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Diesel engine bearing

April 19, 2023

Diesel engine bearing


A part of a diesel engine bearing bearing loads on a rotating shaft. The main bearing parts of the diesel engine are made of plain bearings, which are generally divided, and the two halves are shaped like tiles after being divided, so it is also called bearing bush. The greatest load on a diesel engine is on the main bearing that supports the crankshaft and the connecting rod bearing that connects the crankshaft to the connecting rod.
The plain bearing consists of a shingle back made of high quality carbon steel and anti-friction gold attached to it. According to the different thickness of the tile back, it is divided into thick wall bearing and thin wall bearing. Bearing wall thickness and diameter ratio of 0.065~0.095, alloy layer thickness of 0.75mm~2mm called thick wall bearing; The ratio of wall thickness to its diameter is 0.02~0.065, and the thickness of alloy layer is 0.3mm~0.7mm, which is called thin wall bearing. Thick wall bearing is mainly used for single piece or small batch production; Thin wall bearing is used for mass production.
The anti-wear metal material of sliding bearing requires fatigue resistance, corrosion resistance and good anti-wear performance. The materials suitable for making bearing antifriction gold are babbitt alloy, copper lead alloy and tin aluminum alloy. Babbitt alloy is mostly used in the engine with low load, and its fatigue strength is poor. Copper - lead alloy has high strength, high bearing capacity, but poor surface performance. In order to improve its surface performance, a layer of lead tin alloy can be plated on the copper-lead alloy to form a three-layer alloy bearing bush with steel back - copper-lead alloy - coating, which is widely used in locomotive diesel engine. There is a layer of aluminum oxide film on the surface of tin aluminum alloy, so its wear resistance and corrosion resistance are good. Alloys containing 20% tin have the highest fatigue resistance. Generally, the higher the tin content, the better the anti-bite properties, because tin acts as a lubricant. Stann-aluminum alloy has the tendency to replace copper-lead alloy, especially the performance of three-layer alloy shingles coated with lead alloy is better.
In order to supply lubricating oil between the shaft and the bearing, there is an oil hole on the bearing bush with less load, and there is a cloth oil groove along the circumference, so that the oil can be distributed along the circumference. In addition to lubrication, oil can also reduce the temperature of bearings and improve the bearing capacity of bearings. In the wider bearing, in order to facilitate the oil along the axial distribution, in the bearing section at the opposite end of the oil groove, called garbage groove, groove can store impurities in the oil. The fit of bearing bush and bearing seat hole, thin wall bearing is guaranteed by circumferential interference. To facilitate assembly, the bearing bush is flushed out of the locating lip, and a matching locating slot is milled out in the bearing seat hole. There should be an appropriate gap between the shaft and the bearing. The size of the gap should be calculated according to the working condition of the diesel engine and the load of the bearing. At the same time, the structure and material of the bearing bush should be considered. In order to prevent the axial movement of the shaft, sometimes it is necessary to configure thrust bearings. Thrust bearings can be flanged on the ordinary bearing bush, and two semi-circular thrust retaining rings can be set on the thrust bearing seat and positioned on the bearing seat and bearing cover by pins or other methods.
Bearing damage forms are wear, fatigue and corrosion. In the process of diesel engine starting and stopping, the lack of oil supply causes the dry friction of shaft and bearing. The abrasive wear caused by hard particles entering the bearing pair is the main cause of bearing wear. The uneven wear of adjacent bearings will form the wear ladder between bearings. The fatigue damage of bearings is caused by the alternating oil film pressure. The oxidation of oil produces organic acid, which causes corrosion and damage to bearing alloy.
Bearings are expendable parts of diesel engines and are replaced during overhaul.

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