Home About us Contact
|
Home About us Contact | ||
|
|
||
Lubrication
Terms modified by Lubrication Selected AbstractsUseful Adjuncts to Harvest Split-Thickness Skin GraftsDERMATOLOGIC SURGERY, Issue 12p2 2004Hunter H. Sams MD Background. Split-thickness skin grafts are useful for repair of defects that are not amenable to primary closure or secondary intention healing. Because of the thinness of split-thickness skin grafts, damage to the graft and curling are common with standard harvesting techniques. Adjunctive methods for harvesting split-thickness skin grafts have not been well elucidated in the literature. Methods. Lubrication and a tongue depressor facilitate even harvesting of the split-thickness skin graft. A semipermeable membrane is applied to the split-thickness skin graft donor site before harvesting the skin graft. This aids with harvesting and minimizes trauma to the graft. Conclusion. Use of lubrication, a tongue depressor, and a semipermeable membrane are useful adjuncts to harvesting split-thickness skin grafts. [source] Viscocapillary model of slide coating: Effect of operating parameters and range of validity,AICHE JOURNAL, Issue 10 2009K. Tjiptowidjojo Abstract Slide coating is one of the premetered high-precision coating methods. The layer thickness is set by the flow rate and web speed. The uniformity of the layer, however, can be affected by other operating conditions. Modeling the flow in the coating bead is necessary in developing the range of operability conditions where the layer is adequately uniform. Lubrication and viscocapillary models have been used to describe the flow and some of the operability limits of different coating processes. However, the available models of slide coating were developed with adhoc hypotheses that compromise their accuracy. We present a critical review of the available viscocapillary models and proposed changes to improve its range of applicability. The accuracy of the model is tested by comparing its predictions to the solution of the full two-dimensional Navier-Stokes equation. The model is valid at low capillary and Reynolds number regime and at low gap-to-wet thickness ratio. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] TEXTURE PROFILE ANALYSIS , HOW IMPORTANT ARE THE PARAMETERS?JOURNAL OF TEXTURE STUDIES, Issue 5 2010ANDREW J. ROSENTHAL ABSTRACT A starch-glycerol gel was subjected to a two-bite compression test using two sample-instrument geometries, various speeds of compression and strain levels, both with lubrication or not. Results were interpreted using the primary characteristic terminology previously defined in Texture Profile Analysis. Compression speeds from 0.1 to 10 m/s showed a logarithmic relationship with hardness, cohesiveness, corrected cohesiveness and adhesiveness. Gels survived compression to strains of 0.90 without failing, strain levels from 0.25 to 0.90 resulted in an exponential rise in hardness with increasing strain and linear reduction in corrected cohesiveness. Lubrication had no significant influence on any of the measured parameters and an application of force with different sample-instrument geometry revealed that parallel plates and plungers only had an influence on gel hardness. Caution is urged when researchers modify the test protocol from 75% deformation with parallel plates. A minimum crosshead speed of 2 mm/s is recommended. PRACTICAL APPLICATIONS Texture Profile Analysis has been widely applied to test solid and semisolid foods; however, some researchers deviate from the original test protocol. This article attempts to show how modifying the parameters in the test protocol can influence the apparent properties of the sample. [source] Approximate Formula for the Contact between Truncated Surfaces and Frictional Characteristics of a Journal Bearing in Mixed LubricationLUBRICATION SCIENCE, Issue 3 2004M. Nonogaki Abstract This paper presents an approximate formula for the contact of a non-Gaussian distribution of truncated surfaces, which is useful for mixed lubrication theory, and gives a method for the determination of the truncation parameters in this formula from a measured roughness profile. Using this approximate formula for a contact, the approximate formula for the friction coefficient of a journal bearing in mixed lubrication, which was previously proposed by the authors, is modified for truncated surfaces, and the frictional characteristics are demonstrated for various parameters of truncated roughness using the modified formula. [source] Lubrication of the i-gel supraglottic airway and the classic laryngeal mask airwayANAESTHESIA, Issue 1 2010D. Chapman No abstract is available for this article. [source] The use of lubrication in flexible fibreoptic nasendoscopy: a randomized controlled trialCLINICAL