Bearings

What?
 A bearing is a machine part whose function is to support a moving element and to guide or
confine it's motion, while preventing motion in the direction of applied load.
 The word "bearing" incorporates the meaning of "to bear," in the sense of "to support," and "to
carry a burden." This refers to the fact that bearings support and carry the burden of revolving
axles.
 Today, bearings are one of the most commonly used machine components because their rolling
motion makes almost all movements easier while reducing friction. Bearings have two key
functions:
1. Transfer motion, i.e. they support and guide components which turn relative to one another
2. Transmit forces
PAGE 2
Radial Bearing Axial Bearing

Why?
 Function 1: Reduce friction and make rotation more smooth.
 Function 2: Protect the part that supports the rotation, and maintain the correct position for the
rotating shaft
PAGE 3
Motor overheating due to heating because
of the friction in between shaft and load
Misaligned and causing burn in the shaft

When?
 Since ancient times humankind has developed multiple ways of reducing friction. For now let's
just look at the example of the building of the pyramids of Egypt.
 But Leonardo da Vinci was the one who first thought of using bearings with cages, and became
Father of Modern Bearing.
PAGE 4
Block of a brick sliding over the
logs of wood, hence reducing
friction.
Still this design is the basis of the
modern advanced design and modern
day bearings are using this concept.

How?
 This figure shows how the "shaft" rotates, causing the rolling elements ("balls" or "rollers") inside
the bearing to roll. Bearings reduce friction by means of this rolling motion.
 The "rolling bearing", with its rolling motion, reduces friction more than the "plain bearing" with
its sliding motion, allowing for a greater decrease in the amount of energy consumption during
rotation.
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Components-
 The components that make up the bearing are as follows:
● Bearing rings (races) ... The ring-shaped components
● Rolling elements ... The components that roll between the bearing rings (races); rolling elements
can be either "balls" or "rollers"
● Cage ... The component that maintains a fixed gap so the rolling elements don't contact with each
other
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The structures of radial bearings The structures of thrust bearings

Which roller is required?
 There are a variety of different rolling elements designed to suit the specific conditions of the
bearings, such as the strength of the supporting force or the speed of the rotation.
PAGE 7

Why cage is required?
 when the bearing's inner ring rotates this causes the rolling elements to roll. When this happens,
unless the bearing has a cage, the rolling elements next to each other will make contact.
 When their surfaces come in contact, the rolling elements' rolling direction will be inverted
relative to each other, and the rolling motion of the rolling elements will be disrupted.
 In this way, bearing rings (races), rolling elements and cages all play a role in allowing bearings to
function, and it is by combining these functions that bearings can rotate smoothly.
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The categorization of bearings-
 Bearings support forces applied from various directions, and so they can be categorized based on
the "direction of the force".
 The force applied to a bearing is called the "load".
 The force applied perpendicularly to the shaft is called the "radial load", and that applied in the
same direction as the shaft is called the "axial load".
PAGE 9

The categorization of bearings-
 Bearings can be categorized into four groups based on the direction of the force supported and
the shape of the rolling elements.
PAGE 10
Rolling element
Ball Roller
Direction in which force is
mostly applied
Perpendicular to the shaft
(radial load)
Radial ball bearing Radial roller bearing
The same direction as the
shaft
(axial load)
Thrust ball bearing Thrust roller bearing

Radial ball bearings
 "Radial ball bearings" are ball bearings that can support a force that is applied perpendicularly to
the shaft.
 The contact angle of the radial and axial loads-
The contact angle is the angle formed by the direction of the load applied to the bearing rings
(races) and rolling elements, and a plain perpendicular to the shaft, when a "radial load" and "axial
load" are both applied to a bearing.
PAGE 11

Deep groove ball bearings Angular contact ball bearings

Radial roller bearings
 Radial roller bearings are roller bearings that can support a force perpendicular to the shaft. They
can support an even greater load than radial ball bearings, and there are bearing types that are
made to suit the type of roller.
PAGE 13
Cylindrical roller bearings Needle roller bearings
These use cylindrical rollers as
their rolling elements.
Cylindrical roller bearings can
support an even greater radial
load than deep groove ball
bearings, and are used in
machinery where they will
experience strong impacts.
These use needle rollers as
their rolling elements. Needle
rollers have a smaller
diameter than cylindrical
rollers, and so (as can be seen
in Figure) the bearings have a
smaller cross-sectional height
and contributed to the down-
sizing of machinery.

Cylindrical roller bearings Needle roller bearings

Tapered roller bearings
 These use tapered rollers in the shape of tapered trapezoids as their rolling elements.
 Tapered roller bearings are the most widely used among all roller bearings, and can support a
radial load and a one-directional axial load at the same time.
 When axial loads coming from both directions are to be supported, two or more tapered roller
bearings are combined together.
PAGE 15
A combination of tapered roller bearings to support axial
loads coming from both directions

Spherical roller bearings
 These use barrel-shaped convex rollers as their rolling elements. As shown in Figure, they are
inserted between a spherical outer ring raceway surface and an inner ring raceway surface. This is
why the inner ring, rolling elements and cage in a spherical roller bearing are able to rotate while
inclined toward the outer ring. Spherical roller bearings can support a large load, and are used in
machines where the shaft is easily bent.
PAGE 16

Which one?
 Bearings are used in many machines and are a very important machine component, When
designing a machine, it is important to select the bearing that is right for that machine.
PAGE 17

What are the criteria for selecting bearings?
 When selecting from among these many varied types of bearings, the bearing that is right for
your machine, the following two criteria are very important.
-Criterion 1: It should be appropriate for the machine's usage environment and the operating
condition that is being demanded of the bearing
-Criterion 2: It should be easy to acquire replacement bearings and it should facilitate
maintenance/inspection of the machine
 If these criteria are met, damage of the machine can be reduced, the time needed to replace the
bearings when performing repairs can be shortened, and the machine can be used for a longer
period of time.
PAGE 18
Extra-small
(miniature)
bearings
Ultra large
slewing rim
bearing

The order of priority for selecting bearings
ORDER Examination item Major points to confirm
1 Bearing type What magnitude and direction of load do you need? Will
it fit in the installation space?
2 Bearing arrangement Are you using two (or more) bearings on a single shaft?
3 Bearing dimensions and service life Do the dimensions and service life satisfy your needs?
4 Bearing limiting speed, running accuracy,
fits and internal clearance
Does it have the necessary running accuracy and rigidity
for the machine?
Does it have the fits and internal clearance to satisfy its
service life?
5 Bearing preload and rigidity Does it have the necessary rigidity for the machine?
6 Bearing lubrication Can the bearing rotate stably over a long period of time?
7 Components around the bearing What bearing surrounding structure/assembly are you
looking for?
8 Bearing mounting and dismounting Will it facilitate maintenance/inspection of the machine?
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How to select the type of bearing
 When designing a machine, most people first decide on the dimensions of the shaft to satisfy the
strength requirement, and then select the bearing based on that.
1) If the load will be mostly radial (perpendicular to the shaft), use a radial bearing, and if the load
will be mostly axial* (same direction as the shaft), use a thrust bearing. * Axial loads are
sometimes called thrust loads.
2) If the load on the bearing will be light, use a ball bearing, and if it will be heavy, use a roller
bearing.
3) If a radial load and an axial load are both placed on a single bearing at the same time
(combined load), a light combined load calls for a deep groove ball bearing or an angular
contact ball bearing, while a heavy combined load calls for a tapered roller bearing.
PAGE 20
combined load applied to an
angular contact bearing

Bearing installation space
 Using the table of boundary dimensions, select a bearing type that will fit in the installation space
based on the dimensions of the shaft or housing.
1) In the table of boundary dimensions, the dimensions such as bearing outside diameter and width
(or height in the case of a thrust bearing), corresponding to a specific bearing bore diameter, are
shown in series.
2) The "dimension series code" refers to a combination of the width series and the diameter series
that has a stepped bearing outside diameter with respect to the bearing bore diameter.
3)Even if a bearing has the same bore diameter, there are several types of width and outside
diameter, so select the appropriate bearing from among them. Some people choose bearings based
on the outside diameter of the bearing that matches the dimensions of the housing.
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An example of the bearing boundary dimensions table (a spherical roller bearing)

Bearing dimensions and service life
 When selecting a bearing, we need to determine the appropriate dimensions of the bearing so
that it can rotate stably inside the machine. What kind of things do we need to look out for when
doing this?
PAGE 23

Bearing service life
 As there is a service life for every object to make a thing economical we don’t want to spend extra
money so we decide choose the bearing which will met our required minimum time of operation.
Usually this is the operating hours.
PAGE 24

Defect in bearing caused in service life
 When the bearing that supports the load rotates, the load is repeatedly applied to the raceway
surfaces of the inner and outer rings each time rolling elements (balls or rollers) pass. Due to this
repeated load, high pressure is generated on the raceway surfaces of the inner and outer rings
that are in contact with the rolling surfaces of the rolling elements. Consequently, material flakes
from the surfaces of inner and outer rings or rolling elements by fatigue arising from repeated
contact stress.
PAGE 25

 When extremely heavy load is applied to a bearing that is not rotating, or that is rotating at a low
speed, an indentation (permanent deformation) occurs in the contact area between the rolling
element and the raceway surface of the inner and outer rings. This dent grows with the increasing
load and prevents smooth rotation of the bearing above certain limits.
PAGE 26

