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A PRESENTATION BY WG CDR ARVIND KUMAR. BEARINGS, FAILURES CAUSES & REMEDIES.

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Presentation on theme: "A PRESENTATION BY WG CDR ARVIND KUMAR. BEARINGS, FAILURES CAUSES & REMEDIES."— Presentation transcript:

1 A PRESENTATION BY WG CDR ARVIND KUMAR

2 BEARINGS, FAILURES CAUSES & REMEDIES

3 CONCEPT CONSTRUCTION BEARING MATERIALS TYPES OF LOADS & BEARINGS BEARING CLEARANCES WHY BEARING FAILS! FAILURES, CAUSES & REMEDIES :FEW EXAMPLES PATH PATTERN INTERPRETATION OTHER IMPORTANT POINTS TV-2 STATISTICS PRACTICAL DEMONSTRATION

4 CONCEPT OF ROLLING BEARING

5 Things roll better than they slide. Hence the invention of WHEEL. Rolling friction is far lesser (>100 times less) than sliding friction. Microscopic contacts get peeled off and not sheared off in rolling.

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7 Cage/ Retainer Inner ring / race Rolling element Outer ring / race Side faces Outer ring raceway Shoulder Inner ring raceway Shoulder 7 ROLLING BEARING CONSTRUCTION

8 7 BEARING DIA Outside Diameter Bore

9 BEARING CONSTRUCTION-2 SealRolling ElementsInner Ring Outer RingCageSeal

10 BEARING CONSTRUCTION-3 Outer Ring Cage Inner Ring Side faces W33 Lubrication Groove and Hole Rolling Element Guide Ring Inner Ring Raceway

11 VARIOUS ROLLING ELEMENTS Spherical roller (asymmetrical) Taper roller Spherical roller (symmetrical) Needle roller Cylindrical roller Ball

12 POINT / LINE CONTACT

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14 PROPERTIES : BEARING MATERIALS High wear resistance High rolling fatigue strength Non-metallic inclusions like O, S etc. increase fatigue cracking High dimensional stability Heat treatable to high hardness in depth High corrosion resistance High wettability with oil Low coefficient of semi-dry friction Good heat conductivity Good antiseize properties

15 MATERIALS-SKF BEARINGS BEARING RINGS AND ROLLING ELEMENTS THROUGH-HARDENING STEELS CARBON CHROMIUM STEEL CONTAINING APPROXIMATELY 1 % CARBON AND 1,5 % CHROMIUM CASE-HARDENING STEELS CHROMIUM-NICKEL ALLOYED STEEL AND MANGANESE-CHROMIUM ALLOYED STEEL CONTAINING APPROXIMATELY 0,15 % CARBON

16 SKF BEARING MATERIALS -2 ~SAE 52100 C-Cr Bearing steel ( ISO 683 -17:1999) Ceramics like Si 3 N 4 for ultra high speed applications Stainless steels like X65Cr14 (ISO 683-17:1999)

17 BEARING MATERIALS -3 Highly alloyed steels like 80MoCrV42-16 for temperature > 250°C (SKF) Case Hardening Steel for shock loads DMRL analysis for Russian bearing (6-7000108B, Central Drive B.B on Ist support assy of TV-2 engine of Mi-8 heptr) C~1.0% Cr~1.8% Si~0.23% Mn~0.33% steel nearly equivalent to AISI-52100 Original Russian material is Sh Kh 15

18 SPECIAL FEATURES Hard Surfaces HRC 58-65 for C-Cr bearing steel (SKF) DMRL analysis of Russian Bearing - HV/5Kg : 930 (HRC : 68) Perfectly round and incredibly smooth Very high surface finish : CLA ~ 0.5 microns Addition of Si to improve heat resistance dimensional stability) at 150-200°C

19 Radial loads Axial Loads Combined loads

20 AXIAL / THRUST LOADS BAR STOOL BEARINGS (Mans wt. causes thrust load) Thrust load Bearings

21 RADIAL LOADS Motors & Pulley Shaft Support Bearings Radial load MotorTension

22 COMBINED LOADS Car Wheel Bearing

23 CYLINDRICAL ROLLER BRG : Radial load only (Heavy) BALL BRG : Both axial & radial TAPERED ROLLER BRG : Radial load & Axial load in one direction also Axial load is also called as Thrust load

