In the present study, the tribological behavior of polyaryletherketones (PAEKs) and their composites was investigated in air and vacuum environment. Polymer matrices were filled with either glass or carbon fibers and compared with a standard bearing material containing 10% carbon fiber (CF), 10% graphite, and 10% polytetrafluoroethylene (PTFE). The samples were tested in a pin-on-disk configuration under continuous sliding against a rotating steel disk (AISI 52100) at different sliding speeds. The results indicated that the tribological performance of these materials in vacuum depends on both compositions and test conditions. At low sliding speed, a very low friction and wear coefficients were obtained while at higher speed, severe wear occurred. In particular, CF filled composites showed excessive wear that led to the ignition after opening the vacuum chamber. Experimental results are discussed by analyzing the transfer film and wear debris.

This work examined friction-reducing and antiwear behaviors of multialkylated cyclopentanes (MACs) oil with Mo and W nanoparticles as additives under vacuum condition (∼10 −4 Pa). The tribological evaluation was conducted on a vacuum four-ball tribometer. The results suggested that the MACs oil exhibited the transient high friction in vacuum, resulted into severe adhesive wear to the steel friction pairs. The Mo and W nano-additives could effectively eliminate the severe adhesive wear. When added with Mo nanoparticles, the lubricating life of MACs oil could be prolonged due to the retarded decomposition of MACs, which should be ascribed to the formation of Mo metallic boundary films on steel ball surfaces that was confirmed by the surface analysis. As for W nanoparticle additives, the rolling effect as nano-bearings and the abrasive wear of larger particles due to the aggregation of W nanoparticles are the dual tribological mechanisms.

Ti-6Al-4V pins were slid against SS316L disks in pin-on-disk arrangement using pins of different diameters; with the contact pressure maintained the same for all experiments under ambient and vacuum conditions. Characterization of the tribological samples was performed using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD). The tribological behavior was found to be governed by strain rate response (SRR), tribo-oxidation (TO), formation of a mechanically mixed layer (MML), and frictional heating which can affect each of the above factors. For a particular set of experiments (ambient/vacuum), variation of wear-rate with respect to sliding speed were found to follow the heat flux in each set. Propensity of this material to undergo softening due to frictional heating and strain rate effects is reflected in the tribological response.

This paper configured an improved grip system for gripping and transferring large flat sheets in a noncontact manner. The conventional method for changing the direction of large flat sheets in a conveyor system is to turn the system itself. The new configured grip system applied a noncontact pneumatic head in the vertical direction, with the use of an air levitation table, and L-shaped latches, to lift and rotate large flat sheets to change their direction in the conveyor system. The pneumatic heads made efficient use of a vortex flow and an internal flow guide to improve the swirling flow. The gripping force for the improved head with the inner flow guide was 10% higher than that for the conventional head. To construct a rotational grip system, 12 improved noncontact heads and eight pairs of L-shaped latches were used to provide gripping force against an eight generation liquid crystal display (LCD) glass as a 4:6 ratio, each other. With a partial levitation force from the air blow table, the head-and-latch configuration resulted in the overall glass flatness approaching within 3.0 mm on the lower side at a selected grip rotation height of 40 mm.

In order to investigate the vacuum tribological properties of a Ti-46Al-2Cr-2Nb alloy, dry-sliding tribological tests of the alloy against AISI 52,100 steel ball under different sliding speeds and loads were performed at a high vacuum of 4.0 × 10−4 Pa by ball-on-disk rotating configuration, and the same tests were done in air for comparative purposes. It is an important finding that the TiAl intermetallics have good wear resistance in vacuum, not like that in air. The wear rate of the Ti-46Al-2Cr-2Nb alloy in vacuum is almost lower by an order of magnitude than that in air.

