Aqueous Lubrication Research Articles

High-pressure lubrication with lamellar structures in aqueous lubricant

The lubrication mechanisms of water-based fluids are not yet well understood, especially when extreme load conditions are applied. The example of lamellar crystallite particles in water, provided by an emulsion-like technology, is described in this paper. It is shown, for the first time, that the presence of such nanostructures in the sliding interface can provide extreme-pressure lubrication. This water-based lubricant is particularly efficient when one of the two solid surfaces is made of brass. In this case, a multilayer is created in the contact. It is formed by a brass layer transferred to the counter face, the brass surface itself and a lamellar film adherent to the former layers. This lamellar system is able to sustain pressures up to a few GPa and to maintain a low friction coefficient.

The tribological behaviors of various metallic cations in tapping of a titanium alloy

In this paper, various metallic cations, including Na +, K +, Ca 2+ and Ba 2+, were introduced into water-based lubricating additives. Their tribological behaviors were investigated by the tapping test of a Ti-6Al-4V alloy. Among them, Ba-containing compound showed the best lubricating performance. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the surface morphology and chemical states of elements, respectively. It was found that the worn surface consisted of multiple oxides, which implies that tribooxidation predominated during the frictional process under aqueous lubrication. Furthermore, barium titanate (BaTiO 3) could be detected on the tapped surface, the existence of which was proposed to be responsible for its corresponding performance.

Reaction Pathways and Kinetics in the Degradation of Forging Lubricants

The stability of a hot forging lubricant determines its effectiveness during operation. Aqueous lubricants, which are increasingly popular because of environmental issues, contain an organic ingredient, a stabilizer, and other species including biocides and corrosion inhibitors. The stability of a model forging lubricant containing dipotassium o-phthalate and sodium silicate in water has been measured over a wide range of temperatures and initial concentrations. The oxidation of the organic species is correlated using kinetic analysis, which reveals that decomposition occurs through a first-order reaction with an activation energy of ≈58.2 kJ/mol. The kinetic result is consistent with a proposed free radical reaction mechanism that is also shown to be consistent with theoretical calculations and results reported for other types of lubricants.

Tribochemical investigation of tungsten carbide/titanium alloy tribo-couples under aqueous lubrication

The present paper deals with the fundamental understanding on the tribochemical mechanism of tungsten carbide (WC) coating and titanium alloy tribo-couples system. The tribological experiments were performed with a Timken-type tester. Water containing water-soluble additives was employed as the lubricating media. The rubbed surfaces of the carbide coating were characterized with scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Significant titanium transfer was observed. Results of XPS analyses show that the interfacial layers formed consist of multiple oxides which suggests that oxidative reactions predominate in frictional processes under aqueous lubrication. It is proposed that the oxide layer is responsible for the tribological behavior because it controls the diffusive and adhesive wear.

Tribochemical Polishing of Silicon Nitride

Tribochemical polishing (TCP) is a new technique for polishing materials that is based on the friction‐stimulated dissolution of material in a liquid. It differs from chemomechanical or mechanochemical polishing in that it does not use abrasives. Tribochemical polishing of silicon nitride was explored as a function of the mechanical parameters and the nature of chemical solutions and their concentrations. Over 30 chemical solutions such as acids, bases, salts, and inorganic and organic oxidizers were studied for material removal, polishing rate, and surface quality. Optical, scanning electron, and atomic force microscopy have been used to explore the polishing rate and the surface morphology. Distilled water produces purely tribochemical material removal and very smooth surfaces at low contact pressures. In hydrogen peroxide, the polishing rates are higher and increase with concentration; 3 vol % hydrogen peroxide gives a high polishing rate and smooth surfaces by pure tribochemical reaction. Chromium (VI) oxide in all concentrations less than the solubility limit shows the best, purely tribochemical polishing results and the smoothest surface. Combinations of chromium oxide and hydrogen peroxide, and many of the chromates (VI) show excellent efficiencies. Some chemical solutions containing excess oxygen also present high performance of tribochemical polishing. Some strong organic oxidants which have excess oxygen and some inorganic chemical solutions show 10–250 times lower polishing rates than water. These low material removal rates suggest their use as antiwear agents in aqueous lubricants.