24 RADIAL LOAD Cylindrical Roller Bearing

25 Deep groove B.B Angular contact B.B Self-aligning B.B Ball Bearings Radial loadAxial load SpeedAccommodates carrying capacity carrying capacity capabilitymisalignment

26 Radial Load Axial Load (one direction) Tapered Roller Bearing

27 Radial Load Thrust Thrust Double Tapered Roller Bearing Radial Load Thrust Thrust Double Tapered Roller Bearing

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29 360° ~150° LOAD ZONE

30 Radial clearance / play Axial clearance / play BEARING CLEARANCES

31 C1 - less than C2 clearance C2 - less than normal clearance CN - normal clearance C3 - greater than normal clearance C4 - greater than C3 clearance C5 - greater than C4 clearance Russian System ? Example: A 6210 /C3 ball bearing has 18 - 36 µm (microns) or 0.0007 - 0.0014 radial internal clearance CLEARANCE DESIGNATIONS

32 AXIAL INTERNAL CLEARANCE Example: A 5210 / C3 ball bearing has 33 - 54 µm or 0.0013 – 0.0021 axial internal clearance 25-126114P ball bearing used in TV-3 aeroengine 2nd Support should have 140-220 µm axial internal clearance

33 EFFECT OF TEMPERATURE ON CLEARANCE COLD (by 5-10°C) WARM Reduced radial clearance Expansion Compression

34 EFFECT OF FIT ON CLEARANCE INTERFERENCE FIT between shaft and bearing (inner race) reduces radial clearance by approx 80% of the fit. Because the inner ring expands and the outer ring contracts.

35 EFFECT OF LOOSE FIT N = 3 000 10 hours/day 30 days = 18 000 min Sliding motion =0,013 x π x 3 000 x 18 000 = 2,2 x 10 6 mm = 2,2 km (1.4 miles) creep

36 LOAD DISTRIBUTION & CLEARANCE Less Clearance More Clearance Pressure between rolling element and races can reach 4 lakhs PSI

37 EXCESSIVE CLEARANCE Loading area reduces & stress increases Bearing rigidity reduces Alignment of rolling elements decreases Vibration increases at high speeds Noise increases Running and locating accuracy reduces

38 PRELOAD Small amount of loading before running of brg Causes negative clearance Elastic deformation & compressive stress at contact area Bearing rigidity improves Vibration at high speeds reduces Noise reduces Alignment of rolling elements improves (Thrust brgs) Running and locating accuracy improves

39 EFFECT OF CLEARANCE ON BEARING LIFE Excessive preload causes high stress and heat generation Life PreloadClearance

40 BEARING LIFE Repeated compressive stresses (rolling fatigue) cause flaking of material of raceways and rolling elements and hence failure. Basic Rating Life L 10 (90% reliability) of the bearing is the total number of revolutions in millions which 90% of the bearings out of the lot reach before or at which the first signs of flaking occur under identical operating conditions.

41 BEARING LIFE-2 L 10 = (C / P) n C = Design Load {Basic dynamic rating load (constant radial or axial load when brg is rotating) in N that will give bearing life of 10 6 revs in accordance with ISO 281:1990} P = Actual equivalent dynamic load in N n = 3 for ball bearings 3.33 for roller bearings

42 BEARING LIFE-3 If actual load is half of the rated load, life of a ball bearing will increase by 8 times. (Min. Load*) If actual load increases by 25% above the rated load, the life of a ball bearing gets nearly halved. Actual service life may be reduced even further below the calculated value because of factors like contamination, misalignment, improper installation or lubrication etc. Effect of overload is more severe on roller brg.

