Brazing of hard alloy and steel-2

       

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(2) Commonly used protective coatings

There are two types of protective coatings commonly used in hard alloy brazing.

① The black ink used for printing and the quartz powder of 240 grit are mixed evenly according to the ratio of 1:2, and adjusted into a paste, ready for use.

② After mixing 20% Al2O3 powder and 80% graphite powder evenly, it is mixed with 5% water and 50% water glass (modulus 1.2, density 1.6g/cm3) liquid. The more alumina, The higher the strength of the coating.

(3) Measures to be taken in brazing

When the crucible for copper immersion brazing is heated to 450-550°C, the brazing filler metal is started, and when it is heated to 750-780°C, borax is put into it. During the heating process, borax melts first, and then the brazing filler metal. When the solder is melted, borax floats on the solder. Borax can not only prevent the oxidation of the solder, but also avoid the volatilization of the metal in the solder, and make the temperature of the solder uniform. Whether the temperature of the iron wire solder can be used before brazing is moderate. Insert the iron wire into the copper liquid and then pull it out. If a thin layer of copper is evenly adhered to the iron wire, it indicates that the temperature of the solder is suitable and can be soldered; if the copper sticking on the iron wire is too thick, it indicates that the temperature of the solder is too low ; If there is too little copper sticking to the iron wire, and the copper liquid drops continuously after the iron wire is taken out, it indicates that the temperature of the solder is too high.

Before immersion copper brazing, the workpiece should be preheated at 400～500℃, and then put into the borax solution for the second preheating. When the temperature reaches 700℃, it can be immersed in the copper liquid. weld. The time of dip soldering varies with the shape and size of the tool. Calculated according to the smallest size of the section, it takes 12s per millimeter. In order to prevent the paint on the surface of the workpiece from falling off, the workpiece cannot be swayed back and forth when dipping in copper liquid. After the dip soldering reaches the specified time, the workpiece should be lifted slowly to prevent the solder from being lost due to condensation in time. After welding, the workpiece should be kept warm and slowly cooled to reduce stress. Some substrates require hardened workpieces, which can be quenched while heating and brazing.