Recirculating Screw Mixer
The recirculating screw mixer was designed as a
laboratory intensive mixing machine
with a well understood flow field for fundamental studies.
It primarily consists
of a small single screw extruder with a closed
discharged and a hole bored
down the center to allow for recirculation.
The design goals for the recirculating screw mixer were:
- Sample volume of 10 cm3, large enough to
provide samples for analytical techniques such as
spectroscopy and microscopy but small enough for use of expensive or experimental polymers.
- Intensive mixing with high shear rates.
- Periodic reorientation to improve mixing.
- Capability for handling high or low viscosity materials.
- Well-understood flows to allow for modeling.
The first recirculating screw mixer made was designed to be used with
a Haake torque rheometer and the Rheomix 600 base. With a 1.6 cm barrel,
it has a free volume of 10.2 cm3.
In addition to the standard metal barrel, a poly(methyl methacrylate)
provided to allow for
of the mixing
The combination of well understood flow fields (channel flow in single
screw extrusion and pressure driven flow through a tube) allows the
recirculating screw mixer to be
modeled in detail.
Modeling< of the flow of
Newtonian and power law fluids in the recirculating screw mixer provided the
velocity field, operating diagrams, and methods for use of the mixer
as a melt rheometer.
of the recirculating screw mixer were
tested with a polymer blend and a composite. Results were compared with
a benchmark laboratory mixer and found to be similar.
Details of this equipment and a few experiments which were
conducted with it can be found in:
- "The Recirculating Screw Mixer: a New Small-Volume
Intensive Mixer for the Polymer Laboratory,"C.E. Scott and
C.W. Macosko, Polym. Engr. Sci., 33, 1065 (1993).