JPH07148823A - Breaker plate for extruder - Google Patents

Abstract

PURPOSE:To obtain an extruder breaker plate capable of suppressing the occurrence of phenomena, such as early wear and early break of a screen mesh, and extruding a high-quality melt material for a long time. CONSTITUTION:In an extruder breaker plate 4, a material through part 5 is provided by perforating a disc with a large number of material through holes 6. In the extruder breaker plate 4, a conical projection 8 without the material through holes 6 is provided at the center of the material through part 5 of the disc opposedly to the top of an extruder screw. In this manner, an occurrence of wear and break of a screen mesh in use is reduced, and all foreign particles of a size corresponding to a mesh size can be caught. Thus, a high- quality melt material can be extruded for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a breaker plate for an extruder used in an extruder for rubber, plastics and the like.

[0002]

2. Description of the Related Art When an insulating layer or a sheath layer is extrusion-molded by coating an electric conductor or an electric cable core with rubber or plastic by extrusion, or when a hose or a pipe is extruded. An extruder with a built-in extrusion screw is used. In the extruder with a built-in extrusion screw, the foreign matter and dust mixed in the material to be extruded are screened and the back pressure of the material to be extruded is adjusted. A breaker plate in which a large number of material passage holes are bored in a metal disk to provide a material passage portion is provided. FIG. 5: is explanatory drawing of the front-end | tip part of the extruder 3 incorporating the conventional extrusion screw 2 equipped with such a breaker plate 4. As shown in FIG.

The extruder 3 shown in FIG. 5 comprises a cylinder 1, a screw 2 built in the cylinder 1 and a crosshead 9 connected to the tip end side of the cylinder 1. The cylinder 1 of the extruder 3 and the crosshead. A breaker plate 4 is provided between the connecting portion and the breaker plate 9. The breaker plate 4 is made of a disc-shaped metal plate, and the material passage portion 5 has a honeycomb structure in which a large number of material passage holes 6 are formed in the thickness direction. On the screw 2 side of the breaker plate 4, a plurality of screen meshes 7 (for example, 7a, 7a
b, 7c) are set.

[0004]

Generally, the tip of the extruder 3 having the extrusion screw 2 built in the cylinder 1 is
In order to make the retention of the extruded material as small as possible, it was common to make the tip of the screw 2 a conical shape as shown in FIG. On the other hand, the viscosity characteristics of a thermoplastic material such as rubber or plastic in a molten state are as shown in FIG.
It is a function of the shear rate, and there is a relationship that the viscosity decreases as the shear rate increases and the viscosity increases as the shear rate decreases. Therefore, at the tip of the screw 2 having a low peripheral speed, the shear rate is naturally low and the viscosity of the molten material is high. At the central portion of the screen mesh 7 mounted on the breaker plate 4 through which the high-viscosity molten material passes, the metal wire, which is the material of the screen mesh 7, is abraded by the high-viscosity molten material passing through, and finally the metal. The wire was broken, and the broken metal wire was mixed in the extruded product. Further, when the metal wire, which is the material of the screen mesh 7, is broken, the foreign matter capturing ability is significantly reduced, and the screen mesh becomes meaningless.

As an example, in the case of extrusion molding of a composition for a semiconductive layer for a power cable in which 50% by weight or more of carbon black is mixed with an ethylene-vinyl acetate copolymer (hereinafter referred to as EVA polymer), the peripheral speed is At the tip of the small screw, of course, the shear rate will be small and the viscosity of the molten composition will exceed 150000 poise,
With a 400-mesh screen mesh having a wire diameter of 30 μm, the central part was broken after a continuous extrusion time of about 20 hours. In view of the above-mentioned problems, the present invention suppresses the occurrence of phenomena such as premature abrasion and premature rupture of the screen mesh, and completely captures foreign matter of a size corresponding to the opening of the screen mesh, so that a high-quality molten material can be obtained. An object is to provide a breaker plate for an extruder that can be extruded over time.

[0006]

That is, in the breaker plate for an extruder of the present invention, as shown in FIG. 1, a metal disc is provided with a material passage portion 5 formed by punching a large number of material passage holes 6. In the breaker plate 4 for an extruder, a conical projection portion 8 in which a material passage hole is not formed is provided on the surface side of the material passage portion 5 of the metal disk facing the tip of the screw of the extruder. It is characterized by. In addition,
As shown in FIG. 3, if a conical protrusion 8a provided on the surface side of the material passing portion 5 of the metal disk facing the screw tip of the extruder is detachable, a donut type screen mesh is obtained. The doughnut-shaped screen mesh can be set in the breaker plate 4 by sandwiching it, and it is possible to prevent the inner diameter side of the donut-shaped screen mesh from being turned up due to the flow of the molten material.

