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During the time, the specific characteristics and the efficient lifetime of oil progressively decrease, due to complex pollution, ultimately making the oil unsuitable for the initial applications. The strategy to regenerate and to valorise waste oils is investigated using improved combinations of sclerometric and topometric tests on ductile nodular cast iron. Tribo-abrasive tests are performed in critical conditions, with base oil, waste oil and regenerated oil, of similar viscosities in order to discriminate their interfacial performances. The forms of the scratch traces indicate wear resistance and tendency to elasto-plastic deformation. The mechanisms of deformation and frictional behaviours were evaluated using optical and Scanning Electron Microscopy and measured for various tribological conditions with tactile and optical profilometry. The Energy Dispersive X ray Spectroscopy completes the chemical superficial distribution of pertinent elements. The surface topography metrology is used to characterize the scratch profiles and to determine the volume of the displaced and removed material, as well as maximum pit height. The originality of this paper is that it is a unique approach specifically devoted to transformer oil concerning tribological conditions.

In order to better understand superficial abrasive wear and metal processing sclero-topometric investigations have been developed and applied to spheroidal cast iron at boundary lubrication regime with new, waste and regenerated oils. Recycling of waste oils is the major challenge of worldwide society today, specifically for petroleum resources, and therefore, for derivatives like transformer oil. The contradictory characteristics from physical approach of transformer oil, requiring and insuring simultaneously a high thermal conductivity as well as an electrical resistivity, are specific for their applications. During the efficient lifetime, these characteristics progressively decrease, due to complex pollution (divers pollutions, water absorption, Polychlorobiphenyl (PCB), etc) and degradation (acids, resins, polluted oils, biological invasions, wear debris's du to local frictions, fretting, etc…), ultimately making the oil unsuitable for the initial application. [1] The strategy to upgrade the waste oil is investigated in the presented work using improved sclerometric and topometric characterisations [2,3] on deliberately selected heterogeneous material - ductile cast iron (with spheroidal graphite precipitations) widely manufactured for various transport industry[4].

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