CAVITY TRANSFER MIXING EXTRUDER

Abstract: A cavity transfer mixing extruder comprises an extrusion unit and a mixing unit, arranged coaxially. The extrusion unit comprises a barrel provided with a feed opening through which materials are fed into the barrel, and a screw shaft coaxially and rotatably extended through the barrel. The mixing unit comprises a housing (20), a stator (21) fixedly fitted in the housing (20) and a first cavity group including circumferential cavity rows of cavities (23) in its inner circumferencial portion, and a rotor (22) joined coaxially to the front end of the screw shaft, coaxially rotatably extending through the stator (21), and provided with a second cavity group including circumferential cavity rows of cavities (24) in its outer circumferencial portion. The respective cavities of the first and second cavity groups, when developed on a plane, each has a parallelogrammic shape defined by a pair of opposite, parallel straight walls extending perpendicularly to the axial direction, and a pair of opposite, parallel straight walls inclined at an angle to the axial direction. The longitudinal axes of the cavities of the first cavity group, and the longitudinal axes of the cavities of the second cavity group are inclined in opposite directions, respectively, with respect to the axial direction so that the materials filling the cavities are mpelled forward as the rotor is rotated relative to the stator.

Description: The present invention relates to a cavity transfer mixing extruder for uniformly mixing and extruding highly viscous materials, such as molten plastics or fluid rubbers, and, more specifically, to a cavity transfer mixing extruder having a stator provided with cavities of improved shape in the inner circumference and a rotor provided with cavities of improved shape in the outer circumference, and capable of achieving satisfactory extrusion of the materials. Cavity transfer mixing extruders for uniformly mixing and extruding highly viscous materials, such as molten plastics or fluid rubbers, are disclosed in Japanese Patent Provisional Publication Nos. 60-107306 and 57-87344. The cavity transfer mixing extruder disclosed in Japanese Patent Provisional Publication No. 60-107306 is illustrated in Figs. 10 to 12. As illustrated in Fig. 10, the cavity transfer mixing extruder has a cylindrical housing 1, a cylindrical stator 2 fixedly fitted in the cylindrical housing 1, a cylindrical rotor 3 coaxially and rotatably extended within the stator 2. The rotor 3 is connected at one end thereof to an extruding member such as a screw shaft, and is driven for rotation by a motor. As illustrated in Fig. 12, a group of cavities 8 comprising cavity rows 6 arranged along the axial direction Y-Y and each having a plurality of cavities 4 arranged side by side along the circumferential direction X-X, and a cavity group 9 comprising cavity rows 7 arranged along the axial direction Y-Y and each having a plurality of cavities 5 arranged side by side along the circumferential direction X-X are formed in the inner circumference of the stator 2 excluding the opposite ends thereof and in the outer circumference of the rotor 3 excluding the opposite ends thereof, respectively. The respective cavities 4 and 5 of the cavity groups 8 and 9 are arranged close to each other at very small intervals so that the cavities 4 and 5 are densely distributed. The respective cavities 4 and 5 of the succeeding cavity rows 6 and 7 of the cavity groups 8 and 9 are spaced by a distance ℓx along the circumferential direction in the respective directions or relative rotation of the cavity groups 8 and 9, namely, in a direction opposite the direction R of rotation of the rotor 3 for the cavity group 8 of the stator 2 and in the direction R of rotation of the rotor 3 for the cavity group 9 of the rotor 3, relative to the respective adjacent cavities 4 and 5 of the adjacent preceding cavity rows 6 and 7, respectively. The cavities 4 of the cavity rows 6 of the cavity group 8 of the stator 2 are spaced by a distance ℓy corresponding to a half the axial pitch (interval along the axial direction Y-Y) of the cavity rows 6 and 7 relative to the corresponding cavities 5 of the cavity group 9 of the rotor 3. Accordingly, the cavities 4 of each cavity row 6 of the cavity group 8 overlap the adjacent cavities 5 of the two adjacent cavity rows 7 of the cavity group 9. As illustrated in Fig. 11, each cavity 4 (5) has an oblong shape consisting of a rectangular section 10 (11) and a pair of semicircular sections 12 (13) formed at the opposite ends of the rectangular section 10 (11). The respective