Vacuum brazing of high temperature alloy cast honeycomb assemblies

Abstract

This invention discloses a vacuum brazing method for high-temperature alloy casting honeycomb components, comprising the following steps: S1. After cleaning the casting, the entire surface of the casting to be brazed is brush-plated with nickel, the thickness of the nickel layer being 0.015-0.02 mm; S2. Filling the outer cylindrical surface of the honeycomb component with brazing filler metal; S3. Assembling the honeycomb and the casting and spot welding them; S4. Filling the brazing joint between the honeycomb and the casting with paste-like brazing filler metal and allowing the paste-like brazing filler metal to dry; S5. Clamping the honeycomb component using multiple clamps, the multiple clamps being evenly distributed around the circumference of the honeycomb component; S6. Brazing cycle. This brazing method adds sandblasting to the cleaning of the brazing surface, removes the oxide film on the surface of the casting substrate, and then applies nickel plating to the entire surface. This increases the wettability of the entire brazing surface while preventing incomplete soldering. The nickel layer thickness is selected to take into account the diffusion of the nickel layer during the brazing process, ensuring the protective effect of the nickel layer on the brazing surface. The introduction of a fixture to tightly attach the honeycomb and the casting overcomes the defects such as weak spot welding between the honeycomb and the casting after the honeycomb module is treated with nickel plating, and ensures the gap at the honeycomb brazing joint.

Description

Technical Field

[0001] This invention relates to the field of brazing technology for aero-engine parts, specifically to a vacuum brazing method for high-temperature alloy casting honeycomb components. Background Technology

[0002] Aero-engine sealing structures include grate seals, graphite seals, and honeycomb seals, among which honeycomb seals are most commonly used in engines due to their excellent sealing performance. In the aero-engine field, the current status of honeycomb seal processing is as follows: For easily weldable materials, such as stainless steel and forged high-temperature alloys, the processing technology for honeycomb seal components is relatively mature, resulting in good brazing appearance and a high brazing pass rate. However, with the improvement of aero-engine performance, to ensure weight reduction and structural simplification, more and more structures are being directly brazed from cast casings to honeycomb. However, the base material of the honeycomb assembly is a cast high-temperature alloy with a high content of easily oxidized elements (Al, Ti), forming a dense oxide film on the surface that is difficult to break under high-temperature vacuum, resulting in poor vacuum brazing performance. Furthermore, honeycomb is a flexible component, making it difficult to control the brazing gap. All these factors contribute to the difficulty of brazing cast honeycomb components, often resulting in problems such as non-wetting of the brazing filler metal on the base surface, substandard weld appearance, and low brazing pass rate.

[0003] Patent CN113878189A discloses a vacuum brazing process for aero-engine honeycomb assemblies, comprising the following steps: S1, preparing a honeycomb ring and filling it with adhesive brazing filler metal; S2, the brazing surface between the honeycomb ring and the outer ring includes a nickel-plated area and a non-nickel-plated area. The non-nickel-plated area of ​​the outer ring is protected by a protective element, and the brazing surface near the outer end face of the outer ring is a nickel-plated area, which is then sandblasted; S3, a special nickel plating is applied to the nickel-plated area of ​​the outer ring, followed by a rapid nickel plating, and the protective element is removed; S4, the honeycomb ring filled with adhesive brazing filler metal is assembled with the outer ring; S5, the honeycomb ring is spot-welded for positioning; S6, a paste-like brazing filler metal is filled at the connection between the outer end face of the honeycomb ring and the nickel-plated area of ​​the outer ring to obtain a pre-brazed part; S7, the pre-brazed part is vacuum brazed. This invention's vacuum brazing process for aero-engine honeycomb assemblies, with partial nickel plating on the outer ring, solves the problems of weak spot welding and discontinuous brazed seam surfaces in honeycomb assemblies made of difficult-to-weld materials.

[0004] The aforementioned patent also addresses the brazing of cellular modules, but it mainly targets the problems of weak spot welding and discontinuous welds. It does not address the gap control of brazing welds, and it only involves localized nickel plating. Some parts of the cellular module may have incomplete welds, and the welding quality still cannot meet the delivery requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a vacuum brazing method for brazing high-strength high-temperature alloy casting honeycomb components, ensuring that the honeycomb and the outer ring of the casting are tightly attached and the weld quality is high.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A vacuum brazing method for high-temperature alloy casting honeycomb components includes the following steps:

[0008] S1. After cleaning the casting, the brazed surface of the casting is coated with nickel by brush, and the thickness of the nickel layer is 0.015-0.02mm.

