A degassing apparatus which has a housing of substantially circular cross-section provided with inlet and outlet apertures for the material to be treated is known.
U.S. Pat. No. 3,470,584 discloses such an apparatus. Such apparatus includes a degassing arrangement which is disposed between two extrusion devices mounted in tandem with respect to one another. The material to be degassed is conveyed, by the first extrusion device, into a chamber formed in the degassing arrangement through the intermediary of a spring-loaded cone or tapered sleeve. This causes the material to enter such chamber in the form of thin layers of material. The interior of the chamber is subjected to a vacuum or to a reduced pressure. The vacuum causes residual monomers and similar volatile substances contained in the molten mass to be removed from the thin layers. The molten mass is then supplied to the second extrusion device and further processed. The degassing effect produced by such an apparatus is, however, minimal, because the creation of the thin film of molten material only during its extrusion into the vacuum chamber limits the amount of gas which can be removed.
In German Patent Specification No. 30 30 541, there is disclosed a multi-shaft kneading disc reactor for the continuous production of degassed polymers. Conveying shafts are disposed in a circular manner around the periphery of a degassing chamber. Each conveying shaft meshes with the conveying shafts disposed adjacent thereto. The intermeshing conveying shafts effectively form the outer periphery of the degassing chamber with the result that a film of molten material is formed on such periphery. Since a vacuum prevails in the degassing chamber, these layers of molten material are degassed.
Such an arrangement therefore provides a degassing chamber having a large surface area and thus produces good degassing results. However, such an arrangement suffers from the disadvantages of the difficulty in sealing the degassing chamber and the difficulty of driving the individual, intermeshing conveyor shafts. Thus, for example, it is necessary to provide a plurality of individual shaft seals, one such seal being required for each conveying shaft. The shafts, which rotate about their own axis but are otherwise static, are disposed in a housing. Such an assembly is described in detail in European Patent Specification No. 0 208 139A.
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