Bearing Basics 6f1cm

Bearing basics Have you ever wondered how things like inline skate wheels and electric motors spin so smoothly and quietly? The answer can be found in a neat little machine called a bearing. The bearing makes many of the machines we use every day possible. Without bearings, we would be constantly replacing parts that wore out from friction. The concept behind a bearing is very simple: Things roll better than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be a lot more difficult to push down the road. That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced. Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly. Bearings typically have to deal with two kinds of loading, radial and thrust. Depending on where the bearing is being used, it may see all radial loading, all thrust loading or a combination of both.

Types of bearings: According to design, load and shape, there are many types of bearings used in industries. The mains bearings can be classified as follows. 1) According to the Friction: on the basis of friction bearings are classified as 

Friction bearing: As the name implies, in this bearings the bearing surface is in with moving surface or the shaft which produces more friction. These bearing are made up of cast iron, bronze, brass and white metal having hollow round shape. Lubricant is used for slow moving and heavy weighted running on shaft. These bearings to crack shaft, rocker arm of IC engine. Friction bearing are also subdivided into following types a) Solid bearings: It is a simplest hole made in cast iron to the shaft and form running fit. These are made up of cast iron or bronze in the form of bush and press-fitted in fabricated or cast iron housings. This is used for small and light shafts moving at low speed. A hole is provided on its face of lubrication.

b) Split bearings: Split bearings are same like solid bearings but have an arrangement of split. Split bearings are made in halves and assembled in special plumber blocks. It has collar on its external surfaces and also made in two parts as shown in figure.

c) Self-aligning bush bearings: It consist mainly two parts. The first one is cast iron block and other is bush. These bearing bush are made up of brass or any other soft material in round shape. To protect it from moving, a screw is fixed at one end and this screw is fixed half to the bush and half in block.

d) Adjustable slide bearings: It can adjust the tightness between bearings and the shaft. This type of bearing has provision for wear adjustment. The bearing is fitted in the tapered hole of the housing for adjustment of wear. The bearing is drawn inside by means of a slotted ring nut.

Advantages and disadvantages of friction bearings:

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Advantages: Friction bearings are cheap to produce and have noiseless operation. They can be easily machined, occupy small radial space and have vibration damping properties. They can cope with tapped to the foreign matter.

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Disadvantages: It damages machines. It restricts early movement of machine It produces a lot of heat energy.

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Anti-friction bearing: The main purpose of these bearings is to minimize the friction in bearing. Due to this reason, the speed of an object increases while friction and temperature decreases. Such bearing have long life.

Why rolling bearings? Rolling bearings and guide, with minimal friction, rotating or oscillating machine elements – such as shafts, axles or wheels – and transfer loads between machine components. Rolling bearings provide high precision and low friction and therefore enable high rotational speeds while reducing noise, heat, energy consumption and wear. They are cost-effective and exchangeable machine elements that typically follow national or international dimension standards. The two basic types of rolling element distinguish the two basic types of rolling bearing: 

ball → ball bearing

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roller → roller bearing

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Balls and rollers are different in how they make with the raceways. Balls make point with the ring raceways. With increasing load acting on the bearing, the point becomes an elliptical area. The small area provides low rolling friction, which enables ball bearings to accommodate high speeds but also limits their load-carrying capacity.

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Rollers make line with the ring raceways. With increasing load acting on the bearing, the line becomes somewhat rectangular in shape. Because of the larger area and the consequently higher friction, a roller bearing can accommodate heavier loads, but lower speeds, than a same-sized ball bearing. a) Ball bearings: A ball bearing is a rolling element bearing that used ball to maintain the separation between the bearing races. The width of these bearing is smaller than the bore diameter or ball. On the basis of load and groove cut, ball bearings are classified in the following types. 

Single row ball bearings: These bearing have only one groove cut in outer and inner rings with the ball in identical line.

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Double row ball bearing: These bearing have two grooves cut in inner and outer ring lie in two rows of the bearing.

