Pig iron

“ Pig-iron, or, as it is sometimes called, crude iron, being saturated with carbon and oxygen, and containing also a portion of scoria, is too brittle for any other purpose than castings. Many of these, such as stoves, grates, mill-irons, plough-irons, and kitchen utensils, are commonly manufactured at blast furnaces, and in many cases nearly all the iron is used for these purposes. In such cases, the metal is taken in a liquid state, from the hearth, in ladles. ”

“ The best grey pig iron of American manufacture, superior in strength, and equal in all other respects to the Scotch, is now sold in the New York market at $45 per ton. Good grey iron of the usual character, is worth $35 per ton, and there is no question that forge pig could be obtained by the manufacturer of bar iron, for $25. If it were even to cost $30, it is still cheaper than Staffordshire iron, far less fit for the purpose, can be imported. ”

“ Thus part at least of the carbon which a high-carbon steel is to contain may be supplied by the pig iron from which it is made. The length of the process increases with the proportion of pig used. Thus in the Westphalian pig and scrap practice, scrap usually forms 75 or even 80% of the charge, and pig only from 20 to 25%, indeed only enough to supply the carbon inevitably burnt out in melting the charge and heating it up to a proper casting temperature ”

“ Cast iron melts at about 1200° C., and when cold is hard and brittle. It is not malleable or ductile, and cannot be tempered. Of the several elements named, carbon and silicon are of value in steel-making, which is the chief purpose for which cast iron is produced at the present time; but sulphur and phosphorus are generally highly objectionable. In using the term cast iron here, the chemical nomenclature has been retained. The foundryman generally gives the name pig iron to the direct product of the blast-furnace, and the term cast iron to the form which pig iron assumes after remelting. ”

“ In this as much pig iron from the various blast furnaces of a works as is sufficient for a large number of Bessemer charges, say from seven to twelve charges, or, in other words, from 70 to 120 tons of pig iron, is placed in a mixing vessel. Only a portion of pig iron placed in the mixer is taken for further treatment for steel, while new supplies of pig iron are brought from the blast furnace. ”

“ If the pig iron is to follow path 2, the purification which converts it into wrought iron or steel consists chiefly in oxidizing and thereby removing its carbon, phosphorus and other impurities, while it is molten, either by means of the oxygen of atmospheric air blown through it as in the Bessemer process, or by the oxygen of iron ore stirred into it as in the puddling and Bell-Krupp processes, or by both together as in the open hearth process. ”

“ Pig iron, which was the original basis for the manufacture of all iron and steel, is made by the reduction of iron ore in large blast furnaces, which are filled with layers of ore, charcoal or coke, and flux. By the agency of this the iron is melted out and falls to the bottom of the furnaces, is drawn out through openings for that purpose into canals, and finally into molds, where it solidifies into what are termed pigs. Prior to the invention of Sir Henry Bessemer, steel was manufactured from a pig-iron base by a tedious and expensive process of refining in furnaces adapted to that purpose. ”

“ They test iron all the way along, from the ore in the mine to the sticks of pig iron piled up in our yard.”
“Some of it is in cakes,” said Billy.
“Is that so?” asked Uncle John, as he took another sandwich out of his pail. “Now I think of it, they did tell me that cakes are the new style in pig iron.
“Well,” continued Uncle John, “there are men testing and experimenting all the time; and some of them found out that old iron and pig iron together make better new iron than they can make from pig iron alone. Since they found that out, scrap iron has kept on going up in price. ”

“ This great temperature boils the slag or impurities out of the metal, and after it has been drawn off into ladles it becomes "pig."
From the blast furnaces the pig, red-hot in its molds, is conveyed to the open-hearth furnaces, where it is subjected to a still further boiling process at the same temperature as before, and then it is steel. Steel is pig-iron combined with carbon and with the impurities boiled out. ”

