A vacuum brazing method for an aero-engine screen throttling hydraulic valve assembly

Abstract

The application is a vacuum brazing method for an aero-engine throttling hydraulic valve assembly with a filter screen, which designs a special welding device for the structure of the throttling hydraulic valve with a filter screen on both sides, solves the two-way welding problem through precise control of brazing material amount, heating temperature, vacuum pressure and other means, and realizes the detection of the welded assembly through an industrial computed tomography (industrial CT), well controls the welding quality of the assembly, and makes the aero-engine throttling hydraulic valve assembly with a filter screen meet the design requirements.

Description

Technical Field

[0001] This invention relates to a vacuum brazing method for a hydraulic valve assembly with filter screen in an aero-engine, belonging to the field of heat treatment technology for vacuum brazed components. Background Technology

[0002] According to the construction plan, measures were implemented to add a filter screen to the throttling hydraulic valve. While maintaining the same dimensions and functional performance as the current throttling hydraulic valves used in mass production, this part of the product's structure was optimized and improved, and a throttling hydraulic valve with a filter screen was designed, such as... Figure 1 As shown. While keeping the valve body orifice diameter constant, filters are added before and after the valve body to further filter contaminants, addressing the issue of insufficient oil supply caused by particles larger than 0.3mm entering the pump regulator's booster valve area through the throttle valve. Initially, electron beam welding of the components was planned, but during testing, the small filter melted. This was because although the small filter and the throttle hydraulic valve were made of the same material (1Cr18Ni9), the wall thickness difference at the welding point was too large. When the electron beam emitted at minimum power irradiated the contact surface between the filter and the throttle hydraulic valve, the filter, with a wall thickness of only 0.2mm, reached its melting temperature first, and its edges melted into liquid droplets. At this time, the throttle hydraulic valve had not yet melted, and an effective molten pool could not be formed between them, thus electron beam welding could not be used. Summary of the Invention

[0003] The present invention addresses the aforementioned existing technical situation by providing a vacuum brazing method for an aero-engine filter-equipped throttling hydraulic valve assembly, the purpose of which is to enable the aero-engine filter-equipped throttling hydraulic valve assembly to meet design requirements.

[0004] To achieve the above objectives, the technical solution of this invention employs vacuum brazing. The design concept relies on the melting, flow, and solidification of the brazing filler metal to form a dense weld and a robust joint. Therefore, this type of filter-equipped throttling hydraulic valve assembly does not use traditional pre-embedded closed welding, but rather a completely open welding method, meaning the solder is exposed. However, because the solder is sensitive to furnace environmental factors, controlling the volatilization of elements in the solder is more difficult. Simultaneously, since the two filters are placed at opposite ends of the valve body, it is a bidirectional welding process. This structure results in the filter welding at one end being an anti-gravity brazing operation, which is detrimental to solder wetting and easily leads to incomplete solder filling of the weld. To overcome the above technical difficulties, the technical solution of this invention adopts the following approach:

[0005] The vacuum brazing method of the aero-engine filter screen throttling hydraulic valve assembly, the aero-engine filter screen throttling hydraulic valve assembly comprises a valve body 7 and filter screens 8 at the upper and lower ends of the valve body 7, the wall thickness of the filter screen 8 is 0.2 mm, and the materials of the valve body 7 and the filter screens 8 are both 1Cr18Ni9, characterized in that: the valve body 7 and the filter screens 8 at the upper and lower ends are connected by vacuum brazing, the valve body 7 and the filter screens 8 at the upper and lower ends are vertically placed before brazing, the selected welding filler material is Bag54CuPd900 / 950 in the national standard GB / T18762-2017 'Specification of Precious Metal and Its Alloy Filler Metal', the welding filler material is in the form of a ring with an inner diameter of φ2.5 mm, the thickness of the filler ring 9 at the connection between the upper end of the valve body 7 and the filter screen 8 is 0.33-0.35 mm, and the thickness of the filler ring 9 at the connection between the lower end of the valve body 7 and the filter screen 8 is 0.30-0.32 mm.

[0006] During brazing, synchronous bidirectional welding is performed on the connections between the valve body 7 and the filter screens 8 at the upper and lower ends, the welding temperature is increased from 920 DEG C to 990 DEG C, the time for the temperature increasing process is 6-8 min, the pressure during the welding process should be greater than or equal to 300 Pa, after the welding is completed, the workpieces are cooled by the argon filling method when the workpieces in the furnace are cooled to 780 DEG C, and the workpieces are taken out of the furnace after the temperature of the workpieces is reduced to below 80 DEG C.

[0007] In implementation, the valve body 7 and the filter screens 8 at the upper and lower ends are vertically placed on a clamp to keep the vertical state, the clamp comprises upper, middle and lower three-layer structures, the upper layer is an upper filter screen protection plate 1 to keep and fix the installation position of the upper end of the valve body 7 and the filter screen 8, the middle layer is a fixing plate 2 of the valve body 7 to keep and fix the vertical state of the valve body 7, and the lower layer is a lower filter screen fixing plate 3 with a circular arc groove, the filter screen 8 at the lower end of the valve body 7 is seated in the circular arc groove to keep and fix the installation position of the lower end of the valve body 7 and the filter screen 8.

[0008] Further, the materials of the clamp and the valve body 7 and the filter screens 8 at the upper and lower ends are all 1Cr18Ni9.

[0009] Further, the upper, middle and lower three-layer structures of the clamp are arranged on corresponding upper, middle and lower square plates, so that the welding method can simultaneously weld the connections of multiple valve bodies 7 and filter screens 8 at the upper and lower ends, guide columns 4, cylindrical pins 5 and rhombic pins 6 are arranged on the upper, middle and lower three-layer square plates to ensure that no displacement occurs between the three-layer structures.

[0010] Further, a load control temperature thermocouple is installed at the center position of the upper, middle and lower three-layer square plates to control the real-time temperature in the brazing process.

[0011] Further, the upper, middle and lower three-layer square plates are integrally dry sand blasted before welding, and then vacuum purification treatment is performed.

[0012] In the implementation, the valve body 7 and the upper and lower end filters 8 are subjected to uniform temperature treatment at 870-880 DEG C in a furnace before brazing.

[0013] In the implementation, the workpiece and the solder are cleaned by ultrasonic cleaning with anhydrous ethanol before brazing, the solder ring 9 is first placed in the welding process groove of the valve body 7, then the filter 8 is installed, visual inspection is performed on the filter 8 to check whether the filter 8 is installed without skew, and then a layer of solder resist is applied between the filter holes of the filter 8 to prevent the solder from blocking the filter holes.

[0014] The technical scheme has the following characteristics and advantages:

[0015] 1. The welding fixture guarantees reliable brazing results. The fixture guarantees that the assembled throttling hydraulic valve assembly can be vertically placed during heat treatment, effectively avoiding dislocation of the thin filter during vacuum brazing, and obtaining reliable brazing results. Because the material strength of the parts is not high and the filter wall is thin, it is easy to cause bruising and crushing, so in the design of the welding device, the lower filter fixing plate 3 for supporting the whole assembly adopts circular arc grooves to form surface contact with the filter, avoiding point contact and reducing the stress on the filter. At the same time, according to the test results, the upper filter protection plate 1 does not form the initial design of applying pressure to the filter, which eliminates the filter crushing caused by improper force application. In order to guarantee the dimensional stability during brazing, the fixture should be subjected to simulated brazing cycles before use to eliminate stress, and the welding device should be subjected to dimensional stability and surface cleaning under high temperature and high vacuum conditions.

[0016] In addition, the welding temperature is accurately monitored by using a load-controlled thermocouple to achieve a high level in the heat treatment industry. In order to improve the processing efficiency, the fixture can load multiple workpieces, and in order to guarantee that each workpiece can achieve the same brazing result at the process temperature, the actual heat treatment temperature needs to be mastered. Multiple thermocouples are installed in the furnace temperature field, and the measurement results are combined with the actual quality to determine that the center position of the fixture does not place parts, but installs a load-controlled thermocouple, which can accurately control the actual temperature during brazing.

