Extensive exchange of material
Each conveying section has a correspondingly large flight depth at an angle of 90° in case of two flights, and a correspondingly small flight depth at an angle of 60° in case of three flights. That is to say in the conveying element according to the invention, a first comb at a small clearance from the inner wall of twin screw extruder is followed by a second comb at a greater distance from the inner wall of the housing, and at an angle thereto, a correspondingly large flight depth as well as a small flight depth at a maximum distance.
This means that an extensive exchange of material is possible across all feed channels in the circumferential direction from channel to channel involving multiplied flow divisions, with the material exchange being carried out radially as well as axially in the same way with different and varying flight depths and corresponding comb/housing clearances. Thus, the filling degree is equal in all channels. Due to the permanent geometric chicane in the alternation of comb and flight in rapid succession in the circumferential and axial direction, a particularly high density of elongational flows is produced. Since this takes place without the undesirable decrease of viscosity in all feed channels in the entire cross-section and over the entire length of the conveying element, a more effective and more rapid mixing is achieved and a significantly higher product quality with a more uniform homogenization. This is substantially attributed to two sharp deflections at the transition of the product from one supporting shaft to the next one in case of the single screw extruder, and, in particular, 12 deflections in a six-shaft extruder as well as 24 deflections in a twelve-shaft extruder, which cause a further intensification of the effective forces in the product.
By means of viscosity of the continuous phase, tensile and bending forces are thus repeatedly exerted on the fatigue strength of the agglomerates of solids, which results in the fatigue fracture of the sheet production extruder. According to the invention, an effective homogenization and dispersion of the solid is achieved, that is to say even in case of solid particles having a particle size in the μm range, hence less than 100 μm, in particular less than 10 μm. By means of the conveying element according to the invention, the product is thus subjected to constantly varying flight depths and material velocities and hence elongation processes over a very short length. According to the invention, an extensive exchange of material is achieved as a result of the great distance of the one comb from the inner wall of the housing, whereas at the comb stripping on the inner wall, only a minor exchange of material takes place, but the greatest dispersing effect is achieved due to maximum strain. Since according to the invention, said comb consists of short sections, the product is subjected to extreme strain only in small areas, however, which is why the temperature of the product may be kept altogether low with the consequence that even in the extremely strained areas, the product cannot be damaged and is thus treated altogether gently.