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The fracture of the crankshaft is usually from the beginning of the minimum crack, crack fracture site is mostly in the head cylinder or the end cylinder connecting rod neck at the round corner and crank arm connection part. In the process of operation, the crack expands gradually and breaks suddenly when it reaches a certain degree. In the fracture surface observation will often find the brown part, which is obviously the old crack, shiny tissue is developed to later suddenly broken traces. Today, let's take a look at the cause of crankshaft fracture.
The fracture of the crankshaft is usually from the beginning of the minimum crack, crack fracture site is mostly in the head cylinder or the end cylinder connecting rod neck at the round corner and crank arm connection part. In the process of operation, the crack expands gradually and breaks suddenly when it reaches a certain degree. In the fracture surface observation will often find the brown part, which is obviously the old crack, shiny tissue is developed to later suddenly broken traces. Today, let's take a look at the cause of crankshaft fracture.
1. The rounded corners of the crankshaft journal are too small
When grinding THE crankshaft, THE grinder fails to control the crankshaft's journal fillet correctly. In addition to the rough processing of the arc surface, the radius of the fillet is too small, so the stress concentration at the fillet is large when the crankshaft is working, and the fatigue life of the crankshaft is shortened.
2. crankshaft spindle axis offset
The deviation of crankshaft spindle neck axis destroys the dynamic balance of the crankshaft components, and the powerful inertia force is generated when the engine runs at high speed, leading to the fracture of the crankshaft.
3. the crankshaft cold contest is too large
The crankshaft is used for a long time, especially after the accident of burning tile or pounding cylinder, there will be a large bending, which should be unloaded for cold pressing correction. Because the internal metal plastic deformation of the crankshaft will produce a great additional stress during the correction, so as to reduce the strength of the crankshaft, if the cold contest is too large, it may be the crankshaft damaged or crack, this crankshaft installed machine will be broken soon after use.
4. The flywheel is loose
If the flywheel bolt loosens, the crankshaft assembly will lose its original dynamic balance, and the engine will jitter after operation, and generate a lot of inertia force, resulting in crankshaft fatigue and easy to fracture at the tail end.
5. the spindle tile is not coaxial
During crankshaft assembly, if the center line of each spindle tile on the cylinder block is not coaxial, the engine is prone to burn tile and hold shaft accident after work, and the crankshaft will also break under the strong action of alternating stress.
6. crankshaft assembly clearance is too large
If the clearance between crankshaft journal and bearing bush is too large, the crankshaft will impact the bearing bush after the engine runs, resulting in alloy shedding and burning tile holding shaft, and the crankshaft is easy to be damaged.
7. the oil supply time is too early or the oil quantity of each cylinder is uneven
If the injection pump oil supply time is too early, the piston has not yet to TDC combustion work, will cause engine detonation, and make the crankshaft by the impact of alternating stress. If the amount of oil supplied to each cylinder is uneven, the force on each crankshaft neck will be uneven because of the inconsistent explosive force of each cylinder, resulting in premature fatigue and cracks.
8. Crankshaft lubrication is poor
If the oil pump is worn seriously, the lubricating oil passage is dirty and the circulation is not smooth, it will make the oil supply is insufficient and the oil pressure drops, leading to the formation of a normal lubricating film between the crankshaft and the bearing bush, resulting in dry friction and causing a burning tile holding shaft, broken crankshaft and other major accidents.
9. Improper operation triggers crankshaft fracture
If the throttle is too large or too small, the brake is too frequent or the overload operation for a long time, the crankshaft will be damaged by excessive torque or impact load. In addition, when the diesel engine has accidents such as flying car, ramming cylinder and top valve, it is easy to make the crankshaft fracture.
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