Bearing units with concentric clamping collar

Abstract

A bearing unit (10) comprises: a fixed radial outer ring (31); a radial inner ring (33) which is rotatable about a central axis of rotation (X) of the bearing unit (10) and is provided with at least one raceway (33'), and at least two circular sectors are provided at the end (36) of the radial inner ring; at least one row of rolling elements (32) is located between the radial outer ring and the radial inner ring; and a concentric collar (20) for clamping the radial inner ring on a rotating shaft, wherein an induction hardening heat treatment is applied to a portion of the radial inner ring containing the at least one raceway.

Description

Technical Field

[0001] The invention relates to a bearing unit provided with a collar for clamping a radial inner ring on a rotating shaft. Such a bearing unit is suitable for use in the manufacturing industry, in particular the agricultural industry, because it is simple and inexpensive to produce.

[0002] In particular, the bearing unit according to the invention is provided with rolling elements and with an optimized clamping system involving the use of concentric collars capable of gripping and clamping a plurality of circular sectors separated by grooves in a radial inner ring to the shaft, and with an innovative heat treatment for the radial inner ring. Background Art

[0003] Bearing units provided with rolling elements and systems for clamping said bearing units on a rotating shaft are known.

[0004] Bearing units are used to allow relative movement of a component or assembly relative to another component or assembly. Bearing units usually have a first component (e.g. a radial inner ring) fixed to a first component (e.g. a rotating shaft) and a second component (e.g. a radial outer ring) fixed to a second component (e.g. a fixed seat). Typically, according to the above example, the radial inner ring is rotatable and the radial outer ring is fixed, but in many applications, the outer element can rotate and the inner element can be fixed. In any case, in a rolling bearing unit, the rotation of one ring relative to the other is allowed by a plurality of rolling elements located between the cylindrical surface of one component and the cylindrical surface of the other component (these cylindrical surfaces are usually called raceways). The rolling elements can be balls, cylindrical or tapered rollers, needle rollers or similar rolling elements.

[0005] Also known are bearing units provided with a clamping collar for mounting on a rotating shaft. This solution is simpler and less costly than solutions involving an interference fit of the radial inner ring on the rotating shaft. However, the use of a clamping collar leads to disadvantages associated with noise generation and excessive vibrations, which may damage the shaft on which the clamping collar is mounted. In an attempt to overcome these problems, a known solution consists in shaping the end of the radial inner ring to have a plurality of circular segments separated by grooves, i.e. a series of "grooved fingers", on which the clamping collar engages. The greater flexibility of these circular segments contributes to the bending of the circular segments against the shaft when the clamping collar is mounted and tightened.

[0006] This solution has not proven to be effective, since the thickness of the circle sectors cannot be reduced sufficiently to ensure the necessary flexibility, since there would be a risk of excessively weakening the end of the radially inner ring and causing it to break due to overtightening.

[0007] Furthermore, the radial inner rings must be sufficiently hardened, usually using a case-hardening heat treatment, to ensure correct operation of the bearing unit. In particular, the Hertzian contact between the rings and the rolling elements (balls, rollers, etc.) of the bearing unit requires sufficiently hardened contact surfaces to avoid deformations and the resulting vibrations and noise. However, the result of the heat treatment is precisely a reduction in the flexibility of the circular sectors in contact with the clamping collar, with the result that the solutions according to the prior art are not very effective.

[0008] Therefore, there is a need to define a bearing unit provided with a clamping collar such that the clamping action is reliable from a mechanical strength point of view, ensures the concentricity of the shaft and the radial inner ring, does not generate excessive noise and / or vibrations, and is economically sustainable. Summary of the invention

[0009] The object of the present invention is to provide a bearing unit comprising a clamping collar which has properties which ensure a more effective clamping action and which therefore does not have the above-mentioned disadvantages.

