A superabrasive cutting element for use with a drill bit for drilling subterranean formations and having a superabrasive table, or cutting face, in which a conglomerate of superabrasive particles is dispersed and bonded, or sintered, and in which at least one exposed cutting region of the superabrasive table develops a rough, asperital surface for improving the cutting efficiency of the drill bit, particularly in but not limited to relatively hard, relatively nonabrasive formations. The superabrasive table may include superabrasive particles of substantially differing size, or quality or a combination of differing size and quality. A rotary drill bit including cutting elements embodying the present invention is also disclosed.

1. Field of the Invention
This invention relates generally to superabrasive cutting elements and, more specifically, to polycrystalline diamond compact cutting elements and drill bits for subterranean drilling equipped with such cutting elements.
2. State of the Art
Superabrasive elements are used extensively in drilling, cutting, milling, and other operations relating to the removal of portions of hard materials. A superabrasive element useful in subterranean drilling conventionally includes a polycrystalline diamond (PCD) table, having a cutting surface, or face, of natural or synthetic diamond particles or, less typically, cubic boron nitride (CBN) particles sintered under high-pressure, high-temperature conditions into a coherent conglomerate mass. Such tables are referred to herein generally as superabrasive tables. In order to support the very hard but relatively brittle PCD table, the PCD table is typically bonded to a substrate of tungsten carbide or other similarly tough cemented carbide substrate by way of high-pressure, high-temperature (HPHT) sintering techniques known within the art to form a unified structure which is typically cylindrically shaped and referred to within the art as a polycrystalline diamond compact cutting element, "PDC cutting element" or "PDC cutter." A plurality of such PDC cutting elements, or cutters, may be mounted in a wide variety of patterns on at least the face portion of a rotary drill bit to provide a bit that is particularly useful for drilling subterranean formations. Typically, such PDC cutting elements are formed by placing a cemented tungsten carbide substrate preform into a specially designed press and placing a superabrasive material such as diamond particles, or grains, of a preselected size as well as a sintering agent, or catalyst, such as cobalt, atop the substrate preform and enclosing them in a protective metal enclosure. Under the previously mentioned high-pressure and high-temperature conditions, which may respectively exceed approximately 50 kbars (approximately 5000 Mpa) and approximately 1200° C., the diamond grains are sintered or bonded together to form the previously described PCD table while simultaneously sintering, or bonding, the superabrasive table and the tungsten substrate together to form a unified PDC cutting element that may then be securely installed in a drill bit by way of brazing or other bonding techniques known within the art.
In the past, the diamond grains, or particles, generally used as feed stock in forming a superabrasive table, whether natural or synthetically derived, had nominal diameters, or sizes, which fell within a preselected relatively narrow range, or size distribution. Such a narrow size distribution resulted in superabrasive tables being formed of a diamond feed stock which would have a homogenous structure of essentially uniform, like-sized, like-quality diamond particles, or grains. That is, the feed stock of diamond grains, or particles, used to form a superabrasive table would generally be of a similar quality and a quite similar small, or fine, size. The grain size of such conventional diamond feedstocks typically ranges from 1 micron (1 μm) to 100 microns (100 μm), with a nominal size of 30 μm to 60 μm being common.
Currently, manufacturers and vendors of cutting elements used for industrial purposes such as in the drilling of subterranean formations are using "multimodal" feedstocks in making superabrasive tables for cutting elements such as PDC cutting elements. Such "multimodal" feedstocks typically consist of a mixture of superabrasive particle sizes that tend to vary over a wider range than the feedstocks used to make superabrasive tables in the past. However, these "multimodal" feedstocks tend to comprise superabrasive particle sizes in the range of zero to thirty microns (0–30 μm). The lower end of the range, being designated as zero, indicates the presence of submicron-sized particles. However, it is important to note that even the modem "multimodal" feedstocks typically used in forrming superabrasive tables of cutting elements such as PDC cutting elements installed on subterranean drill bits, will typically have an average particle size ranging from 15 to 25 μm, although multimodal superabrasive tables having an average particle size of 30 to 60 μm are known.
PDC cutting elements have been commercially available for more than 25 years and have become widely accepted and heavily relied upon by the oil and gas industry. For example, PDC cutting elements are installed in rotary drill bits, such as "drag bits" used extensively in the drilling, or boring, of wells in subterranean formations in the exploration and production of hydrocarbons in the form of crude oil and natural gas, as well as for the drilling of geothermal wells and special purpose wells, such as steam injection wells and monitoring wells. The use of PDC cutting elements in rotary drag bits for earth boring has resulted in major increases in penetration rates and overall reductions in drilling costs for a broadened range of subterranean formation types.
