Brazing method of heat exchanger assembly

Abstract

The invention provides a brazing method of a heat exchanger assembly, the heat exchanger assembly comprises a heat exchanger body and a heat exchange tube, and the outer surface of the heat exchanger body is provided with a heat exchange groove. The brazing method comprises the steps that S1, the heat exchange pipe is coiled into the shape matched with the heat exchange groove in advance through a profiling mold; s2, the surfaces of the heat exchange tube and the heat exchanger body are plated with nickel; s3, the heat exchange tubes are embedded into the heat exchange grooves, and the heat exchange tubes are pressed and fixed through pressing blocks with chamfers; s4, the brazing filler metal is applied to the edge of the contact face of the heat exchange pipe and the heat exchange groove in a differentiated mode, and the surface, where the brazing filler metal possibly flows through, of the heat exchanger body is coated with a solder resist; and S5, the heat exchanger assembly is brazed in a stepped heating mode. According to the method, through cooperative implementation of multiple steps such as heat exchange tube preforming, composite nickel plating, precise fixing, differential brazing filler metal applying and stepped temperature rising, tight attachment of the thin-walled tube and the complex curved surface heat exchanger is achieved, the bonding strength and stability of a brazed joint are improved, brazing defects are effectively eliminated, and the product percent of pass is increased.

Description

Brazing method for heat exchanger components Technical Field

[0001] This invention relates to the field of brazing dissimilar metal materials, specifically to a brazing method for heat exchanger components. More particularly, it relates to a highly reliable vacuum brazing method for ultra-long thin-walled tubes to complex curved heat exchanger bodies. Background Technology

[0002] In certain high-end fields, the demand for high-performance heat exchange and fluid transport components is becoming increasingly urgent. Such components require the connection of ultra-long, thin-walled heat exchange tubes with excellent thermal conductivity to complex curved heat exchanger bodies with superior high-temperature strength via brazing, thereby balancing the component's high thermal conductivity with structural reliability.

[0003] However, heat exchanger tubes are mostly made of copper or aluminum, while the heat exchanger body is mostly made of stainless steel or nickel-based alloys. When using conventional brazing methods to connect these dissimilar materials, the following problems arise: 1. Heat exchanger tubes are slender and thin-walled structures, and because their hardness is lower than that of the heat exchanger body, directly bonding the heat exchanger tubes to the heat exchanger body for coiling can easily cause deformation or surface damage; 2. The coefficients of thermal expansion of copper and aluminum differ significantly from those of stainless steel and nickel-based alloys, resulting in high residual stress at the brazed joint, which easily leads to failure; 3. Copper and aluminum, along with stainless steel and nickel-based alloys, present different challenges in thermal expansion coefficients. When directly brazing steel and nickel-based alloys, problems such as poor wettability of the brazing filler metal and insufficient interfacial bonding strength are often encountered. Furthermore, the matrix is ​​prone to oxidation at high temperatures, which further affects the connection quality. Fourth, it is difficult to accurately position and reliably fix ultra-long copper or aluminum tubes in the spiral grooves of complex curved heat exchanger bodies. Traditional fixing methods have poor positioning accuracy and are prone to damaging the workpiece. Fifth, the brazed heat exchanger components need to work for a long time in a complex environment of over 200°C, several atmospheres of pressure, and vibration, which places extremely high demands on the strength and long-term stability of the brazed joints.

[0004] Patent document CN121402735A discloses a heat exchanger processing method and a heat exchanger, including the following steps: assembling and welding a heat exchange tube and a first tube, both made of stainless steel; the fins are made of aluminum or aluminum alloy; a portion of the surface of the heat exchange tube may be coated with a nickel coating with a thickness of 5–20 μm or an aluminum coating with a thickness of 30–150 μm; and then assembling and welding the fins and heat exchange tube to complete the heat exchanger processing. The above-mentioned coating process improves the welding reliability of the fins and heat exchange tube.

