Seal block section of Extruder
A sheet production extruder is formed of a container having a container liner for receiving a billet therein, an extrusion stem situated near the container for disposing the billet into the container, and a two-piece seal block installed between the container and the extrusion stem for sealing there between. The seal block is formed of two seal block sections for sandwiching the extrusion stem there between.
Each seal block section includes a base piece having a press member, and a holding block detachably attached to the base piece to be moved by the press member and having a first sealing member facing the extrusion stem and a second sealing member facing the container. A moving device is attached to the seal block sections for moving the seal block sections relative to the extrusion stem. The holding block is urged to the extrusion stem by the moving device, and to the container by the press member to thereby seal between the container and the extrusion stem.
After a billet the diameter of which is slightly smaller than the inner diameter of a container is inserted into the container, the billet is pressed against a die with an twin screw extruder stem from the rear side of the container which is called as "upsetting" 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 slightly backed to release the compressed air to the atmosphere from a space between the die and the container. After that, the extrusion is started by advancing the container and the extruding stem to the original positions. The deaeration step for eliminating compressed air as mentioned above is referred to as a "verp cycle" which causes a waste of time in the extrusion cycle.
Moreover, this process remains air in a small space like a film at atmospheric pressure between the inner surface of the container and the outer surface of the billet when the container is pressed against the die after the deaeration of the verp cycle. That is, the sufficient deaeration can not be obtained by this process. This may produce blisters in an extruded product. Such an extruded product including blisters should be removed, thereby reducing the yield of end products. In this process, the residual air is eliminated by providing metallic bellows to form a sealed chamber between a container and an extruding stem, sealing by metallic packing between one end of the bellows and the container and between the other end and the extruding stem by metallic packing, and pressing the metallic packing from the outside by a cylinder using air or fluid to eliminate air in the sealed chamber to the outside.
Further, It discloses a method of vacuum deaeration from a container through a space between a dummy block and the container with the inside of the container being sealed with sealing material, through a supporting member being sealingly in contact with disc-like supporting plates, arranged in suitable positions of single screw extruder with carbon sealing material, elastically by a spring disposed between the rear wall of the container and the supporting plates.