[0010] According to the invention, the radial inner ring is provided with a plurality of circular sectors separated by grooves in the end (i.e. the end in contact with the clamping collar), and the collar used in this solution serves to make the radial inner ring concentric with respect to the shaft on which it must be stably fixed.

[0011] In particular, the induction hardening is not through-hardening but only surface hardening.

[0012] More particularly, according to the invention, the radial inner ring is not case-hardened, but is subjected to a local induction hardening heat treatment. In this way, the necessary hardness around the surface of the radial inner ring in contact with the rolling elements is ensured, while the ends of the radial inner ring comprising the circular sectors remain sufficiently flexible, thereby improving the flexibility of the circular sectors intended to be clamped by the concentric clamping collars.

[0013] Therefore, according to the present invention, there is provided a bearing unit provided with a concentric clamping collar and comprising a radial inner ring having the characterizing features described in the appended independent claim. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will now be described with reference to the accompanying drawings, which show a number of non-limiting examples of embodiments of the bearing unit, in which:

[0015] - Figure 1shows a cross-sectional view of a bearing unit provided with a concentric clamping collar according to an embodiment of the present invention;

[0016] - Figure 2 Shown as Figure 1 An axonometric view of a bearing unit provided with a collar is shown, in which the means for fastening the collar around the radial inner ring are visible;

[0017] - Figure 3 Shows something like Figure 1 A bearing unit wherein the portion of the radial inner ring subjected to the induction hardening heat treatment is visible;

[0018] - Figure 4 Shows Figure 3 a first detail of which more clearly shows the different areas of the radially inner ring which are subjected to the induction hardening heat treatment; and

[0019] - Figure 5 Shows Figure 3 A second detail in which the end region of the radially inner ring which has not been subjected to the induction hardening heat treatment is more clearly visible. DETAILED DESCRIPTION

[0020] Referring now to the aforementioned drawings, embodiments of a bearing unit according to the present invention will be described below, by way of example only.

[0021] Special reference Figure 1 A bearing unit 10 for applications in agriculture and / or manufacturing industries (e.g. textile, mining, automotive and food industries) may be arranged, for example, between a rotating shaft and a housing element, which do not form part of the present invention, and comprises:

[0022] - a stationary radial outer ring 31;

[0023] - a radial inner ring 33 rotatable about a central axis of rotation X of the bearing unit 10 ;

[0024] - at least one row of rolling elements 32 , in this example balls, between the radially outer ring 31 and the radially inner ring 33 ;

[0025] - a cage 34 for accommodating rolling elements to hold the rolling elements of the row of rolling elements 32 in place;

[0026] - A concentric collar 20 for clamping the radial inner ring onto the shaft.

[0027] Throughout the present description and claims, terms and expressions indicating positions and orientations such as “radial” and “axial” are to be understood as referring to the central rotation axis X of the bearing unit 30 .

[0028] The radially outer ring 31 is provided with a radially outer raceway 31', while the radially inner ring 33 is provided with at least one radially inner raceway 33', for allowing the rolling of the arrayed rolling elements 32 between the radially outer ring 31 and the radially inner ring 33. For the sake of simpler illustration, the reference numeral 32 will be attributed to both the single ball and the array of balls. Again for the sake of simplicity, the term "ball" may be used by way of example in this specification and the drawings, instead of the more general term "rolling element" (and the same reference numerals will be used as well). Without departing from the scope of the present invention, some examples of embodiments and associated drawings may envisage the use of rolling elements other than balls (e.g. rollers).

[0029] The bearing unit 10 is also provided with a sealing member 35 for sealing the bearing unit from the external environment. In the following, the sealing member 35 may also be more simply indicated as a seal 35, which should obviously be understood to indicate the same component.

[0030] As mentioned, the concentric clamping collar 20 has the function of clamping the end 36 of the radial inner ring 33 on the rotating shaft.

