Patent Application
20160214232
Bonded abrasive articles have abrasive particles bonded together by a bonding medium. There is an increasing demand for high-performance abrasive articles such as grinding wheels that abrade material faster while meeting tight tolerances without damaging workpieces.
Abrasive articles such as stones, hones and wheels may be driven by a stationary-mounted motor such as, for example, a bench grinder, or attached and driven by a hand-operated portable grinder. Hand-operated portable grinders are typically held at a slight angle relative to the surface of the workpiece, and may be used to grind, for example, welding beads, flash, gates, and risers off castings.
Disposing a grinding layer at a surface of or within the interior of a bonded abrasive article was found to surprisingly enhance cutting and grinding performance compared to conventional bonded discs. In particular, among other advantages, the total cut surprisingly increased.
In one aspect, the present disclosure provides a bonded abrasive article comprising a matrix and a grinding layer. The matrix comprises matrix abrasive particles and a matrix binder. The grinding layer comprises erectly-oriented abrasive particles and a grinding layer binder. The grinding layer is disposed on an exterior surface of the bonded abrasive article or is disposed at least partly within the interior of the bonded abrasive article.
In another aspect, the present disclosure provides a method of forming a bonded abrasive article. The method comprises dispersing erectly-orientable abrasive particles on a first support, applying a grinding layer binder to a second support, contacting the grinding layer binder with the erectly-orientable abrasive particles; and curing the grinding layer binder.
In yet another aspect, the present disclosure provides a method of forming a bonded abrasive article, the method comprising applying a matrix mixture to a grinding layer, the matrix mixture comprising a curable matrix binder and matrix abrasive articles, the grinding layer comprising erectly-oriented grinding abrasive particles; and curing the matrix binder.
Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure.
As used herein, variations of the words “comprise”, “have”, and “include” are legally equivalent and open-ended. Therefore, additional non-recited elements, functions, steps or limitations may be present in addition to the recited elements, functions, steps, or limitations.
“Bonded abrasive articles” are abrasive articles having bonded abrasives, including, without limitation, grinding wheels, grinding discs, grinding cylinders or abrasive articles in any other forms.
While the above-identified drawing figures set forth several embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. The figures may not be drawn to scale. Like reference numbers may have been used throughout the figures to denote like parts.
Referring now to
The matrix 13 includes matrix abrasive particles 12 and a matrix binder 14. The matrix 13 may be shaped like a disc, a wheel, a cylinder or any other suitable shape known in the art. The matrix 13 may have openings, including central openings, such as central holes. The matrix 13 may have a depressed center with a central hole. The matrix 13 may have a backing, including paper, fabric, or film backings, or any other backing known in the art or described below or combinations thereof.
The matrix binder 14 holds the matrix abrasive particles 13 in a fixed configuration within the matrix 13 and provides a rigid structure to the matrix 13. The matrix binder 14 may contain any suitable organic, resin, metallic, vitrified or any other binder known in the art such as binders described below or combinations thereof.
The matrix abrasive particles 12 may be any abrasive particles known in the art, including conventional crushed abrasive particles, shaped abrasive particles, or any abrasive particles described below or their combinations thereof. The matrix abrasive particles 12 may be randomly dispersed within the matrix 14, or may be dispersed in a predetermined pattern within the matrix 14. The matrix abrasive particles 12 may be randomly oriented within the matrix 14, or may be oriented in predetermined orientations within the matrix 14. Some, all or none of the matrix abrasive particles 12 may be oriented in substantially similar or parallel orientations within the matrix 13. Some, all, or none of the matrix abrasive particles 12 may be of substantially same, similar or different sizes. Some, all, or none of the matrix abrasive particles 12 may have substantially same, similar or different shapes. The matrix abrasive particles 12 can contain abrasive particles of the same or different chemical compositions, with the same, similar, dissimilar or different chemical and physical properties such as electrostatic attraction, hardness, and fracture toughness. Some, all or none of the matrix abrasive particles 12 may be completely immersed within the matrix 14. Some or all of the matrix abrasive particles 12 may be incompletely immersed within the matrix 14. The matrix abrasive particles 12 abrade surfaces to a varying extent, such as low abrasion, medium abrasion, high abrasion or any other known abrasive extent, depending on factors such as size, geometry, orientation and material of the matrix abrasive particles 12, and factors such as the pressure and speed at which surfaces are exposed to the matrix 13.
The grinding layer 16 contains erectly-oriented abrasive particles 18 bonded and held in an erectly-oriented configuration by a grinding layer binder 20. In an embodiment, the grinding layer 16 also contains abrasive particles that are not erectly-oriented. In an embodiment, the grinding layer 16 has a thickness that is less than the thickness of the matrix 13. In an embodiment, the grinding layer 16 has a thickness that is 95%, or 90%, or 85%, or 80%, or 75%, or 70%, or 65% or 60% or 55% or 50% or any other percentage that is less than 100% but greater than 0% of the thickness of the matrix 13. In another embodiment, the grinding layer binder 20 is sufficiently thick that all the erectly-oriented particles are immersed within the grinding layer 16. In yet another embodiment, the grinding layer binder 20 has a thickness that is less than the height of the erectly-oriented particles 18 such that the erectly-oriented particles 18 at least partially protrude from the exposed surface of the grinding layer binder 20.
The grinding layer 16 may optionally be bonded to the matrix 13 by an adhesive. The grinding layer 16 may optionally be bonded to the matrix 13 by the grinding layer binder 20. The grinding layer 16 may be optionally bonded to the matrix 13 by an additional binder layer containing any suitable binder known in the art, including any one or more suitable binders described below, including organic, resin, metallic, or vitrified binders.
