Patent Publication Number: US-2023160433-A1

Title: Bearing unit with a sealing device

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
     This application is based on and claims priority to Italian Patent Application No. 102021000029606 filed on Nov. 24, 2021, under 35 U.S.C. § 119, the disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a bearing unit having a sealing device. Such a bearing unit may be suitable for use in manufacturing, and in particular in the agricultural sector, mining and for other heavy-duty applications featuring a dusty environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will now be described with reference to the appended drawings which show exemplary embodiments thereof, in which: 
         FIG.  1    is a cross sectional view of a bearing unit according to exemplary embodiments of the disclosure, 
         FIG.  2    is a detail view, on a larger scale, of the bearing unit of  FIG.  1   , 
         FIG.  3    is a detail view, on an even larger scale, of a detail of the bearing unit of  FIG.  1   , and 
         FIG.  4    is a cross-sectional view of a shaped screen of the bearing unit of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     In general, the bearing unit may have a first component, for example a radially outer ring, which is secured to a stationary element, generally a containment casing, and a second component, for example a radially inner ring, which is secured to a rotary element, typically a rotating shaft. In other applications, it may be that the radially inner ring is stationary while the radially outer ring is rotary. In any case, in rolling bearing units, the rotation of one ring with respect to the other is made possible by a plurality of rolling bodies which are positioned between the two surfaces of the components, referred to as raceways. The rolling bodies may be balls, cylindrical or conical rollers, needle rollers and similar rolling bodies. 
     Bearing units may have sealing devices to protect the raceways and rolling bodies from external contaminants and to create a seal with respect to lubricant. The sealing devices may have an elastomer seal co-molded on a first shaped metal screen mounted by interference or chamfer in a seat of the rings of the bearing unit, for example of the radially outer ring. The seal may have at least one sealing lip, contacting or non-contacting, which performs its sealing function by frictional contact with the other ring of the bearing unit or by a labyrinth formed with the ring. 
     A second metal screen with the function of protecting the seal and in any case constituting a first barrier against external contaminants may be mounted in an axially external position with respect to the seal. This second metal screen may be shaped and mounted by interference on the radially inner ring, which may be rotatable, and may face, with play, a radially internal surface of the radially outer ring. 
     Unlike other applications, the bearing units used for agricultural applications often only have the seal and do not use the axially external second metal screen. This is because, in agricultural applications, plant fibers often get in between the second screen and the seal to the extent that the screen comes off the bearing unit, directly exposing the seals to the action of contaminants. The ingress of plant fibers into the space between the second screen and the seal can be prevented if the second screen is also housed in a seat of the radially outer ring in a position closer to the seal. However, this arrangement is not feasible since the production process and the axial play of the bearing cannot guarantee that there is always a minimum distance between the screen and the seal: in such a case, therefore, there is the risk of contact between the screen and the seal. 
     Therefore, for agricultural applications only the seals may be used, the performance of which is enhanced through the use of a greater number of sealing lips, for example five. However, as well as increasing the axial space requirement, this arrangement also leaves the seal directly exposed to contaminants. 
     In any case, regardless of whether use is made of a standard sealing device—seal and screen—or only the seal with a greater number of sealing lips, a further drawback is encountered in applications, for example in mining, in which performance is validated by passing a test specially developed for this type of application known as “Sand&amp;Stone”. During such a test it is often found that the seals are damaged by being hit by stone chippings, to the extent that they become deformed and are no longer able to perform their protective function. 
     Various embodiments of the present disclosure increase the protection for the bearing unit, i.e., providing the bearing unit with a protection disk, which is suitable in particular for agricultural applications but also for all other applications operating in dusty external environments, for example in the mining industry. This disk may include a screen and an elastomer coating having two lips, may be axially external with respect to the sealing device and may be in contact with an axially external surface of the radially outer ring through the elastomer coating. 
     With reference to  FIG.  1   , a bearing unit for use in the agricultural or mining sector may include a stationary radially outer ring  31 , a radially inner ring  33 , rotatable with respect to a central rotation axis X of the bearing unit  10 , and rigidly secured to a rotating shaft  45  by an eccentric locking collar  47  or other securing means, for example socket screws, a row of rolling bodies  32 , in this example balls, interposed between the radially outer ring  31  and the radially inner ring  33  to allow them to rotate relative to one another, and a casing  40 , inside which the rings of the bearing unit  10  are housed. 
     Throughout the present description and the claims, terms and expressions indicating positions and orientations such as “radial” and “axial” are intended with reference to the rotation axis X of the bearing unit  10 . 
     For simplicity, the reference sign  32  designates both individual rolling bodies and the row of rolling bodies. Again for simplicity, the term “ball” may be used by way of example in the present description and in the attached drawings instead of the more generic term “rolling body” (with the same numerical references also being used). Some embodiments and the related drawings may use rolling bodies other than balls, without this departing from the scope of the present disclosure. 
     The bearing unit  10  may also include a sealing device  50 , which may include an elastomer seal co-molded on a shaped metal screen mounted by interference in a seat of the radially outer ring and having a plurality of sealing lips. 
     According to the present disclosure and with reference also to  FIGS.  2  and  3   , the bearing unit  10  may have a protection disk  55 , mounted in an axially external position to the sealing device  50 , and may include a screen  60  shaped and made of metallic material, and an elastomer coating  70  over-molded on part of the screen  60 . The screen  60  may be fixed to the radially inner ring  33  by coupling by interference between a radially internal cylindrical surface  61 ′ of the screen  60  and a radially external cylindrical surface  33 ′ of the radially inner ring  33 . The disk  55  may provide additional protection against external contaminants while at the same time protecting the sealing device  50  or sealing devices of different configuration. 
     With reference to  FIG.  4   , the screen  60  may include cylindrical portion  61 , radially internal, which may include the surface  61 ′ and, therefore, the coupling by interference with the radially inner ring  33 , and a distal portion  62  oblique in a radially external and axially internal direction. Screen  60  may further include a first flange portion  63  steadily connected to the distal portion  62 , a second flange portion  64 , steadily connected to the cylindrical portion  61 , and an oblique portion  65  for connection between the two flange portions  63 ,  64 . 
     To prevent plant fibers from getting in between the disk  55  and the sealing device  50 , the protection disk  55  may be in contact with an axially external surface  31 ′ of the radially outer ring  31 , and this contact takes place via the elastomer coating  70 , which is over-molded, in particular, on the distal portion  62 . The elastomer coating  70  may be provided with two lips, a first lip  71 , non-contacting or contacting and radially external, and a second lip  72 , contacting and radially internal. 
     The first lip  71  may be delimited axially by an annular surface  71   a , which defines a channel  71 ′ with the axially external surface  31 ′ of the radially outer ring  31 . This channel  71 ′ forms a labyrinth seal, thereby increasing the protection of the bearing unit. The value of the axial width of the channel  71 ′, in other words, the value of the meatus g between the first lip  71  and the surface  31 ′, in nominal conditions may be equal to 0.06 mm. Considering the axial play of the components of the bearing unit, the positioning tolerances of the disk  55  with respect to the bearing unit  10 , and the extent to which the second lip  72  deforms on mounting, as will be explained in more detail below, the first lip  71  may come into frictional contact with the surface  31 ′ of the radially outer ring  31 , or interference, albeit only slight, may be created between the first lip  71  and the surface  31 ′. 
     Alternatively, again considering the above, the first lip  71  may also possibly move away from the surface  31 ′, thus increasing the value of the meatus g. The bearing unit provides that the meatus g, or the axial width of the channel  71 ′, may not exceed, under extreme conditions of axial play between the components of the bearing unit, a value equal to 0.2 mm, in order to continue to ensure the labyrinth seal effect. 
