Influence of Kneading Disc Thickness
According to different thicknesses of 45° kneading discs (30, 40, 50mm), three screw combinations are set, numbered 1#, 2#, and 3# in sequence.
1-3# Tensile mild of pp sample fifilled with calcium carbonate under screw combination and energy consumption per unit production of extruder
It can be seen that with the increase of the thickness of the kneading disc, the tensile strength of the sample decreases sequentially and the energy consumption of the co-rotating twin-screw extruder increases sequentially. This is because with the increase of the thickness of the kneading disc, the dispersed mixed components per unit mixing length increase, and the distributed mixed components decrease, that is, the filling effect of calcium carbonate powder in PP is weakened, resulting in a decrease in mechanical properties.
At the same time, when the thickness of the kneading disc increases, the energy consumption of the extruder under the screw combination increases significantly, and the torque required by the screw increases.
It can also be seen from Figure 1 that when the thickness of the 45° kneading disc is 30mm and 40mm, the tensile strength of the sample and the energy consumption of the extruder are not much different, so the thickness of the 45° kneading disc can be selected as 30mm or 40mm.
Influence of staggered angle of kneading discs in plasticizing section
On the basis of the 2# screw combination, a group of kneading discs with different staggered angles were added before the 45° kneading discs in the plasticizing section. °), 3 screw combinations are set, numbered 4#, 5#, 6# in turn.
From this, it can be seen that by changing the staggered angle of the kneading discs in the plasticizing section, the mechanical properties of the samples under the 5# screw combination are the highest, 4# is slightly lower, and 6# is the worst; The energy consumption per unit output of the extruder increases with the angle increases of kneading discs in the plasticizing section. And the energy consumption of the 4# and 5# screw combinations is not much different, but the energy consumption of the 6# screw combination increases significantly.
This is because when the material enters the plasticizing section from the feeding section, it has not yet melted. Since the staggered angle of the kneading blocks of the 6# screw combination is 90°, the shear force is too large, the leakage flow is too large, and the conveying capacity of the screw is reduced. The local residence time increases, and the material filling at the screw conveying part is too high, resulting in poor material mixing effect, increased energy consumption, and rough surface of the extrudate.
When the staggered angles of the kneading discs in the plasticizing section are 30° and 45°, the tensile strength of the sample and the energy consumption of the twin-screw extruder are not much different. Therefore, the staggered angle of the kneading discs in the plasticizing section can be selected as 30° or 45°.
Influence of position of rotor-like threaded elements on energy consumption
To further enhance the mixing effect, a set of kneading discs can be replaced with rotor-like threaded elements.
It differs from conventional large-pitch threaded elements in that it creates a large gap between the threaded element and the inner wall of the barrel, the top of the flight is narrow, and the profile of the leading edge and trailing edge of the thread is also different.
Its flight is composed of 2 segments, one is left-handed and the other is right-handed. This element is installed on both screws, and the parts that mesh with each other have the same helical direction. When this element rotates, the material is “extruded and pressed” to achieve the purpose of enhancing the mixing effect.
According to the positions of different rotor-like screw elements, two screw combinations are used, numbered 7# and 8#, as shown in Table 4.
7# and 8# screw combination and its material extrusion state
7-8# Tensile mild of pp sample fifilled with calcium carbonate under screw combination and energy consumption per unit production of extruder
We can see from the above figure that the tensile strength of the sample under the 7# combination is higher than that of the 8#, and the energy consumption of the extruder is lower than that of the 8#.
This is because the rotor element of the 8# combination is placed behind the first group of kneading discs, the material is not completely melted, and the shearing and refluxing at this time are of little significance to its dispersion and distribution and mixing, and it is easy to increase energy consumption. The rotor element of the 7# ore combination is arranged behind the second group of kneading discs. At this time, the material has been completely melted, so the mixing effect and energy consumption are better.
Influence of Continuous Arrangement of Multiple Groups of Kneading Discs
The screw combination of some twin-screw extruder manufacturers is a continuous arrangement of multiple sets of kneading discs, and the extruded material has good performance. The difference between this combination and the previous 8 combinations is that all the conveying elements between the three groups of 45° kneading disks are replaced with kneading disk elements to form a combination of multiple groups of kneading disks arranged in a row.
Combination form of continuous arrangement of multiple sets of kneading discs And the extrusion state of its materials, tensile strength of samples and energy consumption per unit output of extruder
Compared with the above 8 combinations, after replacing all the conveying elements of the plasticizing and mixing sections with multiple sets of kneading discs with strong shearing force, the energy consumption does not increase significantly, and the tensile strength of the sample does not greatly increase. decline. Therefore, this screw combination has applicability in practical production applications, and can be applied to extrusion production for high shear materials.