THE EIGHTY-ONE TON GUN.

Nelson Evening Mail, Volume IX, Issue 307, 12 September 1874, Page 2

THE EIGHTY-ONE TON GUN.

The first step towards the production of the 81-ton gun has just been taken. All the built-up guns made at the Royal Arsenal, Woodwich, are lined with a steel tube. This tube is derive! from a solid ingot, supplied from the works of Messrs Firth and Sons, of Sheffield. The casting of the tube for the enormous gun now designed was carried out at these works lately in the most successful manner. Tbe ingot is made of crucible steel, and required for its construction 620 crucibles, each containg seventy pounds of metal, the total weight being thus very nearly twenty tons. The casting occupied forty-two minutes, and employed 194 men. The ingot thus produced measures forty-two inches in diameter anrl thirteen feet in length. This will have to be re-heated and hammered out to the proper dimensions for the tube in the rough, after which it will be bored, turned, and tempered in the Royal Gun Factories at Woolwich. After being cast, the ingot is covered with hot ashes and other non-conducting substances, under which conditions it is allowed to cool very slowly. s W]/en cold, a portion is cut off the top"^\the ingot being cast in an upright mould), and the lower end, being the denser, is marked for the breach. The block thus formed is drawn out by a series of heatings and hammerings, which occupy several days, until is forma a cylinder of sufficient length. The forging or drawing out of the cost block under the hammer imparts. to it the desired properties of great and density. In order to provide for forging ingots of such size as fifteen tons and upwards the Messrs Firth have erected in their works two of Nasmyth 's steam, hammers of twentyfive tons weight, eacb, at a cost of £33,000. After the ingot bas been roughly bored outsat Woolwich it undergoes a process w>f " toughening," which consists iv heating the tube in a vertical furnace, and then plunging it bodily into a bath of rape-oil, in which it is allowed to cool aud soak until next day, generally for twelve hours or more. The tank or bath contains several hundred gallons of oil, and has an enclosed space around it, in which s supply of cold water circulates for the pnrpose of keeping the oil below a certain temperature. The necessity far this process, w.herej»y.*.the steel is tempered, will be seen .from the fact that steel in its natural state aftet^ casting snd forging is nearly as solt and inelastic as malleable iron. If heated aud plunged into cold water the steel becomes bard but is at the same time btittle. But oil, being a bad conductor of heat, anW having a high .boiling point, operates differently. The hot. steel lhat is plunged into it parts with its heat much more slowly than when water is used, and the metal becomes toughened as well as hardened. Cast steel is the most expensive of all cannon metals. It is used by the authorities of the Royal Gun Factories not for the sake of imparting strength to the gun, but in order to give smoothness aud hardness to the bore. Roughly speaking, wrought iron is reckoned twice as hard as cast iron. Excepting the steel tube the Woolwich 'guns are entirely made of wrought iron. The total length of the monster gun will be twenty-seven feet, the length of bore twenty-four feet ; the calibre, in the first instance fourteen inches, may be increased to sixteen inches if desirable. Neither the weight of projectile nor the quantity of powder to be contained in the cartridge, has been fixed but it is stated that the first will probably range between 10001 b. and 12001 b., while the second may be estimated at one'sixth of the amount. As to the penetrating power of the T gun, experiment can alone decide, but we may reasonably estimate it as capable of penetrating at least nineteen or twenty inches of armour plates and their backing at a distance of, say, five hundred yards. Will such a coluasus as this„ satisfy the requirements of the modern artillerist ?