Patent Application
20240271664
This application claims priority to Italian Application No. 102023000002274, filed Feb. 10, 2023, the entirety of which is hereby incorporated by reference.
The present disclosure relates to a bearing unit. Said bearing unit is suitable for use in the manufacturing sector, in particular for use in the marble cutting sector.
In the manufacturing sector, and in particular in applications in the marble cutting sector, known bearing units have to have very limited axial dimensions as they are assembled axially side by side, and said size limit creates the need for technical solutions that are particularly sophisticated or even expensive in terms of the components used, which have to be high performance despite their small axial size.
In the context described above and with reference to
It is also known for bearing units to have sealing devices 5 to protect against external contaminants and to seal the lubricating grease. Typically, the sealing devices are made up of a shaped shield interference fitted in a seat in the rings of the bearing unit, for example the radially outer ring, and are made of metal or plastic, for example PTFE, or composite material.
The shaped shield is designed to create an axial seal with the radially outer ring and a labyrinth seal with the radially inner ring.
This solution, which belongs to the applicant, has given satisfactory results. In any case, it should be noted that the sealing devices for these applications must be high performance, both in terms of function and in terms of reliability, throughout the service life of the bearing unit.
In this regard, for example, the sealing devices must not deteriorate over time and must always remain in their seat, otherwise their functionality is entirely lost.
In terms of functionality, it should be noted that the marble sector is a particularly demanding application for bearing units, with different types of contaminants in notable quantities, including water, marble dust (specifically a white calcium carbonate dust) and diamond dust from the marble cutting tools (typically diamond wires).
The sealing devices must therefore provide excellent functional performance. This task is made even more challenging because the aforementioned known bearing units are not only axially thin, but also have rather large diameters, which makes it even more technically complex to find solutions for the related sealing devices, which tend to wave and/or undulate and/or sag in relation to planes transverse to the axis of rotation by up to several centimetres as a result of these axial dimensions, further emphasizing the aforementioned problem of the large volume of contaminants.
The present disclosure is therefore intended to provide a bearing unit that does not have the drawbacks described above. This objective is achieved by a novel component of the sealing device that helps to define a highly efficient labyrinth seal for the bearing units in marble cutting machines.
The present disclosure provides a bearing unit having the features set out in the attached claims.
The present disclosure is described below with reference to the attached drawings, which show some non-limiting example embodiments of the bearing unit, in which:
In
Throughout the present description and in the claims, terms and expressions indicating positions and orientations, such as “radial” and “axial”, should be understood with reference to the axis of rotation X of the bearing unit 10.
The bearing unit 10 is also provided with two sealing devices 35 arranged axially on opposite sides of the bearing unit 10, to seal said unit from the external environment.
With reference to
The first and second shields may be made of metal or composite material.
The first shield 40 is in turn provided with:
The first shield 40 therefore creates a radially outer axial seal between the first flange portion 41 and the support surface 31′ of the radially outer ring 31.
The first shield 40 is held in a stable position in the first seat 31a by an anchoring element 60, which may be an elastic ring 60 made of metal, for example a Seeger ring, and is interference fitted in a second seat 31b of the radially outer ring 31, axially outside the first seat 31a to axially press the first shield 40, in particular the first flange portion 41 thereof, towards the surface 31′ of the outer ring 31.
The second shield 50 is in turn provided with:
To accommodate the second shield 50 such that it can be interference fitted on the radially inner ring 33, the latter has a toroidal recess 33c, the dimensions of which can be defined by a depth Pa in the axial direction and by a height Hr in the radial direction. Compared to other known solutions, for example the solution in
Essentially, the second shield 50 creates a radially inner radial seal between the cylindrical portion 55 and the radially outer surface 33a of the radially inner ring 33.
Furthermore, according to the present disclosure, the second shield 50, which is designed to match practically the entire geometry of the first shield 40 and is shifted axially outwards therefrom, creates a labyrinth or a tortuous path P inside the first shield 40 and the second shield 50 that hinders the ingress of contaminants into the bearing unit.
In particular, following the direction of travel of any contaminant wedged in the tortuous path P (direction indicated in the figure by the arrows along the path P), some noteworthy stretches of said path can be highlighted:
This tortuous path P therefore becomes very long and defines a labyrinth that is particularly advantageous for preventing the ingress of contaminants into the bearing unit 10 as much as possible. The addition of the second shield 50 nearly triples the length of the labyrinth compared to other known solutions (for example the solution in
Furthermore, since neither the first shield 40 nor the second shield 50 have any sliding contact with one another or with other components of the bearing unit (the second shield 50 is stationary and is separated from both the first shield 40 and the anchoring element 60), the improved protection of the bearing unit against contaminants does not have any adverse effects in terms of friction losses.
In particular, the absence of any contact between the first shield 40 and the second shield 50 is ensured by providing an axial distance Da not less than 0.8 mm therebetween in the second stretch P2 of the tortuous path P. This distance ensures that there is no contact between the two shields, even under the worst axial-clearance conditions.
