Vacuum Brazing Furnace for Aluminum Alloy Radiator

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With the continuous growth of national economy and the continuous improvement of science and technology, the development of industrial industry has made a qualitative leap. As an advanced cooling equipment, aluminum alloy plate fin radiator is widely used in various industries. Its remarkable advantages are light weight, high efficiency and simple structure. In order to ensure the quality of aluminum alloy plate fin radiator, we must give full play to the role of vacuum brazing process. The factory should take effective measures to solve the problems existing in the process of vacuum brazing in combination with the actual application, so as to avoid all kinds of quality problems of radiators and effectively meet the needs of market users. This paper will further analyze and discuss the vacuum brazing process of aluminum alloy radiator.

At present, it is an era of economic globalization. The development of industrial industry should keep pace with the times and keep up with the pace of the times. If processing enterprises want to produce more high-quality aluminum alloy plate fin radiator products, to ensure that they can create the maximum economic benefits at the lowest cost, and to meet the needs of market development and product users, they must carry out in-depth research on vacuum brazing technology. The processing technicians must fully grasp the basic theoretical knowledge of vacuum brazing technology, define its standard process, and reasonably set up various process parameters, so as to effectively guarantee the safety and quality of aluminum alloy plate fin radiator production.

Working principle of vacuum brazing for aluminum alloy radiator
In the practical production process of aluminum alloy plate fin radiator, the application principle of vacuum brazing technology is based on the vacuum degree environment, by reasonably controlling the temperature in the vacuum furnace under the melting point of the base metal and above the melting point of the solder, so that the solder in the vacuum furnace can be effectively melted into the required liquid. Then the capillary force is used to make the solder in liquid state fill the space between the solid base metal, and the interaction between them will occur until the temperature is cooled and solidified. At present, the working mechanism of vacuum brazing technology mainly includes three processes: the process of removing oxide film in vacuum environment, the process of filler metal filling solid base metal gap in liquid state and the process of interaction between liquid filler metal and solid base metal.

The vacuum brazing technical application personnel must understand that in the production of aluminum alloy plate fin radiator, a stable and dense oxide film is easy to form on the surface of aluminum alloy material, which will affect the combination of solder and base metal in the process of brazing to a certain extent, resulting in the vacuum crack at the sealing part of radiator seal. Therefore, the processing personnel must attach great importance to the removal of oxide film of aluminum alloy materials. The mechanism of removing oxide film mainly includes the following aspects:
(1) the effective volatilization of metal Mg into mg vapor is promoted by heating treatment, so as to destroy and eliminate the oxide film on the surface of aluminum alloy;
(2) the coefficient of thermal expansion of metal Mg is much smaller than that of aluminum alloy. The oxide film with low expansion rate will crack at the first time through heating treatment;
(3) mg vapor will react with the water vapor left in the vacuum furnace. When Si diffuses to the surface of the base metal, Mg vapor will penetrate through the oxide film and penetrate into the base metal, so that the surface of the membrane material will effectively form Al Si mg low melting alloy, and the oxide film will be removed automatically after the melting reaction;
(4) after the solder is melted, its adsorption can reduce the strength of oxide film on the surface of aluminum alloy to the greatest extent, and promote the oxide film to break and penetrate into the solder at the same time, so that the liquid solder can successfully wet the base metal.

Analysis of vacuum brazing process for aluminum alloy radiator
Characteristics of vacuum brazing equipment
In order to produce high quality aluminum alloy plate fin radiator, the processing enterprise must actively introduce and apply advanced vacuum brazing furnace equipment. According to the different heating methods in the furnace, we usually divide the vacuum brazing furnace equipment into two types, one is hot wall vacuum brazing furnace, the other is cold wall vacuum brazing furnace. Among them, the hot wall vacuum brazing furnace is a widely used vacuum brazing equipment in the early days. Its most remarkable characteristics are high efficiency, low cost and simple production. It is suitable for manufacturing various small and medium parts. The disadvantage is that the temperature distribution in the furnace is not uniform enough to effectively meet the production of large parts with complex structure. As the most advanced equipment in modern vacuum brazing furnace, the cold wall vacuum brazing furnace is characterized by adopting the double-layer circulating water-cooling structure, effectively combining the vacuum chamber with the heater, which can maximize the heat radiation rate in the vacuum environment, avoid a large amount of heat consumption in the furnace, so as to ensure a more uniform temperature distribution in the furnace. With the development of time and the improvement of vacuum brazing technology, the equipment of cold wall vacuum brazing furnace has changed from bell jar structure to multi-functional structure, and the space in the furnace has become larger and larger, which can meet the demand of manufacturing large parts in the market.

