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  • The Stribeck curve and lubrication design for non-fully wetted surfaces
    Kalin, Mitjan ; Velkavrh, Igor ; Vižintin, Jože
    Tailoring the properties of tribological interfaces is difficult, but it can be a very efficient way to reduce wear and friction and so increase service life - providing it can be done successfully. ... However, when considering the interface properties it is necessary not only to take into account the solid-solid contacts, we also need to consider the solid-liquid interfaces, which can have a very significant impact on the micro- and macro-contacts, andwhich cannot be neglected. In this investigation we show that it is essential to consider the wetting, or slip, properties of the non-fully wettedsurfaces when designing the lubrication, and that this is also to a large extent predictable and relatively simple to implement. We discuss the differences between several types of contacts, using steel and DLC as model materials for fully wetted and non-fully wetted surfaces, respectively. We studied steel/steel, steel/DLC and DLC/DLC pairs, and we present the experimental evidence for how the Stribeck curve changes if one or two surfaces in the contact are non-fully wetted. Firstly, in the EHL regime the friction of non-fully wetted surfaces decreases significantly; in our case by around 15% and by more than 20%, respectively, while at minimum friction (the EHL > ML transition) the reduction in friction is lower, but still about 6%, and as high as 9%. Secondly, the film thickness of the non-fully wetted contacts is reduced, which causes a shift in the minimum friction (the Stribeck curve) to higher v/F values. This suggests a lower bearing capacity for these contacts and the potential danger of a transition in the lubricationregime and, as a result, increased wear. However, we have derived several "ready-to-use" diagrams that are generally valid for any oil and surface properties and which allow us to define the film thickness, the lambdaparameter and the regime transition for different wetting/slip properties. These diagrams can be used directly to improve the prediction and design of the lubrication quality and the regimes of the macro-scale contacts by employing a currently used, conventional methodology and equations. Moreover, based on the experimental results and the "ready-to-use" diagrams derived in this investigation for non-fully wetted contacts, the slip at the solid-liquid interface, i.e., the DLC-PAO oil, was estimated independently from the data of two Stribeck curves to be about 20%.
    Source: Wear. - ISSN 0043-1648 (Vol. 267, issues 5-8, 15. jun. 2009, str. 1232-1240)
    Type of material - article, component part
    Publish date - 2009
    Language - english
    COBISS.SI-ID - 10955035
    DOI

source: Wear. - ISSN 0043-1648 (Vol. 267, issues 5-8, 15. jun. 2009, str. 1232-1240)
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