In dipped (splash) lubrication, a rotating component, such as a gear, is partly submerged in a reservoir of liquid lubricant and acts to distribute it within the lubricated machine. Dipped lubrication is widely used for low to medium speed applications in the industrial and automotive sectors and there is a significant interest in the associated energy loss (the “churning” loss) because of its influence on efficiency and fuel consumption. In this study, a simple test rig consisting of a spur gear rotating in a cylindrical enclosure, partly filled with a liquid, was used to study the effect of fluid properties on the churning loss. The inertia rundown method was used to determine the power losses. Lubricating oils, water and aqueous glycerol solutions were among the fluids used. Correlations with Froude and Reynolds and Bond numbers are presented. It was found that the churning losses were significantly affected by the fluid disposition within the housing. In turn this was affected by the ratio of inertial forces to gravity (Froude number) and by air pressure. The influence of the pressure of the air within the enclosure was also investigated. When the air was evacuated from the enclosure, the churning losses increased, by a factor of up to 4.5 times. This can be explained by the effect of air (windage and aeration) on the liquid disposition, factors neglected in most previous work.

A Frictionally constrained condition implies dependence of friction force on tangential displacement amplitude. The condition may occur due to chemical, physical, and/or mechanical interaction between the contacting surfaces. The condition, sometimes also referred to as the presliding condition or partial slip condition, is characterized under fretting. Under such conditions, various experimental studies indicate the existence of two distinguishable regions, that is, stick region and slip region. In the present study, frictionally constrained conditions are identified and the evolutions of stick-slip regions are investigated in detail. Investigations have been performed on self-mated stainless steel and chromium carbide coated surfaces mated against stainless steel, under both vacuum and ambient conditions. Contact conditions prevailing at the contact interface were identified based on the mechanical responses and were correlated with the surface damage observed. Surface degradation has been observed in the form of microcracks and material transfer. Detailed numerical analysis has also been performed in order to understand the energy dissipation and the damage mode involved in the surface or subsurface damage. It has been observed that under frictionally constrained conditions, the occurrence of annular slip features are mainly due to the junction growth, resulting from elastic-plastic deformation at the contact interface. Ratcheting has been observed as the governing damage mode under cyclic tangential loading condition.

There are disk-drive data storage applications best served by single-sided recording configurations. These include situations where (i) storage requirements can be achieved on a single side of a disk and (ii) dimensional constraints on the disk drive prohibit the presence of a recording head and its associated mounting device on each side of the disk. Even if dimensional requirements are not a concern, the most cost-effective and operationally efficient slider-disk air-bearing interface for single-sided recording is one that does not include an air-bearing slider, pressure pad, or other air-bearing structure on the nondata side of the disk. A metal foil disk offers some of the best characteristics of both the hard disk and floppy disk for digital data storage. It offers hard disk recording densities, increased shock resistance, reduced manufacturing cost, and requires less operational energy than a hard disk. However, use of a conventional recording head slider assembly without opposing air-bearing support for single-sided recording on a high-speed metal foil disk presents a fundamental problem because the air-bearing surface of the slider produces a net transverse force to the disk. This force causes the disk to deflect and can result in flying height and stability problems at the slider-disk interface. The current work describes an air-bearing interface for low flying height single-sided recording on a high-speed metal foil disk that minimizes disk deflection and instability without the presence of air-bearing components on opposing sides of the disk. The new interface utilizes a vacuum cavity-type air-bearing with little or no preload. Examples will be presented and discussed for the new interface that illustrate the flying characteristics of a picosized slider on a 1.8 in . stainless steel disk with thickness of 25.4 μ m .

In order to improve the durability of metal-film magnetic tapes, novel lubricants, A20H, X-1P, and X, a modified phosphazene, were deposited on the tapes. The adhesion, friction, and wear of the unlubricated/lubricated tapes were investigated using an atomic force microscope (AFM). The degradation of the lubricants was studied using a mass spectrometer in high vacuum. The durability of various unlubricated/lubricated tapes was compared in ambient and in humid air. The AFM test results show that the A20H lubricated tape exhibited lower adhesion and friction than X-1P and X lubricated tapes. The lubricants were believed to be mainly degraded by tribochemical reaction and mechanical shear in high vacuum. In high humidity air, the various lubricated tapes exhibit higher friction than in ambient air. By comparing the tribological performances of the various lubricated tapes to metal particle (MP) tape, it was found that the lubricated metal-film tapes exhibit lower adhesion, friction, and wear than the MP tape.

