JP2001334112A - Mesh filter and cable insulator extrusion process using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mesh filter which is used for extruding a resin composition and by which problems with respect to a finer screen mesh can be solved and also any foreign matter having larger size than the opening size of such a screen mesh can be prevented from passing through the screen mesh. SOLUTION: In this cable insulator extrusion process, this mesh filter having a laminated structure formed by closely sticking a plurality of sheets of screen meshes each of which has a fine mesh structure, to each other, is used, wherein the plurality of sheets of screen meshes are laminated to each other in such a state that the direction of weaving of each of the plurality of sheets of screen meshes is different from those of the others.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mesh filter for removing foreign matters in a resin composition, and a method for extruding a cable insulator using the same.

[0002]

2. Description of the Related Art In manufacturing rubber and plastic insulated power cables, an insulating resin composition such as rubber or plastic is extruded around a conductor to form an insulating layer. FIG. 4 schematically shows a method of extruding such a cable insulator. The insulating resin composition is kneaded by the screw 3 inside the cylinder 2 of the extruder 1 and extruded into the crosshead 4 in a molten state. The cable conductor 5 is inserted through the crosshead 4, and an insulating resin composition is extruded around the crosshead 4 to form an insulating layer of the cable. Usually, a mesh filter 6 is provided in the resin flow path inside the extruder for removing foreign substances, and is supported by a breaker plate 7 from the rear. As the mesh filter 6, a wire mesh woven with stainless fine wires is usually used, and has a function of rubbing foreign substances in the molten resin. The foreign matter in the insulating resin composition causes deterioration of insulation properties and dielectric breakdown due to concentration of an electric field in a power cable. Therefore, in order to increase the voltage and improve the reliability of the power cable, removal of foreign matter is an important issue.

Further, in recent years, there has been a remarkable tendency to use a crosslinked polyethylene insulated power cable manufactured by the above-described extrusion process for an ultrahigh-voltage line of about 275 kV to 500 kV. In such a power cable, the management of foreign matter becomes a more important problem, and it becomes necessary to remove even finer foreign matter. For example, 500 kV
In a cross-linked polyethylene insulated power cable for use, there is no foreign substance of 50 μm or more in the insulator, so-called 5
It is required to remove foreign matter at a free level of 0μ.

In order to remove such fine foreign matter,
Efforts have been made to use finer screen meshes as mesh filters. Currently, # 500 mesh (the number of meshes per inch is 500) and mesh size is 26 μm is used in the extrusion process, and finer # 635 mesh (mesh size 20 μm) is being used.

[0005]

However, efforts to make the screen mesh finer have almost reached their limits. In order to reduce the size of the mesh by reducing the size of the screen mesh, it is necessary to knit the screen mesh with a thinner metal wire. However, in the above-mentioned # 635 mesh screen mesh, fine stainless steel wires of φ20 μm are used, and further thinning is becoming practically difficult from the viewpoint of securing strength and durability. At present, this # 635 mesh is the finest in supply as a practical product.

[0006] Further, such a screen mesh has a problem that a foreign substance having a size about three times as large as the size of the opening passes. This phenomenon that foreign matter larger than the mesh opening passes is presumed to be caused by the deformation of the mesh or the passing direction of the foreign matter, and will be described later with reference to the drawings.
Therefore, even if a screen mesh of # 635 mesh is used, foreign matter of about 60 μm may pass through,
This would not be enough to achieve the 50μ free level described above. Furthermore, fibrous foreign substances and foreign substances called amber, which are fine aggregates generated by over-crosslinking of cross-linked polyethylene, are deformed when pressed against the mesh of the screen mesh because they themselves have flexibility. Since the particles pass through the mesh, there is a problem that a sufficient effect cannot be obtained even if the screen mesh is miniaturized.

[0007]

A first means is a mesh filter for use in removing foreign matter in a resin composition, in which a plurality of screen meshes having a mesh structure are laminated in close contact with each other. A mesh filter characterized by having a structure is used (Claim 1), and the plurality of screen meshes are stacked in a state where their weaving directions are different from each other (Claim 2). ). By using such a mesh filter, it is possible to efficiently capture a foreign substance having a size substantially equal to the size of the mesh filter.

