A90 Series Correspondence Lessons PART B. Measuring Bearings and Bearing Basics

Transcription

1 A90 Series Correspondence Lessons PART B Measuring Bearings and Bearing Basics Lesson A9004 Measuring and Identifying Bearings Lesson A9005 Friction and Bearing Basics Lesson A9006 Anti-Friction Bearing Basics

2 PART B Measuring Bearings and Bearings Basics Series 90 Training

3 PART B Measuring Bearings and Bearings Basics Lessons A9004 to A9006 Correspondence Course LESSON A9004 Measuring and Identifying Bearings Table of Contents Applications 6 Bearing Interchange 6 Customer Information 6 Digital Calipers 9 Digital Calipers Operating Precautions 11 Dimensions 4 IBI Guide 7 Measuring and Identifying Bearings 3 Measuring Instruments 7 Micrometers 7 Part Numbers 4 Vernier Calipers 7,8 Vernier Scales 8 Structured Training Plan This lesson is the fourth of a series of Correspondence lessons in the BSC Structured Training Plan. Objectives The objective of this lesson is to teach students the correct methods of measuring and identifying bearings and the use of vernier callipers and micrometers. Pre-requisites Completion of lessons A9001 to A9003. Methods Achievement of the objectives is by presentation of lessons in an 'On-Line' or Correspondence Course format. The lessons in a Correspondence Course style are conducted for internal students in a lecture situation. Assessment A formal test is provided with this lesson. LESSON A9004 Series 90 Training

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5 Measuring and Identifying Bearings When a customer contacts us by phone or at the counter with a request to supply bearings we need to be able to identify his requirements by establishing part numbers and quantities. This lesson covers the system of measuring and/or identification of bearings. There is also a sales technique to be aware of and various procedures to follow but these items will both be covered in the sales lessons, later in the course. The simple steps to making a correct identification are listed below: 1) Find out as much information as you can about the bearing e.g. i) Part numbers stamped on the bearing ii) Dimensions iii) Application - what equipment, vehicle, etc. and where is it fitted on that equipment or vehicle. Perhaps the customer has a record of the part number from having previously replaced it, or a manual with genuine part numbers shown. With experience you will learn how much information you need to identify any particular item. 2) If the item is straightforward (E.G. a 6206VV bearing) you may be able to go straight to the shelf and pick it for the customer. Alternatively, you may need to refer to a bearing manual, interchange listing or applications catalogue to find out our part number equivalent. 3) Confirm your choice, if possible, by comparing the selected item with the original. Of course, physical comparison over the phone is not practical although you may be able to confirm quantities and approximate sizes. We will now look at these steps in more detail. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 3

6 Part Numbers If a part number is stamped on the bearing, this may be one which BSC uses or it may need to be converted to our numbering system. If you recognize the part number as a BSC number, watch out for any additional characters at the beginning or end of the number and if you are not sure what these mean, ask someone who knows. Note that in the example the number stamped on the seal is 6205V, but since the bearing has 2 rubber seals - one each side, the part number is actually 6205VV. For NON-BSC part numbers you will need to convert by using a bearing interchange. Before you do this, however, ask yourself if one of the other methods of identification would be easier. More information is given below on using conversion tables. Dimensions There is a standard sequence in the bearing industry for giving bearing dimensions. This is: Inside diameter (or Bore) - Outside diameter - Width The location of these dimensions is shown in the diagrams below. Note that the common abbreviations for these three dimensions are I.D., O.D., and W. Radial Ball Bearing Ball Thrust Bearing Cylindrical Roller Bearing Tapered Roller Bearing It is essential to get accurate measurements to correctly identify each bearing. Sometimes customers on the phone may not be able to give you the standard of accuracy you need - even engineers rulers are not really suitable, so you may have to ask for the bearing to be brought to the counter so that you can measure it with a vernier calliper. Once again, other methods of identification may be easier. Use of vernier callipers is covered later in this lesson. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 4

7 Whilst taking dimensions, look for any other features, for example seals, shields, snap rings. Note the bearing type and construction - ball, roller, tapered roller, needle roller etc. What is the cage made from and are there any other important characteristics? Using the bearing data listed in Appendix A, what is the part number for the following bearings: Test Yourself Answer: 1) ID.: 30mm OD.: 62mm W: 16mm Type: Ball Bearing Comments: the bearing has no seals, shields, groove or ring 2) ID.: 25mm OD: 47mm W: 12mm Type: Ball Bearing Comments: The bearing has 2 steel shields If you need more help, check Lesson A9001 page 4. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 5

