Rigid-flexible form adjustable coal seam reaming cutter and reaming method

Abstract

The invention belongs to the technical field of coal seam gas extraction reaming, pressure relief and permeability increasing, and particularly relates to a rigid-flexible form adjustable coal seam reaming cutter and a reaming method. The rigid-flexible form adjustable coal seam reaming cutter comprises a hydraulic driving assembly and a folding sleeve assembly connected with the hydraulic driving assembly, and further comprises a motor, and an output shaft of the motor is rotationally connected with the folding sleeve assembly through a bearing; a torque sensor and a tachometer are further arranged on an output shaft of the motor, a drill bit is arranged at the tail end of the folding sleeve assembly, two sliding ways arranged in the length direction are further arranged in the folding sleeve assembly, a pneumatic spring is arranged in each sliding way, and a rigid-flexible conversion cutter assembly is arranged at the tail end of each pneumatic spring. The side wall of the end of the folding sleeve assembly is symmetrically provided with two guide sliding grooves for the rigid-flexible conversion cutter assembly to pass through, the sliding ways are communicated with the guide sliding grooves, the folding sleeve assembly is further internally provided with built-in water passing pipelines communicated with the hydraulic driving assembly, and the built-in water passing pipelines are communicated with the sliding ways through water flow channels respectively. Forward and reverse rotation of the motor is controlled, and the arrangement form of asymmetric tool sections on the tool is utilized, so that stress points of the tool in different rotation states are changed, and rigid-flexible conversion of the tool is controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam gas extraction hole expansion, pressure relief and permeability enhancement, and in particular relates to a rigid-flexible and adjustable coal seam hole expansion tool and a hole expansion method. Background Art

[0002] The occurrence environment of "three highs and one disturbance" in the deep earth and the harsh geological conditions make deep coal mining difficult. Accidents such as gas outbursts and gas explosions have become obstacles to coal mining. Coal seam pressure relief and permeability increase have become prerequisites for coal mining. Hydraulic permeability enhancement technology has been applied and promoted in many large-scale mining areas in China, effectively suppressing the occurrence of gas disasters. However, these conventional hydraulic measures still have their limitations. For example, hydraulic fracturing technology is affected by the original ground stress, resulting in a single morphology of hydraulic fractures, which is easy to form a permeability enhancement "blank zone", and the coal body has a high fracture initiation pressure, which is easy to damage the roof and floor of the coal seam, resulting in difficulties in the later coal mining support; hydraulic punching and hydraulic cutting technology have a small permeability enhancement range and a large drilling workload due to the existence of water cushion effect and pressure drop. When encountering soft coal seams, the softening effect of water on the strength of the coal body makes it difficult to form the coal body, and it is very easy to collapse and block the hole. The injected water is easy to be retained in the micropores of the coal seam to form a water film, which blocks the gas migration channel, restricts the gas desorption efficiency, and reduces the permeability by 30%-50%. The alternation of mining and excavation in the mine is unbalanced, and the production capacity succession target is challenged.

[0003] In order to break through the bottleneck of pressure relief and permeability enhancement technology, setting a mechanical tool at the end of the drilling rig for hole expansion can solve the above-mentioned problems. However, in actual engineering applications, due to structural defects, the mechanical tool causes coal slag or gangue to collapse into the mechanical tool folding device during the pressure relief and permeability enhancement operation, which makes it difficult to fold the mechanical tool and make it difficult to withdraw the drill rod. The patent number CN202211676849.1 discloses "a built-in high-pressure water-driven flexible tool retracting device and hole expansion method". By placing the flexible tool in the retracting sleeve assembly, the tool is flexible along the axial direction of the borehole when it is retracted, which solves the problem of conventional mechanical tools getting stuck in the borehole. However, under the conditions of complex coal seams with gangue, the flexible characteristics of the tool make it inefficient in destroying gangue, and the gangue breaking efficiency is less than 1 / 3 of that of rigid tools. For this reason, a forward and reverse driven rigid-flexible adjustable hole expansion tool and a control method are proposed to realize the rigid-flexible collaborative coal breaking pressure relief and permeability enhancement technology, providing a new solution for the safe and efficient mining of deep complex coal seams. Summary of the invention

