Analysis of Causes of Damage to Weichai Engine Bearing Bush Folding Shopping Cart, marketing Shopping cart. Folding Shopping Cart Shopping cart Ningbo Mywin Caster Co., Ltd. , https://www.mywin-caster.com
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Weichai http:// (1) The burning of the bearing bush of the bearing bush, which is also known as the burning tile (chemical tile), due to insufficient supply or supply of lubricating oil, or the oil film between the bearing bush and the crankshaft journal is not formed, in the crankshaft The semi-dry friction or dry friction between the journal and the bearing bush causes the engine bearing bush to melt, the bearing bush is melted, and the crankshaft is locked by the bearing bush. It is a serious mechanical accident of the concrete mixer truck, and the consequences are believed to have been known to everyone. How did this happen? I have summarized the following points:
1 Improper use. When the mixer truck engine is in overload operation for a long time, the temperature of the lubricating oil of the mixer truck is increased, the viscosity of the lubricating oil is lowered, the oil pressure is low, the oil film between the shaft and the bearing bush is not easy to form, and the heat generated by the friction cannot be very high. Good being carried away, causing increased friction and wear, resulting in the vicious wear of the bearing bush and melting.
2 The winter mixer truck is not properly started. In the winter, when the ambient temperature is lower than 0 degrees, the engine is quickly and forcibly started. At this time, due to the low temperature, the viscosity of the oil is large, and the lubricating oil film between the shaft and the bearing bush has not been formed, causing the bearing bush to melt. Starting the engine in winter should stop the engine when the engine is first started for the engine to be ignited. The purpose is to let the oil pump pump oil and deliver it to the oil passage. After a little stop for 1-3 minutes, start the engine until ignition. The number of revolutions should be 650r/min, and the operation should be about 5 minutes. After the standby oil pressure and water temperature rise, start again. If the starting temperature of the mixer is too low (less than 10 degrees), I suggest that you can use a heating device such as a blowtorch to heat the oil pan to reduce the oil resistance of the oil pump and speed up the oil circulation.
3 Oil film is difficult to form. If the quality of the lubricating oil is too bad or the use period is too long, it will not be replaced in time, or the oil will deteriorate due to other reasons, which will destroy the formation of the oil film and cause the engine bush of the mixer to be melted. What needs to be noticed here is that sometimes the injector is stuck, so that the diesel injected into the cylinder is not atomized, and then the combustion is insufficient or not burned, so that excess diesel flows into the oil bottom along the cylinder wall, so that the oil is Dilution, viscosity becomes low, oil film formation is difficult, when the oil dipstick is inspected, there will be a large diesel smell, and the oil surface will also rise accordingly. In addition, the internal leakage of the diesel oil pump can also cause this to happen. Everyone pays attention.
4 The oil is seriously lacking. Engine oil plays four main roles in operation, namely lubrication, cooling, sealing and anti-corrosion. If the oil level of the engine oil is insufficient, the oil is seriously lacking. Due to lubrication, insufficient cooling, the temperature of the engine bush of the mixer is suddenly increased, the bearing bush and the crankshaft The neck expands and deforms, the gap disappears, and the direct contact between the metals is more serious. The lubricating oil on the crankshaft journal is burned off, causing the engine bearing bush temperature to rise sharply, and the burning of the tile is inevitable.
5 Assembly problems. The gap between the journal and the bearing bush has the greatest relationship to the lubrication of the bearing bush. The small pinch clearance of the bearing bush will limit the flow of lubricating oil, making the oil difficult to enter, so that the friction heat can not be taken away well, which increases the bearing deformation and The possibility of burning tile failure; if the bearing clearance is too large, the arc length of the bearing bush and the journal will be reduced, which greatly increases the pressure load of the oil film, exacerbates the fatigue of the bearing bush, and also increases the vibration shock of the crankshaft. The lubricating oil is squeezed out, losing the adhesion of the oil film and increasing the wear of the bearing bush. Here to remind everyone, if the crankshaft has a burning tile failure, it is best to replace the new one, do not go to the small shop for simple grinding.
