Production of aluminum sheet entail as many as five steps, the first of which is preparation for hot rolling. This includes quality check of aluminum ingotting, heat evening, cutting, milling, aluminum covering and heating etc. The quality of finished aluminum sheet can only be guaranteed by high quality of aluminum ingotting. Ingotting for modern manufacturing, commonly obtained by half-continuous casting method, boasts large size and density.
During the process of half-continuous casting aluminum ingotting for aluminum sheet cools so quickly that solid materials can not spread in time, therefore, problems about chemical elements and structures like crystal segregation are likely to arise, which reduces workability of aluminum ingottings. That’s why some aluminum ingottings, especially those of hard aluminum, must go through a homogenizing treatment to eliminate or decrease unevenness of chemicals and structures. During the treatment temperature should be kept between 10 and 15℃ and then the ingotting should experience a heat maintaining process of 12 to 24 hours. For hard aluminum ingottings the two time periods should be respectively 480 to 495℃ and 12 to 15 hours. For aluminum alloys containing Al, Zn, Mg and Cu, the temperature should be from 450 to 465℃ and heat maintenance 24 hours.
Many ingottings of aluminum sheet have floating materials and cracks on the surface. In such circumstance the surface should be milled until it get smooth and bright. The thickness of milled surface depend on depth of defects, normally from 4 to 10mm. Regarded as a special process in aluminum sheet production, aluminum covering refers to cover both sides of an aluminum ingotting with covering aluminum plates. The three are then pressed together by hot rolling. The purpose is to improve corrosion resistance, protect base metal of production lines and enhance processing properties of aluminum ingottings. A piece of covered aluminum plate should be of proper chemical compositions and thickness. Heating aims to strengthen workability and reduces deformation force of aluminum ingottings.