Hollow Metal Castings
The Encyclopedia of Founding (1892)
Hollow or shell castings, in lead, tin, zinc, and their alloys, are obtained by using a brass mould, which is filled with metal, and, after due time has been allowed for a skin to congeal on the surface, inverted, to allow the molten portion to escape. What remains, forms a crust of metal answering to the form of the mould. See STATUARY-FOUNDING. Hollow Shot are made similar to other hollow castings, except that the flasks containing the moulds are reversed a few times immediately the gates have set. This forces the fluid iron equally against the sides both in top and bottom parts, prevents flattening of the top side, and thus preserves a true spherical form in the casting. The same with solid shot: the moulds are reversed as soon as possible, which allows the fluid metal to first congeal on the sides and the shrinkage to be made good from the more fluid mass inside the ball, which naturally leaves the centre in a spongy condition, yet is preferable to a flattened upper surface. See SHOT; PROJECTILES; FEEDING. Hollow-ware Moulding is not necessarily different from the moulding of other fine objects so far as the processes are concerned. This class of moulding is especially confined to boilers, pots, pans, kettles, including all those cast vessels for domestic use. Owing to the necessity of having most of these patterns and flasks in sections, considerable ingenuity is exercised in their arrangement, and the patterns, usually of iron or brass, are elegantly fitted together and finished. The iron part-flasks are, in some instances, marvels of ingenuity; the system of pins, latches, clamps, and runners being well worthy of copying by founders engaged in the production of castings that are similar in design and only differ in name.
What Has Changed in the Last Century
The "slush" method the Encyclopedia of Founding described in 1892 — filling a brass mould with molten lead, tin or zinc, letting a skin freeze and pouring the rest back out — still exists, but it survives mainly for decorative work such as lamp bases, figurines and toy soldiers. For production parts it was displaced by pressure die casting, which spread rapidly in the zinc and aluminium alloys after 1900 and made thin-walled hollow shapes repeatable to close tolerance, and later by plastic injection moulding, which took over most of the cheap hollow goods entirely. The section on hollow shot is now purely historical: spherical shot for smooth-bore guns was already obsolete when this was written, and no foundry rolls flasks to keep a cannonball round today. Cast-iron hollow-ware has had the most mixed fate — pressed steel, aluminium and enamelled ware pushed the old pots and kettles aside, yet cast-iron skillets and Dutch ovens are still sand-cast in quantity and have enjoyed a strong revival among cooks.
Written for this edition, 2026.