Pulley group for multi-wire machines

Abstract

Pulley group (100) for multi-wire machines, the group having a central rotation axis (A) and including at least two thin-section bearing units (10), which are arranged axially side-by-side along the axis (A), and each of which includes: - a stationary inner ring (20), - a rotatable flanged outer ring (30) having axial dimensions smaller than an axial dimension of the inner ring (20), and - a hydraulic grease-distribution network (60) provided with at least one axial duct (61) passing through the inner ring (20) parallel to the axis (A), wherein for each pair of axially adjacent bearing units (10), there is a corresponding sealing device (70) axially interposed between the two units of the pair of bearing units (10).

Description

[0001] PULLEY GROUP FOR MULTI- WIRE MACHINES

[0002] DE S CRIP T I ON

[0003] Technical field of the invention

[0004] The present invention relates to a pulley group for multi-wire machines.

[0005] In particular, the present invention relates to a pulley group comprising at least two thin-section bearing units.

[0006] Prior art

[0007] In multi-wire machines, blocks of stone-like material, such as stone, marble, concrete and the like, are cut into slabs using diamond cutting wires, which are arranged parallel to one another along a cutting path, and are run along that path by tensioner pulleys. To make relatively thin slabs, the tensioner pulleys are assembled tightly together on a common support shaft, axially beside one another, and are made rotatable about the support shaft itself by interposing respective thin-section bearing units.

[0008] Known thin-section bearing units for multi-wire machines are therefore also fitted tightly together, side-by-side along a common central rotation axis defined by the support shaft, and, although the respective outer diameters thereof are relatively large, the axial thicknesses thereof must necessarily be very small to enable them to be fitted axially as close as possible to the tensioner pulleys, and the combination of large diameters and small axial thicknesses requires particularly sophisticated technical solutions to guarantee consistently high performance.

[0009] These bearing units comprise:

[0010] - respective stationary inner rings, arranged axially against one another,

[0011] - respective rotatable outer rings, conversely having an axial dimension slightly smaller than the axial dimension of the inner rings thereof, to enable them to rotate independently of one another and to enable the independent rotation of the respective tensioner pulleys, and

[0012] - respective sealing shields arranged on the axially opposite sides of the bearing units and interposed between the related inner and outer rings, both to prevent contaminants, such as water mixed with stone powder, from entering the bearing units, and to prevent the internal lubricating grease from leaking out.

[0013] Each outer ring is provided with a respective bearing flange connected to a related pulley, while each inner ring is laterally delimited by respective annular surfaces arranged directly in contact with the annular surfaces of the inner rings of the axially adjacent bearing units.

[0014] The high contamination of the working environment of the bearing units described above, related to the processing of stone-like materials, requires frequent maintenance actions, including to extend the life cycle of the bearing units. Indeed, despite the presence of the sealing shields, contaminants still enter the bearing units during the operation thereof, causing damage to the bearing units and deteriorating the lubricating grease. During these maintenance actions, the bearing units are carefully and thoroughly cleaned, and substantially all of the lubricating grease in the bearing units is reconditioned, since the life cycle of said bearing units also depends on the purity of this grease.

[0015] Since these maintenance actions essentially involve disassembling both the tensioner pulleys and the bearing units, these actions are in practice carried out at the substantial expense of the production efficiency of the related multi-wire machines.

[0016] Users of multi-wire machines are familiar with the possibility of replenishing the lubricating grease to extend the life cycle of the bearing-unit pulley group, but without necessarily having to uninstall and / or disassemble the bearing units themselves. For this purpose, a hydraulic network for distributing the lubricating grease that is in fluid communication with the grease containment grooves in the rings of the bearing units is used. However, the known solutions for the bearing units do not ensure that the replenished lubricating grease does not leak to the external environment.

[0017] Summary of the invention

[0018] The purpose of the present invention is to provide a pulley group for multi-wire machines, which minimizes the ingress of contaminants into the individual bearing units of the group and the loss of lubricating grease from the individual bearing units, thereby enhancing the production efficiency of the related multi-wire machines.

[0019] The present invention provides a pulley group for multi-wire machines having the features set out in the appended claims.

