US 3026190 A
Description (OCR text may contain errors)
March 20, 1962 MCMAHON ETAL 3,026,190
ELASTOMER BONDED ABRASIVES Filed Dec. 2, 1958 3 Sheets-Sheet 1 I 40- g o FAE 550- A- RUBBER COATED msc 32%, cc 24 MESH GRAIN 8L8. LOAD 20. ll] 2 3' comm-:acuu. PAPER also, 5 24 MESH GRAIN- 8L B. LOAD 5 IO 15 2o 25 TIME- MINUTES March 20, 1962 H. o. MCMAHON ETAL 3,025,190
ELASTOMER BONDED ABRASIVES Filed Dec. 2, 1958 5 Sheets-Sheet 2 March 1962 H. o. MCMAHON ETAL 3,026,190
ELASTQMER BONDED ABRASIVES Filed Dec. 2, 1958 3 Sheets-Sheet 3 United States Patent Ofllice 3,026,190 Patented Mar. 20, 1962 3,026,190 ELASTOMER BONDED ABRASIVES Howard 0. McMahon, Lexington, and Paul C. Watson, North Quincy, Mass, assignors, by mesne assignments, to American Viscose Corporation, Philadelphia, Pa.,
a corporation of Delaware Filed Dec. 2, 1958, Ser. No. 777,725 4 Claims. (Cl. 51-295) This invention relates to fibrous bodies such as reticulated webs or mats formed of elastomeric fibers and to methods and apparatus for preparing the same. More particularly, the invention relates to abrasive pads or mats, especially to elastomer bonded abrasive pads or mats. The present application is a continuation-in-part of our application Serial No. 400,240 filed December 24, 1953, and now Patent No. 2,950,752.
In the manufacture of abrasive devices, there has been a constant effort to develop an abrasive material which is economical, easy to manufacture and use, and one which has a useful life substantially longer than can be obtained with conventional paper and cloth-backed grinding discs. One approach to the problem has been to intermix abrasive particles with a molten plastic material which is then cast into a desirable block shape. The primary disadvantage of this form of abrasive material is that the abrasive particles are coated with a relatively thick layer of plastic material which must be removed during use before a satisfactory grinding surface is presented. Another proposal has been to impinge abrasive particles onto the exterior surfaces of freshly extruded plastic fibers while they are still in a tacky condition. Unfortunately, the abrasive particles, especially particles of large size, are not sufiiciently embedded within the fibrous material to provide a good bond. Pressing the freshly formed fibers and abrasive grains in this last described procedure does provide a more satisfactory bond between these materials, but is accompanied by a sacrifice in the porosity of the end product.
It is a primary object of this invention to provide a new or improved and more satisfactory abrasive material and methods of making the same.
Another object of the invention is to provide a method of making a fibrous abrasive material from a fiber-forming mixture, including a composition of elastomeric material and abrasive particles, which is extruded to form a mass of individual randomly oriented fibers adhered to each other at their crossing points and together forming a unitary mat or web.
Still another object is to provide an abrasive material in which only small portions of the individual abrasive particles are exposed at any one time, thus permitting the use of larger, and hence less expensive abrasive grains.
A further object is to provide an abrasive material in which the abrasive particles are coated with a relatively thin layer of elastomeric material, the latter of which wears away constantly during use to expose new abrasive grains and thus facilitate grinding or polishing at a uniform rate.
A still further object is to provide a flexible abrasive material which can readily conform to complex or nonuniform surfaces.
A still further object is to provide an abrasive material which produces a minimum of sparks during use, and one which is highly porous yet strong so as to reduce any tendency to overheat or clog.
Other and further objects, features and advantages of the invention will become apparent as the description of certain preferred embodiments thereof proceeds.
