摘要:

The elastohydrodynamic (EHD) film-forming properties of several refrigeration oils placed in pressurized refrigerant environments were investigated by an interferometric EHD tester equipped with a pressurized vessel. It has been shown that the oils with dissolved refrigerants formed EHD films at the point of contact in the same manner as lubricant base fluids. It was also found that greater amounts of dissolved refrigerant in the oil decreased not only the viscosity but also the viscosity-pressure coefficient of the oil. In this paper, the authors describe a method to predict the viscosity-pressure coefficient of oils with dissolved refrigerants.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

ISSN:1040-2004    

DOI:10.1080/10402009708983622

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The body of revolution finite element solution of the previous report (1) is extended to asymmetric loading by Fourier analysis. The solution has the advantage of covering the technologically relevant cases of torque and eccentricity of the shaft relative to the bore of the seal, with only a marginal increase in the computational space required. However, to obtain a solution in which harmonics are decoupled, linear strain displacement relations must be used. For a particular seal the tangential displacement of the area under the lip in contact with the shaft is almost all monotonically increasing along the axis of the shaft, with only a minor portion of the area “unwrapping” in the opposite direction of the torque. For another seal design, the program predicts that loading of the seal eccentrically due to misalignment between the seal bore and the shaft will cause a gap to appear on the side opposite to the load, in the absence of radial load. Comparison of the program results with analytical solutions of the linear theory and the outline of a semiautomatic meshing routine for the program are presented in the appendices.

ISSN:1040-2004    

DOI:10.1080/10402009708983623

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experiments were conducted to investigate and compare the self-lubricating performance of two types of modified, 25 mm-bore ball bearings: a hybrid bearing with Si3N4ceramic balls, and an all-steel bearing. The modified bearings had a single outer land-guided retainer with elliptical pockets and a narrow axial pocket clearance to reduce wobbling of the retainer. The bearings were tested under high thrust loads to 2840 N and at speeds up to 50,000 rpm in liquid hydrogen (LH2), liquid oxygen (LO2), or liquid nitrogen (LN2). Testing showed that the bearing torque of the modified all-steel bearing was drastically decreased to about one-half that of the conventional double outer land-guided bearing at a speed of 50,000 rpm in LH2Furthermore, the hybrid bearing had relatively stable variation of bearing torque and better load capacity than those of the all-steel bearing in both LH2and NH2. However, in LO2, the all-steel bearing exhibited excellent performance with high load capacity at high speeds, contrasted with poor self-lubrication by the hybrid bearing.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

ISSN:1040-2004    

DOI:10.1080/10402009708983624

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Si3N4bearings were tested for more than 1400 hours at temperatures up to 650°C in a vacuum on the order of 10−7to 10−6Pa. The bearings were lubricated with a precoated sputtered MoS2film and a self-lubricating composite retainer. The test bearings were 20 mm-bore angular contact ball bearings (7204 size). The tests were carried out at a rotational speed of 600 rpm under a thrust load of 50 N.

ISSN:1040-2004    

DOI:10.1080/10402009708983625

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experiments and theoretical analyses were carried out in this research to study the operating and lubrication conditions in highspeed, high-load rolling/sliding contacts with liquid oxygen (LO2). A cryogenic traction tester having a single rolling/sliding contact conjunction was used in the experiments. Contact between two AISI 440C stainless steel rolling elements was studied at a rolling velocity of 47 m/s and at a load that generates a Hertzian peak pressure of 2.2 GPa. Tests were run with a slide-to-roll ratio up to one percent, and traction and specimen wear were measured. Experiments were also conducted at rolling velocities of 1.0 m/s and 11.7 m/s to provide evidence of LO2load support at high speeds and to deduce parameters for subsequent theoretical analyses. The measured total traction and asperity friction were then used as inputs to an analytical model to determine the load-carrying capacity and average film thickness of LO2. The analyses show that the traction is mainly due to asperity friction; however, LO2can support a large portion of the total load despite its extremely low viscosity. This analytical result is also supported by the specimen wear data. The analyses in conjunction with the experimental data also provide a meaningful estimate of the average film thickness and LO2viscosity in the contact nip.Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

