Nanjing GIANT Machinery Co.,Ltd.

By the transfer from the sheet production extruder screw into the region of the extruder sleeve, and back, the mixing of the starting materials is to be improved, which represents an important qualify feature of the extruded material. To avoid losses, the cross-sectional areas of the flow channels are precisely coordinated, and the extruder screw runs exactly in the extruder sleeve, with the exception of the structurally required gap of, for example, 100 μm in conformity with the bearing play and the bending of the extruder screw during the rotation and stress.

It has also been proposed to change the flow cross-section in a defined manner in order to generate shear flows that are intended to improve the mixing. By reducing the cross-sectional surface there results, with rubber mixtures, which to this extent act like Newton's liquids, an elongated flow that corresponds to an acceleration of the mixture in an axially parallel direction of the twin screw extruder. However, this unfortunately results in a reduction of the retention time of the extruded material in the extruder. The discontinuous pitch in the screw lands of the transfer mixture region to this extent reduces the homogenization; the temperature behavior also becomes worse. The discontinuous pitch is therefore only well suited for rubber mixtures that are easy to process.

Pursuant to the invention, it is particularly expedient that, due to the provision of a transfer gap, a shear flow profile is produced that at the same length of the extruder offers a significantly improved homogenization. Due to the inventively induced elastic or shear flows, there is effected in a defined manner an improved thorough mixing, which makes the temperature level significantly comparable. Colder regions of the mixture can flow into the inventive width gap. The polymer chains that are present there are inclined to slide along one another and to thereby be heated in an efficient manner. Pursuant to the invention, the retention time of the mixture in the extruder is clearly increased, whereby the length of the retention time can be controlled in a defined manner via the dimensioning of the inventive width gap.

In an advantageous embodiment of the invention, it is provided that the gap be provided with respective inlet or leading inclines that further improve the tendency of the material to flow in. The angle and the precise configuration of the inlet inclines can be adapted over a wide range to requirements. Pursuant to the invention, the transfer is preferably effected using a linear characteristic. It is to be understood that instead of such a characteristic, it is also possible to select a characteristic that deviates from a linear course, for example a characteristic according to which the increase is negative in short regions, in other words, the flow cross-section of the flow channels of the single screw extruder screw increases and in conformity therewith the flow cross-section of the flow channels of the extruder sleeve decreases.