FI86227C - FOERFARANDE OCH ANORDNING FOER FRAMSTAELLNING AV SEKUNDAERMANTELKONSTRUKTION FOER OPTISK KABEL. - Google Patents

Description

1 86227

Method and apparatus for fabricating a secondary sheath field for an optical cable

The invention relates to a method and an apparatus for manufacturing a secondary sheath structure of an optical cable. According to the method of the invention, the optical fibers are passed to the press end of a plastic press on a torpedo and further out of at least one torpedo head, a loose secondary jacket tube is extruded around the optical fibers at the press head. The apparatus according to the invention thus comprises a fixed matrix fitted to the press end of the extruder, a torpe-15 through which the fibers are passed, the Torpedo and the matrix together forming an annular gap from which the plastic is extruded, and means for providing the fibers with the desired extra length.

It is generally known to protect a primary coated or bare optical fiber or a fiber bundle of 20 such fibers with a loose secondary sheath. The main purpose of the secondary sheath, which is usually a plastic tube, is to protect the fiber or bundle of fibers from external mechanical stresses and stresses. The function of the loose 25 secondary sheath tube is also to give the fibers ·; ··! undisturbed Movement space for thermal dimensional changes or dimensional changes due to mechanical forces on the housing. In secondary sheathing, the fibers are intended to be given a certain extra length (bias) to allow the fibers. . 30 would not be stretched, even if the diaper stretches a bit.

Typically, the value of such an excess length is less than * · ['1 ° / 00 · · Due to the loose secondary sheath tube and the excess length of the fibers: * · [: the fibers have room to move inside the tube as the tube lengthens and shortens, e.g., 35 heat and stretching cases. However, due to the relatively small size of the tube, the low modulus of elasticity (<2500 N / mm2) and the high coefficients of thermal expansion (~ 10-4 / ° K) of the plastics used, the tube coating alone does not guarantee a very high "elongation / compression window" for the fibers.

To remedy this shortcoming, it is known to manufacture an optical cable in such a way that the secondary sheath tubes are wound either helically or in the reverse direction (so-called SZ-repetition) on a common central element. The central element, which is typically a metal or plastic composite, increases the strength of the structure and reduces thermal movement. In addition, the repetition increases the clearance of the fibers for geometrical reasons already: the spiral or oscillating rotation of the secondary jacket tube around the central element also means bringing it to a certain bending diameter. This, in turn, together with the radial play of the fibers, results in a significant increase in the relative clearance of the fibers with respect to elongation and compression.

Optical cables made as described above are generally reliable even in difficult environmental conditions and effectively protect the fibers from tensile and compressive stresses. However, they lack the high cost of several successive and delicate work steps required by the manufacturing process. Such a cable typically consists of 5 to 8 secondary sheath tubes, each of which generally contains 1 to 25 6 fibers. Manufacturing thus requires 5-8 secondary coatings, followed by a common repetition, the possible failure or discovery of a defect in one of the fibers after the repetition nullifies all previous successful work steps. Such a structure is also not optimal in terms of, for example, watertightness or compressive strength, and therefore requires a large number of other work steps and structural components to improve these properties.

The structure closely resembling the previous structure-35 they is the so-called. V-groove cable in which the secondary sheath tubes are replaced by helical or oscillatingly rotating grooves in the common central element in which the optical fibers are placed. There are fewer work steps than in the previous structure, although they are laborious and require a lot of special equipment. In particular, the placement of fibers in their grooves is a sensitive and disruptive procedure.

A cable structure that differs significantly from the structures described above is disclosed in PCT application WO86 / 06178. This cable consists of a single tube 10 of relatively large diameter, filled with grease and containing a bundle or bundles of fibers. The pipe is reinforced with steel wires and consists of several overlapping layers of plastic and, if necessary, moisture and / or rodent protection. The entire cable structure is manufactured in one work step, and its obvious advantage is the speed and straightforwardness of manufacture as well as the simplicity of the structure. However, such a structure is unable to take advantage of the increase in fiber working capital brought about by the repetition. Admittedly, the fibers are provided with a certain slight excess-20 length, and the steel wire reinforcement must be dimensioned so that that elongation is not exceeded under any circumstances. In the case of compression, as the structure cools to lower temperatures, a large inner diameter tube allows the fibers or fiber bundles to be twisted without being subjected to compression stress. However, the fibers or fiber bundles are free to settle at any bending plane that is unfavorably different from the helical space. In this case, the minimum bending radii of the individual fibers may be lower, resulting in attenuation. . 30 growth or shortening of fiber life. A large diameter hole • also requires the use of a rigid filling grease, which contributes to the phenomenon described above. The function of the steel wires is obviously also to stabilize the structure against crushing.

