Agitating – Rubber or heavy plastic working – With specified feed means
Reexamination Certificate
2002-01-02
2004-01-27
Cooley, Charles E. (Department: 1723)
Agitating
Rubber or heavy plastic working
With specified feed means
C366S076600, C366S081000, C366S085000, C366S090000
Reexamination Certificate
active
06682213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a twin-screw continuous kneading apparatus suitable for efficiently kneading high-polymer resin materials, such as plastic and rubber mixed with additives, to obtain a plastic compound and a rubber compound. The present invention also relates to a kneading method using the twin-screw continuous kneading apparatus.
2. Description of the Related Art
Generally, composite resin materials, such as a plastic compound and a rubber compound, are produced by supplying a powdery additive, such as talc, into a barrel of a kneading extruder, and extruding a high-polymer resin material to be kneaded downstream using a kneading screw, which is inserted in the barrel, while kneading the high-polymer resin material together with the additive. The extruded material is then shaped into products by a post-treating apparatus such as a granulating machine.
A twin-screw continuous kneading apparatus for producing such composite resin materials comprises a barrel having a pair of left and right kneading chambers formed therein in communication with each other, a pair of left and right kneading screws rotatably inserted in the kneading chambers, a first supply unit constituted by, e.g., a screw feeder connected to the upstream end of the barrel and supplying a material to be kneaded into the kneading chambers, and a second supply unit constituted by, e.g., a side feeder connected to a midstream portion of the barrel and supplying an additive into the kneading chambers. A kneading zone for kneading and mixing the additive into the kneaded material is defined along the kneading screws in an area downstream of the second supply unit.
In the kneading zone, rotor segments each having a tip clearance, which allows the kneaded material to positively pass through it, are employed so that high shearing forces are imparted to the kneaded material even under low temperatures. Also, to control a filling rate of the material, a plurality of kneading disks having phases shifted in a direction to push back the material or screw segments having flights twisted in a direction to push back the material are usually provided in the kneading zone.
However, providing those kneading disks or screw segments acting to push back the resin flow in the kneading zone immediately downstream of a point, at which the additive is added to the resin material, may cause the problem in that the filling rate of the material is locally increased in the kneading zone to such an extent as impeding a gas purge toward the downstream side, and the additive cannot be supplied through the side feeder any more. In that event, the feeding capability is reduced and the stable operation is no longer continued.
One conceivable method for overcoming the above-mentioned problem is to construct the kneading zone, which is positioned immediately downstream of the addition point of the additive, only by rotor segments having flights twisted in a direction to feed the resin material without providing the kneading disks and the screw segments.
However, the tip clearance of the rotor segment is set, as mentioned above, to be comparatively larger than those of other kneading segments. Accordingly, if the kneading zone positioned immediately downstream of the addition point of the additive is entirely constructed using such conventional rotor segments, the kneaded material passing through the tip clearances is more likely to adhere to inner wall surfaces of the kneading chambers in the form of layers and to reduce the effective diameter of each kneading chamber. This may result in a reduced throughput and insufficient kneading of the resin material with the mixed additive.
Also, employing the kneading zone, in which the rotor segments having the tip clearances comparatively larger than those of other kneading segments are successively arranged, raises another problem in that a kneading screw is more susceptible to a mechanical damage because of an increased deflection during the rotation thereof, and the kneading screw cannot be rotated at high speeds. This also impedes an improvement of the throughput.
The above-described problems arise not only in the case of mixing a powdery additive into a material to be kneaded, but also in the case in which the material to be kneaded is itself a powdery material having a very small bulk density.
SUMMARY OF THE INVENTION
In view of the state of the art set forth above, it is an object of the present invention to provide a twin-screw continuous kneading apparatus and a kneading method using the twin-screw continuous kneading apparatus, which can stably supply a powdery additive or a powdery material to be kneaded without reducing the production capability, and can greatly increase the throughput of a high-quality compound.
To achieve the above object, a twin-screw continuous kneading apparatus according to the present invention comprises a barrel having a pair of kneading chambers formed therein in communication with each other; a pair of kneading screws rotatably inserted in the kneading chambers; a first supply unit connected to an upstream end portion of the barrel and supplying a material to be kneaded into the kneading chambers; a second supply unit connected to the upstream end portion or a midstream portion of the barrel and supplying an additive into the kneading chambers; an additive feed zone provided by a part of each of the kneading screws corresponding to the second supply unit, the additive feed zone being made up of screw segments; a downstream feed zone provided by a part of each of the kneading screws downstream of the additive feed zone, the downstream feed zone being made up of screw segments; and an additive mixing zone provided by a part of each of the kneading screws downstream of the additive feed zone and between the additive feed zone and the downstream feed zone, the additive mixing zone being made up of rotor segments arranged successively in an axial direction of the kneading screw. A segment group constituting the additive mixing zone satisfies conditions (a) and (b) given below: (a) the segment group comprises only feed segments having flights twisted in a direction to feed the kneaded material downstream with rotation of the kneading screw, or comprises the feed segments and neutral segments having flights parallel to the axial direction of the kneading screw, and (b) each of the rotor segments making up the segment group has flights formed by arranging a high-height tip portion providing a comparatively small tip clearance relative to an inner wall surface of the kneading chamber and a low-height tip portion providing a comparatively large tip clearance alternately in the axial direction in succession.
With the arrangement set forth above, the segment group constituting the additive mixing zone, which is made up of a plurality of rotor segments arranged successively in the axial direction of the kneading screw, comprises only the feed segments or comprises the feed segments and the neutral segments. Thus, any segments, which develop an action to push back a flow of resin (kneaded material) upstream, are not present in the additive mixing zone. It is therefore possible to prevent the filling rate of the kneaded material from being locally increased in the additive mixing zone to such an extent that degassing toward the downstream side would be impeded. As a result, the feeding capability is avoided from deteriorating due to reduced supply of the additive from the second supply unit, and hence the stable operation is ensured.
Also, with the above arrangement, the flights of each rotor segment of the segment group constituting the additive mixing zone are formed by arranging the high-height tip portion providing the comparatively small tip clearance relative to the inner wall surface of the kneading chamber and the low-height tip portion providing the comparatively large tip clearance alternately in the axial direction in succession. Therefore, mixing of the additive into the kneaded material is accelerated
Inoue Kimio
Miyake Koichi
Cooley Charles E.
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sorkin David
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