MXPA00009489A - Abrasive tools - Google Patents

Abstract

Abrasive tools suitable for precision grinding of hard brittle materials, such as ceramics and composites comprising ceramics, at peripheral wheel speeds up to 160 meters/second are provided. The abrasive tools comprise a wheel core (2) attached to an abrasive rim of dense, metal bonded superabrasive segments (8) by means of a thermally stable bond (6). A preferred tool for backgrinding ceramic wafers contains graphite filler and a relatively low concentration of abrasive grain (4).

Description

ABRASIVE TOOLS DESCRIPTIVE MEMORY This application is a continuation in part of E.U.A Serial No. 09 / 049,623, published March 27, 1998. The invention relates to abrasive tools suitable for accurately grinding strong brittle materials, such as ceramics and mixed materials comprising ceramics, at peripheral wheel speeds of up to 160 meters / second, and suitable for grinding surfaces of ceramic wafers. Abrasive tools comprise a hub or wheel hub bonded to a superabrasive edge bonded with metal with a binder that is thermally stable during grinding operations. These abrasive tools grind ceramic at high material removal rates (eg, 19-380 cm3 / min / cm), with less wheel wear and less damage to the workpiece than conventional abrasive tools. A suitable abrasive tool for grinding sapphire and other ceramic materials is described in U.S.-A-5,607,489 to Li. The tool is described as containing coated metal diamond bonded in a vitrified matrix comprising from 2 to 20% by volume of solid lubricant and at least 10% by volume of porosity.

An abrasive tool containing diamond bonded in a metal matrix with 15 to 50% by volume of selected fillers, such as graphite, is described in U.S.-A-3,925,035 to Keat. The tool is used to grind cemented carbides. A cutting wheel made with abrasive diamond fragment bonded with metal is described in U.S.-A-2,238,351 to Van der Pyl. The binder consists of copper, iron, tin and optionally nickel and the bonded abrasive fragment is sintered in a steel center, optionally with a welding step to ensure adequate adhesion. It is reported that the best binder is one that has a Rockwell B hardness of 70. An abrasive tool containing fine diamond fragment (industrial diamond) bonded in a metal binder of relatively low melting temperature, such as a binder of bronze, is described in US -Re-21, 165 The low melt binder serves to prevent oxidation of the fine diamond fragment. An abrasive edge is constructed as an individual, annular abrasive segment and then attached to a central disk of aluminum or other material. None of these abrasive tools has proven to be satisfactory in the precision grinding of ceramic components. These tools do not meet the exacting specifications for part shape, size and surface quality when working at commercially possible grinding speeds. Most commercial abrasive tools recommended for use in such operations are vitrified bonded superabrasive wheels or resin wheels designed to operate at relatively low grinding efficiencies to avoid damage to the surface and subsurface of the ceramic components. The grinding efficiencies are further reduced due to the tendency of ceramic workpieces to stick to the front of the wheel, requiring frequent wheel sharpening and alignment to maintain precision shapes. As the market demand for precise ceramic components in products such as motors, refractory equipment and electronic devices (for example, wafers, magnetic heads and display windows) has grown, the need for improved abrasive tools for precision grinding has grown. of ceramic In high-performance finishing ceramic materials, such as alumina-titanium carbide (AITiC), for electronic components, surface grinding or "after-grinding" operations demand high quality smooth surface finishes in low-level grinding operations effort, and relatively low speed. When grinding these materials later, the grinding efficiency is determined both by the surface quality of the workpiece and the control of the applied force as well as by material removal speeds and wear resistance of the abrasive wheel.

The invention is an abrasive tool for surface grinding comprising a center, having a specific minimum resistance parameter of 2.4 Mpa-cm3 / g, a center density of 0.5 to 8.5 g / cm3, a circular perimeter, and an abrasive edge defined by a plurality of abrasive segments; wherein the abrasive segments comprise, in amounts selected to give a maximum total of 100% by volume, from about 0.05 to 10% by volume of superabrasive fragment, from 10 to 35% by volume of deleterious filler, and from 55 to 89.95 % by volume of matrix agglutinated with metal having a fracture toughness of 1.0 to 3.0 MPa M1 / 2. The specific resistance parameter is defined as the ratio of the lower yield strength or fracture strength of the material divided by the density of the material. The deleznable filler is selected from the group consisting of graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline syenite, pumice stone, calcined clay and glass spheres, and combinations thereof. In a preferred embodiment, the matrix bonded with metal comprises a maximum of 5% by volume of porosity.

DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a continuous edge of abrasive segments bonded with the perimeter of a metal center to form an abrasive grinding wheel of type 1A1.

Figure 2 illustrates a discontinuous edge of abrasive segments bonded with the perimeter of a metal center to form a cup wheel. Figure 3 illustrates the relationship between the amount of material removed and the normal force during the grinding of an AITiC workpiece with the grinding wheels of example 5. The abrasive wheels of the invention are grinding wheels comprising a center having a central hole for mounting the wheel on a grinding machine, the center is designed to support a super abrasive edge bonded with metal along the periphery of the wheel. These two parts of the wheel are held together with a binder that is thermally stable under grinding conditions, and the wheel and its components are designed to tolerate stresses generated at peripheral wheel speeds of up to at least 80 m / sec, preferably up to 160 m / sec. Preferred tools are type 1A wheels, and cup wheels, such as type 2 or type 6 wheels or bell-shaped cup wheels of type 11 V9. The center is substantially circular in shape. The center may comprise any material having a specific minimum strength of 2.4 MPa-cm3 / g, preferably 40-185 MPa-cm3 / g. The center material has a density of 0.5 to 8.0 g / cm3, preferably 2.0 to 8.0 g / cm3. Examples of suitable materials are steel, aluminum, titanium and bronze, and their mixed materials and alloys and combinations thereof. Reinforced plastics that have the designated minimum specific strength can be used to build the center. Mixed materials and reinforced center materials typically have a continuous phase of a metal or plastic matrix, often in powder form, to which fibers or fragments or particles of harder, more elastic and / or less dense material, it is added as a discontinuous phase. Examples of reinforcing materials suitable for use in the center of the tools of the invention are glass fiber, carbon fiber, aramid fiber, ceramic fiber, ceramic particles and fragments, and hollow filling materials such as glass spheres, mulita, alumina and Zeolite® spheres. Steel and other metals having densities of 0.5 to 8.0 g / cm 3 can be used to make the centers of the tools of the invention. For manufacturing centers that are used for high-speed grinding (eg, at least 80 m / sec), lightweight metals are preferred in powder form (i.e., metals having densities of about 1.8 to 4.5). g / cm3), such as aluminum, magnesium and titanium, and alloys thereof, and mixtures thereof. Aluminum and aluminum alloys are especially preferred. Metals having sintering temperatures between 400 and 900 ° C, preferably 570-650 ° C, are selected if a co-sintering assembly procedure is used to make the tools. Low density filling materials can be added to reduce center weight. Porous fillers and / or ceramic or glass hollows, such as glass spheres and mullite spheres are suitable materials for this purpose. Inorganic and non-metallic fiber materials are also useful. When indicated by the processing conditions, an effective amount of lubricant or other processing aids known in the field of metal binder and superabrasive can be added to the metal powder before pressing and sintering. The tool must be strong, durable and dimensionally stable to withstand the potentially destructive forces generated by high-speed operation. The center must have a minimum specific resistance to operate the grinding wheels at the very high angular speed necessary to reach the tangential contact speed between 80 and 160 m / s. The minimum specific strength parameter required for the core materials used in the invention is 2.4 MPa-cm3 / g. The specific resistance parameter is defined as the ratio of the elastic limit of center material (or fracture) divided by the center material density. In the case of brittle materials, which have a fracture strength less than the elastic limit, the specific resistance parameter is determined using the lowest number of fracture resistance. The elastic limit of a material is the minimum force applied in tension in which the deformation of the material increases without additional increase in force. For example, ANSI 4140 steel hardened to more than about 240 (Brinell scale) has a tensile strength in excess of 700 MPa. The density of this steel is around 7.8 g / cm3.

