Device and method for testing friction coefficient in bulk material

Abstract

The invention provides a device and method for testing the internal friction coefficient of a bulk material, and belongs to the technical field of bulk material characteristic measurement, the device comprises a support, a rotating unit, a shearing unit, a pressure applying unit and a testing unit, the support comprises an upper support and a lower support which are connected through an optical axis, and the shearing unit comprises a lower shearing box, an annular pressing plate and an upper shearing box; the lower shearing box is used for containing materials, the lower end of the lower shearing box is connected with the rotating unit, the upper end face of the annular pressing plate is connected with the lower end of the upper shearing box, the ball upper cover is arranged on the upper shearing box, and the pressure applying unit comprises a vertical driving motor, two lead screws and a pressure applying plate. The testing unit comprises a PLC (Programmable Logic Controller), and a normal pressure testing piece and a horizontal shearing force testing piece which are electrically connected with the PLC; and the testing method comprises the following steps of: filling materials, rotating the lower shearing box, descending the pressure applying plate and testing the shearing force. The device is accurate in testing and can be automatically controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of bulk material property measurement, and particularly relates to a test device and a test method for the internal friction coefficient of bulk materials. Background Art

[0002] Bulk materials are a type of particulate matter, composed of many loose, separated, and differently shaped discontinuous solid particles, with their unique properties and motion laws. In recent years, with the rapid development of granular mechanics and the discrete element method, instruments for studying the properties of bulk materials have received increasing attention. Chinese Patent Application CN110160952 A discloses an internal friction tester, which includes a frame, a shear box, a discharge box, a vertical pressing device, a shear driving device, a reaction support, and a temperature control device. The frame includes a bottom plate, an upper plate, a middle beam, and four groups of columns. Linear bearings are provided at the left front end, left rear end, right front end, and right rear end of the middle beam. A discharge box track assembly is provided at the bottom end of the discharge box. The shear driving device includes a horizontal driving motor, a horizontal speed reducer, a shear force sensor, and a horizontal transmission lead screw. The vertical pressing device includes a normal force driving motor, a normal force speed reducer, a normal force sensor, a normal force transmission lead screw, and a pressing head. The shear box includes an upper shear box and a lower shear box, and a shear box track is provided between the upper shear box and the lower shear box. The above-mentioned device for testing the internal friction coefficient has low accuracy, the shear surface gradually decreases during the shear process, it cannot ensure that the bulk material is sheared under continuous displacement conditions, and it cannot achieve precise control of the shear speed and normal pressure. Summary of the Invention

[0003] The technical problem solved by the present invention is that the existing test device for the internal friction coefficient of bulk materials has low accuracy, the shear surface gradually decreases during the shear process, it cannot ensure that the bulk material is sheared under continuous displacement conditions, and it cannot achieve precise control of the shear speed and normal pressure.

[0004] The present invention provides a test device for the internal friction coefficient of bulk materials, which includes a support, a rotation unit, a shear unit, a pressing unit, and a test unit. The support is an upper support and a lower support connected by an optical axis. The shearing unit includes a lower shearing box, an inner cup, an outer cup, an annular pressing plate, and an upper shearing box. The lower shearing box is an annular box for placing materials. The lower end of the lower shearing box is connected to the rotating unit. The inner and outer cups are cylindrical glass cups with openings at both the top and bottom. The inner and outer cups are coaxially arranged inside the lower shearing box and are respectively in contact with the inner and outer ring walls of the lower shearing box. A number of press claws are symmetrically arranged along the circumference at the bottom of the lower shearing box. The annular pressing plate is used to directly contact the materials. A number of press claws are symmetrically arranged along the circumference on the lower end surface of the annular pressing plate. The upper end surface of the annular pressing plate is connected to the lower end of the upper shearing box. The upper end of the upper shearing box is provided with a central axis. The ball upper cover is arranged through the central axis at the upper end of the upper shearing box. The lower surface of the ball upper cover is provided with an annular raceway. The upper shearing box is provided with a number of universal ball bearings corresponding to the raceway. The annular raceway is in contact with the universal ball bearings. The pressing unit includes a vertical driving motor, two lead screws, and a pressing plate. The pressing plate is arranged above the upper shearing box. The two lead screws are arranged on both sides of the pressing plate. The upper ends of the lead screws are connected to the vertical driving motor, and the lower ends are connected to the lead screw fixing seats. The vertical driving motor is arranged on the upper support. The two ends of the lead screw fixing seats are respectively connected to the lower parts of the two optical axes. The testing unit includes a PLC controller, a normal pressure testing component for the materials, and a horizontal shearing force testing component for the materials. The normal pressure testing component is arranged between the pressing plate and the upper shearing box. The horizontal shearing force testing component is arranged on the upper shearing box. The normal pressure testing component and the horizontal shearing force testing component are both electrically connected to the PLC controller.

