Screw-type extruder

Abstract

This screw-type extruder comprises: a tapered screw that includes a shaft section and a flight; a drive section that rotates the tapered screw; a casing including a passage opening through which a material is allowed to pass; and a die plate that is attached to the casing so as to block the passage opening. The die plate comprises a first discharge hole disposed at a position corresponding to the tapered screw. When the tapered screw rotates, the size of a region where the tip surface of the flight of the tapered screw and the first discharge hole overlap when viewed in an extrusion direction of the material varies cyclically. An increase in the size of the region where the first discharge hole and the tip surface of the flight overlap causes the material extruded by the tapered screw to be cut.

Description

Screw Extruder

[0001] The present invention relates to a screw extruder provided with a pair of tapered screws.

[0002] Conventionally, as disclosed in JP-A-2018-122478, JP-A-2011-73428, JP-A-6-155547, Utility Model Laid-Open Publication No. 57-76832, and JP-A-58-36425, a screw extruder provided with a pair of tapered screws is known. Each of the pair of tapered screws has a shaft portion and a spiral flight. The pair of shaft portions are arranged so as to approach each other toward the tip and are inclined so that the tip is downward. Therefore, when the material is sent toward the tip by the flight, the material is gradually pressurized and also flows toward the tip by its own weight. For this reason, the retention of the material can be suppressed, and the material can be efficiently extruded.

[0003] By the way, in the screw extruders disclosed in JP-A-2018-122478 and JP-A-2,011-73428, a pair of rolls are provided at the material outlet, and the material is formed into a sheet shape by the pair of rolls. As a result, the handling property including the weight control of the material in the subsequent process is improved. However, in recent years, the demand for low-fuel-consumption tires has been increasing, and silica is often blended in a high proportion with rubber, which is a raw material for low-fuel-consumption tires. For this reason, it is difficult to form the material into a sheet shape in a screw extruder, and there are problems in the handling property including the weight control of the material in the subsequent process.

[0004] An object of the present invention is to provide a screw extruder that can handle materials that are difficult to form into a sheet shape.

[0005] A screw extruder according to one aspect of the present invention comprises a pair of tapered screws arranged so as to approach each other towards the tip, each of which has a shaft portion and a flight spirally provided on the outer circumference of the shaft portion and including a flat tip surface; a drive unit that generates a driving force for rotating the pair of tapered screws; a casing that houses the pair of tapered screws and has a receiving port for receiving material and a passage for passing material; and a die plate attached to the casing so as to close the passage. The die plate has a plurality of discharge holes arranged at positions corresponding to each of the pair of tapered screws, and the positions and shapes of the plurality of discharge holes are set so that when the pair of tapered screws are rotated by the drive unit, the size of the overlapping region between the tip surface of each of the pair of tapered screws and the corresponding discharge hole, when viewed in the direction of material extrusion, changes periodically. As the size of the overlapping region between the corresponding discharge hole and the tip surface of the flight increases, the material extruded by the pair of tapered screws is cut.

[0006] This is a cross-sectional view of a screw-type extruder according to an embodiment, viewed from above. This is a cross-sectional view of the screw-type extruder, viewed from the side. This is an enlarged view of a part of the screw-type extruder shown in Figure 2. This is a diagram showing a die plate provided in the screw-type extruder. This is a diagram showing a modified die plate. This is a diagram showing a modified die plate. This is a diagram showing a modified die plate.

[0007] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[0008] The screw-type extruder 1 according to this embodiment is an extruder for extruding materials such as rubber into pellets. The extruder 1 comprises a pair of left and right tapered screws 2 and 3, a casing 4 that houses the tapered screws 2 and 3, and a die plate 5 attached to the casing 4. Figure 1 shows the screw-type extruder 1 with the tapered screws 2 and 3 viewed from above, and Figure 2 shows the tapered screws 2 and 3 viewed from the side.

[0009] The first tapered screw 2 and the second tapered screw 3 each have a shaft portion 10 and a flight 11 spirally provided on the outer circumferential surface 10b of the shaft portion 10. The first tapered screw 2 and the second tapered screw 3 have the same structure except that the direction in which the flight 11 twists is opposite to that of the first tapered screw 2 and the second tapered screw 3 are driven by the drive unit 7 and rotate in opposite directions at the same rotational speed.

