We investigate the thermal behavior of the friction property of ultra-thin perfluoropolyether (PFPE) lubricant film on diamond-like carbon (DLC) overcoats of magnetic disks. We use a newly developed pin-on-disk tester with laser irradiation heating. Results show that the friction coefficient of a lubricated DLC surface with Z-tetraol decreased with increased temperature, while for lubricated disks with Z-03, it gradually decreased at around 120°C and increased over 120°C. This minimal point may indicate the transition temperature. The friction coefficient of both lubricant films on the DLC surface varied with the kinematic viscosity of the lubricant materials, and decreasing the kinematic viscosity decreased the friction coefficient.
This study investigated how the surface roughness of steel disks coated with a Si-containing diamond-like carbon (DLC-Si) film affects the dependence of the friction characteristics, in an oil-lubricated condition via the use of friction experiments and numerical analyses using mixed lubrication models. This study clearly demonstrated that a DLC-Si film with a surface roughness of RzJIS = 3 to 4 μm was an effective means of suppressing frictional vibration caused by stick-slip. In addition to finding that the surface roughness of steel disks coated with DLC-Si film could be used as a design guideline for the sliding surface of an electromagnetic clutch to provide excellent μ-v characteristics, it was also found that providing the mating plate with micro grooves that have a depth of 10 μm and a pitch of about 100 μm was an effective means of improving the friction characteristics. The results of this study suggested that the surface roughness and the micro grooves maintain solid contact even if the formation of oil film is enhanced as the sliding velocity increases, since these results in boundary lubrication.
Fuel economy is a major challenge for the automotive industry. A key way to improve lubricant fuel efficiency is by using polymers as viscosity index improvers to maximise the viscosity index of the lubricants. The viscosity index of automotive lubricants has an upper limit of around 250 because usage of high treat rates can lead to shear stability and flash point issues. To overcome this, the concept of two phase lubricants was reported in former literature but the practical application had not been examined. In this paper, the practical application with an additional ability to control viscosity and separation temperature simultaneously of a two phase lubricant is reported. It is possible to formulate a two phase lubricant with mineral or synthetic base oil and polyalkylene glycol to achieve viscosity index of 500 and keeping the properties of shear stability and flash point on a competitive level as of commercial single phase lubricants. Also, there is little evidence of issues with the lubrication properties. It was shown that additions of Di-isononyl adipate acting as a control element simultaneously control the viscosity and separating temperature of the two phase lubricants.
This paper is focused on the roughness induced effects in EHL contact under high sliding conditions when thermal effects can be expected. High sliding conditions include both the case when both surfaces are moving in the same direction and that when they move in the opposite directions. The presented results show that increasing magnitude of sliding connected with high in-contact temperatures has almost no effect on roughness deformation until the dimple phenomenon occur. The observations of film variations evolution, caused by roughness pass (complementary effect), can give information about flow processes in an EHL contact under dimple phenomenon conditions. Essentially different behavior was observed in a classic EHL contact and in a contact when dimple phenomenon has occurred.
In this paper, an attempt has been made to study the effects of MHD and couple stress fluid lubricants on the steady state and dynamic behaviour of plane slider bearings by considering the squeezing action. The modified Reynolds equation is derived for the plane slider bearing with squeeze effects for the MHD and couple stress fluid. The dynamic stiffness and damping characteristics of one-dimensional MHD and couplestress plane slider bearings are computed. The effect of MHD and couple stress fluid lubricant improves the steady state and dynamic stiffness and damping characteristics of the plane slider bearings.
Lubricant reflow for Z-Tetraol is characterized for heat-assisted magnetic recording (HAMR). The thickness-dependent diffusion constant, D(h), is determined from flow experiments for submonolayer Z-Tetraol films between 2.5 and 13 Å. Fickian diffusion using experimental D(h) values are used to numerically simulate lubricant reflow into HAMR laser-depleted troughs as a function of trough number, trough depth, trough distance and trough width. Reflow is computed to be slower for multiple, wider and deeper troughs. Reflow kinetics as a function of trough separation distance is complicated by adjacent trough interactions. Two major kinetic regimes are identified. Multiple troughs that have not coalesced recover more quickly. Once multiple troughs coalesce into a single larger trough, reflow kinetics is drastically slowed. The crossover time between the two kinetic regimes is computed to be approximately 400 millisec for the system under investigation here, but will be a strong function of trough number, width, depth and separation distances. The simulation of multiple troughs provides significant insight into HAMR conditions. Single trough lubricant studies may be misleading for HAMR systems.
In contact analysis, creating a machined surface model depends on traditional mathematical models, such as statistics and fractal methods. However, these models do not provide an exact representation of the complex information about the machined surface. This raises the need for a method to precisely create the engineering contact surface. This paper solves this problem by measuring the profile of the machined surface, processing position data, inputting position data directly into the finite element software directly by ANSYS parameter design language (APDL) programming and creating a solid model for the real rough surface. Then, statistical analysis of the contact between the rough surface and a rigid flat plane is carried out and relationships for contact area, load, pressure deformation and so on are obtained. Results show that this method used for simulation is promising. From the results, contact deformation was found to exponentially increase with contact pressure, and downward normal contact stiffness exponentially increases with average pressure.