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Vacuum Brazing Furnace

Aluminum alloy vacuum brazing

For the brazing of precision parts, vacuum brazing is a more suitable process, and it does not require a flux removal process after brazing. Vacuum brazing is a welding method in which the brazing filler metal and brazing components are clamped and debugged with fixtures, and then placed in a vacuum brazing furnace for overall heating, heat preservation, and cooling to achieve brazing. Vacuum brazing has the advantages of small size deformation, no cleaning after welding, multiple weld seams, simultaneous welding of multiple parts, and environmental protection. Complex and precise aluminum alloy brazing parts can be vacuum brazed.

Vacuum brazing furnace

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 and turn gray during the heating process, and the brazing filler metal cannot wet the base metal. Only when the pressure is ≤5× 10^-3 Pa, and the temperature is raised slowly before 500 ℃, and the temperature is kept at 450 ℃ for 30 minutes to ensure that the pressure is kept at ≤ 5 × 10^-3 Pa during the heating process, brazing can be realized.

The pressure rise rate of the vacuum brazing furnace is an important indicator to ensure the quality of brazing. The pressure rise rate is the rate of rise of the furnace pressure per unit time after the pressure of the vacuum furnace is pumped to the working pressure and the vacuum system is turned off to stop pumping. It is A technical index reflecting the air leakage performance of the brazing furnace seal, also known as the leakage rate, the pressure rise rate of the vacuum brazing furnace < 0.3Pa·h^-1 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 pumping system can cover up the gas leakage indicators, although the gas leaked into the furnace is quickly pumped out, the brazing parts are still oxidized.

The heating rate in the heating stage of 500 ℃ to 600 ℃ has an important impact on the welding quality. The heating rate is low, and the low melting point components of the solder volatilize rapidly in the vacuum environment, leaving the high melting point components unmelted, and even forming a diffuse flow. The cooling rate after the heat preservation is also very important. Too slow cooling is equivalent to prolonging the heat preservation time, which will cause defects such as flooding, solder leakage, and erosion.

The ultimate pressure of the vacuum brazing furnace should be ≤10^-4 Pa, the working pressure should be ≤1 × 10^-3 Pa, and the pressure rise rate should be < 0.3Pa·h^-1. There should be enough heating power to be able to rapidly raise the temperature, and the heating rate should be ≥12 ℃·min^-1. The vacuum brazing furnace should be equipped with an air cooling system, capable of rapid cooling. The fastest cooling rate is applied under the premise of ensuring the shape and position tolerance of the part. The quality of aluminum alloy brazing has high requirements on the temperature control accuracy and furnace temperature uniformity of the vacuum brazing furnace, and ±5 ℃ can meet the vacuum brazing of small parts. The aluminum vacuum brazing furnace with ±1 ℃ temperature control accuracy and ±3 ℃ furnace temperature uniformity can braze high-quality parts.

Aluminum alloy vacuum brazing process:

Due to the differences in the grades of aluminum alloy and brazing material, the shape and size of the parts, and the different requirements for brazing quality, the composition, concentration, corrosion temperature and corrosion time of the alkali solution for removing the oxide film on the surface, the vacuum degree and temperature rise of vacuum brazing Process parameters such as rate, holding time, and cooling rate will be slightly different, and should be screened and optimized through experiments according to different situations, and finally determine the best combination of process parameters.