The Composition of Twin Screw Extruder
A twin screw extruder comprising a cylinder having twin bores therein to receive the twin screw of the extruder and a circular casing with at least one passage to permit heating or cooling fluid to flow between the cylinder and the casing, in which the cylinder has a generally circular outside contour with a first set of grooves and a second set of grooves forming parts of said at least one passage, extending obliquely to the longitudinal axis of the cylinder and formed in the outer surface of the cylinder, the bottom walls of the grooves extending parallel to a plane which includes the two longitudinal axes of the twin bores with the first set of grooves lying on one side of said plane, and the second set of grooves lying on the other side of said plane, the inclination of said first set of grooves to said axis being opposite to the inclination of said second set of grooves to said axis, and the inside of the casing containing spaced recesses forming further parts of said at least one passage and, except for end ones of said recesses, each connecting one end of a respective one of the grooves of the first set of grooves to one end of a respective one of the grooves of the second set of grooves.
The invention relates to single screw extruder comprising a cylinder having bores therein to receive the screw and enclosed by a cylindrical casing, with at least one passage to allow heating or cooling fluid to flow between the cylinder and the casing.
A difficulty encountered in the heating or cooling of cylinders in sheet production extruder where the bores partially overlap, is that the portions of the cylinder which absorb the greatest quantity of heat per unit are inwardly directed wedge-shaped projections at the sides of the region where the twin bores overlap. Such wedge-shaped projections can be cooled adequately only with a large technical outlay.
In previously proposed twin screw extruder, the cylinder enclosing the twin screw is in extended form, i.e. it is constructed with two flat outer faces each extending parallel with the plane in which the axes of the twin bores lie. This cylinder, which is difficult to produce in single screw extruder. The cylinder is surrounded by a circular casing and the gaps between the upper and lower surfaces of the cylinder and the inner wall of the casing are filled with separate chordal segments. Such a twin screw extruder is expensive to manufacture and it is difficult to maintain a seal between the cylinder and the segments.