Mixing in the Melt Filled Screw Channel

This melt pumping stage is expected to provide polymer mixing whether for additive incorporation, blending or thermal homogenisation to give a uniform melt temperature. 

The basic starting point is the laminar shear flow of a viscous fluid between a stationary and moving plate. There is a velocity gradient within the viscous polymer melt between the moving and stationary surfaces. 

Pj = channel inlet pressure 2 = channel outlet pressure N = cylinder rotation speed Vq = plate or cylinder velocity = TtND W = channel width H = channel height L = length D = diameter 

1) Increasing channel width, W, increases pressure, but it is limited by inlet and exit problems. 

2) Channel depth, H at a given flow rate there is an optimum channel depth for a maximum pressure i.e., it depends on the extruder output rate and the die restriction a drinking straw (high) or a water pipe (low). 

---