Filtering a Heavy-Section Di Casting—New Opportunities

Abstract

Because of the increasing requirements for the quality of heavy-section ductile iron castings, foundries that manufacture large castings have been using ceramic filters regularly since around 2000.

Standard ceramic materials were used in the past, which required a high number of filters per mould. Considering the high cost to manufacture a large iron casting, which includes moulding, resin bonded sand preparation, finishing, transport and machining, the design of such an ingate system requires a lot of attention because of the use of filters. Large castings require a high number of filters. It is difficult to design an ingate system so that each filter will receive the same amount of iron and therefore avoid overloading a single filter. Furthermore, an ingate system with 60 to 100 filters requires a lot of space in the mould.

Even filter materials developed for steel foundries with higher temperature resistance, mainly ZrO or graphite, have a maximum capacity of 800 kg to 1.2 ton per 8 in. diameter filter. Around 100 filters are used in a 100 ton casting.

This paper compares the cost to use current filter materials to the cost of substituting with a high-temperature and high-strength filter in the mould. It includes a short explanation of the risks of filter breakages and also some new ideas of simple ingate designs. These new designs will avoid the risk of overloading single filters due to asymmetric ingate systems.