977 



IRON MANUFACTURE AND TRADE. 



IRON MANUFACTURE AND TRADE. 



978 



now unquestionably observed in the manufacture is due to this cause, 

 the rest being traceable to other improvements. He shows this by 

 adducing the important fact that furnaces, in which the hot-blast has 

 never been employed, continue to increase their produce. This has 

 been especially observable at the great Dowlais Works, near Merthyr 

 Tydvil, where the economising of fuel has been very great without any 

 change in the temperature of the blast. Mr. Truran attributes these 

 improvements partly to an increased use of carbonaceous ironstone, 

 and partly to an enlargement in the throat of the furnace, which 

 facilitates the use of raw coal as a substitute for coke. At the Ply- 

 mouth and Duffryn Works, one in Glamorganshire and the other in 

 Monmouthshire, the yield has gradually increased to 130 tons of 

 pig-iron per week, from an average of much less than half that 

 quantity, without any departure from the old cold-blast. Some of 

 the steam-engines now employed to send the blast into the furnaces 

 are quite stupendous. The blowing cylinder of the engine at the 

 Dowlais Works is 144 inches in diameter, and makes 19 strokes per 

 minute, with a length of stroke of 12 feet : it sends in 50,000 cubic 

 feet of air per minute, at a pressure of 3 Ib. on the square inch ; and 

 its boiler-furnaces consume a ton of coal per hour to raise the neces- 

 sary steam. 



The blast, whether hot or cold, having done its work, the metal 

 contained in the ore has become liquefied, and is then ready for 

 removal. The iron is run from the furnace every twelve hours, by 

 tapping it in the front, on a level with the bottom of the hearth, at 

 the side on which, as will be seen from the diagram, there is no tuyere 

 introduced. When the furnace is tapped, the metal is allowed to run 

 into channels formed in the sand of the smelting-house floor. The 

 names of twc-metal and pig-metal, which were originally given by the 

 workmen, signify in one case the blocks of iron which are formed in 

 the large main channels, and in the other case the smaller blocks which 

 are formed in smaller side channels communicating with the larger 

 ones ; these names were adopted from the fancied resemblance of the 

 cast metal to a sow and her litter of pigs. This is iron in its crudest 

 state. The weight of materials lost in its production is somewhat 

 greater than that of the fuel used ; taking into account the refuse 

 cinder and ashes with the metal, the whole does not weigh quite so 

 much as the ore and lime that have been put into the furnace. Large 

 heaps of cinder are gradually accumulating in the neighbourhood of 

 iron-works, and give a dreary aspect to the country. 



The quality of pig-iron varies according to the purposes for which it 

 is intended, and depends not only upon the quality of the ore, but also 

 upon that of the fuel. The principal division is into foundry-iron and 

 forge-iron , the former being used for castings, the latter for conversion 

 into malleable iron. Foundry-iron is further divided into three 

 qualities, distinguished by the numbers 1, 2, and 3. No. 1 contains a 

 Urge proportion of carbon, which it has acquired from the coke used 

 in smelting, and the quality of which has been chosen with a view to 

 the production of this kind of iron ; it is soft and very fluid when 

 melted, so that it will run into the finest and most delicate forms the 

 moulder can produce. No. 2 contains a smaller proportion of carbon ; 

 it is harder than No. 1, closer grained, and of more regular fracture ; it 

 is more refractory in the furnace, and does not run so freely when 

 melted as No. 1 ; but as it is harder and stronger, it is preferred for 

 purposes where strength and durability are required in preference to 

 delicacy of form : these two kinds are unfit for conversion into bar- 



Fig. 4. Canting Iron Pipes. 



iron. No. 3 varied in the same direction as No. 2, but in a greater 

 degree, from the qualities of No. 1 ; it is used for many kinds of heavy 



ARTS AND SCI. DIV. VOL. IV. 



work, where it has to bear great strains and is exposed to constant wear. 

 Forge-iron is divided also into three qualities, and is distinguished as 

 bright-iron, mottled-iron, and white-iron, which names are indicative 

 of the appearance each quality presents to the eye. They all of 

 them contain some carbon, but less than foundry-iron, and in propor- 

 tions diminishing in the order in which they are here mentioned, white- 

 iron having the smallest proportion of any, and being exceedingly hard ; 

 its fluidity too is so small that it runs with difficulty into the channels 

 provided to receive it at the first smelting, and it is altogether 

 incapable of being afterwards used for foundry purposes. 



Cast Iron. Of casting or founding we ueed not speak here ; it has 

 been sufficiently noticed under FOUNDING, and under other headings 

 cited in that article. One of the modes of casting iron-pipes is shown 

 in fig. 4. 



Malleable-iron. This, which is also called forge- or bar-iron, is pig- 

 iron freed from carbon and oxygen. The first operation for producing 

 this change is called refining. It is performed in small low furnaces 

 about three feet square at the base, having the bottom or hearth of 

 fire-bricks, and the sides of cast-iron, made hollow to allow a stream 

 of water to pass constantly through, which prevents their being quickly 

 burnt away ; near the top are holes for the insertion of blast-pipes. 

 These refineries have iron doors at the back, but are open in front ; 

 the whole is surmounted by a chimney of brick- work carried to the 

 height of 20 feet from the ground. At the level of the hearth in front is 

 a hole similar to that in the smelting-furnace for running out the melted 

 metal. This communicates with a flat mould of cast-iron 20 feet long 

 and 2 feet wide, placed over a cistern of water with which its under 

 surface is in contact, and which serves to cool the metal rapidly as it 

 nins into the mould. The iron is kept in a state of fusion in the 

 refinery for some time, exposed to an intense heat produced by a 

 strong blast. From the sudden cooling to which it is exposed, the 

 plate when run into the mould is very brittle : when broken the 

 fracture presents a bright silvery appearance. From 22 to 23 cwt. of 

 pig-iron is required to produce one ton of refined iron, and from 

 10 to 12 cwt. of coke is used for the purpose. 



The iron being refined, the next process employed for making bars 

 is called puddling, and is performed in a reverberatory furnace, thence 

 called a ptiddliny-furnace. The structure of this furnace will be ex- 

 plained by fig. 5. In this diagram a IB the grate, which is supplied 



Fig. 5. Section of Fuddling Furnace. 



with coal through a door in the side. The refined metal broken in 

 small fragments is placed in the body of the furnace 5, over which the 

 flame is made to play in its passage to the chimney, c. The degree of 

 the draft is regulated by a damper on the top of the chimney, which 

 is about 30 feet high. Such is the intenseness of the heat in these 

 furnaces, that when the damper is raised the flame is sometimes 

 carried to the top of the chimney. Compare this cut with one in 

 the article FURNACE, col. 240, for a few additional details. The quantity 

 of refined metal put into this puddling-furnace at each charge is from 

 34 to 4 cwt. In about half an hour from the charging of the furnace 

 the metal begins to melt. The puddler then observes, through a small 

 hole provided for that purpose and for the introduction of his tools, the 

 progress of the work. The business of the puddler is so to dispose of 

 the pieces of metal, moving them by means of his tools, as to ensure an 

 equable application of heat to the mass. When the whole quantity is 

 fully melted, the puddler stirs the metal about briskly, changing his 

 tools continually that they may not be melted. By means of this 

 agitation the metal gives off an elastic fluid, and after a time becomes 

 thick, and grows increasingly so, until it loses all fluidity and forms 

 into lumps. The contents of the furnace are then divided into five or 

 six portions by the puddler, and each is made up by means of his tools 

 into a roundish form. These balls are technically called blooms. Being 

 taken from the puddling-furnace they are subjected each to several 

 blows from a heavy hammer (called shingling), which makes them more 

 compact and gives them a shape more convenient for going through the 

 rollers. The form and construction of these rollers are shown in the 

 following diagram. The bloom is passed in succession through the 

 holes in a, beginning with the largest and proceeding to the smallest ; 

 or through the grooves in the second roller 6 / and is thus reduced 

 to the requisite width and thickness. By these rollings the iron is 

 converted from a fusible, hard, and brittle substance, to a tough 

 and elastic bar which is hardly fusible, and which from its property 

 of yielding and altering its form under the hammer has acquired the 

 name of malleable iron. The quantity of refined metal required to 



