JPH09117954A - Twin-screw extruder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extruder reduced in the dragging between a screw and a barrel, extended in the life of both of them and enhanced in extrusion capacity. SOLUTION: In twin-screw extruder wherein a perfectly meshed screw consisting of a feed part, a kneading part and a weighing part is arranged in a barrel, kneading part screws 9a, 9b are arranged to at least a part of the kneading part screws 11a, 11b and the outer diameter of the kneading discs 9a, 9b and the kneading part screws 9a, 9b, 11a, 11b is made smaller than that of the screw outer diameter of the part other than the kneading part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-screw extruder for molding a product made of a thermoplastic resin or the like, and more particularly to a completely meshing twin-screw extruder.

[0002]

2. Description of the Related Art Generally, in order to mold a product with a plastic material, an extruder for kneading the plastic material while melting and extruding from a die, and the above-mentioned molten plastic An injection molding machine is used which injects and molds a material into a mold.

As an extruder for extruding and molding the above-mentioned molten plastic material from a die, there is a multi-screw extruder having a plurality of screw shafts arranged side by side. The multi-screw extruder is generally a twin-screw extruder or a three-screw extruder or more. The screw extruder is classified into a screw extruder, and the twin-screw extruder is classified into a fully meshing screw extruder and a non-meshing or incomplete meshing screw extruder.

FIG. 2 is a diagram showing a schematic structure of the above-described completely meshing twin-screw extruder, in which a cylindrical barrel 3 having a hopper 2 at one end is supported on a bed (not shown). The screws 4 a and 4 b are inserted into the barrel 3, and the die 5 is provided at the tip of the barrel 3. A vent port 6 is provided in the middle of the barrel 3.

However, when a plastic material is put into the hopper 2 and the screws 4a and 4b are driven by a motor (not shown) through the speed reduction mechanism 8 and the drive mechanism, the screw 4a and 4b in which the put material is rotating are rotated. Are transported forward, gradually heated from the barrel side, melted and sequentially kneaded. When the melted material reaches the position of the vent port 6, the pressure temporarily falls and the gaseous volatile matter contained in the material is discharged, and then the material is pressurized through the metering section and passes through the die 5 to form the product. Done.

That is, in the barrel 3, a feed section, a kneading section, and a measuring section are sequentially formed in the longitudinal direction from the position where the hopper 2 is provided.

In the fully meshing twin-screw extruder as described above, there are a co-rotating type in which both screws rotate in the same direction and a different-direction rotating type in which the screws rotate in opposite directions. In screw extruders, for the purpose of positively melting and kneading the materials, a narrow disk-shaped kneading disk is incorporated into the screw of the kneading section, and a part of the screw of the kneading section is kneaded. It is formed by the binding disks 9a and 9b.

By the way, in such an extruder,
In the region of the plasticizing zone of the screw to be heated and kneaded, the resin used is still hard and a high pressure is generated inside the two meshing screws. Therefore, the resin is kneaded and plasticized while the screw is pressed against the inner wall of the barrel by the internal pressure.

However, in this plasticizing zone, since the resin is not yet melted and there is no molten film between the screw and the barrel, the screw rotates while making metal contact with the inner surface of the barrel. The pressing force (contact pressure) of this screw against the inner surface of the barrel varies depending on the operating conditions, but the screw configuration, including the screw dimensions, has a large effect. If the screw configuration is not appropriate, the shearing action in the screw kneading zone will cause There are problems that the extrusion performance reaches a peak due to uneven kneading, local heat generation, etc., and the contact pressure increases, causing galling between the screw and barrel.

Further, as the contact pressure increases, the speed of wear of the screw increases, and a bending load is applied to the screw shaft during the progress of wear, and a burden load is also applied to the screw element, and depending on the case, the screw shaft or screw may be applied. There are problems such as damage to the element.

3 (a), 3 (b) and 3 (c) are views showing the flow of the molten resin in the kneading disk in the above twin-screw extruder. Both kneading disks are located near the center of the barrel 3. The resin sandwiched between 9a and 9b exerts an outwardly directed force F1 on both kneading disks, so that both kneading disks 9a and 9b are particularly strongly pressed against the inner surface of the barrel 3. Therefore, in the kneading part, wear due to a biting phenomenon occurs particularly between the screw and the barrel.

Therefore, as shown in FIG.
It has also been proposed that a and 4b have a small diameter over their entire length so that the gap between the a and 4b and the inner surface of the barrel 3 is large. However, when the diameters of the screws 4a and 4b are reduced in this way, the contact pressure and the shear stress on the barrel can be relaxed. However, there is a problem that the amount of extrusion decreases due to the runout of the screw in the feed section and the decrease in the boosting capacity in the metering section.

Further, as shown in FIG. 5, the large diameter portion 10 in which the inner diameter of the barrel 3 is made larger only at the kneading portion as compared with the other portions.
It has also been proposed to. However, in this case, since the distance between the screws 4a and 4b and the inner surface of the barrel 3 becomes large in the kneading section, there is little biting between the screw and the inner surface of the barrel, and there is little run-out of the screw, and a sufficient extrusion amount is secured. Both screws 4a and 4b can be used
Since the gap between them is relatively small like the conventional one,
The resin pressure acts as a bending load on the shafts of both screws on the left and right of the kneading section in the same size as before. Therefore, there is a problem that the bending load leads to early damage.