[0020] Brief description of the drawings

[0021] The invention is described below with reference to the attached drawings, which show a non-limiting example embodiment thereof, in which:

[0022] - Figure 1 is a cross-sectional view of two axially adjacent thin-section bearing units forming part of a pulley group for multi-wire machines, according to a preferred embodiment of the present invention,

[0023] - Figure 2 is a cross-sectional view of a sealing device interposed between the two bearing units in Figure 1, and

[0024] - Figure 3 is a side view of the sealing device shown in Figure 2.

[0025] Detailed description

[0026] With reference to Figure 1, a pulley group for multi -wire machines, comprising at least two thin-section bearing units 10, is indicated as a whole by reference number 100. In particular, Figure 1 illustrates a pair of thin-section bearing units 10, which are identical and axially adjacent to one another.

[0027] To simplify the graphical representation, given that the two bearing units shown are identical to one another, some reference numbers are not shown on both bearing units, but on one or the other.

[0028] Each bearing unit 10 has very small axial dimensions in order to be fitted, together with other identical bearing units 10, in the pulley group 100, where the group 100 may include between 2 and more than 100 (for example, between 30 and 115) bearing units 10, all identical to one another and arranged side-by-side along a respective common central rotation axis A.

[0029] The group 100 of thin-section bearing units 10 according to the present invention can be advantageously used in multi-wire machines, and the remainder of the document refers to such machines by way of example, while remaining generally applicable. In these multi- wire machines, blocks of stone-like material are cut into slabs by the action of diamond cutting wires arranged parallel to one another along the blocks themselves and are run along these blocks by means of tensioner pulleys (not shown). To make these slabs, these tensioner pulleys are assembled tightly together axially side-by-side on a common support shaft (not shown) defining the central axis A, and are made rotatable in relation to the support shaft by interposing a respective bearing unit 10.

[0030] As also shown in Figure 1, a single bearing unit 10 of the pulley group 100 comprises:

[0031] - a stationary inner ring 20, fitted on a stationary shaft of the multi-wire machine (of a known type and therefore not shown in the figure) and limited axially by respective annular surfaces 21 transverse to the axis A,

[0032] - 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 a cylindrical gap 90 with the inner ring 20,

[0033] - a plurality of rolling elements 40, preferably balls, arranged in the gap 90 and interposed between the inner ring 20 and the outer ring 30 to allow the relative rotation thereof about the axis A, and

[0034] - two sealing shields 50 arranged on the axially opposite sides of the bearing unit 10 and interposed between the inner ring 20 and the outer ring 30, both to prevent contaminants, such as water mixed with stone powder, from entering the gap 90 of the bearing unit 10, and to prevent the lubricating grease contained within the gap 90 from leaking out. The sealing shields 50 are fitted on the outer ring 30 and are therefore also rotatable and have respective outer annular surfaces 51.

[0035] The inner ring 20 and outer ring 30 have respectively an outer raceway 22 and an inner raceway 32, radially facing one another and the gap 90, in which the rolling elements 40 can slide, while the outer ring 30 is also provided with a support flange 31, which extends radially outwards from the outer ring 30 in a direction transverse to the axis A, and is connected to a related pulley of the multi-wire machine.

[0036] The inner ring 20 is radially delimited on the inside by a cylindrical surface 24 coaxial to the axis A and orthogonal to the two annular surfaces 21. In the bearing unit 10, the ratio of an inner diameter of the surface 24 to the axial thickness SI of the inner ring 20 varies from a minimum of 8 to a maximum of 12. Furthermore, the inner ring 20 has a circumferential groove 23 in the outer raceway 22.

[0037] The circumferential groove 23 advantageously contains lubricating grease to keep the raceway 22 lubricated, and the bearing unit 10 also includes a hydraulic network 60 for distributing lubricating grease to replenish this lubricating grease, thereby extending the life cycle of the bearing unit 10 without having to uninstall and / or disassemble the bearing unit 10 itself.

[0038] The hydraulic network 60 distributes new lubricating grease inside the bearing unit 10, and comprises at least one axial duct 61 passing through the inner ring 20 parallel to the axis A, and a related radial duct 62 formed in the inner ring 20 between the duct 61 and the circumferential groove 23.

[0039] Evidently, in order to ensure that the bearing units 10 arranged towards the centre of the group 100 also receive the necessary quantity of lubricating grease, the ducts 61 of each bearing unit 10 are perfectly aligned with the ducts 61 of the immediately adjacent bearing units 10.

