Casting coating sagging tester

Abstract

A casting coating sagging property tester comprises a base, a placing piece is arranged on the base, a sample is arranged on the placing piece, and a scraping piece is movably arranged on the placing piece. When the sagging property of the casting coating is tested, a standard sample pressing template is provided, the blade coating surface of the molding sand casting template is ensured to be flat and compact in a pressing and scraping manner before casting, and the molding sand casting template can be protected through the provided mold, so that the service life of the molding sand casting template is prolonged, and the service life of the molding sand casting template is prolonged. And the problem of slag falling or damage of the molding sand casting template in the blade coating process is avoided, so that the sagging property test is not influenced. Wherein the dropped molding sand slag is doped in the coating due to the occurrence of the slag dropping problem, so that the uniformity of the blade coating thickness of the casting coating is influenced.

Description

Technical Field

[0001] This invention relates to the field of casting coating testing technology, and in particular to a casting coating sagging tester. Background Technology

[0002] In the casting process, casting coatings are widely used to coat the surfaces of sand molds or cores to improve the surface quality of castings, prevent molten metal penetration, and enhance refractoriness and anti-sand adhesion properties. The flowability of the coating is one of its key application properties, directly affecting the uniformity and thickness control of the coating. If the flowability is too high, the coating is prone to flowing, accumulating, or even dripping on vertical or inclined surfaces, leading to localized excessive thickness or defects; if the flowability is too low, it may cause problems such as difficult coating and uneven coverage.

[0003] Currently, in the research and development and quality control of casting coatings, viscosity is often measured to indirectly assess sagging tendency. However, viscosity only reflects the flow resistance of the coating under shear action and cannot fully characterize its anti-sagging ability under static or quasi-static conditions, especially making it difficult to simulate the behavior of the coating under gravity after actual application.

[0004] Therefore, the industry has gradually adopted the direct sag test method as a more intuitive and engineering-guided evaluation tool. This method typically simulates actual coating conditions. A certain amount of coating is applied to the surface of a standard sample (such as a pressed molding sand slab), forming a series of coating strips with varying thicknesses using a specialized scraping tool. The sample is then placed vertically and allowed to stand for a period of time under specified environmental conditions. By measuring the sag length or thickness change of each coating strip under gravity, the anti-sag performance of the coating at different initial thicknesses can be quantitatively evaluated. Compared to viscosity testing, this type of sag test method has the following advantages: it is closer to actual application scenarios, truly reflects the dynamic behavior of the coating on the sand mold surface, requires a smaller sample size, is suitable for rapid screening of small-batch new formulations in the laboratory, and provides intuitive and quantifiable results, facilitating the establishment of a correlation between sag properties and application parameters.

[0005] However, this testing method has several drawbacks. First, the lack of limiting mechanisms when moving the specialized squeegee (i.e., the flow squeegee) results in coating strips that are not perfectly straight. Second, due to the poor flatness of the molding sand plate surface, the squeegee is prone to bouncing when passing over protruding areas, leading to uneven coating thickness in some areas, which affects the test results. Finally, when the molding sand plate is placed vertically, the lack of necessary limiting mechanisms requires repeated adjustments to achieve balance, which in turn affects the appearance of the coating strips. Summary of the Invention

[0007] This invention provides a casting coating sag tester to overcome the shortcomings of the prior art and solve the problems in casting coating sag testing, and has strong practicality.

[0008] In order to achieve the objectives of this invention, the following technologies are proposed: A casting coating sag tester includes a base, a placement component on the base, a sample on the placement component, and a scraper movably mounted on the placement component.

[0009] Furthermore, the placement component includes a first shaft rotatably mounted on one end of the upper side plate of the base, a second shaft fixed to the other end of the upper side plate of the base, a pair of rotating feet fixed on the first shaft, the rotating feet being located inside the side plate, a placement plate welded to the other end of the rotating feet, skirts formed by bending downwards on both sides of the placement plate, a first hole opened on the skirts, a pair of insertion holes opened at one end of the placement plate, a support foot welded to the other end of the lower side of the placement plate, the support foot being located inside the side plate, and a slot opened at the lower end of the support foot.

[0010] Furthermore, an end piece is fixed to the upper side of one end of the placement plate; A second hole is provided at one end of the placement plate, and a limiting member is movably provided on the upper side of the other end of the placement plate. A limiting rod is connected to the limiting member, and the limiting rod passes through the second hole. A lower moving plate is connected to the lower end of the limiting rod, and the lower moving plate is located on the lower side of the placement plate. The sample includes a mold placed on the upper side of the placement plate. The upper end of the mold is open. A sand casting template is pressed and formed inside the mold. A pair of insert rods are welded to each end of the mold. One pair of insert rods is inserted into the end piece, and the other pair of insert rods is inserted into the limiting piece.

[0011] Furthermore, a horizontal plate is fitted on the first shaft and the second shaft respectively. An inner abutment plate is formed on the upper and lower sides of one end of the horizontal plate. A third hole is opened on the horizontal plate. The first shaft and the second shaft pass through the third hole. One end of the horizontal plate is connected to the other through a connecting middle plate.

[0012] Furthermore, a tension spring is hung on the second shaft, and the other end of the tension spring is hung on a hook on the inner side of the connecting plate. A circular end groove is opened at one end of the third hole, and the diameter of the circular end groove is larger than the width of the third hole. A pair of symmetrically arranged limiting protrusions with arc-shaped outer ends are welded to both ends of the first shaft. The width of the limiting protrusions is smaller than the width of the third hole, and the outer ends of the limiting protrusions abut against the inner wall of the circular end groove.

[0013] Furthermore, a pair of limit screws are connected to the connecting plate, and a movable plate is movably provided on the rod part of the limit screw. A pair of locking rods are connected to the lower end of the movable plate, a pair of locking holes are opened at one end of the bottom plate, and a gripping opening is opened at the upper end of the movable plate.

[0014] Furthermore, the scraper includes a kit fitted onto the skirt plate, the kit having an outer vertical plate, a central through rod connected to the outer vertical plate, and the central through rod passing through the first hole; A pair of fourth holes are provided on the outer vertical plate. A connecting rod is movably installed in the fourth hole. An inner seat is connected to the inner end of the connecting rod on the same side. The inner seat is located inside the outer vertical plate. An outer top plate is connected to the outer end of the connecting rod on the same side. The outer top plate is located outside the outer vertical plate. A rotating arm is rotatably provided at the upper end of the outer vertical plate. A pull rod is connected between the other ends of the rotating arm. One end of the rotating arm abuts against the upper wall of the outer top plate. A concave part is welded between the upper ends of the inner seat. A scraper is provided in the concave part. Multiple scraping grooves are provided on the lower wall of the scraper.

[0015] Furthermore, a roller is rotatably provided on the inner side of the inner seat, and the outer circumference of the roller abuts against the upper end of the mold.

[0016] Furthermore, a positioning pin is fixed on the outer side of the outer vertical plate. The positioning pin and the second hole are located at the same end, and the positioning pin is located below the hinge screw. A sixth shaft is rotatably provided at the upper end of the outer vertical plate, and a rotating pressure plate is fixed at the upper end of the sixth shaft.

[0017] Furthermore, the upper inner wall of the scraper abuts against a constraint member, the inner wall of the constraint member abuts against the inner wall of the scraper, and the other end of the constraint member is formed with a pair of lower protrusions. The lower protrusions are located on the outer side of the concave part, and a guide rod is passed through the lower protrusions. An inner pressure plate is fixed to the inner end of the guide rod, and the inner wall of the inner pressure plate abuts against the outer side of the concave part. A pair of locking rods are passed through the inner pressure plate, and the inner ends of the locking rods are fixed to the concave part. A protrusion is welded on the constraint member, and a pressure head is rotatably provided on the protrusion. The pressure head is located on the lower side of the protrusion.

[0018] The advantages of the above technical solution are: In the flowability test of casting coatings, this invention provides a standard sample pressing template. Before casting, pressing and smoothing are used to ensure that the coating surface of the molding sand template is flat and dense. The provided mold protects the molding sand template from slag shedding or damage during the coating process, which would affect the flowability test. Slag shedding can lead to the molding sand residue becoming mixed into the coating, thus affecting the uniformity of the casting coating thickness.

[0019] This invention ensures the regularity of the formed coating strips by stably limiting the scraper, and also ensures the uniformity of the thickness of each coating strip, thus improving the accuracy of the scraping test.

