The conveying rate of the extruder screw
A screw extruder conveys on the basis of the internal friction, and produces a drag flow along the extruder screw. In contrast, a planetary pump is a volumetric conveyor, so that here the conveying rate is considerably less dependent upon the viscosity of the material that is to be conveyed. Thus, the inventive approach also makes it possible to convey in a manner that is relatively independent of viscosity, whereby none-the-less a good efficiency can be achieved with the inventive planetary pump.
It has furthermore already been proposed to construct a pump in the manner of a planetary gearing. For the sake of simplicity, such a pump will here be signified as a planetary pump. With this approach, the sun or central gear can be connected directly with the extruder screw of the single screw extruder, so that there is no need for a separate mounting of the end of the screw. Rather, the support of the end of the screw can be provided on the downstream side of the planetary pump. A drawback of this approach is that the conveying properties of elastomeric materials such as rubber or rubber mixtures for the tire industry are greatly dependent upon differing parameters. If due to the prevailing viscosity of the material the planetary pump must be advanced to a greater extent than the extruder screw, an underpressure or partial pressure results in the transition zone. This can lead to the formation of bubbles, so that the quality of the conveyed material is not acceptable.
In order to be able to preclude this with certainty, it would be possible to increase the conveying rate of the extruder screw. However, there then results an overpressure in the transition zone, which stresses the construction and impairs the efficiency or output rate. It is therefore an object of the present invention to provide an extruder arrangement of the aforementioned general type that provides an improved quality of the material that is to be extruded, whereby none-the-less an economical manufacture should be necessary. The outer ring can be provided with a brake that is controllable. It is then merely necessary to have a drive motor for the extruder screw that can then also at the same time drive the central gear or the planetary carrier of the planetary pump. The setting or adjustment is effected such that even with the greatest viscosity of the material that is to be conveyed, the conveying rate of the planetary pump is still sufficient to prevent an overpressure on the input side of the planetary pump. In this state the brake is then activated, so that the outer ring does not, or nearly does not, rotate along.