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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Aluminum plate-fin type heat exchanger and vacuum brazing

Aluminum plate-fin type heat exchanger (hereinafter referred to as heat exchanger) is a pressure vessel, and must meet the corresponding pressure requirements during its application. Due to its structural characteristics, its welding process can only be achieved through vacuum brazing.

Vacuum brazing is an advanced welding method that heats and insulates the structural parts under vacuum, so that the brazing material melts within a suitable temperature and time range, and fully infiltrates, dissolves, diffuses, and welds with the solid metal under the action of capillary force, thereby achieving the purpose of welding. The outstanding advantages of vacuum brazing are that it can connect different metals and realize simultaneous welding of complex structures. The welded joints are smooth and dense, with small deformation and excellent mechanical properties and corrosion resistance. However, vacuum brazing has very strict requirements on the structural design and assembly quality of the heat exchanger, the chemical composition of the aluminum alloy composite plate (hereinafter referred to as the composite plate), the thickness of the brazing material layer, the brazing process system, the working environment, etc. Otherwise, it is very easy to have quality defects such as fin bending and lodging, discontinuous brazing seams, false welding, melting, and even leakage. Among them, leakage is a major quality defect.

The structure of the heat exchanger is mainly composed of partitions, fins, side plates, seals, etc., as shown in the figure. Among them, the partition is the composite plate that plays an important role in vacuum brazing.

Production process

(1) Material preparation: shape and size the composite plate, fins, seals, etc.

(2) Surface treatment process: alkali washing → water washing → acid washing → water washing → hot water washing → drying.

(3) Assembly: mechanically combine and shape the composite plate, side plate, fins, seals, etc.

(4) Vacuum brazing: After the vacuum brazing furnace is evacuated, three stages of heating and insulation are carried out. That is: the first stage (a) preheating and temperature setting; the second stage (b) energy storage and temperature setting; the third stage (c) brazing and temperature setting; power off. Wait until the furnace temperature drops to the specified temperature before taking out of the furnace.

(5) Shaping: The deformation of the heat exchanger after vacuum brazing is corrected by mechanical methods.

(6) Guide plate welding: Use argon arc welding to weld the guide plate of the heat exchanger, that is, the large seal position at both ends of the heat exchanger.

(7) Pressure test: Use air blowing to test the pressure bearing capacity of the heat exchanger, that is, leakage test.

(8) Spraying: Clean, dry, spray and dry the heat exchanger to improve the appearance quality.

(9) Packaging and delivery.

Vacuum degree of vacuum brazing furnace

When the vacuum degree is low under high temperature, the residual O₂, H₂O and other oxidizing gases in the furnace are easy to react chemically with Al to form a hard oxide film, namely Al₂O₃. Al₂O₃ has a dense, stable structure and a high melting point. It is not easy to decompose at ordinary brazing temperature. After the brazing material is oxidized, its fluidity and wettability deteriorate; after the metal to be welded is oxidized, it becomes difficult to wet, which leads to the deterioration of the welding performance between the solder and the substrate. Therefore, it is necessary to increase the vacuum degree during brazing as much as possible, reduce the content of oxidizing gases such as O₂ and H₂O, and control the generation of Al2O3. Generally, the vacuum brazing furnace adopts multi-zone temperature control, the furnace temperature uniformity is: ±5℃, the working vacuum degree should be guaranteed to be no greater than 2.0×10^-3Pa, and the ultimate vacuum degree of pre-vacuuming must be on the order of 10^-4.