Synthetic Plastic Powders
It is well known to plasticize synthetic plastic powders or granulates in an extrusion cylinder wherein the material is heated while being acted upon by an twin screw extruder screw. The latter receives motion from a drive whose output element is coupled to the screw. As a rule, the end faces of neighboring end portions of the screw and output element are formed with grooves for a torque-transmitting wedge, and the end portions are then confined in a two-piece sleeve. A drawback of such couplings is that they are prone to malfunction. The useful life of the wedge is short and the end portion of the screw is likely to crack or break in response to the application of forces which arise if the axis of the output element does not coincide with the axis of the screw.
A single screw extruder, for plastic materials wherein an end portion of the extruder screw extends from the extrusion cylinder and is coupled to the adjacent end portion of the drive shaft by a U-shaped coupling element which partially surrounds the two end portions and by a claw-shaped coupling element which overlies flats on the end portions of the extruder screw and drive shaft and is secured to the U-shaped coupling element by a screw. The flat on the end portion of the extruder screw is inclined with reference to the axis of the extruder screw if the shaft is to transmit torque to and to reciprocate the extruder screw. A U-shaped clamping device is used to secure the U-shaped coupling element to the end portion of the shaft.
The improved sheet production extruder itself, however, both as to its construction and the mode of assembling the same, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.
The screw is rotatable about a predetermined axis, and the motion transmitting member of the drive means can constitute a rotary shaft whose axis coincides with the axis of the screw. The fastening means can be located between the end portions of the screw and shaft; for example, one of the coupling elements can have a tapped bore and the fastening means can include a fastener having an externally threaded shank in the tapped bore of the one coupling element.
It relates to single screw extruder in general, especially to extruders which can be used to make shaped articles from plastic material. More particularly, it relates to improvements in connections between the screw of an extruder and a drive which serves to impart to the screw a rotary and, if necessary, a reciprocatory movement.