Part 31

Copper Zinc Tin Lead I 63.70 33.55 2.50 0.25 II 64.45 32.44 0.25 2.86 III 70.90 24.05 2.00 3.05 IV 72.43 22.75 1.87 2.95

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Their special advantage is that they can be readily cast, worked with file and chisel, and easily gilded.

«To Cast Yellow Brass.»—If good, clean, yellow brass sand castings are desired, the brass should not contain over 30 per cent of zinc. This will assure an alloy of good color and one which will run free and clean. Tin or lead may be added without affecting the property of casting clean. A mixture of 7 pounds of copper, 3 pounds of spelter, 4 ounces of tin, and 3 ounces of lead makes a good casting alloy and one which will cut free and is strong. If a stronger alloy be desired, more tin may be added, but 4 ounces is usually sufficient. If the alloy be too hard, reduce the proportion of tin.

«Leaf Brass.»—This alloy is also called Dutch gold, or imitation gold leaf. It is made of copper, 77.75 to 84.5 parts; zinc, 15.5 to 22.25. Its color is pale or bright yellow or greenish, according to the proportions of the metals. It has an unusual degree of ductility.

«Malleable Brass.»—This metal is affected less by sea water than pure copper, and was formerly much used for ship sheathing, and for making nails and rivets which were to come in contact with sea water. At the present day it has lost much of its importance, since all the larger ships are made of steel. It is usually composed of copper, 60 to 62 parts; and zinc, 40 to 38 parts. It is sometimes called yellow metal, or Müntz metal (called after its inventor), and is prepared with certain precautions, directed toward obtaining as fine a grain as possible, experience having shown that only a fine-grained alloy of uniform density can resist the action of the sea water evenly. A metal of uneven density will wear in holes. To obtain as uniform a grain as possible, small samples taken from the fused mass are cooled quickly and examined as to fracture. If they do not show the desired uniform grain, some zinc is added to the mass. After it has permeated the whole mass, a fresh sample is taken and tested, this being continued until the desired result is reached. It is scarcely necessary to remark that considerable experience is required to tell the correct composition of the alloy from the fracture. The mass is finally poured into molds and rolled cold. Malleable brass can be worked warm, like iron, being ductile in heat, a valuable quality.

Experiments with malleable brass show that all alloys containing up to 58.33 per cent of copper and up to 41.67 per cent of zinc are malleable. There is, in addition, a second group of such alloys, with 61.54 per cent of copper and 38.46 per cent of zinc, which are also malleable in heat.

The preparation of these alloys requires considerable experience, and is best accomplished by melting the metals together in the usual manner, and heating the fused mass as strongly as possible. It must be covered with a layer of charcoal dust to prevent oxidation of the zinc. The mass becomes thinly fluid, and an intimate mixture of the constituents is effected. Small pieces of the same alloy are thrown into the liquid mass until it no longer shows a reflecting surface, when it is cast into ingots in iron molds. The ingots are plunged into water while still red-hot, and acquire by this treatment a very high degree of ductility. The alloy, properly prepared, has a fibrous fracture and a reddish-yellow color.

«Sheet Brass» (For Sheet and Wire).—In the preparation of brass for the manufacture of wire, an especially pure quality of copper must be used; without this, all efforts to produce a suitable quality of brass will be in vain. That pure copper is indispensable to the manufacture of good, ductile brass may be seen from the great difference in the composition of the various kinds, all of which answer their purpose, but contain widely varying quantities of copper and zinc. The following table shows the composition of some excellent qualities of brass suitable for making sheet and wire:

───────────────────+──────+──────+──────+───── Brass Sheet—Source │Copper│ Zinc │ Lead │ Tin ───────────────────+──────+──────+──────+───── Jemappes │ 64.6 │ 33.7 │ 1.4 │ 0.2 Stolberg │ 64.8 │ 32.8 │ 2.0 │ 0.4 Romilly │ 70.1 │ 29.26│ 0.38 │ 0.17 Rosthorn (Vienna) │ 68.1 │ 31.9 │ — │ — Rosthorn (Vienna) │ 71.5 │ 28.5 │ — │ — Rosthorn (Vienna) │ 71.1 │ 27.6 │ 1.3 │ — Iserlohn & Romilly │ 70.1 │ 29.9 │ — │ — Lüdenscheid │ 72.73│ 27.27│ — │ — (Brittle) │ 63.66│ 33.02│ 2.52 │ — Hegermühl │ 70.16│ 27.45│ 0.79 │ 0.20 Oker │ 68.98│ 29.54│ 0.97 │ — │ │ │ │ Brass Wire— │ │ │ │ England │ 70.29│ 29.26│ 0.28 │ 0.17 Augsburg │ 71.89│ 27.63│ 0.85 │ — Neustadt │ 70.16│ 27.45│ 0.2 │ 0.79 Neustadt │ 71.36│ 28.15│ — │ — Neustadt │ 71.5 │ 28.5 │ — │ — Neustadt │ 71.0 │ 27.6 │ — │ — (Good quality) │ 65.4 │ 34.6 │ — │ — (Brittle) │ 65.5 │ 32.4 │ 2.1 │ — For wire and sheet │ 67.0 │ 32.0 │ 0.5 │ 0.5 ───────────────────+──────+──────+──────+─────

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As the above figures show, the percentage of zinc in the different kinds of brass lies between 27 and 34. Recently, alloys containing a somewhat larger quantity of zinc have been used, it having been found that the toughness and ductility of the brass are increased thereby, without injury to its tenacity. Alloys containing up to 37 per cent of zinc possess a high degree of ductility in the cold, and are well adapted for wire and sheet.

«Gilders’ Sheet Brass.»—Copper, 1 part; zinc, 1 part; tin, 1⁠/⁠10 part; lead, 1⁠/⁠10 part. Very readily fusible and very dense.

«White Brass.»—Birmingham platina is an alloy of a pure white, almost silver-white color, remaining unaffected by tolerably long exposure to the atmosphere. Unfortunately this alloy is so brittle that it can rarely be shaped except by casting. It is used only in the manufacture of buttons. The alloy is poured into molds giving rather sharp impressions and allowing the design on the button (letters or coat of arms) to stand out prominently with careful stamping. The composition of this alloy, also known by the name of platinum lead, is as follows:

I II Copper 46.5 4 Zinc 53.5 16

III.—Zinc, 80 parts; copper, 10 parts; iron, 10 parts.

«BRITANNIA METAL.»

Britannia metal is an alloy consisting principally of tin and antimony. Many varieties contain only these two metals, and may be considered simply as tin hardened with antimony, while others contain, in addition, certain quantities of copper, sometimes lead, and occasionally, though rarely on account of its cost, bismuth. Britannia metal is always of a silvery-white color, with a bluish tinge, and its hardness makes it capable of taking a high polish, which is not lost through exposure to the air. Ninety per cent of tin and 10 per cent of antimony gives a composition which is the best for many purposes, especially for casting, as it fills out the molds well, and is readily fusible. In some cases, where articles made from it are to be subjected to constant wear, a harder alloy is required. In the 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.