[0020] This invention helps to maintain and determine the vertical posture of the molding sand casting template, so as to avoid the impact of multiple adjustments on the thickness of the coating strip. Attached Figure Description

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0022] Figure 1 A three-dimensional structure of one embodiment is shown. Figure 1 .

[0023] Figure 2 A three-dimensional structure of one embodiment is shown. Figure 2 .

[0024] Figure 3 A three-dimensional structure of one embodiment is shown. Figure 3 .

[0025] Figure 4 A three-dimensional structure of one embodiment is shown. Figure 4 .

[0026] Figure 5 A three-dimensional structure of one embodiment is shown. Figure 5 . Detailed Implementation

[0027] like Figures 1-5 As shown, a casting coating sag tester includes a base 1, a placement component 2 on the base 1, a sample 3 on the placement component 2, and a scraper 4 movably mounted on the placement component 2.

[0028] The base 1 includes a rectangular base plate 10, with side plates 11 folded upwards on both sides of the base plate 10.

[0029] The placement component 2 includes a first shaft 200, which is rotatably mounted on one end of a side plate 11 and limited by a pair of nuts. A second shaft 211 is fixed to the other end of the side plate 11 by a pair of nuts. A pair of rotating feet 201 are fixed to the first shaft 200, located inside the side plate 11. A placement plate 202 is welded to the other end of the rotating feet 201. The placement plate 202 has a rectangular structure, and skirts 203 are formed by bending downwards on both sides of the placement plate 202. A second shaft 203 parallel to the length direction is formed on the skirt 203. A hole 2030 is provided. A second hole 206 parallel to its length direction is provided at one end of the placement plate 202. A pair of rectangular insertion holes 204 are provided at one end of the placement plate 202. The insertion holes 204 and the rotating foot 201 are located at the same end. A support foot 210 is welded to the other end of the lower side of the placement plate 202. The support foot 210 is located inside the side plate 11. A slot 212 is provided at the lower end of the support foot 210. When the placement plate 202 is in a horizontal position, the second shaft 211 passes through the slot 212.

[0030] An L-shaped end piece 205 is fixed to the upper side of one end of the placement plate 202 by screws. The end piece 205 and the insertion hole 204 are located at the same end.

[0031] An L-shaped limiting member 208 is movably provided on the upper side of the other end of the placement plate 202. A limiting rod 207 is connected to the limiting member 208 by a thread. The limiting rod 207 passes through the second hole 206. A lower moving plate 209 is connected to the lower end of the limiting rod 207 by a thread. The lower moving plate 209 is located on the lower side of the placement plate 202.

[0032] A horizontal plate 213 is fitted onto the first shaft 200 and the second shaft 211 respectively. An inner abutment plate 233 is formed on the upper and lower sides of one end of the horizontal plate 213. A third hole 214 is opened on the horizontal plate 213. The first shaft 200 and the second shaft 211 pass through the third hole 214. The horizontal plate 213 is located inside the rotating foot 201 and the supporting foot 210. One end of the horizontal plate 213 is connected to the other end by a connecting middle plate 215. The connecting middle plate 215 and the supporting foot 210 are located at the same end. A pair of limiting screws 216 are threadedly connected to the connecting middle plate 215. The rod part of the limiting screw 216 is movably provided with an L-shaped movable plate 217. The end cap of the limiting screw 216 is located outside the movable plate 217. A pair of locking rods 220 are threadedly connected to the lower end of the movable plate 217. A pair of locking holes are opened at one end of the bottom plate 10. A gripping opening 218 is opened at the upper end of the movable plate 217.

[0033] A tension spring 232 is suspended on the second shaft, and the other end of the tension spring 232 is suspended on a hook on the inner side of the connecting plate 215. A circular end groove 231 is formed at one end of the third hole 214. The diameter of the circular end groove is larger than the width of the third hole 214. A pair of symmetrically arranged limiting protrusions 230 with arc-shaped outer ends are welded to both ends of the first shaft 200. The width of the limiting protrusions 230 is smaller than the width of the third hole 214.

[0034] The sample 3 includes a mold 30 placed on the upper side of the placement plate 202. The mold 30 has a rectangular structure and its length direction is parallel to that of the placement plate 202. The upper end of the mold 30 is open. A molding sand casting template 31 is pressed and formed inside the mold 30. A pair of insert rods 32 are welded to both ends of the mold 30 along its length direction. One pair of insert rods 32 is inserted into the end piece 205, and one end of the mold 30 abuts against the inner wall of the vertical section of the end piece 205. The other pair of insert rods 32 is inserted into the limiting member 208, and the other end of the mold 30 abuts against the inner wall of the vertical section of the limiting member 208.

[0035] The scraper 4 includes an L-shaped kit 400 fitted onto the skirt 203. The outer end of the horizontal section of the kit 400 is bent upward to form an outer vertical plate 401. A central through rod 402 is threaded onto the outer vertical plate 401 and passes through the first hole 2030.

[0036] A pair of vertically arranged fourth holes 403 are provided on the outer vertical plate 401. A connecting rod 404 is movably installed in the fourth hole 403. The inner end of the connecting rod 404 on the same side is threadedly connected to an inner seat 406, which is located inside the outer vertical plate 401. The outer end of the connecting rod 404 on the same side is threadedly connected to an outer top plate 405, which is located outside the outer vertical plate 401. A roller 424 is rotatably installed on the inner side of the inner seat 406 via a third axis. The outer circumference of the roller 424 abuts against the upper end of the mold 30. The upper part of the outer vertical plate 401... The end is connected to a hinge screw 410 by a thread. The rod part of the hinge screw 410 is rotatably provided with a rotating arm 411 with an L-shaped structure. The two ends of the rotating arm 411 are semi-arc structures. The other end of the rotating arm 411 is connected to a pull rod 412 by a thread. A positioning pin 413 is fixed on the outer side of the outer vertical plate 401. The positioning pin 413 is located at the same end as the second hole 206, and the positioning pin 413 is located below the hinge screw 410. One end of the rotating arm 411 abuts against the upper wall of the outer top plate 405. A concave part 407 is welded between the upper ends of the inner seat 406.

[0037] The upper end of the outer vertical plate 401 is rotatably provided with a sixth shaft 414, and the upper end of the sixth shaft 414 is fixed with a rotating pressure plate 415. When the lower wall of the rotating pressure plate 415 abuts against the transverse section of the rotating arm 411, the outer top plate 405 is positioned at a low position.

[0038] The concave part 407 is provided with a C-shaped scraper 408. The lower wall of the scraper 408 has multiple scraping grooves 409. The groove depth of the scraper 409 increases or decreases sequentially along the length of the scraper 408. The upper inner wall of the scraper 408 abuts against an L-shaped constraint member 416. The inner wall of the vertical section of the constraint member 416 abuts against the inner wall of the scraper 408. The other end of the horizontal section of the constraint member 416 is formed with a pair of lower lugs 417. The lower lugs 417 are located on the outside of the concave part 407. A guide rod 420 passes through the lower lugs 417. The inner end of the guide rod 420 is fixed with an internal pressure. The inner wall of the inner pressure plate 419 abuts against the outer side of the concave part 407. A pair of locking rods 418 are provided on the inner pressure plate 419. The inner end of the locking rods 418 is fixed to the concave part 407. A protrusion 421 is welded on the constraint member 416. A long strip-shaped pressure head 423 is provided on the protrusion 421 through a fifth axis. The pressure head 423 is located on the lower side of the protrusion 421. When the length direction of the pressure head 423 is parallel to the length direction of the bottom plate 10, the inner wall of the inner pressure plate 419 abuts against the outer side of the concave part 407, and the inner end of the pressure head 423 abuts against the outer wall of the inner pressure plate 419.

[0039] The casting coating sag tester described above is used to test the sag properties of casting coatings using the following method: Step 1: Pour the selected standard molding sand into mold 30, and press it several times to form a shape within mold 30 as shown in the image. Figure 1 The sand casting template 31 shown in the figure needs to be scraped flat at the top during several pressing processes so that the upper wall of the sand casting template 31 and the upper wall of the mold 30 are in the same plane. The provided standard sand casting template 31 can be used to verify the flowability of the casting coating after scraping, thus significantly improving the authenticity of the test.

[0040] Step 2: Ensuring the placement plate 202 is horizontal, the operator places the mold 30 on the placement plate 202. During placement, first insert one pair of insert rods 32 into the end piece 205, with one end of the mold 30 abutting against the inner wall of the vertical section of the end piece 205. Then, move the limiting member 208 so that the other pair of insert rods 32 are inserted into the limiting member 208, with the other end of the mold 30 abutting against the inner wall of the vertical section of the limiting member 208. At this point, the mold 30 will be confined on the placement plate 202.

