Abrasive article and method of making same

Abstract: Abrasive article using sintered sol gel abrasive particles mixed with other particles having greater friability, and carried in a bond.

Description: BACKGROUND OF THE INVENTION It is well known that the nature and content of the abrasive grains in a bonded abrasive article have significant influence on the grinding performance of such articles. The term "nature", as herein used, refers to chemical composition, morphology, shape, and size for both the individual abrasive grain and any microcrystalline components thereof. For example, each grit of the sintered sol gel alumina abrasive grains of Cottringer, et al, (U.S. -A-4,623,364), is composed of an assemblage of alpha alumina crystallites each no larger than 0.4 µm. The sol gel alumina particles of Cottringer are generally described as "seeded". Other sol-gel alumina abrasive are described in, for example, U.S. -A- 4,314,827 (Leitheiser et al) and U.S. -A-4,744,802 (Schwabel). The invention described in the US Patent 4,314,827 provides a calcium ion-free and alkali metal ion-free, dense, non-fused, synthetic, aluminium oxide-based granular abrasive material, having a substantially homogeneous microcrystalline structure of randomly oriented crystallites of alumina and a modifying component with the alumina being a dominant continuous phase. Leitheiser et al describes unseeded and Schwabel seeded sol gel alumina abrasives. It is found that vitreous bonded articles prepared from sol gel alumina abrasive grits may outperform identical articles prepared from conventional fused alumina abrasive by as much as 600% or more in wheel life and in the ratio of metal removed to wheel wear, while consuming less power and removing metal at a higher rate. However, in organic bonded abrasive articles, sintered sol gel abrasives, while superior to normal fused alumina abrasives, have hitherto not shown the dramatic improvement seen in vitreous bonded articles. At high grinding pressures, organic bonded abrasive articles wear too rapidly to take advantage of the superiority of the individual sol gel alumina grits and at low force levels not enough pressure is exerted on individual grains to microfracture for self-sharpening. EP-A2-0 280 463 describes erodable agglomerates comprising individual grains of abrasive mineral disposed in an erodable matrix. This matrix comprises a binder, preferably a resinous binder, and hollow bodies which facilitate breakdown of the agglomerates during their utilization in an abrasive product. The hollow bodies render the agglomerates sufficiently durable to avoid premature destruction under severe abrading conditions. It is well known in the art that dilution of the abrasive grit portion of bonded abrasive articles with softer more friable particles will increase the cutting rate. Hartmann, in U.S. -A- 1,830,757, teaches a self-sharpening wheel in which friable particles of calcined clay, porous alumina, magnesia or glass, all softer than the abrasive grits, are incorporated to break out during grinding leaving an open, free-cutting grinding face. Similarly, Robie, in U.S. -A- 2,806,772 teaches the use of thin walled balloons, resin micro balloons, porous clay pellets, and other friable particles to provide pore support and increase freedom of cut. Sandmeyer, in U.S. -A- 2,986,850, recognized the unique ability of hollow alumina spheres to serve as both abrasive grit and pore spacer in bonded abrasive articles. Grinding wheels of 100% alumina bubbles, made according to the Sandmeyer patent, wear very rapidly and are only suitable for grinding soft materials such as cork, rubber, fiber board, etc. Fukada, in U.S. -A- 4,226,602, incorporates pore-forming blowing agents with or without alumina bubbles in a continuously-formed resin bonded abrasive article of improved cutting ability. Zimmer, in South African Disclosure 82/0339, describes resin bonded abrasive articles of less than 14% interconnected porosity containing silane-treated porous support material, including alumina bubbles, and multicellular glass modules. The function of the porous materials in this instance was to prevent slumping during cure and reduce infiltration of water during wet grinding. Bloecher, U.S. -A- 4,799,939, teaches forming abrasive aggregates particles comprising abrasive particles and glass micro balloons in a