Improving seizure resistance in plastic working is a major issue in tribology, but there are few clear guidelines for achieving this using surface treatment. This is likely due to the lack of a method for theoretically and quantitatively evaluating seizure resistance of tool surface treatments. Therefore, the authors focused on the adhesion strength between seizure and the tool surface as a quantitative index of seizure resistance. In this study, Friction pressure welding (FPW) was adopted as a measurement technique. And the effect of tool surface treatments on seizure resistance during hot rolling and FPW strength was investigated. The respective bonding mechanisms with the tool surface were also examined. The results showed the same orders of FPW strength and degree of seizure in hot rolling: polished surface > Cr plating > oxide film. Observation and analysis of bonding interfaces showed that the FPW interface had a higher temperature than the seizure interface during hot rolling, but the bonding mechanism was inferred to be very similar. These results show it is possible to quantitatively evaluate seizure resistance by evaluating seizure point strength using FPW with a controlled amount of friction heating.
Friction reduction by engine oil under low temperature as well as high temperature conditions are required because of the increasing number of hybrid vehicles where bulk oil temperature is low. Friction modifier (FM) technology to realize it is required. Friction performance of MoDTC, which works well at high temperature, used with adsorption type friction modifiers, which work well at low temperature, was investigated. Low molecular type, glycerol monooleate (GMO) inhibited friction reduction performance of MoDTC while polymer type FM showed little inhibition. Surface analysis indicated that the reaction film by MoDTC was not existed when the GMO was used together while it existed when it is used with polymer FM (PFM). The cause of the difference was studied by their adsorption performance examined by quartz crystal microbalance. GMO showed high adsorption density, while PFM showed low adsorption density compared to that of MoDTC. The result indicated that GMO competitively adsorbed on the surface, inhibiting the reaction film formation by MoDTC while polymer FM does not. The study indicated that use of the polymer FM with MoDTC is one of the solutions of FM design that works under both high and low temperature.
Metal-to-metal seals in premium threaded joints (PJ) for Oil Country Tubular Goods need to have high-pressure gas tightness. The gas tightness of such seals is affected by sliding of contact surfaces during integration, the kind of applied greases, temperature and pressure. In this study, a new fundamental testing method is proposed that enables quantitative evaluation of the impact of these factors on the gas tightness. In the proposal method, specific greases as well as helical sliding are employed in order to simulate the sliding conditions in practical PJ. In addition, the seal portions are baked at 180°C to simulate the high temperature condition of oil or gas wells. The gas pressure was applied until leakage was occurred. The proposed method provides more realistic contact conditions of PJ than those of conventional method in which seal surfaces are subject to rotary sliding before gas tightness tests. It is found that the gas tightness of the grease specified by American Petroleum Institute standards is about 2.8 times higher than that of the environmentally friendly grease.