[0005] The drawback of the aforementioned patent literature's technical solution is that it merely forms a nickel or aluminum coating on the heat exchange tube surface through a simple coating method, without employing a composite nickel plating process of "impact nickel plating + chemical nickel plating." It only controls the coating thickness parameter without precisely regulating the phosphorus content of the coating. This simple coating method cannot form uniform catalytic active sites on the substrate surface, resulting in poor adhesion between the coating and the substrate, failing to meet the bonding strength requirements of the coating in this invention. Furthermore, due to the lack of phosphorus content control, the coating cannot simultaneously meet the requirements for brazing wettability and melting point compatibility, and it is difficult to form a dense protective coating, thus having limited effectiveness in improving the high-temperature oxidation resistance of the substrate.

[0006] In summary, existing technologies cannot systematically solve the above problems, resulting in low product qualification rates and insufficient reliability, which seriously restricts the development process of related high-end equipment. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a brazing method for heat exchanger components.

[0008] According to a brazing method for a heat exchanger assembly provided by the present invention, the heat exchanger assembly includes a heat exchanger body and a heat exchange tube, the outer surface of the heat exchanger body is provided with a heat exchange groove for accommodating the heat exchange tube, and the heat exchanger body and the heat exchange tube are made of dissimilar metals.

[0009] The brazing method includes the following steps: S1: pre-winding the heat exchange tube into a size and shape that matches the heat exchange tank; S2: chemically plating nickel onto the outer surface of the heat exchange tube and the entire heat exchanger body; S3: fitting the nickel-plated heat exchange tube into the heat exchange tank and fixing the heat exchange tube; S4: applying brazing filler metal to the edge of the contact interface between the heat exchange tube and the heat exchange tank; S5: brazing the heat exchanger assembly.

[0010] Preferably, in step S1, the heat exchange tube is a copper tube or an aluminum tube, and a conforming mold is used to coil the heat exchange tube. The surface of the conforming mold is provided with a conforming groove that is consistent with the size and shape of the heat exchange groove, and the conforming mold is a non-metallic material with a hardness lower than that of the heat exchange tube.

[0011] Preferably, the nickel plating process in step S2 forms a medium-phosphorus nickel-phosphorus alloy coating. When the heat exchange tube is a copper tube and the heat exchanger body is made of stainless steel or a nickel-based alloy, the nickel plating process includes: first performing impact nickel plating to form uniform catalytic active sites on the substrate surface, and then performing chemical nickel plating.

[0012] Preferably, the impact nickel plating process parameters are as follows: the nickel chloride content in the plating solution is 150-200 g / L, the hydrochloric acid content is 100-150 ml / L, the temperature is 15-35℃, and the current density is 2-4 A / dm²; the electroless nickel plating process parameters are as follows: the nickel ion content in the plating solution is 5.2-6.0 g / L, the pH value is 4.6-5.0, the temperature is 86-92℃, and the nickel plating time is 15-30 min.

[0013] Preferably, in step S3, a pressure block is used to press and fix the heat exchange tube, and the inner edge of the pressure block in contact with the heat exchange tube is chamfered.

[0014] Preferably, the pressure block is made of stainless steel, and the pressure block is fixed to the heat exchanger body by spot welding with a cold welding machine; during spot welding, welding wire is added to form weld points between the four corners of the edge of the pressure block and the heat exchanger body. The weld points avoid the heat exchange tube and do not interfere with the heat exchange tank. After spot welding, the weld point position is cleaned.

[0015] Preferably, in step S4, brazing filler metal is applied differentially to both sides of the contact interface between the heat exchange tube and the heat exchange tank, with one side being higher than the other side, and brazing filler metal is applied to both sides of the contact interface between the pressure block and the heat exchange tube, and to the surface of all welds formed by spot welding at the edge of the pressure block.

[0016] Preferably, step S4 further includes coating the surface of the heat exchanger body through which the brazing filler metal may flow with a solder resist, wherein the solder resist and the brazing filler metal are spaced apart during coating.

[0017] Preferably, step S5 uses vacuum brazing, in which the heat exchanger assembly is placed on a heat-resistant steel base and placed together in a vacuum brazing furnace. The upper and lower surfaces of the heat-resistant steel base are coated with a zirconia or alumina ceramic coating with a thickness of 0.1 to 0.15 mm. When placing the heat exchanger, the side with the greater brazing height on the heat exchange tube is positioned at the top.