[0009] S2. Fill the outer cylindrical surface of the cellular module with brazing filler metal;

[0010] S3. Assemble the honeycomb structure and casting and spot weld them together;

[0011] S4. Fill the brazing joints of the honeycomb and castings with a paste-like filler metal and allow the paste-like filler metal to dry;

[0012] S5. Multiple clamps are used to clamp the honeycomb assembly, and the multiple clamps are evenly distributed around the honeycomb assembly.

[0013] S6. Brazing cycle;

[0014] The fixture described in S5 includes a pressure plate, an I-beam clamp, and bolts. The pressure plate is fitted to the inner cylindrical surface of the honeycomb. The I-beam clamp has a first bent end and a second bent end that are parallel to each other. The first bent end extends to the inner hole countersunk platform of the casting and fits against the countersunk platform wall. The second bent end is located outside the casting. Threaded holes are provided on both the first bent end and the second bent end for the bolt to pass through. The end of the bolt passing through the first bent end abuts against the pressure plate, and the end of the bolt passing through the second bent end abuts against the outer cylindrical surface of the casting.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1) The cleaning of the brazing surface adopts the method of washing + baking + sandblasting. Sandblasting can remove the oxide film on the surface of the casting substrate. Then, the entire surface is brush-plated with nickel, which is compatible with the high strength of the weld of high-temperature alloy casting. It increases the wettability of the entire brazing surface while preventing incomplete welding. The nickel layer thickness of the brush-plated nickel is thicker than the traditional nickel layer thickness, taking into account the diffusion of nickel layer during the brazing process to ensure the protective effect of nickel layer on the brazing surface.

[0017] 2) When brazing the honeycomb module, a fixture is introduced to press the honeycomb and the casting tightly together. This can overcome the shortcomings of the honeycomb module after brush-plating nickel treatment, such as weak spot welding between the honeycomb and the casting, low weld strength, and the honeycomb may spring open during the brazing process, thus ensuring the gap at the honeycomb brazing point.

[0018] 3) The clamping plate and I-beam clamp are made of the same material as the casting matrix, so that the clamp and the honeycomb assembly have the same coefficient of linear expansion. They expand synchronously during the brazing process, ensuring that the honeycomb and the casting are pressed together at all times to ensure the gap. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of the clamp described in Example 1 on the honeycomb assembly;

[0020] Figure 2 This is a top view of the cellular component clamping fixture described in Example 1;

[0021] Figure 3 This is a schematic diagram showing the clamping sequence of the fixture described in Example 1 on the honeycomb assembly;

[0022] Figure 4 This is a schematic diagram of spot welding in step S3 of Example 2. Detailed Implementation

[0023] To clearly illustrate the technical features of this solution, the following detailed description, in conjunction with the accompanying drawings, will explain the technical solution in detail.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0025] Furthermore, it should be understood in the description of this application that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0027] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0028] Example 1

[0029] This embodiment provides a brazing method for brazing honeycomb components on an aero-engine. The castings in the honeycomb components are high-temperature alloy castings, which have high strength but are prone to incomplete welds. The brazing method includes the following steps:

[0030] S1. After cleaning the casting, the brazed surface of the casting is coated with nickel:

[0031] Cast parts often have a porous matrix, and the machining process involves the presence of large amounts of cutting fluid and coolant. These liquids can easily penetrate the porous areas of the casting during machining. Due to the vacuum environment and high-temperature heating during brazing, impurities and contaminants from the machining fluids evaporate and precipitate, contaminating the brazing surface and hindering the spread and wetting of the brazing filler metal, thus affecting the weld quality. To address these issues, the cleaning process can be divided into three steps: ultrasonic cleaning, baking, and sandblasting, performed sequentially. This effectively removes oil stains from the brazing areas of cast parts, especially deep-seated oil stains on the brazing surface, thereby improving the quality of the brazed joint after welding.

[0032] Specifically, after ultrasonic cleaning, the parts are placed in a vacuum brazing furnace for baking at 400℃~700℃ for 30min~3h, ensuring the vacuum level is below 0.2Pa during the baking process. Specifically, the vacuum brazing furnace is evacuated to below 0.1Pa before heating to 500~700℃, and held at 500~700℃ for 0.5h~2h. The negative pressure and high temperature of the vacuum remove contaminants and oil. After baking, the brazed surface is dry-blown with corundum abrasive to remove surface residues and oxide layers. The abrasive particle size is 180~240 mesh, and the blowing pressure is below 0.5MPa. After blowing, no contaminants should seep out from the part surface.

[0033] Afterwards, nickel is brush-plated onto the brazing surface. In traditional brazing methods, such as those described in the prior art, localized nickel plating is typically used, with the nickel layer thickness controlled within 0.01 mm. During brazing, slag inclusions and oxide films can form in the weld, resulting in low component strength. This invention considers that cast parts are highly susceptible to oxidation. To improve the wettability of the brazing filler metal on the casting substrate surface, nickel is brush-plated onto the entire brazing surface to minimize oxidation of the casting surface and reduce the possibility of subsequent incomplete soldering. Furthermore, the quality of the brush-plated nickel layer directly affects the brazing quality of the parts. If the nickel layer thickness is insufficient, the nickel layer will diffuse into the substrate and filler metal during brazing, and the brush-plated nickel area will oxidize after exiting the furnace, and the nickel layer will not be able to wet the filler metal. If the nickel layer thickness is too thick, the nickel layer will peel off and fall off, and the nickel layer will not be able to completely diffuse into the weld and substrate, thus affecting the brazing quality and joint structure. Therefore, in this embodiment, the nickel layer thickness is controlled at 0.015-0.02 mm to ensure the protective effect of the nickel layer. Because the nickel layer is thick, even if there is nickel layer diffusion during the brazing process, the filler metal will always have a nickel layer on the brazing surface, thus ensuring the wettability of the filler metal. The parts can be protected from oxidation before the filler metal melts and diffuses into the substrate and filler metal after the filler metal melts and spreads.

[0034] Brush plating of nickel includes brush plating of special nickel and brush plating of fast nickel. The voltage for brush plating of special nickel is 8-10V and the time is 30-60s; the voltage for brush plating of fast nickel is 8-10V and the time is 8-30min.

[0035] S2. Fill the outer cylindrical surface of the cellular module with brazing filler metal.

[0036] The honeycomb strips are spliced ​​with energy storage spot welding to form honeycomb rings. A 0.3-0.6 mm thick layer of BNi82CrSiB adhesive brazing filler is rolled on the outer cylindrical surface of the honeycomb. The residual brazing filler on the core grid surface is scraped off until the core grid metal surface is exposed.

[0037] S3. Assemble the honeycomb and casting and spot weld them together.

[0038] After assembling the honeycomb with the casting, an energy storage spot welder or a resistance spot welder is used to spot weld and position the honeycomb and the outer ring of the casting around the entire circle. The upper electrode is positioned with the honeycomb, and the lower electrode contacts the outer ring, forming a weld point at the spot weld, thus initially ensuring that the honeycomb and the outer ring of the casting are tightly fitted together.

[0039] S4. Apply solder paste to the brazing joints of the honeycomb and castings and allow the solder paste to dry.

[0040] A certain amount of BNi82CrSiB paste brazing filler metal is added to the side of the honeycomb. After brushing on the paste brazing filler metal, a flow-blocking agent should be brushed near the paste brazing filler metal to prevent the brazing filler metal from overflowing.

[0041] The drying of the paste-like brazing filler metal is achieved by baking or natural air drying. If baking is used, the drying temperature is 50-200℃ and the drying time is 15-120 minutes.

[0042] S5. Multiple clamps are used to clamp the honeycomb components, and the multiple clamps are evenly distributed around the honeycomb components.

[0043] Although spot welding can bring the honeycomb structure to the outer ring of the casting before it enters the furnace, ensuring a proper brazing gap, the nickel plating on the parts may lead to weak spot welds, resulting in low weld strength. Furthermore, thermal expansion and contraction between the honeycomb and the casting substrate during brazing can cause the honeycomb to spring back. In addition, large brazing gaps between the overlapping surfaces can significantly impact the brazing results. Because the honeycomb is a flexible component with a hexagonal structure within the lattice holes, the requirements for the gap between the honeycomb and the outer ring of the casting are even stricter, demanding a tight fit with no gaps at the brazing points. Therefore, to ensure a constant fit between the honeycomb and the casting during the brazing process, this embodiment also introduces a fixture for clamping the honeycomb assembly to guarantee the gap at the brazing points.

