Engineering Wonders of the World
Volume III

270 ENGINEERING WONDERS OF THE WORLD. the middle and top rolls. For rolling plates is employed a “ two-high ” reversing rolling- mill—that is, the mill has two rolls, one fixed roll at the bottom and one adjustable roll at the top, as in the ordinary domestic mangle. These reversing mills are usually steam- the longest plates rolled by the mill. The controllers for operating the tables are placed upon an elevated platform in front of the mill, so that the operator can see all that is going on, and cause the plate to travel back- wards and forwards to the rolls as required. AN “ ALLIGATOR ” GRIP SLAB CHARGER INSERTING A 12-TON PLATE INTO A REHEATING FURNACE. driven, although electric driving is now suc- cessfully employed. The rolls are made of specially hardened steel, and for a mill rolling ship or boiler plates up to 7 feet wide and 40 feet long, are about 16 inches in diameter. They are mounted in massive cast-iron guide- frames or housings with a screw-down gearing for adjusting the rollers, which in large mills is operated by electric motors. At both back and front of the mill is a table of rollers, driven generally by an electric motor, and extending over a distance sufficient to take The rolls themselves are driven by a powerful steam-engine through a double helical spur- gear reduction, the type of gearing rendered necessary by the large power required and the heavy shocks to be borne at the commence- ment of each pass. Thirty to forty ingots an hour are dealt with quite easily. For drawing the slabs out of the reheating furnace and bringing the billets or slabs to the plate-mill a machine called a slab charger is used. It consists of a pair of girders mounted on carriages running upon overhead