Solid anti-friction devices – materials therefor – lubricant or se – Solid anti-friction device – article or material therefor – Elemental or alloyed metal
Reexamination Certificate
1997-10-03
2004-05-11
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Solid anti-friction device, article or material therefor
Elemental or alloyed metal
C508S105000, C508S106000, C508S107000, C508S109000, C508S113000, C508S123000, C508S124000, C508S125000, C508S126000, C508S127000, C508S128000, C508S129000, C508S130000, C508S131000, C508S148000, C508S150000, C508S151000, C508S155000, C508S156000, C508S157000, C508S159000, C508S162000, C508S165000, C508S167000, C508S171000, C508S176000, C508S177000, C508S179000, C508S362000, C508S451000, C508S459000, C508S464000, C508S469000, C508S473000, C508S474000, C508S491000, C508S507000, C508S512000, C508S590000, C508S
Reexamination Certificate
active
06734147
ABSTRACT:
FIELD OF THE INVENTION
The field of the invention is lubricants and especially lubricant compositions comprising a superabsorbent polymer in combination with a lubricant material.
DESCRIPTION OF RELATED ART
Lubricant materials function by separating moving surfaces to minimize friction and wear. Archeological evidence dating to before 1400 B.C. shows the use of tallow to lubricate chariot wheel axles. Leonardo da Vinci discovered the fundamental principles of lubrication and friction, but lubrication did not develop into a refined science until the late 1880's in Britain when Tower produced his studies on railroad car journal bearings in 1885. In 1886 Reynolds developed this into a theoretical basis for fluid film lubrication.
Lubrication principles vary from the separation of moving surfaces by a fluid lubricant through boundary lubrication, to dry sliding. In many respects, these principals are coextensive.
Fluid Film Lubrication
In fluid film lubrication, the load on moving surfaces is supported entirely by the fluid between the surfaces which is a film under pressure. The pressure on the film develops through the motion of the surfaces, which in turn delivers the lubricant into a converging wedge-shaped zone. The behavior of the moving surfaces is totally dependent on the fluidity or viscous behavior of the lubricant. Film pressure and power loss are dependent on the viscosity of the lubricant as well as the configuration of the moving surfaces, and lubricant shear strength. Hydrodynamic or squeeze-film action cannot provide adequate load support in some instances for bearings lubricated with oil or water. Pumping the lubricant into the moving surfaces sometimes provides the necessary hydrodynamic or squeeze-film properties for bearings used for handling heavy loads in low speed equipment. This practice is especially common with low viscosity lubricants such as water. It would therefore be advantageous to provide additives to these types of lubricants to overcome these difficulties.
Oil film lubricants on surfaces are limited in their lubricating capabilities and as such have load limits. Asperities or high spots-on the moving surfaces will in turn support the load when the load limit of the lubricant is reached so that the lubrication moves from full-film to mixed-film to complete boundary lubrication with an increase in coefficient of friction between the moving surfaces. High load, low speed, low viscosity lubricants, misalignment, high surface roughness or an inadequate supply of lubricant causes this change from full-film to boundary lubrication. Chemical additives, however, can reduce resultant wear and friction.
Surface contact through asperities on the moving surfaces can result in tearing of the surfaces and is especially a problem with increasing loads. Plastic deformation, temperature buildup and welding of the surfaces with eventual seizure of the surfaces occurs as a result. This problem is especially prevalent in hypoid gears used in automobile differentials. Extreme pressure lubricants combat welding of the surfaces in these circumstances and contain organic compounds that react at these elevated temperatures and form high-melting inorganic lubricant films on the surfaces. Sulfur, chlorine, phosphorous and lead compounds in these additives provide low shear strength layers that minimize surface tearing, or coat the moving surfaces to prevent- fusing. Since extreme pressure additives function by chemical action, they are not used where the metal surfaces will be severely eroded. Increasing the lubricant or oil viscosity by means of an additive, lowering the unit bearing loading, improving the finish on the moving surfaces and use of external pressurization offer alternatives to extreme-pressure additives.
Dry rubbing or dry sliding involving solid-to-solid contact occurs in fluid lubrication systems as for example in machine start-up, run-in misalignment or inadequate clearance, reversal of direction of moving surfaces, or any unforeseen or unplanned interruptions in lubricant delivery. Conventional lubricants such as greases or oils also are not used on moving surfaces in extreme temperature, high vacuum, radiation or contamination environments. Dry lubricants applied as thin coatings or as particulate materials in these environments reduce wear and friction of moving surfaces. These films or particulate materials may comprise or incorporate solid or particulate carbon-graphite, lead babbitt, bronze, aluminum, polyethylene or polytetrafluoroethylene solid or particulate materials in a binder where the film or particulates are adhered to one or both of the moving surfaces. The effectiveness of the dry lubricant film or particulates is controlled to some degree by the binder where solid or particulate lubricants are employed as well as conditions of use such as the load, surface temperatures generated during use, speed of the moving surfaces, hardening, fatigue, welding, recrystallization, oxidation and hydrolysis. It would be an advantage therefore to have a binder that is strongly adherent and resistant to some of the conditions generated while in use.
In elastohydrodynamic lubrication carrying the load on rolling contacts in ball and roller bearings, gear teeth, cams or friction drives, minimizes lubrication problems. Focusing the load on a small contact area on these moving surfaces results in high elastic contact stresses. Lubricant films help support the load which is described as “elastohydrodynamic,” because of the close relationship between the formation of a thin hydrodynamic fluid lubricant film and elastic deformation.
The lubricant viscosity and film conditions at the entry of the contact zone in these systems generally fix the lubricant film thickness which is substantially uniform over most of its length along the contact. It is believed that high contact pressures lead to excessive lubricant viscosity and pressure distribution close to the Hertz pattern for simple static elastic contact theory. It has also been noted that only a slight reduction in film thickness results with increasing loads with pronounced contact deformation. In plotting contact pressure in psi (pounds per square inch) against distance and direction of lubricant flow, it appears that optimum lubricity is obtained with a sharp pressure spike at the exit portion of the lubricant film; however, this does not take into account changes in temperature, relaxation time or other variables in the lubricating system. It would therefore be an advantage to provide an additive that would enhance viscosity and film formation and retention under these and other conditions.
Load capacity with a full elastohydrodynamic film is limited by fatigue strength of the moving surfaces in rolling contact systems. The working of grain boundaries beneath the contact surface, where shear stress is at a maximum, generates damage. Fatigue cracks occur within this heavily stressed zone with repeated stress cycles. Particles are loosened, which is characterized as surface flaking, and represents the depth of the zone of maximum shear stress. The fatigue cracks are started by focal points of oxide particles and stringers of impurities.
Where the lubricant film thickness becomes less than the surface finish of the moving or rolling surfaces, under high load, low speed or low lubricant viscosity, boundary lubrication comes into play which is dependent upon the chemical nature of the lubricant. The drop in fatigue life can be avoided under such conditions as well as surface wear with the proper lubricant additives.
Petroleum Lubricants
Petroleum based lubricants are extensively used because of their wide availability and consequent low cost. Petroleum lubricants are well known in the art and generally comprise low viscosity and low density paraffins having relatively high freezing points. When combined with oxidation inhibitors to obtain high temperature stability, oxidation resistance is improved and sludging tendency is minimized.
Aromatic petroleum lubricants such as napthenes are generally oxidation s
LCC County Mosquito Control
Medley Margaret
The Law Offices of Robert J. Eichelburg
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