Extruding Stem
A sheet production extruder has a cylindrical container into which a billet is loaded; a two-piece seal block disposed on an end surface of the container at an extruding stem side; a vacuum deaerating hole formed in the seal block; and a fixed dummy block, having an internal cooling function, fixed to an end of the extruding stem, wherein the seal block is allowed to be opened and closed in a direction perpendicular to the axial direction of the container and the seal block comes in close contact with an outer surface of the extruding stem and the end surface of the container when the seal block is closed.
After a billet is inserted into a container wherein inner diameter is slightly larger than that of the billet, the billet is pressed against the die with an twin screw extruder stem from the rear side of the container and is "upset" so that the billet is pressed to be deformed to compress air trapped between the container and the billet. For eliminating the compressed air, the extruding stem and the container are backed slightly and the compressed air is released into the atmosphere through a space formed between the die and the container. After that, the extrusion is started by advancing the container and the extruding stem once again. The breathing step for eliminating compressed air as mentioned above is referred to as a "Veep cycle", which causes a waste of time in the extrusion cycle.
Moreover, Japanese Utility Model Publication No. 55-19605 discloses an single screw extruder provided with a two-piece seal block allowed to open and close in a direction perpendicular to the axial direction of a container. In this extruder, the inner surface of the seal block comes into close contact with the outer surface of an extruding stem when the seal block closes. Such a two-piece seal block opens and closes along a guide plate fixed to upper and lower portions of an end surface of the container at the extruding stem side. In addition, sealing members for sealing the container from the extruding stem are arranged between a cover plate and the seal block and between the extruding stem and the inner surface of the seal block, respectively. The container is provided with a deaerating groove at an upper portion thereof at the extruding stem side, thereby facilitating deaeration.
Since the deaerating groove is formed in the inner surface of the container, i.e. the upper portion of the inner surface of the container at the extruding stem side, such a container is not allowed to be used in a general purpose sheet production extruder because of the limitation so that the container must be exchanged with another one without deaerating groove whenever used for another purpose, thereby taking a lot of time for exchanging containers.