Transcript Document
Tomislav Skračić, MA Undergraduate English Course for MARINE ENGINEERS 3rd Semester Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2, Pomorski fakultet, Rijeka 2009. LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka 2003. Crankshaft alignment Crankshafts are aligned to determine load reactions on each bearing. This is done by laser tehnicques and computer calculations. CHECKS Frequency Once a year After replacing the main bearing If the ship has grounded Techniques The deflections are measured through one revolution of the crankshaft by inserting a dial gauge / dial indicator gauge betwee the webs. Measurements are taken at TDC, BDC and two horizontal web positions. Misalignment CAUSES Wear of main bearings; Distortion of engine bedplate transverse members; Damage to supporting ship’s structure. CONSEQUENCES Hogging is closing of the crank throw at TDC. Sagging is opening of the crank throw at TDC. Crankshaft, Main Bearings and Shaft Alignment REPORTS Main engine crankshaft deflection report; Main / auxiliary engine crankshaft deflection record; Crankshaft and engine bearing data sheet. Exercise 1 - Read the following text: When a crankshaft has to be handled outside the engine, it should be carefully supported to avoid high bending moments on it by its own weight. In the engine it is essential to ensure that the bearings carrying it are in good alignment, as bearing misalignment will cause the crankshaft to bend and eventually break it. Exercise 1 – Complete the sentences: When a crankshaft has to be handled outside the engine, it should be carefully supported to __________ high bending moments on it by its own weight. In the engine it is essential to ensure that the bearings carrying it are in __________ alignment, as bearing misalignment will __________ the crankshaft to bend and eventually break it. Exercise 2 - Read the following text: The main bearing shells are made of steel with a lining of bearing metal which can be white metal, copper-lead or aluminium-tin alloy. A thin flash of lead or indium is often added to provide a layer giving protection against corrosion. The shells are held in position and shape by seatings of the bedplate or frame. To ensure efficient and reliable operation the crankshaft should be checked periodically for alignment by measuring the deflection of the webs. Exercise 2 – Complete the sentences: The main bearing shells are made _____ steel with a lining _____ bearing metal which can be white metal, copper-lead _____ aluminium-tin alloy. A thin flash of lead or indium is often added _____ provide a layer giving protection _____ corrosion. The shells are held _____ position and shape _____ seatings of the bedplate or frame. To ensure efficient and reliable operation the crankshaft should be checked periodically _____ alignment by measuring the deflection _____ the webs. Crankshaft, Main Bearings and Shaft Alignment Questions & Discussion 1. Why should special care be taken when handling crankshafts outside the engine? 2. How are the main bearing shells protected from corrosion? 3. How are crankshafts positioned in the engine with respect to their connection to the shaft? 4. What is a journal bearing? What other types of bearings do you know? 5. What is the function of the webs? 6. How are the main bearings examined for possible wear?