Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Of varying cross-sectional area or with intermittent...
Reexamination Certificate
1998-09-17
2001-03-20
Michl, Paul R. (Department: 1714)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Of varying cross-sectional area or with intermittent...
C425S382300
Reexamination Certificate
active
06203740
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an extrusion method in which material is extruded by an extruder comprising at least two annular conical feed gaps one within the other, provided between a rotatable rotor and a stator, in the method, extrudable material is extruded from the extruder by means of primarily helical curve-shaped grooves located in the rotor and/or the stator between the rotor and the stator and by means of flights located between the grooves.
The invention also relates to an extruder that comprises at least two annular conical feed gaps one within the other, provided between a rotatable rotor and a stator; the rotor and/or stator comprising at least primarily helical curve-shaped grooves and flights between them to extrude the extrudable material from the extruder.
BACKGROUND OF INVENTION
The invention further relates to a product extruded with the method.
U.S. publication 3,314,108 discloses an extruder comprising two conical stators and a conical rotor rotatably arranged between the stators. The plastic material to be extruded is supplied via two different conduits to different sides of the rotor. The rotor is provided with helical grooves by means of which the material is transferred towards an orifice at the narrower end of the extruder. The flows of material on different sides of the rotor exert a force on the rotor, whereby the bearings of the rotor must be very firm. Further, the clearances between the rotor and the stator should be adjusted carefully so as to prevent a back flow of the extrudable material back toward the material inlet. A small clearance is naturally a difficult structure to implement, and excess friction is easily generated between the rotor and the stators. On the other hand, a bigger clearance would add to the back flow and thereby reduce extruder output.
EP 0,422,042 discloses an extruder with a plurality of conical stators and conical rotors rotatably arranged between them. The extrudable material is fed via one conduit to the forward end of each rotor, the rotor comprising, at the inlet, holes through which the material can also flow to the other side of the rotor. The material is transported to the end of the extruder by means of grooves arranged on both sides of the rotor. The different sides of the rotor are also subject to great forces in this device, requiring firm bearings. A further problem is a back flow over the flights between the grooves back toward the material inlet and an accurate arrangement of clearances between the rotors and stators.
U.S. Pat. No. 3,689,181 discloses an extruder comprising a plate-like rotor and a plate-like stator. Recesses and protrusions are arranged in the rotor and the stator so as to improve the mixing of the material. The material is extruded from the extruder mainly by centripetal force, making the extruder quite ineffective. Furthermore the structure of the extruder is such that it requires very firm bearings.
GB 2,202,783 describes an extruder with a plurality of partially conical rotors on top of each other. The rotors are provided with grooves that transport the extrudable material out of the extruder. The grooves may be provided with mixing means, e.g. rods, to reduce the cross-sectional area of the groove. These means mix the material, but they significantly hamper material flow and thus reduce extruder output.
SUMMARY OF INVENTION
It is an object of this invention to provide an extrusion method and an extruder in which the above drawbacks can be avoided. It is a further object of the invention to provide an extruded product with good characteristics.
The extrusion method of the invention is characterized in that at least part of the extrudable material is subjected alternately to higher and lower pressure in the feed gaps of the extruder, the flow rate of the material alternately increasing and decreasing, and that at least part of the extrudable material is led from one groove to another.
The extruder of the invention is further characterized in that the extruder is arranged to subject at least part of the extrudable material alternately to higher and lower pressure and to lead at least part of the extrudable material from one groove to another.
The extruded product of the invention is further characterized in that the product contains orienting material, such as liquid crystal polymer.
It is an essential idea of the invention that the extruder comprises at least two annular conical feed gaps one within the other, and that at least part of the extrudable material is subjected alternately to a higher and then to a lower pressure in the different feed gaps of the extruder. The idea of a preferred embodiment that in order to provide the desired pressure effect, at least part of the extrudable material is led alternately to a lower and then to a higher space. It is the idea of another preferred embodiment that the flights between the grooves that supply the extrudable material are bevelled so that the extrudable material can flow in the circumferential direction of the device, but owing to the pressure effect, axial back flow can be prevented. The idea of a third embodiment that the groove supplying material is arranged to become shallower and deeper in the flow direction of the material, and at the end of the shallowing portion the rotor or stator between the feed gaps comprises an hole via which at least part of the material can flow to the other side of the rotor or stator. If desired, the holes can be formed conical, i.e. they can be arranged to converge.
It is an advantage of the invention that by a varying pressure effect on different sides of the rotor or stator the rotor or the stator enables balancing the rotor or stator between two different feed gaps so that the pressure effect provides a hydrodynamic bearing, the other bearings of the rotor or the stator being subject to little or no force at all during operation of the extruder, whereby the structure of the other bearings can be lighter since they do not need to endure great forces during their whole service life. A further advantage is that the extrudable material can be efficiently mixed. When the material is led alternately to a lower and a higher space, the extrudable material can be heated further by friction heat generated by shear forces. At the same time heat transmission and consequently temperature equalization improves as the materials pass via a lower space. Furthermore, as the product is subjected to a higher pressure, a product can be produced in which orientation can be generated as the flow cross-sectional surface converges. By arranging holes in the rotor or the stator through which the material supplied to the lower point can flow from one feed gap to another, the possible pressure difference in different parts of the rotor or stator can be evened out, which further reduces the force exerted on the rotors or the stators. When the holes are arranged to converge, the material passing through can be oriented in the converging through-holes. When the flights between the grooves that transport the material are bevelled, in the flight will be formed a pressure function, by the action of which the axial back flow of the equipment can be reduced. The clearance between the rotor and the stator can, however, also be made bigger without excessive increase in the back flow, the friction between the rotor and the stator being reduced to a minimum.
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patent: 3776679 (1973-12-01), Hegler
patent: 4006599 (1977-02-01), Hegler
patent: 4300840 (1981-11-01), Kishihiro
patent: 5060698 (1991-10-01), Anastassakis
patent: 5156785 (1992-10-01), Zdrahala
patent: 5387386 (1995-02-01), Kirjavainen
patent: 5538411 (1996-07-01), Gates
patent: 5690972 (1997-11-01), Planeta
Jarvenkyla Jyri
Kirjavainen Kari
Ladas & Parry
Michl Paul R.
Nextrom Holdings S.A.
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