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Wpływ nierównoległości osi pierścieni łożyska walcowego typu NU na jego trwałość zmęczeniową.

Warda B.

Zagadnienia Eksploatacji Maszyn

1999

Vol. 34, nr 1

131-137

W pracy przedstawiono wyniki obliczeń trwałości zmęczeniowej promieniowych łożysk walcowych typu NU z niewspółosiowymi pierścieniami. Wyniki obliczeń porównano z zaleceniami producentów łożysk tocznych dotyczącymi dopuszczalnego wychylenia kątowego pierścieni. Trwałość łożysk wyznaczono za pomocą metod numerycznych. Posłużono się przy tym zarówno konwencjonalnym modelem obliczeniowym, zakładającym zawsze ograniczoną trwałość łożyska, jak i nowym, opartym na hipotezie nieograniczonej trwałości zmęczeniowej.

Calculation methods of bearing fatigue life presented in catalogues do not take into consideration many factors that remarkably influence a bearing fatigue life. One of these factors is the angular misalignment of bearing rings, caused by errors of alignment between shaft and housings resulting from machining or mounting, insufficient stiffness of housings or by a shaft deflection under load. The misalignment occuring in the radial cylindrical roller bearing effects in a tilt of rollers and in stress concentrations at the contact between roller and race, and it decreases the bearing fatigue life. The calculation of the fatigue life of the roller bearing with the misalignment is possible only by using computer. For such case the calculation method requires examining the local values of subsurface stress deciding the bearing fatigue life. In the present paper the influence of the angular misalignment of bearing rings on the fatigue life of the radial cylindrical roller bearing of NU type was discussed. For this purpose the method described in paper [1], based on the unlimited fatigue life hypothesis, was applied. The analysis of influence of the angular misalignment of bearing rings on the bearing fatigue life was achieved for the NU 213 EC and the NU 2213 EC type radial cylindrical roller bearing. Calculations of fatigue life were carried out for radial loads from Fr=0.05C to Fr=C (where C is a basic dynamic load rating of the bearing) and for tilt angles of bearing ring axes from Xi=0 to Xi=5'. The calculations were performed with the aid of the computer program described in paper [2]. On the base of the calculation results it can be stated, that the bearing fatigue life decreases with the increase of the tilt angles of bearing rings. The reduction of fatigue life is greater for low values of bearing radial load. However the method based on the unlimited fatigue life theory better enhances the influence of the angular misalignment of bearing rings on the fatigue life. The analysis of calculation results confirms the recommendations of the rolling bearing manufacturers concerning the permissible angular misalignment of the bearing rings. The computer program applied in the present work allows anticipating the fatigue life of the arbitrary radial cylindrical roller bearing, for the definite case of load, misalignment and correction of the roller generators. It can be useful for the fatigue life calculation of responsible or mass-production bearing arrangements.