FR2765249A1 - METHOD FOR LAYING A TUBE SHAFT ON A TENSIONED MEMBRAGE AND DEVICE FOR SPACING A TUBE SHAPE - Google Patents

Abstract

The present invention relates to a method for placing a tube-shaped sheath (7), made of a thermoplastic synthetic material, on a tensioned frame (4). The invention exploits the fact that a thermoplastic synthetic material whose section is subjected to a strong bending, certainly undergoes a creep effect, but which does not cause plastic deformation of the synthetic material. In addition, cutting a slit in a closed hollow profile results in a reduction in the shape of the section due to the presence of internal stresses. The method of the invention comprises the following steps: cutting a slit in the sheath (7) in the form of a tube in the longitudinal direction, spacing of the sheath section along the longitudinal edges (8) of the slot, fitting of the sheath (7) spaced apart on the stretched member (4). Device for implementing the method.

Description

A The present invention relates to a method for laying a shaped sheath

  of tube, made of a thermoplastic synthetic material, on a stretched frame, as well as a device for spreading a sheath in the form of a tube of thermoplastic synthetic material, split in the longitudinal direction, and another device for spreading and laying the sheath in tube shape, in material

thermoplastic synthetic.

  Tensile members of this type are used, in general, in the field of construction and public works as guy lines for structural elements, but in particular as guy lines for cable stayed bridges. Said shrouds are formed by a large number of individual steel support elements, such as rods, cables or strands, which are assembled in

  bundle and are surrounded by a tube-like sheath.

  Tensile members of this type are not only subjected to heavy stresses, but they are also exposed to mechanical and chemical influences, so that the sheath exerts above all a protective function. In addition, wind resistance is reduced

through the sheath.

  The installation of a tube is particularly problematic when the members have already been assembled and tensioned. In this case, the ends of the tensioned member are no longer free, so that it is no longer possible to slide the tubes on the tensioned member. This case occurs regularly during

  the renovation of stretched members.

  In this context, it is already known to place a tube-shaped sheath formed on the stretched member, formed by longitudinal sheet metal strips. For this purpose, the sheet metal strips are placed around the tensioned member and assembled by crimping to each other along the longitudinal edges of said strips (DE 34 37 350 C2). Another solution has been explained in DE 36 26 886 Ai: a strip of sheet metal is wound in a helical line around the stretched member, the juxtaposed turns of the strip being assembled by crimping along their lateral edges with the lateral edges of the contiguous turns. These solutions are relatively expensive because, on the one hand, the material used for the sheathing is expensive in itself and, on the other hand, it is necessary to use specific machines designed in particular for laying or shrinking, and in particular

for crimping.

  Not only for reasons of profitability, but also because of the weight, the anticorrosive protective sheaths intended for tensile members of this type, can also be plastic tubes, in which, however, the different tube elements must be generally strung one after the other in the longitudinal direction. This means that it is not possible to use sheaths of this type every time the tensile member concerned is mounted in a non-removable manner, that is to say that no end of it remains free. In this case, it is already known to place shell-shaped elements around the tensioned member, which are provided on their longitudinal edges with assembly parts adapted to one another (EP 0 156 441 B1). Said assembly parts are designed on one edge of the shell-shaped elements in the form of a spring, and on the other edge in the form of a groove; said assembly parts have sawtooth profiles and can be brought against each other by a pressure acting tangentially with respect to the section, to form an assembly by embedding. Since the reliability of this assembly by embedding depends on the resistance of the material used for the shell-shaped elements, it has already been proposed to provide an assembly by positive engagement with dovetail projections (DE 43 19 888 Ai ): this assembly is obtained by the engagement of the elements under the effect of axial forces. Also in these assemblies, the expenses necessary for a sealed assembly are relatively high. Furthermore, German patent application 196 06 574.7 describes the installation of a plastic tube on a stretched frame, the wall of the tube being substantially opened by a cut along a helical line made over the entire length of the tube. The helical strip thus obtained can then be placed from the side on the tensioned member, using a device intended to advance said helical strip on the tensioned member. Then the tube is closed again

  directly by welding the edges of the slot made.