Therefore, its specific resistance parameter is around 90 MPa-cm3 / g. Similarly, certain aluminum alloys, for example Al 2024, Al 7075 and Al 7178, which can be treated with heat at Brinell hardness above about 100 have higher tensile strengths than about 300 MPa. Said aluminum alloys have a low density of about 2.7 g / cm 3 and therefore show a specific resistance parameter of more than 110 MPa-cm 3 / g. Titanium alloys and mixed materials and bronze alloys manufactured to have a density of no more than 8.0 g / cm2, are also suitable for use. The center material must be tough, thermally stable at temperatures reached in the grinding zone (for example, around 50 to 200 ° C), resistant to chemical reaction with coolers and lubricants used in grinding and resistant to erosion due to to the movement of cutting residues in the grinding zone. Although some alumina and other ceramic materials have acceptable failure values (ie, in excess of 60 MPa-cm3 / g), they are generally very brittle and structurally fail in high-speed grinding due to fracture. Therefore, the ceramic is not suitable for use in the center of the tool. Metal is preferred, especially quality steel for hardened tool. The abrasive segment of the grinding wheel for use with the present invention is a segmented or continuous edge mounted on a center. A segmented abrasive edge is shown in Fig. 1. The center 2 has a central hole 3 for mounting the wheel to a shaft of a motorized impeller (not shown). The abrasive edge of the wheel comprises embedded superabrasive fragments 4 (preferably in uniform concentration) in a metal matrix bond 6. A plurality of abrasive segments 8 form the abrasive edge shown in Figure 1. Although the embodiment illustrated shows ten segments, The number of segments is not important. An individual abrasive segment, as shown in Figure 1, has a truncated rectangular ring shape (an arcuate shape) characterized by a length I, a width w, and a depth d. The mode of a grinding wheel shown in Figure 1 is considered representative of wheels that can operate successfully in accordance with the present invention, and should not be seen as limiting. The various geometric variations for segmented grinding wheels include cup-shaped wheels, as shown in Fig. 2, wheels with openings through the center and / or spaces between the consecutive segments, and wheels with abrasive segments of different width than the center. The openings and spaces are sometimes used to provide paths to drive the cooler to the grinding zone and to direct the cutting residues out of the area. A segment wider than the width of the center is occasionally used to protect the structure of the erosion center through contact with chip material as the wheel radially penetrates the workpiece.

The wheel can be manufactured by first forming individual segments of pre-selected dimension and then joining the preformed segments to the circumference 9 of the center with a suitable adhesive. Another preferred manufacturing method involves forming segment precursor units of a mixture of abrasive fragment and binder powder, molding the composition around the center circumference, and applying heat and pressing to create and join the segments, in situ (i.e. co-sinter the center and the edge). A co-sintering process is preferred for making cup wheels for surface grinding used for subsequent grinding of wafers and hard ceramic flakes such as AITiC. The abrasive edge component of the abrasive tools of the invention may be a continuous edge or a discontinuous edge, as shown in Figures 1 and 2, respectively. The continuous abrasive edge may comprise an abrasive segment, or at least two abrasive segments sintered separately into molds, and then individually mounted at the center with a thermally stable binder (i.e., a stable binder at temperatures encountered during grinding in the portion of the segments directed away from the grinding face, typically around 50-350 ° C). The discontinuous abrasive edges, as shown in Figure 2, are manufactured from at least two of said segments, and the segments are separated by slots or spaces at the edge and do not align from end to end along their lengths , I, as in the continuous segmented abrasive edge wheels. The figures illustrate preferred embodiments of the invention, and do not attempt to limit the types of tool designs of the invention, for example discontinuous edges can be used on the continuous wheels 1A and edges can be used on the cup wheels. For high-speed grinding, especially grinding of workpieces having a cylindrical shape, a type 1A wheel with a continuous edge is preferred. Continuous segmented abrasive edges are preferred over a single continuous abrasive edge, molded as a single piece in a ring shape, because it is easier to achieve a truly round flat shape during the manufacture of a tool from multiple abrasive segments. For grinding at lower speed (eg, 25 to 60 m / sec), especially surface grinding and flat finishing of workpieces, discontinuous abrasive edges are preferred (eg, cup wheel shown in Figure 2) . Because surface quality is critical in low speed surface finishing operations, slots can be formed in the segments, or other segments can be omitted from the edge to help remove waste material that could scratch the surface of the surface. Workpiece. The abrasive edge component contains superabrasive fragments held in a metal matrix binder, typically formed by sintering a mixture of bonded metal powder and the abrasive fragment into a mold designed to produce the desired size and shape of the abrasive edge or segments of the abrasive. abrasive edge. The superabrasive fragments used in the abrasive rim can be selected from diamond, natural and synthetic, CBN, and combinations of these abrasives. The selection of size and type of fragment will vary depending on the nature of the work piece and the type of grinding procedure. For example, in sapphire grinding and polishing or AITiC, a superabrasive fragment size ranging from 2 to 300 microns is preferred. To grind another alumina, a superabrasive fragment size of about 125 to 300 microns (grain 60 to 120) is generally preferred.; grain size of Norton Company). To grind silicon nitride, a fragment size of about 45 to 80 microns (200 to 400 grain) is generally preferred. Finer grain sizes are preferred for surface finishing and larger grain sizes are preferred for internal diameter or profile or cylindrical grinding operations in which larger amounts of material are removed. As a percentage of volume of the abrasive edge, the tools comprise from 0.5 to 10% by volume of superabrasive fragment, preferably from 0.5 to 5% by volume. A smaller amount of a scorch filler material having a hardness less than that of the metal binder matrix can be added as a binder filler to increase the wear rate of the binder. As a volume percentage of the edge component, the filler can be used from 10 to 35% by volume, preferably from 15 to 34% by volume. The suitable filleting filler material should be characterized by adequate thermal and mechanical properties to survive the sintering temperature and pressure conditions used to manufacture the abrasive segments and assemble the wheel. Examples of useful deleterious filler materials are graphite, hexagonal boron nitride, empty ceramic spheres, feldspar, nepheline syenite, pumice stone, calcined clay and glass spheres, and combinations thereof. Any suitable metal binder for bonding superabrasives and having a fracture toughness of 1.0 to 6.0 MPa m1 / 2, preferably 2.0 to 4.0 MPa-m1 / 2, may be employed herein. Fracture tenacity is the stress intensity factor at which a crack initiated in a material will propagate into the material and lead to fracture of the material. Fracture tenacity is expressed as K-? C = (sf) (p1 / 2) (c1 / 2), where K? C is the fracture toughness, sf is the stress applied to the fracture, and c is half the length of the crack. There are several methods that can be used to determine the fracture toughness, and each has an initial step where a crack of known dimension is generated in the test material, and then a stress load is applied until the material fractures. . The fracture stress and the crack length are replaced in the equation and fracture toughness is calculated (for example, the fracture toughness of steel is around 30-60 MPa m1 / 2, alumina is about 2-3 MPa m1 / 2, silicon nitride is around 4-5 MPa m1 / 2, and zirconium is around 7-9 MPa-m1 / 2 .To optimize the life of the wheel and the grinding performance, the binder wear rate should be equal to or slightly greater than the wear rate of the abrasive fragment during grinding operations, fillers, such as those mentioned above, can be added to the metal binder to decrease The wheel wear velocity Metal powders which tend to form a relatively dense binder structure (i.e., less than 5% by volume porosity) are preferred to activate higher material removal rates during grinding. materi Useful metals in the edge metal binder include, but are not limited to, bronze, copper and zinc alloys (brass), cobalt and iron, and their alloys and mixtures thereof. These metals can optionally be used with titanium or titanium hydride, or other superabrasive reactive materials (ie, active binder components) capable of forming a chemical bond of carbide or nitride between the fragment and the binder on the surface of the superabrasive fragment under the conditions of sintering selected to reinforce fragment / binder posts. Stronger fragment / binder interactions will limit premature fragment loss and damage to work pieces and will shorten the tool path caused by premature fragment loss.

In a preferred embodiment of the abrasive edge, the metal matrix comprises from 55 to 89.95% by volume of the edge, most preferably from 60 to 84.5% by volume. The deleznable filler comprises from 10 to 35% by volume of the abrasive edge, preferably from 15 to 35% by volume. The porosity of the metal matrix binder should be maintained at a maximum of 5% by volume during the manufacture of the abrasive segment. The metal binder preferably has a Knoop hardness of 2 to 3 GPa. In a preferred embodiment of a type 1A grinding wheel, the center is made of aluminum and the rim contains a binder of bronze made of copper and tin powders (80/20 wt%), and, optionally with the addition of 0.1 at 3.0% by weight, preferably 0.1 to 1.0% by weight, of phosphorus in the form of a phosphorus / copper powder. During the manufacture of the abrasive segments, the metal powders of this composition are mixed with abrasive diamond fragments of grain 100 to 400 (160 to 45 microns), molded into segments of abrasive edge and sintered or densified in the scale of 400- 550 ° C at 20 to 33 MPa to produce a dense abrasive edge, preferably having a density of at least 95% of the theoretical density (ie, comprising no more than about 5% volume of porosity). In a typical co-sintering wheel manufacturing process, the center metal powder is poured into a steel mold and cold-pressed at 80 to 200 kN (about 10-50 MPa pressure) to form a green part which has an approximate size of 1.2 to 1.6 times the desired final thickness of the center. The part of the green center is placed in a graphite mold and a mixture of the abrasive fragment (grain size 2 to 300 micrometers) and the metal binder powder mixture is added to the cavity between the center and the outer edge of the graphite mold. A fixing ring can be used to compact the abrasive powders and metal binders to the same thickness as the center preform. The content of the graphite mold is hot pressed at 370 to 410 ° C under 20 to 48 MPa pressure for 6 to 10 minutes. As is known in the art, the temperature can be increased rapidly (for example, from 25 to 410 ° C for 6 minutes, maintained at 410 ° C for 15 minutes) or gradually increased before applying pressure to the mold content. After hot pressing, the graphite mold is separated from the part, the part is cooled and finished by conventional techniques to produce an abrasive edge having the desired dimensions and tolerances. For example, the part can be finished using vitrified grinding wheels on grinding machines or carbide cutters on a lathe. When the center and the edge of the invention are co-sintered, little material removal is needed to put the part in its final form. In other methods to form a thermally stable binder between the abrasive edge and the center, machining of the center and edge may be required before a step of carburizing, ligation or diffusion, to ensure a suitable surface for alignment and joining of the parts .

