A material surface corrosion resistance accelerated test system

Abstract

The utility model relates to a kind of material surface corrosion resistance accelerated test system, including marine environment simulation box, still including test stand, drive motor and controlled by the test seat of drive motor, test stand horizontal reciprocating sliding connection is in marine environment simulation box, test stand lower end is inserted into marine environment simulation box, test stand height is adjustable, test stand lower end is provided drive motor, test seat is connected with drive motor output shaft;Test stand lower end is also provided with limit component, limit component includes extension rod, connecting plate and limit bolt group, extension rod is symmetrically set in test stand lower end, connecting plate is set between extension rod, connecting plate middle part is circular, set in test seat outside, connecting plate middle part is provided with limit bolt group, limit bolt group is tightly resisted on test seat.The utility model can simulate fixed, passive or active motion actual use state for different types of samples to be tested, so as to study the corrosion resistance of samples to be tested under real application.

Description

Technical Field

[0001] This utility model relates to the technical field of testing the corrosion resistance of materials, and in particular to an accelerated testing system for the corrosion resistance of material surfaces. Background Technology

[0002] Marine fisheries, maritime transportation, and marine engineering all rely heavily on corrosion-resistant materials. Both metallic and non-metallic materials are affected by the marine environment, leading to a reduction in their lifespan. To protect these materials, coatings are often applied to their surfaces to increase their corrosion resistance and extend their service life in the marine environment.

[0003] To study the corrosion resistance of material surface coatings, a simulated marine environment is often conducted in a laboratory. The material to be tested is then placed in this environment and immersed in simulated seawater for an extended period of time, thus simulating the marine corrosion environment in which the material is subjected. For example, a test device for simulating seawater erosion disclosed in patent publication number CN221765179U involves placing the specimen on a test platform (23) and then simulating seawater erosion to scour the specimen when a corrosion resistance test is required.

[0004] For example, a marine environmental corrosion testing device disclosed in patent publication number CN221426397U can be used to put samples into an immersion tank for immersion testing. At the same time, when water is pumped into the immersion tank, certain measures are taken to reduce the disturbance to the samples in the immersion tank.

[0005] It can be seen that the materials under test are mostly kept in a fixed state during the test, but the actual motion states of different materials are different. For example, the support legs of offshore oil platforms and the cylinder of wind turbine towers are in a fixed state; the propellers of ships and the hulls of ships sailing at high speeds are in a state of high-speed active motion; while the buoys and floats of moored vessels and some components of aquaculture cages are in a state of passive motion.

[0006] Therefore, when faced with test materials under different practical application conditions, if they are uniformly fixed in a simulated marine environment for testing, it will not be able to truly reflect the impact of the marine environment on material corrosion under actual application conditions. Summary of the Invention

[0007] To address the problem that existing testing devices are unable to simulate the actual application conditions of the materials under test, this invention provides an accelerated testing system for the corrosion resistance of material surfaces. Based on simulating marine environmental conditions, it can realize the fixing, active rotation, and passive rotation of the test sample, thereby simulating different application conditions of the test sample and facilitating the realistic study of the corrosion resistance performance of the test sample under actual application conditions.

[0008] To achieve the above objectives, the technical solution adopted by the present utility model is: An accelerated corrosion resistance testing system for material surfaces, comprising a marine environment simulation box, further comprising a test frame, a driving motor, and a test base controlled by the driving motor, wherein the test frame is horizontally slidably connected to the marine environment simulation box in a reciprocating manner, the lower end of the test frame extends into the marine environment simulation box, and the horizontal sliding facilitates disturbing the liquid in the marine environment simulation box; the height of the test frame is adjustable, the driving motor is arranged at the lower end of the test frame, the test bases are arranged at the lower end of the test frame, and the test bases are connected to the output shaft of the driving motor and controlled by the driving motor; A limiting assembly is further arranged at the lower end of the test frame, the limiting assembly comprises an extension rod, a connecting plate and a limiting bolt set, the extension rods are symmetrically arranged on both sides of the lower end of the test frame, the connecting plate is arranged between the extension rods, the middle part of the connecting plate is annular and sleeved outside the test base, the limiting bolt set is arranged in the middle part of the connecting plate, and the limiting bolt set tightly abuts against the test base for installing a sample to be tested, so as to conveniently limit the rotation of the test base or improve the rotation stability of the test base.

