Abstract:
The invention relates to an element ( 10 ) for sealing two parts ( 2, 3 ) that can be rotated in relation to one another. Said element comprises at least one first sealing ring ( 11 ) consisting of a permanently elastic material, which is fixed to one of the two rotatable parts and comprises at least one sealing lip ( 21 ) and at least one second sealing ring ( 12 ), which is fixed to the other rotatable part and comprises a strip ( 19 ) consisting of another material that runs along its periphery. At least one sealing lip of the first sealing ring lies against said strip.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an element for sealing two parts that can be rotated in relation to one another, with at least one sealing ring consisting of a permanently elastic material that is fixed to one of the two parts that can be rotated in relation to one another, and at least one sealing lip. 
     2. Description of the Prior Art 
     Commercial seals generally comprise a ring consisting of an elastic material fastened to one of the two parts that can be rotated in relation to one another, and that is provided with a sealing lip that is tightly pressed against a surface of the other of the two parts that can be rotated in relation to one another. For the sealing lip not to wear out prematurely, the contact surface should be as smooth as possible. A machined and/or polished surface area of the relevant rotating part is ordinarily used for this, which may also be protected against corrosion by a grease film. However, this arrangement has drawbacks: 
     In large bearings, in particular in plant construction, for example in the case of a pitch bearing of a wind energy system, but also in much medical equipment, the relevant rotating part is often so large that it is uneconomical to use stainless steel for this. The use of ordinary steel that rusts, on the other hand, leads to relatively rapid corrosion from the weathering of exposed bearings, since a protective grease film is quickly washed away by rain. Especially in coastal regions (wind energy systems) or even on the high seas (ships), the air is also very corrosive because of the salt water. However, as soon as corrosion sets in, the seal is damaged by the roughened surface it causes, and is finally destroyed. 
     In other uses, and in the medical technology sector, no grease film, or emergence of grease, is permissible, so that here also there is no corrosion protection, and without using a variety of stainless steel that substantially increases the cost of the equipment in question, corrosion would be unavoidable. 
     Many bearings can also be serviced only at great expense, so that it would be desirable for such applications to have available a special sealing element that does not have to be serviced, even in systems with a life expectation of 20 years. 
     The above considerations result in the problem behind the invention, of providing a seal that operates without wear even under rough or even corrosive environmental conditions, and/or without a protective grease film, for as long a time as possible. 
     SUMMARY OF THE INVENTION 
     This problem is solved with a seal of this type by at least one second sealing ring that is fixed to the other of the parts that can be rotated in relation to one another, and that carries a strip made of another material that contacts the at least one sealing lip of the first sealing ring and that runs along its periphery. 
     The second sealing ring serves only as the carrier for the strip that serves as the contact surface for the opposite sealing lip, and can therefore be matched optimally to this task with regard to the choice of its material. For example, it can have higher elasticity than the sealing strip to compensate for tolerances of the components. The assembly and fastening of the sealing strip are considerably facilitated, which is important also with regard to a continuous strip surface. The sealing strip can also be relatively thin, for example 0.5 to 2 mm thick, and because of its small weight, a high-value, low-wear material can be used for it. 
     It has proved to be desirable for the material of the second sealing ring to have a higher specific electrical resistance ρ than the material of the strip it carries. The second sealing ring is preferably made of an electrically insulating material, for example, of a material with a specific electrical resistance ρ of more than 10 3  Ωm, particularly of more than 10 6  Ωm. Therefore, it sees to it that the strip pursuant to the invention, together with the relevant rotating part, does not constitute a local chemical voltaic cell. 
     Special benefits are obtained by manufacturing the first and second sealing rings from the same material. The invention prefers for this a vulcanized, i.e. crosslinked, material, for example vulcanized rubber, because this is not only elastic but is permanently elastic as a consequence of the molecules crosslinked with one another, in contrast to uncrosslinked rubber. Therefore, the result is that the post-vulcanization that gradually reduces the elasticity existing initially in uncrosslinked rubber is largely or even completely eliminated. 
