Screw extruding machine

Abstract: A screw extruding machine for extruding a material such as rubber, plastics or the like kneaded and blended into a sheet-like form. The screw extruding machine comprises two screws (2) horizontally and rotatably supported on a casing (1), a top-open hopper (3) provided on the side of a screw base portion of the casing (1), an outlet (4) opened in an axial direction of the screw (2) on the side of a screw front end of the casing (1), and a roller die (11) in proximity of the outlet (4), the screw (2) having a feed portion (5) which corresponds to a portion face to the hopper (3) and a compression portion (6) which corresponds to a front end side, whereby material to be extruded supplied from the hopper (3) is extruded into a sheet-like form by the roller die (11) from the outlet (4) via the feed portion (5) and the compression portion (6) by the rotating twin screws (2), the hopper (3) being arranged over the feed portion (5) of each screw (2).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a screw extruding machine, Description of the Prior Art A screw extruding machine of this kind is known, for example, from Japanese Patent Publication No. 11177/1986. In this conventional screw extruding machine, a uniaxial screw 21 is supported horizontally and rotatably within a cylinder casing 20, as shown in FIGS. 9 and 10. This screw 21 is forcibly rotated with a base portion thereof connected to a driving device not shown. A hopper 22 is provided on the side of the screw base portion of the casing 20. This hopper 22 is provided with a pusher device 23 for intruding the material. The casing 20 is provided at the front end of the screw with an outlet 24. A pair of upper and lower roller dies 25 are arranged facing to the outlet 24. The roller dies 25 are rotatively driven by a driving device 26. The screw 21 has a feed portion 27 which corresponds to a portion facing to the hopper 22, and a compression portion 28 which corresponds to a portion closed by the cylinder casing 20 at the front end. According to the above-described uniaxial screw extruding machine, the material supplied into the hopper 22 is forcibly intruded into the feed portion 27 of the screw 21 by reciprocation of a pusher ram 30 by an air (or a hydraulic cylinder 29) of the pusher device 23. The intruded material is carrried by the rotating screw 21 from the feed portion 27 to the compression portion 28, where pressure is applied to the material, and the material is extruded from the outlet 24 at the front end. The extruded material stays spread widthwise on the front surfaces of the roller dies 25 and passes through the roller dies 25 and is shaped into a rolled sheet 31. In the above-described conventional screw extruding machine, since the pulling activity of the material with the feed portion of the screw is not enough, the pusher device is provided in an attempt of forcibly intruding the material within the hopper into the feed portion. From the GB-A 180 638 a screw extruding machine is known which is provided with two screws, the threads of which have the same pitch but are disposed in contrary directions , said screws entering into each other and rotating in opposite directions in the body of the machine which is provided with two bores respectively containing the screws and with a die plate at the discharge end. SUMMARY OF THE INVENTION It is the object underlying the subject matter of the application to produce a screw extruding machine for extruding material with a relatively large width, having a small size and requiring little driving power. According to the application the object is solved by the features of the new claim 1. In the screw extruding machine according to the application the hopper is arranged over the feed portion of each screw and the ratio of the length L of the compression portion to the diameter D of said screws has the completely unusual value of 0.3 to 0.6. Thus, the compression portions of the screws are comparatively short and the diameters of the screws are relatively large. Due to this design a machine is produced which, in comparison to customary machines having a comparatively large material outlet - normally the material outlet largely corresponds to the diameter of the screws - is substantially shorter since the compression portions of the screws are extremely short. Due to the short length of the compression portions the machine also requires only a relatively small driving power since only little friction results at the short compression portions due to the small surface in contact with the material to be extruded. By the arrangement of the hopper over the feed portion the weight of the material to be extruded is used for pressing it into the compression portions. So far, experts have held the prejudice against a structure realized as in case of the subject matter of the application that a screw extruding machine would have to comprise an L/D ratio of larger than 1 in order to ensure a satisfactory extrusion process. Experiments made in the past confirm this view, which led to customary screw extruding machines comprising an L/D ratio which is considerable larger than 1. This prejudice of the experts was for the first time overcome by the structure according to the application. By means of the synergistic