[0040] Although the ducts 61 are perfectly aligned with one another, to avoid potential and unwanted leakage of grease to the outside, the pulley group 100 according to the present invention comprises a plurality of sealing devices 70, each of which is axially interposed between each pair of axially adjacent bearing units 10. These sealing devices 70 perform the function of containing leaks of lubricating grease to the outside and are therefore well suited to solutions, such as the one described, of groups of bearing units for multi-wire machines in which the lubricating grease can be replenished without external maintenance actions.

[0041] Simultaneously, these sealing devices 70 perform an additional function of blocking external contaminants, assisting the sealing shields 50 of the individual bearing units 10.

[0042] With reference also to Figure 2, the sealing device 70 is made of an elastomer and comprises: - a central discoidal element 71 having a radially outer end portion 71a, a radially inner cylindrical surface 71” and a pair of outer annular surfaces 71’ in axial contact with respective annular surfaces 21 of corresponding inner rings 20 of two axially adjacent bearing units 10. The two bearing units 10 and the sealing device 70, which is axially interposed therebetween, are therefore clamped tightly together,

[0043] - at least one through-hole 80, formed through the discoidal element 71 and in fluidic communication with the duct 61 of each bearing unit 10 axially adj acent to the sealing device 70. In addition to enabling grease to pass through adjacent ducts 61 of the hydraulic network 60, the through-hole 80 performs the function of sealing the lubricating grease and preventing it from leaking out. For this reason, the diameter of the through-hole 80 must be 10% to 30% greater than the diameter of each duct 61. In other words, the diameter of the through-hole 80 is between 110% and 130% of a diameter of each duct 61.

[0044] Preferably, the number of through-holes 80 is greater than one and equal to the number of ducts 61 in each bearing unit. The through-holes 80 are arranged symmetrically with respect to the rotation axis A of the bearing units and there are an even number of through-holes, for example eight, so as to balance the design in terms of mass. Furthermore, this design facilitates the fitting of the bearing units and of the sealing device, since any duct 61 can be coupled with any through-hole 80 to align the other ducts and through-holes automatically. On the other hand, asymmetrical through-holes would require a defined assembly direction, which would complicate the assembly work, and

[0045] - a pair of discoidal lips 72, which extend radially outwards from the discoidal element 71 and are located on opposite sides of a plane P of symmetry of the sealing device 70. The lips 72 therefore extend from a common base, the discoidal element 71, that is axially thick enough to withstand crushing and not to cause the lips 72 to open.

[0046] The pair of lips 72 is oblique and therefore defines within itself an annular groove 73 having a substantially “V” shape in cross-section.

[0047] More specifically, the groove 73 is defined by two tapered surfaces 73’ connected together by a curved surface 73”. Each lip 72 is delimited axially on the inside of the groove 73 by the tapered surface 73’ and axially on the outside by a respective tapered surface 72’.

[0048] The curved surface 73” performs substantially two functions. A first function is to collect the contaminant without any risk of said contaminant “overflowing” out. A second function is that the friction caused by any contact between the shield 50 and the sealing device 70 will be very low, because the lips 72 can bend easily, as there is a wide taper therebetween defining the “V” shape.

[0049] This specific geometry of the sealing device 70 enhances the protection of the bearing units 10 of the group 100 of bearing units because:

[0050] - the lips 72 and groove 73 together define a deflector for external contaminants coming from the pulleys of the multi-wire machine, for example water and dust (in particular diamond dust), with most of these contaminants collecting in the centre of the groove 73. The presence of the water (which is one of the main contaminants) causes the dust to be drawn in a circumferential direction by the water itself and then to fall by gravity once it reaches the underside of the bearing units (therefore moving through an angle of approximately 180°). To remove the contaminants, the groove thus formed provides “greater” capacity and facilitates (by falling) the discharge of the contaminant, since the fuller it gets, the greater the force of gravity, causing the contaminant to slide away. Furthermore, the greater the taper, the more effective the removal of contaminants, since the contaminants are higher up than neighbouring contaminants,

[0051] - under nominal geometric conditions, the lips 72 are axially close to the sealing shields 50 of the adjacent bearing units 10. Therefore, a passage L is created between each lip 72 and each sealing shield 50, which is likely to form a labyrinth seal. Indeed, the passage L, along the path of the contaminants, is upstream of the sealing shield 50 and may cooperate with the shield itself to further hinder the passage of contaminant residues that have not been collected in the groove 73.

