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Brazing knowledge summary(2)

Jan 28, 2019

Application feature editing

(1) Brazing heating temperature is low, the joint is smooth and flat, and the structure and mechanical properties change little.

Brazed diamond grinding wheel

Brazed diamond grinding wheel

The deformation is small and the workpiece size is accurate.

(2) The same kind of metal can be welded, and the dissimilar materials can be welded, and the thickness difference of the workpiece is not strictly limited.

(3) Some brazing methods can weld multiple weldments and multiple joints at the same time, and the productivity is high.

(4) The brazing equipment is simple and the production investment cost is small.

(5) The joint strength is low, the heat resistance is poor, and the pre-weld cleaning requirements are strict, and the brazing material is expensive.

Application

Brazing is not suitable for the welding of general steel structures and heavy-duty, dynamic-loaded parts. Mainly used in the manufacture of precision instruments, electrical components, dissimilar metal components and complex thin-plate structures, such as sandwich components, honeycomb structures, etc., also used to braze all kinds of different wire and carbide tools. During brazing, after the contact surface of the brazed workpiece is cleaned, it is assembled in a lap joint manner, and the solder is placed near the joint gap or directly into the joint gap. When the workpiece is heated with the solder to a temperature slightly above the melting temperature of the solder, the solder will melt and wet the surface of the weld. The liquid solder spreads along the joint by capillary action. Then, the brazing metal and the brazing filler metal dissolve each other and penetrate each other to form an alloy layer, and after condensing, a brazing joint is formed.

Brazing has been widely used in machinery, motors, instruments, radios and other departments. Carbide tools, drilling bits, bicycle frames, heat exchangers, ducts and various types of containers; brazing is the only possible connection method in the manufacture of microwave waveguides, tubes and electronic vacuum devices. 

Brazing characteristics

First, the surface of the joint is smooth, airtight, stable in shape and size, and the microstructure and properties of the weldment are not changed much, and the same or different metals and some non-metals can be connected. When brazing, it is also possible to heat the entire workpiece and weld a lot of welds at a time, which improves productivity. However, the strength of the brazed joint is low, and the lap joint is often used to increase the joint strength by increasing the lap length; in addition, the preparation work before brazing is required to be high.

The second is that the solder melts and the weldment does not melt. In order to make the brazing portion firmly connected and enhance the adhesion of the brazing material, a flux is used in the brazing to remove the oxide on the brazing material and the surface of the weldment. Brazing filler metal (such as copper base, silver base, aluminum base, nickel base, etc.) has high strength and can be connected to load-bearing parts for a wide range of applications, such as carbide tools and bicycle frames. Solder (such as tin, lead, antimony, etc.), low welding strength, mainly used for welding weldments that do not bear the load but require good sealing, such as containers and instrument components.

Brazing uses an alloy with a lower melting point than the base material as the brazing material. When heated, the brazing material melts and is filled and maintained in the joint gap by wetting and capillary action, while the base metal is in solid state, relying on liquid brazing material and solid mother The interdiffusion between the materials forms a brazed joint. Brazing has little influence on the physical and chemical properties of the base metal, and the welding stress and deformation are small. The dissimilar metals with different welding properties can complete multiple welds at the same time. The joint appearance is neat and tidy, the equipment is simple, and the production investment is small. However, the brazed joint has low strength and poor heat resistance.

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