parameters of extruder screw exhaust section

the exhaust performance of the exhaust screw of the extruder is mainly determined by the parameters of the exhaust section, and there are many factors that affect the exhaust effect. the simulation device shown in figure 14-2 is used to study the exhaust effect of the exhaust screw of the exhaust extruder. the results show that the length of the exhaust section l, the residence time of the molten material in the exhaust section t, and the shear rate of the molten material in the exhaust section γ, finally, the filling degree of the plastic in the screw groove of the exhaust section (expressed by the filling coefficient f) is directly related to the exhaust effect
in order to ensure a good exhaust effect, the screw groove of the exhaust section shall not be filled with molten material. to measure its filling degree, the filling coefficient f is introduced, which is the ratio of the sectional area of molten material to the area of the screw groove. for the convenience of calculation, it can also be called the ratio of the screw groove depth h1 of the first metering section to the screw groove depth h2 of the exhaust section figure 11-13, namely:
through experiments and analysis of the existing machine, it is shown that for general exhaust screw, under the condition of exhaust section length l ≥ 3d and filling coefficient f ≤ 0.5, better exhaust effect can be obtained if shear force k is greater than 100.
for the exhaust screw with a length diameter ratio of 24-30, the length l of the exhaust section is between 2-6d, but mostly 4d. the screw groove depth of the exhaust section is about m times the screw groove depth h1 of the first metering section (m=2.5-6), which can be selected according to the statistical curve in figure 11-14. then, the formula of anti-inflammatory fullness factor f and shear strength k can be used. finally, the screw strength of the exhaust section must be verified.