The transportation segment of the lubricant industry gets all the buzz and glory associated with innovative lubricants, and it should. Much has been written about this sector of the market. However, industrial lubricants haven’t been standing idly by. Currently, several motivating factors offer interesting challenges and opportunities to formulators of finished fluids.
Such factors include reductions in unscheduled system maintenance and equipment downtime, overall cost savings to the end-user, and minimization of any negative impact to the environment. Together, they have raised the performance requirement bar for industrial lubricants such as turbine oils, circulating oils and hydraulic fluids.
Long Lubricant Life
Resistance to thermo-oxidative degradation and hydrolysis, prevention of rust and adequate surface characteristics are qualities that enhance a fluid’s long-term performance in a given application. Several industrial lubricant specifications have incorporated changes to address these performance trends. General Electric’s GEK 325 68 E, Denison’s HF-O, Cincinnati Machine’s P68, P69 and P70 have all increased the thermo-oxidative requirements of the lubricants that they cover. Similarly, Denison’s HF-O and the relatively recent ASTM D6518 direct attention to surface characteristics such as demulsibility and air release and foam-inhibition characteristics.
The trend toward increasing use of Group II and III mineral oils in industrial lubricants continues in the U.S., Canada and Asia Pacific regions. These base stocks contribute to improvement in long-term oxidative performance of industrial lubricants as evaluated by the Turbine Oil Stability Test (TOST) (ASTM D943) test. Typical ranges for this test show an increase in performance (Table 1) as compared to less expensive solvent refined Group I mineral oils.
Synergistic combinations of aminic and phenolic antioxidants, metal deactivators and corrosion inhibitors play a crucial role in achieving this present level of performance. There are indications that current zinc-containing packages, when used to formulate Group II and III base oils, can be brought up to present levels of TOST life performance through top treatments (retrofitting additives into in-service lubricants) consisting of synergistic blends of antioxidants.
The higher thermo-oxidative stability obtained with industrial lubricants formulated with Group II and III base oils has led many in the industry to question the relevance of the D943 test, as it is presently run, to actual oxidative field performance of the fluid. Modifications of the test, which runs the lubricant for specific periods of testing (1,000 hours, 2,000 hours, 3,000 hours, etc.) and evaluates changes in oxidative performance of the finished fluid, are starting to be adopted by members of the industry. Some of the additional challenges presented by the higher viscosity versions of these oils are additive solubility and antirust performance of the finished fluid.
Additive and Water Compatibility
Fluids must be chemically compatible with all system components including seals and coatings. Of particular interest in recent years has been compatibility of the lubricant with contaminants such as water and trace amounts of zinc or calcium-containing additives. Incompatibility can result in precipitates that can plug the fine filters currently employed in industrial equipment, thereby ruining system performance and increasing costs to the end-user in terms of labor and equipment downtime.
Water can find its way into the oil through ingression or condensation of atmospheric moisture in the equipment. Contamination of the lubricant with trace amounts of calcium or zinc-containing additives can take place when blending/storing multiple lubricants in the same tank, or when topping or recharging a system with a fluid of different formulation to the one previously employed.
The Denison HF-O and MIL-17331H specifications include procedures for assessing the compatibility of a fluid with water. In order to assess the compatibility of trace calcium or zinc-containing contaminants with a particular formulation, variations of the Association Francais de Normalisation (AFNOR) test have been employed by the industry. Additives that are particularly affected by these requirements are corrosion inhibitors and antiwear/extreme pressure agents, and there are products in the market presently that meet these performance requirements.
Raising the Bar on Wear
Aside from the obvious need for an appropriate lubricant film between moving surfaces, protection of the equipment against all wear, under boundary conditions, has gained greater significance as a result of improved requirements for fluid cleanliness and the increasing use of compact systems with smaller oil reservoirs operating at higher temperatures and pressures. The industry is presently requesting higher antiwear additive reserves (concentrations) for industrial lubricants.
The Denison HFO specification now has a requirement for FZG performance (antiscuff control). Modifications of this test are employed to show that the fluid can consistently meet failure load stage pass levels that are higher than 12 (the current upper testing limit). There is presently antiwear chemistry in the market that will meet this need.
Regulatory - Controlling Zinc
The Environmental Protection Agency considers zinc a primary (toxic) pollutant. It is in the process of finalizing regulations that will limit the amount of zinc in effluent discharges from metal products and machinery facilities. These facilities are involved in operations such as metal forming, electroplating, milling, grinding, solvent degreasing, etc. These manufacturing processes fall under several categories such as general metals, nonchromium anodizing, metal finishing and printed circuit board. The final rule is expected by December 31, 2002.
The category of highest interest to the industrial lubricants industry is general metals. If the EPA decree for reduction in zinc levels is significant, facilities that treat waste under this category will need to spend capital in order to implement measures that comply with the regulatory requirements. Some manufacturers may look at ways to minimize these costs by removing as many sources of zinc from their facilities as possible. One potential option is a shift toward the use of ashless or nonzinc containing industrial lubricants at these sites.
While these market factors for industrial lubricants pose a challenge to the formulator of these products, the result of their implementation will offer greener, more cost-effective and higher-performing finished fluids to the end-user.
This article is reprinted with permission from the Independent Lubricant Manufacturers Association (www.ilma.org).