Flame brazing method and flame brazing apparatus

Abstract

The present application relates to the technical field of welding, and provides a flame brazing method and a flame welding device.The flame brazing method comprises the following steps: controlling a brazed workpiece and filler metal to be preheated to a preheating temperature on a preheating fire grate; controlling the brazed workpiece and the filler metal to a brazing fire grate, so that the brazed workpiece and the filler metal are heated from the preheating temperature to a brazing temperature, so that the filler metal starts to melt; controlling the brazed workpiece and the filler metal to a holding fire grate, so that the brazed workpiece and the filler metal are maintained at the brazing temperature, and the filler metal is heated to complete melting, so that the filler metal flows and fills in a joint gap of the brazed workpiece; and controlling the brazed workpiece to a cooling area, so that the brazed workpiece is cooled from the brazing temperature to a cooling temperature.The flame brazing method provided by the present application adds a holding step in the brazing step, so that the filler metal can be completely melted, the joint of the brazed workpiece is uniformly filled, the gap and welding defects of the joint of the brazed workpiece are reduced, the reliability of the welded joint is improved, and the welding quality of the brazed workpiece is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding technology, in particular to a flame brazing method and a flame brazing device. BACKGROUND

[0002] In modern industrial production, especially in the field of manufacturing refrigeration and air conditioning equipment, flame brazing technology is a key technology for connecting metal components such as copper pipes and copper heat exchangers. Brazing operation requires heat treatment to ensure the sealing and mechanical strength of the joint of the brazed workpiece. In the related art, during the process of flame brazing, the filler metal may not completely melt or fail to uniformly fill the gap in the joint of the brazed workpiece, resulting in a joint that is not tightly sealed or has insufficient welding strength. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the related art. To this end, the present application proposes a flame brazing method to improve the welding quality of the brazed workpiece.

[0004] The present application also proposes a flame brazing device.

[0005] The present application proposes a flame brazing method, comprising:

[0006] controlling the brazed workpiece and the filler metal to be preheated to a preheating temperature by a preheating fire grate;

[0007] controlling the brazed workpiece and the filler metal to a brazing fire grate to heat the brazed workpiece and the filler metal from the preheating temperature to a brazing temperature, so that the filler metal begins to melt,

[0008] controlling the brazed workpiece and the filler metal to a holding fire grate to maintain the brazed workpiece and the filler metal at the brazing temperature, heat the filler metal to complete melting, and make the filler metal flow and fill in the joint gap of the brazed workpiece;

[0009] controlling the brazed workpiece to a cooling area to cool the brazed workpiece from the brazing temperature to a cooling temperature.

[0010] The flame brazing method according to the present application, by adding the step of placing the brazed workpiece and the filler metal to the holding fire grate in the brazing step, continues to heat the brazed workpiece and the filler metal in the brazing temperature range, so that it is maintained in the brazing temperature range, so that the filler metal can completely melt and uniformly fill the joint of the brazed workpiece, reduce the gap and welding defects of the joint of the brazed workpiece, improve the reliability of the welded joint, and thus improve the welding quality of the air conditioning heat exchanger.

[0011] According to one embodiment of the present application, the temperature rising rate of the brazed workpiece and the filler metal in the preheating burner is greater than the temperature rising rate of the brazed workpiece and the filler metal in the soaking burner, the temperature of the brazed workpiece and the filler metal in the soaking burner is greater than or equal to the temperature of the brazed workpiece and the filler metal in the brazing burner, and the maximum temperature of the brazed workpiece and the filler metal in the soaking burner is not greater than the liquidus temperature of the filler metal.

[0012] According to one embodiment of the present application, the flame fuel of the soaking burner is compressed air and fuel gas.

[0013] The flame fuel of the preheating burner is oxygen and fuel gas, or the flame fuel of the preheating burner is compressed air and fuel gas.

[0014] The flame fuel of the brazing burner is oxygen and fuel gas.

[0015] According to one embodiment of the present application, the temperature difference between the brazing temperature and the solidus temperature of the filler metal is greater than 30 degrees Celsius, and the solidus temperature of the filler metal is greater than the brazing temperature.

[0016] According to one embodiment of the present application, the flame temperature of the preheating burner is 2100 degrees Celsius to 2300 degrees Celsius, the preheating temperature is greater than 500 degrees Celsius and less than 730 degrees Celsius.