     The lips  71  and  72  may also be delimited radially by a radially external conical surface  71   b  and, respectively, by a radially internal conical surface  72   b  which are parallel to one another and inclined with respect to the rotation axis X of the bearing unit by an angle with dimensions equal to the dimensions of an angle of inclination of the oblique distal portion  62 . The inclination of the distal portion  62  and of the lips  71 ,  72 , in a radially external and axially internal direction, is such as to encourage contaminants which hit against the disk  55  to return to the outside. 
     The protection disk  55  may be located in a radially internal position with respect to a radially internal spherical surface  41  of the casing  40 . Since the disk  55  is covered by the casing, this further reduces the risk of plant fibers getting in between the disk  55  and the sealing device  50 . 
     The second lip  72 , radially internal with respect to the first lip  71 , may be a lip contacting the surface  31 ′ of the radially outer ring. The lip  72  is delimited axially by an annular edge  72   a  which extends axially beyond the annular surface  71   a  of the lip  71  so as to come into contact with the surface  31 ′ preventing contact of the lip  71 . The lip  72  is shown in a non-deformed configuration in which, in use, the annular edge  72   a  tends to be compressed axially. In other words, the annular edge  72   a  collapses on itself, allowing the annular surface  71   a  of the upper first lip  71  to move closer, this surface  71   a  always being perpendicular to the rotation axis X of the bearing unit  10 . The value of the meatus g of the channel  71 ′ also depends on the extent to which the second lip  72  deforms on mounting. 
     The second lip  72  may provide the bearing unit with additional protection. The value of interference between the second lip  72  and the surface  31 ′ will also depend on the axial play between the components of the bearing unit and on the positioning tolerances of the disk  55  with respect to the bearing unit  10 . Therefore, the bearing unit according to various embodiments provides for a minimum interference of 0.1 mm in the worst combination of the tolerances. The presence of a further contacting lip slightly increases the friction torque of the bearing unit, although to a negligible degree with respect to the existing friction torque generated by the sealing device  50 , and therefore has a negligible effect on the performance of the bearing unit. 
     The particular geometry of the screen  60  and of the elastomer coating  70  may result in the formation of two chambers. A first chamber  73  is radially compressed between the first lip  71  and the second lip  72  of the elastomer coating  70 . More specifically, the first chamber  73  is delimited by a radially internal conical surface  71   c  of the first lip  71 , by a radially external conical surface  72   c  of the second lip  72  (forming between them an angle α of the order of 105°) and by the surface  31 ′ of the radially outer ring  31 . The axial width a of the first chamber  73  is between 0.25 mm and 0.55 mm, greater than the meatus g of the channel  71 ′ and therefore this first chamber  73  does not constitute a labyrinth seal but rather a volume for accumulation of lubricating grease. 
     A second chamber  74  may be formed between the disk  55  and the sealing device  50 , radially internal with respect to the second lip  72 . These two chambers act as a volume for accumulation of lubricating grease which creates a further barrier to the ingress of contaminants from the external environment. The presence of lubricating grease in both chambers is also useful as it lubricates the contact lips  71 ,  72 . Due to the effect of the centrifugal forces, in the event of loss of grease, this grease may emerge in a radially external direction and escape the first chamber  73  of the external contaminant. Because the first lip  71  may have a small meatus (or in any case a small interference) with the surface  31 ′ of the radially outer ring  31 , with respect to the greater interference of the second lip  72  with the surface  31 ′, it will be easier for contaminants and grease to get out of the first chamber  73  than the second chamber  74 . Therefore, the function of retention of grease is important as the latter, with the aid of the geometry defined by the two lips  71 ,  72 , may block the external contaminant in the first chamber  73 , preventing it from getting as far as the second chamber  74 , thus effectively protecting the sealing device  50  of the bearing unit  10 . 
