Lubrication and Bearing Module.

IHRDC

Course Manual Lubrication & Bearings

Course Manual Lubrication & Bearings

IHRDC

GRADUATE ENGINEER

DEVELOPMENT PROGRAMME

MECHANICAL DISCIPLINE

LUBRICATION

&

BEARINGS

Total Pages (65)Lubrication and Bearings

Graduate Development Programme Module (M 03 )5D( This Module is designed for AFPC existing Mechanical Graduates, provide hands-on experiences as well as understanding on lubrication system, antifriction bearing and sliding bearings .

( This Module focuses on the principle of lubrication, journal bearing types and troubles and antifirction bearings types configuration and troubles.

Principles of lubrication.

Journal bearing principles, types and troubles.

Axial thrust bearings types and troubles.

Antifriction bearing types and configurations.

Antifriction bearing mounting and shaft preparation.

.Antifriction bearing troubleshooting.

Audience :

Prerequisites :

Location :

Format :

Mechanical Graduates.

English comprehension and communication.

AFPC Training Center, D. Z.

Lecture, discussion and OJT workshop practices.

This module is one of thirteen modules, which together cover the theoretical aspect of the Technical Training for the AFPC Mechanical Graduates Development Programme. This programme has been developed specifically for AFPC Graduate Development to enhance the dynamic Nationalization drive adopted by the company.

SAFETY REQUIREMENTS

1. GENERAL

Participant must become thoroughly familiar with the following safety requirements and first aid procedures, and must observe the safety requirements at all times. Maximum safety of personnel is of primary importance, followed closely by protection of equipment from damage. Careful observation of these safety requirements will minimise hazards or injury to personnel and equipment.

There are three types of Safety Requirements: Warning, Cautions, and Notes, which are intended to emphasise critical information. Safety Requirements also include procedures to be observed in the event of certain operating malfunctions and important precautions to be observed when personnel are working in a special environment (such as in an explosive atmosphere) or with a special substance.

Warnings, Cautions, and Notes are listed in order of significance as follows:

WARNING

A WARNING points out a procedure, practice, condition, or precaution which, if not heeded, could result in personal injury or loss of life.

CAUTION

A CAUTION points out a precaution which, if not observed, could result in damage or destruction of equipment.

Note:

A Note highlights information necessary to understand or follow a procedure, practice, condition, or description.

2. COURSE SAFETY REQUIREMENTS

Participant has to use the following safety precautions during his course:

-Coverall.

-Safety helmet.

-Safety shoes/boots.

-Leather gloves.

Course Contents:

Page

1. Course objectives. 5

2. Course outline. 6

3. Equipment / resources. 8

4. Course manual (hand out for participants). 9

5. Training aids. 52

6. Lesson plan. 53

7. Course final test. 62

1-Course Objectives

On completion of this course, the trainee should be able to:-

Section-I : Lubrication

Understand the characteristics of friction.

Explain the boundary lubrication.

Explain-film lubrication.

Understand the rolling friction.

Explain the six purposes of lubrication.

Section-II Journal bearing, tilting pad and axial thrust

Understand the principle of operation.

Understand journal bearing types.

Describe tilting pad / axial thrust bearing.

Explain vibration due to journal bearing.

Perform journal-bearing maintenance.

Understand failure modes and causes.

Section-III: Antifriction bearing

Understand bearing types.

Understand bearing configuration.

Explain the preparation for mounting.

Perform mounting / dismounting.

Understand troubleshooting.

2- Course Outlines

This course is designed for AFPC existing mechanical technicians, provide understanding and hands-on experience related to lubrication and bearings. Duration of this course is five days (30 Hrs.) the maximum number of participants shall be four in one batch.

This course to be conducted at AFPC training centre classrooms and assembly workshop.

Course Time Plan:-

Instruction time: 12 Hrs.

Workshop time: 12 Hrs.

Final test time: 6 Hrs.

Day-1 (6.0 Hrs.)

Time (Hrs.)ActivityLocation

1

1

21- lubrication

1. Characteristics of friction

1.1 Boundary lubrication

1.2 Full-film lubrication

1- Rolling friction

2- Purposes of lubrication

Classroom

1.30

0.302-Journal bearing

1-Principle of operation

2-Journal bearing types

Assessment

Classroom

Day-2 (6.0 Hrs.)


2

1

2- Journal bearing

3. Tilting pad bearing

4. Axial thrust bearing

5. Vibration due to bearing.

6. Bearing materials.

7. Journal bearing maintenance.

8. Bearing failure modes.

Classroom

2.30

0.302-Journal bearing maintenance

(workshop practice)

Measurements

Assembly/ disassembly

Check clearance

Check failure modes

Assessment

Workshop

Day-3 (6.0 Hrs.)


1

13- Antifriction bearings

1. Bearing types

2. Bearing configuration

3. Shaft and housing preparation

4. Mounting and dismounting

5. Troubleshooting

Classroom

2.30

0.30-Antifrction bearing (workshop practice)

-Assembly and disassembly

-Measurements and checking clearances

-Assessment

Workshop

Day-4 (6.0 Hrs.)


3

3 Journal bearing assembly and disassembly (workshop practice)

Roller bearing assembly and disassembly

(workshop practice)

Workshop

Day-5 (6.0 Hrs.)


1Final Assessment

Classroom

5Final assessment (practical)Workshop

3-Equipment and Resources

1. Samples of bearings (different types).

2. Single stage centrifugal pump (Union).

3. Multistage centrifugal pump (Tayssen).

4. Reciprocating pump (Ingersoll-rand).

4 Course Manual

(Hand out for Participants)Section-I

1-Lubrication

1-Principles of Lubrication

Lubrication

Form the moment you walk through the doors of your plant; you can find all kinds of machinery with moving parts that must b lubricated. Even the hinges on the doors must be oiled or greased. Moving parts of air compressors, machine tools, power presses, and conveyor systems all need lubrication.

To lubricate means to make a surface smooth and slippery. It also means to apply a lubricant. A lubricant is any substance that reduces friction by starting creating a slippery film between two surfaces. This film permits one surface to move easily over the other surface.

1-Characteristics of Friction

Th primary purpose of a lubricant is to reduce friction. Lubrication is merely a means of separating moving surfaces by providing a film for the surfaces to travel on.

Take the simplest case of a flat-sided object moving over a flat surface. If you move Block A across Block B, you feel a considerable amount of resistance to the effort you apply. That resistance is friction.

You recall that static friction is the force that must be overcome to start one surface sliding over another. To get Block A to begin to move over Block B, for example, you must first exert force equal to the maximum static friction between their surfaces. Static friction could be called the friction of bodies at rest.

Once an object is moving, things become little easier. The force required to keep an abject moving is always less than the static friction for the force of resistance acting when one surface slides over another is called kinetic sliding friction force, In other words, this is the friction of motion.

If Blocks A and B are left standing for some time without a layer of lubrication between them the static friction force between their surface tends to get a little greater.

If the normal force between Blocks A and B increases greatly, as it does when parts expand due to high temperatures, the starting effort required may be so great that it is almost impossible to get one surface to slide over the other.

The surfaces have partially fused together, and the parts have seized up. This condition occurs where there has been no lubrication.

But what happens when you apply a lubricant? Figure -2 shows the result.

Oil is drawn between the two blocks, and produces a film between them. When the film is spread evenly across the areas where Blocks A and B are allowed to slide, the blocks remain separated and continually slide on the liquid film.

Neither block ever contacts the other.

Fluid friction result from the cohesion of molecules. Anytime you cause one sheet of fluid molecules to move with respect to another sheet of molecules, you disrupt the forces between them. This causes a resisting force.

Fluid friction can be illustrated in the action of a boat going through the water. The water molecules in contact with the surface of the boat hull tend to adhere to the hull. Therefore, that layer of molecules travels at the boats speed.

