Brass Moulding
So far as the actual moulding is concerned there is very little to distinguish it from the ordinary course pursued for producing castings in iron. For the larger castings in dry-sand and loam, exactly similar moulds are made, but for the very light brass castings in green sand it is necessary to have a very fine silex sand, which contains a slight portion of clay. When the sand contains clay in excess it favors the production of the finest work; but there is always danger of blown spots when this is used, only to be remedied by drying the moulds, or introducing more open sand, to permit the gases generated at pouring to escape. It is not necessary to cast brass any hotter than will result in clear, sharp outlines in the casting.
As a rule, most brass castings will be freer from honeycombs, if the metal is forced in at the lowest part of the mould, taking care that suitable vents are provided for carrying off the gas as it generates in the mould. The fact that all sands taken from the earth must contain more or less vegetable matter, which burns out as soon as the metal strikes it, making a rough and unfinished looking casting, has prompted some dealers to prepare a composition of minerals, crushed and put through a process known alone to themselves, where every trace of vegetable or any other matter not standing a high fire-test is extracted, the sand being usually ground and bolted. See BRASS; FACING-SAND; ROCK-CRUSHER.