Vacuum brazing device for plate-fin heat exchanger, and method

Abstract

A vacuum brazing device for a plate-fin heat exchanger, and a method, relating to the field of welding. Structures such as a hydraulic control system (10), an upper water-cooled sealed conductive electrode head (20), a lower conductive base (30), and tooling (40) are additionally provided on conventional vacuum brazing equipment. The structures are integrated with a furnace liner (60). An upper electrode (24) of the upper water-cooled sealed conductive electrode head (20) is of a distributed structure, and can move up and down by means of the hydraulic control system (10). The upper water-cooled sealed conductive electrode head (20) works in conjunction with the tooling (40).

Description

Vacuum brazing equipment and method for plate-fin heat exchangers Technical Field

[0001] This invention belongs to the field of brazing technology in the manufacturing technology of high-end industrial machine tools, specifically relating to a high-efficiency vacuum brazing equipment and method for plate-fin heat exchangers. Background Technology

[0002] Titanium alloy plate-fin heat exchangers possess excellent properties such as lightweight, high strength, and corrosion resistance, and are widely used in industrial fields such as petroleum, chemical, light industry, power, metallurgy, machinery, and energy. Large titanium alloy plate-fin heat exchangers are core components of the power and environmental control systems of high-end equipment such as aircraft and submarines in cutting-edge fields such as aerospace technology and deep-sea exploration. Their design and manufacturing capabilities constrain the improvement of the power systems for major national equipment. my country currently has shortcomings in the manufacturing of high-efficiency titanium alloy heat exchangers for extreme service conditions such as large size, high pressure, heavy load, strong vibration, and high-temperature corrosion.

[0003] Because large-size titanium alloy plate-fin heat exchangers have multi-layer assembly and interlayer self-shielding structure characteristics, using traditional vacuum brazing equipment usually presents the following prominent problems:

[0004] (1) Brazing quality control is difficult, resulting in a low yield. To ensure the high strength and toughness of brazed joints, the brazing process typically requires the overall temperature uniformity of the product to be controlled within ±5℃ at the brazing temperature, and the total holding time must be sufficiently short. The thermal conductivity of titanium is about 1 / 20 that of copper and 1 / 15 that of aluminum. Using a single vacuum radiation heating method, after the heat exchanger surface reaches the brazing temperature, it needs to be held for at least 30 minutes (longer for large-sized heat exchangers) to achieve overall temperature uniformity. This leads to quality problems such as severe surface embrittlement, easy cracking defects, and severe thin-wall corrosion in large titanium alloy plate-fin heat exchangers, making it difficult to guarantee the yield.

[0005] (2) The thin-walled structure of the product is prone to deformation, and its dimensional performance is difficult to guarantee. In order to ensure that the brazing of tens of thousands of seams is firm and reliable, plate-fin heat exchangers require uniform contact stress at the brazing seam positions during initial furnace loading and to maintain it within a suitable stress range throughout the entire brazing process. Using traditional special tooling for brazing, for large-size heat exchangers, only providing appropriate pre-tightening force during initial assembly, can easily cause uneven contact stress at the edges and core of the workpiece. Furthermore, during the heating process, the thermal expansion under strong constraints is more likely to cause uncontrollable deformation, resulting in product dimensional deviations or low strength of local welded joints.

[0006] (3) The brazing process has a long cycle and extremely low production efficiency. In order to ensure the overall dimensional accuracy of the heat exchanger and reduce thermal stress deformation, the brazing process usually requires the product to be relatively uniform during heating and cooling, with a surface and core temperature difference of ≤50℃. As we all know, vacuum heating and cooling are extremely slow, especially in the low-temperature range below 500℃. Due to the structural characteristics of the heat exchanger, it is only possible to frequently maintain the temperature during radiant heating to ensure the overall temperature uniformity of the product. Therefore, the brazing heating time for large-size titanium alloy plate-fin heat exchangers is more than 20 hours and the cooling process is more than 7 hours, resulting in extremely low efficiency.

[0007] The above problems are even more pronounced for large-size plate-fin heat exchangers. Therefore, in order to achieve high-quality vacuum brazing of large titanium alloy plate-fin heat exchangers, it is necessary to break through the technologies of rapid and uniform heating and small deformation control. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a vacuum brazing device and method for plate-fin heat exchangers. The device is structurally reliable and easy to install. It improves the load distribution on the brazed workpiece, ensuring uniform stress and controllable deformation throughout the brazing process, thus enhancing product dimensional accuracy. Furthermore, based on radiant heating, it incorporates a hydraulic control system, an upper water-cooled sealing voltage conductor assembly, and a lower conductive base. While meeting the specific cooling and sealing requirements of the vacuum brazing device, it also provides self-resisting heat generation, solving the problems of low heating efficiency and difficult deformation control caused by the structural characteristics of plate-fin heat exchangers and the properties of vacuum radiant heating.

[0009] According to one aspect of the present invention, a vacuum brazing apparatus for a plate-fin heat exchanger is provided. The apparatus includes: a hydraulic control system for providing constant-range, constant-pressure control for the vacuum brazing apparatus; a furnace body fixed to the main frame of the hydraulic control system, the furnace body providing a vacuum environment and interfaces for various subsystems, and accommodating the workpiece to be brazed, wherein the interfaces include a temperature control coupler and an infrared thermometer interface; the output signal of the temperature control coupler is a first feedback signal, serving as the primary temperature control feedback signal to regulate the power of each heating element; the output signal of the infrared thermometer is a second feedback signal, used to monitor the temperature of the plate-fin heat exchanger and assist the control board. The finned heat exchanger features self-resistance rapid heating electrode power. The furnace body temperature is controlled using a dual-feedback series control method based on the first and second feedback signals. The furnace chamber, located within the furnace body, includes a furnace chamber frame, a heat insulation screen, and multiple heating tapes. Each heating tape is evenly distributed on the inner wall of the furnace chamber and can be independently controlled. It is used for vacuum radiation heating and insulation. A dynamic sealing structure, fixed to the furnace body, provides a translational sealing interface to maintain the system's working vacuum level. A vacuum system, connected to the furnace body, is used to exhaust gas from the furnace body to obtain a vacuum environment. An upper water-cooled seal is also included. The upper water-cooled sealed voltage conductor is connected to the hydraulic control system. Its lower end passes through the top of the furnace body and maintains the vacuum level inside the furnace through a dynamic sealing structure. The upper water-cooled sealed voltage conductor includes a water-cooled sealed pressure head seat, a pressure head pad, an upper insulating heat insulation plate, an upper electrode, and a first electrode lead-out device. The water-cooled sealed pressure head seat, pressure head pad, upper insulating heat insulation plate, and upper electrode are connected sequentially. The water-cooled sealed pressure head seat includes a flange, a pressure head column, a water inlet pipe, a water outlet pipe, a sealing sleeve, and a sealing ring. The pressure head column is welded to the pressure head through the flange. The upper end face of the sealing sleeve is welded to the flange. The sealing sleeve is a hollow circular tube, and water inlets are welded to the upper outer circumference of the sealing sleeve. The system includes an inlet pipe and an outlet pipe, with the inlet pipe extending to the bottom of the sealing sleeve. The lower end of the inner circle of the sealing ring is welded to the pressure head column, and the upper end of the outer circle is welded to the sealing sleeve. A first electrode lead-out device is connected to the upper electrode and is used to lead out the current of the upper water-cooled sealing voltage head. Together with the lower conductive base, it is used for the self-resistance rapid heating and uniform loading of the workpiece to be welded. The lower conductive base includes a base pad, a lower insulating heat insulation plate, a lower electrode, and a second electrode lead-out device connected in sequence. The second electrode lead-out device is connected to the lower electrode and is used to lead out the current of the lower conductive base. Together with the upper water-cooled sealing voltage head, it is used for the self-resistance rapid heating and uniform loading of the workpiece to be welded. A tooling fixture is used to provide constraints for the plate-fin heat exchanger.

[0010] In one embodiment, the furnace body temperature is controlled using a dual-feedback series control method based on a first feedback signal and a second feedback signal. Specifically, this includes: if neither the first nor the second feedback signal temperature reaches the set temperature, a heating stage is entered, where PID control is used to simultaneously heat the heating element and the self-resistance rapid heating electrode. When the second feedback signal temperature minus the first feedback signal temperature is greater than a set first temperature difference threshold, the self-resistance rapid heating electrode heating is stopped. When the second feedback signal temperature minus the first feedback signal temperature is less than a set second temperature difference threshold, the self-resistance rapid heating electrode is controlled to heat, where the first temperature difference threshold is greater than the second temperature difference threshold. When the second feedback signal temperature reaches the set temperature, a workpiece heat preservation stage is entered. When the second feedback signal temperature equals the set temperature, the self-resistance rapid heating electrode heating is stopped. When the set temperature minus the second feedback signal temperature is greater than a set third temperature difference threshold, the self-resistance rapid heating electrode heating is resumed. When the first feedback signal temperature reaches the set temperature, a furnace liner heat preservation stage is entered, at which point the self-resistance rapid heating electrode heating is completely stopped.

