CRD mixing technology for extrusion and injection screws uses elongational flow to achieve effective mixing while maintaining low melt temperatures. The CRD mixers are also used in blowmolding and compounding. They are well suited to foam extrusion and compounding of color concentrates, as both applications place great importance on mixing and melt temperature control.
A significant advantage of elongational mixing devices is that they disperse gels, a benefit in the extrusion of film, fiber, and thin-walled tubing. The concept is also applied to fluted mixing sections and barrier screws. Many custom screws now use CRD-fluted mixers or barrier sections. The mixing technology now extends into single-screw compounding extruders. These machines are competitive with twin-screw compounding extruders with regard to mixing capabilities; however, they offer a significant cost advantage.
Single-screw compounding extruders based on CRD mixers are expected to become commercially available in 2003 or 2004. The units also offer advantages in direct extrusion because they can handle filler levels up to 50 to 60 percent and have good pressure-generating capability.
Rauwendaal Extrusion Engineering, Los Altos Hills, CA
(650) 948-6266; www.rauwendaal.com