Notwithstanding the many benefits offered by PDC cutting elements when drilling certain hard but not necessarily highly abrasive rock formations such as, but not limited to, the drilling of formations of limestones, marble, dolomite, and some evaporites, PDC cutting element-equipped drill bits may have a tendency to produce a relatively smooth, flat surface, or wear scar, on the cutting edges and related surfaces of each of the PDC cutting elements, reducing the ability of the drill bit to cut the formation. That is, it is not uncommon when drilling in hard but not necessarily abrasive formations over an extended period of time with drill bits provided with currently available PDC cutting elements for the wear scars of the individual PDC cutting elements to, in effect, form a bearing surface, or contact area, between each of the PDC cutting elements secured to the drill bit and the formation being drilled. Such bearing surfaces in effect stop or severely reduce the rate of formation cutting as the conventional PDC cutting elements are not able to adequately engage and efficiently remove the formation material from the area of contact. This type of unwanted bearing surface, or contact area, is also referred to within the art as a "wear flat" in addition to being referred to as a "wear scar."
Therefore, the rate of penetration (ROP) or speed in which the drill bit progresses through such hard, nonabrasive formations may often be reduced, or slowed, because the superabrasive table of the cutting elements, being composed of a homogeneous structure of substantially fine, like-sized, like-quality diamond particles, or grains, as previously described, is unable to provide cutting surfaces or edges which will optimally engage and remove formation material as efficiently as would be desired to maintain a given ROP as compared to the ROP of the same drill bit in other formations, including, but not limited to, formations that are relatively less or more hard, but which are relatively more abrasive. Additionally, relatively fine, homogeneous diamond particle sizes with homogeneous wear characteristics used to manufacture a superabrasive table may allow an initially sharp cutting edge to become rounded with use. Such rounding or dulling of the cutting edge also reduces the ability and effectiveness of the cutting elements to remove the formation material.
U.S. Pat. Nos. 5,011,514 and 5,151,107 to Cho et al. disclose superabrasive cutting elements, backed compacts, and methods for their manufacture wherein superabrasive particles such as diamonds are provided with a metal coating prior to being sintered to form a polycrystalline compact. In one embodiment, metal-coated superabrasive particles of a preferably uniform size are combined with uncoated superabrasive particles of a smaller size within a preselected binder to form a "bimodal" cutting element. Cho et al. further discloses that an additional, yet smaller, superabrasive powder may be added to form a "trimodal" cutting element.
U.S. Pat. No. 5,096,465 to Chen et al. discloses a superhard cutting element manufactured by a low-temperature, low-pressure infiltration process suitable for use within an earth-boring bit being formed by metallic-coated abrasive particles of a single large size within a range of 50–2000 μm, with about 400–600 μm being preferred, and being combined with a binder alloy so that the diamond particle component ranges from approximately 40–75% by volume of the superabrasive table with the remainder of the volume being a suitable infiltrating alloy such as nickel, cobalt, iron, aluminum, and copper-based alloys. Alternatively, a bimodal distribution of larger-sized coated superhard particles within a range of 400–600 μm combined with smaller-sized superhard particles selected from a size range of about 50–65 μm may be used with an alloy binder to form a superhard cutting element in accordance with Chen et al. In the bimodal alternative, the larger-sized coated superhard particle concentration is taught as being approximately 90% by volume of the total diamond component and the smaller-sized coated superhard particle concentration is taught as being approximately 10% by volume of the total diamond component wherein the total diamond component may reach as high as 75% by volume. A further embodiment is disclosed in Chen et al., featuring a superhard product having a trimodal distribution of particles wherein the third charge of yet smaller superhard or abrasive particles is sized to be about ⅙ to 1/9 the size of the secondary charge of particles.
A diamond cutter for use in a drill bit fabricated by assembling a plurality of prefabricated thermally stable PCD elements of preselected geometric shapes and sizes placed and bonded together in a preselected array within a cutting slug is disclosed in U.S. Pat. No. 5,028,177 to Meskin et al. Embodiments having the thermally stable PCD elements sintered within a metallic matrix material having diamond grit therein are set forth in Meskin et al.
In U.S. Pat. Nos. 4,988,421 and 4,992,082 to Drawl et al., a tool is formed by coating a plurality of layers of separated diamonds or diamond-like particles onto a nondiamond, or nondiamond-like tool substrate wherein a planarized binding material extends between and on each of the separated diamond particles to secure the diamond particles.
U.S. Pat. No. 4,604,106 to Hall et al. discloses a PCD compact having precemented carbide pieces interspersed in polycrystalline diamond and a binder to provide a composite abrasive compact. One embodiment comprises a compact formed of a composite material wherein the concentration of the diamond particles is at its highest near the working surface and the concentration of the carbide pieces is at its highest away from the working surface. Another embodiment is disclosed having a plurality of layers wherein a transition layer having a mixture of diamond crystals and pieces of precemented carbide together with a catalyst/binder material is provided.