Other layers of water molecules nearby are drawn along by the motion. But the layers travel at slower and slower speeds; the farther they are from the boat.

The forces of attraction among all these layers of water molecules tend to retard the motion of the boat. The same effect occurs in a bearing. The friction caused by metal-to-metal contact is eliminated when a film of lubricant is applied. That friction, however, is replaced by another friction, fluid friction, because the metal surfaces are moving through the liquid oil. Fortunately, fluid friction force is usually much smaller than kinetic sliding friction force.

Fig. 1 Dry surfaces in contact Fig. 2 Lubricated surfaces separated by oil film.

1.1 Boundary Lubrication:

It occurs as a machine starts-up and continues almost to the point of full operational speed.

The boundary film lubricates a plain journal bearing from the time it starts up until a full film of lubricant is established in the bearing, In Fig. 3, you see a graph of rotational speed vs. friction force for such a bearing, as it gets up to speed.

This shows the effects of boundary and full-film lubrication. The downward slope of the curve is the boundary lubrication portion. Here, friction decreases as the boundary film is established and the shaft comes up to operating speed.

Then, the lubrication pattern changes from boundary to full-film lubrication, and the curve turns and beings to slope gradually upward. This part of the curve represents the gradual increase in fluid friction (operating under full-film conditions).

Fig. 3 Journal speed vs. friction force for plain journal bearing

1.2 Full-film Lubrication: Full-film lubrication is the ideal condition in which the two moving surfaces are completely separated from each other.

Full-film lubrication can be classified into two types or categories. The first, is hydrodynamic full-film lubrication? The second is hydrostatic full-film lubrication.

Hydrostatic full-film lubrication occurs only in those cases in which a machine part, even when it is completely at rest, is fully supported by a cushion of liquid.

In hydrodynamic full-film lubrication, a pressure builds up in the lubricant as a result of the machine parts being in motion. The pressure comes from the resistance of the lubricant to movement and compression. This internal fluid pressure lifts and separates the two moving surfaces. As a shaft begins to rotate in a plain journal bearing, for example, the fluid pressure lifts the shaft away from the bottom of the bearing. You can see this happening in Fig. 3.

Fig. 4 The development of full-film lubrication in a plain journal bearing

Bearings or other moving parts must always be designed so that a liquid wedge can form as the part beings to move. Then, as motion increases, the machine part moves up on the wedge of lubricant in sled fashion. Because of the confined spaces, the lubricant resists the efforts of the moving parts to squeeze it out of the way. The pressure thus formed keeps the surfaces apart.

Hydrostatic full-film lubrication has exactly the same effect as dynamic full-film lubrication.

That is the lubricant completely separates the parts being lubricated. The difference between the two is that the pressure is supplied by an outside source, rather than by the action of the rotating parts. For example, pressure may be developed and maintained by a pump.

The advantage of hydrostatic lubrication is that it can be used to control the clearance between two moving surfaces.

2. Rolling Friction

Fig. 5 Rolling friction is low because of small contact area

Another type of kinetic friction that must be mentioned is rolling friction. The rolling action is different from sliding action because only a small part of the roller is actually touching the surface on which it is rolling.

As a roller, ball. Or wheel moves across a firm surface, the surface is deformed a little by the extra load it has to bear. This deformation moves ahead of the roller like a wave, as shown in Fig. 6.

Fig. 6 Deformation, of a surface by a rolling object.

Fig. 7 an oil film completely surrounds each ball in a lubricated ball bearing

The wave is microscopic in size and cannot be seen with the naked eye. Nevertheless, it does cause some resistance to rolling, which is called rolling friction.

Rolling friction is much slighter than sliding friction. When roller bearings or ball bearings are installed on a shaft, the total rotating friction is much less than if the shaft were rotating in plain journal bearings. Rolling friction can be reduced still more by adding a lubricant.

When oil is applied to a ball bearing, for example, each ball is completely coated with a film of lubricant, As shown in Fig. 7; the film separates the ball from the metal surfaces it had been touching. Now, as the ball rolls along, it produces a small shock wave in the fluid oil instead of in the solid bearing surfaces.

Since deforming a liquid causes less resistance than deforming a solid, the total friction has been reduced still more by the oil.

Because considerable fluid movement occurs in a lubricated ball or roller bearing, fluid friction is an important part of the total friction.

Oil is churned and moved about in many directions. As a result, internal friction within the oil itself can become rather large, and the oil can begin to heat up.

3. The six Basic Purposes of Lubrication

The six basic purposes of lubrication

1. To reduce friction.

4. To cool moving elements.

2. To reduce wear.

5. To prevent corrosion.

3. To help dampen shock.

6. To seal out dirt, other contaminants.

The table lists six reasons for lubricating machines. You have examined the first reason, to reduce friction in some detail. Now consider each of the other five reasons.

2- Reducing Wear

The wearing down of machine parts is caused by friction. If you reduce friction through lubrication, you also reduce wear. The thickness of the lubricant film is important. If the film is thick enough, the two surfaces will never actually contact each other. If the film is no quite thick enough to separate the two pieces, then some of the high points will break off. In many industrial applications, the film is not thick enough to separate the moving parts completely. This is one reason why even lubricated parts do wear out.

3- Dampening Shock

The way a lubricant dampens shock is by making use of its ability to distribute pressure. A practical example of this property is found in gear lubrication. Lubricant is squeezed by the gear teeth as they mesh together. The squeezing action forces the lubricant to squirt out between clearance points in the meshed teeth.

Refer to Fig. 1-8 According to logic. If the left-handgear in Fig. 8 is the driving gear. The pressure on the lubricant should be much greater at point A than at point B. Since fluids quickly equalised any pressure differences, however, the excessive pressure is instantly drawn from A and added to B. This reduces the shock at point A.

Fig. 8 Dampening shock in a pair of gears

4- Cooling Action of lubricants

By itself, a lubricant does not have much cooling action; it prevents excessive friction so that less heat will be generated. But lubricants also carry away some heat from the points where it is generated to coolers areas, where it is then dispelled into the air.

In many systems, hot oil circulates through an oil cooler the oil cooler may simply have metal fins to radiate heat into the air, The Figure shows the path of heat flow in a pressurised lubrication system

5- Corrosion Prevention

Another useful function of lubricants is to prevent or retard rust and corrosion. A lubricant does this when it forms a protective film on metallic machine parts. The film blocks the direct contact of metal with oxygen in the air, so that the metal cannot oxidise.

6- Sealing Action of Lubricants

Lubricants serve as seals in machines in two ways. First, a lubricant can seal itself into the place where it is needed. Second, a lubricant can also seal out dirt and other contaminants from the contact areas.

A very small amount of grease at the end of the shaft is exposed to the air. It oxidises just a bit, and becomes a little stiffer than the rest of the grease. The result is a very thin skin or scab that forms on the exposed grease.

This scab seals the grease in place and keeps dirt from entering the bearing.

Fig. 9 A grease-packed journal bearing, showing the self-sealing action

Section-II

1- Journal bearing, tilting pad and axial thrust bearings

1- Oil Film principles of Operation:-

A journal bearing is essentially a viscous pump, and it derives load capacity by pumping the lubricant through a small clearance region. Referring to Fig. 1, the fluid is dragged along by the rotating journal. To generate pressure, the resistance to pumping must increase in the direction of flow. This is accomplished by a movement of the journal such that the clearance distributed takes on the form of a tapered wedge in the direction of rotation, as shown in Fig. 1.

The eccentricity e is the total displacement of the journal from its concentric position. The attitude angle-y in Fig. 1 is the angle between the load direction and the line of centres. Note that because of the necessity to form a converging wedge, the displacement of the journal is not along a line that is coincident with the load vector. A positive pressure is produced in the converging region of the clearance. Downstream of the minimum film thickness, which occurs along the line of centres, the film becomes divergent. The resistance decreases in the direction of pumping, and either negative pressure occurs or the air in the lubricant gasifies or cavitates and a region of atmospheric pressure occurs in the bearing area. This phenomenon is known as fluid bearing cavitation.

Fig. 1 two-groove cylindrical bearing

2- Journal Bearing Types

1- Cylindrical Bearing

The most common type of journal bearing is the plain cylindrical bushing shown schematically in Fig. 1. It may be split and have lubricating feed grooves at the parting line. A ramification is to incorporate axial grooves to enable better cooling and to improve whirl stability.

2- Cylindrical Bearing with Axial grooves

A typical configuration of this type of bearing is plain cylindrical bearing with four equally spaced longitudinal grooves extending most of the way through the bearing. There is usually a slight land area at either end of the groove to force the inlet flow to each groove into the bearing clearance region (Fig. 2) rather than out the groove ends.

Fig. 2 Cylindrical Bearing with Axial Grooving

3-Elliptical and Lobe Bearings

Elliptical and lobe bearings have noncircular geometeries. Figure 3 shows two types of three-lobe bearings, with the clearance distribution exaggerate so that the lobe geometry is easily discernible. An elliptical bearing is simply a two-lob bearing with the major axis along the horizontal axis.

a. The lobe bearing shown in Fig. 3a is a symmetric lobe bearing, where the minimum concentric clearance occurs in the centre of each lobed region. Thus, at the leading edge region converging clearance produces positive pressure, but downstream of the minimum full thickness there occurs a divergent film thickness distribution with resultant negative, or cavitation pressures.

Fig. 3 (a) symmetric lobe bearing (b) canted lobe bearing

b. The canted lobe shown in Fig. 3b, on the other hand, generally develops positive pressure throughout the lobe because the bearing is constructed with a completely converging film thickness in each lobed region.

This design has excellent whirl resistance and reasonably good load capability.

They are generally used for high-speed, low-load applications where whirl might be a problem.

Standard journal bearing

3- Tilting- pad Bearing

|Tilting-pad bearings (Fig. 4 are used extensively, especially in high speed applications, because of their whirl-free characteristics. They are the freest of all bearing configurations. An important geometric variable for, tilting-pad bearings is the preload ratio, defined as follows: where c = machined clearance. C= concentric pivot film thickness. The variable c is an installed clearance and is dependent upon the radial position of the pivot. In Fig. 5 are shown two pads. Pad 1 has been installed such that the preload ratio is less than 1. For pad 2 the preload ratio is 1. The solid line represents the position of the journal in the concentric position. The dashed portion of the journal represents its position when load is applied to the bottom pads (not shown). Pad 1 is operating with a good converging wedge even through the journal is moving away from it. Pad 2, on the other hand, is operating with completely diverging film, which means that it is totally unloaded. Thus, bearings with installed pad preload ratios of 1 or greater will operate with unloaded pads, which reduces overall stiffness of the bearing and results in a deterioration of stability. So, it is important to design bearing with preload.

C

Ratio ( 1

C

Fig. 4 Five-pad tilting-pad baring

Fig. 5 Tilting-pad bearing preload

Tilting Pad Journal Bearing

4- Axial Thrust Bearings

1- The Collar Bearing

The bearing shown in Fig. 10 is used for combined radial and axial loads.

The radial load is absorbed in the normal manner using white metal covered bearing shells.

In order to carry the axial load a fixed collar is machined on the shaft. This collar is supported by thrust pads. Each of these thrust pads is made self-aligning by using balls as pivots. During operation the thrust pad adjust to that the material of the collar and the pads are separated by a wedge of oil. The bearings shown are used in large pumps and centrifugal compressors.

Fig. 10 Collar Bearing with Thrust pads

2- The Michell Axial Thrust Bearing

When a turbine or electric motor rotates the shaft has a constant speed, which results in a constant axial load. It is impossible for the oil to penetrate the space between the collar and the thrust pads. An engineer, A. Michell, invented a bearing, which can bear high surface pressure without any damage to the lubrication. The design is such that the sliding surfaces do not touch each other because of the layer of oil, which is always present between the sliding surfaces. The friction between these surfaces is therefore very small, as it only fluid friction. This means that the thrust pad can carry a much larger surface pressure, between 25-30 Bar, normal collar bearings can take an axial load corresponding to 4 Bar.

The method of operating of the Michell thrust bearing is shown in Fig. 11. The rear of pad a has a ridge R that allows the pad to pivot. This ridge is slightly out of centre and placed to the left of the collar C (relative to the direction of rotation).

If C is rotated while at the same time a load K is applied then an interval pressure will be created in the oil layer. The area to the right of ridge R is larger than the area to the left the force which is produced as a result of the oil pressure will be larger on the right hand side than on the left hand side, this will cause the pad A to pivot and take up the position as shown. In this way a wedge shaped space has been created between A and C so that when C exerts great pressure into the pad the lubricating oil will always be able to enter this area when C moves towards A.

As the gap in the direction of rotation keeps getting smaller the interval pressure in the left hand side will increase which will prevent the surfaces A and C from touching. The thrust pad will pivot just enough to allow the higher press (caused by the wedge form) multiplied by the area of the block left of the pivot to balance the lower oil pressure at the entrance multiplied by the area to the right of pivot R. This results of course in fluid friction only and no metal to metal contact.

Fig. 11 The Michell Axial Thrust Bearing

3- Kingsbury Thrust Bearing

Double horizontal equalising Kingsbury thrust bearing (6 ( 6) & (6 ( 0) with forced lubrication.

General Description

1. The 6(6 thrust bearing is of the Kingsbury equalising type having six thrust segments or shoes on each side of the collar and is consequently capable of full designed thrust load in either direction. The 6(0 bearing has 6 shoes on the side of normal thrust and a bumped ring on the unloaded side. In either case the thrust of the rotating element is transmitted through the thrust collar to the shoes, by the shoes to the shoe supporting elements, and hence to the stationary housing and the foundation.

2. The general designs of the bearing are shown in the accompanying illustration and the load equalising means in the diagram below. As will be evident upon referring to the diagram.

The load transmitted by the collar to any one thrust shoe causes that shoe to press against the upper levelling plate immediately behind it. Each levelling plate, in turn is supported upon one edge of each of two adjacent lower levelling plates, the other edges of which take part in supporting the next upper levelling plates an either side. As a result of this arrangement, any incipient excess of thrust on one show is immediately shared through the interaction of the levelling plates, by the adjacent shoes, and this interaction and load sharing is distributed all around the circle so that all the shoes automatically receive equal loading.

3. The terms upper and lower levelling plate do refer to the accompanying

drawing (in which the lower levelling plate- appears above the shaft centreline, while the upper is below it). The upper plates are the ones in contact with the shoes and lower the ones in contact with the, base ring regardless of their apparent relative positions in the illustration.

4. If the bearing is not to be used immediately, all parts- especially the collar should be protected against dampness, rust and bruises.

Equalising Construction used in six-shoe bearings

6(0 Shoe Bearing

6(6 Shoe Bearing

Axial thrust Bearing

Sliding Bearing Illustration

Modified journal bearing half with pressure dam cut into bearing bore.

Tilting pad journal-bearing halves and shoe (disassembled).

Tilting pad thrust bearing, shoe and collar (disassembled).

5- Vibration Due to plain (Journal) Bearings

Problems with plain journal, which result in high levels of vibration, are:

1- Bearing misalignment of a sleeve type bearing, with its shaft will cause vibration if accompanied with unbalance.

Misalignment of a sleeve-type bearing with its shaft will only cause axial vibration if accompanied by unbalance.

2- Oil Whirl

Oil whirl is another problem associated with plain or Journal-type bearing that produce vibration.

