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the manufacture of alloys.
301
with open regenerators. The fuel used was producer gas made from
wood, and condensers were employed to rid the gas of its water.
It was not till the eighties that the process began to win general
confidence. Since that time, as will be seen from Table 60, the production
of open-hearth steel has developed steadily and at a rapid rate. The greater
cheapness of the method, the greater choice with regard to raw materials,
the greater certainty with which the carbon content of the final product
can be determined and the superior quality of the product for certain
purposes explain the rapid encroachment of the open-hearth steel in quarters,
where Lancashire iron and Bessemer steel hitherto practically held the
field.
The output of open-hearth steel exceeds the output of Bessemer steel
from the jrear 1894 and the output of wroiight iron from 1900.
Concurrently with this rapid development, the furnaces were built of
larger size — to begin with for from 5 to 10 tons, now for 12, 15,
to 20 tons and upwards, — ore began to be used for the refining, the
regenerators were made larger and closed, seperate channels and ports for
gas and air were arranged and producer gas was used as fuel.
A preceding map shows the situation of the Siemens-Martin
furnaces actually running in 1912.
Open Hearth Furnace.
The Acid Open-licarth Process. The acid process, like the acid Bessemer
process, demands a raw material practically free from phosphorus and sulphur,
for neither of these bodies are removed in the acid furnace. In Sweden both
pig iron and scrap with extremely low phosphorus and sulphur contents are
used for the acid process.
The ratios between the pig iron and the scrap vary considerably, according
to the supply of raw material and the purpose for which the product is intended.
The charge may be, for example, 73 % of pig iron + 7 % of scrap + 20 % of
ore, or, at the opposite extreme, 26 % of pig iron + 74 % of scrap.
Pig iron for the acid open-hearth process contains as a rule from 0-50 to
0’76 % of silicon. The finery ore should contain as much iron as possible. Ore
of this kind often contains from 65 to 70 % of iron.
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