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Self-aligning ball bearings: These bearings can withstand with journal loads. These loads are generally inclined due to shaft misalignment. These types of bearings have a spherical bore on the outer race.

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Angular ball bearings: These bearings are designed to take an axial thrust as well as radial loads.

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Thrust ball bearings: These bearings are useful for taking vertical thrust load but cannot take any radial load. Some special thrust bearings are available which can also take horizontal end thrust.

b) Roller bearings: Roller bearings are available with the grooved race in the outer and inner . Roller bearings are capable of carrying the journal (radial) loads. It can work with greater load than ball bearings. To use this bearing, race is required to be locked. On the basis of uses, roller bearings are classified in following types. 

Self-aligning roller bearings: These bearings are self-adjustable and it is not affected by non-centering of shaft deformation flexure of shaft and bearing block, so it can compensate the concentricity error caused by these reason.

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Tapered roller bearings: These bearings are used to take thrust only one direction. For opposing thrust, the bearings must be mounted in opposite pair. Tapered roller bearings are mainly used for high axial thrust loads.

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Needle roller bearings: These types of bearings have very small roller diameter. Rolling element is called needle roller. Needle roller bearings are used where the outside diameter of bearing restricted due to limited bearing space in the housing. The needles fitted in a circular cage which is push-fit in its housing.

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Cylindrical roller bearings: These bearings are used in such places, where more load is to be bear. These are made of hollow cylindrical roller.

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Barrel roller bearings: The roller fitted in this type of bearing has barrel shape. Its diameter up to full length is uneven. These bearings are self-alignment type bearing, so due to this reason, it has no difficulty to maintain shaft in straight line.

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Spherical roller bearings: These bearings are used in such places, where chance of angular condition in shaft may be possible. In these bearings, rollers are fitted in ball cage in such a way that in angular condition, in inner and outer race, the energy transfer can be possible in full capacity.

Advantages and disadvantages of anti-friction bearings:    

Advantages: Special shielded bearing does not required lubrication again. It is easy to replace. It has very long life and has very less friction. It easy operates on high speed and required less lubrication.

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Disadvantages: Initial cost is usually high. Greater diameter space required for comparable shaft diameter. Dirt, metal chips and so on, entering the bearings can limit their life causing early failure. Lesser capacity to withstand shock

2) According to the load: On the basis of load applications bearings are classified as follows, a) Radial or Journal bearings: Radial bearings accommodate loads that are predominantly perpendicular to the shaft. Some radial bearings can only pure radial loads, while most can additionally accommodate some axial loads in one direction and, in some cases, both direction.

b) Thrust bearings: Thrust bearings accommodate loads that act predominantly along the axis of the shaft. Depending on their design, thrust bearings may pure axial loads in one or both directions and some can additionally accommodate radial loads. Thrust bearings cannot accommodate speeds as high as same-sized radial bearings. The angle determines which group the bearing belongs to. Bearings with a angle ≤ 45° are radial bearings, the others are thrust bearings.

Thrust bearing for pure axial load

Thrust Bearing for combined load

c) Pivot bearings: These bearings are used to the give to the shaft in

stationary position wherever bearings are in parallel to the axis of the shaft and one edge of the shaft is in the inside of the bearing. These bearings are also known as foot bearing.

d) Slipper bearings: These bearings provides s to the moving part or

part in the straight line such as cross head which in used in steam engine.

3) According to the shape: On the basis of shape bearings are classified as a) Flat shape bearings: These types of bearings are flat in shapes which provide

to the sliding parts. Therefore, these bearings are also called slide bearing or guide bearing such as the movement of carriage on lathe bed.

b) Round or cylindrical bearings: These bearings are in round shape which provides

to the moving parts as in case of solid bearing, ball bearing or roller bearing.

