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<\/p>\n<\/p>\n
Classification of bearings-<\/strong> 1. MAIN BEARINGS<\/strong> 2. TOP END BEARINGS<\/strong> 3. BOTTOM END \/ CRANKPIN BEARINGS<\/strong> Bearing Operation<\/strong>: Depends on Bearing Loads<\/strong>: Combustion forces, Inertia forces & Centrifugal force of rotating masses Bearing Material Properties<\/strong><\/p>\n \udbc0\udc90 Mechanical Strength<\/strong> \udbc0\udc90 Soft & low melting point material<\/strong> \u2666\u00a0Soft metal flows locally without damaging the harder steel called conformability \udbc0\udc90 Corrosion resistance<\/strong> \u2013 to withstand corrosive attack from lub oil<\/p>\n \udbc0\udc90 Compatibility between bearing & journal under boundary condition<\/strong> \udbc0\udc90 Antifriction & wear properties \u2013depends upon type of oxide film that material forms on reaction without lube<\/strong> additives.<\/strong><\/p>\n Bearing Material<\/strong> \udbc0\udc90 Copper Lead & Lead Bronze<\/strong> = Brass (Cu + Zn) & Bronze (Cu + Sn) \udbc0\udc90 Aluminum Tin<\/strong> = Al Matrix + Si (minor) + Overlay7 (Pb+Sn) + Steel Backing Bearing Material \u2013 Shaft Material \u2013 Lubricant<\/strong> THIN SHELL BEARING<\/strong> – Recessed below bearing joint face. What is nip ?<\/strong> Advantages of Thin Shell Bearings<\/strong> Oil Grooves on Bearing Shell<\/strong> Main Bearing Groove<\/strong> Different between conventional and thin shell bearing ?<\/strong> \u2666\u00a0Thin shell bearing<\/strong> Cause of thin shell bearing shifting ?<\/strong> Crosshead Bearing Construction Features.<\/strong> Crosshead Bearing Working Condition<\/strong> Modification of Crosshead Bearings Over Last Few Decades:<\/strong> Bearing Housing Design Feature<\/strong> \udbc0\udc90 No fretting marks at the back of bearing shell and crush at bearing shell ends within limits BEARING CAPS<\/strong> BEARING BOLTS<\/strong> INSPECTION OF BEARING & JOURNAL FOR DEFECTS<\/strong> BEARING<\/strong> JOURNAL<\/strong> Bearing checking<\/strong> Bearing Clearance: Depends\u00a0on —<\/strong> Bearing Clearance Methods:<\/strong> Effect of excessive bearing clearance ?<\/strong> C \/E’s Procedure for Complete Inspection of a Crosshead Emphasizing Areas of Significant Interest (extract form B & W manual)<\/strong> 1. Check without opening up<\/strong> 2. Inspection & Overhaul<\/strong> \u2666<\/strong>\u00a0Loaded part is heavily worn \udbc0\udc31 Coin test for roughness, No vibration heard or felt when lightly held coin is passed over the surface What point to be check after removing X head bearing ?<\/strong> Types or Crosshead Bearing failure:<\/strong> Causes of Crosshead Bearing failure:<\/strong> How to check the bearing ? (Bearing overhaul) ****** Before removal<\/strong> After removing<\/strong> What points to be check after removing main bearing ?<\/strong> What points to be checked after removing big end bearing ?<\/strong> What points do you check after removing upper half bearing ? ****<\/strong> What points do you check after removing crank pin bearing ?<\/strong> What points do you check on thin shell bearing during overhaul ?<\/strong> For new thin shell<\/strong> Check new bearing before fitted<\/strong> How to decide that shell to be replaced ?<\/strong> How to check bearing wear down (Main bearing) without bearing removal ?<\/strong> Bearing Problems & Diagnostics<\/strong> Wiping of Bearings Surface<\/strong> Nitride surfaces<\/strong> Fretting<\/strong> Causes of fatigue cracking is due to poor bonding of white metal to its steel shell.<\/strong> Acid Corrosion<\/strong> Thermal Ratcheting<\/strong> Electrical Potential<\/strong> Cavitation Erosion<\/strong> Cause of white metal squeezing is when bearing metal is pressed out into the oil groove due to load on bearing exceed its compressive strength. \udbc0\udc40 Improper viscosity of oil (lower) Big end\/crank pin bearing bolts failure<\/strong> What do you do if intermediate bearing or tunnel bearing or plumber block bearing temperature is increase ?<\/strong> How to check plumber block at sea ?<\/strong> Main bearing removing procedure.<\/strong> Big end bearing removing and fitting procedure.