phenolic resin bond. These particulate aggregates can then be used to manufacture abrasive products. Other methods of introducing pores into organic bonded abrasive articles are well known, as exemplified by Pohl, in U.S. -A- 1,986,850 in which uniformly distributed hollow spaces are produced in abrasive bodies by gas evolution and use of soluble or sublimable spheres. This increase in cutting rate is, however, usually accompanied by a significant increase in the rate at which the abrasive article is worn down. This ratio of the volume of work material removed to volume of abrasive article worn away is known as the "G-ratio". Generally, high G-ratios are clearly preferred but have not hitherto been obtained with conventional abrasive particles. It is therefore the object of the present invention to provide an abrasive article which has increased cutting rates with decreased wheel wear, i.e. obtaining high G-ratios. This object is solved by the invention by providing an improved abrasive article according to independent claim 1 and a method of making same according to independent claim 11. Further advantageous features of the invention are evident from the dependent claims and the following description and examples. It has been found that the substitution of friable filler particles such as bubble alumina spheres or softer, more friable, particles for a portion of the sintered sol gel alumina grains not only increases the cutting rate, but decreases the wheel wear for unexpectedly high G-ratios. This is a most unexpected result and runs counter to the teachings of the prior art. The present invention provides an abrasive article comprising a uniform mixture of sintered sol-gel aluminous abrasive particles, filler particles and a resinous bond in which all the said particles are mounted and held and yet providing increased cutting rates with decreased wheel wear. The said filler particles provide from 20% to 70% of the volume of particulate matter selected from the group consisting of hollow oxide spheres, friable silicate particles and hollow or solid organic polymer spheres. The invention also provides an abrasive article offering the advantages of sintered sol gel alumina abrasive particles without unacceptable wheel wear. The invention further provides an abrasive article combining excellent cutting rate and acceptable wheel wear characteristics with relatively inexpensive material cost. The invention according to another aspect provides an abrasive article which, for a given grinding rate, uses less power and is less likely to damage a workpiece metallurgically. In view of the above as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto. In general, the invention relates to an abrasive article comprising sintered sol gel alumina abrasive particles such as those described by Leitheiser, Schwabel, and Cottringer, and friable filler particles, all such particles being bonded in a resinous matrix. In describing the filler particles as friable it is intended to convey that, when the abrasive article is in use and abrasive forces act upon both the abrasive particles and the friable filler particles, the filler particles are worn away significantly more rapidly than are the abrasive particles. Friable filler particles as the term is used herein include bubble alumina and other filler particles of about the same or greater friability. Conveniently, the friable filler particles may be present in an amount of up to about 50%, such as from about 5 to 40%, and preferably from 5 to 30% of the total particle weight. This represents from about 20 to 70% and preferably up to about 50% by volume of the particulate material. It is preferred that each sintered sol gel alumina abrasive particle be made up of a multitude of sintered alpha alumina crystals having a size in the order of 0.4 µm or finer. The most preferred sol-gel alumina particles are those that have been produced by a seeding technique such as that described in U.S. -A- 4,623,364. The abrasive article may have the form of a wheel or a block or other structure suitable for an abrading use. This is done prior to curing the resinous matrix such that the article has an essentially uniform structure throughout. According to a further aspect, the present invention provides an abrasive article, comprising a uniform mixture of: (a) sintered sol-gel aluminous abrasive