Adjustable bearing device for adjusting the position of the shaft center of a deep-well hoisting drum and a load capacity calculation method

Abstract

The present application belongs to the technical field of deep well hoisting, and discloses an adjustable bearing device for adjusting the shaft center position of a deep well hoisting drum and a bearing capacity calculation method. The adjustable bearing device is introduced into the adjusting wafer-shaped magnetic steel, and the eddy current damping effect is generated with the deep well hoisting drum shaft to realize the function of speed regulation at any time. In the limit position, the wafer-shaped magnetic steel is adjusted up and down to realize the forced constraint by compaction. At the same time, the shaft center position adjusting device is designed to adjust the position of the deep well hoisting drum stator shaft, and the adjustment of the shaft center trajectory is realized according to the actual working state. The bearing capacity calculation method of the adjustable bearing device is adjusted by using the thread bearing device itself and the gravity of the drum, adjusting the number of turns, and solving the maximum bearing capacity of the adjustable bearing device to prevent the device from failing due to excessive load during use. Only the key mechanism parameters are needed to quickly analyze whether the adjustment mechanism meets the bearing demand, prevent the device from failing due to overload, and the calculation is simple, universal and short in calculation time.

Description

Technical Field

[0001] This invention belongs to the field of deep well hoisting technology, and relates to an adjustable bearing device and a method for calculating the load-bearing capacity of a deep well hoisting drum shaft. Background Technology

[0002] In the energy and power sector, deep well hoisting equipment is commonly used in underground mineral resource extraction. With the gradual depletion of surface energy resources, the extraction of deep and even ultra-deep energy is becoming increasingly urgent, evolving from depths of 500-1000 meters to 1500-2000 meters. The hoisting drum is the core component of deep well hoisting equipment, directly determining the efficiency and stability of deep well hoisting. Typically, the speed braking control of deep well drums uses motors and frequency converters, and its control reliability heavily depends on the reliability of electrical components. However, energy extraction environments often face harsh conditions such as strong dust, humidity, and extreme temperatures, which can easily induce electrical component failure, thus affecting the normal operation of the hoisting drum. Mechanical structures, on the other hand, have advantages in terms of immunity to environmental interference, strength, and reliability. Furthermore, considering the potential for eccentricity during drum operation, a braking device with slow speed regulation, forced constraint braking, and adjustable center position must be designed to meet the high-performance and high-reliability operation requirements of deep well equipment drums. Conventional braking devices, such as mechanical gears, worm gears, and belts / steel belts, are space-consuming, require lubrication systems, and have high maintenance costs. They cannot currently meet the requirements for slowing down, braking, and self-aligning the lifting of deep well drums. Therefore, a braking device capable of adjusting the axis position of deep well lifting drums is needed to solve the aforementioned engineering challenges.

[0003] Regarding braking devices for deep well hoisting drums, China University of Mining and Technology, in its patent "Floating Disc Brake for 1000-meter Deep Well Hoisting Machine" (ZL201610144214.5), proposed a floating disc brake for 1000-meter deep well hoisting machines that integrates monitoring of braking positive pressure, clearance, wear, and fatigue state. This effectively and automatically compensates for brake shoe wear to achieve self-alignment of the brake disc. However, it requires a complex sensor system and active control system, resulting in a complex structure and lacking a real-time deceleration function. This makes it unsuitable for the urgent needs of higher performance, greater flexibility, and convenience in hoisting equipment at greater mining depths. In their paper "Calculation of Braking Torque in Dynamic Hoisting Process of 1000-meter Deep Well Hoisting Machine," Zhai Weidong et al. established the safe braking torque and working braking torque of deep well hoisting equipment brakes through dynamic analysis, obtaining the braking dynamic characteristics under frictional hoisting processes in 1000-meter deep wells. However, this paper lacks a mapping relationship between braking force and braking device parameters, failing to provide direct support for the design of braking devices for deep well equipment with deceleration constraints. Therefore, an adjustable bearing device is proposed to adjust the position of the shaft center of the deep well hoisting drum, which has important reference for guiding the performance improvement of deep well hoisting equipment. Summary of the Invention