Bearing Terminology Radial bearings 1. Inner ring 2. Outer ring 3. Rolling element: ball, cylindrical roller, needle roller, tapered roller, spherical roller, toroidal roller 4. Cage 5. Capping device Seal – made of elastomer Shield – made of sheet steel 6. Outer ring outside surface 7. Inner ring bore 8. Inner ring shoulder surface 9. Outer ring shoulder surface 10. Snap ring groove 11. Snap ring 12. Outer ring side face 13. Recess for capping device 14. Outer ring raceway 15. Inner ring raceway 16. Recess for capping device 17. Inner ring side face 18. Chamfer 19. Bearing pitch circle diameter 20. Total bearing width 21. Guide flange 22. Retaining flange 23. angle

Thrust bearings 24. Shaft washer 25. Rolling element and cage assembly 26. Housing washer 27. Housing washer with a sphere seat surface 28. Seat washer

Components and materials A typical rolling bearing consists of the following components 

an inner ring

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an outer ring

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balls or rollers, as rolling elements

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a cage

Bearing rings: The pressure at the rolling area and the cyclic over rolling creates fatigue in the bearing rings when the bearing is in operation. To cope with such fatigue, rings that are made of steel must be hardened. The standard steel for bearing rings and washers is 100Cr6, a steel containing approximately 1% carbon and 1,5% chromium. SKF bearing rings and washers are made of steel in accordance with SKF specifications. They cover all aspects that are relevant to providing a long service life for the bearing. Depending on specific requirements, SKF uses stainless steels or hightemperature steels.

Rolling elements: The rolling elements (balls or rollers) transfer the load between inner and outer rings. Typically, the same steel is used for rolling elements as for bearing rings and washers. When required, rolling elements can be made of ceramic material. Bearings containing ceramic rolling elements are considered hybrid bearings and are becoming more and more common. Cages: The primary purposes of a cage are: 

separating the rolling elements to reduce the frictional heat generated in the bearing

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keeping the rolling elements evenly spaced to optimize load distribution

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guiding the rolling elements in the unloaded zone of the bearing

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retaining the rolling elements of separable bearings when one bearing ring is removed during mounting or dismounting Cages are radially centered either on:

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the rolling elements

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the inner ring

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the outer ring

Cages centered on the rolling elements permit the lubricant to enter the bearing easily. Ring centered cages, which provide more precise guidance, are typically used when bearings must accommodate high speeds, high vibration levels or inertia forces stemming from movements of the whole bearing.

The main cage types are: 

Stamped metal cages Stamped metal cages (sheet steel or sometimes sheet brass) are lightweight and withstand high temperatures.

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Machined metal cages Machined metal cages are made of brass or sometimes steel or light alloy. They permit high speeds, temperatures, accelerations and vibrations.

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Polymer cages Polymer cages are made of polyamide 66 (PA66), polyamide 46 (PA46) or sometimes polyetheretherketone (PEEK) or other polymer materials. The good sliding properties of polymer cages produce little friction and, therefore, permit high speeds. Under poor lubrication conditions, these cages reduce the risk of seizure and secondary damage because they can operate for some time with limited lubrication.

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Pin-type cages Steel pin-type cages need pierced rollers and are only used together with large-sized roller bearings. These cages have relatively low weight and enable a large number of rollers to be incorporated.

Integral sealing Integral sealing can significantly prolong bearing service life because it keeps lubricant in the bearing and contaminants out of it. Bearings are available with various capping devices: 

Shields There is a small gap between the shield and inner ring. Bearings fitted with shields are used where the operating conditions are relatively clean, or where low friction is important because of speed or operating temperature considerations.

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Seals Bearings with seals are preferred for arrangements where contamination is moderate. Where the presence of water or moisture cannot be ruled out, seals are typically used. These seals make positive with the sliding surface on one of the bearing rings. Low-friction seals and non- seals can accommodate the same speeds as bearings with shields, but with improved sealing effectiveness.

Bearing arrangements Back-to-back arrangement In a back-to-back arrangement, the load lines diverge along the bearing axis. Axial loads acting in both directions can be accommodated, but only by one bearing or bearing set in each direction. Bearings mounted back-to-back provide a relatively rigid bearing arrangement. The wide span between bearing effective centers makes this arrangement particularly well suited to moment loads.

