When a casting is released from the mound in which it was formed it is not in a finished condition. It may have “spruces” and “flashes” of excess metal where the mold halves came together or where the molten metal was added. There may be some surface blemishes. The casting will be “dressed” or “fettled” to remove this material. This may be automated but is usually done by hand using hand held grinders or a bench mounted grinding wheel. During the process sparks, metal fragments, and sand particles will become airborne and must be drawn away to protect the operator and the indoor work environment. If the duct work is sufficiently long to allow the sparks to cool to a point where they are no longer incandescent then there is no need for a spark arrest to protect the main filter. An AAF OptiFlo RC with flame retardant cartridges is the ideal filter.