Vacuum brazing furnace for aluminum alloy parts

Aluminum has high chemical activity and is easy to oxidize. When the pressure is ≥ 6 × 10-3 PA, the base metal and brazing filler metal are oxidized to gray in the process of heating up, and the brazing filler metal cannot wet the base metal. Only when the pressure is ≤ 5 × 10 – 3 Pa, and the temperature rises slowly before 500 ℃, and stays at 450 ℃ for 30 min, in order to ensure that the pressure remains ≤ 5 × 10 – 3 PA in the process of temperature rise, can brazing be realized.

The pressure rise rate of vacuum brazing furnace is an important index to ensure the brazing quality. The pressure rise rate is the rate of pressure recovery of the furnace in unit time after the pressure of the vacuum furnace is pumped to the working pressure and the vacuum system is shut down to stop pumping. It is a technical index reflecting the sealing air leakage performance of the brazing furnace, also known as the leakage rate, The pressure rise rate of vacuum brazing furnace is less than 0.3pa · H – 1, which can weld high quality aluminum alloy parts. If the pressure rise rate is large, even if the working pressure is maintained at ≤ 1 × 10-3pa, the brazing quality of aluminum alloy parts is not easy to guarantee. Because the high-power extraction system can cover up the leakage index of the seal, although the gas leaked into the furnace is rapidly extracted, the brazed parts are still oxidized.

In the heating stage of 500 ℃ ~ 600 ℃, the heating rate has an important influence on the welding quality. The heating rate is low. In the vacuum environment, the low melting point components of solder volatilize rapidly, leaving the high melting point components not melting, and even forming a diffuse flow. The cooling rate after heat preservation is also very important, too slow cooling is equivalent to prolonging the heat preservation time, which will produce defects such as diffuse flow, missing welding and melting corrosion.

The limit pressure of vacuum brazing furnace shall be ≤ 10 – 4 PA, the working pressure shall be ≤ 1 × 10 – 3 Pa, and the pressure rise rate shall be < 0.3pa · H – 1. There shall be enough heating power, which can raise the temperature rapidly, and the heating rate shall be ≥ 12 ℃ · min-1. The vacuum brazing furnace shall be equipped with an air cooling system capable of rapid cooling. On the premise of ensuring the geometrical tolerance of parts, the fastest cooling rate shall be applied. Aluminum alloy brazing quality requires high temperature control accuracy and furnace temperature uniformity of the brazing furnace, ± 5 ℃ can meet the vacuum brazing of small parts. Now, aluminum vacuum brazing furnace with temperature control accuracy of ± 1 ℃ and furnace temperature uniformity of ± 3 ℃ on the market can braze high-quality parts.

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