Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/339

IRON 323 pig, fettling, and slag mechanically; Bessemer proposed to employ an ovoid oscillating chamber fired by flame pass ing in through a hollow trunnion on one side and escap ing similarly on the other side, whilst Oestlund (of Sweden) invented a rotating globular vessel into which the flame was directed from the front. Practically none of these machines ever came much into use. A considerable measure of success, however, has attended the improved form of rotary puddling furnace invented by Banks of Cincinnati, and represented in fig. 37. The fuel is burnt in an ordinary fireplace, a blast B being admitted under the bars and another over them A, level with the firing hole, so that by regulating the two streams of air the atmosphere can be kept reducing or oxidizing at will. A circular chamber or drum C is supported on massive friction rollers and arranged so that its axis is about level with the top of the bridge; at the other end is a movable terminal shaped like the frustum of a cone D, supported by chains or rods from a crane so that it can be swung on one side if required, thus serving as a door : this is connected by a lateral tube with the flue ; a small orifice E closed by a stopper allows the interior of the furnace to be viewed when at work. The movable end being swung on one side and the blast turned off, the pigs are introduced at the end, and the terminal replaced ; on turning on the blast and causing the drum to rotate slowly the pig is melted and incorporated with the fettling, &c., by the rotation; motion is communicated by means of a large external cog wheel F gearing into a pinion. Through a small cinder hole G the fluid slag is drawn off. The main difficulty experienced by previous inventors was to obtain a furnace lining that would last for any length of time, silicious bricks and analogous substances being used by them ; this difficulty was overcome by Danks in the following way. The iron external drum is cased inside with fire brick, or preferably a cement composed of crushed ore and lime ; a fusible iron ore such as hammer slag or mill scale is then introduced and melted down, the drum being slowly rotated; the rotation being stopped, the melted mass collects as a pool at the lowest level ; large irregular lumps of an infusible ore (American iron mountain ore in preference, or Marbella lumps when this is not attainable) are then thrown into the pool ; the cooling effect of these soon sets the liquid mass, which then acts as a cement, binding the lumps to the lining. This operation is repeated several times, so that finally Fio. 37. Danks Rotary Puddling Furnace. the whole inside is lined, the pool being formed in a new place each time. The performance of the Danks puddler was very fully in vestigated a few years ago by a special commission of the Iron and Steel Institute, whose various reports are given in the Journal of the I. and S. Inst. for 1872 (see also Hid., 1871, i. 258); the general results of the experiments being that the production from the rotator is several times that from a hand furnace using the same pig, and that a larger yield of iron is obtained, more being in fact taken out of the furnace than is put in as pig, the surplus arising from the reduction of the fettling; moreover, with suitable fettling the quality of iron produced is always at least equal to that yielded by the hand furnace, and is usually much superior owing to the more complete elimination of phosphorus due to the less " acid nature of the slag ; the consumption of fuel per ton of iron made is much about the same, but usually somewhat less with the rotator than with the hand furnace; thus whilst something like 21 cwts. of pig were required to give a ton of wrought iron by the hand process, slightly less than 18f sufficed with the Danks furnace ; i.e., 100 parts of wrought iron were obtained from 107 5 and from 93 6 parts of pig in the two processes respectively. It is to be noticed, how ever, that further practical experience jjas not altogether confirmed the results of the commission, and that so far as England is con cerned the advantages derived from mechanical puddling by the Danks machine (and also by others subsequently introduced) have not proved as great in actual practice as the success of the machine in America at first seemed to indicate would be the case in other countries. In order to avoid the damage done to the lining by introducing solid pigs, Wood proposes to granulate the iron by means of a machine somewhat analogous to his slag granulator ( 17), whilst fusion of the pigs in a separate furnace or cupola has also been often employed, the molten metal being then tapped into the rotary puddler. A large number of modifications of Dariks s furnace and many other more or less analogous rotating arrangements for puddling have been subsequently constructed by various inventors ; thus Williams (Pittsburg, United States) makes the rotating chamber of the Danks furnace to be separated from the combustion chamber a little way, the flame being led in through a movable flue analo gous to that at the chimney end, so that access to both ends of the rotator is possible. 1 Amongst other rotating puddling furnaces may be noticed the following. Seller s Furnace. In this arrangement the flame does not pass through the chamber to the chimney, but turns back on itself as 1 See Iron, vol. x. p. 456, 1877, from the Metallurgical Review.