The semi-cylindrical piece which lies in the centre of the room, toward the fore-ground, is part of a locomotive boiler, and is of course much smaller in size than the others, though it is constructed in the same manner with the large boilers used for sea-going ships. The process of riveting, as will be seen by the engraving, is the same. One man holds up against the under side of the plate a support for the rivet, while two men with hammers form a head above – striking alternately upon the iron which protrudes.
From the boiler we proceed to the cylinder, which is in fact the heart of the engine, – the seat and centre of its power. It is to the cylinder that the steam, quietly generated in the boiler, comes to exercise its energy, by driving, alternately up and down, the ponderous piston. The cylinder must be strong so as to resist the vast expansive force which is exercised within it. It must be stiff, so as to preserve in all circumstances its exact form. It must be substantial, so as to allow of being turned and polished on its interior surface with mathematical precision, in order that the piston in ascending and descending, may glide smoothly up and down, without looseness, and at the same time without friction. To answer these conditions it is necessary that it should be formed of cast iron.
The cylinders are cast, accordingly, in the iron foundry, which, as will be seen by the plan, is on the left, as the visitor enters the works. There is a range of monstrous cranes extending through the interior of the room, as represented in the plan, one of which is exhibited conspicuously in the engraving below. At different places in the ground, beneath this foundry, for it has no floor, there have been excavated deep pits, some of which are twelve feet in diameter and eighteen feet deep, the sides of which are secured by strong inclosures, formed of plates of boiler iron riveted together. These pits are filled with moulding sand – a composition of a damp and tenacious character, used in moulding. The mould is made and lowered into one of these pits, the pit is filled up, the sand being rammed as hard as possible all around it. When all is ready, the top of the mould, with the cross by which it is to be lifted and lowered surmounting it, presents the appearance represented on the right hand lower corner of the engraving below.
A reservoir to contain the melted metal necessary for the casting is then placed in a convenient position near it, with a channel or conduit leading from it to the mould. This reservoir may be seen in the engraving near the centre of the view, at the foot of the crane. An inclined plane is then laid, as seen in the engraving, to the left of the reservoir, up which the workmen carry the molten metal in ladles, which, though they do not appear very large, it requires five men to carry. A party carrying such a ladle may be seen in the engraving in the back-ground on the left. These ladles are filled from the various furnaces, the iron throwing out an intense heat, and projecting the most brilliant scintillations in every direction, as it flows. In the case of the largest castings it requires sometimes four or five hours to get together, from the furnaces, a sufficient supply of metal. The largest reservoir thus filled will hold about thirty tons of iron.
The flowing of the metal from the reservoir to the mould in a great casting, forms a magnificent spectacle. The vast mass of molten iron in the reservoir, the stream flowing down the conduit, throwing out the most brilliant corruscations, the gaseous flames issuing from the upper portions of the mould, and the currents of melted iron which sometimes overflow and spread, like mimic streams of lava, over the ground, present in their combination quite an imposing pyrotechnic display. In fact there is a chance for the visitor, in the case of castings of a certain kind, that he may be treated to an explosion as a part of the spectacle. The imprisoned vapors and gases which are formed in the mould below, break out sometimes with considerable violence, scattering the burning and scintillating metal in every direction around.
When the casting is completed it is of course allowed to remain undisturbed until the iron has had time to cool, and then the whole mass is to be dug out of the pit in which it is imbedded. So much heat, however, still remains in the iron and in the sand surrounding it, that the mould itself and the twenty or thirty men engaged in disinterring it, are enveloped in dense clouds of vapor which rise all around them while the operation is proceeding.
It is necessary that the sand which surrounds these moulds should be rammed down in the most compact and solid manner to sustain the sides of the mould and enable them to resist the enormous pressure to which it is subject, especially in the lower portions, while the iron continues fluid. In the case of iron, the weight of four inches in height is equivalent to the pressure of a pound upon the square inch. In a pit, therefore, eighteen feet deep, as some of the pits at this foundry are, we should have a pressure at the bottom of fifty-four pounds to the inch. Now, in the most powerful sea-going steamers, the pressure of steam at which the engines are worked, is seldom more than eighteen pounds to the inch; that of the Cunard line is said to be from twelve to fifteen, and that of the Collins line from fifteen to eighteen. In other words there is a pressure to be resisted at the lower ends of these long castings equal to three times that at which the most powerful low pressure engines are worked, and which sometimes results in such terrific explosions.
When the cylinder is freed from the pressure of the sand around it, in its bed, the great iron cross by which the mould was lowered into the pit, as seen in the engraving of the Casting, is once more brought down to its place, and the stirrups at the tops of the iron rods seen in the engraving below, are brought over the ends of the arms of the cross. The lower ends of these rods take hold of a frame or platform below, upon which the whole mould, together with the cylinder within it, is supported. The arm of the crane is then brought round to the spot. The hook pendant from it is attached to the ring in the centre of the cross, and by means of the wheels and machinery of the crane, the whole is slowly hoisted out, and then swung round to some convenient level, where the ponderous mass is freed from its casing of masonry, and brought out at last to open day. It is then thoroughly examined with a view to the discovery of any latent flaw or imperfection, and, if found complete in every part, is conveyed away to be the subject of a long series of finishing operations in another place, – operations many and complicated, but all essential to enable it finally to fulfill its functions.
These cylinders though very massive and ponderous are not the heaviest castings made. They are much exceeded in weight by what is called a bed plate, which is an enormous frame of iron cast in one mass, or else in two or three separate masses and then strongly bolted together, to form a foundation on which the engine is to rest in the hold of the ship. The bed plate can not be seen in the view of the engine room already given, as it lies below the floor, being underneath all the machinery. A bed plate weighs sometimes thirty-five tons – which is the weight of about five hundred men. Such a mass as this has to be transported on ways, like those used in the launching of a ship. It is drawn along upon these ways by blocks and pullies, and when brought alongside the ship is hoisted on board by means of an enormous derrick, and let down slowly to the bottom of the hold – the place where it is finally to repose, unless perchance it should at last be liberated by some disaster, from this dungeon, and sent to seek its ultimate destination in the bottom of the sea.
The engraving below represents the forges, where all those parts of the machinery are formed and fitted which consist of wrought iron. The room in which these forges are situated is called the smith's shop, in the plan. In the back-ground, a little to the right, is one of the trip hammers, in the act of striking. The trip-hammer is a massive hammer carried by machinery. The machinery which drives it may at any time be thrown in or out of gear, so that the blows of the hammer are always under the control of the workman. The iron bar to be forged is far too heavy to be held by hand. It is accordingly supported as seen in the engraving, by a crane; and only guided to its place upon the anvil by the workmen who have hold of it. The chain to which this bar is suspended comes down from a little truck which rests upon the top of the crane, and which may be made to traverse to and fro, thus carrying whatever is suspended from it further outward, or drawing it in, as may be required. All the cranes, both in the smith's shop and in the foundry, are fitted with the same