U.S. Pat. No. 4,525,178 to Hall (Reexamination Certificate issued Mar. 27, 1990) is directed toward a material comprised of a polycrystalline material and preferably larger precemented carbide masses dispersed and sintered in the presence of a binder. The placement, shape, and size of the carbide masses may be varied to optimize performance of the subject material.
A process for forming a composite compact is disclosed in U.S. Pat. No. 4,311,490 to Bovenkerk et al., wherein a mass of abrasive crystals, a mass of metal carbide, and a bonding medium are sintered together. Bovenkerk et al. sets forth a process of placing a mass of abrasive crystals, and quantity of metal carbide, and bonding material or a catalyst within a protective shield metal enclosure and subjecting the contents of the enclosure to high-pressure and high-temperature. The process further includes disposing the abrasive crystals in two separate layers comprised of coarser abrasive crystals having a largest dimension of between about 75 to 500 μm disposed in one layer and the finer abrasive crystals having a largest diameter of less than 10 μm disposed in a second layer.
A cutting element formed from a plurality of polycrystalline diamond compact elements of a varying thickness and/or varying hardness to provide a cutting edge having a nonuniform wear pattern is disclosed by the assignee of the present invention in U.S. Pat. No. 5,238,074 to Tibbitts et al. The PCD elements may be of varying thickness and/or hardness to provide a cutting edge having a wear ratio which varies with cutter wear.
U.S. Pat. No. 3,885,637 to Veprintsev et al. sets forth a boring tool in which cutting elements having coarse abrasive grains embedded in a matrix layer ranging in thickness of about one-half to about two-thirds of the height of the coarse abrasive grains and in which the matrix layer contains fine abrasive grains embedded therein. The remaining portion of the large grains is covered with a second metallic layer. The coarse abrasive grains range in size from 1 to 2.5 mm and the fine abrasive grains range in size from 50 to 800 μm with layer 5 ranging from 0.3 to 0.6 mm.
U.S. Pat. No. 6,102,140 to Boyce et al. sets forth rotary cone cutter inserts having coated or encrusted diamond particles dispersed within a matrix body in a zone of the insert intended to engage earthen formations. The zone of the insert includes encrusted diamond pellets, tungsten carbide, and metallic cobalt which are fused together. The coating, or encrustation, is taught to be of a thickness equal to approximately one half the nominal diameter of the associated diamond particles. The encrusted diamond particles are taught as being distributed in the earthen formation-engaging zone of the insert in an amount of approximately 25% to approximately 75% by volume with up to 100% by volume being mentioned. Discrete sintered tungsten carbide particles are taught as forming a portion of the earthen formation-engaging zone of the insert.
Notwithstanding the preceding patents regarding the forming of cutting surfaces and/or cutting elements having superabrasive tables, there remains a need for cutting elements and/or superabrasive tables that offer improved cutting efficiencies over cutting elements known within the art when drilling in certain hard rock formations.
Thus, further advancements in the art are needed to increase the rate of penetration (ROP), or speed, in which a drill bit provided with PDC cutting elements is able to drill through not only certain hard, nonabrasive formations but any formation. Furthermore, the art seeks drill bits having increased ROP while retaining, if not improving, the desired attributes that drill bits provided with PDC cutting elements are known to have such as formation versatility, high impact toughness, high abrasion resistance, and generally high longevity in the very harsh conditions that are typically encountered in a downhole environment.
The cutting element of the present invention is particularly suited for being installed on a rotary drill bit and preferably comprises a superabrasive table of a nominal thickness and shape and which has at least one exposed cutting surface for engaging and cutting a subterranean formation. At least a portion of the superabrasive table may be formed by mixing a plurality of superabrasive particles exhibiting certain wear characteristics, such as synthetic or natural diamonds, with another plurality of superabrasive particles exhibiting different wear characteristics, such as synthetic or natural diamonds and, optionally, a binding catalyst such as cobalt powder. Upon the superabrasive particles being bound, or sintered, together by known high-pressure, high-temperature sintering processes, the surface or cutting face of the table of the cutting element is ground, lapped or even polished to exhibit a smooth, uniform exterior.
