D. J. Carré

Perfluoropolyalkylether Oil Degradation: Inference of FeF3 Formation on Steel Surfaces under Boundary Conditions

The formation of iron fluoride (FeF3) through the interaction of perfluoropolyalkylether (PEPE) oil with steel surfaces was investigated under boundary lubrication conditions. Ball-bearing rolling action was simulated by a specially designed wear-test apparatus that incorporated noncoaxial wear members to give a skid/roll ratio of ∼0.16. The contact stress was 8.3 × 108 N·m−2 (∼120 000 psi), and the speed was 1750 rpm. Under these conditions, FeF3 formation on the wear surfaces was inferred using x-ray photoelectron spectroscopic (XPS), Auger electron spectroscopic (AES), and secondary ion mass spectrometric (SIMS) surface analysis techniques. These findings support the hypothesis that, under the low oxygen environment of spacecraft earth orbit, formation of FeF3 and subsequent FeF3 catalyzed degradation of PEPE can constitute an important PFPE degradation pathway under boundary lubrication conditions. Presented at the 40th Annual Metting in Las Vegas, May 6–9, 1985

The Performance of Perfluoropolyalkylether Oils under Boundary Lubrication Conditions

Perfluoropolyalkylether (PFPE) oils and greases are being used with increasing frequency on spacecraft as a result of their purported outstanding properties. Previously we demonstrated that, under boundary lubrication, these materials degrade by way of an autocatalytic mechanism. As a result, they have serious limitations that cannot be improved using additives because of the inability of the PFPE fluids to dissolve antiwear additives. A series of wear tests comparing PFPE oils and greases with hydrocarbon fluids under boundary conditions were performed which augment the fundamental studies. As predicted, the performances of the PFPE fluids were below that of the hydrocarbon fluids. The results of the wear tests are discussed in terms of the effect that additives would have on the PFPE degradation mechanism and the overall usefulness of the PFPE fluids under boundary lubrication conditions. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in San ...

The use of solid ceramic and ceramic hard-coated components to prolong the performance of perfluoropolyalkylether lubricants

Abstract The performance of perfluoropolyalkylether (PFPE) oils under boundary lubrication conditions was tested using 440C stainless steel, silicon nitride/440C hybrid, and titanium nitride hard-coated ball-bearing components. By limiting the chemical interactions between the lubricant and iron, the performance was extended by a factor of 5–10 using the ceramic materials instead of 440C components. The maximum performance enhancememt for the PFPE oils under our test conditions was limited by thermal degradation at the high temperatures generated in the asperity contact region.

Chemical Analysis of Hydrocarbon Grease from Spin Bearing Tests

The rotor bearing running torque levels of certain spin bearing units were found to increase significantly during extended life testing. Samples of the greases from these tests were analyzed to determine if lubricant degradation was linked with the increased torque levels. By means of chromatographic and spectroscopic techniques, we were able to determine that oxidation of some of the greases had occurred and that the oxidative degradation was most easily observed in the soap-thickener portion of the grease. A correlation between the disappearance of the fatty acid salts and the appearance of degradation products was observed. Polymerization of the greases war observed in all samples. We also determined that the grease degradation was symptom of adverse mechanical condition in the bearings and not the primary cause of mechanical problems. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in Washington, D.C., October 5–7, 1982

Oil Exchange Between Ball Bearings and Cotton-Phenolic Ball-Bearing Retainers.

Experiments have been performed that determine for the first time the transfer of oil between cotton-phenolic ball-bearing retainers and operating ball bearings. A full retainer exchanges oil with the metal park of the bearing, probably by diffusional mixing. There is no net delivery of oil from the retrainer to the metal parts of the bearing. A partially filled retainer (such as one that has been incompletely impregnated) absorbs oil from the bearing even during operation, this drying the bearing. A fully-impregnated retainer does not deliver any significant amount of additional oil to the metal parts of a poorly lubricated bearing. The retainer will not prevent lubricant degradation and premature bearing failure under the conditions of these experiments. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Modeling and Measurement of Aryl Phosphate Ester Vapor Pressures at 50°C

The vapor pressure of TCP was determined by measuring the loss rate under vacuum conditions at 50°C. The mass loss of a four-component aryl phosphate ester additive mixture was also measured. The loss-rate was modeled, and the component vapor pressures were determined by fitting the model to the experimental loss data. The values measured were significantly lower than those obtained through extrapolation of higher-temperature vapor pressure data.

