An extruder comprises an end face
The billet in the container is pressed from the rear side against the die by the single screw extruder, so that the billet is squeezed and air trapped between the container and the billet is compressed. The compressed air must be vacuumed form the rear side of the container before the billet is extruded from the die. In addition, air must be vacuumed from the container just before the end of the billet comes into contact with the die. According to the present invention, the air in the container is forcibly vacuumed at the extruding stem side before the billet is compressed by the extruding stem, thereby omitting the step for eliminating compressed air after the billet is compressed by the extruding stem, called as a breathing process.
The seal block comprises base pieces and sealing material holding blocks and the sealing material holding blocks are capable of performing vacuum aspiration by engaging to a fixed dummy block or the sheet production extruder and is arranged slidably in the lateral direction and detachably relative to said base pieces. The sealing material holding blocks are fixed to the base pieces with engaging pins each having a stopping plate which is engaged to an engaging portion by turning the stopping plate.
For achieving the objects mentioned above, according to a first aspect, an extruder comprises an end face, at an extruding stem side, of a container having a container liner in which a billet is loaded; a two-piece seal block allowed to be opened or closed in a direction perpendicular to the axial direction of the extruding stem; and a press member. When the seal block is closed, the seal block is brought sealingly in contact with the end face of the container and the outer surface of the extruding stem simultaneously by sealing members fixed to the seal block. The press member is arranged to be moved in a direction of pressing the sealing members of the seal block against the end face of the container.
Air in the container is vacuumed with the container being sealed by the seal block having a press member arranged to press the seal block against the end face of the container at the twin screw extruder. For smoothly removing the air in the container, container is provided with a ring-like deaerating groove at the entrance thereof at the extruding stem side, the diameter of which is greater than that of the fixed dummy block, so that a ring-like space is formed between the inner surface of the container and the outer surface of the fixed dummy block when the billet is loaded into the container. Therefore, air trapped between the container and the billet can be easily eliminated to the outside of the container, thereby preventing the inclusion of blister and thus significantly improving the yield of the end products.