Title:
LOW-FRICTION, WEAR-RESISTANT MATERIAL
United States Patent 3787229


Abstract:
A material, and the process therefor, having at least a surface layer of highly densified, uniformly disposed spheres or spheroids partially embedded in a matrix with the exposed segments thereof forming a uniformly wavy finish with low-friction and wear-resistant characteristics.



Inventors:
RUDNESS R
Application Number:
05/116180
Publication Date:
01/22/1974
Filing Date:
02/17/1971
Assignee:
UNION CARBIDE CORP,US
Primary Class:
Other Classes:
75/232, 75/236, 75/238, 242/157C, 242/157R, 242/615.4, 428/418, 428/472, 428/609, 428/639, 428/640, 428/687
International Classes:
C04B35/01; C04B35/10; C23C4/04; C23C4/18; C23C24/00; C23C24/08; C23C28/00; (IPC1-7): B65H57/24; B23P3/00; B32B27/20
Field of Search:
161/162,168 242
View Patent Images:
US Patent References:
3646746BALLOON CONTROL RING1972-03-07Murray et al.
3619231CONTINUOUS METAL COATING PROCESS WITH FUSIBLE PULVERULENT MATERIALS1971-11-09Johnson
3388027Graphic materials incorporating microsphere distributions for the presentation of visual information1968-06-11Altman
3130938Thread guide1964-04-28Dysart
3086722Yarn traverse mechanism1963-04-23Altice et al.
3080135Textile apparatus1963-03-05Steijn
3080134Textile filament guide1963-03-05England et al.
3036975Rapid-curing epoxy resin compositions and method of making1962-05-29Taub
2895389Coatings for the traffic bearing surfaces of grating1959-07-21Nagin
2646227Self-traversing drive roll1953-07-21Calhoun et al.
2555319Bead coated tympan sheet1951-06-05Cross



Other References:

Lee et al., Handbook of Epoxy Resins, McGraw Hill Book Company, New York, N.Y. 1967, pages 4-2, 14-21 and 21-24. TP1180E6L4.C4..
Primary Examiner:
Drummond, Douglas J.
Assistant Examiner:
Bokan, Thomas E.
Attorney, Agent or Firm:
Humphreys, Harrie Cummings Robert Aruontes James M. C. C.
Claims:
1. A low friction, wear-resistant material for guiding moving lengths of textile films and fibers, said material having at least a surface composed of uniformly disposed spheroidal to spherical shaped wear-resistant particles having a microhardness of at least about 500 Diamond Pyramid Hardness and a size between about 270 Tyler mesh and about 325 Tyler mesh, said particles partially embedded in a matrix such that the surfaces of the particles are exposed to provide a uniformly wavy low friction surface

2. The material of claim 1 wherein said wear-resistant particles are uniformly dispersed throughout the material to provide a homogeneous

3. The material of claim 1 wherein said material consists of a substrate having at least one outer layer of the wear-resistant particles embedded

4. The material of claim 3 wherein said substrate is selected from a group consisting of metals, metal alloys and plastics; said wear-resistant particles are selected from at least one of the groups consisting of metal oxides, metal carbides, metal borides, metal nitrides and metal silicides; and said matrix is selected from at least one of the groups consisting of

5. The material of claim 2 wherein said wear-resistant particles are selected from at least one of the groups consisting of metal oxides, metal carbides, metal borides, metal nitrides and metal silicides, and said matrix is selected from at least one of the groups consisting of rubber,

6. The material of claim 4 wherein said metal oxide is selected from at least one of the groups consisting of alumina, silica, chromium sequioxide, beryllium oxide, zirconium oxide, stannic oxide, titanium

7. The material of claim 5 wherein said metal oxide is selected from at least one of the groups consisting of alumina, silica, chromium sequioxide, beryllium oxide, zirconium oxide, stannic oxide, and titanium

8. The material of claim 4 wherein said resin matrix is selected from a

9. The material of claim 5 wherein said resin matrix is selected from a

10. The material of claim 4 wherein said substrate is low carbon steel; said matrix is epoxy resin; and said wear-resistant particles are substantially spherical alumina particles.

Description:
FIELD OF THE INVENTION

This invention relates to a low-friction, wear-resistant material and to a process for producing it. Specifically, the material consists of a variably shaped metallic or non-metallic substrate having an outer layer composed of uniformly disposed spheroidal to spherical shaped particles partly embedded in a matrix secured to the substrate so as to provide a substantially uniformly wavy surface void of any sharp projections. The substrate may also be composed of the uniformly disposed particles thus forming a homogeneous material.

DESCRIPTION OF THE PRIOR ART

The textile industry is one example of a prime user of low-friction, wear-resistant materials. These materials are used mainly as the component parts of the textile apparatus, such as rolls, pins, guides and the like, that commonly come in surface contact with running fibers. The surface of these parts is frequently required to have a low-friction value so that when the fiber moves over the surface, the coefficient of friction between the two surfaces will be at a minimum. The fiber is usually under tension coming off these component parts and any unnecessary increase or change in the coefficient of friction between the surfaces will not only result in non-uniform and erratic performance of the apparatus but could also cause actual breakage of the fiber.

Ceramic materials have wear-resistant characteristics and therefore have been extensively used as component parts in apparatuses designed for textile applications. However, ceramic parts are susceptible to breakage and in addition, ceramic material is unsuitable for transferring the heat buildup associated with the contact friction between the moving fibers and the surface of the ceramic parts. Moreover, it is very difficult to produce a low-friction surface on ceramic parts. To compensate for the mechanical strength deficiencies and poor heat transfer capabilities of ceramic parts, the textile industry has resorted to the use of component parts composed of metallic substrates coated with an outer layer of ceramic material. Although these coated metallic parts are sufficiently strong to withstand breakage and are capable of dissipating the heat buildup during a production run, they are not as desirable as the pure ceramic parts because the as-sprayed or other wise deposited ceramic outer layer is usually too rough and jagged for textile applications. Attempts for abrasively smoothing the as-deposited outer ceramic layer has succeeded in producing a low-friction surface part but upon subjecting it to a textile production run environment, the surface layer wears thus increasing the coefficient of friction between it and the moving fibers. It is suggested that the as-deposited ceramic layer be contacted with an abrasive material for a time period only sufficient to smooth the sharp peaks resulting from the protruding particles of the coating material on the surface. Although an improved as-coated part would be produced, there is no commercial means avaiable for insuring that only the protruding peaks would be abrasively removed and that such removal would result in a rounded surface for the protruding particles rather than a flat surface at their uppermost extremities.

A further advancement in the textile industry was achieved with the production of chromium plated metallic parts having a "matte" type finish on the surface resembling the surface of the common orange. These chromium plated surfaces are admirably suited for use in providing low-friction surfaces which are gentle to textile materials. Chromium plated materials, however, are expensive to produce and do not exhibit a high degree of wear resistance.

Articles having a wear-resistant coating applied by various high temperature flame spraying techniques, such as detonation gun plating and plasma arc spraying, are also in wide use throughout the textile industry. While flame sprayed coatings are generally well suited for many textile applications, a uniform deposition of a coating to a complex surface configuration is difficult to apply since most spraying processes are limited to the line of sight travelled by the coating particles. Also flame spraying requires complex processing steps in their application thus rendering them even more expensive to apply than chromium platings.

Although the high temperature flame spraying techniques provide an advancement in the art of producing textile component parts, the need for producing complex configured parts having a low-friction, wear-resistant surface is still desired. The present invention is directed to fulfilling this desired need.

SUMMARY OF THE INVENTION

This invention relates to materials having a low-friction, wear-resistant surface and to a process for producing it. Specifically, the invention relates to a variably shaped material having at least one outer layer of highly densified, uniformly disposed spheroidal to spherical shaped wear-resistant particles, such as metallic-oxide particles, protruding outward from a matrix secured to a metallic or non-metallic substrate thus providing a "matte" type surface finish resembling a sinusoidal polar waveform. When the substrate is also composed of the same uniformly disposed particles, the only requirement is that the outer surface have a "matte" type finish.

The criteria of the spheroidal particles are that they have wear-resistant characteristics, a melting point above the temperature of the heat buildup in its intended use which is usually above 200°C., and be amenable to the particular material intended to contact them in their designed application. In addition, the wear-resistant particles have to be capable of being formed into spheroidal to spherical shapes so that once they are uniformly disposed and partly embedded in a matrix of plastic or the like, their protruding segments will produce a "matte" type finish. Thus when tension-subjected, long, thin, film or fibrous materials are pulled over a surface so formed, the materials will tangentially contact the rounded protruded wear-resistant particles only, thereby greatly minimizing the actual contact between the materials and the finished surface. This minimum contact area between the fibrous material and the finished surface is highly desirable in achieving low-friction characteristics.

Suitable wear-resistant particles for use in this invention include metal oxides, metal carbides, metal borides, metal nitrides and metal silicides in any combination or mixture thereof. Examples of some metal oxides include such compounds as alumina (Al2 O3), silica (SiO2), chromium sesquioxide (Cr2 O3), hafnium oxide (HfO2), beryllium oxide (BeO), zirconium oxide (ZrO2), stannic oxide (SnO2), magnesium oxide (MgO), yttrium oxide (Y2 O3), rare earth oxides, and titanium dioxide (TiO2) in any and all mixtures. Suitable metal carbides include silicon carbide (SiC), boron carbide (B4 C), hafnium carbide (HfC), columbium carbide (CbC), tantalum carbide (TaC), titanium carbide (TiC), zirconium carbide (ZrC), molybdenum carbide (Mo2 C), chromium carbide (Cr3 C2) and tungsten carbide (WC). Suitable metal borides include titanium boride (TiB2), zirconium boride (ZrB2), columbium boride (CbB2), molybdenum boride (MoB2), tungsten boride (WB2), tantalum boride (TaB2) and chromium boride (CrB). Suitable metal nitrides include aluminum nitride (AlN), silicon nitride (Si3 N4), titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), vanadium nitride (VN), niobium nitride (NbN), tantalum nitride (TaN) and chromium nitride (CrN). Suitable silicides include molybdenum silicide (MgSi2), tantalum silicide (TaSi2), tungsten silicide (WSi2), titanium silicide (TiSi2), zirconium silicide (ZrSi2), vanadium silicide (VSi2), niobium silicide (NbSi2), chromium silicide (CrSi2) and boron silicide (B4 Si2). For clarity and illustrative purposes only, the invention will be mainly directed to the use of alumina particles as the wear-resistant particles although any of the particles listed above can be used successfully according to this invention.