To create a thermally stable binder between the edge and the center using segmented abrasive edges, any thermally stable adhesive having the strength to withstand peripheral wheel speeds of up to 160 m / sec may be used. The thermally stable adhesives are stable at grinding process temperatures that are frequently found in the portion of the abrasive segments directed away from the grinding face. These temperatures typically vary from 50-350 ° C. The adhesive binder must be mechanically very strong to withstand the destructive forces that exist during the rotation of the grinding wheel and during the grinding operation. Two-part epoxy resin cements are preferred. A preferred epoxy cement, Technodyne® HT-18 epoxy resin (obtained from Taoka Chemicals, Japan), and its modified amine hardener, can be mixed in the ratio of 100 parts of resin to 19 parts of hardener. The filler, such as fine silica powder, can be added at a ratio of 3.5 parts per 100 parts of resin to increase the viscosity of cement. The segments can be mounted around the full circumference of the wheel centers for grinding, or a partial circumference of the center, with the cement. The perimeter of the metal centers can be cleaned with sandblasting to obtain a degree of roughness before joining the segments. Thickened epoxy cement is applied to the ends and bottom of the segments that are placed around the center substantially as shown in Figure 1 and mechanically fixed during healing. The epoxy cement is allowed to cure (for example, at room temperature for 24 hours followed by 48 hours at 60 ° C). The drainage of the cement during the curing and the movement of the segments is kept to a minimum during the cure by the addition of sufficient filler to optimize the viscosity of the epoxy cement. The adhesive binder strength can be evaluated by rotating test at an acceleration of 45 rev / min, as is done to measure the breaking speed of the wheel. The wheels need demonstrated breaking degrees equivalent to tangential contact speeds of at least 271 m / s to qualify for operation under currently applicable safety standards at tangential contact speed of 160 m / s in the United States. The abrasive tools of the invention are particularly designed for precision grinding and finishing of brittle materials, such as advanced ceramic materials, glass and components containing ceramic materials and mixed ceramic materials. The tools of the invention are preferred for frosted ceramic materials including, but not limited to, silicon, mono- and poly-crystalline oxides, carbides, borides and silicides.; polycrystalline diamond; glass; and mixed ceramic materials in a non-ceramic matrix; and combinations thereof. Examples of typical workpiece materials include, but are not limited to, AITiC, silicon nitride, silicon oxynitride, stabilized zirconium, aluminum oxide (e.g., sapphire), boron carbide, boron nitride, titanium diboride and aluminum nitride, and mixed materials of these ceramics, as well as certain mixed metal matrix materials such as cemented carbides, and strong brittle amorphous materials such as mineral glass. Either individual glass ceramics or polycrystalline ceramics can be ground with these improved abrasive tools. With each type of ceramic, the quality of the ceramic part and the efficiency of the grinding operation increases as the peripheral wheel speed of the wheels of the invention increases up to 80-160 m / s. Among the improved ceramic parts using the abrasive tools of the invention are ceramic motor valves and rods, pump seals, ball bearings and ssories, cutting tool inserts, wear parts, metal forming dies, components refractories, visual display windows, flat glass for windshields, doors and windows, insulators and electrical parts, electronic ceramic components, including, but not limited to, silicon wafers, AITiC flakes, magnetic reading and writing heads, and substrates . Unless otherwise indicated, all parts and percentages in the following examples are by weight. The examples simply illustrate the invention and do not try to limit it.

EXAMPLE 1 Abrasive wheels of the invention were prepared in the form of a diamond wheel bonded with metal 1A1 using the materials and methods described below. A mixture of 43.75% by weight copper powder (Dendritic FS grade, particle size + 200 / -325 mesh, obtained from Sintertech International Marketing Corp., Ghent, NY) was prepared; 6.24% by weight phosphorus / copper powder (grade 1501, particle size + 100 / -325 mesh, obtained from New Jersey Zinc Company, Palmerton, PA); and 50.02% by weight of tin powder (grade MD115, mesh +325, maximum particle size 0.5%, obtained from Alean Metal Powders, Inc., Elizabeth, New Jersey). The diamond abrasive fragment (320 grain size synthetic diamond obtained from General Electric, Worthington, Ohio) was added to the metal powder mixture and the blend was mixed until uniformly combined. The mixture was placed in a graphite mold and hot pressed at 407 ° C for 15 minutes at 3000 psi (2073 N / cm2) until a matrix with a target density in excess of 95% theory had been formed (by example, for wheel # 6 used in example 2:> 98.5% of the theoretical density). The Rockwell B hardness of the segments produced for wheel # 6 was 108. The segments contained 18.75% vol. of abrasive fragment. The segments were ground to the arched geometry required to align the periphery of a machined aluminum center (7075 T6 aluminum, obtained from Yarde Metals, Tewksbury, MA), producing a wheel with an external diameter of around 393 mm, and segments of 0.62 cm thick. The abrasive segments and the aluminum center were assembled with an epoxy cement system filled with silica (Technodyne HT-18 adhesive, obtained from Taoka Chemicals, Japan) to make grinding wheels having a continuous edge consisting of multiple abrasive segments. The contact surfaces of the center and the segments were degreased and cleaned with sandblasting to ensure adequate adhesion. To characterize the maximum operating speed of this new type of wheel, full-sized wheels were purposely rotated to destroy and determine the breaking strength and the maximum operating speed determined according to the operating speed test method. maximum of Norton Company. The following table summarizes the rupture test data for typical examples of the 393-mm diameter experimental metal agglutinated wheels.

Data of resistance to the rupture of experimental wheels agglutinated with metal According to these data, the experimental grinding wheels of this design will qualify for an operating speed of up to 90 m / s (17,717 surface feet / min). The higher operating speeds of up to 160 m / s can be easily achieved by some additional modifications in manufacturing procedures and wheel designs.

