Patent attributes
An apparatus for processing molten material into a desired shape comprises a die or mold forming a cavity to receive molten material and to allow its solidification within the cavity. A source of vacuum is connectable to the cavity for sucking air out. A hollow after-pressure cylinder is in communication with the cavity so as to receive a portion of the material. The after-pressure cylinder has a first end for connection to the cavity, and a second, opposite end. In the region of the second end is a connection opening for connecting the vacuum source. An after-pressure piston is moveable in the after-pressure cylinder to press its portion of material into the cavity to compensate for any shrinkage of the material in the cavity. There is a drive for moving the after-pressure piston in its after-pressure cylinder into three different positions, i.e.:(a) in a first position, the after-pressure piston is in the region of the cylinder's second end, leaving the connection opening in communication with the cavity,(b) in the second position, the after-pressure piston has moved over the connection opening to interrupt the communication with the cavity, and(c) in a third position, said after-pressure piston has moved from said second position towards said cavity to press said portion of material into it.