As the cutting element or, more precisely, the cutting edge of the superabrasive table at a periphery of the cutting face wears, the differences in relative wear characteristics of the different pluralities of superabrasive particles in that region of the cutting face cause the cutting edge to wear unevenly. Upon wearing, numerous vugs or asperities are formed in the cutting edge of the superabrasive table, which accentuate the roughness, or asperitness, of the diamond material contacting the formation. Thus, the cutting edge of the superabrasive table of the cutting element is constantly provided with a "rough cut" surface throughout the life of the cutting element as the diamond particles wear differently. This uneven, disparate wear process is continuously repeated until the entire useful portion of the superabrasive table has been worn away or the cutting element is retired from service. Thus, the preferably more predominant, jagged surfaces of the more wear-resistant diamonds that remain after the less wear-resistant diamonds have more quickly worn away or released from the superabrasive table concentrate the cutting forces in localized regions to better engage, fracture, and more aggressively remove the formation material into which the drill bit incorporating the cutting elements is drilling. Additionally, the conglomeratic nature of the superabrasive table being comprised of different particle size crystals prevents the formation of a uniform rounding or dulling of the cutting edge engaging the formation, thereby maintaining a more efficient cutting structure.
A drill bit equipped with cutting elements embodying the present invention is particularly well suited for drilling in hard, nonabrasive formations such as limestones, dolomites, marbles, and other sedimentary or evaporite formations without sacrificing the performance of such an equipped drill bit when drilling in more abrasive formations. Therefore, a drill bit provided with cutting elements embodying the present invention will have an overall increased level of formation versatility and an overall increased level of cutting efficiency and ROP as compared to prior art PDC cutting elements. Although cutting elements and drill bits embodying the present invention are particularly well suited for use in drilling in sedimentary, or evaporite formations, cutting elements embodying the present invention are not limited to such, as the same benefits and improved performance of cutting elements and drill bits embodying the present invention will also be applicable when drilling in other formations including, for example, hard, abrasive formations.
Differently sized superabrasive particles may be used to fabricate PDC cutting elements, in order to more closely pack the diamond particles. Accordingly, the present invention in one embodiment may incorporate the use of, for example, at least two different size ranges of diamond particles, wherein the relatively larger-sized superabrasive particles of a first size range may have nominal diameters which may range upwards of approximately 600 μm, with an exemplary range of between approximately 100 μm and approximately 600 μm, and the relatively smaller-sized superabrasive particles of a second size range may have nominal diameters in an exemplary range of between approximately 15 μm and 100 μm.
In another embodiment, relatively larger-sized superabrasive particles of a first size range may have nominal diameters which may range upwards of approximately 500 μm, with an exemplary range of between approximately 100 μm and approximately 250 μm. and the relatively smaller-sized superabrasive particles of a second size range may have nominal diameters in an exemplary range of between approximately 15 μm and 40 μm.
Thus, a first volume of relatively larger-sized superabrasive particles will exhibit a wear rate that generally falls within a first distribution range due to materials and processes used in fabrication thereof, and a second volume of relatively smaller-sized superabrasive particles will exhibit another wear rate that generally falls within a second, different distribution range due to the materials and processes used in fabrication thereof. It is contemplated that superabrasive particles in three or more size ranges may also be employed in fabricating cutting elements according to the present invention. Significantly, notwithstanding size differences, the wear characteristics of one volume of superabrasive particles are different than a second or succeeding volumes of superabrasive particles.
For example, a superabrasive table may be manufactured from approximately 85% by weight of 100 μm diameter superabrasive particles and from 15% by weight of 40 μm superabrasive particles exhibiting different wearing characteristics. Cobalt may be used as known in the art as a catalyst in a high-pressure, high-temperature (HPHT) sintering process with the diamond particles to stimulate diamond-to-diamond bonding. Alternatively, particle sizes and percentages may comprise 20% by weight of 40 μm particles, 20% by weight of 100 μm particles, and 60% by weight of 400 μm particles, with at least some of the particles exhibiting substantially different wear characteristics. Other relative proportions by weight of superabrasive, such as diamond, particles of different sizes suitable for use in the present invention include, by way of example only: 60% of 400 μm particles and 40% of 100 μm particles; 70% of 400 μm particles and 30% of 100 μm particles; 85% of 100 μm particles, 10% of 40 μm particles and 5% of 20 μm particles.
Further, the present invention contemplates use of substantially uniformly-sized particles which exhibit substantially different wear characteristics. A superabrasive table may be manufactured, for example, by mixing 50% by weight of 100 μm diamond particles with certain wear characteristics and 50% by weight of 100 μm diamond particles with substantially different wear characteristics. Of course, volumes of diamond particles exhibiting more than two different wear characteristics may also be employed. One exemplary embodiment for creating particles with different wear characteristics may comprise exposure of diamond particles to multiple HPHT sintering processes. Thus, sintered particulate diamond material may be manufactured by an HPHT process as known in the art and then sized to be used in subsequent HPHT processes for making superabrasive tables. Multiple sintering processes for the diamond particles may be employed. Enhanced diamond-to-diamond bonding or improved distribution of catalyst material may also be used to affect wear characteristics. Also, different superabrasive materials and/or processing techniques may be used in production of a superabrasive table comprised of materials with substantially different wear characteristics.
