Adaption of the Check Ring Mixer to Extrusion

By transferring the check ring mixer concept to extrusion, the mixer can be accommodated within the barrel as part of the screw. Being without the non-return valve function required for injection moulding it can be described as a floating 

The disadvantage is that there will be less screw available for melting/pumping, and the length of the mixer is restricted. Although initial costs will be lower than for addon mixers, the need for occasional replacement of worn injection moulding check rings may also apply to extruders. 

A comparison of three floating ring mixers has been made by Myers and co-workers [12] using a 63.5 mm diameter, 21D (diameters) extruder with the screw length reduced to 19D to provide space for the mixers. 

Experiments were performed using black and white acrylonitrile-butadiene-styrene pellets in a ratio of 220 1 white to black, with extruder speeds of 40 and 80 rpm. About 60% of the ABS entering the mixers was white with no black mixed in, which created big demands on the 2.4D mixers. Cross-sections of 1cm diameter strands showed the conventional screw had the most unmixed white sections, some of it unmelted. 

Gale in Proceedings of a Rapra Technology Ltd., Conference on Injection Moulding Advanced Technology for Optimisation of Operational Performance, 1994, Shawbury, Paper No.4. 

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