Lubrication Coefficient Research Articles

Spreading of Liquid Drops over Dry Porous Layers: Complete Wetting Case

Spreading of small liquid drops over thin dry porous layers is investigated from both theoretical and experimental points of view. Drop motion over a porous layer is caused by an interplay of two processes: (a) the spreading of the drop over already saturated parts of the porous layer, which results in an expanding of the drop base; (b) the imbibition of the liquid from the drop into the porous substrate, which results in a shrinkage of the drop base and an expanding of the wetted region inside the porous layer. As a result of these two competing processes, the radius of the drop goes through a maximum value over time. A system of two differential equations is derived to describe the evolution with time of radii of both the drop base and the wetted region inside the porous layer. This system includes two parameters: one accounts for the effective lubrication coefficient of the liquid over the wetted porous substrate and the other is a combination of permeability and effective capillary pressure inside the porous layer. Two additional experiments are used for an independent determination of these two parameters. The system of differential equations does not include any fitting parameter after these two parameters are determined. Experiments were carried out on the spreading of silicone oil drops over various dry microfiltration membranes (permeable in both normal and tangential directions). The time evolution of the radii of both the drop base and the wetted region inside the porous layer are monitored. All experimental data fell on two universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and of the wetted region inside the porous layer on dimensionless time. The predicted theoretical relationships are two universal curves accounting quite satisfactorily for the experimental data. According to our theory prediction, (i) the dynamic contact angle dependence on the same dimensionless time as before should be a universal function and (ii) the dynamic contact angle should change rapidly over an initial short stage of spreading and should remain a constant value over the duration of the rest of the spreading process. The constancy of the contact angle on this stage has nothing to do with hysteresis of the contact angle: there is no hysteresis in our system. These conclusions again are in good agreement with our experimental observations.

Surface Treatment of Acetylsalicylic Acid with Lubricants by the Wurster Method.

Surface treatment of acetylsalicylic acid (ASA) crystals was examined in a Wurster fluid bed system with water-soluble and water-insoluble lubricants. The influence of the coating process on the flowability, the compressibility and the dissolution rate of the crystals was studied, and the results were compared with the corresponding parameters of ASA crystals processed by a conventional (mixing) method. The coating materials were Carbowax® 6000 as water-soluble and stearin as water-insoluble lubricant. The control sample was unprocessed (commercial) ASA crystals. The Strea-l fluid bed coater with the Wurster column could be used for the production of a lubricant coating on crystal surfaces. The coated crystals, in comparison with mixed samples, had very good compactibility, cohesivity and compressibility values. Their lubrication coefficient was higher and the friction work was less than those of mixed crystals. The dissolution of the active agent could be regulated by the lubricant coat. The rate of dissolution of ASA was primarily promoted by a film coat of Carbowax® 6000 from a capsule.

Contribution to the study of new graft copolymer matrices for drug delivery systems. Technological study

Cellulose and starch derivatives have long been used for their ability to sustain the release of drugs. The use of polymer mixtures represents a potential way of achieving the required release properties. It is known that the release of a drug from a matrix system is produced by diffusion through the gel formed. The aim of this work is focused on the study of viscosity, flowability and compactibility values of polymers for drug delivery matrices. Previously synthesized graft copolymers were used: hydroxypropyl starch—methyl methacrylate (HS-MMA), carboxymethyl starch—MMA (CS-MMA) and hydroxypropyl cellulose—MMA (HC-MMA). It is known that polymers with the highest swelling capacity give highest viscosity value. HC-MMA and CS-MMA graft copolymers can be considered pseudogels because through mechanical-dynamical analysis, an intersection point between the storage modulus and the loss modulus can be seen. All the polymers fulfilled in general the requirements for good flow which will predict a good die filling during the tableting. However, L-products have the higher values for the compactibility and lubrication coefficient and the lower values for ejection and maximum upper force. Also, from the study of gel formation done with these products, we can state that L-products will probably lead to more interesting excipients to the obtaining of control release matrices.

In vitro evaluation of sustained-release matrix tablets prepared with new modified polymeric carbohydrates

The study of the rheological and compressional properties of sustained-release matrix tablets prepared with new polymers obtained by graft copolymerization of methyl methacrylate (MMA) on various carbohydrates is the main purpose of this work. All the mixtures had good flow properties, showing cellulose derivatives mixtures the best values. Powders without homopolymers showed a statistically significant lower flow rate than mixtures with homopolymers. All the mixtures with hydroxypropyl starch polymers showed better statistically significant compactibility and plasticity than the hydroxypropyl cellulose derivatives. Practically all the mixtures accomplished with the requirements of direct compression excipients in relation with lubrication coefficient. All the tablets elaborated with mixtures with homopolymers required a total work lower than the mixtures without homopolymers. Tablets from all products passed the test for weight uniformity, except the tablets of carboxymethyl starch (CS-MMA) without homopolymer. Only hydroxypropylcellulose tablets demonstrated an acceptable friability. Only standard tablets and CS-MMA without homopolymers exhibited disintegration times higher than 30 min. A clearly different behaviour between the new polymers and the standards was observed in relation with dissolution test.

水溶性研削油剤の作用に関する研究(第2報)

In this paper propose is a model with which grinding results can quantitatively be given from the viewpoint of cooling and lubricant actions of water soluble type grinding fluids. Experimental results are compared with calculated results by using this model. Main conclusions are as follows: (1) Cooling action is measured as heat transfer rate of grinding fluids and lubricant action is measured as coefficient of lubricant on the grinding wheel surface. (2) Dimensionless grinding results Gr* are given by: Gr*=μ*α·h*-β, where h* and μ* are dimensionless cooling and lubricant moduli defined from heat transfer rate and coefficient of lubricant. (3) Close agreements are obtained between experimental and calculated values of workpiece surface temperature and grinding forces.

