Molybdenum disulfide (MoS.sub.2), for instance, is a well known, versatile inorganic solid lubricant having a lattice layer crystal structure. Inherent basal cleavage occurring within its atomic structure results in low lamellar shear strength and contributes to its superior anti-friction or lubricious properties. There is evidence to show that this property is caused by Van der Waals type bonding between two molecular unit cells on the basal plane connecting the six-fold symmetry of the respective layers comprising the crystal structure as a whole. It is precisely these chemical bonds, relatively long in physical length, which cause low lamellar shear strength and therefore low dry friction measurement on sliding and rotating contact. Conversely, the chemical bonding occurring in the crystal plane located at right angles to the basal plane is more typical of the mono-valent type, shorter in physical length and therefore many times stronger. Recent studies show the hardness for the basal plane as measured on the Vickers Scale to be 32 Kg./mm.sup.2 and that for the crystal plane to be 900 Kg./mm.sup.2, the latter thus being harder by a multiple of nearly 29. Such a difference in physical measurements within a single unit crystal causes anisotropy, a condition which permits implantation of molybdenum disulfide into metal surfaces to be practical and achievable.
In some motor spring applications an inorganic film containing MoS.sub.2 and bonded to the spring material has been utilized to improve the torque consistency of such springs. Motor springs so treated have proved extremely useful in various mechanical time fuzes and in horological mechanisms of the classic escapement types. Indeed, clocks with such springs have sometimes been operated 300% longer than those without coated springs before rewinding is required. The increased performance in these instances is a product of the reduction in the kinetic coefficient of friction between the spring leaves during the unwinding process, that is to say, a reduction in the "stick-slip" phenomenon historically associated with main spring applications.
Application of films of MoS.sub.2 to various metallic substrates is usually by spraying or dipping methods and subsequent drying and/or baking, or even by electroplating the molybdenum directly to the substrate and then heat treating in an atmosphere containing sulfur or sulfide gases. Whatever the technique, however, it is performed after the material has been processed to final or finished size. It has been suggested that transfer of the MoS.sub.2 film to a metallic substrate in these instances is primarily a mechanical process resulting in (a) direct embedding of the solid MoS.sub.2 into a softer surface, (b) deposition of the solid MoS.sub.2 into surface depressions generated in the substrate by an "abrasive" action of the solid MoS.sub.2 itself during movement between the substrate and an opposing surface, and/or (c) deposition of the solid MoS.sub.2 into the depressions indigenous of the original surface finish and hardness of the substrate. But whatever the case may be, and however satisfactory and lasting these techniques may be for certain applications, the results are not satisfactory in the case of items subject to high surface wear. The MoS.sub.2 film, essentially still only a surface film, simply does not endure in these environments but is rather quickly removed or destroyed by abrasion. Such high wear items as piston rings, bearings, journals, valve stems, shafts, and the like, for instance, are composed of various grades of high carbon or stainless steels and though obviously many of them could profit from the low friction characteristics and protection afforded by MoS.sub.2, especially when other lubrication is at a minimum, no feasible way, so far as is known, has emerged for treating them with MoS.sub.2 such that the latter becomes a much more enduring part of the steel itself.
Cold drawn wire for use in stranded wire constructions, such as wire rope for lifting mechanisms, ship board cable systems, aircraft control cable and the like, and for use in coil springs such as compression, extension and torsion types, is also typically manufactured from various high carbon steel alloys. The finished wire is furnished to the spring manufacturer, for example, and the springs themselves are formed by various operations including coiling, grinding, secondary forming, stress relieving, plating and, in many instances, special packing. Likewise, the wire for stranded wire cnstructions is also shipped to a separate place for manufacture of the rope itself. The wire for both springs and rope is produced by a combination of cold working, annealing and final tempering operations to a predetermined diameter and shipped on spools, reels or loose wound coils.
Significant improvement in the performance of stranded wire cables ought also to be achieved by a solid libricant such as MoS.sub.2 applied to the wire strands in view of earlier work done by the Polymer Corporation of Reading, Pa., where crane sheaves made of nylon containing a fine dispersion of MoS.sub.2 were manufactured and tested. The lifetime of wire cable passing over the special sheaves was increased, in comparison to that when using standard sheaves. Eventual failure was caused by friction between individual strands in the wire cable.
Aircraft carrier arresting cables represent another area of utility for a solid lubricant such as MoS.sub.2. Current practice is to reduce friction and corrosion of such cables by repeated applications of a barrier film, such as grease. But the grease is gradually removed from the cable during use and causes the flight deck to become slippery in critical places. In addition, the grease, being flammable, is a fire hazard, and its elimination would thus provide safer operating conditions. Another carrier-related problem is corrosion of internal aircraft control cables by salt air, and those too ought to be improved both in longevity and corrosion resistance by such a lubricant.
In short, a wide range of products formed from certain carbon and stainless steels ought to benefit greatly from treatment by a solid lubricant such as MoS.sub.2 if only the endurance of the treatment could be increased by making the lubricant more a part of the steel itself. Not only would friction be reduced but corrosion resistance increased as well in those applications where corrosion is a problem that must be reckoned with. These are thus the chief objects of the present invention.
USPTO Backgrounds
USPTO Backgrounds