[0044] like Figure 1 As shown, the fixture 01 includes a pressure plate 1, an I-beam clamp 2, and bolts 3. The pressure plate 1 is in contact with the inner cylindrical surface of the honeycomb A. The I-beam clamp 2 has a first bent end 21 and a second bent end 22 that are parallel to each other. The first bent end 21 extends to the inner hole countersunk platform of the casting B and is in contact with the countersunk platform wall. The second bent end 22 is located outside the casting B. Threaded holes are opened on both the first bent end 21 and the second bent end 22 for the bolts 3 to pass through. The end of the bolt 3 that passes through the first bent end 21 abuts against the pressure plate 1, and the end of the bolt 3 that passes through the second bent end 22 abuts against the outer cylindrical surface of the casting B.

[0045] The specific structure of the pressure plate 1 is an arc segment, the curvature of which is consistent with the curvature of the inner cylindrical surface of the honeycomb. The thickness of the pressure plate should be greater than or equal to 1.5mm. In the axial direction of the honeycomb assembly, the size of the pressure plate should completely cover the size of the honeycomb. Preferably, the two ends of the pressure plate in this direction extend beyond the two end faces of the honeycomb. In the circumferential direction of the honeycomb, the spacing between adjacent pressure plates should be designed to be as small as possible to ensure that even if the I-beam clamps are set separately, the gap area between the two clamps can still press the honeycomb and the casting together.

[0046] The I-beam clamp 2 is made of the same material as the casting so that the clamp and the part have the same coefficient of linear expansion, so that the part expands synchronously during the brazing process. That is, the expansion amount of the I-beam clamp is consistent with the expansion amount of the outer ring, ensuring that the I-beam clamp always presses the honeycomb and the casting together to ensure the gap.

[0047] like Figure 2 As shown, among all the clamps distributed circumferentially in the cellular module, the interval between adjacent clamps is 30-50 mm.

[0048] S6. Brazing cycle.

[0049] The honeycomb modules were loaded into a furnace for vacuum brazing. The vacuum brazing process parameters were: (1030~1060)℃×(5~15)min.

[0050] S7. Post-weld treatment.

[0051] After the honeycomb module is produced, the fixture is removed, the residual flow barrier is removed with a clean cloth, and the weld is inspected for appearance and weld rate.

[0052] Inspection revealed that the honeycomb components obtained using the above brazing method had virtually no appearance defects, no incomplete welds, and a weld fusion rate of over 90%. This reduced the rework and repair rate of vacuum brazing for cast honeycomb parts, improved production efficiency, and saved production costs.

[0053] Example 2

[0054] Based on Example 1, this embodiment specifies requirements for the clamping of the fixtures, namely, the clamping sequence of multiple fixtures on the honeycomb assembly shall be as follows:

[0055] S51. Place a pressure plate on the inner cylindrical surface of the honeycomb.

[0056] S52. Pre-assemble the I-beam clamps in groups of 3-5. Screw the bolts into the first bent end of the I-beam clamp to tighten the pressure plate, and screw the bolts into the second bent end to tighten the outer surface of the casting. Note that the bolts do not need to be tightened at this time. Just make sure that the I-beam clamps are installed on the honeycomb assembly and will not wobble.

[0057] S53. For example Figure 3As shown, first install group ①, then install group ② at the opposite diameter, then rotate 90° and install group ③, then install group ④, and so on until the entire cellular module is filled.

[0058] S54. Tighten the bolts in the order of ①②③④•••••……, about 1.5-2 turns, to ensure that the honeycomb is not damaged while tightening.

[0059] The symmetrical clamping and tightening method of the fixture in this embodiment can ensure that the circumferential gap of the honeycomb is uniform and the quality of the honeycomb assembly is guaranteed. Because the honeycomb is a complete ring, its circumferential gap is uniform in the unconstrained state. If it is clamped along the circumference, the gap is smaller at the first clamping position and larger at the later clamping position. If a single fixture is clamped sequentially, it will result in a large difference in the circumferential gap of the honeycomb.

