摘要:

Prolonging the life of engineering components through lubricant formulation to achieve better wear resistance and higher oxidation stability is of paramount importance to many mechanical systems, such as automotive gears and bearings. This can be accomplished with formulated lubricants that limit the generation of wear debris causing severe abrasion and protect the contacting surfaces through the formation of wear-resistant tribofilms. In this study, a ball-on-disk tribometer was used to characterize the friction and wear properties of steel surfaces slid in the boundary lubrication regime. An experimental scheme was developed to allow the statistical screening of various lubricant formulations. Sliding experiments were performed in baths of different lubricants at relatively low and elevated temperatures, approximately 32 and 100°C, respectively, under conditions of constant load and sliding speed. Surface profilometry, optical microscopy, and scanning electron microscopy were used to characterize the dominant friction and wear mechanisms. The tribological properties were found to strongly depend on the temperature and the additives (e.g., borate, phosphorus, and sulfur) present in the blended lubricants. The superior high-temperature wear performance of the lubricant with the higher borate content is indicative of the formation of a durable tribofilm that reduces metal-to-metal adhesion, material transfer, and surface plowing by wear debris.Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

ISSN:1040-2004    

DOI:10.1080/10402000008982380

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Friction tests were conducted with silicone fluids containing iron oxide particles to investigate the effects of friction and wear on the formation of a micro-gel in viscous couplings. Polysiloxane films were formed on the surface of iron oxide particles as sliding distance increased. The relative viscosity of the particle dispersion increased as well. Frictional heat had a significant effect on the formation of polysiloxane films which had an abundance of cross-linking and terminal trimethyl structures of polydimethyl siloxane. The iron oxide surface was indicated to participate in the tribo-chemical formation of polysiloxane films. A model anti-wear agent suppressed the increase in relative viscosity with less polysiloxane films formed on the surface of the iron oxide. The metal-to-metal contact between adjacent VC plates most likely generates chemically active iron oxide surfaces with frictional heat and wear, which promotes the formation of the polysiloxane film on the surface, leading to the micro-gel.

ISSN:1040-2004    

DOI:10.1080/10402000008982381

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A novel analytical approach for piston ring lubrication solution is presented by taking proper account of mass conservation in the cavitated region (JFO boundary conditions). A system of five nonlinear equations is employed to calculate such parameters as oil film thickness, frictional force, power loss, and oil flow rate. For an enclosed cavitation pattern in piston-ring assembly it was found, that JFO boundary conditions give much better accounting of the estimation of friction force, power loss and flow rate. To show the effectiveness of the undertaken approach, the widely accepted Jeng's approach (Jeng, 1992a) was selected, in which the pressure contribution from the cavitated and the second full film regions, as well as the trailing edge pressure, are ignored.Presented as a Society of Tribologiats and Lubrication Engineers Paper at the STLE/ASME Trlbology Conference in Orlando, Florida, October 11–13, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982382

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new model of surface flattening is developed for cold metal rolling in the mixed regime. Longitudinal surface roughness is modeled by two separate wavelengths. The new model follows the asperity crushing analysis of Sutcliffe (1999) for unlubricated rolling but additionally includes a hydrodynamic model to account for the effect of the lubricant. The effect of various parameters including speed, reduction in strip thickness, roughness wavelength and lubricant properties is examined. The results show similar behavior to previous models of mixed lubrication, with a speed parameter Ashaving the most influence, and confirm the results for unlubricated rolling that the short wavelength components of the surface roughness persist more than the long wavelength components. The predicted changes in roughness are in good agreement with experiments.Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982383