The matrix or binder layer can consist of any material which is capable of adhering to a metal or non-metal substrate and which is capable of securely retaining partially embedded rounded wear-resistant particles therein. Such materials as thermoplastic or thermosetting resins, rubber, ceramic, glass and metal, in any and all mixtures thereof, are suitable for this purpose. The thickness of this binder layer should be at least about one-half the diameter of the largest particle size, or the average particle size, so as to insure proper securement of the particles therein. This outer layer thickness requirement is not necessary when the wear-resistant material is molded or cast from a homogeneous composite of particles intermixed with a binder. The only requirement necessary for this latter wear-resistant material is that it contain at least 35 percent by volume of wear-resistant particles and preferably above about 50 percent by volume.

The substrate, when employed, can either be a pure metal, a metal base alloy or a plastic. Where heat transfer characteristics are desirable, as in the textile industry, a metallic substrate would be preferable. Metals such as steel, aluminum, copper, brass, titanium and Monel (Trademark for alloy containing normally Ni 67%, Cu 28%, Mn 1-2%, Fe 1.9-2.5%.) would be well suited for this purpose.

Aside from the casting and molding of wear-resistant parts, a binder, such as a layer of a thermoplastic or thermosetting resin, between about 0.0001 and 0.001 inch thick, preferably about 0.00025 inch thick, is initially deposited on a substrate by any conventional means such as by spraying, painting, dipping or the like. When necessary, the coated substrate is then heated sufficiently to cause the binder to become tacky so that when the wear-resistant particles are deposited on the surface they will partially imbed themselves into the binder and be sufficiently secured therein to withstand the force of gravity. The particles are required to be fabricated into spheroidal to spherical shaped configurations, preferably spherical. One method for producing spherical shaped particles is by fusing boule powder in a Verneuil crystal-growing burner. The particles so produced will be substantially spherical and possibly have minor shrinkage cavities in the center. The exact size of the particles can be regulated by conventional means, such as by regulating the initial powder size or they can be suitably screened once they assume the desired spheroidal to spherical shaped configuration. Preferably the largest particle size should be no more than about 10 times larger than the smallest particle size in monolayer and multilayer materials. For homogeneous materials prepared by casting or molding techniques, this particle size ratio can be increased to 50. Thus by controlling the size of the particles for the outer layer, the density of the particles embedded in the matrix can be regulated thereby producing a uniform distribution of selected size particles on the surface of the part. This will produce a surface with a sinusoidal type polar wave finish admirably suitable for the textile industry.

The selected sized wear-resistant particles can be deposited on and embedded into the tacky binder in a number of ways such as by sprinkling the particles onto the binder-coated surface, or by immersing the binder-coated part into a confined zone containing the particles. Once the deposited particles are uniformly embedded in the matrix, the part can be lightly shaken to remove any unsecured particles thereon. The particle-embedded tacky coated part can then be appropriately cured so as to firmly secure the particles in their embedded positions and to also firmly adhere the binder to the substrate. This will produce a "matte" type surface having low-friction, wear-resistant characteristics ideally suited for textile applications.

To further secure the wear-resistant particles in the matrix, a second binder application may be deposited on the surface of the material to substantially fill the voids or recesses existing between adjacent particles. This second binder application is preferably applied using a diluted resin or the like that has a low viscosity to enable the voids to be substantially filled by capillary action while simultaneously not depositing an excess adhesive layer on the surface of the projecting particles. The initial binder layer and/or the second binder application should preferably fill the voids between adjacent particles to a height at least above a plane defined as being parallel to the surface of the substrate and containing all the cneter points of adjacent particles so as to insure a firmly embedded securement of the particles within the binder.

The materials produced according to this invention can have any desired shape from relatively straight segments to complex curvature segments as is usually associated with pigtails and other textile component parts. The coefficient of friction (Coefficient of friction as defined in H. G. Howell et al. Friction in Textiles, Textile Book Publishers, Inc., N. Y. 1959, page 42.) for such composite materials when used in textile applications for the production of fibers will be between about 0.17 and about 0.35, preferably about 0.21. The uniform particle distribution within the binder layer provides a sinusoidal type polarized waveform on the surface of the substrate which greatly minimizes the contact area between a filament or the like that is made to pass over the surface. This uniform distribution of the particles on the surface of a substrate is best illustrated by referring to the drawings which show:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are greatly magnified, surface traces of chrome plated and flame-sprayed surfaces, respectively, (Prior Art).

FIG. 3 is a greatly magnified, surface trace of a low-friction, wear-resistant material according to this invention.

FIGS. 4 and 5 are scanning electron microscope photographs of unworn and worn surfaces, respectively, of FIG. 1 (Prior Art).

FIGS. 6 and 7 are scanning electron microscope photographs of unworn and worn surfaces, respectively, of FIG. 2 (Prior Art).

FIGS. 8 and 9 are optical photomicrographs of unworn and worn surfaces, respectively, of FIG. 3.

The preferred method of depositing a low-friction, wear-resistant surface on a metal or non-metal substrate having a straight or complex shaped contour is to cover the substrate with a thin layer of a binder by any conventional technique, such as by dipping, painting or spraying. A most desirable class of binders, although not the only class suitable for this invention, are the thermosetting and thermoplastic resins which should be applied between about 0.0001 and about 0.001 inch thick and preferably about 0.00025 inch thick. Binders such as polyamides, polybenzimidazoles, polycarbonates, polyesters, polyethers, polyolefins, polyacrylates, polyacetals, polysulfones, polyurethanes, epoxy and glass frit are but a few of the binders. that can successfully be used as the initial layer on the substrate. Depending upon the particular resin-layer employed, the resin-coated substrate is heated or held for a time period only sufficient to cause the resin to become tacky thus producing a surface somewhat similar to the adhesive surface of common fly paper. This surface layer should be of sufficient thickness and adhesiveness to secure particles deposited thereon from the force of gravity when such surface is freely held in the open atmosphere face down.