[0010] The first tapered screw 2 and the second tapered screw 3 are arranged so that they move closer to each other as they approach the tip. Each shaft portion 10 has a shape in which the outer diameter gradually decreases towards the tip. Therefore, the distance between the tips of the shaft portions 10, 10 is shorter than the distance between the base ends of the shaft portions 10, 10. As a result, the material is gradually pressurized as it is pushed out toward the tip. This makes it easier for the material to bite into the flights 11, 11 and prevents the material from accumulating inside the casing 4. Note that the shaft portion 10 may include a portion at the base end of the shaft portion 10 in which the outer diameter is constant in the axial direction.

[0011] Furthermore, the shaft portions 10, 10 are arranged in an inclined manner so that they are lower in the direction of gravity as they approach the tip. As a result, when the material is pushed out toward the tip, the material is also propelled by its own weight, making it easier for the material to grip the flights 11, 11.

[0012] The flight 11 is provided extending from the base end to the tip of the shaft portion 10. The tip surface 10a of the shaft portion 10 is flat, and the tip surface 11a of the flight 11 is formed as a flat surface that is in the same plane as the tip surface 10a of the shaft portion 10. Hereinafter, the tip surface formed by combining the tip surface 11a of the flight 11 and the tip surface 10a of the shaft portion 10 may be referred to as the tip surfaces 2a and 3a of the tapered screws 2 and 3.

[0013] The protruding height of the flight 11, that is, the height from the outer peripheral surface 10b of the shaft portion 10 to the outer end 11b of the flight 11, decreases as it approaches the tip of the shaft portion 10.

[0014] The casing 4 comprises a base portion 4a configured to support the base ends of both shaft portions 10, 10, and an enclosure portion 4b connected to the base portion 4a and covering the periphery of the pair of tapered screws 2, 3. The base portion 4a has an axial hole 4c through which the shaft portion 10 passes. The portion of the shaft portion 10 that protrudes from the axial hole 4c to the outside of the casing 4 is connected to the drive unit 7. The drive unit 7 generates a driving force that rotates the first tapered screw 2 and the second tapered screw 3 in opposite directions.

[0015] The enclosure portion 4b is positioned around the pair of tapered screws 2 and 3 so as to cover the top, left and right sides, and bottom of the pair of tapered screws 2 and 3. An opening 12 for receiving material into the casing 4 is formed in the portion of the enclosure portion 4b located above the pair of tapered screws 2 and 3. In other words, the casing 4 has an opening 12 for receiving material. The opening 12 is located above the base ends of the pair of tapered screws 2 and 3.

[0016] In the enclosure portion 4b, the end opposite to the base portion 4a is open. This opening is a passage 4d through which the material extruded by the pair of tapered screws 2 and 3 passes. In other words, the casing 4 has a passage 4d.

[0017] The tips of the first tapered screw 2 and the second tapered screw 3 are inserted into the passage opening 4d. That is, the tips of the shaft portion 10 and the flights 11 are positioned within the passage opening 4d so that their tip surfaces 10a and 11a are as close as possible to the inner surface of the die plate 5. Depending on the shape of the die plate 5, the tips of the shaft portion 10 and the flights 11 do not necessarily have to be inserted into the passage opening 4d.

[0018] The die plate 5 is attached to the casing 4 so as to close the passage opening 4d of the casing 4. The die plate 5 has a coupling portion 15 that is coupled to the casing 4 on the outside of the passage opening 4d, and a facing portion 16 that is opposite to the passage opening 4d.

[0019] As shown in Figure 3, the inner surface 15a of the joint portion 15, that is, the surface 15a of the joint portion 15 facing the casing 4, is fastened to the tip surface 4e of the enclosure portion 4b of the casing 4. The inner surface 16a of the opposing portion 16, that is, the surface 16a of the opposing portion 16 facing the casing 4, faces the passage opening 4d. The outer peripheral edge of the inner surface 16a of the opposing portion 16 follows the inner peripheral edge of the passage opening 4d.