In general, the abrasive device of the present invention is formed by extruding a fiber-forming mixture, including a solution of elastomeric material and abrasive particles, through an orifice and into a high-velocity gas stream, the latter of which serves to attenuate and break the extruded material into a plurality of individual fibers of smaller diameter than the diameter of the orifice. The gas stream effects a partial setting of the elastomeric material due to the evaporation of the solvent therefrom. However, the fibers are still in a tacky or adhesive condition as they are collected as a Web or mat of randomly oriented fibers, and thus adhere to each other at their points of contact. The collected Web or mat of fibers is then heated to cure the elastomeric material, and if desired, may be compressed slightly either before or during the heat curing stage to enhance the fiber bonding and to densify the web. As a result of solvent evaporation, the elastomeric material shrinks snugly against and into general conformity with the abrasive particles to thus cover the same with a relatively thin coating.
The elastomeric material suitable for use in the present invention is rubber, both natural rubbers and synthetic rubbers or rubber substitutes. Such elastomeric materials or rubbers, both natural or synthetic, which are soluble in inexpensive, volatile organic solvents are Well suited for the production of the abrasive material of this invention. Elastomeric materials satisfactory for use in the herein described method include natural rubbers such as crepe rubber and synthetic rubbers or rubber substitutes such as chlorop'rene polymers, for example, neoprenes; butadiene-acrylonitrile copolymers known as Buna-N, for example, Butaprene, Paracril, Ameripol-D, Perbunan, Chemigum', and Hycar-OR; butadiene-styrene copolymers, for example, AmeripolF, Hycar-OS and GR-S; isoprene isobutylprene copolymers, for example, GR-l and butyl. Mixtures of specific elastomeric materials may be utilized to provide desired characteristics and it will be understood that the elastomers enumerated above are merely illustrative and are not intended as limitations of the invention.
The fiber-forming solution may be formed by dissolving an elastomeric material in a satisfactory organic solvent such as aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, aralkyl hydrocarbons and the like, those being preferred which will volatilize readily at moderately elevated temperatures. The solvent utilized in forming the fiber-forming solution will be dependent upon the specific elastomer and upon characteristics desired in the solution, such as volatility of the solvent. For example, solvents which are satisfactory include benzene, naphtha, toluene, xylene cyclohexanone, ethylene chloride, methylene chloride, carbon tetrachloride, nitroparaflins, ketones and the like. Such inexpensive volatile solvents as benzene and naphtha are entirely satisfactory for use in elastomeric solutions containing natural rubber. The elastomeric solution may contain from about 5% to about 50%, and preferably between about 10% and about 35% of the rubber or rubber substitutes.
With regard to the abrasive particles, any suitable abrasive material may be used, as for example silicon carbon and/or alumina. The size of the abrasive grains may range from as large as 24-mesh to the finest abrasives available, such as 400-mesh or finer. The principal limit on the largest size abrasives which can be used is the size of the orifice, since the extremely large sized grains more generally tend to plug the orifices during the extrusion process. While the quantity of abrasive particles may vary considerably, the preferred range is from about 30% by Weight to about by Weight of the total weight of the solids in the finished fibers; that is the total weight of the abrasive particles plus elastomer. It will be understood, of course, that the amount of abrasive grains used will depend somewhat upon the size of the abrasive particles, with fewer grains being intermixed when larger sized abrasive materials are employed. Uncoated abrasive particles are satisfactory for use in the present invention. It is preferred, however, to coat the abrasive grains with a phenolic or epoxy resin, or other similar materials which will assist in bonding the abrasive grains to the elastomeric material and thus impart a longer life to the end product.
Gas-forming or blowing agents such, for example, as ammonium carbonate, sodium acid carbonate, diazoaminobenzene and the like, may be added to the elastomeric materials or spraying liquids, if desired. These agents include solids and gases and are commonly employed in the production of sponge rubber and porous rubber sheet and products. They are adapted to release or form a gas such as ammonia, carbon dioxide or other inert gas at temperatures at which the elastomeric material is cured or vulcanized.
The properties and characteristics of the fibers formed from the elastomeric materials may be varied as desired by incorporating other additives in the spraying liquid. Substances such as normally employed in preparing finished rubber articles from crude natural rubbers or synthetic rubbers may be added, for example, carbon black, curing or vulcanizing agents such as sulfur, ac celerators, antioxidants, plasticizers and the like. Coloring agents, such as dyes and pigments may be utilized to produce fibers having desired colors or tints. Filiers such as clay, whiting, kaolin, French chalk and the like may be added to impart desired characteristics and to reduce the cost of the fibers. The amount of the additive may be varied over a wide range as desired. In the case of solid fillers, from about 50% to about 150% filler, such as clay, finely divided pigments and the like, based upon the weight of the elastomer, may be incorporated in the spraying liquid. Lesser or greater amounts, however, may be employed depending upon the type of product desired.
The additive substances may be mixed with the elastomer as by milling the elastomer and the additive, or the additive substance may be mixed with or dIspersed in the solution of the elastomer. By varying the amount of solvent and the amount of additive substances and the degree of milling, the viscosity of the spraying liquId may be varied over an extremely wide range. It is possible to utilize spraying liquids in forming the products of this invention which are totally unsuited for use in the usual or conventional spinning methods.
Referring now to the drawings:
FIGURE 1 is a diagrammatic illustration of one form of apparatus adapted for practicing the invention;
FIGURE 2 is a diagrammatic illustration of another form of apparatus;
FIGURE 3 is a diagrammatic illustration of a third form of apparatus;
FIGURE 4 is a schematic diagram of a production unit for the manufacture of the abrasive mat or pad;
FIGURE 5 is an enlarged longitudinal section through one of the abrasive fibers; and
FIGURE 6 is a graph illustrating the comparative grinding abilities of an abrasive material formed in accordance with the present invention and a commercial paper-backed disc.
Referring now to FIGURE 1 wherein an apparatus for practicing the invention is illustrated diagrammatically. A tower 9 has a spraying unit 11 mounted therein, preferably centrally thereof. The spraying unit comprises a conduit 13 which terminates in a downwardly extending spray tip 15 having a suitable orifice at its lower end, and a. conduit 17 which terminates in a downwardly extending nozzle 19. The spray tip 15 is preferably mounted concentrically within and extends slightly below the nozzle 19. The elastomeric solution is continuously extruded through the spray tip 15 by means of a suitable metering pump 21, as for example a Moyno pump. A stream of gas, such as air, is continuously passed through the conduit 17 and the nozzle 19 by suitable means, such as a blower, not shown, with the velocity of the gas emerging from the nozzle 19 being appreciably higher than the velocity of the extrusion of the elastomeric solution.
The elastomeric solution is forced out of the tip 15 as a single continuous plastic stream which is attenuated and broken transversely into discontinuous fibers of varying length by the high velocity gas stream flowing from the nozzle 19. The velocity of the extrusion and the velocity of the surrounding air may be varied so as to regulate the amount of attenuation and hence the diameter of the fiber, and may be increased sufficiently to regulate the length of the fiber. In general, for a given spraying liquid, the greater the velocity of the gas with respect to the velocity of extrusion, the finer the fiber. The relative velocity of the gas flow to the velocity of extrusion may be increased to provide fibers of shorter length when a web or mat of lower density is desired. Simultaneously with the extrusion 'of elastomeric material, solvent is evaporated from the extruded fibers to partially harden or set the same. If desired, the gas delivered by the nozzle 19 may be heated to control the rate of solvent evaporation and the tackiness of the fibers.
The multiplicity of fibers formed as described above settle on a suitable collecting means disposed at the lower end of the tower 9. Preferably, the collecting means is an endless screen 23 which is trained over a pair of rolls 25, with at least one of the rolls being driven by suitable means, not shown. A suction chest, not illustrated, may be disposed below the upper reach of the endless screen 23 to assist in the recovery of solvent.
