Abstract:
Proposed is a support disk bearing for an open-end spinning rotor. The support disk possesses a body, which, on its circumferential surface, is designed to receive a cover layer. The cover layer is comprised of rubber, in particular nitrile rubber (NBR). In an advantageously favorable formulation, the cover layer contains an additive for the reduction of its electrical resistance.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns a support disk for a support disk bearing for an open-end spin rotor. 
     Generic conventional support disks have been disclosed by DE 33 24 129 A1 describing a bearing for spin rotors. The support disks comprise a body, which, for instance, is constructed of plastic or metal and which, on its circumference, possesses a plastic ring that forms the running surface for the rotor shaft that it bears. The plastic ring, in this case, is applied by spraying on to the body. In the present state of the technology, the material used on the circumference of the disk with the plastic ring and which is driven by the shaft is polyurethane polymer. 
     This elastic plastic ring forming the running surface of the rotor shaft has the characteristic that it possesses damping qualities, so that oscillations may be damped during a vibratory period in the run of the spin rotor. Such vibratory periods can occur, for instance, because of imbalances or through impacts with the driving tangential belts. With the known support disk bearings and support disks equipped with the circumferential surface made of polyurethane, rotational speeds of the rotor shaft of up to 110,00 RPM are possible. 
     Besides the mentioned advantages, the circumferential polyurethane covering of the support disk also has the drawback of excessive wear. Because of the continual deformation, i.e., compression and expansion of the running surface, this component is heated to such a degree, that complete destruction of the layer occurs. In order to repress this behavior of the support disk, it is a conventional practice within the state of the technology to place a cooling groove in this outer layer. This cooling groove is made known by U.S. Pat. No. 5,178,473. 
     Along with this breakdown, the known support disks are deficient in that the polyurethane running surface separates itself from the base part of the support disk, whereby destruction of the support disk follows. 
     In order to avoid problems of this nature, it is a known practice in the state of the technology for such support disks that have the plastic cover layer applied onto the body to provide a form fit connection between the body and the plastic cover layer as seen in a radial direction of the support disk. A support disk of this kind is described in DE 42 27 489 A1. From DE 198 24 286 A1, a support disk has been made known, which is provided with a cleaning groove, as well as a cooling groove. DE 198 24 286 A1 also provides further measures so that, during an operational run of the rotor spinning apparatus, contamination is prevented from getting on the rotor shaft, which would cause additional maintenance. 
     Experience has shown that the support disks of the state of the technology exhibit faults when installed and, in spite of the known measures, have only a very restricted operational life, which limits their employment in modem rotor spinning machines. The stresses thereby brought about lead to an early failure of the support disks so that, besides the high expenditures for the necessary replacement parts, the productivity of the spinning machine is lessened because of the required maintenance work. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Thus, a principal purpose of the present invention is to eliminate the disadvantages of the state of the technology, and to make available support disks, which provide bearings suitable for open-end spin rotors even at the most extreme speeds of rotation without the detriment of an insufficient length of operational life. Additional objects and advantages of the invention will be set forth in part in the following description or may be obvious from the description, or may be learned through practice of the invention. 
     This principal purpose of the present invention is achieved through a support disk with a circumferential surface having a cover layer made of rubber. 
     By means of the formulation of the support disk in accord with the invention, a secure connection is advantageously created between the body and the running surface of the support disk. This connection resists such forces incurred by the in-and-out flexing of the cover layer. Even at the highest speeds of rotation and loadings, the loosening of the applied circumferential layer from the body of the disk does not occur. 
     Furthermore, the support disk constructed in accord with the invention possesses very good rolling characteristics for the carried rotor shaft. In this way, an unsteady phase in the running behavior of the rotor is substantially ameliorated by the excellent damping properties of the support disk, and vibrations are damped. 
     The damping operation in the circumferential cover layer of the support disk advantageously can be carried out by the layer without detriment to the quality of the running surface. In particular, the most favorable damping characteristics of the invented cover layer for the running surface of the support disk make it possible to hold the thickness of the cover layer of the support disk to a minimum. This has the additional virtue in that the heat removal from the cover layer is alleviated. The flexing brought about in the cover layer on this account does not lead to excessive heating of the cover layer. This advantage substantially increases the operational life of the cover layer as well as that of the support disk. 
     In an advantageous development of the invention, the cover layer of the support disk is furnished with a cooling groove for even better dissipation of heat from the cover layer during operation. This cooling groove further increases the wear resistance of the support disk. 
     Providing a design of the body with circumferential profiling in a radial direction is a favorable design to bring about a form fit connection between the body and the cover layer. Even when this may not seem necessary due to a current application, such profiling does enable future higher load demands to be met by the support disk. 
     By the design of the cover layer with a cleaning groove for the suppression of contaminant deposits on the rotor shaft, disturbances in operation are reduced. Such deposits are also hindered by the fact that the cover layer of the support disk has a low electrical resistance, advantageously less than 1.0×10 9  Ohm. In order to achieve this, the rubber material advantageously is treated with an additive for the increase of its electrical conductivity. 
     In an advantageous development of the invention, the cover layer on the support disk consists of nitrile rubber ([acrylo]nitrile-butadiene rubber), hereinafter, “NBR”. 
     This material has especially favorable mechanical characteristics, which cause it to be practically abrasion proof in rough operational conditions. Even better advantageous properties are possessed by the rubber H-NBR. 
     This rubber can contain additives, so that it requires no special aging, which is required, for instance, of the polyurethane used in practice in accord with the state of the technology. NBR or HNBR, as a result of these additives, has the characteristics of an already aged material and thus possesses uniform, unchanging properties from the beginning. 
     Fortunately, there is found in an advantageous development of the invention, a rubber with a tensile strength to meet at least 28 N/mm 2 . Advantageously, a rubber is available for use with a Shore Hardness of A 85 to 105. Thereby, favorable damping values can be achieved for the cover layer. Just as advantageous is a rubber with a hardness between Shore D 45 to 70. The use of a rubber for the support disk with an elasticity of at least 29% assures a high resistance to wear and good damping. 
     If the support disk has one or more grooves on the circumference of the cover layer, then, in an advantageous manner, the support disk cover layer can endure even the highest loadings. The groove can fulfill several purposes. For example, the groove can be used for cooling the cover layer or for the cleaning of the shaft of the open spin rotor. Moreover, by means of the installation of the grooves, the rolling contact friction of the shafts against the support disks is lessened. 
     If the grooves penetrate to the body of the support disk, that is, if the cover layer is essentially made of a plurality of individual elements, independent of one another, then a highly satisfactory cooling of the cover layer and the support disk is assured. The holding qualities of the rubber of the cover layer onto the body of the support disks, especially when this is made of aluminum, are particularly good. Thus, it is possible to fasten the cover layer without lateral restraint directly to the support disk on the circumferential surface. However, for certain technical manufacturing reasons, certain small lateral restraint may be necessary. The scuffing off of the cover layer from the support disks is not to be feared with the invented formulation of the cover layer within foreseeable loadings. 
     If the cover layer has a thickness of less than 4 mm or if it is less than 1.9 times the depth of the deepest groove, then the cover layer possesses an especially good relationship in reference to its structural strength and the cooling and cleaning effects of the groove. 
     Respectively, in accord with each instance, it can be advantageous if one or more cleaning grooves are placed on the cover layer of the support disk. 
     If the body has been surface treated, especially if the body is of aluminum and has been anodized, then other advantages appear. By means of the surface treatment, damage to the material of the body, particularly by oxidation, is prevented. Besides this, by means of the surface treatment, characterizing colorations are possible, so that the installation of different support disks can be chromatically designated in a simple way and thus unwanted exchanges can be avoided. By means of the special characteristics of the material of the invented cover layer of the support disks, it is even possible to put an anodized surface in place after the installation of the circumferential cover layer. By means of the anodized surfacing, that is, the anodizing of the support disk with the cover layer in place, the circumferential cover layer is not affected and its action is not impaired. The anodizing can take place after the finishing work of the support disk. 
     Invented support disks with outside diameters between 50 and 80 mm have performed exceptionally well for installation in the support bearing system for spin rotors. 
     The contact surface between cover layer and rotor shaft shows a width of between 4 and 12 mm. This width is sufficient to see that first, a predominantly slip-free rolling contact of the rotor shaft on the support disk is actuated and, second, the rolling resistance is held to the least possible amount. 
     For a minimum width of the cover layer, a value of around 2 mm is particularly recommended. At this width, it is even possible to work out a direct fastening of the cover layer on the circumference of the body without lateral restraint between the body and the cover layer. When the body is aluminum, a particularly sufficient hold between the invented cover layer and the circumference is obtained. 
