Screw-type extruder

Abstract

A screw extruder which extrudes a kneaded material includes a screw having a helical flight provided on an outer peripheral surface of a shaft portion thereof, and a chamber housing the screw. In the screw extruder, a flight thickening portion is provided at a part which is a tip portion of the flight and is on the reverse side of a rotation direction of the flight.

Claims

1. A screw extruder which extrudes a kneaded material, comprising: a screw having a helical flight provided on an outer peripheral surface of a shaft portion thereof; and a chamber housing the screw, wherein a flight thickening portion is provided at a part which is a tip portion of the flight and is on the reverse side of a rotation direction of the flight; the flight thickening portion extends from the tip portion, along the flight toward the shaft portion, to a reverse surface of the flight thickening portion; the reverse surface of the flight thickening portion is disposed such that a gap is formed between the reverse surface of the flight thickening portion and the shaft portion; and a thickness of the flight is uniform from the tip portion to the shaft portion.

2. The screw extruder according to claim 1, wherein: an outer peripheral surface of the tip portion where the flight thickening portion is provided is formed in an arc shape in the rotation direction of the flight; and at least a part of an inner wall surface of the chamber has an arc shape so that a gap having a uniform dimension is formed between the at least a part of an inner wall surface of the chamber and the outer peripheral surface of the tip portion including the flight thickening portion.

3. The screw extruder according to claim 1, wherein the flight thickening portion decreases in thickness toward a center of the shaft portion.

4. The screw extruder according to claim 1, wherein the chamber includes: a chamber upstream portion including, at a top portion thereof, a kneaded material supply port; and a chamber downstream portion having a periphery surrounded by a wall surface, and wherein the part including the flight thickening portion in the flight is disposed in the chamber downstream portion.

5. The screw extruder according to claim 3, wherein the chamber includes: a chamber upstream portion including, at a top portion thereof, a kneaded material supply port; and a chamber downstream portion having a periphery surrounded by a wall surface, and wherein the part including the flight thickening portion in the flight is disposed in the chamber downstream portion.

6. The screw extruder according to claim 4, wherein the part of the flight disposed in the chamber downstream portion comprises a plurality of flight portions.

7. The screw extruder according to claim 5, wherein the part of the flight disposed in the chamber downstream portion comprises a plurality of flight portions.

8. The screw extruder according to claim 2, wherein the flight thickening portion decreases in thickness toward a center of the shaft portion.

9. The screw extruder according to claim 2, wherein the chamber includes: a chamber upstream portion including, at a top portion thereof, a kneaded material supply port; and a chamber downstream portion having a periphery surrounded by a wall surface, and wherein the part including the flight thickening portion in the flight is disposed in the chamber downstream portion.

10. The screw extruder according to claim 8, wherein the chamber includes: a chamber upstream portion including, at a top portion thereof, a kneaded material supply port; and a chamber downstream portion having a periphery surrounded by a wall surface, and wherein the part including the flight thickening portion in the flight is disposed in the chamber downstream portion.

11. The screw extruder according to claim 9, wherein the part of the flight disposed in the chamber downstream portion comprises a plurality of flight portions.

12. The screw extruder according to claim 10, wherein the part of the flight disposed in the chamber downstream portion comprises a plurality of flight portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A plan cross-sectional view of an extruder with roller-die as an embodiment of a screw extruder in the present invention.

(2) FIG. 2 A cross-sectional view of II-II in FIG. 1 and a longitudinal cross-sectional view of the extruder with roller-die in the embodiment of the present invention.

(3) FIG. 3 A schematic cross-sectional view of a first screw side of a III-III cross-sectional view in FIG. 2.

(4) FIG. 4 A schematic cross-sectional view corresponding to FIG. 3 for explaining analysis conditions for a flow analysis.

(5) FIG. 5 A schematic cross-sectional view corresponding to FIG. 3 for showing a modification of a flight thickening portion.

(6) FIG. 6 A schematic cross-sectional view corresponding to FIG. 3 for showing a modification of a flight.

DESCRIPTION OF EMBODIMENTS

(7) Hereinafter, embodiments for carrying out the present invention are described with reference to the drawings. The screw extruder shown in the following embodiment(s) is a screw extruder with roller-die (hereinafter, referred to as “extruder with roller-die) that extrudes a kneaded material of a high-polymer such as rubber and molds into a sheet form. The screw extruder in the present invention is also usable for a machine called pelletizer that extrudes a kneaded material of a high-polymer from a die having a multiplicity of circular holes, and then, cut it into cylindrical pellets.

(8) (Structure of the Extruder with Roller-Die)

(9) With reference to FIG. 1 to FIG. 3, an extruder with roller-die 1 in an embodiment of the present invention is described. The extruder with roller-die 1 includes two screws (a first screw 2 and a second screw 3) that extrude a kneaded material and a chamber 4 housing the screws 2 and 3. In front of the chamber 4, a pair of upper and lower rollers 9 and 10 are disposed. Between the chamber 4 and the rollers 9 and 10, an accumulation portion 11 where the kneaded material extruded by the screws 2 and 3 accumulates is provided. The rollers 9 and 10 are coupled so as to rotate in directions opposite to each other. The rollers 9 and 10 are called a roller die.

(10) The chamber 4 includes a chamber upstream portion 14 including, at the top, a kneaded material supply port 14a and a chamber downstream portion 24 having its periphery surrounded by a wall surface. The kneaded material such as rubber supplied to the kneaded material supply port 14a from thereabove is extruded into the accumulation portion 11 by the screws 2 and 3 rotating in directions opposite to each other, and then, is formed into a sheet form by passing it between the rollers 9 and 10.

(11) The screws 2 and 3 are described below. Since the first screw 2 and the second screw 3 are the same screws except that the torsion angles of the flights are opposite to each other, the first screw 2 is described as a representative.

(12) The first screw 2 includes a shaft portion 6 and a helical flight 7 provided on the outer peripheral surface of the shaft portion 6. As shown in FIG. 3, a rib 8 as a flight thickening portion is provided at a part which is a tip portion of the flight 7 and is on the reverse side of the rotation direction R of the flight 7. An outer peripheral surface 7a of the tip portion of the flight 7 and an outer peripheral surface 8a of the tip portion of the rib 8 are flush surfaces having no level difference therebetween, and are flush arc-shaped surfaces in the rotation direction R. The rib 8 may be fixed to the reverse surface of the flight 7 by welding or the like, or may be molded integrally with the flight 7. In FIG. 1 and FIG. 2, illustration of the rib 8 is omitted.

(13) Here, as shown in FIG. 3, a part of an inner wall surface 4a of the chamber 4 (the chamber downstream portion 24) is an arc shape so that a uniform gap S is formed between the outer peripheral surface 7a of the tip portion of the flight 7 including the rib 8 and the outer peripheral surface 8a.

(14) Moreover, a reverse surface 8b of the rib 8 is a slanting surface so that the thickness of the rib 8 continuously decreases toward the center O side of the shaft portion 6,

(15) The rib 8 (the flight thickening portion) is continuously provided on the reverse surface of the flight 7 in the rotation direction R, in a direction in which the flight 7 extends helically. That is, the rib 8 (the flight thickening portion) is a belt-like member having a shape shown in FIG. 3 in the cross-sectional shape.

(16) The part of the flight 7 where the rib 8 is provided is disposed inside the chamber downstream portion 24 the periphery of which is surrounded by the wall surface. The rib 8 may be provided on the reverse surface of the tip portion of also the part of the flight 7 disposed inside the chamber upstream portion 14. Further, the rib 8 may be provided on the reverse surface of the tip portion of only the part of the flight 7 disposed inside the chamber upstream portion 14.

(17) While the flight 7 is a single flight from end to end in the axial direction in the embodiment shown in FIG. 1 and FIG. 2, it is preferable that a part of the flight 7 that is inside the chamber downstream portion 24 and where the rib 8 is provided includes a plurality of flight portions, for example, two flight portions.

(18) (Flow Analysis of the Kneaded Material)

(19) A two-dimensional flow analysis was performed for the screw 2 where the rib 8 as the flight thickening portion was provided at a part which was the tip portion of the flight 7 and was on the reverse side of the rotation direction R of the flight 7.

(20) With reference to FIG. 4, the analysis conditions for the flow analysis are described below. First, not twin screws as described above, that is, the two screws 2 and 3 but one screw 2 was housed in the chamber 4 that was circular in cross section.

(21) The common analysis conditions were as follows:

(22) Inner diameter of the chamber 4: D mm

(23) Diameter of the shaft portion 6 of the screw 2: 0.5 D mm

(24) Thickness T of the flight 7 of the part where the rib 8 is not provided: 0.05 D mm

(25) Number of rotations of the screw 2: 15 rpm

(26) Viscosity and density of the kneaded material: 1000 Pa.Math.s and 1000 kg/m

(27) Regarding the flight in a comparative example (flight including, at the tip portion, no flight thickening portion) and also the flight in the present invention, the outer peripheral surface of the tip portion thereof (for the flight in the present invention, the rib portion was included) had a concentric arc shape along the arc of the inner wall surface 4a of the chamber 4.

(28) The gap S between the flight 7 and the inner wall surface 4a of the chamber 4, the thickness W of the tip portion of the flight 7 and the filling ratio of the kneaded material inside the chamber 4 were changed, and the energy applied to the kneaded material was evaluated. The magnitude of the energy applied to the kneaded material was evaluated by the average rotation torque of the screw 2 when the screw 2 was rotated twice. The fact that the torque is high (or low) indicates that the energy applied to the kneaded material is high (or low). The analysis results are shown in Tables 1 and 2. In Tables 1 and 2, the average rotation torques of the flight under each of the conditions are represented by the ratio as the case where the average rotation torque when the gap S is 0.01 D and the filling ratio is 100% regarding the flight in the comparative example (the flight tip portion thickness W: 0.05 D) where the flight thickening portion is not provided at the tip portion is 1,000.

(29) TABLE-US-00001 TABLE 1 Filling ratio: 100% Thickness W of tip Average rotation Gap S portion of flight torque [mm] [mm] [-] 0.01D 0.05D 1.000 Comparative Example 0.01D 0.10D 1.060 Present Invention 0.01D 0.15D 1.167 0.01D 0.20D 1.250 0.02D 0.05D 0.838 Comparative Example 0.02D 0.10D 0.880 Present Invention 0.02D 0.15D 0.912

(30) TABLE-US-00002 TABLE 2 Filling ratio: 90% Thickness W of tip Average rotation Gap S portion of flight torque [mm] [mm] [-] 0.01D 0.05D 0.856 Comparative Example 0.01D 0.10D 0.884 Present Invention 0.01D 0.15D 0.991 0.01D 0.20D 1.213

(31) As is apparent from Tables 1 and 2, the larger the thickness W of the tip portion of the flight 7 is, the higher the average rotation torque (the energy applied to the kneaded material) is. From this, it is found that the dispersion mixing property of the kneaded material is improved by providing the rib 8 (the flight thickening portion) at the tip portion of the flight and increasing the thickness W of the tip portion of the flight.

(32) Regarding the filling ratio of the kneaded material, from the comparison of analysis results when the gap S was 0.01 D mm in Table 1 and Table 2, it is found that the higher the filling ratio is, the higher the energy applied to the kneaded material is. From this, the use of the screw 2 where the thickness W of the tip portion of the flight 7 is large under the condition where the filling ratio of the kneaded material is high is more effective for improving the dispersion mixing property of the kneaded material. That is, the filling ratio of the kneaded material is higher in the chamber downstream portion 24 having the periphery surrounded by the wall surface than in the chamber upstream portion 14 where the kneaded material supply port 14a is provided. For this reason, as mentioned above, it is preferable that the part of the flight 7 where the rib 8 is provided be disposed inside the chamber downstream portion 24 having the periphery surrounded by the wall surface.