[0017] The flame temperature of the brazing burner is 2100 degrees Celsius to 2300 degrees Celsius, and the flame temperature of the soaking burner is 800 degrees Celsius to 1400 degrees Celsius; the brazing temperature is greater than 730 degrees Celsius and less than 820 degrees Celsius.

[0018] According to one embodiment of the present application, the temperature rising rate of the brazed workpiece and the filler metal in the preheating burner is V1, the temperature rising rate of the brazed workpiece and the filler metal in the brazing burner is V2, and the temperature rising rate of the brazed workpiece and the filler metal in the soaking burner is V3, V1≥V2≥V3.

[0019] According to one embodiment of the present application, the value range of V1 is 50 degrees Celsius per second to 70 degrees Celsius per second.

[0020] The value range of V2 is 20 degrees Celsius per second to 50 degrees Celsius per second.

[0021] The value range of V3 is 9 degrees Celsius per second to 20 degrees Celsius per second.

[0022] According to one embodiment of the present application, the step of controlling the brazed workpiece to a cooling area to reduce the brazed workpiece from the brazing temperature to a cooling temperature comprises:

[0023] A nitrogen cooling tube is used to cool the brazed workpiece, and the nitrogen cooling tube is arranged opposite the welding opening of the brazed workpiece.

[0024] According to an embodiment of the present application, the nitrogen gas flow rate ranges from 0 to 2000 liters per minute.

[0025] The present application also provides a flame brazing device, comprising:

[0026] a welding body;

[0027] a preheating fire row arranged in the welding body and used for preheating the brazed workpiece and the filler metal;

[0028] a brazing fire row arranged in the welding body and used for heating the brazed workpiece and the filler metal to a brazing temperature;

[0029] a holding fire row arranged in the welding body and used for maintaining the brazed workpiece and the filler metal at the brazing temperature; the preheating fire row, the brazing fire row and the holding fire row are arranged in sequence in the running direction of the brazed workpiece and the filler metal;

[0030] a controller used for the above-mentioned flame brazing method.

[0031] The flame brazing device according to the present application has the beneficial effects of the above-mentioned flame brazing method, and details are not repeated here.

[0032] According to an embodiment of the present application, the nitrogen cooling assembly is adjacent to the holding fire row.

[0033] According to an embodiment of the present application, the nitrogen cooling assembly comprises a plurality of nitrogen cooling tubes arranged side by side; and / or the width of the nitrogen cooling assembly is greater than or equal to 100 mm.

[0034] According to an embodiment of the present application, the nitrogen cooling assembly further comprises a flow meter electrically connected with the nitrogen cooling tube, so as to control and measure the nitrogen flow rate through the nitrogen cooling tube.

[0035] Additional aspects and advantages of the present application will be given in part in the following description, become apparent from the following description, or be understood through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or the related art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0037] Figure 1 is a flowchart of the flame brazing method provided by the present application.

[0038] Figure 2 is a structural schematic diagram of the flame brazing equipment provided by the present application.

[0039] Figure 3 is a schematic diagram of temperature changes of the brazed workpiece and the filler metal in the flame brazing method.

[0040] Reference signs:

[0041] 100, flame brazing equipment;

[0042] 101, brazing main body; 110, preheating fire grate; 120, brazing fire grate; 130, holding fire grate; 140, nitrogen cooling assembly.

[0043] 200, brazed workpiece. DETAILED DESCRIPTION

[0044] The embodiments of the present application will be further described in detail below in combination with the drawings and examples. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0045] In the description of the embodiments of the present application, it should be noted that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0046] In the description of the embodiments of the present application, it should be noted that unless specifically defined and limited, the terms "connected", "connected to", "connected with" should be interpreted broadly, for example, can be fixedly connected, can be detachably connected, or integrally connected, can be mechanically connected, or electrically connected, can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0047] In the embodiments of the present application, unless specifically defined and limited, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0048] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0049] The flame brazing method is performed by a flame brazing device, and the flame brazing device includes a welding main body 101, a preheating fire grate 110, a brazing fire grate 120, and a holding fire grate 130. The welding main body 101 can provide a flame brazing scene, and the type of the vacuum brazing device for performing the flame brazing method is not limited, and the welding condition capable of providing vacuum for the welded workpiece

[0050] The flame brazing method described below is suitable for welding processing of various welded workpieces. In the embodiments of the present application, an air conditioner heat exchanger is taken as an example, the air conditioner heat exchanger includes a copper pipe, and the air conditioner heat exchanger is welded and processed by the flame brazing method described below to improve the welding quality of the air conditioner heat exchanger. As shown in Figure 1 The present application provides a flame brazing method, which comprises:

[0051] Step 11: Control the workpiece 200 to be brazed and the brazing filler metal to be preheated to the preheating temperature in the preheating flame bar 110;

[0052] Step 11 can be understood as a preheating step, where the workpiece and the brazing filler metal are heated rapidly to meet the high-speed welding requirements of copper tubes.

