Piston ring materials and manufacturing

[SUPERKYLE]

Hello all,
I'm looking into the design and manufacturing of compression rings (normally aspirated 4 stroke maximum performance engines). Hopefully there are some well informed individuals here that can help? Top compression rings are my primary focus, and I am interested in the different materials, coatings, as well as common manufacturing techniques.

Thanks in advance,
Kyle

 

[EdDanzer]

My experience in sealing is mostly from high pressure hydraulics, but during a patenting process on a piston ring I designed and received a patent on, I learned what some other designs were and some about how other people manufactured them. For internal combustion engines compression rings, most are manufactured from cast iron. There are coating applied and different metallurgies to improve performance.
When choosing materials things to look at are operating temperature, and P/V. PV is pressure (P) projected on to the moving surface, and velocity (V) the speed that the surface is moving. The PV values change with temperature and lubrication for given materials. I haven’t found much published information about PV other than for plain bearings, this will give an idea of how different materials interact in a sealing environment. You may have to experiment with coatings on both the cylinder walls as well as the rings. If a seal is working correctly a portion of the contact surface will be operating dry. Running dry is what causes most wear during sealing.
One major difference in ring is how the ends are designed to stop leakage. A patent search will show many. Steps at the end can reduce leakage if there are tolerance changes between the mating parts. The disadvantage of steps on the end of the ring is structural failure and increased manufacturing costs.
One thing that may help is to use different 1st and 2nd ring designs. The first ring has the most pressure and heat requiring a robust design. The second ring should help control oil as well as compression, and could be used to help center the piston in the bore. A high temperature elastomer under the ring will control shape of the ring, contact pressure (P), and should improve gas and oil sealing.
To make small lot quantities the ring can be turned round in a lathe and split with a milling machine.
Narrow rings can reduce friction and float, but may want to roll in the groove, reducing sealing. Thin cross section rings conform to the bore shape better, but need to be wider to reduce rolling in the groove