Part 30

Castings in bell metal are all more or less brittle; and, when recent, have a color varying from a dark ash-gray to grayish-white, which is darkest in the more cuprous varieties, in which it turns somewhat on the yellowish-red or bluish-red. The larger the proportion of copper in the alloy, the deeper and graver the tone of the bells formed of it. The addition of tin, iron, or zinc, causes them to give out their tones sharper. Bismuth and lead are also often used to modify the tone, which each metal affects differently. The addition of antimony and bismuth is frequently made by the founder to give a more crystalline grain to the alloy. All these conditions are, however, prejudicial to the sonorousness of bells, and of very doubtful utility. Rapid refrigeration increases the sonorousness of all these alloys. Hence M. D’Arcet recommends that the “pieces” be heated to a cherry-red after they are cast, and after having been suddenly plunged into cold water, that they be submitted to well-regulated pressure by skillful hammering, until they assume their proper form; after which they are to be again heated and allowed to cool slowly in the air. This is the method adopted by the Chinese with their gongs, etc., a casing of sheet iron being employed by them to support and protect the pieces during the exposure to heat. In a general way, however, bells are formed and completed by simple casting. This is necessarily the case with all very large bells. Where the quality of their tones is the chief object sought after, the greatest care should be taken to use commercially pure copper. The presence of a very little lead or any similar metal greatly lessens the sonorousness of this alloy; while that of silver increases it.

The specific gravity of a large bell is seldom uniform through its whole substance; nor can the specific gravity from any given portion of its constituent metals be exactly calculated owing to the many interfering circumstances. The nearer this uniformity is approached, or, in other words, chemical combination is complete, the more durable and finer-toned will be the bell. In general, it is found necessary to take about one-tenth more metal than the weight of the intended bell, or bells, in order to allow for waste and scorification during the operations of fusing and casting.

«BISMUTH ALLOYS.»

Bismuth possesses the unusual quality of expanding in cooling. It is, therefore, introduced in many alloys to reduce or check shrinkage in the mold.

For delicate castings, and for taking impressions from dies, medals, etc., various bismuth alloys are in use, whose composition corresponds to the following figures:

I II III IV Bismuth 6 5 2 8 Tin 3 2 1 3 Lead 13 3 1 5

V.—Cliché Metal.—This alloy is composed of tin, 48 parts; lead, 32.5; bismuth, 9; and antimony, 10.5. It is especially well adapted to dabbing rollers for printing cotton goods, and as it possesses a considerable degree of hardness, it wears well.

VI.—For filling out defective places in metallic castings, an alloy of bismuth 1 part, antimony 3, lead 8, can be advantageously used.

VII.—For Cementing Glass.—Most of the cements in ordinary use are dissolved, or at least softened, by petroleum. An alloy of lead 3 parts, tin 2, bismuth 2.5, melting at 212° F., is not affected by petroleum, and is therefore very useful for cementing lamps made of metal and glass combined.

LIPOWITZ’S BISMUTH ALLOY: See Cadmium Alloys.

«BRASS.»

In general brass is composed of two-thirds copper and one-third zinc, but a little lead or tin is sometimes advantageous, as the following:

I.—Red copper, 66 parts; zinc, 34 parts; lead, 1 part.

II.—Copper, 66 parts; zinc, 32 parts; tin, 1 part; lead, 1 part.

III.—Copper, 64.5 parts; zinc, 33.5 parts; lead, 1.5 parts; tin, 0.5 part.

«Brass-Aluminum.»—A small addition of aluminum to brass (1.5 to 8 per cent) {53} greatly increases its hardness and elasticity, and this alloy is also easily worked for any purpose. Brass containing 8 per cent of aluminum has the valuable property of being but slightly affected by acids or gases. A larger percentage of aluminum makes the brass brittle. It is to be noted that aluminum brass decreases very materially in volume in casting, and the casts must be cooled slowly or they will be brittle. It is an alloy easily made, and its low price, combined with its excellent qualities, would seem to make it in many cases an advantageous substitute for the expensive phosphorous bronze.

«Bristol Brass (Prince’s Metal).»—This alloy, which possesses properties similar to those of French brass, is prepared in the following proportions:

I II III Copper 75.7 67.2 60.8 Zinc 24.3 32.8 39.2

Particular care is required to prevent the zinc from evaporating during the fusing, and for this purpose it is customary to put only half of it into the first melting, and to add the remainder when the first mass is liquefied.

«Brass-Iron (Aich’s Metal).»—This is a variety of brass with an admixture of iron, which gives it a considerable degree of tenacity. It is especially adapted for purposes which require a hard and, at the same time, tenacious metal. Analyses of the various kinds of this metal show considerable variation in the proportions. Even the amount of iron, to which the hardening effect must be attributed, may vary within wide limits without materially modifying the tenacity which is the essential characteristic of this alloy.

I.—The best variety of Aich’s metal consists of copper, 60 parts; zinc, 38.2; iron, 1.8. The predominating quality of this alloy is its hardness, which is claimed to be not inferior to that of certain kinds of steel. It has a beautiful golden-yellow color, and is said not to oxidize easily, a valuable property for articles exposed to the action of air and water.

II.—Copper, 60.2 parts; zinc, 38.2; iron, 1.6. The permissible variations in the content of iron are from 0.4 to 3 per cent.

Sterro metal may properly be considered in connection with Aich’s metal, since its constituents are the same and its properties very similar. The principal difference between the two metals is that sterro metal contains a much larger amount of iron. The composition of this alloy varies considerably with different manufacturers.

III.—Two varieties of excellent quality are the product of the Rosthorn factory, in Lower Austria—copper, 55.33 parts; zinc, 41.80; iron, 4.66. Also

IV.—English sterro metal (Gedge’s alloy for ship sheathing), copper, 60 parts; zinc, 38.125; iron, 1.5.

The great value of this alloy lies in its strength, which is equaled only by that of the best steel. As an illustration of this, a wrought-iron pipe broke with a pressure of 267 atmospheres, while a similar pipe of sterro metal withstood the enormous pressure of 763 atmospheres without cracking. Besides its remarkable strength, it possesses a high degree of elasticity, and is, therefore, particularly suitable for purposes which require the combination of these two qualities, such as the construction of hydraulic cylinders. It is well known that these cylinders, at a certain pressure, begin to sweat, that is, the interior pressure is so great that the water permeates through the pores of the steel. With a sterro metal cylinder, the pressure can be considerably increased without any moisture being perceptible on the outside of the cylinder.

Sterro metal can be made even more hard and dense, if required for special purposes, but this is effected rather by mechanical manipulation than by any change in the chemical composition. If rolled or hammered in heat, its strength is increased, and it acquires, in addition, an exceedingly high degree of tenacity. Special care must be taken, however, in hammering not to overheat the metal, as in this case it would become brittle and might crack under the hammer. Sterro metal is especially suitable for all the purposes for which the so-called red metal has been in the past almost exclusively used. Axle bearings, for example, made of sterro metal have such excellent qualities that many machine factories are now using this material entirely for the purpose.

«Cast Brass.»—The various articles of bronze, so called, statuettes, clock cases, etc., made in France, where this industry has attained great perfection and extensive proportions, are not, in many cases, genuine bronze, but fine cast brass. Following are the compositions of a few mixtures of metals most frequently used by French manufacturers: