420 steam-engines--representing together 33,150 horse-power--and twenty-one rolling trains; the daily consumption of coal and coke being 3100 tons by 1648 furnaces. The average daily consumption of water, which is brought from the river Ruhr by an aqueduct, is 24,700 cubic metres. The electric light has been introduced, and the work ceases entirely only on Sunday and two or three holidays. Connected with theEssen works are fifty miles of railway, employing thirty-five locomotives and over 1000 wagons. There are two chemical laboratories; a photographic and lithographic studio; a printing-office, with steam and hand presses; and a bookbinding room, besides tile-works, coke-works, gas-works, &c.
Though, in the popular mind, the name of Krupp is[Pg 41] usually associated with the manufacture of instruments of destruction, yet two-thirds of the work done in his establishment is devoted to the production of articles intended for peaceful uses. The various parts of steam-engines, both stationary and locomotive; iron axles, bridges, rails, wheel-tires, switches, springs, shafts for steamers, mint-dies, rudders, and parts of all varieties of iron machinery, are prepared here for manufacturers. The production is, in Dominie Sampson's phrase, 'prodigious.' In one day the works can turn out 2700 rails, 350 wheel-tires, 150 axles, 180 railway wheels, 1000 railway wedges, 1500 bombshells. In a month they have produced 250 field-pieces, thirty 5.7-inch cannon, fifteen 9.33-inch cannon, eight 11-inch cannon, one 14-inch gun, the weight of the last named being over fifty tons, and its length twenty-eight feet seven inches. Till the end of 1894 the firm has produced 25,000 cannon for thirty-four different states.
Alfred Krupp devoted much attention to the production of steel of the finest quality, and was the first German manufacturer who succeeded in casting steel in large masses. In 1862 he exhibited in London an ingot of finest crucible steel weighing twenty-one
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tons. Its dimensions were nine feet high by forty-four inches diameter. The uniformity of quality of this mass of metal was proven by the fact that when broken across it showed no seam or flaw, even when examined with a lens. The firm can now make such homogeneous blocks of seventy-five tons weight if required. Such ingots are formed from the contents of a great number of small crucibles, each containing from fifty to one hundred pounds of the metal. The recent developments of the manufacture of steel
by the open-hearth process have removed all difficulty in procuring the metal in masses large enough for all requirements, and of a tensile strength so high as thirty-three to thirty-seven tons to the square inch. Crucible steel, however, though more[Pg 42] expensive, still holds its place as the best and most reliable that can be produced; and nothing else is ever used in the construction of a Krupp gun. By the perfected methods in use at the Essen works, such steel can be made of a tensile strength of nearly forty tons to the square inch, and of marvellous uniformity of quality. The ores used in the Krupp works for making the best steel are red haematite and spathic ore, with a certain proportion of ferro-manganese. The crucibles employed are formed of a mixture of plumbago and fire-clay, shaped by a mould into a cylindrical jar some eighteen inches in height, and baked in a kiln. When in use, they are filled with small bars of puddled metal, mixed with fragments of marble brought from Villmar, on the Lahn. They are then shovelled into large furnaces, whose floors are elevated three or four feet above the ground-level. In the earthen floor of the immense room containing the furnaces are two lines of pits, one set to receive the molten metal, the other intended for the red-hot crucibles when emptied of their contents. When the crucibles have undergone sufficient heating, the furnace doors are opened simultaneously at a given signal, and the attendant workmen draw out the crucibles with long tongs, and rapidly empty them into the pits prepared for the reception
of the metal. The empty crucibles when cooled are examined, and if found unbroken, are used again; but if damaged, as is usually the case, are ground up, to be utilised in making new ones.
The production of steel by this method furnishes employment for eight or nine hundred men daily in the Krupp works. The Bessemer process for converting iron into steel is also largely used there for making steel for certain purposes. All material used in the different classes of manufactures is subjected at every stage to extreme and exact tests; the standards being fixed with[Pg 43] reference to the purpose to which the metal is to be applied, and any material that proves faulty when suitably tested is rigorously rejected.
The guns originally manufactured by the Krupp firm were formed from solid ingots of steel, which were bored, turned, and fashioned as in the case of cast-iron smooth-bore cannon. With the development of the power of artillery, the greater strain caused by the increased powder-charges and by the adoption of rifling--involving enhanced friction between the projectile and the bore--had the result of demonstrating the weakness inherent in the construction of a gun thus made entirely from one solid forging, and that plan was eventually discarded. Artillerists have learnt that the strain produced by an explosive force operating in the interior of a cannon is not felt equally throughout the thickness of the metal from the bore to the exterior, but varies inversely as the square of the distance of each portion of the metal from the seat of effort. For example, in a gun cast solid, if two points be taken, one at the distance of one inch from the bore, and the other four inches from the bore, the metal at the former point will during the explosion be strained sixteen times as much as that at the distance of four inches. The greater the thickness of the material, the greater will be
the inequality between the strains acting at the points respectively nearest to and farthest from the interior. The metal nearest the seat of explosion may thus be strained beyond its tensile strength, while that more remote is in imperfect accord with it. In such a case, disruption of the metal at the inner surface ensues, and extends successively through the whole thickness to the exterior, thus entail-ing the destruction of the gun.
This source of weakness is guarded against by the construction of what is termed the built-up gun, in which the several parts tend to mutual support. This gun consists[Pg 44] of an inner tube, encircled and compressed by a long 'jacket' or cylinder, which is shrunk around the breech portion with the initial tension due to contraction in cooling. Over the jacket and along the chase, other hoops or cylinders are shrunk on successively, in layers, with sufficient tension to compress the parts enclosed. The number and strength of these hoops are proportionate to the known strain that the bore of the gun will have to sustain. The tension at which each part is shrunk on is the greater as the part is farther removed from the inner tube; the jacket, for example, being shrunk on at less tension than the outer hoops. The inner tube, on receiving the expansive force of the explosion, is prevented by the compression of the jacket from being forced up to its elastic limit; and the jacket in its turn is similarly supported by the outer hoops; and on the cessa-tion of the internal pressure the several parts resume their normal position.
This system of construction originated in England, and is now in general use. The first steel guns on this principle were those designed by Captain Blakely and Mr J. Vavasseur, of the London Ordnance Works. At the Exhibition of 1862, a Blakely 8.5-inch
gun, on the built-up system, composed wholly of steel, was a feature of interest in the Ordnance section. The plan devised by Sir W. Armstrong, and carried into effect for a series of years at Woolwich and at the Armstrong Works at Elswick, consisted in enclosing a tube of steel within a jacket of wrought iron, formed by coiling a red-hot bar round a mandrel. The jacket was shrunk on with initial tension, and was fortified in a similar manner by outer hoops of the same metal. The want of homogeneity in this gun was, however, a serious defect, and ultimately led to its abolition. The difference in the elastic properties of the two metals caused a separation, af-ter repeated discharges,[Pg 45] between the steel tube and its jacket, with the result that the tube cracked from want of support. Both at Woolwich and at Elswick (described on a later page), therefore, the wrought-iron gun has given place to the homogeneous steel built-up gun, which is also the form of construction adopted by the chief powers of Europe and by the United States of America.
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The failure of some of his solid-cast guns led Krupp, about 1865, to the adoption of the built-up principle.