[0018] Preferably, the vacuum brazing is performed using a stepped heating, holding, and cooling method. First, the temperature is heated to 300-400°C at a rate of 50-150°C / h and held for 0.5-1h. Then, the temperature is heated to the brazing temperature at a rate of 50-120°C / h and held for 15-30 minutes. After the holding period, the temperature is cooled to 400°C at a rate of 50-150°C / h, and then cooled to below 50°C in the furnace before being removed from the furnace.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. By utilizing the hardness change characteristics of copper or aluminum tubes before and after nickel plating, the present invention establishes the process sequence of "precision pre-forming first, then surface treatment", which avoids the problem of poor forming and bonding caused by the increase in tube hardness after nickel plating.

[0020] 2. This invention uses a non-metallic molding die with a hardness lower than that of copper or aluminum tubes for pre-coiling, which ensures that the tube and heat exchange tank fit tightly and eliminates brazing defects caused by uneven gaps, while avoiding damage to the tube surface by the hard die, thus ensuring the long-term safe operation of the heat exchanger assembly under high temperature and high pressure.

[0021] 3. This invention employs a composite nickel plating process that combines impact nickel plating and electroless nickel plating, and controls the plating thickness and phosphorus content. This not only solves the problem of insufficient plating adhesion and effectively prevents plating cracking and peeling, but also solves the problems of poor brazing wettability and insufficient substrate oxidation resistance between copper tubes, aluminum tubes and stainless steel and nickel-based alloys.

[0022] 4. This invention effectively eliminates installation interference by setting a chamfer on the pressure block and combining the mechanical clamping of the stainless steel pressure block with local fixation by cold welding, along with the operation method of spot welding with welding wire. This improves the fit between the pressure block and the copper or aluminum tube, achieving high-precision pre-fixation of ultra-long thin-walled tubes within the spiral groove. This not only enhances the reliability of pre-fixation but also ensures the stability of subsequent brazing quality.

[0023] 5. The present invention adopts a method of differentially and quantitatively applying BNi2 paste brazing filler metal to the upper and lower surfaces, which can ensure that the brazing filler metal is fully filled at the welding interface and forms a reliable weld. At the same time, the surface of the heat exchanger body through which the brazing filler metal may flow is coated with solder resist for effective protection, avoiding damage to non-brazing parts such as threads and holes caused by brazing filler metal overflow, reducing subsequent repair processes, and significantly improving the production efficiency and pass rate of the product.

[0024] 6. The present invention places the heat exchanger assembly on a heat-resistant steel base with a 0.1-0.15mm zirconia / alumina ceramic coating on its surface for brazing, which effectively avoids the problem of adhesion between the workpiece and the base, and between the base and the furnace support during the brazing process. This can prevent damage to parts caused by adhesion, extend the service life of the tooling, and reduce maintenance costs in the production process.

[0025] 7. This invention adopts a multi-stage gradient heating and heat preservation system and formulates a reasonable cooling system after brazing, which can effectively reduce the temperature difference and thermal stress inside and outside the workpiece, avoid deformation and cracking of the components, and prevent excessive internal stress caused by excessive cooling. From the process perspective, it ensures the dimensional accuracy and performance stability of the heat exchanger components. Attached Figure Description

[0026] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 is a schematic diagram of the present invention mainly embodying the conforming mold structure; Figure 2 is a schematic diagram of the present invention mainly embodying the semi-circular annular pressure block structure; Figure 3 is a partial cross-sectional schematic diagram of the present invention mainly embodying the heat exchange tube being assembled in the spiral groove of the heat exchanger and fixed by the pressure block; Figure 4 is a partial enlarged view of the present invention mainly embodying the pressure block being spot-welded and fixed by spot welding.

[0027] Figure reference numerals: 1. Heat exchanger tube; 2. Heat exchanger body; 21. Heat exchanger groove; 3. Press block; 31. Chamfer; 32. Weld point; 4. Contouring mold; 41. Contouring groove. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0029] This invention provides a brazing method for achieving high-quality and high-reliability connection between ultra-long thin-walled copper or aluminum tubes and complex curved stainless steel or nickel-based alloy heat exchangers. The specific implementation is as follows: The heat exchanger assembly includes a heat exchanger body 2 and heat exchange tubes 1. The outer surface of the heat exchanger body 2 is provided with a heat exchange groove 21 for accommodating the heat exchange tubes 1. The heat exchanger body 2 and the heat exchange tubes 1 are made of dissimilar metals, and the material hardness of the heat exchanger body 2 is greater than that of the heat exchange tubes 1. The heat exchange tubes 1 are copper or aluminum tubes, and the heat exchanger body 2 is made of stainless steel or a nickel-based alloy.

