A mechanical grading hoop

Abstract

The cam is provided with a first hole and a second hole for fixing the first and second holes, and the cam is provided with a first hole and a second hole for fixing the first and second holes.

Description

Technical Field

[0001] The present invention relates to the technical field of oil well sealing, and more particularly to a mechanical grading collar. Background Art

[0002] Cementing in oil drilling is a crucial step in drilling operations, primarily used to reinforce the wellbore, isolate the formation, prevent oil and gas crossflow, and provide a stable channel for subsequent production. A staged collar is a special device installed on the casing string that allows cement to be injected in stages during the cementing process. This staged cementing solves problems such as excessive pressure and uneven cement distribution that can occur with a single cementing injection. It is particularly suitable for deep, complex, or horizontal wells.

[0003] The main process of staged cementing is as follows: During the first stage of cementing, the casing string is first lowered, and the staged cementing device is connected to the predetermined position of the casing string (above the well section to be sealed). Cement slurry is pumped into the casing, and the cement slurry returns from the bottom of the casing and enters the annulus between the casing and the wellbore wall, sealing the bottom well section (the upper part of the oil and gas layer). Before starting the second stage of cementing, a top plug of a specific size is inserted into the casing to push the sliding sleeve to move, open the circulation hole, and establish the second stage cementing channel. Then, the second stage of cement slurry is pumped into the casing, and the cement slurry enters the upper annulus through the circulation hole, sealing the remaining well section (such as the middle or shallow formation). After the cement slurry is pushed to the predetermined position, the bottom plug is inserted to close the circulation hole to prevent the cement slurry from flowing back. After the second stage of cement slurry solidifies, a complete sealed annulus is formed between the casing and the wellbore wall.

[0004] During the cementing process in oil drilling, when the displacement fluid pushes the top plug down to the bottom of the casing, it docks with the pre-released bottom plug. Together, they seal the inner cavity of the casing, forming a physical barrier. Once the top and bottom plugs dock, the flow of fluid from the casing to the annular space is completely blocked, preventing the subsequent displacement fluid from flowing. This causes a rapid increase in pump pressure. This sudden increase in pump pressure is a key signal, indicating that cement slurry displacement is complete. It also involves the determination of cementing quality and downhole pressure control.

[0005] Deficiencies of existing technology: The circulation hole size is insufficient, which can easily lead to poor cement slurry flow or tool blockage. In addition, after the top plug and the bottom plug are connected, the pressure exerted on the stage collar by the subsequent pumped displacement fluid increases suddenly. Failure to release the pressure in time will cause the outer casing of the fracturing stage collar to rupture. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a mechanical grading hoop to solve the problems existing in the above-mentioned background technology.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solutions: a mechanical grading hoop, comprising an outer sleeve of the grading hoop, circulation holes are provided on both sides of the outer sleeve of the grading hoop, a first circular hole groove and a second circular hole groove are provided inside the outer sleeve of the grading hoop for fixedly connecting to an inner sleeve, flow holes corresponding to the circulation holes are provided on both sides of the inner sleeve, and the flow holes are of the same size as the circulation holes, an annular groove is provided in the middle of the inner wall of the inner sleeve, a conical hole is provided at the bottom end of the inner sleeve for clamping a gravity bottom plug, a groove with an internal radius greater than the internal radius of the upper pipe section thereof is provided at the bottom of the inner wall of the grading hoop outer sleeve, an annular baffle is provided in the groove, and a top plug for blocking the flow hole is provided inside the inner sleeve;

[0008] A sinking groove is provided at the top of the gravity bottom plug, and a sealing plate is movably connected inside the sinking groove. A telescopic rod for controlling the up and down movement of the sealing plate is fixedly connected to the bottom end of the sealing plate, and a pressure sensor is installed at the top of the telescopic rod. A spring groove for accommodating a spring group is provided at the bottom end of the sinking groove, and pressure relief ducts are provided on both sides of the sinking groove and pass through the bottom end of the gravity bottom plug. An annular groove is provided on the upper side of the side of the gravity bottom plug, and a spring 1 is fixedly connected in the groove, and one end of the spring 1 is fixedly connected to a positioning block.

[0009] Furthermore, the first circular hole groove and the second circular hole groove are opened in an annular array on the inner wall of the outer tube sleeve of the grading hoop, and a block assembly is clamped inside the two. The block assembly includes a cylindrical pin clamped inside the first circular hole groove and the second circular hole groove, a pin fixedly connected to one end of the cylindrical pin located inside the inner sliding sleeve wall shell, and a spring sleeved on the circumferential side of the pin.

