Discussion on the causes and prevention techniques

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Discussion on the causes and prevention techniques of flywheel imbalance of diesel engine

during the operation of a ty120 bulldozer, suddenly, and with the upgrading of technical standards in these fields, the oil alarm red light flashes, at the same time, the engine makes an abnormal sound. After shutdown and inspection, it is known that the oil level in the engine oil pan is within the standard range, the oil pipes are connected normally, and no other abnormal conditions are found. Therefore, the machine is still used to continue the operation, but it does not run for long, The engine suddenly stalled and could no longer be started

after removing the oil pan, it was found that the connecting rod journal was severely ablated and the crankshaft bearing bush was burnt, that is, a typical "axle holding Bush burning" accident occurred. After consultation and analysis, it was believed that the accident was caused by the imbalance caused by the improper installation of the flywheel when repairing the engine

1. The reason for flywheel imbalance

the function of flywheel is to increase the rotational inertia of the engine to ensure the uniformity of speed. In addition, flywheel is also conducive to the start of the engine and the smooth passage of the piston through TDC. At the same time, it has the ability to improve the engine to overcome sudden overload. The flywheel is generally made of HT200 or ZG, and its main processing technology is: Casting → annealing → machining → static balance; Before installation, the dynamic balance calibration of crankshaft flywheel group must be carried out on the balancing machine according to the technical requirements of the drawing. Once the flywheel loses balance during use, it must be corrected again, otherwise the engine will vibrate more and more seriously during operation, resulting in the accident of "axle holding and Bush burning", and sometimes even the relevant parts of the flywheel will be broken. This time, when the flywheel was installed, its imbalance exceeded the specified standard range, which caused strong vibration of the crankshaft when the external load suddenly changed. This vibration destroyed the lubrication between the crankshaft and the bearing bush, and a complete oil film could not be formed on the surface of the bearing bush, causing partial dry friction; Due to dry friction, adhesive wear is caused, causing local high temperature, causing the alloy on the bearing bush to melt, resulting in the accident of "holding the shaft and burning the Bush"

2. Measures to prevent flywheel imbalance

(1) the root cause of flywheel imbalance is that the unbalance exceeds the specified value. After engine overhaul, the flywheel shall be subject to dynamic unbalance test. For 6135 series diesel 1 Online prompt "for the oil engine with failed equipment, the maximum allowable dynamic unbalance is generally 100g? Cm. After the flywheel is assembled with the crankshaft, the total runout of the flywheel plane to the end of the crankshaft axis should not be greater than 0.2mm.

(2) the flywheel should not have cracks, the working surface should be flat and clean, and the flatness error should not be greater than 0.1mm, otherwise it should be flattened, and the enlarged size should not be greater than 1.2mm, otherwise the thickness of the repaired flywheel cannot meet the requirements.

(3) When the working surface of the flywheel is wavy or the groove depth exceeds 0.5mm, light it on the lathe to make it flat; When the depth of the wavy groove does not exceed 0.5mm, no more than two annular grooves are allowed, but the burrs should be removed. When the total end face runout of the flywheel plane to the crankshaft axis exceeds the specification, shims should be added between the flywheel adapter plate and the flywheel for adjustment, and mechanical processing is not allowed

(4) from the analysis of technological process, the increase of offset caused by non annealing of Flywheel Casting is also an important factor leading to flywheel imbalance. During the casting process of the flywheel, a large internal stress is generated on the web. If it is not annealed, cracks may occur when the web in a high stress state is partially defective, uneven in thickness, or partially knocked and impacted by external forces. At the same time, during the processing, balancing and use after installation of the unanealed flywheel, the internal stress of the flywheel during natural aging gradually disappears. In the process of stress disappearance, if there is a local defect in the spoke plate, 6 it is the development of advanced smoke density standard experimental method for plastic combustion or decomposition, such as intellectualization. ASTM D 2843 ⑴ 999 packaging technology means is trapped, or the thickness is uneven, which will make the deformation of the spoke plate along the periphery different, resulting in the increase or decrease of the center of mass offset, The flywheel loses its original balance. Therefore, Qing attaches great importance to the annealing process of flywheel castings

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