UNIT 7 BEARING

UNIT 7 BEARING
Structure
7.1 Introduction
7.2 Types of Bearing
7.3 Journal Bearings
7.4 Thrust Bearings
7.5 Rolling Contact Bearings
7.6 Roller Bearings
7.7 Summary
7.8 Answers to SAQs
7.1 INTRODUCTION
Bearings support the moving object which may have a rotary or translatory motion.
Generally bearing is referred to as that machine part which supports a rotating shaft or
axle. It is interesting to learn about bearings and also how they are supported in machine
frame or in a much larger frame. We shall see the drawing of such bearings and supports
in this unit.
7.2 TYPES OF BEARING
Two basic types of bearing are used in practice :
(a) Sliding contact bearings, and
(b) Rolling contact bearings.
7.3 JOURNAL BEARINGS
In sliding contact bearings the journal of the shaft rotates in the bearing. The bearing on
the inside has the same cylindrical surface as the external surface of the shaft journal. The
inside diameter of the bearing is only slightly greater than the outside diameter of the
shaft. The difference is called clearance and is meant to be filled by lubricating oil which
helps reduce friction and keep bearing cool. To increase the amount of lubricating oil
grooves are often cut on the internal surface of the bearing. The oil gets stored in these
grooves. In many other bearings oil is supplied though especially provided holes to feed
the oil either continuously or intermittently. These bearings are called journal bearing.
A single block bearing in which hole is bored to take shaft journal is called solid bearing.
A bush bearing is the one in which a thin sleeve is inserted in the body and the shaft
journal is supported in the sleeve. In case wear occurs the sleeve is either machined off or
simply pushed out. A set screw (grub screw) is used to prevent any axial movement of
the bush. The body of the bearing is made in cast iron which has two elongated holes in
the base which allow adjustment of any misalignment.
The bush is often made into two semi cylindrical pieces which fit into a perfect bush.
There is a lower part with base in which half the bush is placed and a cap sits on the top.
Such bearings called pedestal bearings or plummer blocks are used for supporting long
shaft away from their ends. There are several split construction which accommodate oil
entry and store holes. The bush normally carries flanges at the end to prevent any axial
displacement. The split bush is normally called brass and ends are so made that rotation
is prevented. To avoid any interference with wall of the pulleys or gears on the long line
shafts the bearing blocks are often supported on especially made brackets of varied
design. Figures 7.1, 7.2 and 7.3 show some journal bearings.
Bearing
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110
Machine Drawing
7.4 THRUST BEARINGS
Figure 7.1 : A Solid Bearing
Figure 7.2 : A Pedestal Bearing
Figure 7.3 : The Cap of a Split Journal Bearing
There are shafts which carry axial thrust in addition to radial loads or only axial thrust.
Bearings are provided either somewhere along the length or at the end of the shaft. For
horizontal shaft collars thrust bearings are used at any suitable section. For vertical shaft
the support provide at the bottom is called pivot or foot step bearing.
SAQ 1
Figure 7.4 shows a bush type journal bearing. Draw
(a) Elevation with right half in section,
(b) Side view with left half in section.
Figure 7.4

SAQ 2
SAQ 3
SAQ 4
Figure 7.5 shows a pedestal bearing. Draw elevation right half in section.
Figure 7.5
(a) Draw side view with left hand half in section of pedestal bearing in
Figure 7.5.
(b) Draw plan in full view of pedestal bearing shown in Figure 7.5.
Figure 7.6 shows the cap of a journal bearing. Draw three views
(a) Elevation
(b) Plan
(c) Side view (full section)
Figure 7.6
Bearing
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112
Machine Drawing
SAQ 5
Figure 7.7 depicts a footstep bearing. Draw elevation right half in section and plan
full in view.
Figure 7.7
7.5 ROLLING CONTACT BEARING
In rolling contact bearings there are three essential elements. There are two concentric
rings (called races) between which balls or rollers are placed such that the ball or rollers
can roll between outer surface of inner race and inner surface of the outer race. The shaft
journal is fitted in the inner race and outer race is supported in body of the machine. To
ensure that the rolling elements do not cluster but they roll at a fixed distance from each
other a fourth element called cage or separator is also placed between the inner and outer
races. Since the coefficient of rolling friction is much smaller than that in sliding these
bearings are also called antifriction bearings. Strictly speaking they are not without
friction. Figure 7.8 shows the cut view of a ball bearing in which rollers are spherical
balls. The rollers can be cylinders, tapered cylindrical with or without curved surfaces.
These bearings are often meant for carrying radial reactions but ball bearings can carry
considerable thrust. Yet some thrust ball bearings are also in use. Figure 7.9 shows some
types of bearing.
Figure 7.8 : A Ball Bearing