[0004] Current deep well hoisting devices suffer from irregular shaft trajectories and excessive torque, severely impacting equipment lifespan and operational stability. To address these shortcomings, this invention presents an adjustable bearing device and a method for calculating the load-bearing capacity of the adjusting mechanism for adjusting the shaft center position of a deep well hoisting drum. The aim is to introduce adjustable, tile-shaped magnets to generate eddy current damping with the drum shaft, enabling real-time slow-speed adjustment. At extreme positions, forced constraint is achieved by compacting the upper and lower tile-shaped magnets. A shaft center position adjustment device is also designed, allowing adjustment of the shaft trajectory based on the actual working conditions by adjusting the position of the stator shaft 1. This innovative braking device employs four symmetrically arranged tile-shaped magnets to achieve both real-time slowing and forced constraint of the deep well hoisting drum, effectively controlling its hoisting speed to ensure safe and reliable operation. It also enables emergency braking in sudden emergencies and allows for adjustment of the drum's center position after prolonged operation, ensuring the drum remains centered within the device. This design significantly improves the reliability of existing deep well hoisting drum braking technology and has broad prospects for other energy machinery fields.

[0005] The technical solution of the present invention: An adjustable bearing device for adjusting the shaft center position of a deep well hoisting drum has the following specific structure: the stator shaft 1 and the deep well hoisting drum 6 form a stator-rotor kinematic pair through a clearance fit, ensuring that the shaft center error meets the standard; the upper bow adjustment frame 3 is fastened to the upper bow end of the stator shaft 1 by the upper bow fastening bolt 2; the upper bow adjustment tile magnet 5 is connected to the upper bow adjustment frame 3 by the upper bow adjustment bolt 4, and the upper bow adjustment tile magnet 5 is secured by the upper bow adjustment bolt 4. The radial clearance between steel 5 and the deep well hoisting drum 6 is adjustable; the upper stern adjustment frame 9 is fastened to the upper stern end of the deep well hoisting drum stator shaft 1 by upper stern fastening bolts 10; the upper stern adjustment tile-shaped magnet 7 is connected to the upper stern adjustment frame 9 by upper stern adjustment bolts 8, and the upper stern adjustment bolts 8 ensure that the radial clearance between the upper stern adjustment tile-shaped magnet 7 and the deep well hoisting drum 6 is adjustable; the lower stern adjustment frame 12 is fastened to the lower stern end of the deep well hoisting drum stator shaft 1 by lower stern fastening bolts 11. The stern-end lower adjusting tile-shaped magnet 14 is connected to the stern-end lower adjusting frame 12 via the stern-end lower adjusting bolt 13. The maximum gap between the stern-end lower adjusting tile-shaped magnet 14 and the deep well hoisting drum 6 is 5mm. The retainer of the stern-end lower adjusting tile-shaped magnet 14 has a pin hole, and the stern-end lower adjusting frame 12 has a threaded hole. The threaded hole, the pin hole, and the stern-end lower adjusting bolt 13 are fitted together to adjust the stern-end axis position, thus enabling adjustable stern-end axis position. The bow-end lower adjusting frame 17 is tightened via the bow-end lower fastening bolt 18. The lower end of the stator shaft 1 of the deep well hoisting drum is fixed to the lower end. The lower end adjusting tile-shaped magnet 15 is connected to the lower end adjusting frame 17 through the lower end adjusting bolt 16. The lower end adjusting bolt 16 ensures that the radial clearance between the lower end adjusting tile-shaped magnet 15 and the deep well hoisting drum 6 is adjustable. The retainer of the lower end adjusting tile-shaped magnet 15 has a pin hole, and the lower end adjusting frame 17 has a threaded hole. The threaded hole cooperates with the pin hole and the lower end adjusting bolt 16 to realize the adjustable position of the bow end axis.

