Introduction to pistons
The piston ring of the engine is working at high temperature, and high pressure the piston does high-speed reciprocating movement, so the piston ring must have wear resistance, corrosion resistance, heat resistance, strong steel degree, and elasticity. The current steel piston ring replaces the former cast iron piston ring, and the wood of the high power diesel engine is usually made of gray cast iron, nodular cast, alloy cast iron, and vermicular cast iron.
In order to further improve the performance of the piston ring and extend its service life, the first circular surface of the gas ring is a porous chrome plating treatment, because the porous chromium layer is high in hardness and can store a certain amount of lubricating oil, which can improve the lubrication conditions. The rest of the air ring is generally treated with tin or phosphating, in order to improve its wear resistance, but also can adopt the molybdenum injection process to improve wear resistance.
The function of the piston ring
1. Good air tightness: the combustion gas in the main sealing cylinder leaks into the crankcase, that is, the phenomenon of “air transmission”, which is usually called, keeps the gas leakage at a controllable minimum, so as to improve the thermal efficiency.
2. Good thermal conductivity: the high temperature and high heat generated by combustion must be transferred to the cylinder wall through the piston ring to cool the piston. The usual price is also the amount of heat emitted to the cylinder wall, 30 to 40 percent of the heat on the top of the piston.
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3. It has the function of supporting pistons. Since the piston diameter is slightly smaller than the inner diameter of the cylinder, if there is no piston ring, the piston will contact friction with the inner wall of the cylinder when moving up and down, resulting in the instability of the piston moving up and down in the cylinder. Therefore, the piston ring has good elasticity to support the piston movement, but does not contact the cylinder wall, but relies on the outer surface of the piston ring to slide with the cylinder wall.
4. Must have good oil tightness (oil ring function): can seal the crankcase oil into the cylinder, and the excess oil on the cylinder wall is scraping off, and at the same time, the cylinder wall cloth has a thin film of oil film, to ensure the normal lubrication of the cylinder and piston ring.
Requirements for engine piston ring installation
1. Load the piston ring into the cylinder liner in the paper, push it gently with the piston, and check the opening clearance at the piston ring joint. The clearance is too small, which will damage the cylinder wall due to heat expansion. Too much clearance will affect sealing. The end clearance should be between 0.2 — 0.5mm, the grub clearance due to different materials, the provisions are different.
2. The piston ring shall be installed in the ring groove of the piston, and the side of the piston ring shall have an upward arrow or “top” logo, which shall be installed face up. If installed, there will be oil burning.
3. The chrome ring should be installed in the first one, opening without facing the vortex pit at the top of the piston.
4. The opening of each piston ring should be at least 120cm staggered to each other, and the piston pin hole is not allowed.
5. When the torsion ring is installed, the chamfering or groove should be upward. When the conical section piston ring and cone reverse torsion ring are installed, the cone surface is kept up.
6. When installing the combined ring, the axial liner shall be installed first, and then the flat ring and waveform ring shall be installed. A flat ring is installed in the waveform ring, and the opening of each ring should be staggered to each other.