"10 common reasons for diesel engine breaking crankshaft fault" are as follows:
1 bad lubrication.
The oil path of the lubricating system of the diesel engine is not smooth, so that the connecting rod bearing and the shaft neck are in the semi friction condition, that is, the failure of the bearing shaft may occur. Because the ablative force of the ablative part is weakened, the radial runout of the shaft will be frequent and the stress changes after the root ablation, that is, it will cause the fracture between the crankshaft journal root and the crank arm. Malfunction.
2 bearings are not working.
Taking the 6135 diesel engine as an example, if the rolling bearing of the spindle bearing is rolling, or the gap is too large for a long time, so that the different axis of the main bearing is too big, that is, the radial round jump of the crankshaft is frequent, and the diesel engine flywheel itself has a certain weight, and the working impact of each cylinder is added, which makes the crankshaft stress uneven. If the assembly clearance of the connecting rod bush is too large or the alloy falls off, the impact load will also increase, resulting in the fracture of the crankshaft at an early stage.
It is one of the important reasons for the early fatigue and fracture of the crankshaft that the 3 main bearing cover nut is loose, the crankshaft loses its bearing, or the coaxiality of each bearing hole of the crankshaft is deviant.
Take a 6105 Diesel engine as an example. If a main bearing nut is loose, the gap between the shaft and the axle must exceed the allowable range, so that the bearing of the main shaft is lost. If the concentricity is deviated from the front and last end bearing holes, the crankshaft will be related to the crankshaft when the crankshaft rotates. Different load will inevitably lead to crankshaft fracture.
4 the crankshaft is oversized in the axial direction.
The large axial clearance of the crankshaft is the main cause of the axial movement of the crankshaft. Take the 6105 Diesel engine as an example, the fourth main bearings are combined with the thrust sheet (commonly known as the combined flanging tiles) to make the crankshaft axial orientation and ensure a certain axial clearance. When the momentum reaches to 0.5~0.6mm or more, the consequence is wood. The crankshaft arm of crankshaft will bear more counterforce when facing the load of the oil turbine. Because of the stress concentration, it is possible to accelerate the development of crankshaft fracture.
The 5 flywheel was open.
If the flywheel bolt is loose, the high-speed rotating crankshaft assembly will lose its original dynamic balance and produce a large inertia force, causing the crankshaft fatigue and easy to break at the tail end. The crankshaft and the flywheel are conformed with the cone hole (such as S195 diesel engine). If the area is less than 75%, the diesel engine will loose at work and thus impact the crankshaft. The shaft causes cracks in the parts matching the outside of the keyway and breaks the crankshaft.
6 the dynamic imbalance.
In the process of maintenance, if the crankshaft is replaced by the unbalanced iron or the unbalanced iron dislocation, it destroys the original balance and makes the crankshaft bear great inertia impact. In addition, the crankshaft, if the crank arm and the crank radius are offset, will cause the imbalance to exceed the allowable value greatly, thereby causing the crankshaft to exceed the allowable value. The unbalanced centrifugal force will cause overload of the bearing and cause strong vibration of the diesel engine, which will cause fatigue fracture of the crankshaft for a long time.
7 improper grinding of the crankshaft.
The most important factor affecting the bending fatigue strength of the crankshaft is the transition round angle between the connecting rod journal and the crank arm, and the transition round angle between the spindle neck and the crank arm. So, when the crankshaft is mended, the coaxiality, parallelism, crank radius, neck shoulder and other repairs of the crankshaft's spindle neck and the connecting rod journal are only paid attention to. The roughness of the surface, as well as the angle between the various connecting rod necks and the angle between the neck of the connecting rod, and neglecting the size and geometry of the transition angle, so that the grinding wheel is unproperly trimmed when grinding the crankshaft neck. Crack now.
The weight of the 8 parts is super poor.
Take the 6110 Diesel engine as an example, the piston is divided into three groups according to the mass, and the piston installed on the same diesel engine should be divided into four groups (A, B, C, and the difference of the same group quality not exceeding the 8g. connecting rod. The connecting rod on the same diesel engine should also be divided into the same quality group (red, blue, white and yellow) and installed in the same one. The total mass of the piston rod assembly on the diesel engine can not exceed 30g. otherwise, that is to say, the explosive force and the inertia force of each cylinder are not consistent with each other. Thus, the force of the crankshaft is not equal. When the crankshaft is struck by vibration, it may cause the fracture of the crankshaft.
9 incorrectly straightening.
When the crankshaft is found to be bent, when the cold straightening method is used to repair the crankshaft, the straightening amount can often be from several um to several mm., but because the cold straightening is a plastic deformation method, sometimes the impact load is very large, so the greater additional residual stress will be produced and the crankshaft strength is greatly reduced. Therefore, the crankshaft will cause fatigue under the action of long term alternating load. And break.
10 overspeed or flying.
In order to make the diesel engine emergency ceasefire, the diesel engine often runs in excess of the rated speed or accidents, so as to make the diesel engine emergency ceasefire, and take the excessive and violent emergency braking measures, so that the crankshaft is overloaded and the stress increases greatly, and it may also cause the accident of accidental fracture of the crankshaft.