<\/strong> Classification of bearings- \u2666 Main bearing \u2666\u00a0Top end\u00a0bearing = Cross Head \/ Gudgeon Pin bearing \u2666\u00a0Bottom End Bearing \/ Crank pin bearing \u2666\u00a0Thrust Pad bearing \u2666\u00a0Pedestal bearing (generator alternator side insulated bearing) 1. MAIN BEARINGS Function : Support crankshaft and keep it aligned. To remove heat produced by friction 2. TOP END BEARINGS Cross head […]<\/p>\n","protected":false},"author":1,"featured_media":5858,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[79],"tags":[],"class_list":["post-5857","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-marine-engineering-competency-exams-study-blogs"],"_links":{"self":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5857","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/comments?post=5857"}],"version-history":[{"count":4,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5857\/revisions"}],"predecessor-version":[{"id":5863,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5857\/revisions\/5863"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media\/5858"}],"wp:attachment":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media?parent=5857"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/categories?post=5857"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/tags?post=5857"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n\u2666 Main bearing
\n\u2666\u00a0Top end\u00a0bearing = Cross Head \/ Gudgeon Pin bearing
\n\u2666\u00a0Bottom End Bearing \/ Crank pin bearing
\n\u2666\u00a0Thrust Pad bearing
\n\u2666\u00a0Pedestal bearing (generator alternator side insulated bearing)<\/p>\n
\nFunction<\/strong> : Support crankshaft and keep it aligned.
\nTo remove heat produced by friction<\/p>\n
\nCross head Engines<\/strong>: Transmit load from cross head pin to connecting rod
\nAllows relative movement of con rod & cross head pin
\nTrunk Piston Engines: Transmit load from gudgeon pin to connecting rod
\nAllows relative movement of con rod & gudgeon pin<\/p>\n
\nFunction<\/strong>: Transmit load from con rod to crankshaft
\nAllows relative movement of con rod & journal<\/p>\n
\n\u2666\u00a0Operating temperature of bearing
\n\u2666 Working temperature of bearing
\n\u2666 Minimum oil film thickness
\n\u2666 Rate of oil flow
\n\u2666 Rate of heat production
\n\u2666 Power loss of bearing.<\/p>\n
\n\udbc0\udcd6 Varying resultant load from gas forces & inertia forces
\n\udbc0\udcd6 Two stroke engine \udbc0\udc8c No load reversal
\n\udbc0\udcd6 Four stroke engine \udbc0\udc8c Load reversals at the end of exhaust stroke hence, wear uniform & lubrication better.
\n\udbc0\udcd6 Fluctuating gas force results fatigue failure in bearing<\/p>\n
\n\u2666\u00a0Fatigue & compressive strength to carry load \u2013 depends upon thickness
\n\u2666\u00a00.3 mm white metal can withstand 141 bar pressure and 0.08 mm white metal can withstand 211 bar pressure
\n\u2666\u00a0Thin lining has poor conformability and too soft material tends to flatten under heavy loads
\n\u2666\u00a0Too hard material withstands high loads, posses high frictional characteristics & may be brittle with poor fatigue characteristics.<\/p>\n
\n\u2666\u00a0Softness & modulus of elasticity of bearing alloy should be as low as possible but hard enough to withstand heaviest continuous loading or chock loading without plastic deformation<\/p>\n
\n\u2666\u00a0Allows abrasive particles to embed to prevent damage to journal<\/p>\n
\n\u2666\u00a0Anti-weld & anti-score property between shaft & journal during start up & stop and by using turning gear.<\/p>\n
\n\udbc0\udc90 White Metal = Tin (Sn) +_ Antimony (Sb) + Copper (Cu)
\n\u2666\u00a0Thin walled bearings, stiff cross head assembly \udbc0\udc8c 88% Sn + 8% Sb + 4% Cu
\n\u2666\u00a0Thick walled bearing, flexible crosshead & Bottom end bearing \udbc0\udc8c 87% Sn + 9% Sb + 4% Cu
\n\u2666\u00a0Tin forms soft matrix to accommodate misalignment
\n\u2666\u00a0Antimony forms hard cubes to withstand load of journal. Tends to float and segregate during casting
\n\u2666\u00a0Copper holds antimony in evenly dispersed pattern, solidifies first.<\/p>\n
\n\u2666\u00a0Can withstand 3 times higher load than white metal
\n\u2666\u00a0Copper \/ Bronze matrix supplies the strength
\n\u2666\u00a0Lead remains in free state, provides bearing properties and Steel strips provides backing
\n\u2666\u00a0Overlay of 0.024 -0.04 mm thickness of lead \u2013tin, lead \u2013tin \u2013copper.
