JP2020121482A - Crosshead die and extruder - Google Patents

Abstract

To realize at low cost a crosshead capable of suppressing an occurrence of weld marks and an extruder equipped with the crosshead.SOLUTION: An extruder 1 comprises a crosshead 3 including a die 60. The die 60 included in the crosshead 3 includes: a first opening 61 serving as an inlet for a molten resin; a second opening 62 serving as an outlet for the molten resin; an inner peripheral surface 60a that faces an outer peripheral surface 40a of a nipple 40 and forms a resin flow path together with the outer peripheral surface 40a; and at least four grooves provided on the inner peripheral surface 60a. The inner peripheral surface 60a of the die 60 is formed in a taper so as to gradually approach the outer peripheral surface 40a of the nipple 40 from an upstream side to a downstream side of the resin flow path. Each of the grooves is formed in a spiral shape extending from a side of the first opening 61 toward a side of the second opening 62 while revolving around a center line of the die 60 as a rotation axis.SELECTED DRAWING: Figure 1

Description

The present invention relates to an extruder for extruding a resin, and a die for a crosshead used in the extruder.

As one of methods for forming a resin layer (for example, a coating layer or an insulating layer) included in a cable, there are a continuous extrusion crosslinking method, an extrusion crosslinking method, and the like (hereinafter collectively referred to as “extrusion crosslinking method”). In the extrusion cross-linking method, a resin layer is extruded around a conductor or the like using an extruder. For example, while moving a conductor inserted through a crosshead included in an extruder in a predetermined direction, resin is extruded around the conductor through a resin flow path provided in the crosshead. Then, the resin extruded around the conductor is exposed to high temperature and high pressure to crosslink.

A part of the resin flow path provided in the crosshead is formed by the head body and the mandrel, and another part of the resin flow path is formed by the nipple and the die. Specifically, a part of the resin flow path is formed by the gap between the outer surface of the mandrel and the inner surface of the head body, and another part of the resin flow path is formed by the gap between the outer surface of the nipple and the inner surface of the die. Are formed.

When extrusion molding is performed using an extruder equipped with the above crosshead, weld marks (sometimes referred to as “weld lines”) may be formed inside or on the surface of the resin molded body. The weld mark is a trace of a plurality of molten resin flows (resin flows) having different flowing directions that merge in the crosshead.

The weld mark generated inside or on the surface of the extrusion-molded resin molded product causes various problems. For example, a weld mark generated on the resin layer of the cable contributes to dielectric breakdown. Therefore, Patent Document 1 describes forming a spiral groove on the outer surface of the mandrel in order to prevent the occurrence of weld marks.

JP-A-59-31118

In order to form the spiral groove described in Patent Document 1 on the mandrel, it is necessary to perform groove processing (cutting processing) on the mandrel. However, the mandrel is a relatively large member among the members forming the crosshead, and it takes a lot of time and labor to form the groove on the mandrel. As a result, the manufacturing cost of the mandrel is increased, which in turn increases the manufacturing cost of the crosshead including the mandrel and the extruder including the crosshead.

An object of the present invention is to realize a crosshead capable of suppressing the occurrence of weld marks and an extruder equipped with the crosshead at low cost.

The crosshead die of the present invention is a die forming a crosshead of an extruder. The crosshead die of the present invention includes a first opening serving as an inlet for molten resin, a second opening serving as an outlet for molten resin, an outer peripheral surface of a nipple, and a resin flow along with the outer peripheral surface of the nipple. It has an inner peripheral surface forming a passage, and at least four grooves provided in the inner peripheral surface. The inner peripheral surface is formed so as to gradually approach the outer peripheral surface of the nipple from the upstream side to the downstream side of the resin flow path. Each of the grooves is formed in a spiral shape extending from the side of the first opening toward the side of the second opening while rotating around the center line of the die as a rotation axis.

The extruder of the present invention comprises a crosshead including a die. The die faces a first opening serving as a molten resin inlet, a second opening serving as a molten resin outlet, and an outer peripheral surface of the nipple, and forms a resin flow path together with the outer peripheral surface of the nipple. It has a peripheral surface and at least four grooves provided on the inner peripheral surface. The inner peripheral surface is formed so as to gradually approach the outer peripheral surface of the nipple from the upstream side to the downstream side of the resin flow path. Each of the grooves is formed in a spiral shape extending from the side of the first opening toward the side of the second opening while rotating around the center line of the die as a rotation axis.

In one aspect of the present invention, each of the grooves ends before the center of the die in the centerline direction.

In another aspect of the present invention, the depth of each groove becomes gradually shallower along the extending direction of the groove.

In another aspect of the present invention, the width of each groove is gradually narrowed along the extending direction of the groove.

In another aspect of the present invention, the inner diameter of the first opening is 50 mm or more.

According to the present invention, a crosshead capable of suppressing the generation of weld marks and an extruder equipped with the crosshead can be realized at low cost.

It is sectional drawing which shows an example of the extruder to which this invention was applied. It is explanatory drawing which shows the spiral groove formed in the inner peripheral surface of a die. It is a figure which shows the structural example of the cable manufacturing apparatus containing the extruder to which this invention was applied.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. Here, a crosshead including a crosshead die to which the present invention is applied, and an extruder including the crosshead will be described.

As shown in FIG. 1, the extruder 1 according to this embodiment includes a cylinder 2 and a crosshead 3, and is used for manufacturing the cable A. Specifically, the extruder 1 is used to extrude a resin layer a2 as a coating layer around the linear conductor a1.

The cylinder 2 schematically shown in FIG. 1 is configured to be heated to a temperature higher than the melting temperature of the material resin (for example, polyethylene, ethylene-vinyl acetate copolymer) of the resin layer a2. There is. A screw for supplying the molten resin in the cylinder 2 to the crosshead 3 is provided in the cylinder 2. The molten resin R supplied to the crosshead 3 along with the rotation of the screw is extruded around the conductor a1 through the resin flow path provided in the crosshead 3 to form the resin layer a2. Specifically, the molten resin R supplied to the crosshead 3 is extruded inside the crosshead 3 around the conductor a1 traveling from the left side of the paper surface of FIG. 1 toward the right side of the paper surface to form the resin layer a2. The traveling direction of the conductor a1 coincides with or substantially coincides with the direction of the central axis of the conductor a1 or the longitudinal direction of the conductor a1. In the following description, the left side of the plane of FIG. 1 is defined as “upstream side” in the traveling direction of the conductor a1, and the right side of the plane of FIG. 1 is defined as “downstream side” in the traveling direction of the conductor a1.

As shown in FIG. 1, the crosshead 3 includes a head flange 4, a head body 10, a nipple holder 20, a mandrel 30, a nipple 40, a balance ring 50, a die 60, a die holder 70, and a die flange 80.

The head flange 4 is interposed between the cylinder 2 and the head body 10, and one end of the head flange 4 is connected to the head body 10. The molten resin in the cylinder 2 is introduced into the head flange 4 as the screw rotates, and is supplied to the head main body 10 via the head flange 4.

The head body 10 holds a plurality of members forming the crosshead 3 and integrates them. The head body 10 is provided with a hollow portion 11 that penetrates the head body 10. The nipple holder 20, the mandrel 30, the nipple 40, and the balance ring 50 are arranged inside the hollow portion 11 of the head body 10. Further, the central axes of the nipple holder 20, the mandrel 30, the nipple 40, and the balance ring 50 are aligned with each other. That is, the nipple holder 20, the mandrel 30, the nipple 40, and the balance ring 50 are coaxially arranged.

The mandrel 30 is formed in a substantially conical shape as a whole, and has a flange portion 31 at the base end. In the following description, a portion of the mandrel 30 other than the flange portion 31 may be referred to as a conical portion 32 to distinguish it from the flange portion 31. However, this distinction is merely for convenience of description, and the flange portion 31 and the conical portion 32 are integrally formed.

The mandrel 30 is provided with an insertion hole 33 penetrating the flange portion 31 and the conical portion 32. The conical portion 32 of the mandrel 30 is inserted into the hollow portion 11 of the head body 10, and the flange portion 31 of the mandrel 30 abuts the rear end surface of the head body 10. In other words, the conical portion 32 is inserted into the hollow portion 11 of the head body 10 until the flange portion 31 hits the rear end surface of the head body 10. As a result, the outer peripheral surface of the conical portion 32 of the mandrel 30 and the inner peripheral surface of the hollow portion 11 of the head body 10 face each other.

The outer peripheral surface of the conical portion 32 and the inner peripheral surface of the hollow portion 11 facing each other are flat, and a part of the resin flow path is formed by these. That is, a part of the resin flow path is formed by the gap between the outer peripheral surface of the conical portion of the mandrel 30 and the inner peripheral surface of the hollow portion of the head body 10. In the following description, in the resin flow path provided in the crosshead 3, a portion formed by a gap between the outer peripheral surface of the conical portion of the mandrel 30 and the inner peripheral surface of the hollow portion of the head body 10 is referred to as an “upstream portion”. ".

The nipple holder 20 has a substantially cylindrical shaft portion 21, a flange portion 22 provided at one end (rear end) of the shaft portion 21, and a first through hole 23 penetrating the shaft portion 21 and the flange portion 22. .. The shaft portion 21 of the nipple holder 20 is inserted into the insertion hole 33 of the mandrel 30, and the tip of the shaft portion 21 penetrates the insertion hole 33 and projects from the mandrel 30. A holding portion 24 is provided at the tip of the shaft portion 21 protruding from the mandrel 30, and the nipple 40 is held by the holding portion 24. That is, the nipple 40 is held by the nipple holder 20 and arranged in front of the mandrel 30.

The nipple 40 is formed in a substantially conical shape, and has a second through hole 41 that communicates with the first through hole 23 of the nipple holder 20. The first through hole 23 of the nipple holder 20 and the second through hole 41 of the nipple 40 form a series of through holes into which the conductor a1 is inserted. That is, the conductor a1 is inserted into the through hole provided in the crosshead 3 and advances in the through hole from the upstream side to the downstream side. The outer diameter and the inner diameter (diameter of the second through hole 41) of the nipple 40 are gradually reduced from the upstream side to the downstream side in the traveling direction of the conductor a1.

The balance ring 50 is formed in an annular shape, and is arranged around the tip of the nipple holder 20 and the root of the nipple 40 so as to surround them. As a result, the outer peripheral surface of the tip portion of the nipple holder 20 and the base portion of the nipple 40 and the inner peripheral surface of the balance ring 50 face each other.

The outer peripheral surface of the tip portion of the nipple holder 20 and the root portion of the nipple 40 and the inner peripheral surface of the balance ring 50 are flat, and these form the other part of the resin flow path. That is, the annular gap between the outer peripheral surface of the tip portion of the nipple holder 20 and the outer peripheral surface of the root portion of the nipple 40 and the inner peripheral surface of the balance ring 50 forms another part of the resin flow path. In the following description, of the resin flow path provided in the crosshead 3, it is formed by a gap between the tip outer peripheral surface of the nipple holder 20 and the root outer peripheral surface of the nipple 40 and the inner peripheral surface of the balance ring 50. The part that is marked may be called an "intermediate part".

A die flange 80 is provided in front of the head body 10. The die flange 80 holds the die holder 70, and the die holder 70 holds the die 60. The die 60 held by the die holder 70 is arranged around the tapered tip of the nipple 40 so as to surround it. In other words, the tapered tip of the nipple 40 has entered the inside of the die 60 held by the die holder 70. As a result, the outer peripheral surface 40a of the tip portion of the nipple 40 and the inner peripheral surface 60a of the die 60 face each other.

As shown in FIG. 2, a first opening 61 is provided at one end of the die 60 in the axial direction, and a second opening 62 is provided at the other end of the die 60 in the axial direction. The first opening 61 is an opening that serves as an inlet into which the molten resin that has passed through the intermediate portion of the resin flow path flows into the die 60. On the other hand, the second opening 62 is an opening that serves as an outlet through which the molten resin that has passed through the inside of the die 60 flows out toward the periphery of the conductor a1 (FIG. 1).

As shown in FIG. 1, the tip of the nipple 40 enters the inside of the die 60 from the first opening 61 of the die 60. The inner diameter of the first opening 61 of the die 60 shown in FIGS. 1 and 2 is 150 mm, and the inner diameter of the second opening 62 of the die 60 is 110 mm. That is, the first opening 61 has a larger diameter than the second opening 62. Further, the tip end surface of the nipple 40 and the opening surface of the second opening 62 are flush or substantially flush with each other.

As shown in FIG. 1, the outer peripheral surface 40a of the tip portion of the nipple 40 and the inner peripheral surface 60a of the die 60 facing each other form another part of the resin flow path. That is, the other part of the resin flow path is formed by the annular gap between the outer peripheral surface 40a of the tip portion of the nipple 40 and the inner peripheral surface 60a of the die 60. In other words, the inner peripheral surface 60a of the die 60 forms a part of the resin flow path together with the tip end outer peripheral surface 40a of the nipple 40. In the following description, of the resin flow path provided in the crosshead 3, a portion formed by an annular gap between the tip outer peripheral surface 40a of the nipple 40 and the inner peripheral surface 60a of the die 60 will be referred to as " It may be called "downstream part".

As described above, the crosshead 3 is provided with the resin flow path including the upstream portion, the intermediate portion, and the downstream portion. The upstream portion is formed between the head body 10 and the mandrel 30, the intermediate portion is formed between the nipple holder 20 and the nipple 40, and the balance ring 50, and the downstream portion is formed between the nipple 40 and the die 60. Formed between. Of course, the resin flow passage includes the upstream portion, the intermediate portion, and the downstream portion described above, but the upstream portion, the intermediate portion, and the downstream portion are not all the resin flow passages. Further, FIG. 1 does not show all the resin flow paths provided in the crosshead 3.

The die flange 80 is provided with a pair of aligning bolts 81 and 82. The pair of aligning bolts 81 and 82 face each other in a direction orthogonal to the traveling direction of the conductor a1. Specifically, the pair of aligning bolts 81 and 82 face each other with the die holder 70 interposed therebetween, one aligning bolt 81 is on the upper surface of the die holder 70, and the other aligning bolt 82 is the lower surface of the die holder 70. Are in contact with each other. Further, a clearance is provided between the upper surface of the die holder 70 and the die flange 80, and between the lower surface of the die holder 70 and the die flange 80.

Therefore, when the aligning bolt 81 is tightened and the aligning bolt 82 is loosened, the die holder 70 moves downward in the drawing, and the die 60 held by the die holder 70 also moves in the same direction. On the other hand, when the aligning bolt 82 is tightened and the aligning bolt 81 is loosened, the die holder 70 moves upward in the drawing, and the die 60 held by the die holder 70 also moves in the same direction. That is, by operating the pair of aligning bolts 81 and 82, the die 60 can be moved up and down, and the center of the die 60 and the center of the nipple 40 can be aligned. In other words, the width of the gap between the nipple 40 and the die 60 (=the width of the downstream portion of the resin flow path) can be made uniform, which in turn makes the thickness of the resin layer a2 to be extrusion molded uniform. be able to.

As shown in FIGS. 1 and 2, the inner peripheral surface 60a of the die 60 is tapered so as to gradually approach the outer peripheral surface 40a of the nipple 40 from the upstream side to the downstream side of the resin flow path. .. As shown in FIG. 2, at least four (eight in this embodiment) grooves 63 are formed in the inner peripheral surface 60a of the die 60 at predetermined intervals along the circumferential direction. Each groove 63 is formed in a spiral shape extending from the side of the first opening 61 toward the side of the second opening 62 while swirling around the center line X of the die 60 as a rotation axis. Therefore, in the following description, the groove 63 may be referred to as the “spiral groove 63”.

As shown in FIG. 2, each spiral groove 63 ends before the center of the die 60 in the center line direction. Specifically, the spiral groove 63 in the present embodiment ends approximately 44 mm before the center of the die 60 in the center line direction. The total length of the die 60 in this embodiment is 86.5 mm. The total length of the mandrel 30 shown in FIG. 1 is 640 mm.

The depth of each spiral groove 63 shown in FIG. 2 becomes gradually shallower along the extending direction thereof. Specifically, the maximum depth (depth of the starting end portion) of the spiral groove 63 in the present embodiment is 2.0 mm, and the minimum depth (depth of the end portion) is 0.5 mm. Moreover, the width of each spiral groove 63 is gradually narrowed along the extending direction thereof. Specifically, the maximum width (width of the starting end portion) of the spiral groove 63 in the present embodiment is 10 mm, and the minimum width (width of the end portion) is 5 mm. 2 is an explanatory view for helping understanding of the spiral groove 63 formed on the inner peripheral surface 60a of the die 60, and does not accurately show the shape (particularly, the outer shape) of the die 60.

