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Aluminum radiators vacuum brazing oven
New Technology of Aluminum Vacuum Brazing Radiator
1.Overview of aluminum vacuum brazing radiator
As a key part of the car cooling system, the radiator plays an important role in the whole car. It forms the cooling system with the cooling fan, rubber tube, engine water jacket, thermostat, cooling water pump, grille and wind deflector. The heat dissipation effect of the engine ensures that the engine can run stably and efficiently.
With the development of raw materials, machinery and metallurgical industries, automobile radiators have mainly experienced three generations of radiators according to materials and manufacturing processes, namely copper and brass radiators, aluminum assembled radiators and aluminum vacuum brazed radiators. So far, aluminum vacuum brazed radiators have become the mainstream and are widely used in cars, commercial vehicles and trucks. Vacuum brazing is an emerging joining technique in the manufacture of aluminum heat sinks.
2.The processing principle of aluminum vacuum brazing radiator
Aluminum vacuum brazed radiators are mainly composed of radiator cores, water chambers and rubber gaskets, and there are some bracket accessories. The core of its design and manufacture is the radiator core. The radiator core is composed of four major parts: the main piece, the side plate, the heat dissipation strip and the heat dissipation pipe, which are welded together by the vacuum brazing technology of aluminum. The water chamber is generally made of engineering plastics mainly made of glass fiber reinforced nylon. The radiator core and the water chamber are connected by mechanical undercutting, so that the main wall of the main piece is clamped to the edge of the water chamber to promote the EPDM rubber is compressed to achieve a sealing effect.
The vacuum brazing method used in the manufacture of aluminum radiator cores was adopted after the emergence of composite materials in the aluminum industry. The composite material is formed by combining two different aluminum materials through a hot wheel and then cold rolling. The aluminum material used to make radiator cores is composed of a material matrix (high melting point metal) and a vacuum brazing material (low melting point metal). In order to ensure the service life of the product, there must be an anti-corrosion layer. The melting point of the material of the anti-corrosion layer is higher than that of the vacuum brazing material, and zinc-containing AA7072 is generally used. The whole vacuum brazing process is that when the ambient temperature is heated above the melting point of the brazing material, under the action of the flux, the brazing material begins to melt, spread and flow, and fills the gaps between the materials under capillary action, and through intermolecular diffusion, The base metals of different parts are connected, and as the temperature drops, a brazed joint is finally formed.
3.Vacuum brazing process of aluminum radiator
Vacuum brazing is the key to the whole production. The process parameters to control the quality of vacuum brazing are the temperature of each zone, the speed of the mesh belt and the atmosphere of the vacuum brazing oven. The vacuum brazing temperature directly affects the quality of the product. If the temperature is too low, the solder will not melt or the fluidity will be poor after melting, and the solder will not penetrate through capillary action to fill the gap; if the temperature is too high, the silicon in the solder will diffuse to the base material, reducing the fatigue resistance of the radiator core performance, affecting the service life of the product. During the vacuum brazing process, the temperature is extremely high, and since the parts of the radiator core are all thin-walled parts, it will cause the corrosion of the base material of the radiator core.
The atmosphere of vacuum brazing is an important process parameter that determines the welding rate and the sealing of the heat pipe and the main sheet. The atmosphere for vacuum brazing refers to the oxygen content and dew point. The higher the oxygen content, the easier it is to oxidize the aluminum material, forming dense high-temperature oxides, which reduces the quality of vacuum brazing. The higher the dew point, the more moisture will be contained in the vacuum brazing, and the water will react with the flux to generate HF, which not only affects the muffle life of the vacuum brazing oven, but also has an impact on the environment.
Generally, the oxygen content is controlled at 50×10-6, and the dew point is controlled below -40°C. In mass production, sometimes the atmosphere cannot meet the requirements, which can be controlled by increasing the flux concentration or speeding up the mesh belt to ensure the quality of vacuum brazing.
The speed of the mesh belt not only determines the production efficiency, but also determines the heating rate in the vacuum brazing oven and the brazing time of the brazing section. Generally speaking, the mass of the radiator core is relatively large, and the speed of the mesh belt is relatively slow, so that the radiator core can fully obtain heat in the heating zone, pre-brazing zone and brazing zone, and the surface temperature reaches the optimal process value . For small products, the speed of the mesh belt is relatively faster, because the heat capacity of the small radiator core is small and the heating is fast. If the temperature in the vacuum brazing area is too high, the silicon in the brazing material will diffuse to the base material, which will affect the service life of the radiator core.
Under the above process conditions, when the temperature on the surface of the radiator core reaches above 562°C, the Nocolok flux adhering to the surface begins to melt and spread on the surface of the aluminum material to dissolve the aluminum oxide film. Then the Al-Si alloy solder layer coated on the surface of the base metal begins to melt, and the seam welding is performed by capillary action. As the surface temperature of the radiator core drops, the solder solidifies, and such a complete radiator core is vacuum The brazing process is complete.
The addition of Si lowers the melting point of aluminum, which can be explained by the AL-Si phase diagram (see attached figure).
Vacuum brazing equipment selection: The vacuum brazing oven produced by SIMUWU is a high-quality product for aluminum vacuum brazing radiator technology. Good temperature control accuracy and temperature control uniformity ensure the effective vacuum brazing process. The equipment is easy to manage and maintain, greatly reducing maintenance costs.
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