Description of the twin screw extruder
Description of the twin screw extruder
This invention relates totwin screw extruder and more particularly to temperable casings for such twin screw extruders.
It is known to use single screw extruder 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 occuring in operation, the liners are surrounded by a supporting member.
When tempering casings of screw extruder 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 localisational heat.
In a known tempering means for sheet production extruder of this type, spiral external grooves are formed in the periphery of the liner. A spiral tempering passage is thus formed upon insertion of the liner into the supporting member. However, forming a good seal between the liner and the supporting member has been found to be a problem.
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.
Thetwin screw extruderhas among its objects to provide a casing for a twin screw extruder which can be manufactured with relatively low technical outlay and which nevertheless enables the casing to be satisfactorily tempered.
This invention relates totwin screw extruder and more particularly to temperable casings for such twin screw extruders.
It is known to use single screw extruder 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 occuring in operation, the liners are surrounded by a supporting member.
When tempering casings of screw extruder 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 localisational heat.
In a known tempering means for sheet production extruder of this type, spiral external grooves are formed in the periphery of the liner. A spiral tempering passage is thus formed upon insertion of the liner into the supporting member. However, forming a good seal between the liner and the supporting member has been found to be a problem.
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.
Thetwin screw extruderhas among its objects to provide a casing for a twin screw extruder which can be manufactured with relatively low technical outlay and which nevertheless enables the casing to be satisfactorily tempered.