[0005] Further, the normal pressure testing component is a pressure sensor. The pressure sensor pressing plate is connected to the pressing plate. The pressure sensor is arranged inside the pressure sensor base. The pressure sensor base is arranged at the upper end of the central axis of the upper shearing box. Four connecting rods are arranged along the circumference of the pressure sensor base. The ends of the connecting rods are connected to the optical axes through linear bearings. A pressing shaft is arranged at the lower end of the connecting rod. The other end of the pressing shaft is connected to the ball upper cover.

[0006] Further, the horizontal shearing force testing component is a torque sensor. The torque sensor is arranged on the central axis of the upper shearing box.

[0007] Further, the horizontal shearing force testing component is two tension sensors. Two semi-circular head bolts are arranged on the upper surface of the upper shearing box. The two semi-circular head bolts are symmetrically arranged with the center of the upper shearing box as the center. One end of the tension sensor is connected to the semi-circular head bolt through a swivel bolt, and the other end is connected to the tension sensor base. The tension sensor base is connected to the optical axis through a bushing.

[0008] Further, the rotating unit includes two rotary drive motors, a slewing bearing, and a turntable. Two rotary drive motors are symmetrically arranged on the lower support. A gear is connected to the outer periphery of the output shaft of the rotary drive motor. The slewing bearing is arranged between the turntable and the lower support. The inner ring of the slewing bearing is fixedly connected to the turntable, and the outer ring is fixedly connected to the lower support. An external gear is arranged on the outer periphery of the outer ring, and the external gear meshes with the gear connected to the output shaft of the rotary drive motor. A connecting ring is arranged on the outer ring of the turntable for bolt connection with the lower shear box.

[0009] Further, it also includes a speed sensor and a tie rod displacement sensor. The speed sensor is arranged on the turntable. The base of the tie rod displacement sensor is arranged on the upper support, and the tie rod of the tie rod displacement sensor is connected to the pressure plate.

[0010] The present invention provides a test method for the internal friction coefficient device of bulk materials, including the following steps. Step 1: Start the vertical drive motor to lift the pressure plate, and then lift the upper shear box and the annular pressure plate to a certain height. Turn off the vertical drive motor, place the loading funnel above the lower shear box, start the rotary drive motor, and make the lower shear box rotate at a lower speed for material filling. Step 2: Turn off the rotary drive motor, start the vertical drive motor, lower the pressure plate until the output value of the normal force test piece reaches the set normal pressure value. Turn off the vertical drive motor, start the rotary drive motor for shear force test, and record the output value of the horizontal shear force test piece. Turn off the rotary drive motor after the test is completed. Step 3: Repeat Step 2. Under different normal pressures, test the horizontal shear force of the material and record the data. Step 4: After the test is completed, start the vertical drive motor to raise the pressure plate, remove the lower shear box, clean the device, process the data, and calculate the internal friction coefficient of the material.

[0011] Further, in Step 1, when the material is filled until it overflows the lower shear box, use a ring knife to scrape across the surface of the lower shear box clockwise one or two times, and then scrape counterclockwise. The radial inclination angle a of the ring knife relative to the surface of the lower shear box is 15 - 30°, until the material particles are flush with the upper end face of the lower shear box, and the filling is completed.

