subject: Twin Screw Extruder For Industry [print this page] A twin screw extruder for processing plastic material having a housing provided with a plurality of juxtaposed housing segments arranged axially in succession and defining two longitudinal, overlapping bores respectively containing two coaxially arranged extruder screws, rotatable about respective longitudinal axes, and having intermeshing threads. One of the housing segments serves as a degassing housing segment for degassing the plastic material and it is connected to a degassing chamber. The degassing housing segment has a transverse, radial opening in which an insert member is fitted, the insert member having a degassing opening providing communication between the degassing chamber and the bores in the housing. The degassing opening tapers in widening fashion in the direction from the longitudinal bores to the degassing chamber, and the degassing opening has a longitudinal axis disposed in a plane passing through the longitudinal axes of the screws. The insert member can be mounted at either or both sides of the housing and a sealing insert member is inserted in the opening in the housing segment which is to be blocked. The degassing opening is rectangular in cross-section.
In accordance with a feature of the invention, the inner surface of the projection of the insert member partially covers the circumference of the adjoining longitudinal screw and the inner surface is provided with a localized enlargement to form a gap or pocket with the circumference of the screw in a region where the circumference of the rotating screw travels upwards and away from the insert member. This prevents the melt product from passing into the degassing opening and promotes the surface adhesion of the melt product on the twin screw extruder.
Where this is not the case, such as, for example, in screw housings having degassing openings directed laterally downwards, only plastics within narrow viscosity limits can be processed, so that extensive retooling of the twin screw extruder is necessary for the degassing of different polymer solutions or melts.