The friction and wear properties of Cr 2O 3 coating with aqueous lubrication

To research and develop water-based lubricants suited for use in ceramic tribocouples is very important for the successful use of ceramics in aqueous environments. A block-on-ring tester was used to investigate theeffect of some water-based lubricants on Cr 2O 3 coating/Cr 2O 3 coating contacts at ambient conditions. Relative to water, lithium stearate and magnesium stearate, suspended in water, can greatly reduce the friction coefficient and wear volume of Cr 2O 3 coating, which can be attributed to the adsorption of anion groups arraying in an orderly way on the rubbing surface. However, ethylenediaminetetraacetic acid disodium salt (EDTA-Na), ethylenediaminetetraacetic acid magnesium-dipotassium salt (EDTA-KMg) and polystyrol maleate sodium (PSMS) have slight lubricating actions, due to multipoint adsorption of their polar groups. There exist hydrations of the coating with water in stearates and EDTA-KMg solutions.

Remarkable lubricating capabilities of amniotic surfactant.

Surface-active phospholipid (SAPL) extracted from amniotic fluid or elutriated from the chorioamnionic sacs of placentas recovered from normal full term deliveries has been shown to be a remarkable lubricant. Coefficients of kinetic and static friction were reduced to 0.009 by SAPL from amniotic fluid and 0.011 for a membrane extract, even under high load (3 kg/cm2), compared with 0.04 for the best nonbiological boundary lubricants. The antiwear properties were equally remarkable, giving a mean scar diameter under extreme pressure of only 0.76 mm for amniotic SAPL and 1.00 mm for membrane extract compared with 0.85-0.95 mm for aqueous lubricants commercially available. These results support the hypothesis that premature rupture (PROM) is less likely to occur if movement between the fetus and the amnion or between the decidual surface of the uterus and the chorion is well lubricated.

Remarkable anti-wear properties of joint surfactant.

A standard (four-ball) test has been used to study the anti-wear capabilities of ovine synovial fluid, the phospholipid extracted from it, a synthetic synovial fluid, and the phospholipid removed from the articular surface by a lipid solvent. Despite using speeds and loads that were "extreme" by engineering criteria, i.e., several orders of magnitude in excess of physiological logical loadings, the indices of wear (mean scar diameters) were comparable to those of the best industrial lubricants (0.35 mm for the best oils to 0.8-0.9 mm for the best aqueous lubricants). Synovial fluid had a value as good (low) as 0.65 +/- 0.04 mm, whereas an artificial synovial fluid synthesized from hyaluronic acid and the proposed active ingredient (disaturated phosphatidylcholine) gave a mean value of 0.59 mm. These results are discussed as consistent with the hypothesis that the joints are lubricated by oligolamellar phospholipid as a lamellated solid (graphite-like) lubricant adsorbed onto the articular surface or otherwise deposited from synovial fluid. This lubricant imparts not only phenomenal anti-wear properties, but also the remarkable reduction in friction reported previously.

The Effect of Interfacial Potential on Friction in a Model Aqueous Lubricant

A tilting electrochemical cell was used to study the effect of potential on the static coefficient of friction of iron on mild steel in a model aqueous lubricant consisting of octanoic acid neutralized to pH 9.2 with sodium hydroxide. A sharp fall in friction was observed at potentials positive of −400 mV vs. standard hydrogen electrode. Both impedance and radiotracer measurements indicated that the decrease in friction coincided with an increase in the thickness of a lubricating surface film. This potential dependent behavior is interpreted in terms of electrostatic interactions between the iron and the negatively charged octanoate species.