[0004] The purpose of the present invention is to provide a coal seam reaming tool and reaming method with adjustable rigidity and flexibility. By controlling the forward and reverse rotation of the motor and utilizing the asymmetric arrangement of the tool sections on the tool, the force points of the tool under different rotation states are changed, thereby controlling the rigidity and flexibility conversion of the tool.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A coal seam hole expansion tool with adjustable rigidity and flexibility, comprising a hydraulic drive component, a folding sleeve component connected to the hydraulic drive component, and a motor. The motor output shaft is rotatably connected to the folding sleeve component through a bearing. The motor output shaft is also provided with a torque sensor and a tachometer. A drill bit is provided at the end of the folding sleeve component. The folding sleeve component is also provided with two slides arranged along the length direction, each slide is provided with a pneumatic spring, and a rigid-flexible conversion tool assembly is provided at the end of the pneumatic spring. The side walls of the end of the folding sleeve component are symmetrically provided with two guide grooves for the rigid-flexible conversion tool assembly to pass through. The guide groove has an arc transition groove inside to facilitate the extension and retraction of the rigid-flexible conversion tool assembly. The slide is connected to the guide groove. The folding sleeve component is also provided with a built-in water pipeline connected to the hydraulic drive component. The built-in water pipeline is connected to the slide through a water flow channel.

[0006] Furthermore, the hydraulic drive component includes a water tank, a high-pressure pump connected to the water outlet pipe of the water tank, the water outlet pipeline of the high-pressure pump is connected to the built-in water pipeline so as to send water to the built-in water pipeline, the built-in water pipeline has only one section that then sends water to the cavity formed by the slide and the pneumatic spring through the internal water flow channel, the high-pressure water pushes the piston rod out in the cavity, thereby controlling the ejection of the rigid-flexible conversion tool assembly, and after the supply of high-pressure water stops, the piston rod is sucked back due to the negative pressure suction effect in the closed cavity of the pneumatic spring, thereby controlling the recovery of the rigid-flexible conversion tool assembly.

[0007] Furthermore, the length of the slide is not less than the length of the pneumatic spring when it is fully extended. The pneumatic spring includes a cylinder body and a piston rod arranged in the cylinder body. The piston rod and the cylinder body are connected by a sealing guide sleeve. The right end of the piston rod is connected to the rigid-flexible conversion tool assembly through a connecting piece. The outer diameter of the connecting piece matches the slide. Two symmetrical limiting grooves are axially provided at the left end of the slide. A limiting slider matching the limiting groove is provided on the outer side of the left end of the pneumatic spring. The cooperation between the limiting groove and the limiting slider limits the free rotation of the pneumatic spring in the slide when the retracting sleeve assembly rotates, so that the rigid-flexible conversion tool assembly can be directionally constrained to respond to the switching of the rigid-flexible mode. The outlet of the water flow channel is located on the slide at the left end of the connecting piece. The purpose of this setting is to enable high-pressure water to push the connecting piece to drive the piston rod to extend, thereby driving the rigid-flexible conversion tool assembly to start hole expansion.

[0008] Furthermore, the rigid-flexible conversion tool assembly includes a plurality of asymmetric tool sections connected end to end, and adjacent asymmetric tool sections are connected by a cross axis. The cross axis is a cube and is provided with connecting through holes in the radial and axial directions. Adjacent asymmetric tool sections are connected by hinge axes passing through the through holes in the radial and axial directions. The setting of the cross axis plays a limiting role on the one hand, and a connecting role on the other hand, cooperating with the structure of the asymmetric tool section to control the conversion between the rigid form and the flexible form of the asymmetric tool section.

