Engine Diagnosis and Service: Block, Crankshaft, Bearings, and Lubrication System
BS3 Tjedan04 Crankshaft and Main Bearings Part 1
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Transcript of BS3 Tjedan04 Crankshaft and Main Bearings Part 1
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Essential reading:SPINI, A., PRITCHARD, B.,An English Textbook For
Marine Engineers 2, Pomorski fakultet, Rijeka 2009.LUZER, J., SPINI, A., Gramatika vjebenica engleskog
jezika za pomorce, Pomorski fakultet, Rijeka 2003.
Tomislav Skrai, MA
Undergraduate English
Course for
MARINE ENGINEERS
3rd Semester
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Lesson 2
Crankshaft, Main Bearings and Shaft Alignment
KEY WORDS
crankshaft (n.) - koljenasto vratilo / osovina, radilica
main bearing - glavni / temeljni leajshaft alignment - centriranje osovine
reciprocating motion - stapno gibanjeat a top center - u gornjoj mrtvoj tokibending stress - naprezanje zbog savijanja
connecting rod thrust - potisak ojnice
crankpin (n.) - oslonac koljena, osovina leteeg leajaadjacent bearing - pokrajnji leaj, "odrivni" leaj, "thrust" bearingtorsional forces - torzijske / zaokretne sile
semi-built design - izraen od vie dijelovacrank web (n.) - 'pruti' za uravnoteenjeforge (v.) - kovati
solid-forged - izraen u jednom dijelu
cast (v.) - lijevati
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Lesson 2
Crankshaft, Main Bearings and Shaft Alignment
KEY WORDS
shrink on to (v.) - navui u toplom stanjucrank journal - oslonac temeljnog leaja
journal (n.) - blazinica, leajna aa (materijal koji se troi)journal bearing - letei leaj
carbon steel - ugljini elik (FeC)alloy steel - legura elikanickel - nikal chromium - krom molybdenum - molibden (Mo)
crank (n.) - koljeno vratila
multi-throw shaft - osovina s vie koljena,
viecilindarska koljenasta osovinafiring order - redoslijed paljenja
torque (n.) - zakretni moment
torque wrench - moment-kljuload (n.) - optereenje
exhaust arrangement - ispuni sustav / raspored ispuha
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Lesson 2
Crankshaft, Main Bearings and Shaft Alignment
KEY WORDS
misalignment (n.) - loe centriranje, nepoklapanje osibearing shell - blaznica temeljnog leaja / kouljica leajalining (n.) - obloga, sloj
copper-lead - bakar-olovo
aluminium-tin alloy - legura aluminija i kositraflash (n.) - sloj obloge
lead (n.) - olovo indium - indij
seating (n.) - sjedite, postoljetransverse sadles - popreni nosai
thrust bolts - vijci temeljnog leaja preoptereeni na tlakshim (n.) - podlona ploicabearing play - zranost leajapressure lubricated - tlano podmazivanetie rod - kotveni vijak
tensioned - stegnut
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Crankshaft, Main Bearings and Shaft Alignment
DEFINITION OF A CRANKSHAFTThe crankshaft converts reciprocating motionin the
cylinder into rotary motionof the propeller shaft.
PARTSThe crankshaft is made up of throws and journals. A throwconsists a pin(secured or attached to big / bottom end
bearings) and two websor cranks. Journalsrest or lie in
the main bearings.
STRESSES (fluctuating)Bending(when the piston is at TDC);
Sheer stress(in operation);
Torsion(due to speed change)
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Crankshaft
MANUFACTURING
Solid forgedbuilt in a single piece (small-slow speed
engines)
Semi-builtdesign (large medium-speed engines).
Crankpins & webs are forged or cast in one pieceand
shrunk on to thejournals.
Fully-built(cast in single piecewebsare shrunk on
to the crankpinsandjournals).
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Crankshaft
MATERIALS
Carbon steelAlloy of nickel, chromium & molibdenumSpecialy alloyed grey cast steel
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The crankshaft, which converts thereciprocating motionof the piston to rotatingmotion, must resist the bending stresses
caused by the connecting rod thrust when thepiston is at the top dead centre.
Then the maximum gas pressure acts straightdown on the crankpin and tends to bend theshaft between the adjacent bearings. Thecrankshaft must also withstand the torsionalforcesproduced by the change of speed.
Exercise 1 - Read the following text:
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The crankshaft converts ... ... to .... ....
It must resist the bending stresses caused by
the connecting rod thrust when ... ... .
Then the maximum gas pressure acts straight
down on the crankpin and tends to ... ....
The crankshaft must also withstand the ... ....
Exercise 1Complete the sentences:
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Medium speed engines have crankshaft usuallysolid forged, i.e. made from a single piece, whileslow speed engine crankshafts are mostly ofsemi-built designwith crankpins and websforged or cast in one piece and shrunk on to the
journals. The type of steel used, which is carbonor alloy steel containing nickel, chromium andmolybdenum, is chosen for its strength,
resistance to fatigue and hardness of bearingsurface.
Exercise 2Read the text:
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Medium speed engines have crankshaft usually
solid forged, i.e. made ... ...
Slow speed engine crankshafts are mostly of
semi-built designwith ... ... They are ... or ... in one piece and ... on to the
journals.
The type of steel used for crakshafts is ... ... It contains nickel, ... and must be resistant to ...
Exercise 2Complete the sentences:
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The cranks of a multi-throw shaftare set atappropriate angles giving a firing orderforthe engine. The firing order is chosen primarily
to obtain a smooth torqueand the bestmechanical balance. However, main bearingsloads, exhaust arrangements suitable forturbocharging and torsional vibration may also
be taken into account. Although the crankshaftappears to be robust, they rely on the mainbearingsto develop their full strength.
Exercise 3Read the text:
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cranks of a multi-throw shaft are set at appropriateangles giving ... ...
The firing order is chosen primarily to obtain ... ...
and ... ...
However, we must also take ito account:
... loads,
exhaust arrangements suitable for ... and
... ...
Crankshaft rely on the ... ... to develop their full
strength.
Exercise 3Complete the sentences:
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1. State the function of the crankshaft.
2. What forces is a crankshaft subjected to?
3. What kind of crankshafts are used in: a) Mediumspeed diesel
4. Slow speed diesel
5. 4. What does the choice of steel type for crankshaftdepend on?
6. What is the firing order?
7. What else is taken into consideration in designing acrankshaft?
Crankshaft, Main Bearings and Shaft Alignment
Questions & Discussion