Preparation method of copper-chromium alloy mixed powder shielding cylinder

Abstract

The invention discloses a preparation method of a copper-chromium alloy mixed powder shielding cylinder, which comprises the following steps: S1, mixing copper powder and chromium powder, and then loading into a ball-milling powder mixing tank for ball-milling to obtain copper-chromium alloy mixed powder; s2, filling a mold with the copper-chromium alloy mixed powder, and pressing to obtain a biscuit with the density of 88-90%; s3, the biscuit is placed on a graphite substrate, a graphite cylinder is placed in the center of the biscuit, then the biscuit is sintered, and a sintered biscuit is obtained; and S4, separating the sintered biscuit and the graphite cylinder, and processing and slotting to obtain the copper-chromium alloy mixed powder shielding cylinder. According to the method, the shielding cylinder can have extremely low gas content by controlling the compaction density of the shielding cylinder and the process route of later-stage solid-phase sintering, the inner ring space of the biscuit is filled with the graphite cylinder, deformation of the biscuit in the sintering process is effectively avoided, the gas content of the shielding cylinder is further reduced, and the service life of the shielding cylinder is prolonged. And the insulating strength of the shielding cylinder in the vacuum arc-extinguishing chamber in the using process is improved.

Description

Technical Field

[0001] The invention relates to the technical field of powder sintering, and in particular to a method for preparing a copper-chromium alloy mixed powder shielding tube. Background Art

[0002] As the core component of vacuum switch, vacuum interrupter can only ensure stable and reliable operation of vacuum switch if it has good mechanical strength, high insulation level and breaking capacity. This determines that the parts of vacuum interrupter located on the shell structure must be able to maintain the vacuum degree inside the tube for a long time, and there must be no defects that cause chronic leakage. The shielding tube used in vacuum interrupter is an indispensable supporting component of vacuum interrupter.

[0003] The invention of CN112941426A relates to the technical field of shielding tube preparation, and specifically to a method for preparing a copper-chromium alloy shielding tube with low gas content and high strength. The gas content in the prepared shielding tube is reduced by lowering the melting temperature, adding Mg for degassing, and using a CaO crucible with low high-temperature degassing. A W fiber preform skeleton is buried inside the CuCr alloy substrate, and the load bearer is changed from CuCr alloy to W fiber, which effectively enhances the strength of the shielding tube during operation and makes up for the shortcoming of insufficient strength of CuCr alloy. ZrB is coated on the surface of the shielding tube to reduce the gas content in the prepared shielding tube. 2 layer, which can not only enhance the strength and conductivity of the shielding tube, but also utilize ZrB 2 The high melting point and low volatility properties suppress the evaporation of copper during soldering of the shield tube.

[0004] However, in the prior art, the preparation process of the shielding tube is complicated, the production efficiency is low, the material utilization rate is low, and the energy consumption is high. In addition, many types of elements are added to manufacture the shielding tube, and it is difficult to control the performance of the material. Therefore, a method for preparing a shielding tube using copper-chromium alloy as material is proposed to solve the above problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a copper-chromium alloy mixed powder shielding tube.

[0006] The technical solution of the present invention is: a method for preparing a copper-chromium alloy mixed powder shielding tube, comprising the following steps:

[0007] S1, ball milling powder mixing: copper powder and chromium powder are mixed and put into a ball milling powder mixing tank for ball milling to obtain copper-chromium alloy mixed powder;

[0008] S2. Pressing and molding: filling the copper-chromium alloy mixed powder into the mold, controlling the core rod to vibrate 10 to 12 times, and adjusting the pressure of the press to 4.5 to 5.0 MPa, to obtain a green blank with a density of 88 to 90%;

[0009] S3, solid phase sintering: placing the green blank on a graphite substrate, and placing a graphite cylinder 1 to 2 mm smaller than the inner diameter of the green blank at the center of the green blank, and then sintering the green blank to obtain a sintered green blank;

[0010] S4, processing and shaping: separating the sintered green billet and the graphite cylinder, and then processing and grooving the inside and outside of the sintered green billet to obtain a copper-chromium alloy mixed powder shielding tube.

[0011] Description: This method effectively ensures that the shielding tube has an extremely low gas content by controlling the compact density of the shielding tube and the process route of the later solid phase sintering, thereby further ensuring the insulation strength of the shielding tube prepared by the present invention in the vacuum interrupter during use;

[0012] At the same time, by using graphite cylinders to fill the inner ring space of the blank during the sintering preparation process, the deformation of the blank during the sintering process is effectively avoided, and the yield of the shielding tube is further improved. In addition, the graphite cylinder can react with the oxygen in the furnace in an appropriate amount during the sintering process, thereby achieving a further degassing effect, so as to obtain a shielding tube with a lower gas content, thereby improving the use effect of the shielding tube.