As heretofore mentioned, the temperature of gas discharged frcm the nozzle 19 is maintained at a desired degree to control the rate of solvent evaporation and thus assure that the fibers are still in a tacky or adhesive c0ndition as they settle upon the endless screen 23. In this tacky condition, the collected fibers will adhere to each other at their crossing points and provide a unitary web structure 27. A more tenacious bond between the adjacent web fibers may be obtained by pressing the web 27 between rollers 29 as it is carried toward a heating chamber or oven 31. The degree of compression of the fibrous web or mat 27 will be primarily determined by the grinding or cutting rate desired in the final abrasive material, and thus the greater the compression of the web 27, the greater will be the cutting rate of the final ab rasive product. Care should be exercised, however, in this pressing procedure to avoid an excess densification of the web 27 which may tend to induce overheating during actual grinding operations.
The collected web 27 may be stripped from the screen 23 in its unvulcanized condition and collected or may be folded upon itself or with supplementary reinforcing or strengthening members. For example, the uncured fibrous web may be laminated with a backing sheet of glass fibers to provide an end product of desired strength. It is preferred, however, to pass the unvulcanized web 27 into and through the chamber or oven 31 where final curing or vulcanization of the web is effected. If desired, the: web 27 may be pressed while in the chamber 31 instead of or in addition to the compression effected by the rollers 29.
As illustrated in FIGURE 5 the elastomeric material, upon evaporation of the solvent therefrom, shrinks snugly against and into general conformity with the abrasive particles. In comparing the structure of FIGURE 5 with a conventional plastic abrasive block, it will be noted that the abrasive grains in the material formed in accordance with the present invention are covered with a relatively thin layer of elastomeric material. During actual grinding operations, this coating material is rapidly worn away, continuously exposing new abrasive surfaces and thus assuring a uniform grinding or polishing rate. Since the abrasive grains are well embedded within the elastomeric material, the actual scratches made by the grains are not as deep as those made by comparable particles in conventional abrasive products. Thus, larger mesh, and hence less expensive abrasive materials may be used in the present invention to give the same results as the finer abrasive particles employed in the ordinary abrasive devices. For example, 120-mesh abrasive particles may be used in the elastomer bonded device here described to obtain the same fine finish as would be achieved with 300-mesh abrasive grains attached to a paper-backed disc. The following specific examples are set forth herein to illustrate the production of fibrous abrasive webs or mats formed of natural and/or synthetic rubbers when employing apparatus such as illustrated in FIGURE 1.
Example I A rubber solution weighing 500 grams was prepared from compounded No. l pale crepe rubber dissolved in naphthol solvent and had a solid content of 36% by weight. This solution was then mixed with 2% of menthol, by weight of the solvent, to adjust the viscosity to 12,000 centipoises at 75 F. Abrasive particles, having an average diameter corresponding to 24-mesh, were coated with a phenolic resin and then stirred into the rubber solution at room temperature. After thorough mixing, the slurry was fed through a Mayno pump and extruded through an orifice of 0.10 inch in diameter. A half-inch diameter nozzle was used to deliver air at c.f.m. around the extrusion orifice and the fibers were extruded into a chamber maintained at 70 C. During the passage on the fiber through the air some of the solvent was removed and the resulting tacky or adhesive fibers collected in a random orientation on a small mesh screen to provide a web having a thickness of about onequarter inch. The abrasive content of the fibrous mat was about 32% of the total weight.
The fibrous mat was rolled lightly under a few pounds of pressure merely to smooth out the surface and was then cured for minutes in an air circling oven maintained at a temperature of 250 F. The finished rubber bonded abrasive material was cut into 7 inch diameter discs and adhesively aifixed to a vulcanized fiber backing to form a flexible abrasive disc. The abrasive characteristics of this particular material were then evaluated by periodically measuring the amount of metal which was ground from a cylindrical metal blank under a load or pressure of 8 pounds. The results of this test were then transposed into a graphical illustration, such as shown in FTGURE 6, wherein curve A shows that the rubber bonded disc had a substantially constant rate of metal removal throughout the grinding period. To compare and better appreciate the improved characteristics of the abrasive disc formed in accordance with the present invention a commercial paper-backed disc, having the same size abrasive particles and maintained under the same load or pressure of 8 pounds, was employed in grinding a similar test cylindrical metal blank. The grinding results obtained with the commercial paper-backed disc have been graphically illustrated as curve B in FIGURE 4. It will be noted that the commercial paper-backed disc initially removed a larger quantity of metal but that its grinding ability, after approximately 5 minutes of use, increased at a very slight rate during the remainder of the grinding period.
The improved results obtained with the fibrous rubber disc can be attributed in part to the porous nature of the fibrous material which prevented overheating and clogging of the disc, and perhaps to a greater extent to the fact that new abrasive grains were continuously being exposed as the thin coating of elastomeric material on the particles was worn away.
Example II Using the same rubber solution as described in Example I, a mixture of 400 grams of elastomeric solution and 400 grams of 400-mesh abrasive silicon carbide particles, coated with a phenolic resin, were thoroughly mixed and then extruded in the same manner as described above. The extruded fibers were collected into a mat of approximately one-quarter inch in thickness which was then passed between rubber rolls and reduced in thickness to approximately one-sixteenth of an inch. The abrasive content represented about 74% by Weight of the total weight of the resulting mat. Curing was accomplished in the same manner as described in Example I, after which the fibrous mat was utilized as a finishing or polishing abrasive sheet for which purposes it was found to be highly satisfactory.
Substantially similar products to that described above may also be obtained by an alternative method which may be practiced with the aid of apparatus such as illustrated diagrammatically in FIGURE 2, to which attention is now directed. A tower 40 which may be cylindrical in form is provided with a spraying unit 41 preferably centered within the tower. The spraying unit comprises a conduit 42 which terminates in an upwardly extending spray tip 43 having a suitable orifice at its upper end and a conduit 44 which terminates in an upwardly extending nozzle 45. The spray tip 43 is preferably mounted concentrically within and extends slightly above the nozzle 45. The fiber-forming liquid is continuously extruded through the spray tip by means of a suitable pump, not shown. A stream of gas such as air is continuously passed through conduit 44 and nozzle 45 by suitable means such as a blower, not shown, the velocity of the gas emerging from the nozzle being appreciably higher than the velocity of extrusion of the spraying liquid. The elastomeric composition is forced out of the tip 43 as a single continuous plastic stream which is attenuated and broken transversely into discontinuous fibers or fibrils of varying length by the high velocity primary gas stream. The velocity of the extrusion and the velocity of the gas may be varied so as to regulate the amount of attenuation and hence the diameter of the fiber or fibrils, and may be increased sufiiciently to regulate the length of the fiber. Simultaneously, solvent is evaporated to partially harden or set the elastomeric fibers.
The relative velocities of extrusion of the spraying liquid and the gas emerging from nozzle 45 may be varied to some extent so as to provide the desired size and length of fiber within certain limits. In general, for a given spraying liquid, the greater the velocity of the gas with respect to the velocity of extrusion, the finer the fiber or fibrils. The relative velocity of the gas flow to the velocity of extrusion may be increased to provide fibrils of shorter length for the production of lower density products. It is not necessary and in many cases not desirable to heat the primary gas stream.
A secondary stream of gas such as air is passed upwardly through the tower 40 by means of a blower 46 and surrounds or envelops the primary stream of gas. This main column of gas in passed upwardly at a velocity lower than that of the gas which is sup-plied through nozzle 45. As the extruded liquid is attenuated and the velocity of the gas from nozzle 45 approaches the velocity of the main stream of gas, the attenuated fibers are then carried upwardly by the main stream of gas. In order to increase the drying or setting rate of the fibers, the temperature of the secondary gas stream may be elevated above 50 C. so that the fibers as they reach the top of the tower 40 are in an adhesive or tacky condition, or the conditions may be varied so that the fibers are deposited in a non-tacky condition with little or no adhesion between the fibers.
