The present disclosure relates to the field of rolling element bearings.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Rolling contact fatigue: The term "Rolling contact fatigue" hereinafter refers to the failure, driven by crack propagation that is caused by a near-surface or sub surface alternating stress field.
Specific film thickness: The term "specific film thickness" hereinafter refers to the ratio of the minimum film thickness to the composite surface roughness of two surfaces in contact and is represented by X.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
The current trend in automotive industries is to improve fuel efficiency by reducing frictional losses of components of the automotive, which is achieved by the use of thin viscous lubricants. Additionally, the thickness of the lubricant film reduces and the wear and surface related fatigue failure is induced. As a result, rolling element bearings of the automotive are made to operate under severe condition wherein the lubricant forms a thin film and the compact design of the rolling element bearings is subjected to higher load.
Typically, rolling element bearings tend to experience rolling contact fatigue when subjected to load. The rolling contact fatigue is either sub-surface oriented or surface oriented. The sub surface oriented fatigue is called as classical failure which depends on the material and location of maximum shear stress, and occurs

due to nature of the lubricant film, operating conditions, and near-surface micro-contacts. Generally, the bearing is subjected to grinding process to ensure high precision and low surface roughness of the surface of the bearings. However, unwanted residual tensile stresses are generated on the surface of the bearing after grinding. As a result, micro-cracks are propagated on the surface of the bearing thereby, compromising the fatigue life of the bearing.
Generally, the mating components of the bearings are lubricated by means of a lubricant film. However, while in operation, the thin viscous fluid produces a thin lubricant film that increases the friction between the mating components. The bearing surface further deteriorates and increases the probability of wear and the subsequent premature failure of the bearings. Further, the fatigue life of the bearings is reduced due to friction in between the mating components of the rolling element bearing.
There is therefore, felt a need for a process to enhance life and mechanical properties of rolling element bearings with lubricant retention that alleviates the aforementioned drawbacks.
OBJECTS
Some of the objects of the present disclosure are described herein below:
An object of the present disclosure is to provide a process to enhance life and mechanical properties of rolling element bearings with lubricant retention.
Another object of the present disclosure is to provide a process that reduces surface roughness of the rolling element bearings.
Yet another object of the present disclosure is to provide a process that reduces friction between mating parts of the rolling element bearings.
Still another object of the present disclosure is to provide a process that enhances the fatigue life of the rolling element bearings.

Another object of the present disclosure is to provide a process that enhances the performance of the rolling element bearings.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a process to enhance life and mechanical properties of rolling element bearings with lubricant retention. The process comprises the following steps: (a) forming a raceway of a rolling element bearing; (b) grinding the raceway to obtain a smooth surface; (c) exposing the smooth surface of the raceway to a first shot peening action to obtain a first shot peened surface; (d) surface finishing the first shot peened surface of the raceway of the rolling element bearing; and (e) exposing the surface of the raceway to a second shot peening action at an intensity lesser than the intensity at which the first shot peening action is performed, to obtain a second shot peened surface.
In an aspect of the present disclosure, the step of forming includes at least one sub-step of hardening or quenching of the raceway.
In another aspect of the present disclosure, the step of first shot peening action includes bombarding the smooth surface of the raceway by a first plurality of media balls at a first intensity level.
In another aspect of the present disclosure, the step of surface finishing is a chemically assisted surface finishing performed by a mass finishing machine.
In another aspect of the present disclosure, the step of surface finishing includes at least one phase of surface finishing.
In yet another aspect of the present disclosure, the step of second shot peening action includes bombarding the surface of the raceway by a second plurality of media balls at a second intensity level.

In yet another aspect of the present disclosure, which includes selecting media balls of a specific diameter for performing the first shot peening action and selecting media balls of a specific diameter for performing the second shot peening action and ensuring that the diameter of the media balls selected for performing the first shot peening action is greater than the diameter of the media balls selected for performing the second shot peening action.
The present disclosure also envisages a raceway of a rolling element which is hardened and quenched and comprises a surface which is ground and shot peened at least twice by media balls, where the diameter of a first plurality of the media balls of a first shot peening action is larger than diameter of a second plurality of the media balls of a second shot peening action
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
A process to enhance life and mechanical properties of rolling element bearings with lubricant retention, of the present disclosure, will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a flow chart that depicts the steps for carrying out the process of the present disclosure, in accordance with an embodiment of the present disclosure;
Figure 2A illustrates an enlarged 3-Dimensional profile of a portion of a conventionally treated surface of a rolling element bearing;
Figure 2B illustrates an enlarged 3-Dimensional profile of a portion of a surface of a rolling element bearing, treated in accordance with an embodiment of the present disclosure;
Figure 3 A illustrates an enlarged SEM (Scanning electron microscope) image of a portion of the surface of the rolling element bearing, after primary shot peening;
Figure 3B illustrates an enlarged SEM (Scanning electron microscope) image of a portion of the surface of the rolling element bearing, after secondary shot peening;