43 LIFE ADJUSTMENT FACTOR Higher the expected reliability, the lesser is the bearing life. L 5 (95% reliability) = 0.62 L 10 L 3 (97% reliability) = 0.44 L 10 L 1 (99% reliability) = 0.21 L 10

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45 WHY BEARINGS FAIL! Study in Scandinavian countries indicates : - ~1/3 brgs fail because of Poor Lubrication - ~1/6 brgs fail because of Contamination - ~1/3 brgs fail because of Fatigue - ~1/6 brgs fail because of Bad Installation

46 WHY BEARINGS FAIL!-2 In India, there is likely to be greater percentage of failures because of :- Contamination Improper installation and lubrication Lesser percentage of failures because of :- Fatigue

47 FAILURE MODE CLASSIFICATION-1 As per ISO 15243:2004, there are 15 main failure modes classified as: Fatigue (Repeated compressive stresses) -Subsurface -Surface initiated (metal to metal contact) Wear -Abrasive -Adhesive

48 FAILURE MODE CLASSIFICATION-2 Corrosion - Moisture, - Fretting - False Brinelling Electrical Erosion -Excess voltage - Current leakage

49 FAILURE MODE CLASSIFICATION-3 Plastic Deformation - Overload - Indentation from debris - Indentation by handling Fracture - Forced - Fatigue - Thermal Cracking

50 SYMPTOMS OF BEARING FAILURE - Overheating - Noise - Vibration - Obstruction of movement (RDT reduces) - Shaft jammed - Others ?

51 FAILURES, CAUSES & REMEDIES – FEW EXAMPLES

52 CORROSION

53 AppearanceCauseAction Grey black streaks across the raceways, mostly coinciding with the rolling element spacing. At a later stage, pitting of raceways and other surfaces of the bearing. Presence of water, corrosive substances in the bearing over a long period of time. Improve sealing. Use lubricant with better rust-inhibiting properties.

54 WEAR-ABRASIVE PARTICLES Fig 19 Outer ring of a spherical roller bearing with raceways that have been worn by abrasive particles. It is easy to feel where the dividing lines goes between worn and unworn sections.

55 WEAR-ABRASIVE PARTICLES AppearanceCauseAction Small indentations around the raceways and rolling elements. Dull, worn surfaces. Lack of cleaning before and during mounting operation. Ineffective seals. Lubricant contaminated by worn particles from brass cage. Do not unpack bearing until just before it is to be mounted. Keep workshop clean and use clean tools. Check and possibly improve sealing. Always use fresh clean lubricant. Wipe the grease nipples. Filter the oil.

56 WEAR-INADEQUATE LUBRICATION Fig 20 Cylindrical roller with mirror- like surface on account of lubrication starvation Fig 21 Outer ring of a spherical roller bearing that has not been adequately lubricated. The raceways have a mirror finish

57 WEAR-INADEQUATE LUBRICATION AppearanceCauseAction Worn, frequently mirror-like surfaces. At a later stage blue to brown discoloration Lubricant has gradually been used up or has lost its lubricating properties. Check that the lubricant reaches the bearing. More frequent lubrication.

58 WEAR DUE TO VIBRATION

59 AppearanceCauseAction Depressions in the raceways. These depressions are rectangular in roller bearing and circular in ball bearing. The bottom of these depressions may be bright or dull and oxidized. The bearing has been exposed to vibration while it was stationary. Secure the bearing during transport. Provide a vibration damping base. Where possible use ball bearing instead of roller bearing. Employ oil bath lubrication, where possible.

60 INDENTATIONS - FOREIGN PARTICLES Fig 31 Indentations caused by dust in one of the raceways of a roller bearing-50 x Magnification

61 INDENTATIONS - FOREIGN PARTICLES AppearanceCauseAction Small indentations distributed around the raceways of both rings and the rolling elements. Ingress of foreign particles into the bearing. Cleanliness to be observed during the mounting operation. Uncontaminated lubricant. Improved seals.

62 FRETTING CORROSION

63 AppearanceCauseAction Areas of rust on the outside surface of the outer ring or in the bore of the inner ring. Raceway path pattern heavily marked at corresponding positions. Fit too loose. Shaft or housing seating with error of form. Proper fit and housing.

64 SMEARING

65 AppearanceCauseAction Scored and discolored roller ends and flange faces Sliding under heavy axial loading and with inadequate lubrication. More suitable lubricants.

