JPH0684034B2 - Screw for twin screw extruder - Google Patents

Description

TECHNICAL FIELD The present invention relates to an extruder screw used in a twin-screw extruder made of a plastic material such as synthetic resin or rubber.

(Prior Art) Conventionally, as a twin-screw extruder, for example, Japanese Patent Publication No.
The one described in Japanese Patent Publication is known. This is a screw for a twin-screw extruder rotating in the extrusion cylinder of such an extruder, in which screws having a flight structure in which they mesh with each other are cantilevered in the extrusion cylinder and driven in opposite directions. The transfer of the plastic material, in addition to the function of extruding, has a function of mixing, kneading and has an excellent function, on the other hand, when compared to the screw for a single screw extruder, as described later, Since the force that pushes the screw toward the inner wall of the extrusion cylinder works, there is a drawback that abrasion due to friction between the inner wall of the extrusion cylinder and the flight top surface of the screw easily occurs.

Therefore, as a means for improving the wear resistance, it is generally performed to subject the inner surface of the extrusion cylinder and the surface of the screw to quenching, carburizing, induction hardening, nitriding or lining of a sintered alloy for surface hardening. .

(Problems to be Solved by the Invention) However, although the extrusion cylinder and the screw of the twin-screw extruder have improved wear resistance due to nitriding treatment, etc. When a large amount of an inorganic filler such as calcium carbonate, which has excellent heat resistance and weather resistance, is mixed as a modifier and used, the abrasion of the extrusion cylinder and the screw is further promoted by the inorganic filler. The wear progresses remarkably when the amount is increased, and such a problem has not been solved yet.

The cause of this wear is that, as shown in FIG. 4, when the biaxial screws 1a, 1a rotate in the directions of arrows E, there are portions H where the flight parts 3a, 3a mesh with each other. This is because the pressure of the molten material rises just before H. In the example of the figure, this pressure increase is a combined force F of the force F ₁ that tries to lift the screws 1a, 1a upward and the force F ₂ that tries to separate the screws 1a, 1a from each other.
a, the axis C _1, C ₁ of 1a is eccentric to the point of C _2, C _2, the flight portion 3
Since the top surfaces of a and 3a (indicated by a chain double-dashed line) are strongly pressed against the G and G points on the inner wall surface of the extrusion cylinder 4a, the flight top surface and the inner wall surface of the extrusion cylinder will be worn at that portion. .

Therefore, in order to prevent such a pressure increase, as shown in FIG. 5, side wall gaps (flight gaps d) of the flight parts 3a, 3a, the flight top surface 31a and the screw groove 2 are formed.
It is easily conceivable to widen the gap (meshing gap e) between the a and the bottom wall 21a, but the so-called backflow in which the molten material flows backward becomes large, and therefore the residence time in the extrusion cylinder becomes long, so plasticity is increased. It cannot be adopted because the material is deteriorated by heat and the extrusion rate is reduced.

The object of the present invention is to eliminate the above-mentioned drawbacks of the conventional screw for a twin-screw extruder, and to prevent the screw from being strongly pressed against the inner wall of the extrusion cylinder while suppressing the backflow to the same extent as the conventional screw, To provide a screw for a twin-screw extruder, which has a flight structure in which a pressure rise of a molten material generated in an engagement portion of a flight portion is suppressed as much as possible, and which can reduce wear between an inner wall of an extrusion cylinder and a flight top surface of the screw. It is in.

(Means for Solving the Problems) A screw for a twin-screw extruder according to the present invention is a screw for a twin-screw extruder in which flight parts that rotate in mutually different directions and mesh with each other are formed. It is characterized in that it is formed as a grooved curved surface that is continuously recessed in the middle portion in the height direction.

(Operation) According to the present invention, with the above-described configuration, both screws are rotated in different directions in the extrusion cylinder of the twin-screw extruder to transfer, extrude, mix, and knead the molten material.
At this time, the molten material passes through the wide gap at the interlocking part of the flight part and at the intermediate part where the flight side walls consisting of the groove-shaped curved surfaces face each other, so that no size backflow occurs, and moreover the flight part The pressure rise in the portion just before the meshing portion is reduced. Therefore, the top surface of the flight part is not strongly pressed against the inner wall of the extrusion cylinder due to the eccentricity of the screw shaft, and wear of the flight surface of the screw is prevented.

(Example) Hereinafter, an example of the screw for twin screw extruders of the present invention is explained with a drawing.

2 in which the screw for the twin-screw extruder of the present invention is mounted in FIG.
The outline of the axial extruder is shown. 1 is an extrusion cylinder,
The cylinder 1 is provided with a plastic material supply port 2 and an extrusion port 3, and a heating device (not shown) is provided on the peripheral wall of the extrusion cylinder 1.

Reference numerals 4,4 'are screws having flight portions 5,5' which rotate in different directions in the extrusion cylinder 1 and engage with each other.

FIGS. 2 to 3 show flight parts 5, 5'where both screws 4, 4'rotate in different directions and engage with each other. The engagement portion S of the flight portions 5, 5'shown in FIG. 2 is a portion where pressure is generated when the molten material is conveyed, and as shown in FIG.
51 'is formed as a grooved curved surface that is continuously depressed in the middle portion in the height direction, and an oblong-shaped gap D having a flat cross section is provided between the side walls 51, 51' of the engagement portion S of the flight portions 5, 5 '. Has been formed. This gap D is an elliptical curve represented by the following equation at the cross-section connecting the axes C and C'of both screws 4 and 4 '. It is preferable that the gap D is surrounded by and the top surfaces 52, 52 'have a wide width. However, even if the arc R that approximates this elliptic curve is drawn, the flight parts 5, 5' The side walls 51, 51 ′ of the ′ may be wide on the base side and narrow on the top side and may be inclined when viewed in the cross-section connecting the axes C, C ′. In short, the flight side walls 51, 51 'are formed as grooved curved surfaces that are continuously recessed in the middle portion in the height direction.
It suffices that the gap 1'is narrow on both top surfaces of the flight parts 5, 5'and wide on the middle part of the height.

Among the symbols used in the above equation, X, Y and Z are the origins in FIGS. 2 to 3 with the center O of the meshing portion S of the flight portions 5 and 5'of both screws 4 and 4'as the origin. Screw
The X-axis is the direction connecting the axes C and C'of 4,4 ', and the screw 4,4'
It is a variable in the coordinates in which the axis parallel to is the Z axis and the axis perpendicular to the X axis and the Z axis is the Y axis. That is, Z represents the opening state of the gap between the side walls 51, 51 'of the flight parts 5, 5',
Z ₀ is the maximum point at that time. Y ₀ is a position where the top surfaces 52, 52 ′ of the flight parts 5, 5 ′ intersect. L is the distance between the axes C and C'of both screws 4 and 4 ', and R ₀ is the radius centered on the axes C and C'of the screws 4 and 4',
The outer circumference of the circle drawn with the radius R ₀ is equal to the top surfaces 52, 52 ′ of the flight parts 5, 5 ′.

The reason why it is preferable that the clearance D is surrounded by the elliptic curve in the meshing portion S of the flight portions 5 and 5'as described above is as follows.

That is, in the screw (hereinafter referred to as the former) in which the flight gap is constant at the meshing portion S of the flight portions 5, 5 ', the molten material in the screw groove is
When passing through the meshing part S, the inner wall side of the extrusion cylinder (arrow j side) rather than the bottom side of the screw groove (arrow i side)
Is a long distance to pass through. The longer the distance is, the greater resistance is exerted, and the amount of the molten material passing through the inner wall of the extrusion cylinder is small, while the amount of the molten material passing through both bottom sides of the screw groove is large.

On the other hand, in the screw of the present invention (hereinafter referred to as the latter) in which a clearance D surrounded by an elliptical shape is formed in the flight engagement portion S, the space between the intermediate portions is widened, and therefore, the melt passing through the flight engagement portion S is melted. The material is the flight part 5,5 '
Is evened over the entire width of the height.

On the other hand, in the former case, when the pressure difference before and after the flight engagement portion S is constant and the flight gap is equal, the amount of molten material passing through the flight engagement portion S passes through the engagement portion S. The resistance is small on both bottom sides of the screw groove, so the amount of passage through it is extremely large. In comparing the former and the latter, if the pressure difference before and after the meshing portion S is the same, the amount of the molten material (the amount of backflow) passing through the meshing portion S in the former becomes larger than that in the latter.

