The weakness of wrought iron, or the enormous penetrating power of the modern projectiles, put it in either way, may be estimated by the following figures:-6-inch Krupp armour is equal to from 15 to 18 inches thickness of wrought iron. This is impenetrable to the shot from a 6-inch gun at moderate ranges. The Vickers' 6-inch gun has a penetration at the muzzle of 23-65 inches for the 45 calibre, and 26-9 inches for the 50 calibre gun. The Vickers' 7.5-inch gun has a penetration of 29.5 inches for the 45 calibre, and 31.8 inches for the 50 calibre gun. The Vickers' 12-inch gun of 45 calibre has a penetration of 51.9 inches at the muzzle. All the above applies to wrought iron. The Armstrong 12-inch guns have a penetration of wrought iron at the muzzle of 50.9 inches in the case of the 50 calibre. Such figures are almost inconceivable to the lay mind.

Perhaps the largest armour plate ever rolled

power. An ingot is squeezed in the 8,000ton press at Messrs Vickers' Works, from its thickness of 4 ft. 3 in., as cast, down to 14 in. thick, in about an hour. After a plate is slabbed, it is reheated and rolled, the sizes often being from about 26 to 28 feet long, by about 10 feet wide. The rolls at this works are made of steel forgings 3 feet in diameter, and 12 feet long, and all the details of the machine are on a similar massive scale. Plates are sometimes rolled down from a thickness of 29 in. to 6 in. at one heat. Plates which have to be bent are placed on an anvil under the press, and receive their curvature from a hollow mould attached to the crosshead.

The plates are planed subsequently, many edges being bevelled, some bolt holes are drilled, the faces hardened, and the edges then corrected by grinding, since their hardness precludes the possibility of bringing cut

ARMOUR PLATE

B

is that which stood in front of the Krupp Hall at the Düsseldorf Exhibition of 1903. It weighed 104 tons, and measured 43 ft. 2 in. in length, by 11 ft. 2 in. in breadth, by 11 in. in

thickness.

The total cost of armour plate per ton is about £80. This seems a big sum, but the plant is costly, the orders fluctuating, and the chances of plant being displaced by better methods are very great.

Armour plates are rolled from cast ingots which often weigh as much as 70 tons or more, to which about 25 per cent. is added for ingates, necessary to ensure soundness. The next operation is reheating in a furnace for 18 to 24 hours preparatory to slabbing under an hydraulic press. The presses used range in power from 3,000 or 4,000 to 14,000 tons

The

ting tools into operation upon them. drilling of such bolt holes as are required in the faces of the plates is done before hardening. As these occur at different angles, portable drills, rope, or electric driven, are used, and the tapping done. These are then plugged with clay to protect them from injury during the subsequent final chilling of the plates, as this hardening produced by super-carbonising extends to a depth of from 1 to 1 inches. Subsequent correction of the edges is done by a grinder having a swivelling head, so avoiding the necessity for adjustment of the plates. Finally the bolt holes for the attachment of the armour plates to the hull are drilled from the back. These are undercut at the bottom for allowing air space, see Fig. 145, and clearance for the tap, and usually go to a

depth equal to the diameter. A special bolthole drilling machine is used for this, having spindles with swivel movements in two directions, at right angles.

Armour-Plate Bolt.-See preceding para

graph.

Armour-Plate Grinding Machine.-See Armour Plate.

Armour-Plate Mill. The machinery and appliances employed here differ chiefly in their greater mass from those in the ordinary plate mill. The two may be combined, but armourplate rolling results in some roughening of the rolls, which make it difficult to turn out smooth plates in the same rolls. Properly, therefore, the two sets should be distinct, even though operated in the same shop.

An armour-plate mill includes, besides the roughing and finishing rolls; engines, and boilers, an ingot furnace, reheating furnaces, annealing furnaces, shears, plate-straightening machine, cooling bed, overhead travellers, roll lathe, &c.

The armour-plate rolling mill seen in Fig. 146, Plate IX., is driven by triple engines of the vertical marine type, of 10,000 HP. The housings of the rollers are of forged steel-in fact, they are themselves large armour plates with the centre cut out to receive the roll chocks. The main rollers are 4 ft. 2 in. diameter, by 13 ft. 6 in. on the face, and are hollow forgings made of Whitworth fluid pressed nickel steel, each roller weighing 65 tons.

One of the largest mills in existence is that at Creusot. The following leading particulars will afford some idea of the massive scale of the plant and machinery, by means of which armour plates of from 60 to 65 tons are produced, and ship and boiler plates up to 65 ft. 7 in. long, or 13 ft. 7 in. wide, or circular plates 13 ft. 9 in. diameter.

The roughing and finishing rolls each measure 3 ft. 11 in. diameter, by 13 ft. 11 in. long, with necks 2 ft. 5 in. diameter, and 3 ft. 11 in. long. Each roll weighs 42 tons 12 cwt. They are carried in standards of 54 tons weight, operated by massive screws 133 in. diameter outside the threads, and of 1 in. pitch; to turn which a reversing electric motor, working normally at from 10 to 12 HP., is used.

A

twin cylinder reversing steam engine drives the rolls, having cylinders 5 ft. 7 in. diameter, with a 4 ft. 11 in. stroke, the reversing of which is done by an auxiliary steam engine.

The main reversing gears on the engine have the usual double helical teeth. They measure over 3 ft. on the face, and are of nickel steel. The wheel weighs 47 tons, and the rim is cast distinct from the centre.

The feed rollers have their mechanism below the floor level, the top edges standing only 23 above the level. These measure 28 diameter, and make on an average 12 revolutions per minute, and require an engine working at 35 HP. to drive them. Underground galleries receive the scale, and through which it is removed.

Five reheating furnaces are erected, one of which is for the reception of the ingots. These are coal-fired, and have air blast. The areas of the hearths of these vary from 144 sq. ft. to 205 sq. ft. The waste gases from them are utilised to heat water-tube boilers, most of which are fitted with economisers. Cranes of from 8 to 85 tons capacity serve the shop areas. A large cooling area is left, where plates are inspected after they have cooled down. They then pass to the shearing machines where they are cross-cut, and shorn at edges, and test pieces taken. These have their feed rollers worked electrically.

Annealing furnaces, and a plate-straightening machine are used for boiler and ship plates.

The roll lathe has its centres 37 high. It has forty-eight different speeds, from 0.26 to 26 revolutions per minute, and is designed for using tools of high-speed steel.

Armour-Plate Press.-There is no special form of press used for this work, the ordinary vertical press of several thousand tons power being employed. It is used for slabbing, bending plates for turrets, and curves generally. An illustration is seen in Fig. 147, Plate X. Forging Press, for general construction.

See

Armour-Plate Shop. The shop in which the planing, drilling, grinding, &c., of these plates is done. An illustration is given in Fig. 148, Plate XI., and the nature of the operations is described briefly under Armour Plate.

PLATE XI.

Fig. 148.-ARMOUR-PLATE MACHINE SHOP. (Messrs Vickers, Sons, & Maxim, Ltd.)

To face page 196.