BEARING UNIT

A bearing unit (10) has radially outer and inner rings (31), (33), rolling bodies (32), a cage (34) containing the rolling bodies, and two sealing devices (35) arranged axially on opposite sides of the bearing unit (10) and interposed between the radially inner ring (33) and the radially outer ring (31). Each sealing device (35) is provided with first shield (40) and a second shield (50). The first shield (40) is sealed, axially inwards, against a support surface (31′) of the radially outer ring (31) and is stably inserted in a first seat (31a) of the radially outer ring (31). The second shield (50) is interference fitted on a radially outer surface (33a) of the radially inner ring (33) and axially outside the first shield (40). The first and second shields (40), (50) generate a tortuous path (P) therebetween to hinder the ingress of contaminants into the bearing unit (10).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Italian Application No. 102023000002274, filed Feb. 10, 2023, the entirety of which is hereby incorporated by reference.

FIELD

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.

BACKGROUND

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 toFIG.1, the bearing unit1usually has a first component, for example a radially outer ring2, that is fastened to a rotary element, and a second component, for example a radially inner ring3, that is fastened to a stationary element. As is known, it is often the case that the radially inner ring is rotary whereas the radially outer ring is stationary, although in other applications, such as that described, the outer ring rotates (in the marble sector, rotation speeds are typically around 750 rpm) while the inner ring is stationary. In any case, the rotation of one ring in relation to the other inside the roller bearing units is enabled by a plurality of rolling bodies4that are positioned between the cylindrical surface of one component and the cylindrical surface of the second component, normally referred to as raceways. The rolling bodies may be balls, cylindrical or conical rollers, needle rollers, and similar rolling bodies.

It is also known for bearing units to have sealing devices5to 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.

SUMMARY

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.

DETAILED DESCRIPTION

InFIG.2, reference sign10denotes a bearing unit as a whole for use in the marble cutting sector, and that comprises:a radially outer ring31that is rotary about a central axis of rotation X of the bearing unit10, provided with a raceway31r,a stationary radially inner ring33provided with a raceway33r,a row of rolling bodies32, in this example balls, interposed between the radially outer ring31and the radially inner ring33to enable relative rotation,a cage34for containing the rolling bodies to hold the rolling bodies of the row of rolling bodies32in position.

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 unit10.

The bearing unit10is also provided with two sealing devices35arranged axially on opposite sides of the bearing unit10, to seal said unit from the external environment.

With reference toFIG.3, the sealing device35is interposed between the radially inner ring33and the radially outer ring31and comprises:a first shield40sealed, axially inwards, against a support surface31′ of the radially outer ring31and stably inserted in a first seat31aof the radially outer ring31, anda second shield50interference fitted on a radially outer surface33aof the radially inner ring33and axially outside the first shield40.

The first and second shields may be made of metal or composite material.

The first shield40is in turn provided with:a radially outer first flange portion41stably inserted in the first seat31aof the radially outer ring31,a radially inner second flange portion42,an annular central portion43,a frustoconical first connecting portion44connecting the first flange portion41to the central portion43, anda frustoconical second connecting portion45connecting the second flange portion42to the central portion43.

The first shield40therefore creates a radially outer axial seal between the first flange portion41and the support surface31′ of the radially outer ring31.

The first shield40is held in a stable position in the first seat31aby an anchoring element60, which may be an elastic ring60made of metal, for example a Seeger ring, and is interference fitted in a second seat31bof the radially outer ring31, axially outside the first seat31ato axially press the first shield40, in particular the first flange portion41thereof, towards the surface31′ of the outer ring31.

The second shield50is in turn provided with:a frustoconical, radially outer first flange portion51, radially facing the anchoring element60and radially and axially facing the first connecting portion44of the first shield40on the outside,an annular central portion52, axially facing the central portion43of the first shield40on the outside,a radially inner second flange portion53, axially facing the second flange portion42of the first shield40on the outside,a frustoconical connecting portion54connecting the second flange portion53to the central portion52and axially facing the second connecting portion45of the first shield40on the outside, anda radially inner cylindrical portion55interference fitted on the radially outer surface33aof the radially inner ring33.

