Cavitation is a special form of corrosion. It is the product of a combination of physical damage and chemical damage. It often occurs on the outer wall of the cast iron cylinder liner in the engine cooling system. It ignites in the engine combustion chamber and the piston “slaps” with greater power. “Cylinder liner. The cylinder liner vibrates violently. When it vibrates in the direction away from the coolant, a low-pressure area will be formed between the outside of the cylinder liner and the coolant. In the low-pressure area, the coolant vaporizes to form bubbles. When it vibrates in the direction closer to the coolant, At this time, the low-pressure bubble explodes violently on the outer wall of the cylinder liner with a pressure as high as 60,000ps (about 420MPa). Continuous vibration causes the bubbles to explode continuously, and the material on the outer wall of the cylinder liner falls off due to fatigue.Over a long period of time, many small holes are formed in the outer wall of the cylinder liner. The bubbles subsequently generated can easily stay in these small holes, and then the bubbles continue to burst, causing the original holes to continue to expand. , some can penetrate the cylinder liner, forming honeycomb cavitation on the outer surface of the cylinder liner.
1. The concept of cavitation
The so-called cavitation of the wet cylinder liner refers to the honeycomb-shaped holes that appear on both sides of the outer surface of the cylinder liner along the swing direction of the connecting rod after the generator has been used for a period of time (in severe cases, it often runs for dozens of hours under high load). Group (usually its diameter is 1~5mm and its depth is 2~3mm). Sometimes, the inner wall of the cylinder of the generator has not been used to the wear limit, that is, it is broken down by cavitation.
2. Causes of Cavitation ① There are microscopic pores, cracks and grooves in the cylinder liner material. ②When the machine is running, the cylinder liner vibrates. When the machine is running, the impact of the combustion explosion and the knocking of the piston when it moves up and down cause the cylinder liner to vibrate, causing the cooling water coating on the outer wall of the cylinder liner to generate local high pressure and high vacuum. Under the action of the high vacuum, the cooling water evaporates. Forming bubbles, some vacuum bubbles and bubbles are squeezed into by vibration or directly occur in the tiny pinholes on the outer wall of the cylinder liner. When they are ruptured by high-pressure impact, a pressure shock wave is generated near the rupture area, and the pressure can reach tens of Atmospheric pressure, it impacts the outer wall of the cylinder in a very short time, producing strong destructive force on the cylinder. This constant and repeated action causes rapid fatigue damage to the metal surface, resulting in cavitation. If the cylinder liner is broken down by cavitation, greater harm will occur: water will enter the cylinder and the machine will not shake. Currently, there is still a lack of effective solutions to cylinder liner cavitation, and some methods or measures can only be taken to prevent or reduce the destructive effect of cavitation on the cylinder liner.
3. The harm of cavitation
Cavitation corrosion may occur in high-pressure oil pumps, high-pressure oil pipes and injectors, and its hazards are as follows:
① Cavitation causes penetration of the high-pressure oil pump body, resulting in poor sliding performance of the plunger couple or jamming.
②Cavitation causes the hole diameter of the high-pressure oil pipe to change or the oil pipe to break, further affecting the change in oil volume.
③ Cavitation also causes poor atomization of the injector needle valve assembly, oil dripping or even no atomization at all..
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