Treating giant papillary conjunctivitis while wearing contact lenses

Patients (114) with bilateral giant papillary conjunctivitis (GPC, grades 1 to 4, continued to wear contact lenses while treated for 30 or more days with aqueous lubricating eyedrops containing the antioxidants polysorbate 80 and vitamin A (0.012%) four times daily. GPC was associated with hydroxyethyl methacrylate (HEMA) lenses in 104 patients (91%) and rigid gas permeable (RGP) lenses in 10 patients (9%). Part of the treatment was to replace soiled HEMA and RGP lenses for 96 patients (84%). The most common lens replacement was from low water (38%) HEMA lenses to high water (55%) hydrophilic lenses. Treatment reduced signs and symptoms in all cases. Biomicroscopic examination of the palpebral conjunctiva showed complete resolution or barely detectable GPC in 210 of 228 eyes (92%). Many individuals continued using the drops after GPC resolution to enhance general comfort. The combination of the antioxidant lubricating eyedrops and new lenses in many cases are believed to have contributed to this successful alternative treatment of GPC.

The effects of the electroejaculation procedure on sperm motility.

Electroejaculation is becoming more available for obtaining semen from spinal cord injured men wishing to father children. This study was undertaken to determine what effect the electroejaculation procedure itself had on sperm motility. Factors which were found to impact on sperm motility were osmolarity, electric current and aqueous jelly lubricant used for bladder catheterisation. pH did not affect sperm motility.

The mechanisms governing crack and pit formation in steel in rolling sliding contact in aqueous lubricants

AbstractThis paper presents the results of an investigation of the fatigue damage of steel surfaces operated in rolling/sliding contact conditions in the presence of water glycol‐based fire resistant fluids. It has been shown that pitting life depends on the relative magnitude of fluid film thickness and the lubrication regime in which the system is operated. A minimum in pitting life is shown to occur in the mixed‐elastohydrodynamic region.Mechanisms for crack initiation, propagation and subsequent pit formation in aqueous lubricants are proposed.

Recent developments in the performance properties of water based cutting and hydraulic fluids

AbstractLubricants and functional fluids may be grouped into those based on natural oils and those having man‐made (‘synthetic’) base stocks. This paper is concerned with the ‘dilute synthetic lubricant’ in which the man‐made component is blended with a major proportion of water. The developments covered include hydraulic and metal‐cutting fluids, with examples drawn from experience with solutions and dispersions. The performance required from these fluids in service is discussed with particular attention to improvements in corrosion protection, antiwear performance, extreme‐pressure properties, foam inhibition, air release, rolling bearing fatigue and resistance to erosion pitting. Water quality can have a significant impact on the performance properties of the fluids already listed. The service properties of aqueous lubricants may be classified according to their response to chemical additives. Examples are given of properties which respond well to additives and of those which are governed largely by the bulk physical properties of water. Manufacturers of equipment are continuing to develop new machinery. Fluid formulators are seeking to extend the current operating limitations of aqueous fluids. Future development relies on close co‐operation between users, equipment suppliers and lubricant formulators.

The Pitting and Cracking of SAE 52100 Steel in Rolling/Sliding Contact in the Presence of an Aqueous Lubricant

The use of aqueous lubricants is well established in applications where their fire-resistant properties are of prime importance. A major disadvantage of the use of such fluids, however, is their relatively poor performance in high-stress rolling-contact bearings where components suffer fatigue cracking and pitting at an earlier stage than with mineral oils. In this investigation, factors affecting the cracking and pitting of SAE 52100 steel in the presence of a water-glycol-based fluid have been studied using an Amsler two-disk machine. A Stribeck curve was plotted and has shown that pitting damage is dependent on the region of the curve in which the system is operated, pitting life being a minimum in mixed-elastohydrodynamic lubrication. Good correlation was found betwen pitting life and specific film thickness λ above λ = 0.05. Below this value, inverse correlation was observed. Finally, a mechanism for crack initiation, propagation, and subsequent pitting in aqueous fluids is proposed.

