LUBRICATION AND LOADED TOOTH CONTACT ANALYSIS FOR SPIRAL BEVEL AND HYPOID GEARS

An preliminary design tool -LLTCA (lubrication and loaded tooth contact analysis) for spiral bevel and hypoid gears is presented, which combines the thermal -EH L analysis with LTCA. The LTCA is used to predict the contact behavior, the geometry of tooth surfaces, normal load, and kinematics for thenmal-EHL analysis between the mating surfaces. From the results of thermal-EHL the designer can predict the lubrication performance which usually include the oil film forming ability, film pressure and the increment of temperature. In the LLTCA model the con- tact behavior, lubrication performance, running condition and tooth geometry which is the resultant of manufacturing parameters are all considered.

Study of lubrication behavior of pure water for hydrophobic friction pair

The perfluorooctyltrichlorosilane molecular layer was self-assembled on glass plate. The tribological properties of the molecular layer in water were studied with the method of ball on disk. An interesting phenomenon was found that low friction coefficients of 0.02―0.08 were obtained when the friction pair was lubricated with only a water droplet. Whereas, when the friction pair was encircled with large amount of water or fully immersed in water, the friction coefficient was higher than that under a droplet lubrication. A mechanism of water droplet lubrication was proposed that the surface tension caused by the solid-liquid-air three-phase interface makes water molecules enter into the contact zone, which separates the two friction surfaces and provides a low friction coefficient. However, water film can hardly form when more water encircles the friction pair, due to the attraction between water molecules.

Investigation of X-1P coating on magnetic head to enhance the stubility of head/disk interface

Stable lubrication is essential to slider/disk interface of computer hard disk drive. Inertlubricant perfluoropolyether （PFPE） on magnetic hard disk in computer is still prone to catalyticdecomposition by Al2O3, which is one of the materials in slider. A partial fluorinated hexaphenoxycyclotriphosphazene chemical, X-1 P, was analyzed to research on its function to reduce the cata-lytic decomposition of lubricant. The surface free energy of X-1 P coated on head surface was alsoinvestigated. Contact start-stop （CSS） tester was employed to investigate the reflow effective ofX-1 P on lubricant PFPE. Results indicate that thermal stability and reflow of lubricant will be im-proved in the presence of X-1 P on the slider.

Atomistic structural change of silicon surface under a nanoparticle collision

This study investigates the effect of the incident angle on the trajectory of a nanoparticle and the damaged region on a silicon surface, by molecular dynamic simulation of the collision and recoil of a nanoparticle with a monocrystlline silicon surface. With the change of the inci-dent angle, the recoil angle of the particle changes in a large range from an obtuse angle to an acute angle. The incident angle determines which part of the particle is in contact with the surface when the particle penetrates into the deepest position. Furthermore, it is the contacting part of the particle that the released elastic deformation energy of the surface acts on. These lead to the phenomenon that the recoil angle is sensitive to the incident angle in the collision process at a nanoscale. A depressed region is formed on the surface after the collision. The shape of the damaged region changes from a deep scoop to a flat arc, which is consistent with the trajec-tory of the particle. Some silicon atoms on the surface are extruded out by the incident particle, and form a pileup at the rim of the depressed region.

Failure characterization at head/disk interface of hard disk drive

The characterization of sub-micron features and particles between hard disk interface(HDI) is becoming even more important to the hard disk industry in the fields of corrosion, tribologyand the contamination. In this paper, media scratch and particles are characterized with AES,TOF-SIMS, SEM/EDX and LPC. The main causes resulted in serious media scratch have beenanalyzed and discussed.

Effect factors of wear particles deposition in the ferrogram based on grey relative analysis

In this paper, a lot of ferrographic experiments have been made by means of rotary fer-rograph and ferroscope. The oil sample of the experiments has been collected from slip diesel en-gines. The data of the experiments has been analyzed based on grey relative analysis and relativeorder. The result of grey relative analysis shows that the effect of the dilution ratio of the oil sampleis the most key factor, in which the volume and the dilution ratio of the oil sample, and the effect ofthe rotation speed of the magnetic disc on the deposition state of wear particles are investigated.This conclusion is in accordance with the orthogonal experiment based on the same oil sample. Itprovides a new practical method for ferrographic experimental analysis.

Excellent tribological behavior of hexadecylphosphonic acid films formed on titanium alloy

Titanium alloy(Ti6Al4V)surfaces are generally modified to achieve some specific surface properties to satisfy requirements of clinical medicine.In our work,hexadecylphosphonic acid(HDPA)films were successfully formed on Ti6Al4V and subsequently confirmed by X-ray photoelectron spectroscopy(XPS)and atomic force microscopy(AFM)measurements.The tribological properties of the HDPA-modified Ti6Al4V were investigated using a ball-on-disk tribometer with a linear reciprocating movement.Experimental results indicate that the HDPA-modified Ti6Al4V can maintain a low friction coefficient(approximately 0.06)for 4 h when sliding against polytetrafluoroethylene(PTFE)balls under a load of 0.8 N in comparison to bare Ti6Al4V(approximately 0.2);the friction coefficient of the HDPA-modified Ti6Al4V shows a 70%decline.In addition,the wear rate of PTFE balls sliding against bare Ti6Al4V was almost twenty times that of PTFE balls sliding against the HDPA-modified Ti6Al4V.Moreover,results of tribological experiments for different speeds(from 3 to 24 mm/s)and loads(from 0.8 to 3.2 N)proved that the HDPA-modified Ti6Al4V was not sensitive to both velocity and load.The friction coefficients were still low and stable even under a high load of 3.2 N or at a high speed of 24 mm/s.This indicates that this soft modification is an optional method of improving tribological properties of Ti6Al4V.

Dynamic characteristics of hard disk drive spindles supported by hydrodynamic bearings

Most hard disk spindles currently used are supported by grease lubricated deep-groove ball bearings.However, in the trend of increasing spindle speed and reducing size and cost, the shortcomings of ball bearing spin-dles, such as high non-repeatable run out, high acoustic noise and short life time at high running speed, make themunsuitable for high performance hard disk drives (HDD). On the contrary, the dynamic characteristics of hydrody-namic bearing spindles are superior to that of ball bearing spindles. Therefore, they are considered to be the substi-tute of ball bearing spindles in HDD. In this paper, a simulative setup of HDD is build up. The dynamic characteristicsof liquid lubricated spiral groove bearing(SGB) spindles are studied. The effects of both operating condition andbearing clearance are investigated. It is found that running speed of the spindle has significant influence on its dy-namic performance, while the load has little influence. The effect of clearance is also evident.

Analysis of thermal expansion effects on leakage in self-sealed journal bearings

This paper, based on a simplified model, researched the problem of liquid lubricantleakage caused by thermal expansion effects in a self-sealed journal bearing, The analysis indi-cated that mismatch between thermal expansion coefficient of oil-holding-space in bearing, σT, andthat of liquid lubricant, αoi, is a subtle factor inducing leakage when bearing temperature varies.Measures like properly selecting liquid lubricant and carefully designing bearing structure could betaken to reduce the leakage by matching αT and αoil, Several such ideas concerning bearing mate-rial choosing and structure designing were presented.