OTOLARYNGOLOGY, Issue 4 2005D.D. Pothier Objectives:, To determine how lubrication of the endoscope prior to flexible fibreoptic nasendoscopy affects levels of patient discomfort and pain during endoscopy. To assess the extent to which lubrication affects the ease of nasendoscopy and the quality of the image obtained. Design:, Single blind, randomized controlled trial. Setting:, Outpatient clinic of the Department of Otolaryngology at a secondary level referral centre. Participants:, A total of 150 participants selected sequentially from patients requiring a nasendoscopy where the endoscope would be passed far enough to view the larynx. Patients requiring topical anaesthetic were excluded. All participants who were entered in the study completed the study. Endoscopy was performed by all grades of medical staff. Main outcomes measures:, Levels of discomfort and pain experienced by the participants were assessed by a visual analogue scale (VAS). Difficulty of passing the scope was indicated by the endoscopist using a VAS, as was the quality of image obtained. Results:, There was no significant difference between mean scores for pain or discomfort of the lubricated and unlubricated groups (P = 0.46 and P = 0.82 respectively). Scores for difficulty of passing the scope were significantly lower in the lubricant group (P = 0.003) but loss of image was significantly greater (P = 0.008). Conclusions:, Lubrication of the endoscope prior to nasendoscopy does not reduce levels of discomfort or pain for the patient, but increases ease in insertion for the operator. However, this may be at the expense of reduced image quality. [source] Useful Adjuncts to Harvest Split-Thickness Skin GraftsDERMATOLOGIC SURGERY, Issue 12p2 2004Hunter H. Sams MD Background. Split-thickness skin grafts are useful for repair of defects that are not amenable to primary closure or secondary intention healing. Because of the thinness of split-thickness skin grafts, damage to the graft and curling are common with standard harvesting techniques. Adjunctive methods for harvesting split-thickness skin grafts have not been well elucidated in the literature. Methods. Lubrication and a tongue depressor facilitate even harvesting of the split-thickness skin graft. A semipermeable membrane is applied to the split-thickness skin graft donor site before harvesting the skin graft. This aids with harvesting and minimizes trauma to the graft. Conclusion. Use of lubrication, a tongue depressor, and a semipermeable membrane are useful adjuncts to harvesting split-thickness skin grafts. [source] Decreased Tear Expression with an Abnormal Schirmer's Test Following Botulinum Toxin Type A for the Treatment of Lateral Canthal RhytidesDERMATOLOGIC SURGERY, Issue 2 2002Seth L. Matarasso MD background. Inactivation of muscles of facial expression by chemodenervation with botulinum toxin remains an off-label indication. Nevertheless, it continues to be a safe and effective technique to improve dynamic rhytides and is the treatment of choice for the hypertrophic lateral fibers of the orbicularis oculi muscle that can cause the superimposed crow's feet. objective. Although infrequent and self-limiting, the complication of unexpected muscle weakness from toxin diffusion or erroneous placement is documented. methods. However, injection into the pretarsal portion of the orbicularis oculi muscle resulting in unilateral ocular irritation and diminished tear expression as evidenced by a dry eye and an abnormal Schirmer's test has rarely been reported. Direct injection into the pretarsal fibers of the muscle as opposed to diffusion of the toxin into the muscle fibers or the lacrimal gland was consistent with the onset of action of the toxin and the prolonged duration of the ocular symptoms. results. Treatment consisted of ocular lubrication until the effects of the toxin dissipated and muscle tone returned. Subsequent treatment did not result in a result in a recurrence of adverse sequelae. conclusions. Facial muscles are small, not isolated, and often have fibers that interdigitate. An important factor in the administration of botulinum toxin is the identification of the muscles responsible for the corresponding rhytide. Precise knowledge of muscular anatomy and function will aid in minimizing this and other potential complications. [source] Ultrastructural localization of salivary mucins MUC5B and MUC7 in human labial glandsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2010Monica Piras Piras M, Hand AR, Tore G, Ledda GP, Piludu M. Ultrastructural localization of salivary mucins MUC5B and MUC7 in human labial glands. Eur J Oral Sci 2010; 118: 14,18. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci As a result of their presence throughout the mouth in the submucosa or between muscle fibers, minor salivary glands secrete directly and continuously into the oral cavity, providing mucosal surfaces with highly glycosylated proteins that are active in bacterial aggregation and in oral tissue lubrication. In this study, we investigated the ultrastructural localization of the MUC5B and MUC7 mucins in human labial glands by means of a postembedding immunogold technique. Thin sections of normal human labial glands, obtained during surgery, were incubated with polyclonal antibodies to human salivary mucins MUC5B and MUC7, and then with gold-labeled secondary antibodies. Specific MUC5B reactivity was found in the secretory granules of mucous cells of all glands examined, and was associated with the luminal membrane of duct cells. MUC7 labeling was observed in the granules of both mucous and seromucous secretory cells of the glandular parenchyma. Quantitative analyses demonstrated that seromucous granules have higher immunogold labeling densities for MUC7 than mucous granules. Our immunohistochemical data extend the results of previous light microscopic studies of MUC5B and MUC7 localizations, pointing out the significant contribution of human labial glands in the secretion process of these two mucins. [source] The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling,sliding contactFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2000D. I. Fletcher Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum,disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth. [source] Coupled lubrication and Stokes flow finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003Matthew S. Stay Abstract A method is developed for performing a local reduction of the governing physics for fluid problems with domains that contain a combination of narrow and non-narrow regions, and the computational accuracy and performance of the method are measured. In the narrow regions of the domain, where the fluid is assumed to have no inertia and the domain height and curvature are assumed small, lubrication, or Reynolds, theory is used locally to reduce the two-dimensional Navier,Stokes equations to the one-dimensional Reynolds equation while retaining a high degree of accuracy in the overall solution. The Reynolds equation is coupled to the governing momentum and mass equations of the non-narrow region with boundary conditions on the mass and momentum flux. The localized reduction technique, termed ,stitching,' is demonstrated on Stokes flow for various geometries of the hydrodynamic journal bearing,a non-trivial test problem for which a known analytical solution is available. The computational advantage of the coupled Stokes,Reynolds method is illustrated on an industrially applicable fully-flooded deformable-roll coating example. The examples in this paper are limited to two-dimensional Stokes flow, but extension to three-dimensional and Navier,Stokes flow is possible. Copyright © 2003 John Wiley & Sons, Ltd. [source] Change of sexual function after midurethral sling procedure for stress urinary incontinenceINTERNATIONAL JOURNAL OF UROLOGY, Issue 8 2008Duk Yoon Kim Objectives: To compare sexual function in women before and after the midurethral sling procedure for stress urinary incontinence (SUI). Methods: A total of 75 women undergoing surgery for SUI between September 2005 and September 2006 were recruited for this study. Those who completed the Female Sexual Function Index (FSFI) preoperatively and 6 months postoperatively were included in the analysis. The FSFI is a validated, 19-item questionnaire, which assesses six domains of sexual function, including desire, arousal, lubrication, orgasm, satisfaction, and pain. Results: Data were analyzed for 47 patients. Overall sexual function after the midurethral sling procedure was not significantly different. There were no significant differences in overall sexual function or any of the individual FSFI domain scores between patients with and without concomitant posterior colporrhaphy. There were no significant differences in sexual function between the transobturator and the retropubic surgical routes. Conclusions: There is no significant change in overall sexual function in women undergoing the midurethral sling procedure. Posterior colporrhaphy and operative methods do not affect overall sexual function. [source] Preparation and tribological properties of polyetheretherketone compositesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2010Dangsheng Xiong Abstract Polyetheretherketone (PEEK) is a thermoplastic engineering plastic with excellent mechanical properties. In this article, PEEK and its composites filled with ultrahigh-molecular-weight polyethylene (UHMWPE) were prepared by vacuum hot-pressing method. Tribological properties of these materials were investigated