FR2499757A1 - COATING FOR PROVIDING THE CENTERING OF A CABLE CORE IN ITS ENVELOPE, CABLE COMPRISING SUCH A DEVICE AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

THE SUBJECT OF THE PRESENT INVENTION IS A COATING INTENDED TO ENSURE THE CENTERING OF A CABLE CORE, A CABLE INCLUDING SUCH A DEVICE AND ITS MANUFACTURING PROCESS. A DEVICE FOLLOWING THE INVENTION IN PARTICULAR A COATING 8 INCLUDES ELASTIC FINS 10 AND IS INTENDED TO BE ARRANGED AROUND THE CORE OF A CABLE. THESE CAN BE SHAPED BY AT LEAST ONE TAPE LAYED IN LONG AND THE EDGES OF WHICH ARE SOLIDARIZED BETWEEN THEM OVER PART OF THEIR WIDTH. A METAL ENCLOSURE 12 IS THEN ARRANGED AROUND THE DEVICE SO AS TO COMPLETE THE CABLE.

Description

COATING INTENDED TO PROVIDE CENTERING

  A CABLE SOUL IN ITS ENVELOPE, CABLE

COMPRISING SUCH A DEVICE, AND

ITS MANUFACTURING METHOD

  The present invention relates to a coating intended to ensure the centering of a cable core in its envelope, a cable

  comprising such a device and its manufacturing method.

  It is already known from the French patent 1,593,816 filed by the Applicant that can be disposed inside a metal casing, including corrugated, a grooved sheath made by extrusion and serves both as a heat shield and locking between sheath and envelope. However, since the locking is obtained by crushing by the envelope of the fins of the grooved sheath, locking centering is not very satisfactory in practice, in particular because it transmits to the core of the cable all the constraints. to which his envelope is subject. This represents a rather awkward inconvenience, particularly in the case of

fiber optic cables.

  The subject of the present invention is thus a coating which ensures the centering of a cable core in its envelope and which at the same time ensures mechanical decoupling between the core of the cable.

cable and its envelope.

  The coating according to the invention is constituted by a sheath provided with at least one elastic fin, so that the mechanical stresses are supported by the casing and the sheath.

  without being retransmitted to the actual soul of the cable.

  The invention also relates to a method of manufacturing such a coating where the edges of at least one edge are brought into coincidence

  ribbon over a predetermined width, around the soul of a cable e.

  o these edges are secured to each other on at least a portion of

  said width so as to achieve at least one elastic fin.

  The invention will be better understood on reading the description

  BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a cladding of the prior art; FIG. FIG. 3 represents a device intended for the manufacture of a coating according to one embodiment of the invention; FIG. 4 a shows in section a detail of an extruded coating according to the invention; FIG. represents a variant of a fin according to the invention. Figure 1 shows a cable described in the aforementioned French Patent 1,593,816. It comprises a core 1 coated with ribbons 2 of plastic and a sheath 3 also made of plastic provided with fins 4 longitudinal or very long pitch, called to delimit voids 6 between the sheath 3 and its metal shell. The metal shell 5 is tightened rather strongly on the

  carrying ends of the fins 4 so as to avoid slipping

  cable inside the envelope. As has been said above, this rigid anchorage does not ensure a satisfactory centering, because it retransmits to the cable core all the constraints to which the envelope is subjected when unrolling and winding the cable

  or when the cable is in operation.

  FIG. 2 represents a cable according to the invention whose core 7 is surrounded by a coating 8 provided with elastic fins 10 and

  of an envelope 12 possibly corrugated. Spaces

  between the coating 8 and the envelope 12 and the fins 10 have a height p at least equal to the size of the spaces 11 in a

  radial direction, referred to below as depth, which corresponds to

  to the existing game between the soul of the cable and the envelope.

  According to the invention, the centering of the core with respect to the enve-

  loppe is not a centering imposed by a mechanical lock, but a self-centering which is achieved through the elastic recovery of the fins 10 when they are removed from a state of equilibrium. When winding or unrolling the cable, the self-centering of the core of the latter makes it possible to avoid stresses due to the winding or unwinding lengths that would be different for a web and a web. off-center envelope. On the other hand, since the connection between the core and its envelope is achieved simply by the friction forces between the fins and the inner face of the envelope, the mechanical and / or thermal stresses to which the envelope is susceptible to be submitted on the site of exploitation will result in a relative translation of the envelope and the soul without however this one is subjected to constraints. Indeed, the only forces present in practice are those corresponding to the friction of 1S the soul with respect to the envelope or ovalization of the envelope,

  and the resulting constraints are almost entirely absorbed

dropped by the wing or fins.

  By way of example, for a telecommunication cable whose envelope has an outside diameter of 15 mm, a 0.2 mm thick polypropylene coating and 0.4 mm fins were used. thickness and 1 mm in height, this height being at least equal to the depth of the spaces 11. For a fiber optic cable of 4 mm diameter surrounded by an envelope

  the respective thicknesses of a polyethylene coating.

  high-density film and fins are, for example, 0.1 mm

  and 0.2 mm and secondly the height of the fins is 0.4 mm.

  To determine the fins, we will take into account a certain

number of parameters.

  The clearance between the core of the cable and its envelope is generally determined by the maximum ovality at which the envelope will be liable to be subjected during the use of the cable or by the average clearance required between the core of the cable. cable and its envelope, which

  allows to determine the ninimale height of the fins.

  The specifications of the cable considered per se; determining

  the maximum eccentricity tolerated for the cable core in relation to-

  its envelope. As has been said above, any eccentricity results, during the winding and unwinding operations, by a different length due to the fact that the winding radii are not quite identical, which generates constraints at the cable core. The setting of a maximum value of eccentricity makes it possible to limit correlatively the stresses on the cable core. This is important in the case of fiber optic cables,

  optical fibers can only withstand

  Vees. Otherwise, their performance deteriorates.

  rent. The definition of the maximum permissible eccentricity then makes it possible to choose the nature of the fin material according to its modulus of elasticity E as well as the thickness of the fins so that the weight of the core only produces at rest lower eccentricity

at the maximum eccentricity tolerated.

  In fact, the known laws of mechanics make it possible to determine the geometry to be given to the fins as a function of the linear density of the cable and the average clearance between the core of the cable and its envelope. The compression force that the fin will undergo must be at all points below the critical load of Euler Pc so as to avoid buckling. In practice, it will be limited to a load at rest less than 0.7 times the critical load of Euler. The method of

  Dutheil can calculate the resulting deformation. Deformity

  maximum when the cable is at rest in the horizontal position shall correspond to an eccentricity smaller than the eccentricity

maximum tolerated.

  Finally, it is also preferable that the frictional forces between the lining of the lining and the lining of the cable are sufficient to prevent relative sliding of the core and the envelope when the cable is vertical, and / or presence of

  vibration when the cable is laid.

  According to an advantageous embodiment, the height of the fin or fins will be chosen greater than the clearance existing between the core of the cable and its envelope so that the or fins 10 "

  (Figure 4b) exhibit initial deformation, with or without

  during the laying of the envelope, creating in the first case a prestressing force increasing the friction (the folding of the fins has been exaggerated in Figure 4b). The deformation and the bending moment of the vanes are then also given by known relationships and in this case also care will be taken to remain well below the load.

Euler's criticism.

  In any case, it may be advantageous to use

  fins of section other than rectangular to obtain a structure

  of equal strength, for example by extrusion. It is thus possible to use fins with a truncated parabolic profile or with a profile

  trapézoTdal. The calculation is then done according to the same laws.

  FIG. 3 illustrates a method of manufacturing a coating according to the invention, in which strips 18 arranged on coils 14, here four in number, distributed around the core 7 to be coated,

  are brought into coincidence on their edges, over a corresponding width.

  laying at the desired height for the fins, their edges then being welded at this level. To do this, the core is driven by an axial translational movement along the arrow F and the ribbons 18 see their edges in contact with 21 as and when they unfold, at the grooves 20 formed on the face internal of a guide cylinder 19 whose axis is the axis of displacement of the core 7. At the outlet of the guide cylinder 19, are arranged heads or pairs of solder heads to perform the soldering portions ribbon put in contact by the grooves 20. It goes without saying that one can use only a ribbon laid for example in a helix and realize

it is a single wing.

  Alternatively, the cylinder 19 is replaced by pairs of axis rollers parallel to the axis of movement of the core 7 of the cable, and which are spaced so as to clamp two thicknesses of ribbons 18. For example, two pairs of rolls per groove 10 will be used and the weld of the ribbon portions will be made between

the two pairs of rollers.

  A coating 8 made from ribbons welded at their edges will have the shape shown in FIG. 2, i.e., the ribbon edges 18 are secured to a thinner portion corresponding to about two thicknesses of the ribbon. 'to a projecting portion forming a thicker portion 9 which is on a

  diameter slightly greater than the average diameter of the coating 8.