  In this context, the object of the present invention is to place a protective sheath on a stretched member, in the simplest and most cost-effective way possible. This object is solved according to the invention by a process consisting of various steps consisting respectively in splitting the tube-shaped sheath in the direction of its longitudinal axis, in spreading the section of the tube-shaped sheath along the edges of the longitudinal slot made using spacer elements, to place the sheath in the form of a spaced apart tube on the stretched member, and to end the spacing process; as well as by a device which is designed in the form of a frame open on one side, intended to receive the tube-shaped sheath, the free ends of which form branches, a traction device being mounted on the end of each branch, so that their tensile forces can be exerted in the plane of the frame, from the center of the frame towards each branch of said frame; and by another device which comprises at least one spacer element provided with at least two rollers, which spacer element is arranged in the longitudinal direction of the tensioned member so as not to slide inside the section of the sheath and with roller housings oriented perpendicularly

  to the longitudinal axis of the stretched member.

  The present invention is based on the surprising observation that a thermoplastic synthetic material whose section is subjected to strong bending, certainly undergoes a creep effect, but which does not cause plastic deformation of the synthetic material. On the contrary, in the state not subjected to a load, the part of deformation due to creep is again canceled. In addition, it has been found that in thermoplastic plastics with closed section profiles, internal stresses occur on the section due to the cooling process during manufacture. If the closed section is then opened, the internal stresses disappear, while the shape of the section changes. In a tube-shaped profile, this results in a reduction in cross-section, the ends

  free from the overlapping split circular section.

  Both effects can also occur so

cumulative.

  The present invention exploits this behavior of a tube made of thermoplastic synthetic material, which gives rise to various advantages. As it is now known that a tube-shaped sheath, split in the longitudinal direction, returns again to its initial position after a large spacing, it is possible to design the tube-shaped sheath in one piece. This greatly simplifies the handling during assembly of the sheath, compared to solutions in which it is necessary to assemble two half-shells to form a single part. In the process according to the invention, it is certainly necessary to firstly separate the split tube, but it is then possible to mount it without

difficulty on the stretched member.

  If the spacing is eliminated after the installation of the sheath on the stretched member, the method according to the invention has the advantage that the tube-shaped sheath closes automatically. To do this, it is not necessary to apply a separate working process, as is the case for example with two half-shells, which must be joined together along their edges . On the contrary, the tube-shaped sheath returns in a more closed form than the shape of the initial tube, that is to say a form in which the

  opposite longitudinal edges even overlap.

  The restoring forces which prevail inside the material of the sheath are, moreover, so great that, for static reasons, it is no longer necessary to envisage an assembly by adhesion of the edges of the slit produced. Therefore, the method according to the invention has a significant economic advantage compared to conventional methods, in which, despite the assembly by adhesion of the half-shells, there still occurs a failure of the assembly element, which requires the application of additional safety measures (such as the mounting of steel strips), otherwise, we could lead

  the fall of the half-shells from great heights.

  It is only necessary to assemble the edges of the slot where the tube-shaped sheath must be sealed. This is above all the case when the tensioned member is exposed to chemical influences, such as corrosion. A tight assembly is generally carried out by thermal welding along

  join points to assemble.

  If it is not desired to weld the edges, it is then advantageous to execute the longitudinal slit not in the radial direction through the sheath, but in a direction which deviates as far as possible from said direction. As a result, oblique surfaces are obtained in the cutting area which, in the overlapping area, give

  practically a continuous shape at the wall of the sheath.

  The wind forces then meet minimal grip surfaces, which prevents the formation of vortices

  and therefore oscillations of the stay cable.

  In order to obtain, during the welding of the edges, a sheath of constant diameter, it is provided in a particular embodiment of the present invention to mount, at the same time as the return of the sheath to its initial shape. , spacers between the longitudinal edges, which ensure a constant width of the overlap. According to the present invention, it is proposed to place the sheath in the form of a tube on the member stretched from below, on one end of the tensioned member, and then to slide upwards the part of the sheath already mounted, by moving towards the other end of the stretched member. In this way, it is also possible to lay the sheath without difficulty on areas

  hardly accessible from the stretched member.

  In principle, the method according to the invention can be carried out in two different ways. On the one hand, it is possible to carry out a continuous laying of the tube-shaped sheath on the stretched member. This variant is particularly advantageous with the roller spreader device, described below, since in this way it is possible to place the tube-shaped sheath on the stretched member, very quickly and with

  a minimum of large manual operations.

