Closed, often laterally installed riser with an inserted or molded conical or pyramid shaped tip in the upper port (Williams core, see also Williams riser).
Ideally, a sharp sand edge is sufficient in this range. These deformations protrude in the riser and are consequently more heated by the material than the adjacent riser wall and cannot yet solidify for this reason (see Sand edge effect).
As a result of the volume contraction beginning with solidification, a interior cavity is formed in the casting and negative pressure occurs. As the sand edge, sand tip or the Williams core (see also Williams riser) keeps an opening in the solidifying metal surface layer as a result of heating and thus delayed solidification (Fig. 1), the external (atmospheric) air pressure applies and presses the metal from the riser into the casting. However, this requires a solid shell on all sides of the casting.
The range of atmospheric risers can also exceed their height. This way, sections of the casting above the riser may also be fed. In any case, the casting yield is considerably improved.