Finding New Value in Lost Foam Casting

This 300-kg ceramic mold will require 2.5 metric tons of ASTM A217 Grade C12A steel to produce a finished casting that achieves a 27% weight savings versus a comparable sand casting. Firing the ceramic mold at 1,000°C removes all traces of carbon that would otherwise prevent the use of polystyrene patterns for the manufacture of steel castings. (Photo by Castings Technology International)

Castings Technology International (Cti), is a member-based R&D organization with capabilities in casting design, materials development and selection, specifications, manufacturing technologies, quality control, testing and performance. Several years ago, Cti developed the Replicast^® process to mitigate the quality and machining problems associated with sand-molded steel castings, and to circumvent the carbon pick-up from the polystyrene pattern in the Lost Foam process that has such a detrimental effect on most steel casting grades.  The aspiration was to achieve the high standards of integrity, surface finish and precision of the Lost Wax investment casting process, and for much larger and far heavier castings than can be made with the current Lost Wax technology.  This was success was achieved by replacing the wax pattern used in the Lost Wax process with one made from polystyrene – a precise replica of the casting required by the customer – and on which a thin ceramic mold is produced in a like manner to the Lost Wax process. 

Over the years, it has been proven time and again that the physical characteristics of polystyrene enable manufacturing costs to be reduced to a level competitive with sand molded castings; that the use of a replica pattern provides greater freedom in the design of the feeding system, thereby reducing shrinkage defects; and that the use of a fired, inert ceramic mold reduces sand inclusions and gas defects associated with resin bonded sand molds.  These and other attributes enable higher as-cast integrity to be achieved reliably and consistently, resulting in more predictable and shorter lead times due to a substantial reduction in weld-repair — factors that are becoming of greater commercial significance with the tightening of acceptance standards following the Deepwater Horizon disaster, and the enforced customer acceptance of severe penalty clauses for late delivery or under-performance.