摘要:

Synthetic oils have come into widespread use due to their inherent stability, consistent physical properties, and reproducible composition. As ever increasing demands are being placed on oil performance in magnetic recording disk drives by increasing rotation rates up to 10,000 rpm, it is important to know the ultimate limitations of these functional fluids due to oxidation; In this study, the authors focus on a pentaerythritol ester oil. Accelerated aging tests were carried out on the oil at elevated temperature. Tests were also done with 50 ppm of dissolved iron in the oil. The progress of oxidation was followed by analytical techniques including UV/visible, infrared, and proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography, thin layer chromatography, viscometry, and differential scanning calorimetry. A new technique of laser desorption mass spectrometry with jet cooling, which provides the parent ion mass spectrum, provided the mass distribution of intermediate oxidation products. These techniques enabled determination of the predominant oxidation products. Oxidation proceeds through interchain and intrachain proton abstraction. Hydroxyl groups form on alkyl chains. Intrachain proton abstraction leads to formation of oxetane and conjugated ketone on the original alkyl chain and to cleavage of the alkyl chain with the formation of methyl ketone and carboxylic acid end groups. Dissolved iron increased the formation rate of hydroxyl and oxetane without changing the hydroperoxide concentration. Oligomers were absent from the mass spectrum of the oxidized oil. The increase in oil viscosity with accelerated aging is due to increasing intermolecular hydrogen bonding between hydroxyl groups formed on alkyl chains.

ISSN:1040-2004    

DOI:10.1080/10402009908982239

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The elastic contact of rough surfaces and the subsurface stresses caused by the contact have been analyzed by means of a numerical model based on fast Fourier transforms (FFT) and minimization of complementary energy. The elastic contact has been modeled mathematically as a linear complementarity problem and solved by a robust algorithm, Conjugate Gradient Method, while the force-displacement relation is determined through a FFT approach. After solving for the pressure distribution, the subsurface stress field is obtained by calculating the stresses due to the application of a point force, and then integrating over the contact region. In comparison with the matrix based method published in recent years, the numerical approach presented in this study is more efficient, more stable and requires less memory. It has great potential in application to problems with general contact geometry and three-dimensional surface roughness. The results show that high frequency roughness could lead to very sharp impulses and significant oscillations in pressure distribution. The amplitude and location of the maximum shear stress in the subsurface region are constantly changing when the contacting rough surfaces are in relative motion.Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

ISSN:1040-2004    

DOI:10.1080/10402009908982240

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Numerical techniques have been developed and used to evaluate the contact temperature distribution between real surfaces in sliding contact. The contact temperature is evaluated for the entire range of Peclet numbers. In the case of “slow sliding” problems a stationary numerical technique was used, whereas for “intermediate and fast sliding” problems transient finite element (FE) solutions were preferred.

ISSN:1040-2004    

DOI:10.1080/10402009908982241

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Perfluoropolyethers (PFPEs) are widely used as lubricants on magnetic recording media. The mobility of the PFPE on the protective carbon overcoat of the media is widely accepted to be intimately coupled to the resulting tribological performance. The flow properties of molecularly thin films of nonpolar PFPEZ and polar PFPE Zdol fractions on solid surfaces were investigated by measuring the spreading profiles. The spreading of Zdol exhibits terraced profiles with the formation of a molecular foot, a shoulder and a vertical step. To describe these features of Zdol spreading, we measured the Zdol thickness dependence of the surface energy, which is then used to calculate the thickness dependence of the disjoining pressure. The polar component of the Zdol surface energy exhibits oscillations as a function of PFPE thickness. The resulting oscillations in the disjoining pressure can be used to qualitatively describe the origins of terraced spreading. The characteristic Zdol spreading profile and surface energy oscillations of Zdol are attributed to molecular layering induced by polar interactions between the Zdol end-groups and the surface.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

ISSN:1040-2004    

DOI:10.1080/10402009908982242

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Applications of high-pressure waterjets directed onto the cutting tool have shown many advantages in metal machining. Tests have shown improvement in machinability of high-strength alloys using carbide tools. This paper presents an experimental investigation of the viability of having a 360 MPa waterjet directed onto the tool/chip interface when cutting a nickel-based superalloy with a SiCw-reinforced ceramic cutting insert. The resulting very localized cooling action was found to profoundly change the chip shape and tool wear behavior. Microscope studies of tools and chips indicate a significantly affected wear and cutting mechanism which can provide further knowledge of the mechanisms associated with this type of machining.

ISSN:1040-2004    

DOI:10.1080/10402009908982243

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper describes a study of the elastohydrodynamic and boundary film-forming properties of solutions of simple surfactants in water. Such solutions are finding increasing use both as highly fire-resistant and environmentally-friendly hydraulic fluids. They also provide a vehicle to help clarify the origins of the film-forming behavior of oil-in-water emulsions.

ISSN:1040-2004    

DOI:10.1080/10402009908982244

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Experiments to identify the leakage and dynamic force coefficients of a plain annular gas (air) seal are presented. The test rig consists of a rigid shaft and a seal housing supported from elastic rods. Two orthogonal impact guns excite the test seal and housing, and displacement and acceleration sensors measure the seal dynamic forced response. A frequency domain parameter identification technique allows accurate estimations of the system stiffness and damping force coefficients. Tests with no journal rotation and at 3600 rpm are conducted for pressure ratios (Ps/Pa) from 1.5 to 3.0 for centered and eccentric (50 percent of clearance) seal conditions. In all cases, measured mass flow rates and identified direct damping coefficients steadily increase with increasing pressure ratios. The direct stiffnesses, however, exhibit a peculiar behavior at and around a pressure ratio of 2.0. As the pressure ratio increases from 1.5 to 2.0, the direct stiffnesses decrease and become negative. Then, as the pressure ratio rises to 3.0, the stiffnesses steadily increase and become positive. A bulk-flow model, which includes the effect of transition flow from laminar to turbulent, demonstrates reasonable agreement with the experimental observations.Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

ISSN:1040-2004    

DOI:10.1080/10402009908982245

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Solid lubricants such as molybdenum disulfide can provide very low friction, but their effectiveness especially in the geometrically constrained sliding pairs is limited by plowing of coated surfaces by wear particles. Even in the presence of solid lubricants wear particles cause higher friction by plowing the interface. To minimize plowing, undulated surfaces with microgrooves perpendicular to the sliding direction can be used to trap wear particles. Smooth and undulated stainless steel surfaces were coated with molybdenum disulfide by pulsed laser deposition (PLD) and friction tested. Under identical test conditions, the friction coefficient of coated undulated surfaces is between 20–40 percent lower than that of coated smooth surfaces. The friction coefficient of undulated uncoated surfaces is about 100–350 percent less than that of smooth uncoated surfaces. Moreover, the entrapment of wear particles at the interfaces of geometrically constrained bearings may lead to seizure even when bearing surfaces are coated with solid lubricants. The use of undulated surf aces on these sliding systems has shown improved operating time and a reduced maintenance cycle.Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

ISSN:1040-2004    

DOI:10.1080/10402009908982246

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Despite the widespread use of surface hardened materials, pitting failures in gears nearly always originate at the surface. This is because the extreme surface is usually subjected to very high local stresses arising from the roughness of the contacting tooth flanks. One potential solution to the problem is reinforcement of the extreme surface using a suitable steel-treatment combination.

ISSN:1040-2004    

DOI:10.1080/10402009908982247

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An analytical model is developed to predict the relation between the opening force and operating conditions in a mechanical seal with laser textured microsurface structure in the form of micropores. The model is valid for any desired shape of the micropores. An optimization is performed for spherical shape micropores evenly distributed on one of the mating rings face to maximize the opening force and fluid film stiffness. Results of a parametric study are presented showing the effect of the main design parameters on the seal performance. Some results of an experimental investigation with water-lubricated seal rings are also shown and compared with the theoretical model.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

ISSN:1040-2004    

DOI:10.1080/10402009908982248

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor