Piston ring breakage is one of the common forms of piston ring damage. Generally, the first and two-way piston rings are prone to break, and the broken parts are mostly near the lap. The piston ring can be broken into several sections, or it may be crushed or even missing. The broken piston ring will increase the wear of the cylinder. The broken ring of the two-stroke diesel engine may be blown into the exhaust pipe or scavenging box, or even blown into the turbo end of the supercharger to damage the turbine blades, causing serious accidents.
Then let me talk about the nine reasons for the broken piston ring
Common causes of broken piston rings
Except for material defects and low processing quality, it is mainly caused by poor maintenance management and poor assembly quality during use.
The gap is too small
When the lap gap is smaller than the assembly gap, the temperature of the piston ring during operation increases, so that there is not enough room for metal expansion at the lap.
Ring groove carbon deposit
Poor combustion, overheating of the cylinder wall, oxidation or burning of the lubricating oil will cause serious carbon deposition in the cylinder. When the carbon deposit is serious, the ring movement is hindered, the ring and the cylinder wall are strongly acting, the scraped oil and metal scraps are mixed, and a local hard carbon deposit is formed on the lower end surface of the ring groove under the action of leakage gas. There is a local hard carbon deposit under the piston ring, and the periodic gas pressure on the top causes the piston ring to bend and break.
Cylinder sleeve grinding table
Long-term relative movement of the piston assembly and the cylinder liner causes the cylinder liner to wear and a grinding table appears on the upper part of the cylinder liner. When the piston moves up to the top dead center, the first piston ring hits the grinding table and is broken by impact.
Excessive ring groove wear
The lower end surface of the ring groove becomes inclined (horn shape) after excessive wear. When the piston is near the top dead center, the pressure of the gas causes the ring to cling to the lower end surface of the inclined ring groove, the piston ring is twisted, and the piston ring groove is excessively worn and fatigue breaks.
Piston ring catches air port
Two-stroke diesel engines often suffer from damage caused by the piston ring catching on the sweep and the exhaust port. Because the tension at the opening of the piston ring is the largest, the deformation due to heat is large, and the ribs between the air ports on the cylinder liner are easily deformed by heating. When the piston moves, the ring meets the air port. As long as the ring opening slightly catches the air port, the ring will break.
Piston ring radial expansion and contraction fatigue
When the elastic force of the piston ring is insufficient or the cylinder liner is excessively worn, the piston ring and the cylinder wall cannot be in close contact, that is, the airtightness cannot be maintained, so that the high-pressure gas leakage will press the ring into the ring groove. When the piston descends, the gas pressure in the cylinder decreases, and the piston ring pops out from the ring groove. The piston ring continuously expands and contracts radially, resulting in fatigue breakage.
The excessive wear of the piston ring makes the strength of the ring fail to meet the requirements and the ring is broken
Most of the current piston ring materials are brittle materials such as gray cast iron, alloy cast iron, and ductile iron. During the casting process, pores, cracks or segregation of ingredients may occur in the internal structure, which causes local strength to drop or stress concentration at the crack, causing impact during work. Fracture or fatigue fracture.
Severe wear of cylinder liner
Stepped wear at the top and bottom dead spots causes shoulders, large wear at the large end of the connecting rod, or the original dead spot position changes after repair of the large and small end bearings of the connecting rod, resulting in impact breakage due to inertial force .
Oil and fuel coordination
Analysis from the nature of fuel oil, some fuel oil contains higher sulfur content, so when the fuel burns, it produces more SO2 and SO3.
However, SO2 and SO3 are in a gaseous state at high temperature, and directly interacting with metals will cause gas corrosion. And promote the hardening of carbon deposits and colloidal deposits, increasing the wear of cylinder liners and piston rings. If the main engine does not use the cylinder oil matched with the fuel or replace the cylinder oil with engine oil, the acid capacity of the lubricating oil to neutralize the combustion decreases, resulting in more serious corrosion of the piston and piston ring by the acid substance, resulting in frequent occurrence Piston ring breakage.