\n\u2666\u00a0Running in prevents acid attack against lead but poor embeddability & conformability<\/p>\n
\n\u2666\u00a0Soft Aluminum forms the matrix and provides embedability & conformability
\n\u2666\u00a0Tin held in suspension provides bearing properties
\n\u2666\u00a0Lead Tin Overlay of 0.02 mm for initial running in
\n\u2666\u00a03 times load carrying capacity than white metal but requires hardened journal
\n\u2666\u00a0Resistant to acid attack and fatigue strength same as Cu & Pb<\/p>\n
\n\udbc0\udc90 High local pressure at the point of contact
\n\udbc0\udc90 Localized welding at these points
\n\udbc0\udc90 Alloy formed at welds
\n\udbc0\udc90 Shear strength at welds.
\n\udbc0\udc90 Shear strength (alloy) > Shear strength (metal)<\/p>\n
\n\udbc0\udc99 Wall thickness to diameter ratio varies 0.05 mm for 40 mm shaft diameter and 0.02 mm for 400 mm shaft diameter.
\n\udbc0\udc99 Interference fit or bearing crush
\n\udbc0\udc99 Fretting \u2013 Interference fit resists relative movement, prevents fretting.
\n\udbc0\udc99 Locating Tags – For correct axial location of shell but not intended to resist motion<\/p>\n
\n\udbc0\udc99 Free spread – Bearing shell in snapped into bearing housing
\n– Bearing can be held in place when inverted during assembling.<\/p>\n
\nThe external circumference of a pair of bearing shell is slightly larger than the bore of housing. The difference is called nip.<\/p>\n
\n\udbc0\udc26 High load carrying capacity; approximately 5 time > conventional bearing
\n\udbc0\udc26 Uniform wall thickness permits better metallurgical control of white metal casting process.
\n\udbc0\udc26 High Bond Strength and ultrasonic method of bond testing between layers is accurate.
\n\udbc0\udc26 Reduced thickness & absence of keying grooves results in higher fatigue strength
\n\udbc0\udc26 Blistering on bearing surface due to H2 emission form is less.<\/p>\n
\n\udbc0\udcd6 Oil Grooves to avoid at pressure areas as oil tend to escape high to low pressure zones
\n\udbc0\udcd6 Circumferential grooves to compensate with increase length of the shell
\n\udbc0\udcd6 Longitudinal groove is not extended to ends to avoid excessive side leakage.<\/p>\n
\n\udbc0\udcd6 Circumferential groove most effective and satisfactory
\n\udbc0\udcd6 Oil supply at all angle and wide variation of load angle.<\/p>\n
\n\u2666\u00a0Conventional bearing<\/strong>
\n(a1) It is made of forged steel and running face is lined with white metal.
\n(a2) Vertical clearance is adjusted by shims.
\n(a3) Not easy to replace and must be done remodeling.
\n(a4) Not easy to handle, transport and store.
\n(a5) Suitable oil grooves design is required.
\n(a6) Lower load carrying capacity.
\n(a7) More cost in manufacturing.<\/p>\n
\n(b1) It is made of tri-metal, they are steel shell, copper or lead alloy and thin layer of soft metal surface.
\n(b2) Easy replacement incase of bearing worn out. ( Re-metalling method no longer required)
\n(b3) No need to adjust by shim ( can not be adjusted by shims.)
\n(b4) Easy handling, transport and storage as spare.
\n(b5) Higher bearing load carrying capacity.
\n(b6) More economy in manufacturing.
\n(b7) No need to take lead reading.<\/p>\n
\n\u2666 Defective tag
\n\u2666 Insufficient nip clearance
\n\u2666 Suddenly applied extreme load.( pounding)
\n\u2666 Improper fitting
\n\u2666 Incorrect size of bearing use
\n\u2666 Due to over tightening bolts
\n\u2666 Frictional force from the back of the shell and keep.<\/p>\n
\n\udbc0\udc90 Thin shell bearings are used and bearing on either end of crosshead pin.
\n\udbc0\udc90 No shim used with thin shell bearing
\n\udbc0\udc90 Oil grooves or gutter used on bottom half to distribute oil.
\n\udbc0\udc90 Grooves do not extend to end and grooves are small because of loaded half.
\n\udbc0\udc90 Grooves to be limited otherwise reduce bearing surface.
\n\udbc0\udc90 Lubricating oil is directly supplied to crosshead bearing
\n\udbc0\udc90 Bearing material usually Sn-Al with Pb-Sn overlay.<\/p>\n
\n\udbc0\udcd6 High sudden load \u2013 Effect of combustion is directly on bearing
\n\udbc0\udcd6 High bearing pressure \u2013 Bearing is placed high in engine. – Space limitations. \u2013 Assembly reciprocating.