[0009] Furthermore, the asymmetric tool section includes a longitudinal support end and a radial bending end arranged up and down, and also includes a smooth transition part connecting the longitudinal support end and the radial bending end. The longitudinal support end, the radial bending end and the smooth transition part are integrally formed into a cylindrical shape, the length of the longitudinal support end is greater than the length of the radial bending end, and both ends of the longitudinal support end and the radial bending end are provided with threaded holes for the hinge shaft to pass through. A U-shaped connecting notch is formed between the longitudinal support end and the radial bending end on the same side of the asymmetric tool section and the smooth transition part, and a cross axis is provided in the cavity formed by the mutual engagement of the connecting notches between adjacent asymmetric tool sections, that is, the hinge axis at one end of the asymmetric tool section on the left is vertically arranged in space with the hinge axis of the adjacent asymmetric tool section on the right; when the motor rotates forward, the longitudinal support end between the asymmetric tool sections is subjected to force and is squeezed with the cross axis to form a mechanical self-locking; when reversed, the radial bending end of the asymmetric tool is rotated to switch the tool to a flexible bending state. According to engineering needs, the rotation angle of the tool section can be controlled by adjusting the size of the tool section gap.

[0010] Furthermore, a pick assembly is provided at the end of the rigid-flexible conversion tool assembly, and the pick assembly includes a pick base, on which are provided a plurality of evenly arranged carbide picks. When the rigid tool is breaking gangue, the picks mainly break the gangue by impact, thereby improving working efficiency; when the flexible tool is breaking coal, the picks mainly break the coal by cutting, thereby maintaining the stability of the hole shape.

[0011] Another object of the present invention is to provide a method for expanding a coal seam hole with an adjustable rigidity and flexibility, comprising the following steps: S1. In the initial state, the rigid-flexible conversion tool assembly is retracted into the retractable sleeve assembly, the high-pressure water pump is started to increase the water pressure to 4 MPa, the pneumatic spring is initially extended to unfold the tool, and the motor is controlled to reverse at a low speed of 200 rpm to drill into the soft coal surface layer; S2. When the torque sensor detects a sudden increase in the coal-breaking torque, the drill enters the hard gangue layer, switches the motor to the forward mode, increases the water pressure to 6 MPa, fully extends the pneumatic spring to the target hole diameter, increases the motor speed to 800 rpm, and the rigid-flexible conversion tool assembly triggers the longitudinal support end to take effect under the centrifugal force and collision with the coal body, forming a geometric constraint with the cross axis, and the rigid-flexible conversion tool assembly forms a rigid structure to impact the hard gangue; S3. After penetrating the hard gangue layer, the motor is switched to reverse mode, the water pressure is reduced to 4 MPa, the speed is reduced to 200 rpm, and the rigid-flexible conversion tool assembly is transformed into a flexible form and bent along the radial bending end on the other side to adapt to the hole wall shape, maintaining the hole shape stable when breaking coal; S4. After the hole expansion is completed, the high-pressure water pump is stopped, the pneumatic spring is reset and contracted, and the rigid-flexible conversion tool assembly is retracted until the retractable sleeve assembly exits the hole.

[0012] The advantages of the present invention are: 1. The present invention controls the forward and reverse rotation of the motor and the driving force of high-pressure water, combines the design of the longitudinal support end and the radial bending end of the asymmetric tool section, and develops a forward and reverse rigid-flexible conversion structure to achieve seamless switching between efficient crushing of hard rock and maintaining hole shape in soft coal seams; 2. The front end of the retractable sleeve assembly is equipped with a drill bit to achieve integrated drilling and expansion, efficient coal breaking, and ensure smooth completion of mining and excavation alternation to achieve the goal of continuous production capacity; 3. A limit groove and a limit slider are set between the closing device and the pneumatic spring to prevent the tool from rotating and thus affecting the control of the tool's rigidity and flexibility switching by forward and reverse rotation; 4. A guide slot structure is provided at the end of the retractable sleeve assembly of the device to reduce the friction and collision between the tool and the retractable sleeve assembly, ensuring smooth extension and retraction of the tool; 5. This device controls the rotatable angle of the cutter segments by changing the size of the radial bending end gap, thereby meeting the engineering requirements under different coal seam conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0014] Figure 2 It is a schematic diagram of the structure of the folding sleeve assembly in the present invention.

[0015] Figure 3 It is a cross-sectional view of one end of the retractable sleeve assembly connected to the motor output shaft.

[0016] Figure 4 It is a cross-sectional view of the connection between the water flow channel and the slideway in the retractable sleeve assembly.

[0017] Figure 5 It is a structural schematic diagram of the rigid-flexible conversion tool assembly in the present invention.

[0018] Figure 6 It is a structural schematic diagram of the asymmetric tool section in the present invention.

[0019] Figure 7 It is a structural schematic diagram of the cross axis in the present invention.

[0020] Figure 8It is a structural schematic diagram of the pick assembly in the present invention.

[0021] Fig. 9 It is a working state diagram of the rigid-flexible conversion tool assembly in the present invention; the left figure is a force diagram for a rigid tool, and the right figure is a force diagram for a flexible tool. DETAILED DESCRIPTION

[0022] As shown in the figure, a coal seam reaming tool with adjustable rigidity and flexibility includes a hydraulic drive component, a folding sleeve component 1 connected to the hydraulic drive component, and a motor 2. The motor output shaft is rotatably connected to the folding sleeve component through a bearing. A torque sensor and a tachometer are also provided on the motor output shaft. A drill bit 3 is provided at the end of the folding sleeve component. Two slideways 4 arranged along the length direction are also provided in the folding sleeve component. A pneumatic spring 5 is provided in each slideway. A rigid-flexible conversion tool assembly 6 is provided at the end of the pneumatic spring. The side walls of the end of the folding sleeve component are symmetrically provided with two guide slides 7 for the rigid-flexible conversion tool assembly to pass through. The interior of the guide slide is an arc transition groove, which is convenient for the rigid-flexible conversion tool assembly to extend and retract. The slide and the guide The slide is connected, and the folding sleeve assembly is also provided with a built-in water pipeline 8 connected with the hydraulic drive assembly, and the built-in water pipeline is connected with the slide through a water flow channel 9; the hydraulic drive assembly includes a water tank 10, and a high-pressure pump 11 connected to the water outlet pipe of the water tank, the water outlet pipeline of the high-pressure pump is connected with the built-in water pipeline, so that water is sent to the built-in water pipeline, and the built-in water pipeline is only provided with a small section, which then sends water to the cavity formed by the slide and the pneumatic spring through the internal water flow channel, and the high-pressure water pushes the piston rod out in the cavity, thereby controlling the push-out of the rigid-flexible conversion tool assembly, and after the high-pressure water stops supplying, the piston rod is sucked back due to the negative pressure suction effect in the closed cavity of the pneumatic spring, thereby controlling the recovery of the rigid-flexible conversion tool assembly.The length of the slide is not less than the length of the pneumatic spring when it is fully extended. The pneumatic spring includes a cylinder body 51 and a piston rod 52 arranged in the rigid body. The piston rod and the cylinder body are connected by a sealing guide sleeve. The right end of the piston rod is connected to the rigid-flexible conversion tool assembly through a connecting piece 12. The outer diameter of the connecting piece matches the slide. Two symmetrical limiting grooves 13 are axially arranged at the left end of the slide. A limiting slider matching the limiting groove is sleeved on the outer side of the left end of the pneumatic spring. The cooperation of the limiting groove and the limiting slider limits the axial movement of the pneumatic spring when the retracting sleeve assembly rotates, making the rigid-flexible conversion tool assembly more stable during cutting. The outlet of the water flow channel is located on the left side of the connecting piece. On the slideway at the end, the purpose of this setting is to enable high-pressure water to push the connecting piece to drive the piston rod to extend, thereby driving the rigid-flexible conversion tool assembly to work; the rigid-flexible conversion tool assembly 6 includes a plurality of asymmetric tool sections 61 connected end to end, and adjacent asymmetric tool sections are connected by a cross shaft 62. The cross shaft is a cube and is provided with interconnected through holes in the radial and axial directions. Adjacent asymmetric tool sections are connected by hinge shafts 63 that pass through the through holes in the radial and axial directions. The setting of the cross shaft plays a limiting role on the one hand, and a connecting role on the other hand, and cooperates with the structure of the asymmetric tool section to control the conversion of the rigid form and the flexible form of the asymmetric tool section; the asymmetric tool section includes an upper and a lower A longitudinal support end 611 and a radial bending end 612 are provided, and also include a smooth transition portion 613 connecting the longitudinal support end and the radial bending end. The longitudinal support end, the radial bending end and the smooth transition portion are integrally formed into a cylindrical shape. The length of the longitudinal support end is greater than the length of the radial bending end. Both ends of the longitudinal support end and the radial bending end are provided with threaded holes for the hinge shaft to pass through. A U-shaped connecting notch is formed between the longitudinal support end and the radial bending end and the smooth transition portion on the same side of the asymmetric tool section, and a cross axis is provided in the cavity formed by the mutual engagement of the connecting notches between adjacent asymmetric tool sections, that is, the hinge shaft at one end of the asymmetric tool section on the left and the hinge shaft of the adjacent asymmetric tool section on the right are vertical in space. When the motor rotates forward, the longitudinal support end of the asymmetric tool segment is stressed and becomes mechanically self-locking with the cross shaft; when the motor rotates reversely, the radial bending end of the asymmetric tool is rotated to switch the tool to a flexible bending state. According to engineering needs, the rotation angle of the tool segment can be controlled by adjusting the size of the tool segment gap; a pick assembly 14 is also provided at the end of the rigid-flexible conversion tool assembly, and the pick assembly includes a pick base 141, on which a plurality of evenly arranged carbide picks 142 are provided. When the rigid tool breaks gangue, the pick mainly breaks gangue by impact, thereby improving work efficiency; when the flexible tool breaks coal, the pick mainly breaks coal by cutting, thereby maintaining the stability of the hole shape.