[0011] In one embodiment, the vacuum brazing equipment for the plate-fin heat exchanger further includes a temperature control system, which comprises: an infrared thermometer output module for transmitting a second feedback signal output by the infrared thermometer; a thermocouple output module for transmitting a first feedback signal output by the thermocouple; a temperature controller for receiving the first and second feedback signals and outputting a digital signal according to a dual-feedback series control method; an analog output module for converting the digital signal into an electrical signal; and a thyristor voltage regulator module for precisely controlling the voltage according to the electrical signal, thereby controlling the self-resistance rapid heating electrode and the radiant heating.

[0012] In one embodiment, the hydraulic control system employs a pressure-temperature coupling control method to maintain the pressure at different set values ​​in different temperature ranges.

[0013] In one embodiment, the dynamic sealing structure includes a sealing seat, a sealing ring, a spacer ring, and a gland. One end of the sealing seat has an outer flange edge, which is fixed to the furnace body by bolts. The other end of the sealing seat has an inner truncated cone surface. Multiple sealing rings and spacers are stacked in sequence and pressed together by the gland. The gland is fixedly connected to the sealing seat.

[0014] In one embodiment, the upper electrode consists of an upper electrode plate, an upper electrode post, and an insulating ceramic tube. The upper electrode plate is connected to the upper insulating heat insulation plate. The lower end of the upper electrode passes through the electrode ceramic tube at the top of the furnace chamber. The upper surface of the upper electrode has countersunk holes for the upper electrode post evenly distributed, and the lower surface has countersunk holes for bolts and threaded holes for the first electrode lead-out device evenly distributed. The insulating ceramic tube has an inner hole. The upper electrode post is placed in the countersunk hole of the upper electrode post on the upper electrode plate and is in contact with the upper insulating heat insulation plate. The insulating ceramic tube is placed in the countersunk hole of the bolt on the upper electrode plate.

[0015] The lower electrode consists of a lower electrode plate, a lower electrode post, and an insulating ceramic tube. The lower electrode plate is connected to the lower insulating heat insulation plate. The upper end of the lower electrode passes through the electrode ceramic tube at the bottom of the furnace. The lower electrode plate is evenly distributed with blind holes for the lower electrode posts and countersunk holes for bolts. The lower end of the lower electrode post is located in the blind hole of the lower electrode post on the lower electrode plate, and the insulating ceramic tube is located in the countersunk hole for bolts.

[0016] In one embodiment, the first electrode lead-out device includes a first copper busbar, a first copper braid assembly, a first water-cooled sealing electrode, and a first connecting plate. The first copper busbar adopts a double lead-out structure, is rectangular in shape, and is connected to the upper electrode plate. The first copper braid assembly is located on both sides of the rectangular frame of the first copper busbar. There are two sets of the first copper braid assembly, located on the left and right sides of the rectangular frame of the first copper busbar, respectively. Each set has two copper braids. One end of each copper braid is connected to the first copper busbar, and the other end is connected to the first water-cooled sealing electrode through the first connecting plate. The length of the first copper braid assembly is greater than the working stroke of the upper water-cooled sealing voltage conductor. The first water-cooled sealing electrode is connected to the furnace body.

[0017] The second electrode lead-out device consists of a second copper busbar, a second copper braid assembly, a second water-cooled sealing electrode, and a second connecting plate. The second copper busbar adopts a double lead-out structure and is rectangular in shape, connected to the lower electrode plate. The second copper braid assembly is located on the left and right sides of the rectangular frame of the second copper busbar. There are two sets of the second copper braid assembly, located on the left and right sides of the rectangular frame of the second copper busbar respectively. Each set has two copper braids. One end of the copper braid is connected to the second copper busbar, and the other end is connected to the second water-cooled sealing electrode through the second connecting plate. The second water-cooled sealing electrode is firmly connected to the furnace body.

[0018] According to another aspect of the present invention, a brazing method for a plate-fin heat exchanger is provided. The method uses the vacuum brazing equipment provided by the present invention. The plate-fin heat exchanger brazing method specifically includes: processing the baffles, fins, and sealing strips of the plate-fin heat exchanger according to dimensional requirements and cleaning them; applying a brazing filler metal layer to the upper and lower sides of the baffles; assembling the plate-fin heat exchanger parts on a fixture, placing the upper thick plate, pad, plate-fin heat exchanger, pad, and lower thick plate sequentially from bottom to top, using screws to pass through the edge through holes of the upper thick plate, pad, and lower thick plate and fastening them with nuts at both ends; and using a material cart to move the above fixture as a whole. Place it on the lower conductive base and press it with the upper water-cooled sealed conductive head. Loosen the tooling and tighten the lower nut to maintain constant pressure. Turn on the vacuum system and evacuate to the working vacuum level. Use a dual feedback series control method to heat and maintain the temperature of the plate-fin heat exchanger. Use a pressure-temperature coupling control method to keep the pressure constant at different set values ​​in different temperature ranges. Heat the plate-fin heat exchanger to the brazing process temperature ±5℃ and hold it for 10-60 minutes to complete the brazing. Cool the welded plate-fin heat exchanger evenly to below 150℃, turn off the vacuum system, and then continue to cool it to room temperature.

[0019] In one embodiment, the pressure-temperature coupling control method sets the pressure-temperature coupling relationship as follows: temperature < 150℃, pressure 0.1 MPa; 200℃ ≤ temperature < 400℃, pressure 0.08 MPa; 400℃ ≤ temperature < 600℃, pressure 0.06 MPa; 600℃ ≤ temperature < 800℃, pressure 0.04 MPa.

[0020] The present invention has the following beneficial effects:

[0021] 1) By adopting the solution of the present invention, the existing multi-stage heat preservation heating process can be changed into a short composite heating heating process, and the temperature of the large-size titanium alloy plate-fin heat exchanger can be kept uniform throughout the heating process, thereby improving the heating efficiency.

[0022] 2) By adopting the solution of the present invention, the overall load distribution of the large-size titanium alloy plate-fin heat exchanger is uniform and adjustable and controllable during the brazing process, thus ensuring the dimensional precision requirements of the product's flatness.

[0023] 3) By adopting the solution of the present invention, the heat holding time of the large-size titanium alloy plate-fin heat exchanger at the brazing process temperature is short enough, and the stress at the weld is uniform enough, which can ensure the consistency of the brazing quality of tens of thousands of products.

[0024] 4) By adopting the solution of the present invention, heat loss is reduced by shortening the heating process time, thus reducing energy consumption.

[0025] In conjunction with the structure and method of the present invention, it will be explained how the present invention solves the following technical problems:

[0026] Compared to traditional vacuum brazing equipment, this invention adds the functions of rapid self-resistance heating and uniform ballast on the workpiece. Through the design of the conductive voltage load device and tooling, dual-feedback series control is adopted to achieve dual-heat source heating, shortening the heating process time. The pressure-temperature coupling control method ensures uniform stress and reduces deformation, improving heating efficiency and welding quality consistency. Specifically, it adds a hydraulic control system, an upper water-cooled sealed conductive voltage head, a lower conductive base, and tooling. This structure is integrated with the furnace chamber. The upper electrode of the upper water-cooled sealed conductive voltage head adopts a distributed structure, which can be moved up and down by the hydraulic control system. Combined with the tooling, it can ensure that the workpiece is always subjected to uniform stress and that the rapid self-resistance heating and energization are continuously stable. During brazing, the above structural scheme, as well as the dual-feedback series control and pressure-temperature coupling control method, can achieve rapid and uniform heating and small deformation control of the workpiece. It can also be extended to the vacuum brazing of large-size plate-fin heat exchangers used in the aerospace and marine fields, fundamentally solving the problems of low heating efficiency and difficult deformation control caused by the structural characteristics of plate-fin heat exchangers and the characteristics of vacuum radiation heating. Attached Figure Description

[0027] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0028] Figure 1 is a front view of a vacuum brazing equipment for a plate-fin heat exchanger according to a specific embodiment of the present invention;

[0029] Figure 2 is a top view of a vacuum brazing equipment for a plate-fin heat exchanger according to a specific embodiment of the present invention.