[0006] A method for calculating the load-bearing capacity of an adjustable bearing device for adjusting the shaft position of a deep well hoisting drum is described below: Step 1: Determine the tightening torque and theoretical preload; applied tightening torque T The nominal diameter of all adjusting bolts d Torque coefficient K Represented as: in, K 1 is the thread friction influence factor, which ranges from 0.25 to 0.45; K 2 is the roughness factor of the gasket or contact surface, which is 0.8-1.2; K 3 is the deep well environment humidity correction factor, which is 1.1-1.3; Theoretical preload F p0 for: The second step is to calculate the radial clearance and normal magnetic attraction force between the magnet and the roller to obtain the initial combined axial force of the bolt. Let δ be the radial clearance between the working surface of the magnet and the outer circle of the drum after adjustment; the normal magnetic attraction force generated by the magnet on the ferromagnetic material of the drum under this radial clearance. F m for: in, B r The residual magnetic flux density of the tile-shaped magnet is expressed in tons (T). A m The effective magnetic pole area of ​​the magnet is expressed in meters (m²). 2 ; m 0 =4π×10 -7 H / m; l The gap reluctance attenuation coefficient ranges from 0.5 to 1.2. The normal magnetic attraction force generates an equivalent additional axial tensile force on all adjusting bolts. F ma : in, or The transfer coefficient for converting axial tensile force into bolt axial force is taken as 0.2-0.8; Initial combined axial force of the bolt: Under prolonged continuous pressure, creep will occur at the contact surfaces of the adjusting bracket and the connected parts. The initial combined axial force decays exponentially, and the final axial force on the bolt is: in, It is the creep time constant, taken as 10. 7 -10 8 s; t For time; No. i Axial stress of each bolt s i (t) : in, A s The cross-sectional area under bolt stress is expressed in meters (m²). 2 ; The third step is to calculate the fatigue life of the bolts. Extracting axial stress s i (t) is a cycle, a cycle consisting of one tension and one compression, stress amplitude s a With average stress s m : in, s max This indicates the maximum axial stress that the bolt withstands in a single stress cycle. s min This indicates the minimum axial stress that a bolt withstands in a single stress cycle; The equivalent stress amplitude is: in, s b The tensile strength of the bolt is given in MPa. Damage caused by a single cycle D i =1 / N f , N f Total bolt damage was determined from the SN curve: in, N f It is the number of cycles before the bolt fails. D total Bolt fatigue life is reached when =1; The fourth step is to compare the actual stress conditions with the allowable load of the thread; The main evaluation criteria include: 1 Applicable to all bolts; 2. Maximum axial stress max s i ( t )≤ Bolt tensile strength / 2.5; 3 Total Damage D total ≤0.8.

[0007] The beneficial effects of this invention are as follows: This invention proposes an adjustable bearing device for adjusting the shaft center position of a deep well hoisting drum. It comprehensively considers the speed control, emergency shutdown, and centering requirements of the deep well hoisting drum. By adjusting the eddy current deceleration effect between the tile-shaped magnet and the drum rotor, it achieves stable deep well hoisting while simultaneously providing deceleration and forced constraint functions. It also significantly reduces auxiliary facilities and improves the space utilization rate for drum speed control. Two adjusting bolts allow for real-time adjustment of the drum center position, preventing excessive bending moment and eccentricity from affecting operational stability. Furthermore, this invention proposes a method for calculating the load-bearing capacity of the adjustment mechanism. Utilizing the threaded load-bearing device of the adjusting bolt itself and the drum's gravity, the number of turns is adjusted to quickly calculate whether the external load meets the design limits, preventing failure due to overload. In summary, the adjustable bearing device for adjusting the shaft center position of a deep well hoisting drum and the load-bearing capacity calculation method proposed in this invention provide innovative configurations and rapid solution methods for the optimized design and performance improvement of similar equipment. It has practical guiding value for the engineering application of deep well hoisting equipment in the energy field and can also improve equipment reliability. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of an adjustable bearing device for adjusting the position of the shaft center of a deep well hoisting drum; Figure 2 This is a cross-sectional schematic diagram of an adjustable bearing device that can adjust the position of the shaft center of a deep well hoisting drum. Figure 3 This is a flowchart of a method for calculating the load-bearing capacity of an adjustment mechanism; In the diagram: 1. Stator shaft of deep well hoisting drum; 2. Upper bow fastening bolt; 3. Upper bow adjusting frame; 4. Upper bow adjusting bolt; 5. Upper bow adjusting tile magnet; 6. Deep well hoisting drum; 7. Upper stern adjusting tile magnet; 8. Upper stern adjusting bolt; 9. Upper stern adjusting frame; 10. Upper stern fastening bolt; 11. Lower stern fastening bolt; 12. Lower stern adjusting frame; 13. Lower stern adjusting bolt; 14. Lower stern adjusting tile magnet; 15. Lower bow adjusting tile magnet; 16. Lower bow adjusting bolt; 17. Lower bow adjusting frame; 18. Lower bow fastening bolt. Detailed Implementation

