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METAL MOULDS FOR PEWTER WORKS.
ensure their taking their true positions. These remarks, however, are only advanced by way of general illustration, as figurecasting is the most refined part of the art of moulding.
Metal moulds are employed for many works in the easilyfused metals, which are required to be produced in large quantities, and with great similitude and economy: the examination of which moulds will serve to demonstrate many of the points of construction and proceeding. Thus the common bullet mould is made like a pair of pliers, the jaws of which are conjointly pierced with a hole or passage leading into a spherical cavity; the aperture is equally divided between the two halves of the mould, so that in fact the division is truly upon the diametrical line both of the sphere and the runner, or the largest part of each, otherwise the pliers could not be opened to remove the bullet when cast. Iron shot for great guns, are likewise cast in iron moulds, by which they also possess great accuracy of form and size. Figs. 142.
Figs. 142 to 145 represent the moulds for casting a pewter inkstand : these are a little more complex, and are made in four parts ; the black portions represent the sections of the inkstand to be cast. The moulds each consist of a top piece or cap t, a bottom or core b, and two sides or cottles, s s; in fig. 145, the one side is removed, in order to expose the casting, and the top piece t is supposed to be sawn through to make the whole more distinct.
METAL MOULDS FOR PEWTER WORKS.
It will be seen, the top and bottom parts have each a rebate like the lid of a snuff-box, which embrace the external edges of the two side pieces s s, and the latter divide as in the bullet mould, exactly upon the diametrical line of the inkstand, which in a circular object is of course the largest part; the positions of the parts are therefore strictly maintained.
When the mould has been put together, laid upon its side, and filled through x, the ingate, or as it is technically called, the tedge, it is allowed to stand about a minute or two, and then the top t is knocked off by one or two light blows of a pewter mallet ; the mould is then held in the hand, and the center part is knocked out of the casting by the edge ; lastly, the two sides are pulled asunder by their handles, and the casting is removed from the one in which it happens to stick fast; but it requires cautious handling not to break it. The face of the mould is slightly anointed with red ochre and white of egg, to prevent the metal adhering to the same, and to give the works a better face : the first few castings are generally spoiled, until in fact the mould becomes warm.
Most of the works made in the very useful material, pewter, are cast in gun-metal moulds, which require much skill in their construction ; thus a pewter tankard, with a hinged cover and spout, consists of six pieces, each of which requires a different mould, thus,
1. The body has a mould in four parts, like that for the inkstand, but it is filled in the erect position through two ingates, which are made through the top piece t, of the mould :
2. The bottom requires a mould in two parts, and is poured at the edge:
3. The cover is cast in the same manner; and thus far the moulds are all made in the lathe, in which useful machine these castings are also finished Fire 146. before being soldered together :
4. The spout requires a mould in two parts:
5. The piece, fig. 147, by which the cover is hinged to the handle requires a much more complex mould,
METAL. MOULDS FOR PEWTER WORKS.
which divides in four parts, as shown in fig. 146, and much resembles, except in external form, the remaining mould: namely,
6. For the handle, which mould, like the last, consists of four pieces fitted together with various ears and projections; they are represented in their relative positions in fig. 149, with the exception of the piece a, fig. 150, which is detached and shown bottom upwards. Fig. 148 shows the pewter handle separately, with the three knuckles for joining on the cover ; and on reference to fig. 149, of the five parts through which the pin p, is thrust, the two external pieces belong respectively to the sides c, and d, of the mould, the others are parts of the casting, and the two hollows are formed by the two solid knuckles fixed to the detached piece of the mould a, fig. 150. At the time of pouring, the pin p, serves to connect the three parts a, c, d, together, and also to form the hole in the casting, for the pin of the joint.
Fig. 151 shows the section of the mould upon the dotted lines : by this it will be seen the handle is cast hollow, as almost immediately the mould has been filled through t, all but the thin external shell is poured out again, and the weight is reduced to less than half. To extract the handle, the pin p, is first twisted out; then the joint piece a, is removed ; next the back piece b; and lastly the two sides c, d, are pulled asunder.
Tin or pewter bearings for locomotive carriages, have been cast in appropriate metal moulds ; and such materials are very
METAL MOULDS FOR PRINTING TYPES.
useful to the mechanist for many temporary purposes, such as collars, bearings, screws, nuts, &c., either for difficult positions, or where no screw tap is at hand and the resistance is moderate; in such cases the parts of the machine constitute one portion of the mould, the apertures being closed with moist loam : the processes are most successful when the parts can be made warm and the clay is nearly dry.
The most important, exact, and interesting example of casting in metallic moulds is that of type-founding, the description of which, as well as drawings of the mould, have been repeatedly given; some of the peculiarities only of this art, will be therefore noticed. Each complete set of types consists of five alphabets, A, a, a, A, a, besides many other characters, in all about two hundred, and which are required to be most strictly alike in every respect, except in device and width, the latter is the greatest for the W and M, and the least for the i and !. Every required measure of the types, (represented on an enlarged scale in fig. 152,) is determined by the mould alone, and not by any after correction.
If the moulds for the rectangular shafts of the types were made as in figs. 153 or 154, the usual forms of square moulds, they would not admit of alteration in width, as shifting a, fig. 153, would produce no change, and fig. 154 would thereby produce the form b. The mould which is used, is made in two parts as in fig. 155 ; whence it follows that shifting the part a, to the
TYPES, CLICHÉE PROCESS.
right or left increases or decreases the width of the type without interfering with its thickness, or as it is technically called, its body, (B, fig. 152,) the width, w, is adjusted by a piece called the register, fixed at the bottom of the mould.
The device is changed by placing across the bottom of the mould one of the two hundred little pieces of copper, fig. 156, called matrices, into which the face of the letter is impressed by very beautifully formed punches. The length of the letter is determined by a contraction at the upper part of the mould, as shown at c, fig. 157, which represents the type as it leaves the mould, the metal is poured with a jerk, to make a sharp impresssion of the matrix : the mould, which is held in the left hand, and the ladle in the right, being jerked simultaneously upwards, at the moment of filling the mould, and without which the face of the type would be rounded and quite imperfect. The breaks c, or the runners, of the types are first broken off, and after a slight correction of the sides, the hollows or channels in the feet are planed out of a whole column of them, fixed between bars of wood, without touching the square shoulders which determine the lengths of the types.
In some types with a large face and much detail, such as the illustrations given on the last page, the motion of the hand is barely sufficient to give the momentum required to throw the metal into the matrix, and produce a clean sharp impression. A machine is then used, which may be compared to a small forcingpump, by which the mould is filled with the fluid metal ; but from the greater difficulty of allowing the air to escape, such types are in general considerably more unsound in the shaft or. body; so that an equal bulk of them only weigh about threefourths as much as types cast in the ordinary way by hand, and which for general purposes is preferable and more economical *.
* Some other variations are resorted to in type founding ; sometimes the mould is filled at twice, at other times the faces of the types are dabbed, (the clichée process,) many of the large types and ornaments are stereotyped, and either soldered to metal bodies, or fixed by nails to those of wood. The music type, and ornamental borders, dashes, &c., display much very curious power of combination.
The clichée process is rather stamping than casting. The melted alloy, (see page 266,) is placed in a paper tray, and stirred with a card until it assumes the pasty condition. The metal die, or mould, is then “dabbed” upon the soft metal as in sealing a letter, but with a little more force.