[0041] Step 3: Move the concave part 407 to the end where the limiting part 208 is located, then place the scraper 408 inside the concave part 407, then put the constraint part 416 on the upper end of the scraper 408, and then move the inner pressure plate 419 inward so that the locking rod 418 is inserted into the inner pressure plate 419. Then the operator rotates the pressure head 423 so that the inner end of the pressure head 423 abuts against the outer wall of the inner pressure plate 419, and at this time the length direction of the pressure head 423 is parallel to the length direction of the placement plate 202.

[0042] Step 4: The operator moves the scraper 408 to one end of the molding sand casting template 31, and then rotates the rotating arm 411 by the pull rod 412, so that the other end of the rotating arm 411 acts on the upper end of the outer top plate 405, thereby causing the outer top plate 405, the scraper 408 and the roller 424 to move downward, so that the outer periphery of the roller 424 abuts against the upper end of the mold 30, while the lower end of the scraper 408 abuts against the upper wall of the molding sand casting template 31. After that, the operator rotates the rotating pressure plate 415 inward, so that the lower wall of the rotating pressure plate 415 abuts against the horizontal section of the rotating arm 411, and the outer periphery of the positioning pin 413 abuts against the outer wall of the vertical section of the rotating arm 411.

[0043] Step 5: The operator injects the casting coating into one end of the molding sand casting template 31 and into the scraper 408. Then, the operator moves the scraper 408 by pulling the pull rod 412. When the scraper 408 moves, the casting coating will form multiple coating strips of different thicknesses under the action of the scraper groove 409.

[0044] Step 6: The operator rotates the placement plate 202 upwards around the first axis 200 to make the placement plate 202 and the molding sand casting template 31 vertical. When the placement plate 202 rotates, the first axis 200 also rotates accordingly, causing the limiting protrusion 230 to rotate from a vertical position to a horizontal position within the circular end groove 231. At this time, since the limiting protrusion 230 is directly opposite the third hole 214, the horizontal plate 213 will then move under the elastic force of the tension spring 232, so that the front end of the horizontal plate 213 is inserted into the insertion hole 204, and then the front end of the inner abutment plate 233 abuts against the inner side of the placement plate 202. During the abutment, the movable plate 217 moves downwards under its own weight, causing the locking rod 220 to be inserted into the locking hole on the base plate 10. At this time, the entire molding sand casting template 31 will be in a vertical position.

[0045] Step 7: After standing for a period of time, measure the length of the coating strip and the thickness of the coating strip at different locations, and determine the sag rating of the casting coating by comparing it with the standard table.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A casting coating sag tester, characterized in that, It includes a base (1), a placement part (2) is provided on the base (1), a sample (3) is provided on the placement part (2), and a scraper (4) is movably provided on the placement part (2).

2. The casting coating sag tester according to claim 1, characterized in that, The placement component (2) includes a first shaft (200) rotatably mounted on one end of the upper side plate (11) of the base (1), a second shaft (211) fixed on the other end of the upper side plate (11) of the base (1), a pair of rotating feet (201) fixed on the first shaft (200), the rotating feet (201) being located on the inner side of the side plate (11), a placement plate (202) welded to the other end of the rotating feet (201), a skirt plate (203) formed by bending downwards on both sides of the placement plate (202), a first hole (2030) opened on the skirt plate (203), a pair of insertion holes (204) opened on one end of the placement plate (202), a support foot (210) welded to the other end of the lower side of the placement plate (202), the support foot (210) being located on the inner side of the side plate (11), and a slot (212) opened at the lower end of the support foot (210).

3. The casting coating sag tester according to claim 2, characterized in that, An end piece (205) is fixed to the upper side of one end of the placement plate (202); A second hole (206) is provided at one end of the placement plate (202), and a limiting member (208) is movably provided on the upper side of the other end of the placement plate (202). A limiting rod (207) is connected to the limiting member (208), and the limiting rod (207) passes through the second hole (206). A lower moving plate (209) is connected to the lower end of the limiting rod (207), and the lower moving plate (209) is located on the lower side of the placement plate (202). The sample (3) includes a mold (30) placed on the upper side of the placement plate (202). The upper end of the mold (30) is open. A molding sand casting template (31) is pressed and formed inside the mold (30). A pair of insert rods (32) are welded to both ends of the mold (30). One pair of insert rods (32) is inserted into the end piece (205), and the other pair of insert rods (32) is inserted into the limiting piece (208).

