BEARINGS A bearing is a mechanical element that

BEARINGS A bearing is a mechanical element that permits relative motion between two parts i. e. shaft and housing with minimum friction. The functions of the bearing : 1) The bearing ensures free rotation of the shaft with minimum friction. 2) The bearing supports the shaft and holds it in correct position. 3) The bearing takes up the forces that act on the shaft and transmits them to the frame or the foundation.

TYPES OF BEARINGS • 1) Sliding contact bearing- The bearing in which the contacting surfaces either make a sliding contact or separated by a film of lubricant. • 2) Rolling contact bearings- The bearing in which the contacting surfaces have rolling contact are known as rolling contact bearings. • They are also known as anti-friction bearings.

CLASSIFICATION OF BEARINGS

TYPES OF ROLLING CONTACT BEARING • (Depending upon the type of rolling element) • Ball Bearing- The ball bearings use the spherical balls as the rolling elements. The contact between the inner race and the ball or the outer race and the ball is a point contact. • Roller Bearing- The roller bearings use the cylindrical roller, taper roller or spherical roller as the rolling elements. The contact between the inner race and the roller or the outer race and the roller is a line contact. Starting friction is high.

ROLLING CONTACT BEARING

ROLLING CONTACT BEARING

TYPES OF ROLLING CONTACT BEARINGS • 1) Depending upon the direction of the force that act on them • Radial and thrust bearings. • A radial bearing supports the load, which is perpendicular to the axis of the shaft. • A thrust bearing supports the load, which acts along the axis of the shaft.

USES OF BEARINGS • • • Sliding contact bearings : Crankshaft bearing in petrol and diesel engines. Centrifugal pumps Large size electric motors. Steam and gas turbines Concrete mixer, rope conveyor and marine installations Rolling contact bearings : Machine tool spindles Automobile front and rear axles Gear boxes Small size electric motors Rope sheaves, hoisting drums.

ADVANTAGES OF ROLLING CONTACT BEARINGS OVER SLIDING CONTACT BEARINGS

Comparison Between Ball and Roller Bearings Comparison parameter Ball Bearing Roller Bearing Rolling Element Spherical Balls Cylindrical rollers, taper rollers, spherical rollers Nature of contact Point contact Line contact Load carrying capacity Low High Axial Dimensions Less More Radial Dimensions More Less

STANDARD DIMENSIONS OF BEARING

DESIGNATION OF ROLLING CONTACT BEARINGS • 1) Bearing Type- The first number indicates the bearing type. • Ex. 6204 • Single, two digit or alpha-numeric. • Deep groove ball bearing • Light Series • Bore Dia. 20 mm First Number Type 6 Deep groove ball bearing 2 Self aligning bearings 3 Double row angular contact ball bearing 30 31 32 Taper roller bearing NU 2 Cylindrical roller bearing

DESIGNATION OF ROLLING CONTACT BEARING BORE 6204 (Two digit no. ) BEARING SERIES 6204 Load carrying capacity Second No. 0 Bearing series Extra Light 2 Third No. Bore”d” mm 00 10 Light 01 12 3 Medium 02 15 4 Heavy 03 17 04 onwards 5 x number

RADIAL BALL BEARING

TYPES OF ROLLING CONTACT BEARINGS Ball bearings • Spherical balls. • Point contact. - Least friction. Roller bearings • Cylindrical or taper rollers. • Line contact. • Higher load carrying capacity.

TYPES OF BALL BEARINGS Deep Groove Ball Bearing- • • Use in almost all kinds of product. Radius of the ball is slightly less than the races. Balls and races may roll freely w/o any sliding. Takes radial and thrust load.

DEEP GROOVE BALL BEARING Advantages • High load carrying capacity. • Can take loads in radial and axial direction. • Due to point contact, frictional loss is less. • Generates less noise. • Available with bore dia. from few mm. to 400 mm. Disadvantages • Not self aligning • Poor rigidity compared with roller bearings.

