A sealing structure and sealing method for an ultra-low temperature refrigeration device

Abstract

This invention belongs to the field of cryogenic refrigeration technology and discloses a sealing structure and sealing method for a cryogenic refrigeration device. A first opening is formed at the bottom of the housing. A heat transfer bus is installed inside the housing, with one end extending out of the first opening and circumferentially sealed to it. A boss is provided inside the housing, with a threaded hole penetrating the housing. A set screw is threaded into the threaded hole, and the gap between the set screw and the threaded hole is filled with sealant. A heat transfer rod is circumferentially sealed to the first opening, and an end cap is circumferentially sealed to a second opening. A saturated solution of magnetic material is injected into the housing through the threaded hole, and crystals grow on the heat transfer wire. After crystal growth is complete, the residual solution inside the housing is emptied through the threaded hole and dried. Sealant is applied to the set screw, and the set screw is screwed into the threaded hole and tightened. This device can effectively withstand huge internal and external pressure differences, is reliable for a long time in cryogenic environments, and is in force balance under the magnetic field of a superconducting magnet. Furthermore, the manufacturing process is simple, the operation is convenient, and it is easy to produce.

Description

Technical Field

[0001] This invention relates to the field of cryogenic refrigeration technology, and in particular to a sealing structure and sealing method for a cryogenic refrigeration device. Background Technology

[0002] Adiabatic demagnetizing refrigerators are the mainstream equipment for obtaining sub-Kelvin and even milliKelvin levels of extremely low temperatures. Their core component is a magnetothermal module (commonly known as a salt pellet). This module is filled with hydrated salt magnetothermal materials such as chromium potassium alum (CPA) and ferric ammonium alum (FAA) as the refrigerant. These hydrated salt magnetothermal materials have stringent requirements for the working environment. Once they lose water, they will completely fail. Therefore, they need to be sealed in an airtight metal container.

[0003] A typical magnetocaloric module structure includes a metal shell with an internal cavity, a highly thermally conductive heat bus structure disposed inside the metal shell for conducting heat, and a heat transfer section thermally connected to the heat bus structure and extending to the outside of the shell. During the fabrication process, a saturated salt solution is injected through one or more small holes (growth ports) opened in the sidewall of the metal shell to allow crystals to crystallize and grow on the heat bus. After the crystal growth is completed, the growth port must be permanently sealed.

[0004] The most common sealing method currently is to directly fill and cover the growth port with epoxy resin after crystal growth is completed. However, the above sealing method has many drawbacks: The magnetothermal module operates in a high vacuum environment, while its internal pressure is typically maintained at about one atmosphere due to residual gas or material volatilization. This means that the sealing structure must withstand a huge pressure difference from the inside out. In the above sealing method, the adhesive acts as a "plug," relying solely on its adhesion to the smooth metal wall to bear this pressure. Since the surface of the metal shell is relatively smooth after machining, and if there are contaminants such as water molecules on the surface of the growth port during bonding, it will seriously affect the interfacial bonding strength between the adhesive layer and the adhered object. This will cause the adhesive to easily creep, detach, or even be "push open" entirely under long-term pressure, ultimately leading to seal failure. The thermal expansion coefficients of epoxy resin and stainless steel differ greatly. When the magnetothermal module is cooled from room temperature to extremely low temperature (such as 4K), the drastic shrinkage will generate huge shear stress at the interface between the adhesive layer and the metal, causing the adhesive layer to crack or debond and the seal to fail. Magnetothermal modules are typically suspended from the center of a superconducting magnet's cylindrical cavity by a delicate suspension system consisting of thin wires with low thermal conductivity (such as Kevlar wires) or thin-walled organic materials. These suspension components are designed to be as fragile as possible to minimize heat leakage, with limited strength margins. However, conventional side-sealing methods create glue protrusions on the sidewalls of the outer casing. To avoid collisions between these glue protrusions and the inner wall of the magnet, two compromises must be made in the design: one is to increase the diameter of the magnet's central hole, but this would multiply the volume and weight of the magnet and magnetic shield; the other is to arrange the magnetothermal module eccentrically, but this would result in uneven stress on the suspension points, with some suspension components bearing excessive additional stress. Under extremely low temperature cycling and external vibration environments, these components are prone to fatigue fracture or debonding, seriously threatening the long-term reliability of the system. Summary of the Invention

[0005] The purpose of this invention is to provide a sealing structure for an ultra-low temperature refrigeration device that can effectively withstand huge internal and external pressure differences, maintain long-term reliability in ultra-low temperature environments, and achieve force balance under the magnetic field generated by a superconducting magnet.