This vibration occur on machines equipped with pressure lubricated sleeve bearings and operating at a relatively high speed, normally above the critical sped of the rotor. Oil whirl vibration is often quite severe, but is easily recognised because the frequency produced is slightly less (3% - 8% less) than one half the R. R. M of the shaft.

The mechanism of oil whirl can be explained by referring to the diagram shown as follows:

Under normal operation, the shaft of the machine will ride up the side of the bearing slightly, as shown. The shaft, operating at an eccentric position from the bearing centre, draws oil into wedge to produce a pressurised load-carrying film. This oil film is made up of molecules, and those oil molecules adjacent to the shaft tend to stick to the shaft and rotate at shaft rpm.

However, those oil molecules adjacent to the bearing tend to adhere to the bearing, which is not rotating. As a result, the oil between the shaft and bearing will be in shear and will tend to rotate at a speed that is the average between shaft speed and bearing rpm, which of course is zero, as a result, the average rotating speed of the oil film between the shaft and bearing is approximately one-half shaft rpm, and if friction losses are considered, the average speed of the oil film will be slightly less than one-half, shaft rpm.

The fact that all oil-lubricated sleeve bearings will have an oil film rotating at slightly less than one-half shaft rpm makes all such machines susceptible to oil whirl.

The average rotating speed of the oil film will be slightly less than one half shaft RPM due to friction losses.

This analysis data shows a severe oil whirl condition on 3600-RPM turbo- generator.

2.1 Why Oil Whirl Occurs:

1- Improper bearing design.

2- Excessive bearing wear.

3- Eccentricity of the shaft within the bearing.

4- Increase in lube-oil pressure or viscosity.

2.2 Journal Bearing Design to Minimise Oil Whirl:

Several special bearing configurations are available to minimise the possibility of oil whirl.

The axial-groove bearing is normally used on smaller machines such as light gas turbines and turbo-charges.

The three-lobed bearing provides improved bearing stability against oil whirl.

The three individual bearing surfaces generate pressurised oil films that centre the shaft within the bearing. By minimising the eccentric position of the shaft within the bearing, the rotor will be less subject to oil whirl. Axial grooves are sometimes included at the intersection of the lobe segments to increase whirl resistance.

The titling-pad bearing is common choice on large high-speed industrial machinery such as centrifugal compressors or high-speed centrifugal pumps. In a manner similar to the lobed bearing, each segment or titling pad provides a pressurised oil wedge, which tends to centre the shaft in the bearing.

These and other special bearings have been designed to improve stability and resistance to oil whirl by minimising the eccentricity of the shaft within the bearing.

3-Dry Whirl

Improper lubrication of a plain journal bearing can also cause vibration. If the bearing lacks lubrication, or if the wrong lubricant is used, the result may be excessive friction between the rotating shaft and stationary bearing. This friction excites vibration of the bearing and other related parts of the machine in a manner similar to the vibration generated by simply rubbing a moistened finger over a pane of glass. This vibration is called dry whirl. The vibration resulting from dry whirl is generally high frequency and thus will often produce the distinctive squeal normally associated with a dry bearing.

Whenever the vibration characteristic of dry whirl is encountered, the lubricant, lubrication system, and bearing clearance should be inspected. This condition has been found on bearings having excessive as well as in sufficient clearance.

6-Plain (Journal) Bearing Materials:

Types of Journal Bearing Materials:

The bearing is mainly made of a weaker and softer material as this makes it easier to adjust the bearing relative to the shaft.

The most common materials are:

1-Bronze

2-White metal

1.1-Bronze

Used for high and shock loads. Bronze is an alloy of copper and tin.

Zinc bronze: Copper and zinc

Lead bronze: Copper and lead

Zinc lead bronze: Copper zinc and lead

1.2- Cintered bronze

Cintered bronze is used for self-lubricating bearings.

This bush is made of bronze or lead bronze, and it is porous and self lubricated.

2-White metal (Babbitt )

It is used as a lining in bearings.

It is used when:

a. Shaft circumferential speed is high.

b. Surface pressure between shaft and bearing is high; this can be up to 200 bar.

The white metal is an alloy of tin, lead, copper and antimony. The composition as follows:

a) 90 % Tin

5% Copper

5% Antimony

b) 50 % Tin

33 % Lead

14 % Antimony

3 % Copper

The advantages of white metal are:

(a) The bearing adjusts to differing loads.

(b) If the bearing gets too warm the lining will melt.

(c) Casting of warm, melted bearings is easy.

7-Journal Bearing Maintenance

Carefully inspect bearings and journals for uneven wear or damage. If required, polish journals using belt-type crocus clothe and remove high spots. Sleeve and thrust bearings should be thoroughly incepted for correct clearance, high spots, flaking of babbitt, scoring, and using the following procedures.

1- Bearing Clearance (Setting)

The journal bearings used in high-speed gears must have clearance between the shaft journal and the bearing. The amount of clearance necessary depends on the oil viscosity, the journal speed, and the bearing loading. Manufacturers consider each of these parameters in calculating a bearing clearance that will produce hydrodynamic lubrication as well as a flow of oil sufficient to cool the bearing.

A rough rule of thumb is .001 in. per in. of journal diameter plus .0015 in. up to 9000 ft per minute journal velocity.

Above this speed, clearance should be .002 in. of journal diameter for shafts larger than 2.5 in.

Measurement of bearing clearances may be done by lifting the shaft and measuring the distance travelled by the shaft with a dial indicator. Also, feeler gauges or plastic gauge material can be used. The bearing may be considered operational as long as the measured clearance does not exceed the design clearance by more than .004 to .005 in. for bearings in the 3 to 8 in. diameter range. This value for clearance increase is acceptable for most applications.

Note: If high shaft vibration develops, this clearance increase may not be acceptable.

The thrust bearing clearance provides room for the formation of an oil film between the bearing face and the gear hub and for thermal expansion of the shafting. Normally, wear of the thrust bearing is not very critical unless it is enough to cause loss of oil pressure in the lubrication system.

Measurement of thrust bearing clearance wear may be done by pushing the slow speed shaft axially to one side of the unit, setting a dial indicator and then pulling the shaft axial to the other side of the unit against the dial indicator.

2- Bearing High Spots Repair

Evidence and location of high spots in the bearing are indicated by bright spots or areas. These spots are caused by wear resulting from a ruptured oil film around the high point. Bright spots are slightly scraped and polished with fine steel wool or crocus cloth until they blend in with the rest bearing. Caution: Do not use sandpaper.

To check the bearing contact, install the lower half of the bearing in the housing with the journal and thrust face clean and dry.

Check outside diameter of bearing with a .0015 in. feeler gauge to be sure the

lower half is seated in the housing.

Apply a light coat of soft blue to the journal and to each thrust face. The journal should show blue transfer for a minimum of 80 percent of bearing length. Thrust faces should show a minimum contact of 60 percent of load area. Repeat the checking process until the contact area is satisfactory.

3- Flaking of babbitt Repair

Flaking of babbitt in the loaded area of the bearing is caused by vibration or shock loading of the bearing material, which causes the babbitt to fatigue and break loose from the steel shell. Not only do the flakes cause scoring as they pass through the bearing, but they also contaminate the oil. In the advanced stages of flaking, the load-carrying area of the bearing is destroyed, and the bearing must be replaced. However, if flaking is caught in the early stages, the bearing may be repaired be scraping and polishing. Whatever the case, the cause of vibration or hammering should be corrected before the unit is put back into service.

4- Scoring Repair

Scoring is the scratching, or marring, of the bearing babbitt or the journal riding in the bearing, or both. It is caused by dirt or metal particles present in the oil that passes through the bearing. A little scoring is not serious, and the bearing may be polished with fine steel wool to remove any rough edges caused by scoring. Any foreign particles imbedded in the babbitt who could score the journal should be carefully picked out, and that area should then be polished smooth. Scoring becomes serious when it significantly reduces the bearing area. In this case, the bearing should be replaced, and the gear unit or pump drained and flushed out with a solvent.

5- Wiping Repair

Wiping is the melting and wiping away of a spot or area of the babbitt due to the bearing temperature rising above the pour point of the babbitt.

Abnormally high bearing temperatures can be causes by one or more of the following, conditions: insufficient bearing clearances, insufficient oil pressure, excessively high oil temperature in the bearing, a high spot in the bearing, extreme bearing loading caused by poor bearing contact, or a gear mesh failure.

A gear mesh failure. If wiping is localised in a small spot, the bearing may be repaired by scraping and polishing the spot until it blends in with the remainder of the bearing; otherwise, the bearing must be replaced.

Before replacing a wiped bearing, determine the cause of the wipe and take corrective measures. If new bearings are necessary, the following precautions should be taken.

1. Remove all nicks and burrs from the housing and bearing shell.

2. Be sure that journal and thrust faces are free of nicks and high spots. These spots can be removed using a fine hone and polishing with crocus cloth.

3. Obtain the proper bearing contact as described previously.

4. After the bearings are fitted and the lower halves are installed in the housing, check the radial clearance using plastic gauge. Check thrust clearance by moving shaft axially in both directions while an indicator pointer is positioned against the shaft. In many cases it may be necessary to use a small hydraulic jack to move the large gears axially to check the clearance.

8-Plain (Journal) Bearing Failure Modes

Failure Modes

The failure modes most commonly found are fatigue, wiping, overheating corrosion, and wear. Fatigue occurs because of cyclic loads normal to the bearing surface. Figure 7 shows babbitt fatigue in a 7in (178mm) diameter journal bearing from a steam turbine. Wiping results from surfacetosurface contact and smears the babbitt, as shown in Fig.8 Usual causes of wiping are bearing overload, insufficient rotational speed to form a film, and loss of lubricant. Overheating is manifest by discoloration of the surface and cracking of the babbitt material. Corrosion is failure by chemical action. It is more common with leadbased babbitts, which react with acids in the lubricant. Figure 9. shows corrosion damage of a 5in. (127mm) diameter leadbased babbitt bearing. Wear results from contaminants in the film and is evidenced by scoring marks that may be localised or persist around a large circumferential region of the bearing.

Fig. 7 Babbitt fatigue in a 7-in

Fig. 8 Bearing wipe on a 3-in

(178mm diameter turbine bearing(76mm) diameter bearing due to temporary

loss of lubricant

Fig. 9 Corrosion on a 5-in (127mm) diameter lead-based babbitt bearingOverheating

Section-III

3-Antifriction Bearings

1- Antifriction Bearings Types

A- Non Separable Bearings

1. Single Row Deep Groove Ball Bearing: The bearing has a deep groove (running Track) in both rings. Used for both radial and axial loads for this type, Tightening and alignment should be done precisely. Can be used in high speed.

2. Double Row Self-Aligning Ball Bearing: two rows of balls, each have its own groove in the inner ring. They share a curved track on the inside of the outer ring. The inner ring with balls can align relative to the outer ring.

3. Single Row Angular Contact Ball Bearing: Carry radial loads combined with axial loads in one direction.

4. Double Row Angular Contact Ball Bearing: The bearing can carry radial loads as well as axial loads in both directions.

5. Double Row Spherical Roller Bearing: It has two rows of rollers, which share a common spherical shaped Track in the outer ring. This means that the bearing can align itself.

The bearing has a large radial load carrying capacity and large axial loads, also used with shock loads.

B. Separable Bearings

1- Single Row Cylindrical Roller Bearing: In a ball bearing the ball is only in contact with the inner and outer ring at one point.

When a roller is used in a bearing it bears along its whole length and line contact is obtained. Cylindrical roller bearings therefore have a higher load carrying capacity than ball bearings.

Single row cylindrical roller bearings have two interval flanges on one ring; the other ring normally has no flanges. The rings can therefore move axially relative to each other. This is an advantage when changes in length of the shaft have to be accommodated, for example due to temperature changes.

The rings can be mounted independently which makes assembly easier especially in cases where both the outer and inner rings have to be assembled using a force fit. This type of bearing has a large radial load carrying capacity and is suitable for operation at high speeds. It cannot accommodate axial loads.

2- Taper Roller Bearing

Due to their design taper roller bearings can carry a radial load combined with an axial load in one direction. The bearing must always be adjusted against a bearing, which can carry an axial load in the opposite direction.

This type of bearing is separable, the inner ring with rollers and the outer ring are mounted independently. Due to the tapered form of the rollers and the angled tracks on the outer and inner rings the clearance can be adjusted very accurately and can also be readjusted if necessary.

3- Thrust ball Bearing

This type of bearing is only suitable for axial loads in one direction and must not be loaded in the radial direction. This type of bearing is very sensitive to misalignment between the shaft and housing. In these bearings there is a difference between the rings. One ring is called the shaft ring and the other housing ring. The difference is in the bore diameters of the rings; the shaft ring is a few tenths of a millimeter smaller than the housing ring. The housing ring remains stationary and the shaft ring rotates with the shaft. This means that the shaft ring must be fixed to the shaft. The number on the housing ring has a small cross in order that the difference between both rings can be easily seen.

4- Double Direction Thrust Ball Bearing.

Can carry an axial loads in both directions.

5- Spherical Roller Thrust Bearing.

Spherical roller thrust bearings have a spherical shaped track and can align themselves in the same way as a self aligning radial bearing; a small misalignment of the shaft relative to the bearing housing can accommodated. The axial load carrying capacity is very high. In contrast to other types of axial bearings these bearings can also carry radial and axial load at the same time. They can operate at relatively high speeds.

Basic ball bearing components

Non-Separable Bearings

Separable Bearings

2-Bearing Configuration

1-Duplex Bearings:

It is a specific combination of two single row angular contact bearings to provide greater thrust capacity and shaft rigidity it carries pure radial or thrust loads, or combination. Contact angle is the nominal angle between the line of action of the ball loads, and a plane perpendicular to the bearing axis. Essentially, this means that when a load is applied to a bearing, it forces the balls to contact the inner and outer race way at other than a right angle.

2-Basic Mounting methods for Duplex Bearings

Duplex bearings can be mounted in three different ways to suit different loading conditions. The three positions bear the symbols, DB, DF, and DT.

1- DB back-to-back bearings are placed so that the stamped backs (high shoulders) of the outer rings are together. In this position, the contact angle lines diverge inwardly.

2- DF face-to-face bearings are placed so that the unstamped face (low shoulders) of the outer rings are together. Contact angle lines of the bearing will then converge inwardly, toward the bearing axis.

3- DT Tandem bearings are placed so that the stamped back of one bearing is in contact with the unstamped face of the other bearing. In this case the contact angle lines of the bearings are parallel.

3-Fit on Shaft for Duplex Bearings

Duplex bearings generally have a looser fit on the shaft than other standard types of bearings. Push fits; (finger pressure fits) are generally employed. This helps prevent a change of internal characteristics and facilities removal and remounting of the bearings.

3-Shaft and housing Preparation

1- Bearing seats on shaft

The inner ring must be tight enough not to turn or creep significantly under load.

2- Shaft Shoulders

The shoulder in Figure 2. A is tapered. This results in poor seating of the bearing against the corner of the inner ring. The shaft shoulder in Figure 2.B is so low that the shoulder actually contacts the bearing corner rather than the locating face of the bearing. With the condition shown in Figure 2.C, contact between the shoulder and the bearing face is not sufficient. Under heavy thrust loads, the shoulder might break down. Figure 2.d is exaggerated to illustrate distortion of the inner ring when forced against off-square shoulder. An off-square bearing shortens bearing life.