This paper investigates the performance of a seal system for an aerostatic journal bearing used in a high vacuum chamber. The seal system consists of axially spaced viscous seals and annular exhaust grooves that are located between the viscous seals. Each exhaust groove is coupled to a separate vacuum pump in order to achieve a vacuum chamber pressure of less than 10 − 3 Pa. The vacuum chamber pressure is affected by design parameters such as the number of viscous seal stages, seal length, seal gap, and exhaust tube conductance. The influence of these design parameters on the pressure distribution across seal regions and the vacuum chamber pressure are discussed theoretically. It is subsequently shown that an aerostatic journal bearing with three-stage seal system installed can obtain a reduction in the vacuum chamber pressure almost to the ultimate pressure of a vacuum pump, providing there is no leak or outgassing from materials.

The sensitivity of clean and oil-impregnated cotton-phenolic retainers to atmospheric humidity has been measured. The cleaning procedure used here, and vacuum oil-impregnation did not change the dimensions of the retainers. Absorption of water caused the diameter of the retainers to increase by 0.2 to 0.4 percent, depending on the humidity. Oil impregnation of the retainers retarded, but did not stop, the absorption of water. Oil was displaced from the impregnated retainers by water; one-third to one-half of the oil was removed, depending on the atmospheric humidity.

This paper completes previous studies concerning the mechanisms governing friction and wear of a steel/graphite couple under an external applied magnetic field. Friction tests were performed in a controlled chamber with a magnetised steel pin sliding against a graphite disk exposed to oxygen, argon, and vacuum environments. Wear debris and friction tracks generated by reactions with the gases after sliding, with and without magnetic field, were identified ex situ by scanning electron microscopy and energy-dispersive X-ray analysis. It shows that the magnetic field modifies the third body behavior which depends on the gases surrounding the contact; this governs the friction state, the type of graphite wear (fatigue or abrasive wear), and the surface reactivity.

Compressible Narrow Groove Analysis, as derived in a companion paper (Pan, 1998), is a model implementation of Thin Film High-Resolution Modeling for gas films. This paper describes the numerical procedure to compute the pressure field in a centered spherical device, which has general design features originally intended for a high performance gas bearing gyroscope (Keating and Pan, 1968). The number of groove patterns is varied to bring out the significance of the local compressibility number. Increased local compressibility, associated with reduced number of groove patterns, causes successive degradation of the pressurization capacity until it is entirely suppressed at 32 groove patterns. Further study is made with reversed rotation to create a high vacuum state in the gas film concurrent with a large compressibility number. The evacuation operation (with reversed rotation) is relatively insensitive to the number of groove patterns, but is highly dependent on the accommodation coefficient. Experience in preparing these examples lends evidence to the robustness of Thin Film High-Resolution Modeling. Trouble free iterative computations are routinely performed for the local Knudsen number in excess of 10 9 and the effective local compressibility number larger than 100.

Regardless of environment (ultrahigh vacuum, humid air, dry nitrogen, or water), ion-beam-deposited diamondlike carbon (DLC) and nitrogen-ion-implanted, chemical-vapor-deposited (CVD) diamond films had low steady-state coefficients of friction (<0.1) and low wear rates (≤ 10 −6 mm 3 /N·m). These films can be used as effective wear-resistant, self-lubricating coatings regardless of environment. On the other hand, as-deposited, fine-grain CVD diamond films; polished, coarse-grain CVD diamond films; and polished and then fluorinated, coarse-grain CVD diamond films can be used as effective wear-resistant, self-lubricating coatings in humid air, in dry nitrogen, and in water, but they had a high coefficient of friction and a high wear rate in ultrahigh vacuum. The polished, coarse-grain CVD diamond film revealed an extremely low wear rate, far less than 10 −10 mm 3 /N·m, in water.

The NASA Ball on Plate Tribometer was built for the investigation of boundary lubricated rolling. Its contact conditions are easily calculated, and can be adjusted to match a range of real hearing applications for stress, surface velocity, pivot, and contact severity. The rig operates under high vacuum at room temperature. Lubricant charge and specimen preparation are well-controlled and well-characterized. Mass spectroscopy instrumentation allows an indication of lubricant degradation during rolling. Other tribological quantities immediately available are contact resistance, friction coefficient, transverse creep, and orbit velocity deficit. Simple specimens allow post-test surface analysis such as FTIR, XPS, microscopy, and profilometry. Here we describe the Tribometer and discuss representative results obtained with liquid, solid, and no lubricant.