A layer of spheroidal shaped wear-resistant particles is then deposited on the adhesive surface of the substrate by any conventional means such as by immersing the resincoated substrate into a confined zone containing the particles. The resin-coated substrate is then removed from the particle-containing zone and slightly tapped to remove any excess and/or loosely secured particles thus leaving a monolayer of densified and uniformly disposed particles protruding from the resin-layer. The composite is then heated at a temperature and for a time period sufficient to fully cure and/or treat the resin thereby securing the particles in the resin matrix. The exact temperature and time period required for curing and/or treating the resin depends on the particular resin selected from the large group of resins available. If the particles completely imbed themselves in the resinous layer then a final finishing step, such as grit blasting, vibrating or brush finishing, will be required to remove the excess resin off the surfaces of the particles thereby providing an exposed particle-imbedded surface having low-friction and wear-resistant characteristics.

The exact size of the wear-resistant particles required to produce a low-friction surface for textile application is variable with a size about 80 Tyler mesh and finer suitable, a size between about 270 Tyler mesh and 325 Tyler mesh desirable, and a size about 325 Tyler mesh and finer preferable.

It is also within the purview of the invention to have more than one layer of wear-resistant particles deposited on a substrate to produce a low-friction surface. This can be accomplished by adding a second resinous layer on top of the particle-embedded surface and then depositing additional particles thereon, such particles being the same size or a different size than the particles in the initial layer. This process can be repeated to produce a multilayer surface of any desired thickness with the final layer preferably having the smaller size particles.

It is also within the purview of this invention to provide a homogeneous material composed of wear-resistant particles uniformly dispersed in a binder or the like. This material can be prepared by uniformly intermixing wear-resistant particles of a preselected size in a binder and then subjecting the composite to conventional molding or casting techniques to obtain predesired shapes. The finished part can then be grit blasted or the like to remove any excess binder so that the rounded surfaces of the wear-resistant particles can be exposed thereby providing a "matte" finish.

In the monolayer or multilayer material, it may be desirable to add a final resinous layer to substantially fill any voids existing between adjacent particles up to at least a level defined by a plane containing the center points of each of the adjacent particles and being parallel to the substrate. This final resinous layer should be employed only when it is desired to increase the adhesive bond between the particles and the resinous layer so as to provide a strong textured surface. This additional resinous application should be applied in the diluted state in which the viscosity of the resin will be such that it will fill the void spaces between adjacent particles through capillary action while at the same time limiting the buildup of excessive resinous adhesive on the other surface of the particles. A diluted resin having a viscosity below about 100 centipoises is desirable for this application.

The final resinous layer, if applied, is then cured by appropriately heating the material at a temperature and for a time period depending on the particular resin used. If an excess of this final resinous layer adheres to the surface of the particles then any of the finishing techniques, such as a slight brushing operation or a chemical dissolving application, can be employed to remove such resin thus exposing the rounded protruding particles. In certain applications the contact with the product of its intended use may be used to remove any of the excess resin that may adhere to the particles.

The finished material so obtained according to this invention will have at least one outer layer of highly densified, uniformly disposed, wear-resistant, spheroidal to spherical shaped particles partly embedded in a matrix with the smooth surfaces of the particles exposed thereby forming a uniformly wavy surface. The spheroidal to spherical shaped particles in this wear-resistant surface will have a microhardness of at least 500 Diamond Pyramid Hardness and when used as a component part in a textile apparatus, the surface will have a coefficient of friction of 0.35 or lower between it and the fibers being produced.

EXAMPLE I

Alumina particles of various sizes were poduced by fusing boule powder by putting it through a Verneuil crystal-growing burner. The particles appeared substantially spherical in shape and were screened into different particle size ranges.

2-1/2-inch size low carbon steel pigtails were cleaned to remove grease and the like by washing them in chloroform. They were then dipped into a resin mixture consisting of 3.3 percent by weight suspension of one-component epoxy powder (commercially available from the Hysol Division of Dexter Corporation as Hysol A7-4314) prepared in chloroform. The coated pigtails were then removed and allowed to dry in ambient air for 5 minutes. This produced a thin tack-free epoxy layer on the pigtails. The coated pigtails were then immersed in a receptacle containing the alumina spheres. The receptacle was tapped several times to insure an adequate supply of the spheres came in contact with the pigtails. The assembly, consisting of the pigtails and the alumina spheres in the receptacle, was heated in an oven to 195°C. and held thereat for 20 minutes. This softened the epoxy layer enough to pick up a single layer of the alumina spheres. The assembly was then removed from the oven and cooled down to ambient. The coated pigtails were then removed from the receptacle and each was tapped several times to remove loosely adhering alumina spheres. The pigtails were than given final cure at 195°C. for 1 hour. The above procedure was repeated for various sizes of the alumina particles and for various concentrations of the powdered resin and chloroform mixture. In addition some samples were subjected to the above procedure more than once so as to produce a multilayer surface.

