Long-life linear Stirling cryocooler piston and cylinder sleeve metal friction pair

Abstract

The invention discloses a long-life linear Stirling cryocooler piston and cylinder sleeve metal friction pair, belongs to the technical field of metal friction pair preparation, and aims to solve the technical problem that the friction resistance and high and low temperature resistance of a friction pair in the prior art need to be further improved. The piston comprises a piston, the piston is formed by connecting a piston body and a piston plug through laser welding, the two ends of the piston body are provided with a tail end conical surface and a front end conical surface correspondingly, and the piston body is obtained after a piston body blank is subjected to surface treatment. A nitriding layer and a sulfurizing layer are combined to replace a traditional polymer coating, so that the friction coefficient and the wear rate of a friction pair are effectively reduced, and the high and low temperature resistance of a sample is also improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal friction pair preparation, in particular to a long-life linear Stirling refrigerator piston and cylinder liner metal friction pair. Background Art

[0002] As a highly efficient and environmentally friendly refrigeration equipment, the Stirling refrigerator has broad application prospects in the fields of cryogenic science, space observation, reconnaissance, solid-state electronics and cryogenic biology. A friction pair refers to a system composed of two objects that are in direct contact and produce relative friction motion. The piston in the refrigerator is a typical sliding friction pair.

[0003] At present, the piston in the refrigerator mainly adopts the surface treatment of coating (plating). The cylinder and the piston substrate are dissimilar metal materials with different thermal expansion coefficients. The piston surface coating is generally a high-molecular composite material based on polytetrafluoroethylene, and its thermal expansion coefficient is more than 10 times larger than that of metal materials. When the piston works for a long time, its temperature gradually rises, and the coating on the surface of the piston expands thermally, making it difficult to maintain a relatively small dynamic sealing gap, which leads to wear of the piston. In addition, the coating has low bonding strength on the piston substrate, cracking, unstable quality, and a long process time. In addition, the wear chips fall off in the form of powder, which pollutes the working medium and blocks the heat return channel, reducing the refrigeration efficiency.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, which is used to solve the technical problem that the friction resistance and high and low temperature resistance of the friction pair in the prior art need to be further improved.

[0006] The purpose of the present invention can be achieved by the following technical solution: A long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, comprising:

[0007] A piston, wherein the piston is formed by connecting a piston body and a piston plug by laser welding, and the two ends of the piston body are respectively provided with a tail end cone surface and a front end cone surface, wherein the piston body is obtained by surface treating a piston body blank;

[0008] The cylinder liner is installed in cooperation with the piston to form a friction pair.

[0009] Furthermore, the tail end conical surface and the front end conical surface are both conical surfaces, and the semi-apex angle of the conical surface is 3 to 5 degrees, and the height of the conical surface is 3 to 5 mm.

[0010] Furthermore, the piston body, piston plug and cylinder liner are all made of high-speed steel, the piston body and cylinder liner have the same wall thickness, the diameter matching clearance between the piston body and the cylinder liner is 6 to 8 μm, and the cylindricity and coaxiality of the piston body and the cylinder liner are 0 to 5 μm.

[0011] Furthermore, a connecting thread is provided at the rear end of the piston body, and a plurality of U-shaped grooves are circumferentially spaced apart on the outer surface of the piston body, wherein the groove depth of the U-shaped groove is 0.2-0.4 mm, and the groove width is 0.2-0.4 mm.

[0012] Furthermore, the surface treatment method comprises the following steps:

[0013] A1. Pre-treating the piston body blank to obtain a pre-treated blank;

[0014] A2. Placing the pretreated blank on the cathode plate at the bottom of the ion nitriding furnace, with the pretreated blank as the cathode and the furnace wall as the anode, performing nitriding treatment, forming a nitriding layer with a thickness of 10-15 μm on the pretreated piston body blank, and obtaining a nitrided blank;

[0015] A3. Place the nitrided blank in a low-temperature ion sulfurizing furnace, use the nitrided blank as the cathode and the furnace wall as the anode, and perform sulfurizing treatment to form a sulfurized layer with a thickness of 5-8μm on the nitrided blank to obtain a piston body.