by block-on-ring friction and wear rig. An alloy (CoCrMo) ring and a ceramic (Si3N4) ring were used as friction pairs. The experiments were conducted under deionized water lubrication (DWL), saline lubrication (SL), and calf serum solution lubrication (CSSL). Worn surfaces morphology was observed and analyzed by metallographic microscope. The results indicated that friction coefficients of PEEK/UHMWPE composites were effectively reduced when compared with pure PEEK. When the materials slid against the alloy (CoCrMo) ring, wear rates of PEEK/UHMWPE were also effectively reduced when compared with pure PEEK. Wear mechanisms of PEEK were mainly ploughing and slight scratches under CSSL condition, whereas the quantity of the ploughing and scratches for PEEK/20%UHMWPE were significantly reduced. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Phospholipid composition of articular cartilage boundary lubricantJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2001A. V. Sarma The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of molecules separate opposing surfaces, occurs under severe loading. This study was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a boundary lubricant. The different types of phospholipid adsorbed onto the surface of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes identified were quantified by a phosphate assay. Gas chromatography and electrospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanolamine (27%) and sphingomyelin (32%) were the major components of the lipid layer on the normal cartilage surface. For each lipid type, a mixture of fatty acids was detected, with a higher percentage of unsaturated species compared to saturated species. The most abundant fatty acid observed with all three lipid types was oleic acid (C18:1). Additional work to further quantify the molecular species using electrospray ionization mass spectrometry is recommended. © 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] TEXTURE PROFILE ANALYSIS , HOW IMPORTANT ARE THE PARAMETERS?JOURNAL OF TEXTURE STUDIES, Issue 5 2010ANDREW J. ROSENTHAL ABSTRACT A starch-glycerol gel was subjected to a two-bite compression test using two sample-instrument geometries, various speeds of compression and strain levels, both with lubrication or not. Results were interpreted using the primary characteristic terminology previously defined in Texture Profile Analysis. Compression speeds from 0.1 to 10 m/s showed a logarithmic relationship with hardness, cohesiveness, corrected cohesiveness and adhesiveness. Gels survived compression to strains of 0.90 without failing, strain levels from 0.25 to 0.90 resulted in an exponential rise in hardness with increasing strain and linear reduction in corrected cohesiveness. Lubrication had no significant influence on any of the measured parameters and an application of force with different sample-instrument geometry revealed that parallel plates and plungers only had an influence on gel hardness. Caution is urged when researchers modify the test protocol from 75% deformation with parallel plates. A minimum crosshead speed of 2 mm/s is recommended. PRACTICAL APPLICATIONS Texture Profile Analysis has been widely applied to test solid and semisolid foods; however, some researchers deviate from the original test protocol. This article attempts to show how modifying the parameters in the test protocol can influence the apparent properties of the sample. [source] Friction Behavior of Dental Porcelain with Different Leucite Particle SizesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008Yi Zhang The effect of leucite particle size on the friction behavior of dental ceramics was investigated using a ball-on-disc tribometer. The experimental loads were 20, 30 and 40 N and the tests were conducted unlubricated and under the lubrication of an artificial-saliva. Dental ceramics with different leucite particle sizes, i.e. 0.5±0.2, 1.2±0.3 and 5±2 ,m, were prepared by sintering the mixture of a low temperature frit and leucite powders with different average particle sizes (0.4, 1 and 5 ,m). The results showed that the leucite particle size, experimental load and lubrication media had not significant effects on the steady-state friction coefficient of the samples. However, the evolution of the friction coefficient was different, which could be generally classified into two categories, i.e. with and without an abrupt increase in the friction curve. The changes in experimental condition and leucite particle size were attributed to such difference. [source] Dietary effects on growth, plasma lipid and tissues of rats fed with non-conventional oil of Telfairia occidentalisJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 13 2004Ibironke A Ajayi Abstract The nutritional value of