Lubrifiant (mécanique)

Résumé

vignette|Burette à lubrifiant synthétique. En mécanique, les lubrifiants ont notamment pour rôle de lubrifier, réfrigérer ou les deux à la fois ; pour réduire le frottement d'une pièce par rapport à une autre ou pour l'usinage mécanique. Typologie Les trois principales familles de lubrifiants sont :

les lubrifiants solides : ** graphite, disulfure de molybdène, biséléniures, cires ; ** polymères : fluoropolymères, polyamides ;
les lubrifiants liquides : ** huiles de lubrification : voir paragraphe ci-dessous : « Fluides lubrifiants » ; ** polyglycols à faible masse moléculaire : polyéthers glycols (comme le polyéthylène glycol (PEG)), polyesters glycols ; ** silicones ;
les lubrifiants pâteux : ** graisses de lubrification : graisses à base d'huile de pétrole, lanoline, suif, brais ; ** polyglycols à masse moléculaire moyenne : polyéthers glycols (comme le polyéthylène glycol), polyesters glycols ; ** silicones (graisse de silicone).

Additifs Les lubrifia

Source officielle

https://fr.wikipedia.org/wiki/Lubrifiant_(m%C3%A9canique)

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This introductory course in tribology (science of friction, lubrication and wear) has specific goals : to present the basic principles of tribology, to develop the attitude to analyse tribological and to illustrate correlations between materials and tribological properties.

Ce cours introduit les bases de la mécanique des structures : calcul des contraintes et déformations provoquées par les forces extérieures et calcul des déformations. Ces enseignements théoriques sont appliqués à la conception des éléments importants des mécanismes de précision.

The course is an introduction to heterogeneous catalysis for environmental protection and energy production. It focusses on catalytic exhaust gas cleaning as well as catalytic systems relevant for gaseous and liquid fuel production. The course ends with two days of experimental exercises at PSI.

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Reducing friction and wear is essential for building efficient systems with low energy consumption and a long lifetime. Surface texturing is one of the methods to reduce friction and wear, especially in oil-lubricated systems. However, there is still a lack of knowledge about the fundamental aspects involved in the improvement of tribological performance, especially for the mechanical parts sliding under starved lubrication conditions. Moreover, failure in such lubricated contacts is poorly understood and there are little agreements regarding the mechanisms leading to scuffing. The present research focuses on three main objectives. The first is to characterize a cast iron-steel tribo-system under starved lubrication conditions, and to improve its tribological performance by laser surface texturing. All tribo-tests are performed using a flat-on-flat set-up with reciprocal movements. This set-up simulates specific industrial operating conditions of a semi-journal bearing used in a cutting machine. A Design of Experiments (DoE) approach is selected to investigate the effect of the different geometrical micro-texture parameters on the coefficient of friction (COF) and the lifetime of the cast iron samples. An optimum micro-texture geometry leading to a low COF and a long lifetime is determined based on a fractional factorial design. The second goal is to investigate the failure mechanisms of the selected tribo-pair. Failure of the tribo-system is characterized for both textured and un-textured surfaces. Scuffing is found to be the failure mechanism for the un-textured cast iron samples. For the textured cast iron samples, in contrast, two different failure mechanisms are observed depending on the distance between the micro-textures in direction of sliding (DMS). The textured surfaces with a DMS > 3.5 mm fail via the scuffing mechanism, whereas the surfaces with a DMS < 3 mm fail by a different mechanism named the oxidation mechanism. In contrary to the scuffing mechanism, the oxidation failure is found to be more a gradual failure. Based on the experimental observations, two hypotheses are suggested for the scuffing mechanism, and one for the oxidation mechanism. Finally, predicting the lifetime of a tribo-system is of the utmost importance to save costs. The DoE model developed for the lifetime was found to be a weak predictive model due to the sudden nature of scuffing. The accuracy of this model could only be improved by performing large statistics, which is not time and cost effective. Consequently, the last objective of this work is to employ an acoustic emission (AE) technique to detect precisely the surface state of our tribo-system. The application of wavelet packet decomposition, as an advanced signal processing method used for AE signals, is found to be promising for early detection of scuffing. The extension of this work using random forest regression shows the possibility of predicting scuffing 5 min before it occurs.

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Miniaturized tube fixed plug drawing: determination of the friction coefficients and drawing limit of 316 LVM stainless steel

Nicolas Paul Henry Chobaut, Bastien De Marco, Stéphane Dobler, Jean-Marie Drezet, Stefano Mischler, Vance Nguyen

Tube drawing with a ﬁxed plug is investigated experimentally and numerically in order to optimise an industrial pass sequence. Tube drawings are performed on a laboratory drawing bench equipped with force, displacement and temperature sensors. The drawing limit of 316 LVM stainless steel (SS) tubes is determined by varying the plug position and the eﬀect of lubricant is discussed. The numerical model relies on the precise die geometry measured using a contact method and on the mechanical behaviour of SS 316 LVM characterised by tensile tests between 20 °C and 200 °C on annealed tubes. The friction coeﬃcients between tube and die and tube and plug are determined by FE modelling by comparing measured and simulated plug, die and drawing forces. The use of a solid lubricant together with the lubricating oil prevents stick and slip and lowers the friction coeﬃcients. Friction is further decreased by preheating the die. The identiﬁed friction coeﬃcients are discussed in terms of the classic Stribeck friction curves and lubrication is found to be in the hydrodynamic regime.

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Structure and functionality of polyelectrolyte brushes, a surface force perspective

Mark Billing, Harm-Anton Klok, Xingyu Xu, Jing Yu

The unique functionalities of polyelectrolyte brushes depend on several types of specific interactions, including solvent structure effects, hydrophobic forces, electrostatic interactions, and specific ion interactions. Subtle variations in the solution environment can lead to conformational and surface structural changes of the polyelectrolyte brushes, which is discussed mainly from a surface interaction perspective in this review. A brief overview is given of recent theoretical and experimental progress on the structure of polyelectrolyte brushes in various environments. Two important techniques for surface force measurements are described, the Surface Forces Apparatus (SFA) and the Atomic Force Microscope (AFM), and some recent results on polyelectrolyte brushes are shown. Lastly, this review highlights the use of these surface‐grafted polymer films to create functional surfaces for various applications, including non‐fouling surfaces, boundary lubricants, as well as stimuli‐responsive surfaces.

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