Working process of vacuum brazing for aluminum alloy radiator
When the aluminum alloy plate fin radiator is manufactured by vacuum brazing process in the processing plant, the relevant staff must carry out the operation according to the strict and standardized work flow, rather than relying on their own experience. At present, the working process of vacuum brazing in the manufacturing of aluminum alloy plate fin radiator is as follows:
(1) prepare qualified manufacturing materials;
(2) clean and assemble the vacuum brazing furnace equipment;
(3) carry out brazing operation;
(4) carry out quality inspection on the manufactured finished products;
(5) dry and clean the qualified products. When selecting the vacuum furnace equipment, the relevant personnel of the processing plant must select and apply the vacuum brazing furnace equipment according to the actual size and complexity of the radiator welding. The operation involved in the whole brazing process mainly includes vacuumizing, furnace heating, heat preservation and cooling, etc.

Vacuum brazing process parameters
In the application process of vacuum brazing process of aluminum alloy plate fin radiator, the staff should correctly recognize the importance of this process parameter setting, in which the vacuum degree is the core process parameter of vacuum brazing process, and the setting of vacuum degree directly determines the final welding quality [3]. Therefore, when the vacuum brazing furnace is put into use for a long time in the processing plant, the equipment must be operated in advance to let it run without load for a period of time before it is used to process and produce aluminum alloy plate fin radiator. At the same time, the setting of heating rate parameters of vacuum brazing furnace equipment will also affect the welding quality of products. If the heating rate is too fast, the surface of parts will lose color and affect the cleanness and smoothness of parts. If the heating rate is too fast in the furnace, the temperature of processing parts will be uneven and the parts will be deformed. If the heating rate is too slow It will cause volatilization of the components with lower melting point in the solder, while the parts with higher melting point will remain solid, so it is difficult to effectively wet the base metal, and the final parts cannot be accurately brazed. Therefore, the operators of vacuum brazing furnace equipment should control the brazing holding time and furnace temperature scientifically. Among them, it is most appropriate to control the brazing heat preservation time within 3 minutes after the processing parts reach the solder liquidus temperature. Too short or too long heat preservation time will affect the welding quality of parts to a certain extent, which is not conducive to the high-quality processing and production of parts in large quantities. The temperature in the vacuum brazing furnace should be strictly controlled between the liquidus temperature of the solder and the solidus temperature of the base metal. If the temperature in the furnace is too low, the solder will not melt completely, so the strength of the brazed joint of the parts will be too low. If the temperature in the furnace is too high, it will lead to corrosion defects and other problems.

When the temperature in the vacuum brazing furnace is less than 365 ℃, the operator can quickly improve the temperature in the furnace. At this time, only the temperature difference between the vacuum brazing furnace and the actual temperature of the production parts should be controlled within 25 ℃. When the temperature in the furnace exceeds 365 ℃, the operator must strictly control the holding time in the furnace to ensure the continuous diffusion of Si. When the temperature in the furnace reaches 525 ℃, the metal Mg will undergo sublimation reaction. In this stage, the temperature control requirements in the furnace are the highest. The operator must ensure that the temperature difference between the temperature in the furnace and the temperature of the processed parts is controlled within 20 ℃. When the temperature in the furnace has reached 597 ℃ in the figure, the metal Mg almost sublimates, the oxide film on the surface of aluminum alloy will be eliminated, and the solder can effectively wet the base metal parts in the furnace, so as to realize the best brazing operation for the parts.

In conclusion, in order to produce high-quality aluminum alloy plate fin radiator products and meet the needs of the vast market users, the processing plant must scientifically apply the vacuum brazing technology, complete the relevant equipment, arrange professional personnel to operate the vacuum brazing furnace, reasonably set the parameters of the vacuum brazing process, and operate in accordance with the standard process.