A series of experiments were carried out to verify the sealing and lubricating performance of the surface structure for mechanical seals with the functions of the low-friction, the low-leakage, and also the pumping effect. The thrust bearing structures were formed in the higher pressure side as a lubricating mechanism, and the reversed thrust bearing structures were formed in the lower pressure side as a sealing mechanism in the mechanical seals’ surfaces. The fluid film thickness and the friction coefficient were measured and compared with the numerical calculation results of our previous report. Cavitation regions formed in the sliding surface were observed with the direct observation system of mechanical seals. Furthermore, the magnitude of the cavitation pressure was also discussed. The experimental results indicated that the theoretical results discussed in our previous report were proved to be valid. Thus we conclude that the novel sealing and lubricating mechanisms for mechanical seals with the functions of the low-friction, the low-leakage and the pumping effect can be technically feasible.
Friction properties of the oils containing polyalkylmethacrylate with different alkyl group were studied in relation to adsorption and desorption ability of polymers. First, the coefficient of friction with a pendulum type tester were roughly correlated with a magnitude of frequency shift ΔF obtained using a quartz crystal microbalance with dissipation tester, in which ΔF was related to adsorption ability of polymers onto a metal surface. This suggests that the friction under the mild contact conditions is governed by surface coverage capacity of polymers. On the other hand, tribological properties under the severer conditions with a steel ball-on-steel disk type tester were evaluated under a temperature of 100°C, a mean Hertzian pressure of 0.73 GPa and a mean rolling speed of 0.05 m/s and a slide/roll ratio of 50%. Among the polymers, a mixed alkyl group containing methyl group was superior to the other polymers in terms of stability in friction with time, friction reducing effect and antiwear properties. It is inferred that the friction under the severe conditions was influenced by surface coverage capacity of polymers as well as adsorption preservation capability, which was evaluated as a separation degree during the tribotest.