THE ROYAL ARTILLERY INSTITUTION. 
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viously used—with “ burnt sand ” — i.e., sand which has been used for 
casting—in about equal proportions (about J th coal-dust being added for 
moulds), mixed by passing through a revolving sieve. Bor making cores, a 
larger proportion of burnt sand is employed, to make the core break up easily. 
Coal-dust is added to all moulds and cores. Where any tool work is required 
it is necessary to use coal-dust, as it prevents the sand adhering to the sides 
of the shells, which would injure the tools employed for turning them. It 
is useful in the cores, as it prevents the core from adhering to the sides of 
the shell, and makes it break up better. Beer dregs are used to paint over 
the moulds and cores. They give a smooth surface, and render the mould or 
core less liable to chip. All cores are dried, after they are made, in the hot 
rooms, and all moulds from 10-in. and upwards. 
The cores are formed in cast-iron boxes, which represent the interior of 
the shell, but have an allowance made for the shrinking of the metal. They 
are formed on perforated iron spindles; and for all except small shell the 
core is supported by small pegs of wood.* Some spun yarn is wrapped 
round the spindle. Both sticks and yarn are charred by the heat, and allow 
the core to break up readily and separate from the spindle. A projection 
round the neck of the core makes a groove in the neck of the shell, which 
facilitates breaking it off, on trimming the shell. The spindle fits into a 
cast-iron neck, which is coned to fit into a conical recess in the top of the 
moulding-box (which is made in two parts), and slotted to receive a key, 
which keeps it in its place. The core-box is filled with the mixture of sand 
and coal-dust, and well pressed in. The top of the core is formed by placing 
a cup-shaped top or lid over the mouth of the core-box, working it round 
and giving it a few smart blows. With large cores a hook is inserted at the 
base, for convenience in hanging the core up. This is removed before placing 
the core in the mould, and the hole filled up. 
The chief thing to remark in the construction of the moulding-box is the 
manner in which the rod carrying the core fits into the coned hole in top of 
the moulding-box. When the core is keyed up, its position is tested by a 
gauge, and great care must be taken that it is accurately placed, as the least 
error would render the shell eccentric, thus making the wall thin on one 
side. The limits allowed are very small, ± *05 in. 
The mould is divided into two parts horizontally, which are keyed together; 
the lower box forms the base,t the upper contains the rest of the shell, also the 
runners and curved opening leading from the runners into the shell, The object 
of having the runner arranged in this way is to prevent injury to the base of 
the mould, which would happen if the metal was allowed to flow directly 
into the shell. The curved passage gives the metal entering the mould a 
sweeping direction, which tends to throw any scoriae, &c., to the outer part 
of the shell. The model on which the mould is formed is larger than the 
shell, to allow of its being turned down in subsequent manufacture. A rod 
projecting from the top of the model forms the hollow in which the core- 
spindle is inserted ; and two projections on the model form ears on the shell. 
* Some large shells have the core supported by cast-iron rings with arms, nicked so as to break 
easily. 
t On the mould which forms the base are the letters R.L. and the |, the day and month of 
casting, and upon 7-in. and upwards the calibre of the shell. 
