Hollow casting

Moulded hollow parts, e.g. jugs and tureens, are "cast" from a liquid porcelain mass - the slagger - in plaster moulds. This process is known as hollow casting or hollow part production because the porcelain mass introduced does not harden completely into a solid.

After a short standing time, the plaster mould begins to extract the water from the porcelain mass. The mass solidifies on the walls of the plaster mould until the raw article has reached its wall thickness after a predetermined time. The remaining mass is simply tipped out and used for the next production cycle. The most common production systems are casting benches, casting moulds or casting lines.

In terms of craftsmanship, moulding is a demanding method of porcelain production. Once the mould shells have stood, they have to be opened and the soft porcelain body removed from the mould. This production step is particularly sensitive because the body is easily deformed. The body is still quite soft and a little finger pressure is enough to deform the article. According to special experience and time values, also depending on the type of hollow body and the climatic conditions, the slip must "stand" in the plaster mould for between 3 and 20 minutes.

The removal of water through the plaster mould must be as uniform as possible so that the hollow body has a uniform wall thickness at the end. For this reason, the hollow casting mould, unlike the solid casting mould described below, must be constantly moved. To avoid having to operate this process individually by hand, the moulds are placed on rotating cones, belts or on rotating discs to achieve the uniformity of the body thickness.

Despite state-of-the-art developments and constantly advancing technology, it has not yet been possible to replace this method of hollow body production with an automated process.