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Manufacture > The great steam-hammer
The conditions which are essential to the safety and efficiency of a big gun having already been explained, it only remains to give a description of how these are practically carried out in the great industry which has its head-quarters at Woolwich. An account of how the work is done will best fall under four headings. They are, first, the appliances necessary to obtain the temperature required for the softening, welding, and preliminary treatment of the materials; second, those necessary for dealing with it, so as to secure the highest capacity for resisting excessive strains in particular directions; third, those contrivances which are needed to manipulate large masses of iron in conveying them from place to place, more especially when heated to a high temperature; and fourth, the processes required for finishing the work of the forge, and rendering the masses of iron practically serviceable for the duties of the field or of the fortress.
As in other branches of the iron trade, the furnace is the method employed for the puddling, heating, and welding of the iron. Though there has never been any disposition shown by the authorities to look askance upon the more recent improvements of private enterprise, nor yet upon the proposals of inventors, there are reasons why such methods as those of the modem regenerative furnaces of Siemens, and other improvements, should not be readily adopted at Woolwich. These reasons are to be discovered in the fact that the scale upon which the work is carried out is not so extensive as to make it by any means certain, that much economy would be effected by the introduction of appliances, which are essentially applicable to works that are conducted with different objects in view. It is not that the Arsenal at Woolwich is in any sense a small establishment, or that the number of the workmen employed is less than in other great establishments connected with the iron trade, but in most of these works the object that is desired is to be able to turn out large quantities of manufactured iron in the form of rails, or plates, or bars, whereas at Woolwich the iron that is made is all consumed upon the establishment. What would be a small amount of plant in a work that supplied outside customers whose demands may amount to thousands of tons in a single order, is nevertheless sufficient for the turning out of malleable iron in the quantities that are necessary for the making of big guns, on which a vast amount of labour, employing great numbers of workmen, is necessary before they are ready to be sent to the proof butts upon their final trials. It follows from this that though the authorities are quite alive to the value of improvements, they have not yet adopted those appliances which are common elsewhere, where the scale upon which they are used justifies the outlay of a large amount of capital; and although everything is very complete and perfect of its kind, the visitor will find that in the puddling department at Woolwich, there is much the same sort of plant that might have been seen some years ago, in the leading establishments of the iron trade depending upon private enterprise for their development, or which may still be seen in the smaller works throughout the kingdom, that have not yet adopted the improvements referred to. The puddling furnace, however, in use in the Royal Gun Factories, is a product of that department, and the invention of Mr. Price, the forge manager. Puddled iron can be produced by it at a considerable saving in fuel, and steel ingots are made from it with the same quickness and facility as from the Martin-Siemens furnace. The methods and designs are novel, and their efficiency has been proved practically over a period of years. A step has been made in one direction, however, which it would be well for other iron-masters to follow, in the adoption of mechanical means for working, or rather assisting to work, the iron in the puddling furnace. Immense exertion is required on the part of the puddler, more especially when the stage of “balling” has been reached, by the iron in its process of conversion, and any one who sees how much this labour is curtailed in the simple and effective machinery employed at the Arsenal cannot but wish that its adoption had become universal. Among the appliances upon which experiments have been made with more or less success for doing away with the labours of the puddler altogether, and substituting machinery, which in itself would afford the requisite labour, there is one at least which has received the most careful consideration of the authorities at the Arsenal, and we wish it every success.
But although the puddling process at Woolwich is not characterised by any novelty, and the furnaces used for fagging the scraps of iron are of the type ordinarily employed in forges throughout the country, no one can fail to be struck by the great size and completeness of those which are used for heating the huge coils of the big guns, and raising them to the temperature for welding them in solid masses under the blows of the steam-hammers. Their dimensions are alone sufficient to strike even the professional visitor, who has seen them for the first time, with astonishment, and when the great door of fire-brick, braced and bound together by its massive iron bands, rises and reveals the molten depths within, an impression is conveyed to the mind not only of the energy and ingenuity of those who have subjected such an element to their use but of their courage as well.
