JP5456430B2 - Screw for molding machine - Google Patents

Description

  The present invention relates to a screw for a molding machine, and particularly relates to a screw for a molding machine for achieving a high extrusion rate and discharge rate while maintaining a uniform kneaded state of a material resin.

  A full flight screw having a flight over the entire length is often used as a screw for a resin molding single screw extruder or injection molding machine (in this specification, these are called molding machine screws). This flight, combined with a heater that heats the cylinder, has a function of transporting or melting the material resin. However, the optimization of the flight shape and dimensions alone limits the homogeneity of the extrusion capability and product quality that can be obtained.

  Therefore, various mixing sections are attached to the tip of the screw in order to make the material resin in a uniform kneaded state. In particular, a barrier type mixing section is used to prevent the unmelted material from being extruded as it is.

  4 is one of the conventional barrier type mixing sections, FIG. 4 (1) is a front view of the conventional mixing section, and FIG. 4 (2) is a cross-sectional view taken along the line CC in FIG. 4 (1). . As shown in FIG. 4, the resin inflow groove 95 has an upstream side (the right side in FIG. 4 (1)) communicating with the upstream screw groove 92, and a downstream side (the left side in FIG. 4 (1)). Is blocked. The resin outflow groove 96 is closed on the upstream side and open on the downstream side. Thus, four pairs of resin inflow grooves 95 and outflow grooves 96 adjacent to each other are formed on the circumference of the screw.

  Among the walls on both sides in the circumferential direction of the inflow groove 95, the top of the wall on the pushing side with respect to the screw rotation direction (arrow P in FIG. 4) is a barrier 94, and through a gap δ with the inner wall 98 of the cylinder 97. The molten resin can flow into the adjacent outflow groove 96. When the molten resin passes through the barrier 94, the molten resin receives heat and generates heat, and gradually flows in the outflow groove 96 while increasing the melting degree. However, since the unmelted resin cannot pass through the gap δ, it flows through the inflow groove 95 toward the downstream, gradually melts by the heating and shearing received in the meantime, and flows into the next outflow groove 96 from the downstream side. The gap δ between the barrier 94 and the inner wall 98 of the cylinder 97 varies depending on the inner diameter of the cylinder, but is usually about 0.3 to 1 mm.

  On the other hand, the gap between the wall 93 on the opposite side of the inflow groove 95, that is, the top 93 of the wall on the back side with respect to the screw rotation direction (arrow P in FIG. 4) and the inner wall 98 of the cylinder 97 is smaller than the gap δ. The distance between the flight 91 and the inner wall 98 of the cylinder 97 is approximately the same, and the molten resin cannot pass through this gap. As described above, the material including the unmelted resin supplied from the upstream screw becomes a uniform molten state in the mixing section and is sent to the downstream side.

  Further, in order to avoid the problem of insufficient feeding ability while maintaining the uniform melting effect of the mixing section of FIG. 4, the mixing section shown in Patent Document 1 has been developed. FIG. 5 is a front view showing the mixing section of Patent Document 1, and is geometrically obtained by twisting the mixing section shown in FIG. 4 about the central axis of the screw. The direction of twisting is the same as that of flight 91. Therefore, the mixing section itself can be provided with a feeding capacity of the material resin. Further, in this mixing section, the depth of the resin inflow groove 95 becomes shallower as it goes downstream, so that the possibility of the resin staying portion is reduced.

  However, the conventional screw having the mixing section shown in FIGS. 4 and 5 has the following problems. The first problem is that the cross-sectional area of the resin flow path rapidly decreases at the inflow portion into the mixing section. That is, the conventional mixing section has the same number of outflow grooves 96 as the inflow grooves 95, and considering that the depth of the normal inflow groove 95 is almost the same as the depth of the screw groove 92 immediately upstream thereof, This is because the flow passage cross-sectional area of the inflow groove 95 is less than half of the flow passage cross-sectional area of the screw groove 92 immediately before the inflow groove 95. As a result, a large pressure loss occurs when the resin flows into the inflow groove 95. Therefore, in the screw having such a mixing section, the extrusion ability of the material resin is considerably lowered.

