Piston rings

Piston rings are rings with a small gap, unclosed. They are located in the grooves on the outer walls of the pistons in all types of reciprocating 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. Rings contribute to the heat dissipation from the piston, thereby 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 ends of the piston 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.

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 together with fuel. Currently, there are either cast iron or composite steel rings with sprinkler expanders. Composite is easier and cheaper to manufacture, so they are much more common than cast.

Compression piston rings protect the crankcase of the engine 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 working, the rings are somewhat twisted (this provides a gap in the groove), which facilitates their running-in.

Manufacture of piston rings

Technologies and methods of manufacture should provide the form of the product, which in a free state would create the necessary level of pressure in its working condition. The piston ring is usually made of high-strength gray cast iron, since it has good stable values of elasticity and strength, high wear resistance, excellent antifriction properties. Also used alloying additives (special coating of porous chromium, surfacing molybdenum, sputtering in a plasma jet, ceramic coating, diamond particles), which contribute to a significant increase in heat resistance products.