The Japanese Society of Tribologists starts this electronic online journal in celebration of the jubilee of the society.
In developing science and technology of tribology to meet the modern demands, rapid and worldwide communication of new ideas has become crucially important. However, there are a number of valuable works in progress which are reported domestically but are seldom shared worldwide. To publish these high quality works should be important for both the researchers and a large number of people in relevant fields. Short letter papers will be an effective medium.
Tribology Online is completely electronic, and is open to the world for free access through Internet. Initially, Tribology Online publishes original Short Communication Papers, which are intended to be preliminary reports of new concepts, findings, technological developments, reviews and opinions whose rapid publication will be important.
The ultra thin film interferometry and conventional optical interferometry techniques are used to measure the central film thickness and friction force as a function of the dimensionless speed parameter. Experiments were conducted in point contacts with a mineral bright stock oil and a disk-like chemical compound by changing the temperature, entrainment velocity and surface roughness at a fixed slide-roll ratio. It has been found that the friction coefficient curve, i.e., the relationship between the friction coefficient and the dimensionless speed parameter, changes depending on lubrication regimes, even when the relationship between the central film thickness and the dimensionless speed parameter obeys EHL theory.
This paper describes the appearance of abnormal film thickness features formed in elastohydrodynamic contacts lubricated by a fatty alcohol. Experiments were conducted by varying the slide to roll ratio between a steel ball and a glass disk in a ball-on-disk type device. Lauric alcohol was used as lubricant and film thickness was measured in the contact area by optical interferometry. Experimental results showed that the film thickness distributions under pure rolling conditions remained classical whereas the film shape changed when the slide to roll ratio was increased. The thickness in the central contact area increased and in the same time inlet and exit film thicknesses were modified. In addition, the film shapes observed when the ball surface was moving faster than the disk one and those obtained in the opposite case were different, i.e. when opposite signs but equal absolute values of the slide to roll ratio were applied.
The effects of composition of alloy steel on the friction and wear characteristics of molybdenum dithiocarbamate MoDTC were studied in reciprocated sliding contact using a ball-on-plate type tester. The oil used was squalane of a pure hydrocarbon. The excellent friction and wear characteristics were obtained with high speed steel M50 containing Mo at 4.25 and Cr at 4.12 mass % and bearing steel SUJ2 containing Cr at 0.45 mass %. Especially, M50 with high Mo and Cr content used as the upper ball specimen gave a very low coefficient of friction. A MoO3 surface film formed in advance was confirmed to be effective in improving the friction and wear characteristics of MoDTC.
Even though solid lubricants or low-volatile greases are used for lubrication of mechanical equipments in space satellites, the life of grease is longer than that of solid lubricants because of the hydrodynamic effects and replenishment. New grease using multiply alkylated cyclopentane (MAC) as base oil was developed for space applications. In this paper, the lubrication characteristics of the new grease have been investigated by experiments using the basic friction tester under high vacuum condition. The results clearly show that the difference of thickener influences the lubrication characteristics even if the greases consist of the same base oil, and MAC grease used with non-soap urea thickener was superior to the others.
Many investigators have frequently assumed polynomial temperature profiles across the film thickness in the mathematical modeling of lubricating films in the hydrodynamic bearings in order to make computations simpler. Thus, to verify the validity of such temperature profile approximations in computations, it is essential to access the accuracy of results achieved with such approximations. In this study two different temperature profile approximations (Legendre polynomial and Parabolic polynomial) across the film thickness in energy equation have been assumed and comparison of computed results with these two temperature approximations have been carried out. The results obtained have been examined for their accuracies. Based on the present analysis, it has been observed that the temperature approximation across the film thickness taken by Legendre polynomial yields more accurate results in comparison to parabolic temperature profile assumption.
Micro-Traction-Drive is made by modified angular contact ball bearings. It is developed for the purpose of transmitting high torque with small drive size. Structure of Micro-Traction-Drive is as follows: The traction force is generated by the thrust preload between inner race and outer race. The retainer connected to the output shaft transmits the driving torque. The retainer is made from copper alloy. The test-runs of Micro-Traction-Drive (outer ring diameter 42mm) have been carried out as tandem stage type (reduction ratio 7.3). The test results demonstrate that Micro-Traction-Drive has been successfully operated at 20,000rpm. Furthermore, material of retainer has been examined. Effect of retainer material on efficiency of Micro-Traction-Drive was revealed.