Kreivaitis, Raimondas

Water is attractive as a base fluid due to its availability and environmental friendliness. To enhance its lubricity, environmentally friendly additives must be applied. This study combined protic ionic liquid and several nanoparticles to form hybrid additives for an oil-in-water lubricant. The performance of these additives was evaluated using wettability, tribo-testing, and worn-surface analysis. The tribo-test employed a ball-on-plate reciprocating tribometer that used bearing steel/bearing steel and WC/bearing steel friction pairs. The results were compared with those obtained using two commercial additives. It was found that the investigated additives are promising candidates for water-based lubricants, as they exhibit comparable wettability. Moreover, they outperform the reference samples in terms of lubricity. According to the results, the suggested lubrication mechanism includes enhanced wettability, composite tribo-film formation, surface polishing, and mending.

Lubricity is critical for maintaining the reliability of mechanical systems. Consistent monitoring of in-service lubricants and the development of new formulations require reliable test equipment and standardised procedures. The four-ball tribo-test is among the most widely used and acknowledged methods. Like other methods, its effectiveness depends on the procedures and specimens used. Therefore, in this study, we aim to emphasise the influence of ball-specimen surface parameters on lubricity results, a factor that is often insufficiently acknowledged in reported experiments. Accordingly, lubricity tests of the same motor oil were performed using balls obtained from different suppliers. The experimental procedure was identical for all ball specimens. It was found that balls from different series exhibit distinct surface properties, leading to differences in lubricity even when the same lubricating oil was used. Based on the results obtained, it was concluded that the outcome is a multiparameter solution and not the result of a single surface parameter. On the other hand, if balls from the same series are used, the results will meet the standard requirements for repeatability regardless of their surface conditions.

In general, the properties of alloy steels and special steels provide significant advantages to the end product. However, these properties often complicate the machining process, particularly in terms of machinability. The formation of a built-up edge (BUE) is a widely recognized phenomenon in the machining of austenitic stainless steels. It is closely associated with changes in cutting performance, tool wear, and surface integrity. Complex adhesive and plastic deformation processes drive BUE development under severe contact conditions at the tool–chip interface. Consequently, the geometrical characteristics and surface roughness of cutting inserts are expected to significantly influence the initiation and growth of adhered material layers on the cutting edge. The insert shape dictates the cutting forces and chip flow. In contrast, insert roughness (and micro-geometry) strongly influences friction and material sticking at the tool–chip interface. This article analyzes the processes in the material-tool contact system and their relationship to geometry, rake-face surface parameters, and BUE development when turning AISI 316L steel under dry and minimal lubrication conditions. The results indicate that BUE development is associated with the combined effects of chip-breaker geometry, rake-face roughness parameters (Rq, Rsk, and Rku), and cutting conditions. Cooling, including the use of an ionic liquid–water suspension, reduces the insert’s susceptibility to adhesion.

Guolių plieno rutulių paviršiaus kokybė yra vienas iš veiksnių, galinčių turėti reikšmingos įtakos trinties ir dilimo procesams tepamose mechaninių sistemų trinties porose. Skirtingų gamybos serijų guolių plieno rutuliai dažnai pasižymi nevienoda paviršiaus mikrogeometrija – nuo lygaus ir poliruoto iki grublėto, pabraižyto ar turinčio kitokius defektus, šių skirtumų įtaka tribologiniam elgesiui lieka nepakankamai išnagrinėta. Šiame darbe atlikta keturių skirtingų gamybos serijų guolių plieno rutulių palyginamoji tribologinė analizė. Pradinė paviršiaus būklė įvertinta optiniu mikroskopu, medžiagos kietumas nustatytas Vikerso metodu. Tribologiniai bandymai atlikti keturių rutulių mašinoje pagal DIN 51350 standartą, naudojant variklinę alyvą SAE 5W-30. Bandymo metu fiksuojamas sukimo momentas ir trinties koeficientas, o po bandymų išmatuoti nudilimo dėmių dydžiai. Tyrimo rezultatai atskleidė ryšį tarp medžiagos kietumo, pradinės paviršiaus kokybės ir tribologinių charakteristikų: didesnio kietumo serijos pasižymėjo mažesniu trinties koeficientu ir mažesnėmis nudilimo dėmėmis. Vizualiai lygiausio paviršiaus serija demonstravo didžiausią nudilimą dėl žemesnio kietumo, kas rodo, jog kietumas yra svarbesnis ilgaamžiškumo veiksnys nei paviršiaus išvaizda. Gautos išvados gali būti naudingos inžinieriams, priimantiems sprendimus dėl guolių parinkimo ir kokybės vertinimo.

