Excursus: Production steps in detail
1. The blank
Grey cast iron has proven its worth particularly for the manufacture of valve guides used in large diesel engines such as shipsí engines, electricity generators or truck engines. It has very good thermal conductivity properties, and, moreover, grey cast iron with a higher phosphorus content has very good dry-running properties due to its favourable graphite structure and its oil retaining pockets. The following is a description of the cast iron valve guide production in four steps from the blank to the ground final part.
2. Internal machining
The valve guide secures the valveís axial location, and thus the bore must be machined with the highest precision.
During the first turning process, the outside diameter is machined. During this process, the coaxiality of the bore to the outside diameter needs to be considered. Subsequently, various forms and grooves are turned on both the outside and in the bore of the workpiece.
Centreless grinding is the last machining operation. The outside diameter of the valve guide is ground on CNC grinding machines within very narrow tolerances. Here, particular attention needs to be paid to the surface roughness and the geometry of the outside diameter.