bs3 tjedan04 crankshaft and main bearings part 1

8/11/2019 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


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


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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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 ...



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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.



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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?


Questions & Discussion

bs3 tjedan04 crankshaft and main bearings part 1

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