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By:
1. Sachin kumar(2010JE0751)
2. Vipin Sharma(2010JE0857)
3. Shashi Ranjan(2010JE0772)
PRESENTATION ON CRANKSHAFT
INTRODUCTION TO CRANKSHAFT
CRANKSHAFT is a part of the engine that translates reciprocating linear piston motion into rotation
• Has crank pins which is attached to big end of theconnecting rod
• Typically connects to a flywheel to reduce the pulsation characteristic of the 4-S cycle• Sometimes torsional or vibrational damper are connected to the other end to reduce the torsional vibrations• Counterweights to improve engine balance
FORCES IMPOSED ON A CRANKSHAFT• If the gas pressure is assumed to be 200bar and piston diameter of 10cm, the force on
crankshaft will be of the order of 16,000kgf.
• This level of force produces substantial bending and torsional moments and the resulting tensile, compressive and shear stresses.
• The combined weight of the piston, ring package, wristpin, retainers, small end of connecting rod and a small amount of oil are continuously accelerated from rest to very high velocity and back to rest twice each crankshaft revolution.
• Combustion forces and piston acceleration are also the main source of external vibration produced by an engine.
• Rotating mass associated with each crankpin, weight of the big end of connecting rod , connecting rod bearing(s), some amount of oil, and the mass of the crankshaft structure comprising the crankpin and cheeks.
• These rotating forces are counteracted by counterweight masses located in appropriate angular locations opposing the rod journals
TORSIONAL VIBRATIONS• Crankshaft has its own torsional resonant frequency as it has mass and its own torsional
stiffness
• Torsional resonant frequency of the crankshaft system is a function of:
• Crankshaft length
• Crankshaft torsional stiffness
• Crankshaft stroke
• Balance masses
• Moments of inertia of rotating items attached to or driven by the engine
• Crankshaft has very little inherent damping as it is made of lump of high-strength steel. Therefore, vibration attenuating device is provided at the free end of engine crankshaft.
CRANKSHAFT TORSIONAL ABSORBERS• Difference between damper and absorber
• Damper dissipates energy, mainly in the form of heat
• Absorber is a device which is designed to oscillate in direct opposition to a vibration at either a specific frequency or a specific order, depending on the design.
• Types of absorber
• Elastomer absorber
• Pendulum absorber
MATERIALS USED IN MANUFACTURE OF CRANKSHAFTS• Crankshaft are subjected to shock and fatigue loads. Therefore material should be tough
and fatigue resistant.
• The crankshafts are generally made of carbon steel, special steel or special cast iron.
• Medium-carbon steel alloys are composed of predominantly the element iron, and contain a small percentage of carbon (0.25% to 0.45%)
• Several alloying mix are carefully mixed carefully in order to produce specific qualities in target alloy.
• These qualities are hardenability, nitridability, surface and core hardness, ultimate tensile strength, yield strength, endurance limit (fatigue strength), ductility, impact resistance, and corrosion resistance.
• Alloying elements typically used are manganese, chromium, molybdenum, nickel, silicon, cobalt, vanadium, and sometimes aluminium and titanium.
• In industrial engines, the crankshafts are generally made from carbon steel such as 40C8, 55C8 and 68C4
• In transport engines- managanese steel such as 20-Mn-2, 27-Mn-2 and 37-Mn-2
• In aero engines- Nickel Chromium steel such as 35-Ni-1-Cr-60 and 40-Ni-2-Cr-1-Mo-28
MANUFACTURING OPERATIONS• Forging
• Crank web milling, Journal milling, Crank pin milling
• Drilling of flywheel flange, Drilling of crankpin, Drilling of crossed oil hole
• Grinding
• Crack Detection
• Nitriding
• Dynamic Balancing
• Lapping and Super finish
• Journal Grading and Bearing Selection
Drilling of crankpin Drilling of flywheel flange Drilling of crossed oil hole
Milling cutter used for journal and crankpin milling
• Grinding- Surface grinding is done for main journal and crank pin. Grinding of sidewalls is a critical step
• Crack detection- For a forged material there is possibility of internal flaws. Hence before sending materials for further operations, cracks are detected by magnaflux method.
• Nitriding- Higher surface hardness is obtained, extremely resistant to abrasion and high fatigue strength
• Lapping and Superfinishing- Crankshaft is super-finished so as to avoid cyclic fatigue failure
• Journal Grading and bearing selection