Lubricant Loss Research Articles

Catalytic Degradation of a Perfluoroalkylether in a Thermogravimetric Analyzer

Catalytic degradation of perfluoroalkylethers (PFAEs) by various substrates can be a significant problem, resulting in the formation of corrosive degradation products and loss of lubricant. The determination of catalytic degradation of a linear PFAE (PFAE-D) by various substrates was made by controlled-diffusion thermogravimetric analysis. The use of a sealed gold pan with a small pinhole in the lid allowed for the measurement of catalytic degradation of PFAE-D by increases in the rate of volatilization relative to a control. Catalytic degradation was observed under ramped conditions (to 500°C) for most commonly used metals and alloys except Inconel 600, silver and pure silicon nitride. Analysis of degradation products confirmed that degradation was occurring by a molecular disproportionation reaction. Milder isothermal conditions (300° C) resulted in catalytic degradation for aluminum, M-50 steel, carbon-carbon composite and some binder components used in silicon nitride balls. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Studies on the interactions between ZDOL perfluoropolyether lubricant and the carbon overcoat of rigid magnetic media

Current high performance magnetic storage devices, i.e., hard disk drives, typically operate at elevated temperatures of nominally 45–60°C. As a consequence, understanding the thermal response of the materials used in the construction of the drive becomes imperative. In this report, we focus on the thermal behavior of a common perfluoropolyether lubricant (ZDOL) used on the carbon-overcoated, hard disk. In particular, we show that evaporative loss of this disk lubricant, as well as bonding of the lubricant to the carbon-overcoated disk, can occur at the temperatures encountered in the hard-disk drive. Surface energy measurements show that the interaction of the hydroxyl-terminated perfluoropolyether ZDOL occurs principally through the end-groups. On unannealed disks, the interaction between this “mobile” lubricant and the carbon overcoat is characterized by hydrogen bonding with the strength of these interactions being only slightly stronger than the intermolecular hydrogen bonding characteristic of bulk ZDOL. Upon annealing at temperatures in the range of 60–150°C, the ZDOL lubricant becomes “bonded” to the disk. The surface energy of the bonded lubricant is substantially lower than the mobile lubricant reflecting the increased interaction strength that occurs as a result of bonding. Since the bonded state is the lower energy state, transitions from the mobile state to the bonded state are thermodynamically favored. The kinetics of this bonding transition, as well as the kinetics of lubricant evaporation were studied as a function of temperature. Using a model of two competing reaction channels, the activation energies for both lubricant bonding and lubricant evaporation were determined to be 3.6 kcal/mole and 5.4 kcal/mole respectively. Ab initio quantum chemical modelling was used to investigate possible interaction sites on the carbon surface. Both experiment and theory indicate that interaction of the hydroxyl-terminated ZDOL to the carbon overcoat occurs via hydrogen bonding to oxygenated species on the carbon overcoat, with a binding energy of 5–8 kcal/mole. An esterification reaction between the hydroxyl end-groups of ZDOL with carboxyl groups on the carbon surface as a result of annealing is shown to be consistent with the both the surface energy data and the kinetic data.

Low-Contamination Fabric Tapes for Disk Polishing, Texturing, and Buffing

Fabric tapes are used in many areas of magnetic media (thin-film disk) preparation in the data storage industry: polishing, texturing, and lube buffing. Tapes are more commonly used than pads for such applications, partly because the continuous supply of new tape during operation provides improved uniformity in comparison to the inherent discontinuities involved in pad conditioning/use/conditioning/use. (Simple modeling shows tapes tend to produce more uniform material removal than pads, although this is not universally true.) An important quality issue (in addition to reproducibility, uniformity, and planarity) is contamination control. Contamination by particles will be even more important as slider flying heights are reduced. Molecular contaminants are also important because some species can lead to the loss of lubricant on areas of the disk. Ionic species adsorb water preferentially from the air and thus can accelerate corrosion. Steps taken to minimize fabric contamination include careful selection of starting materials, control of the processing environment and processing variables, and cleaning the fabrics before they are made into tapes. New tape materials are likely to give new operating options, as well as new quality control problems, and some of these are discussed.

Stagnation of Ice Stream C, West Antarctica by water piracy

The dynamic behavior of the West Antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea‐level rise. Attention is focused on the fast‐moving and rapidly responding ice streams that drain the ice sheet. One of these, ice stream C, largely stopped about a century ago, and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice‐sheet. Here, new data are presented indicating that the slowdown of the ice stream is restricted to its lower part, and occurred because of loss of lubrication on localized “sticky spots” at the bed of the ice stream. The increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream B, together with slow drawdown of the ice sheet, rather than from any general stabilizing feedbacks.