The above-mentioned screen mesh has an advantage of the present invention particularly when it is a fine mesh having a mesh size of 50 μm or less (claim 3). The present invention overcomes the problem of making the screen mesh finer, and also reduces the problem of ultra-high voltage power cables.
This is because removal of foreign matter at the μm level is mainly used.

The screen mesh is a fine mesh having a mesh structure having a mesh size of 50 μm or less.
The laminated screen mesh can be reinforced by being sandwiched from both sides by a support mesh having a larger opening (claim 4).

In a method for extruding a cable insulator by extruding an insulating resin layer around a conductor by using an extruder, a mesh filter is provided in a resin flow path inside the extruder, and the mesh filter is configured as described above. (Claim 5).

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a laminated structure of a mesh filter according to the present invention. The two screen meshes b and c having a fine mesh structure are stacked with their weaving directions shifted by 45 degrees. The screen meshes b and c have a mesh structure in which a stainless wire is plain-woven, the mesh fineness is # 500 mesh, the wire diameter of the stainless wire is 25 μm, and the mesh size is 26 μm. The screen meshes b and c are tightly integrated by a sintering process, and are reinforced by being sandwiched between support meshes a and d from both sides. Support meshes a and d
Uses # 120 mesh. A screen mesh e (# 40 mesh) and a screen mesh f (# 20 mesh) are further laminated from below, and these constitute a set of mesh filters. This mesh filter is mounted in the resin flow path in the extruder 1 described with reference to FIG. 4, and is used for extruding the insulator of the power cable. The mesh filter is mounted in the extruder 1 such that the lower side in FIG. 1 faces the downstream side.

The operation of the foreign matter trapping by the mesh filter of the present invention will be described with reference to FIGS. FIG.
FIG. 2 is an enlarged view of a fine screen mesh used for extruding a cable insulator. In a fine screen mesh of about # 500 mesh, stainless steel wire 1
0 is about 25 μm, and the size of the aperture and L
It is almost the same size.

Generally, in a screen mesh,
It is desirable that the ratio of (the size of the mesh L / the wire diameter D) is large. This is for reducing the pressure loss by increasing the ratio of the openings. Therefore, in a coarse mesh filter, the size L of the openings is larger than the wire diameter D. However, when the aperture is reduced to catch fine foreign matter, even if the stainless wire is to be similarly thinned, a problem arises in strength and durability and there is a limit. In a fine screen mesh of about # 500 mesh, the size L of the opening and the wire diameter D are made substantially the same.
It is difficult to further reduce the diameter of the stainless wire, and if only the aperture is reduced with a stainless wire having the same diameter, the pressure loss of the screen mesh increases. Aperture 20μm
The degree is the limit of mesh refinement.

AA of the screen mesh shown in FIG.
A schematic diagram of the cross section is shown in FIG. In the figure, 10a is a vertical line of the mesh, and 10b is a horizontal line, and the cross section is shown.
11 is a foreign substance in the resin composition to be filtered.

The aperture of the screen mesh is indicated by L in the figure. However, the actual interval between the horizontal lines 10b is L 'which is larger than the apparent opening L. And foreign matter 1
When 1 enters from the direction shown in the figure, the horizontal line 1
0b is slightly deformed and moved, and the aperture is further increased. Therefore, in the case where one screen mesh 10 is used, as shown in the figure, even the foreign matter 11 having a thickness of about twice the size of the opening L and a length of about three times as infiltrated from a specific direction. In such a case, it will pass through the screen mesh 10.

Therefore, in the present invention, as shown in FIG. 3B, two screen meshes 10 and 12 are used in the form of being laminated in close contact with each other. Screen mesh 12
Indicates that the weaving direction of the screen mesh 10 is 4
The layers are stacked at an angle of about 5 degrees. 12a, 12b in the figure
Means vertical and horizontal lines when the cross section is taken along the line BB in FIG.