In view of the above points, the present invention aims to provide a twin-screw extruder capable of reducing the bite between the screw and the barrel, extending the life of the screw and the barrel, and improving the extrusion capability. To aim.

[0015]

SUMMARY OF THE INVENTION The present invention is directed to a feed section,
In a twin-screw extruder in which a complete mesh type screw consisting of a kneading section and a measuring section is arranged in a barrel, a kneading disk is arranged in at least a part of the kneading section screw, and the kneading disk 7 and the kneading disk are arranged. The outer diameter of the partial screw is smaller than the outer diameter of the screw other than the kneading portion.

[0016]

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 is a plan sectional view of a twin-screw extruder according to the present invention. In a barrel 3 having a hopper 2 at one end thereof, a pair of co-rotating, completely meshing screws 4a, 4b is rotatably accommodated, and the screws 4a and 4b are composed of a feeding section, a kneading section, and a measuring section in order from a portion adjacent to the hopper 2. A die 5 is provided at the downstream end of the barrel 3, and
A vent port 6 is provided in the barrel 3 immediately downstream of the kneading section.

By the way, the screw 1 in the above kneading section
Kneading disks 9a and 9b for kneading and melting a resin material are incorporated in at least a part of the la and la 11b. Then, the screw 11a of the kneading section,
The outer diameters of 11b and the kneading disks 9a, 9b are
The diameter is smaller than the outer diameters of the screws 4a and 4b in the feed section and the measuring section. That is, the inner diameter of the barrel 3 is D
When it is o, the screws 11a, 11 in the kneading section are
b, the outer diameter of the kneading disks 9a, 9b is (0.9
5 to 0.98) Do.

The material charged in the barrel of the extruder is sent to the kneading section through the feed section by the rotating screws 4a and 4b, and the screw 11 is fed in the kneading section.
a, 11b and kneading discs 9a, 9b are melted and kneaded, and are further extruded from a die through a measuring section by screws 4a, 4b.

In the kneading section, although the screws 11a and 11b receive a force in a direction in which they are separated from each other, and in particular, a strong force in a direction in which the kneading disks 9a and 9b are separated from each other, as described above, Screws 11a, 11b and kneading disks 9a, 9b
The outer diameter of the kneading part is smaller than the outer diameter of the screw of the other part, and the gaps between the kneading part screws 11a and 11b and the kneading disks 9a and 9b and the inner surface of the barrel 3 are large. Screw 11a, 11
The contact pressure between the b and the kneading disks 9a, 9b and the inner surface of the barrel 3 is small, and the occurrence of wear due to biting is reduced.

Since the kneading section screws 11a, 11b and the like have a small diameter, the left and right screws 11 are
The gap between a and 11b and the kneading discs 9a and 9b is large, so that both screws 11a and 1b
1b and the pressure of the resin sandwiched between the kneading disks 9a, 9b becomes relatively small, and the kneading section screw 1
The bending load applied to 1a, 11b, etc. is reduced, and it is possible to reliably prevent early damage or the like of the relevant portion.

Moreover, since the whole screw shaft is supported by the inner surface of the barrel 3 at both ends, the runout of the whole screw is small and the extrusion capability can be improved.

[0023]

[Table 1] Table 1 shows the kneading section screw and the kneading disk having a diameter of 0.98 Do (Example 1), 0.94.
9 is a table showing the experimental results of the sample of D (Example 2) and the conventional sample, in which the outer diameter of the kneading section screw or the like is (0.98).
.About.1.0) Do resulted in early damage of the screw and less than 0.95 Do caused poor kneading. The numerical setting of 0.95 to 0.98 varies depending on the resin and the operating conditions, but it is close to 0.95 Do for small diameters and 0.98 Do for large diameters.

In the above embodiment, the same-direction rotating twin-screw extruder has been described, but it is also applicable to different-direction rotating twin-screw extruders.

[0025]

As described above, according to the present invention, the outer diameter of the kneading disk and the screw in the kneading part is made smaller than the outer diameter of the screw in the other parts in the completely meshing twin-screw extruder. It is possible to reduce biting due to metal contact between the screw and kneading disk and the inner surface of the barrel, and to reduce the bending load of the screw, thereby extending the life of the screw and barrel and improving the extrusion capability.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a twin-screw extruder according to the present invention.

FIG. 2 is a plan sectional view of a conventional twin-screw extruder.

3 (a), (b) and (c) are views showing a flow of a molten resin in a kneading disk portion of a twin-screw extruder.

FIG. 4 is a diagram showing another example of a conventional twin-screw extruder.

FIG. 5 is a view showing still another example of a conventional twin-screw extruder.

[Explanation of symbols]

 2 Hopper 3 Barrel 4, 4a, 4b Screw 6 Vent port 9a, 9b Kneading disk 11a, 11b Screw of kneading section

Claims (3)

[Claims] 1. A twin-screw extruder in which a fully meshing type screw consisting of a feed section, a kneading section and a measuring section is arranged in a barrel, and a kneading disk is arranged at least in part of the kneading section screw. A twin-screw extruder characterized in that the kneading disk and the screw outer diameter of the kneading part are smaller than the screw outer diameter of the parts other than the kneading part. 2. The kneading disk and the kneading section screw outer diameter relative to the barrel inner diameter Do (0.95 to 0.98)
The twin screw extruder according to claim 1, wherein the twin screw extruder is Do. 3. The twin-screw extruder according to claim 1, wherein the length of the kneading section screw having a small diameter is Do (3 to 6) Do when the barrel inner diameter is Do.