effect of the hopper arranged over the feed portions, which permits a sufficient material density, it became possible for the first time to obtain a satisfactory extrusion result despite the small L/D ratio. A screw extruding machine according to the present invention, comprises screws supported rotatably in a casing, a top-open hopper is provided on the side of a screw base portion of the casing, an outlet open in a unidirection of the screw is provided on the front end of the screw in the casing, and a pair of roller dies are provided in proximity of said outlet, said screw having a portion face to the hopper as a feed portion and a front end side as a compression portion, whereby material to be supplied from the hopper is extruded by said roller dies from the outlet via said feed portion and said compression portion into a sheet-like form by the screw. In the above screw extruding machine, two screws as described are arranged in one and the same plane, said hopper being arranged over the feed portion of both of the screws; the length L of the compression portion to the screw diameter D is in the relationship of L/D = 0.3 to 0.6; the two screws are of the engaged type or non-engaged type and can be disposed by varying a phase by approximately 0° or approximately 180° (which is an angle formed by a thread blade in the same section at the right angle to the axis) depending on the content of the composition and characteristics of the material to be extruded; the ratio C/S between the sheet width S to the outlet width C is 0.6 or over; and the ratio A/E between the die diameter E and the distance A of the surface at the front end of the outlet and the surface of the roller die is 0.4 or less (refer to FIG. 11 for C/S and FIG. 12 for A/E). According to the above-described technical means of the present invention, two screws are arranged in one and same plane within the casing, and the hopper for supplying the material to be extruded is formed over the feed portions of both the screws. Therefore, torsional directions of the thread blades of both the screws are made opposite to each other, and one of both the screws is rotated clockwise whereas the other counterclockwise whereby the material to be extruded supplied from the hopper are brought into engagement with the feed portion of the screw, fed under pressure toward the outlet by the rotation of the thread blade, intruded into the roller die arranged in proximity of the outlet to obtain an extruded material in the form of a wide sheet. According to this arrangement, the pusher device is not required as is so required in the uniaxial screw system. Further, since the outlet is provided over two parallel screws, a lateral opening area thereof becomes widened as compared with the outlet of the conventional uniaxial screw whereby the material can be widely extruded with low pressure extrusion without requiring high pressure. This results from the fact that the length L of the compression portion of the screw is made to have L/D=0.3 to 0.6, which is shorter than L/D= 1.3 to 1.7 of prior art, and in addition, the screw driving power can be reduced and the overall length of the screw can be shortened to make the apparatus compact. Furthermore, according to the present invention, it is possible to install said two screws in parallel with each other, wherein the optimum phase can be set depending on the content of composition and characteristics of the material to be extruded with the result that the engaging ability of the screw with respect to the material to be extruded and the extrusion ability may be enhanced. This comprises a great merit for a screw extruding machine which uses roller dies of this kind to perform sheeting process of rubber and plastics. Moreover, according to the present invention, the ratio C/S between the sheet width S and the outlet width C is made 0.6 or more whereby a sufficiently wide sheet can be obtained with low extrusion pressure. Furthermore, in the present invention, the ratio A/E between the roller die diameter E and the distance A of the surface of the front end of the outlet and the roller die surface is made to be 0.4 or less whereby the material having been discharged is not forced out and pressure required for sheeting can be sufficiently secured. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front sectional view of an embodiment according to the present invention; FIG. 2 is a cross-sectional view of the same; FIG. 3 is a cross-sectional view of an embodiment with 0° phase; FIG. 4 is a sectional view taken on line A-A of FIG. 3; FIG. 5 is a cross-sectional view of an embodiment with 180° phase; FIG. 6 is a sectional view taken on line A′-A′; FIG. 7 is a sectional view showing essential parts of one embodiment of an engaging-type screw; FIG. 8 is a graph showing comparison of extrusion amount; FIG. 9 is a plan view of a conventional example; FIG. 10 is a side view of the same; FIG. 11 is a plan view showing a sheet width and an outlet; FIG. 12 is a sectional view showing a roller die diameter and a distance between a surface of a front end of the outlet and a surface of a roller die; FIG. 13 is a view showing the relationship between C/S and the lowest pressure required; and FIG. 14 is a view showing the relationship between A/E and the maximum pressure