     Beyond this, the 2 mm is enough to avoid a lateral kinking of the cover layer. In the following, the invention will be described with the aid of illustrative presentations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a presentation of the principles of a bearing system for an open-end spin rotor; 
     FIG. 2 shows a cross-section through a support disk of the bearing system of FIG. 1; 
     FIG. 3 shows a cross-section through a support disk with a flat circumferential surface; and 
     FIG. 4 shows various embodiments of a support disk in accord with the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the principles of a bearing system  1  for an open-end spin rotor  2 , as this is standard where such open-end equipment is installed. The bearing system is comprised generally of a bearing block  11  which carries the support disk bearings  12 . The support disk bearings  12  each carry one shaft  13 , which, on each of their ends, a support disk  14  is connected by press fit. Together, the support disks  14  form a disk pair so that a wedge shaped opening  141  is formed between them. The support disks carry the rotor shaft  21  of the open-end spin rotor  2 . If the open-end spin rotor  2 , for instance, is driven by a tangential belt (not shown), it rolls in the wedge shaped opening  141  on the support disks  14 . Thereby, these are set into rotary motion. The support disks  14  are provided with a cleaning groove  3 , which traverses with its edges  31  along the contact line of the rotor shaft upon the rotation of the support disks  14 . The cleaning groove  3  is installed in the cover layer  143  in the form of an endless groove. 
     Since the run of the rotor shaft connected to the support disks is not entirely slipfree, it is assured that the groove edge  31  reaches every position of the rotor shaft and keeps this shaft free from contaminating deposits. 
     The shafts  13 , which serve as bearing for the support disks  14 , are set in their own bearings not parallel to one another, but slightly inclined so that an axial thrust will be exercised on the rotor shaft  21  by the support disks  14 . The rotor shaft  21  is axially supported by the axial bearing  101  in a known manner. This axial bearing, for example, can be designed as a thrust bearing as indicated in FIG. 1 in the form of an aerostatic axial bearing. 
     The positioning of the rotor shaft  21  in the wedge shaped opening  141  of the support disks  14  results in a relatively high pressure on the rotor shaft against the cover layer  143  of the support disks  14 . This pressure is produced since the tangential belts running over the rotor shaft  21  are pressed on their own account with a radial force on the rotor shaft  21 . The direct pressure is necessary in order to hold the slippage between the tangential belts and the rotor shaft  21  as low as possible. This pressure would permit the rotor shaft  21  and thus the open-end spin rotor  2  to be driven without loss. This pressure must be absorbed by the circumferential cover layer  143  of each support disk  14 . Because of the fact that the support disks rotate with the rotor shaft  21 , an alternating pressure force is exercised on the cover layer  143 , which further stresses the cover layer  143 . The stressing due to this alternating pressure leads to a heating of the cover layer  143  and therewith a thermal load is added. 
     Besides this type of stress to which the cover layer  143  is subjected, a continual frictional contact of the rotor shaft  21  perpendicular to the plane of the support disk  14  is exerted against the cover layer  143 . The friction contact has its origin, as already mentioned above, in the arrangement of the two shafts  13  to each other. The frictional contact by means of the rotor shaft leads to a stressing of the surface of the support disk in a mechanical way and again leads to a heating of the cover layer  143  produced by this situation. 
     The support disk  14 , shown in FIG. 2 in cross-section, possesses a cleaning groove  3  in the cover layer  143 . The cover layer  143  forms on its circumference the running surface  144  on which the rotor shaft  21  rolls. The support disk  14  comprises a body  5 , which, for example, can be aluminum, whereupon it could be made by precision molding, or it can also be plastic. The support disk  14  possesses in its center a boring  51  by means of which it is fastened to the shaft  13  of a support disk bearing  12  by means of a press fit (see FIG.  1 ). In the area of the transition of the body  5  to the cover layer  143 , the outer circumference of the body  5  is shaped (not shown) in a special manner, for instance, V-shaped or hammer shaped. This shaping leads to an improved adherence between the body and the cover layer  143 , so that a better holding power between the body  5  and the cover layer  143  can be assured. 
     In a favored construction, the body  5  is designed so that a sufficient depth of the cover layer is available to accommodate a cleaning groove. 
     The assured secure fastening of the cover layer  143  on the body  5  of the support disk is carried out not only by means of a form fit connection between the body  5  of the disk  14  and the cover layer  143 , as shown in FIG. 2, but also by inherent bonding between the cover layer  143  and the body  5 . This bonding in the case of a support disk constructed in accord with the invention is essentially greater than is found in support disks in which the cover layer  143  is made of polyurethane. The invented cover layer of rubber has inherently a substantially higher holding power on the body than do cover layers conventionally used in the state of the technology. Furthermore, the invented support disk cover layer of rubber has a lesser tendency to form shrinkage cavities, and thus, its adhesiveness is once more increased. 
