Lubrication Science最新文献

Discarded tempering lubricants retained significant reuse potential, making their recycling a vital step in reducing resource wastage and wastewater treatment costs in the strip steel industry. Hence, developing an accurate, rapid evaluation indicator for recycled fluid concentration was essential for facilitating this process. Research showed that among common evaluation indicators for metal fluids, three—electrical conductivity, refractive index and total base number (TBN)—due to their high linear correlation with tempering lubricant concentration (R ² > 0.995), could be utilised to monitor the dynamic changes in the concentration of tempering lubricants. Subsequent experiments on reused tempering lubricants revealed that electrical conductivity, significantly altered by iron powder (7%–24% variance), and refractive index, impacted by hydraulic oil (3% deviation), highlighted contaminant challenges; yet, filtration effectively mitigated iron powder's effect on TBN. Finally, A 17-day reused tempering lubricants simulation demonstrated consistent effectiveness of the three indicators in monitoring the need to update tempering lubricant concentration. However, in terms of sensitivity, precision, and particularly stability and relative mean deviation, the TBN concentration evaluation indicator outperformed, with TBN (3.38%) < Refractive Index (7.92%) < Electrical Conductivity (11.05%). This indicates the TBN method's superior stability over conductivity and refractive index methods, with its accuracy deviation below 2%, making it a stable, simple and reliable metric worthy of broader adoption.

Used lubricating oil is generated by various machinery after extended operation. It is also referred to as spent mobile oil. Extremely hazardous waste lubricating oil is detrimental to the environment because it produces oxidative products when additives break down. Used lubricating oil is classified as a hazardous waste substance and has a negative impact on the environment. Polychlorinated biphenyls (PCBs), carcinogenic substances and other impurities make lubricating oil poisonous and pose a serious threat to human health and the environment. Re-refining is considered the preferred technology for resource conservation, waste minimisation and reduced environmental hazards. The present study focuses on optimising the method of re-refining waste lubricating oil. The effects of various operating parameters such as refining time, refining temperature, solvent-to-used oil ratio and flocculant dosage have been extensively studied to maximise the percentage recovery of lubricating oil. Optimum process parameters are (i) a refining time of 80 min, (ii) a refining temperature of 48°C, (iii) solvent-to-waste oil ratio of 5:1 (w/w) and (iv) a flocculant dosage of 2 g/kg of solvent; the optimum yield was found to be 75% with the solvent extraction method and 78% with the extraction–flocculation method, respectively. The purity and physico-chemical properties of the recovered oil were thoroughly analysed using Fourier transform infrared spectroscopy and ASTM standard methods. It was concluded that refined oil can effectively reduce the ongoing oil crisis and create a clean, healthy environment.

The study involved the modification of a melamine sponge (SP) through the introduction of polydopamine (PDA) and octadecylamine (ODA), resulting in the creation of three distinct sponge types: PDA/ODA@SP, PDA@SP and ODA@SP. The successful modification of PDA and ODA onto the surface of the sponge was confirmed through the utilisation of scanning electron microscopy and x-ray photoelectron spectroscopy. Consequently, the resulting sponges exhibited a unique micro–nano composite structure. Wettability testing was conducted to assess the properties of the sponges, revealing that the PDA/ODA@SP sponge demonstrated hydrophobic superlipophilic characteristics. Moreover, a series of 10 repeated oil–water separation experiments indicated that the PDA/ODA@SP sponge achieved an impressive separation efficiency of up to 97%, demonstrating its exceptional oil–water separation capabilities and reusability. Additionally, investigations utilising soybean oil and engine oil demonstrated the composite sponge's superior absorption capabilities for fatty acids and hydrocarbons.

This article presents the preparation of environmentally friendly water-soluble lubricant additives. Adipic acid (AA), sebacic acid (SA) and dodecanedioic acid (DA) were individually subjected to esterification reactions with polyethylene glycol 1500 (PEG1500) to prepare a class of water-soluble polyether esters (AAPEE1500, SAPEE1500 and DAPEE1500) (referred to as XAPEE1500s) that exhibit excellent water solubility and do not contain environmentally harmful elements. First, the molecular structure characterisation and functional group analysis of these additives will be conducted using an infrared spectrometer and a nuclear magnetic resonance spectrometer. Subsequently, the frictional properties of the additives in the base liquid (deionised water) will be investigated using an SRV-V tribometer, Falex pin-on-disc tribometer and screw torque tester. The surface morphology of wear scars will be characterised and analysed using scanning electron microscopy (SEM) and a non-contact 3D profilometer. Finally, the lubrication mechanism of the DAPEE1500 additive will be analysed using X-ray photoelectron spectroscopy (XPS). The results indicate that the optimal lubrication performance is achieved when the added mass fraction of DAPEE1500 is at 3%. Compared with 0.5 wt% DAPEE1500, the average friction coefficient of 3 wt% DAPEE1500 decreased from 0.285 to 0.122, and the wear volume decreased from 25.52 × 10⁻⁵ μm³ to 10.96 × 10⁻⁵ μm³. The lubrication mechanism of polyether ester is the result of the combined action of its polar ester functional groups and long carboxylic acid chains in the structure. These polar functional groups can form a relatively firm adsorption film on the friction surface, while the long carboxylic acid chains act as a brush-like isolating layer, thus demonstrating superior anti-wear and anti-friction performance.

This article presents an experimental study about boundary slippage on the film thickness of hydrodynamic lubrication (HL) using a custom-made slider-on-disc bearing testing apparatus. The interfaces with different affinity were obtained by surface energy modification of sliders with various oleophobic coatings, which are characterised by their contact angle (CA) and contact angle hysteresis (CAH). To study the mechanism of interfacial slip on HL under different wettability constraints, the film thickness and velocity profiles under shear were measured using interference and fluorescence photobleached method, respectively. The results showed that the CAH could better characterise the influence of interface effect on the film thickness of HL, which was explained by the correlation between CAH and the interface potential barrier. Furthermore, it was found that the slip velocity increased with lubricant viscosity and shear rate, which can be explained by the spatial heterogeneity of the flow in conformal contact and the critical shear stress slip model.

The ILs ([Li (synthetic esters)] NTF₂) were prepared by the in situ synthesis method. The tribological behaviour of the ILs to friction pairs of Ti-6Al-4V titanium alloy against silicon nitride was studied by SRV-V under different concentrations and friction frequencies; the wear scar was studied by SEM, XPS and TOF-SIMS. The results showed that the friction coefficient and wear loss decreased gradually with the increase of the LiNTF₂ content; when the LiNTF₂ content reached a certain value (10%), the friction coefficient and wear loss did not change much. Tribofilm composed of titanium oxide, Al₂O₃, TiFO₂, AlOF₂, Ti₂O₄F and Al₂O₃F plays a major role in lubrication and anti-friction effect.

A key issue for nano-additive to effectively exert tribological function is to ensure its entrance to and adhesion on the frictional contact surfaces. But the adhesion of nano-additive on the rubbed surfaces under oil lubrication faces the challenge of the competitive adsorption of lubricant base oil thereon. In this study, oleic acid–modified ultra-small cerium oxide (OA-CeO₂) nanoparticle was synthesised by one-pot liquid-phase surface-modification method in the presence of OA as the surface modifier. The susceptibility of non-polar poly–alpha olefin 6 (PAO6) and polar diisooctyl sebacate (DIOS) base oils to the as-prepared OA-CeO₂ nano-additive was investigated, and the effect of the OA-CeO₂ nano-additive on the friction-reducing and anti-wear abilities of the two kinds of base oils towards a steel–steel sliding contact was investigated with four-ball friction and wear tester. Furthermore, the tribological mechanism of the adsorption and deposition of the OA-CeO₂ nano-additive on the surface of friction steel and the competitive adsorption of base oil were discussed. Characterisations by scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy demonstrate that the as-prepared OA-CeO₂ nanoparticle is of a spherical shape and has an ultra-small average size of 1.2 nm. As the lubricant additive in PAO6 and DIOS base oils, the OA-CeO₂ nano-additive exhibits different tribological properties, which is attributed to the difference in the base oils' polarity. Namely, the CeO₂ nanoparticle in the non-polar PAO6 base oil is more easily adsorbed on the rubbed surface of the steel–steel sliding contact, thereby forming the CeO₂ deposition film to improve the tribological properties of the base oil. However, the CeO₂ nanoparticle added in polar DIOS base oil is difficult to form the CeO₂ deposition film, because of the competitive and preferential adsorption of the polar base oil on the rubbed steel surface. Therefore, it is imperative to select the base oils with proper polarity to better exert the friction-reducing and anti-wear functions of the OA-CeO₂ nano-additive.

As an emerging two-dimensional material, black phosphorus (BP) has excellent tribological properties, but the poor dispersion of BP in oil inhibits its application in friction to some extent. Surface modification is one of the effective methods to solve the dispersibility of BP, and the use of nano-Fe₃O₄ dotted on the surface of BP improves the dispersion stability of BP in soybean from 3 days to about 15 days. Compared with pure soybean oil, friction coefficient and wear rate of the addition of 0.12 wt% BP/Fe₃O₄ are reduced 65% and 78%, respectively. To elucidate the excellent tribological mechanisms of BP/Fe₃O₄ as additives in soybean oil, the compositional and structural characterisation of the abrasion mark surface was studied accordingly. On the one hand, soybean oil reacts with BP/Fe₃O₄ to form a composite tribo-film during the scraping process. This tribo-film composed of amorphous carbon, iron oxide and phosphorus oxide nitrides prevents direct contact between the sliding interfaces. On the other hand, BP and Fe₃O₄ nanoparticles form a mechanical rollerball structure, which can further reduce interfacial friction and wear through synergistic lubrication. The results provide new insights into the design of additives in biomass lubricating oils and propose new application prospects for BP in the field of lubricating additives.

Interaction between the cold rolling oil and substrate at the roll bite has always intrigued the tribologists. In plant conditions, it has been observed that occurrences of surface defects on cold-rolled FHCR coils increase with the ageing of cold rolling emulsion. In this study, the rolling oil was aged at different lab conditions to replicate 6 and 11 months of rolling oil ageing from a particular cold rolling mill. The studies indicated an increase in acid number of the oil. Tribological studies indicated an increase in CoF along with an increase in wear phenomenon on the substrate. The removability of the surface oil becomes difficult with ageing which could lead to potential surface oil residues remaining on the strip after degreasing, resulting in surface defects and dirty coils after annealing. Deterioration in anti-stain property is also observed as ageing progresses. The deterioration in performance is mainly governed by the depletion in additives and generation of free fatty acids within the rolling oil bath. Proper maintenance of the bath ensures lesser defect formation.