Completion of extrusion
When the single screw extruder is backed to the original position after completion of extrusion of the billet, for scrapping off aluminum residues stuck to the inner surface of the container liner by the outer surface of the fixed dummy block fixed to the end of the extruding stem, the scrapped aluminum residues enter into a groove of the guide plate so that the seal block is difficult to open and close, thereby deteriorating sealing performance.
Since the flexible sealing device such as a metallic bellows, a spring, or an elastic member of telescopic type, which is expandable from the extruding stem side toward the rear end of the container, is used to seal the container to completely eliminate the residual air in the container for the extrusion of the billet, it necessitates a larger deaerating space and a longer deaerating time, and the atmosphere is easily entered into the container because of insufficient sealing thereby causing the degree of vacuum lower.
The sealing device is backed to a ram (a base portion of the sheet production extruder) side during loading the billet into the container and then the inside of the container is sealed by advancing the sealing device after the billet is completely loaded by the forward movement of the extruding stem so as to vacuum air in the container, thereby making the idle time longer for the operation of the sealing device. It needs large pressure to press the sealing device from the ram side to the container so that the container comes in sufficiently contact with the end face of the container, thereby making the structure complex.
There are many kinds of sealing methods previously improved. In this method, a container and an extruding stem separately move relative to each other and a two-piece seal block is attached to the container. An outer sealing member of a ring-like projection and an stem sealing member are both integrally fixed to the two-piece seal block to seal the container and the stem in the same direction, respectively. Therefore, a minute space may be generated in a portion sealed by one of the sealing members so that the sealing members can not come in sufficient contact with the container or the stem, thereby making sealing performance lower. In a condition that the flexible sealing device is compressed at the backmost position, the extruding press device is longer than the conventional extruding stem (conventionally, the extending stem necessitates a length sufficiently for extruding the billet loaded in the container) for the size of the sealing device in the compressed state, thereby increasing the whole length of the extruding press and thus necessitating a wider area for installing the extruding press.
Since a deaerating groove is formed in the inner surface of the container, i.e. the upper portion of the inner surface of the container liner at the extruding stem side, such a container is not allowed to be used in a general purpose twin screw extruder because of the limitation so that the container liner must be exchanged with another one without deaerating groove whenever used for another purpose, thereby taking a lot of time for exchanging container liners.