One of the most important but complicated issues for mechanical seals is how to realize two contradictory functions: the sealing and the lubricating performance between the seal surfaces. Various studies have been carried out to solve the problem. However, few fundamental solutions have been presented so far. In our previous report, the surface structure for achieving the low-friction and low-leakage mechanical seals was proposed. In this report, the fundamental characteristics of sealing and lubricating function for the surface structures that we proposed in previous report were investigated by numerical calculations. JAKOBSSON-FLOBERG’s boundary condition was applied in order to consider the mass conservation at the cavitation boundary. Moreover, the effect of cavitation pressure on the sealing and lubricating performance were also investigated. The results indicated that the surface structure could simplify and clarify the surface design procedure for mechanical seals, and could predict and control the leakage rate and the film thickness based on hydrodynamic lubrication theory.

The high-pressure viscosity expression for base oils by HATA et al. was applied to binary system mixtures. The characteristic parameters necessary for the calculation of the high-pressure viscosity are atmospheric pressure-viscosity coefficient (α_ot), effective cohesion energy density (CED_eff), effective molecular weight (MW_eff) and characteristic reference temperature (θ_p). We can obtain α_ot and CED_eff from the bulk properties which are viscosity, density and molecular weight of base oil under the atmospheric pressure. Mixing rule for these characteristic parameters, named α_ot-mix, CED_eff-mix, and θ_p-mix, was analyzed using eight kinds of binary system mixture consisting of thirteen kinds of base oil. As a result, the mixing rule of these characteristic parameters was fundamentally expressed to the same form as the formula of the number-average molecular weight. However, as for α_ot-mix of two kinds of mixture, in mixtures of mineral oils of the same hydrocarbon group and mixtures of synthetic naphthene and polyalphaolefin, the weight-average rule and a modified number-average rule were more preferable respectively.

The nitriding of tool steel was performed in electron beam excited plasma using neutral nitrogen species and nitrogen ions. The plasma apparatus is composed of three regions: the discharge region, the acceleration region and the processing region. This set up has the advantage of controlling the energy and number of electrons involved in producing the plasma independently. Here, the effects of controlling the nitrogen concentration on the formation of a compound layer that is formed on the surface of the tool steel were investigated. EPMA (Electron Probe Micro Analyzer) results revealed that nitrogen concentration of the neutral nitrided samples had a threshold treatment time to attain the 6% nitrogen concentration that is necessary for the formation of the compound layer. The results of our experiments show that in nitriding the tool steel for 6h, below the threshold treatment time, a mirror finish surface with a deep diffusion layer and a surface hardness of more than two times that of the untreated sample were produced.