     Other benefits are available by manufacturing the strip of metal, especially a noble metal or a refined metal, for example, stainless steel. Because of its relatively great hardness, metal is relatively wear resistant. The development of material-destroying local voltaic cells can be avoided by the insulated fastening to the second sealing ring as the carrier. Finally, noble or refined metal is not subject to corrosion. 
     It is a great advantage for the material of the strip to have a lower coefficient of friction μ than the second sealing ring. This spares the sealing lip even with no grease film, which likewise has a beneficial effect on the achievable service life. The capability of reducing the coefficient of friction μ exists if the surface area of the strip serving as the contact surface for a sealing lip of the first sealing ring is smoothed or polished. 
     The sliding of the sealing lip along the strip pursuant to the invention with as little friction as possible is also supported if the surface area of the strip serving as the contact surface for a sealing lip of the first sealing ring follows somewhat a surface of rotation, especially a cylindrical envelope surface. This distributes the pressure of the sealing lip uniformly on the entire circumference, and there are no points with elevated wear. 
     Inasmuch as the strip is closed in a ring, on the one hand, it in turn is given the rotational symmetry necessary to minimize wear of the sealing lip running along it, and on the other hand an annular structure is advantageous for fastening the strip to the second sealing ring. An annular structure, i.e. a structure that is doubly coherent, can be achieved by welding or cementing the two end faces of the strip, preferably abutting blunt ends, optionally followed by smoothing or polishing the joint, particularly the weld bead or cement point. The strip ends can be joined before or after assembly with the relevant sealing ring, as needed; however, the invention prefers to join the strip ends before assembly with the relevant sealing ring, or before installing the seal. 
     A constant cross section of the strip along its entire periphery serves the same purpose, namely, optimal rotational symmetry. The invention prefers a somewhat rectangular cross section with the sealing lip finding an optimal contact surface on one of the wider circumferential surfaces of such a strip, while the thickness perpendicular to this surface can be as small as possible to impart flexibility to the strip. 
     With a view to automatic fastening of the strip, it is recommended to fasten it, using the second sealing ring, to a preferably somewhat cylindrical envelope surface of the relevant rotating part, where fastening is achieved solely because of geometric characteristics, so that the use of adhesive is unnecessary. 
     Especially suitable for this is a convex domed outer envelope surface of the relevant rotating part around which the strip pursuant to the invention can be wrapped like a belt and can thereby have an optimal grip. 
     Since the tiniest points of contact between a metallic strip pursuant to the invention and a likewise metallic rotating part can lead to a local voltaic cell, the encircling strip should be fixed on the second sealing ring in such a way that no contact at all exists with either of the two parts that can be rotated in relation to one another. 
     To avoid migration of the strip, it can be held in an encircling trough-like recess in the second sealing ring. 
     If the depth of the trough in the second sealing ring that holds the strip is less than the corresponding cross-sectional height, i.e. the thickness, of the strip laid in it, then the surface area of the ring serving as the actual contact surface for the sealing lip of the other rotating part rises above the delimiting surface areas of the second sealing ring. Even if there is a small clearance between the parts that can be rotated in relation to one another, permanent contact between the sealing lip on the first sealing ring and the second sealing ring is precluded, and so is damage to these parts caused by friction. 
     Pressure forces exerted by the sealing lip on the strip pursuant to the invention—perhaps together with fastening forces produced by the annular strip itself—act on the bottom surface of a trough in the second sealing ring holding the strip. To be able to be passed on from there to the relevant rotating part, the bottom of the trough in the second sealing ring holding the encircling strip runs generally parallel to the surface area of the rotatable part to which the second sealing ring is fastened. 
     The strip pursuant to the invention is carried in the trough of the second sealing ring; because of its guidance task, the second sealing ring needs orientation or anchoring relative to the actual rotatable part. This is achieved by a stud or the like, which is formed on a peripheral area of the cross section of the second sealing ring opposite the trough and is laid in a somewhat complementary groove-like recess in the relevant surface area of the rotatable part. 
     The fastening stud of the second sealing ring can be provided with projections that stand out cross-sectionally on its radially inner and/or outer surface, which increase its elasticity and permit its complete immersion in a groove-like recess in the rotatable part, on the one hand, and on the other hand guarantee it. These projections can be configured as encircling ribs, or with wavelike or sawtooth-shaped cross sections, or the like. 
     The second sealing ring can also have a sealing lip that is formed on at least one encircling surface area. If the second sealing ring comprises a vulcanized, i.e. crosslinked (rubber) material, it has permanently elastic characteristics as required by a sealing lip. It is therefore obvious to provide the second sealing ring with a sealing lip also, in order to be able to realize a double or multiple seal at low cost. 
     Such a sealing lip on the second sealing ring can contact a surface area of the opposite rotatable part. If, as the invention further foresees, the additional sealing lip on the second sealing ring lies within the cavity preferably filled with grease or similar lubricant, that is closed off by the first sealing lip, then corrosion of the surface area of the rotatable part cooperating with the second sealing lip is precluded, so that damage to the second seal is avoided without additional corrosion protection measures. 
     Alternatively, and/or in addition to the additional sealing lip on the second sealing ring, a surface area that encircles it can be provided as the contact surface for another sealing lip. Such a third seal can lie outside the main seal formed by the strip pursuant to the invention and the first sealing lip contacting it, and then protects the main seal against mechanical influences, for example against impacts. 
     A particularly simple construction is obtained when the sealing lip contacting a contact surface of the second sealing ring is formed on the first sealing ring. 
     An arrangement has proved especially beneficial in which the back of the first sealing ring opposite the sealing lip contacting the strip is turned to the outside, or faces the surface of the relevant ring. If it faces the surface of the relevant ring, then it can be supported there as the case may be, so that the sealing lip, even after it is worn, still remains in tight contact with the strip. If it is turned outward, then it can be held in shape easily with a spring element on the front of the area carrying the sealing lip, which can then be retightened, or replaced, at any time because it is accessible from the outside, or can at least be inspected and optionally brought back into shape manually during maintenance. If the back of the sealing lip is covered by another part of the seal, perhaps by another section of the sealing ring itself, then the correct position of the sealing lip can scarcely be inspected during maintenance, not to mention corrected. 
     The invention is also distinguished by a spring element that presses a sealing lip of the first sealing ring against the strip of the second sealing ring. This can considerably increase the pressure of the sealing lip of the main seal, and with it also its sealing action. 
     An encircling wire or the like, for example, is suitable as a spring element. It can absorb large tensile forces that result in a far greater radial pressure of the sealing lip than can be brought about by the sealing lip alone. To be able to fulfill its task permanently, even under corrosive environmental conditions, the spring element should be corrosion resistant; for example, it should consists of stainless steel, or the like. This feature can be highly important when the spring element is located outside the sealed-off area. 
     To avoid problems when assembling the seal, the spring element can have a somewhat circular cross section, so that unintended twisting does not impair its uniform force action. 
     The spring element is preferably located on the back of the sealing lip of the first sealing element contacting the strip. From there, the pressure preferably acting radially inwardly can act precisely toward the free edge of the sealing lip, so that symmetrical forces are set up in the area of this edge and deformation of the sealing lip is reduced to a minimum. 
     To hold the spring element permanently in place, it should be laid in an encircling, somewhat trough-shaped recess in the first sealing element. Then it cannot slip, and the pressure action of the sealing lip is supported, even after a very long time of operation. If this trough is located outside the sealed-off area, the spring element is accessible from the outside and can easily be installed after inserting the other sealing elements, and/or can be removed and/or optionally replaced and/or tightened at a later time for maintenance purposes. 
     For safety reasons, the invention recommends that the trough in the first sealing element has a circular cross section to hold the spring element, preferably along a cross-sectional peripheral angle of more than 180°. In such a case, the spring element cannot be loosened from this trough, even by severe vibrations. 
