Synthetic fiber cable
Description The invention relates to a synthetic fiber cable for transport, preferably of aromatic polyamide, according to the generic concept of claim 1. The rotating cables constitute in the transport technique, especially in the case of elevators, in the cranes and in mining, a mechanical element subjected to strong stresses. The stresses on cables driven or deflected by pulleys, as used for example in the construction of elevators, are especially multiple. In traditional elevator installations, the chassis of the cabin driven by the elevator shaft and the counterweight, are connected by a cable. To raise and lower the cab and the counterweight, the cable rotates on a drive pulley driven by a drive motor. The driving moment is applied, under friction force, to the portion of the cable that is in contact with the drive pulley at all times along the span. The cable is subjected to a strong transverse tension. When the cable is wound around the drive pulley under load, the braided cables perform relative movements to compensate for differences in tensile stress. The same applies to cables wound on drums, as used in the construction of elevators and cranes. On the other hand, large cable lengths are required in elevator installations and, for energy reasons, the smallest possible dimensions. The cables of synthetic fiber of high resistance, especially of aramidas or aromatic polyamides with chains of molecules oriented in a high degree, fulfill these requirements. Aramid fiber cables have the same cross section as traditional steel cables, a considerably higher load capacity and a fifth, and up to a sixth, of specific weight. However, due to its atomic structure, aramid fiber has a reduced elongation at break and reduced shear strength compared to steel. With EP 0 672 781 an aramid fiber cable with parallel cord placement has been developed. An intermediate casing is provided between the outer and inner cord layer which prevents the contact of the cords of different layers, thus reducing friction wear. The mentioned aramid cable offers satisfactory values in terms of service life, and a high resistance to abrasion and alternating bending. However, in the braided synthetic fiber cable there is the possibility that the cords move in front of the intermediate envelope, which results in an unequal loading of said cords. This modification of the constructive structure can lead to a reduction of the breaking load of the cable and a failure thereof. The object of the invention is to avoid the disadvantages of the known synthetic fiber cable and to improve the internal transmission of forces in a synthetic fiber cable. This object is achieved according to the invention with a transport cable of the characteristics indicated in claim 1. A transport cable is understood as a rotating and driven cable, which, in some cases, is also known as a traction cable or a motor cable. Advantageous developments and improvements of the invention indicated in claim 1 are indicated in the subclaims. The advantages achieved with the invention consist in the fact that the intermediate shell with surfaces adapted to the adjacent profiles of layers of cords offers a greater contact surface with the cords . Due to a stronger bonding of the inner and outer cord layers, greater torsional rigidity is achieved. With the cable loaded, the intermediate shell with a profile according to the invention, avoids twisting of the cable regardless of the type of torque applied. The intermediate shell according to the invention forms a bridge over the interstices between cords of the layers of cords that are in contact with it, increasing the support surface and / or support when the cable is under load. This, in turn, results in a uniform introduction of the moment across the entire peripheral surface of the envelope on the inside of the cable. The restraining force of the outer layer of strands does not act, as hitherto, mainly as a transverse force on the tops of the different strands, but distributed over a large area on the total peripheral surface of the shell. Due to its elasticity, the intermediate casing can absorb different longitudinal movements of adjacent cords without relative displacement of the cords with respect to the intermediate casing, resulting in advantages in terms of flexibility and the alternating bending behavior of the cable. In the following, further advantageous features are described in more detail with the aid of a type of embodiment shown in the drawings. These show: - Figure 1, a perspective representation of an elevator cable with an intermediate enclosure according to the invention. - Figure 2, a cross section of the elevator cable of Figure 1. Figure 1 shows a cable 1 that is used in elevator installations as a carrier and transport element. The cable 1 is made up of a core cord 2, around which in the first direction of braiding 3 five equal cords 4 and a first layer 5 of cords in helical form and with which have been braided ten cords 4, 7 of a second layer 8 of cords in