensor 9 and the infrared emission device 8 are oppositely arranged in parallel and are fixedly connected to the sealing cover, and the baffle 10 penetrates through the sealing cover and floats between the two devices; the PLC controller 26 is connected with the infrared sensor 9 through a wire 20.
The liquid nitrogen replenishing device comprises a motor 14, a gear 28, a rack bar 21, a piston 16, a liquid nitrogen tank 15, a replenishing pipeline 24 and a valve 25; wherein the motor 14 is connected with the PLC 26 through a wire 20, and the infrared sensor 9 transmits signals to the PLC 26 and then controls the motor 14 to operate according to the signals of the PLC 26; the rack bar 21 is closely contacted with a gear 28 on the motor 14, and the lower end of the rack bar 21 is connected with the piston 16, so that the working state of the piston 16 and the working state of the motor 14 are synchronous; the liquid nitrogen tank 15 has good tightness and heat insulation, the lower side wall of the liquid nitrogen tank is communicated with one end of a supply pipeline 24, the other end of the supply pipeline 24 is communicated with the lower side wall of the nonmetallic heat insulation sleeve 2, and a valve 25 is arranged on the supply pipeline 24.
The industrial CT scanning device comprises an X-ray source 7, a receiver 19 and a computer 27; wherein the X-ray source 7 and the receiver 19 are fixedly arranged on two sides of the outer part of the non-metal heat-insulating sleeve 2 through a bracket (common technical means are not shown in the drawing) and are respectively provided with a space between the non-metal heat-insulating sleeve 2; the center of the imaging plane of the receiver 19, the center of the coal sample 4 and the center of the X-ray source 7 are positioned on the same horizontal straight line, and the imaging plane of the receiver 19 is vertical to the straight line; the X-ray source 7 receives an image of the internal structure of the coal sample 4 by emitting X-rays and receiving the X-rays by the receiver 19, and transmits the image to the computer 27 for storage.
The coal rock mechanical testing method under the impact of low-temperature liquid nitrogen utilizes the coal rock mechanical testing device under the impact of low-temperature liquid nitrogen, and comprises the following steps:
step one, preparing experiments, taking out coal blocks from ores, drilling and cutting the coal blocks intoΦStandard coal sample 4 of 50×100 mm;
step two, placing a coal sample 4 in the center of the heat insulation base 1, and placing a gasket 5 on the upper part of the coal sample 4; placing the foam board 3 together with the baffle plate 8 into the nonmetallic heat insulation sleeve 2, wherein the upper part of the foam board 3 is embedded into a sleeve groove 12 on the wall surface of the nonmetallic heat insulation sleeve 2 as shown in fig. 3, so as to facilitate the fixation of the foam board 3; placing the prepared nonmetallic heat-insulating sleeve 2 on the heat-insulating base 1, wherein the bottom of the nonmetallic heat-insulating sleeve 2 is inserted into the base groove 11, and coating silica gel on the contact part of the nonmetallic heat-insulating sleeve 2 and the heat-insulating base 1 to prevent liquid nitrogen from escaping; the sealing cover 18 is covered, the infrared emission device on the sealing cover 18 is parallel and opposite to the infrared sensor 9 on the nonmetallic heat insulation sleeve, and the baffle 10 is arranged between the infrared emission device and the nonmetallic heat insulation sleeve; then placing a pressure head 6, wherein the bottom of the pressure head 6 is aligned with a groove on the gasket 5;
connecting the lead wire 20 on the infrared sensor 9 with the motor 14 through the PLC 26; the first infrared emitter 22 is adjusted to the position with the same scale as the height of the coal sample 4 by 100mm, the second infrared emitter 23 is adjusted to the position with the same scale by 150mm, namely, the scale with the 100mm of the first infrared emitter 22 is the height of the coal sample, and the highest height of the liquid nitrogen surface exceeding the coal sample 4 is set to be 50mm; the first infrared emitter 22 and the second infrared emitter 23 are turned on, the power supply of the motor 14 is turned on, and the valve 25 is turned on;
the automatic supply of liquid nitrogen can be realized through an infrared control device, and the working procedure of the infrared control device is as follows: (1) the baffle 10 is below the scale of 100mm, the infrared sensor 9 receives two infrared signals, the motor 14 rotates to drive the rack rod 21 and the piston 16 to be pressed into liquid nitrogen; with the addition of liquid nitrogen, the baffle 10 is continuously raised; (2) when the baffle 10 rises to the position of 100mm, which shields the first infrared emitter 22, the infrared sensor 9 receives an infrared signal, the original command is kept, the motor 14 continues to work, and liquid nitrogen continues to be added; (3) when the baffle 10 rises to the position of 150mm to cover the second infrared emitter 23, the infrared sensor 9 cannot receive infrared signals, the motor 14 is controlled to stop working, liquid nitrogen is not added any more, and the liquid nitrogen level is lowered; (4) when the baffle 10 just falls below the scale 150mm, the second infrared emitter 23 leaks out, the infrared sensor 9 receives an infrared signal, the original command is kept, the motor 14 does not work, and the liquid nitrogen surface continues to descend; (5) when the baffle plate is lowered to be below 100mm of the scale, the actions (1) - (4) are automatically repeated;
step four, starting a servo loading instrument to apply axial pressure 17 in the liquid nitrogen immersing process of the coal sample 4, so that the coal sample is simultaneously in an ultralow temperature field and an axial stress field; simultaneously, the X-ray source 7 is turned on to emit X-rays 13, and the receiver 19 is utilized to collect the internal structure of the coal sample 4;
turning off the X-ray source 7 after the experiment is finished, and unloading the axial pressure 17 by using a servo loader; closing the infrared emission device, and closing the power supply of the motor 14; taking down the pressure head 6, the nonmetal heat insulation sleeve 2 and the gasket 5, taking down the coal sample 4 and storing; valve 25 is closed and the remaining liquid nitrogen in liquid nitrogen tank 15 is kept sealed and insulated.