The multiplicity of fibers is carried by the secondary gas stream to a suitable collecting means at the top of the tower such as a porous surface 47. In the preferred I form, the collector is a moving endless screen or a porous drum. As the fibers collect and deposit on the screen, the resistance of the collected reticulated mat 48 to the flow of gas increases and for the production of thicker webs or mats, a suction chest 49 may be provided above the conveyor screen. The suction chest also may be employed to aid in the recovery of the solvent, if desired. The tendency of the airborne attenuated fibers to contact and adhere to the walls of the tower may be reduced by providing a conical annular ring 50 in the tower positioned above the spinning tip. The velocity of the main column or secondary stream of gas through the tower may be controlled to deposit the fibers on the collecting means 47 in a desired condition. The temperatures of the gas streams may be varied so as to control the evaporation of solvent and the vulcanizing of the elastomeric material so as to deposit the fibers in a desired condition. The temperature and velocity of the secondary gas stream are so controlled that the fibers are deposited on the conveyor screen 47 in a somewhat adhesive or tacky, unvulcanized condition whereby they become bonded together at their points of contact.
The collected web 48 may be stripped from the conveyor screen 47 and passed through a suitable heater 51 wherein the elastomeric material is vulcanized. The reticulated web or mat 48 is then accumulated on a take-up roll or drum 52. The sheet or web is reticulate in structure having the fibers arranged in a completely and totally random or haphazard order and is highly porous and permeable.
Relatively thick bodies or structures may be produced by a laminating technique. The unvulcanized, reticulated web may be stripped from the conveyor screen and folded upon itself to provide the desired thickness. As alternatives, the unvulcanized web may be cut to a desired size and a plurality of such cut webs assembled, or a plurality of uncut Webs of desired lengths may be assembled to form the desired thickness. Since the fibers of the unvulcanized webs are tacky and adhesive, the fibers on contiguous surfaces adhere to each other upon contact so as to bond the adjacent layers into a unitary structure. Additional bonding between adjacent layers may be obtained by the application of pressure to theassembly whereby the exposed fibers lying beneath the plane of the surface fibers of adjacent layers are brought into contact. The pressed assembly is then vulcanized so as to provide a unitary body of the desired thickness. Such unitary body remains permeable and has substantially the same elasticity and strength characteristics in all directions in the plane of the laminations.
The formation of the laminated body before vulcanizing the sprayed elastomeric fibers preserves the reticulated structure Whereas the use of a rubber adhesive or solvent which would be required if the layers were first vulcanized might reduce the porosity of the product.
Although the chamber or tower 40 is shown as being provided with a spraying unit 41 consisting of a single spray tip and nozzle, it is to be understood that such illustration is merely for purposes of simplifying the drawing and the foregoing discussion. A plurality of spaced spray tips may be mounted within a large chamber provided with a single secondary gas blower. In a preferred embodiment of the apparatus, a plurality of chambers are employed, each containing a number of spaced spray tips and nozzles. It is necessary to provide an appreciable spacing such as to 12 inches between the spray tips or orifices so as to avoid contact between the formed fibers before a majority of the solvent has vaporized. In any case, each spray tip is provided with its separate primary gas nozzle surrounding it.
A product of uniform thickness over the width of the web may be produced by utilizing a tower 53 having a square or rectangular section. A plurality of spraying units 54 are positioned in spaced relationship at or adjacent the base of the tower. Each spraying unit comprises a spraying liquid conduit 55 provided with a plurality of spaced, upwardly projecting spray tips 56 and a gas conduit 57 provided with a plurality of spaced, upwardly projecting nozzles 58 surrounding the tips. A spraying liquid is continuously extruded through the spray tips and a stream of gas is continuously passed through the nozzles.
