Lubricant Deposition Research Articles

Comparison of the mixed flow and heat transfer characteristics in the evaporator of a vapor compression heat pump in normal gravity and microgravity

As a thermal control system for space applications, the vapor compression heat pump is crucial for the future development of aerospace technology. The evaporator in the heat pump is significantly affected by the space environment. Lubricant is present in the system during the operation, and the gas-liquid separation is difficult to achieve in a microgravity environment. The oil-containing refrigerant may form an oil film on the evaporator wall, and deposition may occur. A mixed flow and heat transfer model of the refrigerant and lubricating oil in the evaporator of the vapor compression heat pump was established to investigate the gas-liquid separation and lubricating oil deposition of the vapor compression heat pump in microgravity. The heat flux effects on the flow and heat transfer characteristics were simulated in normal gravity and microgravity using FLUENT. The simulation and experimental results of the evaporator outlet temperature in normal gravity were compared, and the simulation results of the heat transfer coefficient of the refrigerant R134a were compared with experimental data obtained from the literature. The results demonstrate that the velocity field exhibits a large gradient and an asymmetric distribution in normal gravity and an asymmetric distribution with lower values in the lower and upper right positions in microgravity. The heat transfer performance of the evaporator is lower in microgravity than in normal gravity for the same heat flux. For the same heat flux (100000 W/m2), the vapor phase volume ratio of the evaporator outlet is 0.95-1 in normal gravity and 0.6-0.7 in microgravity. After the phase change of the refrigerant and lubricant mixture in the evaporator, the lubricant deposition is not affected by the heat flux in normal gravity and microgravity, and normal oil return occurs. A maximum deviation of 14.9% is observed between the simulated and experimental values of the evaporator outlet temperature in normal gravity. The heat transfer coefficient of the R134a obtained from the simulation is within the range of the experimental values in the literature. This work expands our understanding of microgravity two-phase flow heat transfer and provides theoretical guidance for the development of the evaporator in vapor compression heat pumps for aerospace applications.

Optimization of Pulsed Fiber Laser Texturing for Solid Lubricant Deposition on a Ti/TiN Coated Aerospace Alloy

AA2219 is a superior performance Al-base alloy which promises toughness, strength and creep resistance which allows the deposition of titanium nitride (TiN) coating at 200 °C. The present research addresses the issue of poor wear properties of the alloy, using state of the art technologies, to deposit hard and adherent thin TiN layer followed by laser surface texturing. The thickness of sub-micron size coating is determined by appropriate modification of the existing mathematical model and composite microhardness values. Laser energy density of 20.8 J/cm2 and 4 repeated pulses is optimized to produce regular size and shape of micro-holes on TiN-coated samples. Epoxy-based MoS2 lubricant is deposited on laser textured samples to produce ultra-low friction surfaces. The micro-holes act as a micro-reservoir of MoS2 solid lubricant. Field emission scanning electron microscope and optical profilometer were used to estimate the topology, shape, size, and depth of micro-holes. The cross-sectional view shows the successful impregnation of epoxy-based MoS2 due to the chemisorption of functional groups with an Al oxide surface.

Solid lubricant mass contact transfer technology usage for vacuum ball bearings longevity increasing

A contact mass transfer technological method of solid lubricant deposition on components of vacuum ball bearings is presented. Physics-mathematical model of process contact mass transfer is being considered. The experimental results of ball bearings covered with solid lubricant longevity in vacuum are presented. It is shown that solid lubricant of contact mass transfer method deposition is prospective for ball bearing longevity increasing.

Investigation of subsequent deposit growth on pre‐existing lubricant deposits: a substitutional growth model

AbstractThe Penn State Micro‐Oxidation (PSMO) test was used in an inverse manner to pre‐cover metallic pan surfaces with polymeric, transitioning and carbonaceous films. These pre‐coated pans were then used as the initial test specimen/surface upon which fresh lubricant samples were aged. The effects of pre‐deposits of varied ages were gauged against the baseline of a virgin metallic surface to decouple the lubricant‐deposit system towards resolving their effect upon further deposit growth. From such data, a uniform deposition model describing deposit formation and aging was developed. Chemical characterisation of PSMO deposits by Fourier transform infrared‐attenuated total reflectance and energy‐dispersive X‐ray spectroscope analyses provide additional supporting evidence of changes in chemical bonding (alkyl C–H and carbonyl C=O bond stretching vibrations) and composition (C‐ and O‐atom content) as the deposits undergo deoxygenation and dehydrogenation reactions. Across different aged oils and films, the substitution tests show a declining activity towards mass deposition with film age, interpreted as decline in reactivity. Copyright © 2016 John Wiley & Sons, Ltd.