[0053] Step 12: Control the workpiece 200 to be brazed and the brazing filler metal to the brazing torch 120, so that the workpiece 200 to be brazed and the brazing filler metal are heated from the preheating temperature to the brazing temperature, so that the brazing filler metal begins to melt. It should be noted that the brazing temperature is a temperature range. When preheating the workpiece 200 to be brazed and the brazing filler metal, it can be heated to any temperature within the brazing temperature range.

[0054] Step 13 involves controlling the workpiece 200 to be brazed and the brazing filler metal to the heat-insulating heat exchanger 130, maintaining them at the brazing temperature, and heating the filler metal until it is completely melted, allowing it to flow and fill the gap in the joint of the workpiece 200. Steps 12 and 13 can be understood as the brazing process. If the filler metal does not completely melt during melting, particles inside the filler metal will affect the welding quality. Therefore, adding step 130 based on step 120 ensures that the filler metal melts completely. By controlling the complete melting and uniform filling of the filler metal, voids and welding defects can be reduced, improving the reliability of the welded joint and thus enhancing the welding quality of the air conditioning heat exchanger. It should also be noted that in step 13, the temperature of the workpiece 200 to be brazed and the filler metal can rise slowly within the brazing temperature range, but will not exceed the maximum temperature value of the brazing temperature range.

[0055] Step 14 involves moving the workpiece 200 to a cooling zone, reducing its temperature from the brazing temperature to the cooling temperature. Step 14 can be understood as a cooling step, where the workpiece is cooled rapidly to allow the molten filler metal to solidify quickly, forming a strong weld and joint, ensuring the performance of both the workpiece and the filler metal. It should be noted that after the brazing step, the filler metal fills the weld seam of the workpiece, fusing it with the workpiece. In steps 14 and subsequent steps, the workpiece is collectively referred to as the "workpiece to be brazed."

[0056] According to the flame brazing method proposed in this invention, by adding step 13 to the brazing process, the workpiece 200 to be brazed and the brazing filler metal, which are in the brazing temperature range, are kept at the brazing temperature range, so that the brazing filler metal can be completely melted and uniformly filled into the joint of the workpiece 200 to be brazed, thereby reducing the gap and welding defects of the joint of the workpiece 200 to be brazed, improving the reliability of the welded joint, and thus improving the welding quality of the air conditioning heat exchanger.

[0057] like Figure 3 As shown, Figure 3The temperature and time curve of the brazed workpiece 200 and the filler metal under the flame brazing method, wherein the temperature of the brazed workpiece 200 and the filler metal is divided into four stages, which are preheating temperature, brazing temperature, holding temperature and cooling temperature, wherein the preheating temperature corresponds to the case that the brazed workpiece 200 and the filler metal are heated by the preheating fire grate 110, indicating that the brazed workpiece 200 and the filler metal are heated from room temperature to preheating temperature. The brazing temperature corresponds to the case that the brazed workpiece 200 and the filler metal are heated by the brazing fire grate 120, indicating that the brazed workpiece 200 and the filler metal are heated from the preheating temperature to the brazing temperature. The holding temperature corresponds to the case that the brazed workpiece 200 and the filler metal are heated by the holding fire grate 130, indicating that the brazed workpiece 200 and the filler metal are maintained at the brazing temperature.

[0058] Wherein the temperature rising rate of the brazed workpiece 200 and the filler metal in the preheating fire grate 110 is greater than the temperature rising rate of the brazed workpiece 200 and the filler metal in the holding fire grate 130, and the temperature of the brazed workpiece 200 and the filler metal in the holding fire grate 130 is greater than or equal to the temperature of the brazed workpiece 200 and the filler metal in the brazing fire grate 120, wherein the solidus temperature of the filler metal is 850 degrees, and the maximum temperature of the brazed workpiece 200 and the filler metal in the holding fire grate 130 is not greater than 850 degrees, so as to avoid the filler metal from exceeding the solidus temperature to cause sublimation phenomenon, resulting in waste of the filler metal, and leading to the decline of the filler metal flow filling performance, or leading to the temperature of the copper pipe being too high to cause grain coarsening.