center axes 14 and 15 of the cavities 4 and 5 of the cavity groups 8 and 9 are inclined at the same angle ϑ to the direction of extrusion Z, hence to the axial direction Y-Y, to the left and to the right, respectively. In mixing operation, the rotor 3 and the extruding member are rotated by the motor to press a plurality of highly viscous materials, such as molten plastics or fluid rubbers through the inlet into the stator 2. Then, the mateials are moved in the extrusion direction Z from the cavities 4 and 5 to the overlapping cavities 4 and 5 successively by the thrusting force of the extruding member. Since the rotor 3 is rotating, the materials which differ in quality or color are dispersed and mixed uniformly as they are transferred from the cavities 4 and 5 to the adjacent cavities 4 and 5 by the complex combined action of deflective thrust force and circumferential shearing force. However, the oblong cavities 4 and 5 of this known cavity transfer mixing exturder, extending at an angle to the axial direction have not been satisfactory in respect of its ability to advance the materials through the extruder. Referring to Fig. 13 showing a portion of the development the inner circumference of the stator 2 and that of the outer circumference of the rotor 2, the cavities 4 of the stator 2 move in the direction of the arrow R1 relative to the outer circumference of the rotor 3, while the cavities 5 of the rotor 3 move in the direction of the arrow R2 relative to the inner circumference of the stator 2. Then, the materials filling the cavities 4 and 5 are compelled to move toward the front of the cavities 4 and 5, namely, in the extrusion direction Z, by the edges of the cavities 5 and 4. However, the materials are impelled in the opposite direction in the front semicircular portions of the cavities 4 and 5, and hence the materials tend to stagnate in portions A of the cavities 4 and in portions B in the cavities 5. This phenomenon will be understood more clearly when the oblong cavities 4 and 5 are simulated by rectangular cavities 4′ and 5′ as illustrated in Fig. 14. The edges C corresponding to the semicircular edges of the oblong cavities 4 and 5 impel the materials in a direction opposite to the extrusion direction Z, and hence the materials tend to stagnate behind the edges C. Fig. 32 illustrates another known cavity transfer mixing extruder having a vent for discharging moisture and volatile substances contained in the materials. This cavity transfer mixing extruder comprises a barrel 90, a screw 91 coaxially and rotatably extended within the barrel 90, a housing 94 and a stator 95 fitted in the housing 94. The barrel 90 has an inlet opening 92 at the rear end and a vent 93 at the middle. The housing 94 is joined to the front end of the barrel 90. The screw 91 has a first feed section 96 corresponding to the inlet opening 92, a first metering section 97 extending behind the vent 93, a vent section 98 corresponding to the vent 93, a second metering section 99 before the stator 95, and a rotor section 100 corresponding to the stator 95. The housing 94, the stator 95 and the rotor section 100 constitute a cavity transfer mixing unit. Generally, the productivity of the cavity transfer mixing extruder of this type is dependent on the extruding capacity of the second extruding zone, namely, a section after the vent 93, which is reduced due to pressure drop in the cavity transfer mixing unit joined to the front end of the extruding unit. Furthermore, since heat is generated in the cavity transfer mixing unit due to the cavity transfer mixing action of the cavity transfer mixing unit, the rotating speed of the screw 91 has been limited to a certain level and it has been impossible to extrude a material having a viscosity exceeding a certain level. Still further, since the first zone extending before the vent 93 needs to be sufficiently long to heat the material so that the material is sufficiently plasticized, an elongate screw having a very large L/D ratio, for example, and L/D ratio in the range of 18 to 20 for rubber and in the range of 28 to 35 for plastics, is necessary, which is disadvantageous in respect of mechanical stability. We will describe a cavity transfer mixing extruder having cavities capable of always causing the material to move in the extrusion direction. We will describe a cavity transfer mixing extruder having a vent, capable of operating at a high extrusion rate regardless of the type of materials and having a short extrusion screw as compared with the conventional extrusion screw. According to one aspect of the present invention, as illustrated in Fig. 9, the respective cavities 23 and 24 of the stator and the rotor are formed so that the ridges 29 and 30 defining the opposite longitudinal edges of the cavities 23 and 24 extend parallel to the direction R1 of the rotation of the stator relative to the rotor and to the direction R2 of the rotation of the rotor relative to the stator. Consequently, any force that acts in a direction opposite the extrusion Z direction will not be produced. That is, each of the cavities formed in the inner circumference of the stator and in the outer circumference of the rotor has, as viewed in a development, the shape of a parallelogram having a pair of opposite side extending in a direction perpendicular to the axial direction and a pair of opposite sides extending at an angle to the axial direction. According to another aspect of the invention, an annular restricting member is provided detachably mounted at the junction of the screw and the mixing rotor so as to divide the extruding section and the mixing section. In operation, the screw and the mixing rotor are rotated by a motor, and a plurality of kinds of materials are fed through a feed opening into the cylinder 4 and are advanced by the screw. The screw is of the deep-groove type exterting an extrusive force on the materials at a small work rate, so that less heat is generated in the materials in the extruding unit. In some cases, air bubbles are formed in the materials in the extruding unit. However, since the annular restricting member dividing the extruding unit and the mixing unit increases the pressure of the materials in the front portion of the extruding unit, the air bubbles contained in the materials are eliminated. Since the annular restricting member is detachable, an annular restricting member having a diameter suitable for adjusting the pressure of the materials to a desired degree can be employed. According to the further aspect of the present invention, a cavity transfer mixing extruder comprising a barrel having a feed opening in the rear end, a vent in the middle and an outlet opening in the front end, and a screw coaxially and rotatably extended within the barrel is provided with a cavity transfer mixing unit before the vent. Materials fed through the feed opening into the barrel is conveyed to the cavity transfer mixing unit, where the materials are melted and mixed. Then, moisture and volatile substances contained in the materials are discharged through the vent as the molten and mixed materials are conveyed further toward the outlet opening. Thus, in the first section before the vent, the excellent mixing action and heat generating action of the cavity transfer mixing unit is utilized effectively for melting and mixing the materials, and hence the length of the first section necessary for plasticizing or melting the materials can be reduced. Furthermore, the molten or plasticized materials and the unmelted or unplasticized materials are mixed uniformly and efficiently by the excellent mixing performance of the cavity transfer mixing unit. Still further, since the cavity transfer mixing unit is provided in the first section, only a pressure corresponding to a pressure drop in the cavity transfer mixing unit is required for passing the materials through the cavity transfer mixing unit, the reduction of the extruding rate due to the provision of the cavity transfer mixing unit is limited to a small extent. The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 9 are illustrations to assist in explaining a cavity transfer mixing extruder according to the present invention, and Figures 10 to 12 are illustrations to assist in explaining a conventional cavity transfer mixing extruder, in which: Figure 1 is a longitudinal sectional view of a cavity transfer mixing unit, comprising a preferred embodiment, of the present invention; Figure 2 is a partially sectional side elevation of a stator; Figure 3 is a sectional view taken on line A-A in Fig. 2; Figure 4 is a development of a portion of the inner circumference of the stator of Fig. 2; Figure 5 is a sectional view taken on line B-B in Fig. 4; Figure 6 is a side elevation of a rotor; Figure 7 is a development of a portion of the outer circumference of the rotor of Fig. 6; Figure 8 is a development showing the relative disposition of the cavity groups; Figure 9 is an illustration to assist in explaining the action of cavities according to the present invention; Figure 10 is a fragmentary longitudinal sectional view of a conventional cavity transfer mixing unit; Figure 11 is an enlarged view of a cavity of the cavity transfer mixing unit of Fig. 10; Figure 