Mathematical model of a ferromagnetic lubricant in the presence of a porous coating in the bearing structure

Based on the flow equation of a ferromagnetic liquid lubricant for a “thin layer”, the continuity equation and Darcy’s equation describing the flow of a lubricant in a porous body, an exact self-similar solution of wedge-shaped sliding support with a porous coating of the surface of the support ring is found, taking into account the dependence of the viscosity of the ferromagnetic lubricant and the permeability of the porous coating with the incomplete filling of the working gap. Analytical dependencies for the velocity and pressure fields in the lubricating and porous layer are obtained. Also, the main operating characteristics are determined load-bearing capacity and friction force. The numerical analysis of the theoretical results showed that the bearing capacity of the bearings can be increased by 8-12% in the range of the studied load-speed modes. At the same time, the coefficient of friction is reduced by 14-16%. To verify and confirm the effectiveness of the obtained theoretical models, an experimental study of a modified wedge-shaped sliding support on TP-22C, MS-20 oil and their mixture with various additives was carried out. As a result of theoretical and experimental studies, tribotechnical characteristics were determined that allow us to judge the presence of a long-term friction mode.

Methods for determining the bearing capacity and extreme pressure properties of lubricants used in heavy-loaded tribodynamic couplings of metallurgical machines and units

To solve contact problems related to the study of the interaction between a lubricated or non-lubricated friction pair, we used standard equipment - friction machines and tribometers. However, the use of factory-made research equipment does not always allow us to accurately answer the questions concerning the tribotechnical characteristics of friction and wear processes under specific operating conditions. A review of the literature on the technical capabilities of testing machines showed that their main drawback is the inability to programmatically set the modes of acceleration of the tribological system and tracking slippage in real-time. The study revealed the need to develop a methodology for investigating the extreme pressure properties of liquid lubricants in the tribocoupling acceleration mode, which is caused primarily by the effect of high contact loads acting in the contact areas of friction pairs, e.g. gears, rolling bearings, etc. when technological machines and equipment start and reach the operating speed. The paper considers a modernized friction machine capable of programmatically setting acceleration modes and investigating tribodynamic processes of lubricated frictional couplings. We developed a technique that makes it possible to evaluate the efficiency of a liquid lubricant during acceleration and its effect on the wear of a lubricated contact based on the use of the modernized friction machine.

DEVELOPMENT OF THE COMPONENT COMPOSITION OF THE BIODEGRADABLE LIQUID LUBRICANT FOR SAW CHAINS

The procedure of working out of the component composition of the biodegradable liquid lubricant for the saw chains is shown. The experimental statistical mathematical model is developed for the optimization of the formulation of the main base taking into account the necessary viscosity and temperature parameters. At the same time the kinematic viscosity of the base body at the temperature of 40 °C and its pure point are chosen as the optimization criteria and the following three factors are used as the optimization parameters: the content of vegetable (rapeseed) oil in the composition, the viscosity of mineral oil at the temperature of 40 °C and the content of an adhesive additive in the base composition. The component composition of the lubricant is adjusted to achieve the required level of tribological properties of the saw chain oil and to ensure the stability of all its characteristics during storage (at least 12 months) and operation at a given level of biodegradability (at least 90 %). In particular, the biodegradable calcium sulfonate grease OIMOL KSC BIO was selected as an additive to improve tribological parameters. The special adhesive additive for vegetable oils of the Petrolad 484BD brand is used to increase the sedimentation stability, and the highly refined oil of group III according to the API standard is recommended to use as a mineral component. The developed lubricant has the following characteristics: density at 15 °C — 926 kg/m3, kinematic viscosity at 40 °C — 47.3 mm2/s, kinematic viscosity at 100 °C — 9.9 mm2/s, viscosity index — 202, pour point — –28 °C, flash point — 272 °C, critical load — 872 N, welding load — 1,600 N, wear index at 200 N — 0.39 mm, biodegradability — 93 %.

Experimental Investigation on the Wind-driven Runback Motion of Water Droplets over Solid Surfaces with Different Wettabilities

