FIELD

The present disclosure relates to the field of roller bearings.

DEFINITION

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 whic5 h
they are used indicate otherwise.
Green Compact – The term “Green Compact” hereinafter refers to pressed but not
yet sintered part.
Sacrificial insert – The term “Sacrificial insert” hereinafter refers to a sheet used
10 during the fabrication process of an element to deposit microstructures, and which
is removed towards the end of the fabrication process so that the sacrificial insert
has no role in the operation of the element.
BACKGROUND
The background information herein below relates to the present disclosure but is
15 not necessarily prior art.
Roller bearings are employed for smooth functioning in vehicles and equipment
like constructional machineries such as excavators and dumpers. During
operation, foreign particles come in contact with the rolling elements of the
bearings, thereby causing pitting and wear of the rolling elements. As a result,
20 clearance between the rolling elements increases, and the life of the roller bearing
is reduced. To increase the wear resistance, the rolling elements are surface
hardened by techniques such as carbonitriding, nitriding and case carburizing.
However, surface hardening causes increase in the percentage of retained
austenite in the rolling elements, which causes dimensional instability during
25 operation. As a result, the clearance of the rolling elements alters, thereby
decreasing the bearing life.
3
Thus, the surface of the rolling elements should have high wear resistance, shock
loading capability and dimensional stability for improved performance of the
bearings. These factors are dependent on the material composition and the process
by which the rolling elements are manufactured.
There is therefore, felt a need of a process for manufacturing rolling elements 5 s of
roller bearings to alleviate the aforementioned drawbacks associated with the
conventional rolling elements.
OBJECT
Some of the objects of the present disclosure, which at least one embodiment
10 herein satisfies, are as follows:
An object of the present disclosure is to provide a process for manufacturing
rolling elements of a roller bearing.
Another object of the present disclosure to provide a process for manufacturing
rolling element that increases the performance of the roller bearing.
15 Yet another object of the present disclosure to provide a process for
manufacturing rolling element that is simple.
Still another object of the present disclosure to provide a process for
manufacturing rolling element that is cost effective.
SUMMARY
20 The present disclosure envisages a process of manufacturing a rolling element of a
roller bearing. The process comprises the following steps:
 pulverizing a first material and a second material separately to obtain
finely ground particulates having a predetermined grain size;
 providing a bi-layered die cavity comprising a core portion and a
25 shell portion;
4
 charging the core portion of the die cavity with the particulates of the
first material;
 disposing a sacrificial insert over the first material;
 charging the shell portion of the die cavity with the particulates of
the second material over the sacrificial insert, such 5 that the
particulates of the second material are separated from the particles of
the first material;
 compressing the particulates in the die cavity at a predetermined
pressure to obtain a green compact having a desired shape of the
10 rolling element; and
 sintering the green compact at a predetermined temperature to obtain
a rolling element.
In an embodiment, the step of pulverizing is performed in a ball mill.
In another embodiment, the step of pulverizing is performed in a milling vessel
15 having an inner lining of hardened steel, and partially filled with dry ceramic
milling balls.
In still another embodiment, the first material is pulverized for a time period of 14
to 16 hours.
In one embodiment, the second material is pulverized for a time period of 18 to 22
20 hours.
In another embodiment, the volume ratio of milling balls to the particulate is 30:1.
In an embodiment, the first material is a steel alloy.
In another embodiment, the first material is AISI 52100 steel.
In yet another embodiment, the second material is a titanium alloy.
25 In still another embodiment, the second material is Ti3SiC2.
5
In one embodiment, the sacrificial insert is of low density polyethylene resin or of
polypropylene resin.
In an embodiment, the predetermined pressure required for compressing the
particulates in the die cavity is in the range of 350 MPa to 500MPa.
In another embodiment, the predetermined temperature required for sintering 5 the
green compact is in the range of 1100°C to 1250°C.
In yet another embodiment, the green compact is sintered for a time period
ranging from 90-120 minutes.
In still another embodiment, the process further includes the step of surface
10 finishing the sintered rolling element of the roller bearing.
The present disclosure also envisages a roller element of a roller bearing having a
core made of steel alloy and a shell made of titanium alloy.
The present disclosure further envisages a roller bearing having a plurality of
rolling elements.
15 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A process of manufacturing a rolling element of a roller bearing, of the present
disclosure, will now be described with the help of the accompanying drawing, in
which:
Figure 1 illustrates a flowchart representing the steps involved in the process of
20 the present disclosure;
Figure 2 illustrates a schematic view of a roller bearing;
Figure 3 illustrates a schematic view of a rolling element of the roller bearing of
Figure 1;
Figure 4 illustrates a graphical representation of comparison of coefficient of
25 friction of rolling elements manufactured by conventional techniques and
6
coefficient of friction of rolling elements manufactured by the process of the
present disclosure; and
Figure 5 illustrates a graphical representation of comparison of wear depth of
rolling elements manufactured by conventional techniques and wear depth of
rolling elements manufactured by the process of the present disclosure5 .