12 is a development showing the relative disposition of the cavity groups of the cavity transfer mixing unit of Fig. 10; Figures 13 and 14 are illustrations to assist in explaining the action of the conventional cavities; figure 15 is a fragmentary longitudinal sectional view of a cavity transfer mixing extruder, comprising a second embodiment according to the present invention; Figure 16 is a sectional view taken on line A-­ A in Fig. 15; Figure 17 is a partially sectional view of the stator of the cavity transfer mixing extruder of Fig. 15; Figure 18 is a development showing the disposition of the cavity groups of the cavity transfer mixing extruder of Fig. 15; Figure 19 is a fragmentary sectional view of a portion of the cavity transfer mixing extruder of Fig. 15, provided with an annular restricting member; Figure 20 is a fragmentary cutaway view showing another annular restricting member; Figure 21 is a development showing the disposition of cavity groups of a cavity transfer mixing extruder comprising a third embodiment, of the present invention; Figure 22 is an enlarged plan view of a cavity employed in the third embodiment; Figure 23 is a graph showing the variations of extrusion rate and extrusion temperature with the rotating speed of the screw; Figure 24 is a longitudinal sectional view of a cavity transfer mixing extruder, comprising a fourth embodiment, of the present invention; Figure 25 is a partially sectional view of the stator of the fourth embodiment; Figure 26 is a sectional view taken on line B-­ B in Fig. 25; Figure 27 is a development of the inner circumference of the stator of the fourth embodiment; Figure 28 is a fragmentary side elevation of the rotor of the fourth embodiment; Figure 29 is a sectional view taken on line C-­ C in Fig. 28; Figure 30 is a development of the outer circumference of the rotor of the fourth embodiment; Figure 31 is a sectional view taken on line D-­ D in Fig. 31; and Figure 32 is a longitudinal sectional view of a conventional cavity transfer mixing extruder. A cavity transfer mixing extruder, comprising a first embodiment, of the present invention will be described hereinafter with reference to Figs. 1 to 8 particularly illustrating the cavity transfer mixing unit. In Fig. 1, there are shown a cylindrical housing 20, a cylindrical stator 21 fixedly fitted in the housing 20, and a generally cylindrical rotor 22 coaxially and rotatably extending within the stator 21. The rotor 22 is coupled at one end thereof with a extruding member, namely, a screw, not shown. The rotor 22 is rotated by a motor, not shown. As illustrated in Figs 2 to 8, cavity groups 27 comprising circumferential cavity rows 25 arranged along the axial direction (Y-Y) and each having a plurality of cavities 23 arranged side by side in the circumferential direction (X­ X) are formed in the inner circumference of the stator 21 (excluding the opposite ends of the stator 21), and cavity groups 28 comprising circumferential cavity rows 26 arranged along the axial direction Y-Y and each having a plurality of cavities 24 arranged side by side in the circumferential direction X-X are formed in the outer circumference of the rotor 22 (excluding the opposite ends of the rotor 22). The respective cavities 23 and 24 of the cavity groups 27 and 28 are disposed at very small spacing so that the cavities are distributed densely. The cavity groups 27 and 28 are the same, when developed on a plane, in arrangement, shape and size except that the cavities 23 and 24 of the cavity groups 27 and 28 are inclined in opposite directions, respectively, with respect to the axial direction Y-Y. As best shown in Fig 8, the cavities 23 of the cavity rows 25 of the cavity group 27 of the stator 21 are spaced by a distance ℓy corresponding to a half the axial pitch, namely, the axial interval between the adjacent cavity rows 25 and 26, relative to the corresponding cavities 24 of the cavity rgroup 26 of the rotor 22. Accordingly, the cavities 23 of each cavity row 25 of the cavity group 27 overlap the adjacent cavities 24 of the two adjacent cavity rows 26 of the cavity group 28. When developed on a plane, the cavities 23 and 24 each has a parallelogrammic shape defined by a pair of opposite, parallel straight walls 29 and 30 extending perpendicularly to the axial direction Y-Y, and a pair of opposite, parallel straight walls 31 and 32 extending at an angle to the axial direction Y-Y. The corners of the bottom surface of each one of cavities 23 and 24 is rounded as shown in Fig. 5 to prevent the stagnation of the material in the cavities 23 and 24. The respective longitudinal center axes 33 and 34 of the cavities 25 and 26 of the cavity groups 27 and 28 are inclined at the same angle ϑ to the axial direction Y-Y to the left and to the right, respectively, with respect to the extrusion direction Z. In operation, the rotor 22 and the screw are rotated by the motor to squeeze a plurality of kinds highly viscous materials, such as plastics or rubbers, through the feed opening into the stator 21 by the screw. The materials thus squeezed into the stator are moved in the extrusion direction Z by the squeezing pressure applied thereto by the screw from the cavities 23 and 24 to the overlapping adjacent cavities 23 and 24. Since the rotor 22 is rotated, the materials are subjected to the complex combined action of deflective thrust force and circumferential shearing force as they are transferred from cavities 23 and 24 to the cavities 23 and 24, whereby materials which are different from each other in color or quality are mixed and dispersed uniformly. Since the cavities 23 and 24 are parallelogrammic cavities each are defined by a pair of the parallel straight walls 29 and 30, and pair of the parallel straight walls 31 and 32. The longitudinal axis of each cavity is inclined at an angle to the axial direction Y-Y, the materials filling the cavities 23 and 24 substantially in the extrusion direction Z by an additional force, which is different from the squeezing force produced by the screw, as the materials are sheared between the stator 21 and the rotor 22. Since the walls 29 and 30 are parallel to the circumferential direction of the stator 21 and the rotor 22, no force that acts on the materials in a direction opposite the direction of extrusion is produced, and hence the materials never staagnate within the cavities 23 and 24. Thus, the materials are advanced through the stator 21 by the combined action of the squeezing pressure produced by the screw, namely, the extruding member, and the pressure produced by the rotor 22, and the stagnation of the materials in the cavities 23 and 24 is prevented. Accordingly, the materials can be changed in a short time, and the loss of material in this changeover is reduced. Furthermore, the rotation of the rotor 22 reduces resistance against the flow of the materials through the stator 21, prevents the stagnation of the materials in the stator 21 effectively and reduces pressure drop in the stator 21. Consequently, the extrusion efficiency is improved, the extrusion rate is increased and the productivity is enhanced. Still further, since the resistance against the flow of the materials through the stator 21 is reduced, heat generation in the materials is mitigated, which enables the satisfactory mixing of materials sensitive to heat. A cold-feed type cavity transfer mixing extruder for rubber, providing a second embodiment of the invention will be described hereinafter with reference to Figs. 15 to 20. In Fig. 15, there are shown an extrusion unit 1 and a mixing unit 2 disposed after the extrusion unit 1 with respect to the extrusion direction Z The extrusion unit 1 comprises a barrel 4 provided with a feed opening 3, and a screw 5 coaxially extending through the barrel 4. The screw 5 is of a deep-groove type having a length shorter than the conventional screw. The screw is rotated by a motor, not shown. As illustrated in Fig. 15, the mixing unit 2 comprises a stator assembly 6 consisting of a housing 8 and a stator 9 fitted in the housing 8, and a rotor 7 coaxially extended through the stator 9. The rotor 7 is joined detachably to the front end of the screw 5 by screwing the threaded portion of the same into the screw 5. As illustrated in Fig. 18, a cavity group 14 comprising cavity rows 12 arranged along the axial direction Y-Y and each having a plurality of cavities 10 arranged side by side along the circumferential direction X-X, and a cavity group 15 comprising cavity rows 13 arranged along the axial direction Y-Y and each having a plurality of cavities 11 arranged side by side along the circumferential direction X-X are formed in the inner circumference of the stator 9 and in the outer circumference of the rotor 7, respectively. The respective cavities 10 and 11 of the cavity groups 14 and 15 are arranged at very small intervals so that the cavities are distributed densely. The respective cavities 10 and 11 of the succeeding cavity rows 14 and 15 of the cavity groups 14 and 15 are spaced by distance ℓx in the circumferential direction in the respective directions of relative rotation of the cavity groups 14 and 15, namely, in a direction opposite the direction R of rotation of the rotor 7 for the cavity groups 14 of the stator 9 and in the direction R of rotation of the rotor 7 for the cavity group 15 of the rotor 7, relative to the respective adjacent cavities 10 and 11 of the adjacent preceding cavity rows 12 and 13, respectively. Thus, the cavities 10 and 11 are densely distributed by shifting the respective cavities 10 and 11 of the succeeding cavity rows 12 and 13 relative to the adjacent cavities 10 and 11 of the preceding cavity rows, respectively. The relative distribution of the cavities 10 and 11, and shape of the cavities, and the inclination of the longitudinal axes of the cavities 10 and 11 are the same as those of the first embodiment. As illustrated in Fig. 19, an annular restricting member 18 is fitted detachably on the rear portion of the rotor 7, and is held fixedly between the rotor 7 and the screw 5. The restricting member 18 has an outside diameter greater than those of the screw 5 and the rotor 7, so that the extrusion unit 1 and the mixing unit 2 are divided by the restricting member 18. Fig. 20 illustrates another restricting member according to the present invention. This restricting member 18 is provided with axial grooves 19 formed in the circumference thereof at regular angular intervals to facilitate the passage of the materials across the restricting member 18 from the extrusion unit 1 into the mixing unit 2. Therefore, this restricting member 18 is effective for preventing the burning of the materials, particularly, in extruding the mixing highly viscous materials such as rubbers. A cold-feed type cavity transfer mixing extruder, comprising a third embodiment, of the present invention will be described hereinafter with reference to Figs. 21 and 22. The constitution of the third embodiment is substantially the same as that of the second embodiment, except that the respective cavities 10 and 11 of the stator 6 and the rotor 7 are different from those of the second embodiment. Accordingly, the third embodiment will be described only in terms of the shape and distribution of the cavities 10 and 11. The cavities 10 and 11 have the same oblong shape. The cavities 10 and 11 consists of rectangular sections 21 and 22, and a pair of semicircular sections 23 and a pair of semicircular sections 24 joined to the opposite axial ends of the rectangular sections 21 and 22, respectively. Only the cavities 11 of the rotor 7 each has a longitudinal axis inclined at an angle ϑ with respect to the axial direction Y-Y. The cavities 10 of the stator 6 are arranged so that the circumferential distance ℓx′ between the center of the cavity 10 of one of the cavity rows 12 and the center of the adjacent cavity 10 of the adjacent cavity row 12 is a half the circumferential distance between the respective centers of the cavities of the same cavity row 12. The distance ℓx′ is considerably greater than the circumferential distance ℓx between the center of the cavity 11 of one of the cavity rows 13 and the center of the adjacent cavity 11 of the adjacent cavity row 13. Only the cavities 10 of the stator 6, instead of the cavities 11 of the rotor 7, may be inclined with respect to the axial direction Y-Y, and the cavities 10 and 11 may be elliptic cavities. The performance of a cold-feed type cavity transfer mixing extruder incorporating the present invention was confirmed experimentally. The cold-feed type cavity transfer mixing extruder has a screw having an L/D ratio of eight, a stator provided with three cavity rows, and a rotor provided with three cavity rows. Blue natural rubber compound ribbons and yellow natural rubber compound ribbons (Mooney viscosity MLH4: 60 at 100°C) were subjected to experimental mixing extrusion on the cold-­ feed type cavity transfer mixing extruder. The results of the experimental operation are shown in Fig. 23 showing the variations of the extrusion rate and extrusion temperature with the rotating speed of the screw and the rotor. It is known from Fig. 23 that the extrusion rate was 580 kg/hr and the extrusion temperature, namely, the temperature of the materials extruded, was 93°C, when the rotating speed of the screw and the rotor was 80 rpm. Well mixed and kneaded green natural rubber compound having a small variation in temperature distribution was obtained. The rubber compounds were mixed satisfactorily, the extrusion temperature remained at a low level, and the temperature variation in the extruded compound was as small as ± 1°C, regardless of the rotating speed of the screw and the rotor. It was proved that the performance of the cold-feed type cavity transfer mixing extruder incorporating the present invention is superior to that of the conventional cold-­ feed type cavity transfer mixing extruder. When the cold-feed type cavity transfer mixing extruder was operated without the restricting member 18, some air bubbles were contained in the extruded rubber compound. Thus, according to the present invention, the heat generation of the cavity transfer mixing extruder can be reduced even in mixing and extruding highly viscous materials without sacrificing the degree of mixing and productivity, and even materials which require the severe restriction on the extrusion temperature can be uniformly and satisfactorily mixed and extruded at high efficiency. The provision of the restricting member between the screw and the rotor prevents materials containing air bubbles being squeezed into the mixing unit. Furthermore, since the restricting member is detachable, the squeezing pressure can be adjusted to a desired value by choosing a suitable restricting member from among a plurality of spare restricting members. A cavity transfer mixing extruder, comprising a fourth embodiment, of the present invention will be described hereinafter with reference to Figs. 24 and 31. In Fig. 24, there is shown a cavity transfer mixing extruder comprising a fourth embodiment of the present invention, comprising a barrel 1 consisting of a first barrel section 2 and a second barrel section 3, a housing 4 disposed between and fixedly joined to the first and second barrel sections 2 and 3, a stator 5 fixedly fitted in the housing 4, and a screw shaft 9 coaxially and rotatably extending through the barrel 1. A feed opening y is formed at the rear end of the first barrel section 2; a vent 7 is formed at the rear end, namely, at a position near the housing 4, of the second barrel section 3; an outlet opening 8 is formed at the front end of the second barrel section 3. A die, not shown, is attached to the front end of the second barrel section 3. The screw shaft 9 has a first screw section 10 corresponding to the first barrel section 2, a rotor section 11 corresponding to the stator 5, a second screw section 12 corresponding to a portion having the vent 7 of the second barrel section 3, and a matering screw section 13 corresponding to the front portion of the second barrel section 3. The housing 4, the stator 5 and the rotor section 11 constitute a mixing unit. As illustrated in Figs. 25 to 27, the stator 5 is provided at its inner circumferencial portion with cavities 14 each having a longitudinal axis extending at an angle to the axial direction Y-Y as viewed in a development best shown in Fig. 27. As illustrated in Figs. 28 to 31, the rotor section 11 is provided at its outer circumferencial portion with cavities 15 each having a longitudinal axis extending at an angle to the axial direction Y-Y as viewed in a development best shown in Fig. 30. Thus, the relative circumferential movement of the cavities 14 and 15 causes the material to advance. The cavities 14 and 15 are formed close to each other, respectively, so that the upper surfaces of the lands, namely, the walls, defining the cavities 14 and 15 are of small width to reduce the pressure loss due to the resistance of the inner circumference of the stator 5 and the outer circumference of the rotor section 11 against the flow of the material to the least extent in order that heat generation in the mixing unit attributable to the resistance of the stator 5 and the rotor section 11 against the flow of the material is reduced. In mixing and extruding raw rubber compounds on the cavity transfer mixing extruder, the raw rubber compounds fed through the feed opening are pushed forward by the first screw section 10 into the mixing unit, where the raw rubber compounds are mixed between the respective cavities 14 and 15 of the stator 5 and the rotor section 11, and are plasticized by being heated uniformly. While the mixed rubber compounds are pushed forward by the second screw section 12, moisture and volatile substances contained in the mixed rubber compounds are discharged through the vent 7. Then, the mixed rubber compounds thus deaerated are pushed further forward, and then the mixed rubber compounds are extruded through the die, not shown, after passing the metering section 13. Since the respective cavities 14 and 15 of the stator 5 and the rotor section 11 are arranged with their longitudinal axes inclined at an angle to the axial direction Y-Y, the material are urged forward by the lands of the cavities 14 and 15 as the screw shaft 9 is rotated. Accordingly, the pressure loss and the increase of temperature in the mixing unit is reduced; consequently, the screw shaft 9 may be