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Brazing knowledge summary(1)

Jan 28, 2019

Brazing refers to a welding method in which a solder and a weldment lower than the melting point of the weldment are simultaneously heated to the melting temperature of the solder, and the gap between the solid workpieces is filled with the liquid solder to connect the metal. In brazing, the oxide film and oil stain on the contact surface of the base metal are first removed to facilitate the capillary action after the solder is melted, and the wettability and capillary fluidity of the solder are increased. Brazing is divided into brazing and soldering according to the melting point of the solder. 

The brazing deformation is small, the joint is smooth and beautiful, and it is suitable for welding precision, complex and components composed of different materials, such as honeycomb structural plates, turbine blades, carbide tools and printed circuit boards. Before the brazing, the workpiece must be carefully processed and strictly cleaned to remove oil and excessively thick oxide film to ensure the interface assembly gap. The gap is generally required to be between 0.01 and 0.1 mm.

Brazing process: The surface-cleaned workpieces are assembled together in a lap type, with the brazing material placed near the joint gap or between the joint gaps. When the workpiece and the brazing material are heated to a temperature slightly higher than the melting point of the brazing filler metal, the brazing material melts (the workpiece is not melted), and is sucked into and filled with the gap between the solid workpieces by capillary action, and the liquid brazing material and the workpiece metal mutually diffuse and dissolve. After the condensation, a brazed joint is formed.

Brazing is one of the earliest methods of material joining used by humans. When humans have not started using iron, they have invented brazing to join metals. In the ancient relics unearthed in Egypt, the tubes brazed with silver-copper brazing materials and the talisman boxes connected with gold brazing materials were examined for items 5,000 years ago and nearly 4,000 years ago. In the ruins of Pompeii, which was buried in the volcanic eruption in 79 AD, there are remains of brazed household brazing pipes. The brazing filler metal has a composition ratio of Sn:Pb=1:2, similar to the brazing filler metal used in modern times. . China also used tin-lead alloy brazing filler metal in the early 5th century BC, and also used brazing technology in the Terracotta Warriors and Horses. The earliest known brazing in the literature in China was that there was a cloud in the Han Shu written by Ban Gu in the Han Dynasty: "Hu Tong has tears like tears, and can be welded with gold and silver. It is used by artisans today." In the Ming Dynasty Song Yingxing's masterpiece "Tiangong Kaiwu" published in 1637, "Chinese small brazing powder with white copper foam, the big brazing is trying to force the hammer to strengthen it. If the Hutong juice is combined with silver, it is as strong as stone. Today's jade knife The flux such as the handle, plus one point of silver, will never leave. Try to use a round pot of spot welding flux on it, its medicine is self-propelled, and it is also a cycle. This description clearly indicates that copper brazing should use borax as the flux and silver brazing can use the Hutong resin as the flux, and a wonderful description of the sealing behavior of the brazing filler metal. Although the brazing technology appeared earlier, it has not been greatly developed for a long time. After entering the 20th century, its development is far behind the welding technology. Until the 20th century in the 1930s, on the basis of the development of metallurgical and chemical technology, brazing technology developed rapidly and gradually became an independent industrial production technology. Especially after the Second World War, due to the development of new technologies such as aviation, aerospace, nuclear power, electronics, etc., the adoption of new materials and new structural forms puts higher demands on the connection technology, and the brazing technology has been greatly enhanced. Emphasis on and rapid development, many new brazing methods have emerged, and their applications have become more widespread. For example, the manufacture of various tools for machining, in particular carbide tools, drilling tools for drilling and mining, various pipes and containers, water tanks for automobile tractors, heat exchangers of different materials and different structures for various purposes, Brazing technology is widely used for the manufacture of components such as motor parts and turbine blades and lacing. In light industrial production, brazing technology is widely used in medical equipment, metal implant prostheses, musical instruments, household appliances, cookware, and bicycles. For the electronics industry and instrument manufacturing industry, brazing is the only feasible connection method in a wide range. For example, in the production of components, a large number of non-metal connection problems between metals and ceramics, glass, etc., and heating must be prevented in wiring connections. Damage to components depends on brazing technology. In nuclear power plants and ship nuclear power plants, important components such as fuel element positioning frames, heat exchangers, and neutron detectors are also often brazed.

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