[0016] Furthermore, in step A2, the nitriding time is 8 hours, the gas atmosphere in the nitriding furnace is composed of nitrogen and hydrogen in a volume ratio of 1:3, the cathode temperature is 450-500°C, the voltage between the cathode and the anode is 680V, ​​and the pressure of the nitriding furnace is 180-200Pa. In step A3, the vacuum degree of the sulfurizing furnace reaches 8-10Pa, the voltage between the cathode and the anode is 700-900V, the reaction gas in the sulfurizing furnace is sulfur vapor, the temperature in the sulfurizing furnace is 250-300°C, and the insulation treatment time is 4-5h.

[0017] Furthermore, the preprocessing in step A1 includes the following steps:

[0018] B1. Shot peening the piston body blank using a pneumatic shot peening machine to obtain a shot peened piston body blank;

[0019] B2. Use 1000# sandpaper to thin the surface of the shot-peened piston body blank by 25-30 μm, place it in an ethanol solution, ultrasonically clean it for 20-30 minutes, and wipe it dry to obtain a pre-treated blank.

[0020] Furthermore, in step B1, the steel shots used in the shot peening treatment are composed of large steel balls with a diameter of 0.8 mm and small steel balls with a diameter of 0.1 mm in a weight ratio of 3:1, the shot peening speed is 80-110 m / s, and the shot peening treatment time is 10-13 min.

[0021] The present invention has the following beneficial effects:

[0022] 1. The piston and cylinder liner of the present invention are made of the same high-speed steel material and are subjected to appropriate heat treatment, precision machining, surface strengthening and structural optimization, thereby reducing the friction resistance and wear rate between the piston and the cylinder, avoiding jamming under different working temperature environments, maintaining a relatively unchanged dynamic sealing gap, and meeting the high-efficiency and long-life working requirements of the refrigerator; in the preparation process of the friction pair, the preparation process of the wear-resistant coating on the piston surface is omitted, and the piston surface is treated with nitriding and sulfurizing instead, so as to adapt the friction pair to maintain good refrigeration efficiency under different ambient temperatures of the refrigerator and reduce the power consumption of the refrigerator.

[0023] 2. The metal friction pair of the piston and the cylinder sleeve of the present invention has a taper set on the end face in structure to prevent the expansion of the piston in a high temperature environment from being larger than other places and causing it to get stuck in the cylinder sleeve. In addition, it plays a role of gas dynamic lubrication during the rapid reciprocating motion of the piston to reduce wear. The U-shaped groove plays a role of accommodating trace wear debris and labyrinth sealing. By shot peening the piston body and optimizing the shot peening process, a higher residual compressive stress is introduced into the piston body, the microstructure is optimized, and the wear resistance and fatigue life of the piston are improved. After nitriding, the nitride layer can greatly improve the hardness of the piston surface, reduce the wear and heat generated by metal friction, and further improve the hardness and wear resistance of the piston surface, thereby extending the service life of the piston; the sulfurized layer has good friction reduction and can significantly reduce the friction coefficient. The nitride layer formed by the nitriding treatment has provided a good wear resistance foundation, and the sulfurization treatment further reduces the friction coefficient and improves the resistance to adhesive wear. The two work together to significantly improve the wear resistance and surface lubrication performance of the piston, reduce friction and noise, and improve the overall performance of the friction pair. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the structure of the metal friction pair of the piston and the cylinder liner in the present invention;

[0026] Figure 2 It is a schematic cross-sectional structure diagram of the metal friction pair of the piston and the cylinder liner in the present invention;

[0027] Figure 3 It is a schematic diagram of the cross-sectional structure of the piston in the present invention.

[0028] In the figure: 1. piston; 11. tail end cone; 12. U-shaped groove; 13. front end cone; 14. piston plug; 15. connecting thread; 16. piston body; 2. cylinder liner. DETAILED DESCRIPTION

[0029] The technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a piston for a long-life linear Stirling refrigerator, comprising the following steps:

[0032] S1. A piston body blank made of high-speed steel is selected, and a conical surface with a semi-apex angle of 3° and a conical surface height of 3 mm is set on the tail end conical surface 11 and the front end conical surface 13 of the piston body blank. A connecting thread 15 is set at the tail end of the piston body blank, and a plurality of U-shaped grooves 12 are circumferentially spaced apart on the outer surface of the piston body blank. The groove depth of the U-shaped groove 12 is 0.2 mm, and the groove width is 0.2 mm;

[0033] S2. A large steel ball with a diameter of 0.8 mm and a small steel ball with a diameter of 0.1 mm are mixed in a weight ratio of 3:1 to form steel shots. The steel shots are used as raw materials and a pneumatic shot peening machine is used to eject the steel shots at a shot peening speed of 80 m / s. The piston body blank is shot peened for 10 min to obtain a shot peened piston body blank.

[0034] S3, using 1000# sandpaper to thin the surface of the shot-peened piston body blank by 25 μm, placing it in an ethanol solution, ultrasonically cleaning it for 20 minutes, and drying it to obtain a pretreated blank;

[0035] S4, placing the pretreated blank on the cathode plate at the bottom of the ion nitriding furnace, with the pretreated blank as the cathode, the furnace wall as the anode, and a mixed gas consisting of nitrogen and hydrogen in a volume ratio of 1:3 as the gas atmosphere of the nitriding furnace, setting the cathode temperature to 450°C, the cathode and anode voltage to 680V, ​​and the nitriding furnace pressure to 180Pa, performing nitriding treatment for 8 hours, forming a nitrided layer with a thickness of 10 μm on the pretreated piston body blank, and obtaining a nitrided blank;

[0036] S5. Place the nitrided blank in a low-temperature ion sulfurizing furnace, with the nitrided blank as the cathode and the furnace wall as the anode. The sulfurizing furnace is evacuated to 8Pa, the voltage between the cathode and the anode is set to 700V, the reaction gas in the sulfurizing furnace is sulfur vapor, the temperature in the sulfurizing furnace is 250°C, the insulation treatment time is 4h, and sulfurizing treatment is performed to form a sulfurized layer with a thickness of 5μm on the nitrided blank to obtain a piston body 16.

[0037] Example 2

[0038] This embodiment provides a method for preparing a piston for a long-life linear Stirling refrigerator, comprising the following steps:

[0039] S1. A piston body blank made of high-speed steel is selected, and a conical surface with a semi-apex angle of 4° and a conical surface height of 4 mm is set on the tail end conical surface 11 and the front end conical surface 13 of the piston body blank. A connecting thread 15 is set at the tail end of the piston body blank, and a plurality of U-shaped grooves 12 are circumferentially spaced apart on the outer surface of the piston body blank. The groove depth of the U-shaped groove 12 is 0.3 mm, and the groove width is 0.3 mm;

[0040] S2. A large steel ball with a diameter of 0.8 mm and a small steel ball with a diameter of 0.1 mm are mixed in a weight ratio of 3:1 to form steel shots. The steel shots are used as raw materials and a pneumatic shot peening machine is used to eject the steel shots at a shot peening speed of 95 m / s to shot peen the piston body blank for 11.5 min to obtain a shot peened piston body blank.

[0041] S3, using 1000# sandpaper to thin the surface of the shot-peened piston body blank by 28 μm, placing it in an ethanol solution, ultrasonically cleaning it for 25 minutes, and drying it to obtain a pretreated blank;

[0042] S4, placing the pretreated blank on the cathode plate at the bottom of the ion nitriding furnace, with the pretreated blank as the cathode, the furnace wall as the anode, and a mixed gas composed of nitrogen and hydrogen in a volume ratio of 1:3 as the gas atmosphere of the nitriding furnace, setting the cathode temperature to 475°C, the cathode and anode voltage to 680V, ​​and the nitriding furnace pressure to 190Pa, performing nitriding treatment for 8 hours, forming a nitrided layer with a thickness of 13μm on the pretreated piston body blank, and obtaining a nitrided blank;

[0043] S5. Place the nitrided blank in a low-temperature ion sulfurizing furnace, with the nitrided blank as the cathode and the furnace wall as the anode. The sulfurizing furnace is evacuated to 9Pa, the voltage between the cathode and the anode is set to 800V, the reaction gas in the sulfurizing furnace is sulfur vapor, the temperature in the sulfurizing furnace is 280°C, the insulation treatment time is 4.5h, and sulfurizing treatment is performed to form a sulfurized layer with a thickness of 7μm on the nitrided blank to obtain a piston body 16.