Head–Disk Lubricant Transfer and Deposition During Heat-Assisted Magnetic Recording Write Operations

Lubricant accumulation was found on the media surface the instant when the laser is turned OFF during heat-assisted magnetic recording write operations. By changing the write cycles, laser ON/OFF duration, media, and head temperatures, we find that this lubricant accumulation is related to the change in head-media temperatures. The observed lubricant deposition process is restricted to a short time window (1-2 μs) after the laser is turned OFF. An equilibrium model of thermal displacement due to evaporation and condensation processes is presented and used to discuss the effect of the head-media temperature changes on the lubricant accumulation. Possible solutions to minimize the lubricant transfer and deposition are discussed.

Tribological Behaviour of Lubricants in Hot Stamping of AA6016

The increasing demand for fuel-efficient vehicles has led automotive industry to introduce new alloys in car manufacturing, characterized by a high stiffness and strength-to-weight ratio. Due to their mechanical and chemical properties, aluminium alloys appear potential candidates to replace traditional steels for several parts of the car-body-in-white, even if the limited formability at room temperature, the marked springback and the severe tribological behaviour have often represented important drawbacks in traditional properties. Recently, the use of temperature-assisted processes, such as hot stamping, allows overcoming such limits thanks to substantial increase of the formability and, at the same time, a drastic reduction of springback. However, the choice of proper process parameters, in terms of lubrication at the interfaces between the dies and the blank, and thermal parameters of the dies materials still represent critical points for the feasibility of the process. Recent investigations have proved the limits of assuming constant friction for all the areas of the dies and the steps of the deformations, especially with variable pressures and non-constant temperatures at the interfaces. Such factors, together with the lubricants and the lubricant deposition on the blank, the blank and dies coatings, the surface roughness, the stamping speed are not always considered, despite their considerable influence on the process tribology. In this paper the friction behaviour of commercially available automotive aluminium (AA6016 alloy) is studied. The friction coefficient is measured by means of a new machine for strip draw test at different levels of pressure, temperature, sliding speed and type of lubricant. The results report the investigation of the surface topography of the metal sheets, investigated by Energy-Dispersive X-ray spectroscopy and optical profilometry.

Application of temperature-programmed oxidation (TPO) in studying the mechanism of deposits formation from the degradation of lubricants on metal surfaces

Temperature-programmed oxidation (TPO) was used to investigate the mechanism of lubricant-derived deposit formation on metal surfaces. The relationship between the crystalline structures of different carbonaceous specimens, along with their chemical reactivity, was used to distinguish between more reactive and less reactive lubricant deposits. Multiple CO2 peaks obtained were attributed to differences in the oxidation reactivity of the deposits with respect to their structural characteristics. Findings from this work suggest that as deposits evolve, they become more complex (varied) due to loss of O and H atoms during a carbonisation-type process. As these deposits undergo visible changes over time (lacquer deposit transforming into dark carbon), the average peak temperature (weighted average oxidation temperature) monotonically increases. Characterisations of lubricant deposits by TPO indicate that the global change in carbonaceous structure proceeds across the deposits in a uniform layer deposition model. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of fully and partially additized lubricant deposits by Temperature Programmed Oxidation

Temperature Programmed Oxidation (TPO) was used to analyze carbonaceous deposits derived from the thermal decomposition of a Group 1 base oil and a fully-formulated lubricant. Deposits generated from thermal decomposition of concentrated blends of detergents, dispersants, viscosity modifiers, and antioxidants additives were also analyzed. Results obtained from each of the deposit specimens featured “unique” oxidation profiles. For fully-formulated lubricants and base oil-derived deposits, two characteristic peaks with an overlapping tendency were observed. The first evolved at a relatively lower oxidation temperature and the second at a higher oxidation temperature. Similarities between formulated lubricant and base oil TPO profiles were attributed to the common base oil found in both samples. However, higher thermal stability of the fully-formulated lubricant led to minimal deposition and less intense TPO peaks compared to the base oil-derived deposit profiles. For concentrated additive-derived deposits, deposits showed distinct oxidation profiles, unique to each category of additive and not comparable to any other deposit type.

