Popular Science Monthly/Volume 27/August 1885/Modern Bronzes
By PERRY F. NURSEY, C. E.
WE had in the earlier ages of mankind a rough and a polished stone age, a bronze age, and an age of iron, each distinguished by the character of the material that was predominantly used by men for their weapons and tools, and have now added to those ages one of steel. In a similar manner we are now entering upon a revival of the bronze age, in which that substance in its varieties is to be put through stages of improvement like those that iron and steel have undergone. Many varieties of bronze have been produced within the last few years that possess features strongly distinguishing them from the ancient alloys, and some very remarkable qualities as compared with them, in view of which they are frequently used in place of even iron and steel, The bronzes of the ancients were composed of copper and tin, as is also what is now regarded as bronze pure and simple, mixed in proportions varying according to the purpose for which the compound is intended. Other substances, however, are often added, without un-classifying the product, which is still called bronze, provided copper and tin are the chief constituents. Among these substances are zinc, lead, phosphorus, manganese, silicium, iron, nickel, arsenic, antimony, and sulphur. It is the addition of certain proportions of one or other of such substances that constitutes the modern development of bronze manufacture, and which has given us some of the most useful and at the same time some of the most remarkable alloys known. These comprise no fewer than eleven distinct products, all of which find their uses in connection with the practice of engineering. They are: phosphor-bronze, silicium-bronze, manganese-bronze, delta-metal, phosphor-copper, phosphor-manganese bronze, phosphor-lead bronze, phosphor-tin, aluminum-bronze, silveroid, and cobalt-bronze. There are also other bronzes which are used as substitutes for gold in cheap imitation jewelry, but they do not come within the scope of the present paper.
The action of phosphorus on copper alloys is principally due to its reducing qualities, by virtue of which the oxygen absorbed by the molten metal is removed, or the oxides formed thereby are eliminated, and the degree is imparted of homogeneity, strength, and toughness peculiar to the chemically pure metal. The phosphorus, by producing these effects, is converted into a cuprous oxide, which floats on the surface of the molten metal in the shape of a very fluid slag, while the superfluous quantity combines with the metal. It is not, therefore, desirable to add to the bronze a larger quantity of phosphorus than will suffice to reduce the oxide present.
Phosphor-bronze was first prepared by Dr. Kunzel, of Dresden, and was brought into practical use in England early in 1873. The alloys of this class are composed of copper, tin, and phosphorus, and other ingredients in variable proportions, and are made to be either as ductile as copper, as tough as iron, or as hard as steel, according as the proportions of the constituents are varied. The alloys used for rolling and drawing have very different proportions from those employed for castings, bearings, and parts of machinery. The castings of this metal are perfectly sound and homogeneous. Wherever strength, toughness, and durability are desired, phosphor-bronze is found to be better adapted than gun-metal and brass, and in many cases than iron and steel. Having the advantage of not becoming crystalline under the action of repeated shocks and bendings, it is well adapted for making wire-rope, and, not being acted upon by corrosive liquids or the atmosphere, its value as a metal remains constant. The principal varieties of phosphor-bronze, which are produced by slightly varying the proportions of the constituents, are phosphor-bronze duro A, a very dense metal, adapted for bearings carrying heavy wheels running at great velocities, and generally for all quick-speed purposes; and phosphor-bronze duro B, which is intended for the bearings of hot-neck rolls, and for all bearings having to withstand great pressure.
Silicium-bronze was invented by M. Lazare Weiller, of Angoulême, in the search for a material for telegraph-wires, which, together with all the desirable properties of phosphor-bronze, should have a better conducting power. In it phosphorus is replaced by a silicious metalloid, by the incorporation of which a wire is produced offering the same resistance to rupture as phosphor-bronze wire, by the use of which telegraph lines may be furnished with a light, unoxidizable wire, having all needed electrical efficiency. It is also affirmed of wires of this bronze that they are of equal strength with ordinary wires, while not one tenth as heavy; and that, if broken, they will not fall to the ground as ordinary wires do, but, by virtue of their high elasticity, will spring back and coil up close to the standards.
It has long been known that the hardness of bronze could be increased by adding iron to it, but that quality appears to be acquired at the expense of ductility and toughness, and for that reason, probably, such alloys have never come into general use. Mr. Alexander Parkes, and the late Mr. J. D. Morries Stirling, were probably the first to propose and carry into practice the use of manganese for improving the quality of bronze. Mr. Parkes combined manganese alone with copper, and used this alloy to form improved alloys of brass and yellow metal, of which to make sheathing, rods, wire, nails, and tubes. Mr. Stirling, in 1848, proposed to employ manganese in various brass alloys in which iron was present; and a metal introduced by him was used for some time in railway-carriage bearings. It, however, lacked strength, hardness, and ductility, and has long since been superseded.
A manganese-bronze having all the requisites of a useful alloy was introduced in 1876 by Mr. P. M. Parsons. It is prepared by mixing a small proportion of ferro-manganese with copper, after which various alloys are formed. The ferro-manganese is melted in a separate crucible, and is added to the copper when in a fluid state. The effect of this combination is similar to that produced by the addition of ferromanganese to the decarburized iron in a Bessemer converter. According to Mr. Parsons, while a part of the manganese cleanses the copper of any oxides it may contain by combining with them and forming a slag, another part, with the iron, becomes permanently combined with the copper, whereby the strength, hardness, and toughness of the compound are modified, according as the proportions of the constituents are varied. Five different qualities of manganese-bronze are made. In the number one quality the zinc alloyed with the copper is considerably in excess of the tin. It may be worked hot or cold, and has great tensile strength and elasticity. Manganese-bronze number two is stronger, and can be cast in sand for special purposes where strength, hardness, and toughness are required; but it has to be melted in crucibles. One of its most important applications is to the production of articles cast in metal molds under pressure; and the articles thus made have the strength, toughness, and hardness of cast-steel, without any of its defects. It is perfectly homogeneous, and, while not possessing a fibrous texture derived from rolling or hammering, is still fibrous in character, in all directions alike, and, when broken, shows a beautiful silky fracture. It can be cast upon any object, on which it will shrink with a force equal to its elastic limit, and, when released, will show an amount of resilience about double that of steel. Its hardness is about equal to that of mild steel.
