معدن الفولاذ

steel Billets are the feedstock for long products of small cross section. In cases when they are not directly cast by a continuous caster, they are rolled from blooms by billet mills. One method of rolling billets, which are usually 75 to 125 millimetres square, is to use a three-high mill with box passes, as shown in A in the figure. After a rectangular bloom is rolled into a square cross section at the lower rolls, it is lifted to the next pass on the upper rolls and rolled back into a rectangular one; this is turned 90° while being lowered on a roller table for another square rolling in the lower pass, and so on. In another method, alternating horizontal and vertical stands are arranged in tandem, using diamond and square passes without turning or twisting the billet (as shown in B in the figure).