History of metal casting



For the manufacture of stereotype plates, plaster of Paris, of the consistence of a batter-pudding before baking, is poured over the letter-press page, and worked into the interstices of the types with a brush. It is then collected from the sides by a slip of iron or wood, so as to be smooth and compact. In about 2 minutes the whole mass is hardened into a solid cake. This cake, which is to serve as the matrix of the stereotype plate, is now put upon a rack in an oven, where it undergoes great heat, so as to drive off superfluous moisture. When ready for use, these moulds, according to their size, are placed in flat cast-iron pots, and are covered over by another piece of cast-iron perforated at each end to admit the metallic composition intended for the preparation of the stereotype plates. The flat cast-iron pots are now fastened in a crane, which carries them steadily to the metallic bath, or melting pot where they are immersed and kept for a considerable time, until all the pores and crevices of the mould are completely and accurately filled. When this has taken place the pots are elevated from the bath by working the crane, and are placed over a water trough, to cool gradually. When cold the whole is turned out of the pots, and the plaster being separated by hammering and washing, the plates are ready for use; having received the most exact and perfect impression.

_White Metal._

Melt together 10 oz. of lead, 5 oz. of bismuth, and 4 drs. of regulus of antimony.

Another.--Melt together 2 lbs. of regulus of antimony, 8 oz. of brass, and 10 oz. of tin.

_Common Hard White Metal._

Melt together 1 lb. of brass, 1 1/2 oz. of spelter, and 1/2 oz. of tin.

_Tutenag._

Melt together 2 parts of tin and 1 of bismuth.

_Fusible Alloy._

Put into a crucible 4 oz. of bismuth, and when in a state of fusion throw in 2 1/2 oz. of lead, and 1 1/2 oz. of tin; these metals will combine, forming an alloy fusible at the temperature of boiling water. Mould this alloy in bars and take them to a silversmith's to be made into a half-adozen teaspoons. If one of these be given to a stranger to stir his tea as soon as it is poured from the teapot, he will be not a little surprised to find the spoon melt in the teacup.

The fusibility of this alloy is certainly surprising, for the fusing temperature of each of its components, singly, is higher than twice that of boiling water. Bismuth fuses at 476, lead at 612, and tin at 442; whilst water boils at 212.

Another.--Melt together 1 oz. of zinc, 1 oz. of bismuth, and 1 oz. of lead. This alloy will be found to be remarkably fusible (although each of the metals, separately, requires considerable heat to melt it), and will melt even in hot water; it will likewise remain in a fused state on a sheet of paper, over the flame of a lamp or candle. Both of these alloys expand on cooling, and are well adapted for taking casts of medals, etc.

_Wood's Fusible Metal._

Melts between 150 and 160 Fahr. It consists of 3 parts cadmium, 4 tin, 8 lead, and 16 bismuth. It has a brilliant metallic lustre, and does not tarnish readily.

_Casts from Fusible Metal._

A combination of 3 parts of lead, with 2 of tin and 5 of bismuth, forms an alloy which melts at the temperature of 197 Fahr.

In making casts with this and similar alloys it is important to use the metal at a temperature as low as possible; as, if but a few degrees elevated, the water which adheres to the things from which casts are to be taken forms vapor, and produces bubbles. The fused metal must be allowed to cool in a teacup until just ready to set at the edges, and then pour it into the moulds, procuring in this way beautiful casts from moulds of wood, or of other similar substances. When taking impressions from gems, seals, etc. the fused alloy should be placed on paper or paste-board, and stirred about till it becomes pasty, from cooling, at which moment the gem, die, or seal should be suddenly stamped on it, and a very sharp impression will then be obtained.

_Metallic Injection._

Melt together equal parts of bismuth, lead, and tin, with a sufficient quantity of quicksilver.

This composition, with the addition of a small proportion of mercury, is used for injecting the vessels of many anatomical preparations; also for taking correct casts of various cavities of the body, as those of the ear. The animal structure may be corroded and separated by means of a solution of potassa in water, and the metallic cast will be preserved in an isolated state.

_For Cushions of Electrical Machines._

Melt together in a crucible 2 drs. of zinc and 1 of tin; when fused, pour them into a cold crucible containing 5 drs. of mercury. The mercury will combine with those metals and form an alloy (or amalgam, as it is called) fit to be rubbed on the cushions which press the plate or cylinder of an electrical machine. Before the amalgam is applied it is proper to rub the cushion with a mixture of tallow and beeswax.

_For Varnishing Figures._

Fuse 1/2 oz. of tin with the same quantity of bismuth in a crucible; when melted add 1/2 oz. of mercury. When perfectly combined take the mixture from the fire and cool it. This substance, mixed with the white of an egg, forms a very beautiful varnish for plaster figures, etc.

Moiree Metallique.--A Method of Ornamenting the Surface of Tin Plate by _Acids._

The plates are washed by an alkaline solution, then in water, heated, and sponged or sprinkled with the acid solution. The appearance varies with the degree of heat and the nature and strength of the acids employed. The plates, after the application of the acids, are plunged into water slightly acidulated, dried, and covered with white or colored varnishes. The following are some of the acid mixtures used: Nitro-muriatic acid, in different degrees of dilution; sulphuric acid, with 5 parts of water; 1 part of sulphuric acid, 2 of muriatic acid, and 8 of water; a strong solution of citric acid; 1 part nitric acid, 2 sulphuric, and 18 of water. Solution of potash is also used.

_To Plate Looking-glasses._

This art is erroneously termed silvering, for, as will be presently seen, there is not a particle of silver present in the whole composition.

On tin-foil, fitly disposed on a flat table, mercury is to be poured, and gently rubbed with a hare's-foot: it soon unites itself with the tin, which then becomes very splendid, or, as the workmen say, is quickened. A plate of glass is then cautiously to be slid upon the tin-leaf, in such a manner as to sweep off the redundant mercury which is not incorporated with the tin; leaden weights are then to be placed on the glass, and in a little time the quicksilvered tin foil adheres so firmly to the glass that the weights may be removed without any danger of its falling off. The glass thus coated is a common looking-glass. About 2 oz. of mercury are sufficient for covering 3 square feet of glass.

The success of this operation depends much on the clearness of the glass; and the least dirt or dust on its surface will prevent the adhesion of the amalgam or alloy.

_Liquid Foil for Silvering Glass Globes._

Melt together 1 oz. of clean lead, and 1 oz. of fine tin, in a clean iron ladle; then immediately add 1 oz. of bismuth. Skim off the dross, remove the ladle from the fire. and before it sets add 10 oz. of quicksilver. Now stir the whole carefully together, taking care not to breathe over it, as the fumes of the mercury are very pernicious. Pour this through an earthen pipe into the glass globe, which turn repeatedly round.

Another.--To 4 oz. of quicksilver add as much tinfoil as will become barely fluid when mixed. Let the globe be clean and warm, and inject the quicksilver by means of a pipe at the aperture, turning it about till it is silvered all over. Let the remainder run out, and hang the globe up.

Another.--For this purpose 1 part of mercury and 4 of tin have been used; but if 2 parts of mercury, 1 of tin, 1 of lead, and 1 of bismuth are melted together, the compound which they form will answer the purpose better. Either of them must be made in an iron ladle, over a clear fire, and must be frequently stirred.





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