A device and method for tightening and loosening a piston nut of a large piston compressor
By designing the frame and screw nut mechanism in large piston compressors, the problems of insufficient preloading force and complex operation during the tightening and loosening of the piston nut are solved, and efficient and safe piston nut connection is achieved, extending the piston and The service life of the piston rod.
Patent Information
- Application Number
- CN202311152098.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-07
- Publication Date
- 2024-12-24
- Estimated Expiration
- 2043-09-07
AI Technical Summary
During the tightening and loosening process of large piston compressors, there are problems such as insufficient preloading force, abnormal noise, rust and inconvenient operation. Traditional sledge hammer strike method is difficult to achieve accurate preloading, and it is complex in operation and has high safety risks.
A device including a frame, clamping mechanism and a screw nut mechanism is designed. The piston is fixed through the clamping mechanism, and the plum wrench is driven to tighten or loosen the piston nut, and multi-point compression and screw drive are used. This method improves the tightening torque to ensure reliable connection between the piston and the piston rod.
It realizes efficient tightening and loosening of piston nuts, avoids abnormal noise and rust, reduces working strength and safety risks, improves the service life of pistons and piston rods, and simplifies the operation process.
Smart Images
Figure CN117182529B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of mechanical equipment, and in particular to a device and method for tightening and loosening a piston nut of a large piston compressor. Background Art
[0002] The main transmission device of the piston compression is a crank-connecting rod mechanism. The rotational motion of the crankshaft is converted (transmitted) through the crank pin, connecting rod, and crosshead to make the piston rod and piston perform linear reciprocating motion, compressing the medium in the cylinder to do work.
[0003] The piston rod and the piston nut are connected by threads, making the piston and the piston rod one component. If the pre-tightening force of the piston nut and the piston rod thread is insufficient, the piston will make abnormal noises during operation; the piston rod will creep and elongate under the impact force of the piston and the tensile stress generated by the pre-tightening force for a long time, and the piston will make abnormal noises during operation; the piston will run in a cold and hot alternating environment for a long time, the nut and the piston rod thread will rust, and foreign matter (lubricating oil carbide, scale, impurities) will enter and adhere to the thread connection gap, making it difficult to unscrew the nut during maintenance.
[0004] The conventional method for tightening and loosening the piston nut is to use a sledgehammer to hit the plum blossom percussion wrench, which is prone to the following shortcomings: the piston cannot be positioned in the circumferential direction, and the piston will rotate when struck, resulting in insufficient tightening torque for the nut; the piston nut of a large compressor is large in size, and the percussion wrench is large in size and mass. When struck, the wrench has large inertia and absorbs a lot of the hammer's percussion energy, resulting in insufficient tightening torque for the nut; hitting with a sledgehammer requires very high skills; the sledgehammer may deviate from the target when striking, damaging the piston; the percussion wrench may fly out and injure people; the hammer head may be thrown out and injure people or damage equipment; the ground may be damaged, etc.
[0005] Therefore, the present invention designs a tightening and loosening device for a piston nut of a large piston compressor, a clamping mechanism fixes the piston and the piston rod, and then rotates the piston nut wrench through the nut rotating mechanism to achieve a larger tightening or loosening torque acting on the piston nut, which can complete the tightening of the piston nut of the large piston compressor and achieve the required tightening torque, so that the piston and the piston rod are reliably connected; and the piston nut can be smoothly disassembled during disassembly. Summary of the invention
[0006] In response to the technical problems raised above, a device and method for tightening and loosening a piston nut of a large piston compressor is provided.
[0007] The technical means adopted by the present invention are as follows:
[0008] A large piston compressor piston nut tightening-loosening device comprises: a frame, a clamping mechanism and a nut screwing mechanism. The piston rod and piston of the piston compressor are placed in the frame, one end of the piston rod is connected to the piston through the piston nut, and the other end of the piston rod is fixedly connected to the frame away from the piston; the clamping mechanism is installed on the frame, and is closely connected with the outer cylindrical surface of the piston at multiple locations, and is used to fix and position the piston;
[0009] The nut-screwing mechanism is installed on the frame and comprises a plum wrench. The middle part of the plum wrench is sleeved on the piston nut. The plum wrench is driven by the nut-screwing mechanism to rotate clockwise or counterclockwise to tighten or loosen the piston nut.
