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Application of potassium cryolite
- Oct 31, 2018 -

Potassium cryolite is used in some industries of the national economy, but the most used is aluminum and aluminum alloy brazing. Potassium cryolite as a flux has become an indispensable part of the connection of aluminum parts. material.


1.1 Flux


1.1.1 Aluminum workpiece brazing joint flux


Because aluminum alloy has a series of advantages such as low density, strong electrical and thermal conductivity, abundant resources, high recoverability, high mechanical properties, good formability, strong corrosion resistance and non-magnetic properties, it has been obtained in various sectors of the national economy. Widely used, it has become the second largest metal material after steel, especially in transportation equipment (aerospace aircraft, rail vehicles, automobiles, motorcycles, magnetic levitation vehicles, etc.). Consumption and reduction of pollutant emissions play a key role. However, the surface of aluminum and aluminum alloy has a very thin dense aluminum oxide film, which on the one hand protects aluminum from further oxidation, makes aluminum highly resistant to atmospheric corrosion, and on the other hand hinders aluminum-aluminum, as well as aluminum and other metals. Brazed joint of material. Corundum silicon carbide diamond grinding wheel abrasive grinding saw blade abrasive cloth belt


In the brazing process of aluminum and its alloys, chloride flux has been widely used because of its good activity, enhanced fluidity of the brazing filler metal, stable and non-failure when heated, convenient to use, and low in cost. However, their biggest disadvantage is that they have strong electrochemical corrosion, strong hygroscopicity and are not easy to store. The post-weld residue in the brazing zone or the cleaning is not completely wetted, and the weldment is severely corroded. It is easily hydrolyzed during heating to deteriorate or even defeat the flux. In addition, the cleaning of the residue after welding is required to be very high and slightly residual, that is, corrosion due to moisture. Fluoride flux is far superior to chloride flux in terms of the internal quality of the braze after brazing and the degree of corrosion of the parent metal; in addition, the fluxing flux, the flowability, the brazing rate, The shear strength and coating properties are also slightly better than the chloride flux.


1.1.2 Application of potassium cryolite in Nocolok brazing method


With the development of the automotive industry, the aerospace industry and the weapon industry, there are an increasing number of aluminum and aluminum alloy parts that need to be brazed. For example, commonly used radiators are brazed by aluminum alloy composite materials, among which radiators and condensers The evaporator and radiator core are all made of aluminum alloy, the surface layer is Al-Si alloy, the composition is equivalent to the Si content of the eutectic point, the melting point is low, 577 °C, in order to facilitate brazing, the Al-Si alloy is brazing. . Corundum silicon carbide diamond grinding wheel abrasive grinding saw blade abrasive cloth belt


In the 1970s, Alcan, which merged with Rio Tinto in 2009, changed its name to Rio Tinto-Alcan, but still operates in the name of Canadian Aluminum Corporation. The vacuum brazing line, called the Noclolk line, is called the Nocolok method. Brazing parts of almost all heat exchange systems today are brazed by this method. Corundum silicon carbide diamond grinding wheel abrasive grinding saw blade abrasive cloth belt.


The role of the flux in the brazing process is: removing the oxides on the brazing metal and the surface of the solder, creating the necessary conditions for the liquid solder to spread on the surface of the soldered base material, covering the brazing base material with a liquid film layer and The surface of the solder is isolated from the harmful effects of oxygen in the air; it acts as an interface to improve the wetting of the surface of the soldered metal by the liquid solder. Corundum silicon carbide diamond grinding wheel abrasive grinding saw blade abrasive cloth belt


In the Nocolok brazing furnace, when the aluminum to be welded is heated to a certain temperature, the organic solvent is mixed with the potassium cryolite powder to the surface of the brazing material. The potassium cryolite powder is dissolved immediately, and the organic solvent volatilizes, which hinders the dissolution of the Al2O3 film on the brazed material to be dissolved in the liquid potassium cryolite. The brazing can be smoothly carried out, and a high-quality brazed joint can be obtained, and the solidified Potassium cryolite is easy to remove, even if the residual potassium cryolite on the weld and the base metal does not cause corrosion in the future, which is the biggest advantage of the potassium cryolite flux. Corundum silicon carbide diamond grinding wheel abrasive grinding saw blade abrasive cloth belt


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