Extruders with material supplying port
The extruder of the present comprising a cylinder which has the rear tubular part with large diameter, the front tubular part with small diameter and the tapered intermediate part between said front and rear tubular parts. The twin screw extruder is provided with the material supplying port for supplying the material at the periphery of the rear tubular part and the material extruding outlet for extruding the material at the front tubular part. A screw, which is provided with a spiral ridge on its periphery, is rotatably housed in said cylinder and has the rear part with large diameter, the front part with small diameter and the tapered intermediate part corresponding to said parts of said cylinder respectively. A material flow passage, which is formed by said spiral ridge between the external surface of said screw and the internal surface of said cylinder, communicates with said material supplying port and said material extruding outlet whereby the internal capacity per turn of said spiral ridge in a tapered throttle part formed by and between the tapered intermediate parts of said screw and cylinder decreases as the taper advances from the rear side to the front side.
A blended resin compound of an extremely low viscosity when it is melted as compared with general thermoplastic resins (usual viscosity: 1,000,000 cps or over) can be widely used for other applications such as, for example, coating, painting, printing, etc. in addition to the bonding applications, and the blended resin compounds can be integrally referred to as the hot-melt materials. In general, hot-melt materials are supplied to users in the form of pellets, biscuits or small blocks; however, it is difficult to mold the hot-melt material by the single screw extruder for general plastic materials for its specific characteristic, that is, extremely low viscosity when it is melted.
When sheet production extruder for general plastic materials is used to extrude the hot-melt material, the molten hot-melt material has a small low friction with the internal surface of the extrusion cylinder, the hot-melt slips and the extrusion screw cannot perform conveying function of the hot-melt material. In a plant like this, the melting tanks, strainers and pump should be heated to maintain the temperature of the molten material at a certain specified temperature. For this purpose, the heating medium boiler B and feeder F should be installed to form the pipe passage of the heating medium as shown with broken line A2 in the figure, flow passage A1 for the molten material should be made by dual piping and heated by said heating medium and many valves and cocks should be provided in the piping. In addition, the cooling water piping is required for the pump. As described above, the conventional plants have been complicated and expensive in their constructions. In actual operation, these plants are disadvantageous in that it takes long until the material is melted and the hot-melt material should be completely discharged from all the pipings after extruding operation.
Furthermore, the pump type machines cannot process the hot-melt material of high viscosity (100,000 cps or over) for which the demands are expected to increase. Another object of the present invention is to supply an extruder which is capable of extruding a hot-melt material as described above likewise general extruding machines and to vastly improve the efficiency and economy in melting and molding operations of the hot-melt material. Further another object of the present invention is calrified in the detailed description of the construction based on the drawings.