Piston rings are metallic gaskets that serve three important functions in an IC engine
SEALING Prevent the combustion gases from escaping into the crankcase.
HEAT DISSIPATION Transfer heat away from the combustion chamber and into the cooling media, and
Garima Global has developed an extensive range with the leading manufacturers of piston rings in India. We specialize in developing custom made rings according to the requirements of our customers.
Size Range of Piston Rings in AutoGRACE Brand
In a typical three-ring automotive piston, the top ring performs the sealing function and also dissipates heat away from the combustion chamber.
Usually second from top, these rings help to seal the combustion gases in, while scraping off excess oil from the liner surface.
The oil ring, in combination with the scraper ring above it, regulates the oil film on the liner surface so that there is minimal friction between the rings and the liner.
Piston rings have been designed with numerous cross sections Rectangular, Bevelled, Double Trapezoid / Keystone, Single Trapezoid / Keystone, Taper Face, With Inside Chamfer, Napier, L shaped to serve the particular design requirements of various engines.
Oil control rings also incorporate slots to regulate the flow of oil and could be multi-piece rings consisting of a 2-piece design with an outer ring that is spring loaded on the inside or an expander-backed 3-piece design.
The peripheral surface is further shaped into a straight face, barrel face, asymmetric barrel, taper face or a taper face rounded / lapped partially.
The top inside edge may be bevelled or stepped to achieve a positive twist in the ring, promoting better oil consumption, while creating a bevel / step in the bottom inside edge creates a negative twist in the ring which promotes better sealing against the liner wall.
While installing rings, care should be taken that the rings gaps of all the rings do not line up with each other, or this will create a passageway for combustion gases to escape into the crankcase. To further fool-proof against this eventuality, Convex or Angle Step Joints are used which provide improved sealing as compared to the most popular and simple Butt Joint Design. Other designs like Hook Joints, Overlap Joints and Angle Joints provide no advantage in terms of sealing and are suitable for hydraulic / compressor / automatic transmission applications.
Alloyed and hardened SG Iron is the material of choice for performance compression rings due to its hardness and high resistance to flexure.
For compression rings in low speed engines as well as scraper and oil rings, alloyed and unhardened Grey Cast Iron usually serves the purpose due to its good wear-in and emergency running properties.
For especially low ring heights or in diesel engines with steep pressure gradient, steel is the material of choice. It is also preferred for spacers and rails in three-piece oil control rings due to its higher breaking strength.
Phospho Bronze, Sintered Iron and Sintered Bronze are also being used for specific applications.
It is of utmost importance that the material of the liners and rings be compatible to prevent premature wear and tear of either one of these components. Hence we recommend our customers to use AutoGRACE brand piston rings with AutoGRACE brand cylinder liners to optimize the life of their engines.
Below are some of the main coatings developed for the running face of the piston rings. These coatings in general increase wear resistance of the rings and also generate lower wear of liner surface.
Hard chrome is plated or deposited into a groove on the ring circumference. This prolongs the ring life but may prematurely wear out the liner if its material is not compatible with the ring.
These can withstand metal-to-metal wear better than hard coatings like Chromium, and hence have better anti-scuffing properties. The important ones are:
PVD coatings follow base metal contour perfectly and are extremely scuffing and wear-resistant.
DLC coatings help reduce friction between ring and liner.
Usually used in rings for gasoline engines to improve scuff behaviour and improve wear resistance.
To improve performance of the ring early in its lifecycle after installation, and their cosmetic appeal, as well as to enhance shelf life by protecting the rings against corrosion, a variety of surface treatments have been developed, some of the important ones being:
A 2 5 micron layer of phosphate crystals is deposited which improves the run-in characteristics of the ring since it is softer than the base ring material.
An excellent and economical anti-corrosion treatment.
Reduce the surface hardness and have a lubricating effect when the tin or copper melts due to combustion temperatures.
Improve corrosion resistance and increase fatigue strength.
Used in piston rings for industrial hydraulic applications where loss of lubrication may be anticipated.