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WEAR REDUCTION USING CYCLIC AMIDE
BACKGROUND OF THE INVENTION
1. Field of the Invention 5 The invention is generally related to methods of reducing
wear of rubbing surfaces using cyclic amides.
2. Description of the Prior Art
Wear has been defined as the progressive loss of a 1Q substance from the operating surface of a body as a result of relative motion at the surface of the body (see, Furey, "Tribology", Encyclopedia of Materials Science & Engineering, Pergamon Press, Oxford, pp. 5145-5157, 1986). When elements rub together, whether made of the 15 same or different materials, wear can occur. The rate of wear tends to increase under harsh temperature and pressure conditions which, for example, exist inside ceramic or metal engines, propulsion engines, and the like. In addition to limiting the useful life of the part in which the ceramic or 2Q metal is used, wear of ceramics or metal can be costly because the ceramic or metals materials themselves are expensive to produce. Other significant problems associated with wear include, e.g., down time for equipment, reduced safety, and diminished reliability. 25
Therefore, lubrication, particularly under boundary friction conditions, is extremely important for rubbing materials. Lubrication is a process that reduces friction and/or wear (or other forms of surface damage) between relatively moving surfaces by the application of a solid, liquid, or 30 gaseous substance (i.e., a lubricant). Therefore, the primary function of a lubricant is to reduce friction or wear or both between moving surfaces in contact. However, lubricants can also serve other ancillary functions, such as acting as a hydraulic fluid, coolant, gas seal and carrier for adhesives; 35 they may also protect metal surfaces from corrosion and aid in the removal of debris and deposits. Examples of conventional lubricants are widespread and diverse. They include automotive engine oils, wheel bearing greases, transmission fluids, electrical contact lubricants, rolling oils, cutting 40 fluids, preservative oils, gear oils, jet fuels, instrument oils, turbine oils, textile lubricants, machine oils, jet engine lubricants, air, water, molten glass, liquid metals, oxide films, talcum powder, graphite, molybdenum disulfide, waxes, soaps, polymers, and even the synovial fluid in 45 human joints.
Also, the environments where lubrication needs arise continue to evolve. For instance, in machinery, the classical lubricants and additives more typically have addressed applications involving rubbing parts made of metal, in 50 particular, steel or its alloys. However, more recently there also has been increased interest in using ceramic materials and fiber-reinforced plastics (i.e., composites) in a wide variety of applications which traditionally have utilized metals. Ceramic and composite materials have several 55 advantageous engineering properties. For example, ceramics generally can be used at much higher temperatures than metals, are relatively inert and resist corrosion, and are resistant to abrasive wear owing to their hardness. Additionally, some ceramics are lighter in weight than 60 conventional steel-based materials. Alumina, silicon nitride, partially stabilized zirconia, and silicon carbide, for example, are ceramic materials being used in high temperature wear environments.
Ceramics thus have attracted increased interest for uses 65 along side, in combination with, and/or in lieu of metals, such as in automotive engines, gas turbines, turbomachinery,
cutting tools for super alloys, and aerospace bearings, which are driven by a need for industrial materials that can tolerate high temperature, corrosive environments and/or result in better efficiency. However, the surface characteristics of ceramics are very different from those of metals. For these and other reasons, conventional metal lubricants generally have lacked the versatility for successful use in the lubrication of ceramics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for reducing wear and surface damage to rubbing components.
The foregoing and other objects are achieved by the use of cyclic amide compounds for the boundary lubrication of rubbing solid surfaces. The cyclic amide compounds can be used to reduce wear of rubbing surfaces. The term "rubbing" as used herein refers to solid surfaces in frictional contact with each other. The wear reduction achieved with cyclic amides is applicable to many types of solid surfaces in rubbing contact such as ceramics, metals, composites, plastics, wood, and the like.
The use of cyclic amides to reduce wear combines economic advantages of low cost and wide availability of starting materials with technical advantages such as high solubility in carriers and efficacy at low concentrations.
Cyclic amides useable in the present invention have the following general formula I:
alkylene chain segment is acceptable as long as the same conditions are met.
The cyclic amide compounds may be used in pure form, or as dissolved, partly dissolved or dispersed in a carrier medium. To reduce material costs, the cyclic amide can be 5 dispersed or dissolved in a carrier medium. A carrier fluid is used as a medium for the cyclic amides. The term "fluid" means any material or substance that changes shape or direction uniformly in response to an external force imposed upon it. The term can apply not only to liquids, but also to 10 gases and to finely divided solids. For example, the region of rubbing contact (i.e., the interface) between a first solid part and a second solid part can be flooded with, immersed in, or exposed to the lubricating carrier medium (e.g., liquid, gas, semi-solid) containing the cyclic amides. Experiments 15 described herein have been conducted which show that fluid compositions containing even very low concentrations of cyclic amides significantly reduce the amount of wear and surface damage otherwise suffered by ceramics and metals in rubbing or wearing contact. 20
Specific applications of the present invention are widespread and diverse.
The cyclic amides can be used to reduce wear between mechanical parts in contact with each other, such as between gears, between a valve lifter and a cam of an automotive 25 engine, and between a piston and cylinder in a motor. The cyclic amides also can be used in lubricating and reducing wear of bearings (e.g., steel bearings, ceramic bearings). The cyclic amides also can be used in machining and cutting operations to reduce wear of a machining/cutting tool 30 (ceramic or metal) used in a machining operation such as lathing, broaching, tapping, threading, gear shaping, reaming, drilling, milling, hobbing, grinding, turning operations, and the like.
The cyclic amides also can be used as fuel lubricity and 35 anti-wear additives in combustion fuels, such as hydrocarbon fuels, including gasolines, aviation turbo fuel, jet fuel, rocket fuel (e.g., kerosene), and diesel fuels. The cyclic amides can be added in effective amounts to the engine fuel itself such that a sufficient amount of unburned cyclic 40 amides remains present in the cylinder during the engine cycle to lubricate and reduce wear between the piston and cylinder. For example, methods of the present invention can be applied to lubrication of gasoline engines, such as twostroke engines, where the cyclic amide compounds of the 45 invention can be used as a fuel additive to lubricate and reduce wear of rubbing and contacting engine parts during operation. The cyclic amides can be added directly to the engine gasoline, or to gasoline via a separate carrier fluid such as a lubricating mineral or synthetic oil to be added to 50 the gasoline, to reduce engine wear. The lubricating compositions of the invention can be added to diesel fuel to control wear of diesel fuel injector pumps where metal-tometal contact occurs, while at the same time reducing exhaust emissions. 55
The cyclic amide compounds used in the present invention may be used as the sole additive in the fuel medium or in conjunction with other performance-enhancing additives added to the fuel, such as detergents, corrosion-inhibitors, alcohols (e.g., ethanol) or ethers (e.g., methyl-tertiarybutyl 60 ether).
The cyclic amides used in the invention also can be used as an anti-wear agents in automotive engine oil lubrication applications. For example, the cyclic amides can be used in conjunction with or in place of a conventional engine oil 65 antiwear additives (e.g., zinc dialkyl dithiophosphate or "ZDDP") in liquid lubricating oils. Methods of the invention
can be applied to the lubrication of four-stroke engines, for instance, where the cyclic amides are introduced into the engine as an additive to the lubricating oil. Also, the cyclic amides could be used in short duration "dry" testing of four-stroke engines in which the cyclic amides are introduced via the oil inlet of the engine, such as by vapor phase injection, without any liquid lubricating oil being added or needed in the engine.
Other types of combustion engines where cyclic amides are contemplated to be useful for wear reduction in rubbing engine parts include, for example, adiabatic or low heatrejection engines in which ceramic components are employed, advanced propulsion systems using turbomachinery, and any engine or power-producing device in which hydrocarbon or fossil fuels are used as the source of energy.
The compositions of this invention, where used as an anti-wear additive for engine oils or fuels, offer an important advantage in that the cyclic amide compounds used are devoid of metals, phosphorus, or sulfur, which could lead to solid residues, soots, and deposits in a combustion chamber of an engine (in the case of metals and phosphorus), or interfere with the action of emission catalyst systems. The absence of ash or soot deposit formation, for example, by use of the compositions of the invention is advantageous as ash and soots also might interfere with the antiwear action of any another supplemental antiwear additives being used such as ZDDP. The cyclic amides, when combusted in a high temperature environment, such as in a combustion engine, form ashless, gaseous combustion products (e.g., H20, C02), and, as such, pose no threat to foul the catalyst in a catalytic converter and pose reduced environmental concerns.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of the preferred embodiments of the invention with reference to the drawings, in which:
FIG. 1 is a diagram showing an apparatus used to conduct liquid phase high contact stress pin-on-disk experiments.
FIG. 2 is a graph showing wear reduction achieved with caprolactam as an antiwear agent for an alumina-on-alumina rubbing system.
FIG. 3 is a graph showing wear reduction achieved with caprolactam as an antiwear agent for an alumina-on-alumina rubbing system at different concentration levels of caprolactam.
FIGS. 4A, 4B, 4C, and 4D are graphs showing wear reduction achieved with caprolactam as an antiwear agent for an alumina-on-alumina rubbing system at different speed and load combinations for a given concentration level of caprolactam.
FIG. 5 is a graph showing wear reduction achieved with caprolactam at different concentration levels, and laurolactam, as antiwear agents for an alumina-on-alumina rubbing system.
FIG. 6 is a graph showing wear reduction achieved with caprolactam as an antiwear agent for a steel-on-steel rubbing system.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS OF THE
The present invention concerns use of cyclic amide compounds to significantly reduce the amount of wear and