EXAMPLE 2 Performance evaluation of grinding: Three segmented wheels agglutinated with experimental metal with central hole of 127 mm, diameter of 393 mm and thickness of 15 mm (15.5 inches x 0.59 inches x 5 inches) made according to the method of example 1, previous, (# 4 having segments with a density of 95.6% of theory, # 5 to 97.9% of theory and # 6 to 98.5% of theoretical density) were evaluated for grinding performance. The initial evaluation at 32 and 80 m / s established the # 6 wheel as the wheel that has the best grinding performance of the three, although all the experimental wheels proved to be acceptable. The evaluation of wheel # 6 was carried out at three speeds: 32 m / s (6252 sfpm), 56 m / s (11,000 sfpm), and 80 m / s (15,750 sfpm). Two commercial abrasive wheels of the prior art recommended for grinding ceramic materials served as the control wheels and were evaluated together with the wheels of the invention. One was a vitrified agglutinated diamond wheel (wheel SD320-N6V10 obtained from Norton Company, Worcester, MA) and the other was a diamond wheel agglutinated with resin (wheel SD320-R4BX619C obtained from Norton Company, Worcester, MA). The resin wheel was evaluated at three speeds. The vitrified wheel was evaluated only at 32 m / s (6252 sfpm), due to the speed tolerance specifications. More than one thousand 0.35 in. (0.35 in.) Wide and 0.25 in. (0.25 in.) Deep penetration grinding was performed on silicon nitride workpieces. The conditions of the grinding test were: Grinding test conditions: Machine: Studer Grinder Model S40 CNC Wheel specifications: SD320-R4BX619C, SD320-N6V10, Size: 393 mm in diameter, 15 mm in thickness and 127 mm hole. Wheel speed: 32, 56, and 80 m / s (6252, 11000, and 15750 sfpm) Cooler: Inversol 22 @ 60% oil and 40% water Coolant pressure: 270 psi (19 kg / cm2) Removal speed material: varies, starting at 3.2 mm3 / s / mm (0.3 in3 / min / in) Work material: Si3N4 (rods made of NT551 silicon nitride, obtained from Norton Advanced Ceramics, Northboro, Massachusetts) 25.4 mm (1 inch) ) diameter X 88.9 mm (3.5 inches) long Working speed: 0.21 m / s (42 sfpm), constant Working start diameter: 25.4 mm (1 inch) Working finish diameter: 6.35 mm (0.25 inches) For operations requiring alignment and sharpening, suitable conditions for the metal bonded wheels of the invention were: Alignment operation: Wheel: 5SG46IVS (obtained from Norton Company) Wheel size: 152 mm in diameter (6 inches) Wheel speed : 3000 rpm; to +0.8 ratio relative to the grinding wheel Step: 0.015 inch (0.38 mm) Compensation: 0.0002 inch Sharpening operation: Lever: 37C220H-KV (SiC) Mode: Manual lever sharpening The tests were performed in a penetration mode Cylindrical external diameter in grinding of silicon nitride rods. To preserve the best rigidity of the work material during grinding, the 88.9 mm (3.5 inch) samples were held in a jaw with approximately 31 mm (1-1 / 4 inches) exposed for grinding. Each set of penetration grinding tests started from the farthest end of each rod. First, the wheel made a radial depth of 6.35 mm (1/4 inch) in width and 3.18 mm (1/8 inch) of penetration to complete a test. The working rpm was readjusted to compensate for the loss of working speed due to the reduced working diameter. Two more similar penetrations were made in the same location to reduce the working diameter from 25.4 mm (1 inch) to 6.35 mm (1/4 inch). The wheel moved laterally 6.35 mm (1/4 inch) close to the jaw to make the following three penetrations. Four lateral movements were performed on the same side of a sample to complete the twelve penetrations at one end of a sample. The sample was inverted to expose the other end to another twelve frosted. A total of 24 penetration grinds were made for each sample. The initial comparison tests for the metal bonded wheels of the invention and the resin and vitrified wheels were conducted at a peripheral speed of 32 m / s in three material removal speeds (MRR ') from approximately 3.2 mm3 / s / mm (0.3 inches3 / min / inches) to approximately 10.8 mm3 / s / mm (1.0 inch3 / min / inch). Table 1 shows the performance differences, as illustrated by the G ratios, between the three different types of wheels after twelve penetration grindings. The relation G is the ratio without unit of volume material removed on volume of wheel wear. The data showed that the N-grade vitrified wheel had better G ratios than the R-grade resin wheel at the higher material removal rates, suggesting that a softer wheel performs better in the grinding of a ceramic workpiece . However, the wheel (# 6) bonded with experimental metal, harder was superior to the resin wheel and the vitrified wheel at all material removal speeds. Table 1 shows the estimated G ratios for the resin wheel and the new metal bonded wheel (# 6) at all material removal speed conditions. Because there was no measurable wheel wear after twelve grinding at each material removal rate for the metal agglutinated wheel, a symbolic value of 0.01 mil (0.25 μm) of radial wheel wear was given for each grinding. This produced the calculated G ratio of 6051. Although the metal bonded wheel of the invention contained a concentration of 75 diamonds (about 18.75% by volume abrasive fragment in the abrasive segment), and the resin and vitrified wheels had a concentration of 100 and 150 (25% by volume and 37.5% by volume), respectively, the wheel of the invention still shows superior grinding performance. At these high relative fragment concentrations, superior grinding performance of the control wheels containing a higher volume percentage of abrasive fragment is expected. Therefore, these results were unexpected. Table 1 shows the surface finish (Ra) and ripple (Wt) data measured on samples milled by the three wheels at the low test speed. The ripple value, Wt, is the maximum peak at the height of the ripple profile. All data on the surface finish was measured on the surfaces created by cylindrical penetration grinding without low pressure. These surfaces are usually rougher than the surfaces created by transverse grinding. Table 1 shows the difference in grinding power consumption at various material removal speeds for all three wheel types. The resin wheel had less power consumption than the other two wheels; however, the experimental wheel agglutinated with metal and the vitrified wheel had comparable power consumption. The experimental wheel provided an acceptable amount of power for ceramic grinding operations, particularly in view of the favorable G-ratio and surface-finish data observed for the wheels of the invention. In general, the wheels of the invention demonstrated power traction proportional to the material removal rates.

