Effect of Physical Fields on Highly Resinous Oil

This paper studies the effect of physical fields (i.e. ultrasonic and constant magnetic fields) on structural and energy properties (viscosity, limiting shear stress, pour point, activation energy of viscous flow) as well as kinetic (antioxidant) properties of highly resinous problematic oil. The results were obtained via viscometry, determining of pour point and voltammetric method of oxygen electroreduction. It was shown that the treatment of studied oil by acoustic and magnetic fields lead to decrease in viscosity and temperature parameters. Combined treatment displays an additional reduction of viscosity and pour point

Elastohydrodynamic Lubrication

The development of EHL theory from its tentative beginnings is outlined, with an account of how Ertel explained its relation to Hertz contact theory. The problems caused by the failure of the early numerical analysts to understand that the film thickness depends on only two variables are emphasised, and answers of the form H = F ( P , S ) given. Early methods of measuring the film thickness are described, but these became archaic with the development of optical EHL. The behaviour of surface roughness as it passes through the high pressure region and suffers elastic deformation is described, and the implication for the traditional Λ -ratio noted. In contrast, the understanding of traction is far from satisfactory. The oil in the high pressure region must become non-Newtonian: the early explanation that the viscosity reduction is the effect of temperature proved inadequate. There must be some form of shear thinning (perhaps according to the Eyring theory), but also a limiting shear stress under which the lubricant shears as an elastic solid. It seems that detailed, and difficult, measurements of the high pressure, high shear-rate behaviour of individual oils are needed before traction curves can be predicted.

Evaluation of thixotropy of clay-gypsum based plaster

Introduction. Requirements for mineral based plasters are divided into two groups: technological and performance properties. Plasticity and ease of application are attributed to the technological properties. This determines the requirements for rheological characteristics and, first of all, for the thixotropy of mixtures. The technique is developed and tested on plaster compositions based on clay-gypsum binder which belongs to the category of local binders. Russia has significant reserves of this raw material, but at present it is not used industrially. The main reason is the lack of a scientifically based theory of hardening of the clay-gypsum binder and the formation of its properties without and with modifying additives. The purpose of this research is to develop the composition and technology of application of interior plaster compositions based on stabilized binder. The methodology of studying the rheological properties of dry plaster mixtures based on clay gypsum for interior work and wet rooms is presented. The study of the rheology of clay gypsum mixtures is carried out for the first time, it determines scientific novelty. Recommendations for the use of clay gypsum plaster mixtures determine the practical significance of the research. Materials and methods. Methods of evaluation of thixotropic properties of plaster mixtures based on clay-gypsum binder in laboratory environment are realized. Results. The valid intervals of the water-cement ratio are established which ranged from 0.46 to 0.50, determined by the limiting shear stress and the actual sliding from the vertical wall. Conclusions. The possibility of using a clay-gypsum binder in dry plaster mixtures for interior decorative works in the premises, in particular, confirmed by research. It allows us to assess the actual adhesion of plaster coatings to the concrete based surfaces and to brickwork.

Experimental and Numerical Investigations of the Stribeck Curves for Lubricated Counterformal Contacts

The Stribeck curve is an important means to demonstrate the frictional behavior of a lubricated interface during the entire transition from boundary and mixed to full-film lubrication. In the present study, a new test apparatus has been built that can operate under rolling–sliding conditions at a continuously variable speed in an extremely wide range, approximately from 0.00006 to 60 m/s, covering six orders of magnitude. Hence, a complete Stribeck curve can be measured to reveal its basic characteristics for lubricated counterformal contacts. The measured curves are compared with numerical simulation results obtained from an available unified mixed elastohydrodynamic lubrication (EHL) model that is also capable of handling cases during the entire transition. A modified empirical model for the limiting shear stress of lubricant is obtained, and a good agreement between the measured and calculated Stribeck curves is achieved for the tested base oils in all the three lubrication regimes, which thus well validates the simulation methods employed. Both the experimental and numerical results indicate that the Stribeck curves for counterformal contact interfaces behave differently from those for conformal contacts. When the rolling speed increases at a fixed slide-to-roll ratio, the friction continuously decreases even in the full-film lubrication regime due to the reduction of the lubricant limiting shear stress caused mainly by the rise of the surface flash temperature. In addition, the test results indicate that the boundary additives in a commodity lubricant may have considerable influence on the boundary lubrication friction but that on the friction in the mixed and full-film lubrication appears to be limited.