Extruders, Cavity Transfer Mixer

The cavity transfer mixer (CTM) is a distributive mixing device used as an add-on unit to extruders the barrel and screw have hemispheres cut out of their surfaces to give an overlap of half a pitch. 

Fig. 23. Screw sections for enhancing distributive mixing in single-screw extruders (a) Dul-madge mixer, (b) Saxton mixer, (c) pin mixer, (d) pineapple mixer, (e) cavity transfer mixer, (f) slotted screw flight, (g) Kenics and Ross ISG static mixers [148]...

Cavity-transfer mixer n. A two-piece device installed at the end of an extruder screw to accomplish both distributive and dispersive mixing. The stator is a barrel extension into whose inside surface is machined an array of many hemispherical cavities. The rotor is a screw extension whose exterior is similarly contoured. The lands of rotor and stator have the usual close clearance of screw and barrel. As the melt steam passes through, it is smeared between the lands and is repeatedly cut into small globs and recombined, passing from rotor to stator, stator to rotor, until it emerges. 

Internal modifications. Here belong the screw modifications, as well as the devices that need to be attached to the screw, e.g., Barmag s torpedo, RAPRA s cavity transfer mixer (CTM), a multi-screw planetary unit. All three examples also require modification of the corresponding barrel section. By contrast, the developed in the University of Twente torpedo with perforated, freely rotating sleeve, can be used without affecting the barrel, e.g., to improve mixing of the injection molding extruders. 

Following work with an independently driven mixer, subsequent trials with a 38 mm extruder having a cavity transfer mixer attached as a screw and barrel extension gave acceptable transparency. 

Photomicrographs in Figure 7.19 of cross sections of strands extruded at 80 rpm show no significant improvement in mixing by using this particular barrier screw. The cavity transfer mixer is covered in Section 9.4. 

Figure 8.23 Photomicrographs of extruded mixer samples at varying speeds. Reproduced with permission from G.M. Gale, Development of the Cavity Transfer Mixer for Plastics Extrusion, Rapra Members Report No. 104, Rapra Technology, Shawbury, Shrewsbury, UK, 1984)...

Results are presented of studies, carried out using a cavity transfer mixer, of means of avoiding the defect of extruder marking in extmsion strip winding of large rubber articles. FINLAND SCANDINAVIA WESTERN EUROPE... 

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