Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2, Pomorski fakultet, Rijeka LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka Tomislav Skračić, MA Undergraduate English Course for MARINE ENGINEERS 3rd Semester

Lesson 2 Crankshaft, Main Bearings and Shaft Alignment KEY WORDS crankshaft (n.)- koljenasto vratilo / osovina, radilica main bearing- glavni / temeljni ležaj shaft alignment- centriranje osovine reciprocating motion- stapno gibanje at a top center- u gornjoj mrtvoj točki bending stress- naprezanje zbog savijanja connecting rod thrust- potisak ojnice crankpin (n.)- oslonac koljena, osovina letećeg ležaja adjacent bearing- pokrajnji ležaj, "odrivni" ležaj, "thrust" bearing torsional forces- torzijske / zaokretne sile semi-built design- izrađen od više dijelova crank web (n.)- 'pršuti' za uravnoteženje forge (v.)- kovati solid-forged- izrađen u jednom dijelu cast (v.)- lijevati

Lesson 2 Crankshaft, Main Bearings and Shaft Alignment KEY WORDS shrink on to (v.)- navući u toplom stanju crank journal- oslonac temeljnog ležaja journal (n.)- blazinica, ležajna čaša (materijal koji se troši) journal bearing- leteći ležaj carbon steel- ugljični čelik (FeC) alloy steel- legura čelika nickel - nikalchromium - krommolybdenum - molibden (Mo) crank (n.)- koljeno vratila multi-throw shaft- osovina s više koljena, višecilindarska koljenasta osovina firing order- redoslijed paljenja torque (n.)- zakretni moment torque wrench- moment-ključ load (n.)- opterećenje exhaust arrangement- ispušni sustav / raspored ispuha

Lesson 2 Crankshaft, Main Bearings and Shaft Alignment KEY WORDS misalignment (n.)- loše centriranje, nepoklapanje osi bearing shell- blaznica temeljnog ležaja / košuljica ležaja lining (n.)- obloga, sloj copper-lead- bakar-olovo aluminium-tin alloy- legura aluminija i kositra flash (n.)- sloj obloge lead (n.) - olovoindium - indij seating (n.)- sjedište, postolje transverse sadles- poprečni nosači thrust bolts- vijci temeljnog ležaja preopterečeni na tlak shim (n.)- podložna pločica bearing play- zračnost ležaja pressure lubricated- tlačno podmazivane tie rod- kotveni vijak tensioned- stegnut

Crankshaft, Main Bearings and Shaft Alignment DEFINITION OF A CRANKSHAFT The crankshaft converts reciprocating motion in the cylinder into rotary motion of the propeller shaft. PARTS The 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)

Crankshaft 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).

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

The crankshaft, which converts the reciprocating motion of the piston to rotating motion, must resist the bending stresses caused by the connecting rod thrust when the piston is at the top dead centre. Then the maximum gas pressure acts straight down on the crankpin and tends to bend the shaft between the adjacent bearings. The crankshaft must also withstand the torsional forces produced by the change of speed. Exercise 1 - Read the following text:

The crankshaft converts to The crankshaft converts to It must resist the bending stresses caused by the connecting rod thrust when 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 Then the maximum gas pressure acts straight down on the crankpin and tends to The crankshaft must also withstand the The crankshaft must also withstand the Exercise 1 – Complete the sentences:

Medium speed engines have crankshaft usually solid forged, i.e. made from a single piece, while slow speed engine crankshafts are mostly of semi-built design with crankpins and webs forged or cast in one piece and shrunk on to the journals. The type of steel used, which is carbon or alloy steel containing nickel, chromium and molybdenum, is chosen for its strength, resistance to fatigue and hardness of bearing surface. Exercise 2 – Read the text:

Medium speed engines have crankshaft usually solid forged, i.e. made Medium speed engines have crankshaft usually solid forged, i.e. made Slow speed engine crankshafts are mostly of semi-built design with Slow speed engine crankshafts are mostly of semi-built design with They are... or... in one piece and... on to the journals. They are... or... in one piece and... on to the journals. The type of steel used for crakshafts is The type of steel used for crakshafts is It contains nickel,... and must be resistant to... It contains nickel,... and must be resistant to... Exercise 2 – Complete the sentences:

The cranks of a multi-throw shaft are set at appropriate angles giving a “firing order” for the engine. The firing order is chosen primarily to obtain a smooth torque and the best mechanical balance. However, main bearings loads, exhaust arrangements suitable for turbocharging and torsional vibration may also be taken into account. Although the crankshaft appears to be robust, they rely on the main bearings to develop their full strength. Exercise 3 – Read the text:

cranks of a multi-throw shaft are set at appropriate angles giving cranks of a multi-throw shaft are set at appropriate angles giving The firing order is chosen primarily to obtain and The firing order is chosen primarily to obtain and However, we must also take ito account: However, we must also take ito account:... loads,... loads, exhaust arrangements suitable for... and exhaust arrangements suitable for... and Crankshaft rely on the to develop their full strength. Crankshaft rely on the to develop their full strength. Exercise 3 – Complete the sentences:

1. State the function of the crankshaft. 2. What forces is a crankshaft subjected to? 3. What kind of crankshafts are used in: a) Medium speed diesel 4. Slow speed diesel What does the choice of steel type for crankshaft depend on? 6. What is the “firing order”? 7. What else is taken into consideration in designing a crankshaft? Crankshaft, Main Bearings and Shaft Alignment Questions & Discussion