Therefore, if the amount of backflow is set to the same level, the pressure difference in the latter becomes smaller than the pressure difference in the former. That is, the pressure rise of the molten resin immediately before the meshing portion S of the flight is smaller in the latter case.

Further, in the screw of the present invention, the flight part 5,
It is preferable that the width of the top surfaces 52, 52 'of the 5'be as large as possible within the range where they do not come into contact with each other when the screws are engaged with each other.
If this width is increased, the force per unit area by which the flight top surface of the screw is pressed against the inner wall surface of the extrusion cylinder becomes smaller, and wear can be reduced.

[Experimental example]

The twin-screw extruder of the present invention as described above is used by being mounted in the extrusion cylinder of a known twin-screw extruder, and as one embodiment, the screw outer diameter is 90 mm and the screw shaft center is 76 mm in different directions. A comparative test was performed with a conventional screw using a rotating twin-screw extruder screw.

The numerical values of the flight part of the screw according to the present invention are as follows: the screw thread pitch is 35 mm, the maximum recess depth of the grooved curved surface (maximum point Z ₀ ) is 1.75 mm, that is, the maximum value of the flight gap (2Z ₀ ) is 3.5 m.
m, meshing clearance (e) 3.0 mm, flight top face width 14.8 mm, screw rotation speed 17 rpm, when continuously used for the production of heat melt extrusion of PVC resin, before and after the meshing part of the flight part 5, 5 ' The pressure difference of the conventional screw was 21.0kg / cm ² , but it was reduced to 13.0kg / cm ² , and the wear caused by the contact friction between the inner wall of the extrusion cylinder and the top surface of the flight part was significantly reduced. The service life was extended four times compared to the conventional screw. Further, even if the extrusion amount is increased, the extruded product can be uniformly kneaded in the meshing portion, so that the productivity can be improved and an extruded product excellent in impact strength can be obtained.

By the way, the conventional screw had the same conditions as the above-mentioned example of the present invention except that the numerical values of the flight portion were a flight gap (d) of 3.0 mm and a flight top surface width of 13.0 mm. Also,
The amount of backflow when both screws were used was approximately the same when the screws were pulled out and examined.

(Effect of the Invention) According to the screw for a twin-screw extruder of the present invention, since the side wall of the flight part is formed as a groove-shaped curved surface that is continuously recessed in the middle part in the height direction, the cross-section is formed in the engagement part of the flight part A gap surrounded by a substantially elliptic curve will be formed, the pressure difference generated before and after the molten state passes through this gap is small, and the pressure increase immediately before the meshing part of the flight part is reduced, The eccentricity of the twin screw is also reduced.
Therefore, the degree of contact between the inner wall surface of the extrusion cylinder and the top surface of the flight part is significantly reduced, the frequency of repair and replacement of the screw and the extrusion cylinder is reduced, and the kneading is performed evenly at the meshing part. It is possible to improve the product quality and increase the extrusion rate.

[Brief description of drawings]

FIG. 1 is a partially cutaway horizontal sectional view for explaining an example of an extruder adopting the present invention, FIG. 2 is a horizontal sectional view showing a relation in which flight parts of the screw of FIG. 1 are intermeshed, and FIG. FIG. 4 is an enlarged cross-sectional view of an essential part taken along the line III-III in FIG. 2 and viewed in the direction of the arrow. FIG. 4 illustrates the interlocking relationship of the flight parts of the screw in the extrusion cylinder of the conventional screw for a twin-screw extruder. Cross-sectional view, FIG. 5 is the fourth
FIG. 5 is an enlarged sectional view of an essential part taken along line VV in the figure and seen in the direction of the arrow. Explanation of symbols 1 …… Extrusion cylinder, 4,4 ′ …… Screw, 5,5 ′ …… Flight part, 51,51 ′ …… Sidewall

Claims (1)

[Claims] 1. A screw for a twin-screw extruder in which flight parts that rotate in mutually different directions and mesh with each other are formed, and a sidewall of the flight part has a groove-shaped curved surface that is continuously recessed at an intermediate portion in the height direction. A screw for a twin-screw extruder characterized by being made.