**Lubrication and Friction of Porous Oil Bearing Materials**

DOI: 10.5772/intechopen.72620

Lubrication and Friction of Porous Oil Bearing Materials

Yanguo Yin and Guotao Zhang

Additional information is available at the end of the chapter Yanguo Yin and Guotao Zhang

http://dx.doi.org/10.5772/intechopen.72620 Additional information is available at the end of the chapter

#### Abstract

[19] Nakano M, Korenaga A, Korenaga A, Miyake K, Murakami T, Ando Y, Usami H, Sasaki S. Applying micro-texture to cast iron surfaces to reduce the friction coefficient under lubricated conditions. Tribology Letters. 2007;**28**(2):131-137. DOI: 10.1007/

[20] Xiong DS, Qin YK, Li JL, Wan Y, Tyagi R. Tribological properties of PTFE/laser surface textured stainless steel under starved oil lubrication. Tribology International.

[21] Mishra SP, Polycarpou AA.Tribological studies of unpolished laser surface textures under starved lubrication conditions for use in air-conditioning and refrigeration compressors. Tribology International. 2011;**44**(12):1890-1901. DOI: 10.1016/j.triboint.2011.08.005 [22] Li KM, Yao ZQ, Hu YX, Gu WB. Friction and wear performance of laser peen textured surface under starved lubrication. Tribology International. 2014;**77**:97-105. DOI:

[23] Zhang KD, Deng JX, Xing YQ, Li SP, Gao HH. Effect of microscale texture on cutting performance of WC/Co-based TiAlN coated tools under different lubrication conditions.

[24] Grabon W, Koszela W, Pawlus P, Ochwat S. Improving tribological behaviour of piston ring-cylinder liner frictional pair by liner surface texturing. Tribology International.

Applied Surface Science. 2015;**326**:107-118. DOI: 10.1016/j.apsusc.2014.11.059

2015;**82**:305-310. DOI: 10.1016/j.triboint.2014.07.017

2013;**61**:102-108. DOI: 10.1016/j.triboint.2012.11.027

s11249-007-9257-2

112 Lubrication - Tribology, Lubricants and Additives

10.1016/j.triboint.2014.04.017

In order to address poor lubrication of porous bearings due to the seepage flow of oil into the porous medium, multi-layered sintered composite bearings have been developed. Multi-layered bearings achieve a combination of high strength and good lubrication. Lubrication model of the porous multi-layer materials in polar coordinates was established based on Darcy's law. And the effect of surface Darcy flow and porous structure on the lubrication capacity were discussed by using the finite difference method. In the end, the tribology experiments of the multi-layer materials were presented on the end face tribo-tester to verify the simulation results. Results show that the lubrication performance of the multi-layer materials is better than that of the single layer materials. With the decrease of the surface porosity, the lubrication performance becomes better in the given range of surface layer. Also, it can be significantly improved if considering the surface Darcy flow. Within a certain range, the effects of surface Darcy flow on lubrication performance are more obviously with higher speed. There is a good agreement between the numerical analysis and the measurement. Research work provides a theoretical basis for analysis and design of multi-layer sintering bearing material.

Keywords: lubrication, friction, porous bearing, multi-layer materials, Darcy law

### 1. Introduction

Oil bearings with porous matrix have been widely used in industrial applications for its low manufacturing cost and oil self-lubricating properties [1]. As the counterpart picks up speed, the oil impregnated in the porous bearing exuded to the surface and the hydrodynamic oil film formed. Therefore, the oil storage capacity and lubrication performance have an important influence on the operating characteristic of oil bearing [2]. Over the past decades, a considerable number of theoretical models have been proposed on the lubrication characteristic by several researchers. The hydrodynamic theory of porous journal bearings was studied

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© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

