Rapra cavity transfer mixer

Although the term CTM is sometimes used to describe all mixers with overlapping stationary and moving slots and cavities, the term was initially used at Rapra Technology Ltd., to differentiate between the staggered row geometry of hemispherical cavities which followed the parallel row Woodroffe key slots used in the A2-B2 mixer described in Chapter 2. 

From the outset, the cavities were comparatively large in comparison to key slots, as from an Erwin paper [16] the cutting and turning mechanism was an adjunct to the lamina shear mixing for the end result of good distributive mixing. 

When scaling up from a 38 mm laboratory extruder to a 120 mm production extruder producing mains water pipe to British Standards there was concern that the following points needed attention  

2) Lands between cavities should be minimised to avoid excessive generation of shear heat. 

The designs of the Metal Box and Barmag mixers appear to emphasise the cutting action, whereas theoretically there is an optimum balance between shear mixing and cutting/turning stages [16], 

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In order to improve the homogeneity of the compound, a device is sometimes attached to the screw head. Among these the Rapra cavity transfer mixer (CTM) is very effective in improving distributive mixing with least resistance to the flow of compound. Figure 12.7 [4]. The improvement of dispersion is not intended. 

RAPRA cavity transfer mixer F>S- 4.4 Typical designs of mixing zones... 

The Cavity Transfer Mixer (CTM) is primarily designed as a distributive mixing device to be used as an add-on unit to existing extruders. The original concept of the Cavity Transfer Mixer was devised by Gale at Rapra. Both parts of the barrel and screw unit have hemispheres cut out of their... 

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. 

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)...

M.F. Edwards and R.W. Shales in Proceedings of a Rapra Technology Ltd, Conference - Making the Most of the Cavity Transfer Mixer, Shawbury, Shrewsbury, UK, 1986, Paper No.2. 

Two of the three suppliers are machinery manufacturers who have no reason to give away much technical information and hence for these two mixers, reliance is placed on two articles from Barmag and a collection of press release type articles from Reifenhauser. The author has therefore (but not entirely) relied mainly on his own work at Rapra Technology on the cavity transfer mixer (CTM). There are a few papers by others on this device but nothing from processors on any of these interacting mixers, but this situation is not unusual. 

E. de Jong in Proceedings of the Rapra Technology Symposium - Making More of the Cavity Transfer Mixer, Rapra Technology, Shawbury,... 

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