Global economic growth, especially in emerging countries and regions, increasing concern to natural resource conservation, and environmental protection lead to a need to high performance lubricants. This article discusses the recent trends of lubricant formulation, which may impact the use of type of lubricant base stocks, for passenger car motor oils, heavy duty motor oils, automatic transmission fluids (ATF), gear oils, tractor hydraulic fluids, general industrial oils, industrial engine oils, process oils, and metalworking fluids (MWF) followed by global supply and demand trend of lubricant base stocks by region and API group in the last 10 years and forecast to 2026.
In recent years, coordinated global cooperation is getting increasingly important, in order to protect the global environment. Such thorough consideration and efforts on environmental protection initiatives are positioned now in industries as critical part of product development and on corporate visions. Esters are widely used as base fluids in various application in the world of lubricants. In this article, discussion is made on approach to environment, importance of biodegradability and of sustainable renewable feedstocks, initiatives by producers on environmentally friendly esters and on the requirement on ester base fluids.
In order to understand lubricating mechanism for advanced lubricants, lubricating properties of lubricants composed of additives and base oils are reviewed from the viewpoint of chemical interaction of lubricant components and material surface. The structure of lubricating films formed on material surface which affects lubricating property are controlled by the balance of chemical interaction between additives, base oil and surface. Lubricity of organic phosphates as an anti-wear additive and MoDTC as a friction modifier is closely dependent on the solubility of the additives in base oils. Thickness and structure of the tribofilm formed from thickeners, over-based calcium sulfonate and MoDTC are controlled by the balance between formation and degradation of the films. A dynamic model of tribofilm formation is proposed. The important role of nascent surfaces on tribochemical reactions of additives is reviewed. Although additives having a polar functional group such as organic phosphate interact with metal oxide under mild conditions, non-polar additive such as organic sulfide chemisorb on nascent metal surface formed under severe conditions. Additives should be selected on the basis of surface chemistry dependent on lubricating conditions.
Lubricating oil fails to maintain hydrodynamic lubrication under high temperature and high pressure condition, and seizure and welding are likely to occur in the severe condition. To prevent these catastrophic events, extreme pressure agents (EP agents) that produce tribo-film on the metal surface are indispensable. Chlorine, phosphorus, and sulfur are three major types of EP agents, and the use of these EP agents is decided according to their characteristics. In this paper, we discuss the characteristics of sulfur type EP agents and the behavior of its tribo-film in oil.
Because of wax species which essentially exist in mineral oil, which is often used as base oil, lubricating oils can lose its fluidity at low temperatures. In order to mitigate this issue, pour point depressant is widely used in various formulations. In this article, the working mechanism of pour point depressant and how to evaluate its performance as well as the reason why the fluidity of mineral oil based lubricants can be worse at low temperatures are explained. Some studies on pour point depressant selection for engine oil are also illustrated, focusing on low viscosity fluid such as SAE 0W-16 grade, which is going to expand as a new generation grade.
Austenitic stainless steels have excellent characteristics of non-magnetic and high corrosion resistant, but have relatively low hardness and strength, and therefore have limitations in application fields. Although the surface hardness improvement treatment is very effective, gas-nitriding or gas-carburizing/carbonitriding conducted under gas atmosphere at high temperature is generally difficult because of the presence of the surface passivation films composed of hydrated chromium ferrous/ferric oxides, and the deterioration of corrosion resistance or the inability to maintain non-magnetic. However, by the low-temperature carburizing in which the direct-current plasma and the active screen plasma methods are combined, surface hardening can be performed efficiently without affecting non-magnetism or corrosion resistance. The hardened layer is called S-phase (extended austenite phase) and is also excellent in corrosion resistance, wear- and fretting-resistance. Austenitic stainless steels that have been subjected to S-phase formation process have already been applied to chemical plants, the nuclear power industry, food and medical device, as well as biomaterials in Europe, and are expected to expand into the Japanese market. In the future, the development of mass-production equipments with excellent productivity will be required in accordance with the size and needs of the market.
The temperature dependence of friction coefficient of lubricant oils containing MoDTC was evaluated using a ball on disk tribometer at constant temperatures of 25, 40, 60 and 80˚C. In the experiments, the friction coefficient gradually decreased and tended to become lower at steady state. The decreasing slope of the friction coefficient was steeper and the lower friction coefficient at the steady state were obtained at a higher oil temperature. The friction coefficient was also controlled by the concentration of MoDTC in oil. Considering that the results of lubricating tests supported the successive processes involving production and wear of MoS2, the friction coefficient can be controlled by the coverage of MoS2 which is determined by a balance of formation and wear of MoS2. An analysis formula was established based on kinetic assessment of the process in order to obtain the Arrhenius plots of the test results. There were two regions which had different slopes in the plot. The activation energies were 70 and 4kJ/mol for the low and the high temperature regions, respectively. This result suggested that MoS2 production from MoDTC was reaction rate-limiting at low temperature and transport rate-limiting at high temperature.
Deep groove ball bearings can support radial load and axial load in both directions and are widely used as bearings for automobiles and industrial machineries because of advantages such as low torque, low noise and low cost. In recent years, the introduction of automobile fuel economy regulation has been advanced worldwide and will be further strengthened in the future. In the field of industrial machinery, energy saving is also progressing. Deep groove ball bearings used in these fields are required to have lower torque. In many cases, deep groove ball bearings are used for grease lubrication and until now low torque has been promoted by improving grease but there is a limit to the reduction of torque with only improvement of grease, we report on the achievement of low torque by developing a cage of new structure without other performance decreasing.