[0010] Furthermore, the clamping mechanism includes two lower clamping blocks and an upper clamping block, the two lower clamping blocks are installed at the bottom of the frame and are tightly contacted and connected to both sides of the lower part of the outer cylindrical surface of the piston; a movable cross beam A is installed on the frame, and the upper clamping block is installed on the movable cross beam A and is tightly contacted and connected to the upper part of the outer cylindrical surface of the piston.
[0011] Further, the lower clamping block includes a lower brake body, the lower brake body is connected to the movable crossbeam C through the movable crossbeam C, the movable crossbeam C is fixed on the frame, and the elastic body in the cylindrical surface of the lower brake body is tightly fitted with the outer cylindrical surface of the piston;
[0012] The upper clamping block comprises an upper brake body, which is connected to a screw on the movable cross beam A. The screw enables the elastic body in the inner cylindrical surface of the upper brake body to fit tightly with the outer cylindrical surface of the piston.
[0013] Furthermore, the two lower brake bodies and the upper brake body press the piston at three points evenly distributed over a circumference of 120°.
[0014] Furthermore, the nut screwing mechanism also includes a bearing seat, two screw rods, two movable nuts and a movable beam B. The movable beam B is installed on the frame. The two movable nuts are arranged at intervals and are pin-connected with the movable beam A and the movable beam B. Each of the screw rods passes through the movable nut and is screwed with the movable nut. The bottom end of each screw rod is rotatably connected to a bearing seat, and the bottoms of the two bearing seats are respectively rotatably connected to the two ends of the plum blossom wrench; the two screw rods move up and down in the movable nut, driving the plum blossom wrench to rotate clockwise or counterclockwise to tighten or loosen the piston nut.
[0015] Furthermore, a thrust bearing is installed in the bearing seat, and the screw rod is connected to the thrust bearing, and the rotational connection between the screw rod and the bearing seat is realized through the thrust bearing; a locking nut is also connected to the screw rod, and the locking nut is located above the thrust bearing and is tightened in the bearing seat, so as to limit the thrust bearing; the bearing seat is rotationally connected to the plum blossom wrench through a cylindrical pin A.
[0016] Furthermore, a piston rod anti-rotation plate is installed on one end of the piston rod away from the piston, and the piston rod anti-rotation plate is used to achieve a fixed connection between the piston rod and the frame.
[0017] The present invention also provides a method for tightening and loosening a piston nut of a large piston compressor based on the above device, comprising the following steps:
[0018] Step 1: Install the piston rod into the piston, manually screw in the piston nut, and then manually tighten the piston nut with a 12-sided plum wrench;
[0019] Step 2: Install the lower clamping block and the piston rod anti-rotation plate; hoist the piston rod and the piston into the frame, and place the piston on the lower clamping block; move the piston and the piston rod axially, and install the end of the piston rod away from the piston into the piston rod anti-rotation plate; install the movable crossbeam A and the upper clamping block; the two lower brake bodies and the upper brake body press the piston at 3 points evenly distributed at 120° around the circumference, and the elastic body in the cylindrical surface of the lower brake body fits tightly with both sides of the lower part of the outer cylindrical surface of the piston, and the screw on the movable crossbeam A presses the upper brake body on the upper part of the outer cylindrical surface of the piston;
[0020] Step 3. Adjust the screw rod's screw-in length, assemble the plum blossom wrench, cylindrical pin A, movable nut, and movable beam B; the movable nut is connected to the movable beam A and movable beam B pins, and can swing clockwise or counterclockwise; the screw rod is connected to the bearing seat pin, and can rotate relatively, and screwed together with the movable nut to realize the up and down movement of the screw rod, driving the plum blossom wrench to rotate clockwise or counterclockwise, and realize the tightening or loosening of the piston nut.
[0021] Compared with the prior art, the present invention has the following advantages:
[0022] The large piston compressor piston nut tightening-loosening device and method provided by the present invention adopts a nut-spinning mechanism to rotate the piston nut, and the piston nut tightening and loosening effects are good, thereby eliminating the abnormal noise of the compressor caused by the loosening of the piston nut; avoiding the collision and damage of the piston and the piston rod when the piston nut is loose, thereby extending the service life of the piston and the piston rod; the operation skills can be mastered quickly, and the operator is not required to have the skill of using a sledgehammer; the operation has low labor intensity, low safety risk and high efficiency; the required tools and appliances are few, and on-site operation and promotion are convenient.