[0010] Furthermore, the inner edge of the top end of the inner sleeve is rounded, and the bottom radius of the tapered hole is smaller than the inner radius of the inner sleeve.

[0011] Furthermore, the inner radius of the annular baffle is smaller than the inner radius of the outer sleeve of the grading hoop, the bottom end of the annular baffle is fixedly connected to spring 2, the outer sleeve of spring 2 is provided with a corrugated sleeve, and the top end of the corrugated sleeve is fixedly connected to the bottom end of the annular baffle, the bottom end of the corrugated sleeve is fixedly connected to the top end of the sleeve, and the interior of the corrugated sleeve is closed.

[0012] Furthermore, the upper portion of the gravity bottom plug is cylindrical, the diameter of which matches the inner diameter of the inner sleeve, and the bottom of the gravity bottom plug is truncated cone, the shape of which matches the conical hole.

[0013] Furthermore, a positioning groove adapted to the pin of the block assembly is opened at the bottom of the cylindrical section of the gravity bottom plug. After the part of the pin located inside the inner sleeve is broken by the gravity bottom plug, the remaining part is inserted into the positioning groove under the action of the spring.

[0014] Furthermore, the positioning block is adapted to the curvature and size of the annular groove and can be engaged.

[0015] Furthermore, the top plug includes a rubber ring fixedly connected to the top of the top plug, a gasket fixedly connected to the side of the top plug, and a stop block fixedly connected to the bottom end of the top plug, wherein the diameter of the stop block is smaller than the diameter of the sealing plate.

[0016] Technical effects and advantages of the present invention:

[0017] The present invention is provided with a gravity bottom plug, the top of the gravity bottom plug is provided with a sinking groove, and pressure relief pipes are provided on both sides of the sinking groove and connected with the bottom end of the gravity bottom plug. When the top plug is docked with the bottom plug, the pressure exceeds the threshold value, the pressure sensor triggers the telescopic rod to retract, driving the sealing plate to descend, so that the pressure relief pipe is exposed, so that a channel is established between the inside of the inner sliding sleeve and the internal space of the sleeve below the outer sleeve of the grading hoop through the pressure relief pipe, thereby releasing the pressure in the pipe, which is beneficial to protecting the grading hoop and preventing it from being damaged by excessive pressure.

[0018] The present invention provides an annular baffle at the bottom of the outer sleeve of the grading hoop to provide elastic support force for the inner sliding sleeve, so that the pressure caused by cement slurry blockage becomes larger, which is converted into a thrust for forcing the inner sliding sleeve to slide down, thereby increasing the opening aperture of the circulation hole, which is conducive to helping the cement slurry pass through the circulation hole more smoothly. After the blockage is cleared, the pressure becomes smaller, the inner sliding sleeve rises, and the aperture of the circulation hole is restored, thereby controlling the flow rate of the cement slurry passing through, which is conducive to avoiding pressure loss caused by excessive flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 This is a schematic diagram of the cross-sectional structure of the outer sleeve and inner sliding sleeve of the graded hoop of the present invention;

[0021] Figure 3 This is a schematic diagram of the cross-sectional structure of the present invention when the circulation hole is opened;

[0022] Figure 4 It is a schematic diagram of the cross-sectional structure of the present invention;

[0023] Figure 5 Schematic diagram of the cross-sectional structure of the gravity bottom plug of the present invention;

[0024] Figure 6 This is a schematic diagram of the cross-sectional structure of the present invention when the circulation hole is closed;

[0025] Figure 7 Schematic diagram of the cross-sectional structure of the circulation hole of the present invention when the aperture becomes larger;

[0026] Figure 8 It is a schematic structural diagram of the top plug of the present invention.