[0009] The embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0010] This implementation case uses an adjustable bearing device that includes four pairs of adjusting tile-shaped magnets that simultaneously adjust the position of the shaft center of a deep well hoisting drum, and a method for calculating the load-bearing capacity of the adjusting mechanism.

[0011] The adjustment parameters are as follows: inner diameter of the tile-shaped magnet is 32mm; outer diameter is 44mm; width is 30mm; angle is 120°; remanence is 1.25T; gap between the tile-shaped magnet and the deep well hoisting drum 6 is 6mm; downward speed is 0.2mm / s; descent time is 20s; and effective conductivity of the stator shaft 1 of the deep well hoisting drum is 7.6×10⁻⁶. 6 The rotational speed between the stator shaft 1 and the deep well hoisting drum 6 is 3000 r / min, the empirical conversion factor is 0.8, the nominal diameter of the adjusting bolt thread is 12 mm, the maximum engagement length is 20 mm, the thread pitch is 1.75 mm, and the adjustable range of the stator shaft center is ±3 mm.

[0012] An adjustable bearing device for adjusting the shaft center position of a deep well hoisting drum has the following specific structure: the stator shaft 1 and the deep well hoisting drum 6 form a stator-rotor kinematic pair through a clearance fit, ensuring that the shaft center error meets the standard; the upper bow adjustment frame 3 is fastened to the upper bow end of the stator shaft 1 by the upper bow fastening bolt 2; the upper bow adjustment tile magnet 5 is connected to the upper bow adjustment frame 3 by the upper bow adjustment bolt 4, and the upper bow adjustment tile magnet 5 is secured by the upper bow adjustment bolt 4. The radial clearance between steel 5 and the deep well hoisting drum 6 is adjustable; the upper stern adjustment frame 9 is fastened to the upper stern end of the deep well hoisting drum stator shaft 1 by upper stern fastening bolts 10; the upper stern adjustment tile-shaped magnet 7 is connected to the upper stern adjustment frame 9 by upper stern adjustment bolts 8, and the upper stern adjustment bolts 8 ensure that the radial clearance between the upper stern adjustment tile-shaped magnet 7 and the deep well hoisting drum 6 is adjustable; the lower stern adjustment frame 12 is fastened to the lower stern end of the deep well hoisting drum stator shaft 1 by lower stern fastening bolts 11. The stern-end lower adjusting tile-shaped magnet 14 is connected to the stern-end lower adjusting frame 12 via the stern-end lower adjusting bolt 13. The maximum gap between the stern-end lower adjusting tile-shaped magnet 14 and the deep well hoisting drum 6 is 5mm. The retainer of the stern-end lower adjusting tile-shaped magnet 14 has a pin hole, and the stern-end lower adjusting frame 12 has a threaded hole. The threaded hole, the pin hole, and the stern-end lower adjusting bolt 13 are fitted together to adjust the stern-end axis position, thus enabling adjustable stern-end axis position. The bow-end lower adjusting frame 17 is tightened via the bow-end lower fastening bolt 18. The lower end of the stator shaft 1 of the deep well hoisting drum is fixed to the lower end. The lower end adjusting tile-shaped magnet 15 is connected to the lower end adjusting frame 17 through the lower end adjusting bolt 16. The lower end adjusting bolt 16 ensures that the radial clearance between the lower end adjusting tile-shaped magnet 15 and the deep well hoisting drum 6 is adjustable. The retainer of the lower end adjusting tile-shaped magnet 15 