3- Break corner to prevent burrs

When the shaft shoulder or bearing seat is repaired by regrinding, it is desirable to break the corner on the shaft. This will help prevent burrs and nicks, which may interfere with the proper seating of the inner ring face against the shaft shoulder. If left sharp, shoulder corner is easily nicked, producing raised portions, which, in turn, may create an offsquare condition in bearing location.

The usual procedure to break a corner is to use a file or an abrasive stone.

4-Check Shoulders for OffSquareThe shaft shoulder runout should be checked with an indicator contacting the bearing locating surface on the shaft shoulder while the shaft is still supported on centres (or Vblocks) with the centre of the shaft against a stop. Tolerances have been established for this. If the runout is outside these tolerances, the inner ring of the bearing will be misaligned causing vibration when the spindle is in operation.

5-Check Housing Bore Dimensions

The housing bore dimensions and shoulder should be checked to make sure that they are within the recommended tolerance for size, outof-round, taper, and off-square. The gauge commonly used for this purpose is an indicator type

6-Recheck Dimensions It Necessary

It is important to be absolutely sure that all dimensions are correct before any assembly is begun. If there is any question, a recheck should be made. If variations are noted, the shaft should be repaired to obtain the correct measurements and then rechecked for accuracy and compliance with the recommended tolerances.

4-Mounting Rolling Element Bearings

1- Mounting Methods for Bearings with an Interference Fit on the Shaft

It is possible to use either a cold or warm mounting method. In general it is better to use warm mounting as this method is the easiest and eliminates the danger of damage to the shaft. If this is not possible bearings with a bore up to 70 min may be mounted using the cold method. If a hydraulic press is available, it is possible to mount larger bearings. Some types of bearings in particular those with double seals and "greased for life" must only be mounted using the cold method.

1.1 Cold Mounting

The mounting force must be applied evenly on the inner ring. It is advisable to use a mounting tool, which can be made from a piece of pipe.

The contact face must be perfectly flat and the head of the mounting tool should either rounded or has a raised portion in the centre. The mounting tool should be placed against the inner ring the bearing is then slide along the shaft using a press or by means of light taps with a hammer. During this operation constant checks should be made to ensure that the bearing is at right angles to the shaft centre line.

1.2 Warm Mounting

By heating the bearing it is possible to expand the bore so that it is larger than the shaft. This means that the bearing can be along the shaft without any problem. Bearings can be heated to a maximum of 120, C for a short period. Above this temperature the hardness of the bearing material will be adversely affected. The bearing should be heated in an oil bath without allowing it to touch the bottom.

The heated bearing can be fitted onto the bearing surface without difficulty and care should be taken to ensure that the side face of the inner ring is in complete contact with the shoulder of the shaft or a spacer. While the bearing is cooling the inner ring should be hit with a mounting tool from time to time to ensure that the bearing is pushed against the location face.

2-Dismounting Rolling Element Bearings

1.Dismounting Bearings from the Shaft

When a bearing is being removed from a shaft the force should be applied as evenly as possible onto the inner ring. If possible a ball bearing puller should be used.

2. Dismounting a Bearing from its Housing

If the bearing remains in the housing after the shaft has been removed, it is possible to use a bearing puller.

Bearings with a Tapered Bore

Large forces have to be applied in order to dismount bearings, which have a tapered bore. The forces, which are released when these bearings are dismounted, can also be very high. It is recommended that some method is used to brake (or slow down) these bearings.

Bearings Mounted on a Tapered Shaft

The locating ring (end plate or shaft nut) should be loosened but kept in place as a stop. The bearing can then be dismounted by carefully tapping the dismounting tool or punch with a hammer.

It is also possible to use the SKF oil injection method to remove a bearing. As large forces are released when this type of system is used (in particular with tapered bearing seats or adapter bushes) it is important to arrange a suitable stop

Single Row Deep Groove Bearings

It is generally impossible to dismount this type without destroying it. It. is possible to cut through the outer ring, but an alternative is to remove the cage so that the balls can be collected together. It will then be possible to remove the inner ring by using only a slight force.

Single Row Angular Contact Bearings

The only way to dismount this type of bearing is either to force the outer ring over the balls or cut through it. There are a few types, which are easily separable.

Double Row Deep Groove Angular Contact Ball Bearings

These bearings have an opening in the inner and outer rings, which is used to insert the balls between the rings. When these openings are brought opposite one another it ispossible to push the balls out one by one with a thin piece of steel. The others will then fall out themselves.

Dismounting Using Heat

In order to dismount the inner ring of large cylindrical bearings, which have been mounted onto the shaft using an interference fit, use is made of a special tool, which heats the ring. The tool is heated to about 200(C and then clamped to the inner ring, which comes loose within a few seconds. It is possible to use electric tools, which heat the ring by either induction or radiant heat. Direct heating with a naked flame may never be used.

5. Rolling Elements Troubleshooting (Conditions, causes and solutions)

Accurate and complete knowledge of the causes responsible for the breakdown of a

machine is as necessary to the engineer as similar knowledge concerning breakdown

in health is to the physician. The physician cannot effect a lasting cure unless he

knows what lies at the root of the trouble, and the future usefulness of a machine

often depends on correct understanding of the causes of failure.

1. Most bearing failure causes

1. Defective bearing seats on shafts and in housings.

2. Misalignment.

3. Faulty mounting practice.

4. Incorrect shaft and housing fit.

5. Inadequate lubrication.

6. Ineffective sealing.

7. Vibration while the bearing is not rotating.

8. Passage of electric current through the bearing.

1.1-Defective bearing seats on shafts and / or in housings

For bearings to have long troublefree life, the thin inner and outer rings must be mounted on shafts or in housings that are as geometrically true as modern machine shop techniques can produce. In other words, the shaft and bore must be round and free of taper and must completely support the inner and outer rings. Also, the sizes of each must be correct so as not to reduce the internal clearances in the beating nor allow the bearing to fret on the shaft or in the housing bore. When bearing fits are damaged, they should be remachined and returned to their original sizes by metalising or plating.

1.2-Misalignment

Misalignment is a source of premature spalling of the bearing. This condition generally occurs when the inner ring of a bearing is seated against a shaft shoulder that is not square with the journal or when the outer ring is seated against a housing shoulder that is out of square with the housing bore. Also, misalignment can occur when the bores from side of a gear housing are not parallel and square to the centreline.

1.3- Faulty Mounting Practice

Faulty mounting practice contributes greatly to premature bearing failure and usually results from abuse and neglect during the mounting procedure.

The most common faulty mounting practices are foreign matter in the bearing (not properly cleaned), impact damage handling or mounting resulting in brinelling, and overheating when expanding the bearing to slip on the shaft. When heating a bearing for mounting, an oil bath should be used if available; if a torch is used, care should be taken not to overheat in one spot since localised overheating wi11 actually soften the bearing material.

1.4-Incorrect shaft and housings fits

A bearing may need to be fitted either with an interference fit or a slip fit on the shaft and in the housing depending on the conditions present. The degree of tightness or looseness in the bearing is governed by the magnitude of the load, the speed of the journal, and the arrangement of the bearing. In gear unit bearings, the inner ring usually rotates relative to the load, and therefore, it will have an interference fit on the shaft and a light slip fit in the housing. When it is incorrectly fitted, a bearing will creep on the shaft or in the housing and cause wear to the journal or the bearing seat.

1.5-Inadequate Lubrication

Any loadcarrying contact between the rollers and the inner and outer races in a bearing requires the presence of lubricants for reliable operation. The rollers must carry the bearing cage as the bearing rotates, so they also slide on the bearing cage. This sliding motion can be very detrimental to a bearing unless he lubricant film is thick enough to prevent contact between the sliding parts.

