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[Audio] 231ME521 DESIGN OF MACHINE ELEMENTS PRESENTED BY Dr. R. GANAPATHY SRINIVASAN ASSOCIATE PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING VEL TECH MULTITECH Dr. RANGARAJAN Dr. SAKUNTHALA ENGINEERING COLLEGE.

[Audio] . Unit 5 - Bearings Syllabus: • Sliding contact and rolling contact bearings - Hydrodynamic journal bearings, Sommerfeld Number, Raimondi and Boyd graphs, - Selection of Rolling Contact bearings..

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[Audio] . What are Bearings? • A bearing is a device to permit constrained relative motion b/w two parts typically rotation or linear movement. • Bearing may be classified broadly according to the motion they allow and according to their principle of operation..

[Audio] . In a ball bearing, the load is transmitted from the outer race to the ball, and from the ball to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly. But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform or squish, ruining the bearing. Roller bearings like the one illustrated above are used in applications like conveyer belt rollers, where they must hold heavy radial loads. In these bearings, the roller is a cylinder, so the contact between the inner and outer race is not a point but a line. This spreads the load out over a larger area, allowing the bearing to handle much greater loads than a ball bearing. However, this type of bearing is not designed to handle much thrust loading..

[Audio] . Bearing alloys A bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle..

[Audio] . ball Inner surfa e Outer surfac.

[Audio] . Excentricity_ I) Lubricant 2) Shaft 3) Bearing shell 4) Hydrodynamic pressure https://www.youtube.com/watch?v=_cNIE8K I.Jvmk.

[Audio] . nor Real-time picture of Bearings.

[Audio] . Bearing materials 1. White metals Lead base Sb 13%, Sn 12%, cu 0.75%, As 0.25% Pb- Plain tin Bronze, Phosphor bronze, Leaded bronze, 2. Cu-base alloys Sintered bronze Good Load bearin ca aci —Aero en ines utomobiles Domestic equipment Al— base a I Sn 7%, Cu 1.3%, Ni 1.3%, Balance A1 - Automobiles 3. Nylons 4. Plastic materials Teflons Ceramics Alumina Large speed precision 5..

[Audio] . Function of bearing • The main function of rotating shaft (Journal) is to transmit power from one end of the line to the other. • Supports the load. • It needs a good support to ensure stability and frictionless rotation. The support for the shaft is know as "Bearing". • https://gfycat.com/yearlyshoddyarmyworm.

[Audio] . Functions of Bearings.

[Audio] . Types of Bearings • Based on direction of Lo — Radial bearing — Thrust/Axial bearings — Combined bearing • Based on Nature of cont — Sliding contact — Rolling contact.

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[Audio] . Types of bearing • Sliding contact bearing or Plain bearing or Journal bearing or Sleeve bearing — Hydrodynamic bearing (Thick film bearing) — Thin film bearing (Boundary lubricated bearings) Hydrostatic bearing (Externally pressurized lubricated bearing) • Rolling contact bearing or Anti-friction bearing or simply ball bearing:- (1)Deep groove ball bearing (2)Cylinder roller bearing (3)Angular contact bearing (4)Taper roller bearing (5)Self aligning bearing.

[Audio] . Bearing Rolling contact beanng or Anti-fnction beanng or Simply ball bearing Deep groove ball bearing Cylindncal roller beanng Angular contact bearing Sliding contact beanng or Plain beanng Joumal beanng or Sleeve beanng Self aligning beanng Taper roller bearing Hydrodynamic bearing Hydrostatic bearing Classification of bearing.

[Audio] . Hydrodynamic /Journal Bearin s Design of Journal Bearing m) Finding out other parameters using Somerfield's number and Raimondi and Boyd's curve (ßS,h0) Unit 5 Bearings Selection of Ball Bearing (Bearing SKF no.) — Indirect method Roller/Ball Bearings Life related problems on Ball/Roller Bearing — Direct method.

