STEEL.— Open-Hearth Process.

875

melting furnace are described under the articleFuel . In the drawings of the Pernot furnace (Figs.20, 21) a, b is the furnace bed, which is fixed on aninclined pivot, and revolves on rollers by means ofgearing—it can be drawn out from under the rooffor repairs; c, d are the gas and air ports; e, e isthe bath of metal. At St. diamond there are nowone 10-ton, one 15-ton, one 20-ton Pernot furnacesat work, and three more 20-ton furnaces are beingerected.

The gas is made in producers, which are thoroughlydescribed in the article on Fuel . It consists mainlyof carbonic oxide and nitrogen, as will be seen from

the following analyses.

No. 1.

fto. 2.

Carbonic acid,.

... 4-3

.... 5-2

Carbonic oxide,.

. .. 25-6

.... 24-4

Hydrocarbons,.

... 2-8

.... traces.

Marsh gas,.

1-6

.... 2-4

Hydrogen,.

8-6

Nitrogen,.

... 65-7

.... 59-4

100-0

1000

Sample No. 1 was made with the ordinary pro-ducer,, with natural draught; No. 2, with a closedash-pit and artificial blast induced by a jet of steam.Hence the rather large quantity of hydrogen. Thisgas is conveyed in wrought-iron tubes or in under-ground culverts to the furnace, the producers usuallybeing at some distance off. In the modificationsof gas furnaces known as the Bischeroux andPonsard, the producers are placed close to thefurnace. This saves coal, but is not so convenientas Siemens’ plans.

The melting furnace is a rectangular structure,cased with wrought or cast plates, and firmly bracedtogether by a system of girders, which require to bevery carefully tied above and below the furnace; oldbridge rails are often used for the girders, but atCreuzot regular bridge girders are employed, asthey have to resist a great strain to prevent theexpansion of the roof from pushing out the sides ofthe furnace. The side walls of the furnace are builtof the best firebricks; those made at Glenboig inScotland being particularly suited to this portion ofthe work and for the regenerators, on account oftheir being hard, strong, and withstanding greatheat without changing form. The roof of the fur-nace is built with silica or ganister bricks, as noothers will stand the intense heat of this part of thestructure. The bed of the furnace is supported, soas to leave a clear space underneath it and aroundthe gas ports, in order that these parts may be cooleddown by a free circulation of air. The hearth isthickly lined with pxre quartzose sand, which is soonconsolidated by the intense heat. It is shaped intoa shallow dish-like form to hold the metal, which istapped out through a hole in the middle of the sideplates. The tap-hole is stopped with a little cokedust, and then sand and coke dust outside. Thisis easily removed when the metal is to be tapped;while if sand alone be used, it becomes hardened tosuch an extent, that there is often great difficultyin opening the tap-hole. Below the furnace proper,

and sunk in the ground, are four regenerators.These consist of brick chambers, which are looselyfilled with firebricks, and communicate by passagesabove with the furnace, and below with the gas andchimney flues, by means of reversing valves, so thattwo of the chambers can be alternately connected,cither with the gas flue or chimney flue, and twowith the external atmosphere and with the chimneyflue. The passages above open into the furnace by“gas” and “air ports,” which are narrow passagesabout 5 inches wide. The air ports are made toopen into the furnace above the gas ports, for thepurpose of getting a thorough mixture of gas andair. The roof of the furnace dips from each endtowards the centre, at an angle of about 30° withthe horizontal, so as to deflect the flame on to themetal. After combustion in the furnace, the pro-ducts are drawn down by the chimney through apair of the regenerators, and in passing over thelarge surface of brickwork the greater part of theheat is abstracted, to be restored to the incominggas and air, which are made to pass through thesechambers, and out by the remaining pair when thecurrent is reversed by altering the valves. This isdone about every half hour.

The subsidiary apparatus for steel-making by thisprocess is in many respects similar to that describedfor the Bessemer process; but in most of the steelworks arranged by Siemens the furnaces are placedin a line, and the casting pit runs in front of them,sometimes, as at Landore and Panteg, between twosets, and is served by an overhead travelling cranefor the removal of moulds, ingots, &c. At Dowlais,and at Messrs. Spencer’s on the Tyne, hydrauliccasting and ingot cranes are used. At Terre Noirea circular casting-table, moved from below by rackand pinion, brings each mould alternately oppositethe tap hole, thus avoiding the use of an intermediateladle. At Creuzot and at Bolton somewhat similarplans have been employed; but on the whole thehydraulic arrangements of Bessemer, though mostcostly, are best suited for this work.

Methods of Conducting the Process .—There are twodistinct plans of working—the first may be calledthe “scrap” process, the second the “ore” process.In either case a bath of pig iron is the startingpoint. In the scrap process this may be very small,say from 6 to 10 cwts. for a 5-ton charge. The pigiron is usually melted in the furnace itself, as is alsothe other material employed; but at Terre Noire,and most continental works, a small “dandy” fur-nace is placed by the side of the larger furnace forthe preliminary heating of the material. This is avery useful adjunct, and facilitates the processmaterially, while at the same time it saves wear andtear of the large furnace. Having got the bath ofpig iron, small charges of scrap of all kinds are placedon the sloping bank, and as they get heated arepushed down into the metal bath; fresh chargesbeing added as fast as dissolved. In this way, afterthe lapse of eight to ten hours, a bath of 5 to 10tons of metal is obtained, which is practically pureiron, if iron free from sulphur and phosphorus has