Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/260

218 zinc, and as this alloy can be rolled out hot it is much more cheaply and expeditiovisly prepared than ordinary sheet brass.

Wire Drawing.—Brass wire is consumed in enormous quantities, first and chiefly for pin-making, next for shoe- rivets, then for brush-making, for paper-makers wire web, and many other purposes. The metal for wire drawing is rolled into long strips of a suitable thickness and cut into &quot; strands &quot; by means of slitting rolls. The strands, which are square in section, are drawn through a succession of circular holes in a steel draw-plate, till the desired degree of fineness is reached, and are wound upon a rotating drum or block. The wire has to be repeatedly annealed as it passes through the plates of ever-diminishing gauge.

Stamping.—A. large number of useful articles, as well as many ornamental details, which were formerly produced by the process of casting, are now cheaply and expeditiously made by stamping out of sheets of rolled brass. In this way the ornamentation applied to the cheaper kinds of gasaliers, balance-weights, chain-links, &c., are formed, and cornice-pole ornaments and curtain-rings made ; and the process is also applied to the making of door and shutter knobs, finger plates, and lamp-burners, and to the striking up of many useful articles, such as basins and other vessels. In the process of stamping, a die, in which the pattern to be formed is sunk, is prepared by the ordinary process of die sinking, and securely fixed to a heavy iron block sunk into the ground. From each side of this block rise two cast-iron guide pillars, which act as guides to the heavy hammer or ram arranged to slide up and down between them. Into this hammer a &quot; force,&quot; or exact counterpart of the sunk die, is fitted, so that on the fall of the hammer the force exactly fits into the die. The work of the stamper in raising his hammer is much lightened by passing the lifting belt over a pulley attached to a shaft moved by steam-power. By this arrangement the workman has only to hold his cord sufficiently tight to create the friction between the belt and pulley necessary to raise the weight, and by letting go his hold, the stamp is allowed to fall with its full momentum against the die. In a compound of such hardness and brittleness as brass it is necessary to raise any pattern by repeated strokes, annealing the metal between each separate blow. The number of blows neces sary to bring up any pattern depends on the depth and convexity of the die. The &quot; forces,&quot; or counterparts of the die, are made of lead, tin, or other soft metal, while for finishing the stamping when the die contains fine details a &quot; force &quot; made of brass is employed. A modification of the steam-hammer has been adapted for use in the pro cess of stamping. Stamped work as compared with castings is deficient in depth and richness, as it is not practicable to attain any great boldness and sharpness of outline, and the &quot; force &quot; having to fit into every portion of the die, no undercutting is possible. Globular articles, such as balance weights, are stamped in two (or if necessary more) parts and the pieces joined by soldering. Mr James Atkins of Birmingham has patented an ingenious method of filling stamped shells, such as balance-weights, with molten iron by simply keeping the shell in water while it is being filled.

Tube-making.—Brass tubes are of three principal kinds : 1st, ordinary soldered; 2d, cased; and 3d, solid tubing. Plain soldered tubes are made from sheet-brass by cutting off, with circular shears, strips of the breadth necessary for the gauge of the tube to be made. These strips are passed through &quot; cupping-rolls, &quot; by which they are partially bent round. The end of the strip is then formed into a tang, caught and drawn through a tool called a conductor, which folds over the strip into a circular form, bringing the two edges into close contact The tube so formed is tightly tied up with wire at short intervals to keep the edges together in the process of soldering ; a mixture of granu lated brass and borax is filled into the seam, and the tube is passed slowly through a strong heat in the soldering stove, which melts the granulated brass and so unites the edges. The wires are then cut away, and the superfluous solder filed off, the tube is pickled in sulphuric acid, and again passed through the steel conductor. In the case of tubes which require great accuracy of internal gauge, a man dril or solid cylinder of steel is placed inside the tube before it is finally passed through the tool. The external pressure causes the tube to fit closely to its internal support, and while the outside takes the outline of the steel conductor, the inside is made true to the shape of the mandril. Tubes of any given section are thus formed by the use of mandrils having the outh ne required. Ornamental patterns are impressed on plain tubes by fitting them on mandrils and passing them through a tool, which consists of a strong iron frame cany ing three or more rollers so mounted that the open space between their external edges has the sec tional form of the tube to be ornamented. On the external face of these rollers is sunk the design which is to be impressed on the tube, and as it is drawn through them the powerful squeeze they give is sufficient to impress orna ments of considerable depth and boldness. Cased-tubes or rods, that is, tubes or rods of iron cased in brass, were invented in 1803 by Sir Edward Thomason, who thus described his invention : &quot; In watching the operation of drawing brass and copper tubes upon the mandril, I found it required as much power to slide off the hollow tube from the mandril as was required to draw it on. Reasoning from the adhesion of the brass tube to the steel mandril, I found by experiment that the union of copper and iron or brass and iron could be firmly attached by pressure, and conceived that such an application would be useful for making copper bolts for shipping, solid brass rods for stair carpets, solid brass to go round the top of a room to suspend pictures, as curtain rods for drawing-rooms, and as balustrades for staircases.&quot; Wood is cased in brass by a similar process, and used for such purposes as brass cornice-poles. Solid or seamless brass tubes, which are in very extensive demand for locomotive and other steam boilers, are made by drawing down short thick cast cylinders of brass till they reach the desired gauge and thinness. The instrument in which this drawing is accom plished is similar to the apparatus for impressing orna mental patterns on plain brass tubes. Four steel rollers are mounted in a strong frame, the sectional outline of the outer surfaces of which have the eize and form to which the tube is to be drawn, and through a series of such tools the cast cylinders are passed, after annealing at each opera tion. Mr G. F. Muntz in 1852 patented a method of drawing tubes cast in an oval form in the heated state.

Brass Finishing.—The operations in brass finishing com prise &quot; dipping, &quot; &quot; burnishing,&quot; and &quot; lacquering,&quot; and in some cases brass-work is finished by &quot; bronzing.&quot; After the article to be finished has been cleaned by pickling in acid, it is passed for dipping into an earthenware jar con taining a solution of aquafortis (nitric acid). For bright dipping the acid is used strong, and the brass is imme diately withdrawn from the bath, but for &quot; dead &quot; dipping, i.e., for producing a bitten, frosted appearance, the bath is made weaker and the metal left in it till a creamy appear ance is seen on the surface. Burnishing is accomplished by rubbing with polished steel tools, called burnishers, the parts of dead dipped work which are to be brightened. The work is then passed through water soured with acid, rinsed, and dried in boxwood sawdust. For lacquering, the work is heated over stoves, and while it is hot, a coating of varnish, made of seed-lac dissolved in spirit, is carefully 