[0006] To achieve this objective, the present invention adopts the following technical solution: A sealing structure for an ultra-low temperature refrigeration device includes a housing, a first opening at the bottom of the housing, a heat bus inside the housing, one end of the heat bus extending out of the first opening and circumferentially sealed to the first opening, a boss inside the housing, a threaded hole through the housing, a set screw being threaded into the threaded hole, and a sealant filling the gap between the set screw and the threaded hole.

[0007] Preferably, the boss is disposed on the side wall of the housing, the top wall of the housing, or the hot bus.

[0008] Preferably, the heat bus includes a heat-conducting bundle and a heat transfer rod, one end of the heat-conducting bundle is connected to the heat transfer rod, and the other end extends along the length of the housing. The outer wall of the heat transfer rod is circumferentially sealed to the first opening.

[0009] Preferably, a second opening is provided at the top of the housing, and the second opening is circumferentially sealed to the end cap, with the other end of the heat-conducting beam connected to the end cap.

[0010] Preferably, the heat-conducting bundle and the heat transfer rod are integrally formed.

[0011] Preferably, the heat-conducting bundle is cold-pressed onto the heat transfer rod.

[0012] Preferably, both the housing and the set screw are made of stainless steel.

[0013] Preferably, the thickness of the boss is 6 mm.

[0014] Preferably, the sealant is epoxy resin adhesive, polyurethane adhesive, or silicone adhesive.

[0015] Another objective of this invention is to provide a sealing method for an ultra-low temperature refrigeration device, which has a simple processing technology, is easy to operate, and is easy to produce.

[0016] To achieve this objective, the present invention adopts the following technical solution: A sealing method for an ultra-low temperature refrigeration device, applied to the sealing structure of the aforementioned ultra-low temperature refrigeration device, includes the following steps: S1. The heat transfer rod is circumferentially sealed to the first opening, and the end cap is circumferentially sealed to the second opening. S2. A saturated solution of magnetic material is injected into the shell through the screw hole, and the crystal grows on the heat-conducting beam. S3. After the crystal growth is complete, empty the remaining solution inside the shell through the screw hole and dry it. S4. Apply sealant to the set screw, screw the set screw into the screw hole and tighten it.

[0017] The beneficial effects of this invention are: This invention provides a sealing structure and sealing method for an ultra-low temperature refrigeration device. A first opening is formed at the bottom of the housing. A heat transfer line is installed inside the housing, with one end extending out of the first opening and circumferentially sealed to it. A boss is provided inside the housing, with a threaded hole penetrating the housing. A set screw is threaded into the threaded hole, and the gap between the set screw and the threaded hole is filled with sealant. A heat transfer rod is circumferentially sealed to the first opening, and an end cap is circumferentially sealed to a second opening. A saturated solution of magnetic material is injected into the housing through the threaded hole, causing crystals to grow on the heat transfer line. After crystal growth is complete, the remaining solution inside the housing is emptied through the threaded hole and dried. Sealant is applied to the set screw, and the set screw is screwed into the threaded hole. Tightening; the mechanical engagement between the set screw and the screw hole bears the thrust generated by the pressure difference between the inside and outside of the shell, effectively reducing the risk of the sealing structure being "push open" or "collapsed" by the thrust. It can effectively withstand huge internal and external pressure differences, improving the reliability of the seal. The sealant only fills the tiny spiral gap between the set screw and the screw hole and is not a major structural load-bearing component. Even if the sealant develops micro-cracks due to thermal stress, it will not affect the mechanical sealing effect of the sealing structure. It is reliable for a long time in extremely low temperature environments. The boss is set inside the shell, and the outside of the shell maintains a complete cylindrical outline. The overall structure is in force balance under the magnetic field generated by the superconducting magnet, and the processing technology is simple, the operation is convenient, and it is easy to produce. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the sealing structure of an ultra-low temperature refrigeration device provided in Embodiment 1 of the present invention; Figure 2This is a schematic diagram of the shell structure provided in Embodiment 1 of the present invention; Figure 3 This is a partial structural schematic diagram of the sealing structure of an ultra-low temperature refrigeration device provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the structure of the hot bus provided in Embodiment 1 of the present invention.

[0019] In the picture: 1. Housing; 11. First opening; 12. Second opening; 13. End cap; 2. Hot air bus; 21. Heat conduction bundle; 22. Heat transfer rod; 3. Boss; 31. Screw hole; 4. Set screw. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0021] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0023] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0024] Example 1 Please see Figures 1 to 4 This embodiment provides a sealing structure for an ultra-low temperature refrigeration device that can effectively withstand huge internal and external pressure differences, and is reliable for a long time in ultra-low temperature environments. The overall structure is in force balance under the magnetic field generated by the superconducting magnet.

[0025] Please see Figure 1 and Figure 2 The sealing structure of the cryogenic refrigeration device provided in this embodiment includes a housing 1, a first opening 11 at the bottom of the housing 1, a heat bus 2 arranged inside the housing 1, the heat bus 2 is used to make thermal connection with an external load and conduct heat, one end of the heat bus 2 extends out of the first opening 11, and the heat bus 2 is circumferentially sealed to the first opening 11, thereby sealing the housing 1.

[0026] Further, please refer to Figure 1 and Figure 2 A boss 3 is provided inside the housing 1, and a screw hole 31 is opened on the boss 3. The screw hole 31 is provided to penetrate the housing 1 so that the screw hole 31 can be used as an injection port and an exhaust port for internal processing.

[0027] With the above configuration, the boss 3 is placed inside the shell 1, and the outer side of the shell 1 maintains a complete cylindrical outline. The overall structure is in force balance under the magnetic field generated by the superconducting magnet. There is no need to increase the size of the superconducting magnet, nor is there a need for a complex eccentric arrangement to avoid the boss 3. This allows the whole structure to be centrally suspended in the cylindrical cavity of the superconducting magnet, ensuring uniform force at each suspension point and ensuring the long-term reliability of the fragile suspension system.

[0028] In other feasible embodiments, two or more protrusions 3 may be provided at intervals inside the housing 1 to increase the number of injection ports and vent ports for internal processing and improve the processing speed.

[0029] Furthermore, please refer to Figure 3 Use a set screw 4 that matches the aforementioned screw hole 31, apply sealant to the outer wall of the set screw 4, screw the set screw 4 into the screw hole 31 and tighten it. After the sealant has cured, the sealing of the housing 1 is completed.

[0030] With the above settings, the tightened set screw 4 can transmit the thrust generated by the pressure difference between the inside and outside of the housing 1 to the housing 1 through the threaded pair. The thrust is borne by the mechanical engagement between the set screw 4 and the screw hole 31, which can effectively withstand the huge pressure difference between the inside and outside, effectively reduce the risk of the sealing structure being "push open" or "collapsed" by the thrust, and improve the reliability of the seal.

[0031] In addition, the sealant fills the gap between the set screw 4 and the screw hole 31 to prevent minor leaks. It is used to assist the set screw 4 in sealing the screw hole 31 and to block the leakage path of gas molecules. It is not a major structural load-bearing component. Even if the sealant in the spiral gap develops micro-cracks due to thermal stress, it will not affect the mechanical sealing effect of the sealing structure. It is reliable for a long time in extremely low temperature environments. Moreover, the amount of sealant used is very small and does not come into large-area contact with the solution inside the shell 1. It can eliminate the sealing failure caused by the sealant failure due to contaminants at the bonding interface, and further improve the reliability of the seal.

[0032] Preferably, the sealant is made of epoxy resin, polyurethane, or silicone, all of which can fill tiny gaps, have good stability at low temperatures, and can also play an auxiliary sealing role.

[0033] In this embodiment, the housing 1 and the set screw 4 are made of the same material to ensure that their coefficients of thermal expansion are the same, thus eliminating the effects of thermal stress at extremely low temperatures. Specifically, this ensures that the connection between the set screw 4 and the screw hole 31 will not generate destructive stress due to inconsistent shrinkage throughout the entire temperature range from room temperature to extremely low temperatures, further improving long-term reliability in extremely low temperature environments. Preferably, both the housing 1 and the set screw 4 are made of stainless steel.

[0034] In this embodiment, the boss 3 is set on the side wall of the housing 1. In other feasible embodiments, the boss 3 can also be set on the top wall of the housing 1 or the hot bus 2, as long as the screw hole 31 on the boss 3 can connect the inside of the housing 1 with the outside.

