CUTTING AND ABRADING TOOLS

Abstract: A tool having a working surface of metal bonded abrasive particles (22) comprising a metal tool substrate (10), a tape (18) metallically bonded to the substrate and comprising fused metallic brazing material, and a unilayer of abrasive particles (22) projecting from the surface of the fused tape (18).

Description: CUTTING AND ABRADING TOOLS Description Technical Field This invention relates to abrading and cutting tools, more particularly tools of the type having hard abrasive particles embedded in a fused metallic matrix at the surface of a substrate. Background of the Invention Embedding cutting or abrading particles in a metallic matrix has been employed in the manufacture of saw blades, milling cutters, broaching tools, abrading wheels, sanding discs and the like. The actual cutting or abrading is performed by the hard particles which may be diamond, aluminum oxide, silicon carbide, garnet, tungsten carbide or the like. The choice of the material the particles are made of is dictated primarily by the type of work to be performed balanced by the. cost factor and avail¬ ability of the material. United States Patent 2,906,612 to Anthony et al discloses a plurality of cutting tools having tungsten carbide abrasive grits secured to the surface of a steel base member or substrate by an extremely thin coating of brazing metal which, in effect, contacts only the grit's undersurfaces leaving the preponderant portion of the grits exposed on top of the substrate. The space between individual particles is substantially greater than the mean dimension of the particles. This construction is often referred to as an open cut. In each of the Anthony illustrations no particle is shown touching any other. This provides for a fast cutting tool, but it will not particularly produce a smooth surface on the workpiece. Tools of this construction are employed for rough cutting or rasping and would have utility, for example, in the roughing or abrading of a shoe outsole being prepared to be adhesively secured to a similar sur¬ face of a shoe bottom. United States Patent 3,248,189 to Harris discloses another type of cutting or abrading tool intended pri¬ marily to form a honing function. It is constructed so that it will gradually crumble or disintegrate during use to release material (usually metal) removed from the workpiece. Harris, with this -objective in mind, provides a cutting surface made up of a large number of piles or columns of abrasive grits in anchored and spaced apart relation on the substrate. There nay be as many as 6 or 7 individual particles or grits fused together and projecting from the surface of the tool. Each column then becomes an individual dis.- . integratable cutter. Harris secures the grits to the substrate in the following manner: the surface is first shot blasted and then heated to 200°F in a non-oxidizing atmos¬ phere. Next, nickel-chromium-boron alloy in fused condition is applied by a flame spray or metallizing gun. This produces a thin flash layer from abβut .001" to .005" thick. Next, a small layer of matrix material is flame sprayed onto the initial layer. In some instances, grits pre-coated with matrix are flame-sprayed onto the initial layer. Another technique is to use O H grits pre-coated with matrix material plus individual particles of matrix material in the flame spray. The volume of the particles of grits is greater than that of the matrix. The grits or grit-matrix mixture is put into a magazine of a metallizing gun and are introduced into the flame which issues from the nozzle of the gun. The flame heats the matrix material to its fusion temperature without fusing the grits themselves. They are propelled against the layer of bonding material and become deposited in columnar fashion. Harris thus produces an effective tool for its intended purpose. However, tools which depend in large measure on their ability to wear away during usage are not par- ticularly satisfactory for stock removal of non- metallic workpieces, nor is it particularly well-suited for the production of a smooth surface. United States Patent 3,615,309 to Dawson has as its objective the production of a fast cutting saw or abrading tool wherein, like Harris, there is pro¬ vided a surface of abrasive particles randomly applied and often found lying one upon the other. This, pro¬ duces an irregular contour which, in illustrative form, may be said to resemble the profile of a mountain range. The process of producing the Dawson saw in¬ cludes the first step of coating a selected surface area of the base metal or substrate with a mixture of a paste flux adhesive mixed with a brazing ijfetal powder. Alternatively, a coating of the paste^'flux adhesive alone may first be applied and then an over¬ coating of the brazing metal powders next applied. To the resultant coating applied by either procedure, there is a further overcoating of the abrasive parti¬ cles or grits following which the coated surface is OMPI dried. The tool is then subjected preferably to high frequency electrical induction heating sufficient to fusion bond the matrix metal powders to one another