The materials and methods used in making iron and brass moulds are practically the same, although the means of melting these metals for castings are different because brass melts at a lower temperature (brass about 1700° F., copper about 2000° F.) than does iron.

Fig. 134 shows a typical crucible furnace for melting brass. It is shown as arranged for oil fuel, but may be used for hard coal or coke by removing the oil burner, stopping up the burner hole D and removing the bricks K from the grate bars.

There are patented forms of oil furnaces which are self-contained and may be set at any place desired about the foundry floor.

A reverberatory furnace is used to melt brass for a large casting, but if this is not installed, a large casting can be made by assembling in a large ladle the molten metal from several crucibles.

In Fig. 134, the furnace is built of brick in a concrete-lined pit. The melting space H is enclosed by fire-brick walls and covered by a movable lid. A furnace is composed of a number of these melting spaces in a row.

The burner forces oil and air through the opening D into a flame which strikes the corner of the base B and surrounds the crucible C. The chimney conduit G conducts gases of combustion to a tall chimney.

Two bricks on edge, or better, a bed of glowing hard coal must hold the crucible off the grate bars when coal or coke heating is done, otherwise its bottom would be too much cooled from the air through the bars to allow melting of the contents. The ash pit A is large enough to afford a good draft for coke or coal.

Brass is alloyed by melting the required amount of copper and then stirring in the zinc in small pieces with an iron rod. Salt, sal ammoniac, or charcoal may be used as a flux to avoid oxidation of the surface of the molten metal. Scrap brass must not be used in high-grade castings unless its composition is known to be the same as that intended for the castings. Even then, a careful fluxing is required to remove any possible oxidized metal contained in the scrap.

Fig. 135 shows a pair of tongs for lifting crucibles from brass or crucible-steel furnaces. A tackle hooked to the eyebolt B lifts the crucible and lowers it into a ladle shank. The mould is poured from the crucible.