Welding characteristics of cemented carbide-3

       

Selection of base material and groove design

(1)Selection of base material



Cemented carbide is usually used in conjunction with the base material. The choice of base material mainly considers the size of the load on the cemented carbide. The tool base material for general load can be 45 steel or 40Cr steel. The tool body that needs to be hardened can choose 9SiCr steel, because the temperature of the cooling medium for quenching after welding of 9SiCr steel is higher than that of 40Cr, which is beneficial to cemented carbide.

When 9SiCr steel is used as a small knife body, air cooling or compressed air cooling can also be used, which can also make the knife shaft reach a certain hardness. The base material of some cemented carbide tools that are subjected to stress, impact and cutting heat, such as the tool shaft of a large planer, can be 50 steel or 55 steel. High-precision cemented carbide tools can use W18Cr4V high-speed steel as the base material, and use air cooling after welding. Because the linear expansion coefficient of high-speed steel is closer to that of cemented carbide, the welding stress is also smaller, and the tool life is relatively high .

(2)Groove design

The brazing quality of steel and cemented carbide tools also depends on whether the groove design is reasonable. The principle of cemented carbide channel design is as follows.

① Minimize the brazing surface, avoid the use of closed and semi-closed groove structures to reduce brazing stress and prevent cracks, and use free welding grooves to minimize brazing stress as much as possible.

②When assembling the cemented carbide before welding, the cemented carbide should be placed according to the weight of the cemented carbide or the position of the boss, groove and other parts of the base, and try to avoid using fixtures to fix the cemented carbide.

③When designing the groove shape, it is necessary to promote slag removal during the brazing process, so as to avoid reducing the welding strength or de-soldering caused by slag inclusion in the weld.

④After brazing, do not stick too much solder on the cutter head to avoid difficulty in grinding, especially when designing hard alloy multi-blade cutters.

This shape of the sipe increases the welding surface, greatly increases the welding stress of the cemented carbide blade, and complicates the stress distribution, which may cause the cemented carbide to crack. Carbide blades will shorten the life of the tool. The more reasonable groove design of the groove is shown in Figure 2. This design makes the carbide blade only bear the stress of two brazing surfaces during brazing. The possibility of cracking during brazing is less than that of tools with closed or semi-closed grooves, and the tool life is longer.

The groove design of the hard alloy free welding tool is shown in Figure 3. This design can reduce the groove design of the brazing surface, thereby reducing stress and avoiding cracks without increasing the groove processing procedure. This design reduces the welding surface between the cemented carbide blade and the steel blade body to one, and leaves only 30%-40% of the thickness of the blade at the side weld, which plays a role in the positioning of the blade. The design of the free welding groove shape can minimize the brazing stress, can greatly reduce and prevent the generation of brazing cracks, and extend the service life of the tool by 10% to 30%.

For some cemented carbide tools, measuring tools or the groove design of the mold with a larger brazing surface, machining grooves can be used to separate the larger welding surface or several small parts to reduce the brazing stress and avoid cracks . At the same time, the process trench can also play a role in removing slag to ensure that the weld has sufficient strength. The width and depth of the treatment tank can be about 1.5-2 mm, and the number of treatment tanks can be determined according to the size of the brazing surface.

The vertical welding of cemented carbide inserts can double the thickness of the cutting part of the cemented carbide inserts, and the compressive strength of cemented carbide at room temperature or high temperature is much higher than that of steel, and it can withstand greater cutting and cutting forced heating Can prevent rupture or collapse. The double-bladed surfacing method can also stack two different grades of carbide blades, such as YG8 blades for the lower layer and YT15, YT30, YG3X, YG6X and other blades for the upper layer. Since the linear expansion coefficients of the upper and lower layers of the cemented carbide are relatively close, the upper layer of the cemented carbide blade will not crack after brazing, and the residual stress is very small.

The characteristics of using cemented carbide tools for mining are large impact load and large vibration. The cemented carbide plates must be firmly welded, and the brazing stress must be small, so that cemented carbide drills will not appear during use. Desoldering and chipping. When designing this groove shape, there must be enough brazing area to ensure that the weld has sufficient strength, and it is necessary to consider reducing the brazing stress as much as possible. When the length of the cemented carbide block does not exceed 20mm, the width of the groove B = [b + (0.1~0.15)] mm (b is the width of the cemented carbide). When the length of the cemented carbide block is greater than 20mm, the brazing method of the compensation gasket should be considered, and a layer of metal plate with good plasticity should be inserted in the weld to reduce the brazing stress and prevent cracks. At this time, the width of the groove B = [b + 2C + (0.15~0.25)] mm (where C is the thickness of the compensation pad).

In immersion brazing or brazing under certain special conditions, in order to fix the cemented carbide blade or facilitate the positioning of the cemented carbide, a groove shape with a processed wall can be designed, and the processed wall can be minimized. Thickness and height. . Reference tool slots