[0009] Further, the marine environment simulation box is a rectangular box body, the lower end of the marine environment simulation box is provided with a drain pipe, the upper end of the marine environment simulation box is open, a linear module is centrally arranged at the upper end of the marine environment simulation box, and the marine environment simulation box drives the test frame to reciprocate through the linear module. The prior art is adopted to control the movement of the test frame, which improves the convenience of operation.

[0010] Further, box covers are respectively hinged on the marine environment simulation box on both sides of the linear module, and there is a gap between the box covers and the linear module.

[0011] Further, the test frame comprises a mounting plate, lifting rods and a test table, the mounting plate is connected and fixed with the linear module, both ends of the mounting plate extend out of the linear module, the lifting rods are penetrated through both ends of the mounting plate, the lifting rods are vertically arranged, the lower ends of the lifting rods extend into the marine environment simulation box, the test table is arranged between the lower ends of the two lifting rods, and the cross section of the test table and the lifting rods after connection and combination is in a shape of Chinese character '凵'.

[0012] Further, the lifting rod is a threaded rod, the lifting rod is slidably connected with the mounting plate and threadedly connected with the test table, a compression spring is sleeved outside the lifting rod between the mounting plate and the test table, a nut is connected to the lifting rod above the mounting plate, and the nut tightly abuts against the mounting plate. The compression spring urges the test table away from the mounting plate.

[0013] Further, the driving motor is arranged above the test table, and the output shaft of the driving motor is detachably connected with the test base downward. The convenient disassembly and assembly of the test base can facilitate the installation of the sample to be tested.

[0014] Furthermore, the test stand includes an upper plate, a lower plate, and four connecting columns disposed between the upper plate and the lower plate. Both the upper plate and the lower plate are rectangular plates. Each connecting column is provided with two mounting bolts, one above the other. The four mounting bolts located on the same side cooperate to press and fix the test sample, ensuring that the test sample does not shift. A vertical rod is vertically installed in the middle of the test base. The vertical rod passes through the test base and is threadedly connected and fixed to the output shaft of the drive motor.

[0015] Furthermore, the extension rods are arranged vertically, and the cross-section of the extension rods and the connecting plate after connection and combination is "U" shaped; the middle part of the connecting plate is sleeved outside the vertical rod and is arranged coaxially with the inside and outside of the vertical rod; The limiting bolt group includes multiple upper limiting bolts and multiple lower limiting bolts evenly arranged in the circumference. The upper limiting bolts and lower limiting bolts are arranged at intervals between each other. Limiting holes and limiting grooves are opened on the side wall of the vertical rod. The number of limiting holes is multiple evenly arranged in the circumference, and the limiting grooves are arranged around the circumference of the vertical rod. The head of the upper limit bolt is pressed tightly against any of the limit holes to facilitate limiting the rotation of the vertical rod, and the head of the lower limit bolt is pressed tightly against the limit groove to ensure the stability of the vertical rod's rotation.

[0016] The beneficial effects of this utility model through the above technical solution are: This invention features a rationally designed structure. A linear module allows the test sample to reciprocate within the solution, agitating it and simulating the macroscopic reciprocating motion of water caused by ocean waves. The test stand is held in place by the upper limit bolt, enabling precise study of the corrosion behavior of the test sample under relatively static conditions. Furthermore, the angle of the test sample can be adjusted in this fixed position, facilitating the study of the influence of the material surface orientation relative to the flow direction on corrosion and enabling erosion tests at different angles of water flow.

[0017] This invention uses a drive motor to rotate the test sample, thereby simulating corrosion under high-speed relative motion conditions. The rotating sample generates high flow velocity, which washes away corrosion products on the sample surface, keeping the sample surface continuously exposed to the corrosive medium and significantly accelerating the corrosion rate. The test sample can also be passively rotated under the impact of the solution, facilitating the simulation of passive rotation in ocean waves.

