Thin section bearing unit

Abstract

A thin section bearing unit (10) for multiwire machines, the bearing unit having a central axis (A) of rotation and comprising: - a stationary inner ring (20); - a rotatable flanged outer ring (30), with axial dimensions smaller than an axial dimension of the inner ring (20); - a first (41) and a second row (42) of rolling elements (40) axially close to each other, in which an axial distance (D2) between the first row (41) of rolling elements (40) and the second row (42) of rolling elements (40) is between 0.8 mm and 0.9 mm; - a first (43) and a second cage (44) for retaining the rolling elements (40) of the respective first (41) and second row (42), the cages (43, 44) being made of plastic material and configured to retain the rolling elements (40) on one side only of the respective row (41, 42) of rolling elements; - only two sealing screens (50, 50') arranged on the axially opposite sides of the bearing unit (10) and placed between the inner ring (20) and the outer ring (30).

Description

[0001] THIN SECTION BEARING UNIT

[0002] DE S CRIP T I ON

[0003] Technical Field of the Invention

[0004] The present invention relates to a thin section bearing unit.

[0005] In particular, the present invention relates to a thin section bearing unit for multiwire machines, to which the present description will refer without this undermining its general applicability.

[0006] Prior art

[0007] In multiwire machines, blocks of stony material, such as stone, marble, concrete and the like, are cut into slabs by the action of diamond cutting wires, which are positioned parallel to one another along a cutting path, and are drawn along this path by tensioner pulleys. In order to produce slabs of quite small thickness, the tensioner pulleys are assembled as a set, on a shared support shaft, one axially beside the other, and are rendered rotatable with respect to said support shaft by virtue of the interposition of respective thin section bearing units.

[0008] Known thin section bearing units for multiwire machines are, therefore, also mounted as a set, one beside the other along a respective shared central axis of rotation defined by the support shaft, and although their respective outside diameters are rather large, they must necessarily have a very small axial thickness to allow the tensioner pulleys to be axially mounted as close to one another as possible, while the combination of large diameters and small axial thicknesses requires particularly sophisticated technical solutions to ensure consistently high performance.

[0009] Such bearing units comprise:

[0010] - respective stationary inner rings, arranged axially right next to one another;

[0011] - respective rotatable outer rings, having an axial dimension slightly smaller than that of the related inner rings so as to be able to rotate independently of one another and allow independent rotation of the related tensioner pulleys;

[0012] - a row of rolling elements, preferably balls, placed between the inner ring and the outer ring to allow relative rotation thereof, wherein the rolling elements are held in position by a retention cage made of pressed steel which encloses the rolling elements on both axially opposite sides of the row; and

[0013] - respective sealing shields arranged on the axially opposite sides of the row of rolling elements and placed between the related inner and outer rings, both so as to prevent contaminating materials, for example water mixed with stone dust, from getting into said bearing units, and so as to prevent the outward dispersion of the internal lubricating grease. Each outer ring has a respective support flange connected to a related pulley, while each inner ring is delimited laterally by respective annular surfaces placed directly in contact with the annular surfaces of the inner rings of the axially adjacent bearing units.

[0014] Reduction of the axial thickness of these bearing units is a primary objective of solutions designed for multiwire machines as each bearing unit corresponds to a pulley and each pulley corresponds to a diamond wire. This means that any further reduction in the axial thickness of the bearing unit makes it possible to correspondingly reduce the axial bulk of the pulley and, consequently, the centre-to-centre distance between the diamond wires. Ultimately, a further reduction in the axial thickness of the bearing units would make it possible to produce slabs of stony material of increasingly slender thickness.

[0015] A reduction in the axial thickness of the bearing unit does however mean reducing the diameter of the rolling elements and therefore the load capacity of the bearing unit. Summary of the Invention

[0016] It is an aim of the present invention to produce a thin section bearing unit which solves the abovementioned drawbacks, entirely to the benefit of the production efficiency of the related multiwire machines.

[0017] A thin section bearing unit for multiwire machines according to the present invention has the features set out in the attached claims.

