Introduction of vacuum brazing for aluminum heat exchanger
At present, aluminum flat tube heat exchanger has been more and more widely used in automobile air conditioner. Because this kind of heat exchanger adopts fully welded structure, its design index of heat exchange efficiency is about 10% higher than that of segment heat exchanger. In addition, in the bumpy vibration of automobile, its integrity will not reduce the heat exchange efficiency and service life. In the production process of aluminum heat exchanger, vacuum brazing process plays an important role.
Processing of vacuum brazing for aluminum heat exchanger
The material of aluminum flat tube radiator is L. And LF21, it must use aluminum-based solder during vacuum brazing, and aluminum silicon solder can be selected. Its brazing temperature is 590 ℃ - 600 ℃, and the melting point is quite close to the melting point of the base metal. Therefore, the heating temperature should be strictly controlled. Under the condition of ensuring brazing penetration, the brazing holding time should be 3-5 minutes. When the brazing temperature is below 500 ℃, a faster heating rate (about 10 ℃ / min) and a longer holding time can be adopted, or two holding sections can be set. When the brazing temperature is above 500 ℃, a slower heating rate (4-5 ℃ / min) and a shorter holding time need to be adopted to achieve the perfect combination of brazing quality and efficiency. After the completion of brazing insulation, appropriately accelerating the cooling rate is conducive to refining the fiber seam structure and reducing dendrite segregation, so as to improve the brazing strength. However, if the cooling rate is too high, the weldment may form excessive thermal stress and produce cracks. Generally, the cooling rate of 15-20 ℃ / min can be selected.
Features of vacuum brazing for aluminum heat exchanger
Since the temperature control of vacuum brazing can be carried out by computer, it can strictly reach the temperature and time required for brazing, and the uniformity of temperature can reach ± 3 ℃, it is very suitable for vacuum brazing of aluminum radiator, and its vacuum brazing has no pollution, no flux, no pre welding and post welding cleaning (only degreasing treatment before welding), simple operation and high degree of automation, Under the control of optimization and specification, the yield is very high and the manufacturing cost is low on the premise of mass production. Of course, it also has some shortcomings, such as large power consumption, high environmental requirements of the equipment, dust prevention and air drying, and high maintenance costs of the equipment.