[0018] The test platform of this invention can be raised and lowered, thereby raising and lowering the test sample along with it. The test sample can be completely immersed in the solution of the marine environment simulation chamber, partially immersed in the solution, or completely detached from the solution, so as to realize the testing of the corrosion rate of the test sample in gas phase environment, gas-liquid phase environment and liquid phase environment. Attached Figure Description

[0019] Figure 1 This is a top view of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0020] Figure 2 This is a front view of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0021] Figure 3 This is a front view of the test frame of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0022] Figure 4 This is a side view of the test frame of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0023] Figure 5 This is a schematic diagram of the application status of the upper limit bolt of the accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0024] Figure 6 This is a schematic diagram of the lower limit bolt status of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0025] Figure 7 This is an isometric view of the test seat of an accelerated testing system for the corrosion resistance of material surfaces according to this utility model.

[0026] The attached diagram is labeled as follows: 1 Marine environment simulation chamber, 101 Chamber cover, 2 Test frame, 21 Mounting plate, 22 Lifting rod, 23 Test platform, 3 Drive motor, 4 Test seat, 41 Upper plate, 42 Lower plate, 43 Connecting column, 5 Linear module, 51 Slide, 6 Compression spring, 7 Nut, 8 Mounting bolt, 9 Vertical rod, 10 Screw, 11 Extension rod, 12 Connecting plate, 13 Limit bolt group, 131 Upper limit bolt, 132 Lower limit bolt, 14 Limit hole, 15 Limit groove. Detailed Implementation

[0027] The specific embodiments of this utility model are described in detail below with reference to the accompanying drawings: like Figures 1-7 As shown, an accelerated testing system for the corrosion resistance of material surfaces includes a marine environment simulation chamber 1. The marine environment simulation chamber 1 is existing technology and can hold a certain amount of liquid to simulate a seawater environment. Here, the marine environment simulation chamber 1 is a rectangular box with an open top and a drain pipe at the bottom. The drain pipe has a valve, allowing for convenient liquid discharge.

[0028] The entire testing system, in addition to the marine environment simulation chamber 1, includes a test frame 2, a drive motor 3, and a test base 4 controlled by the drive motor 3. The test frame 2 can slide horizontally back and forth on the marine environment simulation chamber 1, with its lower end extending into the chamber 1 to facilitate the reciprocating movement of the test sample within the chamber. The height of the test frame 2 is adjustable, allowing the test sample to be immersed, partially immersed, or removed from the solution in the marine environment simulation chamber 1.

[0029] In this embodiment, the test frame 2 includes a mounting plate 21, lifting rods 22, and a test platform 23. The mounting plate 21 is a horizontally arranged plate, with lifting rods 22 passing through both ends of the mounting plate 21. The lifting rods 22 are vertically arranged and threaded, but they are slidably connected to the mounting plate 21. The lower ends of the lifting rods 22 extend vertically into the marine environment simulation tank 1. The test platform 23 is arranged between the lower ends of the two lifting rods 22, and the lifting rods 22 are threadedly connected to the test platform 23. The mounting plate 21 and the test platform 23 are arranged parallel to each other vertically and with a gap. After the test platform 23 and the lifting rods 22 are connected and combined, the cross-section is U-shaped.

[0030] To enable the sliding of the test frame 2, a linear module 5 is centrally located at the upper opening of the marine environment simulation chamber 1. The marine environment simulation chamber 1 drives the test frame 2 to reciprocate through the linear module 5. The linear module 5 is existing technology. Its principle is that a running lead screw drives the nut 7 seat to move. A slide 51 is installed on the nut 7 seat, and the nut 7 seat and the slide 51 move linearly together.

[0031] When the test frame 2 is installed with the linear module 5, the mounting plate 21 is connected and fixed to the slide 51 of the linear module 5. The linear module 5 extends from both ends of the mounting plate 21 to prevent the linear module 5 from affecting the downward extension of the lifting rod 22. With the test frame 2 controlled by the linear module 5, allowing for horizontal reciprocating linear movement, a compression spring 6 is fitted over the lifting rod 22 between the mounting plate 21 and the test platform 23. A nut 7 is connected to the lifting rod 22 above the mounting plate 21, and the nut 7 is pressed tightly against the mounting plate 21. Tightening the nut 7 compresses the compression spring 6, causing it to shorten, thus moving the test platform 23 upwards closer to the mounting plate 21; loosening the nut 7 causes the compression spring 6 to lengthen, thus moving the test platform 23 downwards away from the mounting plate 21.