  The second problem is that when the resin flows from the respective inflow grooves 95 through the barriers 94 and flows into the adjacent outflow grooves 96, the resin that has flowed into the outflow grooves 96 passes through the outflow grooves 96 to the downstream side as it is. It will flow. Therefore, since the resin is only melted by the heat generated by the shearing force when it passes through the barrier 94 once, the resin is insufficiently melted, and the insufficiently melted resin passes through the outflow groove 96 as it is downstream. Will flow.

  The third problem is that the unmelted or semi-molten resin may not be sufficiently melted even if it flows down to the downstream of the inflow groove 95. This may occur particularly when the amount of extrusion is large. In such a case, if the gap δ between the barrier 94 and the inner wall 98 of the cylinder 97 is large, the semi-molten resin may pass through the gap δ and flow downstream as it is.

Japanese Patent Publication No.43-24493

  It is an object of the present invention to provide a molding machine screw that can obtain a large extrusion amount and discharge amount while maintaining a uniform molten state in a molding machine screw having a barrier type mixing section. To do.

The above problem is solved by the following means. That is, the present invention is formed in a spiral shape on the outer periphery of a screw rotatably inserted into a cylinder, and transports thermoplastic resin supplied to the base of the cylinder to the tip side of the cylinder, and on the outer periphery of the screw. A screw for a molding machine having a formed barrier type mixing section, wherein the mixing section is formed at a predetermined interval on a circumference of an outer periphery of the screw, and the base side of the cylinder and the tip of the cylinder There are a plurality of grooves open on both sides, and the gap between the top of the wall formed on both sides in the circumferential direction of the groove and the inner wall of the cylinder is sized to allow the molten resin to pass through. in the molding machine screw that is, the groove is formed in the twist direction and the same direction of the spiral shape of the flight, the lead angle of the groove is the Light is formed larger than the lead angle, the mixing section, at a distance from each other in the axial direction of the screw formed with a plurality, of the top and the inner wall of the cylinder wall of the front end side mixing section of the cylinder The screw for a molding machine is characterized in that a gap therebetween is formed smaller than a gap between the top of the mixing section wall on the base side of the cylinder and the inner wall of the cylinder.

  In the screw for a molding machine of the present invention, a barrier type mixing section formed on the outer periphery of the screw having a flight is formed on the circumference of the outer periphery of the screw at a predetermined interval, and the base side of the cylinder and the tip side of the cylinder Both have a plurality of open grooves, and the gap between the top of the wall formed on both sides of the groove in the circumferential direction and the inner wall of the cylinder is formed to a size that allows the molten resin to pass through. Yes.

  Accordingly, the total cross-sectional area of the plurality of grooves is almost the same as or larger than the cross-sectional area of the screw groove immediately before the groove. Therefore, when the resin flows into the groove, no pressure loss occurs, and the resin extrusion capability is improved. In addition, the resin that has flowed into the grooves sequentially passes through the gap, flows into the adjacent grooves, and generates heat by receiving the same number of shearing forces as the number of grooves, so that the resin is sufficiently melted and the resin is sufficiently Homogenized.

  Further, the groove is formed in a spiral shape in the same direction as the flight twist direction, and the groove lead angle is formed larger than the flight lead angle. Therefore, since the resin flowing into the groove is given a large feeding component force in the circumferential direction of the screw, the ability to feed the resin into the adjacent groove is improved.

  In addition, a plurality of mixing sections are formed apart from each other in the axial direction of the screw, and the gap between the top of the mixing section wall on the tip end side of the cylinder and the inner wall of the cylinder is set to the top of the mixing section wall on the base side of the cylinder. If the gap is smaller than the gap between the cylinder and the inner wall of the cylinder, the resin will generate heat by receiving a greater shearing force at the mixing section on the tip side of the cylinder. Homogenized sufficiently.

It is a whole sectional view showing a single screw extruder which has a screw for molding machines of an example of the present invention. It is an enlarged view of 3 A of mixing sections of FIG. 1, (1) is an enlarged front view, (2) is AA sectional drawing of (1). It is an enlarged view of the mixing sections 3B and 3C of FIG. 1, (1) is an enlarged front view, (2) is a BB sectional view of (1). It is an example of the conventional barrier type mixing section, (1) is a front view of the conventional mixing section, and (2) is a CC sectional view of (1). It is a front view which shows the other example of the conventional barrier type mixing section.