[0059] In some embodiments of the present application, the temperature difference between the brazing temperature and the solidus temperature of the filler metal is greater than 30 degrees Celsius. For example, the solidus temperature of the filler metal is 850 degrees, and the maximum brazing temperature is 820 degrees. Wherein the flame temperature of the preheating fire grate 110 is 2100-2300 degrees Celsius, the preheating temperature is greater than 500 degrees Celsius and less than 730 degrees Celsius, the flame temperature of the brazing fire grate 120 is 2100-2300 degrees Celsius, the flame temperature of the holding fire grate 130 is 800-1400 degrees Celsius, and the brazing temperature is greater than 730 degrees Celsius and less than 820 degrees Celsius. Wherein the temperature rising rate of the brazed workpiece 200 and the filler metal in the preheating fire grate 110 is V1, the temperature rising rate of the brazed workpiece 200 and the filler metal in the brazing fire grate 120 is V2, and the temperature rising rate of the brazed workpiece 200 and the filler metal in the holding fire grate 130 is V3, V1≥V2≥V3. The value range of V1 is 50-70 degrees Celsius per second, the value range of V2 is 20-50 degrees Celsius per second, and the value range of V3 is 9-20 degrees Celsius per second.

[0060] In addition, in the flame brazing device, the preheating fire grate 110, the brazing fire grate 120 and the holding fire grate 130 are arranged in sequence in the running direction of the brazed workpiece 200 and the filler metal, and each of the fire grates is symmetrically arranged on both sides of the brazed workpiece 200 and the filler metal.

[0061] The combination of the above conditions can make the temperature curve of the brazed workpiece 200 and the filler metal during brazing close to an ideal temperature curve, optimize the welding process, and improve the welding quality and consistency.

[0062] In some embodiments of the present application, the flame fuel of the holding fire grate 130 is compressed air and fuel gas, for example, the flame fuel of the holding fire grate 130 can be compressed air and natural gas, or a combination of compressed air and acetylene. The flame fuel of the preheating fire grate 110 is oxygen and fuel gas, for example, the flame fuel of the preheating fire grate 110 can be oxygen and natural gas, or a combination of oxygen and acetylene. The flame fuel of the brazing fire grate 120 is oxygen and fuel gas, for example, the flame fuel of the brazing fire grate 120 can be oxygen and natural gas, or a combination of oxygen and acetylene. The combination of compressed air and natural gas produces a heating flame with a wider effective heating range and more uniform temperature heating, which facilitates the full flow of the filler metal and the filling of the brazed workpiece 200, and facilitates the improvement of the brazing quality. In addition, the gentle airflow of the brazing flame combined with compressed air and natural gas can prevent the molten filler metal from being blown away by the airflow of the brazing flame to form brazing defects. In this way, the flame heating temperature can be high, which can quickly raise the temperature of the to-be-welded position and ensure the brazing efficiency.

[0063] Alternatively, in some other embodiments, the flame fuel of the preheating fire grate 110 can also be compressed air and fuel gas, for example, compressed air and natural gas, or a combination of compressed air and acetylene.

[0064] In some embodiments of the present application, step 140 further comprises cooling the brazed workpiece 200 by using a nitrogen cooling pipe, and the outlet of the nitrogen cooling pipe is directly opposite the welding opening of the brazed workpiece 200 to reduce the risk of oxidation of the welding opening. It can be understood that nitrogen is an inert gas medium and does not react with high-temperature copper. By using a nitrogen cooling pipe, the contact between oxygen in the air and high-temperature copper can be prevented, and the probability of oxidation of the welded part of the brazed workpiece 200 can be reduced, thereby causing the problem of difficult repair welding. The nitrogen flow rate of the nitrogen cooling pipe is in the range of 0-2000 liters per minute.

[0065] As Figure 2As shown, the present application also provides a flame welding device 100, which comprises a welding body 101, a preheating fire row 110, a brazing fire row 120 and a holding fire row 130. The preheating fire row 110 is arranged on the welding body 101, and is used for preheating the brazed workpiece 200 and the filler metal. The brazing fire row 120 is arranged on the welding body 101, and is used for heating the brazed workpiece 200 and the filler metal to the brazing temperature. The holding fire row 130 is arranged on the welding body 101, and is used for maintaining the brazed workpiece 200 and the filler metal at the brazing temperature. The preheating fire row 110, the brazing fire row 120 and the holding fire row 130 are arranged in sequence in the advancing direction of the brazed workpiece 200 and the filler metal. The flame welding device also comprises a controller, which can control the brazed workpiece 200 and the filler metal to be welded in the flame welding device 100 by using the above-mentioned flame brazing method.