  A coating 8 provided with elastic fins 10 may be made by extrusion in a plodder through a head whose profile corresponds to that of the coating 8. Thus, in Figure 4a} is shown in partial section a coating 8 made by extrusion and having fins 10 'profiled from a wide portion 22, which connect them to the cylindrical contour of the coating, to a narrow portion 23 at their ends, for example according to

  1S a truncated or trapezoidal parabolic profile.

  The fins 10 may be longitudinal. They may also be helicoidal or alternating: in the case of a production from strips, all of the coils 14 and the guide cylinder 19,

  or the pairs of rollers, will be animated by a correspon-

  around the axis of displacement of the core 7; or the core 7 will be rotated about its axis of displacement, for example by rotating a coil which receives it and / or a drum which delivers it, about an axis perpendicular to its longitudinal axis. In the case

  extrusion manufacturing, the equipment of the

  trusion or, as mentioned above, the core of the cable.

  The centering of the cable in its envelope can be carried out using an envelope provided with a single fin, preferably helical or alternating pitch. A propeller or an alternating step will have a fairly short pitch, for example of the order of magnitude of the diameter of the coating, so that the eccentricity of the core of the cable, which will at worst be compensated a half-step further by the elastic recovery

  of the fin, be corrected effectively.

  As it appears from the description and examples above,

  the space or clearance existing between the cylindrical portion of the coating 8 and the envelope 12 is greater than the space or clearance which is tolerated between the core of a cable and its outer casing in cable technology in general, and in particular in the case of a cable as described in French Patent 1,593,816. This more important game is used for the self-centering that allows the coating according to the invention. According to an alternative embodiment of the invention, the. depth of the or fins is periodically variable between a maximum value and a minimum value, this variation being out of phase in the case of several fins. Thus, in the case of a manufacture using ribbons placed lengthwise (see Figure 3), the drums 14 are

  mounted on an excelle whose eccentricity will correspond to the

  amplitude of variation of the depth of the fins and whose rotational speed will define the pitch of the variation, in relation to the running speed of the core of the cable. In the case of an embodiment by extrusion, an extruder will be used provided with a variable extrusion profile at the fins, the variation being controlled by

example by an eccentric.

  The variation in depth of the fins will allow to have an extra length of the core of the cable inside the casing, the cable core coated with its finned sheath positioning itself in a helix due to the periodic variation of the depth fins, and by

  around an average position corresponding to a cen-

  tration. During unwinding of the cable for its installation, traction on the envelope will produce a slight elongation thereof (for example of the order of 0.5%), so that after peeling, the lengths of the cable and soul will find themselves equal. The core of the cable will no longer necessarily be centered, which is of little importance for a laid cable. Indeed, only mechanical (ovalization of the envelope) and / or thermal stresses will be experienced by the cable, and for

  these precise centering of the soul is not important.

  The invention is not limited to the embodiments described above. Thus, it is not necessary that the fins are made in the same material as the cylindrical portion of the coating 8. On the other hand, the fins, whether or not made of the same material as the coating 8 in its cylindrical part, can be reinforced by one or more elastic bands.

Claims (9)

  1. Coating intended to ensure the centering of a cable core in its envelope and comprising at least one fin,   characterized in that said fin (10) is resilient.   2. The coating of claim 1, characterized in that said fin (10) has a thick portion (9,22) which connects to the cylindrical contour of the coating (8) and becomes more thin at the end.   3. The coating according to one of claims 1 or 2, characterized   in that it comprises at least one ribbon (18) whose edges are   secured to each other over part of their width.   4. Coating according to one of the preceding claims,   characterized in that at least one fin is made of polypropylene or   high density polyethylene or polyester.   5. Cable characterized in that it comprises a coating according to   one of the preceding claims, and an envelope (12) this one.   6. Cable according to claim 5, characterized in that the height of at least one fin (10) is greater than the existing set   between the soul and the cable casing.   7. Device according to one of the preceding claims, characterized   characterized in that at least one fin (10) is of periodic height- variable.   8. A method of manufacturing a cable comprising a centering device of its core, cara, :: - ized in that it consists in forming a coating by colliding the edges of at least one ribbon over a given width self ur of the cable core, to join together said edges over a portion of said width so as to achieve au-., n_ - - - wing,! anttique (10.), el c have   an enveloope (12) around: garment S).   9. Method according to claim 8, characterized in that said given width is periodically variable, so as to   vary the height of the fin (10).