  In the following examples, an example in which the present invention is applied to a screw for a molding machine of a single screw extruder will be described. FIG. 1 is an overall cross-sectional view showing a single screw extruder having a screw for a molding machine according to an embodiment of the present invention. 2 is an enlarged view of the mixing section 3A of FIG. 1, FIG. 2 (1) is an enlarged front view, and FIG. 2 (2) is an AA sectional view of FIG. 2 (1). 3 is an enlarged view of the mixing sections 3B and 3C of FIG. 1, FIG. 3 (1) is an enlarged front view, and FIG. 3 (2) is a cross-sectional view taken along line BB of FIG. 3 (1).

  As shown in FIG. 1, a screw 2 on which spiral flights 21A, 21B, 21C, and 21D are formed is rotatably inserted in an inner wall 11 of a cylindrical cylinder 1 of a single-screw extruder. The flights 21 </ b> A, 21 </ b> B, 21 </ b> C, 21 </ b> D are formed in this order from the supply port 12 of the cylinder 1 toward the discharge port 13, and are formed in a spiral shape in the same direction. The gap between the outer peripheral surfaces of the flights 21A, 21B, 21C, and 21D and the inner wall 11 of the cylinder 1 is very small, and is set to a size that prevents molten resin from passing through the gap. Flight 21A, 21B, 21C has one line, and flight 21D has two lines. The lead angle β1 of the flights 21A, 21B, 21C, and 21D is formed at 15 degrees.

  The screw 2 is rotated via a speed reducer by a motor (not shown). When the screw 2 rotates, the solid resin piece introduced into the supply port 12 on the base side of the cylinder 1 moves in the screw grooves 22A, 22B, 22C, 22D of the screw 2 toward the discharge port 13 on the tip side of the cylinder 1. Are transported. The screw grooves 22A, 22B, 22C, and 22D are formed in the flights 21A, 21B, 21C, and 21D, respectively.

  The resin piece is heated and melted by the heaters 14 </ b> A and 14 </ b> B provided on the outer peripheral surface of the cylinder 1 while being transported toward the discharge port 13. The screw 2 is configured from a supply port 12 toward a discharge port 13 in the order of a supply unit A, a compression kneading unit B, and a measuring unit C.

  In the screw 2, barrier type mixing sections 3 </ b> A, 3 </ b> B, 3 </ b> C are formed in the compression kneading part B so as to be separated in the axial direction of the screw 2. The mixing section 3A is formed between the flight 21A and the flight 21B. The mixing section 3B is formed between the flight 21B and the flight 21C. The mixing section 3C is formed between the flight 21C and the flight 21D. The mixing section 3A has the same shape and different dimensions from the mixing sections 3B and 3C. Further, in the embodiment of the present invention, the mixing sections 3B and 3C are formed with the same shape and the same size, but may be formed with the same shape and different size.

  First, the mixing section 3A will be described. As shown in FIGS. 1 and 2, the mixing section 3A includes six grooves 4A to 4F at equal intervals (60 degree intervals) on the circumference of the outer periphery of the screw 2. Is formed. The grooves 4A to 4F have the same shape and are formed in a spiral shape in the same direction as the twist direction of the flights 21A to 21D. Further, the grooves 4A to 4F are open to both the screw groove 22A on the base side (supply port 12 side) of the cylinder 1 and the screw groove 22B on the tip side (discharge port 13 side) of the cylinder 1. The lead angle β2 of the grooves 4A to 4F is formed at 75 degrees and is larger than the lead angle β1 of the flights 21A, 21B, 21C, and 21D.

  Since the grooves 4A to 4F have the same shape, the groove 4A will be described. In the groove 4A, a gap δ1 is formed between the top 51 of the pushing side wall 5 and the inner wall 11 of the cylinder 1 with respect to the rotation direction of the screw 2 (arrow P in FIG. 2). The size is such that the molten resin can flow into the adjacent groove 4B. In the groove 4A, a gap δ2 is also formed between the top 61 of the wall 6 on the back side and the inner wall 11 of the cylinder 1 with respect to the rotation direction of the screw 2 (arrow P in FIG. 2). The gap δ2 is formed in such a size that the molten resin can flow into the groove 4A from the adjacent groove 4F. That is, the gaps δ1 and δ2 between the tops 51 and 61 of the walls 5 and 6 formed on both sides in the circumferential direction of the grooves 4A to 4F and the inner wall 11 of the cylinder 1 are large enough to allow the molten resin to pass. Is formed.

