Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/344

 328 IRON piston movable ; and fig. 45 indicates a form of Condie s hammer 1 which has the piston fixed and the cylinder movable ; in each case the movable part works vertically and carries a heavy hammer head at the lower end, underneath which is a massive anvil resting on a solid foundation. In the case of single-acting hammers, the steam pres sure is only employed to lift the hammer head, the fall being simply that due to gravity ; much greater force of impact is gained in double-acting hammers, where the steam is admitted on each side of the piston alternately, in the one case lifting the head as with the single-acting hammer, in the other adding to the force of gravi tation by its pressure. By suitably working the valves the blow maybe modified or arrested at any desired stage; a cushion of steam being left underneath the piston by closing the exhaust valve before the stroke is complete, the force of the blow is deadened ; so that a FIG. 44. Cave s modification of Nasmyth s Hammer. variable amount of impact can be imparted, it being possible for an expert hammerman to crack a nut without injuring the kernel, and at the next stroke to exert the full power of the machine. It is this adaptability that renders the steam hammer preferable to the old helve and tilt hammers, the blows from which could not be readily modified during the shingling of a given ball ; whilst the ball is excessively pasty and spongy immediately after taking from the paddling furnace, comparatively light blows suffice to shape it into a bloom, the mass being dexterously turned about on the anvil by means of suitable tongs during the forging ; the force of the blow is then greatly increased so [as to squirt out the fused slag on all sides in a shower at each stroke, and forge the bloom into a compact 1 Taken from Bolley s Handluch, vol. vii., part 2, by Dr C. Stolzel. mass ; in this way the steam hammer acts as both squeezer and helve hammer combined. Hammer blocks or &quot; tups&quot; of from 1 to 3 tons weight usually suffice for ordinary puddling furnace work, and lighter ones still for various kinds of smelting and forging work ; but when large masses have to be forged for special purposes, e.g., thick armour plates, large crankshafts, coils for large guns, $c. , much heavier tups are used, weighing many tons ; thus in Krupp s works a 50-ton hammer is in use with a 10-foot stroke, the anvil weighing upwards of 180 tons, whilst at Creusot an 80-ton hammer with a fall of 5 metres (about 16 feet) is employed. The striking faces of both anvil and tup are usually removable, sliding sideways by dovetails into the body of the tup and the anvil block respectively. For certain classes of work curved faces are employed instead of plain ones ; so that a roughly cylindrical bar can be forged by appropriate manipulation. A duplex horizontal modification of the vertical steam hammer is sometimes used (Ilamsbottom s hammer), consisting of two opposed hammer blocks running on wheels or rollers and meeting one another ; the forging being placed between the two is struck by both simultaneously. In one form of this double horizontal hammer the two tups are actuated by the same piston, each being attached thereto by a link rod so that both necessarily approach and recede at equal ratio; in another form two pistons are employed, the steam valves of each being worked simultaneously by the con trolling lever. For forging small articles such as bolts, screws, &c., special machines are in use, striking a large number of blows per minute, the hammer heads and anvil blocks being moulded or curved into the appropriate forms so as virtually to form dies ; the blows are usually struck by means of cams lifting the hammers and bending strong springs which force the hammer back when the cams release them. See also HAMMER, vol. xi. p. 425. For bending into shape large masses of metal such as thick armour plates that have to be curved to the ship s side, powerful hydraulic presses are employed ; by means of the same appliances large weldings of metal that cannot readily be hammered on account of the shape can be readily made ; thus, for welding the spokes and tyres of iron and steel wheels and the like operations, hydraulic forging, squeezing, welding, and bending machines arc found to be eminently satisfactory. Crank axles thus bent are said to be stronger than ordinary forged ones. Rolling Mills. After the bloom has been forged more or less into shape by the steam hammers, it is passed between