[0035] For example, the thickness of the boss 3 is set to 6mm, which ensures the length of the screw hole 31 and the screw strength between the set screw 4 and the screw hole 31, while reducing the internal space occupied by the housing 1.

[0036] Please see Figure 1 and Figure 4 The heat transfer bus 2 includes a heat-conducting bundle 21 and a heat transfer rod 22, both made of copper. One end of the heat-conducting bundle 21 is connected to the heat transfer rod 22, and the other end extends along the length of the housing 1 inside the housing 1. The outer wall of the heat transfer rod 22 is circumferentially sealed to the first opening 11. Alternatively, in other feasible embodiments, a boss 3 may be provided on the heat transfer rod 22.

[0037] In this embodiment, the outer wall of the heat transfer rod 22 is circumferentially welded to the edge of the first opening 11 to achieve a sealed connection between the heat transfer rod 22 and the first opening 11. Furthermore, the heat conduction bundle 21 and the heat transfer rod 22 are integrally formed using wire cutting technology, and there is no connection interface between the heat conduction bundle 21 and the heat transfer rod 22 to ensure unobstructed heat conduction.

[0038] Alternatively, in other feasible embodiments, the heat conduction bundle 21 and the heat transfer rod 22 can be fabricated separately, and the heat conduction bundle 21 can be connected to the heat transfer rod 22 using cold pressing technology.

[0039] In this embodiment, a second opening 12 is provided at the top of the housing 1, and the second opening 12 is circumferentially sealed to the end cap 13. Preferably, the outer edge of the end cap 13 is circumferentially welded to the edge of the second opening 12 to achieve a sealed connection between the end cap 13 and the second opening 12. Further, the other end of the heat-conducting beam 21 is connected to the end cap 13 to ensure that the heat-conducting beam 21 can quickly conduct the overall heat of the housing 1. Preferably, the other end of the heat-conducting beam 21 is welded to the end cap 13.

[0040] By opening a second opening 12 at the top of the housing 1 and providing an end cap 13 at the second opening 12, it is convenient to connect the heat conduction bundle 21 to the end cap 13.

[0041] The sealing structure of the cryogenic refrigeration device provided in this embodiment has the following beneficial effects: By placing the boss 3 inside the housing 1 and maintaining the complete cylindrical outline of the outer side of the housing 1, the overall structure is in force balance under the magnetic field generated by the superconducting magnet. There is no need to increase the size of the superconducting magnet or to make a complex eccentric arrangement to avoid the boss 3. This allows the whole structure to be centrally suspended in the cylindrical cavity of the superconducting magnet, ensuring uniform force at each suspension point and ensuring the long-term reliability of the fragile suspension system. The mechanical engagement between the set screw 4 and the screw hole 31 bears the thrust generated by the pressure difference between the inside and outside of the housing 1. After tightening, the set screw 4 can transmit the thrust generated by the pressure difference between the inside and outside of the housing 1 to the housing 1 through the threaded pair. The mechanical engagement between the set screw 4 and the screw hole 31 bears the thrust, which effectively reduces the risk of the sealing structure being "push open" or "collapsed" by the thrust and improves the reliability of the seal. The sealant fills the gap between the set screw 4 and the screw hole 31 to prevent minor leaks. It is used to assist the set screw 4 in sealing the screw hole 31 and to block the leakage path of gas molecules. It is not a major structural load-bearing component. Even if the sealant in the spiral gap develops micro-cracks due to thermal stress, it will not affect the mechanical sealing effect of the sealing structure. It is reliable for a long time in extremely low temperature environments. Moreover, the amount of sealant used is very small and does not come into large-area contact with the solution inside the shell 1. It can eliminate the sealing failure caused by the sealant failure due to contaminants at the bonding interface, and further improve the reliability of the seal. The housing 1 and the set screw 4 are made of the same material so that the thermal expansion coefficients of the housing 1 and the set screw 4 are the same. This ensures that the connection between the set screw 4 and the screw hole 31 will not generate destructive stress due to inconsistent shrinkage throughout the entire temperature range from room temperature to extremely low temperature, and will not affect the mechanical sealing effect between the set screw 4 and the screw hole 31.

[0042] Example 2 This embodiment provides a sealing method for an ultra-low temperature refrigeration device, which is applied to the sealing structure of the aforementioned ultra-low temperature refrigeration device. The processing technology is simple, the operation is convenient, and it is easy to produce.