Process Smoothing of the Inner Surface of Cylinders after Honing and its Role in Eliminating Wear in the Activation of the Heat Engine

It is known that one of the basic requirements of the market economy is product competitiveness; competitiveness ensures their operating performance and the costs of obtaining them and therefore manufacturing costs. Process smoothing of the cylindrical internal surfaces must ensure a very high diameters precision and a low surface roughness. Cylindrical inner surface smoothing can be achieved through the following processes: indoor spinning roller, honing, lapping, etc. Fine machining processes without material removing, ensures based on the initial surface quality, initial quality metal cutting, work regime that is processed, hardness increasing by (20…60)%, roughness Ra=(1.6…0.4)μm, and fine processing procedures with material removal, ensures a high quality of machined surfaces, resulting in roughness Ra=(0.4…0.02)μm. Deformed layer size reducing at the previous processing, and reducing of micro depths serving as lubricant deposits, contributes to increasing wear resistance of cylinder surface. Cylinder inner surface smoothing by honing machines is performed on honing machines with a specially designed tool called hon. In the honing process, abrasive grain trajectories are forming on the cylinder a network of fine spiral lines. If carried out on a flat surface, these helical lines become straight and intersecting an angle 2α. Processing accuracy depends on the accuracy of the previous bore. In this paper, the focus is on several methods of heat engine cylinder forming the passage of the piston and rings share repair and their effect giving the engine operating parameters specified by eliminating the running operation. With the help of experimental and theoretical data and the methodology of approach to the subject, several aspects have been clarified regarding the depth of the asperities on the honed surface compared to a process-smoothed surface. The influence of all factors on the processing results has not been thoroughly explained. The following research methods shall be discussed in the future: improving the method of adjusting the pressure of the centrifugal rollers with the help of an automatically controlled device and the creation of an auxiliary device to adjust the bars to which the rollers are connected according to the internal diameter of the processed cylinders.

Tribological Performances of Two White Lubricants in Hot Steel Forging

The tasks of a lubricant used in the hot forging of steel is to reduce friction, cool down tool surfaces, and limit tool surfaces pollution by wear debris and oxides scales transferred from work piece surfaces. The most widely used lubricants in hot forging are dispersions of graphite particles in water or in oil. The graphite is involved to reduce friction. The liquid is used, first, to carry the graphite solid particles to the tool surfaces and, second, to reduce tool surface temperature. But graphite and vapours resulting from the lubricant deposition on hot surfaces lead to dirty workspaces. Some new lubricants are then developed in order to reduce friction in a cleaner way. When they are graphite free, those new lubricants are called “white lubricants”. The aim of the present work is to test two different white lubricants. The first one is a mineral salt; the second one is an organic salt. Lubricant performances are classified using the Warm and Hot Upsetting Sliding Test (WHUST). This friction bench simulates tests with contact pressure, sliding velocity, contactor and specimen temperatures similar to industrial ones. Before performing friction tests, work piece are heated up to 1200°C, contactors are heated up to 200°C, and lubricants are sprayed on contactor surfaces. Then the contactor slides against the specimen with a constant penetration, leaving a residual deformed track on its surface. Direct WHUST results are tangential and normal loads measured on contactor, surface roughness and chemical compositions on specimen and contactor surfaces. “Wear markers” are derived from those direct results, and provide useful information on the ability of the tested lubricants to reduce friction and protect tool surfaces. In the present study, tests are performed with different sliding speed and different contact pressure. The two white lubricants are compared to a generic graphite in water dispersion. Results show the tested white lubricants lead to coefficient of friction in the same range of the graphite lubricant one, but white lubricants lose their ability to reduce friction as soon as the sliding lengths becomes greater to 10 mm, where graphite lubricants can undergo sliding length greater than 30 mm.

A methodology to determine surface durability in multifunctional coatings applied to soft substrates

The tribological characterization, in particular the surface durability of multifunctional layers applied to soft, non-magnetic materials, due to their important differences in mechanical and tribological properties, constitutes, by itself, an important challenge to the tribologist. These multifunctional layers consist of a solid lubricant coating on top of a hard, wear resistant and high load-supporting layer. The use of low severity conditions, which are necessary to discriminate between solid lubricants, induce unnecessary and unduly long test times. The use of high severity conditions, which are more adequate to analyse the hard, high load supporting layers, produce shorter tests but are not able to discriminate among the solid lubricant deposits. In this paper, a new methodology allowing short test time with good discrimination between multifunctional layers is proposed. The test protocol is based on a method of incremental loading. By increasing the normal load in increments at a constant time interval the surface durability of both the hard layer and the solid lubricant coating was determined. The suitability, reliability and reproducibility of the proposed methodology were determined by testing commercially available solid lubricants (DLC, Teflon ®, MoS 2 dispersed in an inorganic binder and MoS 2 dispersed in an organic binder) coated on commercial aluminium (as received and as anodised).

