Pushing piston and low-temperature refrigerator applying same
By using coaxially connected secondary pistons and sprayed wear-resistant resin materials in low-temperature refrigerators, the problem of low refrigeration efficiency caused by poor sealing and material differences between the push piston and the cylinder is solved, and more efficient refrigeration is achieved Effects and simplified production process.
Patent Information
- Application Number
- CN202420864125.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-24
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2034-04-24
AI Technical Summary
In existing low-temperature refrigerators, the sealing between the push piston and the cylinder is poor, resulting in low refrigeration gas leakage and heat exchange efficiency, and material differences lead to reduced refrigeration capacity and efficiency, and high processing difficulty and cost.
Coaxially connected primary and secondary pistons, the secondary piston cylinder is made of 316L stainless steel, and the outer circumference is sprayed with wear-resistant resin material to ensure consistent material shrinkage, improve sealing and heat exchange efficiency, and simplify the processing process. .
It effectively improves the refrigeration capacity and efficiency, stability and long life of the low-temperature zone, and reduces production cycle and cost.
Smart Images
Figure CN222210837U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of low-temperature refrigerators, and in particular relates to a push piston and a low-temperature refrigerator using the push piston. Background Art
[0002] Cold storage refrigerators, such as GM refrigerators and Stirling refrigerators, have a cylinder and a reciprocating piston inside. If the seal between the cylinder and the piston is not sufficient or the heat exchange is not sufficient, the refrigerant gas will not be able to exert the expected cooling capacity.
[0003] Currently on the market, especially in the low temperature zone of the two-stage GM refrigerator in the 10K temperature zone, the second-stage push piston is mostly made of phenolic cloth rod or epoxy cloth rod material.
[0004] 1) The piston material is inconsistent with the cylinder material (generally 304 or 316L stainless steel). The shrinkage rates of the two materials are inconsistent at low temperatures, which can easily cause the gap between the piston and the cylinder to become larger, which may cause insufficient sealing, generate a large amount of heat loss, and reduce the cooling capacity and cooling efficiency of the low-temperature zone of the refrigerator.
[0005] 2) At the same time, compared with the cylinder material (generally 304 or 316L stainless steel), the volume specific heat and thermal conductivity of phenolic cloth rods or epoxy cloth rods are much smaller. During the intake process, the piston cylinder cools the refrigerant gas corresponding to the temperature and the exhaust process, the cylinder heats the refrigerant gas corresponding to the temperature, the difference between the two temperatures is relatively larger. That is, within a piston movement cycle, the temperature of the cylinder corresponding to the same position changes greatly, which means that the greater the heat exchange temperature difference, the lower the heat exchange efficiency, which is not conducive to the heat exchange of the leaked gas in the narrow gap between the cylinder and the piston. In this way, the heat exchange efficiency is low, which affects the cooling capacity and cooling efficiency of the low temperature zone of the refrigerator.
[0006] 3) The push piston made of phenolic cloth rod or epoxy cloth rod reciprocates in the cylinder, and there will be a large amount of wear during the reciprocating motion. Due to the wear resistance of the material, after a long period of use (such as 10,000 hours), the piston diameter will exceed the design tolerance range, resulting in a larger gap between the cylinder and the piston, eccentric wear of the seal and other problems. At this time, the sealing performance and heat exchange efficiency will deteriorate, directly causing the cooling capacity and cooling efficiency of the low temperature zone of the refrigerator to decrease.
[0007] 4) When phenolic cloth rods or epoxy cloth rods are used to make the push piston cylinder, the material contains a high moisture content and a large amount of other non-helium impurities. In the blank stage, rough turning to fine turning and other processing stages, long-term temperature-controlled vacuum baking is required, and high requirements are placed on baking and measurement technology to ensure the accurate determination of the moisture content, gas content and size of the material and workpiece. At the same time, the processing environment requirements for the piston cylinder are high (such as constant temperature and humidity, etc.), and the piston is not allowed to be exposed to the atmosphere for a long time after precision processing, which increases the difficulty of product production, processing and assembly, and also lengthens the production cycle and cost.