Prižiūrint automobilį svarbu laiku keisti variklio alyvą. Eksploatuojant automobilį keisti variklio alyvą yra rekomenduojama kas 10000–15000 km. Didėjant kilometražui ir nekeičiant alyvos laiku, pradeda mažėti alyvos tepimo savybės. Kuo mažiau tepami visi variklio komponentai, tokie kaip: cilindrų sieneles, stūmokliniai žiedai, dujų paskirstymo mechanizmas, tuo labiau mažėja variklio tarnavimo laikas. FTIR spektroskopija galima nustatyti, kurie alyvos produktai atsiranda eksploatuojant automobilį ir kaip kinta jų kiekis vis didėjant kilometražui. FTIR spektroskopija yra ištiriamas antioksidantų, vandens, oksidacijos, suodžių, nitratų, sulfatų, glikolio, AW (anti-wear) ir degalų kiekis alyvoje. Atliekant šį tyrimą sutaupoma laiko ir tiksliai išsiaiškinama, kurį alyvos parametrą nagrinėti detaliau. Alyva buvo naudojama nauja ir pirktas reikalingas kiekis to pačio gamintojo. Pravažiavus eksploatacinį laikotarpį (10000 km) buvo pakeista alyva. Gavus rezultatus matoma, kad alyvoje nuo pat pirmų tūkstančių kilometrų atsiranda glikolis iroksidai. Oksidų kiekis priklauso nuo eksploatavimo sezono, važiavimo režimų bei degiojo mišinio teisingo uždegimo. Kuo automobiliu važiuojama agresyviau-aukštesniais sūkiais, žemomis pavaromis, tuo oksidų kiekis didėja labiau. Taip pat jeigu važinėjama su netvarkinga uždegimo sistema, alyvoje taip pat padidėja oksidų kiekis. Glikolis automobilyje atsiranda dėl kelių priežasčių. Tai variklio bloko ir variklio galvos tarpinės defektas ar net variklio galvos ir variklio bloko paviršiaus išsikraipymas. Keičiant alyvąreikėtų atsižvelgti ne tik į pravažiuotą kilometražą, bet ir eksploatavimo laikotarpį, važiavimo režimus irvariklio būklę.

Alyvos tribologinės savybės yra esminis veiksnys užtikrinant efektyvų mechaninių sistemų darbą ir ilgaamžiškumą. Pastaraisiais metais daug dėmesio skiriama nanodalelėmis modifikuotoms alyvoms, kurios gali pagerinti tepimo savybes, sumažinti trintį ir dilimą. Grafeno nanodalelės, pasižyminčios puikiu mechaniniu stiprumu, cheminiu inertiškumu ir aukštu šiluminiu laidumu, yra vienas iš perspektyviausių tribologinių priedų. Tačiau dauguma tyrimų apsiriboja trumpalaikėmis analizėmis, o ilgalaikiai eksperimentai yra itin reti. Šiame darbe buvo tiriama 5W–20 alyva, modifikuota grafeno nanodalelėmis, naudojant keturių rutulių tribologinį bandymą. Eksperimentai atlikti 1500 aps./min. greičiu, esant cikliniam apkrovos modeliui: 100 ciklų su 20s pauzėmis iki 1000 ciklų. Trinties momentas buvo registruojamas viso bandymo metu, o dilimo pėdsakai analizuoti mikroskopinėmis priemonėmis. Gauti rezultatai parodė, kad grafeno nanodalelėmis praturtinta alyva reikšmingai sumažino trinties koeficientą ir dilimo dydį, palyginti su standartine 5W–20 alyva. Tyrimo rezultatai rodo, kad ilgalaikiai tribologiniai eksperimentai su grafeno nanodalelėmis gali suteikti naujų įžvalgų apie jų stabilumą ir veiksmingumą ekstremaliomis sąlygomis, o gautos išvados gali būti naudingos tobulinant variklines alyvas bei optimizuojant jų naudojimą automobilių ir pramonės sektoriuose.

