445
OF EHGINEERINQ FORMULAE.
Stehl ai^uTACXURE—continued.
obtained In one pit in the 24 hours, but the number and
capacity of the converters in a pit is not stated.
The English practice is to blow until the carbon is reduced
to about 0-l per cent., and then to add from 3 to 5 per cent,
of molten spiegeleisen, -which contains 3 or 4 per cent, of
carbon and 8 to 20 of manganese.
Quick “ blows ” and consequently great heat is favourable
to sound ingots.
The loss of weight in the Bessemer process is from 9 per
cent, when the iron is taken direct and 15 when it is remelted
in a cupola.
The American practice is to divide the converter into four
parts, keeping spare top, bottom and nose sections ready in
reserve and relining the trunnion section in place. In this
manner tbe possible make of a pair of 5-ton converters has
been increased to between 45 and 50 blows in the 24 hours.
Open Hearth System.
SIEMENS’ OFEN HEARTH MELTING FUKNACE.
la the Siemens-Martin open hearth process, steel is pro-
duced by the dissolution of pig metal and iron ores (either
raw or more or less reduced) in a bath of pig metal; the
heat of the furnaces being such that the fluid bath of metal
may be maintained in that condition for any reasonable
length of time, during which samples may be taken and
additions, either of pig metal or wrought scrap or spongy
metal or ore, may be made to adjust it to the desired quality.
A sufficient quantity of pig is first melted down, then iron