[0043] This embodiment provides a sealing method for an ultra-low temperature refrigeration device, which includes the following steps: S1. The heat transfer rod 22 is circumferentially sealed to the first opening 11, and the end cap 13 is circumferentially sealed to the second opening 12. S2. A saturated solution of magnetic material is injected into the interior of the shell 1 through the screw hole 31, and the crystal grows on the heat-conducting beam 21. S3. After the crystal growth is complete, empty the remaining solution inside the shell 1 through the screw hole 31 and dry it. S4. Apply sealant to set screw 4, screw set screw 4 into screw hole 31 and tighten.

[0044] Specifically, the other end of the heat conduction tube 21 is welded to the end cap 13, and the heat transfer tube 2 is inserted into the inside of the housing 1 through the second opening 12. The end cap 13 is then covered, and the outer edge of the end cap 13 is circumferentially welded to the edge of the second opening 12. The outer wall of the heat transfer tube 22 is then circumferentially welded to the edge of the first opening 11, thus forming a sealed structure for the housing 1 except for the threads. A saturated solution of magnetic material is injected into the shell 1 through the screw hole 31. Preferably, a saturated solution of chromium potassium alum (CPA) is selected. Crystals are crystallized and grown on the heat transfer rod 22 by controlling parameters such as temperature and flow rate. After the crystal growth is complete, the residual solution inside the shell 1 is emptied through the screw hole 31 and dried. Apply a layer of sealant to the outer wall of the set screw 4, then screw the set screw 4 into the screw hole 31 and tighten it. After the sealant has cured, the sealing of the housing 1 is completed.

[0045] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A sealing structure for an ultra-low temperature refrigeration device, characterized in that, The device includes a housing (1), with a first opening (11) at the bottom of the housing (1). A heat bus (2) is provided inside the housing (1), with one end of the heat bus (2) extending out of the first opening (11) and circumferentially sealed to the first opening (11). A boss (3) is provided inside the housing (1), with a screw hole (31) penetrating the housing (1). A set screw (4) is screwed into the screw hole (31), and the gap between the set screw (4) and the screw hole (31) is filled with sealant.

2. The sealing structure of the cryogenic refrigeration device according to claim 1, characterized in that, The boss (3) is disposed on the side wall of the housing (1), the top wall of the housing (1), or the hot bus (2).

3. The sealing structure of the cryogenic refrigeration device according to claim 1, characterized in that, The heat bus (2) includes a heat-conducting bundle (21) and a heat transfer rod (22). One end of the heat-conducting bundle (21) is connected to the heat transfer rod (22), and the other end extends along the length of the housing (1). The outer wall of the heat transfer rod (22) is circumferentially sealed to the first opening (11).

4. The sealing structure of the cryogenic refrigeration device according to claim 3, characterized in that, The top of the housing (1) has a second opening (12), which is circumferentially sealed to the end cap (13). The other end of the heat-conducting bundle (21) is connected to the end cap (13).

5. The sealing structure of an ultra-low temperature refrigeration device according to claim 3, characterized in that, The heat-conducting bundle (21) and the heat transfer rod (22) are integrally formed.

6. The sealing structure of an ultra-low temperature refrigeration device according to claim 3, characterized in that, The heat-conducting bundle (21) is cold-pressed to the heat transfer rod (22).

7. The sealing structure of an ultra-low temperature refrigeration device according to claim 1, characterized in that, Both the housing (1) and the set screw (4) are made of stainless steel.

8. The sealing structure of an ultra-low temperature refrigeration device according to claim 1, characterized in that, The thickness of the boss (3) is 6mm.

9. The sealing structure of an ultra-low temperature refrigeration device according to claim 1, characterized in that, The sealant is epoxy resin, polyurethane, or silicone.

10. A sealing method for an ultra-low temperature refrigeration device, applied to the sealing structure of an ultra-low temperature refrigeration device according to any one of claims 1-9, characterized in that, Includes the following steps: S1. The heat transfer rod (22) is circumferentially sealed to the first opening (11), and the end cap (13) is circumferentially sealed to the second opening (12); S2. A saturated solution of magnetic material is injected into the interior of the shell (1) through the screw hole (31), and the crystal grows on the heat-conducting beam (21). S3. After the crystal growth is complete, empty the residual solution inside the shell (1) through the screw hole (31) and dry it. S4. Apply sealant to the set screw (4), screw the set screw (4) into the screw hole (31) and tighten it.

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