As described above, in the present embodiment, the plurality of spiral grooves 63 are formed on the inner peripheral surface 60a of the die 60 that forms the downstream portion of the resin flow path. Therefore, the molten resin R flows along the spiral groove 63 in the downstream portion of the resin flow path. In other words, the resin flow direction is aligned in the same direction in the downstream portion of the resin flow path. Therefore, a weld mark, which is a trace of the joining of resin flows having different directions, does not occur in the resin layer a2. That is, in the upstream portion and the midstream portion of the resin flow passage, resin flows having different directions are allowed to join, while in the downstream portion of the resin flow passage, the resin flow directions are aligned in the same direction. As a result, finally, the occurrence of weld marks in the resin layer a2 is prevented.

Further, the spiral groove 63 in the present embodiment ends before the center of the die 60 in the center line direction. In other words, the spiral groove 63 ends before the midpoint of the downstream portion of the resin flow path. Furthermore, in other words, the spiral groove 63 does not reach the outlet of the resin flow passage, and a certain distance is secured between the end of the spiral groove 63 and the outlet of the resin flow passage. Therefore, the spiral groove 63 is provided on the inner peripheral surface 60a of the die 60 forming the downstream portion of the resin flow path, but the trace of the spiral groove 63 does not remain on the surface of the resin layer a2. When a groove similar to the spiral groove 63 is provided on the inner peripheral surface of the mandrel 30 forming the upstream portion of the resin flow path, even if the groove is formed over the entire length of the mandrel 30, the trace of the groove is formed. Will not remain in the resin layer a2. This is because the marks of the grooves formed in the resin flow in the upstream part of the resin flow path disappear while the resin flow flows in the middle part and the downstream part of the resin flow path.

As described above, the mandrel 30 has an overall length of 640 mm, while the die 60 has an overall length of 86.5 mm. That is, the die 60 is smaller than the mandrel 30. In particular, the total length of the die 60 is significantly shorter than the total length of the mandrel 30. Therefore, the grooving of the inner peripheral surface 60a of the die 60 can be performed with less labor and time than the grooving of the inner peripheral surface of the mandrel 30. In other words, the groove processing for the die 60 can be performed at a lower cost than the groove processing for the mandrel 30.

Further, as the crosshead 3 becomes larger, the mandrel 30 and the die 60 also become larger in principle. However, the enlargement ratio of the die 60 accompanying the increase in size of the crosshead 3 is smaller than that of the mandrel 30. In particular, the enlargement ratio of the entire length of the die 60 accompanying the increase in size of the crosshead 3 is significantly smaller than the enlargement ratio of the entire length of the mandrel 30. Therefore, even if the crosshead 3 is increased in size, the cost required for grooving the die 60 does not rise to the cost required for grooving the mandrel 30.

FIG. 3 shows an example of a cable manufacturing apparatus including the extruder 1 according to this embodiment. The cable manufacturing apparatus shown in FIG. 3 includes a metering capstan 90, an extruder 1, a connecting pipe (splice box) 91, a bridging cylinder (vulcanizing cylinder) 92, and a tensioning capstan 93.

The metering capstan 90 is arranged at a predetermined height and sends the conductor to the extruder 1. The extruder 1 is arranged on the downstream side of the metering capstan 90 and adjacent to the metering capstan 90. The extruder 1 extrudes the resin layer around the conductor fed from the metering capstan 90 as described above.

The connecting pipe 91 is interposed between the crosshead 3 (FIG. 1) of the extruder 1 and the bridging cylinder 92, and connects them to each other. The connection pipe 91 is driven by a hydraulic actuator, a pneumatic actuator, an electric motor, etc., and slides in the forward and backward directions of the cable. Thereby, in the preparation process (setup process), the crosshead 3 (FIG. 1) and the bridge cylinder 92 can be connected or disconnected.