[0060] Example 3

[0061] The difference between this embodiment and Embodiment 1 is that the electrode used for spot welding in S3 includes an upper electrode and a lower electrode. The lower electrode is designed as a copper plate that can support the honeycomb module, with the end face of the honeycomb module attached to the surface of the copper plate. The upper electrode is mounted on a spot welding pen. During spot welding, if... Figure 4 As shown, the honeycomb module is placed flat, and the spot welding pen is placed in contact with the inner cylindrical surface of the honeycomb for spot welding positioning. The foot pedal of the spot welding machine is stepped on to trigger the discharge.

[0062] In traditional spot welding, for small-sized honeycomb parts, workers can easily place them vertically between the upper and lower electrodes for spot welding due to their small size and light weight. However, for cast honeycomb components, such as the honeycomb component in Example 1, the parts are large and weigh hundreds of kilograms, making it difficult to stand them upright. Furthermore, the spot welding process requires rotating the parts to ensure complete circumferential welding, necessitating 2-3 workers to move and hold the parts, wasting significant manpower and increasing worker fatigue. In addition, for aero-engine honeycomb components, which typically involve brazing the honeycomb along the sides of the guide vanes, the blades obstruct the view after the casting is placed behind the upper and lower electrodes of the spot welding machine, making it difficult for workers to observe the contact between the electrodes and the parts during descent, thus making spot welding more challenging. Therefore, traditional spot welding electrodes are unsuitable for spot welding cast honeycomb components.

[0063] The improved spot welding electrode in this embodiment saves labor, reduces the labor intensity of workers, and allows one person to easily complete the spot welding work, greatly improving production efficiency.

[0064] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A vacuum brazing method for high-temperature alloy casting honeycomb components, characterized in that, Includes the following steps: S1. After cleaning the casting, the brazed surface of the casting is coated with nickel by brush, and the thickness of the nickel layer is 0.015-0.02mm. S2. Fill the outer cylindrical surface of the cellular module with brazing filler metal; S3. Assemble the honeycomb structure and casting and spot weld them together; S4. Fill the brazing joints of the honeycomb and castings with a paste-like filler metal and allow the paste-like filler metal to dry; S5. Multiple clamps are used to clamp the honeycomb assembly, and the multiple clamps are evenly distributed around the honeycomb assembly. S6. The honeycomb modules are loaded into the furnace for vacuum brazing; The fixture described in S5 includes a pressure plate, an I-beam clamp, and bolts. The pressure plate is fitted to the inner cylindrical surface of the honeycomb. The I-beam clamp has a first bent end and a second bent end that are parallel to each other. The first bent end extends to the inner hole countersunk platform of the casting and fits against the countersunk platform wall. The second bent end is located outside the casting. Threaded holes are provided on both the first bent end and the second bent end for the bolt to pass through. The end of the bolt passing through the first bent end abuts against the pressure plate, and the end of the bolt passing through the second bent end abuts against the outer cylindrical surface of the casting. The I-beam clamp is made of the same material as the casting. The cleaning of castings in S1 includes three sequential steps: ultrasonic cleaning, baking, and sandblasting.

2. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, In S1, brush plating of nickel includes brush plating of special nickel and brush plating of fast nickel. The voltage for brush plating of special nickel is 8-10V and the time is 30-60s; the voltage for brush plating of fast nickel is 8-10V and the time is 8-30min.

3. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, In the clamps of the circumferentially distributed cellular components, the interval between adjacent clamps is 30-50 mm.

4. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, In the calcination step, the calcination temperature is 400℃~700℃, the time is 30min~3h, and the vacuum degree is kept within 0.2Pa during the calcination process; in the sand blowing step, the sand particle size is 180~240 mesh, and the sand blowing pressure is kept within 0.5MPa.

5. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, After applying the paste-like solder in S4, a flow-blocking agent should be applied to prevent the solder from overflowing.

6. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, The paste-like brazing filler metal is dried by baking at a temperature of 50–200°C for 15–120 minutes.

7. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, The electrodes used for spot welding in S3 include an upper electrode and a lower electrode. The lower electrode is a copper plate that can support the honeycomb module. The end face of the honeycomb module is attached to the surface of the copper plate. The upper electrode is mounted on a spot welding pen.

8. The vacuum brazing method for high-temperature alloy casting honeycomb components according to claim 1, characterized in that, The brazing process parameters in S6 are (1030~1060)℃×(5~15)min.

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