The present invention is not limited to the preferred embodiments described above, and any person skilled in the art will recognize that equivalent embodiments with modifications or variations can be made without departing from the scope of the invention.
Claims (5)
1. The coal rock mechanical testing device under low-temperature liquid nitrogen impact is characterized by comprising a liquid nitrogen sealing device, a loading device, a liquid level device, an infrared control device, a liquid nitrogen supply device and an industrial CT scanning device;
the liquid nitrogen sealing device comprises a nonmetal heat insulation sleeve (2), a heat insulation base (1) and a sealing cover (18); the nonmetal heat insulation sleeve (2) is arranged in a base groove (11) of the heat insulation base (1), the sealing cover (18) is positioned at the top end of the nonmetal heat insulation sleeve, and a sleeve groove (12) is formed in the inner side wall of the nonmetal heat insulation sleeve;
the loading device comprises a servo loading instrument, a pressure head (6) and a gasket (5); the pressure head (6) passes through the sealing cover (18) and is pressed on the gasket (5), the gasket (5) is positioned inside the nonmetal heat insulation sleeve and at the top end of the coal sample (4) which is also positioned inside the nonmetal heat insulation sleeve, and the servo loading instrument applies axial pressure to the pressure head (6);
the liquid level elevation device is positioned in the nonmetal heat insulation sleeve and comprises a foam plate (3) and a baffle plate (10); wherein the foam board (3) is in sliding connection with the sleeve groove (12), and the baffle (10) is fixedly arranged on the foam board;
the infrared control device comprises an infrared emission device (8), an infrared sensor (9), a PLC (programmable logic controller) 26 and a wire; the infrared sensor (9) and the infrared emission device (8) are oppositely arranged in parallel, the infrared sensor and the infrared emission device are both arranged on the sealing cover (18), the upper end of the baffle (10) penetrates through the sealing cover and floats between the infrared sensor (9) and the infrared emission device (8), and the infrared sensor (9) is connected with the PLC (26) through a wire;
the liquid nitrogen replenishing device comprises a motor (14), a gear (28), a rack rod (21), a piston (16), a liquid nitrogen tank (15), a replenishing pipeline (24) and a valve (25), wherein the motor (14) is connected with the PLC (26) through a wire; the motor (14) drives a piston (16) positioned in the liquid nitrogen tank to move, so that liquid nitrogen is conveyed to the interior of the nonmetallic heat-insulating sleeve through a supply pipeline (24);
the industrial CT scanning device comprises an X-ray source (7), a receiver (19) and a computer (27); wherein the X-ray source (7) and the receiver (19) are fixedly arranged at two sides of the outer part of the nonmetallic heat-insulating sleeve, and a space is arranged between the nonmetallic heat-insulating sleeve and the nonmetallic heat-insulating sleeve respectively; the center of the imaging plane of the receiver (19), the center of the coal sample and the center of the X-ray source are positioned on the same horizontal straight line, the imaging plane of the receiver is vertical to the straight line, and the image received by the receiver is stored on a computer (27);
in the infrared control device, the frame structure of the infrared emission device (8) is a groove plate with scales, two infrared emitters which can slide, namely a first infrared emitter (22) and a second infrared emitter (23), are arranged on the groove plate, and the positions of the first infrared emitter (22) and the second infrared emitter (23) are selected through the height of a coal sample and the liquid nitrogen liquid level;
in the liquid level elevation device, the main body structure of the foam plate (3) is a circular arc-shaped block body and protrudes to form a tail part at the middle part of the outer edge of the foam plate, the tail part of the foam plate is inserted into a sleeve groove (12) of the nonmetal heat insulation sleeve to be in sliding connection, and the foam plate (3) drives the baffle plate (10) to lift under the action of buoyancy;
in the liquid nitrogen replenishing device, the rack bar (21) is tightly contacted with a gear (28) on the motor, and the lower end of the rack bar is connected with a piston (16), so that the working state of the piston and the working state of the motor (14) are synchronous;
the automatic supply of liquid nitrogen is realized through an infrared control device, and the working procedure of the infrared control device is as follows: (1) the initial baffle is below 100mm in scale, the infrared sensor receives two infrared signals, and the motor rotates to drive the rack rod and the piston to be pressed into liquid nitrogen; the baffle is continuously raised along with the addition of the liquid nitrogen; (2) when the baffle plate is lifted to the position of 100mm of the scale to cover the infrared first infrared emitter, the infrared sensor receives an infrared signal, the original command is kept, the motor continues to work, and liquid nitrogen continues to be added; (3) when the baffle plate is lifted to the position of 150mm of the scale to cover the second infrared emitter, the infrared sensor cannot receive infrared signals, the motor is controlled to stop working, liquid nitrogen is not added any more, and the liquid nitrogen surface is lowered; (4) when the baffle just falls below the scale of 150mm, the second infrared emitter leaks, the infrared sensor receives an infrared signal, the original command is kept, the motor does not work, and the liquid nitrogen surface continues to descend; (5) and (4) automatically repeating the actions of (1) - (4) when the baffle plate is lowered below the scale of 100 mm.