[0012] Further, in Step 4, the data processing method is to calculate the shear strength of the bulk material tested by the torque sensor according to formula (1) , (1) In the formula, r1 and r2 are respectively the inner radius and the outer radius of the lower shear box; Ti is the torque output by the torque sensor during the i-th test. Calculate the normal stress σ of the bulk material on the upper shear surface for each test according to formula (2)i , (2) where W i is the normal pressure on the upper surface of the material particles during the i-th test, Fit the above data to plot the ultimate shear stress line of the bulk material, and calculate the internal friction coefficient μ of the bulk material according to formula (3) b , (3) where ψ is the internal friction angle of the material, that is, the inclination angle of the ultimate shear stress line in the σ-τ coordinate plane.

[0013] Furthermore, in step four, the data processing method is to calculate the shear strength of the bulk material tested by the tension sensor according to formulas (4) and (5) , (4) (5) where r 1 and r 2 are the inner radius and outer radius of the lower shear box respectively; r s is the radial distance between the two tension sensors; r m is the distance of the force arm; F 1i and F 2i are the tensions output by the two tension sensors during the i-th test respectively, Calculate the normal stress σ of the bulk material on the upper shear plane according to formula (2) i , (2) where W i is the normal pressure on the upper surface of the material particles during the i-th test, Fit the above data to plot the ultimate shear stress line of the bulk material, and calculate the internal friction coefficient μ of the bulk material according to formula (3) b , (3) where ψ is the internal friction angle of the material, that is, the inclination angle of the ultimate shear stress line in the σ-τ coordinate plane.

[0014] The present invention has the following beneficial effects: The test device for the internal friction coefficient of bulk materials of the present invention takes granular bulk materials with a particle size of 3.25 - 12.5 mm as the research object. The lower shear box has a wide range of applicable particle sizes, enabling the bulk materials to be in a flowing state within the device, and testing the horizontal shear force on the shear plane during the flow of particulate matter. By means of a pressure sensor, a vertical drive motor, and a lead screw, the pressure applied to the upper surface of the particles can be made more precisely controllable. By setting an inner glass ring and an outer glass ring, the friction between the particles and the inner wall of the lower shear box can be reduced, making the test results more accurate. By using a torque sensor and a tensile sensor, the horizontal shear force can be tested from multiple aspects, and multiple parameters such as the displacement normal pressure and the shear speed can be adjusted. This device has accurate testing, is easy to maintain, and realizes automatic control. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The front view of the test device for the internal friction coefficient of bulk materials of the present invention.

[0016] Figure 2 The side view of the test device for the internal friction coefficient of bulk materials of the present invention.

[0017] Figure 3 The schematic diagram of the position of the core cutter and the lower shear box of the test device for the internal friction coefficient of bulk materials of the present invention.

[0018] Figure 4 The partial enlarged view of the test device for the internal friction coefficient of bulk materials of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not used to limit the present invention.

[0020] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0021] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

[0022] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0023] Example 1, as Figures 1-4 shown, a test device for the internal friction coefficient of bulk materials includes a support, a rotating unit, a shearing unit, a pressing unit, and a testing unit.

[0024] The support includes an upper support 1 and a lower support 2 connected by an optical axis. Guide shaft seats 3 are fixed at the four corners of the upper support 1 and the lower support 2, and the optical axis 4 is connected within the guide shaft seats 3.

[0025] The rotating unit includes two rotating drive motors 5, a slewing bearing 6, and a turntable 7. Two rotating drive motors 5 are symmetrically arranged on the lower support 2. A gear 8 is connected to the outer periphery of the output shaft of the rotating drive motor 5. The slewing bearing 6 is arranged between the turntable 7 and the lower support 2. The inner ring of the slewing bearing 6 is fixedly connected to the turntable 7, and the outer ring is fixedly connected to the lower support 2. An external gear is arranged on the outer peripheral edge of the outer ring, and the external gear meshes with the gear 8 connected to the output shaft of the rotating drive motor 5. A connecting ring is provided on the outer ring of the turntable 7 for bolt connection with the lower shear box 9.

[0026] The shearing unit includes a lower shear box 9, an inner cup 10, an outer cup 11, an annular pressing plate 12, and an upper shear box 13. The lower shear box 9 is an annular box. The inner cup 10 and the outer cup 11 are cylindrical glass cups with upper and lower openings. The inner cup 10 and the outer cup 11 are coaxially arranged within the lower shear box 9 and are respectively in contact with the inner and outer ring walls of the lower shear box 9. The upper end surface of the inner cup 10 is clamped to the inner ring wall of the lower shear box 9 through an inner ring cover 25, and the lower end surface of the inner cup 10 is clamped to the bottom surface of the lower shear box 9. The upper end surface of the outer cup 11 is clamped to the outer ring wall of the lower shear box 9 through an outer ring cover 24, and the lower end surface of the outer cup 11 is clamped to the bottom surface of the lower shear box 9. An annular cavity formed between the outer wall of the inner cup 10 and the inner wall of the outer cup 11 is used to store materials. The inner cup 10 and the outer cup 11 are used to reduce the friction between the materials and the side walls. A plurality of pressing claws 14 are symmetrically arranged along the circumference at the bottom of the lower shear box 9. The pressing claws 14 are detachably connected to the lower shear box 9. A groove is provided at the bottom of the lower shear box 9, and the pressing claws 14 are fitted in the groove and fixed by countersunk bolts 49, which facilitates the replacement of the pressing claws 14, provides a larger variation range for the shearing speed of the materials, and at the same time, when wear occurs, only the specific pressing claws 14 need to be replaced, and the entire lower shear box 9 does not need to be replaced.

[0027] The annular pressing plate 12 is in direct contact with the material. A number of pressing claws 14 are symmetrically arranged along the circumferential direction on the lower end face of the annular pressing plate 12. The upper end face of the annular pressing plate 12 is connected to the lower end of the upper shearing box 13. A central shaft is provided at the upper end of the upper shearing box 13. A thrust bearing 26, an angular contact bearing 27, and a bearing cover 28 are successively arranged on the central shaft of the upper shearing box 13. A snap ring 29 is arranged between the bearing cover 28 and the angular contact bearing 27. The ball upper cover 48 passes through the central shaft and is arranged at the upper end of the upper shearing box 13 and is connected by a number of L-shaped pull plates 30 and T-shaped nuts 40. Two-stage stepped surfaces are arranged on the inner side of the ball upper cover 48 for clamping the thrust bearing 26 and the angular contact bearing 27 respectively. An annular raceway is arranged on the lower surface of the ball upper cover 48. A number of universal ball bearings 31 are arranged on the upper shearing box 13 corresponding to the raceway. The annular raceway is in contact with the universal ball bearings 31 to realize a small rotation of the upper shearing box 13.

[0028] The test unit includes a PLC controller, a pressure sensor 15, a torque sensor 16, a pull rod displacement sensor 17, and a speed sensor 18. The torque sensor 16 is arranged on the upper end face of the central shaft of the upper shearing box 13. A pressure sensor base 19 is arranged at the upper end of the torque sensor 16. Four connecting rods are arranged along the circumferential direction of the pressure sensor base 19. The ends of the connecting rods are connected to the optical axis 4 through linear bearings 32. A pressing shaft 33 is arranged at the lower end of the connecting rod. The other end of the pressing shaft 33 is connected to the guide shaft seat 3 on the surface of the ball upper cover 48. The pressure sensor 15 is arranged in the pressure sensor base 19. The speed sensor 18 is arranged on the lower support 2 for real-time monitoring of the rotation speed of the turntable 7. The pull rod displacement sensor 17 is arranged on the upper support 1. The pull rod of the pull rod displacement sensor 17 is connected to the pressing plate 20. The pressure sensor 15, the torque sensor 16, the pull rod displacement sensor 17, and the speed sensor 18 are all electrically connected to the PLC controller.

[0029] The pressing unit includes a vertical driving motor 21, two lead screws 22, and a pressing plate 20. The pressing plate 20 is connected to the pressing plate 34 of the pressure sensor 15. The pressing plate 34 can move between the top plate 35 and the induction plate of the pressure sensor 15. Connecting rods are arranged on both sides of the pressing plate 20. A lead screw nut 36 is arranged at the end of the connecting rod for installing the lead screw 22. The upper end of the lead screw 22 is connected to the output shaft of the vertical driving motor 21 through a coupling 37. The lower end is arranged in the mounting hole 38 of the lead screw fixing seat 23. The vertical driving motor 21 is arranged on the upper support 1. Both ends of the lead screw fixing seat 23 are connected to the lower parts of the two optical axes 4 through locking rings 39.

