CRD Mixing screw (Patents 5,932,159 & 6,136,246)
The CRD mixer is a revolutionary new design unique in its ability to provide dispersive and distributive mixing with low pressure loss or even pressure gains. The CRD generates elongational flows, which provides the most efficient mixing. There are a number of important benefits to elongational mixing.
First of all, greater hydrodynamic stresses are generated in elongational flow and the stresses are transferred more efficiently to the agglomerates because rotational motion is absent in pure elongational flow. This is why rheologists call this “irrotational” flow.
Secondly, the energy consumption is less in elongational flow relative to shear flow. As a result, the power consumption of the extruder can be reduced while the melt temperatures can be maintained at lower level. Thirdly, in elongational flow it is possible to disperse highly viscous droplets in a low viscosity matrix while this is not possible in shear flow. As a result, gels can be dispersed in elongational flow; however, shear flow is incapable of dispersing gels.
CRD Barrier screw (Patents 5,932,159 & 6,136,246)
The unique feature of the CRD barrier screw is that the barrier flight is designed to generate elongational flow as the plastic melt passes over the barrier flight. This can be done by making the pushing flight flank of the barrier flight curved or slanted. This wedge-shaped region allows the material to accelerate and stretch, causing elongational flow with better mixing and less shear heating. The barrier section is relatively short and located toward the end of the of the melting zone which eliminates plugging and surging.