[0013] Furthermore, the mass fraction of chromium powder in the copper-chromium alloy mixed powder is 8% to 12%; the ball-to-material ratio of the ball mill is controlled to be 1:1 to 1.2, and the ball milling time is 7 to 8 hours.

[0014] Description: Copper-chromium alloy has excellent mechanical properties. The copper-chromium alloy has high hardness and good corrosion resistance and thermal stability when doped with chromium powder with the above mass fraction. In addition, copper and chromium elements are harmless to the human body. Copper-chromium alloy is an environmentally friendly material and meets the requirements of modern industry for green and sustainable development.

[0015] Grinding copper powder and chromium powder by using the above-mentioned ball-to-material ratio can ensure that copper powder and chromium powder are fully collided and rubbed during the grinding process, thereby improving the grinding efficiency. If the ball-to-material ratio is too high, the ineffective collisions between the grinding balls will increase, resulting in increased energy consumption and decreased grinding efficiency; if the ball-to-material ratio is too low, the material may not be fully ground.

[0016] Furthermore, before the copper-chromium alloy mixed powder is filled into the mold, a release agent is applied to the inner wall of the mold cavity, wherein the release agent is a mixture of zinc stearate and alcohol in a mass ratio of 1:8 to 15.

[0017] Note: Applying the release agent with the above ratio on the inner wall of the mold cavity can avoid adhesion between the blank and the mold, facilitate demolding, and at the same time reduce the impact force on the mold during blank forming, reduce the wear of the blank and the mold, and effectively ensure that the mold is not damaged during the extrusion demolding process.

[0018] Furthermore, the pressure holding time of the press is 0.1 to 0.2 s, and the pressure relief time is 1 to 1.5 s.

[0019] Note: The length of the holding time directly affects the degree of bonding between the powder particles. By maintaining the above pressure and time, the powder particles can be more closely combined together, thereby increasing the density of the green billet. The increase in density helps to improve the mechanical and physical properties of the product. Under the above holding time, a green billet with a density between 88-90% can be obtained, which can facilitate exhaust during the subsequent vacuum sintering process while maintaining a certain hardness. During the pressure relief process, if the pressure relief speed is too fast, stress concentration may occur inside the green billet, which may affect the mechanical properties and long-term stability of the green billet. Therefore, controlling the pressure relief time helps to avoid the occurrence of stress concentration.

[0020] Furthermore, the sintering method is as follows: first, the vacuum in the furnace is evacuated to 1×10 -1 After Pa, gradient heating begins, and the temperature rise rate of the furnace is controlled at 3-5℃ / min; the final sintering temperature is controlled at 1020-1050℃, and the temperature is lowered after keeping warm for 4-5h. When the furnace temperature drops to 500℃, the fan is turned on to accelerate the cooling.

[0021] Note: By using the above-mentioned heating rate to carry out gradient heating, the green billet can be gradually and steadily heated from the initial temperature to 1020-1050°C. By accurately controlling the temperature increase, the adverse effects of sudden temperature changes on the green billet can be avoided, and deformation and cracking caused by thermal stress can be avoided. In addition, the above-mentioned solid-phase sintering process route can effectively ensure the extremely low gas content of the shielding tube itself, thereby further ensuring the insulation strength of the shielding tube prepared by the present invention in the vacuum arc chamber during use.

[0022] Furthermore, in the first 30 to 50 minutes of sintering, the temperature of the graphite cylinder is 40 to 70° C. lower than the temperature of the green body, and then the temperature of the graphite cylinder is made the same as the temperature of the green body until the sintering is completed.

[0023] Description: By using graphite cylinders to control the temperature of the inner ring cavity of the blank during sintering, so that it produces a temperature difference of 40 to 70°C, deformation and cracking caused by thermal stress can be further avoided, and the metallographic changes and grain refinement of the blank can be better controlled, which is helpful to optimize the microstructure of the copper-chromium alloy blank, thereby improving the mechanical and physical properties of the shielding tube.

[0024] Furthermore, the graphite cylinder is composed of an inner core consisting of a copper rod and a temperature controller, and graphite wrapped around the inner core.

[0025] Description: The temperature controller is composed of a commercially available temperature sensor and a single-chip microcomputer. There are two temperature sensors, one is set on the copper rod, and the other is set on the graphite cylinder. The single-chip microcomputer is provided with a heat protection cover. The temperature sensor is connected to the single-chip microcomputer and an external commercial refrigerator through a wire. The cooling end of the refrigerator is connected to the copper rod of the graphite cylinder through a cooling pipe. The temperature of the graphite cylinder and the copper rod is monitored by the two temperature sensors, and the temperature of the copper rod is controlled by the single-chip microcomputer according to the value of the temperature monitoring, so as to realize the temperature control of the graphite cylinder, so that the temperature of the blank and the temperature of the graphite cylinder are kept at a temperature difference of 40 to 70°C within 30 to 50 minutes after the start of sintering, thereby promoting the control of the microstructure of the copper-chromium alloy blank.