[0023] Another object of the present invention is to provide a method for expanding a coal seam hole with a rigidity-flexibility adjustable pore size expansion tool, comprising the following steps: S1. In the initial state, the rigid-flexible conversion tool assembly is retracted into the retractable sleeve assembly, the high-pressure water pump is started to increase the water pressure to 4 MPa, the pneumatic spring is initially extended to unfold the tool, and the motor is controlled to reverse at a low speed of 200 rpm to drill into the soft coal surface layer; S2. When the torque sensor detects a sudden increase in the coal-breaking torque, the drill enters the hard gangue layer, switches the motor to the forward mode, increases the water pressure to 6 MPa, fully extends the pneumatic spring to the target hole diameter, increases the motor speed to 800 rpm, and the rigid-flexible conversion tool assembly triggers the longitudinal support end to take effect under the centrifugal force and collision with the coal body, forming a geometric constraint with the cross axis, and the rigid-flexible conversion tool assembly forms a rigid structure to impact the hard gangue; S3. After penetrating the hard gangue layer, the motor is switched to reverse mode, the water pressure is reduced to 4 MPa, the speed is reduced to 200 rpm, and the rigid-flexible conversion tool assembly is transformed into a flexible form and bent along the radial bending end on the other side to adapt to the hole wall shape, maintaining the hole shape stable when breaking coal; S4. After the hole expansion is completed, the high-pressure water pump is stopped, the pneumatic spring is reset and contracted, and the rigid-flexible conversion tool assembly is retracted until the retractable sleeve assembly exits the hole.

