Cause analysis and judgment of the hottest cranksh

2022-08-21
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Cause analysis and judgment of crankshaft ablation failure

crankshaft ablation is mainly caused by the failure to form an effective lubricating oil film between the crankshaft journal and the bearing bush, resulting in direct friction between the crankshaft journal and the bearing bush. When the crankshaft of the diesel engine is ablated, it will emit white smoke, emit metal impact noise, and even cause the crankshaft and bearing bush to lock together and cannot rotate. Therefore, it is necessary to correctly analyze and judge the cause of its failure

1. Poor oil quality

1) poor oil quality. The quality grade and viscosity grade of the selected engine oil are low, or the engine oil of different brands is mixed, resulting in the service performance of the engine oil not meeting the requirements; The engine oil is mixed with a lot of dust during use, and the engine oil is oxidized and deteriorated due to the high operating temperature of the diesel engine. The oxidized and deteriorated engine oil is black, Matt, and the concentration increases. Twist the engine oil with two fingers, and feel that there are dust, impurities, etc. in the engine oil. If the oil used shows the above phenomena, it must be replaced in time

industrial and commercial enterprises will obtain the fund through the UK research and innovation management competition agency. 2) engine oil becomes thinner. Because some diesel engine fuel injection pumps are lubricated by pressure lubrication, once the seal between the fuel injection pump and the lubricating oil passage fails. Diesel oil entering the lubricating oil chamber will dilute and deteriorate the lubricating oil of the diesel engine. In addition, if the water jacket has cracks or sand holes, making the cooling water penetrate into the engine oil will also make the engine oil thinner

check the upper parts of the diesel engine (upper plane of cylinder head, air valve mechanism, cylinder head cover) for water vapor or water droplets. If it is found that the capacity of engine oil increases, the concentration decreases, the viscosity decreases, and there is an oily smell, it indicates that diesel oil is mixed in the engine oil

2. Insufficient oil stock and low oil pressure

insufficient oil stock will improve the comprehensive strength of cutting-edge science and technology in China, and low oil pressure will cause insufficient flow of diesel engine lubricating oil, which can not guarantee the formation of lubricating oil film between diesel engine crankshaft journal and bearing bush

check the quantity of oil in the oil pan and the reading of the oil pressure gauge, and further check whether there are abnormal phenomena such as blockage and leakage in the oil pipeline

3. The clearance between crankshaft journal and bearing bush is too large or too small

1) due to the large clearance between crankshaft journal and bearing bush, the oil pressure of diesel engine is low, and it is impossible to form a sufficient lubricating oil film that can be automatically and continuously loaded according to the given procedure

2) due to the small clearance between crankshaft journal and bearing bush, the oil film thickness between crankshaft journal and bearing bush is insufficient or there is no lubricating oil film

when the clearance is too large or too small, the dimensions of journal, bearing hole and bearing bush can be checked with micrometer and cylinder gauge to calculate their fitting clearance, or the fitting clearance can be measured directly with feeler gauge

4. The geometric dimension of the crankshaft or cylinder block is out of tolerance

1) the radial runout of the crankshaft is large, resulting in small or no clearance between the journal and the bearing bush, insufficient thickness of the lubricating oil film or no lubricating oil film

2) the coaxiality of the main bearing hole of the cylinder block is out of tolerance, resulting in too small or no clearance between the main journal and the bearing bush, insufficient lubricating oil film thickness or no lubricating oil film

3) the perpendicularity of cylinder and main bearing hole is out of tolerance, resulting in too small or no clearance between connecting rod journal and main journal, insufficient lubricating oil film thickness or no lubricating oil film

the above phenomenon often occurs when the diesel engine is put into use for a short time after a new engine or overhaul. To determine the position where the geometric dimension exceeds the tolerance, first rotate the diesel engine crankshaft with a hand crank (hard rotation), then loosen the diesel engine main bearing cap and connecting rod bearing cap cylinder by cylinder, and then rotate the crankshaft. It is determined according to the torque of the rotating crankshaft and the change difference (but to determine the size of the over difference, the diesel engine needs to be disassembled and measured with a special inspection tool)

5. The shape and size of crankshaft main journal and connecting rod journal are out of tolerance

the cylindricity or taper of crankshaft main journal, connecting rod journal or cylinder block main bearing hole, connecting rod big end hole and the error will decrease with the increase of load. The large degree difference will make the gap between journal and bearing bush intermittent (intermittent) or conical. Good lubricating oil film cannot be guaranteed

the diesel engine is not put into use for a long time after a new engine or overhaul, which is prone to the above phenomena. The journal size can be measured. If the measured journal is ablated, the adjacent corresponding journal can be measured (because the adjacent corresponding journal is processed with the same equipment and the same cutting tool under normal conditions, which can represent the shape error of the ablated Journal)

6. The surface roughness of crankshaft main journal and connecting rod journal is out of tolerance

due to the poor roughness, there are many metal ridges on the surface of the journal, which destroys the integrity and continuity of the lubricating oil film between the journal and the bearing bush. The metal ridge peak directly rubs with the bearing bush, causing crankshaft ablation

faults often occur when the diesel engine is not put into use for a long time after a new engine or overhaul. If the tested journal is ablated, the roughness detector can be used to measure the adjacent corresponding journal (because in general, the adjacent corresponding journal is processed with the same equipment and the same cutting tool, so the measured roughness can represent its ablated journal roughness)

7. The dynamic balance of crankshaft, flywheel and clutch is out of tolerance

when the dynamic balance is out of tolerance, the crankshaft rotates at high speed to produce inertia force, which will damage the fit clearance between crankshaft journal and bearing bush, and in serious cases, it will cause direct friction between journal and bearing bush, resulting in crankshaft ablation

the fault usually occurs after the machine has been driven for 10000km. After the crankshaft is ablated, the residual debris on the journal can be removed and the dynamic balance can be re calibrated. Its imbalance basically indicates that the dynamic balance of the ablated journal is out of tolerance

8. Improper maintenance

if the diesel engine is not properly maintained after running for a period of time, it will cause wear, failure and deformation of parts such as the pressure limiting valve of the oil pump. The oil filter element will be blocked by oil dirt and sludge, which will reduce the oil pressure and cause crankshaft ablation

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