4. The casting coating sag tester according to claim 2, characterized in that, A horizontal plate (213) is fitted on the first shaft (200) and the second shaft (211). An inner abutment plate (233) is formed on the upper and lower sides of one end of the horizontal plate (213). A third hole (214) is opened on the horizontal plate (213). The first shaft (200) and the second shaft (211) pass through the third hole (214). One end of the horizontal plate (213) is connected to the other end by a connecting middle plate (215).

5. The casting coating sag tester according to claim 4, characterized in that, A tension spring (232) is hung on the second shaft. The other end of the tension spring (232) is hung on a hook on the inner side of the connecting plate (215). A circular end groove (231) is opened at one end of the third hole (214). The diameter of the circular end groove (231) is greater than the width of the third hole (214). A pair of symmetrically arranged limiting protrusions (230) with arc-shaped outer ends are welded to both ends of the first shaft (200). The width of the limiting protrusions (230) is less than the width of the third hole (214). The outer end of the limiting protrusions (230) abuts against the inner wall of the circular end groove (231).

6. The casting coating sag tester according to claim 4, characterized in that, A pair of limit screws (216) are connected to the connecting plate (215). The rod part of the limit screw (216) is movably provided with a movable plate (217). A pair of locking rods (220) are connected to the lower end of the movable plate (217). A pair of locking holes are opened at one end of the bottom plate (10). A gripping opening (218) is opened at the upper end of the movable plate (217).

7. The casting coating sag tester according to claim 2, characterized in that, The scraper (4) includes a kit (400) fitted onto the skirt (203), the kit (400) having an outer vertical plate (401) formed thereon, a central through rod (402) connected to the outer vertical plate (401), the central through rod (402) passing through the first hole (2030); A pair of fourth holes (403) are provided on the outer vertical plate (401). A connecting rod (404) is movably provided in the fourth hole (403). An inner seat (406) is connected to the inner end of the connecting rod (404) on the same side. The inner seat (406) is located inside the outer vertical plate (401). An outer top plate (405) is connected to the outer end of the connecting rod (404) on the same side. The outer top plate (405) is located outside the outer vertical plate (401). A rotating arm (411) is rotatably provided at the upper end of the outer vertical plate (401). A pull rod (412) is connected between the other ends of the rotating arm (411). One end of the rotating arm (411) abuts against the upper wall of the outer top plate (405). A concave part (407) is welded between the upper ends of the inner seat (406). A scraper (408) is provided in the concave part (407). A plurality of scraping grooves (409) are provided on the lower wall of the scraper (408).

8. The casting coating sag tester according to claim 7, characterized in that, The inner side of the inner seat (406) is provided with a roller (424) that rotates, and the outer periphery of the roller (424) abuts against the upper end of the mold (30).

9. The casting coating sag tester according to claim 7, characterized in that, A positioning pin (413) is fixed on the outer side of the outer vertical plate (401). The positioning pin (413) and the second hole (206) are located at the same end, and the positioning pin (413) is located below the hinge screw (410). A sixth shaft (414) is rotatably provided on the upper end of the outer vertical plate (401). A rotating pressure plate (415) is fixed on the upper end of the sixth shaft (414).

10. The casting coating sag tester according to claim 7, characterized in that, The upper inner wall of the scraper (408) abuts against a constraint member (416), and the inner wall of the constraint member (416) abuts against the inner wall of the scraper (408). The other end of the constraint member (416) is formed with a pair of lower lugs (417). The lower lugs (417) are located outside the concave part (407). A guide rod (420) is passed through the lower lugs (417). An inner pressure plate is fixed to the inner end of the guide rod (420). 419), the inner wall of the inner pressure plate (419) abuts against the outer side of the concave part (407), a pair of locking rods (418) are provided on the inner pressure plate (419), the inner end of the locking rods (418) is fixed on the concave part (407), a protrusion (421) is welded on the constraint part (416), and a pressure head (423) is rotatably provided on the protrusion (421), the pressure head (423) is located on the lower side of the protrusion (421).

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