Piston rings are rings with a smallgap, non-closed. They are located in the grooves on the outer walls of the pistons in all types of piston engines (for example, in steam engines or internal combustion).
Why do we need piston rings?
1. For sealing the combustion chamber. Compression rings significantly increase compression. With the lighter, broken or worn out rings, the engine may not start or lose power.
2. To improve heat transfer through the cylinder walls. The rings contribute to the heat dissipation from the piston, thus preventing overheating.
3. To reduce the consumption of oil for the engine (in two-stroke diesel and all four-stroke ICE).
How are the piston rings arranged?
The joint (the same lock) is located between the endspiston ring. When the piston is in the cylinder, the lock is slightly compressed - up to several fractions of a millimeter. It happens oblique (for four-stroke ICE) and straight. The rings in the grooves are positioned so that the angle between the joints is equal (2 rings - 180 degrees, 3 rings - 120 degrees). The result is a labyrinth that reduces the breakthrough of gases.
The rings are oil-removable and compression. The oil removers protect the combustion chamber from oil entering it from the crankcase. They remove excess engine oil from the cylinder. Install oil-lubricated rings below the compression rings. They have through-cuts. In two-stroke gasoline internal combustion engines, oil scrapers are not used, since engine oil burns along with fuel. Now produced either cast iron or composite steel rings with expanders in the form of springs. Composite is easier and cheaper to manufacture, so they are much more common than cast.
Compression piston rings protect the crankcaseengine from gusts of gas from the combustion chamber. In the free state of the ring, the outer diameter is greater than the inner diameter. For this reason, part of the product is cut out. The place of the cutout is called the lock. Typically, no more than three such rings are mounted on a single piston, for the reason that the degree of compaction of the piston rises slightly, and the friction losses increase. On two-stroke ICE, as a rule, install two rings. The cross section of most of the compression rings is rectangular. The edge has either a chamfer, which narrows, or a cylindrical profile. When the engine is operating, the rings are somewhat twisted (this provides a gap in the groove), which facilitates their running-in.
Manufacture of piston rings
Technologies and manufacturing methods shouldensure the shape of the product, which in a free state would create the desired level of pressure in its operating state. The piston ring is usually made of high-strength gray cast iron, as it has good stable parameters of elasticity and strength, high wear resistance, excellent anti-friction properties. Also used alloying additives (a special coating of porous chromium, surfacing molybdenum, spraying in a plasma jet, ceramic coating, diamond particles), which contribute to a significant increase in heat resistance of products.