LIST OF REFERENCE NUMERALS
200 – Rolling bearing
202 – Rolling element
202A – Core
10 202B – Shell
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
15 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, well20
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
25 forms "a,” "an," and "the" may be intended to include the plural forms as well,
7
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, 5 nts, 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.
10 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
15 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.
20 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.
A preferred embodiment of a process of manufacturing a rolling element (202) of
a roller bearing (200), of the present disclosure, will now be described in detail
25 with reference to Figure 1 through Figure 5.
The process, of the present disclosure, facilitates the use of multiple layers of
materials to produce the rolling element (202) having high wear resistance and
shock loading capability along with high dimensional stability.
8
Figure 1 illustrates a flowchart (100) representing the steps involved in the
process of manufacturing the rolling element (202) of the roller bearing (200).
The process comprises the following steps:
Step 102: pulverizing a first material and a second material separately to obtain
finely ground particulates having a predetermined grain size5 ;
Step 104: providing a bi-layered die cavity comprising a core portion and a shell
portion;
Step 106: charging the core portion of the die cavity with the particulates of the
first material;
10 Step 108: disposing a sacrificial insert over the second material;
Step 110: charging the shell portion of the die cavity with the particulates of the
second material over the sacrificial insert, such that the particulates of the second
material are separated from the particles of the first material;
Step 112: compressing the particulates in the die cavity at a predetermined
15 pressure to obtain a green compact having the desired shape of a rolling element;
and
Step 114: sintering the green compact at a predetermined temperature to obtain a
rolling element (202).
The first material is the material used for forming the core portion of the roller
20 element (202)
In an embodiment, the step of pulverizing the first material and the second
material is carried in a process of ball mill. In another embodiment, the step of
pulverizing the first material and the second material is performed in a milling
vessel. Typically, the milling vessel is a hollow cylindrical shell rotating about its
25 own axis. The inner surface of the milling vessel is usually lined with an abrasionresistant
material. In an embodiment, the milling vessel has an inner lining of
hardened steel. The milling vessel is partially filled with dry ceramic milling balls.
The milling balls are configured to cascade in the milling vessel as the milling
vessel is rotated to pulverize the material such that the size of the material
9
reduces. In an embodiment, the milling balls are dry ceramic balls that enable
pulverization of the first material and the second material at faster rate.
The step of pulverizing is performed with the help of a process control agent. In
an embodiment, the process control agent is toluene.
In an embodiment, the first material is pulverized for a time period of 14 to 5 16
hours.
In another embodiment, the second material is pulverized for a time period of 18
to 22 hours.
In one embodiment, the volume ratio of milling balls to the particulate size is
10 30:1.
The core (202A) of the rolling element (202) is made of soft metal which imparts
soft impact strength and fracture toughness. In an embodiment, the first material is
a steel alloy. In another embodiment, the first material is AISI 52100 steel having
a chemical composition of iron, chromium, carbon, silicon, and sulphur.
15 The shell (202B) of the rolling element (202) is made of material which has high
wear resistance, dimensional stability and reduced friction, more specifically
MAX phase material,. The MAX phase material is typically, carbides and nitrides
having an empirical formula: Mn+1AXn, where n=1 to 3, M is an early transition
metal, A is IIIA or IVA element and X is either carbon and/or nitrogen. In an
20 embodiment, the second material is a titanium alloy. In another embodiment, the
second material is Ti3SiC2, which possesses both ceramic and metallic properties.
Further, Ti3SiC2 is machinable, resistant to thermal shocks, and deforms
plastically at elevated temperatures. Further, Ti3SiC2 is wear resistant, less dense
and can be machined using conventional grinding techniques. Ti3SiC2 provides
25 high wear resistance, low friction and dimensional stability required by the outer
layer of the rolling element (202).
10
The sacrificial insert segregates the particulates of the first material from the
particulates of the second material. As a result, two distinguishable layers of the
roller element (202) i.e., a core (202A) surrounded by shell (202B) are formed (as
shown in Figure 3). The sacrificial insert is configured to evaporate during step of
sintering, thereby not allowing fusing of particulates of the second material 5 ial with
the particulates of the first material, and retain the desired shape of the rolling
elements (202).
In one embodiment, the sacrificed insert is of a material having a rigidity factor
that can withstand pressure applied during compression process, and can
10 evaporate during sintering. In another embodiment, the sacrificial insert is of
polymer material. In yet another embodiment, the sacrificial insert is of low
density polyethylene resin or polypropylene resin.
The predetermined pressure required for compressing the particulates in the die
cavity is in the range of 350 MPa to 500MPa.