[0044] Example 3

[0045] This embodiment provides a method for preparing a piston for a long-life linear Stirling refrigerator, comprising the following steps:

[0046] S1. A piston body blank made of high-speed steel is selected, and a conical surface with a semi-apex angle of 5° and a conical surface height of 5 mm is set on the tail end conical surface 11 and the front end conical surface 13 of the piston body blank. A connecting thread 15 is set at the tail end of the piston body blank, and a plurality of U-shaped grooves 12 are circumferentially spaced apart on the outer surface of the piston body blank. The groove depth of the U-shaped groove 12 is 0.4 mm, and the groove width is 0.4 mm;

[0047] S2. A large steel ball with a diameter of 0.8 mm and a small steel ball with a diameter of 0.1 mm are mixed in a weight ratio of 3:1 to form steel shots. The steel shots are used as raw materials and a pneumatic shot peening machine is used to eject the steel shots at a shot peening speed of 110 m / s to shot peen the piston body blank for 13 min to obtain a shot peened piston body blank.

[0048] S3, using 1000# sandpaper to thin the surface of the shot-peened piston body blank by 30 μm, placing it in an ethanol solution, ultrasonically cleaning it for 30 minutes, and drying it to obtain a pretreated blank;

[0049] S4, placing the pretreated blank on the cathode plate at the bottom of the ion nitriding furnace, with the pretreated blank as the cathode, the furnace wall as the anode, and a mixed gas consisting of nitrogen and hydrogen in a volume ratio of 1:3 as the gas atmosphere of the nitriding furnace, setting the cathode temperature to 500° C., the cathode and anode voltage to 680 V, and the nitriding furnace pressure to 200 Pa, performing nitriding treatment for 8 hours, forming a nitrided layer with a thickness of 15 μm on the pretreated piston body blank, and obtaining a nitrided blank;

[0050] S5. Place the nitrided blank in a low-temperature ion sulfurizing furnace, with the nitrided blank as the cathode and the furnace wall as the anode. The sulfurizing furnace is evacuated to 10Pa, the voltage between the cathode and the anode is set to 900V, the reaction gas in the sulfurizing furnace is sulfur vapor, the temperature in the sulfurizing furnace is 300°C, the insulation treatment time is 5h, and sulfurizing treatment is performed to form a sulfurized layer with a thickness of 8μm on the nitrided blank to obtain a piston body 16.

[0051] Example 4

[0052] The present embodiment provides a long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, comprising: a piston 1 prepared in Example 1 and a cylinder liner 2 matched with the piston 1; the cylinder liner 2 is made of high-speed steel material, the piston body 16 and the cylinder liner 2 have the same wall thickness, the diameter matching clearance between the piston body 16 of the piston 1 and the cylinder liner 2 is 6μm, and the cylindricity and coaxiality of the piston body 16 and the cylinder liner 2 are 2μm.

[0053] Example 5

[0054] The present embodiment provides a long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, comprising: a piston 1 prepared in Example 2 and a cylinder liner 2 matched with the piston 1; the cylinder liner 2 is made of high-speed steel material, the piston body 16 and the cylinder liner 2 have the same wall thickness, the diameter matching clearance between the piston body 16 of the piston 1 and the cylinder liner 2 is 7μm, and the cylindricity and coaxiality of the piston body 16 and the cylinder liner 2 are 3μm.

[0055] Example 6

[0056] The present embodiment provides a long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, comprising: a piston 1 prepared in Example 3 and a cylinder liner 2 matched with the piston 1; the cylinder liner 2 is made of high-speed steel material, the piston body 16 and the cylinder liner 2 have the same wall thickness, the diameter matching clearance between the piston body 16 of the piston 1 and the cylinder liner 2 is 8μm, and the cylindricity and coaxiality of the piston body 16 and the cylinder liner 2 are 5μm.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 6 is that when the piston 1 is prepared, no conical surface is provided on the block and the tail end.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 6 is that, when preparing the piston 1 used, step S5 is omitted, and the nitrided blank prepared in step S4 is used as the piston body.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 6 is that, when preparing the piston 1 used, step S4 is omitted, and the pretreated blank prepared in step S3 replaces the nitrided blank in step S5.