rotated at a high rotating speed to enhance the productivity of the cavity transfer mixing extruder even when mixing and extruding materials which requires the processing temperature to be kept below a certain level to prevent scorching, such as rubber compounds. Furthermore, since the cavities 14 and 15, which are the same as those of the foregoing embodiments in shape and disposition, propel the materials, the cavity transfer mixing extruder of the present invention requires less time for changing the materials as compared with the conventional cavity transfer mixing extruder employing semispherical cavities. In mixing and extruding plastics with the cavity transfer mixing extruder, it is desirable to provide the first screw section 10 with a compressing unit in order that the plasticization and melting of the plastics are accelerated by the shearing action of the first screw section 10. In mixing and extruding rubbers, the use of a combination of a deep grooved screw and the mixing unit enhances the extrusion rate remarkably, whereas it is possible, with some kinds of rubber compounds, that air bubbles are formed in the mixed rubber compounds. However, the cavity transfer mixing extruder of the present invention is able to extrude a satisfactory mixed rubber compound of uniform temperature even when a deep grooved screw is employed as the first screw section, because the air bubbles are discharged through the vent while the mixed rubber compounds are advanced by the second screw section. Although the parallelogrammic cavities are most desirable, the cavities may be semispherical cavities or oblong cavities.

Claims: 1. A cavity transfer mixing extruder comprising: an extrusion unit (1) comprising: a barrel (4) provided with a feed opening (3) in the rear portion thereof; and a screw shaft (5) coaxially and rotatably extended through the barrel (4); and a mixing unit (2) comprising: a housing (20); a stator (21) fixedly fitted in the housing and provided with a first cavity group (27) including circumferential cavity rows (25) of cavities (23) in the inner circumferential surface thereof excluding the opposite ends thereof; and a rotor (22) joined coaxially to the front end of the screw shaft, coaxially and rotatably extending through the stator (21), and provided with a second cavity group (28) including circumferential rows (26) of cavities (24) in the outer circumferential surface thereof excluding the opposite ends thereof, characterised in that the respective cavities (23, 24) of the first (27) and second (28) cavity groups, when developed on a plane, each has a parallelelogrammic shape defined by a pair of opposite, parallel straight walls (29,30) extending perpendicularly to the axial direction, and a pair of opposite, parallel straight walls (31,32) inclined at an angle to the axial direction; the longitudinal axes (33) of the cavities (25) of the first cavity group (27) and the longitudinal axes (34) of the cavities (26) of the second cavity group (28) are inclined in opposite directions with respect to the axial direction; the cavity rows (25) of the first cavity group (27) and the cavity rows (26) of the second cavity group (28) have the same axial pitch; and the cavity rows (25) of the first cavity group (27) are shifted axially relative to the cavity rows (26) of the second cavity group (28) by a distance corresponding to a half the axial pitch so that each cavity (23) of each cavity row (25) of the first cavity group (27) overlaps the adjacent cavities (24) of the adjacent cavity rows (26) of the second cavity group (28). 2. A cavity transfer mixing extruder as claimed in Claim 1, wherein said rotor (7) is joined detachably to the screw shaft (5), and an annular restricting member (58) having an outside diameter greater than those of the screw shaft (5) and the rotor (7) is provided detachably at the junction of the screw shaft (5) and the rotor (7) so as to divide the extrusion unit (1) and the mixing unit (2). 3. A cavity transfer mixing extruder as claimed in Claim 1, wherein in additional barrel (73) having a vent (77) in the rear portion thereof is joined to the front end of the housing so that the vent (77) is disposed near the mixing unit, and a screw shaft having an extruding screw section (82) and a metering screw section (83) is joined coaxially to the front end of the rotor with the extruding screw section (82) extended within a portion having the vent (77) of the additional barrel (73).

Inventors: FUKUMIZU, SHINNICHI, INOUE, KIMIO, KURIYAMA, AKIMASA
Applicants: KOBE STEEL LTD
Application year: 1986
Main classification: B29C47
IPC codes: B29C47