[0008] A push piston and a cryogenic refrigerator using the push piston are disclosed (patent application number: CN201921167755.5). The push piston is placed in a cylinder (13) and can reciprocate along the extension direction of the cylinder (13). A concave spiral groove gas passage (4) is provided on the outer surface of the push piston. A protruding structure (5) protruding from the concave wall surface of the spiral groove gas passage (4) is provided on the concave wall of the spiral groove gas passage (4). The protruding structure (5) is continuously or discretely arranged along the extension direction of the spiral groove gas passage (4). The cryogenic refrigerator comprises the push piston, which is installed in the cylinder (13) of the cryogenic refrigerator.
[0009] This disclosed solution reduces the cooling loss caused by gas leakage between the piston and the cylinder through a spiral groove gas passage, but gas leakage still exists between the piston and the cylinder, and the refrigerant gas cannot be completely introduced into the interior of the piston to fully exchange heat with the cold storage material, which is defective. Utility Model Content
[0010] The present application provides a push piston and a low-temperature refrigerator using the push piston, aiming to solve the problems of gas leakage between the piston and the cylinder of the above-mentioned low-temperature refrigerator, poor sealing, and low cooling capacity and cooling efficiency of the secondary push piston in the existing refrigerator due to material reasons.
[0011] In order to achieve the above purpose, the utility model adopts the following technical solutions:
[0012] A push piston comprises a primary piston and a secondary piston, the primary piston and the secondary piston are coaxially connected and placed in the primary cylinder and the secondary cylinder, the primary piston and the secondary piston reciprocate in the extension direction of the primary cylinder and the secondary cylinder, a circumferential step surface is machined on the outer circumference of the secondary piston cylinder, the circumferential step surface is evenly sprayed with a wear-resistant resin material, a secondary piston front hole, a mounting groove and an exhaust hole are machined on the circumferential step surface, the mounting groove is located between the secondary piston front hole and the exhaust hole, a secondary cold storage material cavity is arranged in the secondary piston, and the secondary piston front hole and the exhaust hole are respectively connected to the front end and the rear end of the secondary cold storage material cavity.
[0013] Preferably, the first-stage piston is provided with a first-stage piston front hole, a first-stage cold storage material cavity and a first-stage piston rear hole, the first-stage piston front hole is connected to the front end of the first-stage cold storage material cavity, and the first-stage piston rear hole is connected to the rear end of the first-stage cold storage material cavity.
[0014] Preferably, the cylinders of the primary piston and the secondary piston are both made of 304L stainless steel or 316L stainless steel.
[0015] Preferably, the wear-resistant resin material includes tetrafluoroethylene.
[0016] A low-temperature refrigerator using any of the above-mentioned push pistons, wherein a primary piston and a secondary piston are installed in a primary cylinder and a secondary cylinder of the low-temperature refrigerator, the low-temperature refrigerator comprises a helium compressor, a gas pipeline and a refrigerator drive, the helium compressor is connected to the refrigerator drive through a gas pipeline, the refrigerator drive is fixed to the primary cylinder, the refrigerator drive is connected to the primary piston to drive the primary piston and the secondary piston to move, a primary cold head is welded to one end of the primary cylinder away from the refrigerator drive, and a secondary cold head is welded to one end of the secondary cylinder away from the refrigerator drive.
[0017] Preferably, a hot chamber is provided between the first-stage piston and the refrigerator drive, the hot chamber is communicated with the first-stage piston, a first-stage expansion chamber is provided between the first-stage piston and the first-stage cold head, the first-stage expansion chamber is communicated with the first-stage piston and the second-stage piston respectively, a second-stage expansion chamber is provided between the second-stage piston and the second-stage cold head, the second-stage expansion chamber is communicated with the second-stage piston.
[0018] Preferably, a primary piston sealing ring is provided between the primary piston cylinder and the inner wall of the primary cylinder, a secondary piston sealing ring is provided between the secondary piston cylinder and the inner wall of the secondary cylinder, the secondary piston sealing ring is installed in the installation groove, and a metal expansion ring is provided between the secondary piston sealing ring and the bottom of the installation groove.