[Audio] . T es of Slidin Contact Bearin (Based on sliding action) 120 When the ang e OJ contact of the bearing with the journal is 3600 as shown in (a), then the bearing is called a full journal bearing. (b) Partial When the angle of contact of the bearing with the journal is 120% as shown in Fig (b), then the bearing is said to be partial journal bearing. (k) Fitted t e diameters of the journal and bearing are equal, then the bearing is called a fitted bearing, as shown in Fig. (c)..

[Audio] . 1. Sliding contact bearing • In these bearing load is transferred though a thin film of lubricant coils (oils)..

[Audio] . 1.1 Hydrodynamics bearing • A journal bearing , in its simplest form is a cylinder bushing made of a suitable material and containing property machine inside and outside diameters. The journal is usually the part of a shaft or pins that rotates inside the bearing. • Its handle high load and velocity because metal to metal contact is minimal due to the oil films. • They are require large supply of lubrication oil..

[Audio] . Hydrodynamic Bearing Stiatt Fig. 18.1: Joumal Bearing lbgb.

[Audio] . 1.2 Hydrostatic bearing bearings • Hydrostatic externally are pressurized fluid bearings, where the fluid is usually oil, water or air, and the pressurization is done by a pump. Bearing BEARING oe EXTERNAL SOURCVNMP..

[Audio] . Oil Ird C eng Load B eanrg H vdrostatic Journal.

[Audio] . 1.2 SLIDING CONTACT BEARINGS - ADVANTAGES AND DISADVANTAGES These bearings have certain advantages over the rolling contact bearings. They are: 1. The design of the bearing and housing is simple. 2. They occupy less radial space and are more compact. 3. They cost less. 4. The design of shaft is simple. 5. They operate more silently. 6. They have good shock load capacity. 7. They are ideally suited for medium and high speed operation. The disadvantages are: 1. The frictional power loss is more. 2. They required good attention to lubrication. 3. They are normally designed to carry radial load or axial load only..

[Audio] . 2. Rolling contact bearing • A load is transfer though rolling elements such as balls straight and tapered cylinders and spherical rollers. • The designer must deal with such matter as fatigue, friction, heat , lubrication etc. Ball Cylindrical Tapered Barrel Needle roller roller roller rot let.

[Audio] . Roller Bearing I.Deep Groove Ball Bearing- 3.Angular Contact Bearing 2.Cylindircal Roller Bearing 4.Tapper Roller Bearing.

[Audio] . Parts of Ball bearing Inner ring Outer ring Cage Ball.

[Audio] . Radial load Shaft Bearing.

[Audio] . Materials used for Sliding Contact Bearings Babbit metal nn base babbits : Tin 90% ; Copper 4.5% ; Antimony 5% ; Lead 0.5%. Lead base babbits : Lead 84% ; Tin 6% ; Anitmony 9.5% ; Copper 0.5%. The gun_metal (Copper 88% ; Tin 10% ; Zinc 2%) is used for high grade bearings subjected to high pressures (not more than 10 N/mm2 of projected area) and high speeds. 80% ; Tin ; Lead 9% ; Phosphorus 1%) is used for bearings subjected to very high pressures (not more than 14 N/mm2 of projected area) and speeds. cast iron bearings are usually used with steel journals. Such type of bearings are fairly successful where lubrication is adequate and the pressure is limited to 3.5 N/mm2 and speed to 40 metres per minute. The silver and silver lead bearings are mostly used in aircraft engines where the fatigue strength is the most important consideration. various non-metallic bearings are made of carbon-graphite, rubber, wood and plastics. The carbon-graphite bearings are self lubricating, dimensionally stable over a wide range of operating conditions,.

[Audio] . Comparison of Bearings + Comparison of Antifriction bearing and Journal/Sliding bearing: Sr. No. 1 2 3 4 5 6 7 Journal Bearing Starting torque is high. Hydrodynamic bearings remains silent at high speeds. Occupies less radial space and more axial space. Sudden failure may take place and create accident. Simple journal bearings capable to sustain both radial and axial load is difficult to design. More clearance is required compared to rolling contact bearings. Maintenance and lubrication is to be done carefully. Rolling Contact Bering Less starting torque. Makes noise at high speeds. Occupies less axial space and more radial Space. Makes noise prior to failure. Certain bearings can be designed to sustain both radial and axial load. Less clearance required comparatively. Maintenance and lubrication is economical and relatively easy..