EFFECTS OF BLADDER DISTENTION ON CANINE AND FELINE RETROGRADE URETHROGRAPHY

Retrograde urethrography with viscous contrast medium was performed in male and female dogs and cats before and after bladder distention. The viscosity of commercially prepared contrast medium was increased by addition of an aqueous lubricant. The diameter of the proximal urethra of female dogs (regions 1 and 2) was larger during urethrography (p<0.05) following bladder distention. The diameter of regions 1 and 2 of the proximal uretha of female cats in lateral recumbency was larger during urethrography (p<0.05) following bladder distention. The diameter of the distal urethra of female dogs and cats was not significantly different before or after bladder distention. The diameter of the prostatic urethra of male dogs was larger (p<0.003) following bladder distention. The diameter of the membranous and penile urethra of male dogs was not significantly different before or after urinary bladder distention. Similarly, the diameter of the urethral lumen in male cats was not significantly different before or after bladder distention. The increased viscosity of the contrast medium due to the aqueous lubricant failed to distend all areas of the male and female canine and feline urethra maximally during urethrography when the bladder was not distended. On the basis of the results of this study, the authors recommend urinary bladder distention with a lubricant‐free positive contrast medium to generate intravesical hydrostatic pressure sufficient to induce urethral distention. The degree of bladder distention should be determined by digital palpation.

Artificial Eyes and Tear Measurements

Ninety-four consecutive persons with unilateral enucleations or eviscerations were tested by the Schirmer I and Schirmer II tests for tear production. The findings on the artificial eye were compared with those on the companion, living (control) eye. The collected data were subjected to statistical analysis. The control eyes were shown to respond in the normal manner, more tears without topical anesthetic than with it. The sockets of artificial eyes produced no more tears without anesthetic than with it. The control eyes produced a normal amount of reflex tears, whereas the sockets of many artificial eyes produced practically no reflex tears. Tear production in persons with no complaints was compared to those with noteworthy problems. Persons with problems had only half as much basic tear secretion as those without problems. Elimination of the stimulus to reflex tear production by removal of the cornea and by the presence of the prosthesis is suggested as the cause of dryness of the eye socket. The potential value of aqueous or oily artificial lubricants is mentioned.

Wear of water-lubricated composite materials

The wear properties of several commercial composite materials on stainless steel in the presence of water were examined. Particular care was taken to ensure that the conditions of the friction process were characteristic of the boundary lubrication regime. Test results show that the presence of water at the interface influences in various ways the wear of the materials examined. The results emphasize the need for care in the selection of materials for conditions of aqueous lubrication.

Evaluation of hydroxyethyl cellulose ether as a thickener for aqueous lubricants or hydraulic fluids

The relevant characteristics of aqueous solutions of hydroxyethyl cellulose ether have been studied in order to assess their potential for use as lubricants or hydraulic fluids. The results have been compared with those obtained for several fully formulated motor oils and hydraulic fluids and their base oils. Studies using a cone-and-plate viscometer over very wide ranges of shear rate and temperature indicate that the solutions have high shear stability and are pseudoplastic. The loss of viscosity due to ultrasonic shear and shearing in a Kurt Orbahn rig appears to be tolerable. Viscosity-temperature properties measured by standard methods, specific gravity. and antiwear performance in the four ball machine have also been investigated. Two antiwear additives have been tested and the results appear promising.

The Surface-Roughness of Bearing-Surfaces and its Relation to Oil Film Thickness at Breakdown

In this paper the relation of surface roughness of bearing surfaces to allowable film thickness is studied quantitatively with a simple Michell pad apparatus. The pads used were faced with white metal and ran against mild steel collars. The lubricants studied were water, soap solution, paraffin, and light oil. There was little difference in the frictional behaviour of any of the lubricants, except that the aqueous lubricants would not run with very finely finished steel surfaces. The onset of metal to metal contact was detected by an increase in the frictional drag, and also by the change in electrical conductivity between the pad and collar—an extremely sensitive method.The paper shows that there is, at any rate for this system, a quantitative relation between the total surface roughness of the rubbing surfaces and the calculated oil film thickness both at the initial metal to metal contact and seizure. Initial contact occurs when the outlet film thickness, calculated from normal hydrodynamic theory, falls to three times the maximum surface roughness and seizure occurs when it is double the average roughness.