[0019] The utility model has the following beneficial effects:
[0020] (1) This solution uses 316L stainless steel as the secondary piston cylinder material to ensure that the shrinkage rates of the two materials are consistent at low temperatures, and that the gap between the piston and the cylinder always maintains the designed gap size in the full temperature range. At the same time, it can effectively ensure the sealing between the hot end of the piston and the low-temperature zone components, effectively improving the cooling capacity and cooling efficiency of the low-temperature zone of the refrigerator;
[0021] (2) This solution uses 316L stainless steel as the secondary piston cylinder material. Compared with phenolic cloth rod or epoxy cloth rod materials, the volume specific heat and thermal conductivity of the stainless steel cylinder are greater. During the intake process, the piston cylinder cools the refrigerant gas to a temperature corresponding to that of the refrigerant gas, and during the exhaust process, the cylinder heats the refrigerant gas to a temperature corresponding to that of the refrigerant gas. The difference between these two temperatures is relatively small. That is, within a piston movement cycle, the temperature change of the cylinder corresponding to the same position is small, which means that the heat exchange temperature difference is lower and the heat exchange efficiency is higher, which is more conducive to improving the heat exchange of the leaked gas in the gap slit, and effectively improving the cooling capacity and cooling efficiency of the low temperature zone of the refrigerator;
[0022] (3) This solution uses 316L stainless steel as the material for the secondary piston cylinder. At the same time, grooves are turned on the front and rear ends of the piston cylinder and the secondary piston sealing ring section where they match the cylinder, and then wear-resistant resin material (generally polytetrafluoroethylene) is sprayed on them. The wear-resistant resin material is turned to the designed size to match the cylinder. Polytetrafluoroethylene has an extremely low friction coefficient and extremely high wear resistance. During long-term movement, it can ensure that the gap size between the outer periphery of the secondary push piston and the inner periphery of the secondary cylinder body does not change significantly. This can effectively improve the stability of the refrigeration capacity and refrigeration efficiency in the low-temperature zone of the refrigerator over a long period of time;
[0023] (4) This solution uses 316L stainless steel as the secondary piston cylinder material, and part of the piston cylinder is sprayed with polytetrafluoroethylene. The two materials used have good machining properties and contain very low amounts of water vapor and impurities, which avoids cumbersome and harsh process requirements such as vacuum baking during processing. At the same time, these two materials allow long-term exposure to the atmosphere, greatly reducing the requirements for storage and assembly time. This makes it easier to produce products, saving production cycles and production costs;
[0024] (5) A secondary piston seal ring is installed between the secondary piston cylinder and the inner wall of the secondary cylinder. A metal expansion ring is provided between the secondary piston seal ring and the bottom of the installation groove to ensure that the secondary piston seal ring is fully expanded and fits perfectly with the inner wall of the secondary cylinder, thereby ensuring sealing and avoiding leakage of refrigerant gas due to gaps. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 It is a schematic diagram of the structure of the push piston and refrigerator drive in the utility model;
[0026] Figure 2 This is a schematic diagram of the structure of the low-temperature refrigerator of the utility model;
[0027] Figure 3 It is a schematic diagram of the secondary piston processing process in the utility model.
[0028] Among them, 1-refrigeration machine drive, 2-first-stage cylinder, 3-first-stage piston, 31-first-stage piston front hole, 32-first-stage cold storage material cavity, 33-first-stage piston rear hole, 4-first-stage cold head, 5-second-stage cylinder, 6-second-stage piston, 601-circumferential step surface, 602-wear-resistant resin material, 603-installation groove, 61-second-stage piston front hole, 62-second-stage cold storage material cavity, 63-exhaust hole, 7-second-stage cold head, 8-helium compressor, 9-gas pipeline, 10-hot chamber, 11-first-stage piston sealing ring, 12-first-stage expansion chamber, 13-second-stage piston sealing ring, 14-second-stage expansion chamber. DETAILED DESCRIPTION
[0029] Example 1
[0030] like Figure 1-3 As shown, a push piston includes a primary piston 3 and a secondary piston 6, which are coaxially connected and placed in the primary cylinder 2 and the secondary cylinder 5, and the primary piston 3 and the secondary piston 6 reciprocate in the extension direction of the primary cylinder 2 and the secondary cylinder 5. A circumferential step surface 601 is turned on the outer circumference of the cylinder of the secondary piston 6, and the circumferential step surface 601 is evenly sprayed with a wear-resistant resin material 602. The circumferential step surface 601 is processed with a secondary piston front hole 61, a mounting groove 603 and an exhaust hole 63, and the mounting groove 603 is located between the secondary piston front hole 61 and the exhaust hole 63. A secondary cold storage material cavity 62 is provided in the secondary piston 6, and the secondary piston front hole 61 and the exhaust hole 63 are respectively connected to the front end and the rear end of the secondary cold storage material cavity 62.
