Skeleton Core-iron
The Encyclopedia of Founding (1892)
A core-iron consisting of wrought or cast iron rods cast in one or more plates or rings. It is the most efficient and convenient core-iron that can be made for any description of belt or jacket-core having metal on all its sides. Owing to their cage-like appearance, they are frequently termed cage-irons. See JACKET-CORES. Skim-gate is any arrangement of runner that will arrest the skim or slag at some part intermediate to the pouring-basin and casting. If two castings are poured together in one flask, and one of the moulds filled by means of a fountain or horn runner connected with the bottom of that which receives the metal direct from the ladle, it is evident that all the dirt will remain in the latter, while the clean iron only will be forced into the former, thus making one casting a skin-gate to the other. Any intermediate receptacle, not necessarily a casting, may be thus employed to intercept the dirt; but by inserting a spherical object, as a ball, etc., for this purpose, and allowing the metal to enter it at a tangent to the circumference with force sufficient to impart a rapid rotary motion to the entering metal, the lighter scum is forced to the centre and there held until the casting or castings gated from the circumference of the ball are filled with clean metal. In order that this may be effective, the metal must enter the ball with force sufficient to keep it full, so that the castings may be fed from a point below where the dirt is held imprisoned. If a large quantity of metal must necessarily pass through a ball of limited size, a riser on the ball permits the accumulations to mount well above the ingates. See GATES; FOUNTAIN-RUNNER.
What Has Changed in the Last Century
The Encyclopedia of Founding described these cage-irons in 1892 as the best reinforcement for any large sand core, and the practice has not vanished — cast-iron core grids and rods are still set into big cores in jobbing foundries today. What has moved is the sand around them: chemically bonded systems, notably the Croning shell process of the 1940s and the cold-box process introduced in 1968, produce cores strong enough to need far less internal ironwork, and many parts once cored in green sand are now die cast or investment cast instead. The 1892 spinning-ball skim gate has largely given way to disposable ceramic foam and mesh filters, standard in foundries since the 1980s, while gating and slag behaviour are now modelled by casting-simulation software rather than judged by eye.
Written for this edition, 2026.