     Because of the advantageous lesser inclination of the cover layer of rubber, particularly NBR or HNBR, to form shrinkage cavities or piping, it becomes possible to apply this material in a thinner layer on the outer circumference of the support disk body. 
     The support disk  14 , depicted in a cross-sectional view in FIG. 3, possesses a body  5 , which has a smooth cylindrical shaped surface as its circumference upon which the rubber cover layer  143  is placed in accord with the invention. Because of the particular physical properties of this rubber, in particular, its favorable tenacity to the body material, it is possible without the body  5  being profiled on the circumference to make a secure bonding between the cover layer  143  and the body  5 . Further, the tenacity can be increased if necessary by bonding means and/or roughening the contact surface. The cover layer  143 , shown in FIG. 3, possesses a groove  30  running centrally around the circumference. This groove  30  has the task of a cooling groove for the cooling of the cover layer  143 . Such grooves  30  applied for cooling are common in the state of the technology. 
     The thickness of the cover layer  143 , as shown in FIG. 3, allows further design possibilities. In accord with the respective application of various installed rubber cover layers, it is possible to construct the cover layers substantially thinner than the state of the technology requires for polyurethane cover layers. By the thinner designed cover layer, the cover layer  143  advantageously contains a lesser mass, whereby its bonding to the body surface experiences an essentially lesser stress from centrifugal action than does the cover layer of the state of the technology. In spite of its being thinner in the case of the invented rubber cover layer  143 , the required characteristics for the damping of the rotor shaft during rolling action remain. Also, by the diminishing of the thickness, the heat caused by the compression and release of the substance is closer to the body  5 , so that heat dissipation, especially when the support disk bodies are of metal, is essentially improved. This improved heat dissipation increases the operational life expectancy of the cover layer  143  and also the support disk  14 . 
     The favorable characteristics of the support disk cover layer  143  make possible a further design improvement, especially concerning the running surface  144 , since the cover layer  143  in accord with the invention is more resistant, that is, has a greater capability to minimize erosive damage. Thus, narrower support disks can be installed whereby the bearing assembly advantageously can be built smaller and will have a lesser mass. Also, an advantageous reduction in size of the diameters of the support disks as a result of the invented materials for the running surface is now possible. 
     In FIG. 4, respectively, various embodiments of a support disk in accord with the invention are presented. FIG. 4A shows an embodiment having a groove  30  in a cover layer  143  which nearly penetrates through to the base (dotted line). By the cohesion of the cover layer at its inner circumferential surface, a very stable embodiment is created, since the two part cover layer extending outwardly at its fastening point is supported on both sides. 
     In FIG. 4B, a support disk  14  is presented which has two circumferential grooves  30 . By this means, three support surfaces are created by the cover layer for the rotor shaft. 
     FIG. 4C depicts an arrangement of three grooves  30  in the support disk cover layer  143 . As this cross-section shows, the outer two grooves are formed less deep in the thickness of the cover layer than is the center, third groove. The center groove  30  is, in this case, similar to the groove depicted in FIG. 4A as it is formed to a depth in the cover layer  143  approaching the body surface  5 . 
     In FIG. 4D, cleaning grooves  3  in the cover layer  143  are slanted, in reference to the central axis of the body  5 . By this device, an axial thrust is generated on any contaminating deposit on the rotor shaft  21 , whereby such contamination is gradually abraded and the rotor shaft  21  in this area is kept nearly free of any deposits of unwanted material. 
     The arrangement in FIG. 4E shows two individual cover layers  143  in support disk  14 . Each of these cover layers  143  is made fast, without contact with the other, on the circumference of the body  5  of the rotor support disk  14 . Because of the characteristics of the material of the cover layer  14 , a good adherence is secured in this design in which no contact with the body  5  of the support disk  14  is present, or possibly only a very small lateral retention will suffice. 
     A support disk bearing system is, in general, less sensitive to manufacturing and mounting tolerances than usual, and thereby makes possible a more favorable manufacturing cost. Thus, the possibility becomes evident, that it is not necessary to subsequently spray onto the support disk covering  143  any means of diminishing a lateral stress of the covering. For a precise work-up, principally, only the circumferential surface need be treated by chemical or mechanical profiling. 
     Further advantages arise from the advantageous material characteristics. Naturally, rubber inherently has a very small electrical conductivity in comparison to the cover layer of the support disk of the state of the technology.