[0023] Based on the above reasons, the present invention can be widely promoted in the fields of disassembly and assembly of pistons with a diameter of more than 500 mm. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.
[0025] Figure 1 It is a structural schematic diagram of the present invention.
[0026] Figure 2 for Figure 1 Schematic diagram of the structure in the A direction.
[0027] Figure 3 for Figure 1 Schematic diagram of the structure in the B direction.
[0028] Figure 4 It is a schematic diagram of the local structure of one direction of the present invention.
[0029] Figure 5 for Figure 4 Enlarged view of point C in the middle.
[0030] Figure 6 There are four structures of the end of the piston rod away from the piston, among which (a) is the first structure, (b) is the second structure, (c) is the third structure, and (d) is the fourth structure.
[0031] Figure 7 It is a schematic diagram of a local structure of another aspect of the present invention.
[0032] In the figure: 1. frame; 2. lower clamping block; 3. piston; 4. piston rod; 5. piston rod anti-rotation plate; 6. nut screwing mechanism; 7. upper clamping block; 8. plum blossom wrench; 9. cylindrical pin A; 10. bearing seat; 11. screw rod; 12. movable nut; 13. movable crossbeam A; 14. movable crossbeam B; 15. thrust bearing; 16. locking nut; 17. movable crossbeam C; 18. cylindrical pin B; 19. lower brake body; 20. upper brake body. DETAILED DESCRIPTION
[0033] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.
[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.
[0036] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values of the parts and steps described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.
[0037] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.
[0038] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.
[0039] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.
[0040] The technical problem to be solved by the present invention is to reliably tighten (loosen) the piston nut of a large piston compressor, and a spiral tightening (loosening) method and device are provided. The piston nut reaches the required pre-tightening force, avoids abnormal noise during operation, and increases the life of the piston and piston rod.
[0041] The present invention is a large piston compressor piston nut tightening-loosening device, which is to make a frame, and install the piston rod 4 and the piston 3 into the frame (see Figure 1 , Figure 2 , Figure 3 ), the piston 3 is positioned and clamped by the lower clamping block 2 and the upper clamping block 7, and the end of the piston rod 4 away from the piston 3 is connected to the piston rod anti-rotation plate 5 to prevent the piston 3 and the piston rod 4 from rotating, and then the two screw rods 11 of the nut mechanism 6 are rotated (see Figure 4 , Figure 5 ) to tighten or loosen the piston nut.
[0042] A method for tightening and loosening a piston nut of a large piston compressor of the present invention is as follows:
[0043] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5As shown, install the piston rod 4 into the piston 3, manually screw in the piston back cap (piston nut), and then tighten it manually with the 12-sided plum wrench 8 in the nut screwing mechanism 6; install the lower clamping block 2 and the piston rod anti-rotation plate 5, and the two lower clamping blocks 2 are installed at the bottom of the frame 1, and the piston rod anti-rotation plate 5 is used to achieve a fixed connection between the piston rod 4 and the frame 1; hoist the piston rod 4 and the piston 3 into the frame 1, and place the piston 3 on the lower clamping block 2; axially move the piston 3 and the piston rod 4, and install the end of the piston rod 4 away from the piston 3 into the piston rod anti-rotation plate 5; install the movable crossbeam A13 and the upper clamping block 7, and the movable crossbeam A13 is installed on the frame 1, and the upper clamping block 7 is installed on the movable crossbeam A13.