[0030] A method for testing the internal friction coefficient of bulk materials using the above device includes the following steps. Step 1: Start the vertical drive motor 21 to lift the pressing plate 20, thereby lifting the upper shear box 13 and the annular pressing plate 12 to a certain height for easy feeding. Considering that the initial arrangement state of granular materials has a certain impact on the test results, the same granular filling method is adopted. Place the loading funnel above the lower shear box 9, start the rotary drive motor 5, and rotate the lower shear box 9 at a low speed for material filling. When the material overflows from the lower shear box 9, stop filling, turn off the rotary drive motor 5, and the lower shear box 9 stops rotating. Use the ring cutter 47 to scrape across the surface of the lower shear box 9 clockwise one or two times, and then scrape counterclockwise. The radial inclination angle a of the ring cutter 47 relative to the surface of the lower shear box 9 is 15 - 30°. For coarse granular materials, scraping may tear the particle surface, and the particles need to be refilled. When the filled particles are flush with the upper end face of the lower shear box 9, the filling is completed. Step 2: Start the vertical drive motor 21 to lower the pressing plate 20 until the output value of the pressure sensor 15 reaches the set pressure value W, and then turn off the vertical drive motor 21. Due to the self-locking property of the lead screw 22, the pressing plate 20 will continuously apply pressure to the upper surface of the particles. Start the rotary drive motor 5 and adjust the rotation speed. Under the interaction between the material and the pawls 14 on the lower surface of the annular pressing plate 12, the upper shear box 13 is subjected to a horizontal shear force, and the torque value measured by the torque sensor 16 will increase rapidly. After it stabilizes, record the torque T output by the torque sensor 16 and the displacement value output by the tie rod displacement sensor 17, and then turn off the rotary drive motor 5. Step 3: Repeat Step 2 to measure the horizontal shear force of the upper shear box 13 at different pressure values, and record the torque Ti output by the torque sensor 16 and the displacement value output by the tie rod displacement sensor 17. Step 4: After the test is completed, start the vertical drive motor 21 to raise the pressing plate 20, remove the lower shear box 9, clean the device, process the data, and calculate the shear strength of the bulk material under different normal pressure conditions according to formula (1). , (1) In the formula, r 1 and r 2 are the inner radius and outer radius of the lower shear box 9 respectively; T i is the torque output by the torque sensor 16 during the i-th test. Calculate the normal stress σ of the bulk material on the upper shear surface for each test according to formula (2). i , (2) In the formula, W i is the normal pressure on the upper surface of the material particles during the i-th test. Fit the above data to plot the ultimate shear stress line of the bulk material, and calculate the internal friction coefficient μ of the bulk material according to formula (3). b , (3) In the formula, ψ is the internal friction angle of the material, that is, the inclination angle of the ultimate shear stress line in the σ-τ coordinate plane.

[0031] Example 2. The difference between this example and Example 1 is that two tensile sensors 41 are selected as the equipment for measuring the horizontal shear force of the upper shear box 13. Two semi-circular head bolts 46 are arranged on the upper surface of the upper shear box 13, and the two semi-circular head bolts 46 are symmetrically arranged with the center of the upper shear box 13 as the center. One end of the tensile sensor 41 is connected to the semi-circular head bolt 46 through a swivel bolt 42, and the other end is connected to the tensile sensor base 43 through a screw 45. The tensile sensor base 43 is connected to the optical axis 4 through a bushing 44.

[0032] In this example, the data processing method is to calculate the shear strength of the bulk material according to formulas (4) and (5). , (4) (5) In the formula, r 1 and r 2 are the inner radius and outer radius of the lower shear box 9 respectively; r s is the radial distance between the two tensile sensors 41; r m is the distance of the force arm; F 1i and F 2i are the tensile forces output by the two tensile sensors 41 during the i-th test respectively.

