also, throughput and screw "speed,

also, throughput and screw "speed, whic can be changed during
extruion, considerably alter vetocity distrit'ution; thereby, more
uniform shear stresses can be achieved with consequent better material homogeneity.
furthermore, in counterrotating screws, the material forceti into
the calcndering gap untlcrgoes, as it has been nncntioned before, a
high shear but only a small fraction of the chamber's volume passes
through it. This adds to the nonhomogcneity of the cxtrudate. Mix-
ing devices as interrupted flights, etc., will arncliorate the results,
although only partially.
In corotating screw systems, the very presence of the area restric-
tion and stiapo cliange in the pasMge between screws further en lianccs
homogeneily without localized high shear at any poirft.
root are greater than in corotating screws, so that in counterrotating
screws these layers of material are greatly mistreated, whereas a large
percentage of material inside the channels is not exposed to enough
shear for good plasticization and dispersion. (2) In counterrotating
screws, the velocity distribution along the channels, which varies
greatly according to depth, can only be influenced by a change m
screw pitch, which, however, is preselected. (3) In corotating screws