15 Sintering the particulates of the first material and the second material in the die
cavity causes the loose particulates to form a compact solid piece. Further,
strength and integrity is imparted to the material of the core (202A) and the shell
(202B). The amount of heat and pressure administered during the sintering
process is slightly less than the melting point of both the materials.
20 The predetermined temperature required for sintering the green compact is in the
range of 1100°C to 1250°C.
The green compact is sintered for a time period ranging from 90-120 minutes.
In an embodiment, sintering is performed by a method selected from the group
consisting of vacuum sintering, pulse discharge sintering (PDS), and spark plasma
25 sintering (SPS).
In an embodiment, the sintered rolling element (202) may be subjected to coining
and sizing to impart dimensional accuracy to the sintered part, strength and better
11
surface finish by further densification of the sintered rolling element (202).
Thereafter, the porous surface of the rolling element (202) is impregnated with a
lubricating fluid to increase the lubricating properties of the rolling element (202).
In an embodiment, the sintered rolling element (202) is immersed in heated
lubricating fluid. The rolling element (202) is then heat treated for 5 obtaining
greater hardness and strength. The rolling element (202) is then machined by
processes like turning and grinding to obtain accurate features of the rolling
element (202).
The process further includes the step of subjecting the rolling element (202) to a
10 surface finishing. The step of surface finishing may include the sub-steps of
honing or lapping. Surface finishing facilitates the rolling element (202) to
achieve improved appearance, surface finish and dimensional accuracy, and
resistance to wear and corrosion of the rolling element (202). The surface
roughness required is 0.025 microns.
15 The process of the present disclosure facilitates the formation of the rolling
element (202) having two layers of dissimilar materials, wherein the materials are
not fused with each other (as shown in Figure 3). As a result, the individual
properties of the two materials are retained.
The present disclosure also envisages a roller element (202), of a roller bearing
20 (200), having a core (202A) made of steel alloy and a shell (202B) made of
titanium alloy.
The core (202A) is of AISI 52100 steel, and the shell (202B) is of Ti3SiC2.
The present disclosure further envisages a roller bearing (200) having a plurality
of rolling elements (202).
25 The simple and cost-effective process of the present disclosure ensures that
properties such as high wear resistance, shock loading capability and dimensional
stability are infused in the rolling elements (202).
12
In one embodiment, the process of the present disclosure is employed to
manufacture tapered rolling elements (202). In another embodiment, the process
of the present disclosure is not limited to manufacturing rolling elements (202),
but can also be used for manufacturing the inner ring and outer ring of the roller
element (200)5 .
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
10 departure from the present disclosure, and all such modifications are considered to
be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments
which are set forth for illustration purpose only and not to be construed for
limiting the scope of the disclosure. The following experiments can be tested to
15 scale up to industrial/commercial scale and the results obtained can be
extrapolated to industrial scale.
Experimental Details:
Example 1:
AISI 52100 steel alloy was pulverized in the milling vessel to obtain particulates
20 of a predetermined grain size. Similarly, Ti3SiC2 was pulverized in the milling
vessel to obtain particulates of a predetermined grain size. The steel alloy and
titanium alloy powder were thereafter, heated at 200°C for a time period of 2
hours to get rid of any moisture that was present in the particulates. The alloy
powders were charged in the die cavity and compressed to obtain a green compact
25 of the desired shape, which was then sintered and finished to obtain the rolling
element (202).
The surface properties of the rolling element (202) were measured as Vickers
hardness of 10.6 GPa under a load of 98N with elastic modulus as 320GPa. On
13
the other hand, the Vickers hardness of the core (202A) was measured as 1100
HV with elastic modulus of 1.8 GPa.
In an exemplary embodiment, the rolling element (202) manufactured by the
process of the present disclosure, and a rolling element manufactured by
conventional processes were subjected to Finite element analysis (FEA), a5 nd
compared with each other. The load conditions for simulating the rolling elements
under FEA are furnished in the following Table 1.
Table 1
Bearing part number N1252
Load 25% Dynamic load
10 The analysis indicates that the maximum shear stress distribution of the bearing as
per the load condition indicates that the rolling element (202), manufactured by
the process of the present disclosure, generates less stresses than the conventional
rolling element, which implies that the stress generation of the rolling element
(202), manufactured by the process of the present disclosure, was decreased by
15 10.7% due to high elastic deformation of the contact between the rolling element
(202) and the raceway. Further the rolling element (202) manufactured by the
process, of the present disclosure, was less deformed.
The tribological advantage of the rolling element (202) manufactured by the
process, of the present disclosure was studied by preparing discs for wear test and
20 then compared the results with conventional material. The results had shown a
significant improvement in friction properties.