[0052] Since the nominal geometric conditions are only theoretical, axial contact may occur between a lip 72 and the corresponding sealing shield 50. Since such contact is between a rotatable metal element (the shield 50) and a stationary elastomer lip, the contact itself is not problematic. It is however advantageous to take additional measures relating to the geometry of the sealing device 70 and to provide a correct procedure for fitting the device itself to ensure that the friction torque of the bearing unit is not increased to any significant extent.

[0053] With regard to the geometry of the sealing device 70, a first measure is to provide the radially outer end portion 74 of each lip 72 with an outer annular surface 75 (surface which may be in contact with the outer annular surface 51 of the shield 50) having a final flatness of not more than 0.1 mm.

[0054] Each lip 72 has a respective internal median plane S which is substantially equidistant from the related surfaces 72’ and 73’, and is inclined with respect to the plane P by an angle a of between 20° and 30°, and is determined so as to contain and limit the friction torque in the event of contact between the lip 72 and the shield 50. Furthermore, the quite narrow angle a helps to limit the axial dimensions of the sealing device 70. On the other hand, a narrow angle a creates a small space at the groove 73 in which the contaminants may accumulate. To prevent this, the lips 72 have been lengthened to keep the dimensions small and to create a space large enough to collect and then drain the dirt.

[0055] Again to limit the friction torque in the event of contact between the lip 72 and the shield 50, the two internal median planes S converge towards the plane P of symmetry and intercept said plane at a circumference C, the radial position of which in relation to the axis A determines both the flexibility and the stiffness of the device 70. In particular, for the same axial dimensions of the device 70, i.e. the lips 72 thereof, moving the circumference C closer to the axis A reduces the size of the axial opening of the two lips 72, i.e. the value of the angle a, and increases the elasticity and flexibility of the device 70. Conversely, moving the circumference C further away from the axis A increases the size of the axial opening of the two lips 72, i.e. the value of the angle a, and reduces the elasticity and flexibility of the device 70.

[0056] Preferably, the circumference C shall be positioned at the axis A of the bearing units and of the holes 80. The circumference C acts as the theoretical centre of rotation of the lips 72 in the event of contact with the shield 50 and / or compression of the discoidal element 71 as a result of being assembled tightly together. This ensures that the contact between the lip 72 and the shield 50 occurs exactly where it is designed to occur, i.e. on the annular surface 75. If the circumference C were lower than the axis A, there would be a risk of the lip 72 coming into contact with the shield 50 along the tapered surface 72’, instead of along the annular surface 75. This would change a small contact (the annular surface 75 has a radial width not exceeding 0.1 mm) to a larger contact, which would increase friction resistance. However, if the circumference C were higher than the axis A, this would increase the size of the angle a and therefore increase the axial dimension of the sealing device 70.

[0057] Finally, the elastomer can be a nitrile rubber, Teflon or other equivalent material. The important factor is that its hardness should neither be so high as to adversely affect the flexibility of the lips 72, nor so low as to cause excessive deformation of the lips themselves, taking into account that the sealing device 70 is required to provide as much resistance as possible against erosion by water with diamond dust. An optimal value for this is a Shore A hardness between 70 and 80.

[0058] This Shore A hardness range is related to the position of the circumference C which, as mentioned above, acts as the theoretical centre of rotation of the lips 72. If the circumference C is lower than the axis A, the hardness of the material should tend towards the maximum (80 Shore A) in order to avoid excessive deformations, which would generate excessive contact. Otherwise, i.e. if the hardness were low, the lips 72 would “bulge” outwards, resulting in excessive contact with the shields 50. If the circumference C is higher than the axis A, the hardness would have to be lower as the lips would have a shorter flex arm (roughly equivalent to the distance between the circumference C and the annular surface 75). Therefore, including in terms of the characteristics of the material, positioning the circumference C at the axis A of the bearing units and of the holes 80 represents the right balance between hardness and flexibility required for the lips 72.

