Funnel Member For Single Screw Extruder
The funnel member of a single screw extruder comprises a housing and a feed twin screw extruder which passes at least partially axially therethrough and is sealed from the drive shaft by a return feed screwthread covered by a bushing which is fixed with respect to the housing. The feed screw is enveloped by a grooved sleeve having take-in grooves which are parallel to the axis and become shallower in the feeding direction. For charging the material, the funnel member is provided with an eccentric filling aperture tangential to the feed screw. To reduce torque and pressure fluctuations caused in the charged thermoplastic masses by the threads of the screw running past the single aperture.
The invention relates to a funnel member for a sheet production extruder, comprising a housing and a feed screw which passes at least partially axially therethrough and is sealed from the drive shaft by a return feed screwthread covered by a bushing which is fixed with respect to the housing, a grooved sleeve enveloping the feed screw and having take-in grooves which are parallel to the axis and become shallower in the feeding direction, and an eccentric filling aperture tangential to the feed screw.
It is known to provide the take-in zone in the region of the funnel member of the cylindrical extruder housing with a so-called grooved sleeve which is provided over a certain axial length with take-in grooves which are parallel to the axis, become increasingly shallower and merge with the cylindrical bore of the housing and inhibit turning of the granulate so as to increase the feeding capacity of the screw extruder. More accurate investigations have shown that, for each revolution of the screw, torque or pressure fluctuations in the order of +/-2% are produced in the thermoplastic mass, which influence the longitudinal tolerances of the extruded product and have a disadvantageous effect.
Funnel members with an eccentric filling aperture tangential to the feed screw are known and they serve to improve the supply of granulate By reason of the eccentric tangential aperture, the width of this aperture amounts to only about half the diameter of the feed screw. In order nevertheless to achieve adequate filling during high screw speeds, the axial length of the tangential aperture was extended up to 2.5 D (where D=diameter of the feed screw). In the known funnel member, the grooved sleeve which is provided on its inner face with uniformly circumferentially distributed take-in grooves extends along the zone of the filling aperture and is provided with an opening corresponding to the aperture cross-section of the filling aperture. Even in known funnel members with an eccentric tangential filling twin screw extruder, one still encounters periodic pressure increasing feed thrusts for each revolution of the single screw extruder.