Lubrication Science最新文献

Polyol-ester lubricants have been used and developed for aviation gas turbine engines for many decades. The newest MIL-PRF-23699 lubricant class, called enhanced ester (EE), provides the best combination of thermal stability, load carrying capability, boundary lubrication and compatibility with fluoroelastomer O-rings. Two candidate EE Class formulations and one high thermal stability class formulation conforming to MIL-PRF-23699G were evaluated for oil degradation with up to 3000 h of bearing operation. Lubricant degradation was studied using VIM VAR M50 bearings with M50 and silicon nitride balls under two operating conditions using two bearing test rigs. Oil degradation in terms of oxidation time, total acid number and viscosity was studied as a function of time with varying results for the three lubricants.

Nanoadditive with multifunctional properties holds commercial importance in the lubricant industry. Herein, GO-N-PPDA was synthesised as nanoadditive by functionalizing graphene oxide (GO) using N-phenyl-p-phenylenediamine and characterised by Fourier transform infrared spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy analysis. The antioxidant behaviour of GO-N-PPDA was analysed by 2,2-diphenyl-1-picryl-hydrazyl-hydrate. The nanoparticles dispersed mineral base oil (N-250) in 0.2%, 0.4%, 0.6% (w/v) concentrations were evaluated for tribological, rheological and thermophysical analysis by ASTM methods. The flow behaviour of the nanolubricant shows shear thickening behaviour with an increase in shear rate. In contrast, tribological results indicate a significant reduction in wear scar diameter and coefficient of friction to the base oil. Furthermore, GO-N-PPDA shows improved thermophysical properties compared with the mineral base oil. Thus, GO-N-PPDA shows multifunctional behaviour in terms of viscosity index, pour point, antioxidant activity, rheology and tribological properties.

To reduce the agglomeration of graphene and improve the synergistic friction-reducing and anti-wear action of graphene loading copper, one-step preparation of reduced graphene oxide/copper(RGO/Cu) nanoparticles by freeze-drying method was used, the influence of process parameters on particles size of RGO/Cu is studied by orthogonal experiments. The microstructures of RGO/Cu nanoparticles are characterized by SEM and AFM, and the tribological properties of RGO/Cu nanoparticles are studied on a tribometer. The results show that the purity of RGO/Cu nanoparticles prepared by freeze-drying was higher, and the copper nanoparticles 100–200 nm are uniformly attached to the graphene surface. It was found that RGO/Cu nanoparticles have better friction reduction and anti-wear properties than graphene mono-agent as lubricant additive. The synergistic anti-friction and anti-wear performance are better at the addition of 0.10 wt% for RGO/Cu nanoparticles. Compared with the base oil, the friction coefficient decreases by 23.1%, and the width of wear scar decreases by 62.5%.

The friction and wear reducing properties of ammonium thiomolybdate as a water-soluble lubricant additive were evaluated using a pin-on-disck tribometer on a steel-steel contact. The tribological performance of aqueous solutions of thiomolybdate prepared at concentrations between 0.1 and 0.3 wt% Mo were evaluated at the same load (10 N), entrainment speed, sliding distance and temperature. Although there is a reduction of friction and wear compared with pure water, a significant difference is observed, depending on the additive concentration. SEM/EDAX and Raman spectroscopy analyses of the wear tracks of specimens tested at concentrations below 0.3 wt% Mo reveal the formation of FeS which is responsible for gradually reducing the coefficient of friction from values between 0.30 and 0.5 down to ~0.11. At 0.3 wt% Mo, the analyses indicated the formation of a MoS₂ which keeps the coefficient of friction in ~0.05, the lowest recorded value.

In this paper, the static performance analysis of journal bearing having full and partial surface waviness has been presented. The surface waviness is to be considered in the full, first half, second half, and pressure-increasing and decreasing regions of the bearing for analysis. The effect of surface waviness is considered by modifying the lubricant flow governing Reynolds equation with the film thickness equation and it is solved with the finite element method to get performance parameters like bearing load capacity, friction coefficient, and so forth operating under eccentricity ratios range of 0.2–0.8. The waviness geometrical parameters like waviness numbers and amplitudes are also considered in circumferential, axial, and both directions in the selected regions. The maximum performance has been found for waviness in the full and pressure-increasing region in the circumferential direction at a high eccentricity ratio.

The performance of cylinder liner piston ring (CLPR) that worked under harsh conditions significantly affected the reliability of diesel engines. Nano-copper lubricant additives have recently been introduced due to their good anti-wear properties. This study aims to gain insights into the interactions between concentrations of nano-copper lubricant additives and the tribological performance of CLPR. Tests are performed on a reciprocating sliding test rig under different operating conditions, and the tribological performances are characterized by the friction coefficient, wear mass losses, and morphologies of worn surface. The experimental results indicated that the optimal concentration of nano-copper additives is 2 wt%. Additionally, deposition of the Cu nanoparticles on the worn surface during the friction process facilitates the formation of the mending layer. These findings would aid to provide a technical reference for the application of nano-copper additives in diesel engines.

Dust stop seals are widely used in powder and rubber mixing industries. Design of the sealing system requires a continuous supply of pressurised lubricant, which is not recycled because of the risk of contamination. There is also the potential of large volume leakage of oil due to poor sealing, increasing operational costs and necessitating remedial measures to avoid environmental protection. Furthermore, the seal faces are prone to failure in relatively short periods of time due to reduced gap and lubricant leakage. The paper presents an analytical method and numerical predictions based on Reynolds equation under combined hydrodynamic and hydrostatic conditions with the entrant lubricant through hydraulically loaded feedholes. The validity of these methods is ascertained through comparison with a more complex but time-consuming solution of Navier–Stokes equations. The numerical predictions allow for determining the prevailing tribological contact conditions and assessing its suitability for evaluating the sealing performance of mixing machinery.

Research was focused on understanding the degradation kinetics of cold rolling oil used in the rolling mill at Tata Steel. Aged rolling oil leads to various surface defects. Ageing phenomenon is influenced through thermo-mechanical behaviour, oxidation, hydrolysis and presence of iron fines. Ageing of cold rolling oil in presence of iron fines was systematically performed at various temperature followed by thermo-mechanical wear tests. With variation in intensity of ageing, change in physico-chemical parameters and fatty acid distribution (FAD) within triglycerides could be observed. The impact of the controlled ageing on performance parameters like lubrication, evaporation kinetics and oxidative stability were also studied. Thermo-oxidative ageing depletes antioxidant concentration within the rolling oil resulting in rapid oxidation of unsaturated fats. This leads to rapid build-up of high molecular weight ingredients resulting in formation of fatty acid soaps or scum. The resultant scum negatively impacts the boundary lubrication and evaporation kinetics of rolling oil.