8 Applications There will be many instances where the customer will ask for a bearing by its application. By application we mean the piece of equipment or vehicle into which the bearing is fitted and it's location. For example, a customer may ask for a front wheel bearing for a 2002 Holden VX Commodore. In this instance you will need to look up the part number in a catalogue or applications data sheet. In your branch sales area you will find various publications, including the BSC auto catalogue on the AS400 (Path ) from which this can be checked. An example screen is shown to the right. Try using the car catalogue to find the correct bearing number for the Holden application above. Answer Customer Information Information submitted by customers needs to be treated with caution since this may be misleading although it can be very useful if checked for validity first. Genuine part numbers maybe converted and records of previous purchases are usually correct. However, the customer may not be aware of modifications made by previous owners, especially in the area of vehicle transmissions. Wherever possible verify all data by employing at least two of the methods of identification listed above. Customers expect and usually receive expert advice from our sales staff. They will very soon pick a salesperson who does not know what to do, However most customers will be prepared to show tolerance if they can see that you are putting some effort into fulfilling their needs. Bearing Interchange Interchange tables are used to convert bearing numbers from one manufacturer's system to our own. An interchange table is available on the AS400 although the Part Number descriptions on the AS400 Item Master also include alternative numbers. There are several other useful interchanges available you can refer to including the IBI guide. On the AS400, select path and enter the part number you wish to convert under Description. Using the Interchange, find the BSC part number for a NAK Seal. Answer LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 6

9 IBI Guide Finding a cross-reference in the IBI guide is a two-step process. The white section is an index of part numbers which are listed in groups in the other sections. To find a cross reference, look it up first in the white pages and then refer to the IBI Group in the coloured sections where you will find a list of alternatives. Look for your part number in the group to confirm that you have selected the correct group, then look for a manufacturer with whom BSC deals - usually NSK or Timken, and note down the conversion. Fully detailed 'how to use' instructions are given in the front of the IBI guide. Apart from the white Index section, there are three coloured sections containing Ball Bearings (pink), Tapered Roller Bearings (green) and Roller and Needle Roller Bearings (yellow). When converting other part numbers to BSC, always check the brand name as well as the part number. Sometimes, the same part number may be used by different manufacturers for different bearings. IBI also produce interchange listings for seals and drive belts. Measuring Instruments As stated previously, Engineers rulers are not accurate enough to measure to the fine tolerances needed to correctly identify bearings. The two alternatives available are VERNIER CALIPERS and MICROMETERS. Verniers Verniers are available in differing styles, the most significant difference being Electronic or Manual. We will begin with a general examination of functions. Verniers are able to measure inside, outside and depth. The large jaws measure outside diameters, the small jaws measure inside diameters, and the tongue which protrudes from the end of the instrument is used for measuring depth. Verniers consist of two parts - the fixed section and the sliding scale. These sections are illustrated in the picture to the left. Micrometers Micrometers are very accurate measuring instruments but are also very expensive. They are often used in engineering workshops but it is unusual to find one in a BSC branch. Vernier callipers are a less expensive alternative and are capable of measuring down to 0.01mm (one hundredth of a millimeter or.001 in. (one thousandth of an inch). LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 7

10 Vernier Callipers To measure the outside diameter of a bearing, move the sliding scale so that the jaws are just wide enough to fit over the object. Then gently push on the slide so that it moves up to a firm but not over-tight closure. Most callipers have a sprung thumb wheel or grip to assist in obtaining the right tension. Measuring ID and Width is a similar operation. When measuring ID or width, always be sure that the jaws are parallel with the surface - if they are slightly cocked, the measurement will not be 100% accurate. Reading Vernier Scales The term 'Vernier' actually refers to the type of scale used on the callipers. In this lesson we will concentrate on explaining how the vernier system works, mainly in relation to metric measurements. The basic principal is illustrated in the drawing below. Notice that 10 divisions on the sliding scale is equal to only 9 divisions on the fixed scale. If the sliding scale is moved along so that the '1's on both scales are aligned, the jaws will be opened one tenth of a division. This system can be extended by progressively moving the sliding scale so that the '2's, '3's, '4's are progressively lined up and the gap will be correspondingly opened by the same fraction - 2/10ths, 3/10ths, 4/10ths. Real life verniers usually have scales spread over a much larger number of divisions. A sliding scale of 50 divisions is common on metric capers and this allows measurements down to 0.02 mm. An imperial scale of 25 divisions can allow measurement to.001 inches (one thou). In addition, the scales slide next to each other so that the alignment of the markers can be easily seen. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 8