[0018] Brief Description of the Drawings

[0019] The invention will now be described with reference to the attached drawings, which illustrate a non-limiting embodiment of the invention, in which:

[0020] - figure 1 shows, in cross section, a thin section bearing unit according to a preferred embodiment of the present invention,

[0021] - figure 2 is a perspective view of a retention cage of the bearing unit of figure 1, - figure 3 shows, in cross section and on an enlarged scale, a detail of the bearing unit of figure 1, and

[0022] - figure 4 is a view in partial cross section of a multiwire machine comprising the thin section bearing unit of figure 1.

[0023] Detailed Description

[0024] With reference to figure 1, the reference numeral 10 generally designates a bearing unit having a thin section.

[0025] The bearing unit 10 takes up very little space axially such that it can be mounted, together with other identical bearing units, in an idler unit of a multiwire machine, wherein the idler unit may include from two to more than one hundred (for example, from thirty to one hundred and fifteen) bearing units 10, all identical to one another and placed side by side along a respective shared central axis of rotation A.

[0026] The thin section bearing unit 10 of the present invention may advantageously be used in multiwire machines, to which the following description will refer, by way of example, without this undermining its general applicability. In such multiwire machines, blocks of stony material are cut into slabs by the action of diamond cutting wires, positioned parallel to one another along said blocks, and drawn across these blocks by tensioner pulleys 100. To produce these slabs, said tensioner pulleys are assembled as a set, one axially beside the other, on a shared support shaft (not shown) defining the central axis A, and are rendered rotatable with respect to the support shaft by virtue of the interposition of a respective bearing unit 10. Throughout the present description and in the claims, terms and expressions indicating positions and directions, such as “radial”, “axial” or “transverse”, are to be understood with reference to the axis A of rotation.

[0027] According to the present invention and as shown in figure 1, the bearing unit 10 comprises:

[0028] - a stationary inner ring 20, mounted on a stationary shaft of the multiwire machine (which is known, and therefore not shown in the figure);

[0029] - a rotatable flanged outer ring 30, having an axial thickness S2 of dimensions smaller than the axial dimensions of an axial thickness SI of the inner ring 20 and defining with the inner ring 20 a cylindrical cavity 90; - two rows 41, 42 of rolling elements 40;

[0030] - two cages 43 and 44 for retaining the rolling elements 40;

[0031] - two sealing shields 50, 50’ arranged on the axially opposite sides of the bearing unit 10 and placed between the inner ring 20 and the outer ring 30. There are only two sealing shields 50, 50’, not four as is the case, in the prior art, of a pair of bearing units with a single row of rolling elements in which respective sealing shields are arranged on the axially opposite sides of each row.

[0032] The inner ring 20 is provided with a first 22 and a second raceway 23, radially external, in which the rolling elements 40 of the respective first 41 and second row 42 roll. On each side L of the bearing unit 10, the inner ring 20 is axially delimited by two annular surfaces 21 and 21’ arranged in series from the outside of the bearing the unit 10 towards the axis A, the two surfaces 21’ being axially set back with respect to the surfaces 21. Furthermore, the inner ring 20 is delimited radially on the inside by a cylindrical surface 24, coaxial with the axis A and orthogonal to the two annular surfaces 21, and radially on the outside by a surface 25, which is also cylindrical, coaxial with the axis A and orthogonal to the two annular surfaces 21, which surface 25 includes the first 22 and the second raceway 23 of the inner ring 20.

[0033] The outer ring 30 is provided with a first 32 and a second raceway 33, radially internal, in which the rolling elements 40 of the respective first 41 and second row 42 roll. The raceways 32, 33 of the outer ring 30 are radially facing the respective raceways 22, 23 of the inner ring. Furthermore, the flanged outer ring 30, on each side L of the bearing unit 10, is axially delimited by an annular surface 34 orthogonal to the axis A. The flanged outer ring 30 is delimited radially on the outside by a cylindrical surface 35, coaxial with the axis A and orthogonal to the annular surface 34, and radially on the inside by a surface 36, which is also cylindrical, coaxial with the axis A and orthogonal to the annular surface 34, which surface 36 includes the first 32 and the second raceway 33 of the outer ring 30. The outer ring 30 also has a support flange 31, which extends radially outwards from said outer ring 30 transversely to the axis A and is connected to a relative radially internal portion 101 of a pulley 100 of the multiwire machine.