(The clearance between the main bearing bush and the main journal is 0.095--0.163mm, and the clearance between the connecting rod bearing and the connecting rod journal is 0.059--0.127mm)
(2) The abrasion of the bearing bush of the bearing bush generally occurs in the case of instantaneous lack of lubrication or instantaneous interruption of the lubricating oil. Its performance is characterized by direct metal contact on the surface of the bearing bush and the journal, which is stained and severely scratched. There are two main reasons for the bearing scratches. One is the use of the problem, and the other is the quality of the lubricant.
1 Problems with use. Mainly after the engine is started, when the temperature and pressure are not raised, the high speed is mentioned a few seconds after starting. Since this fashion did not form a sufficient oil flow, the bearing bush was insufficiently lubricated and scratches occurred. After the engine is started, it takes about 15-40 seconds for the oil to fill the engine oil passage, and the maximum speed can be achieved by forcibly accelerating for 3-8 seconds. If the maximum speed is forcibly mentioned after starting the engine, the bearing bush will be in a lack of oil for about 8 seconds and will run at high speed with load. The bearing bush will be strained. The abrasion will be very fast.
2 Quality problems with lubricating oil. Dust in lubricating oil. There are many impurities, and the use time is too long and not timely replacement; the concrete mixer truck engine often has high load. The high temperature operation, the increase of impurities in the oil will cause the bearing bush to be scratched. The key is the uncleanness of the lubricating oil. .
(3) Cracks in the bearing alloy and the engine bush of the mixer truck may cause alloy shedding and cracking due to unreasonable use, and may also be referred to as “jun (jun) crackingâ€. This is due to the frequent direct contact between the bearing bush and the journal, resulting in an increase in temperature and a decrease in the fatigue strength in the bearing bush. The crack is in the form of a mesh. When the engine is running, the hydraulic force in the crack causes the crack to develop until the lining of the bearing bush peels off and gradually expands. This is also known as the "fried tile" phenomenon. Due to the spalling of the alloy block, the clearance between the journal and the bearing bush becomes larger, the wear of the two is intensified, and the lubricating oil is depressed from the gap, causing the oil pressure to drop and the knocking sound to appear.
The main cause of cracking and spalling of the bearing pads is operational problems. The connecting rod of the engine is much larger than the oil film pressure and load of the main bearing. It bears the alternating load of cyclic changes and is easy to cause fatigue. At the same time, the connecting rod is firstly affected by the pressure drop of the oil, especially the last connecting rod. At the end of the lubricating oil circuit, it is finally lubricated. The driver often starts the engine repeatedly, and the maximum speed is forcibly mentioned before the oil pressure has risen, so that the connecting rod is subjected to a higher load and has a larger linear speed, so the bearing will be slightly pulled. Injury. The scratch becomes a crack and the last peeling. Therefore, we must pay more attention to the operation: after the engine is started, it must be idle for 3-5 minutes. Never force the speed before the oil pressure is low.
(iv) Excessive wear of the bearing bush Excessive wear occurs in the event of transient oil shortage and repeated occurrences. Each time, the metal is oil-lubricated and directly contacted. This time is not long, and the temperature rise of the bearing bush is not enough to cause discoloration of the bearing bush and overheating of the bearing bush, but each time the metal is in direct contact, a part of the bearing alloy is ground down. The gap is increased, and over time, the excessive wear of the bearing bush is caused repeatedly, and the engine oil pressure is lowered, resulting in the last operation.
The main reasons for excessive wear of the bearing bush are as follows:
1 The engine works continuously under the condition that the oil level of the oil is too low, and the oil is not added in time;
2 After the engine is started, the engine oil pressure is not increased and the speed is forcibly increased;
3 The oil filter element is unqualified, and the filter element is seriously blocked and cannot be replaced in time;
4 engine oil temperature is too high;
5 oil grade does not match;
6 The air filter is dirty or the air filter housing is not sealed;
Analysis of Causes of Damage to Weichai Engine Bearing Bush