of outlet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described hereinafter with reference to the drawings. Referring to FIGS. 1 and 2, a cylinder casing for a twin screw extruding machine is indicated at 1. Within this casing 1 two screws 2 and 2 are rotatably arranged in parallel with each other within the same plane. A top-open hopper 3 is provided on the side of a screw base portion of the casing 1, and an outlet 4 opened in a directin of a screw shaft is provided at the front end of the screw. The screw 2 has a feed portion 5 which corresponds to a portion facing to hopper and a compression portion 6 which corresponds to the front end. The hopper 3 is arranged over the feed portions 5 of two screws 2 and 2. The outer peripheral portion of the compression portion 6 is closed by the inner peripheral wall of the cylinder casing 1. The feed portion 5 and the compression portion 6 of the screw 2 are formed with a thread blade 7, thread pitch of which is an unequal pitch in which the pitch is long in the feed portion 5 while the pitch is short in the compression portion 6. The torsional directions of the thread blades 7 of the screws 2 and 2, respectively, are opposite to each other. The outside diameter of the thread blade 7 is the same over the feed portion 5 and the compression portion 6, and the outside diameter of the thread blade 7 of the two screws 2 and 2 is the same. Let D be the outside diameter of the thread blade 7 of the screw 2 and let L be the length of the compression portion 6, the relationship of L/D=0.3 to 0.6 is established. The base end of each of the screws 2 and 2 protrudes from the casing 1, and gears 8 and 8 are formed on the protruded portions, respectively, said gears 8 and 8 being engaged with each other. The protruded portion of the screws 2 and 2 is supported at two points on a gear case 9 through bearing 10 and 10. A driving device (not shown) is connected to the end of one of the screws 2. The pair of screws 2 and 2 are rotated at the same speed in the directions opposite to each other, and this rotational direction is the direction in which material supplied from the hopper 9 is pulled by the pair of screws 2 and 2. The torsional direction of the thread blade 7 is the direction in which the pulled material is transported toward the outlet 4. Frontwardly of the outlet 4 is arranged a roller die 11 slightly spaced apart from the outlet 4. This roller die 11 consists of a pair of upper and lower rollers 12 and 12 disposed in a horizontal axis perpendicular to the axial direction of the screw, said rollers 12 and 12 being forcibly driven by a driving device (not shown). The axial length of the rollers 12 and 12 is slightly longer than the lateral width of the outlet 4, and side guides 13 and 13 for preventing the material extruded from the outlet 4 from being flown out in a lateral direction are provided on both left and right sides of the rollers 12 and 12, respectively. The side guide 13 is fixed by means of a bolt 14 to the front surface of the casing 1, the side guide 13 having its front portion formed to be curved along the peripheral surface of the rollers 12 and 12. According to the embodiment of the present invention, the material supplied to the hopper 3 is engaged into the feed portion 5 of the pair of screws 2 and 2 which rotate in directions opposite to each other and in the engaging direction, carried to the compression portion 6 on the front end side by the thread blade 7 of the feed portion 5 and increased in pressure. However, due to the ratio between the screw diameter D and the length L of the compression portion 6, L/D=0.3 to 0.6, and the shorter length of the compression portion 6, the material is not so increased in pressure and the pressure at the exit of the outlet 4 is set to approximately 20 kg/cm². Despite the low pressure as described, since the widthwise opening area of the outlet 4 is large, the extruded material flows over the full length of the roller die 10 and passes through the roller die 10 into a wide sheet. However, in the conventional uniaxial screw extruding machine, the outlet is small so that high pressure extrusion must be employed to fill the material over the widthwise of the roller die. The pressure of the compression portion was 60 kg/cm² and that of exit of the outlet was approximately 30 kg/cm². As described above, in the embodiment of the present invention, the length L of the compression portion 6 is short and the low pressure is used, and therefore the power for driving the screws can be reduced to 90 kw whereas the power of prior art was 190 kw. Furthermore, the length of the compression portion 6 is made short and the pusher device as in prior art is omitted, and therefore the weight of the machine can be reduced to 5.2 tons from 10 tons of prior art. With respect to the L/D, if L/D is increased, pressure in the compression portion increases to increase heat generation increasing an excess consumption of energy. In addition, it is necessary to withstand high pressure, which gives rise to a defect in that the weight of the machine increases. Therefore, it is desireable that L/D be made less than 1.3. Further, the value of L/D need be set to 0.3 to 0.6 for the reasons below. That is, the reason why the relationship of L/D = 0.3 to 0.6 is established is that if L/D is 0.3 or less, the thickness of the casing 1 becomes thin and is weakened in terms of strength. The upper limit value, 0.6, is the optimum upper limit value because the screw is shortened, the generated pressure is lowered to thereby reduce heat release value to suppress an energy consumption, and the weight of the machine is further reduced. It is noted that the shape of the hopper 3 can be a divergent tapered shape as shown by the broken lines of FIG. 1. In the following, an embodiment of a construction which enables variation in phase of two screws according to the present invention will be described with reference to FIGS. 3 to 8. As shown in FIGS. 3 and 4, the base portions of two screws 2 and 2 having the thread blades 7 and 7 opposite to each other protrude from the casing 1, said protrusions as driving shafts 2a and 2a are rotatably disposed in parallel with each other through front and rear bearing 10 and 10 within a gear case 9 provided separately from the casing 1, and mutually engaging gears 8 and 8 are secured by means of a key fitting or the like to corresponding positions of the driving shafts 2a and 2a, respectively. Accordingly, though not shown, by connecting either driving shaft 2a to a driving source such as a suitable prime mover, a reduction gear or the like, both the screws 2 and 2 are rotated in a direction opposite to each other through the interlocking of the gears 8 and 8. According to this construction, both the screws 2 and 2 can be disposed under the phase of 0° as illustrated in FIG. 4 by varying the engaging position between the gears 8 and 8. Also, the screws 2 and 2 can be disposed under the phase of 180° as illustrated in FIGS. 5 and 6. Here, 0° to 180° are angles formed between both the thread blades 7 and 7 on the same section at right angles to the screw axis. In the embodiments shown in FIGS. 3 to 6, both the screws 2 and 2 are in the non-engaged state but both the screws 2 and 2 can be brought into the engaging state as illustrated in FIG. 7. In the present invention, both the screws 2 and 2 are disposed in parallel with each other in the engaging or non-engaging state and can be disposed with the phase changed to provide the following characteristics. FIG. 8 is a graph of comparison of extrusion amount for the case of a screw extruding machine according to the present invention which employs a pair of screws 2 and 2 with a phase of 0° and a pair of screws 2 and 2 with a phase of 180°, in which kneaded natural rubber as a material is subjected to extrusion sheeting. In FIG. 8, the axis of ordinate shows the extrusion amount kg/min and the axis of abscissa shows numerical values, upper part of which indicates the rpm of screw while the lower part indicates the rpm of calender roll. It has been confirmed that the extrusion amount by the phase 0° shown by the solid line is higher in extrusion amount by 6% on the average than that of the phase 180° shown by the phantom line. The possible reason is that in the case of the phase 180°, the thread blades 7 and 7 of the screws 2 and 2 alternately extrude the material frontwardly of the screws but sometimes fail to perform effective extrusion of material due to the escape (slip), cut or the like of the material itself whereas in the case of the phase 0°, the thread blades 7 and 7 of the screws 2 and 2 simultaneously perform extrusion operation to thereby enhance the sweep-feed ability to improve the engaging performance. In this case, if the material is easily broken in nature, the improvement in engaging property due to the difference of phase is considered to be more conspicuous. As previously illustrated in FIG. 7, in the case where the screws 2 and 2 are arranged in the engaging state, the improvement of the engaging performance can be amply expected with the phase of 180° as shown. Generally, in the screw extruding machine which uses the roller dies of this kind to carry out the extrusion of sheets, rubber and plastics are often used as material. For example, in the case of rubber, materials different in various components and characteristics such as A kneaded material (master batch) mixed with a filler such as a carbon black and B kneaded material( final batch) into which is charged an agent of a vulcanization type in addition to the master batch are used as rubber material. These materials need be applied with sheeting process suitable therefor. In this case, the engaging property and extrusion ability are sometimes low depending on the materials, and therefore, mere use of a pair of screws 2 and 2 under the fixed phase is sometimes unsuitable. The present invention has a great merit in that the phase of the screws 2 and 2 can be made to be optimum according to the material by changing the engaging position of the gear 8. The extrusion function can be improved merely by changing the phase to either 0° or 180° as shown in the embodiment. While in the embodiment, the case of the phases 0° or 180° has been described, it is needless to say that in the case where the phase is in the vicinity of 0° or in the vicinity of 180°, the similar effect is obtained, and the phase in the vicinity of 0° or in the vicinity of 180° is included in the scope of the present invention. In the case of an intermediate phase between 180° and 0°, it is expected that two