particles, the abrasive being preferably seeded sintered sol-gel aluminous abrasive, (b) filler particles having greater friability than the sintered sol-gel alumina abrasive particles, whereby the filler particles preferably constitute from ten volume percent to sixty volume percent of said article and/or wherein said filler particles preferably are bubble alumina, and (c) a resinous bond in which all the said particles are mounted and held. In this abrasive article additional abrasive particles can be used including fused or sintered alumina, silicon carbide, fused or sintered zirconia, fused or sintered alumina-zirconia, diamond, or CBN. The filler particles are selected from the class consisting of hollow oxide spheres, friable silicate pellets, and hollow or solid organic polymer spheres, or preferable from the class consisting of aluminium oxide bubbles, zirconium oxide bubbles, glass beads, vitrified clay bubbles, vitrified clay pellets and glass bubbles. Preferably, the resin bond is selected from the class consisting of phenol-formaldehyde, phenol-furfural, anilin-formaldehyde, urea-formaldehyde, phenoxy, polyimide, epoxy, urethane, polyester, and combinations thereof, and/or the filler matters are selected from the class consisting of iron pyrites, potassium sulfate, cryolite, sodium chloride, potassium fluoborate, silicon carbide, alumina fluorspar, zinc sulfide, chopped glass fibers, copolymer or vinylidene chloride and vinyl chloride, polyvinyl chloride, polyvinylidene chloride, and mixtures thereof. The sintered sol-gel alumina abrasive particles and said other particles advantageously are present in the amount of approximately 50% and 50%, respectively, by weight of the total amount of abrasive particles. The sintered sol-gel alumina abrasive particles preferably are made up of a multitude of crystallites having a size in the order of 0.4 µm or finer. If the hollow oxide spheres or friable silicate pellets are used, they should range in size from 1.00 to 0.074 µm (10 to 200 mesh). The said other particles should range in size from 1.00 to 0.074 µm (10 to 200 mesh). If the abrasive article contains the hollow oxide spheres or friable silicate pellets, those preferably constitute from ten volume percent to sixty volume percent of said article. DESCRIPTION OF THE PREFERRED EMBODIMENT The resin bonded abrasive bodies of the invention make use of sintered sol gel alumina abrasive grits together with bubble alumina or other friable filler granules to achieve the fast cutting action well known and expected from such combinations together with an unexpectedly high G-ratio and wheel life. This unexpected combination of properties is of great economic importance since lesser quantities of expensive sol gel alumina abrasive are required to produce high performance grinding wheels and other bonded abrasive bodies. The abrasive portion of the inventive bodies in selected from seeded or unseeded sol gel alumina grits with the seeded variation being particularly preferred. These may be combined with up to about 70% of other abrasives, such as diamond, CBN, sintered or fused alumina, silicon carbide, zirconia, or sintered or fused alumina-zirconia. These abrasives may be surface treated with hydrophobic compounds, such as silanes, where grinding with water-based coolants in anticipated. Such treatments are well-known in the art. All of the abrasives used in the three examples which follow were treated with 0.2cc of silane A1102 tm per pound of abrasive and dried at 150°C for 24 hours. Silane A1102 tm was obtained from Union Carbide Corporation, Danbury, Connecticut. The abrasive particles are often of irregular shape as result of the way in which they are prepared. This is, however, not essential. Spherical, pyramidal, cylindrical (with an aspect ratio, L/D, of for example 0.5 to 10), cubic or any other configuration may be selected. The abrasive particle sizes employed will depend on end use for which the article in intended. However, commonly abrasive particle grit sizes of from about 10 to about 200 and preferably from about 16 to about 120 such as for example from about 20 to about 60 grit are found to be suitable. The preferable friable filler particles used in the invention are formed from hollow oxide bubbles such an bubble alumina or other hollow silicate particles but may also comprise solid or porous