The fracture of crankshaft usually starts from the smallest crack, and most of the fracture parts are at the connecting part between the head cylinder or the end cylinder connecting rod journal fillet and the crank arm. In the process of operation, the crack expands gradually and breaks suddenly when it reaches a certain degree. The brown part is often found on the fracture surface, which is obviously an old crack. If the broken surface is shiny, it means that it is suddenly broken. This article will summarize three reasons for the fracture of excavator crankshaft.
1. the fillet at both ends of crankshaft journal is too small
When grinding the crankshaft, the grinder failed to correctly control the fillet of the crankshaft. Except that the arc surface is rough, the fillet radius is too small. Therefore, when the crankshaft is working, a large stress concentration will occur at the fillet, and the fatigue life of the crankshaft will be shortened.
2. crankshaft main journal axis offset
The crankshaft main journal axis is offset, which destroys the dynamic balance of the crankshaft assembly. When the diesel engine runs at high speed, it will produce a strong inertia force, which will lead to the fracture of the crankshaft.
3. the cooling ratio of crankshaft is too large
The crankshaft will be greatly bent after long-term use. It should be removed for cold pressing correction. The internal metal plastic deformation of the crankshaft will produce great additional stress during correction, which will reduce the strength of the crankshaft. If the cold strain is too large, the crankshaft may be damaged or cracked. This kind of crankshaft will break soon after installation.