Cylindrical Roller Bearing • When max. load carrying capacity is required in a given space, the point of contact in ball bearing is replaced by the line contact. • High rigidity. • Can’t take thrust load

Continue…. Advantages 1) Due to line contact between rollers and races, the radial load carrying capacity is high 2) More rigid than ball bearings 3) Coefficient of friction is low and frictional loss is less at high speed. Disadvantages 1) Cannot take thrust load. 2) Not self aligning 3) Generates more noise.

Angular contact bearing • The groove in inner and outer races are so shaped, that the line of reaction at the contact between balls and races makes an angle with the axis of the bearing. This reaction has two component- Radial and Axial. • Can take radial and thrust load • Can be used in pairs • The races are angular to the shaft axis.

Continue…. Advantages 1) Can take both radial and thrust loads 2) Due to more no. of balls, takes more load. Disadvantages 1) Two bearings are required. 2) Must be mounted without axial play. 3) Requires initial preloading.

SELF ALIGNING BEARING • Consists of two rows of balls, that rolls on a common spherical surface in the outer race. The assembly. of the shaft, inner race and the balls with cage can freely roll and adjust itself to the angular misalignment of the shaft. • Permits shaft deflections within 2 -3 degrees. • Used in Agriculture machinery, ventilators, and railway axle boxes.

Taper roller bearing • Rollers are in the frustum of a cone. • Axis of individual rolling element intersect in a common apex on the axis of the bearing. • Can carry both radial and thrust loads. • When subjected to pure radial load induces thrust component and vice versa. • Are always used in pairs. • Have separable construction.

Continue…. Advantages 1) Can take heavy radial and thrust load. 2) More rigidity. 3) Easy to assemble and disassemble. Disadvantages 1) To be used in pairs to balance axial force. 2) Can’t tolerate misalignment. 3) Costly.

THRUST BALL BEARING • Consists of row of balls running between two rings. The shaft ring and the housing ring. • Carry thrust load in only one direction and cant take radial load.

Continue…. Advantages. Due to more no. of balls results in high thrust load carrying capacity in smaller space. Disadvantages 1) Can’t take radial load. 2) Not self aligning 3) gives poor service because balls are subjected to centrifugal force. 4) Not good for horizontal shafts.

FACTORS AFFECTING SELECTION OF BEARING • Type of load • Combination of radial and thrust load. • Magnitude of load. • Alignment of shaft w. r. t. housing. • Rigidity of system. • Operating speed. • Compactness.

MATERIAL • Ball, inner race and outer race are made of high carbon chromium steel (SAE 52100) • 1% Carbon and 1. 5 % chromium. • Cages are made of low carbon steel.

TYPES OF LOADS ON ROLLING CONTACT BEARINGS 1) Radial load (Fr)- The load acts perpendicular to the axis of the shaft. 2) Axial load. (Fa)- The load acting in axial direction. 3) Combined load (Fr and Fa)- Combination of radial and axial loads.

BASIC STATIC CAPACITY OF BEARINGS (CO) • Basic static capacity or basic static load rating CO is defined as the static radial load which corresponds to a total permanent deformation of the ball (roller) and race, at the most heavily stressed contact, equal to 0. 0001 times the ball (roller) diameter. • Available in Mfg. catalogue.

STRIBECKS EQUATION FOR BASIC STATIC CAPACITY OF BEARINGS Assumptions in Stribeck’s equation(May-06, May. 07, May-09, May. 11, Dec. 11, Nov. -13 ) 1) The races are rigid and retain their circular shape even after loading. 2) The balls are equally spaced. 3) The balls in the upper half do not support any load. 4) There is a single row of balls.

Continue…. Forces acting on inner race Deflection of inner race

Continue…. where C 0 = Basic static capacity of bearing N K = Constant d = dia. of the balls. Z = No. of balls. For Ball Bearing d = diameter of rollers, mm L = length of Rollers, mm For Roller Bearing

EQUIVALENT STATIC LOAD (P 0 ) • Static load capacity given in mfg. catalogue is pure radial load capacity. • When ball bearings are subjected radial and thrust loads, it is to convert two components into single imaginary radial load i. e. equivalent static load. • It is defined as an imaginary static radial load which, if applied would cause the same total permanent deformation at the most heavily stressed ball and race contact as that which occurs under the actual combined loading.