Oil Exchange between Ball Bearings and Porous Polyimide Ball Bearing Retainers

The kinetics of the absorption of lubricating oils and moisture from air into porous polyimide, as well as the exchange of oil between porous polyimide retainers and oil baths or operating bearings, have been measured. Oil absorption into porous polyimide is much faster than into cotton-phenotic. Water is absorbed by oil-impregnated polyimide, but little or no oil is lost during the process. Oil is absorbed by air-equilibrated polyimide at a slower rate than by dry polyimide. Porous polyimide is much easier to impregnate with oil than cotton-phenolic, and is also much more tolerant, of storage in air once impregnated. Oil within a porous polyimide ball bearing retainer exchanges slowly with oil in a bath in which the retainer is placed. The exchange is due to diffusion of the oils, and the diffusion coefficient is determined to be 3 × 10−9 cm2/s for the oils used in these experiments. Oil is exchanged quickly between polyimide retainers and well-lubricated operating bearings. The exchange is faster than a...

A Model to Calculate Evaporative Oil Loss in Spacecraft Mechanisms

Calculations of oil loss from ball bearings in space are generally limited by the oil vapor pressure data base used in the calculations. The authors have developed a computer model that ties oil loss behavior of linear hydrocarbons to empirical oil loss measurements. This results in more accurate determination of evaporative oil loss. Two oils are modeled. The application of the model for the oils to actual mechanisms is discussed.

Lead naphthenate additive tribochemistry in hydrocarbon oils

There is often ambiguity concerning the antiwear mechanisms of soluble lubricant additives used in bearings. For example, the common spacecraft lubricant additive lead naphthenate is thought to be effective only as long as a measurable concentration is present in the oil lubricant throughout the mechanism lifetime. Recent mechanism tests with several days of operation indicated that a hydrocarbon lubricant was depleted of lead naphthenate, even during successful operation. To elucidate this apparent contradiction we conducted tests on 440C stainless-steel thrust bearings lubricated with Apiezon C hydrocarbon oil that was formulated with 5 wt% lead naphthenate. The remaining oil in the bearings was analyzed using Fourier Transform Infrared Spectroscopy (FTIR) after several tests with varying durations up to 336 h (2 wk). FTIR showed that lead naphthenate chemically changes within 24 h and begins to disappear in 336 h. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical state of the bearing surfaces after testing. XPS spectra indicated that lead naphthenate chemisorbs onto the bearing surface with minimal bearing operation, and further reaction to elemental lead (a solid lubricant) occurs at relatively short interaction times (two weeks in our testing). Ball bearing test data indicate that, despite the early loss of additive from the oil, the lead-containing surface coatings provide continued lubrication for the ball bearing.

Tricresyl Phosphate Retention by Bearing Retainer and Reservoir Materials

Tricresyl phosphate (TCP) is an important extended-pressure additive in lubricating oils. Its depletion from reservoir oil could constitute a failure mechanism for bearing system. The interaction of TCP with bearing retainer and reservoir materials was investigated using an apparatus that mimicked centrifugal oil feed. TCP was not selectively absorbed by cotton-phenolic retainer or wool felt reservoir materials, but was absorbed by nitrile-acrylic and sintered nylon reservoir materials, which exhibited significant TCP retention. The results are discussed in terms of the degree of bulk oil absorption, the availability of polar sites on the sorbents, and the interaction between such sites and the TCP molecules. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984