Aircraft icing is widely recognized as one of the most serious weather hazards to flight safety. Specially designed hydro-/ice-phobic coatings are currently undergoing development for aircraft icing mitigation. It was found that hydro-/icephobic coatings would delay the ice accretion iover airframe surfaces so that the impacted supercooled water droplets could be blown away by the airflow from the airframe surface before being frozen into ice. It is of fundamental importance to understand the wind-driven runback behavior of water droplets over surfaces treated with different coatings, since the corresponding knowledge would be very helpful and essential to develop more efficient anti-/de-icing systems for aircraft icing protection. With the rapid development of surface engineering, a series of specially designed surface coatings succeed in icing mitigation using airflow to remove the remained water. While various hydro-/ice-phobic coatings/surfaces have been developed in recent years, the “state-of-the-art” icephobic coatings/surfaces can be generally divided into three categories, i.e., 1). Lotus-leaf-inspired superhydrophobic surfaces (SHS) with micro-/nano-scale surface textures to achieve very high contact angles (typically > 150°); 2). Pitcherplant-inspired slippery liquid infused porous surfaces (SLIPS) with a layer of liquid lubricant (which is immiscible with water) being sandwiched between ice and solid substrate materials; and 3). Icephobic elastic materials/surfaces with deformable structures/surfaces. SHS has a water droplet contact angle (CA) larger than 150° and a sliding angle (SA) less than 10° . SHS always has a hierarchical structure which is similar to the lotus leaf, and water droplets on SHS appear as water beads which can easily roll off the surface by wind or gravity before frozen. Another strategy to reduce ice adhesion strength to a solid surface is to use a layer of liquid lubricant, which is immiscible with water, between ice and the solid surface. The use of such lubricated surfaces was investigated as early as 1960s, and has gained increasing attentions again recently with the introduction of a concept called Slippery Liquid-Infused Porous Surfaces (SLIPS). SLIPS concept is inspired by the Nepenthes pitcher plants, which have evolved highly slippery, liquidinfused micro-textured rim to capture insects. SLIPS surfaces were not only found to be able to suppress ice/frost accretion by effectively removing condensed moisture even in high humidity conditions, but also exhibit at least an order of magnitude lower ice adhesion than most SHS coatings. More recently, elastic materials/surfaces, such as Polydimethylsiloxane or PDMS in short, which would be structurally deformed/altered dynamically upon applying extra mechanical stress, have also been suggested for icing mitigation. Elastic materials display ultra-low adhesion to ice due to their low work of adhesion and liquidlike deformability, while maintaining good mechanical durability due to their solid-like rigidity. It is found that water droplets would not only be more readily rebounding away from the surface after impingement, but also be able to roll away before frozen due to the hydrophobicity of PDMS. Considering the differences in wettabilities and mechanisms of water repellency, it is necessary to have a systematic understanding of how efficient the surfaces are when the aerodynamic force is applied to remove the adhered water droplets. In the present study, a comprehensive experimental campaign was conducted to characterize the transient runback behaviors of wind-driven water droplets over the surfaces of test plates coated with different hydro-/icephobic coatings (i.e., SHS, SLIPS and PDMS). A high-resolution Particle Image Velocimetry (PIV) system was used to achieve quantitative measurements of the velocity field of the airflow around the wind-driven water droplets on the test surfaces with different wettabilities. With the detailed PIV measurements of the airflow field around the runback water droplets and the droplet profiles, the aerodynamic forces and the adhesion forces acting on the water droplets were estimated. While Fig. 1 shows the experimental setup used in the present study, Fig. 2 to Fig. 3 given some of the typical measurement results. More measurement results and comprehensive analysis and discussions will be provided in the full version of this research paper.

Influence of the heat transfer field on anomalous lubricant film formation in elastohydrodynamic lubrication conditions

The influence of the heat transfer field on anomalous film formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant film shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. 1-Dodecanol was used as the representative lubricant to develop anomalous film shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. The heat transfer field significantly influenced the formation of anomalous film shapes. The anomalous film shapes approximated the shape of a conventional EHL film with increasing ambient temperature. However, a thickened part of the lubricant film remained, although the phase diagram of 1-dodecanol suggested it to be in the liquid state.

Tribological Properties of 2D Materials and Composites—A Review of Recent Advances

This paper aims to provide a theoretical and experimental understanding of the importance of novel 2D materials in solid-film lubrication, along with modulating strategies adopted so far to improve their performance for spacecraft and industrial applications. The mechanisms and the underlying physics of 2D materials are reviewed with experimental results. This paper covers some of the widely investigated solid lubricants such as MoS2, graphene, and boron compounds, namely h-BN and boric acid. Solid lubricants such as black phosphorus that have gained research prominence are also discussed regarding their application as additives in polymeric materials. The effects of process conditions, film deposition parameters, and dopants concentration on friction and wear rate are discussed with a qualitative and quantitative emphasis that are supported with adequate examples and application areas and summarized in the form of graphs and tables for easy readability. The use of advanced manufacturing methods such as powder metallurgy and sintering to produce solid lubricants of superior tribological performance and the subsequent economic gain from their development as a substitute for liquid lubricant are also evaluated.

Biomimetic Slippery PDMS Film with Papillae-Like Microstructures for Antifogging and Self-Cleaning

Transparent materials with antifogging and self-cleaning ability are of extreme significance for utilization in outdoor solar cell devices to alleviate the performance loss and maintenance costs. Herein, with inspiration from the anti-wetting surfaces in nature, regular papillae-like microstructure arrays (PMAs) inspired by lotus leaves were designed via a common UV lithography combined with a soft replication. Subsequently, the biomimetic slippery polydimethylsiloxane (PDMS) film (BSPF) inspired by the pitcher plant was fabricated successfully by infusing with hydrophobic liquid lubricant. The resultant surface has hydrophobic surface chemistry, a slippery interface, PMAs structure. The wettability, optical characteristic, antifogging property and self-cleaning ability of the PMAs-based BSPF were characterized experimentally. The film displays excellent optical transmittance, antireflection, antifogging, and self-cleaning properties, which is superior to the flat PDMS film (FPF). Remarkably, an average reflection of ∼11.3% in the FPF was reduced to ∼8.9% of the BSPF. In addition, after gradient spray test for 120 s, the antifogging efficiency was close to 100% for the BSPF surface in comparison with the flat PDMS film (FPF), biomimetic PDMS film (BPF) and flat slippery PDMS film (FSPF) (35%, 70% and 85%). Furthermore, we also discovered that the BSPF surface exhibited a better self-cleaning performance toward a variety of liquids than solid dust.