The spun fibers are carried by a single secondary stream of air supplied by the blower 46 and are collected as a reticulated web 59 on the collecting screen 60 supported at the top of the tower. A suction chest 61 may be mounted above the conveyor screen 60, as described hereinbefore. The web may be stripped from the conveyor 60 and passed through the heating chamber 51 wherein the elastomer is vulcanized and the web or sheet finally accumulated on the take-up roll 52.
As illustrated in FIGURE 2, a laminated product may be produced by bringing together two or more webs from dilferent chambers or towers between squeeze rolls 62 and 63 while the elastomeric fibers are tacky and adhesive. The tacky fibers on contiguous surfaces adhere to each other upon contact and additional bonding of the layers or plies is obtained by the application of pressures whereby the exposed fibers lying beneath the plane of the surface fibers are brought into contact. The pressed assembly is then vulcanized so as to provide a unitary body by pass ing the laminate through a heating chamber 51. The laminate is finally accumulated upon a suitable take-up drum 52.
If desired, where a plurality of spraying units are positioned within a tower, all of the spraying units may be supplied with the same spraying liquid and each nozzle may supply the primary gas at the same velocity. The resulting reticulated web thus consists of a single composition and the fibers will be of about the same size and length. If desired, the relative velocities of extrusion of the spraying liquid and of the primary gas stream may be varied in diiferent spraying units to provide fibers of dilferent size and length. Products containing fibers of two or more different elastomers or difierent elastomeric compositions may be formed by supplying spraying liquids of the difierent elastomers or of different composition to separate spraying units. Products having color blends may be prepared by supplying spraying liquids containing different coloring agents to separate spraying units.
Our method may also be practiced by passing the secondary or low velocity gas stream in a direction countercurrent to the primary or high velocity gas stream, as illustrated in FIGURE 3. A spraying unit 64 consisting of a spray tip and nozzle, as described hereinbefore, is mounted at the top of tower 65, preferably concentric with respect to the walls of the tower. The primary or high velocity gas stream is supplied to the nozzle by suitable means and the spraying liquid is extruded through the spray tip by suitable means, not shown. The direction of travel of the primary gas stream and the direction of extrusion are downwardly. The attenuation of the spraying solution and evaporation of the solvent by the primary gas stream is identical to that described herein before.
The secondary or low velocity gas stream is passed upwardly through the tower as by means of a blower 66. The secondary gas stream is passed at a velocity sufiicient to support or retard the fall of the attenuated fibers so as to deposit the fibers on the collecting screen 67 in any desired condition. The fibers may be deposited in a tacky or cementitious, unvulcanized condition to cause them to eifect an immediate bonding at their points of contact. The reticulated web may be passed through a suitable heater 68 to eifect a curing or vulcanization of the elastomer. The cured web is then stripped from the conveyor as by means of a doctor blade 69 and the vulcanized web collected on a take-up roll or drum 70.
In forming the fibers, there is some tendency toward the inter-twining or roping of the adhesive fibers as they are carried upwardly in the gas stream. This is particularly noticeable when spinning from multiple spinning units and results in the formation of rope-like or band-like fibrous strands. The resulting reticulated web is thereby formed of single individual discontinuous fibers and band-like fibers formed by individual fibers bonded together longitudinally. There is also a tendency for some fibers to deposit along the walls of the tower to form a very loose and open web in which the fibers are in a more orderly arrangement. This material may be employed for some purposes or the web, since the elastomer has not been vulcanized, may be re-used in an additional batch of elastomeric composition and used as the spraying liquid.
As explained hereinbefore, the fibers may be deposited under conditions so as to provide a high degree of bonding at the points of contact. The sheet or web as thus formed, after suitable treatment to cure or vulcanize the elastomer may be utilized in sheet form or may be secured or laminated to other materials to form a composite laminate.