11 Answer Vernier Callipers - Digital Most BSC branches now have the new electronic callipers and these make the measuring of bearings a simple matter. In this lesson we will explain how to use the callipers to take measurements. The calipers have many other functions and for those interested in expanding their knowledge, a data sheet is included with this lesson as Supplement 3. Before you begin to take measurements close the jaws to a firm closure as explained before. Then press the Clear button and this will turn the unit on and also reset the scale to zero. Imperial measurements are possible down to.0005 (1/2 thou) since an indicator (.5) will appear on the screen when the measurement approaches.005 between whole digits When you have finished using digital callipers, it is not a bad idea to return them to the closed position and check that the reading is still If it is not, the problem may be caused by low battery power, over-fast movement of the sliding scale, or pressing of the reset button whilst the jaws are open. Move the sliding display so that the jaws will fit over the item. To do this you may use the wheels or gently slide the whole moving section along the fixed part. If you move the display too fast the unit will lose track of its calibration and start to flash to indicate an error. If this happens, return the jaws to the closed position and start again. Close the jaws onto the object and read the display. On power-up this will be indicated in millimeters, but you may change to imperial mode by pressing the orange button. You may then take further measurements in imperial mode or switch back to metric. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 9

12 If you pull the jaws open to about 80mm and turn the callipers over, you will notice a small toothed rack inside the rear groove. This is the precision rack which the callipers use to gauge their present position and must be kept clean at all times to permit smooth movement and prevent inaccuracies. Digital Callipers can also measure Depth.. To do this use the depth gauge rod which appears at the end of the callipers when you slide it open. Read the measurements from the sliding scale in the same way. Other functions which the digital calipers can perform are: Holding of absolute values Comparative Measurements Data recording via an interface Upper and lower limit acceptance/rejection Peak value measurements. More information on these functions is given in the instruction sheet which comes with the callipers. These are reproduce here - KC Tools or NSK brand LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 10

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17 A Questionnaire Name: Employee No (from Payslip): Branch (eg QAA) Date: Measuring and identifying bearings Questions Q1. Select the 3 most useful items of information which could be used to correctly identify a bearing. Answers A. Customer B. Part numbers C. Dimensions D. Last Purchase Date E. Application Q2. Select three dimensions from the list which are commonly used to identify a Ball Bearing. A. Variance (V) B. Inner diameter (ID) C. Outer diameter (OD) D. Radius (R) E. Width (W) Q3. In order to convert from another manufacturers part number to BSC part numbers you would use an: A. Interchange table B. Parts listing C. Catalogue Q4. An Engineers Rule is Suitable/Not Suitable for taking accurate bearing measurements. Q5. The Instrument most commonly used for taking accurate measurements is called: A. Suitable B. Not suitable A. Micrometer B. Engineers ruler C. Vernier callipers LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 15

18 A9004 Questionnaire (cont.) Name: Employee No (from Payslip): Branch (eg QAA) Date: Measuring and identifying bearings Q6. Select 2 items which may cause digital callipers to give inaccurate readings: A. Low battery B. Temperature drops to 5 degrees C C. Moving sliding scale too fast D. Resetting whilst jaws not fully closed E. Failure to remove excess grease from bearing Q7. When you have finished using digital callipers, it is a good idea to re check the calibration by: (Select 2) A. Removing and replacing the Battery B. Closing the jaws C. Rechecking that the callipers are still correctly calibrated. LESSON A9004 Measuring and Identifying Bearings Series 90 Training page 16