     The disk  55  is provided with a further feature of the bearing unit  10 . As shown in  FIG.  2   , the radially outer ring  31  may have a spherical surface  31 ″, radially external and in contact with the casing  41 . Thus, the bearing unit  10  may rotate inside the spherical surface  41  of the casing  40 . Typically, this rotation is of the order of ±2° . In  FIG.  3    it can be seen that a third chamber  75  is created between the first lip  71  and the spherical surface  41 . If rotation is clockwise, as shown in  FIG.  3   , this third chamber  75  is restricted and tends to become a further labyrinth with a radial meatus of the order of 0.3 mm. 
     With reference to  FIG.  4   , the thickness s of the screen  60  may have a value greater than the value of the thickness of known screens. In particular, compared to a standard value of 0.5 mm, the thickness s may have values in a range between 0.75 mm and 0.85 mm. This value may be equal to 0.8 mm with an increase of 60% with respect to the thickness of known screens. 
     The increase in thickness makes the screen  60  much more rigid and thus more resistant to the effect of the plant fibers that try to get in between the screen  60  and the seal  50 . The greater thickness is also beneficial for anchoring with the radially inner ring. 
     The rigidity of the screen  60  may be further increased due to the presence of the oblique portion  65  which connects the two flange portions  63 ,  64 . 
     The shape of the distal portion  62  of the screen  60 , this distal portion having a limited length, may also increase the rigidity of the screen  60 , as well as of the elastomer coating  70 . 
     As stated above, agricultural applications provide for sealing devices  50  which use a greater number of sealing lips, for example five. Since such sealing devices may have a bigger axial space requirement, an axially external protection disk of known type would not be mountable on the radially inner ring as it would interfere with the locking collar  47  or with other systems for securing the radially inner ring to the shaft. For this reason, the screen  60  of the disk  55  may be configured to have an anchoring length  1  between the cylindrical surface  61 ′ of the screen  60  and the homologous cylindrical surface  33 ′ of the radially inner ring  33  that is smaller than the anchoring lengths used in known screens. In particular, compared to a standard value of 3 mm, the anchoring length  1  may assume values in a range between 2.3 mm and 2.5 mm. This value may be equal to 2.4 mm with a reduction of 20% with respect to the anchoring length of known screens. 
     The reduction in the anchoring length may be compensated for by, the screen  60  which may have a reinforced thickness and is thus more rigid than known screens. Anchoring may also be provided by a greater interference of 0.1 mm between the screen  60  and the radially inner ring  33 . This is obtained by reducing by 0.2 mm the value of the diameter d of the cylindrical surface  61 ′ of the screen  60 . The value of the total diametral interference, with respect to the prior art, may be between 0.15 mm and 0.25 mm. 
     The geometry of the screen  60  in the area of anchoring to the radially inner ring  33  may form a further channel  76  between the second flange portion  64  of the screen and the sealing device  50 . This channel  76  creates another labyrinth seal for protecting the bearing unit. The value of the axial width of the channel  76 , in other words the value of the meatus h between the first lip  71  and the surface  31 ′, in nominal conditions may be between 0.3 mm and 0.4 mm, while the design of the bearing unit may provide for a meatus h not smaller than 0.2 mm in the worst combination of tolerances involved. 
     By virtue of the abovementioned features, this innovative disk  55  coupled to the sealing device  50  may be suitable for the aims of the present disclosure. On the one hand it ensures greater protection for the sealing device, while on the other, due to its geometry, it makes it possible to increase the length of the labyrinth as a whole—in sequence, chamber  75 , channel  71 ′, chamber  73 , chamber  74 , channel  76 —for the ingress of contaminants into the bearing unit compared to a standard solution without a disk  55  and may include only the sealing device  50 . 
     Note that, in addition to the embodiments of the disclosure described above, many other variants exist. It may also be understood that these embodiments are simply examples and do not limit the subject matter of the disclosure or its applications or its possible configurations. On the contrary, although the description above makes it possible for a person skilled in the art to implement the present disclosure at least according to one exemplary configuration thereof, it may be understood that many variations of the components described may be envisaged without thereby exceeding the subject matter of the disclosure as defined in the attached claims, interpreted literally and/or according to their legal equivalents.