Synthetic fiber cable without shirt
Description The invention relates to a cable of synthetic fibers, preferably of aromatic polyamide, with a casing according to the preamble of claim 1. The cables are an important machine element subjected to great efforts mainly in the transport technique, for example in elevators, in the construction of cranes and in the mining industry. The efforts are multiple, especially in the case of driven cables, cables with changes of direction by pulleys or cables wound in drums, such as are used, for example, in the construction of elevators and aerial cable cars. In these cases, large cable lengths are required and for energy reasons the cable mass is intended to be as small as possible. Cables of high-strength synthetic fibers, for example of aromatic polyamides or aramides with molecular chains oriented to a high degree, meet these requirements better than conventional steel cables. However, materials, such as aramides, are especially sensitive to ultraviolet (UV) light and oxidative and reducing environmental influences, influences that reduce the breaking load and the ability to function. For this reason, aramid cables are usually coated with shirts or braided material resistant to light. For example, with the document EP 0 672 781 Al of the applicant, it has been known to use this type of synthetic fiber cables with a jacket in the elevator installations as supporting elements for joining the frame of a car driven in an elevator box with a counterweight. The cable runs on a drive pulley driven by a drive motor, to raise and lower the cab and the counterweight. The actuation moment is applied under frictional connection on the cable section which is in contact with the arc of the change of direction in each case. In this case, instead of a jacket that surrounds the entire outer layer of cords, each individual cord of said layer is provided with an extruded sleeve of plastic, preferably polyurethane or polyamide, closed around its perimeter. These sleeves together serve as protection against abrasion of the cable and ensure the desired coefficient of friction with respect to the drive pulley. The cohesion forces between the plastic sleeves and the outer layer of synthetic fiber cords are achieved to the extent that the plastic jacket is applied by pressure projection, in such a way that all the interstices between the cords are filled and a positive connection is formed with a large clamping surface. However, the thrust forces generated when the cable is subjected to loading can cause under certain circumstances a displacement or reinforcement of the plastic jacket. These cable alterations are not desirable, since they could lead to failure of the cable. Obtaining the necessary cohesive forces between the cord and the jacket by applying the sleeves to the strands with the pressure spraying process is expensive. Accordingly, the invention aims to reduce the cost of manufacturing a synthetic fiber cable while ensuring that its high functionality is not modified. This objective is solved, according to the invention, with a synthetic fiber cable of the type mentioned at the beginning with the characteristics indicated in claim 1. Extensive tests by the applicant have shown that, instead of a protective jacket, which until now was extruded simply by coating the synthetic fiber cords of the outer layer with a liquid containing UV stabilizers and other abrasion protection additives and environmental influences detrimental to the cable, reliable protection against light can be durably ensured UV and sufficient resistance against abrasion of the cable. The advantages achieved with the invention consist of a durable union of the envelope with the synthetic fiber cords of the outer layer, since the material of the envelope and that of the matrix that fixes the synthetic fibers of the cords are equal. By simply adding and mixing the corresponding additives, the functionality can be simply extended over the entire lifetime of the fiber cables. The wrapper according to the invention does not form undercuts nor can it move on the strands of synthetic fibers. The wrapping process takes place largely without additional expense in terms of the devices, and is simple and inexpensive. From the strands of conventional synthetic fibers manufactured in large series, the strands of synthetic fibers for the outer layer only have to be passed through an already existing impregnation bath to form the coating according to the invention. The layer thickness can be adjusted by the residence time of the synthetic fiber cords in the impregnation bath. In addition, the coating process can be repeated as many times as desired. By the addition of short fibers, for example of aramid, to the impregnation bath, a particularly abrasion-resistant embodiment is achieved. Other advantageous embodiments of the invention are described. In the following, a preferred exemplary embodiment of the invention is described in more detail with an impregnation means in the form of a liquid, with reference to a cross-sectional view, shown in the drawing, of a cable 1 consisting of sixteen strands. Around one core cord 2, five equal cords 3 are arranged helically, with which five cords 4, thicker, are braided in parallel, alternatively with five cords 5, finer, forming an outer layer 6. The cords supporting 2 , 4, 5 used for the cable 1 shown, consist of twisted or spun individual aramid strands. The cords 2, 3, 4 and 5 consist essentially of aramid yarns 8 fixed helically in a polyurethane matrix. To twist or twist the aramid yarns 8, they are treated with a protective impregnating means, for example a polyurethane solution. The proportion of polyurethane in each strand 2, 4, 5 is decisive for the alternative flexural strength of the cable 1. The greater the proportion of polyurethane the greater the alternative bending capacity. Also, the higher the proportion of polyurethane, the lower the fill factor of the whole cable 1 and, therefore, the lower the load capacity and the lengthening behavior of the cable 1. Depending on the desired cable properties, the ratio of polyurethane for impregnation of cords 2, 4, 5 can oscillate, for example, between ten and sixty percent. In the illustrated embodiment, seven aramid yarns 8 have been bound and fixed by impregnation to form a filament 7. The impregnation forms a thin protective layer 9 around each individual filament 7. Seven of the filaments 7 are twisted together from each other. helical shape by forming a cord 2, 3, 4, 5. In the actual configuration, the filaments 7 do not have the circular shape shown in the drawing, but are adapted to the surface of the adjacent filaments and the cords. Up to this point, the structure of all the strands 2, 3, 4, 5 used in the exemplary embodiment is fundamentally the same, but the amount of twists per meter can vary between the different layers of strands and between the strands with different diameters. Each of the thick cords 4 and fine cords 5 braided in the outer layer 6 is coated according to the invention with an additional protective layer 10 of impregnation means. This protective layer is advantageously formed on the surface of the thick cords 4 and the thin cords 5 by soaking in a bath of impregnation medium in a continuous regime. In addition to polyurethane, the impregnation means contains additives of UV stabilizers, preferably silicon crystals, and oxidation and reduction blockers. By the addition of short fibers, preferably of aramid, a protective layer 10 is obtained with greater resistance to abrasion. The thickness 11 of the protective layer 10 around the individual cords 4, 5 is in this case 0.2 mm, but according to the invention it may vary between 0.1 and 1 mm depending on the desired protection effect. The protective layer 10 serves as a protection against abrasion between the thick cords 4 and the thin cords 5 of the outer layer 6 and forms a sheath of the cable 1 in the structure of all the cords 4, 5 of the outer layer 6 towards the outside. as effective as economic. Therefore, an additional plastic cable jacket can be dispensed with. According to the invention, the cords 4, 5 coated with a protective layer 10 can be prefabricated as semi-finished products and then their processing can be continued as required by conventional braiders, which considerably reduces the manufacturing cost of the aramid fiber cable 1. In Instead of a means of impregnation, another liquid with adherent property can also be applied to the cable. In addition to applications such as pure cable support, the cable can be used in the most diverse facilities of the transport technique, for example for elevators, extraction facilities for wells in the mining industry, cargo cranes such as cranes hangars or ships , aerial funiculars and ski lifts, and as a traction organ in escalators.