① Before welding, check the cemented carbide for cracks, bends, or unevenness defects. The brazing surface must be flat. If it is a spherical or rectangular cemented carbide brazing surface, it should also conform to a certain geometric shape to ensure good contact between the alloy and the substrate to ensure the brazing quality.
② Perform sandblasting on the cemented carbide. Without sandblasting equipment, you can hold the cemented carbide in your hand and grind off the oxide layer and black brand letters on the brazing surface on the rotating green silicon carbide wheel. If the oxide layer on the brazing surface of the cemented carbide is not removed, the solder will not easily wet the cemented carbide. Experience has proved that if there is an oxide layer or black brand letters on the brazing surface, it should be sandblasted, otherwise the brazing filler metal will not easily wet the cemented carbide, and there will still be obvious black letters in the brazing seam, which will reduce the brazing area and cause Desoldering phenomenon.
③ When cleaning the hard alloy brazing surface, it is best not to use chemical mechanical grinding or electrolytic grinding, because they all rely on the bonding agent (cobalt) that corrodes the hard alloy surface layer to speed up the grinding or improve the grinding efficiency Yes, and after the cobalt on the surface of the cemented carbide is corroded, it is difficult for the solder to wet the cemented carbide again, which is likely to cause desoldering. Under special circumstances, when the cemented carbide brazing surface must be treated by the above method or wire EDM, the treated cemented carbide can be sandblasted or the surface layer can be ground with a silicon carbide grinding wheel. The cemented carbide after sandblasting can be cleaned with gasoline or alcohol to remove oil stains.
④ Before brazing, check carefully whether the trough shape on the steel substrate is reasonable, especially for easily cracked cemented carbide and cemented carbide workpieces with large brazing surfaces. The knife groove is also sandblasted and cleaned to remove oil stains. When the cleaning volume is large, use alkaline solution to boil for 10-15 minutes. For high-frequency or copper-dip brazing multi-blade tools and complex measuring tools, it is best to boil them with saturated borax aqueous solution for 20-30 minutes, take them out and dry them before welding.
⑤ Wipe the filler metal with alcohol or gasoline before use, and cut it into shape according to the brazing surface. When brazing general hard alloy tools or molds, the thickness of the brazing filler metal is about 0.4-0.5mm, and the size is similar to the brazing surface. When heating with a coke oven, the filler material can be increased appropriately. When brazing hard alloy multi-blade tools, measuring tools and other workpieces, the area of the brazing sheet should be minimized. Generally, the brazing sheet can be cut to about 1/2 of the brazing surface. When the brazing technique is proficient, The solder sheet is reduced to 1/3 or less of the brazing surface. Reducing the solder can make the appearance of the workpiece after welding beautiful and more convenient for sharpening.
(2) Brazing process
Whether the brazing process of cemented carbide tools is correct has a crucial effect on the quality of welding. The heating speed has a significant effect on the welding quality. Fast heating will cause cracks and temperature unevenness in the cemented carbide sheet; but too slow heating will cause surface oxidation and reduce the strength of the joint.