Single Row Radial
Ball Bearing
Double Row Radial
Ball Bearing
Single Row Radial
Thrust Bearing
Figure 7.9 : Some Types of Ball Bearing
Double Row self
Aligning Ball Bearing
The rolling contact bearings are standardized in dimensions and sold in the market under
the trade names such as SKF, Timken, NBC etc. Antifriction Bearing Manufacturing
Association (AFBMA) has evolved code of numbers which give idea about dimensions.
The defining dimensions are bore (d) outer diameter (D), width (B) and corner radius (r)
as shown in Figure 7.10. Manufacturers tables describe these dimensions. The last two
digits of the code number represent a number one fifth of bore or inner diameter. The
D + d
diameter of the centres of the roller is called mean diameter dm
= .
2
SAQ 6
Figure 7.10
SKF 6208 bearing has 9 balls each of 12 mm diameter. The single row bearing has
following dimensions.
Outer diameter, D = 80 mm
Bore or inner diameter, d = 40 mm
Width, B = 18 mm
Corner radius, v = 2 mm
Draw elevation half in section and side view full.
Bearing appears as shown in Figure 7.8.
Bearing
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114
Machine Drawing
SAQ 7
Figure 7.11 shows four bearings fitted in position. Bearings are restrained from
sliding out though they are fitted tight on their seat. Draw the circled part of the
Figure 7.11.
7.6 ROLLER BEARINGS
Figure 7.11
The rolling elements in these bearings are either cylindrical rollers or tapered rollers.
Cylindrical bearings are used for only radial load. Some bearings with thrust lips
provided either in outer or inner race can take minor thrust. Tapered roller bearings can
carry considerable thrust along with radial load. See Figures 7.12, 7.13 and 7.14.
Roller Bearing with
Lips in Outer Race
Roller Bearing with
Lips in Two Race
Figure 7.12
Figure 7.13 : Roller Bearings Shown in Elevation
Taper Roller Bearing

SAQ 8
Figure 7.14 : Elevation of a Taper Roller Bearing and Nomenclature
In a taper roller bearing D = 35 mm, d = 15 mm, B1 = B2 = 11 mm, t1 = 1 mm,
t2 = 1 mm , R = R1 = 1 mm . Draw elevation.
7.7 SUMMARY
Bearings of sliding and rolling contact type were introduced. Several of them have been
drawn. Some drawings have been shown in assemble. The reader will familiarize with
methods of drawing several bearings.
7.8 ANSWERS TO SAQs
SAQ 1
See Figure 7.15.
Elevation (Right Half in Section) End View (Left Hand in Section)
Figure 7.15
Bearing
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116
Machine Drawing
SAQ 2
SAQ 3
See Figure 7.17.
Figure 7.16 : Elevation (Right Half in Section)
Figure 7.17 : Side View of Pedestal Bearing of Figure 7.5
Figure 7.18 : Plan (Full View)

SAQ 4
SAQ 5
Figure 7.19 shows three views.
Figure 7.19
Figure 7.20
Bearing
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118
Machine Drawing
SAQ 6
SAQ 7
SAQ 8
Elevation (Upper Half in Section) Side View (Front Half or Cage Removed)
Figure 7.21
Figure 7.22
Figure 7.23