Exemplary superabrasive tables may have an exemplary thickness ranging between approximately 1 mm to approximately 5 mm; however, the present invention is readily suitable for use with a superabrasive table thickness outside this range. Because newly manufactured cutting elements, or cutters, embodying the present invention will generally have cutting surfaces that are relatively smooth as a result of being ground, lapped or polished, the cutting elements may need to be "broken-in." That is, after the drill bit in which the cutting elements are installed has been placed into service and has actively engaged and removed formation material within a wellbore, the bit will become broken-in after a period of time. Thus, after the drill bit has initially been placed into service, the cutting elements will wear slightly as is expected and desired, which wear will cause the cutting elements to exhibit the roughcut, or asperital, cutting surfaces in accordance with the present invention.
Another embodiment of the present invention, which may be used in lieu of or in conjunction with other embodiments hereof, not only includes using differently sized superabrasive particles, or diamonds, to make superabrasive tables, but also includes the use of substantially different grades. Thus, for example, a mixture of at least two different feed stocks of superabrasive particles, such as diamonds, which have different inherent qualities and strengths may be used to provide a superabrasive table in accordance with the present invention. As such a superabrasive table wears, the superabrasive particles of higher quality and strength will remain bound within the table structure longer than the superabrasive particles of lower quality and strength, which will be more readily fractured or damaged and, as a result, be dislodged from the table or face as the cutting element wears. Thus, the higher-quality particles provide the more pronounced, jagged exposed cutting surfaces, or cutting edges, and the vugs, or asperities resulting from the more readily worn, destroyed, and/or displaced lesser quality particles accentuate the exposed rough, jagged cutting region of the cutter and especially the cutting edge of the superabrasive table of the cutter.
In accordance with this invention, cutting elements particularly suitable for earth-boring drill bits are formed in a manner resulting in and maintaining an asperital, or rough, exposed surface on at least a portion of the cutting edge or other surfaces of the superabrasive table which are located and oriented to engage the formation after a cutting element has experienced some wear. The superabrasive table may include randomly distributed superabrasive particles of at least two substantially different nominal or average sizes resulting in at least one cutting edge or at least one exposed surface of the superabrasive table of the cutting element to generate concentrated cutting forces in localized regions.
An exemplary, but not limiting, drill bit 10 having cutting elements 20 of the present invention is illustrated in FIGS. 1 and 2. Drill bit 10 is known and referred to in the art as a rotary, fixed cutter, or drag, bit useful for drilling in a wide variety of subterranean formations. For example, drill bit 10 is particularly suitable for drilling through subterranean formations to reach targeted areas in which deposits of crude oil and/or natural gas are known or suspected to be present, or which may be used for drilling special purpose subterranean bore holes. Cutting elements 20 of the present invention may be advantageously used in any of a wide variety of drill bit configurations suitable for incorporation of superabrasive cutting elements.
Drill bit 10 of FIG. 1 includes a bit shank 12 having a conventional pin end 14 to provide a threaded connection to a conventional jointed tubular drill string rotationally and longitudinally driven by a drilling rig on the surface. Alternatively, drill bit 10 may be connected in a manner known within the art to a bottomhole assembly which, in turn, is connected to a tubular drill string or to an essentially continuous coil of tubing. Such bottomhole assemblies may include a downhole motor to rotate the drill bit 10 in addition to, or in lieu of, being rotated by a rotary table or top drive located at the surface (not shown within the drawings). Furthermore, conventional pin end 14 may optionally be replaced with various alternative connection structures known within the art. Thus, drill bit 10 may readily be adapted to a wide variety of mechanisms and structures used for drilling subterranean formations. Drill bit 10 also includes a bit body 16 having a face 18 including fluid passages 26 fed by nozzles 22 and to which cutting elements 20 are secured either directly or on bladed structures as shown. Furthermore, and as customary in the art, gage 24 is the maximum diameter in which drill bit 10 is to have about its periphery. Gage 24 will thus determine the minimum diameter of the resulting bore hole that drill bit 10 will produce when placed into service. The gage of a small drill bit may be as small as a few centimeters and the gage of an extremely large drill bit may approach a meter, or more.