and to the base metal or substrate. The tool is then cooled to solidify the matrix metal layer thus perma¬ nently combining the abrasive particles. This results in an irregular surface. As with the Harris tool, the Dawson tool is quite effective for fast cutting; but it is not particularly well-adapted to produce a smooth cut or a surface free of irregularities. U.S. Patent 3,868,235 to Held describes an earlier process of placing a mixture of copper brazing com¬ pound particles and hard carbide particles (grits) upon the surface of a substrate which is then heated i n a furnace. The temperature is selected to melt the brazing compound to cause it to flow around and adhere to the carbide particles for bonding them to the substrate. Held states, however, that this pro¬ cess is inapplicable where the substrate surfaces have been curved or are at various angles relative to the horizontal. Held also refers to a hot spray mixture of parti¬ cles of brazing compound and hard carbide particles as taught by the Anthony patent described above. He refers also to the Harris patent, also described above, and says that the carbide particles oxidize excessively and tend to bounce off during the spraying process. In the Held process, the first step incluΘes roughing the substrate by abrading or bombarding with hard particles to improve the mechanical interlock. A matrix or bonding layer then is hot sprayed onto the substrate. _ c__ Once the matrix or bonding layer is applied, the material is cooled and then a layer of organic adhe¬ sive such as glycerine and water is applied. This is to hold the carbide particles in place temporarily. The carbide particles or grits are then sprinkled on the glycerine-water tacky surface. The thickness of the layer of particles can be varied by either sprink¬ ling on more particles or by applying a thicker binder. The next step is to melt the matrix and volatilize Q . the temporary adhesive. The matrix material has a flow capability, that is, it tends to surround and thinly coat the carbide parti¬ cles which sink into the molten matrix as illustrated in Figure 5, some of them going completely below the surface. As clearly seen in Figure 5 of the Held patent, the invention contemplates more than a unilayer of grits. Held then states "Flow capability is a characteristic of the molten matrix wherein the matrix forms a thin film or covering over the carbide (grits) during the "baking" or volatilization of the binder. A covering film is eroded or worn away after an initial period of use." Disclosure of the Invention With the objectives of producing a tool which has a long life, fast cutting ability and which will pro¬ duce a smooth finish on a workpiece, Applicant^has found that a unilayer or monolayer of abrasive^particles as distinguished from overlapping particles or/multiple layers is most desirable. Applicant has also found that locating the particles in close proximity to one another but not in overlapping relationship produces the most uniform cutting surface. It is also desirable not to completely wet or cover the abrasive particles with molten brazing material because it defeats the purpose of using hard grits. It reduces the speed of cutting until the brazing material wears away exposing the harder cutting edges of the abrasive particles. Applicant has also found that the prior art techniques of flame spraying or depositing of brazing material in powdered form is not particularly benefi- cial in securing the grits in a uniform cutting surface. Applicant has produced a tool having a working surface of metal bonded abrasive particles which tool comprises a metal substrate, a tape metallically bonded to the substrate which tape comprises fused metallic brazing material. Projecting from the surface of the fused tape is a unilayer of abrasive particles, or grits, a portion of each being embedded in the tape • * • with the remainder projecting from the surface. Only a portion of each grit is coated with brazing material leaving a relatively uniform surface of exposed, sharp abrasive particles. The tool is made by securing to the substrate a tape of powdered brazing material which is blended into a soft, flexible matrix. A unilayer of abrasive particles are partially embedded in the tape matri - The tool is then heated to a temperature at least equal to the liquidus temperature of the brazing material to set the abrasive particles. Then, it is rapidly chilled to solidify the brazing material to produce the metallic matrix on the substrate which contains a unilayer of abrasive particles projecting from its surface. The above and other features of the invention including various novel methods of construction and combinations of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular abrading wheel embodying the in¬ vention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention. Description of the Drawings Figure 1 is an illustrative tool embodying the invention, in this instance an abrading wheel in the process of manufacture. Figures 2 and 3 are sectional views on an enlarged scale emphasizing the surfaces of tools made in accordance with prior art teachings. Figures 4 and 5 are sectional views on an enlarged scale of an abrading tool embodying the invention in the process of manufacture and emphasizing its surface features. Figure 6 is a sectional view of another form of tool embodying the present invention. ' . Best Mode of Carrying Out " the Invention The invention will be illustrated as embodied in an abrading wheel and more particularly in a wheel for abrading and finishing the white sidewall por- tions of automobile tires. A tool for performing this function should be capable of producing a smooth, semi polished surface. It should have long life and be resistant to clogging by the abraded rubber par¬ ticles. It will be understood, however, that the illustrative tire abrading tool is but one of many possible embodiments of the invention. The principles of the invention may be embodied in other stock removal tools for cutting, honing, polishing, smagging, grinding, planing and scraping. They apply also to files, rasps, etc., all without departing from the scope or intent of the invention. The illustrative tire abrading tool comprises a tool substrate which is a steel wheel 10 approximately eight inches in diameter mounted on a shaft 12. It has a peripheral face 14 about 1% inches wide measured parallel to the axis of rotation 16 of the wheel. The periphery 14 is initialy finish machined and thenmechanically cleaned with fine emery cloth. Next, the surface is cleaned with a solvent such as acetone or toluol. The next step in the process is the application of specially compounded brazing material in th* form of a tape 18. The tape comprises a dry alloy ' mixture of 19% chromium, 10.2% silicon, and the remainder nickel, in fine powdered form. The dry mixture con¬ tains less than 1% impurities and may be obtained under the trademark NICROBRAZ 30 from the Wall Colomonoy Corporation of 19345 John R. Street, Detroit, Michigan 48203. It has a soliditus melt¬ ing point of 1975°F (1080°C) , a liquidus melting point of 2075°F (1135°C) , and a brazing range of 2100°F to 2200°F (1150°C to 1204°C) . The mixture is blended into a thick paste with a binder of glycerine and then rolled to form a soft, flexible tape having a thickness of approx- imately .003 inches (.0762mm). Other binders may be employed as for example is taught in U.S. Patent 3,293,072 to Doolittle et al. One side of the tape is coated with a water based adhesive. It will be understood that the particular composition of the tape is merely illustrative. Numerous composi¬ tions may be employed depending upon the purpose of the tool and the composition of the other elements such as the substrate and grits. Such material in tape form for other purposes may also be commercially available. The adhesive side 20 of the tape is then applied to the periphery 14 of the wheel and pressed firmly into engagement as by rolling. Excess pressure at this point should be avoided as it would- tend to thin the tape beyond that which is desired for a particular size of grit to be applied. Grits 22 were partially embedded in thejj tape by pressing them into the soft outer surfaσe 23 in a single, unitary layer. As viewed in Figure 4, some grits but not all, are touching each other. In this illustrative embodiment the grits were selected of tungsten carbide, though they might have been any hard abrasive material, ranging from diamond through the various semi-precious stones, etc. The grit size was #120 sieve mesh, also designated as 125u, with a normal approximate sieve opening of .0049 inches (.125mm) producing a mean diameter that size. The ratio of the average of the mean diameter of the abrasize particles (grits) to the thickness of the tape is approximately 5 to 3 although it could be as low as 1 to 1. The prior art products of Anthony and Harris discussed above are represented in Figures 2 and 3. The grits 22 extended to a depth approaching but not penetrating the surface 14 of the wheel, i.e. from about 1/3 to about 1/2 the depth of the tape 18, i.e. from about .001 to .0015 inches (.025 to .038mm). Excess grits were removed to make sure there were no overlying or overlapping particles as in the Figure 2 representation of prior art. The then-coated periphery of the wheel was next sprayed with a water based adhesive to assure adherence of any grits not firmly embedded in the tape. The wheel was next placed in a vacuum furnace and brought to a temperature just below the solidus temperature of the braze material, that is to about 1080°C. The temperature was then increased rapidly through the solidus ranga to approximately 10°C above the liquidus temperature, that is about 1145°C. It was held at this temperature for three minutes. The vacuum furnace was rapidly filled with a cold inert gas to freeze the tape before it could flow or s' slump away. The brazing cycle, and particularly the use of the brazing material in tape form, achieved a full bonding of the individual particles as shown in Figure 5. There was no unrestricted flow of molten alloy, which if it had occurred, would have resulted in clumping and an uneven distribution of particles on the face of the wheel as in many prior art products. O