The grinding layer binder 20 holds the erectly-oriented abrasive particles 18 in a fixed configuration within the grinding layer 16. The grinding layer binder 20 may contain any suitable organic, resin, metallic, vitrified or any other binder known in the art such as binders described below or those used in make coats or combinations thereof. The grinding layer binder 20 can be formed by coating a curable grinding layer precursor onto a major surface of the matrix 13. The grinding layer precursor refers to coatable materials applied to the matrix 13 which can be hardened, for instance, by curing, to form the grinding layer 16. The grinding layer binder 20 can also be formed by coating a grinding layer precursor onto any other suitable holding surface that can be used to assemble the grinding layer 16. The grinding layer precursor or the grinding layer binder 20 may comprise, for example, glue, phenolic resin, aminoplast resin, urea-formaldehyde resin, melamine-formaldehyde resin, urethane resin, free-radically polymerizable polyfunctional (meth)acrylate (e.g., aminoplast resin having pendant alpha,beta-unsaturated groups, acrylated urethane, acrylated epoxy, acrylated isocyanurate), epoxy resin (including bis-maleimide and fluorene-modified epoxy resins), isocyanurate resin, and any binder described below or mixtures thereof.
Erectly-oriented abrasive particles 18 are abrasive particles having a predetermined axis that is erectly-oriented with respect to the grinding layer 16. The predetermined axis can be any geometric axis passing through the article. In an embodiment, the predetermined axis is the longest axis passing through each of the erectly-oriented abrasive particles 18. In another embodiment, the predetermined axis is the shortest axis passing through each of the erectly-oriented abrasive particles 18. In yet another embodiment, the predetermined axis is the axis that passes through a sharp abrasive vertex of each of the erectly-oriented abrasive particles 18. In a further embodiment, the predetermined axis passes through the center of mass of each of the erectly-oriented abrasive particles 18. In still other embodiments, the predetermined axis is any other geometric axis.
Erectly-oriented abrasive particles 18 include particles with a predetermined axis that can assume any suitable angle ranging from, without limitation, 30° to 90° with respect to the grinding layer 16. For instance, in an embodiment, the predetermined axis is substantially normal to the grinding layer 16. A substantially perpendicular or normal predetermined axis has an angle that is close to 90° or is a right angle within a predetermined tolerance with respect to the grinding layer 16. In another embodiment, the predetermined axis assumes non-perpendicular angles that are less than 90°, for instance, any angle within the range of, without limitation, 30° to 89°.
In an embodiment, erectly-oriented abrasive particles 18 include abrasive particles that have at least one vertex that is elevated with respect to the grinding layer erectly-oriented abrasive particles 18 include abrasive particles. In another embodiment, erectly-oriented abrasive particles 18 include abrasive particles that have at least one vertex that protrudes from the grinding layer 16. A vertex is any geometric vertex such as a tip, an end, a point, a protrusion or any other geometric vertex of an abrasive particle.
In an embodiment, all of the abrasive particles in the grinding layer 16 are erectly-oriented abrasive particles 18. In another embodiment, at least 10% by weight of the abrasive particles in the grinding layer are erectly-oriented abrasive particles 18. In yet another embodiment, at least 20% by weight, or at least 30% by weight, or at least 40% by weight, or at least 50% by weight, or at least 60% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight of the abrasive particles are erectly-oriented abrasive particles. In other embodiments, the abrasive particles in the grinding layer contain any amount, ranging from 10% to 100% by weight, of erectly-oriented abrasive particles 18.
The erectly-oriented particles 18 can comprise shaped abrasive particles or formed abrasive particles. In an embodiment, the shaped abrasive particles have polygonal faces and a polygonal base. In another embodiment, the shaped abrasive particles have a triangular face and a trapezoidal base. In other embodiments, the erectly-oriented abrasive particles 18 contain other abrasive particles known in the art, including conventional crushed abrasive particles, shaped abrasive particles, or any abrasive particles described below or their combinations thereof, disposed in the grinding layer 16 such that a predetermined axis of the particles is erectly-oriented. In one embodiment, the predetermined axis is perpendicular to one side of a triangular shaped abrasive particle and extends through the opposing vertex or tip of the triangular shaped abrasive particle such that the erectly-orientated abrasive particles are positioned as shown in
Abrasive particles can include shaped, fractured abrasive particles, as disclosed in U.S. Pat. No. 8,034,137; abrasive shards, shaped abrasive particles with openings, or dish shaped abrasive articles as disclosed in U.S. Pat. No. 8,123,828; dish-shaped abrasive particles with a recessed surface as disclosed in U.S. Pat. No. 8,142,891; shaped abrasive particles with an opening as disclosed in U.S. Pat. No. 8,142,532; shaped abrasive particles with grooves as disclosed in published U.S. Pat. Application No. 2010/0146867; shaped abrasive particles with a sloping sidewall as disclosed in U.S. Pat. No. 8,142,531; shaped abrasive particles with low roundness factor as disclosed in published U.S. Pat. Application No. 2010/0319269; dual tapered shaped abrasive particles as disclosed in P.C.T. Application No. PCT/US2010/057713; and shaped abrasive particles disclosed in published U.S. Pat. Application No. 2011/0146509.
