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Research advances EPC process.

A new approach using a fluidized bed to remove the foam pattern represents a further refinement of the EPC process.

The last few years have seen a great deal of commercial and technical activity in the field of expendable pattern casting (EPC). The results of these activities have shown that the conventional EPC process has limitations that could impede its growth. One limitation is caused by the direct contact between molten metal and the pattern material in the casting process. This limiting factor gives rise to others, such as:

* porosity in aluminum alloys that results in the entrapment of decomposition products in the solidifying metal;

* the decomposition of the foam pattern in casting ferrous alloys resulting in the formation of solid pyrolytic carbon (lustrous carbon). Because this carbonaceous product can be difficult to remove from the casting cavity, it can lead to a superficial or a subsurface defect in the casting;

* the need for heavy-duty compaction that can cause a deformation in high aspect ratio castings;.

* the attempt to minimize gas evolution during the process, dictating the need for low-density patterns (1.0-1.5 lb/cft). Low-density patterns require more careful handling and are vulnerable to damage during compaction;

* the potential release of hydrocarbons and particulate carbon into the foundry atmosphere;

* styrene contaminated sand that must be cleaned, cooled and classified.

Process Variation

Research at Western Michigan University has produced castings by an alternative EPC process that reduces many of the drawbacks of conventional EPC systems while retaining the simplicity of the process. This alternative approach, detailed in Fig. 1, is known commercially as the Polyform Casting Process. It consists of the following steps:

* A pattern with gates and sprues is prepared from injection molded expanded polystyrene beads. Pattern density is not limited to 1.0-1.5 lb/cft, and patterns up to 4.0 lb/cft have been successful.

* A pattern assembly is prepared in the conventional manner, dipped or spray-coated two or more times with a ceramic slurry designed for the process and, air dried.

* The dried pattern assembly is placed in a controlled atmosphere fluidized bed where the media are maintained at a temperature of 800-1100F. Heat from the fluidized particles evaporates the foam after several minutes, leaving a clean ceramic cavity. Decomposition products from the evaporating foam are captured and cleanly incinerated.

* Molten metal is poured into the clean cavity and extracted from the fluidized bed after solidification.

This process differs in one fundamental aspect from the conventional EPC process in that the pattern does not contact molten metal because the pattern is removed in a controlled manner before the molten metal is poured.

Reportedly, the new process eliminates porosity defects in aluminum alloy castings and produces high-quality castings of iron and steel without lustrous carbon defects. It also reportedly facilitates casting peel and cleaning, and reduces emissions.

Initial work with this new process indicates that it advances EPC because it combines the simplicity of the basic technology while improving quality, eliminating the defects and environmental limitations of the conventional EPC process. Detailed information on the Polyform Casting Process is available from Jay Easwaran at 616/387-3366 or Bryan Baker at 205/663-0732.

References:

J. Easwaran: Process for Evaporative Pattern Casting, U.S. Patent No. 4,995,443 (1992).
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Title Annotation:Research Update; expendable pattern casting
Author:Easwaran, Jay
Publication:Modern Casting
Date:Apr 1, 1993
Words:543
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