parallel placement and in a balanced relationship between twisting of cords and the cable. The second layer 8 of strands is composed of alternating arrangement of two types of strands, five equal strands 4 and five equal strands 7. The cross section shown in figure 2 shows another five strands 7 of greater diameter, arranged helically in the strands. concavities formed by the first layer 5 of cords on which they rest, while five cords 4 of the same diameter of the cords of the first layer 5 of cords rest on the tops of the first layer 5 of supporting cords, thus filling the cords. interstices between adjacent cords 7 of greater diameter. In this way, the cable core 9, double-stranded in a parallel manner, acquires a second layer 8 of substantially circular outer contour cords, which offers the advantages described below when acting together with the intermediate enclosure 13. Being the cable 1 low load, the parallel wiring of the cable core 9 generates a twisting moment against the direction of braiding 3. On the core 9 seventeen strands 10 have been braided in a second braiding direction 11 opposite the first braiding direction 3, forming one outer layer 12 of laces 10 in hawser quilting. The ratio of the braiding pitch between the outer cords 10 and the cords 4, 7 of the inner layers 5, 8 is, in the exemplary embodiment shown, 1.6. The wiring of the outer layer 12 of strands generates, under load, a torque that acts in the opposite direction to the second direction of braiding 11. Between the outer layer 12 of strands, braided in the second sense of braid 11 and the strands 4 7, of the second layer 8, there is an intermediate shell 13. This intermediate shell 13 is composed of an elastically deformable material, such as for example polyester or polyurethane elastomer, and has been injected or extruded on the core of cable 9. During this process, the intermediate wrap 13 of recent application, is deformed in a plastic manner resting closely on the contours of the periphery of the layers 8 and 12 of cords, filling all the interstices and keeping the grooves 18, 19 formed by the layers 8, 12 adjacent. The shaped intermediate shell 13 wraps the second layer 8 of hose-like cords, avoiding contact of the cords 4., 7, with the cords 10. In this way, wear of the cords 4, 7, 10 is avoided by mutual friction during the movement of the cable 1 over a idle pulley or a drive pulley (not shown) and due to the relative displacement of the cords 4, 7, 10 that occurs. In addition, the intermediate shell 13 provides a pressure transmission and shape drag of the torque generated by the load of the cable 1 on the outer layer 12 of cords to the second layer 8 of cords and, therefore, to the cable core. , whose parallel braid generates a torsional moment opposite to the direction of braid 3. At the same time the frictional resistance between the strands 4, 7, 10 and the intermediate shell 13 has been selected with u >; 0.15, so that practically no relative movement occurs between the cords and the intermediate shell 13, but the intermediate shell 13 follows the compensating movements due to its elastic deformation. The elasticity of the intermediate shell 13 is greater than that of the impregnation of the cords and that of the material bearing the cords, thus preventing them from deteriorating prematurely. On the other hand, the total elongation of the material chosen for the intermediate shell 13 is in any case greater than the maximum relative movement that takes place between the cords 4, 7, 10. By means of the thickness 20 of the intermediate shell 13, it can be adjusting in a controlled manner the radial distance of the outer layer 12 of cords 12 to the axis of rotation of the cable 1, in order to thus neutralize the ratio of the twisting pairs of opposite action of the outer layer 12 of cords 12 and of the core of cable 9 of parallel braid on cable 1 under load. The thickness 20 of the intermediate casing 13 should be greater as the diameter of the cords 10 or of the cords 4 and 7 increases. In any case, the thickness 20 of the intermediate casing 13 must be dimensioned so that a thickness is ensured of the envelope of 0.1 mm between the cords 4, 7 and 10 of the adjacent layers 8 and 12 in the loaded state and with the interstices 21, 22 between completely filled cords. The intermediate shell 13 plastically deformed, provides a uniform transmission of the moments through the entire peripheral surface of the envelope. The volume of the interstices between cords can be minimized by alternating arrangement of large diameter cords 7 and cords of small diameter 4 in the second layer 8. The cable can be used in different facilities of the transport technique, for example elevators, well conveyors in the mining sector, in cargo cranes such as construction cranes, factory cranes and ship cranes, funiculars and ski lifts, and as a means of traction in escalators. The actuation can take place by the force of friction through pulleys or Koeppe pulleys and also by rotating drums of cables, on which the cable is wound.