     In an arrangement of the spring element in a somewhat common plane with the free edge of the sealing lip, the two edges of the trough holding the spring element lie on both sides of this plane. At least one of the two trough edges in the first sealing element is suitable for fastening the first sealing ring, by lengthening it cross-sectionally away from the first sealing lip. The edge area that projects backward in such a case can be provided with a stud, or the like, at its free end, which is used to anchor the first sealing ring in a somewhat complementary groove-like recess in the relevant surface area of the rotatable part. The groove to hold such a stud does not have to be located on the envelope surface of the relevant rotating part, but can also be recessed in one of its faces. 
     Like the fastening stud on the second sealing ring, that of the first sealing ring can also have cross-sectionally projecting, preferably wavelike or barb-shaped elevations to increase its elasticity. 
     The construction pursuant to the invention undergoes further optimization by the tip of the cross section of the sealing lip of the first sealing element contacting the strip lying somewhat on the straight line connecting the centers of the two troughs for holding the strip on the one hand and of the spring element on the other hand. In such a case, the pressure forces are transmitted in a single plane from the spring element over the free edge of the sealing lip to the central area of the strip pursuant to the invention, with no fear of unsymmetrical deformations of the sealing lip and/or of the second sealing ring. 
     It is within the scope of the invention for the sealing lip of the first sealing element contacting the strip to have a cross section with a blunt tip. Such a blunt-angled tip is only minimally susceptible to unwanted deformations, and can therefore also withstand very high pressure forces over a period of many years and exert them on the strip pursuant to the invention. 
     Finally, the invention is distinguished by a third sealing ring that is fastened to one of the parts that can be rotated in relation to one another and that has a sealing lip that contacts the other of the parts that can be rotated in relation to one another. This sealing ring also can be provided with a stud, or the like, formed on its cross-sectional area opposite the sealing lip, which is used to anchor it in a somewhat complementary groove-like recess in the relevant surface area of the rotatable part. This fastening stud can also be provided with cross-sectionally projecting elevations, preferably hook-shaped or barb-like elevations. 
     Other features, characteristics, advantages, and actions based on the invention are given in the following description of a preferred embodiment of the invention, with reference to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show: 
         FIG. 1  a section through a ball bearing with a seal pursuant to the invention; 
         FIG. 2  the seal from  FIG. 1  in larger illustration; and 
         FIG. 3  another embodiment of the invention in an illustration corresponding to  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The ball bearing  1  in  FIG. 1  comprises two concentric rings that can be rotated in relation to one another. The outer ring  2  is shown on the left in  FIG. 1 , and the inner ring  3  on the right. Fastening bores  4 ,  5  parallel to the axis of rotation pass through both rings  2 ,  3 . Raceways for at least one row of ball-shaped rollers  7  are provided in the area of a gap  6  between the two rings  2 ,  3 , which permit the mutual rotation of the two rings  2 ,  3  as a single degree of freedom of motion. With the ball bearing  1 , faces  8 ,  9 , at the top in  FIG. 1 , are to be exposed to weathering. For this reason, the gap  6  between the two faces  8 ,  9  is sealed with a seal  10  pursuant to the invention. 
     As shown in  FIG. 2 , the seal  10  comprises a first sealing ring  11  and a second sealing ring  12 , each made of vulcanized material, for example vulcanized natural or synthetic rubber. The first sealing ring  11  is fastened to the outer ring  2 , and the second sealing ring  12  is fastened to the inner ring  3 . For this purpose, there is an encircling groove-like recess  13  in the face of the outer ring  2 , in which an annular extension  14  of the first sealing ring  11  engages; in the same way, there is a likewise encircling groove-like recess  16  in the envelope face  15  of the inner ring  3  facing the gap  6 , which serves to hold the annular extension  17  on the second sealing ring  12 . 