screws 2 and 2 will not equally extrude the material, and as the result, pressure at the outlet 4 is possibly uneven, the defective accuracy of shaping sheets carried out by the roller die sometimes brings fortch, and enhancement of the intended engaging property and extrusion ability cannot be expected. FIG. 13 shows the lowermost pressure (P1) required of the outlet of the extruding machine capable of variously varying the ratio of the outlet width (C) to the sheet width (S) to extrude a sheet without breaking both ends of the sheet width (S). As may be understood from this figure, if C/S is made to 0.6 or more, the sheet width as required may be obtained with low pressure. Further, since the pressure can be minimized, L/D of the extruding machine can be made small to contribute to minimization of heat generation at the extruder part, energy saving and reduction in weight of the machine as well as reduction of driving power of the roller die. Accordingly, C/S must be set to 0.6 or more. Next, FIG. 14 shows the maximum pressure (P2) at the outlet of the extruding machine in the case where A/E is varied in the state that material is not forced out through a clearance formed by the exit of the extruding machine and the roller die. As may be understood from this figure, in the case where A/E is 0.4 or less , even if the outlet pressure is increased in order to obtain the required sheet width, the material is not forced out but when A/E exceeds 0.4, if the outlet pressure is increaseed in order to obtain the required sheet width, the material becomes forced out through the clearance. Accordingly, A/E must be set to 0.4 or less. It is noted of course that the present invention is not merely limited to the above-described embodiments. The screw extruding machine for obtaining a sheet-like extruded article using a conventional roller dies according to the present invention is excellent in the following points. Material supplied from the hopper is kneaded and fed under pressure to the outlet by use of two screw shafts 2 and 2 arranged in parallel within the same plane in the casing, and therefore, pressure is applied merely at the front end of the screw and a wide sheet can be extruded with low pressure, and pressure need not be increased within the casing and the screws may be driven by a small power. Furthermore, the length of the compression portion can be made shorter than prior art, and therefore the length of the screw can be also made into compactness and the structure required can be simplified as well as disuse of a pusher device. Moreover, in the present invention, a pair of parallel screws are provided so that a phase thereof may be changed according to the composition content, components and the like of the material to be extruded, and therefore the engaging property and extrusion ability can be also enhanced depending on the various materials to be extruded. Moreover, by setting C/S to 0.6 or more, a sufficiently wide sheet can be obtained with a low extrusion pressure, and by setting A/E to 0.4 or less, a sheet width as required can be obtained while retaining pressure of material after discharged.

Claims: A screw extruding machine comprising screws (2) rotatably supported on a casing (1), a top-open hopper (3) provided on the side of a screw base portion of said casing (1), an outlet (4) opened in an axial direction of the screw (2) on the side of a screw front end of said casing (1), and a roller die (11) in proximity of said outlet (4), said screw having a feed portion (5) which corresponds to a face portion to the hopper (3) and a compression portion (6) which corresponds to a front end side, whereby material to be extruded supplied from the hopper (3) is extruded into a sheet-like form by said roller die (11) from the outlet (4) via said feed portion (5) and said compression portion (6) by the rotating screws (2), wherein said screws (2) are arranged two in number in the same plane, and said hopper (3) is arranged over the feed portion (5) of each screw (2), and wherein the length L of the compression portion (6) to the diameter D of said screw (2) is in the relationship of L/D = 0.3 to 0.6. A screw extruding machine according to claim 1, wherein said two screws (2) are arranged in an engaging state or a non-engaging state, and can be disposed with a phase varied to an angle of approximately 0° or approximately 180°, depending on the composition and characteristics of the material to be extruded, wherein said angle is formed by thread blades (7) on the same cross section at right angles to the axis. A screw extruding machine according to claim 1, or 2, wherein the ratio (C/S) between the outlet width (C) and the sheet width (S) is 0.6 or more. A screw extruding machine according to claim 1, 2, or 3, wherein the ratio (A/E) between the distance (A) of the surface at the front end of the outlet and the surface of the roller die (11), and the diameter (E) of the roller die (11) is 0.4 or less.

Inventors: ASADA MITUNORI, HAGIWARA KATUNOBU, HAMADA YOSHIHIRO, NAKAGAWA KAZUHIKO, NODA TAKEOKI, ASADA, MITUNORI, HAGIWARA, KATUNOBU, HAMADA, YOSHIHIRO, NAKAGAWA, KAZUHIKO, NODA, TAKEOKI
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO ALSO KNOWN AS KOBE STEEL LTD.
Application year: 1988
Main classification: B29C47
IPC codes: B29C47