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Vacuum Brazing Furnace

vacuum Brazing Process Method, Quality Problems and Solutions of Woodworking Tool Carbide and Steel

1. Preparing woodworking tools for welding

(1) Check whether the cemented carbide is defective before welding. The welding surface must meet the technical requirements of the drawing and ensure that there is a parallel gap between the alloy and the substrate, so that the welding quality can be easily guaranteed.

(2) Sandblasting or grinding the welding surface of the cemented carbide to remove the oxide layer and grease on the brazing surface to ensure that the cemented carbide is easily wetted after the brazing filler metal is liquefied, so as to avoid the phenomenon of virtual welding or even de-soldering.

(3) Before welding, check whether the welding surface on the steel base meets the technical requirements of the drawing. The steel substrate is also sandblasted and cleaned to remove oil. Solder after drying.

(4) The solder should be cut and cut in advance and cleaned with alcohol or gasoline; the shape of the solder with specific requirements should be similar to the welding surface.

(5) Practical experience has proved that if there is no requirement for high hardness in the welding position of the steel matrix, the initial state of low hardness in the welding area should be ensured or the part of the overall quenched blank should be subjected to high-frequency local annealing treatment, which can reduce the quenching of the steel matrix. The influence of stress on the quality of the weld; if there is quenching stress in the steel matrix, the brazing heating will generate stress again, and the combined effect is prone to quality problems such as carbide deformation, cracking or weld cracking and carbide falling off.

2. Brazing process and process parameters

(1) The heating speed has a significant impact on the welding quality.

(2) Practice has proved that the order of brazing operations and the position of solder and flux have a direct impact on the quality of brazing. The appropriate sequence is: first sprinkle or apply flux on the welding position of the steel substrate and the cemented carbide, put the brazing filler metal on the fixed steel substrate, and finally put the cemented carbide.

(3) The cooling rate after welding is one of the main factors affecting brazing cracks. When cooling, the surface of cemented carbide produces instantaneous tensile stress. Since the tensile stress of cemented carbide is much lower than the compressive stress, it is very important to control the cooling rate after welding. The usual practice is to immerse the workpiece in lime powder or charcoal powder immediately after welding to cool the workpiece slowly. This method is simple to operate and has a certain effect of tempering to relieve stress, but it cannot control the tempering temperature and effect. It is best to put the workpiece into the tempering furnace immediately after welding, and temper it at 320-350 ° C for 6 h. Timely low-temperature tempering treatment can eliminate part of the brazing stress, reduce cracks, and prolong the service life of cemented carbide tools.

3. Brazing process quality inspection and method

Weld gap (weld thickness) is an important parameter to ensure welding quality. If the weld layer is too thin, the defect of insufficient flow filling (brazing impermeability) will occur, which will reduce the welding strength and increase the welding stress; while the weld layer is too thick, the capillary action will be weakened, which will also lead to insufficient filling (brazing is not enough). Even if the filling is sufficient, the strength of the weld will decrease, and even the strength of the free solder itself. Therefore, the thickness of the weld layer of moderate size has a great relationship to reduce the welding stress and enhance the weld fastness.

To verify the feasible brazing process, generally only check the quality of the welded cemented carbide and the steel matrix and whether the cemented carbide itself has cracks. The seam should be uniform without black spots, pores and cracks; check whether the thickness of the weld meets the design requirements. Whether the position of the carbide brazing blank meets the requirements.