pig bed

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A bed of sand in which pigs of iron is cast.

Wiktionary

1. n. a mold, made in a bed of sand, in which pig iron is cast; a pig

GNU Webster's 1913

1. n. (Founding) the bed of sand in which the iron from a smelting furnace is cast into pigs.

WordNet 3.0

1. n. mold consisting of a bed of sand in which pig iron is cast