Purpose -The purpose of this paper is to investigate the tribological properties of liquid paraffin with SiO 2 nanoparticles additive made by a sol-gel method. Design/methodology/approach -The tribological properties of the SiO 2 nanoparticles as an additive in liquid paraffin are measured using a ball-onring wear tester to determine the optimal additive concentration. The mechanism that wear and friction are reduced is studied using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and atomic force microscope (AFM). Findings -Experimental results indicate that the sizes of the synthesized SiO 2 nanoparticles are distributed uniformly and that the optimal concentrations of SiO 2 nanoparticles in liquid paraffin is associated with better tribological properties than pure paraffin oil, and an anti-wear (AW) ability that depends on the particle size. Originality/value -It is shown in the paper that by reducing friction and AW, the lubricant prepared by the methods described can prolong operating hours of machinery.

PurposeThe purpose of this paper is to study the influence of number of feeding holes on the performance of aerostatic bearings with spindle rotation. In traditional design of aerostatic bearings, the selection of hole numbers is dependent only on spindle size. However, when the hole numbers of air feeding are enough, the performance of the aerostatic bearing cannot be enhanced by increasing the hole numbers.Design/methodology/approachThe Reynolds equation is utilized to model the air film within bearing clearance at constant temperature and the state equation of adiabatic process is for air feeding within bearing clearance. The finite difference method with relaxation algorithm is utilized to determine the pressure distributions from discretized and coupled equations of flow continuity. The eccentricity, spindle speed, and the number and arrangement of feeding holes are considered in the analyses to determine the load capacity, attitude angle, and flow rate for the comparisons between various designs of aerostatic bearings.FindingsIt is seen from the simulation results that the aerostatic bearing designed with a small number of feeding holes and without locating at bearing bottom is most suitable for the spindle operating at high speed, while the bearing designed with a large number of feeding holes is suitable for the spindle operating at low speed, and the load capacity is increased with the increasing number of feeding holes for low journal speed.Originality/valueThe paper proposes an extensive database as a critical requirement in the design for number and arrangement of feeding holes of aerostatic bearings for the spindle operating at low or high speed.

Purpose -The purpose of this paper is to study the influences of both the number and locations of entry holes on the static and dynamic characteristics of a rigid rotor supported by two double-rows, inherently compensated aerostatic bearings. Design/methodology/approach -The air is assumed to be perfect gas undergoing the adiabatic process and passing through entry holes into the bearing clearance. Air film in the clearance is governed by Reynolds equation including the coupled effects of wedge due to rotor rotation and squeezed film due to rotor oscillation. Findings -The method is used to analyze Reynolds equation, which is then solved by the finite difference method and numerical integration to yield static and dynamic characteristics of air film. The equation of motion of the rotor-bearing system is obtained by using the perturbation method and the eigensolution method is used to determine the stability threshold and critical whirl ratio. Originality/value -The paper considers the eccentricity, rotor speed, and restriction parameter in the analysis of the whirl instability of the rotor-aerostatic bearing system for the comparisons between various designs in the number and locations of entry holes of aerostatic bearings.

PurposeThe present paper proposes a theoretical analysis of the stability characteristics of a rigid rotor‐hybrid bearing system. It is intended that on the basis of the numerical results drawn from this study, the optimal restriction parameter for stable operation can be determined for use in the bearing design process.Design/methodology/approachA rigid rotor supported by hybrid oil film bearings with six recesses and capillary‐compensated restrictors is studied. In order to facilitate the calculation of film dynamics, using the perturbation method, the Reynolds equation was linearized and subsequently solved using finite difference techniques, whilst the stability maps were determined by the Routh‐Hurwitz method.FindingsThe data reported here suggest that the stability characteristics of the rigid rotor‐bearing system could be improved by the use of shallow, dual‐recessed hybrid bearings with capillary compensation. For the same restriction parameter and the same land‐width ratio used in large eccentricity case the stability characteristics of a shallow‐recessed bearing is superior to that of a deep‐recessed bearing, however, a deep‐recessed bearing with a small land‐width ratio and a small restriction parameter can provide better stability than a shallow‐recessed bearing with a large land‐width ratio or with a large restriction parameter.Originality/valueThis study proposes an extensive database as a critical requirement in the design of hybrid bearings, in order to ensure that a rotor bearing system is operating stably.

Purpose -The present paper proposes a theoretical analysis of the stability characteristics of a Jeffcott rotor-hybrid bearing system. It is intended that on the basis of the numerical results drawn from this study, appropriate recess depth, land size, orifice location and speed parameter for stable operation can be determined for use in the bearing design process. Design/methodology/approach -A Jeffcott rotor supported by hybrid oil film bearings with dual-row recesses and orifice-compensated restrictors is studied. In order to facilitate the calculation of film dynamics, using the perturbation method, the Reynolds equation was linearized and subsequently solved using finite difference techniques, whilst the stability maps were determined by the Routh-Hurwitz method. Findings -The data reported here suggest that the stability characteristics of the Jeffcott rotor-bearing system could be improved by the use of shallow, dual-recessed hybrid bearings with orifice compensation. In addition to greater eccentricity ratios, smaller land-width ratios and greater shaft stiffness may also provide shallow-recessed bearings with better stability. In all cases, the stability provided by upstream orifice-sited bearings is better than that provided by center orifice-sited bearings, whilst high-speed parameters may also provide a greater stability threshold.Originality/value -This study proposes an extensive database as a critical requirement in the design of hybrid bearings, in order to ensure that a rotor bearing system is operating stably.