US3411182A

US3411182A - Apparatus for extruding helical webs on conductors

Info

Publication number: US3411182A
Application number: US582702A
Authority: US
Inventors: John J Nevin
Original assignee: Phelps Dodge Copper Products Corp
Current assignee: Phelps Dodge Copper Products Corp
Priority date: 1966-09-28
Filing date: 1966-09-28
Publication date: 1968-11-19
Anticipated expiration: 1985-11-19
Also published as: AT283482B; GB1150517A; CH468251A; ES345450A1; GR34665B; DK119117B; FI47820B; BE704063A; FI47820C; SE336459B; NL149424B; NL6712871A; DE1729315A1; DE1729315B2

Description

J. J. NEVlN Nov. 19, 1968 APPARATUS FOR EXTRUDING HELIGAL WEBS ON CONDUCTORS 2 Sheets-Sheet 1 Filed Sept. 28, 1966 IXVLLVIOR. JOHN .1. NE VIN Nov. 19, 1968 J. J. NEVIN 3,411,182

APPARATUS FOR EXTRUDING HELICAL WEBS ON GONDUCTORS Filed Sept. 28, 1966 2 Sheets-Sheet 2 U\\\ y I 1 w 1 1' 1 1i M N L M [1H1 I 1 I I.

United States Patent M 3,411,182 APPARATUS FOR EXTRUDING HELICAL WEBS ON CONDUCTORS John J. Nevin, Yonkers, N.Y., assignor to Phelps Dodge Copper Products Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 28, 1966, Ser. No. 582,702 5 Claims. (CI. 18-13) ABSTRACT OF THE DISCLOSURE The electrical conductor is passed through the main orifice of an extrusion die having an exit end through which the main orifice opens and also having a sub-orifice intersecting the main orifice and extending generally radially outward therefrom, the sub-orifice opening through the exit end of the die with the radially outer portion of the sub-orifice terminating short of the outer periphery of the die. The die is supported for rotation about the conductor and is provided with an inlet to which a plasticized resinous material is supplied under pressure in all rotational positions of the die, to cause the material to be extruded continuously through the exit opening of the suborifice in the form of a generally radial web on the conductor. Driving means are provided to rotate the die so as to spiral the web in a helix about the conductor, the pitch of the helical web being determined by the rotational speed of the die relative to the speed at which the conductor is moved lengthwise through the die by a transport means.

The disclosure This invention relates to extrusion apparatus and more particularly to apparatus for extruding a helical web around and along the length of an electrical conductor. A conductor having a web formed in accordance with this invention is useful as a component of electrical cable, such as coaxial cable wherein the helical web serves to maintain the conductor in concentrically spaced relation to a surrounding outer conductor.

In the past, such helical webs have been formed on conductors by the use of two structurally independent but functionally cooperating elements, one stationary and the other rotatable, which together form the extrusion die. An example of such an apparatus is seen in United States Patent No. 2,465,482. In order to provide perfect concentricity and uniformity of the web thus formed, perfect alignment of the two die elements must be attained and maintained, which is difficult if not impossible and is time-consuming at best. Modification of the desired web, for example, in width or cross section, requires changing one or both elements and therefore requires a realignment of these elements.

A second known type of apparatus, for forming a helical web about an electrical conductor, comprises a rotatable die having a cavity wiih the configuration of the helix and through which the electrical conductor passes. In addition to the need for accurately aligning the conductor within the cavity, the uniformity of the resulting helix is dependent upon the accuracy with which the die cavity is machined. Furthermore, it is necessary to provide a different die for each different helix pitch which is desired. An apparatus of this type may be seen in United States Patent No. 2,834,047.

Accordingly it is one object of this invention to provide an improved extrusion apparatus for forming a uniform helical web about a cylindrical element and in which the extrusion die is self centering with respect to the element.

Another object of this invention is to provide an extru- 3,411,182 Patented Nov. 19, 1968 sion apparatus having sufficient operation flexibility to permit variation in helix pitch without replacement .of the extrusion die.

These and other objects and attendant advantages of the present invention wi.l become apparent and better understood from the following description and accompanying drawings in which FIGURE 1 is a partially cutaway perspective view of an electrical coaxial cable produced by apparatus in accordance with this invention;

FIGURE 2 is a schematic illustration of an extrusion system, including control circuitry, made in accordance with this invention;

FIGURE 3 is a vertical, longitudinal sectional view of the extrusion apparatus of the system of FIGURE 2, and

FIGURE 4 is a sectional view taken along line 44 in FIGURE 3.

Briefly stated, this invention in one form comprises an extrusion apparatus including a feeding means, which may be conventional, for directing a plasticized resinous material under pressure to an extrusion die. The extrusion die is formed with a main orifice adapted to accommodate passage of the conductor on which the web is to be formed. Intersecting this main orifice and extending radially outwardly from it is a sub-orifice through which the resinous material is extruded. This sub-orifice, at least where it opens through the exit end of the die, has the shape of the desired cross-section of the helical web, preferably rectangular, with its radially outermost portion terminating short of the outer periphery of the die, so that the sub-orifice is completely contained within and defined by the die. The extrusion die is held in a die carrier which is mounted for rotation about the conductor in the main on'fice, and driving means are provide-d to rotate the die carrier and hence the extrusion die.

In some instances, it may be desired to extrude the helical web simultaneously with an underlying thin film of the material which completely surrounds the conductor and from which the web protrudes. In such instances, the main orifice of the die is provided with a diameter which exceeds the conductor diameter by twice the desired thickness of the film. Otherwise, the diameter of the main orifice is essentially the diameter of the conductor.

The conductor is fed continuously lengthwise to the extrusion die and through its main orifice by suitable transport means. In order to form the helical web about the conductor, the resinous material is extruded through the sub-orifice and the extrusion die is rotated during this lengthwise movement of the conductor. The pitch of the resulting helical web is determined by the rotational speed of the die relative to the linear speed at which the transport means passes the conductor through the die, and the pitch can be varied as desired by varying the ratio of these two speeds. Because the conductor is supported so that its central axis coincides with that of the main orifice in the die, and because the sub-orifice is completely defined by the die, the helical web will be concentric to the conductor axis and uniform throughout.

Referring now to the drawings, and more particularly FIGURE 1, there is illustrated an air dielectric electrical coaxial cable 8 including an electrical conductor 10 having a helical web 12 extending radially therefrom and formed by the apparatus of this invention. The web serves as a dielectric support to hold the inner conductor 10 concentrically within an outer conductor 14.

The term conductor as used herein refers to an electrical conductor of any conventional material having high conductivity, such as copper or aluminum.

The system as shown in FIGURE 2 includes a payoff reel 18 rotatably supported by any conventional means, such as jackstands 20, which permits free rotation of the reel as the conductor is pulled by an appropriate transport mechanism described below.

The electrical conductor is passed through an extrusion apparatus 22 wherein the helical web 12 is extruded onto the conductor 10. The conductor and web combination is then passed through a conventional cooling apparatus, such as a water trough 24, wherein the web acquires its final solid state. Downstream from the cooling apparatus is a transport mechanism for pulling the conductor from the payoff reel 18. Any conventional transport mechanism 26, such as a tractor capstan, may be employed. The transport mechanism 26 feeds the webbed conductor to a take-up reel 28.

So that the helical web 12 will have a uniform pitch, a coordinating speed control 30 is provided which controls the speeds of the transport mechanism 26 and the extrusion apparatus 22. The control 30 is of the known type which, in response to any increase or decrease in the speed of one, results in a corresponding change in the speed of the other, so that the relative speeds are maintained essentially constant. If desired, however, the control 30 may be adjusted to maintain a different ratio of the speeds and thus provide a uniform helical web of different pitch. This adjustment may be effected automatically according to a predetermined pattern, when it is desired to vary the pitch of the helical web from time to time during a continuous run.

FIGURES 3 and 4 illustrate in detail the extrusion apparatus which forms the helical web 12. The apparatus includes a block 32 containing a cylindrical member 33 and forming therewith an annular cavity 34 for receiving a plasticized resinous material to be extruded. Any conventional, nonconductive, thermoplastic or thermosetting material can be used. The material is supplied by a standard feeding means, such as a feed screw 36, which forces the material through the cavity 34 and into the adjacent entrance end of an extension die 38.

The die 38 is formed with a central orifice 40 which, as shown, receives the conductor 10 with a close sliding fit. Extending radially outwardly from the central orifice 40 is a rectangular sub-orifice 42 through which the res inous material is extruded. The radial dimension of the sub-orifice 42 is slightly larger than the desired Web height in order to allow for shrinkage when the web 12 cools and solidifies. The extrusion die 38 is supported within a die carrier 44 and is adapted to be rotated with this carrier, as through a key 45. The die carrier 44 is located in a cavity 46 formed in an extension of the stationary block 32 and is supported for rotation therein by bearings 48.

In order to provide rotary motion to the die carrier 44 and its extrusion die 38, a drive sprocket 50 is secured to the die carrier by any conventional means, such as bolts 52. The drive sprocket is adapted to be driven by a variable speed motor 53 through a suitable connection 54.

The electrical conductor 10 is fed through a guide 56 centrally located within the cylindrical member 33 and passes from this guide through the central orifice 40 in the extrusion die 38. The die 38 has a conical cavity 39 tapering from the entrance end of the die toward its exit end and forming an inlet to the orifices 40 and 42. The guide 56 has a similarly tapered end 57 centrally located in the die cavity 39, so that the extrusion material is forced from the annular cavity 34 through the tapering annular passage surrounding the guide end 57, and thence through the sub-orifice 42.

In forming the helical web 12, the conductor 10 is pulled lengthwise through the extrusion die 38 by means of the transport mechanism 26. Simultaneously, the resinous material is fed by a screw 36 to the extrusion die 38 and is extruded through the sub-orifice 42 in the form of a radial web having its inner edge in contact with the conductor, since this sub-orifice intersects the main orifice 40 through which the conductor passes. At the same time, the extrusion die 38 is rotated by the variable speed motor 53, resulting in the formation of a uniform extruded web 12 spiralling about the conductor 10 along its length. The spacing of the convolutions of the helix, that is, the pitch of the helix, is determined by the speed at which the conductor 10 is moved through the die 38 and the speed at which the die is rotated. With a fixed speed of conductor movement, an increase in rotational speed of the die decreases the helix pitch. Conversely, with a fixed rotational speed of the die, an increase in speed of conductor movement increases the helix pitch. Accordingly, the coordinating speed control means 30 can be programed to provide any desired pitch by merely adjusting the relative speeds of the transport mechanism 26 and motor 53. It is also necessary to control the rate of material feed in order to insure uniformity in web thickness. For example, if the conductor movement or the die rotation decreases considerably in speed, it is necessary to similarly decrease the rotational speed of feed screw 36 in order to avoid feeding the material at an excessive rate to the extrusion orifice 42. The speed control of the feed screw 36 is coordinated with the operation of the transport mechanism 26 and variable speed motor 53 by means of the speed control means 30.

Any desired web shape can be provided by merely varying the cross-sectional shape of the extrusion orifice 42. Similarly, various size conductors can be accommodated by interchanging the extrusion die 38. This is accomplished by merely removing the die carrier 44 from the block 32 and replacing the extrusion die 38 with the appropriate die. The die and carrier assembly are then reinserted in the cavity 46. i

As will be observed from FIGURES 3 and 4, the extrusion is effected through an orifice 42 extending radially outward from the main orifice 40 but terminating short of the outer periphery of the die 38, so that the extrusion orifice 42 is defined entirely by the die and the conductor 10 passing through the main orifice. Consequently, it is unnecessary to center the extrusion die 38 with any other element of the apparatus, in order to form a uniform helical web 12 which is perfectly concentric to the conductor 10. Such concentricity is assured simply by preventing lateral movement of the conductor relative to the main orifice 40, which movement is avoided by a close sliding fit of the conductor in the orifice or, when the aforementioned thin film is also to be extruded, by the centering action of the resinous material as it is forced through the annular tapered inlet 39 surrounding the conductor. In other words, the present apparatus is entirely self-centering for the purpose of maintaining the helical web concentric to the conductor. Moreover, the helical web is formed without resort to a helical die cavity, which requires accurate and difiicult machining and limits the helix to a predetermined pitch.

The extrusion material supplied by the feed screw 36 may be any of the polyolefins, cross-linked or not, such as polyethylene, polysulfone or Teflon. The cooling apparatus 24 serves to solidify the extruded material before it is engaged by the transport mechanism 26 which pulls the conductor from the extrusion die.

I claim:

1. Apparatus for extruding a helical web along the length of an electrical conductor, said apparatus comprising (a) an extrusion die formed with a main orifice through which said conductor is adapted to pass, the die having an outer periphery and also having an exit end through which said main orifice opens, the die also being formed with a sub-orifice intersecting said main orifice and extending generally radially outward from said main orifice, said sub-orifice opening through said exit end of the die with the radially outer portion of the sub-orifice terminating short of said outer periphery, the die forming an inlet to said sub-orifice,

(b) means supporting the die for rotation about said conductor in the main orifice,

(c) means for supplying plasticized resinous material under pressure to said inlet in all rotational positions of the die, to cause said material to be extruded continuously through said exit opening of the suborifice in the form of a generally radial web on the conductor,

(d) transport means for moving said conductor lengthwise through said main orifice, to draw the extruded material from said exit end of the die, and

(2) driving means for rotating the die in one direction about said conductor to spiral the web in a helix around the conductor, the pitch of the helical web being determined by the rotational speed of the die relative to the speed at which the conductor is moved lengthwise by said transport means, and the radial dimension of the helical web being determined by said sub-orifice within the die.

2. Apparatus as defined in claim 1, in which the die has a conical cavity tapering toward said exit end and forming said inlet to the sub-orifice, the apparatus comprising also a stationary guide member having a conical end disposed in said cavity in spaced relation to the die and tapering toward said exit end, said member having a passage for guiding the conductor to the die and opening through said tapered end, said material supplying means forming an annular supply passage surrounding the guide member and opening into said cavity at the end of the die remote from said exit end.

3. Apparatus as defined in claim 1, comprising also control means operatively connected to said driving means and said transport means for maintaining a predetermined ratio of the rotational speed of the die and said lengthwise speed of the conductor.

4. Apparatus as defined in claim 1, in which said main orifice is dimensioned to receive the conductor with a close I sliding fit.

5. Apparatus as defined in claim 1, in which said transport means include mechanism for pulling the conductor from the extrusion die, the apparatus comprising also cooling means interposed between the extrusion die and said pulling means and operable to solidify said extruded material on the conductor.

References Cited UNITED STATES PATENTS 2,446,057 7/1948 Morin 18l3 RXR 2,805,179 9/1957 Burr 1813 RXR 2,834,047 5/1958 Morin 18-13 R WILLIAM J. STEPHENSON, Primary Examiner.