[0030] Example 1, Step 1: Pre-coiling Forming In existing technologies, achieving precise positioning and reliable fixing of ultra-long copper or aluminum tubes within the spiral grooves of complex curved heat exchangers is challenging. Traditional fixing methods suffer from low positioning accuracy and are prone to damaging the workpiece. To address this problem, this example employs the following solution: A contour mold 4 with a 1:1 external dimension with the stainless steel or nickel-based alloy heat exchanger body 2 is used. The outer surface of the contour mold 4 has a contour groove 41 that matches the size and shape of the heat exchange groove 21. The heat exchange groove 21 and the contour groove 41 have the same spiral structure. A heat exchange tube 1, exceeding 10 meters in length, with an outer diameter of 8–15 mm, a wall thickness of 0.8–1.2 mm, and made of copper or aluminum, is coiled along the contour groove 41, forming a size and shape that matches the heat exchange groove 21 and is consistent with the final assembly state. The contour mold 4 is made of a non-metallic material with a hardness lower than that of the heat exchange tube 1, selected from wood, engineering plastics, or composite materials.

[0031] In this embodiment, CNC machining technology can be used to create a wooden mold 4, with a groove 41 on its outer surface that is identical to that of the heat exchange trough 21 (see Figure 1). A copper tube with a length of 12 meters, an outer diameter of 10 millimeters, and a wall thickness of 0.8 millimeters is used as the heat exchange tube 1. The starting end of the heat exchange tube 1 is fixed to the lower starting point of the groove 41 of the wooden mold 4. Then, along the trajectory of the groove 41 of the mold 4, the entire heat exchange tube 1 is wound evenly and tightly around the mold 4 using a manual method with the aid of tools such as a rubber mallet. After winding, the heat exchange tube 1 forms a size and shape that matches the heat exchange trough 21. Because the surface of the wooden mold 4 is smooth and its hardness is lower than that of the heat exchange tube 1, the entire winding process does not cause any visible scratches on the surface of the heat exchange tube 1 while achieving high-precision bending. Subsequently, the wound heat exchange tube 1 is transferred to the next process for cleaning and nickel plating.

[0032] Step 2: Nickel Plating. When the heat exchanger tube 1 is made of copper and the heat exchanger body 2 is made of stainless steel or nickel-based alloy, the outer surface of the pre-formed heat exchanger tube 1 and the entire heat exchanger body 2 are nickel-plated. The nickel plating process adopts a composite process of impact nickel plating and chemical nickel plating. Impact nickel plating is performed first, followed by chemical nickel plating, ultimately forming a medium-phosphorus nickel-phosphorus alloy coating with a thickness of 5-10 μm and a phosphorus mass percentage of 6%-9%. Among them, the impact nickel plating uses an acidic plating solution to pre-plat a layer of nickel on the substrate surface by electrodeposition, which is used to form uniform catalytic active sites on the non-catalytically inactive surface of the heat exchanger tube 1 and the easily passivated surface of the heat exchanger body 2. The parameters for impact nickel plating are as follows: nickel chloride content in the plating solution is 150–200 g / L, hydrochloric acid content is 100–150 ml / L, temperature is 15–35℃, and current density is 2–4 A / dm²; the parameters for electroless nickel plating are as follows: nickel ion content in the plating solution is 5.2–6.0 g / L, pH value is 4.6–5.0, temperature is 86–92℃, and plating time is 15–30 min.

[0033] In this embodiment, the surface nickel plating is specifically implemented according to the following steps: 1. Pretreatment: The outer surface of the coiled copper tube and the nickel-based high-temperature alloy heat exchanger body 2, which is machined to the dimensions shown in the drawing (outer diameter 600mm, height 600mm), are subjected to pretreatment such as degreasing, pickling and activation.

[0034] 2. Impact nickel plating: The pretreated copper tube and heat exchanger body 2 are immersed in an acidic nickel plating solution. The impact nickel plating process parameters are: nickel chloride 170g / L, hydrochloric acid 120ml / L, temperature 25℃, current density 3A / dm², and time 4min.