TABLE 1 Sample MRR 'Speed Force Power Energy Ratio Finish of Ranging wheel 3 / s Tangende specific G surface area 1 m / s cial N / mm unit W.s / mm3 Ra μm Wt μm mm W / mm Resin 973 3.2 32 0.48 40 12.8 585.9 0.52 0.86 1040 6.3 32 0.98 84 13.3 36.6 0.88 4.01 980 8.9 32 1.67 139 9.5 7.0 0.99 4.50 1016 3.2 56 0.49 41 13.1 586.3 0.39 1.22 1052 6.3 56 0.98 81 12.9 0.55 1.52 293.2 992 3.2 80 0.53 45 14.2 586.3 0.42 1.24 1064 6.3 80 0.89 74 11.8 2.93.2 0.62 1.80 1004 9.0 80 1.32 110 12.2 586.3 0.43 1.75 Vitrified 654 3.2 32 1.88 60 19.2 67.3 0.7 2.50 666 9.0 32 4.77 153 17.1 86.5 1.6 5.8 678 11.2 32 4.77 153 13.6 38.7 1.7 11.8 experimental metal 407 3.2 32 2.09 67 2.1 6051 0.6 0.9 419 6.3 32 4.03 130 20.6 6051 0.6 0.9 431 9.0 32 5.52 177 19.7 6051 0.6 0.8 443 3.2 56 1.41 80 25.4 6051 0.6 0.7 455 6.3 56 2.65 150 23.9 6051 0.5 0.7 467 9.0 56 3.70 209 23.3 6051 0.5 0.6 479 3.2 80 1.04 85 26.9 6051 0.5 1.2 491 6.3 80 1.89 15 24.3 6051 0.6 0.8 503 9.0 80 2.59 210 23.4 6051 0.6 0.8 When the grinding performance was measured at 80 m / s (15,750 sfpm) in an additional grinding test under the same conditions, the resin wheel and the experimental metal wheel had power consumption comparable to material removal speed (MRR ) of 9.0 mm3 / s / mm (0.8 in3 / min / in). As shown in Table 2, the experimental wheels were operated at increasing MRRs without loss of performance or unacceptable power loads. The power traction of the agglutinated wheel with metal was roughly proportional to the MRR. The highest MRR achieved in this study was 47.3 mm3 / s / mm (28.4 cm3 / m¡n / cm). The data in table 2 are averages of twelve grinding passes. The individual power readings for each of the twelve passes remained consistent for the experimental wheel within each material removal rate. Normally an increase in power will be observed as the successive grinding passes are carried out and the abrasive fragments in the wheel begin to dim or the front of the wheel is loaded with workpiece material. This is often observed when the MRR is increased. However, the stable power consumption levels observed within each MRR during the twelve grinders show, unexpectedly, that the experimental wheel kept its sharp cut-off points during the total length of the test at all MRRs. In addition, during the full test, with material removal rates in the range of 9.0 mm3 / s / mm (0.8 in3 / min / in) to 47.3 mm3 / s / mm (4.4 in3 / min / in), it was not necessary align or sharpen the experimental wheel.

The total, cumulative amount of milled silicon nitride material without any evidence of wheel wear was equivalent to 271 cm3 per cm (42 in3 per inch) of wheel width. In contrast, the ratio G for the concentration resin wheel 100 at a material removal rate of 8.6 mm3 / s / mm (0.8 in.sup.3 / min / in.) Was approximately 583 after twelve penetrations. The experimental wheel showed no measurable wheel wear after 168 penetrations at 14 material removal speeds. Table 2 shows that samples milled by the wheel bonded with experimental metal at the 14 material removal speeds maintained constant surface finishes between 0.4 μm (16 μpul.) And 0.5 μm (20 μpul.), And ripple values between 1.0 μm (38 μpul.) And 1.7 μm (67 μpul.). The resin wheel was not tested at these high material removal rates. However, at a material removal rate of around 8.6 mm3 / s / mm (0.8 in3 / min / in), the ceramic bars ground by the resin wheels had slightly better but comparable surface finishes (0.43 vs 0.5. μm, and weaker waviness (1.73 versus 1.18 μm). Surprisingly, there was no apparent deterioration in the surface finish when the ceramic rods were ground with the new metal-bonded wheel as the material removal rate increased. is contrary to the commonly observed surface finish deterioration with increased cutting speeds for standard wheels, such as the control wheels used in the present invention. The general results show that the experimental metal wheel was able to effectively grind an MRR that was 5 times the MRR achievable with a wheel agglutinated with standard resin used commercially. The experimental wheel had 10 times the G ratio compared to the resin wheel at the lower MRRs.

TABLE 2 Sample MRR 'Force Power Power Ratio Finish Ondu- mm3 / s / Tangen specific unit G of the mm-distance W / mm Ws / mm3 surface Wt N / mm Ra μm μm Resin 1004 9.0 1.32 110 12.2 586.3 0.43 1.75 Metal ja Invention 805 9.0 1.21 98 11.0 6051 0.51 1.19 817 18.0 2.00 162 9.0 6051 0.41 0.97 829 22.5 2.62 213 9.5 6051 0.44 1.14 841 24.7 2.81 228 9.2 6051 0.47 1.04 853 27.0 3.06 248 9.2 6051 0.48 1.09 865 29.2 3.24 262 9.0 6051 0.47 1.37 877 31.4 3.64 295 9.4 6051 0.47 1.42 889 33.7 4.01 325 9.6 6051 0.44 1.45 901 35.9 4.17 338 9.4 6051 0.47 1.70 913 38.2 4.59 372 9.7 6051 0.47 1.55 925 40.4 4.98 404 10.0 6051 0.46 1.55 937 42.7 5.05 409 9.6 6051 0.44 1.57 949 44.9 5.27 427 9.5 6051 0.47 1.65 961 47.2 5.70 461 9.8 6051 0.46 1.42 When operated at wheel speeds of 32 m / s (6252 sfpm) and 56 m / s (11,000 sfpm) (table 1), the power consumption for the wheel bonded with metal was higher than that of the wheel. Resin wheel at all material removal speeds evaluated. However, the power consumption for the metal-bonded wheel became comparable or slightly less than that of the wheel resin at the high wheel speed of 80 m / s (15,750 sfpm) (tables 1 and 2). In general, the trend showed that the energy consumption decreased with increased wheel speed when grinding at the same material removal rate for both the resin wheel and the wheel agglutinated with experimental metal. The power consumption during grinding, much of which goes to the workpiece as heat, is less important when grinding ceramic materials than when grinding metallic materials due to the higher thermal stability of ceramic materials. As demonstrated by the surface quality of the ceramic samples milled with the wheels of the invention, the power consumption was not removed from the finished part and was at an acceptable level. For the wheel bonded with experimental metal, the ratio G was essentially constant at 6051 for all material removal speeds and wheel speeds. For the resin wheel, the G ratio decreased with increasing material removal rates at any constant wheel speed. Table 2 shows the improvement in surface finishes and ripple on samples milled at higher wheel speed. In addition, samples milled by the new metal-bonded wheel had the lowest ripple measured under all wheel speeds and material removal rates evaluated.

In these tests the metal-bonded wheel demonstrated superior wheel life compared to the control wheels. In contrast to the commercial control wheels, there was no need to align and sharpen the experimental wheels during the extended grinding tests. The experimental wheel was successfully operated at wheel speeds up to 90 m / s.