19 PART B Measuring Bearings and Bearings Basics Lessons A9004 to A9006 Correspondence Course LESSON A9005 Friction and Bearing Basics Structured Training Plan Table of Contents Anti-Friction Bearings 6 Axial Loads 7 Bearing Basics 8 Early Anti-friction Bearing Designs 6 First True Bearing 7 Friction and Bearing Basics 3 Inner Ring 8 Outer Ring 8 Practical Applications 8 Plain Bearings 5 Resistance to Motion 3 Retainer 8 Rolling Elements 8 Rolling Friction 4 Sliding Friction 3,4 The Wheel 4 This lesson is the fifth of a series of Correspondence lessons in the BSC Structured Training Plan. Objectives The objective of this lesson is to infirm students about friction and bearing basics, and the early development of methods of overcoming resistance to motion. Instructions are given on the principals of ant-friction bearings. Pre-requisites Completion of Correspondence Course lessons A9001 to A Methods Achievement of the objectives is by presentation of lessons in an 'On-Line' or Correspondence Course format. The lessons in a Correspondence Course style are conducted for internal students in a lecture situation. Assessment A formal test is provided with this lesson. LESSON A9005 Series 90 Training

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21 FRICTION What is Friction? The simplest definition is that it is the RESISTANCE TO MOTION between two surfaces in contact. When you walk, you rely on the FRICTION between your shoes and the ground to keep your balance. What happens when you try to walk on ice or a highly polished floor? Your feet have a nasty habit of slipping out from under you >> This is because there is less resistance to motion on ice or a highly polished floor, than on normal ground. From this it should be obvious that friction may vary between different surfaces. In this case, there is less friction between your shoes and the slippery surface than normal. Without FRICTION you would not be able to walk. It is necessary for walking and many other things. However, for many types of work and the efficient operation of machines, as little friction as possible is desirable. Early man had to move things by sliding them over the ground. This required considerable effort (try pushing a filing cabinet over a carpeted area without any assistance of any kind). The resistance to sliding motion is one of two basic types of friction and is called SLIDING FRICTION. After some time, stone age man discovered that loads could be moved with less effort by putting them on sledges with narrow runners. This is not because the smaller contact area reduces the frictional force, as we tend to think, but because the smaller contact area of the narrow runners increases the weight per unit area of the block compared to the large block. This greater weight smoothes and compacts the ground, reducing the resistance between the two surfaces. Unfortunately, it's not only the ground it changes - as many people have found out. LESSON A9005 Friction and Bearing Basics Series 90 Training page 3

22 Still later it was discovered that man could reduce the effort required to move a heavy object with a flat base by rolling it over logs. Many of our ancestors probably regretted this discovery. Rolling motion inherently creates less resistance to motion than sliding motion. This less resistance to motion is the second basic type of friction and is called ROLLING FRICTION. Okay, so what's the difference of effort required to move two identical heavy blocks on a perfectly hard surface with one of the blocks on a sledge with narrow runners? n a perfectly hard surface it requires the same effort to move the two blocks, as the resistance to sliding motion due to friction is not dependent on the amount of surface in contact. Man then discovered that shorter logs rolled easier than long logs and eventually developed the wheel. Unlike sliding friction, the size of the contact area with rolling friction affects resistance to motion. Therefore, it is easier to roll a wheel than a log because the ground contact area is smaller. With a simple wheel, the bore slides around the outside of the axle. The wheel resists rotating around the axle because the two surfaces are constantly rubbing together as SLIDING FRICTION This caused the axle and wheel bore to wear out rather quickly, sometimes with nasty results: LESSON A9005 Friction and Bearing Basics Series 90 Training page 4

23 Then it was discovered that by applying grease between the axle and the wheel hubs of carts and chariots, friction was reduced and the parts lasted longer. Wheels could also turn faster and carry heavier loads. Separating the axle from the wheel hub by a thin film of lubricant is still the basic principle of today's PLAIN BEARING (or sleeve). Plain Bearings (Sleeves) are used in many applications, a typical example being as crankshaft main and con-rod bearing inserts on automobiles. Plain bearings reduce the friction between two moving surfaces by means of a thin film of lubricant, whereas anti- friction bearings use rolling contact elements. If you want to find out more about friction, check out the Wikipedia online. LESSON A9005 Friction and Bearing Basics Series 90 Training page 5

24 ANTI-FRICTION BEARINGS Principle One of the earliest anti-friction bearing designs featured wooden rollers that rotated as the wheel turned, enabling the wheel to roll on the axle instead of sliding around it. This rolling motion of the bearings between the wheel and the axle illustrates the basic purpose of anti-friction bearings. To convert a relatively large amount of sliding friction into rolling motion, with it's smaller amount of rolling friction. The function of bearings can be demonstrated very simply, with a stack of books on a table. Try pushing the books across the table. It requires a fair amount of effort. This is because of sliding friction. Now put several round pencils under the books and try pushing them across the table. Much easier wasn't it! This is because the sliding friction has been converted to LINE CONTACT rolling motion and there is less friction between the objects. If you substitute several marbles or steel balls instead of the pencils, you will find the books even easier still. Now pick up the books from the floor! This is because the sliding friction has been converted to POINT CONTACT rolling motion and there is even less friction between the objects. LESSON A9005 Friction and Bearing Basics Series 90 Training page 6

