A Polymer Process Engineering & Training Company Home of the CRD Mixing Screws
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
The mixer has been commercially available since late 1998 and has successfully proven itself in a number of single screw extrusion applications; these include:
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.