The role of bearing and scan mechanism life testing in the flight qualification of the MODIS instrument

AbstractThis paper describes the results of accelerated and operational life tests on bearings for the Moderate Resolution Imaging Spectroradiometer (MODIS). It also describes the post‐test analysis of the disassembled bearings. Analysis was performed using micro‐Raman, micro‐FTIR, X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and size exclusion chromatography (SEC). In general, the three sets of bearings in each of three test stations were in very good condition after accumulating 68, 144, and 209 million cycles, respectively. Some of the bearings exhibited lubricant degradation, indicated by viscous lubricant deposits on the cage and raceways.

Geometric effects in high‐temperature vapour‐phase lubrication using hydrocarbon feed gases

AbstractThe effectiveness of ‘far‐field’ vapour‐phase lubrication, in which areas of a bearing surface that are cycled through the contact are exposed to vapour while outside the contact, has been demonstrated in both sliding and combined roll slide tests using acetylene vapours to deposit pyrolytic graphite. Friction coefficients as low as μ = 0.008 have been measured for steel at 540°C with far‐field acetylene concentrations as low as 5%. Effective vapour‐phase lubrication depends on solid lubricant deposition that exceeds the contact's capacity to remove solid lubricant through wear. While the rate of removal is increased by increasing the sliding velocity, in far‐field vapour‐phase lubrication the rate of lubricant deposition, and therefore the lubrication effectiveness, is augmented by increased areas available for far‐field deposition, such as those provided by performing wear tests with increased wear‐track diameters. These geometric concepts may be considered in rolling‐element bearing and gear set applications where vapour‐phase lubrication is to be employed.

Atmospheric Degradation Mechanism of CF3OCH3

Recognition of the adverse effect of chlorofluorocarbon (CFC) release into the atmosphere has led to an international effort to replace CFCs with environmentally acceptable alternatives. Hydrofluoroethers (HFEs) are a class of compounds which have been developed to replace CFCs in applications such as the cleaning of electronic equipment, heat transfer agents in refrigeration systems, and carrier fluids for lubricant deposition. HFEs are volatile compounds and are released into the atmosphere when used. CF{sub 3}OCH{sub 3} has not been used commercially but is one of the simplest fluoroethers and serves as a model compound for the group of fluorinated ethers. A smog chamber/FTIR technique was used to study the Cl atom initiated oxidation of CF{sub 3}OCH{sub 3} in 700 Torr of N{sub 2}/O{sub 2} at 296 K. Using relative rate techniques it was determined that {kappa}(Cl + CF{sub 3}OCH{sub 3}) = (1.4 {+-} 0.2) {times} 10{sup {minus}13} and {kappa}(Cl + CF{sub 3}OC(O)H) = (9.8 {+-} 1.2) {times} 10{sup {minus}15} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. At 700 Torr of N{sub 2}/O{sub 2} diluent at 296 K reaction with O{sub 2} is the only loss mechanism of the CF{sub 3}OCH{sub 2}O{sup {sm_bullet}} radical. The infrared spectra of the peroxy nitrates CF{sub 3}OCH{submore » 2}O{sub 2}NO{sub 2} and CF{sub 3}OC(O)O{sub 2}NO{sub 2} were recorded and compared to the nonfluorinated analogues CH{sub 3}OCH{sub 2}O{sub 2}NO{sub 2} and CH{sub 3}OC(O)O{sub 2}NO{sub 2}. The thermal decomposition rate of CF{sub 3}OC(O)NO{sub 2} is (2.3 {+-} 0.1) {times} 10{sup {minus}4} s{sup {minus}1} in 700 Torr of N{sub 2} at 295.8 K. The reaction of CF{sub 3}OC(O)O{sub 2} radicals with HO{sub 2} radicals gives CF{sub 3}OC(O)H in a yield of (80 {+-} 11)%. The results are discussed with respect to the atmospheric degradation mechanism of CF{sub 3}OCH{sub 3} and other ethers.« less

High temperature lubrication of combined rolling/sliding contacts via directed hydrocarbon gas streams

Extended duration solid lubrication of rolling/sliding contacts, typical of gear teeth, comprised of self-mated steel at high temperature (540 °C) by carbon deposits continuously replenished through pyrolysis of acetylene feed gases, has been confirmed using a WAM-1 test machine. Adequate lubrication, denoted by a low traction coefficient (μ < 0.05), depends on a sufficient rate of solid lubricant deposition relative to the removal rate (due to wear). In the absence of lubrication, high traction coefficients (μ > 0.25) and scuffing will occur. Through tests initiated under adequate lubrication conditions, the balance of rates of deposition and removal is found to be adversely affected by decreased temperature or precursor gas feed rate, or by increased normal load or sliding speed. Gradual excursions in the controlled test variables produce transitions to inadequate lubrication and scuffing as demarcated by rapid increases in traction coefficient.