Telfairia occidentalis seed and seed oil available in local market was studied in rats. The average values of the proximate analysis on dry matter basis were 203 g kg,1 crude protein, 536.3 g kg,1 fat, 39 g kg,1 ash, 95 g kg,1 crude fibre and 43.7 g kg,1 carbohydrate, while the moisture content was 75 g kg,1. The mineral analyses showed that T occidentalis seeds contain potassium (3280 mg kg,1), sodium (1230 mg kg,1), magnesium (60.8 mg kg,1), calcium (60.8 mg kg,1) and iron (13.0 mg kg,1). The oil extracted from the seed sample showed physicochemical properties that suggest its suitability for edible and industrial uses. The oil contained high levels of unsaturated fatty acids, oleic and linoleic, which accounted for 63.22% of total fatty acids recovered, while palmitic acid (27.4% of the oil by weight) was the most prevalent saturated fatty acid in the oil. No trace of eleostearic acid was detected in the oil. The effect on physical appearance, weight gain, organ weight, tissue and plasma cholesterol and triacylglycerol levels was determined in rats fed a diet containing 5% T occidentalis oil. These were compared with those of rats fed a control diet (0% T occidentalis oil) over an 8 week study period. Weekly monitoring of the rats showed good physical appearance and steady weight increase. The test rats were not anaemic and no mortality was recorded. While there was a significantly higher (p < 0.05) level of cholesterol in the heart of test rats compared with the control, there was a significantly lower (p < 0.05) plasma cholesterol level, suggesting that T occidentalis seed oil can be used to lower plasma levels of cholesterol. Histological examination of the sections of the heart, liver, kidney and spleen of the test rats revealed varying degrees of pathology. These include artherosclerotic changes in the walls of vasa vasori and lymphatics in the heart and hyaline degeneration of myofibrils, fatty infiltration of hepatocytes, and glomerular and tubular degeneration in the kidneys. These lesions may have been due to the effect of fatty acids, especially erucic acid, in the seed oil, which at 1.24% (less that the 5% conventional allowable limit for edible oils) may be intolerable for rats and may be unsuitable for human consumption. The seed oil may be used for industrial purposes such as soap making, lubrication and cosmetics for which it is well suited. Copyright © 2004 Society of Chemical Industry [source] Lubrication mechanism of poly(vinyl chloride) compounds: Changes upon PVC fusion (gelation)JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2005James W. Summers Poly(vinyl chloride) (PVC) compounds perform best with adequate metal lubrication and polymer-to-polymer lubrication of PVC primary particle flow units. Much of the mechanism for the lubrication of PVC has been elucidated over the years. One point has not been completely understood, which is the "lubricant failure" at higher processing temperatures where the compound is known to become less ductile. This result is contrary to what might be expected with better PVC fusion (gelation). This article discusses the mechanism involved, which is lubricant inversion, where the lubricant goes from the continuous phase, as a surfactant coating all the PVC primary particle flow units at lower melt temperatures, to become the discontinuous phase at higher melt temperatures. J. VINYL. ADDIT. TECHNOL., 11:57,62, 2005. © 2005 Society of Plastics Engineers [source] A general model for porous medium flow in squeezing film situationsLUBRICATION SCIENCE, Issue 2 2010Mohamed Nabhani Abstract The present paper deals with a numerical investigation of the hydrodynamic lubrication of a porous squeeze film between two circular discs. To this purpose, the thin film (reduced) Navier Stokes equations and a generalised porous medium model are solved. The numerical results show that the effect of the porous disc is to reduce the lubricating properties of the fluid film. This effect is increased during the squeezing action. In addition, it is shown that the film pressure, the load-carrying capacity and the velocity field based only on the Darcy model are predicted higher than those obtained from the generalised porous medium model. Copyright © 2009 John Wiley & Sons, Ltd. [source] A friction energy approach to quantifying lubrication under fretting slidingLUBRICATION SCIENCE, Issue 2 2010T. Kolodziejczyk Abstract The problem of a proper lubrication under low-speed small oscillatory movement can be a decisive factor for the reliability of various components. There is a need to characterise the lubricious behaviour of the interface under oil-bath fretting wear conditions for ball bearing applications. Fast and reliable methods to quantify this behaviour for broad range of mechanical