Slabbing Mill

a high-output rolling mill designed for the pressure shaping of large ingots weighing up to 45 tons into large, flat billets, called slabs. Slabs are a semifinished product used in the manufacture of wide sheets. Unlike blooming mills or blooming-slabbing mills, slabbing mills are highly specialized rolling mills with two pairs of rolls—horizontal and vertical. They are installed in metallurgical plants and in rolling shops equipped with high-output strip mills.

General-purpose, two-stand slabbing mills are the most common type. The first stand has two horizontal rolls, each measuring 1,100-1,370 mm in diameter. The second stand has two vertical rolls, each measuring 900–1,220 mm in diameter, and is arranged alongside the first stand in such a way that the slab is rolled simultaneously in both stands, as in a continuous mill. The annual output of such a slabbing mill is 3-7 million tons. The rolls are driven by reversing DC motors. The power rating of the individual drive for each horizontal roll is up to 7 megawatts, and the total power rating of the drive for both vertical rolls is 4 megawatts. The mechanical equipment of a slabbing mill may weigh as much as 9,000 tons.

Modern general-purpose slabbing mills use integrally cast frames for the horizontal stand; the frames are fastened to the foundation plates by means of anchoring collars. The barrel length of the horizontal rolls corresponds to the maximum width of the slabs, which makes it possible to roll the slabs at higher pressures. The screw-down mechanisms incorporate helical and worm gears driven by high-speed motors; these components provide a lift of the upper roll up to 2,000 mm or more and speeds up to 250 mm/sec. The vertical stand consists of three parts, which are also connected by anchoring collars. Rotation is imparted to each vertical roll by means of separate reduction gears and vertical universal spindles.

A slabbing mill proper consists of a work stand, motors, and mechanisms for driving and changing the rolls. Auxiliary equipment includes ingot buggies, roller conveyors, a scarfing machine for cleaning the slabs, shears for cutting the slabs, coolers, stackers, and other mechanisms.

The production process in a slabbing-mill shop consists of several operations. Hot ingots from the smelting shop are delivered to the soaking pits, where they are reheated in a vertical position to 1100°–1280°C, dependent on the type of steel. The ingots are then transported by buggies to the receiving roller conveyor, weighed, and delivered to the rolls. General-purpose stands roll the slabs in 19 to 31 passes. The horizontal rolls provide a compression of 50–120 mm per pass, and excess spread is removed by the vertical rolls. The surface of the metal is scarfed as the slabs are being transported, and the slabs are cut to the required lengths and stamped with markings. The slabs are then transported on a roller conveyor to an intermediate storage location for cooling and inspection or to a wide-strip, hot-rolling mill installed next to the slabbing mill.

Slabbing mills appeared in the USA at the turn of the 20th century as a result of the design development and specialization of cogging and general-purpose mills. The first slabbing mill in the USSR—model 1100 (the numerals indicate the diameter of the horizontal rolls in mm)—was installed in the Zaporozhstal’ Plant in 1937. It was subsequently rebuilt, and its productivity was increased by 30 percent. Modern slabbing mills currently produced in the USSR (model 1150) and designed at the New Kramatorsk Machine-building Plant were introduced in the 1960’s. They are capable of outputs up to 5 million tons per year and have been installed in the Magnitogorsk, Zhdanov, and Karaganda metallurgical works. During the 1960’s and 1970’s, large slabbing mills with horizontal rolls 1,200-1,370 mm in diameter were installed in metallurgical works in the USA, the Federal Republic of Germany, Japan, and other countries. However, because of the intensive development of continuous steel casting, which reduces the production cost of slabs by 8-10 percent, the number of new slabbing mills being put into operation has decreased significantly.