All of the various samples of coated pigtails were then given a final epoxy treatment by impregnating them with a diluted resin mixture prepared from mixing 10 parts by weight of epoxy resin (commercially available as Hysol AS-4318) with 3 parts of an amine type hardener (commercially available as Hysol H9-3486) and then diluting the mixture to 10 percent solid by weight with a glyocol ether thinner (commercially available as Hysol S-4069). The impregnating was accomplished by dipping the top of each pigtail in a closed vessel and allowing the diluted resin mixture to flow up the pigtail by capillary action. The impregnated pigtails were then cured by heating them to 195°C. and holding thereat for 1 hour after which they were cooled to ambient. Some pigtail samples were given a final resin coating using a different resin concentration in the thinning agent and a different per cent solid in the final diluted resin mixture. In addition, some samples were coated by being dipped into the resin mixture rather than by the capillary action technique.

The surface friction value of the processed pigtails were measured on a Shirley frictometer using duPont 70-34-1/2-Z-280-SD nylon multifilament. The results are summarized in Tables 1 and 2 below.

Table I __________________________________________________________________________ Frictional Values of Pigtails With Spherical Alumina Oxide Layer or Layers __________________________________________________________________________ Sample Particle Size Resin Con. % Resin No. of Friction Value Range (Tyler Wt. % in in dilu- Layers mesh) Chloroform ted form __________________________________________________________________________ A -115 to +150 3.3% 10% 1 Fiber broke while threading through pigtail B -170 to +200 3.3% 10% 1 0.25 (fiber shreads) C -270 to +325 3.3% 10% 1 0.215 to 0.23 D -400 3.3% 10% 1 0.20 E -270 to +325 3.3% 10% 3 0.29 F -400 3.3% 10% 3 0.25 first layer G -115 to +150 3.3% 10% 2 0.30 second layer -400 H -400 6.0% 10% 1 0.23 I -400 10.0% 10% 1 0.26 J -400 20.0% 10% 1 Too rough to test __________________________________________________________________________

Table 2 __________________________________________________________________________ Frictional Values of Pigtails Having An Initial Resin Concen- tration of 3.3% by weight in Chloroform (Single Layer) __________________________________________________________________________ Particle Size % Resin in % Solids in Friction Values (Tyler mesh) Thinner diluted form dipped capillary fill __________________________________________________________________________ -400 25 15 0.215 0.21 -400 33 20 0.23 0.22 -400 40 25 0.23 0.22 __________________________________________________________________________

EXAMPLE 2

A Hastelloy Alloy X bar, 1 1/2 inches long and 1 inch diameter, was grit blasted, washed in chloroform, and given an initial resin coating of a resin mixture consisting of 3.3 percent powder (commercially available from the Hysol Division of Dexter Corporation as Hysol A7-4314) prepared in chloroform. The sample was air-dried for 5 minutes at room temperature and while in a track-free state, it was placed in a container whereupon 400 Tyler mesh and finer alumina spheres were added to cover it. The assembly was heated in an oven to 100°C. and held thereat for 1 hour to soften the resin sufficiently to produce a tacky surface which picked up essentially a single layer of the spheres. The sample was then cooled to ambient in about 30 minutes whereupon the sample was removed and given a slight tapping to dislodge any loosely adhering spheres. The sphere coated sample was then cured by heating to 200°C. and being held thereat for 1 hour after which it was cooled to ambient.

A final resin coating was applied by dipping the sphere coated section in an epoxy resin (commercially available as Ciba Products Co. Araldite No. 502) mixed with an amine hardener (Ciba No. 951) in a weight ratio of 10 parts resin to 1 part hardener. This resin mixture was diluted to 35 cc per 100 cc of solution with methyl ethyl ketone before the dipping process. The coated sample was cured for 1 hour at 100°C. after dipping.

The coated sample was then subjected to an accelerated wear test wherein a 30 inch length of No. 24 cotton twine (commercially available from Shuford Mills, Inc., Hickory, N. C.) was knotted to form a loop, saturated with an aqueous slurry of pigment grade titanium dioxide, and traversed over the surface of the coated sample at a linear rate of 150 feet per minute, ± 5 percent. The specimen was affixed to a lever system and counterbalanced to provide a normal force of 210 grams, ± 5 percent, against the twine, which contacted the coated surface over an included angle (wrap angle) of 160 degrees. The twine loop was driven by a pulley affixed to the shaft of a variable speed motor and passed through the titanium dioxide slurry on each revolution. The slurry was continuously recirculated with a pump. Titanium dioxide was chosen as the abrasive since it is used as a delustrant in synthetic fibers.

Wear tests were run for time periods of 300, 600, and 900 minutes. The coefficient of friction in the wear scar and on the unworn surface was determined with a Shirley Frictometer, as described previously.

Friction and wear tests were similarly made with one inch diameter low carbon steel bars containing a 0.002 inch thick coating of matte finished chrome plate (commercially available as Brame Finish No. 3, Brame Textile Machine Co., Greensboro, N. C.) and a 0.002 inch thick coating of flame-sprayed 60% TiO2 - 40% Al2 O3, applied by a detonation gun (commercially available as Type LA-7, Coating Service Dept., Materials Systems Division, Union Carbide Corporation). The surface of the detonation gun coating was finished to a surface roughness of 132 A.A. (Arithmetic Average) microinches using a power driven brush and an aqueous slurry of 220 grit size silicon carbide to provide a low friction, "brush finished" surface. Wear tests were run for time periods of 1 to 30 minutes for the chrome plated sample and 120 to 600 minutes for the brush finished, flame-sprayed sample. The coefficients of friction were determined as described previously.