has a pin hole, and the lower end adjusting frame 17 has a threaded hole. The threaded hole cooperates with the pin hole and the lower end adjusting bolt 16 to realize the adjustable position of the bow end axis. When the deep well hoisting drum 6 is operating normally, the four adjusting tile-shaped magnets remain stationary, allowing for normal hoisting and operation. When deceleration is required, eddy current damping is achieved by adjusting the gap between the four adjusting tile-shaped magnets and the deep well hoisting drum 6, thus slowing down the flow. In case of an emergency requiring a stop, the four adjusting tile-shaped magnets quickly close to lock the deep well hoisting drum 6, providing forced constraint. After prolonged use, the axial eddy current displacement sensor can monitor the axial eddy current displacement of the stator shaft 1 of the deep well hoisting drum. Adjusting the stern-end and bow-end axial position adjusting bolts 13 and 16 based on the axial eddy current displacement allows for changes in the axial position. This invention's structural design saves space compared to traditional frequency converter control, resulting in a more compact design. Such a structure has not been previously reported. It allows for non-contact magnetic adjustment during deep well hoisting, enabling seamless switching between braking and operation, and possesses significant practical value and application potential in the energy sector.

[0013] At this point, the installation of an adjustable bearing device for adjusting the position of the shaft center of a deep well hoisting drum is complete.

[0014] A method for calculating the load-bearing capacity of an adjustable bearing device for adjusting the shaft position of a deep well hoisting drum, characterized by the following steps: The adjusting bolt has an M12 coarse thread and a nominal diameter of [missing information]. d =12 mm, pitch P =1.75 mm, stress cross-sectional area A s =86.3 mm 2 Tightening torque T =60 N·m, magnetic induction intensity B r =1.2T, d =1 mm, t =1 year s b =800 MPa Step 1: Theoretical preload; M12 bolt tightening torque T Approximately 60 N·m, the nominal diameter of all adjusting bolts d Torque coefficient K Represented as: Theoretical preload F p0 for: The second step is to calculate the radial clearance and normal magnetic attraction force between the magnet and the drum to obtain the initial composite axial force. The normal magnetic attraction Fm generated by the magnet on the ferromagnetic material of the drum under the radial gap is: The normal magnetic attraction force generates an equivalent additional axial tensile force on all adjusting bolts. F ma : in, or The transfer coefficient for converting axial tensile force into bolt axial force is set to 0.5.

[0015] Initial combined axial force of the bolt: Under prolonged continuous pressure, creep will occur at the contact surfaces of the adjusting bracket and the connected parts, and the preload will decrease exponentially, resulting in the final axial force as follows: in, It is the creep time constant, taken as 10. 7 s.

[0016] No. i Axial stress of each bolt s i (t) : The third step is to calculate the fatigue life of the bolts. Extracting axial stress s i (t) is a cycle, stress amplitude s a With average stress s m : in, s max This indicates the maximum axial stress that the bolt withstands in a single stress cycle. s min This represents the minimum axial stress within the same cycle.

[0017] Using the Goodman correction, the equivalent stress amplitude is obtained as follows: .

