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Diagnozowanie ułożenia wału korbowego maszyn okrętowych.

Bielawski P.

Zagadnienia Eksploatacji Maszyn

2002

Vol. 37, nr 4

177-193

Scharakteryzowano naprężenia gnące w wałach korbowych i podano przyczyny zmian naprężeń podczas eksploatacji maszyny. Opisano sprężynowanie wykorbień jako miarę ułożenia wału. Przedstawiono związki między sprężynowaniem wykorbień a przemieszczeniem poosiowym wolnego końca wału. Wskazano na możliwość wykorzystania drgań wzdłużnych wału korbowego maszyny w diagnozowaniu ułożenia wału i przedstawiono przydatne miary drgań.

Essential characteristic features of marine machinery have been mentioned: large dimensions and weight, high and very high power or capacity, long life and effects of a breakdown resulting in high costs of troubleshooting, danger to health and life and the loss of ship's manoeuvring capabilities. One of the main groups of causes resulting in a breakdown are those causing additional bending stresses in crankshafts which add up to working stresses. It is necessary to create tools for detecting the stresses and to modify the forecasting algorithm so that it takes into account the time of crankshaft damage. Causes of bending stresses in a crankshaft are given; besides, the fact has been emphasised that the crankshaft deflection is a static measure of crankshaft position. Relations are shown between additional load of main crankshaft bearings, crankshaft deflection and stresses in the crankshaft. The notion of longitudinal displacement of the free pin of the crank fastened on one end only is introduced. A geometric method of describing the dependence of free crank displacement on the value of crank deflection in vertical and horizontal planes, and on positive and negative deflection. The theoretical decomposition of the crankshaft into one-end fastened cranks was applied in order to determine the resultant displacement of the last main crankpin (free end of the crankshaft) of one-end fastened crankshaft. The created model assumes that the longitudinal displacement of the crankshaft free end is the geometric sum of the displacements of non-fastened pins of individual cranks. The measures given, crankshaft-position oriented, are those of crankshaft free end displacement as the function of shaft turning angle. It is assumed that longitudinal vibrations of the free crankshaft end measured as the function of turning angle include crankshaft position oriented components. The following magnitudes are taken as crankshaft position oriented measures of longitudinal vibrations: mean and peak values as well as phase shift of the first harmonic of those vibrations. The created model, presenting the relations between the longitudinal displacement of the free end and crankshaft displacement given as the deflections of individual cranks, has been verified experimentally. A linear relationship is indicated between the crankshaft free end displacement calculated from the measured deflection and the displacement measured at slow revolving crankshaft of an engine. It has been proved that the longitudinal vibrations depend on both crankshaft deflection and the loads on individual engine cylinders. Presented is a concept of longitudinal vibrations reduction to the vibrations occuring at the nominal load and uniform load of all cylinders.