US 3077068 A
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Description (OCR text may contain errors)
Feb. 12, 1963 D. J. MILLER 3,077,068
PAPER TAPING TECHNIQUE FOR ELECTRIC CABLES FIG. 2
- INVENTOR DONALD J. MILLER 3,077,958 Patented Feb. 12, 1963 hire 3,977,068 PAPER TAPlI lG TECHNEQUE FUR ELECTRIC CABLES Donald John Miller, Scarborough, flntario, Canada, as-
signor to Canada Wire and Cable Company Limited, Toronto, Bntario, Canada Filed Sept. 15, 1% filer. No. 138,387 Qiairns. (Cl. 57-15) This invention relates to a method for applying paper insulation to electric power cables.
In the manufacture of electric power cables it is common practice to insulate the copper, current conducting core by winding over the core several layers of paper tape to build up a paper layer on the core which acts as an insulating layer.
Electrically, the paper insulation is admirably suited for this purpose but, mechanically, certain dilliculties and problems exist.
First of all, the paper must not be wrapped onto the conductor so tightly that, when the conductor is bent, the paper kinks and breaks, on the inside and outside of the bend respectively. At the same time, the paper must not be wrapped on so loosely that it is able to move of its own accord and, possibly, create voids in the paper insulating body.
In order to overcome these mechanical problems many methods and processes have been proposed in the past with varying results.
First of all, the taping machines are provided with mechanisms to control the tension on the paper tape as it is wound about the conductor and such mechanisms vary from those which are quite simple mechanically to those which are of great complexity.
Further, it has been proposed, in order to achieve the desired mechanical characteristics, to very closely control the moisture content of the paper tape. For exa l. ple, it has been proposed to wrap the core with a paper tape having a relatively high moisture content which is subsequently reduced by drying. The high moisture content increases the thickness of the paper tape during the taping operation and drying the tape subsequent to applying it to the cable, uniformly loosens the tapes to permit them to slide one upon the other as the cable is bent so that the tapes do not either kink or tear in the bend area.
Ideally, a paper insulated cable should applied to it in such a manner that the adjacent convolutions of paper tape are sufiiciently loose on the conductor that they may slightly slide relative to one another so that the compressive and tensile stresses set up in the insulating layers when the cable is bent may be accon1- moo'ated by this relative movement in the paper tape. It is extremely diilicult, if not impossible, to achieve this lo-oseness in the paper taping only by conventional tension controlling means.
it is an object of the present invention to provide a method of applying paper tape to an electrical conductor which achieves this ideal condition in an extremely simple and uncomplicated manner and which is entirely reliable in operation, readily adaptable to any conventional paper taping machine, readily adjustable and which does not require constant control by the operator.
The invention will be described by way of example with reference to the accompanying drawings in which like reference numerals refer to like parts in the various views and in which;
FIGURE 1 is a side elevation, in simplified form, or" a paper taping machine constructed in accordance with the present invention, and
FIGURE 2 is an enlarged side elevation view of a section of cable having paper tape applied in accordance have the paper with the inventive method described and claimed herein.
Referring now to the drawings and, in particular, to FIGURE 1 the machine may be seen to include three taping heads 19, 11 and 12 which will be supported in a suitable frame and with which may be associated auxiliary equipment, none of which is shown in the drawings since it forms no part of the present invention.
Generally, each taping head comprises a central guide and bearing cylinder 13 upon which is mounted, for rotation, a revolving member 14 upon which, in turn, are mounted tape reels 15 from which paper tape 16 is led to the cable 17 through suitable supporting guides 13. This structure is all well known in the art and various forms of this structure are currently being manufactured by various organizations.
The cable 17 is drawn through heads 1t 11 and 12 in the direction of the arrow 19 and as the cable moves in the direction of its length from taping station it) towards taping station 12, the rotatable member 14 revolves about the bearing support 13 and the paper tape 16 is wound in a helical manner about the core 17 as may be readily understood from a consideration of FIGURE 1.
Convention practice dictates that the cable core 17 should be, at all times, and over the entire length of the cable passing through the taping machine, in a position such that its longitudinal axis coincides exactly with the axis of the rotation of the rotatable member 14 and with the center about which the tape reels l5 orbit on the rotatable member 14. It will be appreciated that this condition appears to be desirable so that no eccentric centrifugal forces are set up in the mechanism during the taping operation which proceeds at a relatively high speed. Suitable guides in the form of rollers are usually rovided to locate the cable in this desirable position.
The present invention resides in a radical departure from accepted practice and provides for the displacei cut of the cable core 17 from this usual position so that, as the cable passes through the taping head, its longitudinal axis lies at an angle of other than degrees to the axis of revolution of the taping head.
This displacement of the cable is achieved by guide rollers Zll and 21 associated with the taping head 10 and the position of these guide rollers may be adjusted by means of lead screws 22 and 23 controlled by hand wheels 24 and 25. A similar assembly of guide rollers is shown generally at 26 in association with taping head 11 and shown generally at 27 in association with taping head 12.
