DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the FIGURE, a convention ingot forming operation is illustrated in which an open-ended mold 10, associated with coolant providing pipes 11, is mounted in fixed position over a platform 12 which is attached to and supported on a lowering device 14.
The platform 12 initially forms the bottom of mold 10, but once the casting process is started the platform 12 is lowered as the ingot 16 is formed, allowing withdrawal of the ingot 16 from the mold at the rate it is formed, or its shell is formed, therein.
It should be understood that the term ingot as referred to herein comprises both generally rectangular ingots and generally cylindrical billets.
In the FIGURE, the casting is shown in progress, with the molten metal 13 being fed to th operation through a spout 9 and at a rate which, taking into account the coolant, the rate of solidification, and the lowering rate of platform 12, maintains a relatively constant level, or head, 15 of molten aluminum in the mold 10 and above ingot 16.
It is also known to eliminate the spout 9, with the mold 10 in such a case being directly fed from the wall of a furnace or other molten metal container.
According to the practice of the present invention, a small quantity, ranging, for example, from about 10 to about 100 grams, of a fine, insulating, nonreacting powder selected from the group consisting of-boron nitride, amorphous silica, diatomaceous earth and talcum is introduced onto the surface of the molten metal 15 in the mold 10 at the beginning of the drop or casting operation, i.
e.
, when platform 12 forms the bottom of mold 10.
The powder may be introduced by sprinkling it onto the surface of metal 15, or, for example, by aspersion from a squeeze bottle.
The powder may be introduced onto the entire molten metal surface, or may be applied to the edges and/or corners of the mold 10.
Once in place, the powder promotes a stable meniscus to the molten metal head 15, promotes stable heat transfer and results in vertical, rather than horizontal, solidification of the ingot 16
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Generators or Motors 