The erectly-oriented abrasive particles 18 may be randomly dispersed across the grinding layer 16, or may be dispersed in a predetermined pattern across the grinding layer 16. The erectly-oriented particles 18 may be oriented in different orientations across the grinding layer 16 such that even though each of the erectly-oriented particles 18 is substantially erectly-oriented, each of the erectly-oriented particles 18 assumes different orientations. Some, all or none of the erectly-oriented abrasive particles 16 may be oriented in a substantially similar or parallel orientation across the grinding layer 16. Some, all, or none of the erectly-oriented abrasive particles 18 may be of substantially the same, similar or different sizes. Some, all, or none of the erectly-oriented abrasive particles 18 may have substantially same, similar or different shapes. The erectly-oriented abrasive particles 18 can contain abrasive particles of the same or different chemical compositions, with the same, similar, dissimilar or different chemical and physical properties such as electrostatic attraction, hardness, and fracture toughness. The erectly-oriented abrasive particles 18 may abrade surfaces to varying extents, such as low abrasion, medium abrasion, high abrasion or any other known abrasive extent, depending on factors such as size, geometry, orientation and composition of the erectly-oriented abrasive particles 18, and factors such as the pressure and speed at which surfaces are exposed to the grinding layer 16 containing the erectly-oriented abrasive particles 18.
The matrix binder 14 and the grinding layer binder 20 may be the same or different (chemically or physically different). For example, the matrix binder 14 can be a first phenolic binder and the grinding layer binder 20 can be a second phenolic binder that is different from the first phenolic binder.
In an embodiment, an optional size layer 22 is optionally coated over the erectly-oriented particles 18 at the surface of the grinding layer 16. The size layer 22 may be coated by any conventional technique, such as knife coating, spray coating, roll coating, curtain coating, rotogravure coating, and the like. The size layer 22 maintains the integrity of the grinding layer 16, including the erectly-oriented abrasive particles 18. The size layer 22 may contain any suitable organic, resin, metallic, vitrified or any other sizing agent or binder known in the art such as binders described below or those used in sizing coats or combinations thereof. The size layer 22 can be formed by coating a curable size layer precursor onto the exposed surface of the grinding layer 16. The size layer precursor refers to coatable materials applied to the grinding layer 16, for example, over the top of the erectly-oriented abrasive particles 18. The size layer precursor can be hardened, for instance, by curing, to form the size layer 22. The size layer precursor or the size layer binder 20 may comprise, for example, glue, phenolic resin, aminoplast resin, urea-formaldehyde resin, melamine-formaldehyde resin, urethane resin, free-radically polymerizable polyfunctional (meth)acrylate (e.g., aminoplast resin having pendant alpha,beta-unsaturated groups, acrylated urethane, acrylated epoxy, acrylated isocyanurate), epoxy resin (including bis-maleimide and fluorene-modified epoxy resins), isocyanurate resin, or any binder described below or mixtures thereof.
The matrix binder 14, the grinding layer binder 20, or the size layer 22 can each further comprise additives known in the art, such as, for example, fillers, grinding aids, wetting agents, surfactants, dyes, pigments, coupling agents, or any other additives described herein and combinations thereof.
In an embodiment, the matrix 13 is a disc having a diameter of 7 inches with a central hole of diameter ⅞ inch. The grinding layer 16 is disposed on one of the major surfaces of the matrix 13. The combined thickness of the matrix 13 and the grinding layer 16 is ⅛ inch. Thus the bonded abrasive article is of diameter 7 inches, with a central hole of diameter ⅞ inch. The bonded abrasive article can have a depressed central region, for instance, as in a type 27 disc.
In an embodiment, the grinding layer 16 further optionally comprises a backing 24. The backing 24 may be disposed at the back face 17 of the grinding layer 16, such that the backing 24 is disposed between the matrix 13 and the back face 17. The backing 24 may be continuous, for instance, extending continuously across the bottom unexposed surface between the grinding layer 16 and the matrix 13. The backing 24 may be discontinuous, for instance, extending in regular or irregular patterns or patches across the bottom unexposed surface between the grinding layer 16 and the matrix 13. The backing 24 helps in retaining the configuration of the grinding layer 16, the grinding layer binder 18, and the erectly-oriented abrasive particles 18. The backing 24 may comprise any backing known in the art, including paper, fabric, or film backings, or any other backing known in the art or described below or combinations thereof. In another embodiment, the backing 24 can comprise a scrim material such as an open weave woven or knitted material to which the erectly-oriented abrasive particles are applied. The scrim backing for the grinding layer 16 can also be used to reinforce the matrix 14; especially, when the grinding layer 16 is primarily disposed within the matrix 14.
In an embodiment, the grinding layer 16 comprises the backing 24, the grinding layer binder 20, erectly-oriented abrasive particles 18, and the size layer 22. In another embodiment, the grinding layer 16 comprises a coated abrasive article comprising the backing 24, the grinding layer binder 20, erectly-oriented abrasive particles 18, and the size layer 22.
The grinding layer 16 is optionally attached to the matrix by an adhesive layer 26. In an embodiment, the grinding layer 16 comprises the adhesive layer 26. In another embodiment, the grinding layer 16 comprises both the backing 24 and the adhesive layer 26. In yet another embodiment, the grinding layer 16 comprises an abrasive article and the adhesive layer 26, the abrasive article comprising the backing 24, the grinding layer binder 20, erectly-oriented abrasive particles 18, and the size layer 22, wherein the adhesive layer 26 is disposed between the backing 24 and the matrix 13.
The adhesive layer 26 can comprise any adhesive known in the art, including but not limited to pressure sensitive adhesives, curable epoxies, phenolics, resins, silicones, acrylics, and styrene-butadiene copolymers or combinations thereof.
In an embodiment, the grinding layer 16 is disposed partly within the interior of the matrix 13, such that the matrix 13 covers at least a portion of the grinding face 19. In another embodiment, the grinding layer 16 is disposed completely within the interior of the matrix 13 such that the matrix 13 substantially covers the grinding face 19.
In an embodiment, the back face 17′ of the first grinding layer 16′ is bonded to the matrix 13. In another embodiment, the first grinding layer 16′ comprises a backing 24 and the matrix 13 is bonded to the backing 24. In yet another embodiment, the first grinding layer 16′ comprises a backing 24 and an adhesive layer 26 and the matrix 13 is bonded to the backing 24 by the adhesive layer 26.
