There are two types of crankshaft produced, which are commonly known as cast and forged. The counterweights can also be forged directly into the crankshaft or can be bolted-on with the threaded bolts. All the pistons of the internal combustion engine transmit their load at the crankshaft. The crankshaft has to undergo high torsional forces, bending forces, pressures, and vibrations. Let’s study more about the types of crankshaft:
Cast Crankshaft:
This refers to the types of crankshaft that are commonly found for a long time and are mostly in diesel and petrol engines. The name clearly suggests that it’s made from the malleable iron through a casting process. They are quite economical in working and therefore are commonly selected by the manufacturers.
A flat plane crank is the one wherein the journals are kept 180 degrees apart from all in-line four engines. Whereas when it comes to a cross-plane crank, they need a mold of multiple parts because the journals and counterweights are not that symmetrical. The cast cranks are hardened through the flame in order to improve the wear resistance in particular areas.
Forged Crankshaft:
These are comparatively more robust crankshaft that are more commonly found, especially higher stressed engines, which comes standard with some 16v engine. Creating a forged crank is totally different. There are different sets of dies that are machined together to the approximate shape of the crank.
These dies are set in a very large hydraulic press, which has a clamping force of many tons. A hot bar of very high-grade steel alloy is placed at the bottom die, and then the dies are closed. Once the dies are closed, the metal gets squeezed very tightly, after which the material is compacted and aligned for a better casting process. These types of cranks are also hardened like the cast cracks but using induction hardening.
Billet Crankshaft:
Billet crankshaft is one of the best types of crank which one can have in the engine, which is normally used to manufacture this kind of crank. This usually contains materials like nickel, chromium, aluminum, and molybdenum, amongst other elements. These cranks are most common due to the lowest crankshaft machining time. Also, these require minimal balancing due to the uniform makeup of the material.
General Crankshaft Faults
Reasons for Crankshaft Misalignment
- Damage or wipe-out of the main bearing
- Loose engine foundation bolt leading to vibration
- Deformation of ship’s hull
- Crack in the bearing saddle
- Loose main bearing bolt leading to damage of main bearing
- The high bending moment is applied on the crankshaft due to the excessive force from the assembly of the piston.
- Grounding of the ship
- Crankcase explosion or fire
- A defective or worn out stern tube or intermediate shaft bearings
- Loose or broken chokes in the foundation
- Bearing pockets cracked
- Bedplate deformed – transverse girder damaged
- Tie bolts slack or broken
- Weakening of structure due to corrosion
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