On the Critical Speeds of Synchronous Backward Precession

Abstract

Although, as has already been reported, the resonance of synchronous backward precession can occur when the bearing pedestals deflect, this resonance can also appear when the pedestals have no flexibility and there is a loose fit of ball bearing in pedestal. Since there are errors in machining the outer ring of ball bearing as well as the inner surface of bearing box where neither are made exact circle, the degree of flt is not equal in all directions and the shaft has an unequal flexibility. Consequently the critical speeds of synchronous backward precession do occur. Similarly these critical speeds appear in the shaft supported by single-row radial ball bearings, because such a shaft has non-symmetrical, non-linear characteristics and unequal flexibility. Because the phenomenon of shaft whipping induced by dry friction takes place, it is undesirable to equip a gard ring to check an increase of deflection of the shaft at the critical speeds of synchronous backward precession.