Two-shaft extruder with screw blade contact preventing mechanism
In a two-shaft extruder, a pair of rotor shafts ( 1 ) is rotatably arranged such that the closer to the head end of the pair, the smaller the distance between the pair. The pair of rotor shafts ( 1 ) is respectively provided with screw blades ( 2 ) mounted on the head end side of the pair. The rotor shafts ( 1 ) are adapted such that one screw blade ( 2 a ) enters gaps of the other screw blade ( 2 b ). Drive devices (M) for rotationally driving the pair of rotor shafts ( 1 ) are mounted on the respective base ends of the pair. The extruder has a screw blade contact prevention mechanism (SS) which, when the pair of rotor shafts ( 1 ) is driven, prevents the pair from having a phase difference greater than a predetermined level.
1. A two-shaft extruder comprising:
a pair of rotor shafts rotatably disposed with a distance therebetween diminishing toward the leading ends thereof; and
a screw blade mounted to the leading end of each one of the pair of rotor shafts, one screw blade intruding into the pitch of the other screw blade; and a drive unit mounted the base end of each one of the pair of rotor shafts for rotatably driving the rotor shaft associated therewith without the use of conical gears for synchronizing the drive of the pair of rotor shafts;
wherein there is provided a screw blade contact preventing mechanism configured to allow a predetermined phase difference between the pair of rotor shafts, while inhibiting a phase difference greater than the predetermined phase difference when the pair of rotor shafts are rotatably driven respectively,
wherein said screw blade contact preventing mechanism includes:
a first abutment member comprised of a plurality of projecting portions formed in one rotor shaft along the peripheral direction thereof and equidistantly or substantially equidistantly from each other; and
a second abutment member comprised of a plurality of projecting portions formed in the other rotor shaft along the peripheral direction thereof and equidistantly or substantially equidistantly from each other;
a path of the projecting portions of the first abutment member and a path of the projecting portions of the second abutment member are configured to interfere with each other; and
between a projecting portion of the first abutment member and a projecting portion of the second abutment member peripherally opposed thereto, there is provided a gap for allowing the predetermined phase difference between the pair of rotor shafts, while inhibiting a phase difference greater than the predetermined phase difference.
2. The two-shaft extruder according to claim 1 , wherein a plurality of sets of the first abutment members and the second abutment members are provided along the longitudinal direction of each rotor shaft;
the projecting portions of the first abutment member belonging in a certain set are made different in position peripherally as seen in the axial direction of the one rotor shaft than the projecting portions of the first abutment member belonging in another set adjacent thereto; and
the projecting portions of the second abutment member belonging in a certain set are made different in position peripherally as seen in the axial direction of the other rotor shaft than the projecting portions of the second abutment member belonging in another set adjacent thereto.
3. The two-shaft extruder according to claim 2 , wherein the extruder further comprises:
a rotational speed detecting means for detecting a rotational speed of each one of the first abutment member and the second abutment member; and
a controlling means for calculating a cycle ratio between the cycle of the first abutment member and the cycle of the second abutment member from the rotational speeds detected by the rotational speed detecting means and also for executing synchronization control scheme for each one of the pair of drive units such that said cycle ratio becomes equal to 1 (one).
4. The two-shaft extruder according to claim 1 , wherein the extruder further comprises:
a rotational speed detecting means for detecting a rotational speed of each one of the first abutment member and the second abutment member; and
a controlling means for calculating a cycle ratio between the cycle of the first abutment member and the cycle of the second abutment member from the rotational speeds detected by the rotational speed detecting means and also for executing synchronization control scheme for each one of the pair of drive units such that said cycle ratio becomes equal to 1 (one).
5. The two-shaft extruder according to claim 4 , wherein the extruder further comprises:
a phase difference generating commanding means for issuing a phase difference generating command; and
wherein in response to input of the phase difference generating command to said phase difference generating commanding means, said controlling means executes a phase difference generating control scheme for each one of the pair of drive units with priority over said synchronization control scheme such that the predetermined phase difference is generated between the pair of rotor shafts.