[0007]

In the breaker plate 4 for an extruder according to the present invention, the conical protrusion 8 is provided at the center of the breaker plate 4,
The structure is such that the molten material does not pass through the central portion of the breaker plate 4, the molten material with high viscosity at the screw tip is dispersed around, and passes through the screen mesh 7 with a high shear rate and passes through the screen mesh. It does not pass through a portion of

[0008]

EXAMPLE An example using the breaker plate for an extruder of the present invention will be shown below. FIG. 2 is an explanatory view of the tip portion of an extruder 3 of 65 mm equipped with the breaker plate 4 for an extruder of the present invention, which is equipped with an extrusion screw 2 inside a cylinder 1 and a crosshead 9 in which the extruder 3 is provided. Is connected to the tip side of the cylinder 1. The extruder breaker plate 4 of the present invention installed between the connecting portion between the cylinder 1 and the crosshead 9 of the extruder 3 has a structure in which conical projections 8 are fixedly provided on both sides of the central portion thereof. And the conical protrusion 8a on the side facing the extrusion screw 2
In the material passage hole 6 portion of the material passage portion 5 that surrounds the, the three screen meshes 7a, 7b, and 7c having a donut shape of 100 mesh, 400 mesh, and 60 mesh are arranged. Using this extruder, a semiconductive composition based on EVA polymer and containing 60% by weight of carbon black was prepared at a resin temperature of 130 ° C. for 24 hours.
Extrusion was continuously performed for more than time, and the frequency of breakage of the screen mesh due to continuous extrusion was examined. For comparison, the conventional extruder breaker plate shown in FIG.
The same semiconductive composition was continuously extruded at a resin temperature of 130 ° C. using three screen meshes of 00 mesh, 400 mesh, and 60 mesh, and the frequency of breakage of the screen mesh due to continuous extrusion was examined. As a result, 2
The frequency of breakage of the screen mesh after continuous extrusion for 4 hours or longer is shown in Table 1.

[0009]

[Table 1]

As is clear from Table 1, in the use of the breaker plate for an extruder of the present invention, even if continuous extrusion for 24 hours or more was performed 18 times, breakage of the screen mesh did not occur even once. On the other hand, in the case of using the conventional breaker plate for an extruder, continuous screen extrusion for 24 hours or more was performed 15 times, and the screen mesh was broken 12 times.

In the above embodiment of the present invention, the conical protrusions 8 are provided on both sides of the central portion of the material passage portion 5 of the disk opposite to the tip of the screw 2 of the extruder 3. Provided only on the side facing the tip of the screw 2,
It is possible to omit the provision of the disk on the surface opposite to the tip of the screw 2 with the disk sandwiched therebetween, and in this case, the same effect as that of the above embodiment can be obtained. By the way, when the conical protrusions 8 are provided on both sides of the central portion of the material passage portion 5 of the disk facing the tip of the screw 2 of the extruder 3 as in the above embodiment, the extruded material that has passed through the breaker plate 4 is provided. Has the advantage that it flows more evenly and smoothly.

[0012]

As described above, according to the breaker plate for an extruder of the present invention, the screen mesh used is less likely to be worn or broken, and the foreign matter having a size corresponding to the opening of the screen mesh is completely captured. As a result, high quality molten material can be extruded for a long time.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of an example of a breaker plate for an extruder of the present invention.

FIG. 2 is a cylinder equipped with an extruder breaker plate of Example 1 and equipped with an extrusion screw in a cylinder of 65 m.
It is explanatory drawing of the front-end | tip part of the extruder of m.

FIG. 3 is a cross-sectional explanatory view of another example of the breaker plate for an extruder of the present invention.

FIG. 4 is a relationship diagram between shear rate and viscosity of a general composition for a power cable semi-conductive layer.

FIG. 5: A 65 mm cylinder equipped with an extrusion screw, equipped with a conventional extruder breaker plate.
FIG. 3 is an explanatory view of a tip portion of the extruder of FIG.

[Explanation of symbols]

 1 ... Cylinder 2 ... Screw 3 ... Extruder 4 ... Breaker plate 5 ... Material passage part 6 ... Material passage hole 7 ... Screen mesh 8 .... Conical projections 9 ... Cross head

Claims (2)

[Claims] 1. A breaker plate for an extruder in which a large number of material passage holes are bored in a disc to provide a material passage portion, on a surface side of the center of the material passage portion of the disc facing the screw tip of the extruder. A breaker plate for an extruder, characterized in that a conical projection having no material passage hole is provided. 2. The extrusion according to claim 1, wherein the conical protrusion provided on the surface of the disk facing the screw tip of the extruder is removable at the center of the material passage of the disk. Machine breaker plate.