In an embodiment, multiple grinding layers 16 are disposed such that some, all or none of the multiple grinding layers 16 are disposed at the surface of matrix 13, some, all or none of the multiple grinding layers 16 are disposed partly within the interior of matrix 13, and some, all or none of the multiple grinding layers 16 are disposed completely within the interior of matrix 13.
The electrostatic field can be generated using any known electrostatic field generating apparatus known in the art. For example, a useful electrostatic field generating apparatus includes electrodes having an electrical potential applied between them with one electrode placed above the matrix 13 and the opposing electrode placed below the first support 28. The electrical potential can be supplied by a suitable A.C. or D.C. power supply. In an embodiment, shaped electrodes are used to apply the abrasive grains 18′ in a predetermined pattern, for example, as disclosed in U.S. Pat. No. 6,511,713.
In an embodiment, the first support 28 is stationary. In another embodiment, the first support 28 comprises a moving belt or surface. In an embodiment, the matrix 13 is stationary. In another embodiment, the matrix 13 is moved as the abrasive particles 18′ are electrostatically attracted towards the matrix 13. In various embodiments, at least some, or a majority, or substantially all, of the abrasive particles 18′ are attracted to the matrix 13 and attach to the coating of the grinding layer precursor 20′.
In an embodiment, the grinding layer binder precursor 20′ is hardened, for example, by curing, after the abrasive particles 18′ have been attached, while retaining their erectly-oriented configuration, to form the cured grinding layer binder 20 with erectly-oriented abrasive particles 18. In another embodiment, the grinding layer binder precursor 20′ is partially cured before abrasive particles 18′ are attached to it, and completely cured after the abrasive particles 18′ are attached.
Abrasive particles, binders, fillers, backings, grinding aids and other additives that can be used in various embodiments are described below.
Useful abrasive particles include conventional abrasive particles including any abrasive particles known in the abrasive art. Exemplary useful abrasive particles include fused aluminum oxide based materials such as aluminum oxide, ceramic aluminum oxide (which may include one or more metal oxide modifiers and/or seeding or nucleating agents), and heat-treated aluminum oxide, silicon carbide, black silicon carbide, green silicon carbide, co-fused alumina-zirconia, diamond, ceria, titanium diboride, cubic boron nitride, boron carbide, garnet, flint, emery, sol-gel derived abrasive particles, and mixtures thereof. The abrasive particles may be in the form of, for example, individual particles, agglomerates, composite particles, and mixtures thereof.
Useful crushed abrasive particles include, for example, crushed particles of fused aluminum oxide, white fused aluminum oxide, ceramic aluminum oxide materials such as those commercially available under the trade designation 3M CERAMIC ABRASIVE GRAIN from 3M Company of St. Paul, Minn., titanium diboride, tungsten carbide, titanium carbide, sol-gel derived abrasive particles, iron oxide, chromia, zirconia, titania, silicates, tin oxide, silica (such as quartz, glass beads, glass bubbles and glass fibers) silicates (such as talc, clays (e.g., montmorillonite), feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate). Examples of sol-gel derived abrasive particles can be found in U.S. Pat. No. 4,314,827 (Leitheiser et al), U.S. Pat. No. 4,623,364 (Cottringer et al); U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.); and U.S. Pat. No. 4,881,951 (Monroe et al.). It is also contemplated that the abrasive particles could comprise abrasive agglomerates such, for example, as those described in U.S. Pat. No. 4,652,275 (Bloecher et al.) or U.S. Pat. No. 4,799,939 (Bloecher et al).
The abrasive particles may, for example, have an average diameter of at least about 0.1 micrometer, at least about 1 micrometer, or at least about 10 micrometers, and less than about 10,000 micrometers, or less than about 8,000 micrometers, or less than about 5,000 micrometers, although larger and smaller abrasive particles may also be used. For example, the conventional abrasive particles may have an abrasives industry specified nominal grade. Such abrasives industry accepted grading standards include those known as the American National Standards Institute, Inc. (ANSI) standards, Federation of European Producers of Abrasive Products (FEPA) standards, and Japanese Industrial Standard (JIS) standards. Exemplary ANSI grade designations (i.e., specified nominal grades) include: ANSI 12 (1842 μm), ANSI 16 (1320 μm), ANSI 20 (905 μm), ANSI 24 (728 μm), ANSI 36 (530 μm), ANSI 40 (420 μm), ANSI 50 (351 μm), ANSI 60 (264 μm), ANSI 80 (195 μm), ANSI 100 (141 μm), ANSI 120 (116 μm), ANSI 150 (93 μm), ANSI 180 (78 μm), ANSI 220 (66 μm), ANSI 240 (53 μm), ANSI 280 (44 μm), ANSI 320 (46 μm), ANSI 360 (30 μm), ANSI 400 (24 μm), and ANSI 600 (16 μm). Exemplary FEPA grade designations include P12 (1746 μm), P16 (1320 μm), P20 (984 μm), P24 (728 μm), P30 (630 μm), P36 (530 μm), P40 (420 μm), P50 (326 μm), P60 (264 μm), P80 (195 μm), P100 (156 μm), P120 (127 μm), P120 (127 μm), P150 (97 μm), P180 (78 μm), P220 (66 μm), P240 (60 μm), P280 (53 μm), P320 (46 μm), P360 (41 μm), P400 (36 μm), P500 (30 μm), P600 (26 μm), and P800 (22 μm). An approximate average particles size of reach grade is listed in parenthesis following each grade designation.
