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Brazing requirements for carbide woodworking tools

Main problems in the vacuum brazing process of carbide woodworking tools
After cleaning before welding, filler metal and flux are added between the blade and the cutter body. After melting, the welding gap is filled to complete the firm welding of the blade and the cutter body. The brazed carbide blade is subjected to reasonable vacuum heat treatment. Reduce welding stress and prevent cracks. There are two main problems in using the welding process to weld the carbide blade to the steel body:

(1) Due to the different linear expansion coefficients and thermal conductivity of the carbide blade and steel (the linear expansion coefficient of carbide is 5~7×10^-6/℃, while that of steel is 11~14×10^-6/ ℃), when the blade is cooled under the high temperature of welding, internal stress often occurs, causing cracks in the blade.

(2) Due to the poor wettability of ordinary solder to cemented carbide, the blades are often not welded firmly and will desolder under the impact of cutting forces. Therefore, in order to prevent welding cracks and desoldering phenomena, it is necessary to study the welding stress, solder wettability, flux and welding process specifications when welding carbide tools.
Vacuum brazing requirements for carbide woodworking tools
①Brazing temperature.
② Solder strength or elastic deformation ability and cooling performance.
③The thickness of the weld.
④The ratio of the thickness of cemented carbide and steel.
Precautions after vacuum brazing of carbide woodworking tools
The quality inspection of woodworking tools after vacuum brazing is to check whether there are pores in the weld and whether there are cracks in the welded workpiece. Tools that have been inspected for defects can be reheated and brazed, but the number of rewelding should be minimized to avoid affecting the quality of the carbide due to repeated heating.

For workpieces that have cracked, the cracked carbide should be removed and re-brazed after analyzing the cause.
Vacuum brazing process of cemented carbide and steel
(1) Preparation before welding
① Before welding, the cemented carbide should be checked for cracks, bends and other defects to ensure that the brazing surface is flat and has a certain geometric shape, and that it maintains good contact with the substrate.
② Sandblast the cemented carbide to remove the oxide layer and black letters on the brazing surface to prevent desoldering.

(2) Vacuum brazing process
① When welding carbide tools, uniform heating of the tool holder and tool head is the basic condition to ensure welding quality. If the temperature of the carbide part is higher than that of the tool holder, the molten filler metal will wet the carbide but not the tool holder, and the strength of the joint will be reduced. When the carbide is sheared along the weld, the filler metal will not be destroyed but will harden as the carbide is sheared. The alloy is detached. If it is the opposite, the phenomenon is opposite.
② Cool after vacuum brazing. During cooling, instantaneous tensile stress occurs on the surface of the cemented carbide sheet, and the tensile stress of the cemented carbide is much lower than the compressive stress. Usually the workpiece is inserted into a lime tank or charcoal powder tank immediately after welding to allow the workpiece to cool slowly. If possible, the workpiece can be placed into a furnace at 220℃-250℃ for tempering for 6h-8h immediately after brazing. The use of low-temperature tempering treatment can eliminate part of the brazing stress, reduce cracks and extend the service life of carbide tools.
③Clean up after welding. The welded carbide workpiece should be cleaned after welding to clean up the residual solvent around the weld. The common cleaning method is to put the post-weld cooling workpiece into boiling water and boil it for about 1-2 hours, and then sandblast it. , to remove residual flux and oxides adhered around the weld.

(3) Quality inspection of vacuum brazing
Normal welds should be uniform without black spots, the welds not filled with filler metal should not be greater than 10% of the total length of the welds, and the width of the welds should be less than 0.15mm. The tendency of cemented carbide to crack can be detected by the following method.
① After the tool is sandblasted, clean it with kerosene and observe it with the naked eye and a magnifying glass. There are obvious black lines when there are cracks.
② Use 65% kerosene, 30% transformer oil and 5% turpentine to make a solution, add a small amount of Sudan red, soak the inspected cutting tools in the solution for 10-15 minutes, take them out, wash them with clean water, apply kaolin clay, and bake Check the surface after drying. If there are cracks, the color of the solution will show in the white clay and can be detected with the naked eye.