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. 

Wang, C. and Manus-Zloczower, I., Flow Field Analysis of a Cavity Transfer Mixer, Polym. Eng. ScL, 34, 1224 (1994)... 

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]...

Add-on s — Barmag add-on torpedo, Staro-mix , Maddox, Cavity Transfer Mixer (CTM), Twente Mixing Ring (TMR), the Extensional Flow Mixer (EFM), Dynamic Melt Mixer (DMX), static or motionless mixers (SM) from Koch, Ross, or Kenics, etc. 

Figure 7.18 Cavity transfer mixer (Courtesy RA PR A, Shrewsbury, UK)...

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. 

See also Dulmadge mixing section, Maddock mixing section, and cavity-transfer mixer. 

Cavity Mixers. One of the well-known cavity mixers is the cavity transfer mixer (CTM). It consists of a screw section and a barrel section, both containing hemispherical cavities (see Fig. 51). 

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. 

Further improvements in the quality of mixing obtained can be brought about by modifying the screw or by the use of special mixing sections, these usually being located in the metering section of the screw. Typical examples of such sections are pins, barriers, Barr type mixing sections and cavity transfer mixers. 

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. 

In Figure 2.3(b) a cavity transfer mixer (CTM) extension (see Chapter 9) has been added to the screw used in Figure 2.3(a) which has eliminated the striations but agglomerates are still present and in the absence of striations are more clearly seen. The greyness gradation is the result of microtomed thickness variation. 

Figure 2.24 Photomicrographs showing improving mix quality over five cavity rows of a cavity transfer mixer nsing HDPE. Adapted with permission from R.W. Shales, Mixing of Thermoplastics in Single Screw Rextruders, Department of Chemical Engineering, University of Bradford UK, 1989. [PhD thesis])...

Figure 2.25 Model Cavity Transfer Mixer with transparent acrylic stator. (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, Figure 8.1. 1984, Rapra Technology)...

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