An exemplary cutting element 20 of the present invention, as shown in FIG. 2, includes a superabrasive table 28 of circular, rectangular or other polygon, oval, truncated circular, or other suitable cross-section. Superabrasive table 28, exhibiting a circular cross-section and an overall cylindrical configuration, or shape, is suitable for a wide variety of drill bits and drilling applications. Superabrasive table 28 of cutting element 20 is preferably formed with a conglomerated superabrasive material such as a polycrystalline diamond compact (PDC), with an exposed cutting face 30. Cutting face 30 will typically have a top 30A and a side 30B with the peripheral junction thereof serving as the cutting region of the cutting face and more precisely the cutting edge 30C of cutting face 30, which is usually the first portion of the cutting face 30 to contact and thus initially "cut" the formation as the drill bit 10 retaining cutting element 20 progressively drills a bore hole. Superabrasive table 28 will also typically have a primary underside, or attachment, interface face 30D joined during the sintering of the diamond, or superabrasive, layer forming superabrasive table 28 to a supporting substrate 32 formed of a hard and relatively tough material such as a cemented tungsten carbide or other carbide, as may be seen in FIG. 4A. Returning to FIG. 2 of the drawings, substrate 32 may be preformed in a desired shape such that a volume of particulate diamond material may be formed into a polycrystalline table 28 thereon and simultaneously strongly bonded to substrate 32 during HPHT sintering techniques practiced within the art. A unitary cutting element 20 will thus be provided that may then be secured to drill bit 10 by brazing or other techniques known within the art.
In order to better illustrate the present invention, features of superabrasive table 28 of cutting element 20 have been exaggerated in FIGS. 3, 4A, 4B, 4B′, 4C, and 4D. In accordance with the present invention, superabrasive table 28 comprises a heterogeneous conglomerate type of PCD layer or diamond matrix in which at least two different nominal sizes and wear characteristics of superabrasive particles, such as diamonds of differing grains, or sizes, are included to ultimately develop a rough, or roughcut, cutting face 30, particularly with respect to cutting face side 30B and most particularly with respect to cutting edge 30C. Referring now to FIG. 3, which is a top view of cutting face top 30A, wherein larger diamonds or superabrasive particles 34 having a wear rate within a first selected wear rate distribution range may be seen to be substantially randomly dispersed within a greater number of smaller diamonds or superabrasive particles 38 having a wear rate within a second, different selected wear rate distribution range. For the sake of convenience, a mean exhibited wear rate of each of the wear rate distribution ranges may be employed to differentiate the respective wear rates. In one embodiment, larger diamonds 34 may range upwards of approximately 600 μm, with a preferred range of approximately 100 μm to approximately 600 μm, and smaller diamonds, or superabrasive particles, 38 may preferably range from about 15 μm to about 100 μm. In another embodiment, larger diamonds 34 may range upwards of approximately 500 μm, with a preferred range of approximately 100 μm to approximately 250 μm, and smaller diamonds, or superabrasive particles, 38 may preferably range from about 15 μm to about 40 μm.
The specific grit size of larger diamonds 34, the specific grit size of smaller diamonds 38, the thickness of cutting face 30 of superabrasive table 28, the amount and type of sintering agent, as well as the respective large and small diamond volume fractions, may be adjusted to optimize cutter 20 for cutting particular formations exhibiting particular hardness and particular abrasiveness characteristics. The relative, desirable particle size relationship of larger diamonds 34 and smaller diamonds 38 may be characterized as a tradeoff between strength and cutter aggressiveness. On the one hand, the desirability of the superabrasive table holding on to the larger particles during drilling would dictate a relatively smaller difference in average particle size between the smaller and larger diamonds. On the other hand, the desirability of providing a rough cutting surface would dictate a relatively larger difference in average particle size between the smaller and larger diamonds. Furthermore, the immediately preceding factors may be adjusted to optimize cutter 20 for the average rotational speed at which the cutting element will engage the formation as well as for the magnitude of normal force and torque to which each cutter 20 will be subjected while in service as a result of the rotational speeds and the amount of weight, or longitudinal force, likely to be placed on drill bit 10 during drilling.
By incorporating at least two groups of superabrasive particles of at least two substantially different mean wear rates, a primary characteristic of the present invention will be manifested by side 30B and cutting edge 30C of cutting face 30 of superabrasive table 28 developing a "roughcut" or asperital texture, as may be seen in the enlarged view of FIG. 4B, which depicts an isolated portion of superabrasive table 28 of exemplary cutting element 20, as shown in FIG. 4A. This particular aspect of the present invention enables cutting element 20 to more aggressively engage and remove the formation per each revolution of drill bit 10 when a bore hole is being drilled, thereby increasing the ROP. That is, the exposed "roughcut," or asperital, surface or surfaces of cutting face 30 may be generally attributable to larger diamonds, or superabrasive particles, 34 being slightly more exposed, particularly on side 30B and cutting edge 30C as shown in FIG. 4B or, alternatively, smaller diamonds 38 may be slightly more exposed.