[0026] Furthermore, the chromium powder is Cr@Cu composite powder.

[0027] Description: A spherical Cr@Cu composite powder with uniform performance and good properties is prepared by attaching a copper layer to the surface of the chromium powder. By using the Cr@Cu composite powder as the introduction of the chromium element, the solid-state bonding effect between the copper powder and the Cr@Cu composite powder can be improved, thereby obtaining a blank with extremely low gas content; at the same time, when the blank is sintered, it can help to increase the grain density of the copper-chromium alloy and further improve the microstructure of the copper-chromium alloy blank, thereby obtaining a shielding tube with excellent performance.

[0028] Furthermore, the preparation method of the Cr@Cu composite powder is:

[0029] 1) OP-10 is added to deionized water at a ratio of 0.2-0.3 g: 250 mL to obtain a mixed solution, and then chromium powder is added to the mixed solution at a ratio of 1 g: 20-30 mL, and magnetic stirring is performed for 10-15 minutes, and the chromium powder is filtered to obtain filtered chromium powder;

[0030] 2) Add the filtered chromium powder into 10% H 2 SO 4 The chromium powder is filtered again, and the filtered chromium powder is added to 30-60 g / L citric acid at a ratio of 1 g: 10-20 mL, and magnetically stirred for 10-15 min to obtain the treated chromium powder;

[0031] 3) The treated chromium powder is spread on a titanium plate as the cathode, and an electrolytic copper plate is used as the anode. The electrolyte is CuSO 4 The solution is electrolytically treated, and after electrolytic treatment, Cr@Cu composite powder with a copper content of 45-50wt.% is collected from the titanium plate. 4The concentration of Cu ions in the solution is 10-20 g / L, and the current density of the electrolytic treatment is 400-600 A / m 2 .

[0032] Description: By using OP-10 mixed with deionized water as a dispersant and degreasing agent for chromium powder, impurities such as oil on the surface of chromium powder can be removed and chromium powder can be fully dispersed; the chromium powder is pickled with dilute sulfuric acid to remove a small amount of oxide on the surface of the chromium powder and corrode the surface of the chromium powder to a certain extent, thereby making the surface of the chromium powder rough to increase the surface area of ​​the chromium powder; then, through citric acid immersion treatment, the use effect of chromium powder can be significantly enhanced, the adhesion of copper layer can be enhanced, and on this basis, combined with 400-600A / m 2 Electrolysis treatment at a current density of can make the copper layer adhere to the chromium powder more uniformly, thereby improving the sphericity of the obtained chromium powder.

[0033] The beneficial effects of the present invention are:

[0034] (1) The method of the present invention can make the shielding tube have an extremely low gas content by controlling the density of the pressed blank and the process route of the later solid-phase sintering. In addition, by using a graphite cylinder to fill the inner annular space of the blank during the sintering preparation process, the deformation of the blank during the sintering process is effectively avoided, and the gas content of the shielding tube is further reduced, thereby improving the insulation strength of the shielding tube in the vacuum arc extinguishing chamber during use.

[0035] (2) The method of the present invention can avoid the adverse effects of sudden temperature changes on the green billet and avoid deformation and cracking caused by thermal stress by optimizing the solid phase sintering process and accurately controlling the temperature increase.

[0036] (3) The method of the present invention controls the temperature of the graphite cylinder and the blank to create a temperature difference, thereby better controlling the metallographic changes, grain refinement and other processes of the blank, thereby optimizing the microstructure of the copper-chromium alloy blank and further improving the use effect of the shielding tube in the vacuum arc extinguishing chamber.

[0037] (4) The method of the present invention can improve the solid-state bonding effect of copper powder and Cr@Cu composite powder by using Cr@Cu composite powder as the introduction of chromium element, and can further improve the microstructure of the copper-chromium alloy blank during sintering, thereby obtaining a shielding tube with excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a metallographic photograph (200 μm) of the copper-chromium alloy mixed powder shielding tube of the present invention.

[0039] Figure 2 This is a metallographic photograph (100 μm) of the copper-chromium alloy mixed powder shielding tube of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with specific implementation methods to better reflect the advantages of the present invention.

