US3549531A - Microsphere solid metal lubricant - Google Patents

Description

Dec. 22, 1970 I R. SANTT 3,549,531 mIcRdsPaERE so w METAL LUBRICANT 7 Original Filed Feb. 24. 1964 lllvllllrl/ 41m 0440/ 55% 9 United States Patent 3,549,531 MICROSPHERE SOLID METAL LUBRICANT Ren Santt, Villefranche par Dun-sur-Meuse, Meuse, France, assignor to Centre National de la Recherche Scientifique, Paris, France, a society of France Continuation of application Ser. No. 346,881, Feb. 24, 1964. This application Feb. 27, 1967, Ser. No. 624,969 Claims priority, application France, Dec. 18, 1963,

rm. (:1. 610m 5/02 US. Cl. 25226 Claims ABSTRACT OF THE DISCLOSURE Solid metal microsphere lubricants used between slidably engaged surfaces.

This application is a streamlined continuation of application Ser. No. 346,881 filed Feb. 24, 1964 and now abandoned.

The present invention relates to the field of lubricants and more particularly to lubricants made from solid materials in the form of microscopic particles.

The advent of commercially available particulated materials of uniformly spherical shape, and having diameters of the order of microns, has led to many new applications which take advantage of their unusual properties. They have come to be used as filters for aircraft panels, as floating protective layers on oil reservoirs, as packing materials for fragile objects, etc. These materials have been found to be quite hard, mainly because their shape prevents their being subjected to tangential stresses, and extremely easy to handle since their solid nature ensures that they will not chemically or mechanically deteriorate their containers.

The present invention seeks to extend the range of uses of these materials to the lubricating field in which they have been discovered to have several extremely valuable applications. In addition these materials present certain striking advantages over prior art lubricants in that they are relatively insensitive to both wide variations of temperature and the passage of time and they do not present the containment problems inherent in the use of liquid or amorphous lubricants. These materials have proven to have excellent lubricating qualities, especially when used in combination with certain temperature-insensitive liquids which have not been previously thought of as effective lubricants.

It is, therefore, an object of this invention to produce a lubricant which is relatively insensitive to wide variations in temperature and pressure and to the passage of time.

It is another object of this invention to produce a lubricant consisting at least in part of solid, spherical particles.

It is yet another object of this invention to achieve a lubricating action which is superior to that previously achieved by conventional, light-weight, liquid lubricants.

These and other objects, features and advantages will become more readily apparent from the following description, when taken together with the accompanying drawings, in which FIGS. 1 and 2 are graphs showing the properties of the lubricants of the present invention in comparison with those of prior art lubricants.

The lubricants envisioned by the present invention are characterized by the fact that the particles forming at least one ingredient thereof are in the form of hard spheres which are calibrated, that is to say sized, so as to be as uniform as possible in diametral size. This sizing is conducted with a view of obtaining spheres the diameter D of which is within the range of D Di These spheres have a diameter of less than 40 micron and preferably less than 8 microns. It is preferred that the materials constituting these particles be taken from the group consisting of iron, nickel, cobalt, tungsten, aluminum, or an alloy of the bronze type. Such spheres are commercially available in a non-calibrated state.

In order to calibrate them, one can have recourse to a sedimentation in the gaseous phase, for example by a passage of the particles without the aid of secondary air in a vortex separator of the Walther or Bahco types, or by a sedimentation in an appropriate liquid medium.

According to another method, one could prepare the spheres by decomposing the metal carbonyl of one of the above named materials, if it exists.

As an example, and purely by way of illustration, one could produce the desired iron spheres, for instance, by injecting the iron pentacarbonyl in a current of ionized hydrogen, the latter being inert with respect to the iron pentacarbonyl, at a temperature above C. The resulting decomposition of the iron pentacarbonyl is followed by the condensation of the alloy around nuclei constituted by the hydrogen ions present. The spheres obtained by this process result from the superposition of successive concentric layers of the alloy and are thus relatively uniform in size. The resulting spheres are thus subjected to a first calibration at the very moment of their production.

Advantageously, one can complete the calibration by one of the methods described above.

Still by way of example such a process was carried out and it resulted in the production of a powder consisting of iron spheres having diameters which were uniform and of about tWo microns, having the following chemical composition:

Percent Percent Carbon 0.6 Nitrogen 0.5 Oxygen 1.0 Iron 97.9

The hardness of these small spheres, expressed in D.P.N. units, was in the neighborhood of 850, being notably superior to that of the hardest steels.

Experimentation shows that the spherical particles thus produced are remarkably resistant to corrosion.

Because of the microscopic size of these particles their emplacement between the surfaces to be lubricated ofter requires special measures. In accordance with the invention, one can utilize, in order to achieve this emplacement, a suspension of the spheres in a volatile liquid, for example alcohol, which evaporates very rapidly after the emplacement operation with the result that only the spheres remain between the surfaces to be lubricated.

With respect to the quantity of lubricant introduced between the rubbing surfaces, it is preferred that there be just enough spheres to form a single layer in which the spheres are in contact with each other.

In the preceding discussion, the lubricant produced according to the present invention consisted solely of the spherical particles described above. However, the present invention is also directed to lubricants which are prepared by mixing these particles with a binder constituted by a substance which can be either a low density liquid or a viscous substance and which does not have any corrosive properties with respect to either the spherical particles or the surfaces to be lubricated.

The respective proportions of particles and binder are chosen so that, once the lubricant has been applied to the surfaces to be lubricated, the particles will present the single, continuous layer described above.

One could select, for the binder, a substance which itself has the properties of a lubricant. Such a substance, which must be able to resist temperature and pressure variations without experiencing an excessive change in its properties, can be in the form of a grease or an oil, either vegetable, mineral, or synthetic.

On can also select a binder material from among substances which do not themselves necessarily have lubricating properties but which possess other properties, for example relative insensitivity to wide variations in temperature and pressure or to other conditions, such as the presence of an ionized medium.

By way of example, there could be mentioned liquids which are stable up to temperatures of 400 C. and which are moreover uninflammable. Such liquids are usually chosen from the group consisting of chlorinated benzene, chlorinated diand polyphenylic derivatives, hexachlorobutadiene and others.

With reference to the binders which are insensitive to ionized environments, diphenyl ether may be mentioned as an example. Other binders which could prove useful are constituted by silicones and petroleum.

In order to give one example of the combinations described above, it has been observed that a pair of rubbing surfaces could be lubricated by spherical particles to which petroleum has been added, the combination of petroleum and spherical particles having been found to have remarkable lubricating properties. In order to clearly point out the value of these properties reference will be made to FIG. 1 which shows curves indicating the operation of a rotating device which was lubricated by a different substance during each run.

The curves of FIG. 1 indicate the motor operating current versus time for a motor driving a small speed reducer, the latter being the element which was lubricated by the various materials. The speed reducer was of the SAGEM brand, type 1070, and was driven by an electric motor running at 7750 rev/min.

Without any lubrication at all (point A) the speed reducer started at a motor current of 10 ma.; when lubricated with petroleum alone (point B) it also started at 10 ma., leading to the conclusion that the petroleum provides no reduction of the friction in the speed reducer; lubricated by a special oil (point C) the device started at 5 ma.

For the next test run, a lubricant representing one of the embodiments of the present invention was used. It consisted solely of tiny calibrated spheres obtained from iron carbonyl, of the type described in detail above, and its use resulted in a motor starting current of 11 ma. (point D). The same motor current was obtained for a lubricant consisting of a suspension of iron particles in alcohol, after the alcohol has had time to evaporate (point E on curve E). This increase with time of curve B is probably due to a clogging of the tiny spheres in the bases of the reduction device gear teeth. The curve B, which had an initial value of 2 ma. (point E represents the increase with time of the motor current as the alcohol evaporated.

The final experimental value, point F, represents the motor current when lubrication is provided by a suspension of the above-described iron carbonyl particles in petroleum of the same type as that used to obtain point B, such a combination having been described above. This current is of the order of 1 ma., or 5 times less than that obtained with a usual high-grade lubricating oil.

These results clearly show that the presence of iron carbonyl spheres in a petroleum medium gives to the combination lubricating properties which are not possessed by petroleum alone.

The presence of the tiny spheres in lubricants applied between rubbing surfaces eliminates all dangers of abrasion or gouging of one surface by the other, the pheres playing the role of tiny balls which roll in contact with one another between the two surfaces to be lubricated and which not only prevent all seizing between the surfaces but are also capable of freeing units which had previously become seized.

Moreover, experiments have shown that the lubricants according to the present invention effect a constant polishing of the friction surfaces, thus continually improving their sliding characteristics. This leads to a continual reduction in both the heat generated by the sliding action of the surfaces and their wear, all of which prevents the formation of deep fissures during operation. Further, the quality of the lubrication provided by the lubricants of the present invention does not deteriorate with time.

In order to establish the verity of this latter assertion, a group of tests were run to determine the friction torque experienced by a device rotating in a ball bearing unit which was successively lubricated by various substances. The results of these tests are shown in FIG. 2, wherein the curves illustrate the characteristic of friction torque versus time obtained by the use of various lubricants.

Curve I represents the friction torque versus time characteristic when the device is run without any lubricant while curve II represents the case where a few drops of petroleum have been added. In both cases, the friction increased rapidly after a short period of operation (one hour in the case of these experiments) and very quickly became so great that the unit stopped running. In the case of curve III, the bearing was lubricated with lightweight oil of the kind used for oiling delicate mechanisms such as watches. After having started at a raised value, the torque therein stabilized itself rapidly at a value of around 0.25 g./cm. a value which is almost double than that measured for the case where no lubrication was used. However, the torque obtained with the use of the light oil remained constant during the entire duration of the experiment, about 96 hours.

Finally, the curve IV shows the torque-time characteristic for the case where the bearing was lubricated by a substance representing one embodiment of the present invention and consisting of the spherical particles suspended in alcohol. The starting torque for this test was in the neighborhood of 0.08 g./cm., and, in proportion to the rate of evaporation of the alcohol and to the rate at which the spheres spread themselves out uniformly between the lubricated surfaces, the torque diminished rapidly until the alcohol was completely evaporated, reaching a final value of 0.05 g./cm. The friction torque remained constant at this value during the entire remaining period of the experiment. Comparison of the foregoing results clearly shows that the use of the lubricant of the present invention caused the friction torque to be five times less than the value produced with the aid of the special light oil, and that the lubricating quality of the spherical particles did not diminish with time.

It should be noted at this point that the effectiveness of the novel lubricants described above is augmented by an appropriate treatment of the surfaces between which they are to be used. Specifically, these surfaces should receive a finish which is of such a smoothness that the deepest irregularities, be they lines or pits be less than one-third of the diameter of the spheres. 'Such a smoothness will insure that the spheres do not become rutted in these irregularities.

The desired polishing can be accomplished mechanical- 1y or electrically, the technique used, of course, depending on the degree of smoothness required. In the case of mechanical polishing, it is necessary that the helical or linear scorings which inevitably result extend in many different directions and intersect each other irregularly in order to prevent the movement of the spheres from being biassed in any particular direction or directions. In other words, the spheres roll at random.

The use of lubricants prepared according to the present invention offers solutions to previously unsolved lubrication problems. For example, by applying the spherical particles alone between two rubbing surfaces, one obtains a lubrication which, for all practical purposes, is independent of variations in ambient temperature and pressure, and can thus be used to lubricate materials which can themselves withstand extreme conditions. One example of such materials would be the new ceramics which withstand extreme temperatures.

The use of the spheres with such materials would be extremely valuable because these ceramics have the ability to withstand extremes of temperature and pressure without changing their properties, and are, therefore, often used to replace metals under these conditions. However, these ceramics have the serious drawback of being incapable of engaging in sliding contact with one another without experiencing excessive friction which tends to permanently damage them. The lubricants of the present invention are able to solve this problem because they possess lubrication properties which are as insensitive to temperature and pressure variations as are the ceramics.