“ The pig iron contains from 2 to 5 per cent of carbon, which it obtains from the coal in the blast-furnace, and it is this particular proportion of carbon which gives it its own peculiar properties. To convert it into wrought iron a workman puts a long iron rod into the furnace and stirs the metal about, thereby exposing it to the air and permitting the carbon to be burnt out. As it loses carbon the iron becomes less and less fluid until it reaches a sticky stage. ”

“ Afterward the contents of the tubs were dumped on the bank of the stream near the furnace. The iron and the cinders can easily be separated, as the iron is heavier and goes to the bottom.
The moulds for the iron are made on the floor of the building with sand. The pig-iron is made in small troughs. In order to keep the metal flowing in the large troughs, men have to loosen it constantly with long poles. The iron as it comes from the furnace looks like melted gold. ”

“ The first operation to which the pig iron is subjected, consists in melting it in a fire called a finery, similar in form and character to the bloomeries and refineries of which we have spoken, but in which the fuel is coke. The melted metal is drawn off by tapping the furnace from beneath, and is cast into thin plates. In this way it assumes the characters of the white cast iron, which has been described as formed, when the reduction of the metal is complete, a form that cannot be given when the blast furnace in which it is made is supplied with coke. ”

“ The ”refinery process” of fitting pig iron for the puddling process by removing the silicon without the carbon, is sometimes used because of this difficulty in making a pig iron initially low in both sulphur and silicon. In this process molten pig iron with much silicon but little sulphur has its silicon oxidized to silica and thus slagged off, by means of a blast of air playing on the iron through a blanket of burning coke which covers it. ”

“ Four other large companies produce more than a million tons of pig iron annually, these being the Republic Iron & Steel Co., with an estimated total capacity from its 11 blast furnaces in Ohio and Alabama of 1,430,000 tons of pig iron, and of 2,500,000 tons of ore from its mines in the Lake Superior district and in Alabama ”

“ The pig-iron is thus cast in handy-sized pieces for the purpose of being transported to other iron foundries; while the clumsy sow metal is broken up and passes through another process of melting, or is reserved for foundry uses at the works where it is produced. After inspecting with great pleasure the machinery connected with the foundry, we took our leave and returned to Edinburgh by steamer from Alloa. ”

“ It may therefore be inferred, that, when the English method is applied to pig iron, that would produce a good wrought metal by the process with charcoal, it will produce one that is equally good by means of coal, but that the latter is capable of hiding the apparent defects of even the worst iron. ”

“ These wonderful developments in the production of iron and steel were even more dependent upon the development of machinery for transporting the material and handling it in the factory than was the case with the textiles. Pig iron cannot be made without having in immediate conjunction three natural materials, iron ore, limestone and some material to produce intense heat. The iron is only found in the form of “ore,” being iron mixed with rocks, earth or other matter which must be removed in order to use the iron. ”

“ Mushet represents, “at Tintern the furnace charge for forge pig iron was generally composed of a mixture of seven-eighths of Lancashire iron ore and one-eighth part of a lean calcareous sparry iron ore, from the Forest of Dean, called flux, the average yield of which mixture was fifty per cent. of iron. When in full work, Tintern Abbey charcoal furnace made weekly from twenty-eight to thirty tons of charcoal forge pig iron, and consumed forty dozen sacks of charcoal; so that sixteen sacks of charcoal were consumed in making one ton of pigs.” ”

“ By rapidly stirring molten iron oxide into molten pig iron in a furnace shaped like a saucer, slightly inclined and turning around its axis, at a temperature but little above the melting-point of the metal itself, the phosphorus and silicon are removed rapidly, without removing much of the carbon, and by this means an extremely pure cast iron is made. ”

“ Now one of the very first requirements for a man who is fit to handle pig iron as a regular occupation that he shall be so stupid and so phlegmatic that he more nearly resembles in his mental make-up the ox than any other type. The man who is mentally alert and intelligent is for this very reason entirely unsuited to what would, for him, be the grinding monotony of work of this character. Therefore the workman who is best suited to handling pig iron is unable to understand the real science of doing this class of work. ”

“ Pig iron is thus the intermediate or semi-raw material from which practically all of our various iron and steel products are made and the transition product through which they pass.
Machine Cast Pig Iron
But the romantic period of the hand-fed furnace and the gloriously beautiful pig beds at casting time are rapidly passing; in fact, are almost past. Modern “skip-hoists” carrying automatically dumped buckets or cars charge the furnace more economically than even low-waged laborers can do it. ”

“ In these furnaces which consisted mainly of a shallow hearth filled with glowing charcoal, with tuyères for blast supply, the pigs of iron were heated until molten. At high temperatures the metalloids of pig iron will readily burn in a blast of air. After the air blown over and upon the molten metal has burned out most of the carbon, the main metalloid, the melting point of the purified metal becomes so much higher that the heat of the furnace is not sufficient to keep it molten. It becomes more and more pasty and stiff therefore. ”

“ One has no difficulty in realizing that these flakes, which cut in every direction through the metal, make it structurally weak, especially toward a sudden blow.
No. 1d shows a typical section of wrought iron cut lengthwise of the rolled bar. It will be noted that, as in photomicrograph No. 99b, there are no graphite flakes.
In the process of wrought iron manufacture practically all of the carbon of the original pig iron is burned out, leaving little besides the iron itself and some viscous cinder or slag. ”

“ It should be understood that in casting pig iron one does little more than form it into some desired shape, the nature of the metal undergoing little or no change. In working it, however, into wrought iron, we change its nature. ”

“ As this in turn has been due to the very men who have developed the iron industry, it can hardly be questioned that, on further analysis, this development must in considerable part be referred to racial qualities. The same is true of the German iron development. We may note with interest that the three great iron producers so closely related by blood—Great Britain, the United States and Germany and Luxemburg—made in 1907 81% of the world’s pig iron and 83% of its steel ”

“ Pig iron melts at about 2100° F., steel at 2500° F., and wrought iron at 2800° F., so the temperature of the puddling furnace is kept high enough to melt pig iron but not hot enough to keep wrought iron in a liquid state. ”

“ It will be observed that in producing the pig iron the chemical action is the separation of oxygen from the metal, while conversely an oxidizing action is set up in the finery and subsequent treatment, in order to burn off the foreign ingredients. ”

“ On its way from the blast furnace to the converter or open hearth furnace the pig iron is often passed through a great reservoir called a “mixer,” which acts also as an equalizer, to lessen the variation in composition of the cast iron, and as a purifier, removing part of the sulphur and silicon. ”

“ But the working door of a puddling furnace is the door through which the puddler does his work. It is a porthole opening upon a sea of flame. The heat of these flames would wither a man's body, and so they are enclosed in a shell of steel. Through this working door I put in the charge of “pigs” that were to be boiled. These short pieces of “mill iron” had been smelted from iron ore; they had taken the first step on their journey from wild iron to civilized iron. There isn't much use for pig-iron in this world. You've got to be better iron than that. Pig-iron has no fiber ”

“ Pig iron contains varying quantities of carbon, and to burn away just enough would necessitate a different length of the blowing for each charge of iron, thus introducing complications difficult to handle. ”

“ Water and carbon dioxide are objectionable only as they replace the iron, while the others exert an influence upon the fluxing properties of the ore and the course of smelting operations. Of greater importance, however, are the small quantities of phosphorus, sulphur, and titanium, these impurities being almost wholly obnoxious in their effect. Phosphorus gives a fluid pig iron that can be converted into steel only by employing special methods of treatment. ”

“ The first step in the conversion of the pig iron usually taken has been, and to a certain extent even is still, to remelt the metal in what is termed a finery furnace, a kind of forge in which a charcoal fire is urged by a cold blast, and so regulated that an excess of oxygen is supplied, or rather more than would suffice to convert all the carbon of the fuel into carbonic acid; although this is perhaps not absolutely necessary, as carbonic acid would itself supply oxygen by suffering reduction to carbonic oxide. ”