Solid lubrication by decomposition of carbon monoxide and other gases

Extended duration high temperature (above 500°C) lubrication of silicon nitride sliding and rolling contacts was accomplished by solid carbon deposited and replenished via the decomposition of carbonaceous gas streams directed towards the tribological surfaces. Injection of carbon monoxide-hydrogen mixtures can lead to reductions in high temperature friction and wear of silicon nitride sliding contacts by factors of up to 10 × and 500 × respectively from the unlubricated case. Similar lubrication is attained by various hydrocarbon gas mixtures, while only a ten-fold reduction in wear is attained by a carbon dioxide-hydrogen mixture. Effective lubrication can be modeled as a favorable balance between carbon deposition from the gas phase and removal by wear. This model is based on the dependencies of solid lubricant deposition and removal processes on temperature, sliding speed, normal load, decomposition activation energy, gas flow rate, and tribosystem properties. The model is checked by the mapping of regions where measured friction indicates that lubrication by CO-H 2 mixtures is adequate, and the identification of a boundary representing the onset of marginally effective lubrication.

On the problem of determination of the distance of the pneumatic rifle shot

The criteria of determination of the distance of the IZH-38 pneumatic rifle shot by peculiarities of lubricant deposits of the barrel bore on the vertical target wthi regard to its remoteness from the barrel cut are presented. The regularity of lubricant deposits on the target of an elliptic form in three zones: continuous, relatively continuous and solitary drops is revealed. The distance of the shot affects the formation, nature, relative position, combination and sizes of zones. The greatest distance of the shot comprises 185 sm wherein lubricant deposits on the target are revealed. The data obtained testify that for the pneumatic low-speed rifle the nature of lubricant deposits of the barrel bore around inlet bullet may serve as one of signs allowing to judge the distance of the shot.

"Organic lubricant evaporation method", a new lubricating surface treatment for thin film magnetic recording media

A new surface treatment method was developed, which improves wear resistance of thin film magnetic recording media. In this method, a thin film of higher fatty acids, their metal salts, amides, esters, etc. is coated on the magnetic film surface by the vacuum deposition method, and it is called the "lubricant deposition method". In this experiment, a still life of more than 60 minutes could be obtained by depositing lithium oleate on the HIN deposition tape.

A Microscale Deposition Test for the Evaluation of Aircraft Turbine Engine Lubricants

The development of a liquid-phase micro panel coker and a vapor-phase micro panel coker is described. The devices are intended primarily for use in screening synthetic lubricants on the basis of deposit formation in instances where only research-size sample quantities are available. Each model requires less than 75 ml of sample per test and is capable of operation to 1000 F panel temperature. Both micro coker models were utilized in an experimental investigation of the effects of lubricants, panel temperature, and dry and moist air on lubricant deposition. In addition, the liquid-phase micro coker data are examined in comparison with full-scale panel coker and bearing deposition test results. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference held in Atlantic City, New Jersey, October 8–10, 1968.

Lubrication of High-Speed High-Temperature Thrust Ball Bearings

High temperatures impose special problems on the operation of high speed axially loaded ball bearings. Among these are fatigue, lubricant deposits, and aggravated friction and surface damage at areas of metal contact. This paper is concerned only with the friction and surface damage aspects of the problem. Since a small scale bearing was to be used in the experimental work, an analysis was made of spinning, one of the major friction sources, and the small-scale operating conditions were chosen to give ball-to-race surface temperatures approaching, as near as practical, the corresponding temperatures for full-scale bearings. Bearing rig tests in a once-through jet lubrication system with silicone fluid, mineral oil, and a synthetic ester lubricant resulted in friction failures at approximately 350F, 650F, and 800F, respectively. This is in agreement with full-scale experience and lends support to the validity of the rig tests. With oil-air mist lubrication failure occurred at a much lower temperature. This...