25 Practical applications - First true bearing In this section we will find out how the principles are turned into practical applications. The first true bearing of modern times was a thrust bearing. Around 1780 a rotating post mill was built at Sprowston near Norwich, England and the whole unit rotated on a bearing consisting of two grooved plates containing 40 cast iron balls each having a diameter of 2-1/4 inches (57.15mm). The mill was burnt down in 1933 but the bearing was salvaged and presented to Norwich Museum where it can be seen today. Most anti-friction bearings are mounted between a shaft and housing and their function is to limit friction in order to minimize the rotational force required to turn a shaft or housing. In the case of the thrust bearing, a circular groove retained the cast iron balls between two flat plates (see illustration above). This is the same with today's thrust bearings. Thrust bearings are so named because they are designed to take axial loads (Thrust loads along the axis of the bearing). With bearings mounted between a shaft and housing, the plates are ring shaped, and indeed are called rings. The balls or rolling elements are still retained by means of grooves. Clutch Thrust Bearing >> LESSON A9005 Friction and Bearing Basics Series 90 Training page 7

26 Practical applications - Ball Bearings The basic components of all anti-friction bearings are INNER RING and OUTER RING that retain the ROLLING ELEMENTS. In most cases the rolling elements are separated and evenly spaced from each other by means of a CAGE or RETAINER. Now if we take another look at the wheel, and insert a bearing between the shaft and the wheel (see above diagram), it can be seen that the SLIDING FRICTION has been converted into ROLLING MOTION. This enables the wheels to turn with even less effort than with a thin film of lubricant between the axle and the wheel. Since the bearing is made of hardened steel it resists wear from loads acting on it. Now that you know the bearing basics we will move on to look at bearings in more detail in the next lesson. LESSON A9005 Friction and Bearing Basics Series 90 Training page 8

27 A Questionnaire Name (eg Tom Brown): Employee No (from Payslip): Branch (eg QAA): Date (eg 12/04/08): Friction and Bearing Basics Questions Q1. Friction may be described as: Answers A. Narrow runners B. Resistance to motion C. Rolling motion D. Moving of heavy loads E. The amount of thrust Q2. For the efficient operation of a machine, friction should be: A. Enhanced B. Maintained C. As little as possible Q3. The two basic types of friction are: A. Sliding B. Angular C. Rolling D. Point Contact E. Thrust Q4. Friction can be reduced by: (select 2) Q5. Which statement is correct? A. Using Runners B. Reducing the contact area C. Using lubrication A. Rolling motion created less friction than sliding motion B. Sliding motion created less friction than rolling motion C. Rolling motion created more friction then sliding motion LESSON A9005 Friction and Bearing Basics Series 90 Training page 9

28 A9005 Questionnaire (cont.) Name (eg Tom Brown): Employee No (from Payslip): Branch (eg QAA): Date (eg 12/04/08): Friction and Bearing Basics Q6. Rolling motion may be described as: A. Point contact Q7. Q8 The first anti-friction bearing was a and contained balls made from: Thrust bearings are made to take: B. Line contact C. Either point or line contact A. Ball Bearing B. Thrust Bearing C. Roller Bearing A. Steel B. Bronze C. Cast Iron A. Radial loads B. Axial Loads C. Combined Loads Q9 The 4 main parts of an anti-friction bearing are A. Inner Ring B. Outer Ring C. Cage or Retainer D. Housing E. Rolling Elements Q10 Anti-friction bearings convert A. Sliding motion to rolling motion B. Rolling motion to sliding motion C. Friction to perpetual motion LESSON A9005 Friction and Bearing Basics Series 90 Training page 10