Loss of lubricant from oil-lubricated near-starved spherical roller bearings

The time to lubricant film breakthrough in an oil-lubricated spherical roller bearing has been measured using SKF Lubcheck for various settings of bearing load, outer ring temperature, shaft speed and oil type and viscosity. The bearings were lubricated once and then run to film breakthrough with the aim of estimating the lubricant losses under different conditions. The result of the experiments supports the theory of lubricant replenishment, and it is shown that high speed combined with high lubricant viscosity will shorten the time to film breakthrough.

Ultrathin Perfluoropolyether Films—Influence of Anchoring and Mobility of Polymers on the Tribological Properties

Abstract The tribological behavior of ultrathin films of hydroxyl terminated perfluoropolyethers attached to smooth silicon surfaces was studied in pin-on-disk experiments. The frictional properties of the films, which consisted of either physically adsorbed or chemically bonded polymer or a combination of both, was measured in sliding contact and lubricant loss was studied simultaneously by scanning microellipsometry. Prior to these experiments the kinetics of attachment of the polymer to silicon surfaces and the behavior of the polymer at high temperatures was investigated in order to obtain reproducible conditions for the deposition of the lubricant films and to rule out the occurrence of thermal degradation during film deposition. The tribological investigations showed that the lifetime of the surfaces with the attached boundary lubricant was strongly dependent on the mode of attachment of the polymer. The best tribological behavior was observed in films which contained both chemisorbed and physically adsorbed material.

Structure and Facies Development in the Niger Delta Resulting from Hydrocarbon Maturation: ABSTRACT

A new depositional model relates the formation of the Niger Delta toe thrusts and growth faults to source rock maturation. Specifically, it is proposed that an oil-prone source rock at early maturity generates enough fluid and pressure to initiate major fault movement by gravity sliding. Recently acquired, high quality, deepwater seismic data show a well defined decollement surface that links toe thrusts, growth faults and counter regional faults in the progradational wedge. It is believed the decollement occurs in an Aptian-aged source rock known to be present in West Africa and Brazil. Regional cross sections were constructed through the delta, using the published positions of shorelines through time and assuming a maximum post Aptian sediment wedge of 8 kilometers. Maturation modeling was performed and the results at various times from Late Cretaceous to Recent were plotted and compared to paleopositions of the shelf edge and toe of slope. The modeling illustrates how the maturation of an Aptian source rock may have significantly influenced structural development and facies distribution in the delta. The present day time slice shows a strong correlation between the location of the early mature oil window of the proposed source rock and the position of the leadingmore » toe thrust in the delta. A, similar correlation is found between the location of the post gas-mature window and the position of significant fluvial facies accumulation. The fluvial facies occurs as the result of shoreline advance caused by the loss of source-related lubrication of the decollement surface.« less

Oil Drop Formation at the Outlet of an Elastohydrodynamic Lubricated Point Contact

The loss of lubricant from grease-lubricated bearing surfaces is determined by a number of different mechanisms such as side-flow out of the contacts, evaporation, drop formation, oxidation etc. Some of the drops formed behind a rolling element in a bearing will be onrolled by the next rolling element but some will be lost from the bearing. This loss of lubricant is dependent to a high degree on the speed of the air flow through the bearing and is one of the reasons for early failure of grease lubrication in bearings operating in strong, axial air streams. To evaluate the most important parameters in drop formation, the droplets being thrown out from the outlet of an elastohydrodynamic contact were analyzed using picture processing and statistical methods. An empirical model has been built to describe mathematically the principal factors involved in the volume flow thrown out into the air at the outlet side of the Hertzian contact area. For example, drops in a ball bearing will contribute to the inlet feed of oil for the next ball if it is not lost by sideways flow out from the bearing.

Effects of Temperature and Humidity on Thin Film Disk Lubricant Mobility

Lubricant loss, degradation and mobility of perfluorinated poly-ether (PFPE) on carbon coated disks were investigated by observing friction during sliding contact while controlling temperature and humidity. Lubricant loss from asperity contacts and its replenishment from adjacent areas were investigated for Al2O3-TiC and Mn-Zn ferrite sliders at various sliding velocities by continuous and oscillating rotation of the disk.

Tribochemistry at lubricated interfaces

High resolution mass spectrometry is used to monitor in situ gaseous wear products that are generated during sliding of lubricated carbon–carbon interfaces in a vacuum. During the initial stages of sliding, significant amounts of polyperfluoroether lubricant fragments are detected, which resemble the mass patterns of scissioned lubricant in the thermal desorption experiment. The intermediate stage of sliding characterized by lower rate of lubricant fragmentation is followed by higher rate before wear of hydrogenated carbon overcoat occurs, which is accompanied by hydrogen emission and friction increase. Lubricant loss, removal, and alteration are precursors of the wear of solids and are determined by scanning microellipsometry. The amount of altered lubricant that is left on the disk and slider surfaces is quantified by x-ray photoelectron spectroscopy and the chemical structure of altered lubricant is evaluated by time-of-flight mass spectrometry. It is found that the dominant process, before the wear of solids occurs, is tribochemical scission of fluorocarbon polymers. Some fragments desorb from the interface, while others containing carboxylic end groups attach by strong physisorption to solid surfaces.

Bestimmung der Bioabbaubarkeit von nicht wasserlöslichen Flüssigkeiten (Schmieröle etc.) nach CEC L-33-A-94

The use of biodegradable lubricants as substitutes for lubricants based on mineral oils is necessary in areas where an impact on ecosystems is inevitable and cannot be excluded. These are applications in which a partial loss of lubricant into the environment occurs, e.g. chain saw oils, two-stroke oils for outboard motors, and hydraulic oils, which are used in sensitive areas as dredging-machines near rivers or ground water sources. The use of commercially available biodegradable base liquids for lubricants is discussed and several current examples are given. These water-insoluble products are frequently examined with the CEC test that can be used for a rough determination of the biodegradability. The development and application of this method has a long tradition at the EMPA Dübendorf. Experimental details, limits, advantages, and disadvantages will be discussed in this paper. Longterm measurements with the calibrating oils RL 130 and RL 110 together with results from a biodegradation study of several hydraulic fluids that are used in agricultural machinery are presented.

Organic buildup on slider leading edge tapers and its effect on wet stiction

The phenomenon of organic mixture buildup on slider leading edge tapers (LETs) was studied experimentally by conducting contact start/stop (CSS) tests in a humidity chamber. The effect of organic buildup on wet stiction performance of head/disk interface (HDI) was investigated. It is found that high humidity leads to higher rate of PFPE lubricant loss at disk landing zone and significant material buildup at the end of head slider LET surfaces. Such changes at the HDI cause irreversible high stiction, large stiction modulation, and, therefore, shorter CSS life. Organic silicone vapor film from silicone outgassing speeds up to the buildup process and leads to early HDI failure. Reducing LET organic buildup can extend wet CSS life.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of surface roughness on the lubrication properties of the piston ring and cylinder of an engine, and calculation of lubrication and power loss analysis of piston-ring pack of a S195 diesel engine

The effect of surface roughness on lubrication of piston ring and cylinder is examined. In particular, the temperature effect is considered, and a model proposed to overcome shortcomings in the previous mathematical model. Further, film thickness was measured by transducer capacitance method in a S195 diesel engine. The results found are consistent with theoretical results. In addition, the authors show quantitatively the value of friction power losses of the ring package of a S195 diesel engine.

Sexual Issues at Menopause

Although the desire for sexual encounters and the frequency of coitus decrease with menopause, sex in the elderly is no longer considered taboo and continues to be an important and acceptable activity for most older persons. Couples in their 50s or older expect continued sexual involvement, but most consider intercourse the only legitimate form of sexual exchange and reject other forms of sexual activity. Sexual dysfunctions which impair coital ability, especially ejaculatory difficulties in the male and genital atrophy and loss of vaginal lubrication in the female, are frequent. Menopausal couples are often not knowledgeable about physiologic aging changes that affect sexual performance and are reluctant to communicate sexual difficulties to their partner. Without professional counseling and/or pharmacologic intervention, these conditions may lead to sexual frustration and abstinence. The identification and treatment of problems, as well as patient education, are imperative in caring for the menopausal patient.

On the two modes of operation of monolithic Ag-C brushes

The previously observed transition from low-temperature (mode I) to high-temperature (mode II) behavior in silver-graphite brushes can be explained either by changes of constriction resistance through the temperature dependence of electrical resistivity and hardness at negligible film resistivity and one to three contact spots, or by loss of graphite lubrication within the interfacial film. These two interpretations were tested by controlling the contact spot temperature: (1) by heating in an oven and (2) by local heat input through friction. Correlated studies of contact resistance, friction, wear rate, wear chip size, wear chip microstructure, and calculations of contact spot temperatures favor the second hypothesis. Micrographic evidence suggests that this occurs through desorption of water vapor from the graphite. It is found that primary wear particles form due to the wedge mechanism and by cutting by graphite fragments steeply inclined to the interface. Silver fragments may consolidate into secondary wear particles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Duplex reactive fluorocarbon films with spin-off resistant characteristics

