Vacuum Brazing of Aluminum Alloy Fin Plate Heat Exchanger

Salt bath dip brazing is the traditional manufacturing process for aluminum plate-fin heat exchangers. The brazing method usually utilizes the characteristics of fast heat conduction and large heat in the liquid medium, which can achieve the purpose of fast and uniform welding, and the production efficiency is relatively high. However, since the liquid salts used in this method contain a large amount of toxic substances such as cyanide, fluoride and chloride, such toxic substances will be released in the form of gas during the operation, which has a great impact on the environment and operators. On the other hand, after immersion brazing in salt bath, chloride salt with high corrosiveness tends to remain on the weldment, which requires post-treatment of the weldment, and the steps are complicated. As the shortcomings of salt bath immersion brazing become more and more prominent, in order to meet the actual production needs, it is inevitable to find a new brazing technology. Under this condition, vacuum brazing technology emerges as the times require.

Vacuum brazing is a joining technology that can be efficiently brazed without flux in a vacuum state. Compared with the traditional brazing method, the method has the advantages of good joint quality, low rejection rate and less environmental pollution, and completely solves the problem of corrosion of welding parts by residual chloride in salt bath immersion brazing.

Process and process parameters of vacuum brazing of aluminum plate-fin heat exchanger:

The general process flow for vacuum brazing of aluminum plate-fin heat exchangers is: raw material preparation → cleaning → assembly → brazing → product inspection → product drying and cleaning. In actual production, the suitable vacuum furnace should be selected according to the welding size, structural complexity and production scale. The brazing process includes vacuuming, heating, heat preservation, cooling and so on.

Temperature control: When the temperature in the furnace is lower than 365°C, the temperature control is relatively unimportant, so the temperature can be raised quickly. It only needs to ensure that the difference between the set temperature in the furnace and the actual temperature of the workpiece does not exceed 25°C to meet the process requirements. After 365 ℃, vacuum brazing begins to enter the cycle process. At this time, Si diffuses. If the workpiece remains soaked for a long time, it is not conducive to generating sufficient temperature difference to promote Si diffusion. Therefore, it is necessary to control the holding time at this stage. When the temperature reaches 525°C, Mg begins to sublime. At this time, the temperature control requirements are higher, and the actual temperature difference between the furnace temperature and the workpiece cannot exceed 20°C. When the set temperature reaches 597 °C, Mg is basically completely sublimated, and MgO is formed, which reduces or prevents Al and the formation of a dense and stable oxide film, so that the solder can smoothly wet the base metal workpiece and achieve the final high-quality brazing effect.

The RVB-L low-temperature vacuum brazing furnace produced by SIMUWU is a high-quality product for handling this type of brazing process. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum brazing process. With more than ten years of sales and manufacturing experience, it is exported to developed regions in Europe, America and Asia. It is a widely acclaimed vacuum furnace product.