[0031] The primary piston 3 is provided with a primary piston front hole 31, a primary cold storage material cavity 32 and a primary piston rear hole 33. The primary piston front hole 31 is connected to the front end of the primary cold storage material cavity 32, and the primary piston rear hole 33 is connected to the rear end of the primary cold storage material cavity 32.
[0032] The cylinders of the primary piston 3 and the secondary piston 6 are both made of 316L stainless steel.
[0033] The wear-resistant resin material 602 includes tetrafluoroethylene.
[0034] In order to improve the consistency of the material yield rate of the secondary piston 6 and the secondary cylinder 5 in the low temperature section and the high volume specific heat and thermal conductivity of the piston cylinder, and at the same time improve the wear resistance of the cylinder, the preparation method of the piston is further described in detail:
[0035] (1) If Figure 3As shown, first, the cylinder of the secondary piston 6 is made of 316L stainless steel, and an appropriate margin is left on the outer diameter for later use. At the same time, a circumferential step surface 601 is turned on the outer circumference of the cylinder of the secondary piston 6. The surface of the turned circumferential step surface 601 needs to be relatively rough to facilitate the adhesion of the subsequent spraying of the wear-resistant resin material 602. At the same time, the length of the turned circumferential step surface 601 needs to be longer to ensure that the secondary piston 6 and the secondary cylinder 5 have sufficient matching and guiding length when assembled.
[0036] (2) Secondly, the wear-resistant resin material 602 is sprayed on the circumferential step surface 601 of the secondary piston 6. After spraying, the diameter of the circumferential step surface 601 must be larger than the maximum diameter of the 316L stainless steel cylinder blank to facilitate subsequent production.
[0037] (3) Finally, the outer diameter of the cylinder of the secondary piston 6 is re-processed to the design size, and the secondary piston front hole 61, the mounting groove 603 and the exhaust hole 63 on the secondary piston 6 are processed. The key here is that the diameter of the wear-resistant resin material 602 after turning must be larger than the maximum diameter of the cylinder 316L part, and the tolerance size must remain consistent.
[0038] In the implementation of this solution, the thickness of the wear-resistant resin material 602 is selected to be between 50 μm and 2 mm according to the wall thickness of the secondary cylinder 5. Considering the processability and adhesion of the wear-resistant resin material 602, a thickness of 100 μm to 1 mm can be further selected. The thickness of the wear-resistant resin material 602 should not be too large, because too thick a material is likely to increase axial heat leakage loss, and a thickness of 100 μm to 800 μm can be selected more preferably.
[0039] Example 2
[0040] like Figure 1 and Figure 2 As shown, a low-temperature refrigerator using a push piston, a primary piston 3 and a secondary piston 6 are installed in a primary cylinder 2 and a secondary cylinder 5 of the low-temperature refrigerator, the low-temperature refrigerator comprises a helium compressor 8, a gas pipeline 9 and a refrigerator drive 1, the helium compressor 8 is connected to the refrigerator drive 1 through the gas pipeline 9, the refrigerator drive 1 is fixed to the primary cylinder 2, the refrigerator drive 1 is connected to the primary piston 3 to drive the primary piston 3 and the secondary piston 6 to move, a primary cold head 4 is welded to one end of the primary cylinder 2 away from the refrigerator drive 1, and a secondary cold head 7 is welded to one end of the secondary cylinder 5 away from the refrigerator drive 1.
[0041] A hot chamber 10 is provided between the primary piston 3 and the refrigerator drive 1, and the hot chamber 10 is communicated with the primary piston 3. A primary expansion chamber 12 is provided between the primary piston 3 and the primary cold head 4, and the primary expansion chamber 12 is communicated with the primary piston 3 and the secondary piston 6 respectively. A secondary expansion chamber 14 is provided between the secondary piston 6 and the secondary cold head 7, and the secondary expansion chamber 14 is communicated with the secondary piston 6.
[0042] A primary piston sealing ring 11 is provided between the primary piston 3 cylinder body and the inner wall of the primary cylinder 2, a secondary piston sealing ring 13 is provided between the secondary piston 6 cylinder body and the inner wall of the secondary cylinder 5, the secondary piston sealing ring 13 is installed in the installation groove 603, and a metal expansion ring is provided between the secondary piston sealing ring 13 and the bottom of the installation groove 603.
[0043] The working principle of this cryogenic refrigerator:
[0044] (1) The helium compressor 8 sucks in and compresses the refrigerant gas, and discharges it as high-pressure refrigerant gas. The gas pipeline 9 supplies the high-pressure refrigerant gas to the refrigerator drive 1. The cylinder is a two-stage cylinder, the main body of which is made of 316L stainless steel. The primary cylinder 2 and the secondary cylinder 5 are coaxially arranged, and the inner diameter of the secondary cylinder 5 is smaller than the inner diameter of the primary cylinder 2. A primary cold head 4 is vacuum brazed on the end (cold end) of the primary cylinder 2 away from the refrigerator drive 1, and a secondary cold head 7 is vacuum brazed on the end (cold end) of the secondary cylinder 5 away from the refrigerator drive 1. The above cold heads are made of oxygen-free copper. A primary piston 3 is provided in the primary cylinder 2, and a secondary piston 6 is provided in the secondary cylinder 5. The primary piston 3 and the secondary piston 6 are coaxially connected and reciprocate together in the cylinder under the drive of the refrigerator drive 1. When the secondary piston 6 moves toward the refrigerator drive 1, the volume of the primary expansion chamber 12 and the secondary expansion chamber 14 increases; otherwise, the corresponding expansion volume decreases. Under the change of the expansion chamber volume, the refrigerant gas passes through the first piston front hole 31 and the first cold storage material cavity 32 to exchange heat with the cold storage material, and then flows out from the first piston rear hole 33 to the first expansion chamber 12; a part of the gas expands in the first expansion chamber 12, and the remaining gas flows into the second piston 6 through the second piston front hole 61, exchanges heat with the cold storage material in the second cold storage material cavity 62 of the second piston 6, and then flows out from the exhaust hole 63 to enter the second expansion chamber 14. In the above process, the refrigerant gas transfers its own heat to the cold storage material, and the temperature changes from normal temperature to low temperature. Along the above gas flow direction, the temperature of the cylinder, the first piston 3, and the second piston 6 continuously decreases, forming a temperature gradient.
[0045] (2) The flow process of the refluxed gas is opposite to the above process. The refrigerant gas flows out from the secondary expansion chamber 14, exchanges heat with the refrigerant material in the secondary refrigerant material chamber 62 through the exhaust hole 63, flows out from the secondary piston front hole 61, mixes with the refrigerant gas in the primary expansion chamber 12, and then exchanges heat with the refrigerant material in the primary refrigerant material chamber 32 through the primary piston rear hole 33, then enters the refrigerator drive 1 through the primary piston front hole 31, and then flows to the low-pressure side of the helium compressor 8. In the above process, the refrigerant gas absorbs heat from the refrigerant material and changes from low temperature to room temperature.
[0046] (3) By repeating the above actions, the cold storage material in the primary cold storage material chamber 32 and the cold storage material and refrigerant gas in the secondary cold storage material chamber 62 are cooled. The low-temperature gas continuously expands and performs work in the primary expansion chamber 12 and the secondary expansion chamber 14, forming a cooling source. The primary cold head 4 and the secondary cold head 7 are cooled by the heat transfer effect.
[0047] (4) For the primary piston 3, the primary piston seal ring 11 is used to seal the gap between its outer peripheral surface and the inner wall of the primary cylinder 2. Since the primary piston seal ring 117 is installed on the room temperature side, that is, close to the refrigerator drive 1 side, the temperature is moderately at a higher temperature during operation, which can effectively prevent the refrigerant gas from entering the primary expansion chamber 12 through the gap between the outer surface of the primary piston 3 and the inner wall of the primary cylinder 2. The temperature of the primary cold head 4 is in the temperature range of 30K to 77K.