Further, the use of the lubricants of the present invention simplifies the construction, the technology and the design of the surfaces of ceramic units because it permits the tolerances between pieces to be reduced to around 1 micron.

It is also possible to construct pillow blocks abutments and pivots carrying cylindrical or frustoconical shafts or spindles turning in ceramic housings which are lubricated by embodiments of the present invention, thus permitting the dimensions of the various parts to be such that adjacent parts experience very little play, of the order of 1 micron, for example.

Further, the employment of such narrow tolerances between moving parts permits the lubricated spaces to be highly impervious to the introduction of foreign particles from the surroundings, and, to a large degree, water tight and gas tight.

Turning to another field of application, it has been found that the lubricants of the present invention can be used to great advantage in the textile, plastics and paper industries to remove certain sources of static electricity, and thus reduce fire hazards. This result is achieved by using the spheres of the present invention, particularly those made from iron or tungsten, as lubricants between the sliding surfaces of machines thus taking advantage of the fact that these lubricants (which, when subjected to no pressure, act as dielectrics having properties equivalent to those of mica), when subjected to even a very slight pressure, become electrical conductors which prevent the accumulation of static electricity on any one part.

Those embodiments of the present invention which consist solely of spherical particles could also solve many lubrication problems of devices designed to travel in outer space. In brief, the spheres, being relatively unaffected by either the extremely low temperatures and pressures of outer space or the extremely high temperatures experienced by a device reentering the earths atmosphere, would provide a consistent, effective lubrication during the entire period of flight of such a unit.

Further, the lubricants of the present invention are insensitive to ionized environments and hence would be very valuable lubricants for devices working in such environments, such as in the nuclear industries.

The foregoing has represented an attempt to describe a few of the possible uses for the lubricants of the present invention. It will be appreciated that the embodiments disclosed herein are capable of a great many variations, applications and modifications without departing from the spirit of this invention and it should, therefore, be understood that its scope is intended to be limited only by the breadth of the appended claims.

What is claimed is:

1. In combination with surfaces engaging each other slidably, a lubricant between said surfaces comprising a plurality of calibrated spherical had particles having a diameter less than 40 microns, such surfaces having a polish sufficient to make possible the rolling at random therebetween of said spherical metallic particles.

2. A combination according to claim 1 wherein said particles are made of a metal selected from the group consisting of iron, nickel, cobalt, aluminum, tungsten and bronze.

3. A combination according to claim 1 wherein said diameter is less than about 8 microns.

4. A combination according to claim 1 wherein said diameter at least equals three times the deepest irregularities of said engaging surfaces.

5. A combination according to claim 1 wherein said slidably engaging surfaces are made of ceramic.

6. A combination according to claim 1 wherein the diametral sizes of said metallic spherical particles calibrated at a determined average value D range within D D D and D+ 10 7. In combination with surfaces engaging each other slidably, a lubricant between said surfaces consisting of a single layer of calibrated spherical hard particles having a diameter less than 40 microns, such surfaces having a polish suflicient to make possible rolling at random therebetween of said spherical particles.

8. In combination with surfaces engaging each other slidably, a lubricant between said surfaces consisting of a nonvolatile organic liquid binder material containing therein calibrated spherical hard particles having a diameter less than 40 microns, such surfaces having a polish sufiicient to make possible the rolling at random therebetween of said spherical particles.

9. In a combination as claimed in claim 8, said binder material having lubricating properties.

10. In a combination as claimed in claim 9, said binder material is mineral lubricating oil.

References Cited UNITED STATES PATENTS 2,021,885 11/1935 Bird 252l9 2,486,130 10/1949 Dietrich et al. 252-19 2,859,181 11/1958 Jordan et al. 25219 3,007,867 11/1961 Allen et al. 25226 3,224,966 12/1965 Li 252--12.2 2,697,028 12/1954 Baker et al. 23209.1

FOREIGN PATENTS 206,706 ll/1923 Great Britain 25226 OTHER REFERENCES The Machinist, Mar. 13, 1954, pp. 433-411.

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R.

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