Following are the experimental conditions required for the wear test conducted by
means of Ball on Disc tribometer:
 Load: 170 N
25  Ball : Steel (AISI 52100)
 Disc : first set :As per present invention & second set is conventional disc
14
 Sliding speed: 0.5 m /s
 Sliding distance: 2000 m
 Oil Quantity: 5 ml
The result of the test results are tabulated in Table 2, as follows:
Table 5 le 2
Test sets
Coefficient of
Friction
Wear Depth (μm)
Conventional rolling element 0.11 250
Rolling element (202)
manufactured by the process of
the present disclosure
0.07 180
The wear test results show that the friction between the rolling elements (202),
manufactured by the process of the present disclosure is 36.36% lesser when
compared to the rolling elements made by conventional techniques (as shown in
Figure 4). The wear of the rolling elements (202) is also 28% lesser than the
10 rolling elements made by conventional techniques (as shown in Figure 5). These
results indicate that the process, of the present disclosure can reduce the increase
in frictional heat as the friction is reduced, and enable the roller bearing to operate
cooler than conventional system.
TECHNICAL ADVANCEMENTS
15 The present disclosure described herein above has several technical advantages
including, but not limited to, the realization of a process of manufacturing a
rolling element of a roller bearing, that:
 increases the performance of the bearing;
 is simple; and
20  is cost effective.
15
The embodiments herein and the various features and advantageous details thereof
are explained with reference to the non-limiting embodiments in the following
description. Descriptions of well-known components and processing techniques
are omitted so as to not unnecessarily obscure the embodiments herein. The
examples used herein are intended merely to facilitate an understanding of way5 s
in which the embodiments herein may be practiced and to further enable those of
skill in the art to practice the embodiments herein. Accordingly, the examples
should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general
10 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
15 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.
20 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, devices, articles or the like that has
been included in this specification is solely for the purpose of providing a context
25 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.
16
The numerical values mentioned for the various physical parameters, dimensions
or quantities are only approximations and it is envisaged that the values
higher/lower than the numerical values assigned to the parameters, dimensions or
quantities fall within the scope of the disclosure, unless there is a statement in the
specification specific to the contrary5 .
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
10 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 of manufacturing a rolling element (202) of a roller bearing
(200), said process comprising the following steps:
 pulverizing a first material and a second material separately to
obtain finely ground particulates having a predetermined gra5 in
size;
 providing a bi-layered die cavity comprising a core portion and a
shell portion;
 charging said core portion of said die cavity with the particulates of
10 said first material;
 disposing a sacrificial insert over said first material;
 charging said shell portion of said die cavity with the particulates
of said second material over the sacrificial insert, such that the
particulates of said second material are separated from the particles
15 of the first material;
 compressing the particulates in said die cavity at a predetermined
pressure to obtain a green compact having the desired shape of a
rolling element; and
 sintering said green compact at a predetermined temperature to
20 obtain a rolling element (202).
2. The process as claimed in claim 1, wherein the step of pulverizing is
performed in a ball mill.
3. The process as claimed in claim 2, wherein the step of pulverizing is
performed in a milling vessel having an inner lining of hardened steel, and
25 partially filled with dry ceramic milling balls.
4. The process as claimed in claim 1, wherein said first material is pulverized
for a time period of 14 to 16 hours.
18
5. The process as claimed in claim 1, wherein said second material is
pulverized for a time period of 18 to 22 hours.
6. The process as claimed in claim 3, wherein in the ball mill, the volume
ratio of milling balls to the particulates is 30:1.
7. The process as claimed in claim 1, wherein said first material is a stee5 l
alloy.
8. The process as claimed in claim 1, wherein said first material is AISI
52100 steel.
9. The process as claimed in claim 1, wherein said second material is a
10 titanium alloy.
10. The process as claimed in claim 1, wherein said second material is
Ti3SiC2.
11. The process as claimed in claim 1, wherein said sacrificial insert is of low
density polyethylene resin or polypropylene resin.
15 12. The process as claimed in claim 1, wherein the predetermined pressure
required for compressing the particulates in said die cavity is in the range
of 350 MPa to 500MPa.
13. The process as claimed in claim 1, wherein the predetermined temperature
required for sintering said green compact is in the range of 1100°C to
20 1250°C.
14. The process as claimed in claim 1, wherein said green compact is sintered
for a time period ranging from 90-120 minutes.
15. The process as claimed in claim 1, which further includes the step of
surface finishing the sintered rolling element (202) of the roller bearing
25 (200).
19
16. A roller element (202), of a roller bearing (200), having a core (202A)
made of steel alloy and a shell (202B) made of titanium alloy.
17. The roller element (202) as claimed in claim 16, wherein said core (202A)
is of AISI 52100 steel and said shell (202B) is of Ti3SiC2.
18. A roller bearing (200) having a plurality of rolling elements (202) 5 ) as
claimed in claim 16 or claim 17.