[0018] Assume the total number of loops is 10 5 Next, obtain materials by referring to the table. N f =10 6 Damage caused by a single cycle D i =1 / 10 6 Total damage to bolts: N f It is the number of cycles before the bolt fails. D total Bolt fatigue life is reached when =1; The fourth step is to compare the actual stress conditions with the allowable load of the thread; The main evaluation criteria include: (1) Applicable to all bolts, meets the requirements; (2) The maximum axial stress 73.7 MPa ≤ 800 / 2.5 = 320, which satisfies the condition; (3) Fatigue injury D total =0.1≤0.8, which satisfies the condition.

[0019] At this point, the load-bearing capacity calculation for an adjustable bearing device and adjustment mechanism for adjusting the shaft position of a deep well hoisting drum has been completed.

[0020] This novel braking device comprehensively considers the needs of speed control, emergency shutdown, and self-alignment for deep well hoisting drums. Through the eddy current deceleration effect between the tile-shaped magnets and the drum rotor, it achieves stable deep well hoisting while simultaneously providing deceleration and forced constraint. This also significantly reduces auxiliary facilities and improves the space utilization rate for drum speed control. During normal operation, adjusting the slow displacement between the tile-shaped magnets and the drum stator shaft generates a large non-contact braking force to quickly decelerate the drum, greatly maintaining operational safety. Two adjusting bolts allow for real-time adjustment of the drum's center position, preventing excessive bending moment and eccentricity from affecting operational stability. Furthermore, this invention proposes a method for calculating the load-bearing capacity of the adjustment mechanism. Utilizing the threaded bearing capacity of the adjusting bolts themselves and the drum's gravity, the number of turns of the bolts is adjusted to quickly calculate whether the external load meets the design limits, preventing failure due to overload. In summary, the adjustable bearing device and adjustment mechanism load-bearing capacity calculation method proposed in this invention provide an innovative configuration and rapid solution method for the optimized design and performance improvement of similar equipment. It has practical guiding value for the engineering application of deep well hoisting equipment in the energy field and can also improve the reliability of the equipment.

[0021] This invention proposes a method for calculating the load-bearing capacity of an adjustment mechanism. Utilizing the threaded bearing capacity of the adjusting bolt itself and the weight of the drum, the number of turns of the bolt is adjusted to quickly calculate whether the external load meets the design limits, preventing failure due to overload. In summary, the adjustable bearing device and adjustment mechanism load-bearing capacity calculation method proposed in this invention provide an innovative configuration and rapid solution method for the optimized design and performance improvement of similar equipment. It has practical guiding value for the engineering application of deep well hoisting equipment in the energy sector and can also improve the reliability of the equipment.

Claims

1. An adjustable bearing device for adjusting the position of the shaft center of a deep well hoisting drum, characterized in that, The specific structure of the adjustable bearing device is as follows: the stator shaft (1) of the deep well hoisting drum and the deep well hoisting drum (6) form a stator-rotor kinematic pair through clearance fit, and ensure that the shaft center error meets the standard; the upper bow adjustment frame (3) is fastened to the upper bow of the stator shaft (1) of the deep well hoisting drum through the upper bow fastening bolt (2); the upper bow adjustment tile magnet (5) is connected to the upper bow adjustment frame (3) through the upper bow adjustment bolt (4), and the upper bow adjustment tile magnet (5) is ensured to be aligned with the deep well hoisting drum (6) along the bow. The radial clearance is adjustable; the upper stern adjustment frame (9) is fastened to the upper stern of the deep well hoisting drum stator shaft (1) by the upper stern fastening bolt (10), and the upper stern adjustment tile magnet (7) is connected to the upper stern adjustment frame (9) by the upper stern adjustment bolt (8), and the upper stern adjustment tile magnet (7) and the deep well hoisting drum (6) are radially adjustable by the upper stern adjustment bolt (8); the lower stern adjustment frame (12) is fastened to the lower stern of the deep well hoisting drum stator shaft (1) by the lower stern fastening bolt (11), and the lower stern adjustment... The stern-end adjustable magnet (14) is connected to the stern-end adjustable frame (12) via the stern-end lower adjusting bolt (13). The maximum gap between the stern-end lower adjusting magnet (14) and the deep well hoisting drum (6) is 5mm. The retainer of the stern-end lower adjusting magnet (14) has a pin hole, and the stern-end lower adjusting frame (12) has a threaded hole. The threaded hole, the pin hole, and the stern-end lower adjusting bolt (13) are used to adjust the stern-end axis position, thereby making the stern-end axis position adjustable. The bow-end lower adjusting frame (17) is fastened to the bow-end lower fastening bolt (18). The lower side of the stator shaft (1) of the deep well hoisting drum has an adjusting tile-shaped magnet (15) on the lower side of the bow end connected to the lower side adjusting frame (17) on the lower side of the bow end through the lower side adjusting bolt (16), and the lower side adjusting bolt (16) ensures that the radial gap between the lower side adjusting tile-shaped magnet (15) and the deep well hoisting drum (6) is adjustable; the retainer of the lower side adjusting tile-shaped magnet (15) on the bow end has a pin hole, and the lower side adjusting frame (17) on the bow end has a threaded hole. The threaded hole cooperates with the pin hole and the lower side adjusting bolt (16) on the bow end to realize the adjustable position of the bow end shaft.

