(1) the brazed surface of tungsten steel shall not be sand treated or polished before welding. The oxide layer on the brazed surface reduces the wetting effect of the solder and weakens the bond strength of the weld.
(2) improper selection and use of welding flux also occur. For example, borax is used as the welding flux. Because there is too much water in raw borax, it can not effectively deoxidize, solder can not be hard welded on the surface, and good wetting and desoldering occur.
(3) suitable brazing temperature should be higher than the melting point brazing filler metal is the most suitable when the temperature is 30 ~ 50 ℃, too high or too low will lead to desoldering. Overheating can cause oxidation of the weld. Use zinc solder to make the weld blue or white. When the brazing temperature is too low, the weld is thick and full of pores and slag. The above two conditions can lead to the reduction of weld strength, and it is easy to desquamate when grinding or using.
In the process of brazing, slag or slag can not be discharged in time, so that a large number of solder slag remains in the weld, so as to reduce the strength of the weld and lead to welding.
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