The exact mechanism of forming the aforementioned asperital surface or surfaces is uncertain and may be related, in a given instance, to the selected proportional mix and number of superabrasive particle sizes as well as relative wear rates of superabrasive particles in the various volumes of such employed in forming superabrasive table 28. However, in one instance, the interstitial smaller diamonds or superabrasive particles 38 may wear away relatively more quickly as the cutting element is in service, resulting in vugs 42 providing asperities in the cutting surfaces. Such a "roughcut" or asperital texture of worn cutting face 30, and especially of worn cutting side 30B and cutting edge 30C, concentrates cutting forces in localized regions, i.e., primarily about the exposed portions of larger diamonds 34, to better engage and remove, or cut, the formation being drilled. Alternatively, larger diamonds 34 may wear away relatively more quickly, creating vugs 42 providing the asperities in the cutting surfaces provided by the remaining "matrix" of smaller diamonds 38. Larger diamond particles are inherently weaker than smaller ones and thus more easily fractured. Further, larger diamonds may be more difficult to sinter during formation of the superabrasive table 28, thus exhibiting weaker bonding thereto and resulting in easier loss therefrom. The foregoing relative bonding strengths of larger and smaller diamond particles within the superabrasive table 28 are encompassed by the term "wear rate" as used herein to indicate the overall tendency of a diamond particle to remain as a portion of a superabrasive table as the table wears during drilling.
Such improved efficiency may be particularly apparent while drilling hard, nonabrasive formations such as, but not limited to, limestones, shales, and evaporites. A portion of cutting face 30 will exhibit a roughcut, or asperital, surface, especially cutting edge 30C, which will be maintained throughout the life of the cutting element 20, because new asperities are constantly formed as the differently sized diamond particles are respectively worn away. However, the majority of culling top 30A, i.e., that portion of culling top 30A located to the right of cutting edge 30C as illustrated in FIG. 4B, will retain its original, preferably smooth finish as rendered by the final grinding, lapping or polishing process performed on the cutting element 20 during its manufacture because of its less aggressive interaction with the formation.
It should be understood that either natural diamonds or synthetic diamonds may be used as feedstock for forming cutting elements in accordance with the present invention. Furthermore, a combination of natural diamonds and synthetic diamonds may optionally be used as particulate feedstock for forming cutting elements in accordance with the present invention. Additionally, more than two selected sizes, or grains, of superabrasive particles may be used in practicing the present invention. For example, three or more different feedstocks of preselected superabrasive particles of a particular size, or falling within a preselected size range, may be used to provide a superabrasive table having at least one cutting surface, or at least a portion thereof, with the desired "roughcut," or asperital, surface preferably having randomly distributed larger superabrasive particles therein and wherein some of the abrasive particles eventually protrude substantially from at least a portion of the at least one cutting surface, or face, as the cutting element wears. Moreover, the at least one cutting surface, or a portion thereof, is provided with randomly distributed vugs of differing sizes to further enhance the effectiveness of the jagged cutting surfaces of exposed portions of the abrasive particles as interspersed, differently sized abrasive particles wear away as the cutting surface, and especially the cutting edge, wears with use.
FIG. 4B′ illustrates another embodiment that may be used in lieu of, or in conjunction, with the prior embodiment. As discussed earlier, the prior embodiment, among other things, features at least two groups or pluralities of at least two differently sized superabrasive particles with differing wear characteristics in the superabrasive table of a cutting element. Instead of relying solely upon a mixture of disparately sized diamonds having differing wear rates to provide a cutting element having a cutting face including at least one cutting surface to eventually exhibit an exposed roughcut, asperital surface as previously described, alternative superabrasive table 28′, a portion of which is illustrated in isolation in FIG. 4B′, comprises superabrasive particles 34′ and 38′ which are generally of the same size but which are of differing inherent quality and strength or, in other words, of a substantially different grade. Thus, the inherently weaker, less strong, less abrasion-resistant, and/or lower grade of abrasive particles or diamonds 38′ will be the first to wear away, fracture, or disintegrate and thereby be removed from a portion of cutting face top 30A′, a portion of cutting face side 30B′, and especially cutting edge 30C′ to repeatedly and continuously form a plurality of preferably randomly distributed vugs 42′ in at least the active cutting surfaces of superabrasive table 28′ as the table wears throughout its service-life. In other words, differences in wear rates of superabrasive particles of differing quality, in lieu of or in combination with diamonds, or superabrasive particles of differing size or sizes, may be used to provide a cutting element having a roughcut, asperital cutting face in accordance with the present invention. Those regions of cutting face 30′, including in most circumstances the vast majority of cutting face top 30A′ and side 30B′, which are generally not actively and directly engaging the formation, as discussed earlier with respect to superabrasive table 28 illustrated in FIG. 4A, essentially maintain the original smooth finish resulting from the grinding or polishing process performed on the cutting element during the manufacturing thereof. However, the active cutting surface or cutting edge 30C′ will, as superabrasive table 28′ wears, exhibit the desired rough, asperital surface of the present invention.
