Cable Jacket Extrusion Apparatus And Die With Wire Positioning Means

Abstract

An extrusion die for cable jackets with embedded drain wires is provided with radially adjustable shoes to position the wires.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

Continuation-in-part of application, Ser. No. 740,594 filed June 27, 1968 now U.S. Pat. 3,531,962.

Description

BACKGROUND OF THE INVENTION

Electric cables in which drain wires are embedded in the cable jacket are described in application, Ser. No. 692,893, assigned to the assignee of the present invention. In the manufacture of such cables the drain wires, which are made undulatory, principally for increased flexibility, are paid into an extruder, along with the cable core to which a jacket is being applied. The circumferential position of the drain wires is established by the spacing of longitudinal slots in an otherwise conventional extrusion guider and the location of these slots also fixes, to some extent, the radial location of the wires. However a fine adjustment of the drain wires radially is highly advantageous particularly if it is desired to protect the wires from corrosion by having them covered with a thin layer of the jacket stock. So far as I am aware, prior to the present invention there has been no means for making such an adjustment.

SUMMARY

My invention encompasses an improvement in apparatus for applying a jacket that has a plurality of embedded strands around a cable core that is continuously advancing downstream through the apparatus. Such apparatus comprises a guider for the core, a die, and means continuously urging a supply of jacketing stock around the core directly downstream of the guider, and my improvement, in combination, comprises a substantial land within the die, and walls in the guider that define a plurality of circumferentially distributed lengthwise passages for the strands. My improvement also comprises a plurality of shoes projecting radially through the stock at a station that is downstream of the guider but upstream of the land. These shoes are aligned with the passages in the guider and press against the strands and means such as cams projecting lengthwise through the die, are provided for adjusting them radially, preferably from the face of the die, to fix the depth of the strands within the jacket. Surprisingly I have found that the extruded stock will blend together again over the embedded strands downstream of the shoes if the land has sufficient length. This length should at least exceed the land radius.

For my apparatus I have invented an extrusion die with an exit face that comprises a metal block with walls defining a tapered entrance, a land coextensive with the entrance, and radial bores located inwardly in the block at least a major portion of the land so that there is sufficient land downstream of the shoes to bridge over the jacket stock. My die also comprises pin members supported in the bores and projecting inwardly from them and a plurality of lengthwise holes that communicate between the bores and the die face. Cam rods are mounted rotatably in the holes and engage the pin members, and camming means are provided whereby the projection of the pin members is adjusted by rotating the rods. These camming means will preferably comprise lateral channels in the pins and eccentrically positioned circular projections on the rods.

Where the strand comprises an undulatory wire applied with the plane of the undulations radial to the cable core the pins will advantageously comprise slots only slightly exceeding the wire gage and having a length of at least a full cycle of the wire undulations. In any case it is advantageous to terminate the pins in narrow shoes aligned with the axis of the die land to minimize obstruction of the flow of jacket stock.

A more thorough understanding of my invention may be obtained by considering the specific embodiments hereinafter described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lengthwise section through an apparatus of my invention.

FIG. 2 shows a section through the lines 2--2 of FIG. 1.

FIG. 3 shows a front view of a pin used in one embodiment of my invention.

FIG. 4 shows a section through the lines 4--4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

My apparatus indicated generally by the numeral 10 comprises a die 11 and guider 12 of a type that are conventionally used for extruding cable jackets except for the improvements hereinafter described. The guider 12 has a plurality of lengthwise slots or passages 13 for the introduction of strands in the form of undulatory wires 14 around a cable core 16 that is being paid through a conventional bore 17 in the guider 12. Jacket stock 18 is urged by the usual means, not shown, to surround the core 16 downstream of the guider 12 at a point 19 within a tapered entrance 21 to the die 11. The die 11 has a land 22 which has a length l greater than the length which would be conventionally used for the extrusion of the stock 18 which, in the illustrated embodiment, comprises polyvinylchloride rendered semiconducting by the inclusion of carbon black. The diameter of a cable 23 covered with a jacket 24 of the stock 18 is fixed by the diameter of the land 22, and the length l should be at least half this diameter (at least one radius). Radial bores 26 in a block 27 of the die 11 are positioned upstream of the land 22 but downstream of the point 19. I have shown the bores 26 opening into the tapered portion of the die but it will be understood that they might open into the land provided there is still sufficient length of land downstream to distribute any jacket stock that is diverted. Each of the bores 26 houses a cylindrical pin 28 in a slide fit. The pins 28 terminate in narrow shoes 29 of which a slotted form 31 is shown in FIG. 3. The shoes 29 press against the wires 14 and serve to determine how deeply the wires are embedded in the jacket 24. To reach the wires 14 the shoes 29 project through the flowing stock 18 and are shaped to offer a minimum obstruction to the lengthwise flow of the stock. Each of the pins 28 has a rectangular channel 32 into which is closely fitted a circular projection 33 eccentrically mounted on the end of a threaded cam rod 34 which is threaded into a tapped hole 36 of the block 27. The pins 28 have slots 37 which, on assembly, are used to determine the proper downstream orientation of the channels 32. The cam rods 34 project through a front face 38 of the die 11 and have slots 39 so that they can be rotated as desired. The depth of the channels 32 and length of the projections 33 are such that at least one half a rotation of the rods 34 can be made, after the projections have engaged the channels, to provide a camming effect adjusting the radial position of the pins 28.

In FIGS. 3 and 4 the pins 28 have been modified so that the shoe portions 31 have slots 41 offering a slide fit to undulatory wires 42 that it is desired to apply with the plane of the undulations radial to the cable 16. Since, in this case, the top of the slot should only touch the crests of the wire the length "L" of the slot must span 2 crests, or be equal, at least to one undulatory cycle as shown in FIG. 4.

The foregoing description has been exemplary rather than definitive of my invention for which I desire an award of Letters Patent as defined in the following claims.

Claims

I claim:

1. In an extrusion apparatus for applying a jacket having a plurality of embedded strands around a cable core continuously advancing downstream through said apparatus and comprising a guider for said core, a die, and means continuously urging a supply of jacketing stock around said core directly downstream of said guider, the improvement comprising, in combination,

A. a substantial land within said die,

B. walls in said guider defining a plurality of circumferentially distributed lengthwise passages for said strands,

C. a plurality of shoes

a. projecting radially through said stock at a station downstream of said guider and upstream of said land,

b. aligned with said passages, and

D. means for adjusting the radial projection of said shoes, said shoes pressing against said strands and fixing the depth of said strands within said jacket.

2. The apparatus of claim 1 wherein said adjusting means comprise cam means projecting lengthwise through said die.

3. The apparatus of claim 2 wherein said cam means are adjustable from the face of said die.

4. The apparatus of claim 1 wherein the length of said land exceeds its radius.

5. An extrusion die having an exit face comprising

A. a metal block,

B. walls in said block defining a tapered entrance,

C. a land coextensive with said entrance,

D. walls defining a plurality of radial bores in said block and upstream of at least a major portion of said land,

E. pin members supported in said bores and projecting inwardly therefrom,

F. walls defining a like plurality of lengthwise holes communicating between said bores and said face,

G. cam rods rotatably mounted in said holes and engaging said pin members,

H. camming means whereby the projection of said pin members is adjusted by the rotation of said rods.

6. The die of claim 5 wherein said camming means comprise lateral channels in said pins and eccentrically positioned circular projections on said rods.

7. The die of claim 5 wherein said pins terminate in narrow shoes aligned with the axis of said land.

8. The die of claim 5 wherein said strand comprises an undulatory wire and said pin members comprise walls defining slots only slightly exceeding the gage of said wire and having a length of at least full cycle of the undulations of said wire.