In the present invention, when the foreign matter 11 shown in FIG. 3B enters from the direction shown in FIG. It will be captured by the mesh 12. By laminating two screen meshes in close contact with each other, a three-dimensional trapping action acts on foreign matters having various shapes. And in this invention, the 2nd screen mesh 12 is laminated | stacked in the state inclined by 45 degrees. In this way, the mesh pattern of the two screen meshes is displaced, and the direction in which the first screen mesh most easily passes foreign matter does not coincide with the direction in which the second screen mesh most easily passes foreign matter. . Therefore, a foreign matter larger than the aperture that could pass through by invading the first screen mesh from a specific direction cannot be passed because the direction does not match in the second mesh, and is caught. The Rukoto. Further, since the mesh filter of the present invention has a three-dimensionally spread network structure, it is possible to remove long and thin fibrous foreign substances and flexible amber with a high probability.

[0018]

EXAMPLES A mesh filter according to the present invention was applied to an extruder, and an evaluation test of a screening effect was performed. Here, with the mesh filter attached to the extruder, 3
The resin mixed with a foreign substance of 0 μm to 200 μm was extruded, and the number of foreign substances in the resin extruded in a tape shape was measured. The measurement was performed on a 100 mm × 400 mm sample. Table 1 shows the specifications of the mesh filter used in the test. In the table, Examples are mesh filters having the structure shown in FIG. 1, Comparative Example 1 uses one screen mesh of # 500 mesh, and Comparative Example 2 uses # 635 mesh.
A single screen mesh is used, or each is reinforced with a support mesh or the like.

Table 2 shows the measurement results. In the embodiment of the present invention, in the region where the size of the foreign material is 20 μm or more, the number of detections is smaller than the values in Comparative Examples 1 and 2 for all the foreign material sizes. Since the number of foreign substances detected in the example is smaller than that in Comparative Example 2 using a finer screen mesh, it can be seen that the lamination of the screen mesh in the present invention has a high effect on foreign substance removal. Further, in the embodiment, the number of detected foreign substances of 40 μm or more is 0,
Required for 500kV class ultra-high voltage power cable5
It is possible to remove foreign matter at a free level of 0 μm.

Incidentally, the number of detected foreign particles having a size of 10 μm is slightly larger than that in Comparative Example 1. However, the foreign matter of the 10 μm level is smaller than the mesh filter used in the examples and comparative examples and is outside the trapping capacity of the filter. It is considered that this reflects the number of foreign substances that are generated.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

As described above, the present invention solves the problem of making the screen mesh finer in the mesh filter used for extruding the resin composition, and foreign matter larger than the screen mesh opening passes. It is to prevent. ADVANTAGE OF THE INVENTION According to this invention, the foreign material larger than the mesh filter opening, a fibrous foreign material, etc. can be efficiently caught, and the 50 micrometer level fine foreign material which becomes a problem in the extrusion of an ultra-high-voltage power cable is reliably removed. Becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a laminated structure of a mesh filter according to the present invention.

FIG. 2 is an enlarged view of a screen mesh used for extruding a cable insulator.

FIG. 3 is a schematic diagram showing a cross section of a screen mesh and a pattern of passage of foreign matter.

FIG. 4 uses a mesh filter according to the invention;
It is explanatory drawing which shows the outline of the extrusion method of a cable insulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 4 Cross head 6 Mesh filter 7 Breaker plate 10 Stainless wire 11 Foreign matter

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) B29L 31:34 B29L 31:34 F term (Reference) 4D019 AA03 BA02 BB02 BD01 BD02 BD06 CB04 4F207 AD15 AH35 AJ08 AJ09 KA01 KA17 KB18 KL38 KL40 KL58 KL98 KM20 5G325 GB29

Claims (5)

[Claims] 1. A mesh filter for use in removing foreign matter in a resin composition, wherein the mesh filter has a structure in which a plurality of screen meshes having a network structure are laminated in close contact with each other. . 2. The mesh filter according to claim 1, wherein the plurality of screen meshes are stacked in a state where their weaving directions are different from each other. 3. The mesh filter according to claim 1, wherein the screen mesh is a fine mesh having a mesh size of 50 μm or less. 4. The screen mesh is a fine mesh having a mesh structure having a mesh size of 50 μm or less,
3. The mesh filter according to claim 1, wherein the laminated screen mesh is reinforced by being sandwiched from both sides by a support mesh having a larger opening. 4. 5. A method for extruding a cable insulator by extruding an insulating resin layer around a conductor by an extruder, wherein a mesh filter is provided in a resin flow path inside the extruder. 5. A method for extruding a cable insulator according to any one of claims 1 to 4.