[0024] During specific use, first, the operator moves the entire device to the working surface to be expanded by the crawler, ensures that the drilling rig is aligned with the drilling axis, then drops and locks the hydraulic support, and applies 20-30 MPa supporting pressure through the hydraulic cylinder to stabilize the fuselage. Start the drilling rig, use the drill bit to drill holes in the coal seam on the working surface, and drive the retracting sleeve assembly slowly into the borehole after the hole is drilled. Open the water pressure valve of the water tank, and start the high-pressure pump to inject water and pressurize the hydraulic pipeline. In the initial stage, the water pressure is controlled within the range of 4MPa±0.2 MPa. The high-pressure water enters the cavity formed by the pneumatic spring and the retracting sleeve cylinder along the built-in water pipeline of the retracting sleeve cylinder. Under the action of pressure, the rigid-flexible conversion tool assembly connected to the end of the piston rod of the pneumatic spring is pushed out from the guide slide groove and gradually unfolded to ΦThe diameter of the hole is 80 mm. At this time, the asymmetric tool section moves along the radial bending end under the low-speed reversal state. The rigid-flexible conversion tool assembly retracts centripetally under the reaction of the coal body, adapting to the non-uniform hole wall morphology of the soft coal seam, and the coal body is broken by cutting through the pick assembly. When the motor detects a sudden increase in the coal breaking torque through the torque sensor, it is considered that the hole is expanded to the hard gangue layer and rigid coal breaking is required. The motor is controlled to rotate forward and the high-pressure pump output water pressure is increased to 6 MPa±0.3 MPa. At this time, the pneumatic spring is extended again, and the motor speed is synchronously increased to 800 rpm±50 rpm; the asymmetric tool section moves along the longitudinal support end under the high-speed forward rotation state, and the longitudinal support end is in surface contact with the cross shaft, so that the asymmetric tool section forms a mechanical self-locking, and the rigid-flexible conversion tool assembly forms a rigid overall structure. At the same time, the pick assembly welds carbide picks to impact the hard gangue layer to achieve efficient crushing. After penetrating the hard gangue layer, the motor is operated in reverse mode, the high-pressure pump water pressure is adjusted back to 4 MPa±0.2MPa, the speed is reduced to 200 rpm±10 rpm, the pneumatic spring is retracted, the asymmetric tool section turns to the radial bending end with a gap of 1-3 mm on the other side, and the rigid-flexible conversion tool assembly is transformed into a flexible bend along the irregular contour of the hole wall during rotation, and the soft coal hole wall is uniformly cut and expanded to maintain the stability of the hole shape. During this process, the operator monitors the value changes of the torque sensor and the tachometer in real time, and adjusts the water tank water pressure valve according to the change of the hardness of the gangue in the hole or the fluctuation of the slag discharge resistance. After the expansion is completed, the gangue or coal slime remaining on the tool is washed through the connection of the asymmetric tool section with 0.5MPa water pressure. After the tool is retracted, the high-pressure pump is turned off, and the device is safely withdrawn from the hole. Finally, the hydraulic support is raised and moved to the next station using the crawler.

Claims

1. A coal seam hole enlarging tool with adjustable rigidity and flexibility, characterized in that: It includes a hydraulic drive component, a folding sleeve component connected to the hydraulic drive component, and a motor. The motor output shaft is rotatably connected to the folding sleeve component through a bearing. The motor output shaft is also provided with a torque sensor and a tachometer. A drill bit is provided at the end of the folding sleeve component. The folding sleeve component is also provided with two slides arranged along the length direction, each slide is provided with a pneumatic spring, and a rigid-flexible conversion tool assembly is provided at the end of the pneumatic spring. The side walls at the end of the folding sleeve component are symmetrically provided with two guide grooves for the rigid-flexible conversion tool assembly to pass through, and the slides are connected to the guide grooves. The folding sleeve component is also provided with a built-in water pipeline connected to the hydraulic drive component, and the built-in water pipeline is connected to the slide through a water flow channel.

2. The coal seam hole enlarging tool with adjustable rigidity and flexibility as claimed in claim 1, characterized in that: The hydraulic drive assembly includes a water tank, a high-pressure pump connected to a water outlet pipe of the water tank, and a water outlet pipeline of the high-pressure pump is connected to a built-in water pipeline.