[0027] The accompanying drawings are marked as follows: 1. outer sleeve of the graded hoop; 11. circulation hole; 12. first circular hole groove; 13. second circular hole groove; 2. inner sliding sleeve; 21. circulation hole; 22. annular groove; 23. conical hole; 24. block assembly; 3. gravity bottom plug; 31. sinking groove; 32. sealing plate; 33. telescopic rod; 34. spring group; 35. spring groove; 36. pressure relief conduit; 37. spring one; 38. positioning block; 4. annular baffle; 41. spring two; 42. corrugated sleeve; 5. top plug; 51. rubber ring; 52. gasket; 53. stop block. DETAILED DESCRIPTION

[0028] The technical solutions of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. In addition, the forms of the various structures described in the following embodiments are merely examples. The mechanical grading clamp involved in the present invention is not limited to the various structures described in the following embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] Reference Figures 1 to 6 The present invention provides a mechanical grading hoop, comprising an outer pipe sleeve 1 of the grading hoop, circulation holes 11 are provided on both sides of the outer pipe sleeve 1 of the grading hoop, a first circular hole groove 12 and a second circular hole groove 13 are provided inside the outer pipe sleeve 1 of the grading hoop for fixedly connecting to an inner sleeve 2, flow holes 21 corresponding to the circulation holes 11 are provided on both sides of the inner sleeve 2, and the flow holes 21 are the same size as the circulation holes 11, an annular groove 22 is provided in the middle of the inner wall of the inner sleeve 2, a conical hole 23 is provided at the bottom end of the inner sleeve 2 for clamping a gravity bottom plug 3, a groove with an internal radius greater than the internal radius of the upper pipe section thereof is provided at the bottom of the inner wall of the outer pipe sleeve 1 of the grading hoop, an annular baffle 4 is provided in the groove, and a top plug 5 for blocking the flow hole 21 is provided inside the inner sleeve 2.

[0030] In this embodiment, before starting to inject the second stage of cement, the gravity bottom plug 3 is first inserted. The gravity bottom plug 3 falls into the outer sleeve 1 of the grading collar, and its bottom end is clamped in the conical hole 23 at the bottom of the inner sliding sleeve 2. The locking relationship between the inner sliding sleeve 2 and the outer sleeve 1 of the grading collar is released, so that the inner sliding sleeve 2 slides down to the top of the annular baffle 4. At this time, the flow hole 21 partially overlaps with the circulation hole 11, opening the channel between the outer sleeve 1 of the grading collar and the well wall, allowing cement slurry to enter the annulus through the hole. After the cementing is completed, the top plug 5 is inserted, and the cement slurry is pushed to the predetermined position of the annulus between the casing and the upper part of the well wall by using the displacement fluid. When the top plug 5 is docked with the gravity bottom plug 3, the cementing is completed.

[0031] Reference Figure 4 and Figure 5A sinking groove 31 is provided at the top of the gravity bottom plug 3, and a sealing plate 32 is movably connected inside the sinking groove 31. The bottom end of the sealing plate 32 is fixedly connected to a telescopic rod 33 for controlling the up and down movement of the sealing plate 32, and a pressure sensor is installed on the top of the telescopic rod 33. A spring groove 35 is provided at the bottom end of the sinking groove 31 for accommodating a spring group 34. Pressure relief conduits 36 are provided on both sides of the sinking groove 31 and pass through the bottom end of the gravity bottom plug 3. An annular groove is provided on the upper side of the gravity bottom plug 3, and a spring 37 is fixedly connected in the groove. One end of the spring 37 is fixedly connected to a positioning block 38, and the positioning block 38 is adapted to the curvature and size of the annular groove 22 and can be engaged.

[0032] The sealing plate 32 is adapted to the size of the sinking groove 31. The pressure applied to the top of the sealing plate 32 is transmitted to the telescopic rod 33 and sensed by the pressure sensor installed at its top. When the pressure suddenly rises after the top plug 5 and the gravity bottom plug 3 are docked, it will exceed the threshold, causing the hydraulic cylinder to activate and control the telescopic rod 33 to descend. When the top surface of the sealing plate 32 drops below the nozzle of the pressure relief conduit 36, the upper and lower spaces of the gravity bottom plug 3 are connected through the pressure relief conduit 36. In addition, when the gravity bottom plug 3 is inserted into the outer sleeve 1 of the grading hoop, the spring 1 37 is in a compressed state, and the outer edge of the positioning block 38 and the outer edge of the gravity bottom plug 3 are on the same curved surface. When the gravity bottom plug 3 falls into the bottom of the inner sleeve 2, the positioning block 38 slides to the same horizontal plane as the annular groove 22. Under the elastic force of the spring 1 37, the positioning block 38 pops out and engages with the annular groove 22, fixing the gravity bottom plug 3 to the inner sleeve 2.

[0033] Reference Figure 2 and Figure 3 The first circular hole groove 12 and the second circular hole groove 13 are opened in an annular array on the inner wall of the outer sleeve 1 of the grading hoop, and a clamping block assembly 24 is clamped inside the two. The clamping block assembly 24 includes a cylindrical pin clamped inside the first circular hole groove 12 and the second circular hole groove 13, a pin fixedly connected to one end of the cylindrical pin located inside the wall shell of the inner sliding sleeve 2, and a spring sleeved on the side of the pin.