[0030] Figure 3 is a schematic diagram of the structure of the water-cooled sealed voltage conductor provided according to a specific embodiment of the present invention;

[0031] Figure 4 is an enlarged schematic diagram of the dynamic sealing structure between the upper water-cooled sealing voltage conductor and the furnace body according to a specific embodiment of the present invention;

[0032] Figure 5 is a schematic diagram of the first electrode lead-out device of the water-cooled sealed conductive voltage head provided in a specific embodiment of the present invention;

[0033] Figure 6 is a schematic diagram of the structural composition of the lower conductive base provided in a specific embodiment of the present invention;

[0034] Figure 7 is a schematic diagram of the second electrode lead-out device of the lower conductive base provided in a specific embodiment of the present invention;

[0035] Figure 8 is a schematic diagram of the tooling provided in a specific embodiment of the present invention;

[0036] Figure 9 is a schematic diagram of a titanium alloy plate-fin heat exchanger.

[0037] Figure 10 is a schematic diagram of a temperature control system for a vacuum brazing equipment for a plate-fin heat exchanger provided in a specific embodiment of the present invention.

[0038] Figure 11 is a process curve diagram of brazing titanium alloy plate-fin heat exchangers using conventional vacuum brazing equipment.

[0039] Figure 12 is a process curve diagram of brazing a titanium alloy plate-fin heat exchanger using a vacuum brazing equipment provided in a specific embodiment of the present invention.

[0040] The above-mentioned figures include the following reference numerals: 10, hydraulic control system; 11, main frame; 12, pressure head; 13, control system; 20, upper water-cooled sealing conductive pressure head; 21, water-cooled sealing pressure head seat; 211, flange; 212, pressure head column; 213, water inlet pipe; 214, water outlet pipe; 215, sealing sleeve; 216, sealing ring; 22, pressure head pad; 23, upper insulating heat insulation plate; 24, upper electrode; 241, upper electrode plate; 242, upper electrode column; 243, first insulating ceramic tube; 25, first electrode lead-out device; 251, first copper busbar; 252, first copper braid assembly; 253, first water-cooled sealing electrode; 254, first connecting plate; 30, lower conductive base; 31, base pad; 32, lower insulating heat insulation plate; 33, lower electrode; 331, lower electrode. 332. Lower electrode post; 333. Second insulating ceramic tube; 34. Second electrode lead-out device; 341. Second copper busbar; 342. Second copper braid assembly; 343. Second water-cooled sealing electrode; 344. Second connecting plate; 40. Tooling; 41. Upper thick plate; 42. Pad plate; 43. Lower thick plate; 50. Furnace body; 51. Perforated flange cover; 52. Blind flange cover; 53. Temperature control coupler; 54. Observation window; 55. Infrared thermometer; 60. Furnace liner; 61. Furnace liner frame; 62. Heat insulation screen; 63. Heat generating tube; 64. Electrode ceramic tube; 65. Observation hole; 70. Dynamic sealing structure; 71. Sealing seat; 72. Sealing ring; 73. Spacer ring; 74. Pressure cap; 80. Vacuum system; 81. Vacuum pump; 82. Vacuum valve; 83. Piping. Detailed Implementation

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0043] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0044] As shown in Figures 1 to 12, a vacuum brazing device for a plate-fin heat exchanger is provided according to a specific embodiment of the present invention. The vacuum brazing device for the plate-fin heat exchanger includes: a hydraulic control system 10, a furnace body 50, a furnace chamber 60, a dynamic sealing structure 70, a vacuum system 80, an upper water-cooled sealing voltage conductor 20, a lower conductive base 30, and a tooling 40. The hydraulic control system 10 provides constant-range and constant-pressure control for the vacuum brazing device. The furnace body 50 is fixed to the main frame 11 of the hydraulic control system 10. The furnace body 50 provides a vacuum environment and interfaces for various subsystems, and accommodates the parts to be brazed. The interfaces include a temperature control coupler 53 and an infrared thermometer 55 interface. The output signal of the temperature control coupler 53 is a first feedback signal, serving as the main temperature control feedback signal to regulate the power of each heating element 63. The output signal of the infrared thermometer 55 is a second feedback signal, used to monitor the temperature of the plate-fin heat exchanger and assist in controlling the self-resistance rapid heating of the plate-fin heat exchanger. The thermoelectric electrode power and the operating temperature of the infrared thermometer 55 are controlled by a dual-feedback series control method based on the first and second feedback signals; the furnace 60 is located inside the furnace body 50 and includes a furnace frame 61, a heat insulation screen 62, and multiple heating tapes 63, with each heating tape evenly distributed on the inner wall of the furnace 60 and capable of independent control; it is used for vacuum radiation heating and heat preservation; a dynamic sealing structure 70 is fixed to the furnace body 50 and is used to provide a translational dynamic sealing interface to maintain the system's working vacuum level; and a vacuum system 80 is connected to the furnace body 50. Next, the vacuum system is used to exhaust the gas inside the furnace body 50 to obtain a vacuum environment; the upper water-cooled sealing voltage conductor 20 is connected to the hydraulic control system 10, and its lower end passes through the top of the furnace body 50 and maintains the vacuum inside the furnace through the dynamic sealing structure 70; the upper water-cooled sealing voltage conductor 20 includes a water-cooled sealing pressure head seat 21, a pressure head pad 22, an upper insulating heat insulation plate 23, an upper electrode 24, and a first electrode lead-out device 25, wherein the water-cooled sealing pressure head seat 21, the pressure head pad 22, the upper insulating heat insulation plate 23, and the upper electrode 24 are connected in sequence, and the water-cooled sealing pressure head seat 21 includes a flange 211 and a pressure head column 25. 12. Water inlet pipe 213, water outlet pipe 214, sealing sleeve 215 and sealing ring 216. The pressure head column 212 is welded to the pressure head 12 through the flange 211. The upper end face of the sealing sleeve 215 is welded to the flange 211. The sealing sleeve 215 is a hollow round tube. The water inlet pipe 213 and the water outlet pipe 214 are respectively welded to the upper end of the outer circle of the sealing sleeve 215. The water inlet pipe 213 extends to the bottom of the sealing sleeve 215. The lower end of the inner circle of the sealing ring 216 is welded to the pressure head column 212, and the upper end of the outer circle is welded to the sealing sleeve 215. The first electrode lead-out device 25 is connected to the upper electrode 24 and is used to lead out the current of the upper water-cooled sealing conductive voltage head 20.Together with the lower conductive base 30, it is used for self-resistance rapid heating and uniform loading of the workpiece to be welded; the lower conductive base 30 includes a base pad 31, a lower insulating heat insulation plate 32, a lower electrode 33, and a second electrode lead-out device 34 connected in sequence, the second electrode lead-out device 34 being connected to the lower electrode 33 for leading out the current from the lower conductive base 30; together with the upper water-cooled sealed conductive head 20, it is used for self-resistance rapid heating and uniform loading of the workpiece to be welded; the tooling 40 is used to provide constraint for the plate-fin heat exchanger.

[0045] The system includes a hydraulic control system 10, a furnace body 50, an infrared thermometer 55, an upper water-cooled sealed conductive head assembly, and a lower conductive base 30. The hydraulic control system 10 is used to provide welding pressure for the vacuum brazing equipment. The furnace body 50 is fixed to the hydraulic control system 10. The furnace body 50 includes a temperature control coupler 53 and multiple heating cables 63. The output signal of the temperature control coupler 53 is a first feedback signal.

[0046] This configuration, through the addition of a conductive voltage-carrying device, enables rapid self-heating of the workpiece. Dual-feedback series control achieves dual-heat-source heating, shortening the heating process time and improving heating efficiency and welding quality consistency. Specifically, a hydraulic control system, an upper water-cooled sealed conductive voltage head, and a lower conductive base are added. This structure is integrated with the furnace chamber. The upper water-cooled sealed conductive voltage head assembly has multiple electrodes in a distributed structure, which can move up and down via the hydraulic control system. This ensures both uniform force on the workpiece and continuous, stable self-heating and energization. The water-cooling system effectively reduces the temperature of the electrodes and surrounding components, extending the equipment's lifespan. During brazing, the above structural scheme and dual-feedback series control enable rapid and uniform heating of the workpiece and minimal deformation control. This can be extended to vacuum brazing of large-size plate-fin heat exchangers used in the aerospace and marine industries, fundamentally solving the problems of low heating efficiency and difficult deformation control caused by the structural characteristics of plate-fin heat exchangers and the characteristics of vacuum radiation heating.

[0047] As an optional embodiment, to achieve dual-heat-source heating, the operating temperature is controlled using a dual-feedback series control method based on the first and second feedback signals. Specifically, this includes: if neither the first nor the second feedback signal temperature reaches the set temperature, the heating stage begins, where PID (Proportional Integral Derivative) control is used to simultaneously heat the heating element and the self-resistance rapid heating electrode. When the second feedback signal temperature minus the first feedback signal temperature is greater than a set first temperature difference threshold, the self-resistance rapid heating electrode stops heating. When the second feedback signal temperature minus the first feedback signal temperature is less than a set second temperature difference threshold, the self-resistance rapid heating electrode continues heating, where the first temperature difference threshold is greater than the second temperature difference threshold. When the second feedback signal temperature reaches the set temperature, the workpiece heat preservation stage begins. When the second feedback signal temperature equals the set temperature, the self-resistance rapid heating electrode stops heating. When the set temperature minus the second feedback signal temperature is greater than a set third temperature difference threshold, the self-resistance rapid heating electrode resumes heating. When the first feedback signal temperature reaches the set temperature, the furnace liner heat preservation stage begins, at which point the self-resistance rapid heating electrode completely stops heating.

[0048] According to a specific embodiment of the present invention, when the temperature of the second feedback signal reaches the set temperature of 680°C, the workpiece enters the heat preservation stage. When the temperature of the second feedback signal equals the set temperature of 680°C, the self-resistance rapid heating electrode stops heating; when the set temperature of 680°C minus the temperature of the second feedback signal is greater than the set temperature difference value of 30°C, the self-resistance rapid heating electrode resumes heating. When the temperature of the first feedback signal reaches the set temperature of 680°C, the furnace liner heat preservation stage begins, at which point the self-resistance rapid heating electrode completely stops heating.

[0049] By applying this configuration, the furnace temperature regulation method is divided into three stages—heating, workpiece heat preservation, and furnace shell heat preservation—based on the temperature range of the first and second feedback signals. The dual-heat source heating method of self-resistance rapid heating and radiation heating is controlled. The dual-heat source heating stage can be carried out in segments, and the segment temperature, heat preservation time, and number of segments can be set according to the size of the titanium alloy plate-fin heat exchanger and the type of brazing filler metal, thereby improving heating efficiency and flexibility.

[0050] As an optional embodiment, to achieve precise temperature control, as shown in Figure 10, the vacuum brazing equipment for the plate-fin heat exchanger also includes a temperature control system. The temperature control system includes an infrared thermometer output module, a thermocouple output module, a temperature controller, an analog output module, and a thyristor voltage regulation module. The infrared thermometer output module transmits the second feedback signal output by the infrared thermometer 55; the thermocouple output module transmits the first feedback signal output by the thermocouple; the temperature controller receives the first and second feedback signals and outputs a digital signal according to the dual-feedback series control method; the analog output module converts the digital signal into an electrical signal; and the thyristor voltage regulation module precisely controls the voltage based on the electrical signal, thereby controlling the self-resistance rapid heating electrode and radiant heating.

[0051] By employing this configuration, the temperature control system can accurately monitor the furnace temperature and automatically adjust it according to the preset dual-feedback series control method, thereby maintaining a stable temperature environment and achieving automatic and precise temperature control.

[0052] As an optional embodiment, to ensure uniform stress and improve weld quality consistency, the hydraulic control system 10 employs a pressure-temperature coupling control method, maintaining constant pressure at different set values ​​across different temperature ranges. This configuration ensures uniform stress, reduces deformation, and improves heating efficiency and weld quality consistency.

[0053] As an optional embodiment, as shown in Figure 4, to achieve effective sealing, the dynamic sealing structure 70 includes a sealing seat 71, sealing rings 72, spacer rings 73, and a pressure cap 74. One end of the sealing seat 71 has an outer flange edge, which is fixed to the furnace body 50 by bolts. The other end of the sealing seat 71 has an inner truncated cone surface, on which multiple sealing rings 72 and spacer rings 73 are stacked sequentially and pressed together by the pressure cap 74, which is fixedly connected to the sealing seat 71. This configuration can meet the special sealing requirements of the vacuum environment in vacuum brazing equipment, improving the overall reliability and stability of the equipment.

[0054] As an optional embodiment, as shown in Figure 3, to effectively achieve electrical insulation and heat insulation between the electrode and the surrounding environment, and to enhance the safety and stability of the equipment, the upper electrode 24 is composed of an upper electrode plate 241, an upper electrode post 242, and a first insulating ceramic tube 243. The upper electrode plate 241 is connected to the upper insulating heat insulation plate 23. The lower end of the upper electrode 24 passes through the electrode ceramic tube 64 at the top of the furnace liner 60. The upper surface of the upper electrode 24 has countersunk holes for the upper electrode post, and the lower surface has countersunk holes for bolts and threaded holes for the first electrode lead-out device 25. The first insulating ceramic tube 243 has an inner hole. The upper electrode post 242 is placed in the countersunk hole of the upper electrode post on the upper electrode plate 241 and is in contact with the upper insulating heat insulation plate 23. The first insulating ceramic tube 243 is placed in the countersunk hole of the bolt on the upper electrode plate. The mounting bolt passes through the inner hole of the first insulating ceramic tube 243, the through hole of the upper insulating heat insulation plate, and the through hole of the pressure head pad in sequence, and is fastened to the water-cooled sealing pressure head seat 21. The lower electrode 33 is composed of a lower electrode plate 331, a lower electrode post 332, and a second insulating ceramic tube 333. The lower electrode plate 331 is connected to the lower insulating heat insulation plate 32. The upper end of the lower electrode 33 passes through the electrode ceramic tube 64 at the bottom of the furnace 60. The lower electrode plate 331 is evenly distributed with blind holes for the lower electrode post and countersunk holes for bolts. The lower end of the lower electrode post 332 is set in the blind hole of the lower electrode post of the lower electrode plate 331. The first insulating ceramic tube 333 is set in the countersunk hole for bolts. The mounting bolt passes through the first insulating ceramic tube 333 and the through hole of the lower insulating heat insulation plate 32 in sequence and is fastened to the base pad 31.

[0055] As an optional embodiment, as shown in Figures 5 to 7, to meet the requirements of vacuum brazing equipment for high-current active electrode connections, the first electrode lead-out device 25 includes a first copper busbar 251, a first copper braid assembly 252, a first water-cooled sealing electrode 253, and a first connecting plate 254. The first copper busbar 251 adopts a double lead-out structure, is rectangular in shape, and is connected to the upper electrode plate 241. The first copper braid assembly 252 is located on both sides of the rectangular frame of the first copper busbar 251. There are two sets of the first copper braid assembly 252, located on the left and right sides of the rectangular frame of the first copper busbar 251, respectively. Each set has two copper braids. One end of the copper braid is connected to the first copper busbar 251, and the other end is connected to the first water-cooled sealing electrode 253 through the first connecting plate 254. The first copper braid assembly 252 is longer than the working stroke of the upper water-cooled sealed conductive head 20. The first water-cooled sealed electrode 253 is connected to the furnace body 50. The second electrode lead-out device 34 consists of a second copper busbar 341, a second copper braid assembly 342, a second water-cooled sealed electrode 343, and a second connecting plate 344. The second copper busbar 341 adopts a double lead-out structure, is rectangular in shape, and is connected to the lower electrode plate 331. The second copper braid assembly 342 is located on the left and right sides of the rectangular frame of the second copper busbar 341. There are two sets of the second copper braid assembly 342, located on the left and right sides of the rectangular frame of the second copper busbar 341, respectively. Each set has two copper braids. One end of the copper braid is connected to the second copper busbar 341, and the other end is connected to the second water-cooled sealed electrode 343 through the second connecting plate 344. The second water-cooled sealed electrode 343 is tightly connected to the furnace body 50. The second water-cooled sealed electrode 343 is tightly connected to the right-angle electrode seat on the furnace body 50 by bolts.

[0056] This configuration, employing a dual-lead structure, enhances the stability and reliability of the electrode lead-out device. It also provides more flexible installation and connection methods, better adapting to complex electrical connection requirements and reducing resistance and heat accumulation. The water-cooled sealed electrode not only provides excellent electrical connection but also effectively reduces the temperature of the electrode and surrounding components through the water-cooling system, meeting the cooling requirements of vacuum brazing equipment.

[0057] As an optional embodiment, as shown in Figure 8, in order to assemble the workpiece and ensure uniform contact stress, the tooling 40 includes an upper thick plate 41, a pad 42 and a lower thick plate 43. The upper thick plate 41 and the lower thick plate 43 are tightly fitted to the upper electrode post 242 and the lower electrode 33, respectively. The edges of the upper thick plate 41, the pad 42 and the lower thick plate 43 are fixedly connected, and the lower thick plate 43 is placed on the lower conductive base 30.

[0058] Traditional brazing with specialized tooling, especially for large heat exchangers, often results in uneven contact stress between the workpiece's edges and core, provided only during initial assembly. Furthermore, the intense thermal expansion under high-constraint conditions during heating makes uncontrollable deformation more likely, leading to dimensional deviations or weak local weld joints. This new configuration, however, ensures that the brazing process remains within a suitable stress range.

[0059] As an optional embodiment, according to another aspect of the present invention, a brazing method for a plate-fin heat exchanger is provided. The plate-fin heat exchanger's baffles, fins, and sealing strips are machined according to dimensional requirements and cleaned. A brazing filler layer is applied to the upper and lower sides of the baffles. The plate-fin heat exchanger components are assembled on a fixture 40, with the upper thick plate 41, pad 42, plate-fin heat exchanger, pad 42, and lower thick plate 43 arranged sequentially from bottom to top. Screws are passed through the edge through-holes of the upper thick plate 41, pad 42, and lower thick plate 43, and secured with nuts at both ends. The fixture 40 is then placed entirely on a lower conductive base using a material cart. Place the plate-fin heat exchanger on the 30th and press it with the water-cooled sealing voltage head 20. Loosen the tooling 40 and tighten the lower nut to maintain constant pressure. Turn on the vacuum system 80 and evacuate to the working vacuum level. Use a dual feedback series control method to heat and maintain the plate-fin heat exchanger. Use a pressure-temperature coupling control method to keep the pressure constant at different set values ​​in different temperature ranges. Heat the plate-fin heat exchanger to the brazing process temperature ±5℃ and hold it for 10-60 minutes to complete the brazing. Cool the welded plate-fin heat exchanger evenly to below 150℃, turn off the vacuum system 80, and then continue to cool it to room temperature.

[0060] By applying this configuration, the vacuum brazing method for plate-fin heat exchangers of the present invention can improve the load distribution of the brazed workpiece, ensure uniform stress and controllable deformation throughout the brazing process, and improve the dimensional accuracy of the product. At the same time, it adds the self-resistance heating function of the workpiece to the function of radiation heating, which solves the problems of low heating efficiency and difficulty in deformation control caused by the structural characteristics of plate-fin heat exchangers and the characteristics of vacuum radiation heating.

[0061] As an optional embodiment, to meet the requirements of vacuum brazing equipment for the uniformity of welding stress and deformation control of plate-fin heat exchangers, a pressure-temperature coupling control method is adopted. The pressure-temperature coupling relationship is set as follows: temperature < 150℃, pressure 0.1 MPa; 200℃ ≤ temperature < 400℃, pressure 0.08 MPa; 400℃ ≤ temperature < 600℃, pressure 0.06 MPa; 600℃ ≤ temperature < 800℃, pressure 0.04 MPa.

[0062] To provide a further understanding of the present invention, the vacuum brazing equipment and method for plate-fin heat exchangers of the present invention will be described in detail below with reference to Figures 1 to 12. As shown in Figures 1 to 10, a vacuum brazing equipment for plate-fin heat exchangers includes:

[0063] The hydraulic control system 10 enables constant range and constant pressure control of the upper water-cooled sealing conductive head. The hydraulic control system 10 includes a main frame 11, a pressure head 12, and a control system 13. The pressure head 12 is located inside the main frame 11, and the control system 13 is electrically connected to the pressure head 12.

[0064] The furnace body 50 is a sealed chamber that can withstand both negative and positive pressure. The furnace body 50 is fixed to the main frame 11 of the hydraulic control system 10 and is equipped with interfaces for various subsystems, including a perforated flange cover 51 for connecting the top pressure head, a blind flange cover 52 for fixed installation at the bottom, a temperature control coupler 53, an observation window 54 at the front, and an infrared thermometer 55.

[0065] The furnace chamber 60 is located inside the furnace body 50. The furnace chamber 60 includes a furnace chamber frame 61, a heat insulation screen 62, multiple heating tapes 63, electrode ceramic tubes 64, and an observation hole 65. The heat insulation screen 62 is installed inside the furnace chamber frame 61. The heating tapes 63 are installed inside the heat insulation screen 62 of the furnace chamber frame 61. The heating tapes 63 are serpentine in shape and are placed inside the square furnace chamber frame 61. They are fixed on the top, bottom, left, and right sides, or on the top, bottom, left, right, front, and back sides. The output power of the heating tape on each side can be independently controlled, which solves the problem of uneven temperature distribution caused by the introduction of the top and bottom electrodes.

[0066] The dynamic sealing structure 70 includes a sealing seat 71, a sealing ring 72, a spacer ring 73, and a pressure cap 74. The upper end of the sealing seat 71 has an outer flange edge, which is fixed to the furnace body 50 by bolts. The lower end has an inner circular platform. Multiple sealing rings 72 and spacer rings 73 are stacked in sequence and pressed by the lower end face of the pressure cap 74. The pressure cap 74 is connected to the sealing seat 71 by bolts.

[0067] Vacuum system 80 includes vacuum pump 81, vacuum valve 82 and pipeline 83. Vacuum pump 81 is connected to furnace body 50 through pipeline 83, and vacuum valve 82 is installed on pipeline 83.

[0068] The upper water-cooled sealed voltage conductor 20 is mechanically connected to the pressure head 12 of the hydraulic control system 10, and maintains the vacuum degree inside the furnace through the dynamic sealing structure 70. The upper water-cooled sealed voltage conductor 20 includes a water-cooled sealed pressure head seat 21, a pressure head pad 22, an upper insulating heat insulation plate 23, an upper electrode 24, and a first electrode lead-out device 25.

[0069] The water-cooled sealing head seat 21 is welded together from a flange 211, a head column 212, an inlet pipe 213, an outlet pipe 214, a sealing sleeve 215, and a sealing ring 216. The head column 212 is a solid cylinder with the flange 211 welded to it, which is fastened to the head 12 with bolts. The sealing sleeve 215 is a hollow cylindrical tube, with the head column 212 located inside it. Its upper end face is welded to the flange 211, and the inlet pipe 213 and outlet pipe 214 are welded to the upper end of the outer circle, respectively. Water pipe 214, wherein the inlet of water pipe 213 extends to the bottom of sealing sleeve 215, the lower end of the inner circle of sealing ring 216 is welded to pressure head column 212, and the upper end of the outer circle is welded to sealing sleeve 215, thereby forming a ring-shaped closed cavity that can be cooled by water; the bottom of water-cooled sealing pressure head seat 21 passes through the perforated flange cover 51 located on the top of the vacuum brazing equipment furnace body, and a dynamic sealing structure 70 is adopted between it and the furnace body 50, which can realize the reliable movement of the upper water-cooled sealing pressure head within the working stroke range.

[0070] Both the pressure head pad 22 and the upper insulating heat insulation plate 23 have through holes and are fastened to the lower end of the water-cooled sealing pressure head seat 21 by bolts. The lower end face of the pressure head pad 22 is provided with the upper insulating heat insulation plate 23, and the upper electrode 24 is provided on the upper insulating heat insulation plate 23.

[0071] The upper electrode 24 includes an upper electrode plate 241, an upper electrode post 242, and an insulating ceramic tube 243. The upper electrode plate 241 is located below the upper insulating heat insulation plate 23. Its upper surface is evenly distributed with countersunk holes for the upper electrode posts, and its lower surface is evenly distributed with countersunk holes for bolts and threaded holes for the first electrode lead-out device 25. The upper electrode post 242 is placed in the countersunk holes for the upper electrode posts on the upper electrode plate 241 and is in contact with the upper insulating heat insulation plate 23. The upper electrode post 242 is a cylindrical long rod with the larger end facing upwards, and its upper end face is higher than the upper plane of the upper electrode plate 241. The insulating ceramic tube 243 has an inner hole and is placed in the countersunk holes for bolts on the upper electrode plate. The mounting bolts pass through the inner hole of the insulating ceramic tube, the through hole of the upper insulating heat insulation plate, and the through hole of the pressure head pad in sequence, and are fastened to the water-cooled sealing pressure head seat 21. The lower end of the upper electrode 24 passes through the electrode ceramic tube 64 at the top of the furnace liner 60.

[0072] The first electrode lead-out device 25 can achieve high current power supply of over 8000A and ensure the safe and reliable movement of the water-cooled sealed conductive head. The first electrode lead-out device 25 includes a first copper busbar 251, a first copper braid assembly 252, a first water-cooled sealed electrode 253, and a first connecting plate 254. The first copper busbar 251 adopts a double lead-out structure, is rectangular in shape, and is placed below the upper electrode plate 241, connected to the upper electrode plate 241 by bolts. There are two sets of the first copper braid assembly 252, located on the left and right sides of the rectangular frame of the first copper busbar 251, respectively. Each set of the first copper braid assembly 252 has two copper braids, one end of which is connected to the first copper busbar 251, and the other end is connected to the first water-cooled sealed electrode 253 via the first connecting plate 254. The first copper braid assembly 252 is connected to the working stroke of the water-cooled sealed voltage conductor 20. The first water-cooled sealed electrode 253 is fastened to the electrode seat on the furnace body 50 by bolts. The motor seat can be a right-angle structure. One end face of the first connecting plate 254 is connected to the first copper braid 252. After the water-cooled sealed voltage conductor 20 is installed, it passes through the right-angle electrode seat on the furnace body 50 together with the first copper braid 252. The other end face of the first connecting plate 254 is fastened to the installed water-cooled sealed electrode 253 by bolts. The first connecting plate 254 is a 90° bent part.

[0073] The lower conductive base 30 is welded to the bottom flange blind cover 52 of the furnace body 50; the lower conductive base 30 includes a base pad 31, a lower insulating heat insulation plate 32, a lower electrode 33, and a second electrode lead-out device 34.

[0074] The base plate 31 has threaded holes and is welded to the flange blind cover 52. The lower insulating heat insulation plate 32 has through holes and is located above the base plate 31. Both the upper insulating heat insulation plate 23 and the lower insulating heat insulation plate 32 are heat resistant to temperatures above 300℃.

[0075] The lower electrode 33 is bolted through the through holes of the insulating ceramic tube and the lower insulating heat insulation plate 32, and then fastened to the base plate 31. The lower electrode 33 includes a lower electrode plate 331, a lower electrode post 332, and an insulating ceramic tube 333. The lower electrode plate 331 has blind holes for the lower electrode posts and countersunk holes for bolts evenly distributed on it. The lower end of the lower electrode post 332 is set in the blind hole of the lower electrode post in the lower electrode plate 331, and the upper end passes through the electrode ceramic tube 64 at the bottom of the furnace 60. The lower electrode post 332 is a long rod of equal diameter, with the lower end set in the blind hole of the lower electrode post in the lower electrode plate 331 and the upper end passing through the electrode ceramic tube 64 at the bottom of the furnace 60. The insulating ceramic tube 333 is set in the countersunk hole for bolts and is a sleeve with a shoulder, with the larger end facing upwards.

[0076] The second electrode lead-out device 34 can provide high-current power supply of over 8000A. The second electrode lead-out device 34 includes a second copper busbar 341, a second copper braid assembly 342, a second water-cooled sealed electrode 343, and a second connecting plate 344. The second copper busbar 341 adopts a double lead-out structure, is rectangular in shape, and is placed above the lower electrode plate 331, connected to the lower electrode plate 331 by bolts. There are two sets of second copper braids 342, located on the left and right sides of the rectangular frame of the second copper busbar 341, respectively. Each set of second copper braid assembly 342 has two copper braids, one end of which is connected to the second copper busbar 341, and the other end is connected to the second connecting plate 344. The second water-cooled sealing electrode 343 is connected to the right-angle electrode seat on the furnace body 50 by bolts. The second connecting plate 344 is a 90° bent piece. One end face of the second connecting plate 344 is connected to the second copper braid 342. After the upper water-cooled sealing conductive head 20 is installed, it and the second copper braid 342 pass through the right-angle electrode seat on the furnace body 50. The other side of the second connecting plate 344 is connected to the installed second water-cooled sealing electrode 343 by bolts. The second connecting plate 344 is a 90° bent piece.

[0077] The fixture 40, comprising an upper thick plate 41, a pad 42, and a lower thick plate 43, is located within the effective heating working area of ​​the furnace 60 between the upper water-cooled sealed conductive voltage head 20 and the lower conductive base 30. The upper thick plate 41 and the lower thick plate 43 have smooth surfaces, are parallel on both sides, and have through holes along their edges, respectively, to tightly fit against the upper electrode post 242 and the lower electrode post 332. The pad 42 has a smooth surface, is parallel on both sides, and has through holes along its edges; it is made of a conductive material that does not chemically react with the plate-fin heat exchanger. The edges of the upper thick plate 41, the pad 42, and the lower thick plate 43 all have through holes. A screw passes through these through holes and is secured with a nut. The upper water-cooled sealed conductive voltage head 20 is placed on the upper thick plate 41, and the lower thick plate 43 is placed on the lower conductive base 30. During loading, the lower thick plate 43, pad 42, plate-fin heat exchanger, pad 42, and upper thick plate 41 are placed sequentially from bottom to top. A screw is passed through the edge through-hole and secured with nuts at both ends. The entire assembly is then placed on the lower conductive base, with the upper water-cooled sealing voltage head pressing against the upper thick plate. The lower nut is then loosened. During operation, constant pressure control is achieved by the control system. During brazing, the hydraulic control system presses the plate-fin heat exchanger firmly through the upper water-cooled sealing voltage head, lower conductive base, and tooling, achieving heating and insulation through radiant heating and self-resistance heating.

[0078] The temperature control system includes a temperature control coupler 53, a radiant heating device, an infrared thermometer 55, a rapid heating resistor, a thermocouple output module, an infrared thermometer output module, a temperature controller, an analog output module, and a thyristor voltage regulation module. The output signal of the thermocouple 53 is the first feedback signal, which serves as the main temperature control feedback signal to regulate the power of each heating element 63 of the radiant heating device. The output signal of the infrared thermometer 55 is the second feedback signal, used to monitor the temperature of the rapid heating resistance plate-fin heat exchanger and assist in controlling the power of the self-resistance rapid heating electrodes 24 and 33 of the plate-fin heat exchanger. The operating temperature is controlled by a dual-feedback series control method based on the first and second feedback signals. The thermocouple output module is used to transmit the first feedback signal output by the thermocouple 53, the infrared thermometer output module is used to transmit the second feedback signal output by the infrared thermometer 55, the temperature controller is used to receive the first and second feedback signals, and outputs a digital signal according to the dual-feedback series control method. The analog output module converts the digital signal into an electrical signal, and the thyristor voltage regulation module uses the electrical signal to achieve precise voltage control, thereby realizing the control of the radiant heating and self-resistance rapid heating electrodes.

[0079] This configuration allows for the use of self-resistance rapid heating to heat the titanium alloy plate-fin heat exchanger in the low-temperature zone, with radiant heating following the furnace heating. In the high-temperature zone, radiant heating is used alone to heat the titanium alloy plate-fin heat exchanger to the brazing temperature. This method significantly improves the brazing efficiency of the vacuum brazing equipment and solves brazing quality problems such as severe surface embrittlement, easy cracking defects, and severe thin-wall corrosion caused by the large temperature difference between the core and the surface and the long holding time at the brazing temperature.

[0080] Figures 11 to 13 show specific embodiments of the brazing method for titanium alloy plate-fin heat exchangers.

[0081] The workpiece dimensions are 300mm (width) × 500mm (length) × 300mm (height).

[0082] The brazing method of the vacuum brazing equipment and method for a plate-fin heat exchanger in this embodiment is as follows:

[0083] 1) Process the titanium alloy plate-fin heat exchanger parts such as baffles, fins, seals, and guide vanes according to the size requirements, and clean them. The material is TC4 titanium alloy.

[0084] 2) Assemble components such as fins, baffles, seals, and guide vanes to form the heat exchanger core, wherein the baffles contain a certain thickness of amorphous titanium brazing filler metal layer on both the upper and lower sides;

[0085] 3) Assemble the plate-fin heat exchanger parts on the tooling 40, and place the upper thick plate 41, pad 42, plate-fin heat exchanger, pad 42 and lower thick plate 43 in sequence from bottom to top. Use screws to pass through the edge through holes of the upper thick plate 41, pad 42 and lower thick plate 43 and fasten them with nuts at the upper and lower ends.

[0086] 4) Place the above tooling 40 onto the lower conductive base 30 using a material cart, and press it with the upper water-cooled sealed conductive head 20. Loosen the tooling 40 and tighten the lower nut to keep the pressure constant at 0.1MPa.

[0087] 5) Close the furnace door, turn on the vacuum system, and evacuate to 5×10-3 Pa;

[0088] 6) The vacuum brazing furnace heats the furnace chamber and the titanium alloy plate-fin heat exchanger through radiation heating. Simultaneously, the titanium alloy plate-fin heat exchanger itself is also heated via rapid resistance heating. The self-resistance rapid heating power supply has a voltage of 5V and a current of 8000A. During the dual-heat source heating stage, the total heating rate of the titanium alloy plate-fin heat exchanger reaches 45.3℃ / min, while maintaining a constant pressure of 0.08MPa.

[0089] In the dual-heat-source heating stage, as shown in Figure 10, a dual-feedback series control strategy is implemented using the same temperature controller. The temperature-controlling thermocouple serves as the main temperature control feedback signal to control the radiant heating component, while the infrared thermometer serves as the auxiliary temperature control feedback signal connected to a specific port of the temperature controller to assist in controlling the self-resistance rapid heating component.

[0090] Specifically, the first feedback signal is a temperature control coupler located near the effective working area of ​​the furnace shell, installed and fixed on the furnace body, used to regulate the heating power of each surface and precisely control the furnace temperature uniformity; the second feedback signal is an infrared thermometer located at the front of the furnace body, which monitors the temperature of the plate-fin heat exchanger through the observation window and furnace shell through-hole, used to assist in controlling the power of the self-resistance rapid heating electrode of the plate-fin heat exchanger; the two temperature feedback signals are simultaneously connected to specific ports of the temperature controller and compared. During the heating stage, if neither the first nor the second feedback signal temperature reaches the set temperature of 680℃, PID control is used to simultaneously heat the heating element and the self-resistance rapid heating electrode. When the difference between the second and first feedback signal temperatures exceeds the set temperature difference value of 100℃, the self-resistance rapid heating electrode stops heating. When the difference between the second and first feedback signal temperatures is less than the set temperature difference value of 30℃, the self-resistance rapid heating electrode continues heating. When the second feedback signal temperature reaches the set temperature of 680℃, the workpiece heat preservation stage begins, and the self-resistance rapid heating electrode stops heating. If the difference between the set temperature and the second feedback signal temperature exceeds the set temperature difference value of 30℃, the self-resistance rapid heating electrode resumes heating. When the first feedback signal temperature reaches the set temperature of 680℃, the furnace liner heat preservation stage begins, at which point the self-resistance rapid heating electrode completely stops heating.

[0091] The dual-heat-source heating stage can be carried out in segments. The segment temperature, holding time, and number of segments can be set according to the size of the titanium alloy plate-fin heat exchanger and the type of brazing filler metal.

[0092] 7) When the temperature of the titanium alloy plate-fin heat exchanger reaches 680℃, stop applying the current. When the workpiece temperature is lower than the furnace temperature, apply the current again. Repeat this cycle until the furnace temperature and the titanium alloy plate-fin heat exchanger temperature both rise to 680℃. Hold the temperature for 25 minutes to make the temperature of each part of the brazed part uniform. This dual heat source heating stage can be carried out in stages.

[0093] 8) The titanium alloy plate-fin heat exchanger is heated by single radiation heating at a rate of 10℃ / min to 780℃, held for 80min, then heated at a rate of 10℃ / min to 840℃, held for 60min, and finally heated at a rate of 10℃ / min to the optimal brazing temperature of 920℃, with an optimal brazing time of 30min.

[0094] 9) Quickly cool the welded titanium alloy plate-fin heat exchanger to below 150°C and shut down the vacuum system to prevent oxidation and discoloration;

[0095] 10) Remove the titanium alloy plate-fin heat exchanger after the temperature drops to room temperature.

[0096] As shown in Figures 11 and 12, the traditional vacuum brazing process curve for the titanium alloy plate-fin heat exchanger (dimensions W×L×H, 300mm×500mm×300mm) in this embodiment takes 1740 minutes for the entire production cycle, with a product flatness of 8mm / m. The dual-heat-source vacuum brazing process curve for the titanium alloy plate-fin heat exchanger (dimensions W×L×H, 300mm×500mm×300mm) using the equipment of this invention takes 870 minutes for the entire production cycle, with a product flatness of 3mm / m, improving manufacturing efficiency by 50% and deformation control accuracy by 62.5%.

[0097] The vacuum brazing method for plate-fin heat exchangers of this invention first loads the plate-fin heat exchanger between the upper water-cooled sealed conductive head and the lower conductive base of the equipment using tooling. Then, it automatically achieves rapid self-resistance heating and uniform ballast loading of the workpiece using a dual-feedback series control and pressure-temperature coupling control method. Based on the vacuum brazing method proposed in this invention, the manufacturing efficiency of the brazing process for titanium alloy plate-fin heat exchangers is improved by 50%, and the deformation control accuracy is improved by 62.5%, fundamentally solving the problems of low heating efficiency and difficult deformation control caused by the structural characteristics of plate-fin heat exchangers and the characteristics of vacuum radiation heating. This invention has significant engineering application value in the vacuum brazing of large-size plate-fin heat exchangers used in the aerospace and marine fields.

[0098] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms 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 the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0099] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0100] Furthermore, it should be noted that the use of terms such as "one" and "two" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

A vacuum brazing device for plate-fin heat exchangers, characterized in that... The vacuum tube of the plate-fin heat exchanger Welding equipment includes: A hydraulic control system (10) is provided for providing constant stroke and constant pressure control for the vacuum brazing equipment; The furnace body (50) is fixed on the main frame (11) of the hydraulic control system (10). The furnace body (50) is used to provide a vacuum environment and interfaces for various subsystems and to accommodate the parts to be welded. The interfaces include a temperature control coupler (53) and an infrared thermometer (55) interface. The output signal of the temperature control coupler (53) is a first feedback signal, which serves as the main temperature control feedback signal to regulate the power of each heating element (63). The output signal of the infrared thermometer (55) is a second feedback signal, which is used to monitor the temperature of the plate-fin heat exchanger and assist in controlling the power of the self-resistance rapid heating electrode of the plate-fin heat exchanger. The temperature inside the furnace body is controlled by a dual feedback series control method based on the first feedback signal and the second feedback signal. Furnace chamber (60), the furnace chamber (60) is set inside the furnace body (50), the furnace chamber (60) includes a furnace chamber frame (61), a heat insulation screen (62) and multiple heating tapes (63), the heating tapes (63) of each zone are evenly distributed on the inner wall of the furnace chamber and can be independently controlled; used for vacuum radiation heating and heat preservation; A dynamic sealing structure (70) is fixed to the furnace body (50). The dynamic sealing structure (70) is used to provide a translational sealing interface to maintain the working vacuum of the system. A vacuum system (80) is connected to the furnace body (50) and is used to exhaust the gas inside the furnace body (50) to obtain a vacuum environment; The upper water-cooled sealing voltage conductor (20) is connected to the hydraulic control system (10). Its lower end passes through the top of the furnace body (50) and maintains the vacuum inside the furnace through the dynamic sealing structure (70). The upper water-cooled sealing voltage conductor (20) includes a water-cooled sealing pressure head seat (21), a pressure head pad (22), an upper insulating heat insulation plate (23), an upper electrode (24), and a first electrode lead-out device (25). The water-cooled sealing pressure head seat (21), pressure head pad (22), upper insulating heat insulation plate (23), and upper electrode (24) are connected in sequence. The water-cooled sealing pressure head seat (21) includes a flange (211), a pressure head column (212), a water inlet pipe (213), a water outlet pipe (214), a sealing sleeve (215), and a sealing ring. (216) The pressure head column (212) is welded to the pressure head (12) through the flange (211). The upper end face of the sealing sleeve (215) is welded to the flange (211). The sealing sleeve (215) is a hollow round tube. The upper end of the outer circle of the sealing sleeve (215) is welded with the water inlet pipe (213) and the water outlet pipe (214). The water inlet pipe (213) extends to the bottom of the sealing sleeve (215). The lower end of the inner circle of the sealing ring (216) is welded to the pressure head column (212), and the upper end of the outer circle is welded to the sealing sleeve (215). The first electrode lead-out device (25) is connected to the upper electrode (24) and is used to lead out the current of the upper water-cooled sealing conductive voltage head (20). Together with the lower conductive base (30), it is used for the self-resistance rapid heating and uniform loading of the workpiece to be welded. The lower conductive base (30) includes a base pad (31), a lower insulating heat insulation plate (32), a lower electrode (33), and a second electrode lead-out device (34) connected in sequence. The second electrode lead-out device (34) is connected to the lower electrode (33) and is used to lead out the current of the lower conductive base (30). Together with the upper water-cooled sealed conductive head (20), it is used for self-resistance rapid heating and uniform loading of the workpiece to be welded. Tooling (40) is used to provide constraints for the plate-fin heat exchanger. A vacuum brazing device for plate-fin heat exchangers according to claim 1, characterized in that, The operating temperature is controlled using a dual-feedback series control method based on the first feedback signal and the second feedback signal, specifically including: If neither the first feedback signal nor the second feedback signal temperature reaches the set temperature, the heating stage begins. PID control is used to simultaneously heat the heating element and the self-resistance rapid heating electrode. When the second feedback signal temperature minus the first feedback signal temperature is greater than the set first temperature difference threshold, the heating of the self-resistance rapid heating electrode is stopped. When the second feedback signal temperature minus the first feedback signal temperature is less than the set second temperature difference threshold, the heating of the self-resistance rapid heating electrode is controlled to continue. The first temperature difference threshold is greater than the second temperature difference threshold. When the temperature of the second feedback signal reaches the set temperature, the workpiece heat preservation stage begins. When the temperature of the second feedback signal equals the set temperature, the self-resistance rapid heating electrode stops heating. When the set temperature minus the temperature of the second feedback signal is greater than the set third temperature difference threshold, the self-resistance rapid heating electrode resumes heating. When the temperature of the first feedback signal reaches the set temperature, the furnace liner insulation stage begins, at which point the self-resistance rapid heating electrode heating is completely stopped. A vacuum brazing device for a plate-fin heat exchanger according to claim 2, characterized in that, The vacuum brazing equipment for the plate-fin heat exchanger also includes a temperature control system, which comprises: Infrared thermometer output module, the infrared thermometer output module is used to transmit the second feedback signal output by the infrared thermometer (55); Thermocouple output module, wherein the thermocouple output module is used to transmit the first feedback signal output by the temperature control coupler; A temperature controller, which receives the first feedback signal and the second feedback signal, and outputs a digital signal according to the dual feedback series control method; The analog output module converts the digital signal into an electrical signal; The thyristor voltage regulator module achieves precise voltage control based on the electrical signal, thereby controlling the self-resistance rapid heating electrode and radiant heating. A vacuum brazing device for plate-fin heat exchangers according to claim 1, characterized in that, The hydraulic control system (10) adopts a pressure-temperature coupling control method to keep the pressure constant at different set values ​​in different temperature ranges. A vacuum brazing device for plate-fin heat exchangers according to claim 1, characterized in that, The dynamic sealing structure (70) includes a sealing seat (71), a sealing ring (72), a spacer ring (73), and a pressure cap (74). One end of the sealing seat (71) has an outer flange edge, which is fixed to the furnace body (50) by bolts. The other end of the sealing seat (71) has an inner circular platform. Multiple sealing rings (72) and spacer rings (73) are stacked in sequence and pressed by the pressure cap (74). The pressure cap (74) is fixedly connected to the sealing seat (71). A vacuum brazing device for plate-fin heat exchangers according to claim 1, characterized in that, The upper electrode (24) is composed of an upper electrode plate (241), an upper electrode post (242) and a first insulating ceramic tube (243). The upper electrode plate (241) is connected to the upper insulating heat insulation plate (23). The lower end of the upper electrode (24) passes through the electrode ceramic tube (64) at the top of the furnace shell (60). The upper surface of the upper electrode (24) is evenly distributed with countersunk holes for the upper electrode post, and the lower surface is evenly distributed with countersunk holes for bolts and threaded holes for the first electrode lead-out device (25). The first insulating ceramic tube (243) has an inner hole. The upper electrode post (242) is placed in the countersunk hole for the upper electrode post on the upper electrode plate (241) and is in contact with the upper insulating heat insulation plate (23). The first insulating ceramic tube (243) is placed in the countersunk hole for bolts on the upper electrode plate. The lower electrode (33) is composed of a lower electrode plate (331), a lower electrode post (332), and a second insulating ceramic tube (333). The lower electrode plate (331) is connected to the lower insulating heat insulation plate (32). The upper end of the lower electrode (33) passes through the electrode ceramic tube (64) at the bottom of the furnace shell (60). The lower electrode plate (331) is evenly distributed with blind holes for the lower electrode post and countersunk holes for bolts. The lower end of the lower electrode post (332) is set in the blind hole of the lower electrode post of the lower electrode plate (331). The second insulating ceramic tube (333) is set in the countersunk hole for bolts. A vacuum brazing device for a plate-fin heat exchanger according to claim 6, characterized in that, The first electrode lead-out device (25) includes a first copper busbar (251), a first copper braid assembly (252), a first water-cooled sealing electrode (253), and a first connecting plate (254). The first copper busbar (251) adopts a double lead-out structure, is rectangular in shape, and is connected to the upper electrode plate (241). The first copper braid assembly (252) is located on both sides of the rectangular frame of the first copper busbar (251). There are two sets of the first copper braid assembly (252), which are located on the left and right sides of the rectangular frame of the first copper busbar (251), respectively. Each set has two copper braids. One end of the copper braid is connected to the first copper busbar (251), and the other end is connected to the first water-cooled sealing electrode (253) through the first connecting plate (254). The length of the first copper braid assembly (252) is greater than the working stroke of the upper water-cooled sealing voltage head (20). The first water-cooled sealing electrode (253) is connected to the furnace body (50). The second electrode lead-out device (34) consists of a second copper busbar (341), a second copper braid assembly (342), a second water-cooled sealing electrode (343), and a second connecting plate (344). The second copper busbar (341) adopts a double lead-out structure, is rectangular in shape, and is connected to the lower electrode plate (331). The second copper braid assembly (342) is located on the left and right sides of the rectangular frame of the second copper busbar (341). There are two sets of the second copper braid assembly (342), which are located on the left and right sides of the rectangular frame of the second copper busbar (341), respectively. Each set has two copper braids. One end of the copper braid is connected to the second copper busbar (341), and the other end is connected to the second water-cooled sealing electrode (343) through the second connecting plate (344). The second water-cooled sealing electrode (343) is tightly connected to the furnace body (50). A vacuum brazing device for plate-fin heat exchangers according to claim 1, characterized in that, The tooling (40) includes an upper thick plate (41), a pad (42) and a lower thick plate (43). The upper thick plate (41) and the lower thick plate (43) are tightly fitted to the upper electrode post (242) and the lower electrode (33) respectively. The edges of the upper thick plate (41), the pad (42) and the lower thick plate (43) are fixedly connected. The lower thick plate (43) is placed on the lower conductive base (30). A brazing method for a plate-fin heat exchanger, characterized in that... The brazing method for the plate-fin heat exchanger employs the vacuum brazing equipment for plate-fin heat exchangers as described in any one of claims 7 to 8, and the brazing method specifically includes: 1) Machin the baffles, fins, and sealing strips of the plate-fin heat exchanger according to the dimensional requirements, and clean them; 2) Apply solder layers to the top and bottom sides of the partition; 3) Assemble the plate-fin heat exchanger parts on the tooling (40). Place the upper thick plate (41), pad (42), plate-fin heat exchanger and lower thick plate (43) from bottom to top. Use screws to pass through the edge through holes of the upper thick plate (41), pad (42) and lower thick plate (43) and fasten them with nuts at both ends. 4) Place the above tooling (40) on the lower conductive base (30) using a material cart, and press it with the upper water-cooled sealed conductive head (20). Loosen the tooling (40) and tighten the lower nut to maintain constant pressure. 5) Turn on the vacuum system (80) and evacuate to the working vacuum level; 6) A dual-feedback series control method is used to heat and insulate the plate-fin heat exchanger; 7) A pressure-temperature coupling control method is adopted to keep the pressure constant at different set values ​​in different temperature ranges; 8) Heat the plate-fin heat exchanger to the brazing process temperature ±5℃, hold for 10-60 minutes, and complete the brazing. 9) Cool the welded plate-fin heat exchanger evenly to below 150°C, shut off the vacuum system (80), and then continue cooling to room temperature. The method according to claim 9, characterized in that The pressure-temperature coupling control method sets the following pressure-temperature coupling relationships: temperature < 150℃, pressure 0.1 MPa; 200℃ ≤ temperature < 400℃, pressure 0.08 MPa; 400℃ ≤ temperature < 600℃, pressure 0.06 MPa; 600℃ ≤ temperature < 800℃, pressure 0.04 MPa.