[0034] The two rows 41, 42 of rolling elements 40, preferably balls, are arranged inside the cavity 90 and placed between the inner ring 20 and the outer ring 30 to allow relative rotation thereof about the axis A. The rolling elements 40 have the same diameter as the rolling elements of known solutions, so as to have the same load capacity. Obviously, the total load that can be supported by the bearing unit 10 is equivalent to the load that can be supported by two bearing units of known type, i.e. with a single row of balls. In order to reduce the axial bulk of the bearing unit as far as possible, the first 41 and the second row 42 of rolling elements 40 are as close as possible to one another axially and therefore the axial distance D2 (shown in figure 3) between the first row 41 and the second row 42 is reduced to the minimum. At the same time, however, it is necessary to ensure that there is no interference between the rolling elements of the different rows. This trade-off (minimum axial distance / axial interference between rolling elements of two different rows) is achieved in the present invention by defining a range of admissible values for the axial distance D2 of between 0.8 mm and 0.9 mm.

[0035] The retention cages 43, 44, which are made of plastic material, retain the rolling elements in respective circumferential positions. They are designed to reduce the axial bulk of the bearing unit and have themselves limited axial and radial bulk. To be specific and with reference to figure 2, which shows the first cage 43 (the following description is also valid for the second cage 44, which is identical to and mirrors the first cage 43), each cage 43, 44 comprises, in turn, a frame 45 with a circular base and a plurality of tenons 46 which are integral with the frame, departing axially from it along a single direction (axially internal), are spaced circumferentially, and, in pairs, define between them a plurality of alveoli 47 to retain respective rolling elements. The fact that the tenons 46 depart from the frame 45 only in an axially internal direction and therefore retain the rolling elements on only one side of the row of rolling elements (whereas, as a reminder, in known solutions the retention cage of pressed steel encloses the rolling elements on both axially opposite sides of the row) makes it possible to reduce the axial bulk of the retention cages 43, 44. The base frame 45 is a continuous annular structural element, which extends circumferentially about the axis A, constitutes a solid base, and gives the cage as a whole the necessary rigidity to retain the rolling elements spaced apart from one another equidistantly. The base frame 45 is delimited radially inwards by a first cylindrical surface 45a, radially outwards by a second cylindrical surface 45b and axially by an annular surface 45c transverse to the axis A. The tenons 46, on the other hand, which contain and retain the rolling elements between them, must exhibit substantially elastic behaviour so that they can move apart to allow insertion of said balls, and then close up again substantially around the balls to retain them inside the related alveoli 47. The tenons 46 are spaced circumferentially and have a curved shape. Two circumferentially adjacent tenons 46 have respective concave surfaces 46’ facing one another and each alveolus 47 will be defined by a pair of circumferentially adjacent tenons 42.

[0036] Of the two sealing shields 50, 50’, a first sealing shield 50 is located axially outwards relative to the first row 41 of rolling elements 40 and a second sealing shield 50’ is located axially outwards relative to the second row 42 of rolling elements 40. The sealing shields 50, 50’ serve both to prevent contaminating materials, for example water mixed with stone dust, from getting into the cavity 90 of said bearing unit 10, and to prevent the outward dispersion of the lubricating grease contained inside the cavity 90. The sealing shields 50, 50’ are mounted on the outer ring 30 and, therefore, are themselves also rotatable.

[0037] With reference to figure 3, each sealing shield 50, 50’ comprises, in series from the outer ring 30 towards the axis A:

[0038] - a first flanged portion 51 mounted on the outer ring 30,

[0039] - an oblique portion 52, stably connected to the first flanged portion 51,

[0040] - a second flanged portion 53, stably connected to the oblique portion by means of its radially external edge 53b, and provided with an annular surface 53a, axially internal, and

[0041] - a cylindrical portion 54 which, interacting with the inner ring, defines a meatus which ostensibly acts as a labyrinth seal.

[0042] Since, in the bearing unit 10 according to the present invention, the diameter of the rolling elements is the same as in known solutions, so as not to be detrimental to the load capacity of the bearing unit, the design solutions described above and, for convenience, set out again and in detail below, are such that the axial thickness of this bearing unit is smaller than the sum of the axial thicknesses of a pair of bearing units with a single row of rolling elements, according to the prior art.

[0043] First of all, the bearing unit according to the invention requires only two sealing shields, whereas an equivalent known solution made up of two bearing units with a single row of balls, axially facing one another, requires four sealing shields overall (two per unit).

[0044] Compared to the equivalent known solution, the present solution therefore makes it possible to dispense with two sealing shields and, in this way, the overall axial thickness of the bearing unit 10, with a double row of rolling elements, may be reduced by the axial bulk of the two sealing shields that have not been used.

[0045] Dispensing with the two sealing shields does not compromise the efficiency in terms of sealing of the bearing unit 10: both of the axially opposite sides of the bearing unit 10 are protected by a sealing shield placed between the inner ring 20 and the outer ring 30, with a design unchanged with respect to the prior art, which has proved to be more than adequate. A further axial reduction in overall thickness is obtained by designing the cages 43, 44 such that the tenons 46 retain the rolling elements 40 on only one side of the row 41, 42 of rolling elements 41.

[0046] Moreover, a further two features of the present invention contribute to reducing the overall axial bulk of the bearing unit 10: a) the cages 43, 44 are designed such that their radial extension is smaller than the radial extension of the second flanged portion 53 of the sealing shields 50, 50’. In other words, the diameter of the second cylindrical surface 45b of the frame 45 of the cages 43, 44 is smaller than the diameter of a circumference passing through the edge 53b, radially external, of the second flanged portion 53 of the shields 50, 50’. This is obtained by making the cage 43, 44 asymmetrical with respect to a plane P tangential to the circumference C of the centers of the rolling elements 40. This prevents the cage 43, 44 from coming into contact with the oblique portion 52. It is therefore possible to place the cage 43, 44 axially close to the shield 50, 50’, in other words to minimize the axial distance DI between the annular surface 45c of the frame 45 of the cage 43, 44 and the annular surface 53a of the second flanged portion 53 of the shield 50, 50’; b) the oblique portion 52 of the sealing shields 50, 50’ has an axial projection whose length L is reduced to a minimum. At the same time, however, it is necessary to ensure the required rigidity of the shields 50, 50’ and therefore the oblique portion 52 is needed. This trade-off (minimum axial length of the oblique portion / sufficient rigidity of the shields) is achieved in the present invention by defining a range of admissible values for the length L of between 1.5 mm and 3 mm.

[0047] Dispensing with the two sealing shields, together with the other arrangements described, ensures a reduction in the axial bulk of the bearing unit 10 which is very considerable and equal to around 20% with respect to the axial thickness of the known solution.

[0048] Therefore, and with reference also to figure 4, compared to the known solution, the bearing unit 10 with a double row of rolling elements thus makes it possible to reduce the axial bulk for the same loading capacity. It is thus possible to provide a pulley 100 having substantially the same axial bulk of the bearing unit 10 and provided with a first channel 105 and a second channel 110 for receiving, in each one, a diamond wire (for the sake of simplicity, the diamond wires are not depicted but shown schematically by respective axes of symmetry X, X’). The centre-to-centre distance between the diamond wires of the pulley 100, and the centre-to-centre distance between diamond wires of adjacent pulleys, will thus be smaller than the centre-to-centre distance between diamond wires of the known solution (pair of bearing units with a single row of rolling elements). Therefore, the bearing unit 10 with a double row of rolling elements, according to the present invention, makes it possible to design multiwire machines with the capacity to produce slabs of stony material which are thinner than what can be obtained with known solutions.

