STEEL.— Bessemer Plant. Cdpola.
863
99-99
The Essential Parts of a Bessemer Plant for con-ducting the process according to present inodes ofworkng are:—
1. The Cupola. —Fig. 15 represents an ordinaryEnglish cupola, -with a double row of twyers.Blast main, d d ; charging door, e ; twyer pipes, f f ;tapping hole, li- cleaning door, K; slag tapping
Fig 15.
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hole, l. It will be seen to consist of a wrought-l iron casing, lined with firebrick. The bosh or con-
stricted part around the twyers is further protectedwith a lining of ganister, rammed in a semi-plasticstate around a core, in order to withstand the ex-cessive heat at this point, which is the zone offusion ; there is a charging-hole at the top, and theportion of the cupola above this point serves toconduct away the waste products of combustion.There is a double row of twyers in order to increasethe melting zone. The twyers are connected withthe blast main, from which they can be shut off bya slide valve. It is advisable to have a hole throughthe twyer, by which a bar can be introduced to cleanaway any slag that may accumulate at the nose of thetwyer. About 12 inches below the twyers there isa tap-hole for the slag, which is allowed to run offcontinuously as soon as it rises to this point; andthe lower portion of the cupola is enlarged to forma well, which is made sufficiently large to hold onecharge of metal, generally about 8 tons, Thecharging of the cupola is now frequently carried oncontinuously, and the metal is tapped off as soon asit rises to the slag-hole. Formerly the full chargeof metal, with its equivalent of coke, was put intothe cupola, and melted down before another chargewas introduced, in order to keep the charges separate,and insure the proper quantity of iron. In practice
this can be kept sufficiently accurate by measuringthe quantity as explained above.
There is an aperture left in the casing of the well,about 2 feet square, through which the residue canbe raked out at the week’s end, or when the cupolahas to be put out for relining. This is made upwith bricks and clay, which are retained by an irondoor, after the fire has been lighted in the cupola.In starting a cupola a good fire of coke is first formedin the well, and when it has thoroughly burnt up,and is red-hot up to a little above the twyers, abed of about 1 cwt. of coke is put in at the charging-hole, and then a layer of broken pig iron, then morecoke with a little limestone as a flux, then more pig,and so on till the cupola is full. The blast is thenput on, and as the charge sinks, more coke and ironare thrown in. The quantity of coke used varies verymuch. In the best practice, about 1^ cwt., or ratherless, suffices to melt a ton of iron; usually, however,the quantity employed is 3 cwts. or even more. Thiswaste of coke is generally due to having too shorta column of material from the charging-hole to thetwyers, so that the whole of the heat of the ascend-ing gases is not absorbed by the descending material.A good deal of useful combustible gas, carbonicoxide, escapes unburnt from the top of the charge,and several plans have been attempted for burningthis among the charge at the top of the cupola.This endangers the regular working of the cupola,by tending to produce what are called scaffolds.These are generally produced by the half-meltedpigs soldering themselves together across the cupola,and leaving little or no passage for the ascendinggases.
Alexander Wilson has devised a better plan ofutilizing the gases, by burning them on the top partof the cupola, and using the waste heat to raise thetemperature of the blast, by causing it to traversea spiral cast-iron pipe placed in the top of thecupola above the charging-door. Cooper heats theblast for the cupola by passing it through a cast-iron hot-blast stove, placed in the chimney abovethe Bessemer convertor. In America , instead ofraking the remaining coke and slag out of a door inthe side of the cupola, a movable bottom is employed,which is dropped down after a few casts (eight orten) have been run. In English practice it is pos-sible to get G800 tons melted in a cupola, beforeputting it out for repairs.
The spiegeleisen is melted in a smaller cupola,having generally only two or three twyers, butsimilar in other respects to the pig-iron cupola.Various plans are adopted for raising the blast forcupolas. Root’s blowers have found great favourin England, and Mackenzie’s in America ; but pro-bably the cheapest and best are either high speedfans, or simple direct-acting blowing engines withlarge blast-cylinders, where first outlay is not mate-rial. When the charge of iron has been melted, itis in England run down channels in sand at onceinto the vessels. In America the metal is run intoan intermediate ladle holding about 12 tons. Thisis placed on a weighing machine, and thus at any