originally by Morgan and Cameron, who gave a solution for a short bearing based on Darcy model [3]. Later, Darcy's equations were extensively used in the study of the lubrication characteristic of oil bearing. The unsteady state, non-Newtonian effect and rough surface were coupling to the lubrication model to improve the numerical accuracy [4–9]. These studies were all focused on single-layer bearing materials, without considering the change porosity in the thickness direction. Meurisse [10] and Usha [11] found that reducing the porosity can prevent the oil leaking into the porous medium and improve the bearing strength and hydrodynamic capacity. But the decreased porosity leads to the decrease of oil content and then will deteriorates the self-lubrication performance. Therefore, it can be concluded that the coexistence of high strength and good lubrication characteristics of the porous bearing are difficult to achieve. This is the biggest problem that oil bearing has encountered in the industrial application. Hence, adjusting the permeability of bearing reasonably is the key to improve the lubrication property. Based on the above studies, Naduvinamani [12] and Rao [13] discussed the effect of the multi-layer structure parameters on the lubrication property, which promoted the theoretical development of the oil bearing. This multiple-layer structure is useful, as it would not only increase the load capacity of the bearing because of reduced oil seepage into its wall but would also help to bring oil between the surfaces, thereby improving the bearing performance when saturated with oil Inadequately. But for now, there is no systematic research on the multi-layer oil bearing materials compared with the single-layer sintered materials. Especially, most researchers ignored the surface Darcy flow to simply the boundary condition in the previous work. It did not coincide with the homogeneity and isotropy hypothesis, which will undoubtedly have a bad effect on the analysis accuracy. In this paper, the multi-layer oil bearing composites with different porosities were made to achieve the unification of high strength and good lubrication property. Hydrodynamic lubrication model of the porous bearing in polar coordinate system was established based on Darcy's law. The effect of surface Darcy flow and porous structure on the lubrication property were also discussed. In the end, the tribology experiments of the multi-layer materials were presented on the end face tribotester to verify the simulation results.

If take b equal to 2 and take c equal to 8, the film thickness is show in Figure 2.

; V<sup>0</sup> <sup>¼</sup> <sup>k</sup><sup>1</sup> η ∂p ∂y

where η is the fluid viscosity, and p is the fluid pressure in porous matrix.

∂2 p ∂x<sup>2</sup> þ

form technology, the Reynolds equation under the polar coordinate shown as

þ ∂ <sup>r</sup>∂<sup>θ</sup> <sup>λ</sup> <sup>∂</sup><sup>p</sup> ∂θ 

þ ∂ <sup>r</sup>∂<sup>θ</sup> <sup>ξ</sup> <sup>∂</sup><sup>p</sup> ∂θ 

<sup>r</sup><sup>λ</sup> <sup>∂</sup><sup>p</sup> ∂r 

Similarly, the Reynolds equation without surface Darcy flow shown as

<sup>r</sup><sup>ξ</sup> <sup>∂</sup><sup>p</sup> ∂r 

∂ ∂r

∂ ∂r

<sup>U</sup><sup>0</sup> <sup>¼</sup> <sup>k</sup><sup>1</sup> η ∂p ∂x

Figure 1. Two rotary parallel disc samples.

directions are all considered.

where <sup>ξ</sup> <sup>¼</sup> <sup>h</sup><sup>3</sup> � <sup>12</sup>k1T<sup>1</sup> � <sup>12</sup>k2T2.

Suppose the porous matrix is homogeneous and isotropic. That means the permeability is equal in any coordinate direction. The flow in porous matrix is governed by the Darcy's law.

Owing to the fluid continuity in the porous bearing, the pressure p satisfies the Laplace equation

Integrating the continuity Eq. (3) over the fluid film thickness and using the Eq. (2) as the velocity conditions, the general Reynolds equation can be obtained. By the coordinate trans-

where <sup>λ</sup> <sup>¼</sup> <sup>h</sup><sup>3</sup> � <sup>6</sup>hk<sup>1</sup> � <sup>12</sup>k1T<sup>1</sup> � <sup>12</sup>k2T2. And the surface Darcy flow in the three coordinate

As we all know, the internal powder particles are sintered at high temperature during the preparation of the oil bearing by powder metallurgy technology. The pores between the spherical particles are connected with each other to form the porous channels of the oil bearing, which is consistent with the modeling idea of the Kozeny–Carman equation. So the

∂2 p ∂y<sup>2</sup> þ η

∂2 p

T<sup>1</sup> þ k2 k1 T2 ∂<sup>2</sup>

¼ �6ηωr

¼ �6ηωr

dh

dh

p ∂x<sup>2</sup> þ ∂2 p ∂y<sup>2</sup>

Lubrication and Friction of Porous Oil Bearing Materials http://dx.doi.org/10.5772/intechopen.72620 115

<sup>∂</sup>z<sup>2</sup> <sup>¼</sup> <sup>0</sup> (3)

(2)

<sup>d</sup><sup>θ</sup> (4)

<sup>d</sup><sup>θ</sup> (5)

; W<sup>0</sup> ¼ � <sup>k</sup><sup>1</sup>