     The second sealing ring  12  fastened in this manner to the inner ring  3  carries an annular, relatively flat trough-like recess  18  on its face opposite the extension  17 , for example with a groove-like cross section. The encircling metal strip  19  is laid in this recess, which is wrapped around by the encircling edges of the trough  18  and is thereby prevented from shifting parallel to the axis of rotation of the rotary bearing  1 . 
     There is the sealing lip  21  of the first sealing ring  11  contacting the outside  20  of the metal strip  19 , opposite the trough  18 . The sealing lip  21  can be formed by an edge with an obtuse open angle, for example, an open angle between 90° and 150°. For this sealing lip  21  to be pressed firmly against the contact surface  20  of the metal strip  19 , even when the elasticity of the sealing ring  11  declines, the sealing lip  21  is positioned on the inside  22  of a somewhat sleeve-like section  23  of the outer sealing ring  11 . The radially outer envelope surface  24  of this sleeve-like section  23 , or the back  24  of the sealing ring  11  opposite the sealing lip  21 , is turned outward in the embodiment according to  FIGS. 1 and 2 , so that the correct position of the sealing lip  21  can be easily inspected for the position of its back  24 . 
     This sleeve-like section  23  at its radially outer envelope surface  24  is also provided with an encircling trough  25  in which the metal spring  26  is laid, which is intended to press the sleeve-like section  23 , and with it the sealing lip  21 , on it constantly against the metal strip  19 . The spring element  26  is preferably a tension spring, optionally with a screw fitting to connect the two ends of the spring. Such an annular closed tension spring can produce maximum tensile stress. 
     The encircling fastening extension  14  is joined to an edge  27  of the trough  25  closest to the face  8  of the outer ring  2 . For this purpose, the edge  27  of the trough  25  is bent toward the face  8 . Two lateral shoulders  28 ,  29  opposite one another are supported on the edges of the groove-like recess  13  in the face  8 , while the extension  14  extends completely into this recess  13 . Since the bending  30  between the edge  27  of the trough  25  and the extension  14  grips the metal spring  26 , in radially outer areas, it can exert a centering action on the metal spring  26  and thus also on the sealing lip  21  of the main seal  19 ,  21 . To lay, tighten, and/or replace the metal spring  26 , the trough  25 , together with the back  24  of the sealing ring  11 , is open toward the outside; the trough  25  is preferably not covered by any other part of the sealing ring  11 , so that the metal spring  26  is readily accessible from the outside. To protect against corrosion, the metal spring  26  should be made of a stainless material. 
     A second sealing lip  31  is provided in the area of the upper face of the sealing ring  11  exposed to the weather, which grips around the metal strip  19  on the outside and on top, and on the other side of it contacts the second, inner sealing ring  12  and is intended to keep pouring rain and other effects, for example impacts, away from the main seal  19 ,  21 . 
     A sealing lip  32  extending radially outward can also be provided on the second, inner sealing ring  12 , inside, i.e. below the trough  18  for the metal strip  19 , which is supported on an envelope face  33  of the outer bearing ring  2 , facing the gap  6 . This internal sealing lip  32 , like a third sealing ring  34  that may be provided even further inward, primarily serves to hold back the lubricating grease in the gap  6 . 
     The embodiment  110  according to  FIG. 3  differs from that of  FIGS. 1 and 2  only in that in this case the fastening extension  114  of the first sealing ring  111 , which engages in an encircling groove-like recess  113  in the face  108  of the outer ring  102 , is not connected to the edge  124  of the trough  125  for the metal spring  126  closest to the face  108 , but to the trough edge  135  further away from the face  108 , likewise by a bend  136 . Because of this, the metal spring  126  arrives at the cavity closed off by the main seal  119 ,  121 , and is also removed from external influences; neither is the back  124  of the sealing lip  121  turned outward, nor does it face the face  108  of outer ring  102 . In this embodiment, the metal spring  126  is replaced only together with the first sealing ring  111 ; in the embodiment according to  FIGS. 1 and 2 , it could also be replaced separately from the first sealing ring  11 .