Development of aerostatic porous bearings manufactured using metal 3D printing technology

Aerostatic porous bearings have been applied widely in precision devices to achieve higher accuracy of motion. Conventional aerostatic porous bearings are made of porous graphite, porous ceramics or sintered metal porous material, having a thickness of several millimetres and a surface-restricted layer. However, during mass production of porous bearings, the time required for the production of the porous materials and the surface restriction treatment leads to an increase in the manufacturing time and cost of the porous bearings. Accordingly, to overcome this problem, an aerostatic porous bearing with a layer thickness of several hundred µm and a support member, manufactured using metal 3D printing technology, is proposed. In this study, the optimum conditions for manufacturing the proposed aerostatic porous bearings with a direct metal laser sintering method 3D printer were investigated, and characteristics of the prototype of the proposed bearings were investigated experimentally.

Effect of journal misalignment and coupled-stress lubricant on the film pressure of a double-layered porous journal bearing

Purpose In the application of hydrostatic double-layered porous journal bearings, misalignment of bearing systems is a major problem. On the other hand, the use of coupled-stress fluid as a lubricant is more practical in the present days. Furthermore, in case of porous bearing, neglecting slip effect and percolation effect of additives into the pores may lead to erroneous result. Hence, this paper aims to address the effect of journal misalignment and coupled-stress lubricant on the steady-state film pressure of the double-layered porous journal bearing with tangential velocity slip and percolation effect. Design/methodology/approach First, considering the tangential velocity slip, the most general modified Reynolds type equation has been derived for the film region and the governing equations for flow in the coarse and fine layers of porous medium, incorporating the percolation effect for a double-layered porous bearing. Here, considering the misalignment caused by shaft displacement. Film thickness expression established considering the effect of misalignment. Steady-state film pressures are obtained by solving modified Reynolds equation based on the coupled-stress lubrication theory. Effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are discussed and demonstrated in the graphical form. Findings In this paper, effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are obtained. In general, higher degree of misalignment gives higher steady-state pressure value in the film region, and this pressure increases due to increase in coupled-stress parameter up to a certain limit. Originality/value To the best of the author’s knowledge, there is no literature available, so far, that addresses the analysis of the steady-state pressure in the film region of a doubled–layered porous journal bearing under misaligned condition with coupled-stress lubricant. But in this paper all these points are included, which makes this article valuable in design purpose.

Effect of percolation on hydrodynamic lubrication of rough bilayer porous bearing with circular contact

Purpose The purpose of this paper was to study the hydrodynamic lubrication of rough bilayer porous bearing to reveal the effect of percolation. Design/methodology/approach The seepage lubrication model of the circular bilayer porous bearing was established in polar coordinates. The digital filtering technique and Darcy’s law were used to simulate the rough surface and the percolation characteristic of the oil bearing, respectively. The influence of the structural parameters on the lubrication performance was analyzed. Findings Compared with the ordinary monolayer oil bearing with high porosity, the bilayer bearing can reduce the whole porosity, prevent oil infiltrating into the porous medium and have better lubrication performance. The lubrication performance of bilayer oil bearing is better than that of the single-layer oil bearing which has a higher porosity. With increasing root-mean-square roughness or decreasing surface porosity, the lubrication performance of the bilayer bearing improves. The lower the porosity of the surface layer, the better the lubrication performance. Originality/value This research provides a theoretical basis for clarifying the lubrication mechanism and influence the mechanism of the bilayer oil bearing.

The effect of the arc on annular-thrust aerostatic porous bearings

Purpose Aerostatic porous bearings are important for guide rails and spindles. It is well-known that flow restrictors made of porous materials offer major advantages over conventional restrictors in such bearings, including design and manufacturing, load-carrying capacity, stiffness, damping and dynamic stability. Thus, this work numerically investigates the effect of the arc on a new combined annular-thrust aerostatic porous bearing. Design/methodology/approach The static characteristics of an annular-thrust aerostatic porous bearing were studied using a fast finite element scheme. The pressure distribution, radial load and thrust load were analyzed as functions of the arc, permeability and eccentricity. Findings The results reveal that the radial load achieves maximal values at an optimal arc value between 200 and 300, and the thrust load increases monotonically with increasing arc. Originality/value This work developed a new combined annular-thrust aerostatic porous bearing to investigate the effect of arc on the annular-thrust aerostatic porous bearings to increase the load-carrying capacity.

Effects of surface roughness and porous structure on the hydrodynamic lubrication of multi-layer oil bearing

Purpose The purpose of this paper is to discuss the combined effects of the deterministic surface roughness and porous structure on the lubrication property of the multi-layer bearing. Design/methodology/approach Digital filtering technique and Kozeny-Carman equation are used to simulate the random Gauss surface and the internal pore structure of the porous bearing, respectively. Effects of surface morphology, structure and pores on the lubrication property are discussed by using the finite difference method. Findings Results show that the lubrication performance of the multi-layer bearing increased with the increase of the surface roughness. Also, the transverse surface is better than that of the longitudinal surface. Moreover, lubricating property is getting worse with the increase of the height of each layer and the porosity. The lower permeability surface is beneficial to improve the lubrication performance when the total porosity is certain. Originality/value The effect of the Gauss roughness parameters on the detail of lubrication performance are analysed, such as the migration of the oil film rupture point position, the expansion of the pressure distribution region and the fluctuation of the pressure distribution curve with the roughness parameters. The combined effects of surface roughness, multi-layer structure and the internal pore parameters on the hydrodynamic behaviours of multi-layer porous bearing are analysed. This work is beneficial for the analysis of the tribological property and the structural design of multi-layer bearing.

Carbon nanotubes and superplasticizer reinforcing cementitious composite for aerostatic porous bearing

Cementitious composites are low cost and readily manufactured materials which can be used for specialist applications such as the production of aerostatic porous bearings. A design of experiment was used to identify the effects of superplasticizer additions and carbon nanotube inclusions on the physical and mechanical properties of cementitious composites which can be applied as porous restrictor in aerostatic thrust bearings. The presence of carbon nanotubes was able to increase the bulk density, the compressive strength and the modulus of elasticity, and also decrease the apparent porosity of the composites. The composite made with 0.4 wt.% of superplasticizer and 0.05 wt.% of carbon nanotubes achieved acceptable properties for the use as double-layered porous restrictor in aerostatic thrust bearings.

Thrust Porous Bearing with Rough Surfaces Lubricated by a Rotem-Shinnar Fluid

In the paper the influence of both bearing surfaces roughness and porosity of one bearing surface on the pressure distribution and load-carrying capacity of a thrust bearing surfaces is discussed. The equations of motion of a pseudo-plastic fluid of Rotem-Shinnar, are used to derive the Reynolds equation. After general considerations on the flow in a bearing clearance and in a porous layer using the Morgan-Cameron approximation and Christensen theory of hydrodynamic lubrication the modified Reynolds equation is obtained. The analytical solutions of this equation for the cases of squeeze film bearing and externally pressurized bearing are presented. As a result one obtains the formulae expressing pressure distribution and load-carrying capacity. Thrust radial bearing with squeezed film is considered as a numerical example.