| 摘要 |
Molten aluminum, magnesium, or their alloys, or other metal is solidified in a mold or casting device from which an ingot is continuously and progressively withdrawn. The ingot as initially formed has a solid shell and a liquid core which progressively solidifies as the ingot is withdrawn through and from the casting device. As the ingot emerges from the casting device it is contacted directly with water or other coolant referred to as direct chill. Improved casting rates can be achieved without cracking the ingot where the direct chill cooling effects are divided into three successive zones. In the first direct chill zone a relatively high chill rate is employed, after which a retarded chill rate is employed in a second direct chill zone followed by a higher chill rate in a third direct chill zone. Thus, the ingot is drawn through a high direct chill rate zone then a lower direct chill rate zone and then a higher direct chill rate zone. The intermediate low chill rate zone is effected preferably by use of a dissolved gas such as carbon dioxide, which establishes a heat insulating film or layer around the solidifying ingot to retard heat extraction. At a predetermined distance from the mold that film is then mechanically disturbed as by a comb, rake or other mechanical action or as by a jet of water, air or other fluid to establish a higher chill rate for the third zone.
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