  On the other hand, it is also possible to place the sheath on the tensioned member, section after section in separate stages. In this variant, a complete section of the future sheath is split and kept open using spacer elements. For this purpose, the length of said section can be between 20 and 30 m, for example, and this section is placed on the tensioned member using

of a crane.

  It is up to the user to choose the variant which suits him for the implementation of the method. In his choice between the different variants, he is guided by the external conditions and he can thus react very flexibly to influences from outside. As regards the implementation of the method, in particular the spacing of the tube-shaped sheath, the present invention provides two devices to those skilled in the art. One of the devices is formed by a large number of frames open on one side, against which is mounted a traction device, by which it is possible to open the tube-shaped sheath along the longitudinal slot. These frames have a simple structure, which gives very robust and cost-effective frames. Their size and weight still allow manual movement of the spacer elements, so that this device is particularly suitable for implementing the process by sections to place the sheath on the

stretched frame.

  The other device is formed by spacer elements provided with rollers and its structure is more complex. Said device is fixedly mounted on the end of the tensioned member and is particularly suitable for implementing the continuous process. To this end, the device simultaneously performs the steps "spacing and fitting of the sheath in the form of

tube "of the process.

  The arrangement of rollers, which can move parallel to the longitudinal axis of the tensioned member and, at the same time, rotate around the longitudinal axis of the tensioned member, makes it possible to reduce the frictional forces when sliding the sheath , which during

  this process tends to twist.

  According to another embodiment of the present invention, it is possible to mount upstream of the device an installation used to split the sheath, and to mount downstream of the device a

  installation intended to weld the longitudinal edges.

  As a result, it is possible to largely automate the duct installation process and to install very quickly

the sheath on the stretched member.

  The present invention is explained in detail below.

  after in support of an embodiment given by way of example, with reference to the drawing in which: FIG. 1 is a view of a cable-stayed bridge, the stays of which are protected by a sheath in accordance with the invention; 2 shows a tube-shaped sheath, split in the longitudinal direction; Figure 3 shows a section of a tube-shaped sheath, in the separated position; Figure 4 is a view of the cable-stayed bridge shown in Figure 1, during a later stage of the process; Figure 5 is another view of the cable-stayed bridge shown in Figure 1, during a next step of the process; Figure 6 is a cross section of a tube-shaped sheath according to the invention, with a detailed representation of the overlapping area of the edges of the slot; Figure 7 is a longitudinal section of a tube-shaped sheath in the region of the junction of two sections; Figure 8 is a cross section of a spacer device, before the start of the spacing process; Figure 9 is another cross section of the spacer device shown in Figure 8 during the spacing process; Figure 10 is a view of another device for spreading and placing a tube-shaped sheath on a taut member; Figure 11 is a view of a spacer element of the device shown in Figure 10; Figure 12 is a cross section of the spacer element shown in Figure 11, along the line

XII - XII;

  Figure 13 is a cross section of another spacer; Figure 14 is a cross section of yet another spacer; Figure 15 is a cross section of a device

of tension intended to spread.

  Figures 1 to 9 and 15 relate to the installation of a sheath in sections on a stretched member, while the

  Figures 10 to 14 describe a continuous process.

  Figure 1 shows a cable-stayed bridge, which includes a pylon 2 and an apron 3. The apron 3 is suspended by means of tensioned members, in the form of stay cables 4, from the part of the pylon 2 situated above the apron 3. The shrouds 4 are arranged on either side of the pylon 2 parallel to one another. Said shrouds are anchored in the deck 3 by their lower ends and

  in pylon 2 by their upper ends.

  As a rule, hard polyethylene tubes are used to sheath the shrouds 4. Before the sheathing, the hard polyethylene tubes, which are delivered in lengths of 12 m, are assembled by welding using a welding device at the end by reflectors to form a 24 m long tube element. Therefore, in this example, the cladding by

  sections are executed on sections 24 m long.

  Then, the tube elements are split in the direction of their longitudinal axis using a circular saw, which makes it possible to obtain two longitudinal edges 8 facing each other. As already explained, the restoring forces exerted inside the tube material cause an overlap on a given dimension of the

  longitudinal edges 8 of the slot made.

  Since, before being placed on the shroud 4, the tube-shaped sheath 7 has to be opened again using a spacer device, it is advisable to prevent the open longitudinal edges from closing. again behind the slot area, mount spacers 9, which prevent overlapping of the longitudinal edges 8 at this stage. In the simplest embodiment, the spacers 9 are formed by screws, which are locked between the longitudinal edges 8. But it is also possible to use specific machined parts. This situation is

shown in figure 2.

  The sheath sections thus prepared are stored in a storage place near the shrouds, before proceeding to the separation along the open longitudinal edges 8 over the entire length of a section 7a of the sheath 7, for later use. . The spacing dimension must be at least equal to the diameter of the tensioned member 4. Details on the spacing process are described in

the explanation of Figures 8 and 9.

  The section 7a of the tube-shaped sheath 7 is held in the spread position over its entire length, then suspended from a crane 10 (FIG. 3) and thus placed on the stretched member 4 to be sheathed. Along the stretched member 4, along the length of a section is mounted a scaffolding 11 which the workers use as a working platform. Once the crane 10 has placed on the stretched member 4 the section 7a of the sheath 7 at the lower end of the stretched member 4, the elements used to spread the tube-shaped sheath are again removed; therefore, the section of the sheath closes again under the effect of the return forces already described and, thus, the open longitudinal edges 8 overlap on a determined dimension. Due to the overlapping of the longitudinal edges 8, it can then happen that the diameter of the sheath becomes smaller than the outside diameter of the stretched member 4, so that the sheath 7 strongly clamps the stretched member 4 and slides with difficulty on the stretched member 4 in the longitudinal direction. For this reason, it is possible, in this case, to place, between the longitudinal edges 8, spacers by which the dimension of the overlap is limited to a determined dimension, so that the diameter of the stretched member is always less than the inner diameter of the tube-shaped sheath 7. The spacers can be designed for example in the form of an S. In cases where it is necessary to design a sealed sheath 7, it is advisable to weld the longitudinal edges 8 of a section 7a of the sheath 7 in this position, even before to raise the section 7a of the sheath 7 along the shroud 4. Otherwise, the working platform for carrying out the welding would be located at a great height. For the welding process, it is first of all necessary to graze the surfaces to be welded and then to carry out the welding of said surfaces using a machine for welding the aggregates starting from the upper end of the section 7a of the sheath 7 to the lower end. Figure 6 shows a cross section of a shroud 4 provided with a sheath 7, hermetically welded in the longitudinal direction. In the center of the cross section, are

  arranged a large number of tension elements 12. These

  these are surrounded by the tube-shaped sheath 7.

  The empty space 13 between the tensioning elements 12 and the sheath 7 can be filled, for example, with a mass

  intended to provide anticorrosive protection.

  At the top of the cross section, the longitudinal edges 8 of the tube-shaped sheath 7 overlap. In order to assemble the longitudinal edges 8 of the section formed by the slit made, and thus to obtain again a closed section, a weld bead 14 is executed in the longitudinal direction, by which the cutting surfaces of one of the edges longitudinal are joined by adhesion with the outer surface of the other longitudinal edge. This is what the

  detailed representation of figure 6.

  The section 7a of the sheath 7, maintained on a constant diameter by spacers or by welding the longitudinal edges, is then pulled up along the length of a section, along the shroud 4. This is done in the manner the simplest with traction devices, mounted at the upper anchoring points of the shrouds 4 and the towing cable of which is hooked against

  the upper end of the section 7a of the sheath 7.

  Now, the process cycle is repeated, while the crane 10 removes from the stock another section 7b of the tube-shaped sheath 7, which has been split and spread apart as described above, and places it on the lower part of the

guy 4.

  This situation is illustrated by FIG. 4. The section 7a of the tube-shaped sheath 7 laid first on the shroud 4 has been pulled upwards on the shroud,

  over a distance equal to the length of a section 7a.

  Thus, the shroud 4 has been released in the part which extends the anchoring zone and can receive a new section 7b of the sheath 7 in the form of a tube. The new section 7b is laid by the mobile crane 10 on the stay

  4, then assembled end to end with the first section 7a.

  The sections 7a, 7b are assembled at the joining point

by annular welding.

  FIG. 7 shows the production of an annular weld at the joining point 15 between two sections 7a, 7b of the sheath 7. Said figure shows two ends facing two sections 7a, 7b of the sheath 7. The cutting surfaces ends of the sections 7a, 7b are respectively bevelled to form a cone widening towards the outside. The ends of the sections are joined end to end, so that a V-shaped cavity is formed on the periphery due to the conicity of the cutting surfaces. The weld bead

16 is placed in this cavity.

  FIG. 5 shows the state obtained: the tube-shaped sheath 7 is almost placed entirely on the stretched member 4. The joining points between the different sections 7a, 7b of the tube-shaped sheath 7 are assembled by welding, if necessary the edges

longitudinal 8 too.

  The process continues as described

  until the shroud 4 is fully covered.

  The sheathing work is then carried out on the

next guy.

  Figure 8 shows a spacer device 17 for a sheath 7 in the form of a tube, and split. The device is formed by a U-shaped frame 18. The ends of the two branches 19, 19 'are provided with a bore 20,' produced in the plane of the frame 18. In each bore, 20 'passes a pin 21, 21 ', which is formed by a threaded rod 22, 22', the end inside the frame carries a hook 23, 23 'and the end outside the frame carries a wing nut 24, 24 'To spread the tube-shaped sheath 7, it is first necessary to pull the pins 21, 21' outwards, so as to release the open side of the frame 18. Then, the frame 18 is mounted above the split sheath 7, until the sheath 7 is placed between the two branches 19, 19 '. In addition, the longitudinal slot made in the tube-shaped sheath 7 is oriented towards the open side of the frame 18. Finally, the two pins 21, 21 'are pushed through the bores 20, 20' until their end provided with the hook 23, 23 ′ can penetrate the longitudinal slot of the sheath 7

  tube-shaped. This state is illustrated in Figure 8.

  By tightening the wing nuts 24, 24 'of the two pins 21, 21', the hooks 23, 23 'move in the direction of the branches 19, 19' of the frame 18 and then spread the tube-shaped section up to that the opening is large enough so that the tube-shaped sheath 7 can be placed around the shroud 4.

  This situation is illustrated in Figure 9.

  In the process executed section by section, it is necessary to mount along the sheath 7 in the form of a tube a large number of said spacer elements 17, arranged at a given distance from each other. In this way, it is possible to keep open over its entire length a section 7a, 7b of a sheath 7 in the form of a tube (FIG.

3) and place it on the shroud 4.

  FIG. 15 shows another variant of the spacer device 17. In this figure, we can see a sheath 7 already split, the peripheral wall of which is enveloped by a tensioning device 50. The tensioning device 50 is formed by a pawl 51, the hooks 52 and 53 and the straps 54 and 55, which connect the pawl 51 with the hooks 52 and 53. The hooks 52 and 53 are hooked around the open longitudinal edges 8 of the slot. The pawl 51 must be actuated to tension the straps 54 and 55, which at the same time spreads the longitudinal edges 8 using the hooks 52 and 53. If the opening of the sheath corresponds at least to the diameter

  of the shroud 4, the sheath 7 can be placed on the shroud 4.

  Finally, the tensioning device 50 is relaxed, which

  causes the sheath 7 to close.

  As with the spacer device 17, it is also possible to mount several tensioning devices 50 fixedly along a cross-member. The cross-member, which then corresponds practically to the length of a section of the tube-shaped sheath 7, serves at the same time to

  hang said section of sheath on a crane.

  The spacer element 17, shown in FIGS. 8 and 9, as well as the tensioning device 50, shown in FIG. 15, can also be used for a continuous process of sheathing a shroud 4. The sheath 7 is then kept open over a determined length in the area where it is placed on the shroud 4. When the finished sheath 7 is slid or pulled up, along the longitudinal axis of the shroud 4, the spacer elements 17 or the tension 50 are driven with the sheath 7, given that they are fixedly assembled therewith. However, to limit the spacing in the area where it is necessary for installation on the shroud 4, the spacer element 17 or the tensioning device 50 is removed from the upper end of the spaced area and mounted on the end lower. In this way, the separated area moves continuously relative to the tube-shaped sheath 7,

  against the direction of the duct mounted upstream. Figures 10, 11, 12, 13 and 14 show a variant 25 of the device

  retractor, used for the continuous process, manual work being reduced to a minimum. Figure 10 shows the foot of a guy 4. The deck is identified at 3. A guy 4 is connected at its lower end with the deck 3 via an anchoring zone. The upper end of the shroud 4 is not shown and leads to the upper zone

anchor in the pylon.