[0044] like Figure 4 , Figure 5 As shown, adjust the screw rod 11 screwing length, assemble the plum wrench 8, cylindrical pin A9, movable nut 12, and movable crossbeam B14 as shown. Figure 4 , Figure 5 . The movable nut 12 is pin-connected with the movable crossbeam A13 and the movable crossbeam B14, and can swing clockwise or counterclockwise; the screw rod 11 can be pin-connected with the bearing seat 10, and can rotate relatively, and screwed with the movable nut 12 to realize the up and down movement of the screw rod 11, driving the plum blossom spanner 8 to rotate clockwise or counterclockwise to tighten or loosen the piston nut. Specifically, the movable crossbeam B14 is installed on the frame 1, and the two movable nuts 12 are arranged at intervals and are pin-connected with the movable crossbeam A13 and the movable crossbeam B14. Each screw rod 11 passes through the movable nut 12 and is screwed with the movable nut 12. The bottom end of each screw rod 11 is rotatably connected to a bearing seat 10, and the bottoms of the two bearing seats 10 are respectively rotatably connected to the two ends of the plum blossom spanner 8; the screw rod 11 moves up and down in the movable nut 12, driving the plum blossom spanner 8 to rotate clockwise or counterclockwise to tighten or loosen the piston nut. A thrust bearing 15 is installed in the bearing seat 10, and the screw rod 11 is connected to the thrust bearing 15, and the rotational connection between the screw rod 11 and the bearing seat 10 is realized through the thrust bearing 15; a locking nut 16 is also connected to the screw rod 11, and the locking nut 16 is located above the thrust bearing 15 and is tightened in the bearing seat 10, and is used to limit the thrust bearing 15; the bearing seat 10 is rotationally connected to the plum wrench 8 through a cylindrical pin A9.
[0045] like Figure 1 , Figure 6 The end of the piston rod 4 away from the piston 3 usually has four structures, and the piston rod anti-rotation plate 5 is manufactured according to different structures.
[0046] like Figure 1 , Figure 7The two lower brake bodies 19 and the upper brake body 20 of the upper clamping block 7 press the piston 3 at three points evenly distributed at 120°. The lower brake body 19 is connected to the movable crossbeam C17 (the movable crossbeam C17 is fixed on the frame 1) through the cylindrical pin B18, so that the elastic body in the inner cylindrical surface of the lower brake body 19 is tightly fitted with both sides of the lower part of the outer cylindrical surface of the piston 3. The screw on the movable crossbeam A13 presses the upper brake body 20 on the upper part of the outer cylindrical surface of the piston 3.
[0047] The present invention is applied to the disassembly and assembly of pistons with a diameter of more than 500 mm, and the larger the piston diameter, the more obvious the advantage.
[0048] Large bolts are often tightened (loosened) by striking with a sledgehammer, but striking with a sledgehammer cannot achieve precise pre-tightening. Compared with the traditional sledgehammer striking method, the present invention adopts a nut-twisting mechanism to rotate the piston nut, which has good tightening and loosening effects on the piston nut and can achieve relatively precise tightening and loosening, eliminating abnormal noise of the compressor caused by loose piston nut; avoiding collision and damage between the piston and the piston rod when the piston nut is loose, and extending the service life of the piston and the piston rod; operators can quickly master operating skills, and are not required to have sledgehammer skills; the operation has low labor intensity, low safety risks, and high efficiency; fewer tools and appliances are required, and on-site operation and promotion are convenient.
[0049] The piston compressor has a wide range of applications, with a large number of sets in metallurgy, petrochemical and other industries. The piston has high-speed linear reciprocating motion and temperature changes alternately. The tightening preload of the piston nut is a key quality control point. The invention has a wide range of application and promotion prospects.
[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A large piston compressor piston nut tightening-loosening device, characterized in that: include: A frame (1), a clamping mechanism and a nut-screwing mechanism (6); a piston rod (4) and a piston (3) of a piston compressor are placed in the frame (1); one end of the piston rod (4) is connected to the piston (3) via a piston nut, and the other end of the piston rod (4) away from the piston (3) is fixedly connected to the frame (1); the clamping mechanism is installed on the frame (1) and is tightly contacted with the outer cylindrical surface of the piston (3) at multiple locations, so as to fix and position the piston (3); The nut-screwing mechanism (6) is mounted on the frame (1) and comprises a spanner (8). The middle part of the spanner (8) is sleeved on the piston nut. The nut-screwing mechanism (6) drives the spanner (8) to rotate clockwise or counterclockwise to tighten or loosen the piston nut. The nut screwing mechanism (6) further comprises a bearing seat (10), two screw rods (11), two movable nuts (12) and a movable crossbeam B (14); the movable crossbeam B (14) is mounted on the frame (1); the two movable nuts (12) are arranged at intervals and are both pin-connected to the movable crossbeam A (13) and the movable crossbeam B (14); each screw rod (11) passes through the movable nut (12) and is screwed together with the movable nut (12); the bottom end of each screw rod (11) is rotatably connected to a bearing seat (10); the bottoms of the two bearing seats (10) are respectively rotatably connected to the two ends of the plum wrench (8); the two screw rods (11) move up and down in the movable nut (12), driving the plum wrench (8) to rotate clockwise or counterclockwise, thereby tightening or loosening the piston nut.
