Lubrication effectiveness, calculating

In all experiments, the measured viscosities of the blends were lower than those calculated by the linear mixing rule. Moreover, this lubricating effect induced by the LCP was greatest with blends having optimal viscosity ratio. 

Dr. R I Tavlor (Shell Global Solutions (U.K.), Chester, UK). Have you compared your micro-ehl calculations with simpler dry contact models where the lubricant effectively acts as a spacer layer and each asperity is treated by Hertz theory ... 

The three most likely types of operational service misuse are overloading, incorrect lubrication and the presence of contaminants. Overloading is primarily due to the use of too small or too weak a gear unit, and this may be the result of false economy (installing an available unit for an application beyond its capacity) or failure to cater for the effects of shock loads in calculations of power rating. 

The methodology discussed previously can be applied to the study of colloidal suspensions where a number of different molecular forces and hydrodynamic effects come into play to determine the dynamics. As an illustration, we briefly describe one example of an MPC simulation of a colloidal suspension of claylike particles where comparisons between simulation and experiment have been made [42, 60]. Experiments were carried out on a suspension of AI2O3 particles. For this system electrostatic repulsive and van der Waals attractive forces are important, as are lubrication and contact forces. All of these forces were included in the simulations. A mapping of the MPC simulation parameters onto the space and time scales of the real system is given in Hecht et al. [42], The calculations were carried out with an imposed shear field. 

An emerging subdiscipline of tribological simulation involves the study of tribochemical reactions—that is, reactions that are activated by pressure and shear. These reactions alter the structure of lubricants and films that are used to protect surfaces from wear. Understanding the effects of these reactions on the intended behavior of these films is of utmost importance. However, simulation studies of tribochemical reactions have been impeded by the difficulty in accurately describing changes in chemical bonding. In a limited number of cases, this can be achieved with the use of reactive FFs, as noted above, whereas in other cases, one must resort to expensive quantum chemical calculations. In this section, we will describe two studies where such methods were used to examine tribochemical reactions. 

The effects of applying 0.48% of Texspray Compound and 1.09% of Spraycot 8853 are summarized in Table I. In both cases there is a marked drop in the number of particles (an average of 84.8%) and in dust concentration (70.5% for the Texspray and 84.8% for the Spraycot). The dg calculated algebraically decreases from 1.88 un for the control cotton to 1.44 urn for the two lubricated cottons. The cumulative probability curves of the dust emitted from the cottons containing additives become bimodal. These changes in the nature of the cumulative distribution curves suggest that the fraction of particles removed is not constant for all dieuneters. 

When the gap width between two particles becomes very small, numerical calculations involved in both the bispherical coordinate method and the boundary collocation technique are computationally intensive because the number of terms in the series required to be retained to achieve a desired accuracy increases tremendously. To solve this near-contact motion more effectively and accurately, Loewenberg and Davis [43] developed a lubrication solution for the electrophoretic motion of two spherical particles in near contact along their line of centers with the assumption of infinitely thin ion cloud. The axisymmetric motion of the two particles in near contact can be approximated as the pairwise motion of the spheres in point contact plus a deviation stemming from their relative motion caused by the contact force. The lubrication results agree very well with those obtained from the collocation method. It is shown that near contact electrophoretic interparticle... 

Lubricating oil often contains additives that react with alkali to form metal soaps, and the saponification number expresses the amount of base that will react with 1 g of the sample when heated in a specihc manner. In the test method (ASTM D-94, IP 136), a known weight of the sample is dissolved in methyl ethyl ketone or a mixture of suitable solvents and the mixture is heated with a known amount of standard alcoholic potassium hydroxide for between 30 and 90 min at 80°C (176°F). The excess alkali is titrated with standard hydrochloric acid, and the saponification number is calculated. The results obtained indicate the effect of extraneous materials in addition to the saponifiable material present. 

An elastohydrodynamic problem customarily involves the calculation of the pressure distribution in the lubricant film, allowing for the effects of pressure on the properties of the fluid and on the geometry of the interface. The shape of the lubricant film and its thickness are functionally related to the pressure distribution. The technologically important solutions are for bounding surfaces of counterformal geometry, which in most cases can be approximated satisfactorily by two opposing circular cylinders. 

The response of scuffing to load can be treated as a temperature effect. Spikes and Cameron [35] showed that for steel rubbing at medium speed (1.34 cm/s) lubricated by palmitic acid in n-hexadecane a linear relation between tog C and is obtained when is calculated from the formula... 

Another semi-empirical expression derives from the widely used work of Frankel Acrivos (1967) who assumed a dense suspension of monomodal spherical particles, where the particle separation is small compared to the particle radius. In this limit the dissipation is taken to be governed by lubrication forces associated with the relative velocity of the particles along their line of centers. In the low volume fraction or dilute limit, this effect vanishes and the dissipation is close to that associated with the externally applied shear rate. Sengun Probstein (1989a) calculated the dissipation in a unit cell assuming the total dissipation at any volume fraction to be given by the linear sum of the two dissipations. 

The ribbon was placed between two split billet halves of the same polyethylene, and the assembly coextruded through conical brass dies which had an included entrance angle of 20 and nominal extrusion draw ratios, EDR, of 12, 25, and 30. No lubricant was used. The EDR calculated from the displacement of the line mark was in good agreement with the nominal EDR defined as the ratio of entrance to exit cross-sectional area of a die. The extruded films were used only for the evaluation of the effect of deformation components on the resultant morphology and properties. The semiperipheral coextrudates obtained simultaneously from the extruded assembly were used for the x-ray study of the deformation mechanism for extrusion drawing. 

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