Toshifumi Mawatari

Effects of coating thickness and slip ratio on durability of thermally sprayed WC cermet coating in rolling/sliding contact

Abstract Using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC–Cr–Ni cermet coating in lubricated rolling or rolling with sliding contact conditions. The coating was formed onto the roller specimen made of an induction hardened carbon steel or a thermally refined carbon steel by high velocity oxy-fuel flame spraying (HVOF). In the experiments, the WC cermet coated roller was mated with the carburized steel roller without coating and a maximum Hertzian stress of P H =1.2 or 1.4 GPa was applied in line contact. First, it was recognized that the life-to-flaking has a tendency to increase as the thickness of coating increases. Secondly, it was shown that the occurrence of flaking depends on the rolling/sliding conditions. Finally, based on the results of elastic–plastic analysis of subsurface layer, the authors discussed the effects of the coating thickness and the slip ratio on the durability of coated roller.

High Pressure Rheology of Environmentally Friendly Vegetable Oils

Environment-friendly lubricant is the key demand in twenty-first century for the issue of global climate change. Vegetable oils as base oil for lubricants and biodiesel fuel are environmentally preferable to petroleum. They are usually excellent boundary lubricants, but their high-pressure behavior is not investigated yet properly. In this research, first solidification characteristics of rapeseed oil, soybean oil, sunflower oil, palm oil, coconut oil, olive oil, camellia oil, mustard oil, castor oil, rapeseed methylester, and soybean methylester were investigated. Next, a very useful viscosity–pressure–temperature relation on the basis of phase diagram was derived for the nine vegetable oil.

Rolling Contact Fatigue Life of Bearing Steel Rollers Lubricated with Low Viscosity Traction Oil

Using a low viscosity synthetic traction oil, the rolling contact fatigue life of bearing steel rollers was examined, and the test results were compared with those obtained using a mineral oil with almost the same viscosity grade. A pair of rollers with smooth surfaces finished to a mirror-like condition were driven under rolling with sliding condition of s=-3.2% and a maximum Hertzian stress in the range of PH= 3.0GPa~4.0GPa was applied in point contact condition. As a result of experiments, it was found that the fatigue life with a low viscosity traction oil is shorter than that with a low viscosity mineral oil and this tendency appears distinctly at higher stress conditions above PH=3.4GPa. From the numerical results of thermal EHL analysis, depending on the lubricating oil, significant differences were recognized in the distributions of pressure, film thickness and temperature in the region of contact ellipse. It is supposed that the shorter rolling contact fatigue life with traction oil is attributed to the thermal effect and the existence of pressure spike as well as the difference in the property of solidified oil at high pressure EHL contacts.

Effects of surface topography and running-in upon rolling contact fatigue life -Evaluation by plasticity index-

Using carburized, thermally refined, normalized, and through-hardened steel discs, the authors examined the effects of surface topography and running-in of two surfaces on the occurrence of pitting under rolling with sliding conditions. In order to evaluate the severity of asperity contacts, the authors adopted a parameter ‘plasticity index’ which governs the degree of elastic and plastic contact conditions. Taking account of the three dimensional roughness parameters and the micro-Vickers hardness of disc surfaces, the changes in plasticity index during operation were followed. As results, it was found that there exists a close relation between the plasticity index and the rolling contact fatigue life.

Slider Air Bearing Design in Consideration of the Pumping Effect

The pumping effect proposed by the authors is used to analyze the contamination of the air bearing in hard disk drive. Three different types of air bearing surface are considered in the focus on the accumulation of the contamination at the rear pad where the minimum spacing is located. It is found that the contamination tends to accumulate at both the front and the rear ends of the air bearing surface pad where the shear stress of air film is interrupted due to due to the dramatic change in the spacing. The accumulation at the tailing edge of the air bearing is the most detrimental. The thickness of adsorbed film at the tailing edge increases suddenly when the terrace length at the tailing edge exceeds a critical value, which is in between 15 μm and 35 μm in this article.Copyright

Dynamic behaviour of ball motion and its effect on oil film formation in ball screw

Using a magnetized ball and hall elements arranged on the nut and the return tube, the authors tried to measure the actual ball motion in a ball screw rotating at various shaft speed conditions. As test screws, a conventional ball screw and its improved type which incorporates resin retaining pieces between the balls were used, and by means of an electric resistance method, the state of oil film formation between balls and raceways was also measured in the grease lubricated condition. As a result of these experiments, a significant effect of retaining pieces on the ball motion and the oil film formation was found. Namely, owing to the retaining pieces which prevent direct contact or skirmishes of balls, the ball motion in the improved ball screw became smooth and the oil film was built up rapidly not only in the steady process but also in the acceleration or the deceleration phase.

Effects of surface topography and hardness combination upon friction and distress of rolling/sliding contact surfaces

Using circumferentially, axially, and obliquely ground steel discs, the changes in the frictional force during the running-in process have been examined under the lubricated rolling with sliding contacts. The results obtained were much different depending on the surface topography, the hardness combination, the slip ratio, etc. Especially, the circumferentially ground discs showed a considerably high friction and severe wear occurred in the different hardness combination. Based on the results of experiments and measurements of the surface temperature, the surface hardness, the surface profile, the state of oil film formation, etc., the authors discuss the mechanisms which cause such differences.