[0017] 2. According to the characteristics of bidirectional welding, the amount of solder is accurately controlled to guarantee the welding strength and prevent the filter holes from being blocked. Generally, the gravity and capillary action of the solder are in the same direction to facilitate solder filling. The welding of the lower end filter of the throttling hydraulic valve conforms to this rule, but the welding of the upper end filter is opposite to the direction of the solder gravity and capillary, which hinders the solder filling. This structure determines that there is a difference in the amount of solder required for the two end filters under the same gap, and the amount of solder required for the lower end filter must be less than that for the upper filter to ensure that the solder spreading degree on both sides is close. Too much solder will block the filter holes and affect the filtering effect, and too little solder will reduce the welding strength and cause the filter to fall off. The appropriate amount of solder is determined through multiple tests.

[0018] 3. According to the structural characteristics of the throttle hydraulic valve, the brazing heat treatment process parameters are determined. Including:

[0019] 3.1 Because of the large difference in the effective heating thickness of the valve body 7 and the filter screen 8 of the throttle hydraulic valve, in order to reduce the stress concentration caused by thermal deformation, uniform temperature treatment of 870-880℃ is carried out before welding;

[0020] 3.2 Since the brazing filler metal contains silver, copper and other volatile alloy elements, in order to prevent the brazing filler metal from volatilizing in a high temperature state, it is necessary to inhibit it by increasing the pressure in the furnace through back-filling gas. According to the brazing filler metal coverage of the test piece, it is found that too high pressure hinders the spread of the brazing filler metal, and too low pressure causes excessive spread of the brazing filler metal to block the filter screen holes. Finally, it is determined that the back-filling high-purity argon gas is ≥300Pa after the preheating uniform temperature treatment is completed.

[0021] 3.3 According to the experiment, the solidus temperature of the brazing filler metal is 900℃, and the liquidus temperature is 950℃. Between these two temperatures, the brazing filler metal exists in solid and liquid states. When the welding temperature is higher than the liquidus temperature of the brazing filler metal, the liquid brazing filler metal wets, capillary flows, fills and spreads in the gap and on the surface of the base material, and cools to form a firm joint. According to the temperature of the test piece in the load couple test and the actual welding condition, it can be calculated that the brazing filler metal starts to melt at 920℃ and completely melts at 990℃. According to the structural characteristics of the throttle hydraulic valve assembly, the brazing heat treatment process temperature is designed to be 920℃ for a certain holding time to complete the melting and spreading of the brazing filler metal, so that the weld filling is full and the brazing filler metal does not excessively spread to block the filter screen holes.

[0022] 3.4 In order to avoid the cracking of the welded joint due to too fast cooling speed, and the oxidation color caused by premature discharge, after the welding is completed, the furnace is cooled to 780℃, the high-purity argon gas is back-filled, and then the furnace is discharged after cooling to 80℃.

[0023] 4. The industrial CT is used to create a new way to check the internal quality of the brazing seam. Generally, X-ray is used to check the internal quality of vacuum brazing parts. Because the throttle hydraulic valve assembly is small in size and the weld is very narrow, it is not suitable for X-ray inspection. Industrial CT is the abbreviation of industrial computer tomography technology. For the weld of the throttle hydraulic valve assembly, the weld section is scanned at a certain distance, the total weld rate is calculated according to the brazing filler metal filling ratio, and the total weld rate is required to be ≥75%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the schematic diagram of the outer shape structure of the throttle hydraulic valve assembly of the aircraft engine

[0025] Figure 2 is the sectional view of Figure 1

[0026] Figure 3 ​This is a schematic diagram of a welding fixture for an aero-engine throttling hydraulic valve assembly with a filter screen, as described in this invention.

[0027] Figure 4 for Figure 3 Top view

[0028] Figure 5 for Figure 3 3D schematic diagram Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0030] See appendix Figures 1-2 As shown, the aero-engine throttling hydraulic valve assembly with filter screen in this embodiment includes a valve body 7 and filter screens 8 at the upper and lower ends of the valve body 7. The filter screen 8 has a wall thickness of 0.2 mm and is made of 1Cr18Ni9 material. See attached figure. Figures 3-5 As shown, the welding fixture and the workpiece are made of the same material, maintaining the same coefficient of thermal expansion, thermal conductivity, and high-temperature strength. Structurally, to minimize thermal stress, the fixture has three layers: an upper filter screen protection plate 1 (upper layer) to maintain workpiece verticality and reduce the impact of gas flow on the upper filter screen 8 during refilling; a middle layer (middle layer) for fixing the throttling hydraulic valve; and a lower layer (lower filter screen fixing plate 3 with arc-shaped grooves) for easy filter screen fixation. The welding fixture uses guide posts 4 at the four corners, two cylindrical pins 5, and a diamond-shaped pin 6 to ensure the three-layer structure remains stable. The welding device can fix the assembled welding components in their respective positions, preventing displacement of the workpiece during brazing. A load-controlled thermocouple is installed at the center to control the real-time temperature during brazing, ensuring reliable brazing results.

[0031] The vacuum brazing process steps for the filter-equipped throttling hydraulic valve assembly of this aero-engine are as follows:

[0032] Step 1: Cleaning of parts, solder, and welding equipment

[0033] Hydrocarbon vacuum cleaners are used to clean parts, solder, and tooling. During the cleaning process, parts should be protected from being bumped or damaged. After cleaning, the surface of the parts should be visually inspected to ensure that there is no obvious dirt.

[0034] Step 2: Pre-treatment of welding fixtures

[0035] The welding fixture should be dry sandblasted as a whole and vacuum purified before use.

[0036] Step 3: Preparation of brazing filler metal

[0037] The selected soldering filler is Bag54CuPd900 / 950 in GB / T18762-2017 "Specification of Precious Metal and Its Alloy Soldering Filler". The soldering filler is in the form of a ring with an inner diameter of φ2.5mm. The thickness of the soldering filler ring 9 at the connection between the upper end of the valve body 7 and the filter screen 8 is 0.33~0.35mm, and the thickness of the soldering filler ring 9 at the connection between the lower end of the valve body 7 and the filter screen 8 is 0.30~0.32mm;

[0038] The soldering filler ring 9 is first polished to remove the oxide layer, and then is wound and processed into a tight annular soldering filler by a lathe. After being cut into individual rings, the cut edges are manually polished to be smooth and tight, thereby ensuring the consistency of the soldering filler diameter. Further, one side of the soldering filler ring is ground into a flat surface to facilitate the placement of the filter screen.

[0039] Step four, assembly

[0040] The parts and soldering filler are cleaned with anhydrous ethanol by ultrasonic wave, and the internal cavity of the throttle nozzle, the φ0.3 hole, and the small holes of the filter screen are further inspected for burrs and other excess materials by a digital electronic microscope. The soldering filler ring is then placed in the welding process tank of the throttle hydraulic valve, and the two filter screens are installed on both sides. Visual inspection is performed to check whether the filter screens are installed without skew. A layer of solder resist is manually applied between the filter holes of the filter screen to prevent the soldering filler from blocking the filter holes.

[0041] Step five, welding device fixing assembly

[0042] The valve body of the throttle hydraulic valve is placed into the welding fixture with the hexagonal one end facing downward, and the lower end filter screen 8 is placed on the circular arc grooves of the lower filter screen fixing plate 3, which are distributed at intervals. Then, the throttle hydraulic valve is placed into the effective heating area of the vacuum furnace.

[0043] Step six, vacuum soldering

[0044] After closing the furnace door, the pre-evacuation is further started, and the temperature is raised to a load couple temperature of 870-880℃ for 6min. Then, high-purity argon is recharged to ≥300Pa. The temperature is further raised to a load couple temperature of 920℃, and the heating is stopped when the temperature reaches 990℃. The welding process time is 6-8min. The pressure during the welding process should be greater than or equal to 300Pa. After the welding is completed, the workpiece is cooled to 780℃ in the furnace with argon charging. When the temperature of the workpiece drops to below 80℃, the workpiece is taken out of the furnace.

[0045] Step seven, industrial CT detection

[0046] The two end welding positions of the throttle hydraulic valve assembly with filter screens are horizontally scanned. Each weld is scanned at an interval of 0.1mm. The total weld ratio is calculated according to the soldering filler filling ratio, and the total weld ratio is required to be ≥75%. The internal cavity of the throttle hydraulic valve assembly with filter screens is not allowed to have excess materials, and the internal oil passage hole wall is not allowed to have soldering filler accumulation.

Claims

1. A vacuum brazing method for an aero-engine screen throttling hydraulic valve assembly, the aero-engine screen throttling hydraulic valve assembly comprising a valve body (7) and a screen (8) at the upper and lower ends of the valve body (7), the wall thickness of the screen (8) is 0.2 mm, and the materials of the valve body (7) and the screen (8) are both 1Cr18Ni9, characterized in that: The valve body (7) and the filter screen (8) at the upper and lower ends are connected by vacuum brazing. Before brazing, the valve body (7) and the filter screen (8) at the upper and lower ends are placed vertically. The selected welding filler metal is Bag54CuPd900 / 950 in the national standard GB / T18762-2017 “Specification of Precious Metal and Its Alloy Filler Metal”. The shape of the welding filler metal is a ring with an inner diameter of φ2.5mm. The thickness of the filler metal ring (9) at the connection between the upper end of the valve body (7) and the filter screen (8) is 0.33~0.35mm. The thickness of the filler metal ring (9) at the connection between the lower end of the valve body (7) and the filter screen (8) is 0.30~0.32mm. ​ During brazing, synchronous bidirectional welding is performed on the connections between the valve body (7) and the filter screen (8) at the upper and lower ends. The welding temperature is raised from 920℃ to 990℃, and the time for this temperature rising process is 6~8min. The pressure during welding should be greater than or equal to 300Pa. After welding is completed, the workpieces are cooled by argon gas in the furnace when the temperature of the workpieces in the furnace cools to 780℃. The workpieces are taken out of the furnace when the temperature drops to below 80℃.

2. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 1, wherein: The valve body (7) and the filter screen (8) at the upper and lower ends are placed vertically on a fixture to maintain their vertical state. The fixture includes upper, middle, and lower three-layer structures. The upper layer is an upper filter screen protection plate (1) to maintain and fix the installation position of the upper end of the valve body (7) and the filter screen (8). The middle layer is a fixing plate (2) of the valve body (7) to maintain and fix the vertical state of the valve body (7). The lower layer is a lower filter screen fixing plate (3) with a circular arc groove. The filter screen (8) at the lower end of the valve body (7) is seated in the circular arc groove to maintain and fix the installation position of the lower end of the valve body (7) and the filter screen (8).

3. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 2, wherein: The material of the fixture and the valve body (7) and the filter screen (8) at the upper and lower ends is 1Cr18Ni9.

4. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 2, wherein: The upper, middle, and lower three-layer structures of the fixture are arranged on the corresponding upper, middle, and lower three-layer square plates, so that the welding method can simultaneously weld the connections of multiple valve bodies (7) and upper and lower filter screens (8). Guide columns (4), cylindrical pins (5), and diamond pins (6) are provided on the upper, middle, and lower three-layer square plates to ensure that there is no positional error between the three layers.

5. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 4, wherein: A load-controlled thermocouple is installed at the center position of the upper, middle, and lower three-layer square plates to control the real-time temperature during brazing.

6. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 4, wherein: Before welding, the upper, middle, and lower three-layer square plates are dry sandblasted as a whole, and then subjected to vacuum purification treatment.

7. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 1, wherein: Before brazing, the valve body (7) and the filter screen (8) at the upper and lower ends are subjected to uniform temperature treatment at 870~880℃ in the furnace.

8. The aircraft engine strainer-throttling hydraulic valve assembly vacuum brazing method of claim 1, wherein: Before brazing, the workpieces and the filler metal are ultrasonically cleaned with anhydrous ethanol. First, the filler metal ring (9) is placed in the welding process groove of the valve body (7), then the filter screen (8) is installed, the installation of the filter screen (8) is visually inspected for any skew, and then a layer of solder resist is applied between the filter holes of the filter screen (8) to prevent the filler metal from blocking the filter screen holes.

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