Converter
The Encyclopedia of Founding (1892)
A pear-shaped vessel resting on trunnions, and provided with hydraulic apparatus for the purpose of rotating the same through an angle of 180 deg., or thereabouts. It consists of an outer casing of wrought-iron plates, held together by rivets, and is suspended by means of a strong steel band carrying two trunnions which is secured on the body of the converter at its widest part. The trunnions run in bearings connected with uprights, one of them being solid, and the other hollow; the latter serves as a passage for the blast, and carries a gear-wheel. It is important that the lining of a converter be material of the most refractory character. Sometimes fire-brick is used, but chiefly gannister, which is found to be better for this purpose than any other substance. The bottom of the converter is flat and contains a tuyere-box, or cylindrical chamber connected by a curved pipe with the hollow trunnion. The tuyeres are round, tapered fire-bricks, each containing seven holes 1/2 inch in diameter. From 5 to 7 of these tuyeres are used, their lower ends protruding through a guard-plate in the top of the air-chamber; the vertical position being maintained by stops which bear against horizontal arms that can be moved aside when any of the bricks are to be replaced, thus saving the necessity of removing the bottom of the converter. To turn the converter, a direct acting water-pressure engine is provided, the pistonrod of which carries a rack which gears into the wheel on the trunnion. See BESSEMER STEEL; GANNISTER.
What Has Changed in the Last Century
The vessel described in 1892 — pear-shaped, ganister-lined, air blown up through seven fire-brick tuyeres in a flat bottom — is a Bessemer converter, and that machine has effectively vanished from steelmaking. The decisive change came in 1952, when works at Linz and Donawitz in Austria began blowing pure oxygen down onto the bath through a water-cooled lance instead of air through the bottom; the basic oxygen converter cut heat times to well under an hour and avoided the nitrogen that air blowing left in the steel. Bessemer shops closed through the 1950s and 60s, and today world steel comes almost entirely from basic oxygen converters and electric arc furnaces melting scrap. The 1892 description remains accurate as engineering history, and the trunnion-mounted tilting vessel it describes is still recognisable in the shape of a modern oxygen converter.
Written for this edition, 2026.