  The tube-shaped sheath 7 is already mounted on the shroud 4 in the zone marked in a. In zone b, it is kept open by the spacer device 25 according to the invention, and in zone c it is prepared to be placed on the shroud 4. In zone c is mounted an end welding machine by reflectors 6, used to butt weld the various hard polyethylene tubes, delivered in lengths of 12 m, to form a continuous tube. It is planned to mount downstream, in zone c, a device 27 intended to split the

  sheath 7 in the form of a tube, along the longitudinal axis.

  When the tube-shaped sheath 7 is split, the sheath 7 is conveyed to the spacer device 25. The spacer device 25 is formed by a large number of spacer elements 28, which are arranged at a given distance from each other and in a different position along the longitudinal axis of the shroud 4, as well as the spacer elements 32 and 33, which start the spacing process. The number of spacer elements 28, 32 and 33 then defines the length over which the sheath 7 is separated. A single spacer element 28 is shown by way of example in the view of FIG. 11 and in the cross section of FIG. 12. It is essentially formed by a cuff 29, two diametrically opposite fork housings and two rollers 30, 30 'inserted in the fork housings. The cuff 29 surrounds the shroud 4 leaving sufficient play, so that the cuff 29 can pivot freely around the longitudinal axis of the shroud 4. The fork housings opposite one another are each formed of two tongues 31, 31 ′, parallel to each other and rigidly mounted at a given distance from each other, so that the housings of the rollers are arranged perpendicular to the longitudinal axis of the shroud, which means that the direction of movement of the rollers 30, 30 'is oriented in the longitudinal direction of the

guy 4.

  The spacer element 28 is mounted inside the sheath 7 in the form of a tube, the rolling surface of the rollers 30, 30 'coming into contact with the inner face of the sheath 7. Consequently, the distance between the two rollers 30, 30 'of a spacer device defines the degree of spacing of the shaped sheath 7

of tube.

  Since the split sheath 7 is brought from the side onto the shroud 4, the spacing of the sheath 7 already begins outside the section of the shroud 4. For this purpose, the spacer elements 33 and 32 described in FIGS. 13 and 14 are arranged at the lower end of the spacer device 25. These begin the spacing process, until the degree of opening is reached allowing the fitting of the sheath 7 on the

guy 4.

  Figure 13 shows the spacer element 33 which, as the first element of the spacer device 25, begins the spacing process. It consists of a sleeve 29 'which surrounds the shroud 4. Unlike the spacer element 28, shown in FIG. 11, the sleeve 29' is, in the present case, fixedly assembled with the shroud 4. On the cuff 29 'is arranged an opening key 35 whose flanks meet at a point, which begins the separation process, because, by its flanks, said key pushes in opposite directions the edges

longitudinal 8 of the sheath 7.

  The spacer element 33 is followed, in the direction of the sheath placed upstream, by the spacer element 32, shown in FIG. 14. It includes a cuff 29 "which surrounds the shroud 4. On the side of said cuff is mounted, by means of an arm 36, a pair of rollers 37 in an eccentric position relative to the longitudinal axis of the shroud 4. The pair of rollers 37 is designed substantially identically to the pair of rollers of the Figure 11. Under the effect of these rollers, which push against the inner face of the sheath 7, the latter is separated and, under the effect of several spacer elements 32, located at a given distance one behind the other, said sheath is

continuously fed on the stay 4.

  In order to guarantee a permanent transition from the closed section to the open section of the sheath 7, the distance between the rollers 30, 30 'of a spacer element 28 and 33 is the smallest at the ends of the spacer device 25 and the greatest in the middle of said spacer device. So that the spacer elements 28, 32 and 33 always remain in the same place with respect to the stay 4, each element 28, 32 and 33 is guyed downwards, towards the zone 26 of the anchoring, the elements 32 and 33 being mounted in an eccentric position relative to the axis of the wire rope. As a variant, it is also possible to assemble in a fixed manner the cuff 29 or 29 "of the spacer elements 28 and 33 with the shroud 4. In order to guarantee, in this case, the free rotational movement of the housings in forks with the rollers 30, 30 'around the longitudinal axis of the shroud 4, the cuff 29 or 29 "must be divided into two parts, that is to say an inner ring fixedly placed on the shroud 4 and a ring outer bearing the fork housing, the outer ring can rotate around the inner ring

  using ball or needle bearings.