Boundary dimensions
 The boundary dimensions of the bearing are dimensions required for bearing installation with
shaft and housing, include the bore diameter, outside diameter, width or height, and chamfer
dimensions.
PAGE 27
The boundary dimensions of radial bearings The boundary dimensions of thrust bearings

Bearing Number
 The "bearing number" is a designation (number) that indicates special characteristics of a
bearing.
 This bearing number systematically indicates bearing specifications including bearing type,
boundary dimensions, running accuracy, internal clearance, and so on. It allows us to easily select
a bearing.
PAGE 28

6001 actually mean? Lets attempt to break it down.
(6)001
This first number relates to the bearing type, as
shown in the table below type 6 is a deep grooved
roller bearing.
Number Type
1 Self-Aligning Ball Bearing
2 Barrel and Spherical Roller Bearings
3 Tapered Roller Bearing
4 Deep Groove Double-Row Ball Bearing
5 Axial Deep Groove Ball Bearing
6 Deep Groove Ball Bearing (Single row
7 Single-Row Angular Contact Bearing
8 Axial Cylindrical Roller Bearings

 6(0)01 This second number relates the bearing series, which reflects the robustness of the bearing. As
you go up the scale below from 9 to 4 the inner and outer race thickness will usually increase along
with the ball size, this will be to help cope with extra load.
I. 9 Very thin section
II. 0 Extra light
III. 1 Extra light thrust
IV. 2 Light
V. 3 Medium
VI. 4 Heavy
 60(01) The 3rd and 4th digits of the bearing number relate to the bore size of the bearing, numbers 00
to 03 have a designated bore size depending on the number.
I. 00 10mm
II. 01 12mm
III. 02 15mm
IV. 03 17mm
 While numbers over 03 simply have a bore size which is 5 times that of the 3rd and 4th digit.
PAGE 30

Bearing limiting speed, running accuracy, and fits
 When selecting a bearing, we need one that rotates stably and with the required accuracy, in a
manner appropriate to the operating speed of the machine. What kind of things do we need to
pay attention to when selecting bearings?
PAGE 31

Limiting speed and running accuracy
 When a bearing rotates, its internal temperature rises due to friction resistance.
 Once the bearing reaches a rotational speed equal to or greater than a certain amount, its
temperature will increase tremendously, impairing the ability of the machine to run smoothly.
This certain amount is called the "limiting speed. "If a machine keeps running above the limiting
speed of the bearing, the temperature of the bearing will increase dramatically, and potentially
cause damage (seizure).
 limiting speed of the bearing is affected not only by the type and size of the bearing but is also
greatly affected by such factors as its tolerance, cage type and material, type and amount of
lubricant, lubrication method, and so on
PAGE 32

Bearing fits and bearing internal clearance
 "Bearing fit" is what we call the relationship between the bore diameter of the bearing inner ring
and the shaft diameter, or the relationship between the outside diameter of the bearing outer
ring and the bore diameter of the housing.
 a) Clearance fit The shaft diameter is smaller than the bore diameter of the inner ring, and even
after mounting the inner ring on the shaft there is a clearance between them. Bearing mounting
is simple.
 b) Interference fit The shaft diameter is larger than the bore diameter of the inner ring, and the
bearing is firmly locked in place on the shaft. This, however, can make it difficult to mount the
bearing on the shaft, so consideration needs to be given to the mounting method.
 c) Transition fit This is somewhere between the clearance fit and the interference fit.
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 Making the wrong decision regarding clearance fit can result in circumferential relative slipping on
the fitting surface (the mounting surface between the bearing and the shaft or housing) and
damage the bearing. For this reason, it is important to take care when deciding on the fits.
 Select a bearing with a limiting speed that is higher than the rotational speed in accordance with
the operating speed of the machine.
 Bearings of class 5 or higher are required for a precise running accuracy and a higher rotational
speed.
 Select the best bearing "fit" based on the load direction and conditions.
 Select the bearing internal clearance based on the operating clearance.
PAGE 35

Bearing lubrication
 The surfaces of bearing rolling elements and rings (inner ring and outer ring) are finished
extremely smooth. But however smooth they are their surfaces still have unevenness.
PAGE 36

 When a bearing rotates, the convex regions of the bearing rings and the rolling elements come in
contact with each other. This contact between the convex regions leads to friction and wear,
inhibiting the smooth rotation of the bearing.
 In order to prevent this friction and wear, oil or some other substance is applied between the
contact regions. This is called "lubrication." With the appropriate lubrication, an oil film makes it
so that the rolling elements and bearing rings do not come in direct contact. This results in less
friction and a massive decrease in wear.
PAGE 37Without Lubrication With Lubrication

Comparison
 As a lubricant material mainly we use either oil or grease, here is a comparison between them.
PAGE 38

Bearings

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Bearings