Figure 4A illustrates COF (Co-efficient of friction) of ball on disc test, a tribological performance graph comparing a conventionally treated disc and disc treated by the process of the present disclosure for sliding velocity 0.5 m/s.; and
Figure 4B illustrates COF (Co-efficient of friction) of ball on disc test, a tribological performance graph comparing a conventional treated disc and disc treated by the process of the present disclosure for sliding velocity 1.0 m/s.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," "including," and "having," are open ended transitional phrases and therefore specify the presence of stated features, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their

performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
When an element is referred to as being "mounted on," "engaged to," "connected to," or "coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc.,when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Terms such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.
The present disclosure envisages a process to enhance life and mechanical properties of rolling element bearings with lubricant retention.
Referring to Figure 1, the steps involved in the process of the present disclosure are now described in detail. The process is described with reference to enhance life and mechanical properties of a rolling element bearing, more specifically the raceways of a rolling element bearing. The enhancement of life and mechanical properties of any component/element of a rolling element bearing by the process is well within the scope and ambit of the present disclosure.
The process involves an initial step of forming (105) a raceway of a rolling element bearing. The step of forming (105) includes at least one sub-step of hardening or quenching of the raceway. The sub-step of hardening includes heating of the component above its austenization transformation temperature. Thereafter, the material can be quenched and tempered to achieve the desired

mechanical properties of the bearing components, especially the hardness of the bearing material.
In an embodiment, the process further includes the step of include grinding (110) and super finishing the raceway to obtain a smooth surface.
Thereafter the surface of the raceway is exposed to a first shot peening action (115). The first shot peening action (115) includes bombarding the surface of the raceway by a first plurality of media balls at a first intensity level. The impact of the first plurality of media balls produces plastic deformation of the raceway. More specifically, a plurality of dimples is formed on the surface of the raceway. The first shot peening action (115) induces residual stresses on the surface of the raceway. Further, the first shot peening action (115) produces asperities on the surface of the raceway. The asperities act as stress inducers on the surface of the raceway and additionally increase the surface roughness. The surface roughness instigates metal-to-metal contact and thereby, increases the friction and wear in the mating elements of the rolling element bearings.
The process further includes a step of chemically assisted surface finishing (120) by using mass finishing machines like vibratory mass finishing, tumbling, centrifugal barrel finishing process and the like to remove surface asperities formed due to the first shot peening action (115).
The chemically assisted surface finishing (120) involves introduction of the component into a non-abrasive chemical solution, which may be of either acidic nature or alkaline nature depending on the components to be processed. More specifically, the chemical solution reacts with asperities of the components and produces soft conversion coating, which is brittle in nature. The non-abrasive media thereafter removes the soft layer. The removal of the peaks of the asperities exposes a new layer of asperities. The chemical solution reacts with the newly exposed layer of asperities to form a soft conversion coating. The step of chemically assisted surface finishing (120) continues till all peaks of the asperities are removed.

In an embodiment, the step of chemically assisted surface finishing (120) is conducted in two phases namely surface enhancement step and burnishing step.
In an embodiment, the step of chemically assisted surface finishing (120) is conducted in one phase.
The process thereafter involves the step of exposing the surface of the raceway to a second shot peening action (125). The second shot peening action (125) includes bombarding the surface of the raceway by a second plurality of media balls at a second intensity level. The second shot peening action (125) ensures that enough residual stress is generated which can be removed during the chemically assisted surface finishing (120) step by removing the asperities (peaks) on the surface of the raceway and maintaining the dimples (valleys) formed.
In an embodiment, the shot peened raceway has improved toughness.
In another embodiment, the hardness of the bearing is maintained in a hardness range of 58-62 HRC.
In an embodiment, the size of the first plurality of media balls used in the first shot peening action (115) is more than the size of the second plurality of media balls. In another embodiment, the size of the first plurality of media balls varies in the range of 0.1mm to 0.5mm. In yet another embodiment, the size of the second plurality of media balls varies in the range of 0.01mm to 0.1mm.
In an embodiment, the first intensity level of the first shot peening action (115) is higher than the second intensity level of the second shot peening action (125). The lesser intensity of the second shot peening action (125) reduces the roughness of the surface of the raceways and thereby, develops a desired depth of the shot peened layer on the surface of the raceway.
In one embodiment, exposing the raceways to the first shot peening action (115), the chemically assisted surface finishing (120) and the second shot peening action (125) eliminates the grinding lines (lay direction) and the asperities on the surface

of the raceways thereby, reducing the resistance to pressure flow factor of the lubricant. As a result, the lubrication of the rolling element bearings is improved.
In an embodiment, exposing the raceway to the first shot peening action (115) and the second shot peening action (125) facilitates removal of the residual tensile stresses imparted during grinding and hardening, and further enhances the residual compressive stresses on the raceway. As a result, the fatigue life of the bearings is improved. Further, the enhanced compressive stresses have a reduced risk of cracking the raceway, thereby increasing the operating life of the bearing. Additionally, the surface compressive stress is several times greater than the sub-surface tensile stress. More specifically, the value of the compressive stresses on the surface of the raceway lies in the range of 300 MPa to 500 MPa in the conventional method. In another embodiment, the first shot peening action (115) and the second shot peening action (125) generate 800 MPa to 1000 MPa upto maximum shear stress location.
In an embodiment, exposing the raceway to the first peening action (115) and the second peening action (125) ensures a desired layer of residual compressive stress under the contact and profile of the raceway maintained, thereby increasing the hardness by small value (around 100 HV).
In an embodiment, the dimples are configured to operate as lubricant sump to retain lubricant therein, thereby maintain an optimal thickness of lubricant film.
In an exemplary embodiment, a first raceway treated by conventional process of surface enhancement and a second raceway treated by the process of the present disclosure were compared. The surfaces of both the raceways were scanned by an electron microscope. It was evident from Figure 2A and Figure 2B, that the surface of the second raceway treated by the process of the present disclosure, has a smooth surface free from any asperity. Further, the smooth surface of the second raceway ensures that all prior grinding lines and asperities formed due to the first shot peening action (115) and the second shot peening action (125) has been removed, thereby facilitating a smooth surface of the raceway (wherein direction

of lay became null i.e., the orientation of the asperities orientation was in a random direction), which subsequently improves the lubrication as less the resistance to pressure flow factor (y=0). Further, the directionless surface provides minimal friction of the mating elements. The process of surface enhancement of the present disclosure thus, ensures that the life of the raceway improves.
In a working example, disc sample was prepared in accordance with a conventional process and the process of the present disclosure. The ball on disc test were conducted and compared under the conditions mentioned in Table 1. The 3-dimensional spatial and amplitude parameters of the surface of both conventional treatment of the surface of the raceway and the surface treated by the process of the present disclosure is compared in table 1. The texture aspect ratio (Str) value determines the direction of lay (formed by grinding marks/orientation of asperities) in any direction, whereas surface texture direction (Std) measured the angular direction of lay.

Test Ball on disc (Ball is stationary, disc is rotating)
Load 170 N
Sliding distance 5000 m
Lubricant ISO VG68
Temperature Normal room temperature
Film thickness (micron)
Sliding velocity at 0.5 m/s 120 nm
Sliding velocity at 1.5 m/s 250 nm
TABLE 1

Specific film thickness ratio (X) Process of the present disclosure Conventional
Sliding velocity at 0.5 m/s 2.8 0.75
Sliding velocity at 1.5 m/s 3.8 1.5
TABLE 2

