A sprue cup is formed and the mold surface leveled. The back of the mold is covered with unheated plastic film.
Vacuum is applied to the flask. Atmospheric pressure then hardens the sand. The vacuum is released, pressurized air is introduced into the carrier and the mold is stripped.
The cope and drag assembly form a plastic-lined cavity. During pouring, molds are kept under vacuum.
After cooling, the vacuum is released and free-flowing sand drops away leaving a clean casting, with no sand lumps. The sand is cooled for re-use.