Tribology Online starts to publish three categories of papers of Article, Short Communication, and Review from Volume 4 this year.
Article is intended to be an original report of researches and technological developments in tribology and relevant fields. There is no page limit for Article. Short Communication is intended to be a preliminary report of new concepts, findings, technological developments and opinions whose rapid publication will be important for a large number of readers in relevant fields. Recommended length for Short Communication is four printed pages. Review is intended to be review of researches and technological developments in tribology and relevant fields. There is no page limit for Review.
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Submission of manuscripts implies that it has not been published previously, and is not currently under consideration for publication elsewhere. Those manuscripts of Papers (Original Contributions) and Short Papers that are written in Japanese and have been published in the Journal of Japanese Society of Tribologists (Toraiborojisuto) may be translated to English and published in Tribology Online; the originality is in the original Japanese papers.
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Machine designers are sometimes confronted with high contact pressure conditions which generate plastic deformation. However there is no clear design method for such severe condition. We investigate the contact condition in the high contact pressure by using a ball-on-glass disc type test. According to the test results, the following conclusions were obtained. 1) The ratio of calculating contact pressure and the hardness in consideration of working hardness, the number of the ratio is settled about 0.4 for any loading condition. 2) In the condition of high contact pressure generating plastic deformation, the contact pressure converges with constant value according to the work hardening behavior of material.
To develop a low-friction and low-wear tribo-system for engine components, the authors have been studying the ZDDP tribofilm formed on iron oxide. Tribotests on iron-oxide / steel sliding pairs were performed in PAO with 1 mass% ZDDP. It was confirmed that the friction coefficient was lower in the PAO with ZDDP than that in pure PAO. The distributions of elements on the wear track of the iron oxide were analyzed by EPMA and found that a zinc-containing layer was distributed on almost entire contact surface.
The new hard porous carbon material called the RH (rice husk) ceramics has been developed by carbonizing rice husk as the main raw material. In order to clarify the friction and wear properties of RH ceramics, a study of the effect of carbonization temperature on the mechanical and tribological properties of RH ceramics was undertaken. RH ceramics samples carbonized at 900, 1400, and 1500 °C were prepared for this study. The RH ceramics samples were inspected using X-ray diffraction, EDX and scanning electron microscopy. Mechanical properties of RH ceramics such as Vickers hardness, compressive strength, and bulk density were also studied. The RH ceramics carbonized at 1500 °C had much higher porosity compared to the ones carbonized at lower temperatures. In addition, the bulk density and compressive strength decreased with increasing carbonization temperature. Whereas, the hardness was higher for the RH ceramics carbonized at higher temperatures. Ball-on-disk sliding tests showed that the RH ceramics carbonized at the conventional 900 °C have better friction and wear properties compared to the ones carbonized at 1400 and 1500 °C under dry condition sliding against austenitic stainless steel (JIS SUS304). The friction coefficient and specific wear rate took very low values of 0.07 and less and 5.0×10-10mm2/N and less, correspondingly, for the RH ceramics carbonized at 900 °C. Based on the experimental results, friction and wear mechanisms have been summarized for each carbonization temperature.
A numerical simulation was carried out to examine the effect of radial and/or circumferential grooves on the frictional surface temperature and torque response in a multidisk wet clutch. The modified Reynolds equation for hydrodynamic lubrication and heat conduction equation for heat transfer were solved by SOR and ADI methods, respectively. The real contact area was given by Greenwoods and Williamson model, the contact pressure was assumed proportional to the real contact area. The simulation results show that the temperature at the surface material can be better controlled by the simultaneous use of radial and circumferential grooving.It was also shown that grooving enhances the torque response in the case of low permeable friction material.
PTFE was reinforced with PAN-based, Pitch-based (carbonized and graphitized) carbon fibers and vapor-grown carbon fibers and their tribological properties were examined. Aluminum alloy was used as the counter face material. The wear rate of PTFE was only reduced by the vapor-grown carbon fiber and the composite filled with the vapor-grown carbon fiber caused minimum wear amount of the aluminum alloy counter face. Aluminum alloy was easily abraded by the carbon fibers other than vapor-grown carbon fibers, and then the abraded rough surface promoted the wear of PTFE composites. There was a correlation between the abrasiveness of carbon fiber and the cylindrical surface area of carbon fiber.
In recent years, metal working oil is required to have lower viscosity and higher lubricity than ever. Controlling oil film thickness is one of the most important in metal working. In this study, we investigated the effect of molecular structure and molecular weight distribution of oil on both lubricity and oil film thickness on friction surface during rolling. Oil film thickness was measured for three oils with the different molecular structures in spite of the same kinematic viscosity. In this result, the polyisobutylene with relative rigid structure formed the thickest film of the three oils. Oils with broad molecular weight distribution (wide-ranged oil) were formulated by mixing a few polyisobutylenes which have different molecular weight distribution. A film thickness with wide-ranged oil was eight times as thick as one with a narrow molecular weight distribution (narrow-ranged oil) in spite of the same viscosity. Increase in the difference of molecular weight increased the film thickness. We could reduce a friction coefficient during rolling even with a low viscosity oil, using a wide-ranged oil.
Micro-hole drilling of engineering ceramics has potential for application to fuel injection nozzles and fiber spinning nozzles, etc. To date among engineering ceramics, less study has been reported on the micro-hole drilling of silicon nitride. We therefore conducted micro-hole drilling of hot-pressed silicon nitride using a chemical vapor deposition (CVD) diamond-coated tool with ethanol as the cutting fluid. As a result, the successful drilling of silicon nitride was achieved with a smooth drilled surface and sufficient accuracy of the hole size. Wear damage of the CVD coated diamond tool and drilling debris of silicon nitride were investigated using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX). As a result, it is suggested that tribochemical reaction of silicon nitride effectively contributed to the micro-hole drilling characteristics; that is, smoother hole surface was obtained due to the polishing action of wear debris and tribochemical reaction products. The hole inlet size, varied during successive drilling process, could be explained in relation to the wear damage of the diamond-coated drill tip.
For successful cold rolling operation at elevated operating conditions, the existence of desirable minimum film thickness at the roll-strip interface and awareness of its controlling by adjusting the process variables such as roll speed, reduction ratio, lubricant types, and roll cooling system etc. are essential. Moreover, the studies of the lubricant's starvation in the inlet zone and its influence on the film thickness at high roll speeds considering viscous shear heating effects are very important issues. Thus, the objectives of this paper are to analyze the inlet zone of cold rolling interface thermohydrodynamically and develop formulas for the prediction of minimum film thickness (for both isothermal and thermal cases) as functions of operating parameters including levels of starvation. Based on the investigations reported herein, it is observed that the existence of starvation up to certain level seems to be beneficial. It causes reduction in the temperature rise in the inlet zone and reduces the quantity of lubricating oil (leading to oil conservation) required during the cold rolling operation provided a thin continuous film exists at the strip-roll interface. Authors believe that the cold rolling industries may be benefited by the formulas reported in this paper.