[0059] Furthermore, the flexibility of the lips 72 is further increased by the fact that the axial thickness thereof lessens in the radially outward direction, since the tapered surfaces 72’ and 73’ of the two lips are not parallel to one another, but have different inclinations with respect to the axis A, making the lips thinner at the tip than at the base.

[0060] The design condition is that the axial width s of a radially outer cylindrical surface 76 of the lips 72 must not be greater than 0.6 mm, so as not to cause an unwanted increase in the stiffness of the lips themselves.

[0061] Also with reference to Figure 3, the sealing device 70 advantageously has centring through-holes 77 to ensure the correct fitting of the sealing devices 70 between respective pairs of bearing units 10. The centring system used in known solutions, without the sealing device 70, may be used: the centring holes 77 are aligned with the corresponding holes in the inner ring 20 and are held in the correct position by centring pins inserted therein.

[0062] Evidently, this centring system also enables the through-holes 80 of the sealing device 70 to be aligned with the corresponding ducts 61 of the inner rings 20.

[0063] Advantageously, the through-holes 80 and the centring holes 77 are uniformly distributed about the axis A and alternate with one another along the circumference.

[0064] Finally, the solution according to the present invention is advantageously applied to solutions in which the group of bearing units does not require frequent maintenance actions as the lubricating grease of the bearing units is replenished without stopping operation of the related multi-wire machines. This is because the present solution prevents the loss of grease, which may be replenished grease or grease otherwise present within the group of bearing units.

[0065] Furthermore, this solution enhances the seal against external contaminants.

[0066] In addition to the embodiments described above, numerous other variants of the invention are possible. Said embodiments are provided solely by way of example and do not limit the scope of the invention, its applications or its possible configurations. Indeed, although the description provided above enables the person skilled in the art to carry out the present invention 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 invention, as defined in the attached claims interpreted literally and / or according to their legal equivalents.

Claims

C LAIM S1. Pulley group (100) for multi -wire machines, the group having a central rotation axis (A) and including at least two thin-section bearing units (10), which are arranged axially side by side along the axis (A), and each of which includes:- 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- a hydraulic network (60) for grease distribution comprising, in turn, at least one axial, through duct (61), obtained through the inner ring (20) parallel to the axis (A); the group (100) being characterized in that it comprises, for each pair of axially adjacent bearing units (10), a respective sealing device (70) axially interposed between the two units of the pair of bearing units (10).

2. Pulley group (100) according to claim 1, wherein each sealing device (70) comprises:- a central discoidal element (71), clamped tightly between two inner rings (20) of two bearing units (10) axially adjacent to each other;- at least one through hole (80), obtained through the discoidal element (71) and in fluid communication with the duct (61) of each bearing unit (10) axially adjacent to the sealing device (70);- a pair of discoidal lips (72), which extend radially outwards from the discoidal element (71) and are located on opposite sides of a plane (P) of symmetry of the sealing device (70).

3. Pulley group (100) according to claim 2, wherein a diameter of the through hole (80) is between 110% and 130% of a diameter of each duct (61).

4. Pulley group (100) according to claim 2 or 3, in which the pair of lips (72) defines an annular groove (73) inside it.

5. Pulley group (100) according to one of claims 2 to 4, wherein each lip (72) of the pair of lips of the sealing device (70) defines a passage (L) with a corresponding sealingshield (50) of the bearing unit (10), axially adjacent to the sealing device (70) and placed between the inner ring (20) and the outer ring (30).

6. Pulley group (100) according to claim 5, wherein a terminal portion (74), radially external, of each lip (72) is provided with an external annular surface (75) having a flatness not exceeding 0.1 mm.

7. Pulley group (100) according to claim 5 or 6, wherein the amplitude of an angle (a) between an internal median plane (S) of the lips (72), and the plane (P) of symmetry is included between 20° and 30°.

8. Pulley group (100) according to any of claims 5 to 7, wherein an axial width (s) of a cylindrical surface (76), radially external, of each lip (72) assumes values not exceeding0.6 mm.

9. Pulley group (100) according to any of the previous claims, in which the sealing device (70) is made of elastomeric material with Shore A hardness between 70 and 80.

10. Pulley group (100) according to any of the previous claims, in which the sealing device (70) has centring through holes (77).

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