[0034] The inner sleeve 2 is fixedly connected to the outer sleeve 1 of the grading hoop through the block assembly 24. In the static state, the cylindrical pin at one end of the block assembly 24 is inserted into the first circular hole groove 12 and the second circular hole groove 13, and the pin at the other end fixes the cylindrical pin and leaves a section on the inner wall of the inner sleeve 2, and the spring is in a stretched state. After the gravity bottom plug 3 enters the outer sleeve 1 of the grading hoop and cuts off the pin, the cylindrical pin will shrink into the inside of the inner sleeve 2 under the restoring force of the spring, that is, the cylindrical pin will break away from the first circular hole groove 12 and the second circular hole groove 13 and no longer engage with them. The inner sleeve 2 loses the fixation of the block assembly 24 and the inner part of the outer sleeve 1 of the grading hoop and slides downward relative to the outer sleeve 1 of the grading hoop.

[0035] Reference Figure 3The inner edge of the top of the inner sleeve 2 is rounded, and the bottom radius of the tapered hole 23 is smaller than the inner radius of the inner sleeve 2.

[0036] Reference Figure 2 The inner radius of the annular baffle 4 is smaller than the inner radius of the outer tube sleeve 1 of the grading hoop. The bottom end of the annular baffle 4 is fixedly connected to a spring 2 41. The outer sleeve of the spring 2 41 is provided with a corrugated sleeve 42. The top end of the corrugated sleeve 42 is fixedly connected to the bottom end of the annular baffle 4. The bottom end of the corrugated sleeve 42 is fixedly connected to the top end of the sleeve, and the interior of the corrugated sleeve 42 is closed.

[0037] The inner diameter of the annular baffle 4 is smaller than the outer diameter of the inner sleeve 2. After the inner sleeve 2 falls, it will fall to the top of the annular baffle 4. At this time, the flow hole 21 partially overlaps with the circulation hole 11, opening the annular channel between the inside of the casing and the well wall. When pressure is applied from the top, the spring 2 41 contracts, the gravity bottom plug 3 slides down, the overlapping part of the flow hole 21 and the circulation hole 11 increases, and the channel becomes larger. When the spring 2 41 is compressed to the limit, the flow hole 21 completely overlaps with the circulation hole 11, and the channel is opened to the maximum. The corrugated sleeve 42 protects the spring 2 41 from the influence of mud and sand in the pipe.

[0038] Reference Figure 5 and Figure 6 The upper part of the gravity bottom plug 3 is cylindrical, and its diameter is adapted to the internal diameter of the inner sleeve 2. The bottom of the gravity bottom plug 3 is truncated cone, and its shape is adapted to the conical hole 23. After the gravity bottom plug 3 falls to the bottom of the inner sleeve 2, its bottom end truncated cone is engaged with the conical hole 23 to achieve sealing of the grading hoop.

[0039] Reference Figure 6 and Figure 7 The bottom of the cylindrical section of the gravity bottom plug 3 is provided with a positioning groove adapted to the pin of the block assembly 24. After the part of the pin located inside the inner sleeve 2 is broken by the gravity bottom plug 3, the remaining part is inserted into the positioning groove under the action of the spring, thereby fixing the inner sleeve 2 and the gravity bottom plug 3.

[0040] Reference Figure 8 The top plug 5 includes a rubber ring 51 fixedly connected to the top of the outer periphery of the top plug 5, a gasket 52 fixedly connected to the side of the top plug 5, and a stop block 53 fixedly connected to the bottom end of the top plug 5, wherein the diameter of the stop block 53 is smaller than the diameter of the sealing plate 32.

[0041] Working principle of the present invention:

[0042] First-stage cementing: Cement slurry is injected into the casing from the wellhead through a cement pump, passes through the conical hole 23 at the bottom end of the inner sleeve 2, reaches the bottom of the casing, and returns from the bottom of the casing to enter the annulus between the casing and the well wall, sealing the bottom well section. At this time, the circulation hole 11 is in a closed state, waiting for the first-stage cement to initially solidify and form a bottom cement ring.

