HOME > Piston Ring Museum > Technologies that Assure Ring Function > Contact Friction & Ring Durability
Technologies that Assure Ring Function
C-5 Contact Friction & Ring Durability

Vehicle and machine operators share a common wish: to have the best fuel economy and to have the longest possible oil change intervals. The periphery (running face) of a piston ring requires a material that reduces contact friction as much as possible and still allows the ring to perform its sealing function against the cylinder wall. Even though the ring's running face is usually gliding on a very thin layer of oil, the friction force can be large. Minimizing such friction losses is therefore another challenge that faces today's piston ring designer.

Although hard chrome plating and nitriding are well-proven coatings for a piston ring's running face surface, current trends in engine design are driving the development of new piston ring materials and face coatings.


Surface Treatment
Recently developed face coatings have been proven under the most severe engine operating conditions.

[a] Top Ring Surface Treatment: IP (CrN) Coating
The IP coating is a type of PVD film that offers the following characteristics:
(1) Low coefficient of friction
(2) High hardness
(3) High adhesion to base metal
(4) Excellent scuff resistance

The table below shows various ion plating coatings offered by Riken.
 
●RIKEN lon plating Film Variations
  IP-100 IP-200 IP-251
Composition TiN CrN CrN
Color Gold
 Metallic Silver Metallic Silver
Hardness 1700～2300 1500～2000 850～1150
File Thickness Difficult to achieve thick film less than 10μm
 Possible to achieve thick film Up to 40μm
 Possible to achive thick film Up to 50μm
Application Range 1st ring for high output gasoline engines
 Oil contorol ring for diesel engines and gasoline engines 1st ring for diesel engine and gasoline engines


[b] Second Ring Surface Treatment: Nitriding
  This family of processes produces a hard surface layer on the base material. In these processes, nitrogen atoms penetrate and diffuse into the base metal, significantly increasing the surface hardness.
  Types and characteristics of nitriding processes
 
Looking at the layer hardness value as a function of distance from the ring surface, it can be seen in the graph below that the hardness at the surface is over Hv 1,100.
 

image


[c] Oil Ring and Side Rail (Segment) Surface Treatment
  Depending on the application, IP film, nitriding, and chrome plating are all surface treatment options.



Coefficient of Friction
It is desirable to make this number as low as practically possible since it plays a large role in engine wear and efficiency. From the table below it can be seen that IP coating has the lowest coefficient of friction of any of the available surface coatings.
  image
 
Exhibit Hall C-4 Exhibit Hall C-6
Page Top