Experimental study on the feasibility of alternative materials for tilting pad thrust bearings operating in transition to mixed friction

In hydrodynamic bearings traditional bearing alloys:Babbitts and bronzes are most frequently utilized.Polymer sliding layers are sometimes applied as a valuable alternative.Hard diamond-like carbon(DLC)coatings,which are also considered for certain applications may show some advantages,as well.Although material selection is of secondary importance in a full film lubrication regime it becomes important in mixed friction conditions,which is crucial for bearings with frequent starts and stops.Experimental research aimed at studying the performance of fluid film bearings in the specific operating regime,including the transition to mixed friction,is described in the paper.The tests were carried out on four tilting pad bearings of different material compositions:Steel/bronze,DLC/steel,steel/polyether ether ketone(PEEK),and steel/Babbitt.The tests comprised stopping under load and reproduction of the Stribeck curve by decreasing rotational speed to very low values,and observing the changes of friction force during the transition to mixed friction regime.Analysis of the transition conditions and other results showed clear differences between the tested bearings,illustrating the feasibility of less popular material compositions for bearings operating in specific conditions.More specifically,the DLC/steel bearing was demonstrating superior performance,i.e.lower friction,transition to mixed friction occurring at higher load,and more stable performance at start-stop regime over the other tested bearings.

Surface roughness characteristics effects on fluid load capability of tilt pad thrust bearings with water lubrication

The effects of surface roughness characteristics on the fluid load capacity of tilt pad thrust bearings with water lubrication were studied by the average flow model.The flow factors utilized in the average flow model were simulated with various surface roughness parameters including skewness,kurtosis and the roughness directional pattern.The results indicated that the fluid load capacity was not only affected by the RMS roughness but also by the surface roughness characteristics.The fluid load capacity was dramatically affected by the roughness directional pattern.The skewness had a lower effect than the roughness directional pattern.The kurtosis had no notable effect on the fluid load capacity.It was possible for the fluid load capacity of the tilt pad thrust bearings to be improved by the skewness and roughness direction pattern control.

NUMERICAL RESEARCH ON WATER GUIDE BEARING OF HYDRO-GENERATOR UNIT USING FINITE VOLUME METHOD

With the consideration of the geometry of tilting pad journal bearing, a new form of the Reynolds equation was derived in this article. The film thickness, the squeeze motion of the journal and the rotation motion of the pad were explicitly contained in the equation. Based on this equation, together with the equilibrium equation of pad pivot, the water guide bearing used in the Gezhouba 10 F hydro-generator unit was numerically researched. The new Reynolds equation for the lubricating film was solved using Finite Volume （FV） discretization, Successive Over-Relaxation （SOR） iteration method and C＋＋ code are included. According to the numerical solution, and the stability of the film and the influences of the film thickness, the journal squeeze effect and the pad rotation effect on film force were discussed. The results indicate that the squeeze effect can not be neglected, although the rotation effect is negligible for both low-speed and high-speed bearings, so the computing time could be greatly reduced.

Effects of Load Direction on Performance of Tiliting Pad Journal Bearings

At the previous works for tilting journal pad bearings （TPJBs）, most TPJBs are designed to operate with the load either directly on-pad（LOP） or directly between-pad（LBP）. However, in practice, in some cases, the load direction can change dramatically in operation. With the current requirements for the analysis of dynamic characteristics of the rotor-bearing systems, the effects of the load direction on the bearing performance must be known. So, in this paper, the effects of load direction on the static and dynamic characteristics of TPJBs are obtained with theoretical analysis based on the hydrodynamic lubrication theory, and the influence of load direction on the performance of TPJBs in different structure and operating parameters is also analysed. The results show that the load direction has considerable effects on the static and dynamic characteristics of the TPJBs, especially for the TPJBs that are operating under heavy load and high rotor speed. And for the operating condition that load direction changed rapidly, TPJBs with more pads, smaller length to diameter ratio, larger clearance ratio and smaller perload ratio can reduce the performance fluctuation with the variation of load direction.