EXAMPLE 3 In a subsequent grinding test of the experimental wheel (# 6) at 80 m / sec under the same operating conditions as those used in the previous example, an MRR of 380 cm3 / min / cm was reached while generating a Measurement of surface finish (Ra) of only 0.5 μm (12 μpul) and using an acceptable level of energy. The observed high removal rate of material without surface damage to the ceramic workpiece that was obtained using the tool of the invention has not been reported for the grinding operation of ceramic material with any commercial abrasive wheel of any type. binder.

EXAMPLE 4 A cup-shaped abrasive tool was prepared and evaluated in sapphire grinding on a vertical-spindle "blanchard-type" machine. A cup-shaped wheel (diameter = 250 mm) of abrasive segments identical in composition to those used in example 1, wheel # 6 was made, except that (1) the diamond was 45 microns in grain size ( USA Mesh 270/325) and was present in the abrasive segments at 12.5% by volume (concentration 50), and (2) the sizes of the segments were 46.7 mm in length of rope (radius 133.1 mm), 4.76 mm in width and 5.84 mm in depth. These segments agglutinated along the periphery of a side surface of a cup-shaped steel center having a central spindle hole. The center surface had grooves positioned along the periphery that formed discrete, hollow pockets that had the same width and length dimensions as the segments. An epoxy cement (Technodyne HT-18 cement obtained from Taoka, Japan) was added to the bags and the segments were placed in the bags and the adhesive was allowed to cure. The finished wheel resembled the wheel of Example 2. The cup wheel was successfully used to grind the surface of a working material consisting of a solid sapphire cylinder 100 mm in diameter producing acceptable flat surface under favorable grinding conditions of G ratio, MRR and power consumption.

EXAMPLE 5 Abrasive cup-shaped tools of type 2A2 (280 mm in diameter) suitable for subsequently grinding AITiC or silicon wafers were prepared with the abrasive segments described in Table 3 below. Except as stated below, the segment sizes were 139.3 mm in radius length, 3.13 mm in width and 5.84 mm in depth. Diamond abrasives containing sufficient batch mixtures to make 16 segments per wheel in the proportions given in Table 3 were prepared by sieving the heavy components through an E.U.A. 140/170 mesh, and mixing the components to combine them evenly. The powder required for each segment was weighed, introduced into a graphite mold, leveled and compacted. The graphite segment molds were hot pressed at 405 ° C for 15 minutes at 3000 psi (2073 N / cm2). After cooling, the segments were removed from the mold. The assembly of a wheel adhering the segments in a machined aluminum center 7075 T6 was done as in example 1. The segments were degreased, sandblasted, coated with adhesive and placed in machined cavities to conform to the periphery of the wheel. After curing the adhesive, the wheel was machined to size, rocked and tested for speed.

TABLE 3 Binder composition % by weight% by volume Sample Cu Sn P Graphite Cu Sn P Graphite Control 49.47 50.01 0.52 0.00 43.71 54.03 2.26 0.00 (Ex.1) d) 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18.30 7. 5/204 0 (2) 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18.30 7. 5/204 0 (3) 45.76 46.26 0.48 7.50 34.02 42.07 1.75 22.16 7. 5/205 1 (4) 46.50 47.01 0.49 6.00 35.70 44.14 1.86 18.30 /2040 (5) 43.53 44.01 0.46 12.00 29.55 36.54 1.53 32.37 /2052 TABLE 4% vol of abrasive segment composition Sample Graphite Diamond Binder3 Porosity Control > 80 0.00 18.75 < 5 (Ex 1) (75 conc) (1) > 80 17.93 1.88 < 5 7.5 / 2040 (7.5 conc) (2) > 80 17.93 1.88 < 5 7.5 / 2040 (7.5 conc) (3) > 75 21.72 1.88 < 5 7.5 / 2051 (7.5 conc) (4) > 80 18.07 1.25 < 5/20/20 (5 conc) (5) > 63 30.35 6.25 < 5 25/2052 (25 conc) a. All the diamond fragments used in the segments were sieve 325 (49 micrometers) grain size, except the sample (1) that was sieved 270 (57 micrometers). Diamond concentration levels are given below% by volume of diamond. b. The porosity was calculated from the observation of the segment microstructure. Due to the formation of intermetallic alloys, the density of test samples often exceeded the theoretical density of materials used in the segments.

EXAMPLE 6 Performance Evaluation of Grinding: Samples of experimental segmented wheels filled with graphite, with a low diamond concentration of 280 mm diameter, 29.3 mm thick, 228.6 mm central hole, (11 x 1.155 x 9 in), made of According to example 5, they were tested for grinding performance. The performance of these tests was compared to that of the back grinding wheel of example 5 that was made according to the diamond abrasive segment composition (concentration 75) of example 1 (wheel # 6) without graphite filler. About 70 frosted, each 114.3 mm (4.5 inches) wide and 1.42 mm (0.056 inches) deep, were made in AITiC work pieces (AITiC grade 210 obtained from 3M Corporation, Minneapolis, MN) of square dimensions of 4.5 inches (114.3 mm) or 6.0 inches (152.4 mm), and the microns of the removed material and the normal grinding force were recorded. The conditions of the grinding test were: Grinding test conditions: Machine: Strasbaugh Grinder Model 7AF Grinding mode: Vertical spindle penetration Wheel specifications: 280 mm in diameter, 29.3 mm in thickness and 229 mm in hole Wheel speed: 1, 200 rpm Working speed: 19 rpm Cooler: Deionized water Material removal speed: Varies, 1.0 micron / sec at 5.0 micron / sec. The wheels were aligned and sharpened with a 6 inch (152.4 mm) bearing bearing sharpening for sharpening specification 38A240-HVS obtained from Norton Company, Worcester, MA. After the initial operation, the sharpening and alignment were conducted periodically as necessary and when the feed rates were changed. The results of the grinding test (normal force against material removed) for example 5, samples 2, 4 and 1, are shown below in table 5, and in figure 3.

