The CRD mixer is the first mixing device that has
been developed using analytical, numerical and experimental techniques. After
only one year on the market, the CRD device has been used very successfully
to replace the barrier-type screw, Maddock, rhomboid and other mixing sections
to provide a finer level of distributive and dispersive mixing
The new CRD mixing technology represents
a radical departure from existing mixers in several respects. The CRD mixer
is the first screw-mounted mixer specifically designed to generate strong
elongational flows. Elongational flow is more effective in breaking down agglomerates
and droplets than shear flow and creates less viscous dissipation - most
existing mixers are based on shear flow. Further, the CRD mixer combines
both distributive and dispersive mixing capability within one device; this
combination is key to achieving highly effective mixing. The CRD mixer is
designed to force the material through the high stress regions several times
to achieve a fine level of dispersion. Many mixers, such as the Leroy/Maddock
only expose the material to a single high stress exposure.
Patented CRD Technology
The patented CRD mixer was developed by Chris Rauwendaal in cooperation with
The Madison Group. The CRD mixer was designed and optimized through full
3D-flow analysis (BEMflow simulation program). The CRD mixer is likely the
first mixing device designed with a solid theoretical basis and developed
with engineering calculations, computer simulation and experimental verification.
Advantages of CRD Technology
- Utilizes elongational flow to achieve excellent mixing
- Multiple high stress exposures to achieve a fine level of dispersion
- Reduced viscous dissipation and melt temperatures
- Low cost and easy to incorporate into existing screw designs
- Can disperse gels (shear based mixers cannot disperse gels)
Proven Technology
The mixer has been commercially available since late 1998 and has successfully
proven itself in a number of single screw extrusion applications; these include:
- Color Concentrates, quote from production manager: "Nothing else comes
close"
- Foamed Plastic, quote from process engineer: "Far superior to the
barrier screw"
- Reactive Extrusion
- Heat Shrinkable Tubing and Medical Tubing
- Post Consumer Reclaim
- Blown Film Extrusion, quote from plant manager: "CRD screw eliminated
gel problems"
- Injection Molding
The CRD mixers are available in a wide range of
configurations. The CRD5 is designed for good mixing and pumping capability;
it can replace the metering section achieving greatly improve mixing capability
without reducing the output capability of the screw. The CRD6 has increased
mixing capability but slightly reduced pumping capability. The CRD7 is the
most intensive CRD mixer used for the most demanding compounding jobs; it
combines the helical geometry of the CRD5 and 6 with a circumferential arrangement
of elongational mixing pins. The CRD mixers are also available for twin screw
extruders, corotating and counterrotating.
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