2. A coal rock mechanical testing device under impact of low-temperature liquid nitrogen according to claim 1, characterized in that the liquid nitrogen tank (15) has good tightness and heat insulation, the lower side wall of the liquid nitrogen tank is communicated with one end of a supply pipeline (24), the other end of the supply pipeline (24) is communicated with the lower side wall of the nonmetallic heat insulation sleeve (2), and a valve (25) is arranged on the supply pipeline.
3. The coal rock mechanical testing method under the impact of low-temperature liquid nitrogen is characterized by comprising the following steps of:
step one, preparing an experiment, namely taking out coal blocks from the mine, and drilling and cutting the coal blocks into standard coal samples (4);
step two, installing equipment, namely placing a coal sample in the center of the heat insulation base (1), and placing a gasket (5) on the upper part of the coal sample (4); placing the foam board (3) together with the baffle (10) into a nonmetallic heat insulation sleeve, and embedding the tail part of the foam board into a sleeve groove (12) of the nonmetallic heat insulation sleeve; inserting the bottom of the non-metal heat-insulating sleeve into a base groove (11), and coating silica gel on the contact part of the non-metal heat-insulating sleeve and the heat-insulating base to prevent liquid nitrogen from escaping; a sealing cover (18) is covered, an infrared emission device (8) on the sealing cover is parallel and opposite to an infrared sensor (9) on the nonmetallic heat insulation sleeve, and a baffle (10) is arranged between the infrared emission device and the nonmetallic heat insulation sleeve; then placing a pressing head (6), and pressing a gasket (5) at the bottom of the pressing head;
step three, connecting an infrared sensor (9), a PLC (26) and a motor (14) through wires; the first infrared emitter (22) is adjusted to the scale position with the same height as the coal sample (4), and the second infrared emitter (23) is adjusted to the scale position with the highest height of the set liquid nitrogen surface; the first infrared emitter (22) and the second infrared emitter (23) are turned on, the power supply of the motor is turned on, and the valve (25) is turned on;
step four, starting a servo loading instrument to apply axial pressure in the liquid nitrogen immersing process of the coal sample, so that the coal sample is simultaneously in an ultralow temperature field and an axial stress field; simultaneously, an X-ray source is turned on to emit X-rays, and a receiver is utilized to collect an internal structure image of the coal sample;
turning off an X-ray source (7) after the experiment is finished, and unloading axial pressure by using a servo loader; closing the infrared emission device (8), and closing the motor (14); taking down the pressure head (6), the nonmetal heat insulation sleeve (2) and the gasket (5), taking down the coal sample and storing; closing the valve, and keeping the residual liquid nitrogen in the liquid nitrogen tank in a sealed and heat-insulating manner.
4. A method for testing coal and rock mechanics under low temperature liquid nitrogen impact as claimed in claim 3, wherein: in the first step, the coal sample isΦStandard coal sample of 50×100 mm.
5. The method for testing the coal rock mechanics under the impact of low-temperature liquid nitrogen as claimed in claim 4, wherein the method comprises the following steps: in the third step, the infrared sensor (9), the PLC (26) and the motor (14) are connected through wires; the first infrared emitter (22) is adjusted to the position with the same height as the coal sample (4) at the position of 100mm, the second infrared emitter (23) is adjusted to the position with the same height as the coal sample at the position of 150mm, namely the position with the same height as the first infrared emitter (22) at the position of 100mm is the height of the coal sample, and the highest height of the liquid nitrogen surface exceeding the coal sample is set to be 50mm; the first infrared emitter (22) and the second infrared emitter (23) are turned on, the power supply of the motor (14) is turned on, and the valve (25) is turned on.
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