[0049] This solution also improves the overall rigidity of the bearing unit, with respect to the rigidity of bearing units with a single row of rolling elements. Indeed, the oscillation of the outer ring 30 in the event of vibration caused by the multiwire machine is vastly reduced since the outer ring is supported by two rows of balls. This is because the solution with a double row of balls creates two points of contact on the inner ring and two points of contact on the outer ring. This results in a reduction in the maximum elastic deflection that the radially outermost point of the support flange 31 (and, therefore, of the pulley 100) can have with respect to the case of solutions with a single row of balls and a single point of contact per ring. The bearing unit according to the present invention is therefore much more rigid than the standard solution. Consequently, the cutting of stony material will be much more precise. To sum up, the solution according to the present invention, a bearing unit with a double row of balls with optimized geometry, makes it possible to reduce the thickness of the slabs of stony material and improve the precision of cutting of the slabs.

[0050] In addition to the embodiments of the invention as described above, it is to be understood that there are numerous other variants. It is also to be understood that said embodiments are merely examples and do not limit the subject matter of the invention, its applications, or its possible configurations. On the contrary, although the above description enables those skilled in the art to apply the present invention according to at least one exemplary configuration thereof, it is to be understood that numerous variations of the components described may be devised, without thereby departing from the subject matter of the invention as defined in the appended claims, interpreted literally and / or according to their legal equivalents.

Claims

C LAIM S1. Thin section bearing unit (10) for multiwire machines, the bearing unit having a central axis (A) of rotation and comprising:- a stationary inner ring (20);- a rotatable flanged outer ring (30), with axial dimensions smaller than an axial dimension of the inner ring (20); and the bearing unit (10) being characterized, in combination, by also comprising:- a first (41) and a second row (42) of rolling elements (40) axially close to each other, in which an axial distance (D2) between the first row (41) of rolling elements (40) and the second row (42) of rolling elements (40) is between 0.8 mm and 0.9 mm;- a first (43) and a second cage (44) for retaining the rolling elements (40) of the respective first (41) and second row (42), the cages (43, 44) being made of plastic material and configured to retain the rolling elements (40) on one side only of the respective ring (41, 42) of rolling elements;- only two sealing screens (50, 50') arranged on the axially opposite side of the bearing unit (10) and placed between the inner ring (20) and the outer ring (30).

2. Bearing unit (10) according to claim 1, wherein a first sealing shield (50) is located axially outwards relative to the first row (41) of rolling elements (40) and a second sealing shield (50') is located axially outwards relative to the second ring (42) of rolling elements (40).

3. Bearing unit (10) according to claim 1 or 2, in which each cage (43, 44) comprises a frame (45) with a circular base and a plurality of tenons (46), which are integral with the frame, departing axially from it along a single direction axially internal, said tenons (46) being spaced circumferentially, and, in pairs, defining between them a plurality of alveoli (47) to retain respective rolling elements (40) on only one side of the respective row (41, 42 ) of rolling elements.

4. Bearing unit (10) according to any of the previous claims, wherein each sealshield (50, 50') comprises, in series from the outer ring (30) towards the axis (A):- a first flange portion (51) mounted on the outer ring (30),- an oblique portion (52), stably connected to the first flange portion (51),- a second flange portion (53), stably connected to the oblique portion (52), and- a cylindrical portion (54).

5. Bearing unit (10) according to claim 4, wherein the oblique portion (52) of the sealing shields (50, 50') has an axial projection whose length (L) is between 1.5 mm and 3 mm.

6. Bearing unit (10) according to claim 4, in which the second flange portion (53) is stably connected to the oblique portion by means of its radially external edge (53b), and is provided with an annular surface (53a) axially internal.

7. Bearing unit (10) according to claim 3, wherein the base frame (45) of the cages (43, 44) is delimited radially inwards by a first cylindrical surface (45a), radially outwards by a second cylindrical surface (45b) and axially by an annular surface (45c) transverse to the axis (A).

8. Bearing unit (10) according to claims 6 and 7, wherein the diameter of the second cylindrical surface (45b) of the frame (45) of the cages (43, 44) is smaller than the diameter of a circumference passing through the edge (53b), radially external, of the second flange portion (53) of the sealing shields (50, 50').

9. Bearing unit according to claim 8, wherein the cage (43, 44) is asymmetrical with respect to a plane (P) tangential to the circumference (C) of the centers of the rolling elements (40).

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