PI As seen in Figure 4, the particular 120-grit (.125mm) particles when initially inserted into the .0762 mm tape, projected above the surface of the tape with about 60% of the grit exposed and 40% below the surface. Contrast this with the prior art representation of Figure 3. The 60-40 ratio was selected for the particular grit size being brazed with a .762 mm tape. However, it is possible to use a tape thickness of as much as .125mm, with the only requirement being that it not be thicker than the nominal dimension of the grit. Otherwise, during the braze cycle, the grits could be completely covered by the molten braze as practiced in some prior art techniques. As seen in Figure 5, on average, approximately 40% of the mean diameter of grit then projects above the surface of the tape and 60% is below the surface. As the tape passes rapidly through the solidus into the liquidus range, the grits settle into the melt somewhat. The non-metallic components volatilize, causing the brazing tape to shrink in volume by about 25% to 35%. Then the ratio of the mean diameter of the abrasive particles (grits) to the mean thickness of the fused tape is approximately 5 to 2. Capillary attraction causes the molten braze material to run slightly up the sides of the particles as shown at 25, in spite of the fact that surface tension between the particles and the braze tends to oppose it, the capillary action being the stronger of the two. ' The result is that there is little chance for the grits to move much from their original embedded positions and there is virtually no running of the melt. Consequently, the particles are uniformly distributed in a mono-layer with a portion of each projecting -12- above the solidified tape and the crevices between grits filled and filleted as at 25. The grits 22 approach but do not penetrate the surface 14 of the abrading wheel 10. This construction produces a variation of only approximately ±025mm in the height of projection of individual grits 12. This contributes to an extremely uniform cutting surface that produces a smooth semi polished surface on a rubber workpiece. Long life and wear resistance results because each of the grits is uniformly embedded in the fused tape matrix as distinguished from the Figure 2 prior art construction which is intended to wear away. The filleted areas 15 between individual grits 22 result in resistance to the wheel clogging with abraded workpiece particles. As another example of a tool made in accordance with the present invention. Figure 6 shows a cross section of a saw blade for fine cutting as in jewelry manufacture. Three sides of the substrate are coated with particles with like reference characters referring to like elements of the abrading wheel.

Claims: CLAIMS 1. A method of making a tool having a working surface of metal bonded abrasive particles comprising the steps of: providing a metal tool substrate; securing to the substrate a tape of powdered brazing material blended into a soft, flexible matrix; partially embedding a unilayer of abrasive particles in the tape matrix; heating the tool to a temperature at least equal to the liquidus temperature of the brazing material to set the abrasive particles; and, rapidly chilling the tool to solidify the brazing material to produce a metallic matrix on the substrate containing a unilayer of abrasive particles projecting from its surface. • • 2. The method of Claim 1 wherein the ratio of the average of the mean diameter of the abrasive particles to the thickness of the unfused tape is approximately 5 to 3. 3. The method of Claim 1 in which the thickness of the tape does not substantially exceed €he average of the mean diameter of the abrasive particles. 4. The method of Claim 1 wherein the abrasive particles are tungsten carbide. 5. The method of Claim 1 wherein the brazing alloy is comprised of chromium, silicon and nickel. 6. The method of Claim 1 wherein the abrasive particles are initially embedded in the tape matrix to a depth of from 1/3 to 1/2 the thickness of the tape. 7. A tool having a working surface of metal bonded abrasive particles comprising: a metal tool substrate, a tape metallically bonded to the sub¬ strate and comprising fused metallic brazing material; and a unilayer of abrasive particles pro- jecting from the surface of the fused tape. 8. The tool as in Claim 8 wherein the mean thickness of the average of the fused tape does not sub¬ stantially exceed the mean diameter of the particles. 9. The tool of Claim 8 wherein the ratio of the average of the mean diameter of the abrased particles to the mean thickness of the fused tape is approximately 5 to 2. Ά 10. The tool of Claim 8 wherein the abrasive particles are tungsten carbide. 11. The tool of Claim 8 wherein the fused tape is an alloy comprised of chromium and nickel. O PI - 15- 12. The tool of Claim 8 wherein approximately 40% of the average of the mean diameter of the abrasive particles project from the surface of the fused tape. -

Inventors: COLE RICHARD F, COLE, RICHARD, F.
Applicants: HALE ENGINEERING INC, HALE ENGINEERING, INC.
Application year: 1983
Main classification: B24D5
IPC codes: B24D18