This study aims to develop a novel, eco-friendly lubricant engineered to meet antiwear requirements, reduce energy consumption, and improve performance reliability. A series of deep eutectic solvents (DESs) was successfully synthesized using a facile, one-step approach by combining eco-friendly L-Proline with diols and two distinct carboxylic acids as hydrogen bond donors. The resulting DES lubricants exhibit favourable physicochemical properties and excellent lubrication performance. Notably, the L-Proline /Oxalic acid DES demonstrates superior lubrication performance, resulting in a substantial decrease in both friction (~46–78 %) and wear volume (~61–91 %) compared to PEG 200 and choline chloride/urea across all tested temperatures. Furthermore, in-depth analysis of the worn surfaces reveals the formation of a tribo-chemical film derived from L-Proline based DESs, consisting of hydrocarbon (CxHy), oxy metal nitride (Ti-N-O) fragments, along with titanium oxide/ hydroxide-rich layer. This film plays a vital role in delivering effective lubrication for titanium alloy surfaces. These findings pave the way for designing eco-friendly, high-performance lubricants for sustainable lubrication practices.

Water as a base lubricating fluid is popular due to its low cost, nontoxicity, fire resistance, and availability. However, water as a base fluid needs to be enhanced to meet the requirements of specific applications. Therefore, this study aims to evaluate the potential of protic ionic liquids (PILs) to improve the tribological properties of water-based lubricants. The lubricity of several PILs, namely diethanolamine oleate and erucate, and tert-octylamine oleate in the water-based lubricating fluid was experimentally investigated using a ball-on-plate tribometer. In addition, kinematic viscosity, corrosiveness, and wettability were investigated. Environmental compatibility, such as soil phytotoxicity, was evaluated. The results show that the wear and friction reduction ability was significantly improved by using up to 1 wt. % of PILs. It was speculated that the polar molecules of PIL adsorb on the lubricated surface. Introducing PILs reduces the surface tension of water, resulting in better wettability. The investigated PILs showed no phytotoxicity, which makes them attractive as environmentally friendly additives.

Water as a base lubricating fluid is popular due to its low cost, nontoxicity, fire resistance, and availability. However, water as a base fluid needs to be enhanced to meet the requirements of specific applications. Therefore, this study aims to evaluate the potential of protic ionic liquids (PILs) to improve the tribological properties of water-based lubricants. The lubricity of several PILs, namely diethanolamine oleate and erucate, and tert-octylamine oleate in the water-based lubricating fluid was experimentally investigated using a ball-on-plate tribometer. In addition, kinematic viscosity, corrosiveness, and wettability were investigated. Environmental compatibility, such as soil phytotoxicity, was evaluated. The results show that the wear and friction reduction ability was significantly improved by using up to 1 wt. % of PILs. It was speculated that the polar molecules of PIL adsorb on the lubricated surface. Introducing PILs reduces the surface tension of water, resulting in better wettability. The investigated PILs showed no phytotoxicity, which makes them attractive as environmentally friendly additives.

The control of lubricity induced by electric potential is appealing for numerous applications. On the other hand, the high polarity of ionic liquids facilitates the adsorption of equally charged molecules onto polar surfaces. This phenomenon and its consequences are well understood at the nanoscale; however, they have recently garnered significant attention at the macroscale. This study investigates the lubricity of trihexyltetradecylphosphonium dicyanamide, a phosphonium ionic liquid, when used as a neat lubricant in reciprocating sliding under electrically charged conditions. Two different polarities with the same potential were applied to the friction pair of bearing steel against bearing steel while monitoring electrical contact resistance. The lubricity was evaluated through measurements of friction, wear, surface morphology, and composition. It was found that the application of electric potential significantly alters the lubricity of the investigated ionic liquid where a positive potential applied to the ball resulted in the least damaging situation. The recorded electrical contact resistance enabled the monitoring of tribofilm formation during reciprocation. It was found that there was minimal to no separation between interacting surfaces when the ball was changing direction.