conditions are proposed and validated. Pure sliding reciprocation induces mixed lubrication mode. It was found that transient film profiles depend on the non-Newtonian response of the oils and the type of motion. Running-in period has a crucial importance for the tribofilm formation, and is a result of the interplay of the oil-sliding surfaces interface and is directly connected with the total energy dissipated from the contact region. The stability of structured tribofilm in steady-state period relies on the balance between the competitive processes: replenishment of the oil to the contact and ejection of the oil pending the oscillatory movement. The phenomenon of starvation was observed when the system was moved away from dynamical equilibrium and the growth of the dissipated energy was spotted. A proposed methodology provides the evaluation of the lubrication properties of the oil in a quantitative way. Copyright © 2010 John Wiley & Sons, Ltd. [source] Tribochemistry of tetrahedral hydrogen-free amorphous carbon coatings in the presence of OH-containing lubricantsLUBRICATION SCIENCE, Issue 2 2008C. Matta Abstract Diamond-like carbon (DLC) films are gaining attention for its use in a wide range of tribological applications because of their low friction coefficient and high wear resistance. Recently, ultra-low friction or superlubricity as low as 0.006 has been observed between hydrogen-free DLC films lubricated with oil containing a glycerol mono-oleate (GMO) additive. Consequently, there are many efforts to understand their detailed tribological behaviour. In this study, first, a characterisation of a pristine hydrogen-free tetrahedral amorphous DLC coating (denoted as ta-C) is presented. The technique used for ta-C characterisation is the energy-filtered transmission electron microscopy studied on a focus ion beam cross section of the coating. Then, to simulate the action of GMO, which is used as an additive in engine oils, and to understand its mechanism of action in boundary lubrication conditions, simple and shorter molecules such as pure glycerol and hydrogen peroxide are used in friction tests. These two molecules and GMO have the same alcohol chemical function. Friction tests in the presence of pure glycerol and hydrogen peroxide are presented. Moreover, to understand the properties of these two molecules, the overtone of GMO and their reaction mechanism in boundary lubrication, liquid phase lubrication was simulated by gas phase lubrication. Results show that very low friction coefficients are obtained with no apparent wear. Finally, the mechanisms of ultra-low friction are investigated by the wetting method and the X-ray photoelectron spectroscopy (XPS) technique. These two techniques are used to identify the physical (wetting method) and chemical (XPS) changes occurring at the ta-C surface after friction. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical evaluation of pressure from experimentally measured film thickness in EHL point contactLUBRICATION SCIENCE, Issue 1 2008Michal Vaverka Abstract This paper is concerned with elastohydrodynamic lubrication, especially the determination of lubricant film thickness and contact pressure within a point contact of friction surfaces of machine parts. A new solution technique for numerical determination of contact pressure is introduced. The direct measurement of contact pressure is very difficult. Hence, input data of lubricant film thickness obtained from the experiment based on colorimetric interferometry are used for the calculation of pressure using the inverse elasticity theory. The algorithm is enhanced by convolution in order to increase calculation speed. The approach described in this contribution gives reliable results on smooth contact and in the future, it will be extended to enable the study of contact of friction surfaces with asperities. Copyright © 2007 John Wiley & Sons, Ltd. [source] Tribological interactions between DLC coatings and lubricantsLUBRICATION SCIENCE, Issue 2 2008B. Podgornik Abstract In the last couple of years a tremendous research work has been done in the field of development and characterization of hard coatings, mainly to boost their use in machine component applications working under normal and extreme operating conditions. Generally, hard coatings improve tribological properties of contact surfaces under dry sliding, while under lubricated conditions their inertness hinder the possibility of boundary film formation. The aim of this paper is to elaborate on the interactions between diamond-like carbon (DLC) coatings and lubricants, and possible tribofilm formation in different tribological contacts. Therefore, relationships between surface properties (i.e. surface tension, surface free energy, contact angle) and tribological properties of the lubricated DLC coated contact, as well as the influence of oil additive type and concentration and contact conditions will be presented. It is believed that this type of knowledge will lead to further coatings modification in terms of improved tribological properties under boundary lubrication. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigation of the mechanism of lubrication in starch,oil composite dry film lubricants,LUBRICATION SCIENCE, Issue 1 2007G. Biresaw Abstract The boundary coefficient of friction (COF) of starch,oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch,oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (,Gads) of the polar oils onto the starch surface. The analysis gave ,Gads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane,starch than that for the polar oil,starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd. [source] Surface roughness effects on thermo-hydrodynamic lubrication of journal bearings lubricated with bubbly oilLUBRICATION SCIENCE, Issue 1 2006A. M. A. El-Butch In this paper, the combined effect of surface roughness and bubbles content on the hydrodynamic performance of journal bearings is studied. In the analysis, it is assumed that the bearing and shaft surfaces are covered with homogeneous isotropic roughness, the air bubbles are evenly distributed through the lubricant and the bubble size is very small. The modified Reynolds equation governing the pressure generation in the bearing gap for compressible fluid is solved simultaneously with the energy equation. Temperature and pressure distributions, coefficient of friction, bearing load capacity and attitude angle as affected by surface roughness, bubble content and some bearing parameters are presented. Results showed that the bearing load carrying capacity is higher at higher values of average roughness and higher bubble content as a direct consequence of the higher pressure values attained, and the average roughness and the bubbles content had no significant effect on the attitude angle. Copyright © 2006 John Wiley & Sons, Ltd. [source] On a test bench for studying lubrication in a spherical bearing: simulations and experimental validationLUBRICATION SCIENCE, Issue 4 2006N.P. Belfiore In this paper a test bench dedicated to the analysis of a lubricated spherical pair is presented. The experimental set-up has been used to validate a numerical code that has been developed by the authors in order to simulate a complex lubricated spherical pair that affects the reliability of a novel continuous variable transmission (CVT). The test bench is modular and can be adapted to other lubricated pairs, either cylindrical or spherical. The stand is equipped with an I/O control card and allows the on-line acquisition of some important parameters. As for the numerical code, the finite-difference method has been used to solve the indirect problem in the lubricated spherical pad, under the condition of hydrodynamic regime, with externally pressurized inlets. Two simulators are needed since the physical properties of the test bench and the real system are different. The one that simulates the behavior of the spherical pair in the test stand has been used to ascertain the numeric approach prediction capability. Indeed, the experimental tests gave results which are in very good correspondence with the numerical predictions. Hence, the second simulator, which has been tailored on the particular spherical pair the CVT is equipped with, gained reliability in predicting the behavior of the real system under different load and speed conditions. These predictions have been useful in achieving new insights into the novel CVT, which, under this new light, has been criticized by making the point that its range of application in automotive is, at the actual state of the art, rather limited, in spite of a high intrinsic complexity. Copyright © 2006 John Wiley & Sons, Ltd. [source] Large-scale specimen testing on friction and wear of pure and internally lubricated cast polyamidesLUBRICATION SCIENCE, Issue 3 2006Pieter SamynArticle first published online: 4 JUL 200 Abstract Due to the casting process for nylons, their composition can easily be modified to cover a wide range of mechanical properties and applications, especially as large wear surfaces in, for example, crane guidances. Presently, selection tests for working conditions up to 40MPa are presented on pure Na-catalysed polyamides, oil-filled polyamides with homogeneous oil dispersions and holes in the surface containing oil lubricant and two types of thermoplastic solid-lubricated polyamides. Pure polyamides are, however, prone to high and unstable sliding at pressures as low as 10MPa with brittle fracture and lumpy transfer. Oil lubrication is not able to remove the sliding instabilities as oil supply to the sliding interface is controlled by migration effects that are restricted by deformation and thermal softening or melting of the polyamide matrix. Although friction and wear are lower and more stable for samples with oil supplied through lubricating holes, additional running-in phenomena are attributed to a relatively thick transfer film that is brittle and easily peels off. A continuous thick molten film or island-like deposition occurs on the polyamide surface. Solid lubricants are able to stabilize friction and lower wear down to the formation of a thin and coherent transfer film. However, increasing the amount of lubricants induces lower mechanical properties and higher deformation of the test samples. The differences in transfer behaviour are discussed with reference to optical microscopy and calculations of bulk and flash temperatures. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effect of coconut oil-blended fuels on diesel engine wear and lubricationLUBRICATION SCIENCE, Issue 4 2005M. A. Kalam This paper presents the results of an experimental investigation into the wear and lubrication characteristics of a diesel engine using ordinary coconut oil (COIL)-blended fuels. The blended fuels consisted of 10, 20, 30, 40, and 50% COIL with diesel fuel (DF2). Pure DF2 was used for comparison purposes. The engine was operated with 50% throttle setting at a constant speed of 2000 rpm for a period of 100 h with each fuel. The same lubricating oil, equivalent to SAE 40, was used for all fuel systems. A multi-element oil analyser was used to measure wear metals (Fe, Cr, Cu, Al, and Pb), contaminant elements (Si, B, and V), and additive elements (Zn, Ca, P, and Mg) in the used lubricating oil. Fourier transform infrared analysis was performed to measure the degradation products (soot, oxidation, nitration, and sulphation products) in the used lubricant. Karl Fischer (ASTM D 1744) and potentiometric titrations (ASTM D 2896) were used to measure water concentration and total base number (TBN), respectively. An automatic viscometer (ASTM D 445) was used to measure lubricant viscosity. The results show that wear metals and contaminant elements increase with an increasing amount of COIL in DF2. An increasing amount of COIL in the blends reduces additive elements, with the reduction for blends of up to 30% COIL being quite similar to that for DF2. Soot and sulphation decrease with increasing COIL in the blended fuels due to reduced aromatics and sulphur in comparison to DF2. The water concentration increases for blended fuels with more than 30% COIL. The TBN and viscosity changes are found to be almost normal. The engine did not appear to have any starting and combustion problems when operating with the COIL-blended fuels. The lubricating oil analysis data from this study will help in the selection of tribological components and compatible lubricating oils for coconut oil- or biofuel-operated diesel engines. [source] Investigation into the traction coefficient in elastohydrodynamic lubricationLUBRICATION SCIENCE, Issue 2 2004Y. S. Wang Abstract The elastohydrodynamic traction coefficients of two Chinese aviation lubricating oils were investigated for various loads, rolling velocities, and lubricant inlet temperatures using a self-made test rig. Traction coefficient versus slide-to-roll ratio curves were generated. The concept of critical load varying with the lubricant temperature is proposed. This paper presents a new empirical formula for the dynamic performance design of high-speed rolling bearings, that relates traction coefficient with normal load, rolling velocity, and lubricant inlet temperature. The coefficients of the formula may be computed by regression analysis of the experimental data. Two example calculations are presented. The predicted results from the formula agree well with experimental observations. [source] Approximate Formula for the Contact between Truncated Surfaces and Frictional Characteristics of a Journal Bearing in Mixed LubricationLUBRICATION SCIENCE, Issue 3 2004M. Nonogaki Abstract This paper presents an approximate formula for the contact of a non-Gaussian distribution of truncated surfaces, which is useful for mixed lubrication theory, and gives a method for the determination of the truncation parameters in this formula from a measured roughness profile. Using this approximate formula for a contact, the approximate formula for the friction coefficient of a journal bearing in mixed lubrication, which was previously proposed by the authors, is modified for truncated surfaces, and the frictional characteristics are demonstrated for various parameters of truncated roughness using the modified formula. [source] | ||||||||||||||||||||||