Sunday, September 22, 2013

Difference between foamcast and lost foam casting process offered in China

During our efforts to promote foamcast - lost foam metal casting technology, of late many foundries have asked us one common question - "How is foamcast different from the lost foam process in use in China?"
Most Lost Foam Casting foundries in China project that lost foam cannot and should not be used to manufacture steel castings. Lost foam foundries in China & Europe have experienced that, with the exception of certain heat-resistant alloys, carbon pick-up from the polystyrene foam patterns during pouring contaminates most steel grades, producing regions within a casting where the mechanical properties are extremely inferior. This problem is commonly known as "lustrous carbon" in the lost foam casting industry.
To compensate for the "lustrous carbon" defect the Chinese use and recommend EPS-PMMA a material that is designed to leave low carbon residue. The problem is EPS-PMMA is four times more expansive than the EPS used in the foamcast Process. EPS-PMMA is not manufactured in India and has to be imported with a minimum order quantity of 17.0 Tons. (1no. Full Container as EPS is termed as hazardous material and part shipment is banned)  EPS-PMMA has a shelf life of 6 months if stored in a moisture free environment at 20.0 degrees C. Due to this limitation and with a foam to metal ration of 1:150 you have pour 2550 Tons of castings within six months so that the imported EPS-PMMA is used within its expiry date.
Most Chinese foundries recommend the metal to be over heated by approx. 200 degrees over the required temperature so that the metal does not loose its fluidity while it is burning the foam. In areas where the metal has lost it fluidity foam inclusion in the casting takes place which is exposed post machining or under pressure testing.
The foamcast Process is alien to all these problems associated with the traditional lost foam process since in the foamcast process we build up a ceramic shell on the polystyrene foam pattern. On firing the ceramic, all traces of the polystyrene foam are removed before the mould is buried in the supporting un-bonded silica sand.
The foamcast process is very much similar to the Lost Wax process but with certain key differentiating characteristics. For example, polystyrene foam is lighter, stronger and insensitive to temperature. Polystyrene foam patterns can be produced in very thin or thick walls (2-200mm). Complex shapes can be formed by gluing sections thus allowing design freedom of the Lost Foam process. The physical properties of polystyrene foam enable thinner ceramic shells as compared to lost wax. Due to the use of thinner shells in the foamcast Process pre-heating the ceramic mould before pouring it not NOT required.
In addition to the above process advantages, on the shop floor level too the foamcast Process is simpler to operate. The foam pattern molding process is done on a vertically moving molding machine. This enables use of bigger molding tools with complex manually operated cores. The Chinese are familiar with horizontally moving machines that limit the size of the molding tools and require very expensive auto core removal devices. The design of the foamcast pattern molding machine allows the use of four different molding tools at any given time which allows us to mold any number of patterns from just a few to thousands. The Chinese molding machine does not allow this flexibility.
Thus, the foamcast® process enables castings of a size commonly associated with sand moulding to be manufactured in a way that achieves the as-cast integrity, surface finish and dimensional accuracy associated with the Lost Wax process. And this has been achieved at lower cost, especially in end-product manufacturing cost, compared with traditional sand castings.
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