6D125 Second Hand Crankshaft For Excavator PC400 - 5 PC400 - 7 6151 - 31 - 1110

Specification

Description

FORCES IMPOSED ON A CRANKSHAFT
The first source of forces applied to a crankshaft is the product of combustion chamber pressure acting on the top of the piston. High-performance, normally-aspirated Spark-Ignition (SI) engines can have peak combustion pressures in the 120 to 130 bar neighborhood, while contemporary high-performance Compression-Ignition (CI) engines can see peak combustion pressures in excess of 200 bar.

A pressure of 120 bar (1740 psi) acting on a 4.00 inch diameter piston wil produce a force of 21,866 pounds. A pressure of 200 bar acting on a 4.00 inch diameter piston produces a force of 36,442 pounds. That level of force exerted onto a crankshaft rod journal produces substantial bending and torsional moments and the resulting tensile, compressive and shear stresses.

There is another major source of forces imposed on a crankshaft, namely Piston Acceleration. The combined weight of the reciprocating components (piston, ring package, wristpin, retainers, the conrod small end and a small amount of oil) is being accelerated from zero to a very high velocity and back to zero velocity twice each crankshaft revolution. This velocity characteristic and the associated accelerations which that motion produces, are presented in detail on the page entitled PISTON MOTION BASICS.

Since the force it takes to accelerate an object is proportional to the weight of the object times the acceleration (as long as the mass of the object is constant), many of the significant forces exerted n those reciprocating components and on the wristpin, conrod, crankshaft, crankshaft, bearings, and engine block are directly related to piston acceleration. A more detailed discussion of those loads and vibrations they can cause is presented on the page entitled FORCES ON RECIPROCATING COMPONENTS.

In addition to these reciprocating forces and the resulting moments, there is a rotating mass associated with each crankpin, which must be counteracted. The rotating mass consists of the weight of the conrod big end(s), conrod 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 conrod journals. A fully-counterweighted inline-4 cylinder engine has a similar layout.

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