friable particles such an calcined clay, pumice, feldspar, nepheline syenite and the like, as well as solid and hollow spheres made from an organic polymer or glass. The friable filler size is preferably the same or loss than that of the abrasive particles and, in general, mesh sizes of from 10 to 200 mesh are found to be suitable. A conventional organic resinous binder may be fixed with a variety off additions or modifiers to bind the abrasive grains and friable grains together. Preferably, the organic binder is a thermosetting phenolic resin with or without modifiers such as rubber or epoxy. Examples of resins which may be employed include phenoxy, phenol-furfural, aniline-formaldehyde, urea-formaldehyde, epoxy, cresol-aldehyde, urethane, polyester, polyimides resorcinol-aldehyde, urea-aldehyde, melamine-formaldehyde, and mixtures thereof. The preferred resin bond is a phenolic resin, such as a phenol/formaldehyde resole or novalac. As is well known, there are various inorganic and organic adjuvants which may be put in organic bonded abrasive bodies for improving strength, reducing cost, and most importantly for improving grinding performance. The adjuvants are usually considered to be part of the bond and are in a finely divided state, much smaller than the primary grinding abrasive grits. Suitable conventional and well known adjuvants include cryolite, fluorspar, iron pyrites, zinc sulfide, magnesia, silicon carbide, sodium chloride, potassium fluoborate, calcium oxide, potassium sulfate, copolymer of vinylidene chloride and vinyl chloride (Saran B), polyvinylidene chloride, polyvinyl chloride, other fibers such as glass fiber, sulfides, chlorides, sulfates, fluorides and mixtures thereof. The abrasive articles of the invention are made by forming a mixture of the abrasive particle(s) and the friable filler particles with the resin in its uncured state, and thereafter forming the mixture into the desired shape and curing the resin. It is often, also, desirable to fire the article to drive off volatile material and to harden it. Typically, the shape of the abrasive article will be an abrasive wheel or other abrasive tool. The invention is now further described with reference to the following Examples which are for the purpose of illustration only and are intended to imply no essential limitation to the shape of the invention itself. Example 1 A series of nine cold-pressed resin bonded wheel compositions were prepared as follows for grinding tests. The batch compositions are given in Table 1. BATCH WEIGHTS IN POUNDS Wheel A C D E G J K Density 2.54 2.38 2.04 2.17 2.11 2.24 1.82 46 grit size seeded sol-gel alumina abrasive 0 6.33 7.39 11.57 7.14 11.21 13.77 46 grit size fused alumina abrasive 20.11 10.58 0 0 0 0 0 Bubble alumina 0.5-1.0mm dia. 0 0 0 0 0 0 3.60 46 grit size Syenite 333 tm 0 2.99 11.65 7.83 11.27 7.58 0 Varcum 29717 tm powdered phenolic resin 2.30 2.46 2.87 2.70 3.79 3.57 4.25 Varcum 2930 tm liquid phenolic resin 0.37 0.40 0.46 0.44 0 0 0 Cryolite -200 mesh 2.10 2.24 2.62 2.46 2.46 2.32 2.76 Carbon black 0.05 0.05 0.06 0.05 0 0 0 Chloroflo 40 tm 50cc 50cc 50cc 50cc 40cc 0 0 Furfural 165cc 156cc 191cc Quicklime 0.54 0.51 0.61 Varcum 2930 tm Oxy Chem Corporation, Niagara Falls, New York. Varcum 29717 tm is a rubber modified powdered phenolic resin available from Varcum Division, Oxy Chem Corporation, Niagara Falls, New York. Chloroflo 40 tm is a liquid chlorinated paraffin obtainable from Dover Chemical Company, Dover, Ohio. Standard mixing procedures for the preparation of resin bonded abrasive mixes were followed, i.e., the abrasive and any friable filler particles were placed in a rotating mixing pan and wet with liquid resin or furfural before the introduction of the powdered resin and any adjuvants. After five minutes of mixing the batch was ready to press into wheels. Wheels were pressed to 5 1/8 inch diameter (130.2 mm) with 1 inch (25.4 mm) hole and 0.563 inch (14.3 mm) in thickness using the proper weight of mix to provide the correct final density. In each case this density was calculated to yield 52 volume percent of abrasive or abrasive plus friable filler particles. The wheels were cold pressed. After pressing the wheel were placed on alumina batts and cured in a convection-type electric oven at 175°C for 15 hours. The cured wheels were then finished to 5 inches (127 mm) in diameter