\n\udbc0\udcd6 Diameter & length \u2013 Diameter & length of bearing are low. \u2013 Bearing area limitations. \u2013High specific loading
\n\udbc0\udcd6 Possibility of bearing distortion \u2013 Bending moment & deflection are maximum at center. Pin bored at center (earlier model engines). Less stiffness & high stress concentration. \u2013 Bearing surface deflection. \u2013 Alignment difficulty.
\n\udbc0\udcd6 Lubrication \u2013 Unsatisfactory or difficult oscillating moment. \u2013 Con rod swings over 25\u00b0 -30\u00b0.
\n\udbc0\udcd6 Oil supply disturbed \u2013 Difficult smooth & uninterrupted oil flow.
\n\udbc0\udcd6 2 stroke engine \u2013 Unidirectional load.<\/p>\n
\n\udbc0\udcd6 Conjugate Deflection \u2013 Sulzer Engines (crosshead pin bored at center)
\n\udbc0\udcd6 Crosshead mounted mechanical lub oil pump \u2013 MAN Engines (oil supplied when load is lowest & oil film is not broken at highest pressure)
\n\udbc0\udcd6 Continuous full length bottoms half of crosshead bearing \u2013 MAN B & W, Sulzer Engines.
\n\udbc0\udcd6 Eccentric bored bearing & machining shell \u2013 Fiat Engines
\n\udbc0\udcd6 Large diameter stiff crosshead pins L\/D ratio less (small con rod and crank throw ratio. Sliding velocity high & lub oil film improved)
\n\udbc0\udcd6 Hardened cross head pin high degree of surface finish < 0.1\u03bc
\n\udbc0\udcd6 Thin shell bearing & improved material.<\/p>\n
\n\u2666<\/strong>\u00a0Bearing shells are in place by interference fit
\n\u2666\u00a0There is no relative movement of housing & shell
\n\u2666\u00a0Effective heat transfer between shell & housing is essential
\n\u2666\u00a0Cap holding bolts are to be closely pitched to prevent distortion
\n\u2666\u00a0Housing is robust to prevent excessive strains on shell.
\n\u2666\u00a0Housing is not too stiff to prevent localized load concentration on bearing.<\/p>\n
\n\udbc0\udc90 Medium & High speed engine’s Con Rod bottom end bearing housing tendency to distort.<\/p>\n
\n\udbc0\udcd6 Load is always on down wards & construction is light
\n\udbc0\udcd6 Load rotates but bearing cap is rigid
\n\udbc0\udcd6 Bolts centers are kept close together.
\n\udbc0\udcd6 Two halves of bearing housing is kept concentric by fitted bolts, stepped cap & serrate cap<\/p>\n
\n\udbc0\udcd6 Adequate tensile strength
\n\udbc0\udcd6 High resilience, capacity to absorb maximum strain before yielding
\n\udbc0\udcd6 Reducing diameter to bottom of thread over the length of the bolt reduces localized stress except at fitted.<\/p>\n
\nBearing should be inspected at the overhaul \/ survey for the following defects<\/p>\n
\n1) Abrasive damage: Fine scratches caused by particles in the lub oil. Very common on HFO burning engines
\n2) Erosion damage: Removal of the overlay in strips caused when the oil supply pressure is low or rapid journal movements occur. More usual on medium speed engines.
\n3) Fatigue damage: The overlay becomes detached from the lining when the bearing load becomes too high. The bearing surface loads cracked paving.
\n4) Corrosion: Discoloration and roughening of the bearing surface indicate4s that the oil has become acidic.
\n5) Wiping: This is overlay removal by melting Wiping can be re-alignment of the bearing to journal, but if too much metal has been removed then clear4aqnces may be affected.<\/p>\n
\n1) Cracks: These will appear at the high stress points of the fillet radii and oil holes. These cracks may be removed by light grinding, but engine derating would be required if deep \/ numerous cracks are found.
\n2) Scoring: Similar problem to the abrasive bearing
\n3) Overheating: As the bearing is weaker than the shaft, the bearing should fail first. However if the engine is run on a failed bearing then shaft overheating will occur. This ‘bluing’ of the shaft increases the hardness of shaft and hence the shaft is less able to resist crack growth. Classification states a maximum hardness for crankshaft journal.<\/p>\n
\n1) Edge wear
\n2) Score & scratch (striation wear)
\n3) Overheating surface (blur\/violent colour show heating cracks)
\n4) Cavitations & erosion (10% bearing surface)
\n5) Corrosion
\n6) Crack in galvanic layer
\n7) Pitting & fretting<\/p>\n
\n\u2666<\/strong> Desired operating temperature \u2013 extremely critical \u2666<\/strong> Engine speed
\n\u2666<\/strong> Oil flow \u221d (clearance) 3 \u2666<\/strong> Oil film thickness
\n\u2666<\/strong> Working viscosity of lubricant \u2666<\/strong> Load carrying capacity
\n\u2666<\/strong> Operating temperature \u2666<\/strong> Engine ambient temperature.<\/p>\n
\nIt is important that regular checking of bearing clearance is carried out, as the clearance determines the effectiveness of lubrication.
\n\udbc0\udc31 Lead wire > Traditional method, but requires that bearing are tightened just to obtain clearance. Accurate as long as load is not over squeezed. Lead is not to squeeze blow 1\/3rd of original diameter.
\n\udbc0\udc29 Turn the crank shaft and set the crank at TDC position.
\n\udbc0\udc29 Remove locking arrangements, mark the nut position.
\n\udbc0\udc29 Slacken the nut and lower the bottom half with bolts.
\n\udbc0\udc29 Then three lengths of lead wires would be laid circumferentially in the bottom half at three places.
\n\udbc0\udc29 Place the bottom half into position and tighten the nut to its tightening torque.
\n\udbc0\udc29 Lower down the bottom half again.
\n\udbc0\udc29 Remove the lead wires and take the measurement.
\n\udbc0\udc29 It must have within the limit, if out of limit, the bearing shell must be replaced with new ones or readjust the clearance by adjusting shims.
\n\udbc0\udc31 Feeler gauge > Quick method, but more difficult to be accurate when using the long feelers as measuring point may not be the minimum point.
\n\udbc0\udc29 Turn the crank shaft and set the crank at BDC.
\n\udbc0\udc29 Insert the feeler gauge between lower half and crank pin.
\n\udbc0\udc29 Take the measurement readings.
\n\udbc0\udc31 Plastigauge > Relies on the width of a plastic strip after compression. More accurate than leads.
\n\udbc0\udc31 Bridge gauge > Depends on bedplate condition and crankshaft rigidity
\nBridge gauge is an instrument for main bearing wears down measuring.
\n\udbc0\udc29 Remove the lube oil supply pipe.
\n\udbc0\udc29 Remove upper bearing half and fit the bridge gauge.
\n\udbc0\udc29 Then take the measurement by inserting feeler gauge.
\n\udbc0\udc31 Micrometer > More accurate<\/p>\n
\n\udbc0\udc40 Low LO pressure
\n\udbc0\udc40 Reduce load carrying capacity
\n\udbc0\udc40 Pounding will case and bearing will damage.
\n\udbc0\udc40 High impact load on crankshaft.<\/p>\n
\n\udbc0\udc99 The cross head bearings consists of steel shells with 1.0 to 1.5 \u03bcmm of white metal (WM) having a 25 \u03bcm lead based overlay for running in.
\n\udbc0\udc99 Complete inspection may be carried out on a time basis i.e. after 8000 operating hours, for a 4 years survey of following inspection carried out without opening up.<\/p>\n
\n\udbc0\udc31 Just after stopping feel over bearing, check that uniform oil jets appear form all the oil outlet grooves in the lower shell.
\n\udbc0\udc31 Check clearance (on top) with feeler gauge and compare with records.’
\n\udbc0\udc31 Visually inspect sides of bearing for signs of white metal squeezed \/ missing
\n\udbc0\udc31 Dismantle & inspect if oil jets are oblique \/ twisted \/ reduced \/ missing \/ if white metal gives cause for concern or if clearances have increased.<\/p>\n
\n\udbc0\udc31 Crosshead opened up, condition of white metal and journal surfaces noted and entered in engine room log. White metal should be checked for wear \/ wiping \/ cracking \/ discoloration due to corrosion \/ bonding defects.
\n\udbc0\udc31 It is quite normal for the overlay to be disturbed at the most highly loaded areas.
\n\udbc0\udc31 Overlay or WH squeezed into the oil wedges and oil grooves or small spots, which have loosened, can be removed with a scraper.
\n\udbc0\udc31 If wiping is less than hand size scrape to blue marking cracks formation which will eventually cause WM to become loosened and dislodged may be due to lack of bonding strength or geometric irregularities causing local overloading.
\n\udbc0\udc31 Areas of small local crack formation discovered at an early stage should be relieved by scraping.
\n\udbc0\udc31 The back side of the shell should be inspected for even contact fretting or cavitation.