EQUIVALENT STATIC LOAD Where Po = equivalent static load, N For = Actual Static radial load, N Foa = Actual static thrust load, N Xo = static radial load factor Yo = static thrust load factor. Co = Equivalent static capacity of bearing. For safety of bearing against the static failure

Values of Xo and Y 0

BEARING LIFE • Life of an individual bearing is defined as the total number of revolutions ( or the number of hours at a given constant speed) which the bearing can complete before the first evidence of fatigue failure develops on the ball or races. • Life of an individual bearing cannot be predicted, it is to define in terms of statistical average performance of a group of apparently identical bearings.

BEARING LIFE 1) Rating Life- (L 10)- (Catalogue life)Rating Life of a group of apparently identical bearings is defined as the number of revolutions (or the no. of hours of service at some constant speed) that 90% of a group of bearings will complete or exceed the first evidence of fatigue failure develops. It is known as minimum life. 2) Median Life (L 50)-(Average life)-

Basic Dynamic Capacity (Basic Dynamic Load Rating of Bearing It is defined as the constant stationary radial load which a group of apparently identical bearings with stationary outer race can withstand for a rating life (L 10 Life) of one million revolutions of inner race.

Equivalent Dynamic Load (Pe) • Equivalent dynamic load is defined as an imaginary constant radial load which, if applied on the bearing with rotating inner race and stationary outer race, would give the same bearing life as do the actual applied combined loading.

EQUIVALENT DYNAMIC LOAD (Pe) Pe = {(X. V. Fr + Y. Fa) Ka} where Pe = equivalent dynamic load, N Fr = radial load, N Fa = axial or thrust load, N X = radial factor. Y = thrust factor. V = rotation factor. ( 1. 00 for inner race rotate) ( 1. 2 for outer race rotate) Ka = where Ka is load factor or service factor or application factor

LOAD FACTOR, Ka Type of Application Load Factor, Ka Precision gearing 1. 0 – 1. 1 Commercial gearing 1. 0 -1. 3 Machinery with no impact 1. 0 -1. 2 Machinery with light impact 1. 2 -1. 5 Machinery with moderate impact 1. 5 -3. 0

LOAD- LIFE RALATIONSHIP (May-10, Dec. -10, Nov. 12) Two groups of identical bearings working under identical conditions but different loads have load life relationship as Where a = 3 for ball bearing = 10/3 for roller bearings When the first group of bearing is subjected to the radial load equal to it basic dynamic capacity ”C” the life of the bearing is one million revolutions. i. e. when P 1= C, L 1= one million rev.

Continue…. If second group of bearings is subjected to radial load equal to the equivalent dynamic radial load, P 2 = Pe and L 2 = L 10 Rating life of bearing milloin revolutions. Where L 10 = Rating life of bearing under load, million rev. C = Basic dynamic load capacity, N Pe = Equivalent dy. load capacity, N L 10 = where, Lh 10 = Rating life of bearing in no. of hours.

SELECTION OF BEARING LIFE Selection of proper size of bearing is dependent on the expected life of the bearing for a given application. 1) Bearing life in million revolutions- Automotive vehicles. • 2) Bearing life in number of hours of service. Industrial machines, electric motors.

SELECTION OF BEARING LIFE Bearing life for vehicle Applications No. Vehicle Life in million rev. 1 Automobile cars 50 2 Trucks 100 3 Rail road cars 1000

SELECTION OF BEARING LIFE Bearing life for Industrial Applications Application Life in. Hrs. (Lh) Machines used for intermittently and whose breakdown is not serious 4000 to 8000 Machines used intermittently and whose breakdown is serious 8000 -12000 Machines use for 8 hrs. per day and not fully utilised 12000 to 20000 Machines use for 8 hrs. per day and fully utilised 20000 -30000 Machines use for continuous 24 hrs. per day. 40000 -60000 Machines required to work with high degree of reliability for 24 hrs. per day. 100000 -200000