  Since all of the six grooves 4A to 4F have the same shape, the top 51 of the push-side wall 5 of the grooves 4A to 4F and the top 61 of the back-side wall 6 of the grooves 4A to 4F adjacent to the push-side wall 5 are It shows the same place. Similarly, the top 61 of the back wall 6 of the grooves 4A to 4F and the top 51 of the push wall 5 of the grooves 4A to 4F adjacent to the back wall 6 indicate the same location. Therefore, the gap δ1 and the gap δ2 have the same dimensions. For example, when the inner diameter of the inner wall 11 of the cylinder 1 is 60 mm, the gap δ1 and the gap δ2 are preferably set to 2 mm. Of course, the size of the gap δ1 and the gap δ2 can be appropriately set according to the size of the inner diameter of the cylinder 1 and the type of resin. Further, the grooves 4A to 4F may have different shapes, and the gap δ1 and the gap δ2 may have different dimensions.

  The push-side wall 5 is formed in a convex arc shape outward in the radial direction so that the gap between the push-side wall 5 and the inner wall 11 of the cylinder 1 gradually decreases toward the top 51. Since the grooves 4 </ b> A to 4 </ b> F are formed in a spiral shape, the resin flowing into the grooves 4 </ b> A to 4 </ b> F is caused by the rotational force of the screw 2 in the circumferential direction and the axial feed force as the screw 2 rotates. Both feed forces are given. The lead angle β2 of the grooves 4A to 4F of the mixing section 3A is larger than the lead angle β1 of the flights 21A, 21B, 21C, and 21D. Therefore, the resin flowing into the grooves 4A to 4F is given a large feeding force in the circumferential direction of the screw 2 as the screw 2 rotates, and the ability to feed the resin to the adjacent grooves 4A to 4F is set large. ing. Accordingly, the resin in the grooves 4 </ b> A to 4 </ b> F is gradually stretched under pressure as the screw 2 rotates, and passes through the gap δ <b> 1 between the top 51 and the inner wall 11 of the cylinder 1 and is adjacent. It smoothly flows into the grooves 4A to 4F.

  The wall 6 on the back side is a convex circle outwardly in the radial direction so that the molten resin that has flowed in through the gap δ2 from the adjacent grooves 4A to 4F smoothly enters the grooves 4A to 4F. It is formed in an arc shape so that convection of the molten resin does not occur.

  When the resin is conveyed from the screw groove 22A on the base side (supply port 12 side) of the cylinder 1 to the mixing section 3A configured as described above, the resin flows into the six grooves 4A to 4F. The total cross-sectional area of the six grooves 4A to 4F is substantially the same as or larger than the cross-sectional area of the screw groove 22A immediately before it. Therefore, no pressure loss occurs when the resin flows into the grooves 4A to 4F. As a result, in the screw having the mixing section 3A of the present invention, the extrusion capability of the material resin is improved.

  As the screw 2 rotates, a large feed force acts on the resin flowing into the six grooves 4A to 4F in the circumferential direction, and pressure is gradually applied by the push-side wall 5. It is stretched and passes through the gap δ1 between the top 51 and the inner wall 11 of the cylinder 1 and flows into the adjacent grooves 4A to 4F. When the resin passes through the gap δ1, the resin receives heat and generates heat, and gradually flows into the adjacent grooves 4A to 4F while increasing the melting degree.

  For example, the resin that has flowed into the groove 4A will be described. The resin that has passed through the gap 4A from the groove 4A and has flowed into the adjacent groove 4B is gradually pressured by the wall 5 on the pushing side of the groove 4B as the screw 2 rotates. Is added, and passes through the gap δ1 between the top 51 of the push-side wall 5 of the groove 4B and the inner wall 11 of the cylinder 1 and flows into the adjacent groove 4C. When the resin passes through the gap δ1, it generates heat by receiving a shearing force and gradually flows into the adjacent groove 4C while increasing the melting degree.

