This document discusses journal bearings and lubrication. It begins by defining hydrodynamic lubrication and types of journal bearings such as full, partial, and fitted. It then covers lubrication mechanisms like hydrodynamic, hydrostatic, and boundary lubrication. Finally, it discusses lubrication principles, terminology used in journal bearings, common bearing materials and their properties, and types of loads carried by different bearings.

1. Journal bearing and
lubrications
What is the Principal of hydrodynamic lubrication ?
What is the meaning of Partial journal bearing?
Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Radial, thrust and hydrodynamic bearing

2. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
In previous video we have already learned about definition and advantages of sliding contact bearing. Let us
start with classification of sliding bearing
Sliding contact bearings are classified in three ways.
1. Based on type of load carried
Thrust or axial bearing
Radial- thrust bearing
2. Based on type of lubrication
Thin film or boundary lubrication
zero film lubrication
3. Based on lubrication mechanism
Hydrostatic lubricated bearings
Elastohydrodynamic lubricated bearings
Boundary lubricated bearings
Solid film lubricated bearings
Radial bearing
Thick film lubrication
Hydrodynamic lubricated bearings

3. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Based on type of load carried – We have already discussed about what is radial or thrust bearing in
previous video of rolling bearing.
(ii) Thrust bearing
Footstep or pivot bearing – In this end of the shaft remains in contact with the bearing.
Collar bearing – A collar fitted with the shaft remains in contact with the bearing.
(iii) Radial – thrust bearing – These bearings can
carry both radial and
thrust load.
Footstep bearing
or pivot bearing
Collar bearing
Single collar
bearing
Multi collar
bearing

4. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Based on type of lubrication- 1. Thick film bearings. - The thick film bearings are those in which the working
surfaces are completely separated from each other by the lubricant. Such type of bearings are also called as hydrodynamic
lubricated bearings.
2. Thin film bearings. - The thin film bearings are those in which, although lubricant is present, the working surfaces
partially contact each other at least part of the time. Such type of bearings are also called boundary lubricated bearings.
3. Zero film bearings. – The zero film bearings are those which operate without any lubricant present.
Terminology of hydrodynamic journal bearing - Let D = Dia of bearing, d = Dia of journal, and l = Length of bearing.
1. Diametral clearance- It the difference between the diameters of the bearing and the journal. c = D – d
2. Minimum oil film thickness ( h0 )- It is the minimum distance b/w bearing and journal, under complete lubrication. it
occurs at the line of centres as shown in fig. Its value may be assumed as c / 4.
3. Radial clearance- It is the difference b/w the radii of the bearing and the journal.
mathematically, radial clearance, c1 = R- r =
𝑫−𝒅
𝟐
=
𝒄
𝟐
4. Eccentricity- It is the radial distance b/w the center (O) of the bearing and the displaced
center (O′) of the bearing under load. It is denoted by e.
5. Attitude or eccentricity ratio- It is the ratio of the eccentricity to the radial clearance.
Mathematically, attitude or eccentricity ratio

5. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
 Based on lubrication mechanism -
1. Hydrodynamic lubricated bearings - already discussed in detail.
2. Hydrostatic lubricated bearings - Hydrostatic bearings are those which can support
steady loads without any relative motion b/w the journal and bearing. This is achieved by
forcing externally pressurized lubricant between the members.
3. Elastohydrodynamic lubricated bearings- This lubrication is the phenomenon
that occurs when a lubricant is introduced between surfaces that are in rolling contact, such as mating gears or rolling
bearing. Since the hydrodynamic film is developed due to elastic deflection of the parts so known as elastohydrodynamic.
Boundary lubricated bearings-
When the speed of the bearing is inadequate, less quantity of lubricant is delivered to the bearing, an increase in the bearing
load, or an increase in the lubricant temperature resulting in drop in viscosity – any one of these may prevent the formation of
thick film lubrication and establish continuous metal-to-metal contact extensively. Often bearings operating in such situations
are called boundary lubricated bearings.
5. Solid film lubricated bearings-
For extreme temperature operations ordinary mineral oils are not satisfactory. Solid film lubricants such as graphite,
molybdenum disulfide or their combinations which withstand high operating temperature are used. These types of bearings
are common in furnace applications, or trunnion bearings of liquid metal handling systems, hot drawing mills etc.

6. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Lubrication of bearing – it is the science of reducing friction by application of a suitable
substance called lubricant. Between the rubbing surfaces of bodies having relative motion.
Objective of lubrication – (i) to reduce friction (ii) To reduce or prevent wear
(iii) To carry away heat generated due to friction (iv) To protect the bearing and journal from corrosion
Classification of lubricants-
Modes of lubrication- Thick film, thin film and zero film. Thick film is further divided in two
groups hydrodynamic and hydrostatic lubrication.
Hydrodynamic lubrication – It is defined as a system of lubrication in which the load supporting fluid
film is created by the shape and relative motion of the sliding surfaces.
Liquid lubricants like mineral or
vegetable oilsSemi solid lubricants like grease
solid lubricants like graphite or molybednum
disulphide

7. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Principal of hydrodynamic lubrication – It can be shown in three stages. Consider a steady load F, a
fixed bearing and a rotating journal .
Stage 1 - At rest, the bearing clearance space is filled with oil, but the load F has squeezed out the
oil film at the bottom. Metal-to-contact exists. The vertical axis of bearing and journal are co-axial.
Load and reaction are in line.
Stage 2 - When the journal starts rotating slowly in clockwise direction, because of friction, the
journal starts to climb the wall of the bearing surface as in Fig. Boundary lubrication exists now. The
wear normally takes place during this period. However, the journal rotation draws the oil between
the surfaces and they separate.
Stage 3 -As the speed increases, more oil is drawn in and enough pressure is built up in the
contact zone to float” the journal . Further increase in speed, additional pressure of the converging
oil flow to the right of the minimum film thickness position (ho) moves the shaft slightly to the left of
center. As a result full separation of journal and bearing surfaces occurs. This is known as
Hydrodynamic
lubrication or full film/thick film lubrication.
At this equilibrium condition,the pressure force
on journal balances the external load F.

8. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Journal or sleeve bearing -The radial bearings are also called journal or sleeve bearings. The portion of
the shaft inside the bearing is called the journal and this portion needs better finish and specific property.
Depending on the extent to which the bearing envelops the journal, these bearings are classified as full,
partial and fitted bearings. Among the sliding contact bearings radial bearings find wide applications in
industries . It has two types full and partial journal bearing.
Full bearing – The angle of contact of the bushing with the journal
is 360˚. Can take load in any radial direction.
Partial bearing – Angle of contact is always less than 180˚. Most of
the bearing in practice have 120˚. They can take load in only one
radial direction.
Clearance bearing – In this the radius of journal < radius of bearing.
Fitted bearing - In this the radius of journal = radius of bearing. Full bearing Partial bearing

9. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Bearing material - The materials commonly used for sliding contact bearings are discussed below :
1. Babbit metal. The tin base and lead base babbits are widely used as a bearing material, because they satisfy most
requirements for general applications. The babbits are recommended where the maximum bearing pressure (on
projected area) is not over 7 to 14 N/mm2. The composition of the babbit metals is as follows :
Tin base babbits : Tin 90% ; Copper 4.5% ; Antimony 5% ; Lead 0.5%.
Lead base babbits : Lead 84% ; Tin 6% ; Anitmony 9.5% ; Copper 0.5%.
2. Bronzes. The bronzes (alloys of copper, tin and zinc) are generally used in the form of machined bushes pressed
into the shell. The bush may be in one or two pieces. The bronzes commonly used for bearing material are gun metal
and phosphor bronzes.
The gun metal (Copper 88% ; Tin 10% ; Zinc 2%) is used for high grade bearings subjected to high pressures (not
more than 10 N/mm2 of projected area) and high speeds.
The phosphor bronze (Copper 80% ; Tin 10% ; Lead 9% ; Phosphorus 1%) is used for bearings subjected to very
high pressures (not more than 14 N/mm2 of projected area) and speeds.
3. Cast iron. The cast iron bearings are usually used with steel journals. Such type of bearings are fairly successful
where lubrication is adequate and the pressure is limited to 3.5 N/mm2 and speed to 40 metres per minute.
4. Silver. The silver and silver lead bearings are mostly used in aircraft engines where the fatigue strength is the most
important consideration

10. Journal Bearing types, lubrication of bearing, principal of hydrodynamic lubrication
Bearing material properties – Properties as discussed below must be considered in selecting the best
material.
1. Compressive strength. - The maximum bearing pressure is considerably greater than the average
pressure obtained by dividing the load to the projected area. Therefore the bearing material should have
high compressive strength to withstand this maximum pressure so as to prevent extrusion or other
permanent deformation of the bearing.
2. Fatigue strength. - The bearing material should have sufficient fatigue strength so that it can withstand
repeated loads without developing surface fatigue cracks. It is of major importance in aircraft and
automotive engines.
3. Comformability. - It is the ability of the bearing material to accommodate shaft deflections and bearing
inaccuracies by plastic deformation (or creep) without excessive wear and heating.
4. Embeddability. - It is the ability of bearing material to accommodate (or embed) small particles of dust,
grit etc., without scoring the material of the journal.
5. Bondability. - Many high capacity bearings are made by bonding one or more thin layers of a bearing
material to a high strength steel shell. Thus, the strength of the bond i.e. bondability is an important
consideration in selecting bearing material.
6. Corrosion resistance. - The bearing material should not corrode away under the action of lubricating
oil.
7. Thermal conductivity. - The bearing material should be of high thermal conductivity so as to permit the
rapid removal of the heat generated by friction.

11. If you found the video knowledgeable then like the video
Refrences – 1. Shigley’s mechanical engineering design
2. Design of machine elements by V B Bhandari
3. A text book of machine design by khurmi
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