Piston ring fracture is one of the common damage forms of piston ring. Generally, the first and second piston rings are easy to break, and the broken parts are mostly near the lap joint. The piston ring can be broken into several sections, or it may be crushed or even missing. The broken piston ring will aggravate the wear of the cylinder, and the broken ring of the two-stroke diesel engine may be blown into the exhaust pipe or scavenging box, or even blown into the turbocharger turbine end to damage the turbine blade, resulting in serious accidents.
Next, let's talk about the nine reasons for piston ring fracture -——
Common causes of piston ring fracture
In addition to material defects and low processing quality, it is mainly caused by poor maintenance and management during use and poor assembly quality.
Overlap clearance is too small
When the lap gap is smaller than the assembly gap, the heating temperature of the piston ring increases during operation, so that there is no sufficient room for metal expansion at the lap. The two ends of the lap bend against the top and break near the lap.
Ring groove carbon deposition
Poor combustion, overheating of cylinder wall, oxidation or burning of lubricating oil will cause serious carbon deposition in the cylinder. When the carbon deposit is serious, the ring movement is blocked, the ring and the cylinder wall act strongly, the scraped oil and metal chips are mixed, and local hard carbon deposits are formed on the lower end face of the ring groove under the action of the leaked gas. There is local hard carbon deposit under the piston ring, which is subjected to periodic gas pressure, causing the piston ring to bend, fatigue and break.
Cylinder liner grinding table
The long-term relative movement between the piston assembly and the cylinder liner causes the wear of the cylinder liner and the grinding table on the upper part of the cylinder liner. When the piston goes up to the top dead center, the first piston ring will be broken due to impact on the grinding table.
Excessive wear of ring groove
The lower end face of the ring groove is inclined (horn shaped) after excessive wear. When the piston is near the top dead center, the gas pressure makes the ring close to the lower end face of the inclined ring groove, the piston ring is twisted and deformed, and the piston ring groove is excessively worn and fatigued.
Piston ring hangs on air port
Two stroke diesel engines often suffer from the damage that the plug ring catches the scavenger and the exhaust port to break the ring. As the tension at the opening of the piston ring is the largest and the heating deformation is large, and the ribs between the air ports on the cylinder sleeve are easy to deform when heated, when the piston moves, the ring meets the air port, as long as the opening of the ring is slightly connected with the air port, the ring will break.
Radial expansion and contraction fatigue of piston ring
When the elasticity of the piston ring is insufficient or the cylinder liner is excessively worn, the piston ring and the cylinder wall cannot be close to each other, that is, they cannot remain airtight, so that the high-pressure fuel gas leaks and presses the ring into the ring groove. When the piston goes down, the gas pressure in the cylinder decreases, and the piston ring pops out from the ring groove. The piston ring expands and contracts continuously in radial direction, resulting in fatigue fracture.
Excessive wear of piston ring makes the strength of the ring unable to meet the requirements and the ring is broken
At present, most piston ring materials are brittle materials such as gray cast iron, alloy cast iron and nodular cast iron. During the casting process, pores, cracks or component segregation may occur in the internal structure, resulting in local strength reduction or stress concentration at the crack, resulting in impact fracture or fatigue fracture during work.
Severe wear of cylinder liner
The shoulder is caused by stepped wear at the upper and lower dead centers. When the big end of the connecting rod is greatly worn or the original dead center position is changed after the bearing at the big and small ends of the connecting rod is repaired, the ring is broken under the action of inertia force.
Coordination of lubricating oil and fuel oil
According to the properties of fuel oil, some fuel oil contains high sulfur content, so there are more SO2 and SO3 produced when the fuel is burned. However, SO2 and SO3 are in gaseous state at high temperature, and direct interaction with metal will cause gas corrosion. It also promotes the hardening of carbon deposits and colloidal deposits, and increases the wear of cylinder liners and piston rings. If the engine does not use the cylinder oil matching with the fuel or uses engine oil to replace the cylinder oil during operation, the ability of the lubricating oil to neutralize the acid generated by combustion will be reduced, resulting in more serious corrosion of the piston and piston ring by the acid, resulting in frequent piston ring fracture.