*: * 35 4 86227

In order to provide a sheath structure for the optical cable that allows the fibers a large amount of movement without the risk of crushing or falling below the minimum bending radii, the secondary sheath should be constructed so that the fiber channel through the tube spirals forward along the tube. Such a structure is known per se from EP-A-22036. The object of the invention disclosed in this EP publication is to provide an optical cable which remains homogeneous throughout its length, including its ends, and which further prevents stresses from being applied to the optical fiber in the cable and in the area of the connectors. To solve this problem, the optical cable has means for positioning the fiber relative to the tube at least at certain points. These positioning means are en-15 essentially cross-beams arranged at regular intervals inside the pipe. However, in one embodiment, these positioning means consist of a guide channel helically rotating in the longitudinal direction of the tube, in which the fiber is placed.

20 However, the EP does not make any reference to how the secondary jacket structure in question is to be manufactured. The production of such a structure has been found to be technically difficult to extrude and to require complex equipment.

It is therefore an object of the present invention to provide a manufacturing method for a secondary sheath structure provided with a helical fiber channel, which enables safe and easy fabrication of the cable and simple equipment.

. . With the method according to the invention, this is achieved by fitting the central axis of the torpedo head at a certain angle with respect to the central axis of the press head by deviating the torpedo and rotating the torpedo about the central axis of the press head, the torpedo head being eccentrically to the central axis of the press head.

5 86227

The apparatus according to the invention, in turn, is characterized by the features described in the characterizing part of claim 3.

The invention will now be described in more detail with reference to an example according to the accompanying drawings, in which Fig. 1a schematically shows a secondary fiber sheath line according to the invention, Fig. Ib shows graphically the relative elongation of the Fig. 1a shows graphically the relative elongation of the secondary jacket relative to the fiber bundle and at the same time the method of generating the fibers over 15 lengths in a situation where the location, dimensions and shape of the helical fiber channel and / or a wheel-20 to facilitate the generation of excess fiber in secondary sheath structures where an excess of fiber must be generated in a pattern as described in Figure 1a, and Figure 2 shows in more detail a part of the secondary sheath line according to Figure 1a for a more detailed description of the method and apparatus according to the invention.

Figure 1a shows an example of a complete secondary jacket line suitable for the manufacture of a secondary jacket structure with a helical fiber channel. The separate fibers 3 leave their own starting coils 10,. . 30 each of which can be individually adjusted to achieve the correct output voltage. In order for the fibers to maintain as regular a helical state as possible during the manufacturing process and subsequently under the conditions of use, and not; ***; in order to form unfavorable, small bending radii, it is advantageous to increase their rigidity by bundling them 6 86227 together. To do this, the fibers first pass through a binder 11, where they are bundled together, e.g. with a detection wire. Bundling can also be performed with a vulcanizable polymer or adhesive, for example a so-called hot melt-5 with glue. For example, the bundle 4 may contain six fibers, which are preferably of different colors, and there may also be more than one bundle 4, each of which has a separately identifiable bond. The bundle 4 further advances through the fat mouthpiece 12 to the press head 13, the torpedo of which is rotated-10 at line speed by a synchronized mechanism 14 in the manner described below in connection with Figure 2. From the press end, the bundle 4 and the filling grease proceed to the melt zone 15 and further to the cooling tank 16.1, surrounded by the coating material, where the coating material crystallizes into a secondary jacket tube The second cooling basin 16.2 controls the temperature and post - crystallization of the tube 1. On the line after the cooling basin 16.2-20 there is a traction device 19, which at the same time acts as a generator of the excess length of the fibers and as the main speed point according to which the other devices in the line are synchronized. The traction device includes a belt traction device 19.1 and a wheel 19.2.

: The traction device 19 is followed by a third cooling basin 16.3, in which the secondary jacket structure is brought to ambient temperature, as well as a tension accumulator 20 and a receiving coil 21.

Fig. 1b graphically illustrates the relative elongation e of the secondary sheath with respect to the fiber bundle 4 by zones in the line according to Fig. 1a and at the same time the excess. . 30 lengths to create and adjust. The relative elongation of the secondary sheath is illustrated by a solid line A1 and the fiber bundle 4 by a dashed line A2, which is straight because the fibers run: * · *: at a constant speed and substantially unstressed from the output coil 10 to the take-up coil 21. In the melt zone 35 15/1 the secondary sheath is drawn

