Question

What is feed metal required of SG iron casting?

Answer 1

Answer:

Shrinkage is the reduction in the metal volume during cooling and solidification of most metals and alloys. Measures to recognize this phenomenon are taken; the solidified casting will exhibit gross shrinkage porosity, which can make it unsuitable for the purpose for which it was designed. To some extent, gray and ductile cast irons are exceptions, because the graphite formed on solidification expands and can compensate for the metal shrinkage. However, even with these alloys, measures may need to be taken to avoid shrinkage porosity. To avoid shrinkage porosity, it is necessary to ensure that there is a sufficient supply of additional molten metal, available as the casting is solidifying, to fill the cavities that would otherwise form. This is known as “feeding the casting,” and the reservoir that supplies the feed metal is known as a “feeder head” or a riser. The feeder must be designed so that the feed metal is liquid at the time that it is needed, which means that the feeder must freeze later than the casting itself. The feeder must also contain sufficient volume of metal, liquid at the time it is required, to satisfy the shrinkage demands of the casting