In FIGURE 4 there is illustrated schematically and in flow diagram fashion, a method for commercially producing a laminated reticulated abrasive fibrous web in accordance with this invention. The elastomeric material and the desired additives such as fillers, vulcanizing agents,
accelerators, anti-oxidants and the like are thoroughly mixed in a conventional type rubber mill 75. After the required milling period, the elastomeric composition is transferred to a conventional jacketed rubber mixer 76 and dissolved in the solvent, supplied from a suitable tank 77, to form the spraying liquid. The abrasive particles are added to the liquid in the mixer 76 from a hopper 78 and thoroughly admixed therein so as to form a homogeneous suspension. The spraying liquid having the abrasive particles suspended therein is then transferred to a suitable storage tank 79 from which it passes to a pump 80. A strainer or filter 81 may be interposed between the storage tank and the pump to filter out any oversize abrasive particles. From the pump 80, the spraying liquid passes to the spray tips 82 mounted in adjacent towers 83. The primary gas stream is supplied to the nozzles 84 by means of a blower 85. The secondary gas streams are supplied to the bottom of towers 83 by means of a blower 86. The spraying liquid is attenuated and the discontinuous elastomeric fibers are formed in the towers as described hereinbefore.
The fibers are collected on endless conveyor screens 87 which are disposed at the top of the towers and the vaporized solvent and gases supplied to the towers are removed through suction chests 88. The reticulate webs are stripped from the collector screens 87 and are brought together under pressure between squeeze rolls 89. The laminated sheet may then be passed through a dusting chamber 90 wherein a detackifier such as tale is applied to the outer surfaces to reduce the tackiness of the surfaces. The sheet then may be passed between another pair of rolls 91 from which it is passed through a precuring or pre-vulcanizing chamber 92. The sheet is then passed over steam heated rolls 93 in a curing chamber 94 to effect a final curing or vulcanization of the elastomeric material. The cured or vulcanized sheet may then be passed through a suitable trimming device 95 to cut the sheet to a desired width. The finished sheet is then dusted with talc in a dusting chamber 96 and collected on a suitable wind-up roll 97.
The fibrous, reticulated web or mat of elastomeric material has much the same feel as foam and sponge rubber. However, because of the completely random or haphazard arrangement of the fibers and due to the fibrous structure of these Webs or mats as compared to the cellular structure of foam and sponge rubber, the permeability of the mats is substantially greater per unit of thickness than foam and sponge rubber. The tear strength and tensile strength of the webs and mats are also substantially greater per unit of thickness than foam and sponge rubber although the permeability is greater.
The products of this invention possess substantially the same elasticity and strength characteristics in all directions in the plane of the web or mat in view of the random arrangement of the fibers. Further, it has been found that holes made in the finished web are localized and have little tendency to induce tearing when the web is stretched. Thus, the webs may be sewed, tacked or nailed by conventional means without any loss in strength. The finished product may be used in variety of ways including hand-held blocks, abrasive wheels, wrapped around forms or mandrels, endless abrasive belts, and household scouring pads.
While the fibrous abrasive web or mat of the present invention has been described as being particularly suited for use as a grinding or polishing material, it will be of course understood that the elastomeric bonded abrasive materials are adapted for use in various other applications. In View of the uniform traction surface provided by the material of the present invention, it can be collected in its uncured state and then vulcanized onto the tread surface of solid or pneumatic tires. Other sug gested uses are as soles for Work or overshoes, stair treads, non-creeping rug pads, and the like.
It is seen from the above description that the objects of the invention are well fulfilled by the structure described. The description is intended to be illustrative only and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.
Having thus described the invention, What is claimed is:
1. As an article of manufacture, a flexible, porous, fibrous sheet-like body of elastomeric fibers disposed in random distribution and bonded to each other at their points of contact, and abrasive particles embedded within the individual fibers and being covered by a thin layer of elastomeric material.
2. An article as defined in claim 1, wherein the elastomeric fibers comprise natural rubber.
3. An article as defined in claim 1, wherein the elastomeric fibers comprise synthetic rubber.
4. An article as defined in claim 1, wherein the elastomeric fibers are shrunk into the general conformity of the embedded abrasive particles.
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