The effective pressure, rotation speed and specific power of modern diesel engine are increasing continuously, the quality is becoming smaller and smaller, the structure is becoming more and more compact, and the wall thickness of cylinder liner is thinning, which makes the ability of pitting corrosion decrease. We found in the maintenance practice, cavitation of modern diesel engine damage is very serious, many Baotou North Benz diesel engine cylinder parts not because more than wear limit and change, is often due to cavitation damage was forced to change. Cavitation has become an important factor affecting the service life and reliability of modern diesel engines.
1, pitting corrosion
Cavitation refers to the surface of the diesel engine cylinder liner and the outer wall of the cooling liquid contact holes are broken into some acicular, these holes gradually expand and deepen, and finally the formation of deep hole or crack; holes generally very clean, no corrosion products. Wet cylinder liner in direct contact with the cooling liquid, inevitably gradually by cavitation; and dry liner while not directly contact with the cooling liquid, but also by the cavitation of cylinder block, cylinder block was gradually cavitation through holes or cracks, will further damage of dry liner.
It is generally believed that cavitation is caused by high-frequency vibration of the cylinder liner. Mechanical vibration results in changes in coolant pressure, causing bubbles and cracks in the coolant. This process is the cause of pitting corrosion. Because the cooling liquid in dissolved gas, when the high-frequency vibration so that the local pressure of the cooling liquid drops to a critical value, the form of soluble coolant gas bubbles will separate these bubbles flow to the high pressure zone, when the pressure exceeds the pressure occurs when the bubble collapse. In the gas bubble state re liquefied or dissolved in the coolant, the volume suddenly decreases, the cooling liquid to the high-speed bubble center and produce water hammer phenomenon, have a great impact and high temperature, and the pressure wave form of supersonic propagation when acting on the cylinder outer surface, have a great impact. Extrusion and high temperature. Under the repeated action of this kind of force, the outer surface of cylinder liner fatigue and gradually fall off, and it is numb point and needle shaped small hole, and gradually expanded with the pitting corrosion.
2, prevention of pitting
(1) using factor A., the coolant temperature which is most likely to occur pitting corrosion is 40 degrees -60 DEG C, so it is necessary to keep the coolant at normal operating temperature (80 -85 C). B. should be added with the cooling fluid provided by the manufacturer, without hard water or with more cooling water (liquid). Experiments have shown that hard water containing salts and alkalis is several times faster than clean soft water holes. C. minimize idling, heavy load and overload operation time. D. adds fuel according to regulations to reduce the harshness of the diesel engine caused by the combustion.
(2) maintenance factor A. change coolant according to regulations and clean the cooling system in time, so that the cooling system often keeps good technical condition. B. according to the regulation, adjust the fuel supply advance angle and fuel system assembly, keep the fuel system good working performance, reduce the harm caused by abnormal combustion. C. maintain good clearance between the cylinder, crankshaft bearing clearance and connecting rod bearing clearance to reduce knock and vibration. D. installation of Baotou North rush spare parts cylinder sleeve, piston, Baotou North Ben relaxation parts, connecting rod and other parts, we should try to achieve vertical, parallel requirements, reducing the piston on the cylinder liner of the normal impact.
(3) manufacturing factor A., applying anti cavitation material and vibration absorption material on the side wall of water jacket. B. improves the hardness of the outer surface of cylinder liner; reduces the roughness of the outer surface as much as possible; selects the material with strong pitting resistance. C. selects the proper cylinder wall thickness to increase its stiffness in order to avoid resonance.