[0066] The preheating fire row 110 is arranged at the starting position of the welding body 101, and can quickly preheat the brazed workpiece 200 and the filler metal to the appropriate preheating temperature, so as to prepare for the subsequent brazing. The brazing fire row 120 is arranged at the middle position of the welding body 101, and can heat the preheated workpiece and the filler metal to the brazing temperature, so that the filler metal starts to melt and fills the joint. The holding fire row 130 is arranged at the end position of the welding body 101, and can continue to maintain the workpiece and the filler metal in the brazing temperature range after brazing is completed, so that the filler metal is fully melted and uniformly fills the gap, and the welding quality is improved. The controller can coordinate the working states of the fire rows, accurately control the temperature, time and flame intensity, and automatically execute the preset brazing steps, so as to ensure that the temperature and processing time of the workpiece in different stages are in the best state.

[0067] The preheating fire row 110, the brazing fire row 120 and the holding fire row 130 are arranged in sequence, the workpiece is gradually heated and processed along the advancing direction, the continuity and automation of the production process are realized, and the intermediate steps and time of workpiece processing are reduced. The fire rows arranged in different stages can uniformly and sufficiently heat the workpiece and the filler metal, and reduce the welding defects caused by uneven temperature. The existence of the holding stage ensures that the filler metal can be completely melted and uniformly filled in the joint gap, and improves the tightness and strength of the welded joint.

[0068] The flame welding device 100 according to the present application has the beneficial effects of the above-mentioned flame brazing method, and thus will not be described here.

[0069] As shown in the drawings, Figure 2 In some embodiments of the present application, the welding body 101 can be a conveyor belt, and the preheating fire row 110, the brazing fire row 120 and the holding fire row 130 are arranged in sequence on both sides of the conveyor belt. The brazed workpiece 200 and the filler metal can be placed on the conveyor belt, so as to be welded.

[0070] AsFigure 2 As shown, in some embodiments of the present invention, the flame welding equipment 100 further includes a nitrogen cooling assembly 140, which is adjacent to the heat-insulating fire bar 130, so that the workpiece 200 to be brazed can be quickly moved into the nitrogen cooling assembly 140 for cooling.

[0071] like Figure 2 As shown, the nitrogen cooling assembly 140 includes multiple nitrogen cooling pipes arranged side-by-side, which can cover a larger cooling area, ensuring uniform cooling of the workpiece throughout the welding area and preventing localized overcooling or overheating of the brazed workpiece 200, thereby reducing internal stress. Multiple pipes can provide a higher flow rate and more uniform nitrogen distribution, making cooling more efficient and helping to quickly reduce the workpiece temperature and increase the cooling rate. The width of the nitrogen cooling assembly 140 is greater than or equal to 100mm, ensuring that the nitrogen flow of the cooling assembly can effectively cover a larger area. The multiple nitrogen cooling pipes make the cooling process more efficient, reducing the workpiece temperature in a shorter time, quickly solidifying the brazing filler metal, shortening the production cycle, and improving production efficiency. Uniform and rapid cooling effectively prevents material deformation caused by uneven cooling, ensuring the shape and dimensional accuracy of the workpiece.

[0072] In some embodiments of the present invention, the nitrogen cooling assembly 140 further includes a flow meter electrically connected to the nitrogen cooling pipe to control and measure the nitrogen flow rate through the nitrogen cooling pipe. The flow meter allows for precise setting of the nitrogen flow rate according to the size, shape, and material of the workpiece, ensuring uniform cooling and avoiding localized overcooling or overheating, thereby improving cooling efficiency and consistency. Adjusting the flow rate based on real-time data enables dynamic adaptation to different cooling requirements, further improving the adaptability and efficiency of cooling. The flow meter can monitor the nitrogen flow rate in real time and feed the data back to the controller, allowing the controller to adjust the nitrogen supply as needed to maintain optimal cooling. Combined with the controller, the flow meter can achieve automatic control, adapting to different workpiece and process requirements and improving the automation level of the cooling process.

