Vacuum brazing connection method for thin-wall capillary tube of xenon proportional flow controller

Abstract

The invention discloses a vacuum brazing connection method for thin-wall capillary tubes of a xenon proportional flow controller. The vacuum brazing connection method comprises the steps that an inner hole of a sealing ball head and an inner hole of a flow divider support are machined; the capillary tube, the sealing ball head and the diverter support are selected and matched; oxide film removal and cleaning are conducted on the surface to be welded; inserting the cleaned end part of the capillary tube into the sealing ball head and the inner hole of the diverter bracket to form a welding seam; after brazing filler metal is preset at the weld joint, the brazing filler metal and the weld joint are put into a vacuum furnace together for vacuum brazing, and a brazing workpiece is obtained; and detecting the quality of the brazed workpiece. The internal quality of the welding seam is high, the mechanical property is high, and the sealing property is high.

Description

Technical Field

[0001] The invention relates to a vacuum brazing connection method for a thin-wall capillary of a xenon proportional flow controller, belonging to the technical field of welding technology. Background Art

[0002] In order to meet the development needs of small celestial body probes, a multi-operating point electric propulsion system was designed. The xenon proportional flow controller is a key component in the electric propulsion subsystem. The sensor in the controller needs to simultaneously realize the reliable connection between the thin-walled capillary and the two sealing ball heads, and the diverter in the controller needs to simultaneously realize the reliable connection between the three thin-walled capillaries and the diverter bracket. The thin-walled capillary can be made of 06Cr19Ni10 (0Cr18Ni9 / 304) stainless steel, GH3030 high-temperature alloy and other materials, and the sealing ball head and diverter bracket can be made of 1Cr18Ni9Ti stainless steel, 022Cr17Ni12Mo2 (00Cr17Ni14Mo2 / 316L) stainless steel, GH3128 high-temperature alloy and other materials. Since the diameter of the thin-walled capillary is only Φ0.5mm and the wall thickness is only 0.1mm, it is extremely difficult to connect with conventional fusion welding methods. The vacuum brazing method is suitable for the connection of small precision components. Therefore, the vacuum brazing method is selected. Through the exploration and optimization of process parameters, on the basis of ensuring the reliable brazing of thin-walled capillaries, the control problem of capillary erosion defects is solved, and the delivery of small-diameter thin-walled capillary brazing joints of flow sensor components and diverter components is achieved. After welding, the brazing rate of thin-walled capillary joints is nearly 100%, the shear strength can reach 278MPa, the dissolved thickness of the capillary base material is ≤3μm, and the leakage rate is ≤1×10 at a pressure of 1.2MPa for 5min. -4 Pa×L / s, the joint performance is higher than the product technical index requirements. At present, dozens of sets of flow sensors and thin-walled capillary joint identification parts of flow divider components have been successfully delivered, laying a good technical foundation for the development of xenon proportional flow controllers for small celestial body detectors.

[0003] Domestic and foreign scholars have carried out some research work on capillary structure welding. The main connection method is brazing. For example, Yaning et al. Bonding Characterization Between 316L and Porous Stainless SteelPipes by Vacuum Brazing[J].(Yaning, Rare Metal Materials and Engineering, 2018, 47(2):474-478.) used BNi-7 brazing filler metal to vacuum braze 316L stainless steel and porous stainless steel pipes, analyzed and tested the microstructure and properties of the joints, and compared the wettability of the brazing filler metal on different base materials; scanning electron beam brazing of four capillaries and one plate structure (Li Shaoqing et al., Mechanical Engineering Materials 2006, 30(2):16-18.) used electron beam as heat source to braze the capillary and the test plate; vacuum brazing of stainless steel capillaries (Jia Zhihua et al., Metal Forging Technology, 2011, 40(23):180-184.) studied the Φ2×0.2 capillary. Vacuum brazing of capillary tubes, the research did not make strict control requirements on parameters such as the amount of brazing filler metal, brazing temperature, and holding time; vacuum brazing of palladium alloy capillary tubes and stainless steel joints (Li Yin'e et al., Metal Forging Technology, 2011, 40(21):140-141.) and others carried out research on brazing palladium alloy capillaries with Ba972Cu filler metal; invention patent: A brazing method for stainless steel pipes (patent number: CN115519205A) discloses a brazing method for stainless steel pipelines; invention patent: A double-station capillary high-frequency brazing device (patent number: CN115229288A) discloses a capillary induction brazing device; German invention patent: Method for producing a heat exchanger, in particular asorption heat transducer (patent number: DE102013222258) discloses a heat exchanger pipeline connection method.

[0004] However, in the relevant literature and patents at home and abroad, there is no report on the brazing of thin-walled stainless steel capillaries using high-temperature brazing filler metals under vacuum. Summary of the invention

[0005] The technical problem solved by the invention is: to overcome the deficiencies of the prior art, to provide a vacuum brazing connection method for a thin-walled capillary of a xenon proportional flow controller, and to solve the problem of high-reliability sealing connection of the thin-walled capillary of a xenon proportional flow controller.

[0006] The technical solution of the present invention is:

[0007] The invention discloses a vacuum brazing connection method for a thin-wall capillary of a xenon proportional flow controller, comprising:

[0008] Machining the inner hole of the sealing ball head and the inner hole of the diverter bracket;

[0009] Select and match the capillary tube, sealing ball head and splitter bracket;

[0010] Remove the oxide film and clean the surface to be welded;

[0011] Insert the cleaned capillary end into the inner hole of the sealing ball head and the diverter bracket to form a weld;

[0012] After the brazing material is pre-placed at the welding seam, the brazing material is put into a vacuum furnace together for vacuum brazing to obtain a brazed workpiece;

[0013] Perform quality inspection on brazing workpieces.

[0014] Furthermore, in the above method, the capillary, the sealing ball head, and the diverter bracket are selected and matched, specifically: according to the outer diameter of the capillary end to be welded and the measured values ​​of the inner hole of the sealing ball head and the inner hole of the diverter bracket, the matching clearance on both sides of the weld assembly between the thin-walled capillary end to be welded and the inner hole of the sealing ball head and the inner hole of the diverter bracket is ensured to be 0.01 to 0.09 mm.

[0015] Furthermore, in the above method, the surface to be welded is deoxidized and cleaned, specifically:

[0016] If there is an oxide film on the surface to be welded, use 800# or above sandpaper to remove the oxide film at the position to be welded, or use a non-fibered wire drawing cloth dipped in pickling liquid to wipe and remove the oxide film. After grinding or pickling, the assembly gap still meets the matching requirements;

[0017] Use anhydrous ethanol or acetone ultrasonic cleaning, the cleaning time should not be less than 10 minutes, then dry or air dry;

[0018] After cleaning, assemble and weld immediately or store in a drying cabinet immediately for no more than 24 hours.

[0019] Furthermore, in the above method, the insertion depths of the two ends of the capillary tube in the ball heads on both sides are kept consistent, and the insertion depths of the three capillaries in the bracket are kept consistent.

[0020] Furthermore, in the above method, the solder is pre-placed at the weld, specifically: the solder is filled at the weld, and the single-side cross-section is triangular; the solder coating width W is 0.2-1 mm, the coating radius R is 0.2-0.8 mm, and the solder is close to the weld.

[0021] Furthermore, in the above method, the vacuum brazing is specifically performed as follows:

[0022] When the furnace temperature rises to T1 = 830 ~ 1030 ° C, keep warm for a time of t1 = 0 ~ 60 min;

[0023] When the furnace temperature rises to T2 = 925 ~ 1220 ° C, brazing begins, and the brazing holding time is t2 = 1 ~ 15min;

[0024] When the furnace temperature drops below 400°C, release the gas and open the furnace door to take out the workpiece.

[0025] Furthermore, in the above method, the vacuum degree of the vacuum furnace is 1×10 -2 ~1×10 -5 Pa.

[0026] Furthermore, in the above method, the quality inspection of the brazing workpiece is specifically performed as follows:

[0027] Check the appearance of the weld with a microscope at a magnification of 10 or more to ensure that the brazing angle is uniform, continuous, and smooth, with no incomplete brazing, incomplete filling, or external cracks;

[0028] Select brazing workpieces in batches and inspect them with an optical microscope to ensure that the brazing rate of the weld is not less than 85%;

[0029] The weld leakage rate was tested using a vacuum helium mass spectrometer to ensure that the pressure was above 1.2 MPa and the weld leakage rate was less than 1×10 -4 Pa·L / s.

[0030] Furthermore, in the above method, the brazing filler metal is a high-temperature Ni-based brazing filler metal that can be used at a temperature above 800°C.

[0031] The beneficial effects of the present invention and the prior art are:

[0032] (1) The present invention uses vacuum brazing technology to achieve a reliable connection between the thin-walled capillary and the sealing ball head in the xenon proportional flow controller sensor assembly, effectively ensuring that the sensor can accurately sense and measure the changes in gas flow in the flow channel.

[0033] (2) The present invention uses vacuum brazing technology to achieve reliable connection between the thin-walled capillary and the diverter bracket in the diverter assembly of the xenon proportional flow controller, effectively ensuring the diversion, connection and sealing of the complex flow channel of the diverter.

[0034] (3) The Φ0.5mm×0.1mm thin-walled capillary used in the present invention can reduce weight by more than 160% compared with the capillary of the same inner diameter specification commonly used on the current satellite, and can effectively control the total weight of the whole machine while ensuring the flow index of the product component.

[0035] (4) The welding assembly gap processing and selection scheme adopted by the present invention realizes the precise control of the welding gap size and consistency between the thin-walled capillary and the sealing ball head and the inner hole of the diverter bracket, providing a guarantee for the reliability and consistency of the weld quality.

[0036] (5) The high-temperature Ni-based solder used in the present invention has a reliable operating temperature of 800-900°C or above, and does not introduce alloy elements that the parent material itself does not have, making the welded joint more adaptable to the harsh aerospace service environment and reducing the risk of failure of the joint under complex working conditions such as alternating hot and cold.

[0037] (6) The solder filling volume control scheme adopted in the present invention can simultaneously realize the precise control and measurement of the usage of different types of solder filling such as powder, foil and molten block, while effectively ensuring that the solder completely fills the weld, and avoiding the risks of clogging the inner hole of the thin-walled capillary and corrosion of the tube wall.

[0038] (7) The present invention uses a dedicated vacuum brazing process to make the surface of the thin-walled capillary joint well formed, the internal quality of the weld is high, the mechanical properties are high, and the sealing performance is high (the weld leakage rate is less than 1×10 -4 Pa·L / s), high reliability.

[0039] (8) The capillary connection methods involved in the prior art are somewhat different from those of the present invention: in terms of the specifications and materials of the capillary, the capillary diameter is Φ2 mm, and the capillary material includes palladium alloy, etc., and the research results are difficult to apply to the connection of Φ0.5 mm thin-walled capillaries; in terms of the connection method, the methods include induction brazing, soft soldering, etc., the equipment used includes induction brazing equipment, etc., and the solders used include P-containing and Zn-containing solders, etc., all of which cannot be used for reliable brazing of Φ0.5 mm thin-walled capillaries. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process flow chart of "a method for vacuum brazing connection of thin-wall capillary tubes of a xenon proportional flow controller" of the present invention;

[0041] Figure 2a ) is a schematic structural diagram of a thin-wall capillary-sealed ball joint of the present invention;

[0042] Figure 2b ) is a schematic diagram of the structure of the thin-walled capillary-diverter bracket joint of the present invention;

[0043] Figure 3 It is a schematic diagram of the position and amount of the pre-set solder of the present invention;

[0044] Figure 4 It is a brazing process parameter curve diagram of the present invention;

[0045] Figure 5 It is a metallographic image of the weld after the thin-walled capillary-sealed ball head welding in a specific implementation manner of the present invention (Example 1);

[0046] Figure 6 It is a metallographic image of the weld after thin-wall capillary-sealed ball head welding in a specific implementation manner of the present invention (Example 2). DETAILED DESCRIPTION

[0047] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0048] like Figure 1 As shown, the present invention provides a method for vacuum brazing connection of a thin-walled capillary of a xenon proportional flow controller, which mainly includes the steps of selecting a capillary 1 and a ball head 2 as well as a capillary and a bracket 4, cleaning before welding, assembling before welding and prefabricating solder, vacuum brazing, etc. The following briefly introduces each step.

[0049] 1. Capillary, ball head and bracket selection

[0050] As shown in Figure 2, the inner hole of the sealing ball head and the inner hole of the diverter bracket can be machined to Φ0.3~Φ0.4mm during mechanical processing, and then the inner hole can be expanded to Φ0.5mm before welding and assembly, and the inner hole processing tolerance is controlled according to the measured value of the outer diameter of the capillary end to be welded. After the hole expansion is completed, the matching is carried out according to the measured values ​​of the outer diameter of the capillary and the inner hole of the sealing ball head and the diverter bracket to ensure that the bilateral gap of the weld 3 is within the range of 0.01~0.09mm, and at the same time, the assembly gap of each weld 3 is kept consistent as much as possible. In order to avoid the formation of a thick oxide film that affects the subsequent welding quality, the parts to be welded should be cleaned, assembled and welded as soon as possible after hole expansion and matching. If it takes a long time to place before welding after hole expansion, the selected parts need to be placed in a sealed bag with desiccant and stored in a drying cabinet.

[0051] 2. Cleaning of the surface to be welded

[0052] Before welding, use anhydrous ethanol or acetone to ultrasonically clean the position to be welded and the pipe joints of the straight pipe. The cleaning time is ≥10min, and then dry or air dry naturally. Avoid touching the workpiece with bare hands after cleaning. If there is an oxide film on the surface to be welded, which may affect the welding quality and needs to be removed by mechanical grinding or pickling, you can use sandpaper of no less than 800# to gently grind and remove the oxide film, or you can use a dust-free cloth without fiber drop to dip in pickling liquid to wipe the oxide film and quickly rinse or soak to remove excess pickling liquid. Note that after mechanical or pickling to remove the oxide film, the pipe diameter and inner hole size should be measured again, and the size that does not meet the matching clearance requirements should be re-selected. After removing the oxide film, the surface to be welded needs to be ultrasonically cleaned again with anhydrous ethanol or acetone. After cleaning, assembly welding should be completed as soon as possible. If welding cannot be done immediately, the workpiece to be welded should be placed in a drying cabinet for storage, and the storage time should not exceed 24 hours. If the storage time is too long, it needs to be cleaned again before welding.

[0053] 3. Assembly before welding and pre-setting of solder

[0054] Insert the polished and cleaned capillary ends into the inner holes of the sealing ball head and the diverter bracket. Note that the insertion depth of the two ends of the capillary in the two side balls should be consistent, and the insertion depth of the three capillaries in the bracket should be consistent. Then press Figure 4 It indicates that solder 5 is pre-placed outside the weld. The solder 5 used is BNi series high-temperature Ni-based solder (GB / T 10859 grades: BNi63~BNi95, etc., AWS American Welding Society grades BNi-1~BNi-13, etc.). Due to the small size of the weld and the small amount of solder used, the volume is used instead of the weight to calibrate the pre-placed solder amount. The filled solder can be approximately regarded as a truncated cone, and the single-side cross-section can be approximately triangular. The solder coating width W on the capillary should be controlled at 0.2~1mm, and the solder coating radius R on the ball head / bracket should be controlled at 0.2~0.8mm. By controlling the volume of the coated solder, it can be ensured that the solder amount meets the joint quality requirements. If powder solder is used, the solder powder needs to be mixed into a paste before coating. If molten block solder is used, the solder should be machined into a solder truncated cone that meets the size requirements before use. If solder foil or solder wire is used, the solder should be shaped to ensure that it meets the requirements of similar size and volume before use. Pay attention to ensure that the pre-set solder is tightly attached to the workpiece and the weld to avoid the solder being unable to fill the weld after melting. After the filling is completed, place the workpiece to be welded on a flat tray made of oxide ceramic. If a metal tray is used, a thick and uniform coating of a flow barrier is required on the surface of the tray. The flow barrier component is an alcohol suspension of Y2O3 ceramic particles. The surface of the tray can also be covered with mica sheets or other substances that do not react with the solder. Pay attention to ensure that the flow barrier layer or mica sheet is flat to avoid tilting or rolling of the workpiece to be welded.

[0055] 4. Weld according to vacuum brazing process parameters

[0056] Place the workpiece to be welded with the tray into the vacuum chamber of the vacuum brazing furnace and evacuate the vacuum. When the vacuum degree reaches 1×10 -2 Heating starts from the beginning until the welding is completed. The temperature in the furnace drops below 400℃ and the vacuum degree should be maintained at 1×10 -2 ~1×10 -5 Pa range. The welding heating curve is as follows Figure 5 As shown. When the furnace temperature is heated to T1 = 830 ~ 1030 ℃, it can be kept warm to promote furnace temperature homogenization. The holding time is t1 = 0 ~ 60min. The actual brazing temperature is T2 = 925 ~ 1220 ℃, and the holding time is t2 = 1 ~ 15min. The specific homogenization temperature time and brazing temperature time can be adjusted according to the type of brazing material used, the size of the vacuum chamber and the amount of furnace loading. After the brazing insulation is completed, it can be cooled. It should be avoided to open the furnace and take out the workpiece when the furnace temperature is higher than 400 ℃, so that the high-temperature workpiece will be severely oxidized in contact with the atmospheric environment. If defects such as partial incomplete brazing and incomplete filling are found after welding, the process parameters can be adjusted appropriately and then repair welding can be performed. The number of repair welding should not exceed 2 times to avoid the deterioration of the brazing seam structure and affect the joint performance.

[0057] The present invention will be further described below in conjunction with the accompanying drawings.

[0058] The present invention "a method for vacuum brazing connection of thin-walled capillary tubes of a xenon proportional flow controller" mainly includes the steps of selecting capillary tubes, ball heads and brackets, cleaning the surface to be welded, assembling before welding and pre-setting brazing materials, vacuum brazing, and quality inspection after welding. The selection of capillary tubes, ball heads and brackets, assembly before welding and pre-setting brazing materials, and vacuum brazing parameters are the key points of the present invention, which involve the key processes for the development of xenon proportional flow controllers, and other process processes belong to conventional process processes.

[0059] The implementation steps of the present invention are as follows:

[0060] 1. Capillary, ball head and bracket selection

[0061] The installation matching clearance is used to select and match the thin-walled capillary, the sealing ball head, and the diverter bracket. The matching clearance between the capillary end to be welded and the inner hole of the ball head and the inner hole of the bracket is required to meet 0.01 to 0.09 mm on both sides.

[0062] 2. Cleaning of the surface to be welded

[0063] (1) Remove oxide film before welding: If there is an oxide film on the surface to be welded, use 800# or above sandpaper to grind and remove the oxide film at the welding position, or use a non-fibered wire drawing cloth dipped in pickling liquid to wipe and remove the oxide film. After grinding or pickling, the assembly gap should still meet the matching requirements.

[0064] (2) Cleaning before welding: Use anhydrous ethanol or acetone for ultrasonic cleaning. The cleaning time should not be less than 10 minutes. Then dry or air dry naturally. Do not touch the workpiece with bare hands. After cleaning, assemble and weld immediately or transfer to a drying cabinet for storage immediately. The storage time should not exceed 24 hours.

[0065] 3. Assembly before welding and prefabrication of solder

[0066] (1) Assembly before welding: Insert the cleaned thin-walled capillary end into the inner hole of the sealing ball head and the diverter bracket. Note that the insertion depth of the two ends of the capillary in the ball heads on both sides should be consistent, and the insertion depth of the three capillaries in the bracket should be consistent.

[0067] (2) Pre-set solder: Figure 3 As shown in the figure, the solder is in the shape of a truncated cone filled outside the soldering seam, and the single-side cross-section can be approximately a triangle. The solder coating width W should be controlled within 0.2-1 mm, the coating radius R should be controlled within 0.2-0.8 mm, and the solder should be close to the weld.

[0068] 4. Vacuum brazing

[0069] (1) Vacuuming: vacuum degree is 1×10 -2 ~1×10 -5 Pa.

[0070] (2) Welding: When the furnace temperature rises to T1 = 830 ~ 1030 ° C, it can be kept warm, and the holding time is t1 = 0 ~ 60 min. When the furnace temperature rises to T2 = 925 ~ 1220 ° C, brazing begins, and the brazing holding time is t2 = 1 ~ 15 min.

[0071] (3) Removing the workpiece: When the furnace temperature drops below 400°C, the air can be released and the furnace door can be opened to remove the workpiece.

[0072] (4) Repair welding: Repair welding can be performed if there are defects such as partial incomplete penetration and incomplete filling on the outside of the brazing seam. The number of repair welding should not exceed 2 times.

[0073] 5. Weld quality inspection

[0074] (1) External quality: Check the appearance of the weld with the naked eye or a 10x microscope to ensure that the weld angle is uniform, continuous, and smooth, with no incomplete or unfilled defects or external cracks.

[0075] (2) Brazing rate: Select product joints from batches or use test pieces with the same structure as the actual joints to cut and grind metallographic test pieces, and inspect them using an optical microscope to ensure that the brazing rate of the weld is not less than 85%.

[0076] (3) Pressure leakage rate: vacuum helium mass spectrometer test, ensure 1.2MPa pressure for 5 minutes, weld leakage rate is less than 1×10 - 4Pa·L / s.

[0077] Example 1

[0078] As shown in Figure 2, 1. The raw material of the thin-walled capillary is 06Cr19Ni10 stainless steel, and the raw material of the sealing ball head and the diverter bracket is 022Cr17Ni12Mo2 stainless steel; 2. The matching clearance between the thin-walled capillary and the two ball heads is 0.02-0.04mm, and the matching clearance between the three thin-walled capillaries and the diverter bracket is 0.03-0.05mm; 3. There is no oxide film on the surface to be welded, and no mechanical or acid washing is required to remove the film. Before welding, anhydrous ethanol is used for ultrasonic cleaning for 20 minutes, and the assembly and welding are immediately performed after natural air drying; 4. The brazing material used is BNi82CrSiBFe powder brazing material, and the brazing material particle size is 200 mesh. The brazing material is adjusted into a paste and then coated on the outside of the weld and shaped into a truncated cone. The coating width value W is about 0.4-0.6mm, and the coating radius value R is about 0.5-0.7mm; 5. The vacuum degree is 5×10 - 3 Pa, homogenization temperature T1 = 950 ° C, homogenization holding time t1 = 15min, brazing temperature T2 = 1034 ° C, brazing holding time t2 = 2min, furnace opening temperature is 100 ° C. VI. Post-weld quality inspection. The appearance quality of the two welds between the capillary and the ball joint and the three welds between the capillary and the bracket joint were checked under a 10x microscope. The brazing angles of all welds were uniform, continuous, and smooth, without any defects such as incomplete brazing and unfilled defects, and no external crack defects. The weld leakage rate was tested using a vacuum helium mass spectrometer. The leakage rate of the capillary and the ball joint was 8.7×10 -5 Pa·L / s, the capillary and bracket joints were kept at 1.2MPa for 5min with a leakage rate of 8.5×10 -5 Pa·L / s; Use an optical microscope to examine the metallographic structure of the two welds between the capillary and the ball joint, and the three welds between the capillary and the bracket joint. The brazing rate of all welds is not less than 85%. Figure 5 shown.

[0079] Example 2

[0080] The difference between this embodiment and embodiment 1 is that: in step 2, 1000# sandpaper is used to slightly grind the end of the thin-walled capillary to be welded to remove the oxide film; in step 5, the brazing temperature T2 = 1050°C and the brazing holding time t2 = 5min, and the rest is the same as embodiment 1. After welding, the brazing angle of all welds is uniform, continuous and smooth, without incomplete brazing, incomplete filling defects, and external crack defects; the leakage rate of the capillary and ball joint is 9.2×10 -5 Pa·L / s, the leakage rate of the capillary and bracket joint is 8.9×10 -5 Pa·L / s; the brazing rate of all welds shall not be less than 85%. Figure 6 shown.

[0081] Example 3

[0082] The difference between this embodiment and embodiment 1 is that the raw material of the thin-walled capillary in step 1 is GH3030 high-temperature alloy, the raw material of the sealing ball head and the diverter bracket is GH3128 high-temperature alloy, and the rest is the same as embodiment 1. After welding, the brazing angle of all welds is uniform, continuous, and smooth, without incomplete brazing, incomplete filling defects, and external crack defects; the leakage rate of the capillary and ball head joint is 7.5×10 -5 Pa·L / s, the leakage rate of the capillary and bracket joint is 7.6×10 -5 Pa·L / s; the brazing rate of all welds shall not be less than 85%.

[0083] Example 4

[0084] The difference between this embodiment and embodiment 1 is that the brazing filler metal used in step 4 is BNi-5 powder brazing filler metal with a particle size of 200 mesh; the homogenization temperature T1=1030°C, the homogenization holding time t1=15min, the brazing temperature T2=1175°C, the brazing holding time t2=2min, and the rest is the same as embodiment 1. After welding, the brazing angle of all welds is uniform, continuous, and smooth, without incomplete brazing, incomplete filling defects, and external crack defects; the leakage rate of the capillary and ball joint is 3.8×10 -5 Pa·L / s, the leakage rate of the capillary and bracket joint is 4.0×10 -5 Pa·L / s; the brazing rate of all welds shall not be less than 85%.

[0085] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

[0086] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for vacuum brazing connection of thin-wall capillary tubes of a xenon proportional flow controller, characterized in that: include: Machining the inner hole of the sealing ball head and the inner hole of the diverter bracket; Select and match the capillary tube, sealing ball head and splitter bracket; Remove the oxide film and clean the surface to be welded; Insert the cleaned capillary end into the inner hole of the sealing ball head and the diverter bracket to form a weld; After the brazing material is pre-placed at the welding seam, the brazing material is put into a vacuum furnace together for vacuum brazing to obtain a brazed workpiece; Perform quality inspection on brazing workpieces.

2. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The capillary, the sealing ball head and the diverter bracket are selected and matched, specifically: according to the outer diameter of the capillary end to be welded and the measured values ​​of the inner hole of the sealing ball head and the inner hole of the diverter bracket, the matching clearance on both sides of the weld assembly between the thin-walled capillary end to be welded and the inner hole of the sealing ball head and the inner hole of the diverter bracket is 0.01~0.09mm.

3. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: Remove the oxide film and clean the surface to be welded, specifically: If there is an oxide film on the surface to be welded, use 800# or above sandpaper to remove the oxide film at the position to be welded, or use a non-fibered wire drawing cloth dipped in pickling liquid to wipe and remove the oxide film. After grinding or pickling, the assembly gap still meets the matching requirements; Use anhydrous ethanol or acetone ultrasonic cleaning, the cleaning time should not be less than 10 minutes, then dry or air dry; After cleaning, assemble and weld immediately or store in a drying cabinet immediately for no more than 24 hours.

4. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The insertion depths of the two ends of the capillary in the ball heads on both sides are kept consistent, and the insertion depths of the three capillaries in the bracket are kept consistent.

5. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The solder is pre-placed at the weld, specifically: the solder is filled at the weld, and the single-side cross-section is triangular; the solder coating width W is 0.2-1 mm, the coating radius R is 0.2-0.8 mm, and the solder is close to the weld.

6. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The vacuum brazing is specifically performed as follows: When the furnace temperature rises to T1 = 830 ~ 1030 ° C, keep warm for a time of t1 = 0 ~ 60 min; When the furnace temperature rises to T2 = 925 ~ 1220 ° C, brazing begins, and the brazing holding time is t2 = 1 ~ 15min; When the furnace temperature drops below 400°C, release the gas and open the furnace door to take out the workpiece.

7. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The vacuum degree of the vacuum furnace is 1×10 -2 ~1×10 -5 Pa.

8. A method for vacuum brazing connection of thin-wall capillary tubes of a xenon proportional flow controller according to claim 1, characterized in that: The quality inspection of the brazing workpiece is specifically as follows: Check the appearance of the weld with a microscope at a magnification of 10 or more to ensure that the brazing angle is uniform, continuous, and smooth, with no incomplete brazing, incomplete filling, or external cracks; Select brazing workpieces in batches and inspect them with an optical microscope to ensure that the brazing rate of the weld is not less than 85%; The weld leakage rate was tested using a vacuum helium mass spectrometer to ensure that the pressure was above 1.2 MPa and the weld leakage rate was less than 1×10 -4 Pa·L / s.

9. A method for vacuum brazing connection of a thin-wall capillary tube of a xenon proportional flow controller according to claim 1, characterized in that: The solder is a high-temperature Ni-based solder that can be used at temperatures above 800°C.

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