66 ELECTRIC CURRENT EROSION

67 AppearanceCauseAction Dark brown or greyish black fluting (corrugation) or crater in raceways and rollers. Balls have dark discoloration only. Sometime zigzag burns in ball bearing raceways. Localised burns in raceways and on rolling elements. Passage of electric current. Re-route the current to bypass the bearing. Use insulated bearings. When welding, arrange earthing to prevent current passing through the bearing.

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69 Working surfaces become dull after operation. Path Pattern (dull surface) varies in appearance according to the rotational and loading conditions. By experience, we can learn to distinguish abnormal paths from normal paths and hence get clues to brg failure reasons.

70 PATH PATTERN INTPT-2 Uni-directional Radial Load

71 PATH PATTERN INTPT-3 Uni-directional Radial Load

72 PATH PATTERN INTPT-4 Uni-directional Axial Load

73 PATH PATTERN INTPT-5 Uni-directional Radial Load + Creeping* Outer Ring

74 PATH PATTERN INTPT-6 Uni-directional Radial Load + Tight Fit / Preloading

75 PATH PATTERN INTPT-7 Oval Compression of Outer Ring

76 PATH PATTERN INTPT-8 Outer Ring Misaligned

77 PATH PATTERN INTPT-9 Inner Ring Misaligned

78 PATH PATTERN INTPT-10 Combined Uni-directional Radial & Axial Loads

79

80 2014-05-31 ©SKF Slide 80 [Code] LUBRICATION MODES

81 GREASE RUN-IN

82 AXIAL LOCATION "Non-located" bearings that can move axially

83 CONDITIONS : BEARINGS SHOULD BE STOCKED IN A SEPARATE STOCKING PLACE * CLEAN (no dust) * DRY (Max 60 % humidity) * DRAUGHTS TO BE AVOIDED (no windows opened) AWAY FROM VIBRATION TEMPERATURE AROUND 20 DEGREES C. * NO TEMPERATURE FLUCTUATIONS (avoid condensation) AIR CONDITIONED IN HOT & HUMID CLIMATES Never touch aviation bearing with hand. BEARING STORAGE ROOM STORAGE AND REPACKING

84 1. FIRST IN, FIRST OUT 2. DO NOT PILE UP TOO HIGH 3A. STOCK LARGE BEARINGS FLAT (O.D. > 420 mm) 3B. MEDIUM SIZE BEARINGS 3C. SMALL BEARINGS * OLDEST BEARINGS ALWAYS IN FRONT AND ON THE TOP OF THE PILE * IT DOES DAMAGE THE PACKING * AT THE BOTTOM OF THE RACKS * STOCK FLAT (not vertical) * STOCK UNOPENED (individually packed in box) * NUMBER READABLE (up front) * NUMBER (designation) UP FRONT) * IN DRAWERS OR BOXES (keep away from dust) * DESIGNATION ON DRAWER (box) STORAGE IN RACKS STORAGE AND REPACKING

85 REMARK : * BEARINGS ARE CLEAN AND ARE PROTECTED WITH A RUST INHIBITIVE OIL. * BEARINGS ARE WRAPPED IN A SPECIAL PAPER OR PLASTIC SHEETING FOR PROTECTION. * BEARINGS ARE PACKED IN CARDBOARD BOXES FOR PROTECTION * LARGE SIZE BEARINGS ARE INDIVIDUALLY PACKED IN WOODEN BOXES FOR PROTECTION. 3 GOOD REASONS TO KEEP BEARINGS IN THE ORIGINAL PACKING : STOCKING RECOMMENDATIONS STORAGE AND REPACKING

86 * WHITE SPIRIT * CLEAN AREA * LET DRY 1. WASH 2. INHIBITING OIL PROTECTION * 40 % QUAKER 5815 BASE AND 60 % WHITE SPIRIT * DIP AND ROTATE * DRY 7 HOURS * CLEAN AREA 3. PACK * WRAP IN POLYETHYLENE COATED "VPI" PAPER * PACK IN (CARTON) BOXES 4. IDENTITY * INDICATE FULL BEARING NUMBER * INDICATE BRAND !! RENEWING ANTI-RUST (AND PACKING) STORAGE AND REPACKING

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