Drilling Fluids for Highly Deviated Wells in North Sea Petroleum Drilling

Summary This paper reviews drilling operations at eight highly deviated wells in three North Sea fields, with emphasis on the use and engineering of drilling fluids to drill the wells and to maintain a stable wellbore until protective casing is set and cemented. Wells with angles deviated more protective casing is set and cemented. Wells with angles deviated more than 500 from vertical are considered highly deviated. The eight wells have an average angle of 560 and an average course length of 3300 m (10,827 ft). In most cases, angle buildup occurs in the measured-depth range of 600 to 1400 m (1,969 to 4,593 ft) at a rate of 20/30 m (98 ft). Figures showing a cross section of the well geometry and pertinent mud and drilling information are presented with each well study. Introduction Drilling fluids play an integral part in any drilling operation. Their main functions are (1) to lubricate and to cool the bit and drillstring, (2) to maintain hole stability (i.e., provide a gauge-size hole), (3) to carry drilled cuttings to the surface, and (4) to prevent the entry of subsurface fluids into the annulus.When a deviated well is drilled, Functions 1 and 2 warrant special consideration because the drillstring tends to lie along the underside of the slope formed by the well in the formations. The increased area of contact between the drillstring and borehole wall, and the increased force of contact as the angle becomes more severe, present the drilling and mud engineers with a challenge. Carrying capacity of the drilling fluid also merits particular attention because the vertical lifting power of the mud decreases as the angle of deviation increases and the cuttings tend to be rolled out of the hole along the low side rather than be lifted out.Pipe rotating torque and drag are important considerations when a deviated well is drilled. Factors affecting the amount of torque and drag are (1) dog-leg severity (in both the horizontal and vertical directions), (2) angle of deviation from the vertical, (3) bottomhole-assembly makeup (number, type, and position of stabilizers), (4) mud lubricity coefficient, and (5) hole stability (torque and drag become more severe if the hole becomes undergauge).Of these factors, the last two can be enhanced by mud engineering. Muds formulated with oil as the continuous phase (oil muds) have a very low lubricity coefficient, as shown by field results (Table 1). At the same time, oil muds provide a very stable borehole wall (especially in claystone) to provide a firm base or area of contact between drillstring/stabilizers and the formation. Also, oil muds have an inherently low fluid loss, giving added assurance against sticking because of differential pressure in underpressured permeable formations (especially produced zones). Most operators do not approve the use of oil muds in the produced zones). Most operators do not approve the use of oil muds in the North Sea until they have proved that water-base muds are unfeasible (too costly in terms of mud cost and drilling time) for drilling development wells through the strata overlying and within the oil field. Specialized products available to treat water-base muds to overcome the problems of products available to treat water-base muds to overcome the problems of drilling highly deviated wells include lubricant surfactants and solid-bead lubricants. These products have been applied with success. Most water-base muds now used for development drilling in the North Sea are inhibited with an electrolyte (potassium chloride, gypsum, lime, or, in some cases, seawater alone, which may contain sufficient electrolyte to inhibit clay hydration) and various types of polymer. The advantages of using efficient and sufficient mud-solids control equipment (maintaining a low mud-solids content without excessive dilution) are recognized by all operators. This is essential to maintain an effective and economical mud system, either water- or oil-base, for development drilling. JPT p. 703

A Study of the Lubrication and Dynamics of Geometrically Perfect, Lightly Loaded, Cylindrical Roller Bearings with Particular Reference to Shaft Loci

The principal objective of this paper is to ascertain and quantify the cyclic movement of the centre of a shaft in a geometrically perfect, lubricated, cylindrical roller bearing exhibiting initial clearance and subjected to a light and steady load. The movement may be important in relation to the accuracy of location of shafts in roller bearings, and it is shown that a detailed consideration of the rolling element assembly predicts some interesting effects. The study also covers more conventional features of bearing performance such as lubricant film thickness and coefficient of friction, and shows the effect of squeeze to be negligible under steady bearing loads.

Quantitative separation of tin from manganese, iron and chromium by electrolysis

Recent developments in nanofluids indicate that the addition of nanoparticles to water-based drilling muds can alleviate many drilling problems, including wellbore instability, lost circulation, torque and drag force, differential pipe sticking, and low drilling rates. In this study, the addition of hydrophilic Gilsonite nanoparticles (HGNs) to water-based drilling mud was investigated, and its effects upon the well-cleaning process, rheological properties, filtration loss reduction, lubricity characteristics, and, more importantly, on the differential sticking of the base fluid were evaluated. Hence, initially, the HGNs were characterized by means of Fourier transform infrared spectroscopy, the dynamic light scattering technique, as well as thermogravimetric and differential thermogravimetric analysis. The results showed that after the addition of HGNs, the rheological behavior of the base mud before the hot roll process was improved, and, interestingly, after the hot roll at 149 °C and 4 h, the characteristics of the sample mud were significantly retained, compared to those of the base mud. Also, after the hot roll, the plastic viscosity (PV) improved, the yield point (YP) was remarkably maintained, and the ratio of YP/PV was enhanced. On the other hand, the American Petroleum Institute (API) filtration loss was reduced by 36%, and, additionally, after the hot roll process, the filtration loss reduction and the mud cake thickness in high-pressure high-temperature conditions diminished by 79.4% and 50%, respectively. After the hot rolling process, the lubricity coefficient and torque percentage dropped by 15% and 13.63%, respectively. Also, the HGNs reduced the differential sticking coefficient and increased the likelihood of differential sticking release of the base fluid by 61.5%.