The bridging cylinder 92 is arranged on the downstream side of the connecting pipe 91 and inclines like a catenary from a high place to a low place. The bridging cylinder 92 includes a hollow portion into which the cable is inserted. The pressurized and heated gas is filled (enclosed) on the upstream side of the bridging cylinder 92. The gas is, for example, an inert gas such as nitrogen or water vapor. On the other hand, the downstream side of the bridging cylinder 92 is filled with cooling water. As a result, the resin layer extruded by the extruder 1 is crosslinked (vulcanized) on the upstream side of the crosslinking cylinder 92 and cooled on the downstream side of the crosslinking cylinder 92.

The tensioning capstan 93 is arranged on the downstream side of the bridging cylinder 92 and at a position lower than the metering capstan 90. The tensioning capstan 93 pulls the cable after passing through the bridge 92 with a predetermined tension. A winder for winding the cable around the drum may be arranged downstream of the tensioning capstan 93.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention. For example, the above-mentioned dimensions regarding each member constituting the crosshead 3 are examples, and can be appropriately changed as necessary. However, from the viewpoint of making groove processing (cutting) for the die 60 easy and inexpensive, the inner diameter of the first opening 61 of the die 60 is preferably 50 mm or more.

Further, in the present specification, as an example of the cable manufacturing apparatus including the extruder 1 according to the above-described embodiment, the cable manufacturing apparatus including the bridging cylinder (vulcanization cylinder) 92 has been described. However, the extruder 1 according to the above-described embodiment is a cable manufacturing apparatus that does not include the cross-linking cylinder (vulcanization cylinder) 92, or a so-called general cable manufacturing apparatus that does not incline like a catenary from a high place to a low place. Can also be applied to.

The application target of the present invention is not limited to the extruder used for cable production and the die for the crosshead provided in the extruder used for cable production.

1 Extruder 2 Cylinder 3 Crosshead 4 Head Flange 10 Head Main Body 11 Hollow Part 20 Nipple Holder 21 Shaft Part 22 Flange Part 23 First Through Hole 24 Holding Part 30 Mandrel 31 Flange Part 32 Conical Part 33 Insertion Hole 40 Nipple 40a Outer Surface 41 second through hole 50 balance ring 60 die 60a inner peripheral surface 61 first opening 62 second opening 63 groove (spiral groove)
70 Die Holder 80 Die Flange 81, 82 Alignment Bolt 90 Metering Capstan 91 Connection Tube 92 Bridge Bridge 93 Tensioning Capstan A Cable R Molten Resin X Centerline a1 Conductor a2 Resin Layer

Claims (6)

A die constituting a crosshead of an extruder,
A first opening serving as an inlet for the molten resin;
A second opening serving as an outlet for the molten resin;
An inner peripheral surface facing the outer peripheral surface of the nipple and forming a resin flow path together with the outer peripheral surface of the nipple;
And at least four grooves provided on the inner peripheral surface,
The inner peripheral surface is formed so as to gradually approach the outer peripheral surface of the nipple from the upstream side to the downstream side of the resin flow path,
Each of the grooves is formed in a spiral shape extending from the side of the first opening toward the side of the second opening while rotating around the center line of the die as a rotation axis.
Die for crosshead. The crosshead die according to claim 1,
Each of the grooves ends before the center of the die in the center line direction,
Die for crosshead. The crosshead die according to claim 1 or 2,
The depth of each groove is gradually shallower along the extending direction of the groove,
Die for crosshead. The die for crosshead according to any one of claims 1 to 3,
The width of each of the grooves is gradually narrowed along the extending direction of the groove,
Die for crosshead. The crosshead die according to any one of claims 1 to 4,
The inner diameter of the first opening is 50 mm or more,
Die for crosshead. An extruder having a crosshead including a die,
The die is
A first opening serving as an inlet for the molten resin;
A second opening serving as an outlet for the molten resin;
An inner peripheral surface facing the outer peripheral surface of the nipple and forming a resin flow path together with the outer peripheral surface of the nipple;
And at least four grooves provided on the inner peripheral surface,
The inner peripheral surface is formed so as to gradually approach the outer peripheral surface of the nipple from the upstream side to the downstream side of the resin flow path,
Each of the grooves is formed in a spiral shape extending from the side of the first opening toward the side of the second opening while turning around the center line of the die as a rotation axis.
Extruder.

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