In practicing the present invention, the guide rollers 20 and 21 are displaced in one sense of a direction transverse to the axis of revolution of the rotatable member 14 and the guide roll mechanism 26 associated with taping head 11 will be adjusted so as to displace the longitudinal axis of the cable in the opposite sense of the transverse direction to the common axis of revolution of taping heads 10 and 11 so that the longitudinal axis of the cable 17, as it passes through the taping head 10 will lie at an angle of other than 180 degrees to the axis of the taping head 11. It has been found that an angle of between 3 and 7 degrees, preferably approximately 4.5 degrees, produces desirable results.
When there are more than two taping heads in succession, the cable will be alternately displaced above and below the common axis of rotation of the successive taping head in a manner which can readily be understood from a consideration of FIGURE 1.
The effect of this displacement may be understood from the following description when read in association with FIGURE 2.
Normally, when the cable passes through the taping head with its longitudinal axis coinciding with the axis the successive taping of rotation of the taping head, the plane in which the taping head rotates will intersect with the cable at 90 degrees to the longitudinal axis of the cable and the cross-section of the cable core, therefore, about which the paper tapes are being applied will be circular. Accordingly, the tapes will be evenly applied in intimate contact with the cable throughout their width and no looseness, slack or play between adjacent convolutions of the tape and between the tape and the core will exist.
When the cable axis, however, is displaced from the axis of rotation of the taping head at a small angle, the plane in which the taping head rotates will intersect with the cable at an angle of other than 90 degrees and the cross-section of the cable, therefore, at the paper taping station will no longer be circular but will be elliptical.
Since the taping head is rotating at a relatively high speed, centrifugal forces will still cause the individual convolutions of the paper tape to assume a circular configuration as they are applied to the core, but under these circumstances, the diameter of the circular configuration of each convolution will be equal to the length of the major axis of the elliptical cross-section of the cable and, as a result, when the cable is subsequently straightened out, the individual paper convolutions will have a diameter slightly greater than the true diameter of the cable and there will be, accordingly, a certain amount of slack available which will enable the adjacent convolutions of the paper tape to slide relative to one another so that when the cable is bent such as, for example, when it is reeled upon a shipping reel, the adjacent convolutions may slide relative to one another and avoid kinking or buckling and tearing.
Obviously, the amount of looseness can be controlled by controlling the angle which the longitudinal axis of the cable makes with the axis of rotation of the taping head. In practice, since the distance between adjacent taping heads is fixed and is known, adjustment is made usually not by measuring the angle which the longitudinal axis of the cable makes with the axis of rotation of the head but by measuring the linear distance through which the cable is displaced at the guide rolls 2t} and 21. In a practical embodiment of the present invention, operated by the assignee of this application, it is found that with a machine having successive taping heads spaced apart by approximately 26", a displacement of 1" on one side of the axis of rotation of the taping head 16 and a displacement of l" on the opposite side of the axis of taping head 11 produces satisfactory results. The displacement, measured in terms of degrees, as set forth above, amounts to approximately 4.5 degrees between the longitudinal axis of the cable 17 and the axis of rotation of the taping head 14.
Obviously, the advantages of the invention will be obtained to a greater or lesser degree as a departure from these preferred limitations is made. As a practical matter, it is believed that a range of from 3 degrees to 7 degrees will produce satisfactory results in most instances and if the angle is reduced below 3 degrees it is believed that the amount of looseness achieved will be insuificient to be of practical value whereas if the angular displacement exceeds 7 degrees, the paper tape will not apply properly to the cable core.
Workers skilled in the art of controlling machines applying paper tape to cable cores will readily be able to select the optimum displacement for any particular set of conditions.
The drawings accompanying this application are intended only to illustrate the principles of the present invention and the accompanying description is intended to be construed in an illustrative rather than a limting sense. Minor modifications of detail are contemplated within the spirit of the present invention and the scope of the appended claims.
What 1 claim as my invention is:
1. The method of applying a tape insulation to an elongated core comprising the steps of feeding the core in the direction of its length through a taping head, revolving the taping head about an axis coaxial with the longitudinal axis of the core over part of its length to wind tape about the core and, as the core passes through the head, altering its direction of travel so that the axis of the core lies at an angle of other than degrees to the axis of revolution of the taping head.
2. The method of app-lying a tape insulation to an elongated core by means of at least two successive coaxial rorating taping heads comprising the steps of feeding the core through the taping heads in the direction of its length along the axes of the taping heads and displacing the cable from its position on the axis of the taping heads in one sense of a direction transverse to the axes on one side of each head and in the opposite sense of the transverse direction on the other side of each head so that the effective cross-section of the core at each taping head is an ellipse.
3. The method of claim 2 wherein the longitudinal axis of the cable intersects with the axis of rotation of each taping head in the plane of rotation of the head at an angle of from 3 degrees to 7 degrees.
4. The method of claim 2 wherein the longitudinal axis of the core intersects with the axis of rotation of each taping head in the plane of rotation of the taping head at an angle of approximately 4.5 degrees.
References (Iited in the file of this patent UNITED STATES PATENTS