New Casting Process for Better Piston Rings

A better process leads to better product, according to Federal-Mogul Corp. Powertrain Segment (federalmogul.com), as it has developed a new casting process for piston rings that it says produces higher quality, stronger, and more wear-resistant rings.

And it is a process that replaces one that it has been using for 80 years.

The replacement process is based on a vertical casting process that uses a special mold design that allows optimization of the blank and gating system design so that material flow is better controlled. The previous process had been horizontal stack casting, which limited both the gate design and the range of ring design options.

The new casting form allows feeding around the complete circumference of the casting, resulting in more uniform graphite formation in the ring. Which results in a stronger part.

In addition to the process itself, the Federal-Mogul engineers worked on other ring-related technologies, such as a finite-element analysis simulation process that they’re calling “Slow-Motion Casting Simulation.” This provides detailed analysis of the mold filling at various temperatures and speeds. Also, they have developed a new cast steel material for diesel rings that can be used as a replacement for high-strength martensitic grey cast iron with nodular graphite, a material with a strength of 1,200 MPa. The new cast steel material, GOE70, has a marten-sitic matrix structure with embedded chromium carbides; it has a strength of at least 1,800 MPa. In addition to which, its wear resistance can be improved by nitriding.

Said Dr. Steffen Hoppe, Federal-Mogul Powertrain director of technology, Rings and Liners, “As engine manufacturers continue to pursue strong engine downsizing and more advanced injection strategies to reduce fuel consumption and CO₂ emissions, the thermal, mechanical and tribological demands on the components around the combustion chamber—particularly the piston rings—increases. While engine friction can be reduced through the use of thinner piston rings, a stronger ring material is necessary in order to maintain the proper bending strength.”