A severe intake wear problem is resolved in a large power generation engine by replacing standard diesel intake materials with a cobalt-base common trade material and special nitrided valve. The turbocharged engine is made up of cylinder blocks to the required load demand up to 1500 hp, at 1800 rpm.
A multitude of engine changes requires higher performance materials to replace the original martensitic cast iron inserts and Sil 1 valves. After many trials, the cobalt-base common trade material proves to be an ideal match with the nitrided valve. The unique chemistry of the insert and valve surface reduces the friction of their respective sliding surfaces. Both materials also retain high hardness levels in the operating environment to maintain smooth sliding surfaces. The nitrided valve face shows light shallow scratches caused by valve rotation on a smooth shiny surface. The cobalt-base common trade material insert surface shows a similar light wear pattern on a shiny surface. This combination has been successfully used in this engine for a variety of off-highway mining, marine, and power generation applications for two years. Solid cobalt-base common trade material inserts and cobalt-base common trade material valves have been successfully combined for the most severe diesel and natural gas intake applications when other materials were not up to the task or other wear reducing engine designs could not be utilized. The success of this combination has been generally attributed to the wear-resistant cobalt-base containing about 40 percent volume of Laves phase. The unique wear behavior comes from the structure and hardness of the intermetallic compound having a low friction coefficient.
Further testing indicates that low cost W10-P® iron-base insert material could be substituted for the expensive cobalt-base common trade material. W10-P® is a material developed as a low-cost iron-base substitute for the cobalt-base common trade material. It contains a high percentage of Laves phase and forms unique oxides to reduce sliding friction at high temperatures. A recent test on the same engine indicates W10-P® also works well with the special nitrided valve, which also maintains a high hardness and relies on a low friction coefficient coating to reduce shear stress. The W10-P® insert surface has a relatively smooth surface that shows the vertical direction of valve closure. The total wear of the nitrided valve and W10-P® combination is 0.022 mm compared to 0.042 mm with the expensive cobalt-base common trade material after a 700 hour test on the same engine.