[0035] 3. Electroless nickel plating: After cleaning the copper tubes and heat exchanger body 2 that have undergone impact nickel plating, immediately transfer them to a medium phosphorus electroless nickel plating solution at 90℃, with nickel ions at 5.6g / L and pH value at 4.8 for 30 minutes to obtain a uniform medium phosphorus nickel-phosphorus alloy coating with a thickness of 7μm and a phosphorus mass percentage of 8%.

[0036] 4. Post-processing: After the coating reaches the required thickness, the parts are removed, washed with water, and dried. The resulting medium-phosphorus nickel-phosphorus alloy coating will serve as a transition layer for subsequent brazing processes.

[0037] Step 3: Assembly and Spot Welding. The pre-formed and nickel-plated heat exchanger tube 1 is installed into the heat exchange tank 21, and a pressure block 3 is used to press the heat exchanger tube 1 firmly. The inner edge of the pressure block 3, which contacts the heat exchanger tube 1, has a chamfer 31. This chamfer 31 allows the heat exchanger tube 1 to easily embed into the concave surface inside the pressure block 3, improving assembly convenience; it also ensures a tight fit between the pressure block 3 and the heat exchanger tube 1, providing a reliable assembly foundation for subsequent brazing. If this chamfer structure is missing, the fit between the pressure block 3 and the heat exchanger tube 1 will be loose, affecting the brazing quality. The preferred dimension of the chamfer 31 is C0.5. Subsequently, a cold welding machine is used for spot welding to fix the pressure block 3 onto the heat exchanger body 2. During the cold welding process, welding wire is added to form weld points 32 between the four corners of the pressure block 3 and the heat exchanger body 2. The weld points 32 are located at the corners of the pressure block 3 and close to its side, avoiding the heat exchanger tube 1 and not interfering with the heat exchange tank 21. After spot welding is completed, use a wire brush to clean the weld point 32.

[0038] As an optional embodiment, the pressure block 3 has a semi-circular annular structure made of stainless steel, as shown in Figure 2. A partial cross-sectional view of the heat exchange tube 1 assembled into the heat exchange groove 21 of the heat exchanger body 2 and fixed by the pressure block 3 is shown in Figure 3. ERNiCr-3 welding wire can be used for spot welding, and a cold welding machine can be used to spot weld and fix the four corners of the pressure block 3. A partial enlarged view of the spot welding and fixing of the pressure block 3 is shown in Figure 4. After spot welding, the weld points 32 are cleaned with a 304 stainless steel brush.

[0039] Step 4: Applying Brazing Alloy and Solder Resist. Considering the different gaps between the upper and lower interfaces of the copper or aluminum tubes in the heat exchange tank 1 and the flow characteristics of the melting brazing alloy, brazing alloy is applied differentially to the upper and lower surfaces of the contact interface between the heat exchange tube 1 and the heat exchange tank 21. The thickness of the brazing alloy on the upper surface is greater than that on the lower surface. The preferred brazing alloy height on the upper surface is 2-3 mm, and on the lower surface is 1-2 mm. The upper surface is the edge surface of the contact interface further away from the base during vacuum brazing, and the lower surface is the edge surface of the contact interface closer to the base during vacuum brazing. Brazing alloy is applied to both sides of the contact interface between the pressure block 3 and the heat exchange tube 1, and to all weld surfaces formed by spot welding on the edges of the pressure block 3. Here, "both sides" refers to the two axial edges of the pressure block 3 on the heat exchange tube 1. Simultaneously, solder resist is applied to the surfaces on the heat exchanger body 2 where the brazing alloy may flow, especially to the threads and holes where the brazing alloy may flow. The solder resist must not come into contact with the brazing alloy; the two must be applied alternately.

[0040] In this embodiment, a syringe can be used to apply BNi2 paste-like brazing filler metal to the upper and lower surfaces, as well as to both sides of the interface between the pressure block 3 and the heat exchange tube 1, and to the surface of the spot weld. The distance between the area coated with solder resist and the brazing filler metal is 3-5 mm to ensure that they are spaced apart. This arrangement ensures that the brazing filler metal fully fills the welding interface and forms a reliable weld, effectively controls the flow of the brazing filler metal, avoids brazing filler metal overflow damaging non-brazing parts, reduces subsequent repair processes, and improves production efficiency and product qualification rate.