[0020] The inner surface of the die plate 5 has a recess 18 that is recessed from the inner surface 15a of the joint portion 15. The recess 18 includes a first bottom surface portion 18a facing the tip surface 2a of the first tapered screw 2, a second bottom surface portion 18b facing the tip surface 3a of the second tapered screw 3, and a side surface portion 18c along the outer circumference of the first bottom surface portion 18a and the second bottom surface portion 18b. The first bottom surface portion 18a is parallel or approximately parallel to the tip surface 2a of the first tapered screw 2. The second bottom surface portion 18b is parallel or approximately parallel to the tip surface 3a of the second tapered screw 3.

[0021] The two shaft portions 10, 10 of the pair of tapered screws 2, 3 extend in a direction that brings them closer together towards each other as they approach their tips, and the tip surfaces 2a, 3a of the tapered screws 2, 3 are flat surfaces perpendicular to the direction in which the corresponding shaft portion 10 extends. For this reason, the tip surfaces 2a, 3a of the tapered screws 2, 3 are not aligned on the same plane, but are slightly inclined with respect to a plane PL perpendicular to a virtual straight line extending in the longitudinal direction (left-right direction in Figure 1) of the casing 4. For this reason, when viewed from above, the first bottom surface 18a is inclined in a first direction with respect to the plane PL (see Figure 2). Also, when viewed from above, the second bottom surface 18b is inclined in a second direction, which is the opposite direction to the first direction with respect to the plane PL. Note that the plane PL is also the direction along the passage opening 4d.

[0022] The gap G between the first bottom surface 18a and the tip surface 2a of the first tapered screw 2 is preferably 10 mm or less, and more preferably 5 mm or less. Similarly, the gap G between the second bottom surface 18b and the tip surface 3a of the second tapered screw 3 is also preferably 10 mm or less, and more preferably 5 mm or less. In other words, the material extruded by the pair of tapered screws 2 and 3 temporarily enters the gap G between the die plate 5 and the tip surfaces 2a and 3a of the pair of tapered screws 2 and 3. As will be described later, this material is cut by the flight 11 when it flows into the discharge holes 21 and 22 described later. For this reason, in order to improve the material cutting performance, it is preferable that the gap G between the die plate 5 and the tip surfaces 2a and 3a of the pair of tapered screws 2 and 3 be as narrow as possible. Accordingly, it is preferable that the gap G between the tip surfaces 2a and 3a of the pair of tapered screws 2 and 3 and the die plate 5 be set to 10 mm or less or 5 mm or less. Furthermore, it is preferable that the tip surfaces 2a and 3a of the pair of tapered screws 2 and 3 and the die plate 5 do not come into contact with each other. If the tip surface 11a of the flight 11 and the tip surface 10a of the shaft portion 10 are not formed on the same plane, it is sufficient that the gap between the tip surface 11a of the flight 11 and the die plate 5 (or the first bottom surface portion 18a or the second bottom surface portion 18b) be set to 10 mm or less or 5 mm or less.

[0023] The outer surface 16b of the opposing portion 16, that is, the surface 16b of the opposing portion 16 facing away from the casing 4, has a first inclined surface 16c parallel to the first bottom surface 18a, a second inclined surface 16d parallel to the second bottom surface 18b, and a connecting surface 16e located between the first inclined surface 16c and the second inclined surface 16d. Therefore, the outer surface of the die plate 5 also has a shape that is recessed from the outer surface of the joining portion 15. However, the outer surface of the die plate 5 is not limited to this shape and may be formed as a flat surface extending across the joining portion 15 and the opposing portion 16.

[0024] The die plate 5 is provided with a plurality of discharge holes 21 and 22. As shown in Figure 4, some of the discharge holes 21 and 22 are positioned to correspond to the tip surface 2a of the first tapered screw 2. These discharge holes are referred to as the plurality of first discharge holes 21. The remaining discharge holes are positioned to correspond to the tip surface 3a of the second tapered screw 3. These discharge holes are referred to as the plurality of second discharge holes 22. Figure 4 shows the outer surface of the die plate 5. The outer surface of the die plate 5 is the surface facing away from the casing 4, or in other words, the surface viewed from the direction of arrow A in Figure 3.