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new technique for fabrication of self-lubricating ceramic-based composites has been developed. Multi-channel ceramic matrices with a predetermined number, diameter, and distribution of channels are fabricated and then filled with a lubricant such as polytetrafluoroethylene or perfluoropolyether. Friction coefficients of lubricant-filled silicon nitride against 52100 steel were found to be 0.1 to 0.2, in contrast with pure silicon nitride for which values of 0.6 to 0.7 were found. This friction reduction is insensitive to applied load or to sliding speed. The controlled pattern of porosity allows these materials to have lubricant loading of 7.5 to 10 volume percent, instead of 20–25% typical of traditional self-lubricating materials. This configuration permits higher crushing resistance and stiffness in comparison with conventional self-lubricating antifriction materials.Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982384

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Recently developed colorimetric interferometry technique was used for the study of both minimum and central film thicknesses for a wide range of operating parameters. Over 300 film thickness maps were obtained for the combination of four values of the materials parameter G, five values of the load parameter W and many values of the speed parameter U. The use of a spacer layer extended the range of film thickness measurement down to 5 nm. An excellent agreement was found between experimental values and data obtained from numerical solution presented by Venner and ten Napel, especially for thin lubrication films. An increase in a speed exponent with increasing material parameter G was observed for both central and minimum film thicknesses. The minimum film thickness and, thereby, the ratio between central and minimum film thickness was confirmed to be of a stronger dependence on material and load dimensionless parameters than Hamrock and Dowson equations predict.Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982385

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The aim of this work is to show the correlation between grease rheological behavior and its composition and structure (base oil viscosity, soap nature, and concentration).

ISSN:1040-2004    

DOI:10.1080/10402000008982386

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In tribology often a closed form solution for calculation of contact stress and real contact area is required for the purposes of, for example, developing wear maps and temperature profiles at asperities. In assuming a Gaussian distribution of asperity heights it is not possible to obtain an analytical solution for the contact load and real contact area for many analytical models such as those developed by Greenwood and Williamson (elastic model), Chang, et al. (elastic-plastic model) and Horng (elliptic elastic-plastic model). In this paper, two exponential functions have been derived from a fitting procedure applied to the numerical results of the Gaussian height distribution thus offering an analytical expression for the above three models. It has been demonstrated that the two exponential functions (φ2* and φ4*) can give a fair approximation to the contact load and the real contact area in the separation of 0 to 4σ. In addition, variations in plasticity index (ψ) and effective asperity radius (γ) do not significantly affect the approximated accuracy. The results obtained by the newly derived exponential functions have been compared with the exponential function φ1*; suggested by Greenwood and Williamson, 1966 and it has been shown that use of φ1* invariably gives a larger error than using two exponential functions over two ranges of separation distances.Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

ISSN:1040-2004    

DOI:10.1080/10402000008982387

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The electrical and frictional properties of axially grooved oil-impregnated sintered-metal bearing (porous metal bearing) with varying loads and speeds were measured. The results were compared with the performance of bearings without grooves and conventionally used ball bearings. The test results showed that the frictional values of the porous bearings were lower than those of ungrooved bearings and ball bearings, and that the porous bearings operated in a full-hydrodynamic lubrication regime. The values of rating current, starting time and jitter revealed that the grooved-bearing had better electrical characteristics than the ungrooved bearing as well as the ball bearing. From the endurance tests on start-stop and continuous operating, it was confirmed that this bearing could be mass-produced for use in a laser scanner unit.Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982388

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Tool wear and machining performance of hardened AISI M2 steel in hard turning has been studied. Ceramic tools were used in the cutting tests without coolants, and the workpiece was heat treated to increase its hardness up to Re 60. Cutting forces, temperature, and tool wear were measured in the experiments and the effects of cutting conditions on these were investigated. Important aspects from the research are summarized as follows:1.Flank wear was the dominant wear mode on the ceramic tool insert in hard turning. In contrast, crater wear was very small due to the ceramics high resistance against chemical reactions at high temperature. A notch was unlikely to be formed in the tool.2.The initial flank wear rate mainly depends on the feed rate. High feed rates cause a high initial flank wear rate.3.Depth of cut was the most important cutting parameter to affect cutting force variation, and the cutting force increased due to tool wear.Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

ISSN:1040-2004    

DOI:10.1080/10402000008982389

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor