Strip begins with a slab, which is inspected and, if necessary, surface cleaned either manually or by scarfing machines with oxyacetylene torches. The slabs are then pushed, or walked on their broadside, through gas-fired furnaces that have a hearth dimension of about 13 metres by 30 metres. In a pusher-type furnace, the slabs slide on water-cooled skids, and, each time a new slab is charged, a heated slab drops through a discharge door onto a roller table. In walking-beam furnaces, several walking beams lift the workpieces from the hearth, move them forward, and set them back down in a series of rectangular movements. These furnaces have the advantage of producing no cold stripes and skid marks across the slabs. Preheating temperature, as with slabs and plates, is about 1,250° C.
Many highly mechanized strip mills have a capacity of three million to five million tons per year, and as much as 60 percent of the raw steel produced in industrial countries is rolled on these mills. There are, however, strip mills designed for smaller production. For example, a semi-continuous strip mill has only one reversing rougher in front of the finishing train. Another rolling system goes even farther and uses one four-high reversing rougher and one four-high reversing finishing mill.