[0025] Multiple first discharge holes 21 are provided so as to penetrate the opposing portion 16 from the first bottom portion 18a of the inner surface 16a to the first inclined surface 16c of the outer surface 16b. On the other hand, multiple second discharge holes 22 are provided so as to penetrate the opposing portion 16 from the second bottom portion 18b of the inner surface 16a to the second inclined surface 16d of the outer surface 16b. However, some of the first discharge holes 21 may extend into the second bottom portion 18b. Also, some of the second discharge holes 22 may extend into the first bottom portion 18a.

[0026] Multiple first discharge holes 21 are arranged at intervals in the rotational direction of the first tapered screw 2. Each first discharge hole 21 has an elongated shape in a direction inclined with respect to the radial direction RD of the shaft portion 10. That is, since the flight 11 protrudes from the outer circumferential surface 10b of the shaft portion 10 in a direction inclined with respect to the radial direction RD of the shaft portion 10, the first discharge holes 21 are also inclined in the same direction as the inclination direction of the flight 11. Note that the direction in which the flight 11 protrudes from the outer circumferential surface 10b of the shaft portion 10 and the longitudinal direction LD of the first discharge hole 21 may or may not be parallel. In the example shown in Figure 4, the longitudinal direction LD of the first discharge hole 21 is inclined with respect to the radial direction RD of the shaft portion 10. For example, the angle θ between the longitudinal direction LD and the radial direction RD may be 30 to 50 degrees. When the angle θ is such an inclination angle, a long first discharge hole 21 can be provided in the longitudinal direction LD, which is effective for a screw-type extruder 1 that discharges larger pellets. Furthermore, the longitudinal direction LD of the first discharge hole 21 can be set to a desired angle with respect to the flight 11. The longitudinal direction LD is the direction that passes through the intersection of the outer circumferential surface 10b of the shaft portion 10 and the radial direction RD, and extends along the longitudinal direction LD of the first discharge hole 21.

[0027] In Figure 4, the first taper cru 2 on the left rotates clockwise, and the second taper cru 3 on the right rotates counterclockwise.

[0028] In the die plate 5, of the inner circumferential surfaces 24 that define each first discharge hole 21, at least the front surface 24a is inclined with respect to the first bottom surface 18a (or inner surface 16a) such that the opening area increases in the direction of material discharge. The front surface 24a referred to here is the side toward which the flight 11 faces during the rotation of the tapered screw 2. In other words, when viewed in the direction in which the shaft portion 10 extends, the flight 11 moves from the rear surface 24b of the first discharge hole 21 toward the front surface 24a during the rotation of the tapered screw 2.

[0029] The inclination angle of the front surface 24a with respect to the first bottom surface 18a (or inner surface 16a) is preferably 40 to 60 degrees. In the example shown in Figure 4, the front surface 24a is inclined with respect to the first bottom surface 18a, while the rear surface 24b is perpendicular to the first bottom surface 18a (or inner surface 16a). However, the inner circumferential surface 24 of the first discharge hole 21 is not limited to this configuration.

[0030] Each first discharge hole 21 is located radially inward from the trajectory TR of the outer end 11b of the rotating flight 11. That is, even at the outermost edge (also referred to as the outer edge 21a) of the shaft portion 10 in the radial direction RD, the first discharge hole 21 is located radially inward from the trajectory TR of the outer end 11b of the flight 11. Here, the outer edge 21a of the first discharge hole 21 refers to the outer edge 21a on the inner surface 16a of the opposing portion 16.

[0031] The innermost edge (also referred to as the inner edge 21b) of the shaft portion 10 in the radial direction RD of the first discharge hole 21 is located radially inward from the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10). Here, the inner edge 21b of the first discharge hole 21 refers to the inner edge 21b of the inner surface 16a of the opposing portion 16.

[0032] The inner edge portion 21b may be formed at a position that coincides with the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10), or it may be located radially outward from the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10). When the inner edge portion 21b is located radially outward from the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10), and the flight 11 is not in an opposing position, the first discharge hole 21 will be completely open.

[0033] As described above, the outer edge 21a of the first discharge hole 21 is located radially inward from the trajectory TR of the outer end 11b of the rotating flight 11. Therefore, when the first tapered screw 2 rotates, there is a period during which the tip surface 11a of the flight 11 overlaps the first discharge hole 21 over the entire length LD of the first discharge hole 21. Note that the state in which the tip surface 11a of the flight 11 overlaps the first discharge hole 21 means that when viewed in the direction in which the shaft portion 10 extends (or in a direction perpendicular to the first inclined surface 16c or perpendicular to the first bottom surface portion 18a), the tip surface 11a of the flight 11 appears to overlap at least a part of the first discharge hole 21.

[0034] As the first taper scru 2 rotates, the flight 11 sequentially overlaps with each first discharge hole 21. Therefore, at each first discharge hole 21, there is a period of overlap between the tip surface 11a of the flight 11 and a period of non-overlap between the tip surface 11a of the flight 11 and the first discharge hole 21, which repeats periodically. In other words, the position and shape of the first discharge hole 21 are set so that the size of the overlapping area between the tip surface 11a of the flight 11 and the first discharge hole 21 changes periodically.

[0035] In the rotational direction of the shaft portion 10, the width of the first discharge hole 21 is smaller than the width of the tip surface 11a of the flight 11. Therefore, when the first tapered screw 2 rotates, the tip surface 11a of the flight 11 overlaps with the first discharge hole 21 over the entire width of the shaft portion 10 in the rotational direction for a period of time. Also, as mentioned above, the outer edge 21a of the first discharge hole 21 is located radially RD inward from the trajectory TR of the outer end 11b of the rotating flight 11. Therefore, when viewed in the material extrusion direction, the entirety of one first discharge hole 21 is temporarily blocked by the tip surface 11a of the flight 11 and the tip surface 10a of the shaft portion 10. In other words, the tip surface 11a of the flight 11 has a shape that, when viewed in the material extrusion direction, cooperates with the tip surface 10a of the shaft portion 10 to block the entirety of the first discharge hole 21 during the rotation of the tapered screw 2. Furthermore, when viewed in the material extrusion direction, the tip surface 10a of the shaft portion 10 may have a shape that completely blocks the first discharge hole 21 during the rotation of the tapered screw 2.

[0036] When the tip surface 11a of the flight 11 is in a position that does not overlap with one of the first discharge holes 21, the material surrounding the shaft portion 10 is pushed out into the first discharge hole 21 by the flight 11 without being divided. In contrast, when the tip surface 11a of the flight 11 passes a position that overlaps with the first discharge hole 21, the material surrounding the shaft portion 10 is divided by the flight 11 in the gap G between the tip surface 11a of the flight 11 and the inner surface 16a of the opposing portion 16 of the die plate 5. In other words, the material is divided as the overlapping area between the first discharge hole 21 and the tip surface 11a of the flight 11 increases. At this time, since the tip surface 11a of the flight 11 overlaps with the first discharge hole 21 sequentially from the inside to the outside in the radial direction, the division of the material also occurs sequentially from the inside in the radial direction.

[0037] As the material is divided, it becomes pellets and is discharged through the first discharge hole 21. At this time, since the front surface 24a of the first discharge hole 21 is inclined with respect to the first bottom surface 18a, it is possible to suppress the divided material from adhering to the front surface 24a.

[0038] The second discharge hole 22 is formed in the same way as the first discharge hole 21, except that it is formed in the opposite direction from the left to right. That is, the multiple second discharge holes 22 are arranged at intervals in the rotational direction of the second tapered screw 3, and each second discharge hole 22 has an elongated shape in a direction inclined with respect to the radial direction of the shaft portion 10. In addition, of the inner circumferential surface 26 that defines the second discharge hole 22 in the die plate 5, at least the front side surface 26a is inclined so that the opening area increases toward the material discharge direction. The rear side surface 26b may or may not be inclined.

[0039] Furthermore, each second discharge hole 22 is located radially inward from the trajectory TR of the outer end 11b of the rotating flight 11. Therefore, the outer edge 22a of the second discharge hole 22 is located radially inward from the trajectory TR of the outer end 11b of the flight 11. Also, the inner edge 22b of the second discharge hole 22 is located radially inward from the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10). However, the inner edge 22b may be formed at a position that coincides with the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10), or it may be located radially outward from the trajectory of the inner end of the flight 11 (or the outer circumferential surface 10b of the shaft portion 10).