The viscosity of a lubricant is the most important characteristic of the oil either as oil itself or as the oil in grease lubrication. Oil with too low a viscosity allows metaltometal contact between the rollers and the inner and outer races, which results in bearing failure. Also, an insufficient quantity of lubricant at medium to high speeds generates a temperature rise, which in turn can cause lubricant failure. Lubricant failure generally causes surface damage in the bearing ranging from frosting to spalling, discoloration, glazing, or smearing.

1.6-Ineffective Scaling

The effects of dirt and other abrasives in bearings can result in changes in bearing internal geometry. Freedom from abrasive matter is so important that some bearings for very high precision equipment are even assembled in air-conditioned white rooms. In addition to abrasive matter, corrosive agents must be excluded from bearings. Water, acid, and other agents that deteriorate lubricants result in corrosion and premature bearing failure. Acids formed in the lubricant with water present etch the bearing surfaces and reduce the loadcarrying capacity.

1.7-Vibration

Rolling element bearings exposed to vibration while the shafts are not rotating are subject to a damage referred to as false brinelling. This is usually indicated by either bright polished depressions at each roller or a corrosive type stain or fretting. The vibrating load causes minute sliding in the area of contact between the rolling element and raceways and sets free small particles of material that are oxidised and cause accelerated wear.

1.8-Passage of electric current through the bearing

In certain applications where electrical machinery or electrical equipment is in use, there is the possibility that electric current will pass through a bearing. Current that seeks ground through the bearing can be generated from magnetic fields in the machinery or can be caused by welding on some part of the machine with the ground attached so that the circuit is required to be completed through the bearing.

When the current is broken at the contact surfaces between rolling elements and raceways, marking results; this marking produces localised high temperature, and consequently, the surfaces are damaged. This damage is usually manifested as very small pits on the raceways and the rollers.

2. Troubleshooting heat, noise and vibration

The most important thing for bearing maintenance is what to look for, how to recognise the reason for the trouble, and what is the practical solution.

The observations of bearing trouble can be classified in three main points:

1. Overheating bearing.

2. Noisy bearing.

3. Vibration.

The following tables A, B, and C will explain conditions of trouble, cause of trouble and practical solution.

The machinist can touch, feel and listen to locate the trouble, he may go thin through the following tables.

5 - Training Aids

1- White board.

2- Video tape MJCPIM03 (Antifriction bearing lubrication)

3- Projector.

4- Transparencies.

Transparencies

Page

T1Objectives5

T2Dry and oil film lubrication11

T3Journal speed VS. friction force12

T4The development of full-film lubrication13

T5Rolling friction13

T6Deformation of rolling object14

T7Oil film or ball bearing14

T8Dampen shock in pair of gears15

T9Self sealing action16

T10Two groove cylindrical bearing17

T11Tilting pad journal bearing20

T12Collar bearing with thrust pad21

T13Michell axial thrust bearing22

T14Kings bury thrust bearing23

T15Basic ball bearing components34

T16Non-separable bearing35

T17Separable bearing36

T18Duplex bearing37

T19A Overheating49

T20B Noisy bearing50

T21C - Vibration51

Lesson Plan

Lesson Number One: Lubrication

Objective:

Understand the characteristics of friction.

Explain the boundary lubrication.

Explain full-film lubrication.

Understand the rolling friction

Explain the six purpose of lubrication.

ContentsActivity

A. Introduction to the course.B. 1. Principles of lubrication characteristics of friction

1.1 Boundary lubrication.

1.2 Full-film lubrication

2. Rolling friction.

3. The six Physical properties

1. To reduce friction.

2. To reduce wear.

3. To help dampen shock.

4. To cool moving elements.

5. Prevent corrosion.

6. Seal out dirt & contaminates.

C. Lesson briefing

D. DiscussionE. Assessment

Show T1 for course objectives

Show T2Show T3Show T4Show T5 & T6 & T7Explain

Show T8Show video tape

Show T9Main topics

Allow for 30 minutes

Lesson Plan

Lesson Number Two: Journal Bearing, tilting Pad and Axial Thrust Bearing.

Objective:

Understand the principle of operation.

Understand journal bearing types.

Describe the titling pad/ axial thrust bearing.

Explain vibration due to journal bearing.

Perform journal bearing maintenance.

Understand failure mode and cause.

ContentsActivity

A. 1. Oil film principle of operation

2. 1. Cylindrical bearing2. Cylindrical bearing with axial groove.3. Elliptical and lube bearing3. Tilting pad and lube bearing.4. Axial thrust bearing.1. Collar bearing.2. Michell axial thrust bearing.3. Kings bury thrust bearing. Sliding bearing illustration.5. Vibration due to journal bearing.1. Misalignment.

2. Oil whirl.

3. Dry whirl.

6. Journal bearing material.

7. Journal bearing maintenance.

1. Bearing clearance.

2. High spot repair.

3. Flaking repair.

4. Scoring repair.

5. Wiping repair.

8. Failure modes

B. Guide participants to work shop.

C. Lesson briefing.

D. Assessment.Show T10Draw on the board

Show T11Show T12Show T13Show T14Show T15Draw on white board

Allow for 2.30 hours at workshop.

Lesson Plan

Lesson Number Three: Antifriction Bearings.

Objective:

Understand bearing types.

Understand bearing configuration.

Explain the preparation of mounting.

Perform mounting and dismounting.

Troubleshooting.

ContentsActivity

A. 1. Antfriction bearing Types.

a. Non-separable bearings.

b. Separable bearing.

2. Bearing configuration.

a. Duplex bearing.

b. Basic mounting.

c. Fit on shaft.

3. Shaft and housing preparation.

4. a. Mounting.

c. Dismounting.

5. Trouble shooting.a. Most bearing failure causes.

b. Trouble shooting heat, noise and vibration.B. Guide participants to workshop practice.

C. Lesson briefing.

D. Discussion.

E. Assessment.

Show T15Show T16

Show T17 board

Show T18Draw on white board

Draw on whiteboard

Show T 19 &T 20& T 21

Allow for 5 hours

Lesson One Assessment

1. What is the meaning of lubrication?

2. What is the meaning of lubricant?

3. What is the friction in lubrication?

4. What is the boundary lubrication?

5. What is the film lubrication?

6. What is the hydrodynamic full- film lubrication?

7. What is the hydrostatic full film lubrication?

8. What are the advantage of a hydrostatic full film lubrication?

9. Why does the ball or roller bearing up in operation, while it is lubricated?

10. What are the six basic purposes of lubrication?

11. Why does lubricant dampen shock?

Lesson Two Assessment

1. How is the hydrodynamic pressure generated in journal bearing?

2. What are the journal bearing types?

3. What is the advantage of the tilting pad bearings?

4. What is the best preload ratio for the tilting pad bearing?

5. What are the types of the axial thrust bearings?

6. What are the components of Kingsbury thrust bearing?

7. What is the oil whirl in a journal bearing?

8. What are the causes of the oil whirl?

9. Hwo can you measure journal- bearing clearance?

10. How can you measure thrust bearing clearance?

11. How can you check a bearing contact surface for a journal bearing after scraping and polishing?

12. What are the failure modes for journal bearing?

Lesson Three Assessment

1. What is the advantage of separable bearing?

2. What is the advantage of a duplex bearing?

3. What is the duplex bearing composed of?

4. What are the basic mounting methods for duplex bearing?

5. What are the preparations needed before assembly of the bearing?

6. Explain how to use a warm oil bath.

7. What are the causes of the bearing failure? (Mention four causes only).

8. What are the common causes for improper assembly that lead to bearing overheating, noise and vibration? (List five causes only).

Final Test (Classroom).

1. Define each of the following:-

A- Hydrodynamic full- film lubrication.

B- Hydrostatic full- film lubrication.