[0031] Reference Figure 2 The clamping of the collar 20 around the circular segment 40 of the end 36 of the radial inner ring 33 is performed using known methods, i.e. using screw components 21, such as cylindrical head screws (Torx head screws) with hexagonal recesses. The collar 20 allows for the provision of raised grooves 22. The collar mounted on the radial inner ring 33 and in particular on the circular segment 40 locks the radial inner ring 33 of the bearing unit 10 to the shaft in a concentric manner without causing damage and / or burrs and exerts a 360-degree clamping force on the shaft with minimal displacement of the arms 23, 24 of the collar 20 to reduce vibrations to a minimum.

[0032] Reference Figure 3 , which shows something like Figure 1 The bearing unit 10 shown has the only difference that it includes rolling elements 32 (in this figure, there are two rows of rollers, while in Figure 1 In the bearing unit of FIG. 1 , there is a single row of balls), the portion 37 of the radial inner ring 33 which has been subjected to the induction hardening heat treatment is visible.

[0033] The particular features of the invention include the fact that a different heat treatment, namely induction-hardening, is also applied to the radial inner ring 33 instead of case-hardening. This allows a cost reduction, since the induction-hardening process is more economical than case-hardening, and allows the inner ring close to the clamping collar 20 to be completely pliable.

[0034] Finally, a known type of heat treatment is case hardening on all the inner surfaces of the radial inner ring 33. Typically, the case hardening can be solid or gas, and since the radial inner ring 33 cannot be divided into two parts, all surfaces are case hardened, including those close to the clamping collar 20.

[0035] In contrast, with the induction hardening process, only certain surfaces of the inner ring can be hardened, particularly those around the raceway 33'. This different heat treatment can result in significant cost savings, since the cost of the heat treatment is proportional to the surface area of ​​the material being heat treated, and the amount of material treated with the induction hardening process is less than with the case hardening process.

[0036] Advantageously, the material of the radial inner ring may be hardened steel, such as 100Cr6 steel, which is also less expensive, rather than case-hardened steel, such as AISI 8620H (21NiCrMo2).

[0037] In order for the induction hardening treatment to effectively achieve the two objectives of providing the necessary surface hardness around the raceway 33 ′ of the radial inner ring 33 on the one hand and keeping the material flexible at the end 36 of the radial inner ring 33 on the other hand, a heat treatment must be performed specifying specific geometrical parameters and hardness in different areas of the radial inner ring 33 .

[0038] More specifically, refer to Figure 4 , Figure 4 yes Figure 3 In the first detail, in which the different areas of the radial inner ring 33 subjected to the induction hardening heat treatment are more clearly shown, it can be noted that the portion 37 of the radial inner ring 33 subjected to the induction hardening heat treatment can be further subdivided into a first central area R and a more peripheral second peripheral area D located on opposite sides of the central area R.

[0039] In order to optimize the induction hardening heat treatment, the axial length K1 of the first central region R must completely surround the axial length of the raceway 33' of the radial inner ring 33, that is, the axial length K1 will be greater than or equal to the axial length of the (multiple) raceways 33'. In addition, over the entire axial length K1, the hardening depth of the region R (that is, the thickness of the material that must ensure a high hardness value) will be equal to at least 10% of the thickness T of the radial inner ring 33.

[0040] Furthermore, if K defines the axial length of the entire portion 37 of the radial inner ring 33 on which the heat treatment is performed, the axial length of each of the second peripheral regions D (which can be calculated as (K-K1) / 2) must be not less than 2 mm.

[0041] Reference Figure 5 , which shows Figure 3 A second detail, in which the end portion 36 of the radial inner ring 33 that has not been subjected to the induction hardening heat treatment is more clearly visible, can define a third area A, which is included in the end 36 of the radial inner ring 33 and is understood as the smallest area that has not been subjected to the induction hardening heat treatment. If A1 defines the axial length of the circular sector 40, the axial length A2 of the third area A must not be less than A1+0.5 mm.

[0042] Finally and according to a preferred embodiment, the regions R, D and A defined above must have hardness values ​​measured, for example, on the HRC scale, as shown in the table below.

