A tally propellor extruder comprising a lodging, two extruder screws substantiated in said protection for turn in the selfsame itinerary near change, longitudinal axes of move, each of said screws including a vertical and a propellor area having wear secured on the related shaft for turning therewith, the threads of the screw part of one airway interengaging with the vesture of the propellor cutting of the another remark to rise a product longitudinally along the screws.

The present invention relates to a twin screw extruder having two extruder screws rotating in the same direction around parallel axes of rotation, the screws having screw sections with interengaging threads for longitudinally advancing a product.

More particularly, the present invention relates to such a twin screw extruder in which the screws are devoid of threads in a zone between screw sections and a baffle element is secured on one of the screws between the screw sections for effecting a mixing of the material.

In order to carry out different processing operations, it is known to form the screws of a twin screw extruder with different screw sections which consist, in particular, of a succession of screw and kneading elements. Such processing operations are, for example, mixing, melting and homogenizing plastic materials upon the addition of additive and filler elements, by developing shearing forces while maintaining a given temperature profile dependent on the material being processed.

In the twin screw extruder the interengaging threads of the two screws in the housing of the twin screw extruder longitudinally advance the material in a plurality of separate streams and these separate streams of material are combined in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement for confinement around one of the screws whereafter the combined stream is divided back into separate streams downstream of the thread-free zone.

An object of the present invention is to provide a twin screw extruder which permits homogenization by deflection of the flow of the material being processed, with only slight shearing stress, particularly for incorporating additive elements.

This object is achieved according to the invention by providing a baffle element of conical shape which increases uniformly in diameter in the direction of advance of the product.

Due to the gentle deflection of the streams of product, both a homogeneous distribution of temperature in the material being mixed, as well as a homogeneous distribution of the mixture components is obtained with low shearing stress. Upon the admixing of long-fiber reinforcing substances such as, for instance, glass fibers, the fiber length is not substantially decreased during the processing in the twin screw extruder and the percentage of fines thereof is limited to a minimum.The twin screw extruder as constructed according to the invention carries out a unique method in which material is longitudinally advanced by the interengaging threads of the two screws in the form of a plurality of separate streams of material as shown in FIG. 2.

In still further accordance with the invention, the baffle element is constructed to be pushed on the associated shaft and fixed for rotation there with so that replacement of individual baffle elements can be effected simply.

This invention relates to twin screw extruders and more particularly to temper able casings for such twin screw extruders. It is known to use twin screw extruders for processing plastics materials where the internal processing chambers are formed by wear resistant liners. The liners have internal layers which are wear resistant to lengthen the life of the extruding cylinder. To enable the liners to be replaced and to absorb the forces occurring in operation, the liners are surrounded by a supporting member.

When tempering casings of twin screw extruders of this type, that is to say controlling the temperature thereof, difficulty is experienced in obtaining a good even tempering action over the periphery of the spectacle shaped combined bore. The greatest quantity of heat per unit appears in wedge shaped projections between the two longitudinal bores of the liner, while lateral portions of the spectacle bore show less localization heat.A temper able screw casing for a twin screw extruder for processing plastics comprises a supporting member and wear resistant liner disposed therein. The liner has a spectacle shaped bore accommodating both screws of the extruder. The supporting member, which engages around the liner, takes over the reinforcing function of the screw casing. Low technical manufacturing cost and satisfactory tempering of the screw casing is achieved by providing the liner with a circular external cross section, surrounded by a supporting member which has a circular internal recess. Axial tempering holes are provided in wedge shaped projections which extend into the spectacle shaped bore of the liner. Axial tempering holes are disposed opposite one another in the supporting member, at the sides of the spectacle shaped bore of the liner. These result in individual tempering systems, by which the liner and supporting member can be tempered independently.

Another known screw casing with a wear resistant liner has two parallel longitudinal bores. These form a spectacle shaped bore in which the two extruding screws are located. The external cross section of the liner is bounded exclusively by convex or by convex and straight curves. The curves of the external cross section extend through the wedge shaped projections without bending inwards. The purpose of this is to obtain accurate surface contact in the supporting member and thus good heat transfer from the liner to the supporting member, while maintaining the possibility of easy replacement. The special shape of the external cross section of the liner requires a recess of the same cross section in the supporting member. Such a recess in the supporting member of the screw casing is technically expensive to provide and usually a two part supporting member is required.

 

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