29 PART B Measuring Bearings and Bearings Basics Lessons A9004 to A9006 Correspondence Course LESSON A9006 Anti-Friction Bearing Basics Table of Contents Angular Contact Load 6,7 Non-Contact Sealed Bearings 8 Anti-friction Bearings 3 Point Contact Rolling Motion 3 Axial Clearance 5 Raceway 4 Ball Bearings 3 Radial Clearance 5 Bearing Loads 6 Radial Load 6 Clearance 5 Retainer 4 Cone, Cup 4 Roller Bearings 3 Contact Sealed Bearings 8 Rollers 4 Inside Diameter 4 Sealed Bearings 8 Interference Fit 5 Shielded Bearings 8 Line Contact Rolling Motion 3 Slip Fit 5 Loaded Zone 7 Snap Rings 7 Open Bearings 8 Tapered Roller Bearings 4,5 Outer Ring 4 Thrust Load 6 Outside Diameter 4 Types, Anti-Friction 3 Names of Parts 4 Width 4 Structured Training Plan This lesson is the sixth of a series of Correspondence lessons in the BSC Structured Training Plan. Objectives The objective of this lesson is to teach students the basic nomenclature used in the bearing industry and also to introduce students to bearings installation, clearance, bearing loads, sealing, rings and ring grooves. Pre-requisites Completion of Correspondence Lessons A9001 to A9005. Methods Achievement of the objectives is by presentation of lessons in an 'On-Line' or Correspondence Course format. The lessons in a Correspondence Course style are conducted for internal students in a lecture situation. Assessment A formal test is provided with this lesson. LESSON A9006 Series 90 Training

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31 Anti-Friction Bearings Types of Anti-friction Bearings There are two basic types of antifriction bearings - ROLLER BEARINGS and BALL BEARINGS. Roller bearings use line contact rollers of differing shapes to convert sliding friction into line contact rolling motion, thereby reducing friction. The area of contact is greater than in ball bearings and as such they can support heavier loads. Ball bearings use point contact balls of different diameters to convert sliding friction into point contact rolling motion, which is a lower friction than line contact. Therefore ball bearings have a higher speed capacity than roller bearings. BALL BEARINGS Less load carrying capacity Higher Speed Capacity ROLLER BEARINGS Greater Load Carrying Capacity Lower Speed Capacity LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 3

32 Names of Parts and Important Dimensions These three illustrations show the important dimensions and Nomenclature for the most widely used types of anti-friction bearings. Bearings are available in many sizes and are available in both 'imperial' and 'metric' dimensions. The most important dimensions in determining bearing size are: INSIDE DIAMETER or BORE - OUTSIDE DIAMETER WIDTH The standard names for the major components are: INNER RING OUTER RING ROLLERS or BALLS CAGE, RETAINER or SEPARATOR The grooves in the rings of a ball bearing, in which the balls run, are called the RACE or RACEWAY. Similarly, the flat contact surface in roller bearings is often called their RACE or RACEWAY. TAPERED ROLLER bearings, unlike other types, are two-piece designs. The inner ring comes with the rollers and cage as an assembly and is called a CONE. The outer ring is separate and is called a CUP. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 4

33 Bearing Installation Now that you know something about bearing components and how they reduce friction, let's look briefly at bearing installation. In most applications, the shaft rotates and the housing is stationary. This requires the inner ring to be pressed or tightly fitted on the shaft with an INTERFERENCE fit. The outer ring is also usually tightly fitted to the housing. However, sometimes the outer ring is installed with a SLIP fit which provides no interference. If the housing rotates and the shaft is stationery, then the outer ring must have an interference fit and the inner ring can have a slip fit. Clearance Internal clearance is one of the most important factors in bearing design for correct component alignment and long bearing life. Internal running clearances are designed into bearings to allow for changes in fits, operating temperatures, and slight deformation of parts caused by heavy loads. For ball bearings and straight cylindrical roller bearings, the difference between the diameter of the ball or roller and the space between the inner and outer ring raceways is called RADIAL clearance. The difference between the width of the ball or roller and the width of the inner and outer ring raceways is called AXIAL clearance. This point is illustrated in the diagram above. Tapered roller bearings are twopart assemblies, and thus, clearance can be adjusted during installation. This gives them certain advantages over other types in some applications. The internal clearance between the cup and cone is called radial and axial clearance. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 5

34 Bearing Loads In theory, rolling elements support loads at a point or a line. However, due to the resiliency, or the elastic quality of steel, a load on a bearing causes the outer and inner rings to be slightly deformed by the rolling elements. Thus, the point contact of a ball bearing actually has an elliptical shape and the line contact of a roller bearing has a rectangular shape. Depending on the application, anti-friction bearings may be subjected to three types of loads. These are generally referred to as: a) RADIAL LOAD b) THRUST LOAD c) ANGULAR CONTACT LOAD RADIAL LOAD is when the load is applied PERPENDICULAR to the centre line of rotation. THRUST LOAD is when the load is applied PARALLEL to the centre line of rotation. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 6

35 ANGULAR CONTACT load is when both thrust and radial loads are acting on the same bearing. Therefore, the resultant load is applied AT AN ANGLE to the centre line of rotation. Generally, the rolling elements do not carry equal loads around the circumference of the bearing. As the direction and magnitude of the load changes, the rollers pass through a LOADED ZONE as shown. This is a RADIAL LOADED bearing with the rolling elements shaded in proportion to the load which each is supporting. The darker shading represents a heavier load and from this it can be seen that the roller 'A' is carrying the greatest load. Snap Rings Most bearings are located (held in place) by means of a shoulder on the shaft or in the housing. However, sometimes this is not possible for many reasons, in which case, the bearing is manufactured with a groove in the OD of the outer ring, and a snap ring is used to locate the bearing in the housing. In such a case, the bearing is identified by the suffix 'NR' in the bearing part number. If the bearing is supplied without the snap ring in the groove then "N" only is included in the part number suffix. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 7

36 Seals and Shields To maximize the service life of bearings, they must be properly lubricated and free of dirt and contaminants. Most bearing failures are due to dirt in the bearings. Therefore, a variety of shields are used to provide a long service life for bearings. However, if a bearing is operating in a clean free-flowing lubricant and is protected from outside dirt, it is probably an OPEN bearing. OPEN bearings do not have seals or shields. Shielded bearings have a stamped metal washer-like disk that is crimped into a groove to resist dirt and abrasive material. One shield is used on bearings with only one side exposed to foreign material. The open side permits lubrication to enter the bearing and the shield limits the flow of lubricant from the bearing. Two shields are used where both sides of the bearing must be protected. These bearings are pre-lubricated and thus require no further lubrication as they are grease-packed for life by the manufacturer. Even greater protection in extremely dirty conditions is provided by the use of rubber sealing elements which are built into the bearing in a similar manner to the shields. Non-contact and contact types are available in either single and double sided styles Bearing Service stocks in the main, non-contact type which are so called because the rubber seal is attached to the outer ring but is just clear of the inner ring. This provides excellent protection in all but the worst of conditions. Contact types are available for extreme conditions. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 8

37 A Questionnaire Name: Employee No (from Payslip): Branch (eg QAA) Date: Anti Friction Bearing Basics Questions Answers Q1. The two basic types of anti-friction bearings are A. Tapered B. Roller C. Ball D. Plain E. Sliding Q2. A. Roller Bearings have???? load carrying capacity than Ball Bearings. A. Higher B. Lower B. Ball Bearings have a???? limiting speed than Roller Bearings A. Higher B. Lower Q3. Inner Rings, Outer Rings, Cage and Rollers are all part of a... A. Ball bearing B. Roller bearing C. Tapered roller bearing Q4. Cup, Cone, Cage and Rollers are all part of a... A. Ball bearing B. Roller bearing C. Tapered roller bearing Q5. The grooves in the rings of a bearing in which the balls run are called the A. Raceway B. Running slots C. Outer ring LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 9

38 A9006 Questionnaire (cont.) Name: Employee No (from Payslip): Branch (eg QAA) Date: Anti Friction Bearing Basics Q6. When the inner ring of a bearing as manufactured, is a tight fit on the shaft, this is known as a... Q7. The difference between the diameter of a ball or roller and the space between the inner and outer raceway is called... Q8. Identify how the load is applied to the shaft for each type of load. A. Contact fit B. Interference fit C. Standard clearance A. Standard clearance B. Angular clearance C. Radial clearance. Load Perpendicular At an Angle Radial A1. A2. A3. Parallel Thrust B1. B2. B3. Angular C1. C2. C3. Q9. The rolling elements do not carry equal loads but pass through a???????? where they carry a heavier load. Q10. In order to locate a bearing within a housing, some bearings are fitted with a... A. Set screw. B. Snap ring and groove. C. Interference fit. LESSON A9006 Anti-Friction Bearing Basics Series 90 Training page 10