Structural-induced lubricity of liquid crystal nanomaterials of cholesterol at metal friction

Experimentally, it was found that with the change in temperature there is a structural-induced increase in the lubricating capacity of liquid-crystal nanomaterials induced by transformations in the cholesteric mesophase. It is shown that in this temperature range, the minimum values of the friction coefficient practically coincide with the peak values of the dynamic viscosity, which together indicates in favor of the ordered state of the cholesterol liquid-crystal structures at these temperatures. As a result, it can be assumed that in this temperature range, spirally twisted layers of liquid-crystal cholesterol molecules with high antifriction action are formed in the friction zone. It is noted that the thickness of the friction-implemented cholesteric liquid-crystal films is sensitive to temperature changes in the contact area, changing the color and energy loss.

Tribology Performance of Surface Texturing Plunger

Plunger pumps are widely used in oil pumping units around the world. The water content of the wellbore is increasing along with the development progress, so the lubricating capacity of the well fluids between the plunger and barrel is decreasing correspondingly. Commonly, the substrate material of the plunger and barrel are stainless steel, and the plunger surface is usually covered with nickel-based coating. Therefore, the performance of the plunger and barrel has been affected due to poor lubrication and eccentric wear. Non-smooth surfaces have been proven to improve the tribology performance in many cases. A surface texturing plunger covered with specific dimples has been prepared by using laser surface texturing technology. The morphology of the surface texturing plunger was characterized and analyzed. The tribology performance of surface texturing plunger samples was tested using standard friction and wear test machines with oil and water lubrication, respectively. The results indicated that surface texturing could effectively reduce the coefficient of friction, and the wear resistance of the surface textured samples has been improved to some extent.

Evaluation of the lubricating power of chemical modified Sesame oil additivated with Cu and Al2O3 nanoparticles

Biolubricant from modified sesame oil (Sesamumindicum L.) was produced. The lubricant base consists of a mixture in a volume ratio of 74 parts of epoxidized sesame and 26 parts of transesterified sesame oil. This mixture was characterized by FT-IR, thermo-oxidative stability was determined and heating and cooling curves were performed, where a crystallization and solidification temperature of -8 °C was obtained. To improve the lubricating capacity of the oil blend concentrations of 0.05, 0.10, 0.15 and 0.20% of copper nanoparticles (NPsCu) and alumina nanoparticles (NPsAl2O3) were added, which had been subjected to tribological tests for the wear scar measurement and characterized by scanning electron microscopy (SEM). The addition of NPsCu and NPsAl2O3 improved the lubricating power of oil base-stock. The NPsCu percentage in modified sesame oil that showed the best lubricating performance was in the interval between 0.15-0.2; as for the oil with NPs2O3 better result was obtained with 0,05% of NPs.

Influence of Coating Thickness and Substrate Elasticity on the Tribological Performance of PEEK Coatings

When a material is subjected to repeated sliding contact, a surface fatigue and crack nucleation may occur on its surface. This damage weakens the material and can lead to debris formation. In many practical engineering assemblies, a thin PEEK (poly-ether-ether-ketone) coating is applied to reduce the damage, since PEEK exhibits wear resistance, corrosion resistance self-lubricating capacity and is lightweight. However, little is known about the effect of coating thickness on the plastic deformation, residual stresses and energy dissipation of PEEK when placed under sliding load. Moreover, the effect of substrate rigidity on coating stresses and deformation under sliding load are also under-researched. Having such knowledge is of significant importance in order to reduce damage of engineering parts and extend their lifetime. In this study, the effects of PEEK coating thickness and substrate elasticity were analyzed using a 3D ball-on-flat finite element model as well as experimental analysis using a linear reciprocating tribometer. The experimental tests were performed with samples that incorporated PEEK coatings of various thicknesses on alumina and steel substrates. It was found that under a constant normal load, stresses, strain and energy dissipation were sensitive to both substrate material and coating thickness. It is shown from both simulation and experiment, the optimum combination, within the range the experiments were conducted, for minimizing residual stress and possible fatigue damage was an alumina substrate with 35μm PEEK coating thickness.

Simulating Design of Magnetic Fluids Lubricating Unit Structure with Porous Material

In order to enhance the lubricating capacity of the magnetic lubrication on the surface of the porous material, a new magnetic lubricating field has been designed by simulating method based on the coupling relationship between the pores and micro-magnets structure. The results show that the output characteristics of magnetic fluids in the pores of the material play a significant role in the design, whereas the output characteristics depend on micro-magnets and the pores’ size such as length and diameter, for example, when the ratio of length/diameter of the pore is larger than 3.2 ,the output capacity of the magnetic fluids in the pores presents a stable value, but when the ratio is smaller than 3.2, the output capacity obviously decreases. It is also found when the distance among the pores changes from 5 mm to 8 mm, the output capacity also presents a stable value; however, the output capacity obviously decreases with the increased distance among the pores beyond 8 mm. Furthermore, the effect of the parameters of micro-magnets structure on the output capacity of magnetic fluids is also investigated in the paper. The research results are helpful to improve the lubricating properties of the magnetic fluids on the surface of the porous material.