  To place the sheath 7 in the form of a tube on the shroud 4, the sheath 7 is pulled in the direction of the longitudinal axis of the shroud 4 towards the pylon 2. For this purpose, two cables of a traction unit are fixed on the corresponding ends of the sheath 7. When the sheath 7 is pulled upwards, it is brought from the side towards the lower end of the spacer device 25. The spacer element 33 opens at this time the longitudinal edges 8 of the sheath 7. In the remainder of the process, the spacer elements 32, 28 push against the inner face of the sheath 7 and thereby cause the sheath 7 to spread apart along the edges.

  longitudinal 8 of the slot made in the sheath 7.

  After the passage of the spacer device 25, the section of the sheath 7 closes again under the action of the restoring forces, the longitudinal edges 8 of the slot overlapping. In this way, a local spacing is produced relative to the shroud 4 and continuously movable relative to the sheath 7 in the form of a tube. The measures applied in the sectional process, described above, to maintain a constant overlap or to perform welding, can also be applied

to the continuous process.

  Since the method described last allows for advanced automation, it is rational to mount downstream of the spacer device 25 an automatic welding machine, which reassembles the longitudinal edges 8 of the slot of the sheath 7 to form a

closed annular section.

Claims (15)

  1. Method for laying a tube-shaped sheath, made of a thermoplastic synthetic material, on a stretched member, characterized by the following steps: a) cutting a slot in the sheath (7) in the form of a tube in the direction of its longitudinal axis; b) spacing of the section of the tube-shaped sheath (7) along the longitudinal edges (8) of the slot, using spacer elements (18, 28, 23, 33, 50);   c) laying the sheath (7) in the form of a tube, spaced apart, on the tensioned member (4); d) end of the separation process.   2. Method according to claim 1, characterized in that the tube-shaped sheath (7) is spaced continuously   and placed continuously on the stretched member (4).   3. Method according to claim 1, characterized in that the tube-shaped sheath (7) is spaced apart by sections, and placed section after section on the frame stretched (4).   4. Method according to any one of claims 1 to   3, characterized in that the edges of the slot (8)   made in the sheath (7) are assembled by welding.   5. Method according to any one of claims 1 to   3, characterized in that the slot in the tube-shaped sheath (7) is made in the direction of its axis   longitudinal in a bias cut.   6. Device intended to separate a tube-shaped sheath, split in the longitudinal direction, according to claim 1, characterized by a frame (18) open on one side, intended to receive the sheath (7) in the form of a tube, of which the free ends form branches (19, 19 '), a traction device (21, 21') being mounted on the end of each branch, so that their traction forces can be exerted in the plane of the frame , from the center of the frame towards   each branch (19, 19 ') of said frame.   7. Device according to claim 6, characterized in that the traction device is formed by a pin (21, 21 ').   8. Device according to claim 6 or 7, characterized in that the spindle (21, 21 ') is provided with a hook (23,   23 ') on its end located inside the frame.   9. Device for spreading and placing the tube-shaped sheath according to claim 1, characterized in that the device comprises at least one spacer element (28, 32), provided with at least two rollers (30, 30 ' ), which is arranged in the longitudinal direction of the tensioned member (4) so as not to slide inside the section of the sheath (7), and whose housings for rollers are oriented perpendicular to the axis   longitudinal of the stretched member (4).   10. Device according to claim 9, characterized in that the spacer elements (28, 32) are arranged so that they can rotate freely around the axis   longitudinal of the stretched member (4).   11. Device according to claim 9 or 10, characterized in that the rollers of a spacer element   (28, 32) are diametrically opposed.   12. Device according to any one of claims   9 to 11, characterized in that the rollers are arranged   on a cuff (29, 29 ") surrounding the tensioned member.   13. Device according to any one of claims   9 to 12, characterized in that several spacer elements (28, 32, 33) are arranged one behind the other in the longitudinal direction of the tensioned member (4).   14. Device according to any one of the claims   9 to 13, characterized in that an installation intended to split the tube-shaped sheath (7) is mounted upstream of said device.   15. Device according to any one of claims   9 to 14, characterized in that an installation intended for welding the cords in the longitudinal direction is mounted downstream of said device.