Martin Ebner

Oil-impregnated open-pored sintered materials can be used to provide the intrinsic self-lubrication of tribological contacts. Although its general functionality was recently confirmed for highly-loaded contacts, detailed analyses on the local effects of surface porosity in tribological contacts are required in order to understand and improve its operating behavior. In this context, this study investigates the influence of different surface finishes at a twin-disk test rig, and the local effects of surface porosity in elastohydrodynamically lubricated (EHL) contacts at an optical tribometer, based on thin film colorimetric interferometry. The results show the detrimental influence of high surface porosity on the operating behavior. Local observations of the lubricant film in EHL contacts indicate the presence of “open” pores, resulting in local film breakdown, and “closed” pores, transporting the additional lubricant into the pressurized zone. An appropriate surface finish technique to manufacture a low permeable layer with an adequate mechanical strength is demanded.

Purpose: The purpose of this study is to investigate lubricant film-forming capability of oil-impregnated sintered material in highly loaded non-conformal contacts. This self-lubrication mechanism is well described in lightly loaded conformal contacts such as journal bearings; however, only a little has been published about the application to highly loaded contacts under elastohydrodynamic lubrication regime (EHL).Design/methodology/approach: Thin film colorimetric interferometry is used to describe the effect of different operating conditions on lubricant film formation in line contacts.Findings: Under fully flooded conditions, the effect of porous structure can be mainly traced back to the different elastic properties. When the contact is lubricated only by oil bleeding from the oil-impregnated sintered material, starvation is likely to occur. It is indicated that lubricant film thickness is mainly governed by oil bleeding capacity. The relationship between oil starvation parameters corresponds well with classic starved EHL theory.Practical implications: To show practical, relevant limitations of the considered self-lubrication system, time tests were conducted. The findings indicate that EHL contact with oil-impregnated sintered material may provide about 40 per cent of fully flooded film thickness.Originality/value: For the first time, the paper presents results on the EHL film-forming capability of oil-impregnated sintered material by measuring the lubricant film thickness directly. The present paper identifies the phenomena involved, which is necessary for the understanding of the behavior of this complex tribological system.