Plastic article or earthenware shaping or treating: apparatus – With separate and distinct upstream agitating or kneading means – Agitator or kneader comprises means rotating about a...
Reexamination Certificate
2000-09-13
2002-10-22
Cooley, Charles E. (Department: 1723)
Plastic article or earthenware shaping or treating: apparatus
With separate and distinct upstream agitating or kneading means
Agitator or kneader comprises means rotating about a...
C366S077000, C366S087000
Reexamination Certificate
active
06468067
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite extruding apparatus of rubber including a screw extruder and a gear pump, and is suitable for use by connecting it to a die head for extrusion-molding of the rubber. Further, the present invention relates also to a method of extruding unvulcanized rubber with the use of the composite extruding apparatus.
2. Description of the Background Art
As a method of producing an extrusion-molded product of rubber such as a tire tread, a weather strip, a door seal, or a hose of an automobile, there are known a method in which a vulcanizable rubber composition obtained by kneading a rubber material with additives such as a reinforcing agent, a filler, a plasticizer, a vulcanizer, and a vulcanization promoter is fed to an extruder and extruded to a desired shape from the extruder via a die head, and vulcanized with a vulcanizing apparatus after being subjected to a lamination process or the like, such as in the case of a tire tread, or a method in which the vulcanizable rubber composition is guided to a vulcanizing apparatus for vulcanization after extrusion, and then is cut to a desired length to obtain a product, such as in the case of a weather strip.
Generally, a screw extruder is used for the above-mentioned extrusion. In this screw extruder, rubber is conveyed by a screw in a barrel, where the rubber is subjected to friction, shear, and compression between an inner surface of the barrel and an outer surface of the screw, whereby the rubber is self-heated and plasticized to have a viscosity that enables molding. In a conventional type extruder in which a die head is directly connected to the screw via a screen mesh, it has been considered that the longer the length L of the aforesaid screw is, the better it is, in view of the necessity of ensuring a predetermined molding pressure to the die head after the rubber passes through the screen mesh. In other words, it has been assumed that the screw must be provided with a feeding part, a compressing part, and a metering and discharging part, and hence the ratio L/D of the length L to the outer diameter D of the screw has been set to be within a range from 12 to 16 for a rubber at room temperature.
However, if the length of the screw is increased, it requires a larger motive force to that extent, and temperature control for heating and cooling will be required that respectively corresponds to the feeding part, the compressing part, and the metering and discharging part, thereby necessitating a complex temperature control mechanism. Moreover, even if the length of the screw is increased as described above, a plasticizing effect comparable to that of a Banbury mixer cannot be obtained. In order to improve the degree of plasticization with the use of the conventional type extruder, the speed of the screw rotation must be increased. This raises the temperature of the discharged rubber too much and generates scorching of the rubber, making the rubber unmoldable and decreasing the throughput. In addition, there is a problem that, by increasing the length of the screw, the material will remain in a larger amount in changing the lots.
On the other hand, it is known in the prior art that, by connecting a gear pump to a tip end of a screw extruder, the pressure of feeding rubber to a die head is maintained constant to enable precision molding (publication of Japanese Patent application No. 05-116200/1993(A1) (which has the same contents as U.S. Pat. No. 5,156,781)). This known art is constructed in such a manner that the metering and discharging part among the feeding part, the compressing part, and the metering and discharging part of the screw is transferred to the gear pump to allow the two functional areas of the feeding and heating part and the compressing part to remain in the screw, and that the pressure loss generated at the screen mesh and the breaker plate, which is a supporting body of the screen mesh, between the screw extruder and the gear pump is restrained to the minimum extent. Therefore, the total length of the screw has been such that the aforesaid ratio L/D is within a range from 4.5 to 8.5, and also the shape of the rubber passageways before and after the screen mesh and the breaker plate has been complex.
SUMMARY OF THE INVENTION
The present invention provides a composite extruding apparatus of rubber in which, as compared with the known composite type extruding apparatus using a gear pump in combination, the ratio L/D is further reduced to decrease the screw length while maintaining the same screw diameter, whereby the material residue is reduced. The present invention also provides a composite extruding apparatus of rubber in which the throughput can be increased while maintaining the same screw diameter, and the screw motive force is reduced. Further, the present invention provides a composite extruding apparatus of rubber in which the temperature control is facilitated to prevent rubber scorching, and extrusion molding of a vulcanizable rubber composition is made possible at a low temperature. The present invention provides a composite extruding apparatus in which the shape of the rubber passageways before and after the screen mesh can be simplified. In another aspect, the present invention provides a method of extruding an unvulcanized rubber with the use of the aforesaid extruding apparatus.
Thus, the present invention provides a composite extruding apparatus of rubber in which a gear pump is connected to a tip end of a screw extruder via a screen mesh having a breaker plate, and a die head is connected to an ejecting side of the gear pump, wherein the screw extruder plasticizes a fed rubber composition mainly by friction with an inner surface of a barrel and by heating from outside and extrudes the rubber composition from the screen mesh to a space on an inlet side of the gear pump; the screen mesh rectifies the rubber composition passing through the screen mesh towards the gear pump while stirring and plasticizing the rubber composition by friction and shear; and the gear pump further stirs and plasticizes the rubber composition, which is fed to the space on the inlet side, by shear and compression, and gives a forcing pressure to the die head.
In other words, the screw extruder used in the present invention needs to be substantially provided only with the feeding part among the feeding part, the compressing part, and the metering and discharging part, which are needed in conventional extruding apparatus, thereby eliminating the need for the compressing part and the metering and discharging part. Therefore, the length of the screw can be reduced to a great extent while maintaining the thickness (D), thereby all the more simplifying the temperature control mechanism.
The ratio L/D of the length L to the outer diameter D of the aforesaid screw is preferably set to be within a range from 1 to 4, particularly within a range from 2 to 3. Further, it is sufficient that the aforesaid screw extruder can plasticize a rubber composition by heating, and can feed the rubber composition to the gear pump by the rotation of the screw against the resistance of the screen mesh, so that the screw extruder does not need a forcing pressure needed for the rubber composition to pass through the die head. Therefore, the driving motor of the aforesaid screw is reduced in scale as compared with conventional ones. However, if the aforesaid ratio L/D is less than 1, the plasticization by heating the rubber composition will be insufficient, whereas if the ratio exceeds 4, the length will be too large to be economical.
Further, the screen mesh equipped with the breaker of the present invention rectifies the rubber composition, which passes through the screen mesh and its supporting breaker plate towards the gear pump, while stirring and plasticizing the rubber composition with friction and shear. Namely, the rubber composition ejected from the screw extruder and having a twisted shape is passed through the screen mesh and the holes of the breaker plate,
Cooley Charles E.
Fulbright & Jaworski L.L.P.
Toyo Tire & Rubber Co., Ltd.
LandOfFree
Composite extruding apparatus of rubber and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite extruding apparatus of rubber and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite extruding apparatus of rubber and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2974745