\n\udbc0\udc31 Journals to be inspected for roughness and ovality; slight ovality is acceptable.
\n\udbc0\udc31 Change journal if _<\/p>\n
\n\u2666<\/strong> More than 1\/3 of the contact area is scratched.
\n\u2666<\/strong> Roughness has caused a large area of the WM to be wiped
\n\u2666<\/strong> Manual polishing with hemp rope will not then be satisfactory.<\/p>\n
\n\udbc0\udc31 Surface roughness \udbc0\udc4a New 0.05 \u03bcm, \udbc0\udc4a Run in 0.1 \u03bcm, \udbc0\udc4a Trouble possible 0.125 \u03bcm.
\n\udbc0\udc31 Roughness will most likely be due to abrasive or corrosive (acid or SW) contamination of the lube oil.
\n\udbc0\udc31 Note that 1% SW contamination of the lub oil can promote galvanic attack of the WM formation of very hard black tin oxide (Sno) which will roughen journal surfaces.<\/p>\n
\n\u2666<\/strong> Check bearing thoroughly.
\n\u2666<\/strong> Check X head pin ovality.
\n\u2666<\/strong> Check bearing clearance.
\n\u2666<\/strong> Lubrication system and oil holes.
\n\u2666<\/strong> Check Guide shoe wear down.<\/p>\n
\nVarious types of failure occur in cross head bearing lining. If it is found early, can be rectified and continue in service. Failure of the white metal in less- severe forms usually progress so that the bearing must be remetalled.
\n\udbc0\udcd6 Cracking of white metal
\n\udbc0\udcd6 Fatigue failure of white metal
\n\udbc0\udcd6 Squeezing of white metal so that oil grooves are partially blocked; oil holes may be partially blocked or wholly blocked in extreme cases.
\n\udbc0\udcd6 Failure of white metal when the bearing surface of the white metal becomes plastic or even melts.
\n\udbc0\udcd6 Corrosion depends on the nature of the contamination of the lubricating oil.<\/p>\n
\nBearing failures may result from any one or combination of the following causes.
\n\udbc0\udcd6 Deterioration of surface finish or cross head pins.
\n\udbc0\udcd6 Poor quality of white metal
\n\udbc0\udcd6 Insufficient supply of lubricant
\n\udbc0\udcd6 Impure lubricant or water contamination
\n\udbc0\udcd6 Excessive firing pressure in cylinder<\/p>\n
\na. Check locking device and nuts tightness.
\nb. Check for wiped out of loose white metal at bearing end.
\nc. Check bearing clearance ( roughly ) by tongue gauge.<\/p>\n
\na. Check pin or key or tag.
\nb. Check holding down bearing surface.
\nc. Check white metal bearing surface (crack and damage)
\nd. If over 30 % of wear or crack in the contact area it should be renewed.
\ne. Check oil grooves and passage holes.
\nf. Check pin diameter & pin ovality<\/p>\n
\n\u2666<\/strong> Check bearing thoroughly ( tag, oil grooves and holes, bearing surface)
\n\u2666<\/strong> Journal ovality-take measurement at least 3 spaces.
\n\u2666<\/strong> Checking bearing clearance-0.4 to 0.6 mm for 550mm shaft diameter.<\/p>\n
\n\u2666<\/strong> After cleaning, inspect the bearing thoroughly at crank pin ovility two halves of bearing together with oil holes and grooves.
\n\u2666<\/strong> Thoroughly, examined the bolts ( no cracks, no extension and no twisting )
\n\u2666<\/strong> Check sign of movement of the joint point such as two halve of bearing joint and between top halve and connecting rod foot.
\n\u2666<\/strong> Bearing clearance.<\/p>\n
\n\u2666<\/strong> Check upper half bearing & bearing keep
\n\u2666<\/strong> Check the bearing wear down by using bridge gauge & feeler gauge ovality of journal pin
\n\u2666<\/strong> Check crack pin condition, oil holes
\n\u2666<\/strong> Check upper bearing clearance by lead wire method
\n\u2666<\/strong> Visual check to edge of lower bearing half, bearing pocket<\/p>\n
\n\u2666<\/strong> Check pin ovality & oil holes
\n\u2666<\/strong> Check two bearing halves with oil holes and grooves (tag, crack, wear,)
\n\u2666<\/strong> Check the bolt (crack & stretching)
\n\u2666<\/strong> Check the movement at the joining point such as two halves of bearing joint and between the top half and connecting rod foot<\/p>\n
\n1. Visual inspection of any wiping & squeezing
\n2. Check axial play
\n3. Check of local temperature after test run<\/p>\n
\n1. Fit into housing and check the contact area after thorough cleaning
\n2. After clean, check bearing running surface (any crack, grooves, tap)
\n3. After renew test run for 30 minute and again, after 5 hours operation, manual checking bearing temperature.<\/p>\n
\n\udbc0\udc31 Bearing thickness, length, crack, surface smoothness, edge, oil hole, groove, tap
\n\udbc0\udc31 Casing & keep surface
\n\udbc0\udc31 Pin ovality,<\/p>\n
\n1. Shell with galvanic layer worn down over 30% of developed working surface to be replaced (X head 5% )
\n2. Running hour excess of 40, 000 to be replaced in any case (O\/H or not)
\n3. Running hour excess of 30, 000 to be replaced when engine overhaul<\/p>\n
\n(1) Remove LO pipe connection from keep a bore has in the keep
\n(2) Hole also be provided in upper bearing half
\n(3) Clean holes & insert the depth gauge & take reading
\nThe different of present reading & previous reading give lower bearing wear down<\/p>\n
\nTypes of bearing defects ?
\n\u2666<\/strong> Crack
\n\u2666<\/strong> Fatigue failure of white metal
\n\u2666<\/strong> Squeezing of white metal, so oil grooves are partially blocked.
\n\u2666<\/strong> wiping
\n\u2666<\/strong> Faulty casting and faulty machining.
\n\u2666<\/strong> Tin oxide Corrosion
\n\u2666<\/strong> Acid Corrosion
\n\u2666<\/strong> Thermal Ratcheting
\n\u2666<\/strong> Electrical Potential
\n\u2666<\/strong> Fretting
\n\u2666<\/strong> Cavitation Erosion<\/p>\n
\n\udbc0\udc40 Wiping is a slight transient phenomenon & is undetected until the machinery is opened up for survey.
\n\udbc0\udc40 In serious cases, complete bearing failure occurs due to over heating of bearing metal which occur owing to –
\n\udbc0\udc96 Temporary lack of oil ` \udbc0\udc96 Very slow start up of engine
\n\udbc0\udc96 Too small bearing clearance \udbc0\udc96 Misalignment of pin and bearing
\n\udbc0\udc96 Fabricated cross girder of bedplate \udbc0\udc96 Tin oxide corrosion<\/p>\n
\n\udbc0\udcd6 Surface to be machined at least by 0.025 mm to prevent bearing damage.
\n\udbc0\udcd6 Stainless steel shafts & white metal bearing surface \u2013 wiping, pick up & seizure
\n\udbc0\udcd6 Failures \u2013 Due to lack of compatibility and the problem is worst at high specific load.
\n\udbc0\udcd6 Ni or Cr Plating: on journals \/ pins must be voided which results in scuffing seizure.<\/p>\n
\n\udbc0\udcd6 In dynamic loaded bearings \/ pivoted pad bearing i.e. thrust pads of thrust bearing
\n\udbc0\udcd6 Fretting occurs on the back of support surface where the interference fit \/ nip is insufficient for dynamic forces involved.
\n\udbc0\udcd6 Caused by the housing, which is insufficiently rigid for the load cycle involved.
\nFatigue
\n\udbc0\udcd6 Bearings carrying high dynamic loads are liable to fatigue damage
\n\udbc0\udcd6 Caused by a concentration of load due to mechanical imperfection i.e. poor geometric form, misalignment and distortion.
\n\udbc0\udcd6 White metal bearings are particularly prone to fatigue since any high loading not only increases the stress in the lining, but the associated temperature rise reduces the strength.<\/p>\n
\nTin Oxide Corrosion<\/strong>
\n\udbc0\udcd6 Tin oxide is extremely hard & brittle and corrosion takes place at tin phase of white metal
\n\udbc0\udcd6 This breaks off rapidly, causing wear of the surfaces & breakdown of oil film
\n\udbc0\udcd6 Appearance \u2013 Grey at initial stage, becomes darker as its thickness increases & particle become detached.
\n\udbc0\udcd6 With high loads when the oxide layer becomes thick, the bearing temperature may rise sufficiently to melt the underlying metal & failure occurs by wiping.
\n\udbc0\udcd6 Cause – Water mixes with LO promoting electro chemical reaction.
\n\udbc0\udcd6 Prevention \u2013 Regular & continuous removal of water from lubricating oil prevent tin oxide formation.<\/p>\n
\n\udbc0\udcd6 Takes place in high temperature condition
\n\udbc0\udcd6 Bearing alloy is attacked by acid (condensation of SO2) form high ‘S’ content fuel.
\n\udbc0\udcd6 Steel working parts corrode more than bearing alloy
\n\udbc0\udcd6 Solution \u2013 Add rust & corrosion inhibitor in lub oil and select proper material.<\/p>\n
\n\udbc0\udcd6 Caused by alternate cooling & heating of bearing
\n\udbc0\udcd6 Results in bearing deformation
\n\udbc0\udcd6 Indication of high bearing temperature
\n\udbc0\udcd6 Place mainly in thrust pad bearing surface<\/p>\n
\n\udbc0\udcd6 This type of damage occurs frequently in electrical machinery due to stray currents.
\n\udbc0\udcd6 The damage consists of uniformly distributed pitting, the pits being generally hemispherical with the intensity increasing to a maximum in the zone of thinnest oil film.
\n\udbc0\udcd6 Caused by incorrect earthlings system which cause spark erosion damage.
\n\udbc0\udcd6 Prevention \u2013 Insulate the non-drying end bearing (pedestal bearing) of electrical machines and sometimes in both bearings.<\/p>\n
\n\udbc0\udcd6 Severe damage to complete bearing area.
\n\udbc0\udcd6 Cavities are usually around at low pressure areas i.e. oil groove or oil holes.
\n\udbc0\udcd6 Caused by an implosion of gas or air bubbles released from a lubricating oil film under particular conditions
\n\udbc0\udcd6 The pressure set up locally during theses implosions are very high , possibly 220 bar & may cause a pitting \/ cavitation
\n\udbc0\udcd6 Prevention \u2013 May be reduced by viscous oil because of damping effect high viscous oil & viscosity must be in limit.<\/p>\n
\nCause of faulty casting and machining is due to premature failure even under normal running conditions.
\nCauses of bearing overheat<\/p>\n
\n\udbc0\udc40 Insufficient lubrication
\n\udbc0\udc40 Improper oil clearance
\n\udbc0\udc40 Foreign matters in oil
\n\udbc0\udc40 Misalignment of shaft and bearing
\n\udbc0\udc40 Scored journal
\n\udbc0\udc40 Poorly fitted bearing<\/p>\n
\n1. Over stressed on bolts (due to piston seizure, over tightening, propeller strike some obstruction)
\n2. Too long in service (renew after 10 years)
\n3. Wear of bolts & enlarge of holes can cause the easing of nuts.
\n4. Too much clearance of bearings, shock resulting fatigue in bolts<\/p>\n
\nOverheating of plumber block bearing can be reduce by following ways<\/strong>
\n\udbc0\udc44 By applying maximum lubrication
\n\udbc0\udc44 By applying maximum cooling
\n\udbc0\udc44 By reducing to suitable engine speed.
\n\udbc0\udc44 By applying the air
\n\udbc0\udc3b By removing the cooling outlet pipe
\n\udbc0\udc3b By filling the L.O into the sump at the same time open the drain valve and drain out the hot oil
\n\udbc0\udc3b By reducing the engine speed to the suitable speed.<\/p>\n
\n\udbc0\udc3b Check L.O level and L.O temperature
\n\udbc0\udc3b Cooling water outlet temperature
\n\udbc0\udc3b Noise and vibration
\n\udbc0\udc3b Overheating of casing by hand touch feeling<\/p>\n
\nMeasure bearing clearance.
\nTurn crank shaft to efficient position.
\nRemove lube oil pipe, locking arrangement and nuts.
\nTook out bearing keep with thrust nut by means of wire sling and chain block or special tool. Took out upper bearing shell.
\nTook out lower bearing shell.
\n1. By fitting lower bearing taking out tool fitted at oil hole at crankshaft or adjacent crank web and turn the crank shaft (the direction is according to the maker instruction, usually opposite to the ahead running direction.)
\n2. By use of hydraulic jack to lift the crankshaft just clear, about 0.1 to 0.3mm and turn the bearing shell without rotating the crank shaft.
\nEye bolt fitted to the back of the shell and lift it out of the engine.<\/p>\n
\n1) Measure bearing clearance.
\n2) Turn TDC position.
\n3) Remove locking arrangement and slackened the nuts. The bottom half lower a few and took out bearing clearance adjusting shim, each set being tied separately and note taken of the side to which each set belongs.
\n4) Chain blocks connected to eye bolts, screw into each bolt. After removing two nuts, bottom half lowered into the sump. If necessary it can be taken out from crankcase.
\n5) Putting hanging bar in position, connect chain blocks to crankcase door frame and eye bolts which is screwed into each side of the top half. Then turn the crankshaft to the position where the top half can be taken out.
\n6) Inspection on crank pin, bearings, oil holes, grooves, bolts cracks, sign of movement and elongation<\/p>\n","protected":false},"excerpt":{"rendered":"