Hot cracks occur in bucket teeth during solidification, when bucket teeth are in plastic deformation state. The liquid metal solidifies from the surface of the castings under the heat transfer of the mold wall. A large number of dendrites appear and form a complete skeleton, resulting in solid shrinkage. At this time, there is a layer of film between dendrites that has not yet solidified.
If the solidification of bucket teeth castings is not hindered by any hindrance, that is, the dendrite is not affected by force, the castings shrink freely, and the internal stress gradually occurs. If the shrinkage of dendrite layer is hindered by core and core, and the shrinkage of dendrite layer is affected by tensile force, the tensile stress of dendrite layer appears. When the tensile stress exceeds the strength limit of the liquid film, the dendrites will be pulled apart. If enough liquid metal flows into the crack area in time, the bucket teeth castings will not produce hot cracks, otherwise hot cracks will occur.
The main reason is the uneven shrinkage of the formed parts. During the filling process of parts, the temperature field of the die is not uniformly distributed, the forming specific pressure is relatively low, and the parts can not be effectively compensated, which will cause the non-uniform shrinkage of the parts after forming.
Because of the thin wall thickness and good thermal conductivity of the workpiece in the bucket tooth cavity, the part solidifies before the hot spot part, which results in a great encapsulation force on the core of the bucket tooth. In the process of core pulling, there will be a tension stress. At the same time, because the runner has solidified at this time, it will have a certain resistance effect on the direction of core pulling. This resistance is a tension stress in the opposite direction as compared with the front tension stress.
If the effect of these two tension stresses is greater than that of the yield stress of the material at high temperature, the workpiece will be pulled apart at the weak point, forming a hot crack, that is, the so-called bucket teeth shrinkage crack.
Huangzuan Machinery established in 2008, is a specialized manufacturer of bucket teeth, bucket adaptor and side cutter which is used Caterpillar, Komatsu, Hyundai, Daewoo, Kobelco, Hensley, Liugong, Hitachi, XCMG, XGMA, Volvo, JCB .etc.
With production facilities covering an area of 18136 square meters and staff of 100, our annual processing capability equals approximately 12,000 metric tons. we currently have the technology of lost wax casting, precoated sand casting, resin sand casting, have the advanced instrument such as spectromaxx, Brinell hardness tester, universal testing machine, metalloscope.