This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.
The ordinary furnace used is of very simple construction.
After lighting the fire, put the pot intended for use bottom upwards over it, so as to warm gradually through. As soon as the fire is burned well through, put the pot into its place, resting the bottom on a fire brick to keep it off the bars, and filling round with lumps of coke to steady it; then put in the copper, either blocks cut up into pieces of convenient size, or if this is not to be had, sheet copper doubled up; as the metal sinks down add more copper or old brass till the pot is nearly full of melted metal; now add the tin, and when this is melted and mixed, put in a piece or two of zinc; if this begins to flare add the rest of the zinc in, stir it well in, lift the pot off at
14* once, skim the rubbish off the top, and pour into the mould. If, however, it does not flare up, put a little coal on to excite the fire, and cover over till it comes to a proper heat. As soon as the zinc begins to flare, add in the rest, and take the pot off the fire. If old brass alone is melted down no tin is required, but a small quantity of zinc. If part copper and part brass, add tin and zinc in proportion to the new copper, with a little extra zinc for the brass.
As soon as the boxes are run, it is the usual custom to open them at once, and to sprinkle the castings with water from the rose of a watering can, this has the effect of making them softer than they would otherwise be; the boxes are then emptied, and fresh moulds made while fresh metal is being melted.
When the casting is completed, draw the bearer forward, and let the bars all drop, so that the furnace can be effectually cleared from the clinkers, and put the pot among the ashes to cool gradually.
The moulding boxes may be of hard wood, well secured at the corners, either by dovetailing or by strong nails and iron corner plates, with guides to keep the boxes fair with one another. A few cross bars in the top box help to carry the sand.
Fresh green sand, the same as used for iron founding, mixed with a small quantity of coal dust, about one-twelfth part, should be sifted over the patterns on all sides to the thickness of about an inch, the box then filled up with old sand, and properly rammed up, and well pricked to let the air and gas escape, then remove the patterns, and dust over the mould with a little charcoal powder from a bag, or with a little flour, cover over the box again, and the mould is ready for pouring.
For long articles, spindles, bars, etc, make a good airhole at the opposite end from where the metal is poured, incline the box slightly, and pour the natal at the lower end; for flat, thin and straggling articles it is necessary to have two or more pouring holes, and to fill them all at the same time.
The pots generally used are the Stourbridge clay pots, and black lead pots, both kinds being made of various sizes up to 60 lbs.; the former are less durable, but much cheaper than the latter, they require to be carefully hardened by gradual exposure to the fire.
Clay pots are made of 2 parts raw Stourbridge clay to 1 of gas coke pulverized; well mixed up together with water, dried gently, and slightly baked in a kiln.
Black lead pots of 2 parts graphite, and 1 of fireclay, mixed with water, baked slightly in a kiln, but not completely until required for use.
The pots are made on a wood mould, the shape and size of the inside of the pot, the clay being plastered round it to (he thickness desired.