Another zone in which the two shields are prevented from coming into contact is the third stretch P3 of the tortuous path P. In this case, the minimum radial distance Dr between the second flange portion 42 of the first shield 40 and the cylindrical portion 55 of the second shield 50 may be equal to 0.3 mm. This value is much lower than the value of the axial distance Da since the radial clearance is ten times less than the axial clearance and the tolerances of the components during assembly (in particular the tolerances of the first shield 40) are very precise.
In the first stretch P1 of the tortuous path P, the minimum distance Dm between the anchoring element 60 and the first flange portion 51 of the second shield 50 is between 0.8 mm and 0.9 mm.
This minimum distance ensures that there is no contact between the anchoring element 60 and the second shield 50, and simultaneously increases the protection of the tortuous path P by creating a further narrow section at the entrance thereof.
Alternatively, by using a composite material for the second shield 50, it is possible to reduce this minimum distance Dm to zero by creating a small contact zone between the anchoring element 60 and the second shield 50. Consequently, in this embodiment, the second shield 50 can also be used to retain the anchoring element 60 in its seat 31b, to prevent disassembly of the anchoring element 60. This is an important function since the functionality of the first shield 40, and consequently the reliability of the bearing unit as a whole, would be adversely affected if the anchoring element came out of its seat. On the other hand, contact between the two components would not create any problems if at least one component is made of composite material. There may be a small amount of wear on the second shield 50 (composite material is obviously less hard than metal), which would reduce local contact between the two components to zero. This would not however affect the function of preventing the anchoring element 60 from accidentally coming out of its seat.
In any case, in addition to having a narrow section of distance Dm, the ingress of external contaminants into the tortuous path P is further hindered by the frustoconical shape of the first flange portion 51 of the second shield 50, which acts as a deflector, preventing contaminants from entering the tortuous path P. Indeed, in applications in the marble sector, the bearing units in machines for cutting marble are assembled closely together, in a number of the order of 80 to 100 bearing units. In particular, the radially inner rings (stationary) are butted against one another, whereas there is a small amount of clearance between the mutually adjacent radially outer rings (rotary). Since external contaminants can only enter through the space between two adjacent outer rings, the frustoconical shape of the first flange portion 51 of the second shield 50 in cooperation with the same mirrored shape of the adjacent shield creates a sort of convergent channel that conveys the contaminants towards the inner ring and in any case away from the tortuous path P.
Having regard to the fourth stretch P4 of the tortuous path P, the axial distance between the second flange portion 42 of the first shield 40 and the surface 33b of the radially inner ring 33 is approximately 0.4 mm, this value already being in use in other known solutions and being known to provide a narrow section in the stretch P4 with no risk of contact between the two components involved, even under unfavourable clearance and tolerance conditions.
The first shield 40 has the shape described above (a central portion 43 and two connecting portions 44, 45) to match the profile of the containment cage 34 axially towards the outside. This feature enables optimization of the space in the axial direction to accommodate the second shield 50 without adversely affecting the axial size of the bearing unit as a whole.
Furthermore, the frustoconical portions 44, 45 increase the rigidity of the first shield 40 so as to minimize any bending of the first shield 40 that could occur in the most demanding applications.
The adopted solution does not have any drawbacks, including any related to the disassembly and reassembly of the bearing unit 10 by an end user. Indeed, the second shield 50 is assembled with an interference of between 0.05 mm and 0.15 mm. This is therefore a very low interference that enables easy disassembly and reassembly by the end user. Furthermore, the use of an anchoring element 60, for example a Seeger ring, has the advantage of enabling the independent disassembly of the Seeger ring and of the first shield 40, insertion of new lubricant into the bearing unit 10, and subsequent reassembly.
Returning to the second shield 50, the assembly interference can be low because, in marble working applications, the radially inner ring is stationary and the radially outer ring is rotary. As already seen, this means that the second shield 50 is a stationary component that is not in contact with other components. Given that the contaminants in this specific application are water and dust, it is not necessary for the second shield 50 to have specific hardness and mechanical strength features. Furthermore, excessively high interference would make it difficult to disassemble the second shield without permanently deforming the structure thereof.
In short, the sealing device according to the present disclosure improves the protection of the bearing unit against external contaminants, and consequently the service life of said bearing unit, without creating drawbacks in terms of friction losses or the possibility of simple disassembly and reassembly of the bearing unit.
Numerous other variants exist in addition to the embodiments of the present disclosure described above. These embodiments should also be understood to be examples and do not limit the scope, applications or possible configurations of the present disclosure. Indeed, although the description provided above enables the person skilled in the art to carry out the present disclosure at least according to one example configuration thereof, numerous variations of the components described could be used without thereby departing from the scope of the present disclosure, as defined in the attached claims interpreted literally and/or according to their legal equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023000002274 | Feb 2023 | IT | national |