Useful abrasive particles also include formed ceramic abrasive particles and, in particular, shaped abrasive particles. Shaped abrasive particles can be prepared according to the disclosures of U.S. 8,142,531. The shaped abrasive particles were prepared by shaping alumina sol gel from, for example, equilateral triangle-shaped polypropylene mold cavities of side length 0.031 inch (0.79 mm) and a mold depth of 0.008 inch (0.2 mm). After drying and firing, such resulting shaped abrasive particles comprised triangular plates that were about 280 micrometers (longest dimension) and would pass through a 50-mesh sieve and be retained upon a 60-mesh sieve. In one embodiment, the triangular shaped abrasive particles comprise a first face, an opposing second face connected to the first face by a sidewall where the perimeter of each face is a triangular and desirably an equilateral triangle. In some embodiments, the sidewall, instead of having a 90 degree angle to both faces, is a sloping sidewall as disclosed in U.S. Pat. No. 8,142,531 having a draft angle a between the second face and the sloping sidewall between about 95 degrees to about 130 degrees, which has been determined to greater enhance the cut rate of the triangular shaped abrasive particles.
As used herein “formed ceramic abrasive particle” means an abrasive particle having at least a partially replicated shape. One process to make a formed ceramic abrasive particle includes shaping the precursor ceramic abrasive particle in a mold having a predetermined shape to make ceramic shaped abrasive particles. Ceramic shaped abrasive particles, formed in a mold, are one species in the genus of formed ceramic abrasive particles. Other processes to make other species of formed ceramic abrasive particles include extruding the precursor ceramic abrasive particle through an orifice having a predetermined shape, printing the precursor ceramic abrasive particle though an opening in a printing screen having a predetermined shape, or embossing the precursor ceramic abrasive particle into a predetermined shape or pattern. Non-limiting examples of formed ceramic abrasive particles include shaped abrasive particles, such as triangular plates as disclosed in U.S. Pat. Nos. RE 35,570; 5,201,916; 5,984,998; 8,034,137; 8,123,828; 8,142,531; 8,142,532; and 8,142,891; and in U.S. patent publications 2009/0169816, 2010/0146867, and 2010/0319269 or elongated ceramic rods/filaments often having a circular cross section produced by Saint-Gobain Abrasives an example of which is disclosed in U.S. Pat. No. 5,372,620. Formed ceramic abrasive particles are generally homogenous or substantially uniform and maintain their sintered shape without the use of a binder such an organic or inorganic binder that bond smaller abrasive particles into an agglomerated structure and excludes abrasive particles obtained by a crushing or comminution process that produces abrasive particles of random size and shape. In many embodiments, the formed ceramic abrasive particles comprise a homogeneous structure of sintered alpha alumina or consist essentially of sintered alpha alumina.
The formed ceramic abrasive particles can be graded to a nominal screened grade using U.S.A. Standard Test Sieves conforming to ASTM E-11 “Standard Specification for Wire Cloth and Sieves for Testing Purposes.” ASTM E-11 proscribes the requirements for the design and construction of testing sieves using a medium of woven wire cloth mounted in a frame for the classification of materials according to a designated particle size. A typical designation may be represented as -18+20 meaning that the formed ceramic abrasive particles pass through a test sieve meeting ASTM E-11 specifications for the number 18 sieve and are retained on a test sieve meeting ASTM E-11 specifications for the number 20 sieve. In one embodiment, the formed ceramic abrasive particles have a particle size such that most of the formed ceramic abrasive particles pass through an 18 mesh test sieve and can be retained on a 20, 25, 30, 35, 40, 45, or 50 mesh test sieve. In various embodiments of the invention, the formed ceramic abrasive particles can have a nominal screened grade comprising: −18+20 (925 μm), −20+25 (780 μm), −25+30 (655 μm), −30+35 (550 μm), −35+40 (463 μm), −40+45 (390 μm), −45+50 (328 μm), −50+60 (275 μm), −60+70 (231 μm), −70+80 (196 μm), −80+100 (165 μm), −100+120 (138 μm), −120+140 (116 μm), −140+170 (98 μm), −170+200 (83 μm), −200+230 (69 μm), −230+270 (58 μm), −270+325 (49 μm), −325+400 (42 μm), −400+450 (35 μm), −450+500 (29 μm), or −500+635 (23 μm).
The average particle size is the expected average size of abrasive particles conforming to the industry specified grade or in the case of sieves, the average between the size of the screen opening the particle passed through and the size of the screen opening the particle was retained on. The number in parenthesis following the grade or screen designation is the average abrasive particle size in μm.
Filler particles may be blended with abrasive particles in the abrasive article. Examples of useful fillers include metal carbonates (such as calcium carbonate, calcium magnesium carbonate, sodium carbonate, magnesium carbonate), silica (such as quartz, glass beads, glass bubbles and glass fibers), silicates (such as talc, clays, montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate), metal sulfates (such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate), gypsum, vermiculite, sugar, wood flour, aluminum trihydrate, carbon black, metal oxides (such as calcium oxide, aluminum oxide, tin oxide, titanium dioxide), metal sulfites (such as calcium sulfite), thermoplastic particles (such as polycarbonate, polyetherimide, polyester, polyethylene, poly(vinylchloride), polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, polypropylene, acetal polymers, polyurethanes, nylon particles) and thermosetting particles (such as phenolic bubbles, phenolic beads, polyurethane foam particles and the like). The filler may also be a salt such as a halide salt. Examples of halide salts include sodium chloride, potassium cryolite, sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides, potassium chloride, magnesium chloride. Examples of metal fillers include, tin, lead, bismuth, cobalt, antimony, cadmium, iron and titanium. Other miscellaneous fillers include sulfur, organic sulfur compounds, graphite, lithium stearate and metallic sulfides.