  In this way, the resin that has flowed into the groove 4A passes through the gap δ1 and sequentially flows into the adjacent grooves 4B to 4F. Each time, the resin is stretched by the push-side wall 5, and is added to the top 51 and the cylinder. When passing through the gap δ1 between the inner wall 11 and the inner wall 11, heat is generated by receiving a shearing force, and the melting degree is increased. The same applies to the other grooves 4B to 4F. Accordingly, the resin that flows into each of the six grooves 4A to 4F generates heat by receiving the same number of stretching and shearing forces as the number of the grooves 4A to 4F, and the resin is sufficiently melted. Homogenized sufficiently. Further, since the axial flow of the screw 2 is given to the resin flowing into the grooves 4 </ b> A to 4 </ b> F, the resin that has entered the grooves 4 </ b> A to 4 </ b> F is efficient toward the discharge port 13 on the tip side of the cylinder 1. Is conveyed.

  Next, the mixing sections 3B and 3C will be described. The mixing sections 3B and 3C are formed in the same shape and different dimensions from the above-described mixing section 3A. In the following description, the same number is used for the same structure part as the mixing section 3A, and the overlapping description is omitted.

  As shown in FIG. 1 and FIG. 3, the mixing sections 3B and 3C include six grooves 4A to 4F at equal intervals (60 degree intervals) on the circumference of the outer periphery of the screw 2 in the same manner as the mixing section 3A. Is formed. The grooves 4A to 4F have the same shape and are formed in a spiral shape in the same direction as the twist direction of the flights 21A to 21D.

  The grooves 4A to 4F of the mixing section 3B are open to both the screw groove 22B on the base side (supply port 12 side) of the cylinder 1 and the screw groove 22C on the tip side (discharge port 13 side) of the cylinder 1. Similarly, the grooves 4A to 4F of the mixing section 3C are opened to both the screw groove 22C on the base side (supply port 12 side) of the cylinder 1 and the screw groove 22D on the tip side (discharge port 13 side) of the cylinder 1. ing. The lead angle β2 of the grooves 4A to 4F of the mixing sections 3B and 3C is formed at 75 degrees, which is the same as the lead angle β2 of the mixing section 3A, and is larger than the lead angle β1 of the flights 21A, 21B, 21C, and 21D.

  Since the grooves 4A to 4F have the same shape, the groove 4A will be described. In the groove 4A, a gap δ3 is formed between the top 51 of the push-side wall 5 and the inner wall 11 of the cylinder 1 with respect to the rotation direction of the screw 2 (arrow P in FIG. 3). Is formed in such a size that the molten resin can flow into the adjacent groove 4B. In the groove 4A, a gap δ4 is formed between the top 61 of the wall 6 on the back side and the inner wall 11 of the cylinder 1 with respect to the rotation direction of the screw 2 (arrow P in FIG. 3). The gap δ4 is formed in such a size that the molten resin can flow into the groove 4A from the adjacent groove 4F. That is, the gaps δ3 and δ4 between the tops 51 and 61 of the walls 5 and 6 formed on both sides in the circumferential direction of the grooves 4A to 4F and the inner wall 11 of the cylinder 1 are large enough to allow the molten resin to pass therethrough. Is formed.

  The gap δ3 and the gap δ4 have the same dimensions and are set to 1.5 mm, and are set to be smaller than 2 mm of the gaps δ1 and δ2 of the mixing section 3A. Further, the grooves 4A to 4F may have different shapes, and the gap δ3 and the gap δ4 may have different dimensions.

  The pushing side wall 5 and the back side wall 6 are formed in the same shape as the pushing side wall 5 and the back side wall 6 of the mixing section 3A. When the resin is conveyed from the screw groove 22B or 22C on the base side (supply port 12 side) of the cylinder 1 to the mixing sections 3B and 3C configured as described above, the resin is transferred to the six grooves 4A to 4F. Inflow. The total cross-sectional area of the six grooves 4A to 4F is substantially the same as the cross-sectional area of the screw groove 22B or 22C immediately before the groove. Therefore, no pressure loss occurs when the resin flows into the grooves 4A to 4F. As a result, in the screw having the mixing sections 3B and 3C of the present invention, the extrusion capability of the material resin is improved.

  The resin that has flowed into each of the six grooves 4 </ b> A to 4 </ b> F is subjected to a large feed component force in the circumferential direction of the screw 2 as the screw 2 rotates, and is gradually stretched by pressure applied by the wall 5 on the pushing side. Then, it passes through the gap δ3 between the top 51 and the inner wall 11 of the cylinder 1 and flows into the adjacent grooves 4A to 4F. The gap δ3 is set to 1.5 mm, which is smaller than 2 mm of the gap δ1 of the mixing section 3A. Therefore, only a resin having a small particle diameter can pass through the gap δ3, and when the resin passes through the gap δ3, the resin receives heat generated by the shearing force larger than that of the mixing section 3A, and gradually increases the melting degree while adjoining the grooves 4A. To 4F.

