Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/303

CONSTRUCTION.] tubes, are suppliel by contractors. They are tested for quality of metal, and toughened after being bored by being raised to the temperature shown by the tests to be most suitable to the particular cylinder, and then plunged in oil. They are subsequently tested by water pressure at 4 tons Fig. 32. p3r square inch. The tubes are not bored quite through for muzzle-loaders ; a solid end is left to form the bottom of the bore. The rest of the gun is made of wrought iron. The material is chiefly received from the contractor in the form of wrought scrap, but a certain proportion of iron piddled in the works is used also. Blooms of these materials are rolled into flat bars, which are fagoted together and rolled into long bars of the section required for the part of the gun for which they are intended. These bars are then placed in a long narrow reverberatory furnace, i-^- 1 Fig. 34. foiling, and raised to a bright red heat. When ready for coiling, one end is drawn out and fixed to a revolving mandril, which pulls the bar out and winds it into a coil, like rope round a capstan. Sometimes a second bar is wound round outside the first coil ; in this case the mandril is made to r Fig. 35. revolve in the opposite direction. The coil is next placed upright in a reverberatory furnace, and raised to a white or "welding" heat. In this state it is placed under a steam hammer, and welded till it becomes a compact hollow cylinder. On cooling it is bored and turned to the proper r Fig. 36. dimensions. Two parts of the gun are made of forged iron (not coiled), the cascable screw which supports the breech end of the tube, and the hoop which carries the trunnions. The latter is either welded to the outer coil or shrunk on. Figs. 32-39 show the method of building up Woolwich Fig. 37. Juilding ordnance as exemplified in the 80-ton guns. The various coils are hooked together by shoulders to prevent slipping or distortion from the shock of discharge. Thus, in fig. 36, shoulders are turned on the exterior of the breech-piece and inside the IB coil; the latter is expanded by being raised to a dull red heat and slipped over the tube from the muzzle end. The expansion enables the shoulders to pass, 289 and on cooling they grip each other as shown, while the IB coil contracts on and slightly compresses the part of the tube within it. A method of strengthening and utilizing as rifled guns Con- some of the old cast-iron ordnance of the service has been verte( largely employed to supply pieces of secondary power and ^ uns excellence for land fronts and for practice. It was brought forward in its present shape by Sir W. Palliser in 1863, and is now being much used in the United States gun factories. The cast-iron block or gun is bored out to the Fig. 38. requisite dimensions, and a tube of coiled wrought iron is thrust into it; no shrinking is here employed, but a toler able fit is ensured by accurate turning. When fitted, the tube is secured by a collar screwed in at the muzzle ; a plug of iron passes through the under side of the gun into the tube near the trunnions to prevent any shift of position. The tube is in two parts, the breech end being turned down and a second tube shrunk over it. The bottom of the bore is formed by a wrought-iron cup, which is forged and stamped into shape under a steam hammer. A screw is Fig. 39. cut on the outside of the cup and inside the end of the tube; the cup is then screwed tightly home. The tube is next severely tested by water pressure, after which the second tube is shrunk on. The whole tube is then fitted into the cast-iron casing, the greatest care being taken that the breech end bears firmly home. The gun is now ready for rifling, an J, after that operation is performed, undergoes proof by firing heavy charges, which expand the tube closely against the cast-iron envelope, which then takes up the strain and affords the necessary support. The relation between the powers of the three classes of guns will be gathered from the following comparison : Nature of Gun. Weight of Gun. Weight of Pro jectile. Weight of Charge. Calibre. Energy of Projectile at 1000 yards. Energy of Projectile at 2000 yards. cwt. It). tt>. ins. foot-tons. foot-tons. Cast-ison 68-pr., 1 smooth bore, . | 95 C8 16 812 298 136 Palliser 80-pr , converted from V 100 80 10 6-30 C02 488 68-pr. above, . ) Wrought - iron ") 7-in. Woolwich > 90 ii5 22 j 7-00 1042 814 gun, . . .) The great German gunmaker, Krupp, employs nothing Steel but steel in the manufacture of his ordnance. His earlier guns pieces were bored from solid blocks of this metal forged under heavy hammers. They were homogeneous, and therefore the exterior did not assist the interior to bear the strain of the powder gas on discharge to the extent which scientific methods of construction admit. Still the excellent quality of the material enabled the artillerist to gat results from these pieces which have been surpassed only by the coil guns, and by Krupp s later productions. As, how ever, progress was made and the ratio of power to weight increased, it was found necessary to introduce a system of building up for steel ordnance also, and Krupp adopted the principle of shrinkage to which the English guns owed so

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