[0041] Step 5: Vacuum Brazing. The assembly formed by spot welding the heat exchanger body 2 and the heat exchange tube 1 is placed on the heat-resistant steel base, with the side of the heat exchange tube 1 with the larger brazing filler material application height facing upwards. Then, the assembly and the heat-resistant steel base are placed together in a vacuum brazing furnace at a vacuum degree lower than 1×10⁻⁶. - Under the condition of 2 Pa, brazing is performed using a stepped heating, holding, and cooling process. The upper and lower surfaces of the heat-resistant steel base are coated with a 0.1–0.15 mm thick zirconia or alumina ceramic coating. The specific steps of stepped heating, holding, and cooling are as follows: heating to 300–400℃ at a rate of 50–150℃ / h, holding for 0.5–1h; then heating to the brazing temperature at a rate of 50–120℃ / h, holding for 15–30 minutes; after holding, cooling to 400℃ at a rate of 50–150℃ / h, and then cooling in the furnace to below 50℃ before removal from the furnace, completing the brazing connection and preparing the heat exchanger assembly.

[0042] In this embodiment, the heat exchanger body 2 and the copper tubes, assembled and spot-welded together, are placed on a 310S heat-resistant steel base with a 0.12mm thick zirconia ceramic coating on both the upper and lower surfaces. During placement, the upper surface of the copper tubes, where the brazing filler metal has a greater application height, is positioned upwards. The assembly and the base are then placed together in a vacuum brazing furnace, and a vacuum of 5×10⁻⁶ is applied. -After ³Pa, the following process is carried out: heating up to 400 °C at a rate of 100 °C / h and holding for 40 min; heating up to 1040 °C at a rate of 80 °C / h and holding for 20 min; after the holding is completed, cooling to 400 °C at a rate of 120 °C / h, then turning off the heating and cooling in the furnace to below 50 °C before taking out of the furnace.

[0043] The ceramic coating on the surface of the heat-resistant steel base can form an anti-adhesion isolation layer during the brazing process, avoiding adhesion between the workpiece and the base, and between the base and the furnace support during brazing, preventing part damage, while prolonging the service life of the tooling and reducing the tooling maintenance cost. The stepped heating, holding, and cooling regime can reduce the temperature difference and thermal stress inside and outside the workpiece, effectively alleviating the problem of excessive residual stress caused by the difference in thermal expansion coefficients between copper tubes, aluminum tubes and stainless steel, nickel-based alloys, avoiding workpiece deformation and cracking, and ensuring the dimensional accuracy and performance stability of the heat exchanger assembly.

[0044] Step 6: Inspection After the brazing is completed, visual inspection is carried out by naked eye observation or with the aid of a magnifying glass with a magnification of not less than 4 times. It is required that the brazing seam is continuous, smooth, with uniform width, without any visible cracks, unfilled, pores and other defects, and there is no oxidation and discoloration on the surface of the brazing seam and the base metal. In this embodiment, after the brazing is completed, a pneumatic test is carried out on the heat exchange tubes, and the test condition is to hold the pressure for 30 min under 2 MPa air pressure. It is required that there is no leakage in the heat exchange tube 1. After detection, both the visual inspection and the pneumatic test of the heat exchanger assembly are qualified.

[0045] After brazing according to the above steps, the product qualification rate reaches 100%. The brazing method of the present invention greatly improves the product qualification rate, reduces the production cost, breaks through the restriction of the existing technology on the development of related high-end equipment, and can promote the industrial application of high-end heat exchange and fluid transmission components; at the same time, it can meet the requirements of the heat exchanger assembly working for a long time under the combined environment of temperature exceeding 200 °C, several atmospheric pressures and vibration, and ensure the strength and long-term stability of the brazed joint.

[0046] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0047] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments and features in the present application can be combined with each other arbitrarily.