[0073] By precisely controlling nitrogen flow rate, excess nitrogen usage is avoided, reducing nitrogen consumption and thus production costs. Optimized cooling processes reduce excessive equipment use and wear, extending equipment lifespan and further lowering maintenance and replacement costs. Flow meters prevent nitrogen overflow, reducing potential risks to equipment and workpieces caused by excessive cooling and improving process safety. Furthermore, flow meters can be equipped with alarm functions to promptly alert when flow abnormalities occur, preventing insufficient cooling or excessive flow.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the present application, but not to limit the present application. Although the present application is explained in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the present application do not deviate from the spirit and scope of the present application, and should be covered in the scope of claims of the present application.

Claims

1. A method of flame brazing, characterized by, The method comprises: controlling the brazing workpiece and the filler metal to preheat fire row to preheat temperature; controlling the brazing workpiece and the filler metal to brazing fire row, heating the brazing workpiece and the filler metal from the preheat temperature to brazing temperature, so that the filler metal begins to melt, controlling the brazing workpiece and the filler metal to holding fire row, maintaining the brazing workpiece and the filler metal at the brazing temperature, heating the filler metal to complete melting, and making the filler metal flow and fill in the joint gap of the brazing workpiece; controlling the brazing workpiece to cooling area, cooling the brazing workpiece from the brazing temperature to cooling temperature; The temperature difference between the brazing temperature and the solidus temperature of the filler metal is greater than 30 degrees Celsius, and the solidus temperature of the filler metal is greater than the brazing temperature; The flame temperature of the preheating fire row is 2100-2300 degrees Celsius; the preheating temperature is greater than 500 degrees Celsius and less than 730 degrees Celsius; The flame temperature of the brazing fire row is 2100-2300 degrees Celsius, and the flame temperature of the holding fire row is 800-1400 degrees Celsius; the brazing temperature is greater than 730 degrees Celsius and less than 820 degrees Celsius; The temperature rising rate of the brazing workpiece and the filler metal in the preheating fire row is V1, the temperature rising rate of the brazing workpiece and the filler metal in the brazing fire row is V2, and the temperature rising rate of the brazing workpiece and the filler metal in the holding fire row is V3, V1≥V2≥V3; The value range of V1 is 50-70 degrees Celsius per second; The value range of V2 is 20-50 degrees Celsius per second; The value range of V3 is 9-20 degrees Celsius per second.

2. The flame brazing method according to claim 1, characterized by, The temperature rising rate of the brazing workpiece and the filler metal in the preheating fire row is greater than that in the holding fire row, the temperature of the brazing workpiece and the filler metal in the holding fire row is greater than or equal to that in the brazing fire row, and the maximum temperature of the brazing workpiece and the filler metal in the holding fire row is not greater than the liquidus temperature of the filler metal.

3. The flame brazing method according to claim 1, characterized by, The flame fuel of the holding fire row is compressed air or gas mixture; The flame fuel of the preheating fire row is oxygen and gas, or the flame fuel of the preheating fire row is compressed air and gas mixture; The flame fuel of the brazing fire row is oxygen and gas mixture.

4. The flame brazing method according to claim 1, characterized by, The step of controlling the brazing workpiece to the cooling area, cooling the brazing workpiece from the brazing temperature to the cooling temperature, comprises: The brazing workpiece is cooled by nitrogen cooling pipe, the outlet of the nitrogen cooling pipe is opposite to the welding opening of the brazing workpiece, and the flow range of the nitrogen is 0-2000 liters per minute.

5. A flame brazing device, characterized by The method comprises: welding body; preheating fire row, arranged in the welding body, for preheating the brazing workpiece and the filler metal; brazing fire row, arranged in the welding body, for heating the brazing workpiece and the filler metal to brazing temperature; holding fire row, arranged in the welding body, for maintaining the brazing workpiece and the filler metal at the brazing temperature; The preheating fire row, the brazing fire row and the holding fire row are arranged in sequence in the running direction of the brazed workpiece and the filler material; A controller for performing the flame brazing method according to any one of claims 1-4.

6. The flame brazing apparatus of claim 5, wherein Further comprising a nitrogen cooling assembly for cooling the brazed workpiece, the nitrogen cooling assembly being adjacent to the holding fire row, the nitrogen cooling assembly comprising a plurality of nitrogen cooling pipes arranged side by side; and / or the width of the nitrogen cooling assembly is greater than or equal to 100 mm.

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