Page:Advanced Automation for Space Missions.djvu/179



Input slabs can be hot-rolled or cold-rolled. However, if a cold aluminum alloy slab is rolled to more than 120% of its input length, cracks appear in the material. To avoid this problem, slabs are annealed between passes or are rolled hot throughout the process. (The final rolling pass should be done cold to improve the structural properties of the output.) Miller and Smith (1979) chose to hot-roll the input slabs, which, therefore, either travel directly from the continuous caster to the rolling mill without cooling or are taken from intermediate storage and preheated before insertion into the mill. Aluminum alloy slabs elongate roughly by a factor of 11 as they are squeezed from a thickness of 2 cm down to 1.77 mm. Rolling also widens the slabs from 70 to 73.5 cm, the width required for structural member ribbon. Input slab length is arbitrary and often is determined merely by handling convenience, though slabs usually are at least as long as they are wide. An 80-cm-long slab produces about 8.8 m of ribbon.