[0043] Table 1

[0044]

[0045] It can be noted how the first central region R and the second peripheral region D subjected to the induction hardening heat treatment can reach very high hardness values ​​of up to 64 HRC, and in any case the region R must have a hardness value of not less than 56 HRC. On the other hand, the third region A not subjected to the heat treatment must not exceed a hardness value of 45 HRC. Therefore, the circular sector 40 included in the third region A must be made of a completely flexible material and will therefore have optimal flexibility when dealing with the clamping action of the concentric collar 20.

[0046] Basically, with this novel induction hardening heat treatment, an improved performance of the clamping system in terms of transmittable dynamics and vibration levels can be achieved compared to the prior art. The circle segments are more flexible, as a result of which, for the same tightening torque of the screw acting on the collar, the closing action of the circle segments can be increased.

[0047] From a functional point of view, with the proposed invention, a "concentric" solution is obtained with all the resulting advantages: coincidence between the axes of the shaft and the bearing unit; speed and nominal limit load do not depend on the tolerances of the shaft; constant or alternating directions of rotation can be used; lower vibration levels do not damage the shaft in any way; reduced corrosion due to friction; easy and fast assembly.

[0048] Furthermore, with the solution shown, savings in production costs can be achieved, in particular those related to the induction hardening heat treatment, the surface area that has to undergo hardening being limited to the raceways of the rolling elements in contact with the radial inner ring.

[0049] In addition to the embodiments of the present invention as described above, it should be understood that there are many further variations. It must also be understood that the embodiments are merely examples and neither limit the scope of the present invention, nor its application, nor its possible configurations. On the contrary, although the description provided above enables those skilled in the art to implement the present invention at least in one of its configuration examples, it must be understood that many variations of the described components are feasible without thereby departing from the scope of the present invention as defined in the appended claims, interpreted literally and / or according to their legal equivalents.

Claims

1. A bearing unit (10), comprising: - a fixed radial outer ring (31), a radial inner ring (33) rotatable about a central axis of rotation (X) of the bearing unit (10) and provided with at least one raceway (33') and at least two circular sectors (40) arranged in the ends (36) of the radial inner ring, - at least one row of rolling elements (32) between the radially outer ring (31) and the radially inner ring (33), - a concentric collar (20) for clamping the radial inner ring (33) on the rotating shaft, The bearing unit (10) is characterized in that an induction hardening heat treatment is applied to a portion (37) of the radial inner ring (33) comprising the at least one raceway (33'), The induction hardening is not full hardening, but only surface hardening. The portion (37) of the radial inner ring (33) includes a first central region (R) and a second peripheral region (D), wherein the second peripheral region (D) is located on opposite sides of the first central region (R), and the induction hardening heat treatment is applied to the second peripheral region (D).

2. The bearing unit (10) according to claim 1, characterized in that The axial length (K1) of the first central region (R) is greater than or equal to the axial length of at least one raceway (33') of the radial inner ring (33).

3. The bearing unit (10) according to claim 1 or 2, characterized in that: The hardening depth of the first central region (R) over the entire axial length (K1) is greater than or equal to 10% of the thickness (T) of the radial inner ring (33).

4. The bearing unit (10) according to claim 1, characterized in that The axial length of each of the second peripheral regions (D) at the periphery relative to the central region (R) is greater than or equal to 2 mm.

5. The bearing unit (10) according to claim 1 or 2, characterized in that: The end portion (36) of the radial inner ring (33) includes a third region (A) to which the induction hardening heat treatment is not applied.

6. The bearing unit (10) according to claim 5, characterized in that The axial length (A2) of the third region (A) is not less than the axial length (A1) of the circular sector (40) plus 0.5 mm.

7. The bearing unit (10) according to claim 1, characterized in that The first central region (R) has a hardness value of not less than 56 HRC.

8. The bearing unit (10) according to claim 5, characterized in that The third region (A) has a hardness value of no more than 45 HRC.

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