The results of the friction and wear tests are shown in Table 3. The average wear rate for the matte chrome plate was 3.0 × 10-2 mils per minute, and the friction value was increased appreciably after 5 minutes. The average wear rate for the brush finished, flame sprayed coating was 1.0 × 10-3 mils per minute, and the friction value was increased appreciably after 120 minutes. The average wear rate for the spherical aluminum oxide was 3.9 × 10-4, and the friction value remained low after 900 minutes.

FIG. 1 is a Talysurf trace across the 5 minute wear scar in matte chrome plate. The vertical magnification is 1,000 and the horizontal magnification is 100. The scar is distinctly smoother than the unworn surfaces on either side, which accounts for the increased friction value.

FIG. 2 shows a similar trace across the 600 minute scar in the brush finished, flame sprayed coating. Again, the scar is quite smooth compared to the unworn surfaces.

FIG. 3 shows a similar trace across the 900 minute scar in the spherical aluminum oxide coating. The wear scar, which is in the center of the Figure, is not so easily distinguished since the roughness in the scar is comparable to that of the adjacent unworn surfaces. The absence of a smooth trace in the scar explains the low friction value which persists after prolonged wear.

FIG. 4 is a Scanning Electron Microscope (SEM) photograph of unworn matte chrome plate taken at a magnification of 300x, showing the rounded nodules which account for the low friction value of the surface. Flattening of some nodules could be detected microscopically in the 1 minute wear scar. More extensive flattening was observed after 2 1/2 minutes of wear and after 5 minutes, relatively large flat areas were observed in the scar as shown in FIG. 5 (SEM, 300x). After 20 minutes of wear, essentially no vestige of the original surface remained visible in the scar area.

FIG. 6 similarly shows the surface features of the unworn, brush finish, flame-sprayed coating (SEM, 300x), and FIG. 7 shows the flattened wear scar after 600 minutes (SEM, 300x).

FIG. 8 is an optical photomicrograph of the unworn spherical aluminum oxide coating taken at a magnification of 240x and showing the close packed spheres. FIG. 9 is a similar photomicrograph of the 900 minute wear scar, and illustrates the appreciable degree of roughness remaining on the surface after prolonged wear.

Table 3 __________________________________________________________________________ Friction and Wear Data for Coated 1-inch Bars Coating Test Duration Friction Value Wear Rate (min) Unworn Wear Scar (mil/min) __________________________________________________________________________ Matte Chrome 1 0.20-0.21 0.22 N.M.* Plate 2.5 0.24 N.M. 5 0.32 3.0 × 10-2 10 >0.40 3.5 × 10-2 10 >0.40 3.0 × 10-2 20 > 0.40 3.5 × 10-2 20 > 0.40 2.5 × 10-2 30 > 0.40 3.0 × 10-2 30 > 0.40 2.7 × 10-2 Brush Finished, 120 0.21-0.22 0.38 N.M.* Flame-Sprayed 300 0.40 1.0 × 10-3 600 0.40 1.0 × 10-3 Spherical Aluminum 300 0.21-0.23 0.23 N.M.* Oxide 600 0.24 3.3 × 10-4 900 0.24 4.5 × 10-4 __________________________________________________________________________ 1 * Not Measurable

Example 3

A steel rod 1 1/2 inches long and 3/8 inch diameter, degreased, acid etched, rinsed and dried, was given an initial resin coating of a resin mixture consisting of 3.3 percent powder (commercially available as Hysol A7-4314) prepared in chloroform. The sample was air dried for 5 minutes at room temperature and while in a tack-free state was placed in a container whereupon fine titanium carbide spheres between 30 and 40 microns diameter were added to cover it. The assembly was heated in an oven to 100°C. and held there for 1 hour. This softened the resin sufficiently to produce a tacky surface which picked up essentially a single layer of the spheres. The assembly was then cooled to ambient whereupon the sample was removed and given a slight tapping to dislodge the loosely adhering spheres. The sphere coated sample was then cured by heating to 195°C. for 1/2 hour after which it was cooled to ambient.

A final resin coating was applied by dipping the ball coated section in a resin (commercially available at Ciba Products Co. Araldite No. 502) mixed with an amine hardener (Ciba No. 951) in a weight ratio of 10 to 1. This resin mixture was diluted to 35 cc per 100 cc of solution with acetone before the dipping process. The coated sample was cured for an hour at 100°C.

The coated sample was subjected to accelerated wear tests for time periods of 240 and 480 minutes on the same testing machine and within the same load and speed limits as described in Example 2. The friction value for the unworn surface was 0.21-0.22. A Talysurf trace across the 240 minute wear scar was similar in appearance to those previously described for the spherical aluminum oxide coating. The scar depth had an average wear rate of 8.3 × 10-4 mils per minute and the friction value in the scar did not increase over that for the unworn surface.

After 480 minutes, the friction had increased to 0.26, still a relatively low value, and the Talysurf trace across the scar still showed a high degree of roughness with smoothly rounded peaks. Optical photomicrographs of the wear scar showed flattened (worn) areas on the TiC spheres. The wear rate was found to be 9.4 × 10-4 mils per minute. The average wear rate for both tests was 8.8 × 10-4 mils/min.