  Thus, in the mixing section 3A on the base side (supply port 12 side) of the cylinder 1, the resin once melted and homogenized is mixed with the number of grooves 4A to 4F in the mixing sections 3B and 3C. Since the heat is generated by receiving the same number of stretching and shearing forces, the resin is sufficiently melted, the resin is sufficiently homogenized, and the resin that is not sufficiently melted remains in the grooves 4A to 4F. It does not flow downstream. Further, the grooves 4A to 4F are formed in a spiral shape in the same direction as the twist direction of the flights 21A to 21D. Accordingly, the resin flowing into the grooves 4A to 4F is also given a feed force in the axial direction of the screw 2, and the resin flowing into the grooves 4A to 4F is efficiently supplied from the discharge port 13 on the tip side of the cylinder 1. Discharged. Further, if the grooves 4A to 4F of the mixing sections 3A, 3B, and 3C are formed in a spiral shape opposite to the twisting direction of the flights 21A to 21D, the resin flows directly downstream in the grooves 4A to 4F. The number of times of passing through the gap between the top 51 and the inner wall 11 of the cylinder 1 and flowing into the adjacent grooves 4A to 4F increases. Therefore, the twist direction of the grooves 4A to 4F of the mixing sections 3A, 3B, and 3C is arbitrarily selected according to the type of resin used and the molded product.

  In the above embodiment, the example in which the present invention is applied to the screw of a single screw extruder has been described. However, the present invention may be applied to a screw of an injection molding machine. Moreover, in the said Example, although the groove | channels 4A-4F of a mixing section are formed at equal intervals on the circumference of the outer periphery of the screw 2, you may form in unequal intervals. In the above embodiment, three mixing sections are formed apart from each other in the axial direction of the screw. However, the number of mixing sections is not limited to three and may be one or four or more. In the above embodiment, the lead angle β2 of the grooves 4A to 4F of the mixing sections 3A, 3B, and 3C is formed at 75 degrees. However, the lead angle β2 is not limited to 75 degrees. Regardless of the left and right of the lead angle, it may be formed at an arbitrary angle in the range of 30 to 90 degrees, that is, in the range of 30 to 90 degrees on the right and 150 degrees (30 degrees on the left). In the above-described embodiment, six grooves 4A to 4F of the mixing sections 3A, 3B, and 3C are formed. However, the number is not limited to six, and any number may be used as long as there are a plurality of grooves.

1 cylinder 11 inner wall 12 supply port 13 discharge port 14A, 14B heater 2 screw 21A, 21B, 21C, 21D flight 22A, 22B, 22C, 22D screw groove 3A, 3B, 3C mixing section 4A, 4B, 4C, 4D, 4E, 4F Groove 5 Push-side wall 51 Top 6 Back-side wall 61 Top 91 Flight 92 Screw groove 93 Back-side wall top 94 Barrier (Top of push-side wall)
95 Inflow groove 96 Outflow groove 97 Cylinder 98 Inner wall

Claims (1)

A flight that is formed in a spiral shape on the outer periphery of a screw that is rotatably inserted into the cylinder, and that conveys the thermoplastic resin supplied to the base of the cylinder to the tip side of the cylinder,
A screw for a molding machine provided with a barrier-type mixing section formed on the outer periphery of the screw,
The mixing section above
A plurality of grooves formed on the circumference of the outer periphery of the screw at predetermined intervals, wherein both the base side of the cylinder and the tip side of the cylinder are open,
In the screw for the molding machine in which the gap between the top of the wall formed on both sides in the circumferential direction of the groove and the inner wall of the cylinder is formed in a size that allows the molten resin to pass through ,
The groove is formed in a spiral shape in the same direction as the twist direction of the flight, and the lead angle of the groove is formed larger than the lead angle of the flight,
The mixing section is formed in a plurality spaced apart in the axial direction of the screw,
The gap between the top of the mixing section wall on the tip side of the cylinder and the inner wall of the cylinder is smaller than the gap between the top of the mixing section wall on the base side of the cylinder and the inner wall of the cylinder. A screw for a molding machine.

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