3. The coal seam hole enlarging tool with adjustable rigidity and flexibility as claimed in claim 1, characterized in that: The length of the slide is not less than the length of the pneumatic spring when it is fully extended. The pneumatic spring includes a cylinder body and a piston rod arranged in the rigid body. The piston rod and the cylinder body are connected by a sealing guide sleeve. The right end of the piston rod is connected to the rigid-flexible conversion tool assembly through a connecting piece. The outer diameter of the connecting piece matches the slide. Two symmetrical limiting grooves are axially provided at the left end of the slide. A limiting slider matching the limiting groove is provided on the outer side of the left end of the pneumatic spring. The outlet of the water channel is located on the slide at the left end of the connecting piece.

4. The coal seam hole enlarging tool with adjustable rigidity and flexibility as claimed in claim 1, characterized in that: The rigid-flexible conversion tool assembly includes a plurality of asymmetric tool sections connected end to end, and adjacent asymmetric tool sections are connected via a cross axis. The cross axis is a cube and is provided with connecting through holes in radial and axial directions, and adjacent asymmetric tool sections are connected via hinge axes passing through the through holes in radial and axial directions.

5. The coal seam hole enlarging tool with adjustable rigidity and flexibility as claimed in claim 4, characterized in that: The asymmetric tool section includes a longitudinal support end and a radial bending end arranged up and down, and also includes a smooth transition part connecting the longitudinal support end and the radial bending end. The longitudinal support end, the radial bending end and the smooth transition part are integrally formed into a cylindrical shape. The length of the longitudinal support end is greater than the length of the radial bending end. Both ends of the longitudinal support end and the radial bending end are provided with threaded holes for the hinge shaft to pass through. A U-shaped connecting notch is formed between the longitudinal support end and the radial bending end and the smooth transition part on the same side of the asymmetric tool section, and a cross axis is provided in the cavity formed by the mutual engagement of the connecting notches between adjacent asymmetric tool sections, that is, the hinge axis at one end of the asymmetric tool section on the left and the hinge axis of the adjacent asymmetric tool section on the right are vertically arranged in space.

6. The coal seam hole enlarging tool with adjustable rigidity and flexibility as claimed in claim 5, characterized in that: A pick assembly is also provided at the end of the rigid-flexible conversion tool assembly. The pick assembly includes a pick base, on which a plurality of evenly arranged cemented carbide picks are provided.

7. The method for expanding a coal seam hole with an adjustable rigidity and flexibility tool as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: S1. In the initial state, the rigid-flexible conversion tool assembly is retracted into the retractable sleeve assembly, the high-pressure water pump is started to increase the water pressure to 4 MPa, the pneumatic spring is initially extended to unfold the tool, and the motor is controlled to reverse at a low speed of 200 rpm to drill into the soft coal surface layer; S2. When the torque sensor detects a sudden increase in the coal-breaking torque, the drill enters the hard gangue layer, switches the motor to the forward mode, increases the water pressure to 6 MPa, fully extends the pneumatic spring to the target hole diameter, increases the motor speed to 800 rpm, and the rigid-flexible conversion tool assembly triggers the longitudinal support end to take effect under the centrifugal force and collision with the coal body, forming a geometric constraint with the cross axis, and the rigid-flexible conversion tool assembly forms a rigid structure to impact the hard gangue; S3. After penetrating the hard gangue layer, the motor is switched to reverse mode, the water pressure is reduced to 4 MPa, the speed is reduced to 200 rpm, and the rigid-flexible conversion tool assembly is transformed into a flexible form and bent along the radial bending end on the other side to adapt to the hole wall shape, maintaining the hole shape stable when breaking coal; S4. After the hole expansion is completed, the high-pressure water pump is stopped, the pneumatic spring is reset and contracted, and the rigid-flexible conversion tool assembly is retracted until the retractable sleeve assembly exits the hole.

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