One SWDM-22 rotary drilling rig, equipped with Cummins M11-C330 diesel engine, has been running for 7 500 hours. During construction, the drilling rig failed to start due to the presence of water in the diesel oil pan. After dismantling the diesel engine, it was found that the six wet cylinder liners had different degrees of cavitation, and the cavitation in some parts was relatively serious.
1. Causes of cavitation of cylinder liner
The cavitation parts of the cylinder liner of the machine appear on both sides of the outer surface of the cylinder liner along the swing direction of the connecting rod, and the shape is a honeycomb hole group with a diameter of 1-5 mm and a depth of 2-3 mm. The main reasons for the analysis of cylinder liner cavitation are as follows:
(1) Shock Vibration
When the diesel engine is working, after the cylinder liner is vibrated, the cooling water on the outer wall generates local high pressure and high vacuum, and then evaporates to form small bubbles that adhere to the outer wall of the cylinder liner. When the bubbles burst, a large impact pressure is generated. The outer wall of the cylinder liner is subjected to repeated strong shock and vibration of the pressure wave for a long time, and the metal surface is fatigued and damaged, which first produces pitting, and then expands into foam-like or sponge-like cavitation, or even perforation.
(2) Manufacturing error
Specifically, it includes: too large matching clearance between cylinder liner and cylinder block hole; too large matching gap between piston and cylinder liner; too large connecting rod deformation and crankshaft axial clearance; relatively thin cylinder liner wall, poor material, and defective manufacturing process.
(3) The cooling water is polluted
Hard water with many impurities and serious pollution is often used, which is easy to cause cavitation damage to the cylinder liner. The temperature of the cooling water is too low, the cooling water is insufficient, and the mixed use of different coolants will accelerate the damage to the outer wall of the cylinder liner.
(4) Chemical corrosion
When the diesel engine is working, the iron and iron carbide in the gas form a micro-battery in the upper part of the cylinder liner with a higher temperature, resulting in chemical corrosion, and the impact and vibration will accelerate the corrosion and cavitation of the cylinder liner.
2. Preventive measures
To reduce the cavitation of the diesel engine wet cylinder liner, corresponding measures should be taken mainly from the aspects of manufacture, maintenance and use.
(1) Improve repair quality
Improve the maintenance and assembly quality of the cylinder block, piston connecting rod group, crankshaft flywheel group, etc., improve the dynamic balance of the diesel engine, and reduce the vibration intensity of the cylinder liner.
(2) Improve the corrosion resistance and wear resistance of the cylinder liner
The design and manufacturing departments should take measures in structural design, material selection, processing technology and surface processing quality to improve the corrosion resistance and wear resistance of the cylinder liner. For example, coating the outer wall of the cylinder liner with a protective layer can improve the ability of the cylinder liner to resist cavitation.
(3) Reduce shock and vibration
Adjusting the fuel injection advance angle, the fuel injection pressure of the injector and the uniformity of the fuel injection of each cylinder, etc., to meet the technical requirements, can reduce the impact of the piston on the cylinder liner.
(4) Rational use of coolant
The coolant temperature should not be too high or too low, and should be kept in the range of 80 to 90°C. You should insist on using soft water, keep the cooling water clean, and remove the dirt in the water jacket in time.