In some embodiments, the abrasive particles are treated with a coupling agent (e.g., an organosilane coupling agent) to enhance adhesion of the abrasive particles to the binder. The abrasive particles may be treated before combining them with the binder material, or they may be surface treated in situ by including a coupling agent to the binder material.
In some embodiments, bonded abrasive wheels according to the present disclosure contain additional grinding aids such as, for example, polytetrafluoroethylene particles, cryolite, sodium chloride, FeS2 (iron disulfide), or KBF4; typically in amounts of from 1 to 25 percent by weight, more typically 10 to 20 percent by weight, subject to weight range requirements of the other constituents being met. Grinding aids are added to improve the cutting characteristics of the cut-off wheel, generally by reducing the temperature of the cutting interface. The grinding aid may be in the form of single particles or an agglomerate of grinding aid particles. Examples of precisely shaped grinding aid particles are taught in U.S. Patent Publ. No. 2002/0026752 A1 (Culler et al).
Useful backings include, for example, paper, fabric, scrim or open weave backings, or film backings. Suitable film backings include polymeric films and primed polymeric films, especially those used in the abrasive arts. Useful polymeric films include, for example, polyester films (e.g., an ethylene-acrylic acid copolymer primed polyethylene terephthalate), polyolefin films (e.g., polyethylene or polypropylene films), and elastic polyurethane films. The film backing may be a laminate of two polymeric films. Examples of elastomeric polyurethanes that may be used to form films include those available under the trade designation ESTANE from B.F. Goodrich and Co. of Cleveland, OH and those described in U.S. Pat. No. 2,871,218 (Schollenberger); U.S. Pat. No. 3,645,835 (Hodgson); U.S. Pat. No. 4,595,001 (Potter et al.); U.S. Pat. No. 5,088,483 (Heinecke); U.S. Pat. No. 6,838,589 (Liedtke et al.); and U.S. Pat. No. RE 33,353 (Heinecke). Pressure-sensitive adhesive-coated polyurethane elastomer films are commercially available from 3M Company under the trade designation TEGADERM. Useful polymeric films are generally from about 0.02 to about 0.5 millimeters in thickness, for example, from 0.02 millimeter to 0.1 millimeter in thickness; however, this is not a requirement.
The binder material typically comprises a glassy inorganic material (e.g., as in the case of vitrified abrasive wheels), metal, or an organic resin (e.g., as in the case of resin-bonded abrasive wheels).
Glassy inorganic binders may be made from a mixture of different metal oxides. Examples of these metal oxide vitreous binders include silica, alumina, calcia, iron oxide, titania, magnesia, sodium oxide, potassium oxide, lithium oxide, manganese oxide, boron oxide, phosphorous oxide, and the like. Specific examples of vitreous binders based upon weight include, for example, 47.61 percent S1O2, 16.65 percent Al2O3, 0.38 percent Fe2 O3, 0.35 percent TIO2, 1.58 percent CaO, 0.10 percent MgO, 9,63 percent Na20, 2.86 percent]¾0, 1.77 percent L12O, 19.03 percent B2O3, 0.02 percent Mn02, and 0.22 percent P2O5; and 63 percent S102, 12 percent Al2O3, 1.2 percent CaO, 6.3 percent Na20, 7.5 percent]¾0, and 10 percent B2O3. During manufacture of a vitreous bonded abrasive wheel, the vitreous binder, in a powder form, may be mixed with a temporary binder, typically an organic binder. The vitrified binders may also be formed from a frit, for example anywhere from about one to 100 percent frit, but generally 20 to 100 percent frit. Some examples of common materials used in frit binders include feldspar, borax, quartz, soda ash, zinc oxide, whiting, antimony trioxide, titanium dioxide, sodium silicofluoride, flint, cryolite, boric acid, and combinations thereof. These materials are usually mixed together as powders, fired to fuse the mixture and then the fused mixture is cooled. The cooled mixture is crushed and screened to a very fine powder to then be used as a frit binder. The temperature at which these frit bonds are matured is dependent upon its chemistry, but may range from anywhere from about 600° C. to about 1800° C.
Examples of metal binders include tin, copper, aluminum, nickel, and combinations thereof.
Organic binder materials are typically included in an amount of from 5 to 30 percent, more typically 10 to 25, and more typically 15 to 24 percent by weight, based on the total weight of the bonded abrasive wheel. Phenolic resin is the most commonly used organic binder material, and may be used in both the powder form and liquid state. Although phenolic resins are widely used, it is within the scope of this disclosure to use other organic binder materials including, for example, epoxy resins, urea-formaldehyde resins, rubbers, shellacs, and acrylic binders. The organic binder material may also be modified with other binder materials to improve or alter the properties of the binder material. Useful phenolic resins include novolac and resole phenolic resins. Novolac phenolic resins are characterized by being acid-catalyzed and having a ratio of formaldehyde to phenol of less than one, typically between 0.5:1 and 0.8:1. Resole phenolic resins are characterized by being alkaline catalyzed and having a ratio of formaldehyde to phenol of greater than or equal to one, typically from 1:1 to 3:1. Novolac and resole phenolic resins may be chemically modified (e.g., by reaction with epoxy compounds), or they may be unmodified. Exemplary acidic catalysts suitable for curing phenolic resins include sulfuric, hydrochloric, phosphoric, oxalic, and p-toluenesulfonic acids. Alkaline catalysts suitable for curing phenolic resins include sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines, or sodium carbonate.
Phenolic resins are well-known and readily available from commercial sources. Examples of commercially available novolac resins include DUREZ 1364, a two-step, powdered phenolic resin (marketed by Durez Corporation of Addison, Texas under the trade designation VARCUM (e.g., 29302), or HEXION AD5534 RESIN (marketed by Hexion Specialty Chemicals, Inc. of Louisville, Ky.). Examples of commercially available resole phenolic resins useful in practice of the present disclosure include those marketed by Durez Corporation under the trade designation VARCUM (e.g., 29217, 29306, 29318, 29338, 29353); those marketed by Ashland Chemical Co. of Bartow, Fla. under the trade designation AEROFENE (e.g., AEROFENE 295); and those marketed by Kangnam Chemical Company Ltd. of Seoul, South Korea under the trade designation “PHENOLITE” (e.g., PHENOLITE TD-2207).
Curing temperatures of organic binder material precursors will vary with the material chosen and wheel design. Selection of suitable conditions is within the capability of one of ordinary skill in the art. Exemplary conditions for a phenolic binder may include an applied pressure of about 20 tons per 4 inches diameter (224 kg/cm̂) at room temperature followed by heating at temperatures up to about 185° C. for sufficient time to cure the organic binder material precursor.
Bonded abrasive articles according to various embodiments may take any of a variety of conventional forms. Preferred abrasive articles are in the form of wheels. Abrasive wheels are typically in the form of a disc or right cylinder having dimensions that may be very small, e.g., a cylinder height on the order of a few millimeters or very large, e.g., a meter or more, and a diameter which may be very small, e.g., on the order of a few centimeters, or very large, e.g., tens of centimeters. Wheels typically have a central opening for support by an appropriate arbor or other mechanical holding means to enable the wheels to be rotated during use. Wheel dimensions, configurations, means of support, and means of rotation are all well known in the art.
The abrasive particles may, for example, be uniformly or non-uniformly distributed throughout the bonded abrasive article. For example, if the bonded abrasive article is a grinding wheel or a cut-off wheel, the abrasive particles may be concentrated toward the middle (e.g., located away from the outer faces of a grinding or cut-off wheel), or only in the outer edge, i.e., the periphery, of a grinding or cut-off wheel. The depressed-center portion may contain a lesser amount of abrasive particles. In another variation, first abrasive particles may be in one side of the wheel with different abrasive particles on the opposite side. However, typically all the abrasive particles are homogenously distributed among each other, because the manufacture of the wheels is easier, and the cutting effect is optimized when the two types of abrasive particles are closely positioned to each other.
Optionally, bonded abrasive articles according to various embodiments may further comprise a scrim that reinforces the bonded abrasive article; for example, disposed on one or two major surfaces of the bonded abrasive article, or disposed within the bonded abrasive article. Examples of scrims include a woven or a knitted cloth. The fibers in the scrim may be made from glass fibers (e.g., fiberglass), organic fibers such as polyamide, polyester, or polyimide. In some instances, it may be desirable to include reinforcing staple fibers within the bonding medium, so that the fibers are homogeneously dispersed throughout the bonded abrasive article.
Objects and advantages of this disclosure are further illustrated by the following non-limiting examples. The particular materials and amounts thereof recited in these examples as well as other conditions and details, should not be construed to unduly limit this disclosure. Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.
Abrasive articles of Example 1 through Example 8 were prepared using conventional and shaped abrasive particles of various sizes.
An abrasive article was prepared in the form of a depressed-center grinding wheel (a type-27 grinding wheel) as follows.
Mix 1 was formed by mixing 860 grams of AP1 and 55 grams of PR1 using an air mixer.
Mix 2 was prepared by mixing 155 grams PR2, 155 grams CRY1 for 1 minute in a paddle type mixer.
Mix 3 was prepared by mixing Mix 1 and Mix 2 in a paddle type mixer for 10 minutes.
Mix 4 was prepared by mixing 860 grams SAP1 and 55 grams of PR1 with a high shear air mixer.
Mix 5 was prepared by combining Mix 2 and Mix 4 and mixing in a paddle type mixer for 10 minutes.
Mix 6 was prepared by combining 700g of Mix 3 and 300g of Mix 5 and mixing in a paddle type mixer for 10 minutes.
A 6.75 in. (17.1 cm) diameter disc of SCRIM was placed in a 7″ (18 cm) cavity die. 250 grams of Mix 6 was spread out evenly on the scrim and a second 6.75 in. SCRIM was placed on top of the mixture. The filled cavity mold was then pressed at 40 ton/38 sq. inch (14.51 MPa) to form a disc.
Multiple resulting discs were then placed on a spindle between depressed center aluminum plates in order to be pressed into type 27 depressed-center grinding wheels. The discs were compressed at 5 ton/38 sq. inch (1.81 MPa). The compressed discs were cured in an oven by heating for 7 hours at 79° C., 3 hours at 107° C., 18 hours at 185° C., and followed by a ramp down over 4 hours to 27° C. to form cured discs. The cured discs had a diameter of 180mm and a thickness of 4 mm, with a central hole of diameter 7/8″.
The cured discs were spray coated with 15 grams of a make resin mix consisting of 51 parts PR3, 42 parts CACO, 6 parts water, and 1 part SURF to be ready for electrostatic mineral coat. A layer of about 47 grams of SAP1 was deposited on top of the sample. Then the discs were cured at 226° F. for 90 minutes.
The mineral coated discs were then sized by spraying the size resin mix consisting of 45 parts PR3, 53 parts CRY2, and 2 parts CB, followed by curing at 190° F. for 80 minutes. Finally, the dried discs were cured for 12 hours at 212° F. to form grinding wheels.
The grinding wheels were tested by grinding by hand for ten 1-minute cycles on a mild steel bar 0.5″ thick and 18″ long using a 6000 RPM air grinder (Ingersoll-Rand). The grinder weight resulted in an applied load of 13 lbs. (5.9 kg) The weight of the steel bar was measured before and after each cycle to measure the cut. The grinding was repeated 16 times from end to end per cycle, approximately 1 minute each. The weight lost from the grinding disc was recorded after each test. The grinding test results are summarized in Table 1.
Grinding wheels were prepared as in Example I, with additional spray coating with 15 grams of the make resin mix of Example 1, in preparation for electrostatic mineral coat after the first curing. A second layer of SAP1 was deposited on top of the first layer of SAP1, weighing about 47 g. Then the sample was cured at 226° F. (108 C) for 90 minutes.
The mineral coated discs were then sized by spraying the size resin mix of Example 1, followed by curing at 190° F. (88 C) for 80 minutes.
Finally, the dried discs were cured for 12 hours at 212° F(100 C) to form grinding wheels. The grinding test results are summarized in Table 1.
Grinding wheels were prepared as in Example 1, substituting the electrostatic mineral coated SAP1 with AP2. The grinding test results are summarized in Table 1.
Grinding wheels were prepared as in Example 1, but Mix 6 was substituted by Mix 7 (40 parts Mix3 and 60 parts Mix4). The grinding test results are summarized in Table 1.
Grinding wheels were prepared as in Example 4, substituting the electrostatic mineral coated precision shaped grain mineral layer with AP2. The grinding test results are summarized in Table 1.
A depressed-center grinding wheel was prepared according to the following procedure.
Mix 8 was prepared by mixing 430 grams of SAP1, 430 grams of AP1, 72 grams of PR1, and 2 grams of CB for 1 minute using a high shear air mixer
Mix 9 was prepared by mixing 175 grams of PR2 and 151 grams CRY1 for 1 minute in a paddle type mixer.
Mix 10 was prepared by combining Mix 8 and Mix 9 and mixing in a paddle type mixer for 10 minutes.
Mix 10 was then screened through a screen with 2x2 mm openings to remove agglomerates. This screened mixture was then pressed in 178 mm diameter dies. SCRIM was placed in the die, 200 grams of Mix 10 was spread out evenly and a second fiberglass mesh was placed on top of the mix. A metal center hole bushing was added. This mix was then pressed at 40 ton/38 sq. inch (14.5 MPa) to form discs.
These discs were placed on a spindle between depressed center aluminum plates in order to be pressed to form type 27 depressed-center grinding wheels. A stack of 5 plates and pressed discs were compressed at 5 ton/38 sq.inch (1.8 MPa). The discs were cured in an oven for 7 hours at 79° C., 3 hours at 107° C., 18 hours at 185° C., and ramp down over 4 hours to 27° C. The cured discs had a diameter of 180mm and a thickness of 4 mm, with a central hole of diameter 22.32.
The working surface of the disc was coated SAP1 by the following procedure. The discs were spray coated with 15 μm of the make resin mix of Example 1. A layer of SAP1 weighing about 42 grams was deposited on top of the disc. Then the disc was cured at 226° F. (108 C) for 75 minutes. Next, in order to have the sized sample, the mineral coated disc was sprayed with the size resin mix of Example 1. Then, it was cured at 190° F. (88 C) for 80 minutes.
Finally, the dried discs were cured for 12 hours at 212° F. (100 C) to produce grinding wheels for testing.
The grinding wheels were tested by grinding by hand for ten 1-minute cycles on a mild steel bar 0.5″ thick and 18″ long using a 6000 RPM air grinder (Ingersoll-Rand). The grinder weight resulted in an applied pressure of 13 lbs. The weight of the steel bar was measured before and after each cycle to measure the cut. The grinding was repeated 16 times from end to end per cycle, approximately 1 minute each. The weight lost from the grinding disc was recorded after each test. The grinding test results are summarized in Table 2.
Commercially available depressed center grinding wheels (92309, 7″×⅛″×⅞″, 3M Company, Thailand) were coated using the method of Example 6. The grinding test results are summarized in Table 2.
7″×⅛″×⅞″ discs were prepared by mixing 23 parts AP3, 38 parts SAP1, 15 parts AP4, 4 parts PR1, 6 parts PR2, 4 parts PR4, 3 parts CRY3, 2 parts APS, 4 parts CRY2, 0.1 part CB, 0.2 parts silane, 0.3 parts solvent, and 0.4 parts oil. The components were mixed for 10 minutes. The prepared discs were compressed, coated and cured into grinding wheels as in Example 6. The grinding test results are summarized in Table 2.
Grinding wheels were prepared as Example 1, without the grinding layer. The grinding test results are summarized in Table 1.
Grinding wheels were prepared as in Example 4, without the grinding layer. The grinding test results are summarized in Table 1.
7″×⅛″×⅞″ depressed center grinding wheels were prepared as in Example 6, without the additional coated abrasive layer. The grinding test results are summarized in Table 2.
Commercially available depressed center grinding wheels (92309, 7″×⅛″×⅞″, 3M Company, Thailand) without the added grinding layer of Example 6. The grinding test results are summarized in Table 2.
7″×⅛″×⅞″ depressed center grinding wheels were prepared as in Example 8, but without the coated abrasive layer. The grinding test results are summarized in Table 2.
Table 3 presents a comparative analysis of the grinding performance of grinding wheels according to Examples 1 through 5 and Comparative Examples 1 through 2.
As can be seen in Table 3, grinding wheels according to various embodiments exhibit significantly improved total cut and grinding performance.
Other modifications and variations to the present disclosure may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present disclosure, which is more particularly set forth in the appended claims. It is understood that aspects of the various embodiments may be interchanged in whole or part or combined with other aspects of the various embodiments. All cited references, patents, or patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/057633 | 9/26/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61886815 | Oct 2013 | US |