[0033] Calculate the normal stress σ of the bulk material on the upper shear surface according to formula (2). i , (2) In the formula, W i is the normal pressure on the upper surface of the material particles during the i-th test. Fit the above data to plot the ultimate shear stress line of the bulk material, and calculate the internal friction coefficient μ of the bulk material according to formula (3). b , (3) In the formula, ψ is the internal friction angle of the material, that is, the inclination angle of the ultimate shear stress line in the σ-τ coordinate plane.

[0034] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and modifications made by those skilled in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

[0035] Other parts not detailed in the present invention belong to the prior art, so they will not be elaborated here.

[0036] Although the present invention has been described in conjunction with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various changes, substitutions of equivalents, and modifications to the subject matter listed herein without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims presented.

Claims

1. A testing device for the internal friction coefficient of bulk materials, characterized in that: Including support, rotation unit, shear unit, pressure unit, test unit, The support is an upper support and a lower support connected by an optical axis, The shearing unit comprises a lower shearing box, an inner cup, an outer cup, an annular pressure plate, and an upper shearing box. The lower shearing box is an annular box for placing materials. The lower end of the lower shearing box is connected to the rotating unit. The inner and outer cups are cylindrical glass cups with upper and lower openings. The inner and outer cups are coaxially arranged in the lower shearing box and are in contact with the inner annular wall and the outer annular wall of the lower shearing box respectively. A plurality of pressure claws are symmetrically arranged along the circumference at the bottom of the lower shearing box. The annular pressure plate is used to directly contact the material. A plurality of pressure claws are symmetrically arranged along the circumference on the lower end surface of the annular pressure plate. The upper end surface of the annular pressure plate is connected to the lower end of the upper shearing box. A central axis is arranged at the upper end of the upper shearing box. A ball upper cover passes through the central axis and is arranged at the upper end of the upper shearing box. An annular raceway is arranged on the lower surface of the ball upper cover. A plurality of universal ball bearings are arranged corresponding to the raceway of the upper shearing box. The annular raceway is in contact with the universal ball bearing. The pressure unit includes a vertical drive motor, two lead screws, and a pressure plate. The pressure plate is arranged above the upper shear box. Lead screws are arranged on both sides of the pressure plate. The upper end of the lead screw is connected to the vertical drive motor, and the lower end is connected to the lead screw fixing seat. The vertical drive motor is arranged on the upper support, and the two ends of the lead screw fixing seat are respectively connected to the lower part of the two optical axes. The testing unit includes a PLC controller, a normal pressure testing piece of the material, and a horizontal shear force testing piece of the material. The normal pressure testing piece is arranged between the pressure plate and the upper shear box, and the horizontal shear force testing piece is arranged in the upper shear box. The normal pressure testing piece and the horizontal shear force testing piece are both electrically connected to the PLC controller.

2. The device for testing the internal friction coefficient of bulk materials according to claim 1, characterized in that: The normal pressure test piece is a pressure sensor, the pressure sensor pressure plate is connected to the pressure plate, the pressure sensor is arranged in the pressure sensor base, the pressure sensor base is arranged at the upper end of the center axis of the upper shear box, the pressure sensor base is provided with four connecting rods along the circumference, the end of the connecting rod is connected to the optical axis through a linear bearing, the lower end of the connecting rod is provided with a pressure shaft, and the other end of the pressure shaft is connected to the ball upper cover.

3. The device for testing the internal friction coefficient of bulk materials according to claim 1, characterized in that: The horizontal shear force test piece is a torque sensor, and the torque sensor is arranged on the middle axis of the upper shear box.

4. The device for testing the internal friction coefficient of bulk materials according to claim 1, characterized in that: The horizontal shear force test piece is two tension sensors. Two semicircular head bolts are arranged on the upper surface of the upper shear box. The two semicircular head bolts are symmetrically arranged around the axis center of the upper shear box. One end of the tension sensor is connected to the semicircular head bolt through a live bolt, and the other end is connected to the tension sensor base. The tension sensor base is connected to the optical axis through a shaft sleeve.