2. What are the purposes of lubrication?

3. How does the lubricant dampen shock?

4. Explain the building- up of lubricant hydrodynamic pressure in journal bearing

5. What is the oil whirl in sliding bearing?

6. What are the causes of oil whirl?

7. Mention seven types of antifriction bearings.

8. Explain one configuration of duplex bearing.

9. What are the causes of improper assembly in antifriction bearing? (Mention five only).

10. What is the effect of inadequate lubrication on both sliding and antifriction bearing?

Final test (practical) Workshop.

Disassembly, inspect, measure the bearing clearance, check bearing seats, check failure modes, clean and assemble the following:-

1. Bearings for single stage centrifugal pump (Union).

2. Bearing for multi centrifugal pump (Tayssen).

3. Main bearing for reciprocating pump (Ingersoll- Rand).

Answers

Lesson One Answer

1- To make a surface smooth and slippery.

2- Any substance that reduces friction, by creating a slippery film between two surfaces.

3- Fluid friction is the force that tend to retard the motion of two moving surfaces.

4- The lubrication that occur as a machine starts-up and continues to the point of full operational speed.

5- Full film lubrication is the ideal condition in which the moving surfaces are completely separated from each other.

6- The hydrodynamic full-film lubrication is the lubrication which occur without external pressure. A pressure builds up in the lubricant as a result of the machine parts being in motion. The pressure comes from the resistance of the lubricant to movement and compression. This internal fluid pressure lifts and separate the two moving surfaces.

7- Hydrostatic full-film lubrication occurs only in those cases in which a machine part, even when it is completely at rest, is fully supported by a cushion of liquid. The pressure is supplied by an outside source.

8- 1) The pressure is developed and maintained by a pump.

2) It can be used to control the clearance between the two moving surfaces.

9- Because of the fluid friction. Oil is churned and moved about in many directions- so the internal friction increase. So heat is the result.

10- 1- Reduce friction.

2- Reduce wear.

3- To help dampen shock.

4- To cool moving parts.

5- To prevent corrosion.

6- To seal out dirts.

11- By making use of its ability to distribute pressure. The lubricant is squeezed by

the gear teeth as they mesh together.

The squeezing action forces the lubricant to squirt out between clearance points

in the meshed teeth. So the shock is dampened by the lubricant.

Lesson Two Answer

1- By rotating the journal in a tapered wedge clearance in the direction of rotation. A positive pressure is produce in the converging region of the clearance, as a result of the hydraulic fluid resistance.

2- 1. Cylindrical bearing.

2. Cylindrical bearing with axial grooves.

3. Elliptical and lobe bearings.

3- Oil whirl free.

Concentric pivot film thickness C1

4- Preload ratio = = C1 / C Less than one

Machined Clearance C

5- 1. Collar bearing.

2. the Michell axial thrust bearing.

3. Kings bury thrust bearing.

6- 1. Thrust collar.

2. Shoes.

3. Leveling plates.

4. Base ring.

7- The rotation of the lubricant between shaft and bearing at less than half rpm of the shaft. This is detected by vibration analysis.

8- 1. Improper bearing design.

2. Excessive bearing wear.

3. Eccentricity of the shaft within the bearing.

4. Increase in lube oil pressure or viscosity.

9- By lifting the shaft, and measuring the distance traveled by the shaft with a dial indicator. Also, feeler gauge or plastic gauge can be used.

10- Push the shaft axially to one side of the equipment, setting dial indicator, and then pull the shaft axially to the other side of the equipment against the dial indicator. The reading is the axial thrust.

11- To check bearing contact, install the lower half of the bearing in the housing, with the journal and thrust face clean and dry. Check out side diameter of bearing with 0.0015 in feeler gauge. Apply a light coat of soft blue to the journal and to each thrust face. Rotate shaft the journal should show blue transfer for a minimum of 80 percent of bearing length. Thrust face should show a minimum contact of 60 percent of load area.

12- Fatigue, wiping, overheating, corrosion and wear.

Lesson Three Answer

1- The rings can be mounted independently, which makes assembly easier, also both bearing rings can be assembled using force fit.

2- Provide greater thrust capacity and shaft rigidity, also carries pure radial or thrust loads or combination.

3- Two single row angular contact bearings.

4- 1. DB back-to-back.

2. DF face-to-face.

3. DT Tandem bearing

5- 1. Bearing inner ring to be tight enough.

2. Shaft shoulder to be clean of burr, square and in correct dimensions.

3. Check housing bore dimension.

6- 1. Heating oil not more than 120 C.

2. Bearing in oil bath should not touch bottom.

3. During mounting, hit the mounting tool slightly to ensure that bearing is pushed against the shaft shoulder properly.

4. use hand gloves and goggle.

5. Be careful for cleaning shaft and bearing during assembly.

7- 1. Detective bearing seats on shaft and in housing.

2. Misalignment.

3. faulty mounting practice.

4. In correct shaft and housing fit.

5. In adequate lubrication.

6. Ineffective sealing.

7. Vibration.

8. passage of electric current through bearing

8- 1. Housing bore: out of round, undersized, oversized distorted and (pounding-out).

2. Bearing seat on shaft: Knurling, oversized, undersized.

3. Two held bearing on one shaft.

4. Adapter tightened excessively on inner ring.

5. In correct method of mounting (hammer blow).

6. In adequate shoulder support.

7. failure to remove chips or dirt.

Final Test Answers (Classroom)

1- A- The hydrodynamic full-film lubrication is the lubrication which occur without external pressure. A pressure builds up in the lubricant as a result of the machine parts being in motion. The pressure comes from the resistance of the lubricant to movement and compression. This internal fluid pressure lifts and separate the two moving surfaces.

B- Hydrostatic full-film lubrication occurs only in those cases in which a machine part, even when it is completely at rest, is fully supported by a cushion of liquid. The pressure is supplied by an outside source.

2- 1- Reduce friction.

2- Reduce wear.

3- To help dampen shock.

4- To cool moving parts.

5- To prevent corrosion.

6- To seal out dirts.

3- By making use of its ability to distribute pressure. The lubricant is squeezed by the gear teeth as they mesh together.

The squeezing action forces the lubricant to squirt out between clearance points in

the meshed teeth. So the shock is dampened by the lubricant.

4- By rotating the journal in a tapered wedge clearance in the direction of rotation. A positive pressure is produce in the converging region of the clearance, as a result of the hydraulic fluid resistance.

5- The rotation of the lubricant between shaft and bearing at less than half rpm of the shaft. This is detected by vibration analysis.

6- 1. Improper bearing design.

2. Excessive bearing wear.

3. Eccentricity of the shaft within the bearing.

4. Increase in lube oil pressure or viscosity.

7- 1. Single row deep groove ball bearing.

2. Double row self aligningg ball bearing.

3. Single row angular contact ball bearing.

4. Double row angular contact ball bearing.

5. Double row spherical roller bearing.

6. Single row cylindrical roller bearing.

7. Taper roller bearing.

8- DB back-to-back configuration. The deep shoulder of outer ring will be back-to-back.

9- 1. Housing bore out of round.

2. Housing bore distorted.

3. Knurling bearing seat on shaft.

4. Bearing seat shaft under or over sized.

5. In adequate shoulder support.

10 . Sliding Bearing:-

In adequate lubrication will destroyed the liquid film, generate excessive friction between shaft and bearing. This leads to dry whirl vibration. This vibration occur at high frequency, and produce distinctive squeal antifriction bearing.

Antifriction Bearing:-

Inadequate lubrication will generate a high temperature rise, which leads to lubricant failure.

Lubricant failure cause surface damage same as spalling, discoloration, glazing and/or smearing.

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1IHRDC L & B-M-03 (Rev. 0) 02 2 1999 P # 20

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Lubrication and Bearing Module.

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Transcript of Lubrication and Bearing Module.