By Mr. A. TRAPPEN.
The success of the Bessemer process when carried out on the small scale
at Avesta in Sweden, as described by Professor Ehrenwerth, and subsequent
experiments of a similar kind made at Pravali, in Carinthia, and
elsewhere, have led the author, who is specially occupied in the building
of Bessemer works, to design a plant suitable for operation upon small
charges. This consists essentially of a converter about 1 meter outside
diameter, and 1.5 meters high, connected by a single trunnion to a
horizontal steel shaft carried by the arm of a hydraulic crane which is
very similar in character to the ladle crane of a large sized converter.
The sweep of the crane is such as to allow the converter to be brought
close up to the tap hole of the blast furnace or cupola, so that the use
of open gutters for the fluid metal may be avoided as much as possible.
The converter is turned on its axis by a screw and worm wheel, which is
manipulated by a workman standing on a platform at the opposite arm of
the crane. The blast is brought in from above by a pipe down the central
pillar of the crane, which is connected with the blast-main by a flexible
tube and packed joint. The outer trunnion bearing is open, so that by
slightly raising and lowering the ram of the crane, the converter may be
left suspended to a weighing machine in front of the furnace, if it is
required to determine the weight of the charge. When the converter is
filled, it is borne by the crane into a convenient position for blowing,
and if the basic method is followed for removing the slag, the converted
metal is cast into ingot moulds, which are manipulated by a small ingot
crane of the ordinary pattern. In the case of small existing
blast-furnaces, which usually have their tap holes near to the ground, it
may be necessary to have a shallow ingot pit (20 to 24 inches deep); but
with cupolas this will not generally be necessary, and the whole of the
operations may be carried on at the ground level. Each crane is intended
to be supplied with two or three converters, so that operations may be
carried on continuously. The weight of charge proposed is 15 cwt., which
should under ordinary conditions give 12 cwt. of ingots. Taking the time
of a single converting operation at half an hour it will be easy to
obtain fifty blows per day, or a production of 30 tons. This may be
easily increased by placing a second converting crane on the other side
of the furnace, for which the same blowing engine will be sufficient, as
the actual blowing time will not exceed twelve minutes. The labor
required for each converter will be about six men per shift.
The blast required has been experimentally determined at 40-50 cubic
meters per minute at 15 lb. pressure. This will be supplied by a single
cylinder engine of 900 millimeters blast, and 786 millimeters steam
piston, diameter 786 millimeters, stroke making fifty revolutions per
minute, which is also to work a Root blower and the accumulator pumps.
Having regard to these very different demands upon the power of the
engine, it will be provided with expansion gear, allowing a considerable
variation in the cut-off. A single boiler of 70 to 75 square meters
heating surface will be sufficient. The accumulator is intended to work
at 300 lb. pressure.
The cost of the plant, including one of each of the following items,
converter, converter truck, blowing engine, accumulator, ingot crane,
centesimal weighing machine, and accumulator pump, is estimated at £2,050
to £2,100; and that of the steam boiler, £325. The buildings may be of
the simplest and cheapest possible character. As the productive power of
such a plant contrasts very favorably with its cost, the author considers
that it may be fairly expected to meet the competition of large works,
especially in the manufacture of a high-class product.--_Stahl und
Eisen_, vol. iv., page 524; through _Proc. Inst. Civ. Eng_.
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