[0048] (5) For the secondary piston 6, the gap between its outer peripheral surface and the inner wall of the secondary cylinder 5 is sealed by the secondary piston seal ring 13. The secondary piston seal ring 13 is installed on the side close to the primary expansion chamber 12 using a low temperature resistant and wear resistant sealing material to prevent the refrigerant gas from entering the secondary expansion chamber 14 through the gap between the outer surface of the secondary piston 6 and the inner wall of the secondary cylinder 5. The temperature of the secondary cold head 7 is in the temperature range of 8K to 20K.
[0049] Example 3
[0050] The difference between this embodiment and the above embodiment is that the cylinders of the primary piston 3 and the secondary piston 6 are both made of 304L stainless steel, and in this case, the material of the cylinder is also 304L stainless steel, ensuring that the material of the cylinder and the piston is the same.
[0051] The above description is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.
Claims
1. A push piston, comprising a primary piston (3) and a secondary piston (6), wherein the primary piston (3) and the secondary piston (6) are coaxially connected and disposed in a primary cylinder (2) and a secondary cylinder (5), and the primary piston (3) and the secondary piston (6) reciprocate in the extension direction of the primary cylinder (2) and the secondary cylinder (5), characterized in that: A circumferential step surface (601) is machined on the outer circumference of the cylinder of the secondary piston (6), the circumferential step surface (601) is evenly sprayed with a wear-resistant resin material (602), the circumferential step surface (601) is processed with a secondary piston front hole (61), a mounting groove (603) and an exhaust hole (63), the mounting groove (603) is located between the secondary piston front hole (61) and the exhaust hole (63), a secondary cold storage material cavity (62) is provided in the secondary piston (6), and the secondary piston front hole (61) and the exhaust hole (63) are respectively communicated with the front end and the rear end of the secondary cold storage material cavity (62).
2. A push piston according to claim 1, characterized in that: The first-stage piston (3) is provided with a first-stage piston front hole (31), a first-stage cold storage material cavity (32) and a first-stage piston rear hole (33); the first-stage piston front hole (31) is communicated with the front end of the first-stage cold storage material cavity (32), and the first-stage piston rear hole (33) is communicated with the rear end of the first-stage cold storage material cavity (32).
3. A push piston according to claim 2, characterized in that: The cylinders of the first-stage piston (3) and the second-stage piston (6) are both made of 304L stainless steel or 316L stainless steel.
4. A push piston according to claim 1, characterized in that: The wear-resistant resin material (602) includes tetrafluoroethylene.
5. A cryogenic refrigerator using the push piston as claimed in any one of claims 1 to 4, characterized in that: The primary piston (3) and the secondary piston (6) are installed in the primary cylinder (2) and the secondary cylinder (5) of the low-temperature refrigerator. The low-temperature refrigerator comprises a helium compressor (8), a gas pipeline (9) and a refrigerator drive (1). The helium compressor (8) is connected to the refrigerator drive (1) through the gas pipeline (9). The refrigerator drive (1) is fixed to the primary cylinder (2). The refrigerator drive (1) is connected to the primary piston (3) to drive the primary piston (3) and the secondary piston (6) to move. A primary cold head (4) is welded to one end of the primary cylinder (2) away from the refrigerator drive (1), and a secondary cold head (7) is welded to one end of the secondary cylinder (5) away from the refrigerator drive (1).
6. The cryogenic refrigerator according to claim 5, characterized in that: A heat chamber (10) is provided between the primary piston (3) and the refrigerator drive (1), the heat chamber (10) being in communication with the primary piston (3), a primary expansion chamber (12) is provided between the primary piston (3) and the primary cold head (4), the primary expansion chamber (12) being in communication with the primary piston (3) and the secondary piston (6) respectively, a secondary expansion chamber (14) is provided between the secondary piston (6) and the secondary cold head (7), the secondary expansion chamber (14) being in communication with the secondary piston (6).
7. The cryogenic refrigerator according to claim 6, characterized in that: A primary piston sealing ring (11) is provided between the primary piston (3) barrel and the inner wall of the primary cylinder (2), a secondary piston sealing ring (13) is provided between the secondary piston (6) barrel and the inner wall of the secondary cylinder (5), the secondary piston sealing ring (13) is installed in the installation groove (603), and a metal expansion ring is provided between the secondary piston sealing ring (13) and the bottom of the installation groove (603).