SELECTION OF BEARINGS FROM MANUFACTURERS CATALOGUE 1 Calculate radial and axial load (Fr and Fa) 2 determine the dia. of shaft. 3 Select the type of bearing. Start with extra light series. 4 Find basic static capacity from catalogue. (Co) 5 Calculate ratios (Fa/ V Fr) and ( Fa/ Co) 6 Find radial and thrust factors (X and Y) from catalogue. The values depend upon (Fa/VFr) and (Fa/ Co) 7 For the given application, find the value of load factor Ka from catalogue.

SELECTION OF BEARING FROM MANUFACTURERS CATALOGUE 8 Calculate equivalent dynamic load, Pe= (X. V. Fr +Y. Fa). Ka 9 Decide expected life L 10 in millions rev. 10 Find required basic dynamic capacity L 10= (Cr/Pe)a 11 Check weather the selected bearing has required basic dynamic capacity. (C > Cr ). If not, go for higher series bearing. 12 If necessary, calculate the equivalent static load by using, Po= Max. {Xo. For + Yo. Foa} or{ For} For safety of the bearing against static failure, C 0 > Po

START INPUT: i) Ft & Fa ii) Shaft Diameter iii) Application SELECT: Type of Bearing SELECT : Bearing of Extra Light Service FIND: i) Co ii) C iii) (Fa/VFr) and (Fa/Co) iv) X and Y SELECT : i) Ka ii) L 10 CALCULATE: Pe= (X. V. Fr +Y. Fa). Ka

Continue…. NO a = 10/3 Is It Ball Bearing ? YES CALCULATE : Required Dynamic Capacity Cr = Pe (L 10)1/a SELECT: Bearing of Next series NO Is C > Cr CALCULATE : Po= Max. {Xo. For + Yo. Foa} or{ For} NO Is Co > P o YES STOP a=3

TAPER ROLLER BEARING

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MOUNTING OF TAPER ROLLER BEARING

Back to Back Mounting Face to Face Mounting

Face to Face ( Direct) Mounting Back to Back (Indirect) Mounting

Bearing With Probability of Survival Higher Than 90 Percent • Reliability of a bearing can be defined as the mathematical probability of a bearing to successfully complete the required life. • If the machine is assembled with total “N” bearings, each having reliability of 90%, then the reliability of the complete system. • RN= (R)N

Continue…. • The Relationship between the bearing life and the reliability can be best approximated by the statistical disribution known as “Weibull Distribution”. • According to Weibull Distribution, the relation between bearing life ‘L’ desired reliability ‘R’ and rating life ‘L 10’ is given by Where, L = Bearing life with desired reliability ‘R’ L 10 = Rating Life

ADJUSTED LIFE OF BEARING § Required reliability higher than 90% § Severe operating conditions § Requirement of different bearing materials in specific conditions. Where: La = actual adjusted life of bearing, million revolution L 10 = Rating life of bearing, million revolution a 1 = life adjustment factor for reliability a 2 = life adjustment factor for operating condition a 3 = life adjustment factor for bearing material

Preloading of Bearings Objectives of preloading- • To remove internal clearance found in bearings. • To improve positional accuracy of shaft. • To decrease the shaft slope at bearing. • To increase the fatigue life of bearing. Types of preloading- § Axial preloading of ball bearing and Taper roller bearing § Radial preloading of cylindrical roller bearing.

TYPES OF FAILURES IN ROLLING CONTACT BEARINGS § Fracture in outer race of the bearing. § Misalignment § Breakage of cages- High speed § Abrasive wear- Contamination. § Corrosive wear- Moisture § Pitting- Faulty mounting / preload. § Scoring- Execessive frictional heat.

Lubrication of Bearings Objectives - • To reduce the friction & wear. • To dissipate the frictional heat. • To protect from corrosion. • To obstruct the entry of foreign material. Guide lines for selection of lubricant – § Operating Speed & Temperature. § Bearing Load § Lubrication System

Faulty mounting