As a group, fluorocarbons are by far the most common disc lubricants used in rotating storage memories. They possess excellent properties including chemical inertness, low surface tension, low volativity and moisture repellancy. They have, however, one serious limitation: the continual loss of lubricant from the rotating disc surface due to centrifugal migration. This leads to increased head to disc interference and may eventually cause complete failure of the head-disc assembly (HDA) unit. A unique solution to this problem is described in this paper. It was arrived at by combining two fluorocarbon films, one chemically and permanently bonded to the media surface, the other a normally applied lubricant which is overcoated onto the primed disc surface. These duplex films retain the excellent lubricant properties of the single film but dramatically reduce the lubricant loss by spinoff. Experimental data for duplex and single lubricant systems are presented including spinoff curves, stiction and friction measurements and start-stop wear testing. Finally, a mechanism based upon polymer chain entanglement is proposed to explain the retention of lubricant in this newly discovered system.

A study on the surface durability of grease lubrication gears. The lubricant stirring loss and its behavior in a gear box.

The purpose of this paper is to measure the lubricant stirring loss and study its behavior in a gear box. The gear sets are made with spur gears having a 2.0 module, and with the number of teeth being Z1/Z2 =28/52. The lubricant used are two greases made form NLGI 0 and 000 gear oil. The stirring loss and lubricant behavior are examined in relation to the velocity Vp, quantities of lubricants, temperature and the face width. The loading force is no load. The results are summarized as follows : (1) the harder grease has a tendency to show channeling, and the softer grease produces churning. (2) the stirring torque of the grease lubrication is much larger than that of the oil lubrication. (3) the stirring torques of both the grease and oil lubrication are evaluated as functions of (v·Vp).

Porous bearings

Much equipment in everyday use, such as small domestic appliances and audio equipment, has porous bearings to support a rotating shaft. The bearings in this type of equipment can only be supplied with lubricant once, during manufacture, so the use of porous bearings is an obvious solution. The porous wall of these bearings functions as a reservoir from which the bearing gap is filled with lubricant. With these bearings, problems are regularly encountered, such as noise, loss of lubricant, premature failure, irregular friction and inaccurate shaft position. In a practical investigation, attempts were made to obtain a better understanding of the causes of these problems and, where possible, to lay down guidelines for restricting or avoiding them. The investigation was concerned exclusively with cylindrical porous bearings, between 2.5 and 5 mm diameter, impregnated with oil having a relatively low viscosity and operating in the mixed lubrication regime

Labyrinth Sealing of Aerospace Mechanisms—Theory and Practice

High-vacuum naphthalene evaporation loss experiments were conducted with a specially designed annular effusion cell to examine the validity of the most frequently used theoretical models of molecular flow, specifically applied to a high molecular weight organic compound. Literature data are similarly correlated to (a) show the respective accuracy of the various formulae and (b) discuss the most prevalent effusion experimental errors often causing orders of magnitude differences between theoretical predictions and experimental results. A simplified molecular flow effusion model is proposed, modified to account for the evaporation rate and rate of vapor pressure change of polymeric lubricating oils. The results and conclusions are useful for accurate predictions of long-term lubricant loss through annular-design labyrinth seals of wet-lubricated aerospace mechanisms and vacuum chamber components.

Wear and friction of two different types of graphite fibre-reinforced composite materials

The wear of epoxy resins reinforced with either of two strongly different types of graphite fibre was studied, in a pin-disc sliding contact wear tester. Composites reinforced (62 per cent by volume) with low modulus, high strength circular fibre (Modmor II) exhibited high wear resistance (threshold wear load∼ 1 kg, maximum bearing load ∼ 5 kg, wear coefficient ∼ 10 −6) when worn by hardened (y ∼ 400 ksi) 52100 steel pins. However, the composite produced extreme abrasion on the steel counter face. Composites reinforced (62 per cent by volume) with high modulus, lower strength, non-circular fibre (GY70) also exhibited high wear resistance (threshold wear load ∼ 1/4 kg, maximum bearing load ∼ 2 kg, wear coefficient ∼ 10 −6) when worn by 52100 steel. However, these composites developed a surface film which prevented abrasion at the steel counter face. Potential applications of the two different types of fibre reinforcement in bearings are discussed. Advantages of these composites in bearings subject to corrosion, vibration, loss of lubrication, or impact, are noted.