2. A method for calculating the bearing capacity of an adjustable bearing device for adjusting the shaft position of a deep well hoisting drum as described in claim 1, characterized in that, The steps are as follows: Step 1: Determine the tightening torque and theoretical preload; applied tightening torque T The nominal diameter of all adjusting bolts d Torque coefficient K Represented as: in, K 1 is the thread friction influence factor, which ranges from 0.25 to 0.45; K 2 is the roughness factor of the gasket or contact surface, which is 0.8-1.2; K 3 is the deep well environment humidity correction factor, which is 1.1-1.3; Theoretical preload F p0 for: The second step is to calculate the radial clearance and normal magnetic attraction force between the magnet and the roller to obtain the initial combined axial force of the bolt. Let δ be the radial clearance between the working surface of the magnet and the outer circle of the drum after adjustment; the normal magnetic attraction force generated by the magnet on the ferromagnetic material of the drum under this radial clearance. F m for: in, B r The residual magnetic flux density of the tile-shaped magnet is expressed in tons (T). A m The effective magnetic pole area of ​​the magnet is expressed in meters (m²). 2 ; μ 0 =4π×10 -7 H / m; λ The gap reluctance attenuation coefficient ranges from 0.5 to 1.

2. The normal magnetic attraction force generates an equivalent additional axial tensile force on all adjusting bolts. F ma : in, η The transfer coefficient for converting axial tensile force into bolt axial force is taken as 0.2-0.8; Initial combined axial force of the bolt: Under prolonged continuous pressure, creep will occur at the contact surfaces of the adjusting bracket and the connected parts. The initial combined axial force decays exponentially, and the final axial force on the bolt is: in, It is the creep time constant, taken as 10. 7 -10 8 s; t For time; No. i Axial stress of each bolt σ i (t) : in, A s The cross-sectional area under bolt stress is expressed in meters (m²). 2 ; The third step is to calculate the fatigue life of the bolts. Extracting axial stress σ i (t) is a cycle, a cycle consisting of one tension and one compression, with stress amplitude σ a With average stress σ m : in, σ max This indicates the maximum axial stress that the bolt withstands in a single stress cycle. σ min This indicates the minimum axial stress that a bolt withstands in a single stress cycle; The equivalent stress amplitude is: in, σ b The tensile strength of the bolt is given in MPa. Damage caused by a single cycle D i =1 / N f , N f The total damage to the bolts was determined from the SN curve. in, N f It is the number of cycles before the bolt fails. D total Bolt fatigue life is reached when =1; The fourth step is to compare the actual stress conditions with the allowable load of the thread; The main evaluation criteria include: (1) Applicable to all bolts; (2) Maximum axial stress max σ i ( t )≤ Bolt tensile strength / 2.5; (3) Total damage D total ≤0.8.

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