[0032] A drive motor 3 is installed at the lower end of the test frame 2. Specifically, the drive motor 3 is installed above the test platform 23, which can drive the drive motor 3 to move up and down. Test seats 4 are arranged at the lower end of the test frame 2. The test seats 4 are connected to the output shaft of the drive motor 3, meaning the output shaft of the drive motor 3 is detachably connected to the test seats 4 downwards. Thus, when the drive motor 3 is started, it can drive the test seats 4 to rotate. When the drive motor 3 is de-energized, the test seats 4 can be passively rotated under external force. The test stand 4 is used to mount the test sample. The test stand 4 includes an upper plate 41, a lower plate 42, and four connecting posts 43 disposed between the upper plate 41 and the lower plate 42. Both the upper plate 41 and the lower plate 42 are rectangular flat plates, arranged parallel to each other with vertical spacing. The upper plate 41 and the lower plate 42 are connected and fixed together by the four connecting posts 43. Each connecting post 43 is provided with two mounting bolts 8, one above the other. The four mounting bolts 8 on the two connecting posts 43 on the same side cooperate to press and fix the test sample.

[0033] It should be noted that when preparing the test sample, it is cut into a rectangle. First, remove the mounting bolt 8, and place the test sample between the upper plate 41 and the lower plate 42. The upper plate 41 and the lower plate 42 clamp the upper and lower ends of the test sample, restricting its vertical movement. Then, tighten the mounting bolt 8, which is located on the left and right edges of the test sample, thereby restricting its lateral movement. After tightening the mounting bolt 8, the tail of the mounting bolt 8 and the connecting post 43 cooperate to clamp the test sample, restricting its forward and backward movement, thus reliably mounting the test sample on the test holder 4.

[0034] When the test base 4 is installed with the drive motor 3, a vertical rod 9 is vertically installed in the middle of the test base 4. The vertical rod 9 is a stepped round rod with a larger diameter at the upper end than at the lower end. The lower end of the vertical rod 9 passes through the test base 4, and the vertical rod 9 is threadedly connected and fixed to the output shaft of the drive motor 3. Specifically, the larger diameter end of the vertical rod 9 is first fitted onto the output shaft of the drive motor 3 and threadedly connected to it. At the same time, a screw 10 passes between the larger diameter end of the vertical rod 9 and the output shaft to ensure a reliable connection and prevent disengagement. The drive motor 3 can directly drive the test base 4 to rotate through the vertical rod 9.

[0035] In order to ensure the stability of the rotation of the test stand 4 and to ensure the fixation of the test stand 4, a limit component is also provided at the lower end of the test frame 2. The limit component acts on the vertical rod 9, which can limit the rotation of the vertical rod 9 and ensure its operational stability when the vertical rod 9 rotates.

[0036] In this embodiment, the limiting assembly includes extension rods 11, connecting plates 12, and limiting bolt groups 13. Extension rods 11 are symmetrically arranged on both sides of the lower end of the test frame 2, and are vertically aligned. The upper ends of the extension rods 11 are connected and fixed to the test platform 23. Connecting plates 12 are arranged between the extension rods 11, and the cross-section of the extension rods 11 and connecting plates 12 after connection and combination is U-shaped.

[0037] Note that the middle part of the connecting plate 12 is annular and is fitted outside the test seat 4. Specifically, the middle part of the connecting plate 12 is fitted outside the vertical rod 9 and is arranged coaxially with the vertical rod 9. The diameter of the vertical rod 9 is smaller than the diameter of the middle part of the connecting plate 12 to ensure that the vertical rod 9 can pass through the middle part of the connecting plate 12.

[0038] A set of limiting bolts 13 is provided in the middle of the connecting plate 12, and the set of limiting bolts 13 abuts against the test seat 4 used to install the test sample. Specifically, the set of limiting bolts 13 includes three upper limiting bolts 131 and three lower limiting bolts 132 arranged circumferentially. The upper limiting bolts 131 and the lower limiting bolts 132 are arranged vertically at intervals and are not on the same height plane. Both the upper limiting bolts 131 and the lower limiting bolts 132 use positioning balls, and the positioning balls have steel balls at their heads. The positioning balls are threaded to the middle of the connecting plate 12.

[0039] Meanwhile, limiting holes 14 and limiting grooves 15 are provided on the side wall of the vertical rod 9. The number of limiting holes 14 is several evenly distributed circumferentially, and the limiting grooves 15 are arc-shaped grooves that surround the circumference of the vertical rod 9. The limiting holes 14 and limiting grooves 15 are arranged vertically at intervals. The limiting holes 14 correspond to the upper limiting bolts 131, and the limiting grooves 15 correspond to the lower limiting bolts 132. In application, after the upper limiting bolts 131 are tightened, their heads are pressed tightly against any of the limiting holes 14, thus restricting the rotation of the vertical rod 9; after the lower limiting bolts 132 are tightened, their heads are pressed tightly against the limiting grooves 15, providing support to the vertical rod 9 from all sides and ensuring the stability of its rotation. The upper limiting bolts 131 and lower limiting bolts 132 are not used simultaneously.

[0040] The principle of this invention is as follows: The test frame 2 is manually operated to move the test platform 23 upwards, closer to the mounting plate 21. Then, the test base 4 is removed, and two pre-prepared test samples are installed on the test base 4. The test base 4 is then fixed to the output shaft of the drive motor 3. Finally, the test platform 23 is moved downwards, bringing the test base 4 and the test samples closer to the bottom of the marine environment simulation chamber 1. A seawater solution is artificially prepared and added to the marine environment simulation chamber 1. The solution level can submerge, partially submerge, or be below the test sample. The height of the test sample can also be adjusted by raising and lowering the test platform 23.

[0041] Depending on the type of the test sample, the user can choose whether to activate the linear module 5 and drive motor 3, and select either the upper limit bolt 131 or the lower limit bolt 132. For example, when the test sample is used to manufacture fixed components such as support legs for offshore oil platforms, the upper limit bolt 131 can be used to fix the vertical rod 9, thereby fixing the posture of the test sample. Simultaneously, the user can choose not to activate the linear module 5 or activate it at a low speed to simulate corrosion resistance in still water or micro-flow environments. Of course, the linear module 5 can also run at high speed to simulate the rigidly fixed state of the test sample in waves. The fixing angle of the test sample can be changed, allowing for the study of the influence of the test sample's orientation relative to the flow direction on corrosion.

[0042] For example, if the test sample is used in the manufacture of passively moving components such as marine buoys, the drive motor 3 is de-energized to ensure that the test base 4 can rotate under external force. After activating the linear module 5, the passive rotation of the test sample in ocean waves is simulated, where the test sample will be passively rotated due to the impact of the solution. Alternatively, if the test sample is used in the manufacture of actively moving components such as propellers, the drive motor 3 is energized to drive the test base 4 to rotate, thus continuously subjecting the test sample to the impact and shear force of the solution, simulating the working state of a high-speed rotating component in ocean waves.

[0043] Whether the test sample rotates actively or passively, the lower limit bolt 132 can be used to hold it against the vertical rod 9, thereby improving the stability of the test sample's rotation. After the test sample has been running back and forth in the marine environment simulation chamber 1 for a certain period of time, the test sample can be removed, and the condition of the two test sample surfaces can be observed to comprehensively judge the corrosion resistance of the test sample.

[0044] Because the top of the marine environment simulation chamber 1 is open and the linear module 5 is centrally located, the upper sides of the marine environment simulation chamber 1 remain open, facilitating the installation and removal of test samples. To maintain the clean appearance of the marine environment simulation chamber 1, lids 101 are hinged to both sides of the linear module 5. The lids 101 are rectangular plates that can be flipped outwards or onto the top of the marine environment simulation chamber 1 for sealing. A gap exists between the lids 101 and the linear module 5 to allow space for the test frame 2 and avoid interfering with its linear reciprocating movement.

[0045] The embodiments described above are merely preferred embodiments of this utility model and are not intended to limit the scope of implementation of this utility model. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the patent claims of this utility model should be included within the scope of the patent application of this utility model.

Claims

1. An accelerated testing system for the corrosion resistance of material surfaces, comprising a marine environment simulation chamber (1), characterized in that, It also includes a test frame (2), a drive motor (3) and a test seat (4) controlled by the drive motor (3). The test frame (2) slides horizontally back and forth on the marine environment simulation box (1). The lower end of the test frame (2) extends into the marine environment simulation box (1). The height of the test frame (2) is adjustable. The drive motor (3) is installed at the lower end of the test frame (2). The test seat (4) is arranged at the lower end of the test frame (2). The test seat (4) is connected to the output shaft of the drive motor (3). The test frame (2) is also provided with a limiting component at its lower end. The limiting component includes an extension rod (11), a connecting plate (12), and a limiting bolt group (13). The extension rods (11) are symmetrically arranged on both sides of the lower end of the test frame (2). The connecting plate (12) is arranged between the extension rods (11). The middle part of the connecting plate (12) is circular and sleeved outside the test seat (4). The limiting bolt group (13) is arranged in the middle of the connecting plate (12). The limiting bolt group (13) is tightly pressed against the test seat (4) used to install the test sample.

2. The accelerated testing system for material surface corrosion resistance according to claim 1, characterized in that, The marine environment simulation box (1) is a rectangular box with a drainage pipe at the bottom and an open top. A linear module (5) is set in the center of the top of the marine environment simulation box (1). The marine environment simulation box (1) drives the test frame (2) to move back and forth through the linear module (5).

3. The accelerated testing system for material surface corrosion resistance according to claim 2, characterized in that, The marine environment simulation tanks (1) on both sides of the linear module (5) are respectively hinged with lids (101), and there is a gap between the lids (101) and the linear module (5).

4. The accelerated testing system for material surface corrosion resistance according to claim 2, characterized in that, The test frame (2) includes a mounting plate (21), a lifting rod (22), and a test platform (23). The mounting plate (21) is connected and fixed to the linear module (5). The linear module (5) extends from both ends of the mounting plate (21). The lifting rod (22) passes through both ends of the mounting plate (21). The lifting rod (22) is arranged vertically. The lower end of the lifting rod (22) extends into the marine environment simulation box (1). The test platform (23) is set between the lower ends of the two lifting rods (22). The cross section of the test platform (23) and the lifting rod (22) is "U" shaped after being connected and combined.

5. The accelerated testing system for material surface corrosion resistance according to claim 4, characterized in that, The lifting rod (22) is a threaded rod. The lifting rod (22) is slidably connected to the mounting plate (21) and threadedly connected to the test bench (23). The lifting rod (22) between the mounting plate (21) and the test bench (23) is fitted with a compression spring (6). A nut (7) is connected to the lifting rod (22) above the mounting plate (21). The nut (7) is tightly pressed against the mounting plate (21).

6. The accelerated testing system for material surface corrosion resistance according to claim 4, characterized in that, The drive motor (3) is installed above the test bench (23), and the output shaft of the drive motor (3) is detachably connected to the test base (4) downwards.

7. The accelerated testing system for material surface corrosion resistance according to claim 1, characterized in that, The test seat (4) comprises an upper plate (41), a lower plate (42) and four connecting posts (43) arranged between the upper plate (41) and the lower plate (42), wherein the upper plate (41) and the lower plate (42) are both rectangular plates, each connecting post (43) is provided with two upper and lower mounting bolts (8), and the four mounting bolts (8) located on the same side cooperate with each other to press and fix a sample to be tested; A vertical rod (9) is vertically arranged in the middle of the test seat (4), the vertical rod (9) penetrates through the test seat (4), and the upper end of the vertical rod (9) is connected and fixed with the output shaft of the driving motor (3) through threads; 8. The accelerated testing system for material surface corrosion resistance according to claim 7, characterized in that, The extension rods (11) are vertically arranged, and the cross section of the extension rods (11) connected and combined with the connecting plate (12) is in a "凵" shape; the middle part of the connecting plate (12) is sleeved outside the vertical rod (9) and is coaxially arranged inside and outside with the vertical rod (9); The limit bolt group (13) comprises a plurality of upper limit bolts (131) and a plurality of lower limit bolts (132) which are annularly and uniformly arranged, the upper limit bolts (131) and the lower limit bolts (132) are arranged at an interval up and down, the side wall of the vertical rod (9) is provided with limit holes (14) and limit grooves (15), the limit holes (14) are annularly and uniformly arranged in plurality, and the limit grooves (15) are arranged around the circumference of the vertical rod (9) for one circle; The head of the upper limit bolt (131) abuts tightly against any one of the limit holes (14), and the head of the lower limit bolt (132) abuts tightly against the limit groove (15).

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