[0043] Second stage cementing:

[0044] The working principle of closing the grading hoop and opening the circulation hole is as follows: a gravity bottom plug 3 is inserted into the casing, the gravity bottom plug 3 enters the outer tube sleeve 1 section of the grading hoop along the casing, and then slides into the inner sleeve 2. The gravity of the falling gravity bottom plug 3 sequentially shears the block assemblies 24 distributed at the upper and lower ends of the inner sleeve 2, so that the pins of the block assemblies 24 set on the inner wall of the inner sleeve 2 are broken, and the cylindrical pins are retracted into the inner sleeve 2 under the action of the spring restoring force, wherein: the cylindrical pin on the upper part of the inner sleeve 2 is pulled out from the first circular hole groove 12 and retracted into the wall shell of the inner sleeve 2; the cylindrical pin on the lower part of the inner sleeve 2 is pulled out from the second circular hole groove 13, and retracts into the interior of the inner sleeve 2, and the end of the cylindrical pin close to the interior of the inner sleeve 2 is inserted into the cylindrical hole opened on the side of the gravity bottom plug 3, fixing the inner sleeve 2 and the gravity bottom plug 3. Afterwards, the inner sliding sleeve 2 separates from the inner wall of the outer sleeve 1 of the grading hoop and slides downward until its bottom end contacts the top of the annular baffle 4. At this time, the flow hole 21 partially overlaps with the circulation hole 11, and the circulation hole 11 is opened, establishing a flow channel for cement slurry between the casing and the well wall.

[0045] The working principle of circulation hole anti-blocking: cement slurry is poured into the casing from the wellhead through the cement pump, and enters the upper annulus between the casing and the well wall through the circulation hole 11. In this process, the opening diameter of the circulation hole 11 is insufficient, and the flow rate is insufficient, resulting in poor flow of cement slurry. The pressure exerted by the cement slurry blocked in the inner sleeve 2 on the gravity bottom plug 3 increases. The increased pressure causes the gravity bottom plug 3 to move downward relative to the outer sleeve 1 of the grading hoop. The gravity bottom plug 3 is locked with the inner sleeve 2 through the clamping block assembly 24, and the bottom end of the gravity bottom plug 3 is clamped at the inner bottom end of the inner sleeve 2, so the inner sleeve 2 and the gravity bottom plug 3 move downward synchronously relative to the outer sleeve 1 of the grading hoop. In this process, the overlapping area of ​​the circulation hole 11 and the flow hole 21 increases, the opening diameter of the circulation hole 11 increases, the flow rate increases, and the cement slurry enters the annulus smoothly through the enlarged aperture. During this process, the annular baffle 4 provides it with elastic support force, so: the blockage of cement slurry causes the pressure to increase, and the increased pressure causes the opening diameter of the circulation hole 11 to increase, helping the cement slurry to pass through the circulation hole 11 more smoothly; after the blockage is cleared, the pressure decreases, and the diameter of the circulation hole 11 decreases and recovers, controlling the flow rate of the cement slurry and avoiding excessive flow rate and pressure loss.

[0046] The working principle of displacement and closing the circulation hole: After the cement slurry is injected, the top plug 5 is put in, and then the displacement fluid (drilling fluid or clean water) is injected into the casing through the cementing pump. The gasket 52 fits against the inner wall of the outer pipe sleeve 1 of the graded collar, isolating the cement slurry from the displacement fluid. When the bottom end of the top plug 5 contacts the top of the gravity bottom plug 3, the rubber ring 51 on the top side of the top plug 5 fits tightly against the inner wall of the inner sliding sleeve 2, isolating the flow hole 21 from the space above and closing the circulation hole 11. The cement slurry is pushed out from the circulation hole 11, enters the annular space between the casing and the well wall, and returns upward to the designed height, forming a continuous cement ring. After the second-stage cement slurry solidifies, a complete sealed annulus is formed between the casing and the well wall.

[0047] The working principle of pressure relief: After the cement slurry is pushed out from the circulation hole 11, when the top plug 5 reaches the position of the gravity bottom plug 3, the channel for the fluid in the casing to flow to the annular space is completely blocked, and the subsequent displacement fluid cannot continue to flow, causing the pump pressure to rise rapidly. At this time, the pressure acts on the sealing plate 32 through the stop block 53, and the sudden increase in pressure is transmitted to the telescopic rod 33, and exceeds the threshold of the pressure sensor at the telescopic rod 33. The telescopic rod 33 contracts, and the sealing plate 32 drops below the pipe mouth of the pressure relief conduit 36 ​​inside the sinking groove 31. The interior of the inner sleeve 2 is connected to the internal space of the casing below the outer sleeve 1 of the grading hoop through the pressure relief conduit 36, which slowly releases the internal pressure of the inner sleeve 2 to prevent the sudden increase in pressure from damaging the outer sleeve 1 of the grading hoop.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mechanical grading hoop, comprising a grading hoop outer sleeve (1), characterized in that: Circulation holes (11) are provided on both sides of the outer tube sleeve (1) of the grading hoop. A first circular hole groove (12) and a second circular hole groove (13) for fixedly connecting the inner sleeve (2) are provided inside the outer tube sleeve (1). Flow holes (21) corresponding to the circulation holes (11) are provided on both sides of the inner sleeve (2). The flow holes (21) are the same size as the circulation holes (11). An annular groove (22) is provided in the middle of the inner wall of the inner sleeve (2). The bottom of the inner sleeve (2) is provided with a circular groove (22). A conical hole (23) is provided at the end for clamping a gravity bottom plug (3); a groove having an inner radius greater than the inner radius of the upper pipe section is provided at the bottom of the inner wall of the outer tube sleeve (1) of the grading hoop; an annular baffle (4) is provided in the groove; the inner radius of the annular baffle (4) is smaller than the inner radius of the outer tube sleeve (1) of the grading hoop; a spring 2 (41) is fixedly connected to the bottom end of the annular baffle (4); a top plug (5) for blocking the flow hole (21) is provided inside the inner sliding sleeve (2); The top of the gravity bottom plug (3) is provided with a sinking groove (31), the interior of the sinking groove (31) is movably connected to a sealing plate (32), the bottom end of the sealing plate (32) is fixedly connected to a telescopic rod (33) for controlling the up and down movement of the sealing plate (32), and a pressure sensor is installed on the top of the telescopic rod (33), the bottom end of the sinking groove (31) is provided with a spring groove (35) for accommodating a spring group (34), both sides of the sinking groove (31) are provided with pressure relief conduits (36) which are connected to the bottom end of the gravity bottom plug (3), the upper side of the side of the gravity bottom plug (3) is provided with an annular groove, a spring (37) is fixedly connected in the groove, and one end of the spring (37) is fixedly connected to a positioning block (38); A positioning groove adapted to the pin of the block assembly (24) is provided at the bottom of the cylindrical section of the gravity bottom plug (3). After the portion of the pin located inside the inner sleeve (2) is broken by the gravity bottom plug (3), the remaining portion is inserted into the positioning groove under the action of a spring.

2. A mechanical grading hoop according to claim 1, characterized in that: The first circular hole groove (12) and the second circular hole groove (13) are formed in an annular array on the inner wall of the outer tube sleeve (1) of the grading hoop, and a clamping block assembly (24) is clamped inside the two. The clamping block assembly (24) comprises a cylindrical pin clamped inside the first circular hole groove (12) and the second circular hole groove (13), a pin fixedly connected to one end of the cylindrical pin located inside the wall shell of the inner sliding sleeve (2), and a spring sleeved around the pin.

3. The mechanical grading hoop according to claim 1, characterized in that: The inner edge of the top end of the inner sleeve (2) is rounded, and the bottom radius of the conical hole (23) is smaller than the inner radius of the inner sleeve (2).

4. The mechanical grading hoop according to claim 1, characterized in that: The outer sleeve of the second spring (41) is provided with a corrugated sleeve (42), and the top end of the corrugated sleeve (42) is fixedly connected to the bottom end of the annular baffle (4), the bottom end of the corrugated sleeve (42) is fixedly connected to the top end of the sleeve, and the interior of the corrugated sleeve (42) is closed.

5. The mechanical grading hoop according to claim 1, characterized in that: The upper portion of the gravity bottom plug (3) is cylindrical, and its diameter matches the inner diameter of the inner sleeve (2); the bottom portion of the gravity bottom plug (3) is truncated cone, and its shape matches the conical hole (23).

6. The mechanical grading hoop according to claim 1, characterized in that: The positioning block (38) is adapted to the annular groove (22) in terms of arc and size and can be engaged.

7. The mechanical grading hoop according to claim 1, characterized in that: The top plug (5) comprises a rubber ring (51) fixedly connected to the top of the outer periphery of the top plug (5), a gasket (52) fixedly connected to the peripheral side of the top plug (5), and a stopper (53) fixedly connected to the bottom end of the top plug (5), wherein the diameter of the stopper (53) is smaller than the diameter of the sealing plate (32).

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