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Power Systems

Power Systems. Overview of structural components. Chapter Two - Objectives. Explain the functional purpose of essential structural parts Understand the constructional features of structural parts. Structural parts. bedplate holding down arrangement frames / columns crosshead guides

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Power Systems

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  1. Power Systems Overview of structural components

  2. Chapter Two - Objectives • Explain the functional purpose of essential structural parts • Understand the constructional features of structural parts

  3. Structural parts ... • bedplate • holding down arrangement • frames / columns • crosshead guides • cylinder block • tie-bolts • cylinder liner • cylinder head

  4. Bedplate • General description • Forces • Developments • Materials • Classification requirements • Problem areas • Inspection & repairs

  5. Bedplate - Holding Down Arrangements • Choking • Choking Materials: Epoxy Resin & Steel • Engine seating requirements • Developments

  6. Forces on Bedplate • Gas Pressure • Inertia Forces • Side Thrust from Guide faces • Static weight of engine components • Torque reaction from propeller • Hull defection • Vibration • Heavy seas

  7. Functions of bedplate • Support the static load of the stationary and running gear • support the crankshaft in perfect alignment • distribute the static and dynamic load onto the ship structure • collect the crankcase lub oil and convey it to the sump tank

  8. Bedplate • Most heavily loaded constructional part • Main propulsion engine bedplates are flat bottom type • Main components: Longitudinal & Cross girders • Bedplate carried on number of chocks

  9. Design Features - Large Bedplate • Box shaped or H-section • Deep section • Single walled • Cast steel bearing saddle • Longitudinals - mild steel fabricated • Tie bolts fitted close to centre line • Double row long bolts

  10. Design - Large Bedplate • Cast steel or epoxy resin chocks • Extra projection forward of bedpaltes • Extra row of bolts

  11. Design - Large Bedplate • High degree of surface finishTop: Frame attachmentBottom: Chocks - Tie Bolts - Oil panSide: ChocksEnd: End chocks - Thrust block

  12. Bedplate - Longitudinal Girders • Mild steel welded construction • Runs along the length of the engine • Main bearing & crank shaft alignment depends on longitudinal rigidity • Box or H-section (MAN B&W) girder • Prevents twisting of engine

  13. Bedplate - Cross Girder • Carries main bearing saddle • Heavily strengthened by ribs • Deep section • No support at the centre of cross girder to prevent direct connection with tank top • Most heavily loaded part of engine • Weakness will result in crankshaft failure

  14. Cross Girder Construction • Classification society Requirements:Steel castingFabrication not to be allowed • Failure bearing pockets & junction welds • Difficult welding & assembly

  15. Pictures of bedplates(click on each picture to enlarge)

  16. Bedplate Construction • Double welded butt joint • Minimum number of joints • No intricate shape • Continuous full strength weld • No intersection • Welding without difficulty • Avoid change of section

  17. Bedplate Construction • Whole bedplate heat treated in FurnaceFull annealing or NormalisingNormalised & Tempered(>550 deg C)

  18. Cast Steel Fabricated Steel

  19. Bedplate problems • Cracks • cross girder central, bearing saddle • junction welds • around tie bolt holes • lightening holes • base of main bearing keeps • Loose chocks • Oil leakage

  20. Why bedplates fail ... • Excessive vibration • slack tie bolts • slack foundation bolts • loose chocks • overloading • excessive bearing wear • poor welding • improper stress relief

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