(33) Further, by disposing the part of the flight 7 where the rib 8 is provided as having a plurality of flight portions (making the number of flights plural) inside the chamber downstream portion 24 where the filling ratio of the kneaded material is high, the energy applied to the kneaded material can be made higher and the dispersion mixing property of the kneaded material can be further improved.

(34) Moreover, from the above-described flow analysis results, it has been found that in a screw in the comparative example where the flight thickening portion is not provided on the reverse side of the tip portion of the flight, the kneaded material readily accumulates on the reverse side of the tip portion of the rotating flight. When the kneaded material accumulates, cooling of the kneaded material is inhibited, so that high temperature state continues for a long time. The continuation of the high temperature state causes deterioration of the kneaded material, so that kneading quality is degraded. From this, as in the above-described embodiment(s), by the provision, on the reverse side of the tip portion of the flight, of the rib 8 (flight thickening portion) having the thickness which continuously decreases toward the center side of the screw shaft, the accumulation of the kneaded material at this portion can be prevented. Thus, the deterioration of the kneaded material can be inhibited.

Modifications

(35) FIG. 5 shows a modification of the flight thickening portion. The rib 8 as the flight thickening portion shown in FIG. 3 and FIG. 4 is formed so that the thickness of the rib 8 continuously decreases toward the center O side of the shaft portion 6 of the screw. Instead of this, it may be a rib with a substantially uniform thickness like a rib 12 (flight thickening portion) shown in FIG. 5.

(36) FIG. 6 is a modification of the flight. The thickness of the flight 7 (flight body portion) shown in FIG. 3 to FIG. 5 is uniform from the base end portion which is the center O side portion of the shaft portion 6 toward the tip portion. Instead of this, it may be a flight that is thick at the base end portion and becomes thinner from the base end portion toward the tip portion like a flight 13 shown in FIG. 6. In other words, it may be a flight that becomes thicker (increases in thickness) from the tip portion toward the base end portion. By adopting such a flight, the flight strength can be enhanced and the accumulation of the kneaded material between flights can be further prevented.

(37) Moreover, while the outer peripheral surfaces of the tip portions of the flights 7 including the ribs 8 or 12 shown in FIG. 3, FIG. 4 and FIG. 5 are all arc-shaped in the rotation direction of the flights 7, they are not necessarily arc-shaped (the same applies to the flight 13 shown in FIG. 6). That is, the gap between the outer peripheral surface of the tip portion of the flight including the flight thickening portion and the inner wall surface of the chamber does not necessarily have uniform dimension.

(38) While the extruder 1 with roller-die shown in FIG. 1 and FIG. 2 is a screw extruder including twin screws, that is, the screws 2 and 3, it may be a screw extruder including only one screw or may be a screw extruder including three or more screws.

(39) In addition, various modifications may be made within the scope that one of ordinary skill in the art can arrive at.

(40) As described above, the present invention is not limited to the above-described embodiment(s) but combining the structures of the embodiment(s) with each other, and modifications and applications by one of ordinary skill in the art based on the description of the specification and known art are also what the present invention targets and are embraced in the scope the protection of which is claimed.

(41) The present application is based upon Japanese Patent Application No. 2016-84212 filed on Apr. 20, 2016, the contents of which are incorporated herein by reference.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

(42) 1: Extruder with roller-die (screw extruder) 2: First screw (screw) 3: Second screw (screw) 4: Chamber 4a: Inner wall surface 6: Shaft portion 7: Flight 8: Rib (flight thickening portion) 7a, 8a: Outer peripheral surface 9, 10: Roller 14: Chamber upstream portion 14a: Kneaded material supply port 24: Chamber downstream portion S: Gap