The number three quality is composed chiefly of copper and tin in about the same proportions as gun-metal, combined with a large percentage of ferro-manganese. Its chief characteristics are great transverse strength, toughness, and hardness, the facility with which it can he cast, and the soundness and uniformity of the castings produced. This quality is used for wheel-gearing, supports and connections of machines, crank-pin brasses, the shells of main and other bearings of engines, axle-boxes, and parts of locomotive-engines. It is also adapted for statuary and for large bells. Its most important application appears to be for making screw-propellers, for which, in its qualities of strength, non-corrosiveness, and perfect trueness in casting, it seems to be superior to any other substance yet found.
The qualities numbers four and five have no particular claim to strength, but are useful for bearings, slide-valves, slide-blocks, piston rings, and other purposes in which friction has to be taken account of.
Delta-metal, the second and latest example of the successful addition of iron to bronze, was introduced, in 1883, by Mr. Alexander Dick, who named it with the Greek equivalent for the initial of his surname. His preliminary experiments were directed to removing the inequalities in the properties of the iron-bronze alloys previously attempted, and he found that all depended on getting exactly the right proportion of iron and preventing its oxidation during the process of remelting. Delta-metal in color resembles gold alloyed with silver. It can be worked hot and cold. When melted, it runs freely, and the castings produced from it are sound and of a fine, close grain. It can not be welded, but can be brazed, and, when of suitable thickness, "burned." The varieties designed for working hot are capable of being stamped or punched, similar to wrought-iron and steel, into a variety of articles which have hitherto been cast in bronze or brass. This property is of much importance, for the articles thus turned out are cheaper and stronger than brass-castings. The iron introduced into the compound by Mr. Dick's process is really chemically combined; and the alloy does not rust, and has no action on the magnetic needle. Delta metal may be used to replace the best brass and gun-metal, and in many instances iron and steel also—for parts of rifles, guns, and torpedoes, tools for gunpowder-mills, parts of bicycles, gongs, various domestic articles, spindles for steam-and water-valves, plungers, pump rods, and boats.
Phosphor-copper is a preparation devised by Mr. W. G. Otto, of Darmstadt, for the purpose of furnishing engineers and founders with a compound, by adding certain proportions of which to a given bulk of metal they can obtain a phosphor-bronze suitable for various purposes.
An article called phosphor-manganese-bronze is in the market, but the manufacturer has not furnished a description of it.
Phosphor-lead bronze, introduced in 1881 by Messrs. K. H. Kuhne & Co., of Löbau, near Dresden, is regarded as specially adapted for all purposes where metal is subjected to constant wear or continuous friction. The introduction of lead into its composition and its homogeneousness are said to give it special properties, by reason of which the advantages are claimed for it of self-lubrication, greater wearing capacity than any other metal or alloy, coolness under friction, great tensile strength combined with hardness, and non-liability to fracture.
Phosphor-tin is a compound designed to be added to copper for the making of phosphor-bronze.
The history of the practical manufacture of aluminum does not extend very far back into the past; in fact, its commencement dates within the limits of the present generation. The three International Exhibitions which have been held in Paris since aluminum began to be worked on a commercial scale form so many landmarks in its progress. In 1855 it was met with for the first time in the Palais d'Industrie, in the form of a large bar, and was exhibited as silver produced from clay. In the Exposition of 1867 it was to be seen in a more advanced stage, worked up into castings and various kinds of useful and ornamental articles. There also for the first time was seen the alloy aluminum bronze. The Paris Exhibition of 1878 witnessed the maturity of the aluminum manufacture and its establishment as a current industry, having a regular demand and supply for certain purposes within the limits permitted by its somewhat high price. A little more than two years ago Mr. James Webster perfected his invention for producing aluminum, which is now being practically worked, and gives, it is claimed, alumina without a trace of iron, and free from contamination with other foreign substances. The process is being worked by the Aluminum Crown Metal Company, and the metal itself combines strength and lightness with elegance of appearance and general utility. The bronze is of two kinds—white and yellow—the former being used for cutlery and other table requisites where silver and plated goods are now employed, for metallic fittings, and for every purpose where a non-oxidizing, bright surface, with strength, is desired. The yellow metal is adapted, and is used for articles and for details of machinery where gun-metal and other alloys are now employed. It is said to stand well in engine-bearings, and to give satisfactory results when used in screw-propellers. The bronze is made in five qualities, and each quality is made hard or soft as may be required.
Silveroid, a metal introduced to public notice early in 1884, is an alloy of copper and nickel adjusted with zinc, tin, or lead, in various proportions, according to the purpose for which it is intended; but the secret of success in the manufacture is said to lie in a special method of treatment at a certain point in the process. This alloy is a metal of great whiteness, brilliancy, closeness of grain, and tensile strength.
Cobalt-bronze has been introduced since silveroid, by the same manufacturers, Messrs. Henry Wiggin & Co., who produced that metal. It is whiter and slightly more expensive than silveroid, and is interesting as containing small quantities of cobalt, with the most desirable qualities of that metal, particularly its malleability. It is manufactured in several qualities, the higher grades of which are eminently suitable for casting purposes, have a close, steel-like surface, are susceptible of a high polish, are hard and tough, and possess great tensile strength.
- From a paper read before the Society of Engineers.