[0063] Performance Test:

[0064] The friction coefficients of the friction pairs prepared in the test examples 4-6 and the comparative examples 1-3 were compared with those of the samples after 5×10 4 After reciprocating friction, the wear rate of the sample was measured. The specific test results are shown in Table 1 below:

[0065] Table 1-Performance test data of the sample

[0066]

[0067] Data Analysis:

[0068] Comparative analysis of the data in the above table shows that the friction coefficient of the friction pair prepared by the present invention is reduced to 0.39. 4Reciprocating friction, after the sample has experienced a process of rising from room temperature to high temperature, the wear rate of the sample is only 0.17mm 3 / Nm, and all performance test data are better than those of the control example, indicating that the present invention optimizes the structure and preparation process of the piston and replaces the traditional polymer coating with a combination of a nitriding layer and a sulfiding layer, which not only effectively reduces the friction coefficient and wear rate of the friction pair, but also improves the high and low temperature resistance of the sample.

[0069] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0070] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0071] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. Long-life linear Stirling refrigerator piston and cylinder liner metal friction pair, characterized by: include: A piston (1), wherein the piston (1) is formed by connecting a piston body (16) and a piston plug (14) by laser welding, and the two ends of the piston body (16) are respectively provided with a rear end conical surface (11) and a front end conical surface (13), wherein the piston body (16) is obtained by subjecting a piston body blank to surface treatment; A cylinder liner (2) is installed in cooperation with the piston (1) to form a friction pair.

2. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 1, characterized in that: The tail end conical surface (11) and the front end conical surface (13) are both conical surfaces, and the semi-apex angle of the conical surface is 3 to 5 degrees, and the height of the conical surface is 3 to 5 mm.

3. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 1, characterized in that: The piston body (16), the piston plug (14) and the cylinder sleeve (2) are all made of high-speed steel material. The wall thickness of the piston body (16) and the cylinder sleeve (2) is the same. The diameter matching clearance between the piston body (16) and the cylinder sleeve (2) is 6 to 8 μm. The cylindricity and coaxiality of the piston body (16) and the cylinder sleeve (2) are 0 to 5 μm.

4. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 1, characterized in that: The rear end of the piston body (16) is provided with a connecting thread (15), and the outer surface of the piston body (16) is provided with a plurality of U-shaped grooves (12) at intervals in the circumferential direction. The groove depth of the U-shaped groove (12) is 0.2-0.4 mm, and the groove width is 0.2-0.4 mm.

5. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 1, characterized in that: The surface treatment method comprises the following steps: A1. Pre-treating the piston body blank to obtain a pre-treated blank; A2. Placing the pretreated blank on the cathode plate at the bottom of the ion nitriding furnace, with the pretreated blank as the cathode and the furnace wall as the anode, performing nitriding treatment, forming a nitriding layer with a thickness of 10-15 μm on the pretreated piston body blank, and obtaining a nitrided blank; A3. Place the nitrided blank in a low-temperature ion sulfurizing furnace, with the nitrided blank as the cathode and the furnace wall as the anode, and perform sulfurizing treatment to form a sulfurized layer with a thickness of 5-8 μm on the nitrided blank to obtain a piston body (16).

6. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 5, characterized in that: In step A2, the nitriding time is 8h, the gas atmosphere in the nitriding furnace is composed of nitrogen and hydrogen in a volume ratio of 1:3, the cathode temperature is 450-500°C, the voltage between the cathode and the anode is 680V, ​​and the pressure of the nitriding furnace is 180-200Pa. In step A3, the vacuum degree of the sulfurizing furnace reaches 8-10Pa, the voltage between the cathode and the anode is 700-900V, the reaction gas in the sulfurizing furnace is sulfur vapor, the temperature in the sulfurizing furnace is 250-300°C, and the insulation treatment time is 4-5h.

7. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 5, characterized in that: The preprocessing in step A1 includes the following steps: B1. Shot peening the piston body blank using a pneumatic shot peening machine to obtain a shot peened piston body blank; B2. Use 1000# sandpaper to thin the surface of the shot-peening piston body blank by 25-30 μm, place it in an ethanol solution, ultrasonically clean it for 20-30 minutes, and wipe it dry to obtain a pre-treated blank.

8. The long-life linear Stirling refrigerator piston and cylinder liner metal friction pair according to claim 7, characterized in that In step B1, the steel shots used in the shot peening treatment are composed of large steel balls with a diameter of 0.8 mm and small steel balls with a diameter of 0.1 mm in a weight ratio of 3:1, the shot peening speed is 80-110 m / s, and the shot peening treatment time is 10-13 min.

Images