Bagley correction evaluation on the basis of measurements in extrusion line
Polimery 2005, No 6, 455
Bagley correction (eB) measurements usually are done using capillary rheometers. In this article a method of eB value determination on the basis of the measurements done in real processing conditions is presented. Extrusion head with exchangeable dies (Fig. 3, Table 2) installed to the single-screw extruder was used as a measuring device. Two commercial grades of low-density polyethylene (PE-LD) (Table 1) were used. The peculiarity of the action of plastifying system of an extruder, far different from plastifying system of capillary rheometer, forced us to elaborate the special measuring - computational procedure allowing to evaluate eB during the process of extrusion (Fig. 4-6). Bagley correction was determined for shear rate range from 27 s-1 up to 629 s-1 (Table 3). Ability of dies to be exchanged allowed estimating the effect of geometric elements of the channel on eB value (Fig. 7-9). On the basis of velocity profiles courses (Fig. 10 and 11) the interpretation of differences in Bagley correction value, dependently on PE-LD grades and measuring dies' dimensions, has been done.
Key words: Bagley correction, measurements in extrusion line, entrance effect, velocity profile, rheological measurementsation