Preparation before vacuum brazing
Inspect cemented carbide for cracks, bends or uneven imperfections. The brazing surface must be smooth. If it is spherical or rectangular, the brazing surface of the hard alloy should also conform to a certain geometric shape to ensure a good contact between the alloy and the matrix, so as to ensure the quality of brazing.
Hard alloy sandblasting treatment. In the absence of sand blasting equipment, the hard alloy can be held by hand and the oxide layer and black brand letters on the brazed 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 filler metal will not easily wet the cemented carbide. Experience has shown that sand blasting should be used if oxide or black lettering is present on the brazed surface. Otherwise, the solder is difficult to wet the hard alloy, brazing joints still appear obvious black letters, reducing the brazing area, causing the phenomenon of unsoldering.
When cleaning cemented carbide brazed surfaces, it is best not to use chemical mechanical grinding or electrolytic grinding methods, as they rely on adhesives (cobalt) to corrode the cemented carbide surface layer to speed up grinding or improve grinding efficiency. When the cobalt on the surface of the hard alloy is corroded, the solder is difficult to wet the hard alloy again and easy to cause peeling. The surface of the material must be cleaned before vacuum brazing.
Rub W3.5 diamond abrasive paste on the cast iron and grind the brazing part of hard alloy until it is bright. The 40Cr steel was also treated: first, the surface dirt was removed on the W150 sandpaper, and then polished on the W40 sandpaper. The solder should also be polished on W150 sandpaper to keep the surface clean.
Wash 40Cr steel, YG8 carbide and filler metals in acetone to remove oil stains from the surface. After treatment, the filler metal is placed between the hard alloy and the 40Cr steel (the hard alloy is at the top) and placed into the fixture. In special cases, when the cemented carbide brazing surface must pass through the above method or WEDM treatment, the treated cemented carbide can be sand blasted or ground with silicon carbide grinding wheel to remove the surface layer. The sanded cemented carbide can be cleaned with gasoline and alcohol to remove grease.
Carefully examine the groove shape on the steel base. Especially for fissionable cemented carbide and large brazing surface cemented carbide workpieces, more stringent requirements should be required. The slots are also sanded and cleaned to remove grease stains. When cleaning a large amount, you can use the alkaline solution to boil for 10-15 minutes. High-frequency or copper dip brazing multi-blade cutting tools and sophisticated measuring tools, preferably with saturated borax solution boiled for 20-30 minutes, removed and dried before welding.
Wipe the filler metal with alcohol or gasoline before use and cut and shape it according to the brazing surface. When brazing cemented carbide tools or dies, the thickness of the filler metal is about 0.4-0.5mm, which is similar to the size of the brazing surface. When the brazing furnace is heated by continuous nitrogen protection, the filler metal can be appropriately added.
The area of brazing plate should be reduced as much as possible when brazing carbide multi-blade cutting tools and measuring tools. Usually, the brazed plate can be cut into about 1/2 of the brazed surface. When brazing is practiced, the brazing plate can be reduced to 1/3 or less of the brazing surface. Reduce solder filler metal can make the workpiece beautiful appearance, grinding more convenient.