[Audio] . Applications of Bearings ROLLING CONTACT BEARINGS machine tool spindles automobile front and rear ax les gear boxes small size electric motors rope sheaves, crane hooks and hoisting drums SLIDING CONTACT BEARINGS crankshaft bearings in petrol and diesel engines centrifugal pumps large size electric motors steam and gas turbines concrete mixers, rope conveyors and marine installations.

[Audio] . Assumptions in Hydrodynamic bearings • Obeys newton law of viscous flow — Relationship between the shear stress and shear rate of a fluid subjected to a mechanical stress. The ratio of shear stress to shear rate is a constant, for a given temperature and pressure. • Pressure is constant through out the film thickness • Lubricant is incompressible • Viscosity is constant • Flow is one dimensional —Side leakage is neglected.

[Audio] . Wedge film formatior Hydrodynamic bearil Oil (a) At rest. (h) Slow speed. • The lubricant, by virtue of its viscosity, clings to the surface of the rotating journal, and is drawn into the wedge, creating a very high pressure (sometimes in excess of 6,000 psi), which acts to separate the journal from the bearing to support the applied load..

[Audio] . Terms used in Hydrodynamic Journal Bearing e sin bearing oil journal Pmax bearing oil journal Pmav GURE 10-8.

[Audio] . PSG databool( (Hydrodynam.

[Audio] . Terms used in Hydrodynamic Journal Bearing GEOMETRIC RELATION FOR ANY (Shown here cteomnce beorbtgJ GEOMETRIC RELATIONS FOR A CLEARANCE BEARING : Clearance ratio CID Eccentricity, e Eccentricity factor or Attitude Eiim thickness at any 2-29 angle c h e — (ecos 1) 2 Minimum film thickness ho (l e) DESIGN TECH journal diameter, cm diametral dearaoce. cm C. tiinimum film thickness, cm attitude dimensionless attitude. angle Leagth of bearing. cm W. Load kgr bearing pressure 00 prc*Eted area. kgf/cm2 eccentricity. cm e. speed or journal, rpm n', speed of journal cps absolute viscosity Of the oil, centipoises Z, 7.33.

[Audio] . Terms used in Hydrodynamic Journal Bearing GEOMETRIC RELAUON FOR BEBANG portbl eteomnce GEOMETRIC RELATIONS FOR A CLEARANCE BEARING . Clearance ratio C/D Eccentricity. e Eccentricity factor Ot Attitude Eiim thickness at any c angle Minimum film thickness ho (I — e) DESIGN TECH journal diameter, cm D, diametral elearuoce. cm C. tiinimum film thickness, em attitude. dimensionless attitude. .angle Length of bearing. cm W. Load, kgr baring pressure 00 pr+cted area, kgf/cm2 eccentrEty, em e. speed or journal, rpm speed Of journal. rps absolute viseosity Of the oil, entipoises 7.33.

[Audio] . Coefficient of Friction for Journal Bearings By McKee *Coefficient of fiiction, 33 ZV d — + k (when Zisinkg/m-sandpisinN/mm2) where Z, N, p, d and c have usual meanings as discussed in previous atticle, and k = Factor to corect for end leakage. It depends upon the ratio oflength to the diameter of the beanng (i.e. I = 0.002 for I / d ratios of 0.75 to 2.8. By Petroff's equation or Petroffs law 2 Zn' g = 27t P d c The Petroff's equation and McKee's equations are employed for lightly loaded bearings..

[Audio] . Sommerfeld Number The Sommerfeld number is also a dimensionless parameter used extensively in the design of journal bearings , Mathematically 2 ZV d Sommetfeld number — For design purposes, its value is taken as follows : 2 ZV d = 14.3 x 106 Critical Pressure of the Journal Bearing Critical pressure or minimum operating pressure, 2 ZV d 4.75 x 106 c 2 N/mm.

[Audio] . Heat Generated in a Journal Bearing Q = p.m. V N-m/s or J/s or watts g Coefficient of friction, = Load on the bearing in N, = Pressure on the bearing in N/'mm2 x Projected area of the bearing in mm2 (l x d), nduV , d is in metres, and r = Rubbing velocity in mis = 60 N = Speed of the joumal in r.p.m. Heat Dissipated in a Journal Bearing C = Heat dissipation coefficient in W/m2/0C, A = Projected area of the bearing in m2 = I x d, tb Temperature of the bearing surface in oc, and t = Temperature of the sunounding air in oc. Heat generated < Heat dissipated.

[Audio] . *VDOOYNASOC EQUATION PSG DB: Pg no- 7.34.

[Audio] . •UBISGS eou,400N r«gorrs 7.34 nov CAP :.

[Audio] . eco 20 OATA—ßC ABSCWTE Viszcsrrs V. 70 n too 'to 120 so 9.41.

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[Audio] . Design Procedure of Journal Bearing I. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Diameter of journal/Shaft (Use 2TtNT/60 & T = Tt DA3 t/16) Select L/D ratio from PSG databook 7.31 Find Clearance from C/D ratio - PSG databook 7.32 Bearing Pressure P=W/LD (Check at PSG databook 7.31 If not satisfied change L/D ratio) Absolute viscosity, Z (PSG databook 7.31) Lubricant oil used and it's viscosity (PSG databook 7.41) Bearing characteristics number (Zn/P) Film thickness (if needed) Coefficient of Friction (From Mckee's Equation - PSG databook 7.34) Materials used Additional cooling system required or not Somerfield number (if needed) Heat generated (PSG databook 734) and Heat dissipation (Hd = q A At) Mass flow rate ( Qt = m cpnt).

[Audio] . Unit Conversion Solving DME problems be like: Forgeting to convert to SI units Cqrrcet Answer.

[Audio] . Problem The load on a journal bearing is 150 kN due to a turbine shaft of 250 Inm diameter running at 1800 rpm. Determine the following (i) Length of bearing if the allowable bearing pressure 1.6 MPa, (ii) Amount of heat to be removed by the lubricant per minute if the bearing temperature is GOUC and the viscosity of the oil at 6COC is 20 centipoises and the bearing clearance is 0.25 mm, (Anna University).

[Audio] . Solution: Given: Load on the journal, Diameter of journal, Speed of journal, Bearing pressure, Operating temperature Viscosity of oil, Bearing clearance, W = 150 150 x 103 N d = 250 mm. n = 1800 rpm. 2 p = 1.6 MPa = 1.6 x 106 = 1.6 N/mm Z=20 cp=20x10-3N-s/m 2 c = 0.25 mm. (i) To find length of bearing: Let I = Length of bearing. The bearing pressure over the projected area is given by, w w p.d 150 x 103 = 375 mm (Answer) 1.6 x 250.

[Audio] . (ii) Amount of heat to be removed: The heat generated in bearing due to turbine shaft rotation is given by Hg=p WV N—m/min. (or) Jimin. where, = Coefficient of friction, 3325 Zn d 108 33.25 0.020 x 1800 108 1.6 250 + 0.002 0.25 1 375 IFor d 250 .0075 + 0.002 = 0.0095 V = Sliding velocity X 250 X 1800 dn k is approximately equal to 0.002) (From Fig. 18.6), (PSG 7.34, JDB 19.24) m/min = 1000 1414 m/min. 1000 Hence, 0.0095 x 150 x 103 x 1414* 2015 x 103 N-m/min = 2015 kN—m/min (i.e., 2015 kJ/min.) This generated heat fihould be removed by the lubricant in order to safeguard the turbine from over heating. Hence, the amount of heat to be removed = 2015 kJ/min Answer).

[Audio] . Problem The load on a 100 mm full hydro-dynamic journal bearing is 9000 N. Speed of the journal is 320 rpms Let l/d = 1, c/d = 0.0011. The operating temperature = 650C and minimum oil film thickness -0.022 mm (i) Select an oil that will closely accord with the stated conditions. For the selected oil, determine (ii) the friction loss (iii) the hydro dynamic oil flow through the bearing, (iv) the amount of leakage (v) the temperature rise of oil passes through the bearing and (vi) maximum oil pressure. (Anna University, Nov. 2010).