and hole was reamed to 1 1/4 inches (31.8 mm) in diameter. The prepared wheels were then tested in a slot-grinding mode on 4340 steel blocks, hardened to Rc48, 16 1/8 inches (409.6 mm) in length. For this test the face of each wheel was reduced to 1/4 inch in width (6.35 mm) and slots were ground lengthwise into the 4340 steel block using three separate infeeds: 0.5 mils, 1.0 mils and 2.0 mils (0.0126 mm, 0.0254mm and 0.1016 mm). Total depth of infeed for each test was 100 mils (2.54 mm). The test was conducted on a surface grinder with table speed set at 50 feet per minute (15.24 meters per minute) and wheel speed set at 6500 surface feet per minute (33.02 meters per second). The test was conducted wet using E55 tm coolant (available from the White & Bagley Co., Worcester, Massachusetts), diluted with 40 parts of city water. Careful measurements were made of wheel wear and metal removal as well as the power consumed in each slot grind. The results of the grinding test are given in Table 2 as follows: SLOT GRINDING TEST RESULTS Friable/Filler Wheel Marking Feed (mils) G Ratio (S/W) Relative G Ratio Relative (start/finish) 100% 57A tm fused alumina A (c) 0.5 13.13 100 100 100 1.0 5.61 100 100 100 2.0 2.51 100 100 100 50% 57A tm 30% sol-gel 20% Syenite C 0.5 50.44 384 71 83 1.0 13.61 243 83 123 2.0 4.65 185 96 92 30% sol-gel alumina 70% Syenite D 0.5 25.53 194 46 88 1.0 10.96 195 70 100 2.0 3.38 135 104 81 50% sol-gel alumina 50% Syenite E 0.5 68.43 521 50 94 1.0 19.79 353 74 124 2.0 6.02 240 92 81 30% sol-gel alumina 70% Syenite G 0.5 67.07 511 50 94 1.0 14.83 264 78 141 2.0 3.79 151 92 96 50% sol-gel alumina 50% Syenite J 0.6 67.69 516 50 100 1.0 19.66 350 87 112 2.0 7.55 301 100 96 50% sol-gel alumina 50% bubble alumina K 0.5 67.59 515 63 106 1.0 44.99 802 117 153 2.0 12.81 510 116 92 57A refers to 57 Alumdum tm which is a fused alumina abrasive and is a product of the Norton Company, Worcester, Massachusetts. Syenite 333 tm is a friable mined mineral, nepheline syenite, available from Indusmin Division, Havelock, Ontario, Canada. It is predominantly a vitrified alumina silicate. All percentages are by volume in the above Table 2. The relative grinding results shown in Table 2 are calculated by dividing the actual value by the value of the standard 57A tm fused alumina wheel A and multiplying by 100. Thus, all relative values for the standard wheel are equal to 100. The preferred invention wheel K, whose abrasive portion is composed of 50% by volume sol-gel alumina and 50% by volume bubble alumina, showed a G-ratio 500 to 800% greater than the standard fused alumina wheel A. Power requirements for wheel K were not excessive; in fact, at the heaviest final downfeed wheel K drew slightly less power than standard wheel A. Wheels C, D, E, G, and J represent another embodiment of the invention in that the diluent for the sol-gel abrasive is a friable silicate particle, in this case, nepheline syenite. From the data in Table 2, the relative G-ratio of these wheels was as much as 516% greater than that of the standard fused alumina wheel A. Wheel J, whose abrasive portion consisted of volume proportions of 50% sol-gel alumina and 50% nepheline syenite, showed a relative G-ratio 516% greater than the standard at the lowest infeed and 300% greater than the standard at the highest infeed without an increase in power. Example 2 A series of six test wheels of the same size as those in Example 1 were prepared from the batch compositions shown in Table 3. BATCH WEIGHTS IN POUNDS Wheel marking 1(c) 2(c) 3(c) 4 5 Density 2.54 2.61 2.6 1.83 1.82 46 grit size seeded sol-gel alumina abrasive 0 0 3.48 4.94 8.27 46 grit size fused alumina abrasive 12.14 11.18 8.31 3.36 0 Bubble alumina 0.5-10mm dia. 0 0 0 2.16 2.16 Varcum 29717 tm powdered phenolic resin 1.39 1.79 1.85 2.62 2.63 Varcum 2930 tm liquid phenolic resin 0.22 0 0 0 0 Cryolite -200 mesh 1.27 1.16 1.20 1.70 1.71 Chloroflo 40 tm 23cc 24cc 24cc 24cc 24cc Furfural 80cc 81cc 114cc 115cc Quicklime 0.26 0.26 0.38 0.38 Methods of mixing, cold pressing and curing were the same as in Example 1. After finishing to size these test wheels were subjected to the same slot grinding test as in Example 1 with the exception that horsepower was measured by dynamometer. The results of grinding these are shown in Table 4. SLOT GRINDING TEST RESULTS Abrasive/Friable Filler Wheel Marking Feed (mils) G Ratio (S/W) Relative G Ratio Relative Power 100% 57A tm fused alumina 1(c) 0.5 15.37 100 100 1.0 6.37 100 100 2.0 3.10 100 100 100% 57A tm fused alumina 2(c) 0.5 18.02 117 192 1.0 9.32 146 125 2.0 5.00 161 137 70% 57a tm fused alumina 30% sol-gel alumina 3(c) 0.5 30.85 201 149 1.0 16.25 255 125 2.0 4.80 155 93 20% 57A tm fused alumina 30% sol-gel alumina 50% bubble Alumina 4 0.5 50.13 326 113 1.0 21.70 341 91 2.0 6.43 207 84 50% sol-gel alumina 50% bubble alumina 5 0.5 81.01 527 72 1.0 38.46 604 80 2.0 16.75 540 87 All percentages given by volume. Wheels 1, 2 and 3 are for comparative purposes. The test results of Example 2 as shown in Table 4 again illustrate the marked increase in G-ratio of the preferred invention wheels. Both wheels 3(c) and 4 contain 30% sintered sol-gel alumina abrasive by volume of total abrasive; however, the remainder of the abrasive portion of wheel 3 is 70% fused alumina. Wheel 4, containing 50% bubble alumina, considerably outperforms wheel 3 in both G-ratio and power even though both contain the same volume (30%) of sintered sol-gel alumina. Wheel 5, whose abrasive portion is 50% sintered sol-gel alumina and which contains 50% bubble alumina, outperformed the standard fused alumina wheel by 527 to 604% in G-ratio and drew 13% to 27% less power. Example 3 In this series of test wheels, various blends of sintered sol-gel alumina with fused alumina and bubble alumina were evaluated. The compositions of the mix batches from which these wheels were pressed are given in Table 5. BATCH WEIGHTS IN POUNDS Wheel marking 6 7 8 9 10 11 Density 2.37 2.02 2.01 2.00 2.09 2.00 46 grit sol-gel alumina 1.69 1.99 5.99 10.03 9.63 10.03 46 grit 57A tm fused alumina 12.13 8.14 4.86 0 0 0 0.5mm-1mm bubble alumina 1.49 4.38 4.40 4.42 4.24 4.42 Varcum 29717 tm powdered phenolic resin 2.70 2.90 3.19 3.20 3.06 3.20 Cryolite -200 mesh 1.75 1.88 2.06 2.07 0 2.07 Iron pyrites 0 0 0 0 2.39 0 Potassium sulfate 0 0 0 0 0.45 0 Chloroflo 40 tm 32cc 32cc 32cc 32cc 32cc 32cc Furfural 118cc 126cc 139cc 139cc 154cc 139cc Quicklime 0.39 0.42 0.46 0.46 0.44 0.46 Methods of mixing, cold pressing and curing were the same as in Example 1. After finishing to size these test wheels were subjected to the same slot grinding test as in Example 1 with the exception that horsepower was measured by dynamometer. The results of the grinding test are shown in Table 6. SLOT GRINDING TEST RESULTS Abrasive/Friable Filler Wheel Marking Feed (mils) G Ratio (S/W) Relative G Ratio Relative Power 70% 57A tm fused alumina 10% sol-gel alumina 20% bubble alumina 6 0.5 22.79 148 105 1.0 11.49 180 93 2.0 2.44 79 89 40% 57A tm fused alumina 10% sol-gel alumina 50% bubble alumina 7 0.5 26.40 172 92 1.0 10.70 168 91 2.0 3.86 124 75 20% 57A tm fused alumina 30% sol-gel alumina 50% bubble alumina 8 0.5 65.58 427 73 1.0 22.67 356 79 2.0 5.14 166 63 50% sol-gel alumina 50% bubble alumina (cryolite filler) 9 0.5 107.47 699 57 1.0 48.93 768 77 2.0 8.54 275 65 50% sol-gel alumina 50% bubble alumina (iron pyrites + K₂SO₄ fillers) 10 0.5 91.49 595 60 1.0 45.31 711 74 2.0 9.92 320 69 50% sol-gel alumina 50% bubble alumina (both silane treated) 11 0.5 67.01 436 59 1.0 45.49 714 69 All percentages are by volume. The grinding test results from Example 3 again show the unexpectedly large increase in G-ratio obtained from combinations of sintered sol-gel alumina and alumina bubbles and other embodiments of the invention. Wheels 9, 10, and 11 which contain 50% sintered sol-gel alumina and 50% alumina bubbles by volume of the abrasive portion gave G-ratios 275% to 768% greater than a standard wheel containing 100% fused alumina. The power expended in grinding was 25% to 40% less for the invention wheel indicating that the invention wheel is much more efficient and would be less likely to cause metallurgical damage to the workpiece. Example 4 The following results were obtained in a commercial hot mill roll grinding operation. The rolls were of high chromeiron and the grinding was done at essentially constant full power. The results obtained are set forth in Table 7 below. Wheel Abrasive Total Metal Remove (in.) Relative G Ratio Metal Removal Rate Comments 12 50% 57A tm 50% Black SiC 1.7 100% 100% Chatter 13 20% Sol-Gel Alumina 80% Green SiC 4.1 240% 125% No Chatter 14 20% Sol Gel Alumina 60% Green Sic 20% Bubble Alumina 5.2 310% 250% No Chatter By replacing 20% of SiC (silicon carbide) with bubble alumina (Wheel 14 compared to Wheel 13) resulted in a large improvement in both Metal Removal Rate and G Ratio. This is a highly unusual result because, normally, improvements in G Ratio are gained at the expense of metal removal rate - and vice versa. The embodiments disclosed herein are illustrative of the unexpectedly high G-ratios obtainable when hollow oxide spheres or friable particles are incorporated into abrasive bodies whose abrasive portion is wholly or in part composed of sintered sol-gel alumina grits and such embodiments are not in any way limiting. Example 5 This example shows a hot mill grinding of a high chrome iron roll. The grinding was carried out in a commercial plant at essentially full power level. The results are set forth in Table 8 below. Wheel Vo. % Composition Total of Steel Removed (inches) Rel. G-Ratio Comments 15 57A - 50% 1.7 100% Chattering 37C - 50% 16 SG - 20% 4.1 240% No chatter 39C - 80% 17 SG - 20% 5.2 310% No chatter 39C - 60% BA - 20% SG = Seeded Sol-Gel alumina 37C = Black silicon carbide 39C = Green silicon carbide BA = Bubble alumina The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

Claims: Abrasive article, comprising a uniform mixture of: (a) sintered sol-gel aluminous abrasive particles, (b) filler particles providing from 20% to 70% of the volume of particulate matter selected from the group consisting of hollow oxide spheres, friable silicate particles, and hollow or solid organic polymer spheres and (c) a resinous bond in which all the said particles are mounted and held. Abrasive article as recited in claim 1, wherein additional abrasive particles are used, selected from the group consisting of fused or sintered alumina, silicon carbide, fused or sintered zirconia, fused or sintered alumina-zirconia, diamond, or CBN. Abrasive article as recited in claim 1 or 2, wherein said filler particles are selected from the group of aluminum oxide bubbles, zirconium oxide bubbles, glass bubbles, glass beads, vitrified clay bubbles, vitrified clay pellets. Abrasive article as recited in one of the preceding claims, wherein the resin bond is selected from the class consisting of phenol-formaldehyde, phenol-furfural, aniline-formaldehyde, urea-formaldehyde, phenoxy and mixtures thereof. Abrasive article as recited in one of the preceding claims further comprising adjuvants which are selected from the group consisting of iron pyrites, potassium sulfate, cryolite, sodium chloride, potassium fluoborate, silicon carbide, fluorspar, zinc sulfide, glass fibers, copolymer of vinylidene chloride and vinyl chloride, polyvinyl chloride, polyvinylidene chloride, and mixtures thereof. Abrasive article as recited in one of the preceding claims, wherein the sintered sol-gel alumina abrasive particles and said filler particles are present in the amount of approximately 50% and 50%, respectively, by weight of the total amount of abrasive particles. Abrasive article as recited in one of the preceding claims, wherein the sintered sol-gel alumina abrasive particles are made up of a multitude of crystallites having a size in the order of 0.4 µm or finer. Abrasive article as recited in one of the preceding claims, in which the said filler particles range in size from 1.00 to 0.074 mm (10 to 200 mesh). Abrasive article as recited in one of the preceding claims, in which the said filler particles constitute from ten volume percent to sixty volume percent of said article. Abrasive article as recited in one of the preceding claims, wherein said sintered sol gel aluminous abrasive is a seeded sintered sol gel aluminous abrasive. A method of forming an abrasive article which comprises: A. forming a uniform mixture comprising: 1) sintered sol-gel aluminous abrasive particles, 2) filler particles providing from 20% to 70% of the volume of particulate matter selected from the group consisting of hollow oxide spheres, friable silicate particles, and hollow or solid organic polymer spheres and 3) a resinous bond in which all the said particles are mounted and held; B. shaping the mixture into that of the desired article; and C. curing the resin bond.

Inventors: NARAYANAN KESH S, RAMAKRISHNAN MUNI S, NARAYANAN, KESH S., RAMAKRISHNAN, MUNI S.
Applicants: NORTON CO, NORTON COMPANY
Application year: 1990
Main classification: B24D3
IPC codes: B24D3, C09K3