[0040] As the second taper scru 3 rotates, the flights 11 of the second taper scru 3 overlap sequentially with respect to each second discharge hole 22. Therefore, at each second discharge hole 22, periods in which the tip surfaces 11a of the flights 11 overlap and periods in which the tip surfaces 11a of the flights 11 do not overlap are periodically repeated. In addition, in the rotational direction of the shaft portion 10, the width of the second discharge hole 22 is smaller than the width of the tip surfaces 11a of the flights 11.

[0041] When the tip surface 11a of the flight 11 is in a position that does not overlap with one of the second discharge holes 22, the material surrounding the shaft portion 10 is pushed out into the second discharge hole 22 by the flight 11 without being cut. In contrast, when the tip surface 11a of the flight 11 passes a position that overlaps with the second discharge hole 22, the material surrounding the shaft portion 10 is cut in the gap G between the tip surface 11a of the flight 11 and the inner surface 16a of the opposing portion 16 of the die plate 5.

[0042] The die plate 5 is equipped with heaters 28 that raise the temperature of the die plate 5. The heating of the die plate 5 by the heaters 28 improves the release properties of the material after cutting. The heaters 28 are located at both ends of the die plate 5 in the longitudinal direction. However, the heaters 28 are not limited to these positions.

[0043] As described above, in the present embodiment, when the pair of tapered screws 2 and 3 rotate and the material is sent toward the tip by the flights 11, the material is gradually pressurized. In this state, the material flows into the plurality of discharge holes 21 and 22 of the die plate 5. When the pair of tapered screws 2 and 3 rotate, the size of the overlapping region between the flat tip surfaces 11a of the respective flights 11 of the pair of tapered screws 2 and 3 and the corresponding discharge holes 21 and 22, as viewed in the extrusion direction of the material, changes periodically. And when the overlapping region between the discharge holes 21 and 22 and the tip surface 11a of the flight 11 becomes large, the material is cut. At this time, since the size of the overlapping region changes periodically, the material continuously flowing into the discharge holes 21 and 22 is cut every predetermined time. Therefore, since there is little variation in the size of the cut material, it is possible to obtain a predetermined weight of the extruded material without forming it into a sheet shape. Therefore, it becomes a screw extruder 1 corresponding to a material that is difficult to form into a sheet shape.

[0044] Further, in the present embodiment, the outer edge portions 21a and 22a located at the outermost side in the radial direction RD of the shaft portion 10 in the discharge holes 21 and 22 are located inside the radial direction from the locus TR of the tip surface 11a of the flight 11. For this reason, when viewed in the extrusion direction of the material, the tip surface 11a of the flight 11 passes through the entire area of the portions of the discharge holes 21 and 22 other than the portions facing the shaft portion 10. Therefore, it is possible to prevent the remaining material from occurring throughout the discharge holes 21 and 22 in the radial direction RD of the shaft portion 10.

[0045] Further, in the present embodiment, since the die plate 5 can be heated by the heater 28, it is possible to suppress the adhesion of the cut material to the die plate 5.

[0046] In addition, in the present embodiment, at least the front side surface 24a of the discharge holes 21 and 22 is inclined so that the opening area increases in the material discharge direction. For this reason, it is possible to suppress the cut material from adhering to and staying on the front side surface 24a of the discharge holes 21 and 22. That is, if the material adheres to the inner peripheral surface 24 of the discharge holes 21 and 22 even after being cut, the material may stay in the discharge holes 21 and 22. In that case, this material may be connected to the material pushed out next. Therefore, since at least the front side surface 24a of the discharge holes 21 and 22 is inclined, the adhesion of the cut material to the front side surface 24a of the discharge holes 21 and 22 is suppressed. For this reason, the adhesion between the cut materials can be suppressed.

[0047] Note that the width of the first discharge hole 21 in the rotational direction of the shaft portion 10 may be the same as or larger than the width of the tip surface 11a of the flight 11. Even when the width of the first discharge hole 21 is larger than the width of the tip surface 11a of the flight 11, there is a period during which the flight 11 overlaps the first discharge hole 21. During that period, not the entire first discharge hole 21 is blocked, but only a part of the first discharge hole 21 is blocked. However, since the outer end 11b of the flight 11 is located outside the outer edge portion 21a of the first discharge hole 21 in the radial direction RD of the shaft portion 10, the flight 11 passes through the entire first discharge hole 21 in the radial direction RD of the shaft portion 10. Therefore, the material can be divided by the flight 11.

[0048] For example, in the die plate 5 shown in FIG. 5, in the rotational direction of the shaft portion 10 of the first tapered screw 2 and the second tapered screw 3, the width of the first discharge hole 21 is larger than the width of the tip surface 11a of the flight 11. Further, the outer edge portion 21a of the first discharge hole 21 is located radially inward of the locus TR of the outer end 11b of the flight 11. The same applies to the second discharge hole 22. However, the first discharge hole 21 has a shape in which the width in the rotational direction of the shaft portion 10 is larger than the length in the radial direction. The same applies to the second discharge hole 22.

[0049] In this configuration as well, the flight 11 of the first tapered screw 2 passes through the entire first discharge hole 21 in the radial direction RD of the shaft portion 10. Therefore, the material can be divided by the flight 11. The same applies to the second tapered screw 3. Note that in Figure 5, the flight 11 has a shape that is wider in the rotational direction of the shaft portion 10 than the flight 11 shown in Figure 4.

[0050] In the die plate 5 shown in Figure 4, the rear surface 24b of the first discharge hole 21 is perpendicular to the first bottom surface 18a. In contrast, in the die plate 5 shown in Figure 6, the inner circumferential surface 24 defining the first discharge hole 21 is tapered so that the opening area increases in the direction of material discharge. In other words, the inner circumferential surface 24 is inclined along its entire circumference, including not only the front surface 24a but also the rear surface 24b of the first discharge hole 21. The second discharge hole 22 is formed similarly.

[0051] In this configuration, each first discharge hole 21 and each second discharge hole 22 are formed as tapered holes. Therefore, it is possible to further suppress the adhesion of cut material to the inner circumferential surface 24 of the first discharge hole 21 and the inner circumferential surface 26 of the second discharge hole 22. Note that the shape of the first discharge hole 21 and the shape of the second discharge hole 22 are not limited to the shapes shown in Figure 6. Also, the shape of the tip surface 11a of the flight 11 is not limited to the shape shown in Figure 6.

[0052] The shape of the first discharge hole 21 and the shape of the second discharge hole 22 may be a round cross-section, as shown in Figure 7.

[0053] The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The present invention is not limited to the embodiments described above, and various modifications and improvements are possible without departing from its spirit. For example, a mechanism may be provided to adjust the gap G between the taper screws 2 and 3 and the die plate 5. For example, by providing shims (not shown) at the base ends of the taper screws 2 and 3, the gap G width may be finely adjusted so that the gap G between the taper screws 2 and 3 and the die plate 5 becomes narrower.

[0054] Here, we will give an overview of the embodiment described above.

[0055] A screw extruder according to one aspect of the present invention comprises a pair of tapered screws arranged so as to approach each other towards the tip, each of which has a shaft portion and a flight spirally provided on the outer circumference of the shaft portion and including a flat tip surface; a drive unit that generates a driving force for rotating the pair of tapered screws; a casing that houses the pair of tapered screws and has a receiving port for receiving material and a passage for passing material; and a die plate attached to the casing so as to close the passage. The die plate has a plurality of discharge holes arranged at positions corresponding to each of the pair of tapered screws, and the positions and shapes of the plurality of discharge holes are set so that when the pair of tapered screws are rotated by the drive unit, the size of the overlapping region between the tip surface of each of the pair of tapered screws and the corresponding discharge hole, when viewed in the direction of material extrusion, changes periodically. As the size of the overlapping region between the corresponding discharge hole and the tip surface of the flight increases, the material extruded by the pair of tapered screws is cut.

