The Raw Materials Sloss Furnace - Sloss-Sheffield Steel & Iron Company, Birmingham Alabama
Improved technology was a perquisite to large-scale iron production, and accelerated the exploitation of Alabama's mineral resources. The State's bituminous coal region encompassed an area of 6,400 square miles south of the Tennessee Valley. The Warrior, the region's largest field, was near Birmingham. Since coke constituted one-third of the furnace burden, and one-half the total cost of production, the low transport cost was a significant advantage.
Two general types of iron ore were found in the district and were used in roughly equal proportions. Red iron ore, or hemitite, was mined on Red Mountain, east of Birmingham. The ore formation ran for 160 miles from north-central Alabama through the northeast corner of the State and into Georgia. 75 miles of it was workable. Red ore was classified as either hard or soft. The soft ore was rich in iron content and could be mined closer to the surface. The hard ore, however, consisted of 12% to 20% lime, and was therefore considered "self-fluxing." Since it reduced the amount of limestone or dolomite necessary for the furnace burden, the use of hard ore increased.
The second type of ore found in Northern Alabama was limonite, or brown ore. Limonite was mined in four major fields: near Birmingham; Bessemer; Tuscaloosa; and in the northwest corner of the State near Muscle Shoals. Brown ore possessed certain advantages over red. It was higher in iron content, could be surface mined, and was more easily improved by washing or slow-burning - methods designed to raise iron content. However, brown ore was not found in extensive seams, as red ore was, nor did it contain "self-fluxing" properties. Each of the ores had its particular advantages, and each was generally mixed in the furnace according to tradition and experience. In the early period, particularly, little attention was paid to chemical analysis, and most manuals of the period noted this with dismay.
The limestone or dolomite used as flux was quarried in the valley bordered by Red Mountain on the east and the Warrior coal field on the northwest. Prior to 1890, limestone was used exclusively. Gradually dolomite, a carbonate of lime and magnesia, came into increasing use. It possessed advantages over limestone because of its greater purity and regularity. 88 tones of dolomite could do the work of 102.19 tons of limestone.
Raw materials were the major cost of production. In the mid-1890's they constituted no less than 70.9% of total annual production costs. Their plentiful supply, and the cheapness with which they could be moved to Birmingham furnaces, gave the area a strong initial advantage. But despite the ringing boosterism of the district's early publicists, there were serious problems. Local red and brown ores were high in phosphorus, an impurity which prevented the production of Bessemer steel and weakened castings made from high phosphorus pig iron. For iron to be converted to steel in the Bessemer process the ore could contain no more than .04% phosphorus to 50% iron. Alabama brown ore had a phosphorus content between .10 and .40, and red ore contained .30 to .40.
Alabama was not alone in this problem. British, French, German, and Belgian ores also contained high amounts of phosphorus. Early efforts to eliminate phosphorus involved lining the converter with materials basic in chemical composition, such as lime or magnesia. The basic Bessemer process was eventually developed by Sidney Gilchrist Thomas between 1877 and 1879- Ironically, the process depended on ore of a higher phosphorus content than that of the Birmingham district. Experiments at Ensley attempted to increase the percentage of phosphorus by the addition of a phosphatic flux, but this was not a long-term solution. Efforts to produce a basic pig iron at the Alice experiments, the Birmingham Rolling Mills produced steel in two small open-hearth furnaces.
There were drawbacks to their success. The basic open-hearth process, superior in many ways to the Bessemer, could be economically operated with large amounts of iron and steel scrap. However, the Birmingham area did not have easy access to sufficient amounts for large-scale production. It was not until the development of the duplex process of steel-making> a process employing both Bessemer and open-hearth principles, that the district was finally able to cast off some of its competitive disadvantages. But the intractable nature of the district's ores left a permanent imprint. Steel production was : seriously limited and Birmingham's challenge to the Northern iron and steel centers of Pittsburgh, Eastern Pennsylvania, and the Great Lakes districts was sharply hindered.
Phosphorus content was not as serious a problem for the pig iron industry and saleable pig iron could be produced for foundries, rolling mills, and cast iron pipe works. There were certain disadvantages; phosphorus could not be eliminated in the blast furnace, and high phosphorus pig iron produced brittle castings and was not suitable for some cast iron products. In foundries where it was used, there is evidence it had to be mixed with low phosphorus pig iron to reduce impurities. In general, this was not a critical disadvantage, at least for the first half of the 20th century.
Besides the problem created by a high percentage of phosphorus, Birmingham district ore was relatively low in iron content. As a result, more coke was necessary to reduce the ore. Since the district's coal had a high ash content, it produced excessive slag, which was destructive. to hearth linings causing "frequent" break-outs of iron and slag, which raised production costs, lowered profits, and endangered workers.