PLATED MANUFACTURE

( Fabrique de plaqué , Fr.; Silber plattirung , Germ.) The silver in this case is not applied to ingots of pure copper, but to an alloy consisting of copper and bra , which po e es the requisite stiffne for the various articles. The furnace used for melting that alloy, in blacklead crucibles, is a common air-furnace, like that for making bra . The ingot-moulds are made of cast iron, in two pieces, fastened together; the cavity being of a rectangular shape, 3 inches broad, 1 1 ⁄ 2 thick, and 18 or 20 long. There is an elevated mouth-piece or gate, to give pre ure to the liquid metal, and secure solidity to the ingot. The mould is heated, till the grease with which its cavity is besmeared, merely begins to smoke, but does not burn. The proper heat of the melted metal for casting, is when it a umes a bluish colour, and is quite liquid. Whenever the metal has solidified in the mould, the wedges that tighten its rings are driven out, lest the shrinkage of the ingot should cause the mould to crack. See Bra . The ingot is now dre ed carefully with the file on one or two faces, according as it is to be single or double plated. The thickne of the silver plate is such as to constitute one fortieth of the thickne of the ingot; or when this is an inch and a quarter thick, the silver plate applied is one thirty-second of an inch, being by weight a pound troy of the former, to form 8 to 10 pennyweights of the latter. The silver, which is slightly le in size than the copper, is tied to it truly with iron wire, and a little of a saturated solution of borax is then insinuated at the edges. This salt melts at a low heat, and excludes the atmosphere, which might oxidize the copper, and obstruct the union of the metals. The ingot thus prepared is brought to the plating furnace. The furnace has an iron door with a small hole to look through; it is fed with cokes, laid upon a grate at a level with the bottom of the door. The ingot is placed immediately upon the cokes, the door is shut, and the plater watches at the peep-hole the instant when the proper soldering temperature is attained. During the union of the silver and copper, the surface of the former is seen to be drawn into intimate contact with the latter, and this species of riveting is the signal for removing the compound bar instantly from the furnace. Were it to remain a very little longer, the silver would become alloyed with the copper, and the plating be thus completely spoiled. The adhesion is, in fact, accomplished here by the formation of a film of true silver-solder at the surfaces of contact. The ingot is next cleaned, and rolled to the proper thinne between cylinders as described under Mint ; being in its progre of lamination frequently annealed on a small reverberatory hearth. After the last annealing, the sheets are immersed in hot dilute sulphuric acid, and scoured with fine Calais sand; they are then ready to be fashioned into various articles. In plating copper wire, the silver is first formed into a tubular shape, with one edge projecting slightly over the other; through which a redhot copper cylinder being somewhat loosely run, the silver edges are closely pre ed together with a steel burnisher, whereby they get firmly united. The tube thus completed, is cleaned inside, and put on the proper copper rod, which it exactly fits. The copper is left a little longer than its coating tube, and is grooved at the extremities of the latter, so that the silver edges, being worked into the copper groove, may exclude the air from the surface of the rod. The compound cylinder is now heated redhot, and rubbed briskly over with the steel burnisher in a longitudinal direction, whereby the two metals get firmly united, and form a solid rod, ready to be drawn into wire of any requisite finene and form; as flat, half-round, fluted, or with mouldings, according to the figure of the hole in the draw-plate. Such wire is much used for making bread-baskets, toast-racks, snuffers, and articles combining elegance with lightne and economy. The wire must be annealed from time to time during the drawing, and finally cleaned, like the plates, with dilute acid. Formerly the different shaped ve els of plated metal were all fashioned by the hammer; but every one of simple form is now made in dies struck with a drop-hammer or stamp. Some manufacturers employ 8 or 10 drop machines. IMG:4147767755307473660_illo0999.png:Die stamp Fig. 878. and 879. are two views of the stamp. A is a large stone, the more ma y the better; b , the anvil on which the die e is secured by four screws, as shown in the ground plan, fig. 880. In fig. 878. , a a are two upright square prisms, set diagonally with the angles opposed to each other; between which the hammer or drop d slides truly, by means of nicely fitted angular grooves or rece es in its sides. The hammer is raised by pulling the rope f , which pa es over the pulley c , and is let fall from different heights, according to the impulse required. Ve els which are le in diameter at the top and bottom than in the middle, must either be raised by the stamp in two pieces, or raised with a hand hammer. The die is usually made of cast steel. When it is placed upon the anvil, and the plated metal is cut into pieces of proper size, the top of the die is then surrounded with a lute made of oil and clay, for an inch or two above its surface; and the cavity is filled with melted lead. The under face of the stamp-hammer has a plate of iron called the licker-up fitted into it, about the area of the die. Whenever the lead has become solid, the hammer is raised to a certain height, and dropped down upon it; and as the under face of the licker-up is made rough like a rasp, it firmly adheres to the lead, so as to lift it afterwards with the hammer. The plated metal is now placed over the die, and the hammer mounted with its lead is let fall repeatedly upon it, till the impre ion on the metal is complete. If the ve el to be struck, be of any considerable depth, two or three dies may be used, of progre ive sizes in succe ion. But it occasionally happens that when the ve el has a long conical neck, recourse must be had to an auxiliary operation, called punching . See the embo ing punches, fig. 881. These are made of cast steel, with their hollows turned out in the lathe. The pieces a , b are of lead. The punching is performed by a series of these tools, of different sizes, beginning with the largest, and ending with the least. By this means a hollow cone, 3 or 4 inches deep, and an inch diameter, may be raised out of a flat plate. These punches are struck with a hand hammer also, for small articles, of too great delicacy for the drop. Indeed it frequently happens that one part of an article is executed by the stamp, and another by the hand. IMG:4147767755307473660_illo1000a.png:Bending machines Cylindrical and conical ve els are mostly formed by bending and soldering. The bending is performed on blocks of wood, with wooden mallets; but the machine so much used by the tin-smiths, to form their tubes and cylindric ve els (see the end section, figs. 882. and 883. ), might be employed with advantage. This consists of 3 iron rollers fixed in an iron frame. A , B , C , are the three cylinders, and a , b , c , d , the riband or sheet of metal pa ed through them to receive the cylindrical or conical curvature. The upper roller A can be raised or lowered at pleasure, in order to modify the diameter of the tube; and when one end of the roller is higher than the other, the conical curvature is given. The edges of the plated cylinders or cones are soldered with an alloy composed of silver and bra . An alloy of silver and copper is somewhat more fusible; but that of bra and silver answers best for plated metal, the bra being in very small proportion, lest the colour of the plate be affected. Calcined borax mixed with sandiver (the salt skimmed from the pots of crown gla ) is used along with the alloy, in the act of soldering. The seam of the plated metal being smeared with that saline mixture made into a pap with water, and the bits of laminated solder, cut small with sci ors, laid on, the seam is exposed to the flame of an oil blowpipe, or to that of charcoal urged by bellows in a little forge-hearth, till the solder melts and flows evenly along the junction. The use of the sandiver seems to be, to prevent the iron wire that binds the plated metal tube from being soldered to it. IMG:4147767755307473660_illo1000b.png:Metal working tools Mouldings are sometimes formed upon the edges of ve els, which are not merely ornamental, but give strength and stiffne . These are fashioned by an instrument called a swage , represented in figs. 884. and 885. The part A lifts up by a joint, and the metal to be swaged is placed between the dies, as shown in the figures; the tail b being held in the jaws of a vice, while the shear-shaped hammer rests upon it. By striking on the head A , while the metal plate is shifted succe ively forwards, the beading is formed. In fig. 884. the tooth a is a guide to regulate the distance between the bead and the edge. A similar effect is produced of late years in a neater and more expeditious manner by the rollers, figs. 886. 887. Fig. 888. is a section to show the form of the bead. The two wheels a , a , fig. 886. , are placed upon axes, two of which are furnished with toothed pinions in their middle; the lower one being turned by the handle, gives motion to the upper. The groove in the upper wheel corresponds with the bead in the lower, so that the slip of metal pa ed through between them a umes the same figure. The greatest improvement made in this branch of manufacture, is the introduction of silver edges, beads and mouldings, instead of the plated ones, which from their prominence had their silver surface speedily worn off, and thus a umed a bra y look. The silver destined to form the ornamental edgings is laminated exceedingly thin; a square inch sometimes weighing no more than 10 or 12 grains. This is too fragile to bear the action of the opposite steel dies of the swage above described. It is nece ary, therefore, that the sunk part of the die should be steel, and the opposite side lead, as was observed in the stamping; and this is the method now generally employed to form these silver ornaments. The inside shell of this silver moulding is filled with soft solder, and then bent into the requisite form. The base of candlesticks is generally made in a die by the stamp, as well as the neck, the dish part of the nozzle or socket, and the tubular stem or pillar. The different parts are united, some with soft and others with hard solder. The branches of candlesticks are formed in two semi-cylindrical halves, like the feet of tea-urns. When an article is to be engraved on, an extra plate of silver is applied at the proper part, while the plate is still flat, and fixed by burnishing with great pre ure over a hot anvil. This is a species of welding. The last finish of plated goods is given by burnishing-tools of bloodstone, fixed in sheet-iron cases, or hardened steel, finely polished. The ingots for lamination might probably be plated with advantage by the delicate pre ure proce employed for silvering copper wire. The total value of the plate, plated ware, jewellery, and watches, exported in the year 1836, was 338,889 l. ; but the value of the plated goods is not given in the tables of revenue. M. Parquin, the greatest manufacturer of plated goods in Paris (or France, for this busine is monopolized by the capital), who makes to the value of 700,000 francs per annum, out of the 1,500,000 which, he says, is the whole internal consumption of the kingdom, states that the internal consumption of the United Kingdom amounts 30,000,000, or 20 times, that of France! He adds, that our common laminated copper costs 26 sous the pound, while theirs costs 34. Their plated goods are fashioned, not in general with stamps, but by the pre ure of tools upon wood moulds in the turning-lathe, which is a great economy of capital to the manufacturer. There are factories at Birmingham which po e a heavy stock of 300,000 different die-moulds. See Stamping of Metals .