| 摘要 |
<p>A riser sleeve is closed at one end into a dome form and the dome's outer surface includes a flattened portion. An elongate member, forming a Williams core, extends from the outside of the sleeve below the flattened portion to a point within the sleeve which is surrounded by molten metal when the sleeve is in use. The sleeve and the Williams core are integrally formed of an air-permeable material so that in use atmospheric pressure acts on molten metal contained in the riser.</p> |