To accommodate the second shield50such that it can be interference fitted on the radially inner ring33, the latter has a toroidal recess33c,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 inFIG.1, the axial depth does not need to be changed, whereas the radial height is slightly increased. In any case, the recess33cis not at all problematic from a structural perspective, on the basis of practical experience with the known solution and considering the fact that the material removed to form the recess33cis material that is not affected by the loads transmitted by the rolling bodies32to the raceway33r.

Essentially, the second shield50creates a radially inner radial seal between the cylindrical portion55and the radially outer surface33aof the radially inner ring33.

Furthermore, according to the present disclosure, the second shield50, which is designed to match practically the entire geometry of the first shield40and is shifted axially outwards therefrom, creates a labyrinth or a tortuous path P inside the first shield40and the second shield50that 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:a first stretch P1arranged radially between the anchoring element60and the first flange portion51of the second shield50. It should be noted that, in addition to the narrow section created between these two components, the centrifugal effects caused by the relative rotation of the first shield40(rotary) relative to the second shield50(stationary) also further hinder the ingress of contaminants into the tortuous path P,a second stretch P2axially interposed between the first shield40and the second shield50,a third stretch P3radially interposed between the second flange portion42of the first shield40and the cylindrical portion55of the second shield50. In this stretch, the tolerances of the radial clearance between the components of the bearing unit, as explained in greater detail below, make it possible to define a very narrow section in this third stretch P3,a fourth stretch P4axially interposed between the first shield40(in particular the second flange portion42thereof) and the radially inner ring33(in particular an axially outer surface33bthereof).

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 unit10as much as possible. The addition of the second shield50nearly triples the length of the labyrinth compared to other known solutions (for example the solution inFIG.1). For a specific application, for example, the length of the labyrinth is increased from 5 mm (known solution inFIG.1) to more than 15 mm in the present solution (FIGS.2and3) with a percentage increase of more than 300%. This improves the protection of the bearing unit against contaminants, and consequently the service life of said bearing unit.

Furthermore, since neither the first shield40nor the second shield50have any sliding contact with one another or with other components of the bearing unit (the second shield50is stationary and is separated from both the first shield40and the anchoring element60), 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 shield40and the second shield50is ensured by providing an axial distance Da not less than 0.8 mm therebetween in the second stretch P2of 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 P3of the tortuous path P. In this case, the minimum radial distance Dr between the second flange portion42of the first shield40and the cylindrical portion55of the second shield50may 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 shield40) are very precise.

In the first stretch P1of the tortuous path P, the minimum distance Dm between the anchoring element60and the first flange portion51of the second shield50is between 0.8 mm and 0.9 mm.

This minimum distance ensures that there is no contact between the anchoring element60and the second shield50, 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 shield50, it is possible to reduce this minimum distance Dm to zero by creating a small contact zone between the anchoring element60and the second shield50. Consequently, in this embodiment, the second shield50can also be used to retain the anchoring element60in its seat31b,to prevent disassembly of the anchoring element60. This is an important function since the functionality of the first shield40, 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 shield50(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 element60from 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 portion51of the second shield50, 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 portion51of the second shield50in 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 P4of the tortuous path P, the axial distance between the second flange portion42of the first shield40and the surface33bof the radially inner ring33is 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 P4with no risk of contact between the two components involved, even under unfavourable clearance and tolerance conditions.

The first shield40has the shape described above (a central portion43and two connecting portions44,45) to match the profile of the containment cage34axially towards the outside. This feature enables optimization of the space in the axial direction to accommodate the second shield50without adversely affecting the axial size of the bearing unit as a whole.

Furthermore, the frustoconical portions44,45increase the rigidity of the first shield40so as to minimize any bending of the first shield40that 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 unit10by an end user. Indeed, the second shield50is 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 element60, for example a Seeger ring, has the advantage of enabling the independent disassembly of the Seeger ring and of the first shield40, insertion of new lubricant into the bearing unit10, and subsequent reassembly.

Returning to the second shield50, 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 shield50is 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 shield50to 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.