2. The large piston compressor piston nut tightening-loosening device according to claim 1, characterized in that: The clamping mechanism comprises two lower clamping blocks (2) and an upper clamping block (7); the two lower clamping blocks (2) are mounted at the bottom of the frame (1) and are tightly contacted and connected to both sides of the lower part of the outer cylindrical surface of the piston (3); a movable crossbeam A (13) is mounted on the frame (1); the upper clamping block (7) is mounted on the movable crossbeam A (13) and is tightly contacted and connected to the upper part of the outer cylindrical surface of the piston (3).
3. The large piston compressor piston nut tightening-loosening device according to claim 2, characterized in that: The lower clamping block (2) comprises a lower brake body (19), the lower brake body (19) is connected to a movable crossbeam C (17) via a cylindrical pin B (18), the movable crossbeam C (17) is fixed on the frame (1), and the elastic body in the inner cylindrical surface of the lower brake body (19) is tightly fitted with the outer cylindrical surface of the piston (3); The upper clamping block (7) comprises an upper brake body (20), which is connected to a screw on the movable cross beam A (13), and the elastic body in the inner cylindrical surface of the upper brake body (20) is tightly fitted with the outer cylindrical surface of the piston (3) through the screw.
4. The large piston compressor piston nut tightening-loosening device according to claim 3, characterized in that: The two lower brake bodies (19) and the upper brake body (20) press the piston (3) at three points evenly distributed over a circumference of 120°.
5. The large piston compressor piston nut tightening-loosening device according to claim 1, characterized in that: A thrust bearing (15) is installed in the bearing seat (10), and the screw rod (11) is connected to the thrust bearing (15), and the rotational connection between the screw rod (11) and the bearing seat (10) is realized through the thrust bearing (15); a locking nut (16) is also connected to the screw rod (11), and the locking nut (16) is located above the thrust bearing (15) and is screwed into the bearing seat (10) to limit the thrust bearing (15); the bearing seat (10) is rotationally connected to the plum wrench (8) through a cylindrical pin A (9).
6. The large piston compressor piston nut tightening-loosening device according to claim 1, characterized in that: A piston rod anti-rotation plate (5) is installed on the end of the piston rod (4) away from the piston (3), and the piston rod anti-rotation plate (5) is used to achieve a fixed connection between the piston rod (4) and the frame (1).
7. A method for tightening and loosening a piston nut of a large piston compressor based on the device according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: Install the piston rod (4) into the piston (3), manually screw in the piston nut, and then manually tighten the piston nut with a 12-sided plum wrench; Step 2: Install the lower clamping block (2) and the piston rod anti-rotation plate (5); hoist the piston rod (4) and the piston (3) into the frame (1), and place the piston (3) on the lower clamping block (2); axially move the piston (3) and the piston rod (4), and install the end of the piston rod (4) away from the piston (3) into the piston rod anti-rotation plate (5); install the movable crossbeam A (13) and the upper clamping block (7); the two lower brake bodies (19) and the upper brake body (20) press the piston (3) at three points evenly distributed at a circumference of 120°, and the elastic body in the inner cylindrical surface of the lower brake body (19) is tightly fitted with both sides of the lower part of the outer cylindrical surface of the piston (3), and the screw on the movable crossbeam A (13) presses the upper brake body (20) on the upper part of the outer cylindrical surface of the piston (3); Step 3, adjust the screw-in length of the screw rod (11), assemble the wrench (8), cylindrical pin A (9), movable nut (12), and movable crossbeam B (14); the movable nut (12) is pin-connected with the movable crossbeam A (13) and the movable crossbeam B (14), and can swing clockwise or counterclockwise; the screw rod (11) is pin-connected with the bearing seat (10), and can rotate relative to each other, and is screwed with the movable nut (12) to realize the up and down movement of the screw rod (11), driving the wrench (8) to rotate clockwise or counterclockwise, so as to tighten or loosen the piston nut.