Claims

1. A brazing method for a heat exchanger assembly, characterized in that, The heat exchanger assembly includes a heat exchanger body (2) and heat exchange tubes (1). The outer surface of the heat exchanger body (2) is provided with heat exchange grooves (21) for accommodating the heat exchange tubes (1). The heat exchanger body (2) and the heat exchange tubes (1) are made of dissimilar metals. The brazing method Includes the following steps: S1: The heat exchange tube (1) is pre-coiled into a size and shape that matches the heat exchange tank (21); S2: The outer surface of the heat exchange tube (1) and the heat exchanger body (2) are nickel-plated as a whole; S3: The nickel-plated heat exchange tube (1) is fitted into the heat exchange tank (21) and the heat exchange tube (1) is fixed; S4: Brazing filler metal is applied to the contact interface edge between the heat exchange tube (1) and the heat exchange tank (21); S5: The heat exchanger assembly is brazed.

2. The brazing method for the heat exchanger assembly as described in claim 1, characterized in that, In step S1, the heat exchange tube (1) is a copper tube or an aluminum tube. The heat exchange tube (1) is coiled using a molding die (4). The surface of the molding die (4) is provided with a molding groove (41) that is consistent with the size and shape of the heat exchange groove (21). The molding die (4) is made of a non-metallic material with a hardness lower than that of the heat exchange tube (1).

3. The brazing method for the heat exchanger assembly as described in claim 1, characterized in that, The nickel plating process in step S2 forms a medium-phosphorus nickel-phosphorus alloy coating. When the heat exchange tube (1) is a copper tube and the heat exchanger body (2) is made of stainless steel or nickel-based alloy, the nickel plating process includes: first, impact nickel plating to form uniform catalytic active sites on the substrate surface, and then chemical nickel plating.

4. The brazing method for the heat exchanger assembly as described in claim 3, characterized in that, The parameters for impact nickel plating are as follows: nickel chloride content in the plating solution is 150–200 g / L, hydrochloric acid content is 100–150 ml / L, temperature is 15–35℃, and current density is 2–4 A / dm²; the parameters for electroless nickel plating are as follows: nickel ion content in the plating solution is 5.2–6.0 g / L, pH value is 4.6–5.0, temperature is 86–92℃, and plating time is 15–30 min.

5. The brazing method for the heat exchanger assembly as described in claim 1, characterized in that, In step S3, the heat exchange tube (1) is pressed and fixed by a pressure block (3). The inner side of the pressure block (3) that is in contact with the heat exchange tube (1) is chamfered (31).

6. The brazing method for the heat exchanger assembly as described in claim 5, characterized in that, The pressure block (3) is made of stainless steel. The pressure block (3) and the heat exchanger body (2) are fixed by spot welding with a cold welding machine. When spot welding with the cold welding machine, welding wire is added to form weld points (32) between the four corners of the edge of the pressure block (3) and the heat exchanger body (2). The weld points (32) avoid the heat exchange tube (1) and do not interfere with the heat exchange tank (21). After spot welding, the weld point (32) is cleaned.

7. The brazing method for the heat exchanger assembly as described in claim 5, characterized in that, In step S4, brazing filler metal is applied differentially to both sides of the contact interface between the heat exchange tube (1) and the heat exchange tank (21), with one side being higher than the other side. Brazing filler metal is also applied to both sides of the contact interface between the pressure block (3) and the heat exchange tube (1) and to the surface of all spot welds formed on the edge of the pressure block (3).

8. The brazing method for the heat exchanger assembly as described in claim 7, characterized in that, Step S4 also includes coating the surface of the heat exchanger body (2) through which the solder may flow with a solder resist, wherein the solder resist and the solder are spaced apart during coating.

9. The brazing method for the heat exchanger assembly as described in claim 7, characterized in that, Step S5 uses vacuum brazing. The heat exchanger assembly is placed on a heat-resistant steel base and put into the vacuum brazing furnace together. The upper and lower surfaces of the heat-resistant steel base are coated with zirconium oxide or alumina ceramic coating. When placing it, the side with the larger brazing material application height on the heat exchange tube (1) is positioned on top.

10. The brazing method for the heat exchanger assembly as described in claim 9, characterized in that, The vacuum brazing is performed using a stepped heating, holding, and cooling method. First, the temperature is heated to 300-400℃ at a rate of 50-150℃ / h and held for 0.5-1h. Then, the temperature is heated to the brazing temperature at a rate of 50-120℃ / h and held for 15-30 minutes. After the holding period, the temperature is cooled to 400℃ at a rate of 50-150℃ / h, and then cooled to below 50℃ in the furnace before being removed from the furnace.

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