De-airing mixer

The following table shows the main components of the de-airing mixer and the most important options regarding the design of these parts ... 

Table 7 Components and design options of the de-airing mixer...

The type of combined de-airing extrusion machine can be defined by, amongst other aspects, the configuration of the auger and mixer shafts, by the method of coimection between the extruder and de-airing mixer, as well as by the construction of the de-airing mixer. One differentiates the features accordingly, as shown below ... 

The presence of a substantial constant vacuum in the space between the de-airing mixer and the extruder exerts a major influence on the quality of the extruded body. 

In addition to such mechanical and process-technological prerequisites as a leakage free system and a finely shredded body to ensure a large specific surface, the crucial factors also include the degree of body compaction, i.e., the pressure in the pressure zone of the de-airing mixer. 

Multiple shaft extruders. Some publications quote a classification for multiple shaft extruders referring to combined de-airing extrusion units defined by the sum of their auger shafts, infeed shafts and mixer shafts. This method of categorization is, however, disputed. 

Hot extrusion. Hot extrusion, which involves heating of the clay by the introduction of steam into the combined de-airing extrusion unit, is primarily aimed at reducing the drying time. Most of the factories in the structural clay industry use the benefits of hot extrusion. The steam is usually added at the mixer via a bottom plate in the mixing trough. As a rule the aim is to reach a column temperature of 50-60°C. 

Compact version combined de-airing extrusion unit. With this version, the extruder and mixer form a conjoined single unit with one only common drive, the latter representing a cost benefit and probably the main motivation for the development of this type of construction (Fig. 13). 

Extruder and de-airing double shaft mixer. Thanks to the high throughput capacity, the good mixing properties and the option of steam... 

Extruder and de-airing single shaft mixer. This machine combination is the superior choice for stiff extrusion purposes in the heavy clay industry. One of the reasons for this is the fact that a stiff body could cause warping of the mixer shaft, which could prove to be problematic with a double shaft mixer. 

In the 1960s Messrs. Uniceram SA of Marseille, France, built a hydraulically-driven piston extruder for the stiff extrusion of structural clay products, combined with a de-airing double-shaft mixer, was operated as a combined de-airing extrusion unit (Fig. 5). On the whole however the piston extruder has been of relatively little importance in comparison to the auger extruder within the field of structural ceramics. 

Fig. 5 Combined de-airing extrusion unit with de-airing double-shaft mixer and piston extruder, built by Messrs. Uniceram, Marseille, about 1960...

Heath Company of Plymouth, Ohio, in 1919 for a de-airing machine, which enabled the clay to be de-aired even twice. This was in fact a double piston extruder followed by a mixer (Fig. 44). 

Fig. 47 Combined de-airing extrusion machine comprising of vacuum doubleshaft mixer and auger extruder, 1937...

Vacuum Mixer. A machine for the simultaneous de-airing and moistening of dry, prepared clay as it is fed to a pug. In the original design (L. Walker, Claycraft, 25,76,1951) the clay fell as a powder through a vertical de-airing chamber where water was added as a fine spray from the bottom of the de-airing chamber the moist, de-aired, clay passed into a pug. There have been several developments of this principle. 

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