Hydrogenated carbon films (CH x ) with different hydrogen content percentages have been examined. Drag tests on CH x coated disks, using 50 percent Al 2 O 3 /TiC sliders, with and without carbon coating on the slider air bearing surfaces (ABS), were conducted in an ultra high vacuum chamber equipped with a mass spectrometer. Mass fragments of lubricant released from the head disk interfaces were recorded in real time along with friction measurements. The results show that a higher hydrogen content in the carbon overcoat can improve wear durability by reducing the friction coefficient and affecting the chemical reactions between the sliders and the lubricant. A carbon overcoat on the slider ABS can protect Z-dol lubricant from catalytic reaction with the Al 2 O 3 in the slider material. The wear durability at the head disk interface is controlled by combined mechanical and chemical factors, which are defined by the atomic structures of the contacting surfaces.

The TNP contour air bearing slider is composed of oversized transverse pressure contour (TPC) outer rails and a central negative pressure (NP) cavity. The NP cavity is separated from the TPC rails by an ambient pressure reservoir which serves two functions. First, it prevents direct hydrodynamic interaction between the various component air bearing surfaces and thus, eliminates pressure distortion and dilution, common causes of problems related to flying height and roll angle control. Second, the ambient reservoir allows the TPC rails and NP cavity to be configured and dimensioned independently so that they will track each other with a nearly constant force difference, resulting in a flying height that has significantly reduced sensitivity to altitude change. The multi-function TPC sections of the outside rails are able to overcome the effects of a changing radius and wide skew angle variation over the disk radius as well as a changing vacuum load and asymmetry of the NP cavity pressure, in order to provide a truly constant low flying height over the entire data surface. The combination of a high air bearing stiffness and a gradually developing cavity vacuum as disk velocity increases produces a rapid slider take-off from the disk surface. Dynamic stability of the TNP slider air bearing is enhanced by the unusual combination of a high air bearing stiffness and high air film damping in each of the three slider excursion modes. Finally, the TNP slider experiences a reduced sensitivity of flying height to manufacturing and operational tolerances as compared to non-NP type sliders. The entire TNP slider air bearing is created by a two-etch process. A shallow etch creates the TPC sections and leading edge step. A deeper etch forms the NP cavity, ambient pressure reservoir, and outermost edge of each side rail.

This paper presents a rheological investigation conducted on three lubricants used in space applications under vacuum. Lubricant behavior was determined for representative pressures and temperatures. Relations between standardized methods and space requirements are discussed. Finally, the elastohydrodynamic load-carrying capacity of the three fluids in the Newtonian domain is computed over a wide temperature range and compared to those of two reference base oils.

Cavitation erosion tests of composite coatings based on vacuum fusion sintered cobalt alloy containing tungsten carbide particles were carried out in 30 percent HCl and 50 percent H 2 SO 4 solutions. The technique used included an ultrasonic vibratory apparatus at 30°C, 25μm amplitude and 30 kHz frequency. Weight loss was measured with an analytical balance and the microstructure was observed with SEM. The test results showed that the cavitation erosion resistance of the composite coatings was increased by increasing the tungsten carbide content. The cavitation erosion is mainly caused by removal of the matrix material. The steady-state erosion rates have a linear relationship with the volume fraction of the tungsten carbide phase.

Calculations of the forces exerted on a journal by a magnetic bearing actuator are presented, along with comparisons to experimentally measured forces. The calculations are based on two-dimensional solutions for the flux distribution in the metal parts and free space, using finite but constant permeability in the metals. Above a relative permeability of 10 4 the effects of changes in permeability are negligible, but below 10 4 decreases in permeability cause significant decreases in the force. The calculated forces are shown to depend on the metal permeability more strongly when the journal is displaced from its centered position. The predicted forces in the principal attractive direction are in good agreement with experiment when a relatively low value of permeability is chosen. The forces measured normal to the axis of symmetry when the journal is displaced from that axis, however, are significantly higher than predicted by theory, even with a value of relative permeability larger than 5000. These results indicate a need for futher work including nonlinear permeability distributions.