Preparation before welding for vacuum brazing

【Summary Description】 1) Before vacuum brazing, check whether the cemented carbide has cracks, bending or uneven defects. The brazing surface must be smooth, if it is spherical or rectangular carbide brazing surface should also conform to a certain geometric shape, to ensure good contact between the alloy and the substrate, in order to ensure the quality of brazing. 2) sandblasting hard alloy. Without sandblasting equipment, hard alloy can be held by hand and the oxide layer and black brand letters on the brazing surface can be ground on the rotating green silicon carbide grinding wheel. If the oxide layer on the brazing surface of the cemented carbide is not removed, the brazing filler metal is not easy to wet the cemented carbide. Experience has proved that if there is an oxide layer or black brand letters on the brazing surface, sandblasting should be carried out, otherwise the brazing material is not easy to wet the hard alloy, and obvious black letters will still appear in the brazing seam, which will reduce the brazing area and cause deswelding. 3) when cleaning the hard alloy brazing surface, it is best not to use chemical mechanical grinding or electrolytic grinding and other methods, because they all rely on the binder (cobalt) that corrodes the hard alloy surface layer to speed up grinding or improve grinding efficiency, and after the cobalt on the hard alloy surface is corroded, the brazing filler metal is difficult to re-wet the hard alloy, which is easy to cause welding off. The surface of the material must be cleaned before vacuum brazing. The method is: apply W3.5 diamond grinding paste on the cast iron block, and polish the hard alloy brazing part until it is bright. Also on the 40Cr steel surface treatment: first in the W150 water sandpaper to remove the surface dirt, and then in the W40 sandpaper sanding. The solder shall also be sanded on W150 sandpaper to make the surface clean. Finally, 40Cr steel, YG8 hard alloy and brazing filler metal are cleaned in acetone to remove surface oil stains. After the treatment, the brazing filler metal is placed between hard alloy and 40Cr steel (hard alloy is located in the upper part), and then put into the fixture together. Under special circumstances, when the hard alloy brazing surface must be treated by the above method or electric spark wire cutting, the treated hard alloy can be sandblasted again or the surface layer can be ground with silicon carbide grinding wheel. The cemented carbide after sandblasting can be cleaned with gasoline and alcohol to remove oil stains. 4) Before vacuum brazing, carefully check whether the groove shape on the steel substrate is reasonable, especially for hard alloy workpieces with crack grades and large brazing surfaces, which should be strictly required. The knife slot is also sandblasted and cleaned to remove oil. When the amount of cleaning is large, the alkaline solution can be boiled for 10~15min. High-frequency or immersion copper brazing multi-blade tools and complex measuring tools, it is best to use saturated borax aqueous solution boiling 20~30min, take out and dry before welding. 5) before using the brazing filler metal with alcohol or gasoline wipe, and according to the brazing surface cutting shape. When brazing general carbide 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 continuous nitrogen protection brazing furnace, the brazing 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 reduced as much as possible. Generally, the brazing sheet can be cut into about 1/2 of the brazing surface. When the brazing technology is skilled, the brazing sheet can be reduced to 1/3 or less of the brazing surface. Reducing the brazing filler metal can make the appearance of the workpiece after welding more convenient.

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Vacuum Brazing Process of Cemented Carbide