Face-to-face arrangement In a face-to-face arrangement, the load lines converge along the bearing axis. Axial loads acting in both directions can be accommodated, but only by one bearing or bearing set in each direction. The shorter span between effective bearing centers makes face-to-face arrangements less suitable to moment loads compared to bearings in a back-to-back arrangement.

Tandem arrangement The use of a tandem arrangement provides increased axial and radial load carrying capacity compared to a single bearing. In a tandem arrangement, the load lines are parallel so that radial and axial loads are shared. The bearing set can only accommodate axial loads acting in one direction. If axial loads act in both directions, or if combined loads are present, additional bearing(s) adjusted against the tandem arrangement must be added.

Examples Universally match able single direction bearings can be arranged in various ways depending on the stiffness and load requirements of the application. The possible arrangements are shown in below figure, including the applicable designation suffixes for matched sets. If misalignment cannot be avoided between the bearing positions, face-to-face bearing arrangements are recommended. They are less sensitive to misalignment than back-toback bearing arrangements. Combinations of tandem arrangements with back-to-back or face-to-face arrangements are usually selected to maximize the stiffness or load carrying capacity of a bearing set in a particular direction. This is the case, for example, when extended, preloaded, vertical or overhung screw drive must be ed.

Bearing Numbers Explained

(1) Prefix : (2) Basic Number: (3) Suffix Prefix K

Cage with roller elements

L

Removable bearing ring

R

Ring with roller set

S

Roll body of stainless steel

W

Stainless steel deep groove ball bearing

*Note: Each bearing company may create their own prefixes. e.g. E2. = SKF Energy Efficient bearings Suffix 2 RS

Bearing with rubber seal on both sides. RS provides a better seal but more rolling friction than 2Z.

RS

Bearing with rubber seal on one side, one side open.

2 Z / ZZ Bearing with a metal seal on both sides. Z

Bearing with a metal seal on one side, one side open.

E

Reinforced Design

P2

Highest precision

K

Bearing with taper bore

Bearing Numbers The example at the header shows a 6001 2RS bearing. So what does the 6001 actually mean?

(6)001 This first number relates to the bearing type, as shown in the table below type 6 is a deep grooved roller bearing.

Self-Aligning Ball Bearing 1 This kind of ball bearing has a spherical outer race, allowing the axis of the bearing to "wande r around". This is important because misalignment is one of the big causes of bearing failure.

2

Barrel and Spherical Roller Bearings

Tapered Roller Bearing 3 Designed to take large axial loads as well as radial loads.

4

Deep Groove Double-Row Ball Bearing Designed for heavy radial loads.

5

Axial Deep Groove Ball Bearing Intended for exclusively axial loads.

Deep Groove Ball Bearing (Single row) 6 Typical ball bearing. Handles light axial loads as well as radial loads.

Single-Row Angular Bearing 7

Specific geometry of angular bearing raceways and shoulders creates ball angles that higher axial loads

Axial Cylindrical Roller Bearings Axial cylindrical roller bearings comprise axial 8 cylindrical roller and cage assemblies and shaft and housing locating washers. The bearings have particularly small axial section height, have high load carrying capacity and high rigidity and can axial forces in one direction.

6(0)01 This second number relates the bearing series, which reflects the robustness of the bearing. As you go up the scale below from 9 to 4 the inner and outer race thickness will usually increase along with the ball size, this will be to help cope with extra load. 9 0 1 2 3 4

Very thin sections Extra light extra light thrust Light Medium Heavy

60(01) The 3rd and 4th digits of the bearing number relate to the bore size of the bearing, numbers 00 to 03 have a designated bore size depending on the number. 00 01 02 03

10mm 12mm 15mm 17mm

While numbers over 03 simply have a bore size which is 5 times that of the 3rd and 4th digit.