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mensions of the models, or globes, should be regulated according to the quality of the metal which in the particular foundry employed is best adapted for casting in sand, or for making most of the common cast iron utensils, and this is generally a mixed metal. The grey metal may also be used if it have the property of remaining liquid, which will be the case when the mixture of ore and fluxes is somewhat refractory; but if the grey metal should become thick and throw out a large quantity of graphite, it would give the projectile a very porous, wrinkled surface, covered with dross, and of an unseemly appearance. What we have said of the kind of metal best adapted for hollow projectiles, does not apply to that which should be used for making shot; white metal, or that which inclines to white, gives very ugly shot. The best is a slightly mixed metal, inclining rather to grey than to white, or else the clear grey metal, very liquid and having a pure slag. Such metal is easily obtained in furnaces fed with coke or charcoal. It is to be observed that the ore which furnishes brittle iron, whatever may be its colour, does not give as good shot as some of the ores from which medium, or tough iron is obtained; but the latter are generally of too much value for the manufacture in question. To obtain shot of an even surface, a certain quantity of the better quality should, however, always be added to the former kind.
We are at no loss to understand that white metal which, when poured into moulds, presents a very even surface, may furnish good shells, and at the same time be unfit for the fabrications of shot; because the latter must be rolled and hammered, and this metal is not adapted to either of those operations; the same may be said of almost all the ores of very brittle iron; they are not sufficiently ductile to take a smooth surface after having been hammered.
Grey metal which is a little thick, occasions, around the superior pole of the projectile, small cavities, very narrow and deep; especially if the metal has been reduced with coke of a bad quality, or from impure ores. In that case it contains a large quantity of silex, a part of which is separated from the metal by oxidation and cooling; if the ore is, besides, very fusible, the metal throws out graphite in cooling. This graphite and the silex thrown out are collected about the superior pole, where, mixed again with a certain quantity of metal, they form a soft spongy matter which gives a very bad appearance to the shot, and should cause its rejection-when metal
ced by the expulsion of the earthy minerals; but these substances are not entirely crystallized, because the metal of this projectile is thin and cools quickly. In the twentyfour pound howitzes these rents are for the same reason' very rarely found, and never in grenades. The pellicles which so often appear on the surface of projectiles, are produced only by the crystallization of the earthy minerals. These troublesome accidents may be prevented by keeping the metal for some minutes in the ladles; when poured into the moulds it then becomes well mixed, and the tendency of the foreign substances to separate from the mass is counteracted; as the metal cools more quickly this separation becomes less easy, and the flaws are neither so great nor so numerous. This precaution should not be neglected in the fabrication of projectiles; if the metal be used too hot, depressions and cavities occur in cooling. These depressions, which are found about the eye, on the interior surface of six inch and eight inch howitzes, and ten inch and twelve inch shells, are caused by rents which often extend from the centre of the thickness of the metal to its interior surface. In some foundries most of the rejections are caused by the faults we have just mentioned, and we cannot too strongly recommend to those charged with the manufacture of hollow projectiles to allow the grey metal, when very hot, to remain a short time in the ladles; especially metal obtained, as it generally is for this purpose, from impure ore.
entirely grey has been obtained by means of charcoal from refractory and rather pure ores, it becomes more liquid, throws out less graphite, and is more suitable for making shot of an even surface; but small cavities may still be seen at the superior pole.
Of casting hollow Projectiles.
The moulds for hollow projectiles are made of sand; clay was formerly used for the cores, but they are now also made of sand; at least it is to be hoped that this improvement will be generally adopted. Pit sand should be used for moulds; river sand has too little adhesiveness. It should be of a fine grain, and of such a consistence that it may stick together when pressed in the hands. If it contain too much earth it adheres to the casting, and gives it a rough surface: if too pure it has not sufficient consistence, and the moulds are easily broken and spoiled. The sand should however be as pure as it is possible to use it, in order that the surface of the casting may be more readily cleaned.
Sand which is too earthy may be easily corrected by the addition of dust from charcoal, coke or mineral coal, a very refractory substance which may be obtained perfectly fine, and which resists, in the strongest manner, the tendency to vitrification, and consequently to the adhesion of the sand to the metal. The dust of coke or of mineral coal is preferable to that of charcoal, and should always be used to give projectiles a fine surface. Calcination also furnishes the means of preventing the sand from adhering too strongly to the metal; and this method is naturally employed, by making use of the sand in which other castings have been made. It is necessary to mix it with fresh sand in order to give it greater consistence, and at the same time a certain proportion of the dust of coke or of pulverized coal is added.
Before using sand it is dried, then sifted, and properly worked and moistened: the quantity of water added should be the least possible to make it fit for use, because too much moisture may cause the casting to fail; there is however no danger to the workman in an excess of moisture, because the steam finding little resistance, passes easily through the sand without causing explosions, which often occur, in using clay moulds.
