Tomislav Skračić, MA Undergraduate English Course for MARI NE ENGINEERS 3rd Semester

Essential reading:Essential reading:SPINČIĆ, A., PRITCHARD, B.,SPINČIĆ, A., PRITCHARD, B., An English Textbook For An English Textbook For

Marine Engineers 2Marine Engineers 2, Pomorski fakultet, Rijeka 2009., Pomorski fakultet, Rijeka 2009.LUZER, J., SPINČIĆ, A., LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog Gramatička vježbenica engleskog

jezika za pomorcejezika za pomorce, Pomorski fakultet, Rijeka 2003., Pomorski fakultet, Rijeka 2003.

Tomislav Skračić, MATomislav Skračić, MA

Undergraduate English Undergraduate English Course forCourse for

MARIMARINE ENGINEERSNE ENGINEERS3rd Semester3rd Semester

Lesson 2Lesson 2Crankshaft, Main Bearings and Shaft AlignmentCrankshaft, Main Bearings and Shaft Alignment

KEY WORDS

crankshaft (n.) - koljenasto vratilo / osovina, radilicamain bearing - glavni / temeljni ležajshaft alignment - centriranje osovinereciprocating motion - stapno gibanjeat a top center - u gornjoj mrtvoj točkibending stress - naprezanje zbog savijanjaconnecting rod thrust - potisak ojnicecrankpin (n.) - oslonac koljena, osovina letećeg ležajaadjacent bearing - pokrajnji ležaj, "odrivni" ležaj, "thrust" bearingtorsional forces - torzijske / zaokretne silesemi-built design - izrađen od više dijelovacrank web (n.) - 'pršuti' za uravnoteženjeforge (v.) - kovatisolid-forged - izrađen u jednom dijelucast (v.) - lijevati

Lesson 2Lesson 2Crankshaft, Main Bearings and Shaft AlignmentCrankshaft, Main Bearings and Shaft AlignmentKEY WORDS

shrink on to (v.) - navući u toplom stanjucrank journal - oslonac temeljnog ležajajournal (n.) - blazinica, ležajna čaša (materijal koji se troši)journal bearing - leteći ležajcarbon steel - ugljični čelik (FeC)alloy steel - legura čelikanickel - nikal chromium - krom molybdenum - molibden (Mo)crank (n.) - koljeno vratilamulti-throw shaft - osovina s više koljena,

višecilindarska koljenasta osovinafiring order - redoslijed paljenjatorque (n.) - zakretni momenttorque wrench - moment-ključload (n.) - opterećenjeexhaust arrangement - ispušni sustav / raspored ispuha

Lesson 2Lesson 2Crankshaft, Main Bearings and Shaft AlignmentCrankshaft, Main Bearings and Shaft AlignmentKEY WORDS

misalignment (n.) - loše centriranje, nepoklapanje osibearing shell - blaznica temeljnog ležaja / košuljica ležajalining (n.) - obloga, slojcopper-lead - bakar-olovoaluminium-tin alloy - legura aluminija i kositraflash (n.) - sloj obloge

lead (n.) - olovo indium - indijseating (n.) - sjedište, postoljetransverse sadles - poprečni nosačithrust bolts - vijci temeljnog ležaja preopterečeni na tlakshim (n.) - podložna pločicabearing play - zračnost ležajapressure lubricated - tlačno podmazivanetie rod - kotveni vijaktensioned - stegnut

Crankshaft, Main Bearings and Shaft AlignmentCrankshaft, Main Bearings and Shaft Alignment

DEFINITION OF A CRANKSHAFTThe crankshaft converts reciprocating motion in the cylinder into rotary motion of the propeller shaft.

PARTSThe crankshaft is made up of throws and journals. A throw consists a pin (secured or attached to big / bottom end bearings) and two webs or cranks. Journals rest or lie in the main bearings.

STRESSES (fluctuating)Bending (when the piston is at TDC);Sheer stress (in operation);Torsion (due to speed change)

CrankshaftCrankshaft

MANUFACTURING Solid forged built in a single piece (small-slow speed engines) Semi-built design (large medium-speed engines). Crankpins & webs are forged or cast in one piece and shrunk on to the journals. Fully-built (cast in single piece – webs are shrunk on to the crankpins and journals).

CrankshaftCrankshaft

MATERIALS

• Carbon steel• Alloy of nickel, chromium & molibdenum• Specialy alloyed grey cast steel

The crankshaft, which converts the The crankshaft, which converts the reciprocating motionreciprocating motion of the piston to of the piston to rotating rotating motionmotion, must resist the , must resist the bending stressesbending stresses caused by the connecting rod thrust when the caused by the connecting rod thrust when the piston is piston is at at the the top top dead dead centrecentre..Then the maximum gas pressure acts straight Then the maximum gas pressure acts straight down on the crankpin and tends to bend the down on the crankpin and tends to bend the shaft between the adjacent bearings. The shaft between the adjacent bearings. The crankshaft must also crankshaft must also withstand the torsional withstand the torsional forcesforces produced by the produced by the change of speedchange of speed. .