[0041] Embodiment 1: A method for preparing a copper-chromium alloy mixed powder shielding tube, comprising the following steps:

[0042] S1. Ball milling powder mixing: copper powder and chromium powder are mixed and put into a ball milling powder mixing tank for ball milling, wherein the ball-to-material ratio of the ball milling is controlled to be 1:1, and the ball milling time is 8 hours to obtain a copper-chromium alloy mixed powder; wherein the mass fraction of chromium powder in the copper-chromium alloy mixed powder is 11%, and the copper powder and the chromium powder are both prepared by gas atomization, but not limited to this method, and the copper powder and the chromium powder can also be prepared by water atomization and other methods;

[0043] S2. Pressing: Apply a release agent to the inner wall of the cavity of the mold, wherein the release agent is a mixture of zinc stearate and alcohol in a mass ratio of 1:10, and then fill the copper-chromium alloy mixed powder into the mold, control the core rod vibration times to 11 times, and adjust the pressure of the press to 4.8 MPa, the holding time to 0.1 s, and the pressure relief time to 1.3 s, to obtain a green blank with a density of 88.41%;

[0044] S3, solid phase sintering: the green blank is placed on a graphite substrate, and a graphite cylinder 1.5 mm smaller than the inner diameter of the green blank is placed in the center of the green blank. The green blank is then sintered. First, the vacuum in the furnace is pumped to 1×10 -1 After Pa, gradient heating was started, and the temperature rise rate of the furnace body was controlled at 4°C / min; the final sintering temperature was controlled at 1030°C, and the temperature was lowered after 4 hours of heat preservation. When the furnace temperature dropped to 500°C, the fan was turned on to accelerate the cooling, and the wind speed of the fan was 3m / s to obtain the sintered green billet;

[0045] S4, processing and shaping: separating the sintered green blank and the graphite cylinder, and then processing and grooving the inside and outside of the sintered green blank to obtain a copper-chromium alloy mixed powder shielding cylinder;

[0046] Taking the shielding tube with specifications of 80mm outer diameter, 70mm inner diameter and 40mm high as an example, the graphite cylinder is a solid graphite cylinder with a diameter of 68.5mm and a height of 45mm.

[0047] The method of Example 1 is now used to perform ball milling and mixing for 8 hours to perform green blank pressing and forming. The green blank density and density of five groups of green blanks obtained are experimentally tested. The results are shown in Table 1 below:

[0048] Table 1 Parameters of green billet formed by ball milling and pressing for 8 hours

[0049] Group <![CDATA[Density / g / cm 3 > <![CDATA[Calculated theoretical density value / g / cm 3 > Density / % 1 7.82 8.784 88.97 2 7.75 8.784 88.20 3 7.77 8.784 88.41 4 7.74 8.784 88.09 5 7.74 8.784 88.13

[0050] It can be seen from Table 1 that the method of the present application can obtain a green blank with a density of 88-90%, thereby meeting the requirements of subsequent solid phase sintering, and the density is greater than 7.7. At the same time, the above green blanks are solid-phase sintered, and the performance indicators of the shielding tube after solid-phase sintering are tested as shown in Table 2 below:

[0051] Table 2 Performance indicators of shielding tube after solid phase sintering

[0052]

[0053] It can be seen from Table 2 that after solid phase sintering of the five groups of blanks in Table 1, the oxygen and nitrogen contents of the copper-chromium alloy mixed powder shielding tube are controlled at: oxygen content ≤ 250ppm, nitrogen content ≤ 20ppm respectively while ensuring the hardness and density of the material, which can effectively ensure the insulation strength of the shielding tube used in the vacuum interrupter. At the same time, we observed the metallographic structure of the two groups with the lowest oxygen content, such as Figure 1 and Figure 2 As shown, it can be seen that the chromium content in its metallographic structure is evenly distributed, there is no aggregation of chromium particles, and the chromium particles are controlled at ≤200μm.

[0054] At the same time, in order to further verify the compact density of the present application and the influence of the graphite cylinder on the finished shielding tube, the following comparison is set:

[0055] Control 1: The copper-chromium alloy mixed powder was filled into a mold to obtain a green billet with a density of 92%, and the other parameters were the same as those in Example 1;

[0056] Control 2: No graphite cylinder was used, and the other parameters were the same as those in Example 1;

[0057] The oxygen content and nitrogen content of the shield tube after solid phase sintering were tested for control 1 and control 2, respectively, as shown in Table 3 below:

[0058] Table 3 Performance indicators of shielding tube after solid phase sintering

[0059] Group Oxygen content / ppm Nitrogen content / ppm Comparison 1 290 25 Comparison 2 260 17

[0060] It can be seen from Table 3 that after the green billet density is increased, its oxygen content is greater than 250ppm and its nitrogen content is greater than 20ppm, which obviously affects the insulation strength of the shielding tube used in the vacuum interrupter. This may be due to the fact that the compaction density of the control 1 is too high, which affects the exhaust in the later vacuum sintering process.

[0061] At the same time, the shielding tube obtained without using the graphite cylinder for auxiliary sintering has an oxygen content significantly higher than that of the shielding tube in Example 1. This may be because after the graphite cylinder is not used, the graphite cannot be used to react with the oxygen in the furnace, so that the oxygen content of the shielding tube is higher; and 50 shielding tubes are produced by the method of Example 1 and the method of Control 2, and the yield rate is statistically calculated. The results are shown in Table 4 below:

[0062] Table 4 Shielding tube yield rate

[0063] Group Finished product quantity Yield / % Example 1 50 100 Comparison 2 38 76

[0064] It can be seen from Table 4 that after the graphite cylinder was not used, the yield rate of the shielding tube decreased significantly, from the original 0 unqualified products to 12. It can be seen that after the graphite cylinder was used, the yield rate of the shielding tube was effectively improved.

[0065] Example 2: This example is different from Example 1 in that the mass fraction of chromium powder in the copper-chromium alloy mixed powder is 8%.

[0066] Example 3: This example is different from Example 1 in that the mass fraction of chromium powder in the copper-chromium alloy mixed powder is 12%.

[0067] Example 4: This example is different from Example 1 in that the ball-to-material ratio is controlled at 1:1.1 and the ball milling time is 7.5 h.

[0068] Example 5: This example is different from Example 1 in that the ball-to-material ratio is controlled at 1:1.2 and the ball milling time is 7 hours.

[0069] Example 6: This example is different from Example 1 in that the release agent is a mixture of zinc stearate and alcohol in a mass ratio of 1:8 to 15.

[0070] Example 7: This example is different from Example 1 in that the release agent is a mixture of zinc stearate and alcohol in a mass ratio of 1:8 to 15.

[0071] Embodiment 8: This embodiment differs from Embodiment 1 in that the vibration times of the core rod are controlled to be 10 times, and the pressure of the press is adjusted to 4.5 MPa, the pressure holding time is 0.1 s, and the pressure relief time is 1 s.

[0072] Example 9: This example is different from Example 1 in that the vibration times of the core rod are controlled to be 12 times, and the pressure of the press is adjusted to 5.0 MPa, the pressure holding time is 0.2 s, and the pressure relief time is 1.5 s.

[0073] In order to verify the influence of different press working parameters on the finished shielding tube, the compactness and density of the pressed green blank are tested by the experimental method of Example 1. The results are shown in Table 5 below:

[0074] Table 5 Parameters of green billet formed by ball milling and pressing for 8 hours

[0075] Group <![CDATA[Density / g / cm 3 > <![CDATA[Calculated theoretical density value / g / cm 3 > Density / % Example 8 7.67 8.784 88.01 Example 9 7.84 8.784 89.12

[0076] It can be seen from Table 5 that after reducing the pressure of the press and the pressure relief time on the basis of Example 1, the density decreased to a certain extent, and the density was basically close to 88%. Considering the fluctuation of the pressing value, Example 8 would be relatively easy to have a situation where the density was difficult to control within 88-90%;

[0077] After increasing the pressure of the press and the pressure relief time on the basis of Example 1, the density is improved to a certain extent, and the density is between 88% and 90%. However, Example 9 adopts a longer pressure holding and pressure relief time and a greater press pressure. From the perspective of economy and production efficiency, Example 1 is relatively better.

[0078] Embodiment 10: This embodiment differs from Embodiment 1 in that a graphite cylinder 1 mm smaller than the inner diameter of the blank is placed at the center of the blank.

[0079] Example 11: This example is different from Example 1 in that a graphite cylinder 2 mm smaller than the inner diameter of the blank is placed at the center of the blank.

[0080] In order to verify the influence of different graphite cylinders on the solid phase sintering of the green blank, 50 shielding cylinders were produced by the methods of Example 10 and Example 11, and the yield rate was statistically analyzed. The results are shown in Table 6 below:

[0081] Table 6 Shielding tube yield rate

[0082] Group Finished product quantity Yield / % Example 10 50 100 Embodiment 11 47 94

[0083] It can be seen from Table 6 that, on the basis of Example 1, the spacing between the blank and the graphite cylinder is reduced, and the yield rate does not change. However, due to the reduction in the spacing between the blank and the graphite cylinder, the difficulty of assembling and separating the graphite cylinder increases, and the blank is prone to scratches. On the basis of Example 1, the spacing between the blank and the graphite cylinder is increased, and the yield rate decreases to a certain extent. This may be because the graphite cylinder cannot play a good supporting role after the spacing is increased, so that part of the blank still deforms during the sintering process. Therefore, the spacing between the blank and the graphite cylinder in Example 1 is relatively better.

[0084] Example 12: This example is different from Example 1 in that the temperature rise rate of the furnace is controlled at 3°C / min; the final sintering temperature is controlled at 1020°C and kept warm for 4 hours.

[0085] Example 13: This example is different from Example 1 in that the temperature rise rate of the furnace is controlled at 5°C / min; the final sintering temperature is controlled at 1050°C and kept at this temperature for 5 hours.

[0086] In order to verify the influence of different sintering conditions on the shielding tube, the hardness, oxygen content and nitrogen content of the pressed green blank are tested by the experimental method of Example 1. The results are shown in Table 7 below:

[0087] Table 7 Performance indicators of shielding tube after solid phase sintering

[0088]

[0089]

[0090] It can be seen from Table 7 that after changing the sintering heating rate and the final sintering temperature, there are certain differences in the performance indicators of the prepared shielding tube. The shielding tube performance of Example 12 is basically the same as that of Example 1, but its heating rate is slower and the process takes longer, while the gas content of Example 13 is relatively higher. Overall, the sintering conditions of Example 1 are relatively better.

[0091] Example 14: This example is different from Example 1 in that, in the first 45 minutes of sintering, the temperature of the graphite cylinder is 60°C lower than the temperature of the blank, and then the temperature of the graphite cylinder is made the same as the temperature of the blank until the sintering is completed; the graphite cylinder is composed of an inner core consisting of a copper rod and a temperature controller, and graphite wrapped around the inner core; it can be understood that the temperature controller is composed of a commercially available temperature sensor and a single-chip microcomputer, two temperature sensors are provided, one is arranged on the top surface of the copper rod, and the other is arranged on the top surface of the graphite, the single-chip microcomputer is arranged on the top of the copper rod, and the single-chip microcomputer is arranged on the top of the copper rod. The machine is provided with a heat protection cover, the temperature sensor is connected to the single-chip microcomputer and an external commercial refrigerator through a wire, the cooling end of the refrigerator is connected to the copper rod of the graphite cylinder through a cooling pipe, the temperature of the graphite cylinder and the copper rod is monitored by two temperature sensors, and the single-chip microcomputer controls the refrigerator to control the temperature of the copper rod according to the value of the temperature monitoring, so as to realize the temperature control of the graphite cylinder; at the same time, the diameter of the graphite cylinder is 68.5 mm, the diameter of the copper rod is 20.5 mm, the thickness of the graphite wrapped on the inner core is 24 mm, the height of the copper rod is 42 mm, and the height of the graphite is 45 mm;

[0092] Example 15: This example is different from Example 14 in that, in the first 30 minutes of sintering, the temperature of the graphite cylinder is 40° C. lower than the temperature of the green body.

[0093] Example 16: This example is different from Example 14 in that, in the first 50 minutes of sintering, the temperature of the graphite cylinder is 70° C. lower than the temperature of the green body.

[0094] In order to verify the influence of the above sintering method on the shielding tube, the hardness, oxygen content and nitrogen content of the shielding tube are tested by the experimental method of Example 1. The results are shown in Table 8 below:

[0095] Table 8 Performance indicators of shielding tube after solid phase sintering

[0096] Group Hardness / HB Oxygen content / ppm Nitrogen content / ppm Embodiment 14 72.4 160 14 Embodiment 15 71.2 170 16 Example 16 72.0 170 15

[0097] It can be seen from Table 8 that by controlling the temperature difference between the graphite cylinder and the blank, the hardness of the shielding tube is effectively improved and the gas content of the shielding tube is reduced. After reducing or increasing the temperature difference between the graphite cylinder and the blank on the basis of Example 14, the hardness and gas content of the shielding tube both change to a certain extent. This may be because the temperature difference between the graphite cylinder and the blank is too large, which will cause the temperature difference between the inside and outside of the blank to be too large, affecting the grain refinement process of the blank; and the temperature difference between the graphite cylinder and the blank is too small, which will reduce the effect of the sintering method of the present application. Therefore, the sintering effect of Example 14 is the best.

[0098] Example 17: This example is different from Example 1 in that the chromium powder is Cr@Cu composite powder, and the preparation method of the Cr@Cu composite powder is:

[0099] 1) OP-10 was added to deionized water at a ratio of 0.25 g: 250 mL to obtain a mixed solution, and then chromium powder was added to the mixed solution at a ratio of 1 g: 25 mL, and magnetic stirring was performed for 12 minutes, and the chromium powder was filtered to obtain filtered chromium powder;

[0100] 2) Add the filtered chromium powder into 10% H 2 SO 4 The chromium powder was filtered again, and the filtered chromium powder was added to 45 g / L citric acid at a ratio of 1 g:15 mL, and magnetically stirred for 12 min to obtain the treated chromium powder;

[0101] 3) The treated chromium powder is spread on a titanium plate as the cathode, and an electrolytic copper plate is used as the anode. The electrolyte is 40°C CuSO 4 The solution was electrolytically treated, and Cr@Cu composite powder with a copper content of 48wt.% was collected from the titanium plate after electrolysis. 4 The Cu ion concentration in the solution is 15 g / L, and the current density of the electrolysis treatment is 500 A / m 2.

[0102] Example 18: This example is different from Example 17 in that OP-10 is added to deionized water at a ratio of 0.2 g: 250 mL to obtain a mixed solution, and then chromium powder is added to the mixed solution at a ratio of 1 g: 20 mL, and magnetic stirring is performed for 10 minutes.

[0103] Example 19: This example is different from Example 17 in that OP-10 is added to deionized water at a ratio of 0.3 g: 250 mL to obtain a mixed solution, and then chromium powder is added to the mixed solution at a ratio of 1 g: 30 mL, and magnetic stirring is performed for 15 minutes.

[0104] Example 20: This example is different from Example 17 in that the filtered chromium powder is added to 10% H 2 SO 4 The chromium powder was filtered again and added into 30 g / L citric acid at a ratio of 1 g:10 mL, and magnetically stirred for 10 min.

[0105] Example 21: This example is different from Example 17 in that the filtered chromium powder is added to 10% H 2 SO 4 The chromium powder was filtered again and added into 60 g / L citric acid at a ratio of 1 g:20 mL, and magnetically stirred for 15 min.

[0106] Example 22: This example is different from Example 17 in that CuSO 4 The Cu ion concentration in the solution is 10 g / L and the current density of the electrolysis treatment is 400 A / m 2 , and a Cr@Cu composite powder with a copper content of 45wt.% was obtained.

[0107] Example 23: This example is different from Example 17 in that CuSO 4 The Cu ion concentration in the solution is 20 g / L, and the current density of the electrolysis treatment is 600 A / m 2 , and obtain Cr@Cu composite powder with a copper content of 50wt.%.

[0108] In order to verify the influence of different chromium powder materials on the performance of the shielding tube, the performance indicators of the shielding tube are tested by the experimental method of Example 1, as shown in Table 9 below:

[0109] Table 9 Performance indicators of shielding tube after solid phase sintering

[0110] Group Hardness / HB Oxygen content / ppm Nitrogen content / ppm <![CDATA[Measured density / g / cm 3 > Density / % Embodiment 17 75.9 120 11 8.68 98.81 Embodiment 18 75.6 120 12 8.67 98.70 Embodiment 19 75.9 120 11 8.68 98.82 Embodiment 20 74.8 130 13 8.59 97.80 Embodiment 21 75.1 120 12 8.61 98.02 Embodiment 22 75.4 120 12 8.65 98.47 Embodiment 23 76.0 120 11 8.68 98.85

[0111] It can be seen from Table 9 that after using Cr@Cu composite powder as the introduction of chromium element, its various performance indicators are better than the method of using chromium powder as the introduction of chromium element. The specific analysis is as follows:

[0112] When adjusting the ratio of chromium powder to the mixed liquid, it can be found through the comparison of Example 18, Example 19 and Example 17 that after reducing the concentration of OP-10 in the mixed liquid, the hardness and density of the shielding tube decreased slightly, which may be due to the influence on the sphericity of the Cr@Cu composite powder, thereby affecting the density of the material after the later solid phase sintering. After increasing the concentration of OP-10 in the mixed liquid, the various performance indicators of the shielding tube did not change significantly, and the amount of the mixed liquid and OP-10 raw materials in Example 19 increased. Considering from the perspective of economy, the comprehensive use effect of Example 17 is the best;

[0113] When adjusting the ratio of chromium powder in dilute hydrochloric acid and citric acid, it can be found through the comparison of Example 20, Example 21 and Example 17 that after reducing or increasing the concentration of citric acid, various performance indicators of the shielding tube have decreased to a certain extent. This may be because an appropriate amount of citric acid can promote the synthesis of Cr@Cu composite powder. Therefore, the Cr@Cu composite powder synthesis method of Example 17 is relatively optimal.

[0114] When adjusting the copper sulfate solution and the electrolytic treatment parameters, it can be found through the comparison of Example 22, Example 23 and Example 17 that after reducing the copper layer coverage of the chromium powder, the hardness and density of the shielding tube prepared therefrom have decreased. This may be due to the poor sphericity of the Cr@Cu composite powder and the relatively low copper content, which affects the density of the shielding tube; after increasing the copper layer coverage of the chromium powder, the various performance parameters of the shielding tube prepared therefrom have not changed significantly, and Example 23 uses more raw materials and consumes more power. Therefore, from the perspective of economy, the comprehensive use effect of Example 17 is the best;

[0115] At the same time, in order to further verify the effect of citric acid on the Cr@Cu composite powder, a control is now set: in step 2), citric acid is not used, and the remaining steps are the same as in Example 17. The experimental method of Example 1 is now used to test the various performance indicators of the shielding tube, as shown in Table 10 below:

[0116] Table 10 Performance indicators of shielding tube after solid phase sintering

[0117] Group Hardness / HB Oxygen content / ppm Nitrogen content / ppm <![CDATA[Measured density / g / cm 3 > Density / % Comparison 72.7 150 14 8.64 97.36

[0118] It can be seen from Table 10 that, after not being treated with citric acid, the gas content of the control was significantly increased compared with Example 17, and the hardness was also decreased. This may be because the sphericity of the Cr@Cu composite powder affects the effect after pressing and sintering. In this regard, we also conducted sphericity statistics on the Cr@Cu composite powder prepared by Example 17 and the control, and the proportion of sphericity above 90% was statistically analyzed, as shown in Table 11 below:

[0119] Table 11 Sphericity distribution of Cr@Cu composite powder

[0120] Group Sphericity ≥ 90% content / % Embodiment 17 93.44％ Comparison 84.37％

[0121] It can be seen from Table 11 that the sphericity of the Cr@Cu composite powder that has not been treated as above is above 90%, which is significantly lower than that of the Cr@Cu composite powder in Example 17. This also confirms our above conjecture that the use of the above-mentioned citric acid effectively improves the sphericity of the Cr@Cu composite powder, thereby further improving the performance of the shielding tube made of copper-chromium alloy material.

Claims

1. A method for preparing a copper-chromium alloy mixed powder shielding tube, characterized in that: The following steps are involved: S1, ball milling powder mixing: copper powder and chromium powder are mixed and put into a ball milling powder mixing tank for ball milling to obtain copper-chromium alloy mixed powder; S2. Pressing and molding: filling the copper-chromium alloy mixed powder into the mold, controlling the core rod to vibrate 10 to 12 times, and adjusting the pressure of the press to 4.5 to 5.0 MPa, to obtain a green blank with a density of 88 to 90%; S3, solid phase sintering: placing the green blank on a graphite substrate, and placing a graphite cylinder 1 to 2 mm smaller than the inner diameter of the green blank at the center of the green blank, and then sintering the green blank to obtain a sintered green blank; S4, processing and shaping: separating the sintered green billet and the graphite cylinder, and then processing and grooving the inside and outside of the sintered green billet to obtain a copper-chromium alloy mixed powder shielding tube.

2. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: The mass fraction of chromium powder in the copper-chromium alloy mixed powder is 8% to 12%; the ball-to-material ratio of the ball mill is controlled to be 1:1 to 1.2, and the ball milling time is 7 to 8 hours.

3. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: Before the copper-chromium alloy mixed powder is filled into the mold, a release agent is applied to the inner wall of the mold cavity, wherein the release agent is a mixture of zinc stearate and alcohol in a mass ratio of 1:8-15.

4. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: The pressure of the press is 4.5-5.0 MPa, the pressure holding time is 0.1-0.2 s, and the pressure relief time is 1-1.5 s.

5. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: The sintering method is: first, the vacuum in the furnace is pumped to 1×10 -1 After Pa, gradient heating begins, and the temperature rise rate of the furnace is controlled at 3-5℃ / min; the final sintering temperature is controlled at 1020-1050℃, and the temperature is lowered after keeping warm for 4-5h. When the furnace temperature drops to 500℃, the fan is turned on to accelerate the cooling.

6. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: In the first 30 to 50 minutes of sintering, the temperature of the graphite cylinder is 40 to 70° C. lower than that of the green body, and then the temperature of the graphite cylinder is made the same as that of the green body until the end of sintering.

7. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 6, characterized in that: The graphite cylinder consists of an inner core composed of a copper rod and a temperature controller, and graphite wrapped around the inner core.

8. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 1, characterized in that: The chromium powder is Cr@Cu composite powder.

9. The method for preparing a copper-chromium alloy mixed powder shielding tube according to claim 8, characterized in that: The preparation method of the Cr@Cu composite powder is: 1) OP-10 is added to deionized water at a ratio of 0.2-0.3 g: 250 mL to obtain a mixed solution, and then chromium powder is added to the mixed solution at a ratio of 1 g: 20-30 mL, and magnetic stirring is performed for 10-15 minutes, and the chromium powder is filtered to obtain filtered chromium powder; 2) adding the filtered chromium powder to 10% H2SO4 at a ratio of 1 g: 10-20 mL and mechanically stirring for 5-10 min; filtering the chromium powder again, and adding the filtered chromium powder to 30-60 g / L citric acid at a ratio of 1 g: 10-20 mL, and magnetically stirring for 10-15 min to obtain the treated chromium powder; 3) The treated chromium powder is spread on a titanium plate as a cathode, and an electrolytic copper plate is used as an anode. The electrolyte is a CuSO4 solution for electrolytic treatment. After the electrolytic treatment, Cr@Cu composite powder with a copper content of 45-50wt.% is collected from the titanium plate, wherein the Cu ion concentration in the CuSO4 solution is 10-20g / L, and the current density of the electrolytic treatment is 400-600A / m 2 .

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