But we must go on to the next part of the subject, which is embraced under the appliances that are necessary for dealing with the iron so as to secure the highest capacity for resisting excessive strains in a particular direction. When the ball of iron, or the faggot of scraps, is taken from the furnace, and subjected to the blows of the steam-hammer, and then allowed to cool, it is impossible to say, with any certainty, what the direction of its greatest strength may be. Every blow which it received must have effected a change in the constitution of its substance, so that its internal structure when it is finally thrown aside and allowed to cool must be a matter of very uncertain guess-work. The first appliance, then, which combines in itself not only the means of reducing the iron to the shape required for further operations, but the disposal of its fibres in the direction best suited for withstanding the ultimate strain of the explosion, is the rolling-mill. Here again we find that the Arsenal differs in no essential respect from other first-rate establishments, though it may safely be said that there is no better rolling-mill in existence. One advantage it has over most others, in being provided with facilities for reversing the revolutions of the rolls, by means of an apparatus which has been adopted with the greatest success, and which greatly simplifies the operation. It is the invention of Mr. R. D. Napier, whose name is associated with many improvements in modem machinery, and who found at the Arsenal at Woolwich, the sympathy and assistance which are essential to the success of a new invention. The apparatus is of too complicated a character to admit of a description in these pages; but we cannot pass from the subject without congratulating both Mr. Napier and the authorities upon having been rewarded for their enterprise by the great success of the appliance. The limits that are placed in practice upon the dimensions of a mass of iron which has to be passed through a rolling-mill, depend upon the space between the rolls when they are separated, so as to leave the widest possible room for its reception; and the length of the bar which is produced from the rolling process is not only dependent upon this condition, but also upon the cooling of the iron, which takes place when it has been too long exposed to the action of the atmosphere. From both these causes – the limited capacity of the rolling-mill for receiving the mass, and its tendency to become hardened during the process of rolling – it is impossible to obtain anything approaching to the full length of a completed bar ready for being coiled. The unit of length, as it comes from the rolling-mill cannot be more at the most than twenty or thirty feet, and it therefore becomes necessary to weld a number of them together in order to obtain what is required for the formation of a complete coil. When the iron has been reduced to the proper shape in the rolling-mill, it is removed to another department, and the different lengths are welded together, so as to form, if necessary, a bar that, in the case of an 80-ton gun, is about 200 feet in length, and considerably over a foot square in section. Much care is required in the welding process, and it would no doubt be of great advantage, if such a bar could be produced directly in the rolling-mill. As this cannot be done, the only course left is to exercise every precaution, so as to ensure, as far as possible, that the bar is homogeneous and continuous in its fibrous structure; and as the blows of the hammer necessary for welding the bars together are made at right angles to their length, there is little doubt that the desired object is, in this manner, to a great extent obtained. When the bar has been completed to the desired length, it is placed in a furnace which stretches from one end of a long workshop to the other, and is not equalled in this respect by any other in the kingdom. The longest furnaces employed in the iron trade are those which are used for preparing the frames of ships for the bending that is necessary to shape them to the form of the vessel; but that which is used at Woolwich for heating the coiled bars of the big guns is more than double the length of the longest of those used in ship-building. As it would be impossible to obtain an equable distribution of heat from one centre of combustion, the firing of the coil furnace takes place at intervals along the length of the bar, and in this way the workmen are enabled to obtain the required temperature throughout.
The coiling of the bars can best be described by comparing it with the winding of a strip of paper round the finger, in which the edges of the paper touch each other throughout, and the result of the process is the formation of a cylinder. The difference between this very simple operation and that which takes place at Woolwich, is that the finger of one hand which forms the centre or mandril in the case of the strip of paper is fixed, and the coil is wound round by the fingers of the other hand, whereas at Woolwich the coil is fixed to the centre-mandril, which is made to revolve, and in that way to coil the bar round it just as a rope is coiled round the barrel of a windlass. The bar having been rapidly drawn out of the furnace when it has been sufficiently heated to render it soft and pliable, is borne up at intervals upon portable supports provided with rollers on which the bar rests, and which render it easier for the workmen to move it backwards and forwards in the direction of its length. As the power required for this operation is very considerable, even when the friction to be overcome has been reduced by means of the rollers on which the bar is resting, a chain is made fast to the end which projects from the furnace, and this being attached to a sort of winch, in connection with a revolving shaft of the workshop, provides a ready means for removing the coil. When the mandril, or centre round which the red-hot coil is twisted, is set in motion, much care and skill is required on the part of the workmen to insure its being wound round so as to leave as little space as possible between the edges, but practice has made perfect in this department, as well as in others where the technical difficulties are even greater, and the result of the operation is so complete that nothing further is required than a welding heat, and a few blows of the great steam-hammer to convert the long unwieldy bar as it came from the coil furnace into a solid cylinder, which is practically homogeneous throughout, and having its fibres arranged in the direction best suited to resist excessive strains. There is one respect in which the coiling machine differs from other appliances of a somewhat similar description, such as rolling-mills, and this arises from the necessity for removing the coil, and detaching it from the mandril upon which it has been wound. This can only be done by withdrawing it, and provision has therefore to be made for removing one of the side framings in which the mandril revolves. When this has been effected, the coil is then free to be drawn away to one side, leaving the mandril behind. No such appliance is necessary in the case of the rolling-mill, where the bars or plates or rails go in at one side and out at the other.