Exercise 1 - Read the following text: Exercise 1 - Read the following text:

The crankshaftThe crankshaft convertsconverts ... ... ... ... to to .... .... .... .... It It must resist the bending stresses caused by must resist the bending stresses caused by

the connecting rod thrust when the connecting rod thrust when ... ... .... ... . Then the maximum gas pressure acts straight Then the maximum gas pressure acts straight

down on the crankpin and tends to down on the crankpin and tends to ... ...... .... . The crankshaft must also withstand the The crankshaft must also withstand the ... ...... .... .

Exercise 1 – Complete the sentences: Exercise 1 – Complete the sentences:

Medium speed engines have crankshaft usually Medium speed engines have crankshaft usually solid forgedsolid forged, i.e. made from a single piece, while , i.e. made from a single piece, while slow speed engine crankshafts are mostly of slow speed engine crankshafts are mostly of semi-built designsemi-built design with crankpins and webs with crankpins and webs forged or cast in one piece and forged or cast in one piece and shrunk on to the shrunk on to the journalsjournals. The type of steel used, which is carbon . The type of steel used, which is carbon or alloy steel containing nickel, chromium and or alloy steel containing nickel, chromium and molybdenum, is chosen for its strength, molybdenum, is chosen for its strength, resistance to fatigue and hardness of bearing resistance to fatigue and hardness of bearing surface. surface.

Exercise 2 – Read the text: Exercise 2 – Read the text:

Medium speed engines have crankshaft usually Medium speed engines have crankshaft usually solid forged, i.e. made solid forged, i.e. made ... ...... ...

SSlow speed engine crankshafts are mostly of low speed engine crankshafts are mostly of semi-built designsemi-built design with with ... ... ... ...

They are ... They are ... or or ...... in one piece and in one piece and ... ... on to the on to the journals. journals.

The type of steel usedThe type of steel used for crakshafts is ... ... for crakshafts is ... ... It It containcontains s nickel, nickel, ... ... and and must be must be resistan resistant t toto ... ...

Exercise 2 – Complete the sentences: Exercise 2 – Complete the sentences:

The cranks of a The cranks of a multi-throw shaftmulti-throw shaft are set at are set at appropriate angles giving appropriate angles giving a “firing order”a “firing order” for for the engine. The firing order is chosen primarily the engine. The firing order is chosen primarily to obtain a to obtain a smooth torquesmooth torque and the best and the best mechanical balancemechanical balance. However, main bearings . However, main bearings loads, exhaust arrangements suitable for loads, exhaust arrangements suitable for turbocharging and torsional vibration may also turbocharging and torsional vibration may also be taken into account. Although the crankshaft be taken into account. Although the crankshaft appears to be robust, they appears to be robust, they rely on the main rely on the main bearingsbearings to develop their full strength. to develop their full strength.

Exercise 3 – Read the text:Exercise 3 – Read the text:

cranks of a multi-throw shaft are set at appropriate cranks of a multi-throw shaft are set at appropriate angles giving angles giving ... ...... ...

The firing order is chosen primarily to obtainThe firing order is chosen primarily to obtain ... ... ... ... and ... ...and ... ...

However, However, we must also take ito account:we must also take ito account: ... ... loads, loads, exhaust arrangements suitable for exhaust arrangements suitable for ... ... and and ... ... ... ...

Crankshaft rely on the Crankshaft rely on the ... ... to ... ... to develop their full develop their full strength. strength.

Exercise 3 – Complete the sentences:Exercise 3 – Complete the sentences:

1.1. State the function of the crankshaft.State the function of the crankshaft.2.2. What forces is a crankshaft subjected to?What forces is a crankshaft subjected to?3.3. What kind of crankshafts are used in: a) Medium What kind of crankshafts are used in: a) Medium

speed dieselspeed diesel4.4. Slow speed dieselSlow speed diesel5.5. 4. What does the choice of steel type for crankshaft 4. What does the choice of steel type for crankshaft

depend on?depend on?6.6. What is the “firing order”?What is the “firing order”?7.7. What else is taken into consideration in designing a What else is taken into consideration in designing a

crankshaft?crankshaft?

Crankshaft, Main Bearings and Shaft AlignmentCrankshaft, Main Bearings and Shaft AlignmentQuestions & DiscussionQuestions & Discussion