2022-01-07 News Views 1226
The common damage of the connecting rod bearing of diesel engine is mainly the damage of the wear resistant alloy layer on the bearing bush. The main damage forms are: early wear and burning, corrosion, abrasion, fatigue crack and peeling, etc. In order to take effective preventive measures to reduce the occurrence of connecting rod bearing bush damage, the following analysis is made on the causes of the damage of connecting rod bearing bush.
1 Common causes of connecting rod bearing bush damage
1.1 Early wear and burn
The early wear of the connecting rod bearing destroys the normal fit gap between the bearing and journal, especially the wear of the upper tile of the connecting rod. Burning tile is the serious damage fault of bearing tile, burning tile refers to the alloy layer burning adhesion on the journal, resulting in the wear of crankshaft journal and shaft holding accident. The reasons for early wear and burning of connecting rod bearing bush are as follows:
(1) the normal wear of connecting rod bearing bush is very small under the condition of maintaining good lubrication. If foreign dust, iron filings, or other metal abrasive particles enter between the journal and the bearing with the lubricating oil, the bearing and bearing will be scratched.
(2) when the lubrication system failure, oil pressure too low or too high, bearing lubricating oil supply is not normal, interruption of lubricating oil and improper fit clearance can cause overheating, the lubricating oil film damage, movement, deputy direct contact between the metal surface, and form abnormal wear and make the local temperature is too high, causing burning-out alloy.
(3) Improper operation and use of diesel engine, such as the engine just started on high speed overload operation, due to the pressure generated by dedetonating gas, engine overheating, easy to lead to bearing burning.
(4) After bearing seat deformation, bearing bush and bearing seat will contact poor. If the position of the bearing bush is not correct, the higher part of the lubricating oil film will be destroyed, and the dry friction between metal and metal will occur.
1.2 Corrosion
The corrosion phenomenon shows that the internal surface of bearing bush presents dark gray or black macular holes and honeycomb pits. The main reason for the corrosion of connecting rod bearing bush: the corrosion of bearing bush is caused by the erosion of acid substances in lubricating oil. Alloy bearing bearing lead is susceptible to corrosion because of the strong interaction between acid and lead. Stress concentration occurs when the alloy layer is corroded, which accelerates the fatigue failure of the alloy layer. So in the use of management to regularly sample the quality of oil test, to judge the degree of deterioration. If exceeds the target, the oil must be replaced to prevent corrosion of the bearing bush.
1.3 Scratch
The surface of the inner circle of the bearing bush appears along the circumferential direction of the linear or banded pull mark. It is an uneven wear, often caused by foreign bodies. It is mainly caused by the impurities in the oil, these impurities may be the diesel engine parts wear products iron powder, rust, dust and carbide. At work, these small particles can be embedded in the soft alloy, large particles will abrade the alloy along the circumferential direction, and large particles can not pass through the bearing clearance may be pressed into the bearing bush alloy to form scars and pits, may also bruise the journal. General bearing bush more or less have scratch marks, which does not affect the normal operation of the diesel engine, but serious, will cause damage accidents. Therefore, in the use of management to regularly check and clean the oil filter and replace the oil.
1.4 Fatigue cracking and spalling
Fatigue can crack the bush alloy, and in serious cases, the alloy flakes off from the bush until the whole bush alloy is destroyed. Or under the action of high load, the oil film is destroyed, forming critical lubrication or direct contact between metals, local temperature rises, and cracks occur. Caused by casting casting quality of crack, generally occurs at the beginning of the diesel engine running, and fatigue cracks are usually occurs after working for a long time, in addition to the above reasons, the manipulation of mismanagement can also cause cracks, such as diesel engine in long-term work overload, too much or excessive load on the start times, all can lead to bearing shell crack, Serious will make small pieces of alloy peeling down, and finally lead to the destruction of the whole bearing bush. Bad matching between the journal and the bearing or the cylindricity deviation of the journal is too large, easy to cause the local surface pressure of the bearing, poor heat dissipation, so that the middle of the bearing is easy to produce axial crack. Irregular local shedding of the alloy is followed. When assembling, if the straightness of the center line of the connecting rod is out of tolerance, the load can not be evenly distributed on the surface of the bearing bush, and the diesel engine may fall out after working for a period of time. According to the requirements of use, the fitting degree between bearing and seat hole should not be less than 86%, and the non-fitting place should be dispersed in more than two places, otherwise it will affect the heat transmission, and lead to fatigue crack and spalling of bearing alloy.
2 Inspection methods
2.1 Visual inspection
On the surface of the bearing bush if there are corrosion pitting, abrasion, cracks, peeling and burning phenomena, can be directly observed by the naked eye. The bonding of alloy layer and tile back can be checked by percussion method. If the above defects are found to be serious, they need to be replaced.
2.2 The wear test
(1) Empirical identification method: install the connecting rod on the crankshaft, tighten the connecting rod bolts according to the specified torque, and then swing the connecting rod. If the connecting rod can be rotated once and there is no loose feeling along the axial direction, the clearance is considered appropriate. Identification of the main shaft tile, the main shaft neck oil is installed in the main bearing bush, torsion crankshaft arm with the torque of the wrist, if you can smoothly turn half a circle, and up and down, left and right to pull the crankshaft, and no obvious movement, the gap is appropriate.
(2) measurement: bearing wear, available diameter micrometer bearing thickness. By comparing the wear thickness of the bearing bush with the original standard thickness, the wear amount of the bearing bush can be obtained. However, in diesel engine maintenance, the absolute wear of the bearing bush is often not used to determine the scrap and replacement of the bearing, but the total wear of the connecting rod journal and connecting rod bearing, resulting in the replacement of the gap exceeds the requirements of the provisions. In order to obtain the connecting rod bearing and journal clearance, it is necessary to measure the inner diameter of the connecting rod bearing, so the bearing bush is installed in the connecting rod big hole, fastening the connecting rod bolt according to the specified torque requirements, and then wear measurement, measurement usually measured two parts three directions a total of six dimensions.
When measuring the inner diameter of connecting rod bearing bush with micrometer or inner diameter dial meter, attention should be paid to: ①For the big head of the connecting rod with a flat cut, when measuring the dimension of the horizontal position of the bearing bush, two measuring positions should be selected at 10 ~ 15 mm below the surface of the bearing bush to avoid the garbage trough. ② For the big head bearing of oblique incision, the maximum size of the bearing bush is the largest value in the two directions of size perpendicular to the connecting rod cover and the connecting rod axis line when measuring. ③ The rounded corners should be avoided when measuring the front and rear positions of the bearing bush.