Foundry Coating Technology: A Review

Abstract

The importance of foundry coating in improving the surface quality of castings cannot be over emphasized. The application of mould and core washes creates a high thermal integrity barrier between the metal and the mould resulting in the reduction of the thermal shock experienced by the sand system. These thermal shock leads to series of surface defects such as veining/finning, metal penetration, burn-on/in, scab, rat tail, erosion etc. The use of coatings reduces the tendency of occurrence of these defects. However, the understanding of the coating, its components, characteristics and mechanism of action is important. In this review, a detailed description of these topics and examples are provided where necessary. A potential area of research in foundry coating development, using sol-gel process is suggested. The application of sol-gel technology in the development of foundry coatings is a novel approach

Evaporative Pattern Casting (EPC) Process

“…As regards the particle size of the refractory coating, Kumar et al [2] and Nwaogu and Tiedje [38] had recommended 200 meshes (75 μm) in their research. In reality, the particle size can be reduced to 65 μm.…”

“…The surface roughness obtained in the castings when the coatings are used is subject to the type of casting method employed. With ceramic investment casting process, Singh et al [42], obtained 2 μm surface roughness but with sand casting method 10 μmto50μm was obtained [38].…”

“…The coating must be permeable to allow gas to escape into the surrounding; otherwise the gas would be trapped, causing defects in the castings [38]. Houzeaux and Codina [31] showed that the escape of the gas from the mold is subject to coating applied on the foam.…”

“…The surface roughness obtained in the castings when the coatings are used is subject to the type of casting method employed. With ceramic investment casting process, Singh et al [42], obtained 2 μm surface roughness but with sand casting method 10 μmto50μm was obtained [38].Usually one of the three methods; spraying, dipping, swabbing, is used to apply the refractory coating to the surface of patterns. Spraying has proved to be the most effective in that uniform spread of the coating is obtained leading to almost uniform thickness.…”

“…This will allow for controlled liquid absorption and gas permeability. The coating layer provides clean and smooth surfaces on the castings because it is easily removed.As regards the particle size of the refractory coating, Kumar et al [2] and Nwaogu and Tiedje [38] had recommended 200 meshes (75 μm) in their research. In reality, the particle size can be reduced to 65 μm.…”