It is inferred from Table 1 and 2, that the surface finish is a critical parameter for the optimal functioning of the rolling element bearings. When the rolling element bearings are operated at a low speed (0.5 m/s), the specific film thickness ratio (X) is less than 2. The specific film thickness ratio can be defined by the following
condition: X = ,, ' .
Wherein, ol is the root mean square value of the inner ring raceway of the rolling element bearing, o2 is the root mean square value the rolling element, and he is minimum film thickness of the lubricant.
In an embodiment, the low value of the specific film thickness ratio obtained for the conventionally treated raceway indicates that the film thickness is less than the peak of the contacting elements. The slow speed condition does not maintain the desired lubricant film thickness, thereby causing metal to metal contact between the elements of the bearing and subsequently resulting into premature failure due to wear. Hence, it can be inferred that the roughness of the surface of the raceways of the bearing should be kept as minimum as possible such as to work better during less velocity conditions.
Further, it is observed from Figures 3 A and 3B, and Table 1 that when the texture aspect ratio was approximately 0, the surface was dominated by direction of lay. When the texture aspect ratio is approximately 1, the surface does not have any dominant direction, thereby influencing better lubrication since pressure flow factor decreases. The lubricant film improves, thereby facilitating better lubrication over the conventionally treated surface. Both texture aspect ratio and surface texture direction confirm that the raceway treated by the process of the present disclosure has better lubrication properties than the raceway treated by conventional process.
Additionally, it is observed that value of the lubricant film does not depend on the roughness of the mating parts. However, the specific film thickness (k) is a proportional relation with the roughness. It is observed that the surface treated by

the process of the present disclosure has an improved surface finish than the conventionally treated surfaces. It is further observed, that at a low sliding speed of 0.5 m/s, the raceway treated by the process of the present disclosure is able to run under EHL (Elastohydrodynamic lubrication) lubrication regime (wherein X<3) whereas the conventionally treated raceway runs under boundary lubrication conditions (X<1). Additionally, at a sliding speed of 1.5 m/s, the raceway treated by the process of the present disclosure is able to run under a full film lubrication regime (X>3), whereas the conventionally treated raceway runs under mixed lubrication condition (X<3). These regimes indicate that the increased lubrication condition prevents the metal-to-metal contact thereby decreasing the friction and the subsequent heat generation (as shown in Figure 4A and 4B).
In another embodiment, the process of the present disclosure can be applicable in various systems where transmission of heavy load increases the possibility of premature failure of the rolling element bearing, more specifically, in automotive vehicles. In such systems, the load rating increases with the increase in service load.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process to enhance life and mechanical properties of rolling element bearings with lubricant retention, that:
• reduces surface roughness of the rolling element bearings;
• reduces friction between mating parts of the rolling element bearings;

• enhances the fatigue life of the rolling element bearings; and
• enhances performance of rolling element bearings.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, apparatus, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

WE CLAIM:

1.A process comprising the following steps:
a) forming (105) a raceway of a rolling element bearing;
b) grinding (110) the raceway to obtain a smooth surface;
c) exposing (115) the smooth surface of the raceway to a first shot peening action to obtain a first shot peened surface;
d) surface finishing (120) the first shot peened surface of the raceway of the rolling element bearing; and
e) exposing (125) the surface of the raceway to a second shot peening action performed at an intensity lesser than the intensity at which the first shot peening action (115) is performed, to obtain a second shot peened surface.

2. The process as claimed in claim 1, wherein the step of forming (105) includes at least one sub-step of hardening or quenching of the raceway.
3. The process as claimed in claim 1, wherein the step of first shot peening action (115) includes bombarding the smooth surface of the raceway by a first plurality of media balls at a first intensity level.
4. The process as claimed in claim 1, wherein the step of surface finishing (120) is a chemically assisted surface finishing performed by a mass finishing machine.
5. The process as claimed in claim 4, wherein step of the surface finishing (120) includes at least one phase of surface finishing.
6. The process as claimed in claim 1, wherein the step of second shot peening action (115) includes bombarding the surface of the raceway by a second plurality of media balls at a second intensity level.

7. The process as claimed in claim 6, which includes selecting media balls of a specific diameter for performing the first shot peening action (115) and selecting media balls of a specific diameter for performing the second shot peening action (125) and ensuring that the diameter of the media balls selected for performing the first shot peening action (115) is greater than the diameter of the media balls selected for performing the second shot peening action (125).
8. A raceway of a rolling element which is hardened or quenched and comprises a surface which is ground and shot peened at least twice by media balls, where the diameter of a first plurality of the media balls of a first shot peening action is larger than diameter of a second plurality of the media balls of a second shot peening action.