[0056] In the screw-type extruder described above, as a pair of tapered screws rotate and the material is fed toward the tip by the flights, the material is gradually pressurized. In this state, the material flows into multiple discharge holes in the die plate. When the pair of tapered screws rotate, the size of the overlap area between the flat tip surfaces of each flight of the pair of tapered screws and the corresponding discharge holes, when viewed in the direction of material extrusion, changes periodically. When the overlap area between the discharge holes and the tip surfaces of the flights increases, the material is cut. At this time, because the size of the overlap area changes periodically, the material continuously flowing into the discharge holes is cut at predetermined time intervals. Therefore, since there is little variation in the size of the material cut, a predetermined weight of material can be obtained by extrusion without forming it into a sheet. Thus, this screw-type extruder is suitable for materials that are difficult to form into a sheet.

[0057] In the corresponding discharge hole, the outermost radial edge of the shaft portion may be located radially inward of the shaft portion than the trajectory of the outer end of the tip surface of the rotating flight.

[0058] In this embodiment, when viewed in the material extrusion direction, the tip surface of the tapered screw passes through the entire area of ​​the corresponding discharge hole. Therefore, it is possible to prevent material from being left uncut throughout the entire area of ​​the discharge hole in the radial direction of the shaft.

[0059] The die plate may be provided with a heater. In this embodiment, the die plate can be heated, which can suppress the adhesion of the material after cutting to the die plate.

[0060] At least the front surface of the inner circumferential surface defining the plurality of discharge holes, which faces away from the rotational direction of the pair of tapered screws, may be inclined such that the opening area increases in the direction of material discharge.

[0061] In this embodiment, it is possible to suppress the adhesion and retention of the cut material on the front surface of the discharge hole. That is, even if the material is cut, if it adheres to the inner surface of the discharge hole, there is a possibility that the material will remain inside the discharge hole. In that case, this material may connect with the next material that is extruded. Therefore, by having at least the front surface of the discharge hole inclined, the adhesion of the cut material to the front surface of the discharge hole is suppressed, and thus the adhesion of the cut material to each other can be suppressed.

[0062] The leading surface of the flight may have a shape that, when viewed in the material extrusion direction, has a period of time during the rotation of the pair of tapered screws that closes the corresponding discharge holes. In this embodiment, the material cutting performance can be improved.

[0063] The gap between the tip surface of the flight and the die plate may be 10 mm or less. In this embodiment, the material cutting performance can be improved.

[0064] As described above, the screw-type extruder according to the embodiment can handle materials that are difficult to form into a sheet.

[0065] This application is based on Provisional Application No. 63 / 707480, filed with the United States Patent and Trademark Office on 15 October 2024, the contents of which are incorporated herein by reference.

Claims

1. A screw-type extruder comprising: a pair of tapered screws arranged so as to approach each other towards the tip, each of the pair of tapered screws having a shaft portion and a flight spirally provided on the outer circumference of the shaft portion and including a flat tip surface; a drive unit that generates a driving force for rotating the pair of tapered screws; a casing that houses the pair of tapered screws and has a receiving port for receiving material and a passage for passing material; and a die plate attached to the casing so as to close the passage. The die plate has a plurality of discharge holes positioned corresponding to each of the pair of tapered screws, and the position and shape of the plurality of discharge holes are set such that, when the pair of tapered screws are rotated by the drive unit, the size of the overlapping region between the tip surface of each of the pair of tapered screws and the corresponding discharge hole, when viewed in the material extrusion direction, changes periodically. A screw extruder in which the material extruded by the pair of tapered screws is cut as the size of the overlapping area between the corresponding discharge hole and the leading surface of the flight increases.

2. A screw extruder according to claim 1, wherein the outermost radial edge of the shaft portion in the corresponding discharge hole is located radially inward of the shaft portion than the trajectory of the outer end of the tip surface of the rotating flight.

3. A screw extruder according to claim 1, wherein a heater is provided on the die plate.

4. A screw-type extruder according to claim 1, wherein at least the front surface of the inner circumferential surface defining the plurality of discharge holes, which faces away from the rotation direction of the pair of tapered screws, is inclined such that the opening area increases toward the material discharge direction.

5. A screw extruder according to claim 1, wherein the leading surface of the flight has a shape that, when viewed in the material extrusion direction, has a period of time during rotation of the pair of tapered screws that closes the corresponding discharge holes.

6. A screw extruder according to claim 1, wherein the gap between the leading surface of the flight and the die plate is 10 mm or less.

Images