Of Sand for Cores.
Sand for cores should of course contain more clay than that used for moulds, in order that after having been dried the cores may be so hard as not to be easily injured, and that they may adhere properly to the spindles. If the sand contain too much clay the core would not dry thoroughly without long exposure to a very high temperature. This inconvenience may be remedied by the addition of pure sand, or of coke dust, and by drying a second time.
In general, the quality of the sand and the degree of heat to which the cores should be exposed are dependent on each other. It is easy to succeed by subjecting them a sufficient length of time to a high heat; but the results are more certain, the operation is quicker and less expensive, when the sand is of the proper quality, having sufficient consistence not to be easily separated, and at the same time not retaining water with so much force as to require exposure to a very high degree of heat. If sand of this quality is not to be found on the spot, it may be composed by mixing the different kinds, or even by adding clay, provided however that it does not contain too great a proportion of calcareous matter, the proportions of the mixture are
soon determined by trial. But it is especially important to regulate the operation of drying according to the quality of the material used; when the casting fails and the projectiles are full of flaws, it may always be attributed to the presence of moisture. Whatever be the quality of the sand, it is prepared as described under the preceding head; that which has been once used cannot be again employed without the addition of fresh sand.
Of Clay for Cores.
Although cores are now made of sand, we shall say a few words on the preparation of them from clay, and consequently on that of the clay itself: our remarks will apply also to the preparation of the nucleus of cores made of sand.
Argillaceous earth retains water with greater force, shrinks more in drying, and has a greater tendency to crack, in proportion, as it contains a greater quantity of alumina. The use of grey earths should be avoided, because they have not sufficient consistence; nearly all the earths which effervesce with acids are of this sort.
The clay is first dried, then pulverized, or rather beaten with a bat, to break the lumps, and sifted for the purpose of separating the pebbles, it is then moistened and well worked, adding at the same time about one third of horse dung. The viscous liquor contained in the dung prevents the clay from cracking, diminishes the shrinking, makes it less compact, less hard after drying, and easier to break when the shell is to be emptied. The clay used for the core of the eye should be passed through a silken sieve, and mixed with a smaller proportion of dung; the same may be said of that used for the last coats of cores made after the old method.
Of the models of Hollow Projectiles.
The globe, or model, is generally made of copper: it consists of two hemispheres joined by a tongue and groove, in such a manner that they touch each other only on the exterior circumference; the inner part should be bevelled at a large angle: this is an essential point, for by this form the seam of the projectile is made thinner than it would be if the two hemispheres touched each other on a larger surface. The metal should be from three to four lines* thick, so that it may not yield when the sand is rammed on it. The diameter of a model for any calibre is variable, on account of the different degrees of expansion and contraction of different kinds of cast iron: it always expands in passing from a fluid to a solid state, and afterwards contracts in cooling. This increase and diminution of volume varies not only in different foundries, but also in different kinds of metal obtained in the same furnace by working it differently.
In general the grey metal expands more in crystallizing, or contracts less in cooling, than the white metal; the former may give projectiles of too great dimensions, whilst those cast with white metal in the same moulds may be too small. The diameter of the model should therefore be regulated according to the quality of metal which, in the furnace employed, appears to be most fit for the object in view, and most frequently obtained. On the other hand
*The French measures are retained in this article without reduction to the corresponding dimensions in English measures, because the former bear nearly the same proportion to the latter that the corresponding calibres bear to each other in the French service and in ours; besides they are easily reduced if necessary, to English measures; a French foot being equal to 12.79 English inches, very nearly. TRANS.
it advantageous for the service that the diameters of the projectiles should agree as nearly as possible with those of the largest gauge used in the inspection; which diameters, for twelve inch mortars and twenty-four and sixteen pounder guns, differ eighteen points from the calibre of the bore, and for other pieces, one line. It is only by trial, making the globe at first too large, that we can obtain the proper diameter, which should be such that the greater number of projectiles shall not pass through the intermediate gauge. To obtain this result it often happens that, for large calibres, the diameter of the model should exceed, by several points, that of the large gauge.
The addition of the dust of coal, or coke, to the sand facilitates the cleaning of the projectile and makes the surface more even, consequently the diameter smaller, so that a greater number pass through the intermediate gauge, or even through the small one. If water be poured on the iron whilst not, it contracts more. (See casting and finishing Projectiles.) Hence the necessity of being well acquainted with all the circumstances of the manufacture, when by the first trials, the dimension of the model is to be determined; if too small it cannot be corrected by a coating of tin, as has been sometimes attempted; it would be necessary to procure a new one, which occasions a considerable expense.
The model should be turned and finished in all its parts with the greatest precision. It was formerly the custom to flatten the models of all projectiles very much at the poles: it was thought that the metal contracted more in the horizontal than in the vertical direction. We have for a long time contended against this opinion. Experiments have proved to us that the alleged difference in the contraction of the metal does not exist. If projectiles, of a medium weight, moulded with spherical models, are sometimes elongated, it is to be attributed solely to the unskilfulness of the workmen, who have not sufficiently compressed the sand about the lower pole: it then happens, especially in the case of large projectiles, that the weight of the ! metal, causing the sand to yield, produces the elongation in question. When the workmen have the requisite degree of skill and intelligence, the models of all hollow projectiles, below the calibre of ten inches, should be perfectly spherical: by flattening them we obtain many flattened, and ill shaped, pro1 jectiles. If, on the contrary, the models are spherical, the workman soon learns to ram the sand properly, so that the number of elongated projectiles very small, whilst nearly all the others are perfectly spherical. Workmen generally prefer flattened models, because they are more afraid of obtaining elongated projectiles which will be rejected, than of producing a quantity of others more or less badly made.
The models of ten inch and twelve inch shells may be flattened from four to six points, as the sand cannot always be rammed sufficiently to prevent it from yielding to the pressure of these heavy castings. This explanation of the cause of the elongation of projectiles overthrows an absurd opinion, which has generally prevailed; there are, however, other causes of elongation which will be explained under the head of moulding.
The upper hemisphere of the model is pierced with a round hole intended to receive an iron spindle; in twelve inch shells the hole is nine lines in diameter; the length of the spindle is seven inches, four lines: it consists of three parts; one part is cylindrical and cut with a screw thread; it serves to fix to the hemisphere of the model a sort of handle by means of which it is managed: the second part is a truncated cone, all the dimensions of which are perfectly similar to another conical part on the spindle of the core, and it serves to prepare for the latter a lodgment in the sand. The third part is VOL. XVIII.-No. 1.-JULY, 1836.
nearly cylindrical, having also a diameter equal to that of the spindle of the core. In speaking of the flasks, we shall return to this subject. The upper hemisphere of the model of shells is pierced besides with two rectangular holes for the ears. Their position and form have undergone several variations; the following is the usual manner of tracing them. On a diameter perpendicular to the axis passing through the eye, lay off on each side three inches three lines, draw perpendiculars at these points, and with the radius of the twelve inch shell increased by that of the hole in the ear, cut the two perpendiculars at points which determine the centres of the holes: all shells being similar figures, the centres of the holes will be always found on the same radii. The diameters of these holes are laid down at four lines six points, for the twelve inch shell; three lines nine points, for the ten inch, and three lines three points for the eight inch. In practise it is necessary to make them a little larger, to afford the requisite play to the rings. It is essential that the mortices for the ears should be large enough to admit of their remaining in the sand, with the rings, after the hemisphere has been removed. Each ear is divided into two parts, which are generally joined by a tenon, so that they may be easily withdrawn in succession, without displacing the ring.
The ears placed as we have said, on a great circle, ought to fit accurately on the sphere, and form with it a continuous surface. The rings which are semi-elliptical, should be made with great precision, and finished with the file, so that the brazing, which is on the straight part, may not be visible. They are made of iron wire about two-fifths of an inch thick: it is necessary that they should play freely in the ears, and should fall down entirely on the surface of the shell. The diameter of the hole which they make should therefore be greater than their own: this is effected by enveloping them with a coat of clay, which should be quite round and well dried. When the shell is cast, this clay being removed, the ring has the requisite play.
The lower hemisphere of the model is also pierced with a hole which receives a piece called the false spindle; its dimensions are arbitrary; it is pierced at the inner end, with a mortice which receives a key. The other end is also pierced with a square hole in which is introduced a bar of iron or small ruler. The object of this spindle is to prevent the model from being detached from the mould when the flask containing it is raised; for this purpose a bit of wood is slipped under the rule; this acting like a wedge against the edge of the flask raises the rule and consequently presses the mould against the sand.
Of the Spindle of the Core, and of the Pattern.
The spindle of the core is divided into two parts by a swell several lines in height, in the form of a truncated cone, the base of which nearest to the core, has a diameter only three or four points less than the greatest diameter of the eye. The diameter of the other base is a little smaller than the first; in order that the spindle of the model, which should be perfectly similar to that of the core, may be withdrawn from the sand without causing any derangement of the mould. The dimensions of the part of the spindle opposite to the core are determined by the height of the flask, as we shall see further on. The part which supports the core, added to that which forms the eye of the projectile is equal in length to the distance from the upper circumference of the eye to the bottom of the shell, less a small quantity, and varying with the calibre: it is not important whether it be a little longer or a little shorter; the only essential point is that the swell and the part of the