II

7 86227 cross-sectional area achieves the desired dimensions. At the same time, its speed and relative elongation e increase. In zone II, the secondary jacket 1 begins to crystallize under the effect of cooling, its density increases, i.e. it shrinks and at the same time its speed 5 decreases in the direction of travel of the line. In Zone III, the jacket structure is maintained at a higher ambient temperature, giving it a certain thermal elongation, and its coefficient of elasticity is lower than at normal temperature (+ 20 ° C). In zone IV, the secondary jacket is stretched by a precisely controlled speed difference between the hih-10 barn device 19.1 and the wheel 19.2, the corresponding elongation of which is indicated in the figure by the reference symbol e #. When the secondary jacket rotates several turns around the wheel 19.2, and when the fiber bundle 4 can slide relatively freely inside the secondary jacket, the bundle 4 settles on the inner circumference of the secondary jacket and locks in it under the influence of the output. In zone V, the secondary jacket detaches from the wheel 19.2, its elongation is removed and when it is brought to ambient temperature (approx. + 20 ° C) in the cooling pool 16.3, it is further shortened, whereby the relative length difference of the fibers inside it increases. In zone VI, the constant tension winding on the take-up reel 21 no longer substantially changes the excess length eQ of the fibers. Thus, in the situation described, the final excess length eQ is the result of a combination of two factors; elongation ee recovery 25 and cooling-induced shortening eT. The above-mentioned biasing method is known per se and will not be explained in this connection as part of the actual inventive idea. The method is described in more detail in Finnish patent application 30 FI-831 928.

Figure 1e graphically illustrates the case where the location, dimensions and shape of the fiber channel and / or the substantially rigid filling fat prevent the fiber bundle from moving freely up to the wheel 19.2. In this case, the locking-35 of the fiber bundle 4, i.e. the adhesion to the inner surface of the secondary sheath, takes place by means of the filling grease and the shape of the channel in zone II. The exact point of adhesion can be adjusted by the initial tension of the fiber bundle and, if necessary, intensified by a freely rotating wheel 32 placed on the line behind the cooling basin 16.1 as shown in Fig. Id. In zones III and IV, the secondary sheath is further cooled and allowed to shrink to create excess fiber. The secondary casing is pulled by the traction device 19.1, but it passes the wheel 19.2 or rotates around it without pre-stretching ee. 10 By controlling the temperatures of the cooling tanks 16.1, 16.2 and 16.3 and the initial tension of the fibers, the generation of the correct amount of excess length eQ is controlled. In practice, the generation of excess fiber is simpler according to Fig. Ib, and in that sense the fiber channels with a straight center channel are advantageous, because in them the center channel ensures the free movement of the fiber bundle up to the wheel 19.2.

Figure 2 shows in more detail a part of the secondary sheath line according to Figure 1a. More specifically, Fig. 2 shows a cross-section of a pressing head 13 according to the invention. However, the direction of travel of the fiber or fibers in Fig. 2 is opposite to Fig. 1a. The fiber bundle 4 is guided under a constant output tension to the tool end of a conventional plastic press, i.e. the press head 13, which contains a fixed matrix 23, a torpedo holder 24 arranged behind it 25 and an inner mandrel extending inside the torpedo holder. 41, into the interior of which the rear portion of the front piece protrudes while engaging the back piece.

. . The front of the front piece 40 is in turn attached to the torpedo 25. The shapes and dimensions * 'of the matrix 23 and the torpedo 25, as well as their relative positions, determine the dimensions and shape of the resulting secondary: ·: sheath element. Feeds pass through the inner mandrel and torpedo up to the torpedo head 25a .1. 35 a guide tube 42 attached at its rear end to a fixed anchoring point 43.

9 86227

A precise dosing pump synchronized to the line speed feeds the filling grease 28 to the grease nozzle 12, where it covers the fiber bundles, and from there they together feed into the guide tube 42. At the same time, the grease nozzle prevents excessive grease 5 28 from flowing backwards. The molten plastic mass 29 from the plastic press grid, depicted by the arrow, fills the empty slits of the press head and advances toward the annular gap formed by the die 23 and the torpedo 25. As stated above, this gap determines the dimensions and shape of the final secondary jacket element. However, since the plastic mass 29 is still in the molten state for a while in the melt zone 15 as it exits the press head 13, it can be stretched, thereby reducing its diameter. Thus, the dimensions of the secondary jacket tube can be influenced by the control ratio 15 of the mass flow of the press and the line drawing speed. From the melt belt zone 15, the secondary jacket pipe advances to the cooling tank 16.1, where it crystallizes to its final dimensions.

Articulated ball surfaces 44 are formed between the torpedo 25 and the torpedo holder 24 and articulated ball surfaces 45 at the rear of the torpedo holder 24. The radii of the ball surfaces are denoted by R1 and R2 and their centers by P. Since the ball surfaces are parallel and have the same center, the inner mandrel and torpedo within the limits of mechanical constraints. 25 The ball surfaces 44 and 45 act as bearing surfaces. In the case of plastic, the spherical surfaces 44 also act as a sealing surface. The cohesiveness of the ball surfaces is ensured by a disc spring pack 46 tuned to a suitable force, which is fitted to the ball of the rear piece 41 of the inner mandrel and the torpedo holder 24. 30 between surfaces 45. A controlled rotational movement of the torpedo 25 according to the invention is obtained by providing the rear part of the press head with a centrally rotating support part 47 mounted on the press head body 13 by a bearing 48. A support plate 49 movable in the direction of the press head diameter is arranged in the support part 47. 86227 eccentric with respect to the central axis Φ of the head with the adjusting screws 50 and 51. A rear portion 41 of the inner mandrel is mounted through the adjusting plate 49.

When the rear piece 41 is deflected by the adjusting plate 49 5 from the central axis Φ of the press head mukaisesti by a dimension n as shown in Fig. 2, the torpedo head 25a moves to the side by a dimension m determined by the ratio of the lever arms a and b, forming an angle α between the press head and the torpedo -10 the rotating support part 47 is wound by means of its drive device, e.g. a toothed belt 14, it rotates the rear piece about the central axis Φ of the press head so that the rear piece is eccentrically with respect to the central axis of the press head during rotation. At the same time, the torpedo 25 also rotates at a mass-rate within the matrix 23 so that the torpedo head is constantly eccentric with respect to the central axis Φ. The ball surfaces 44 and 45 act as bearing surfaces.

In this way, an eccentric fiber channel continuously and in a controlled helical manner 20 is obtained from the pressing head to the secondary jacket to be pressed, the position of which on the cross-sectional surface of the secondary jacket can be determined by means of adjusting screws 50 and 51. The feed and guide tube 42 is made of flexible steel, so that it follows the small rotational movement of the torpedo 25.

*: Although the invention has been described above with reference to the example according to the accompanying drawings, it is clear that it is not limited thereto, but can be modified in many ways by the inventive idea presented by the appended claims and the norm of a person skilled in the art. . 30 within the framework of knowledge.

Il

Claims (9)

11 86227 A method of manufacturing a secondary sheath structure of an optical cable, the structure comprising a secondary sheath tube 5 and optical fibers in a helical fiber channel therein, the method comprising: - guiding optical fibers (3) to a torpedo end (25) and further out of at least one torpedo head 25a), 10. extruding a loose secondary sheath tube (1) around the optical fibers (3) at the press head (13), allowing mutual axial movement between the fibers and the tube, and - providing the fibers (3) with a desired additional length 15 relative to the sheath tube (1), known - adjusting the central axis of the torpedo head (25a) to a certain angle (α) with respect to the central axis (Φ) of the press head by deflecting the torpedo and rotating the torpedo (25) about the central axis (() of the press head (13), the torpedo head (25a) being located during rotation eccentrically with respect to the central axis of the press head. A method according to claim 1, characterized in that the distance (m) of the central axis of the torpedo head (25a) from the central axis of the press head is adjusted by means of adjusting members (49, 50, 51) arranged at the rear of the press head (13). . An apparatus for manufacturing a secondary sheath structure (1) provided with a helical fiber channel of an optical cable, the apparatus comprising. . - a fixed matrix (23), '· *' - a torpedo (25) fitted to the press head (13) of the extruder, through which the fibers (3) are passed, whereby the torpedo and the matrix together form an annular gap from which the plastic (29) is pressed out, and 12 86227 - means (19, 16.3) for providing the fibers (3) with the desired additional length relative to the jacket tube (1), characterized in that it further comprises turning and recirculation means (14,47,40,41,44, 45,46,49,50,51) 5 for rotating the central axis of the torpedo head (25a) at a certain angle (a) to the central axis (Φ) of the press head and for rotating the torpedo (25) about the central axis (Φ) of the press head (13) so that the torpedo head (25a) is located eccentrically with respect to the central axis of the press head during rotation. Apparatus according to claim 3, characterized in that the turning and recirculation means comprise a support part (47) rotating centrally about the central axis (Φ) of the press head (13), a rear body (41) 15 mounted on the support part, members (49,50,51) to deflect it from the central axis (Φ) of the press head and means (40, 44, 45, 46) for transmitting the movement of the rear body to the torpedo (25). Apparatus according to claim 4, characterized in that the movement means comprise a front body (40) attached to the rear body (41) at its rear, which is attached at its front between the torpedo (25) and the torpedo (25) and the torpedo holder (24) and the torpedo holder spherical surfaces (44,45) formed at the rear, the cohesiveness of which is ensured by a spring (46) arranged between the rear body (41) and the rear spherical surfaces (45) of the torpedo holder (24). Apparatus according to claim 4 or 5, characterized in that the deflection means comprise an adjusting plate (49) arranged in the support part (47), on which the rear body (41) is mounted, which adjusting plate is provided with adjusting means (50, 51) to adjust the deflection amount of the rear body (41) mounted thereon. Apparatus according to Claim 6, characterized in that the adjusting elements consist of adjusting screws (50, 51). 13 S6227