5. The device for testing the internal friction coefficient of bulk materials according to claim 1, characterized in that: The rotating unit includes two rotating drive motors, a slewing support bearing, and a turntable. The two rotating drive motors are symmetrically arranged on the lower support. The outer periphery of the output shaft of the rotating drive motor is connected to a gear. The slewing support bearing is arranged between the turntable and the lower support. The inner ring of the slewing support bearing is fixedly connected to the turntable, and the outer ring is fixedly connected to the lower support. An external gear is arranged on the outer periphery of the outer ring. The external gear is meshed with a gear connected to the output shaft of the rotating drive motor. A connecting ring is arranged on the outer ring of the turntable for bolting to the lower shear box.

6. The device for testing the internal friction coefficient of bulk materials according to claim 5, characterized in that: It also includes a speed sensor and a pull rod displacement sensor. The speed sensor is arranged on the turntable, the pull rod displacement sensor base is arranged on the upper support, and the pull rod of the pull rod displacement sensor is connected with the pressure plate.

7. A method for testing the internal friction coefficient of bulk materials, characterized in that: The bulk material internal friction coefficient testing device according to any one of claims 1 to 6 comprises the following steps: Step 1: Start the vertical drive motor, lift the pressure plate, and then lift the upper shear box and the annular pressure plate to a certain height, turn off the vertical drive motor, place the loading funnel above the lower shear box, start the rotary drive motor, and make the lower shear box rotate at a lower speed to fill the material. Step 2: Turn off the rotary drive motor, start the vertical drive motor, lower the pressure plate until the output value of the normal force test piece reaches the set normal pressure value, turn off the vertical drive motor, start the rotary drive motor, perform the shear force test, and record the output value of the horizontal shear force test piece. After the test is completed, turn off the rotary drive motor. Step 3: Repeat step 2 to test the horizontal shear force of the material under different normal pressures and record the data. Step 4: After the test is completed, start the vertical drive motor to raise the pressure plate, remove the lower shear box, clean the device, process the data, and calculate the internal friction coefficient of the material.

8. The method for testing the internal friction coefficient of bulk materials according to claim 7, characterized in that: In step one, when the material is filled until it overflows the lower shear box, use a circular knife to scrape the surface of the lower shear box clockwise once or twice, and then scrape it counterclockwise. The circular knife is radially inclined at an angle of a=15~30° relative to the surface of the lower shear box until the material particles are flush with the upper end surface of the lower shear box and the filling is completed.

9. The method for testing the internal friction coefficient of bulk materials according to claim 7, characterized in that: In step 4, the data processing method is to calculate the shear strength of the bulk material tested by the torque sensor according to formula (1): , （1） Where r1 and r2 are the inner radius and outer radius of the lower shear box respectively; T i is the torque output by the torque sensor during the i-th test, According to formula (2), the normal stress σ of the bulk material on the upper shear surface of each test is calculated: i , （2） Where W i is the normal pressure on the upper surface of the material particles during the i-th test, The above data are fitted to draw the limit shear stress line of bulk materials, and the internal friction coefficient μ of bulk materials is calculated according to formula (3): b , （3） In the formula, ψ is the internal friction angle of the material, that is, the inclination angle of the limiting shear stress line in the σ-τ coordinate plane.

10. The method for testing the internal friction coefficient of bulk materials according to claim 7, characterized in that: In step 4, the data processing method is to calculate the shear strength of the bulk material tested by the tension sensor according to formulas (4) and (5): , （4） （5） Where r1 and r2 are the inner radius and outer radius of the lower shear box respectively; r s is the radial distance between the two tension sensors; r m is the distance of the force arm; F 1i and F 2i are the tension output by the two tension sensors during the i-th test, According to formula (2), the normal stress σ of the bulk material on the upper shear surface is calculated as i , （2） Where W i is the normal pressure on the upper surface of the material particles during the i-th test, The above data are fitted to draw the limit shear stress line of bulk materials, and the internal friction coefficient μ of bulk materials is calculated according to formula (3): b , （3） In the formula, ψ is the internal friction angle of the material, that is, the inclination angle of the limiting shear stress line in the σ-τ coordinate plane.

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