TABLE 5 Normal grinding force against material removed Sample Control Control Control 2a 2a 2b 4 wheel (eg 1) (eg D (eg D MRR 1 3 5 1 2 2 2 (μ / sec): Ground material Normal grinding force Ibs (kg) total (μ) 25 6 (2.7) 8 (3.6) 11 (5.0) 1 1 (5.0) 50 16 (7.3) 20 (9.1) 23 (10.4) 6 (2.7) 7 (3.2) 19 (8.6) 20 (9.1) 75 12 (5.4) 7 (3.2) 23 (10.4) 22 (10.0) 100 24 (10.9) 34 (15.4) 40 (182) 17 (7.7) 7 (32) 27 (12.3) 28 (12.7) 150 27 (12.3) 45 (20.4) 50 (22.7) 22 (10.0) 7 (32) 31 (14.1) 32 (14.5) 200 33 (15.0) 50 (22.7) 59 (26.8) 28 (12.7) 21 (9.5) 34 (15.4) 36 (16.3) 250 37 (16.8) 53 (24.1) 60 (272) 31 (14.1) 30 (13.6) 38 (17.3) 38 (17.3) 300 40 (18.7) 57 (25.9) 63 (28.6) 33 (15.0) 35 (15.9) 40 (182) 36 (16.3) 350 36 (16.3) 39 (17.7) 42 (19.1) 38 (17.3) 400 39 (17.7) 41 (18.6) 40 (182) 33 (15.0) 450 42 (19.1) 42 (19.1) 40 (182) 34 (15.4) 500 42 (19.1) 45 (20.4) 41 (18.6) 34 (15.9) 550 43 (19.5) 46 (20.9) 43 (19.5) 35 (15.9) 600 46 (20.9) 46 (20.9) 39 (17.7) 31 (14.1) to. 2a is sample 2 of table 3 with an edge width of abrasive segment of 3.13 mm. b. 2b is sample 2 of table 3 with an edge width of abrasive segment of 2.03 mm. These results demonstrate that a significant increase in normal force was necessary to remove large amounts of material at higher MRRs (MRR from 1 to 3 microns / second) when the surface was grinded with the control wheel sample that did not have graphite filler and a concentration of 75 diamond abrasive. In contrast, the graphite-filled wheels, of low diamond concentration, of example 5 of the invention (samples 2a, 2b and 4) required significantly less normal force during the grinding. The force required to remove an equivalent amount of material at an MRR of 2 microns / second for the wheel of the invention was equivalent to that required for an MRR of 1 miera / second for the comparative wheel sample. In addition, the wheel samples 2a required approximately equal normal forces to grind at an MRR speed of 1 miera / second or an MRR of 2 micras / second. The wheels of the invention 2a, 2b and 4 of example 5 also presented demands of relatively stable normal force as the amount of ground material progressed from 200 to 600 microns. This type of grinding performance is highly desirable for the subsequent grinding of AITiC wafers because these stable, low-strength conditions minimize thermal and mechanical damage to the workpiece. The control wheel (example 1) could not be evaluated at higher material removal levels (for example, above about 300 microns) because the force needed to grind these wheels exceeded the normal force capacity of the machine to grind, thus causing the machine to turn off automatically and preventing the accumulation of data at the highest material removal levels. Although not intended to be limited by a particular theory, it is believed that the superior grinding performance of the wheels of the invention filled with graphite, of low diamond concentration, is related to the small number of individual fragments per unit area of the segment. abrasive that comes into contact with the surface of the workpiece at any time during the grinding. Although a person skilled in the art will expect a lower MRR at a lower diamond concentration, the grinding force improvement of the invention is met unexpectedly without compromising the MRR. The wheel 2b, having an abrasive segment width of 2.03 mm, required less force to grind at the same speeds and amounts of material removal as the wheel 2a, having an abrasive segment width of 3.13 mm. The wheel sample 2b had a smaller surface area and fewer grinding points in contact with the surface of the workpiece at any time during the grinding operations compared to the wheel sample 2a.

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - An abrasive tool for grinding surfaces comprising a center, having a specific minimum resistance parameter of 2.4 MPa-cm3 / g, a center density of 0.5 to 8.0 g / cm3, a circular perimeter, and an abrasive edge defined by a plurality of abrasive segments; wherein the abrasive segments comprise, in amounts selected to give a maximum total of 100% by volume, from 0.05 to 10% by volume of superabrasive fragment, from 10 to 35% by volume of deleterious filler, and from 55 to 89.95% by volume. volume of matrix agglutinated with metal having a fracture toughness of 1.0 to 3.0 MPa M1 /

2. 2. The abrasive tool according to claim 1, further characterized in that the center comprises a metallic material selected from the group consisting of aluminum, steel, titanium and bronze, mixed materials and alloys thereof, and combinations thereof.

3. The abrasive tool according to claim 1, further characterized in that the abrasive segments comprise from 60 to 84.5% by volume of matrix bonded with metal, from 0.5 to 5% by volume of abrasive fragment, and from 15 to 35% in volume of deleznable filler, and the matrix agglutinated with metal comprises a maximum of 5% by volume of porosity. 4.- The abrasive tool in accordance with the claim 1, further characterized in that the deleznable filler is selected from the group consisting of graphite, hexagonal boron nitride, hollow ceramic spheres, feldspar, nepheline syenite, pumice stone, calcined clay and glass spheres, and combinations thereof. 5. The abrasive tool according to claim 1, further characterized in that the abrasive fragment is selected from the group consisting of diamond and cubic boron nitride and combinations thereof. 6. The abrasive tool according to claim 5, further characterized in that the abrasive fragment is diamond having a grain size of 2 to 300 micrometers. 7.- The abrasive tool in accordance with the claim 1, further characterized in that the metal binder comprises from 35 to 84% by weight of copper and from 16 to 65% by weight of tin. 8. The abrasive tool according to claim 7, further characterized in that the metal binder further comprises 0.2 to 1.0 wt% phosphorus. 9. The abrasive tool according to claim 1, further characterized in that the abrasive tool comprises at least two abrasive segments and the abrasive segments have an elongated, arched shape and an internal curvature selected to align with the circular perimeter of the center, and each abrasive segment has two ends designed to mate with adjacent abrasive segments so that the abrasive edge is continuous and substantially free of spaces between abrasive segments when the abrasive segments agglutinate with the center. 10. The abrasive tool according to claim 1, further characterized in that the tool is selected from the group consisting of type 1A1 wheels and cup wheels. 11. The abrasive tool according to claim 1, further characterized in that the thermally stable binder is selected from the group consisting essentially of an epoxy adhesive binder, a metallurgical binder, a mechanical binder and a diffusion binder, and combinations thereof. same.