A hard chrome plated steel bar, 3/8 inch diameter, was tested under the same conditions and found to have a linear wear rate of 5 × 10-2 mils per minute for test periods of 10, 20 and 30 minutes. The wear scars for each time period were smooth.

EXAMPLE 4

A 1 inch diameter steel rod was coated with -270, +325 Tyler mesh size aluminum oxide spheres and a second one inch diameter steel rod was coated with -325, +400 mesh aluminum oxide spheres according to the process outlined in Example 2, except that the final resin coating was applied by the capillary fill technique with the CIBA 502 resin and CIBA 951 hardener, in a 10:1 weight ratio, diluted to 50 volume per cent with acetone.

Talysurf traces were made across the surfaces of these samples at a vertical magnification of 1,000 and a horizontal magnification of 100 and also across the surfaces of sections from steel pigtails previously described in Example 1 and which contained single layer coatings of either -270, +325 or -400 Tyler mesh size aluminum oxide spheres. The number of distinct rounded peaks was counted over an appreciable length of the traces and converted to a linear density, peaks per inch. These values were compared with the linear density calculated from the minimum and maximum sphere diameter expected for the mesh size used and assuming that the spheres were in a close packed linear array. The results are summarized in Table 4, and show that the measured linear density is in good agreement with that expected.

Table 4 __________________________________________________________________________ Particle Size Range Measured Calculated (Tyler Mesh) No. of Inches Peaks Peaks Peaks Traversed Per Inch Per Inch __________________________________________________________________________ -270, +325 121 0.23 526 480-578 -325, +400 97 0.15 645 578-685 -400 215 0.30 717 >685 __________________________________________________________________________

EXAMPLE 5

Two low carbon steel pigtail samples were cleaned as described in Example 1 and given an initial resin coating of a resin mixture consisting of 3.3 percent powder (commercially available as Hysol A7-4314) prepared in chloroform. The samples were air-dried for 5 minutes at room temperature and while in a tack-free state they were placed in a container whereupon 400 Tyler mesh and finer alumina spheres were added to cover them. The assembly was heated in an oven to 195°C. and held thereat for 20 minutes to soften the resin sufficiently to produce a tacky surface which picked up essentially a single layer of the spheres. The assembly was then cooled to ambient in about 30 minutes whereupon the pigtail samples were removed and given a slight tapping to dislodge the loosely adhering spheres. The sphere coated samples were then cured by heating to 195°C. and being held thereat for one hour after which they were cooled to ambient.

A final resin coating was applied by way of capillary action as described in Example 1 using a resin mixture consisting of 10 parts by weight of epoxy resin (AS-4318) and 3 parts by weight of an amine type hardener (H9-3486) diluted to 33 percent by weight with a glycol ether thinner (S-4069). A red dye (commercially available as Hysol AC-6238) was added to color the resin. The coated samples were heated to 195°C. and held thereat for 1.5 hours after which they were cooled to ambient.

The cured samples were given an additional resin coating following the same procedure as above. After being fully cured each sample was tested on a frictometer and found to have a surface friction value of 0.20.

EXAMPLE 6

Two low-carbon steel pigtail samples were processed as outlined in Example 5 except that only one final resin coating was applied and that coating consisted of one-part epoxy resin diluted to 50 percent solid (commercially available as Hysol A7-4315) which was mixed with a liquid blue dye (AC-6240). This final coating was applied by the capillary-fill technique and then the coated samples were cured at 195°C. for 1.5 hours. The surface friction value of each of the two pigtail samples measured 0.215 and 0.225, respectively.

EXAMPLE 7

Two low-carbon steel pigtail samples were processed as outlined in Example 6 except the final resin coating consisted of resin liquid (commercially available from Ciba Products Co. as Araldite No. 502) mixed with an amine type hardener (Ciba No. 951) in a weight ratio of 10 to 1. This resin mixture was diluted to 60 cc per 100 cc of solution with acetone and then given a blue dye coloring using Hysol dye AC-6240. The overall resin mixture was 60 percent solid. This final resin coating was applied by the capillary-fill technique and then the coated samples were cured at 100°C. for one hour. The surface friction value of each of the two pigtail samples measured 0.195 and 0.21, respectively.

EXAMPLE 8

Two low-carbon steel pigtail samples were processed as outlined in Example 7 except that spherical alumina particles between 270 and 325 Tyler mesh size were used and a green coloring dye (Hysol AC-6241) was added in the final resin coating. The surface friction value of each of the two cured samples measured 0.225 and 0.215, respectively.

EXAMPLE 9

An extruded Nylon rod, 3/8-inch diameter by 6 inches long was passed in front of a gas flame to smooth the surface. The cooled rod was given an initial resin coating of a resin mixture consisting of 3.3 percent powder (commercially available as Hysol A7-4314) prepared in chloroform. The sample was air dried for 5 minutes at room temperature and while in a tack-free state was placed in a container whereupon 400 Tyler mesh and finer alumina spheres were added to cover it. The assembly was heated in an oven to 100°C. and held thereat for 20 minutes to soften the resin sufficiently to produce a tacky surface which picked up essentially a single layer of the spheres. The assembly was then cooled to ambient in about 30 minutes whereupon the sample was removed and given a slight tapping to dislodge the loosely adhering spheres. The sphere coated sample as then cured by heating to 160°C. for four hours after which it was cooled to ambient.

A final resin coating was applied by dipping the sphere coated section in a resin (commercially available as Ciba Products Co. Araldite No. 502) mixed with an amine hardener (Ciba No. 951) in a weight ratio of 10 to 1. This resin mixture was diluted to 35 cc per 100 cc of solution with acetone before the dipping process. The coated sample was cured for an hour at 100°C. The surface friction value of the coated piece was 0.21.

EXAMPLE 10

A cleaned, 1 inch O.D., by 3 inches long steel tube was painted on the outer surface with a mixture of 10 parts by weight epoxy resin (Union Carbide Corp. ERL 2,400) and 3 parts of an amine hardener (Union Carbide Corp. ZZL0822). The piece was then heated in an oven at 100°C. for 13 minutes and cooled. The resin was now in a tacky stage. Minus 250 plus 270 Tyler mesh alumina spheres were immediately sprinkled on the tacky surface and the piece was given a final cure at 100°C. for 2 hours. No second coat of epoxy was applied. After cooling the surface had a friction value of 0.205.

EXAMPLE 11

A low melting ceramic powder (Owens-Illinois substrate glaze, Article No. 01158) was mixed with a liquid fugitive binder (Wall-Colmonoy brazing binder No. 500 standard) in a 1 to 1 weight ratio and painted on a 1/8 in. diameter copper rod. The ceramic was melted by heating the rod to approximately 470°C. After cooling to room temperature, the rod, now having a coating about 0.0005 in. thick, was buried in a pack of minus 400 mesh alumina spheres and heated to the softening point (about 450°C.). The pack was allowed to cool and the sphere covered rod was tested on the frictometer. The friction value was 0.205.

EXAMPLE 12

A mixture of 10 parts by weight epoxy resin (Union Carbide Corporation ERL 2,400) and 3 parts by weight of an amine hardener (Union Carbide Corporation ZZL 0822) was diluted with an equal weight of acetone. Spherical aluminum oxide, -270, +325 Tyler mesh size, was stirred into the above mixture until it had the consistency of a thick pancake batter. A 3/8-inch-diameter steel rod was dipped into the mix to a depth of about 1 inch, removed from the mix with the adhering material, dried in air for 10 minutes, and cured in an oven for 2 hours at 100°C. The so-coated surface had a coefficient of friction of 0.20.

EXAMPLE 13

A mixture of 25 percent by weight of spherical Al2 O3 particles, sized -325 Tyler mesh, and a particulated fine thermosetting phenolic resin (Bakelite), 75 percent by weight, were blended by hand in a glass jar. The blended mixture was placed in a 1-1/4 inch diameter steel mold and a pressure of 4,200 psi. applied with a steel ram. The temperature of the mixture was raised to 150°C. in 10 minutes, held thereat for 10 minutes and then cooled to room temperature. The pressure was released and the body pushed from the mold cavity. The cylindrical surface of the molded body was then grit blasted with an S. S. White air abrasive unit for approximately 20 minutes. The abrasive used was fine calcium carbonate and was carried by 60 psi. air through a nozzle about 0.020 inch in diameter. Care was taken to grit blast the surface uniformly. This operation removed the Bakelite near the surface thereby exposing the rounded spheres thus providing a "matte" finish. The co-efficient of friction of this surface measured 0.20.

EXAMPLE 14

Ten parts by weight of epoxy resin (Union Carbide Corporation ERL-2,400) and 3 parts by weight of an amine hardener (Union Carbide Corporation ZZL 0822) were mixed carefully to produce a homogeneous composite. To this mixture was added 71 percent by weight of spherical Al2 O3 particles, sized -270 to +325 Tyler mesh. The overall mixture was then stirred slowly until the particles were uniformly distributed throughout the composite whereupon the mixture was poured into a steel die with a cavity measuring 3 inches long, 25/32 inches outside diameter, and 1/2 inch inside diameter. The filled die was then placed in an oven and heated to 100°C. for 1 hour. The die was then separated and the epoxy-Al2 O3 tube removed. The outside surface of the tube was grit blasted as in example 13; however, a -325 mesh rutile (TiO2) was used as the abrasive. This removed the excess epoxy layer thus exposing the Al2 O3 spheres which were slightly roughened. The surface was further finished by polishing with a long nap (felt) metallographic wheel, charged with a 1 micron diamond, for about 5 minutes. The coefficient of friction of this surface measured 0.21.

EXAMPLE 15

A quantity of spherical Al2 O3 particles, sized -270 to +325 Tyler mesh, were added to Nicrobraze 500 in a glass beaker until the mixture had the consistency of a thick pancake batter. Nicrobraze 500 is a liquid fugitive binder made by the Wall Colmonoy Co. and is used for fastening powdered brazing compounds to metal surfaces. A 3/8 inch diameter steel rod, grit blasted with 60 mesh Al2 O3, was dipped into the Al2 O3 Nicrobraze mixture to a 1 inch depth and immediately removed. The as-coated rod was then heated for 1 hour at 100°C. to drive off all the solvent and thereafter cooled to room temperature. The rod was further painted with a mixture of 10 parts by weight of epoxy resin (Union Carbide Corporation ERL-2,400) and 3 parts by weight of an amine hardener (Union Carbide Corporation ZZL 0822) and then placed in an oven at 100°C. for 1 hour. The rod, upon removal from the oven, was cooled to ambient and a measurement of its surface revealed a coefficient of friction of 0.195.