Combined de-airing extrusion

In his Types of extrusion units , Willy Bender investigates all the various kinds of extruders and combined de-airing extrusion machines. 

Table 2 Boundary parameters of extruders and combined de-airing extrusion units used in structural clay industry comparing the levels in 1960 and 2005...

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. 

Classification by the Design Version of the Combined De-airing Extrusion Unit... 

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 ... 

Basically there are two options for connection of the machines that form the combined de-airing extrusion unit ... 

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). 

The compact de-airing extrusion unit is only available in a longitudinal arrangement it has lost much of its importance in relation to the combined de-airing extrusion machine. 

Any combined de-airing extrusion machine consists of an extruder and a primary pug sealer, of which several versions do exist, and therefore the following combinations are possible ... 

Fig. 14 Combined de-airing extrusion unit with vertical primary pug sealer and expansion barrel...

Final observation. Only the most important and commonly used types of extruders and combined de-airing extrusion machines have been listed in this contribution. Bearing in mind the vast variety of options available on the market, there is no pretence to completeness. Especially prototype... 

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...

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

It is a wrong approach, often applied in practical operation, to use overdimensioned vacuum pumps with a high rated throughput instead of amply-dimensioned vacuum pumps with a higher ultimate pressme, except for such cases where the vacuum collapses frequently as a result of insufficient material feed into the combined de-airing extrusion unit or inadequate sealing of the vacuum chamber. 

Quite a few experts entertain fairly vague notions about how much vacuum a combined de-airing extrusion machine can achieve as a function of ... 

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