Henley's Twentieth Century Formulas, Recipes and Processes. Various
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proportions given above, the metal is indeed much harder than tin, but would still soon give way under usage.
A table is appended, giving the composition of some of the varieties of Britannia metal and their special names.
| Tin | Antimony | Copper | Zinc | Lead | |
|---|---|---|---|---|---|
| English | 81.90 | 16.25 | 1.84 | — | — |
| English | 90.62 | 7.81 | 1.46 | — | — |
| English | 90.1 | 6.3 | 3.1 | 0.5 | — |
| English | 85.4 | 9.66 | 0.81 | 3.06 | — |
| Pewter | 81.2 | 5.7 | 1.60 | — | 11.5 |
| Pewter | 89.3 | 7.6 | 1.8 | — | 1.8 |
| Tutania | 91.4 | — | 0.7 | 0.3 | 7.6 |
| Queen’s metal | 88.5 | 7.1 | 3.5 | 0.9 | — |
| German | 72.0 | 24.0 | 4.0 | — | — |
| German | 84.0 | 9.0 | 2.0 | 5.0 | — |
| German (for casting) | 20.0 | 64.0 | 10.0 | 6.0 | — |
| Malleable (for casting) | 48.0 | — | 3.0 | 48.0 | 1.0 |
Britannia metal is prepared by melting the copper alone first, then adding a part of the tin and the whole of the antimony. The heat can then be quickly moderated, as the melting point of the new alloy is much lower than that of copper. Finally, the rest of the tin is added, and the mixture stirred constantly for some time to make it thoroughly homogeneous.
An alloy which bears a resemblance to Britannia metal is Ashberry metal, for which there are two formulas.
| I | II | |
|---|---|---|
| Copper | 2 | 3 |
| Tin | 8 | 79 |
| Antimony | 14 | 15 |
| Zinc | 1 | 2 |
| Nickel | 2 | 1 |
Bronzes.
The composition of bronze must be effected immediately before the casting, for bronze cannot be kept in store ready prepared. In forming the alloy, the refractory compound, copper, is first melted separately, the other metals, tin, zinc, etc., previously heated, being then added; the whole is then stirred and the casting carried out without loss of time. The process of forming the alloy must be effected quickly, so that there may be no loss of zinc, tin, or lead through oxidation, and also no interruption to the flow of metal, as metal added after an interval of time will not combine perfectly with the metal already poured in. It is important, therefore, to ascertain the specific weights of the metals, for the heavier metal will naturally tend to sink to the bottom and the lighter to collect at the top. Only in this way, and by vigorous stirring, can the complete blending of the two metals be secured. In adding the zinc, great care {56} must be taken that the latter sinks at once to the level of the copper, otherwise a considerable portion will be volatilized before reaching the copper. When the castings are made, they must be cooled as quickly as possible, for the components of bronze have a tendency to form separate alloys of various composition, thus producing the so-called tin spots. This is much more likely to occur with a slow than with a sudden cooling of the mass.
Annealing Bronze.
—This process is more particularly employed in the preparation of alloys used in the manufacture of cymbals, gongs, bells, etc. The alloy is naturally brittle, and acquires the properties essential to the purpose for which it is intended only after casting. The instruments are plunged into cold water while red-hot, hammered, reheated, and slowly cooled, when they become soft and sonorous. The alloy of copper and tin has the peculiar property that, whereas steel becomes hard through cooling, this mixture, when cooled suddenly, becomes noticeably soft and more malleable. The alloy is heated to a dark-red heat, or, in the case of thin articles, to the melting point of lead, and then plunged in cold water. The alloy may be hammered without splitting or breaking.
Aluminum Bronze.
—This is prepared by melting the finest copper in a crucible, and adding the aluminum. The copper is cooled thereby to the thickly fluid point, but at the moment of the combination of the two metals, so much heat is released that the alloy becomes white hot and thinly fluid. Aluminum bronze thus prepared is usually brittle, and acquires its best qualities only after having been remelted several times. It may be remarked that, in order to obtain a bronze of the best quality, only the very purest copper must be used; with an inferior quality of copper, all labor is wasted. Aluminum bronze is not affected by exposure to the air; and its beautiful color makes it very suitable for manufacturing various ornamental articles, including clock cases, door knobs, etc.
Aluminum bronze wire is almost as strong as good steel wire, and castings made from it are almost as hard as steely iron; its resistance to bending or sagging is great.
I.—A good formula is 90 to 95 per cent of aluminum and 5 to 10 per cent of copper, of golden color, which keeps well in the air, without soon becoming dull and changing color like pure copper and its alloys with tin and zinc (bronze, brass,