ISSN:1040-2004    

DOI:10.1080/10402009708983626

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Recently, several papers have been published reporting measured journal bearing characteristics including the linear dynamic force coefficients. In some instances, analyses were performed to give confidence levels for the data based on uncertainties in the measured data. However, the effect of fluid film nonlinearity on the measured data used to calculate the dynamic coefficients has not previously been reported. This paper presents results of a nonlinear simulation to assess these effects for one particular bearing test rig previously documented. The nonlinearity arises from the finite size orbital motion imposed on the journal or housing during the measurement process to obtain response data used to extract the dynamic coefficients from a linear model of the journal bearing dynamic system. The orbit size may be large enough to introduce nonlinearity in the fluid film forces which may in turn affect the resulting calculation of the linearized force coefficients. The nonlinear simulation includes a time-transient solution of the Reynolds equation for a three-lobe bearing and replicates the testing procedure used in an experimental journal bearing test rig previously reported upon. Comparisons of orbital motion and dynamic force coefficients to data obtained from that rig are reported herein. The fluid film nonlinearity was found to produce an uncertainty in the coefficients of up to 20 percent compared to the linearized coefficients obtained from a small perturbation solution of the Reynolds equation which are commonly used in rotating machinery design and analysis. A further objective of the simulation is to evaluate the effect of different external forcing functions to assist guiding the test procedure in the actual test rig to reduce the influence of fluid film nonlinearity on the test results.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

ISSN:1040-2004    

DOI:10.1080/10402009708983627

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A method to experimentally evaluate and mathematically indicate the energy loss connected -with friction forces in pneumatic semi-rotary actuators is presented in this paper. A proper test bench was designed and constructed. Results obtained for a group of semi-rotary actuators are presented.

ISSN:1040-2004    

DOI:10.1080/10402009708983628

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Perfluoropolyether lubricants have been the lubricants of choice on thin-film magnetic disks because of their superior properties. However, studies have shown that they can degrade at lower temperatures in the presence of metal oxides such as Al2O3and Fe2O3. In this paper, the degradation behavior of three widely used disk lubricants which have a Z-backbone structure were studied in the presence of the following ceramic powders: AlN, Al2O3, Fe2O3, SiC, Si3N4, SiO2, TiC, TiO2, and ZrO2. Experiments involved monitoring the weight loss of a continuously stirred mixture of lubricant containing 1 wt% of powder with lime, at a fixed temperature of 250° C. In the case of ZDOL 4000, there was a 10% loss in the first 60 minutes and then a very low and constant rate of weight loss. TiC, AlN and Al2O3were very aggressive in degrading the lubricant while SiC and Si3N4had no effect at all. ZDOL 2000 exhibited a 60% loss in the first 100 minutes and then a low and constant rate of loss with time. ZrO2, Al2O3, TiC and AlN were very effective in degrading the lubricant, while SiC and Si3N4had negligible effect. Heating the AM 2001 lubricant alone at 250°C caused the lubricant to quickly turn into a black sludge; however, at 180°C, it exhibited a slow and constant weight loss with time. At 180° C, the presence of ceramic powders did not appear to have any effect on the rate of weight loss. X-ray diffraction of residues left behind after degradation tests showed that, except for the tests with SiC and Si3N4, most of the residues left behind after complete lubricant degradation were found to contain fluorides.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kissimmee, Florida, October 8–11, 1995

ISSN:1040-2004    

DOI:10.1080/10402009708983629

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A Kelvin probe apparatus was developed to profile surface potential. Measurements were performed on unlubricated and lubricated carbon overcoated thin film magnetic recording media. The surface potential on perfluoropolyether-lubricated media was more negative than that on the unlubricated carbon overcoat. Sliding, start/slop, and low-flying tests were performed with two-rail sliders, and the surface potential was measured across the test tracks prior to detectable mechanical wear. The surface potential in the lest tracks became more negative with the number of cycles during sliding or start/stop and with decreasing slider-disk spacing during low flying. Degraded lubricants with polar carboxylic acid end groups accumulate and increase the dipole moment in the lest tracks.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

ISSN:1040-2004    

DOI:10.1080/10402009708983630

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A model for asperity contacts at the head/disk interface has been developed that allows for elastic asperity deformations based on an experimentally derived function for the contact pressure. The model predicts the distributed contact pressure, the contact force and the apparent area of contact on the air bearing surface of the slider. A second approach that assumes entirely rigid asperities is employed to verify the asymptotic behavior of the contact force as the asperity stiffness increases. Further results are reported for the elastic asperity method and the dependence of the contact force, contact area and flying height on various operating conditions is investigated. The comparison between numerical calculations and experimental results shows excellent qualitative agreement.Presented as a Society of Tribologlsts and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

ISSN:1040-2004    

DOI:10.1080/10402009708983631

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor