| 摘要 |
PURPOSE:To improve wearing resistance and pitching resistance by forming a cam of a cam shaft from a spherical graphite cast iron substance which has predetermined composition with the ground consisting of mixed tissue of retained austenite and bainite. CONSTITUTION:By rotating a cam shaft 5, a rocker arm 3, having in its one end a roller 3a rollably adapted to a cam 6, is swiveled about a rocker shaft 2 being associated with and through the cam 6 formed in the cam shaft 5, and a valve 4 is opened and closed. The cam 6 in a tappet valve mechanism 1 thus obtained is formed from a spherical graphite cast iron substance being composed of, by weight %, 2.0-4.0% C, 1.5-3.5% Si, 0.1-1.0% Mn, 0.005-0.08% Mg, 0.15% or less P, 0.15% or less S, 0.3-1.0% Cu, 0.03-0.09% Mo and the rest of Fe with the base consisting of a mixed tissue of 30-50% retained austenite by volume and bainite or the like. |