In order to fabricate an exemplary cutting element incorporating another embodiment of the present invention, a first feedstock of superabrasive particles, such as natural and/or synthetic diamonds, wherein the diamonds are of a high inherent quality, high strength, and high abrasion resistance, are combined with a second feedstock of superabrasive particles, such as natural and/or synthetic diamonds of generally the same size as the first feedstock, but wherein the diamonds of the second feedstock are of at least one of a substantially lower inherent quality, lower strength, and lower abrasion resistance than those of the first feedstock. Thus, the fraction of weaker, lower quality diamonds 38′ will be more quickly worn away from the exposed surfaces of the table, such as top 30A′, thereby leaving vugs 42′ as the cutting element wears with the fraction of stronger, higher quality diamonds 34′ staying in place longer to provide the desired randomly dispersed jagged cutting edges, or surfaces, to concentrate the cutting forces in localized regions in accordance with the present invention. If desired, weaker diamonds 38′ may be sized substantially smaller as described above with respect to superabrasive particles 34′. This allows further tailoring, or fine tuning, of the desired degree of asperity, or roughness, of the exposed cutting regions or surfaces of a table or cutting element is to exhibit when constructing cutting elements in accordance with the present invention as well as controlling the superabrasive particle density in the superabrasive table 28.
Superabrasive particles may have differing qualities for any number of reasons. For instance, internal flaws, inclusions, materials used, growth rate, and sintering kinetics may affect the quality of any given superabrasive particle. Catalyst distribution and interaction is also of importance in superabrasive particle quality. One method that may result in a higher quality feedstock is termed "multiple-sintering" processing. Multiple-sintering processing involves exposing superabrasive particles to HPHT processing, then reducing the sintered structure to particles for use in additional HPHT processing. Such multiple-sintering processing may improve the inherent quality of the feedstock and may distribute catalyst more evenly and effectively, thus improving the quality of the final sintered superabrasive table. Therefore, multiple-sintering may be used in accordance with the present invention.
FIGS. 4C and 4D each show superabrasive table 28 composed of homogeneous superabrasive particles 31 of a specified size range and exhibiting substantially uniform wear characteristics. Two problems associated with cutting elements composed of homogeneous wearing of superabrasive table 28 are illustrated in FIGS. 4C and 4D. Specifically, FIG. 4C shows a superabrasive table 28 after being placed into service as taken in the same direction and depicted in the same manner as in FIGS. 4A and 4B with a rounded cutting edge 30C. Rounded cutting edge 30C is formed from an initially sharp edge coming in contact with the formation during drilling. Rounded cutting edge 30C requires considerably more force in order to drill a formation at a given rate of penetration than a sharp cutting element would require, as the load on the rounded cutting edge 30C is applied over a significantly greater surface area. Thus, aggressiveness of the cutting element with a rounded cutting edge 30C is reduced when compared to a cutting element of the present invention. Further, FIG. 4D shows a superabrasive table 28 after being placed into service as taken in the same direction and depicted in the same manner as in FIGS. 4A and 4B with a wear scar surface 33 along the cutting edge 30C. Wear-scarred cutting edge 30C requires even more force in order to drill a formation at a given rate of penetration than a rounded or sharp cutting element would require as a result of its even greater surface area oriented toward the formation. Thus, a cutting element with a wear-scarred cutting edge 30C, as shown in FIG. 4D, is also less aggressive than a cutting element of the present invention.
Referring now to FIGS. 5 and 6, FIG. 5 is a photomicrograph of the top cutting surface of an exemplary cylindrically shaped PCD cutting element exemplifying a preferred embodiment of the present invention, magnified eight times the actual size. The actual size of the exemplary cutting element of FIG. 5 is approximately 1.3 cm in diameter. FIG. 6 is a representative portion of the same top cutting surface photographed in FIG. 5, but is magnified twenty times the actual size of the cutting element photographed in FIG. 5. The larger diamond particles appear as dark-colored shapes dispersed with the lighter-colored smaller diamond particles, all of which are sintered together to provide a superabrasive cutting table embodying the present invention. The larger diamond particles have a nominal diameter of approximately 600 μm and the smaller diamond particles have a nominal diameter of approximately 20 μm.
In practice, it is often difficult to randomly disperse differently sized diamond particles. Often, due to slight differences in packing density and vibrations present or applied during manufacturing, differently sized diamond particles segregate. As illustrated in FIG. 5, the larger diamond particles have segregated somewhat, forming a slight gradient toward edge 50 during the manufacturing process. Such segregation may be used advantageously to produce cutting tables with varying characteristics as the cutting element wears, or to produce a useful portion of a superabrasive table (such as a cutting edge) which exhibits a relatively higher or lower concentration of a particular particle size or sizes with respect to the remainder of the cutting element serving largely for securing the cutting element to a drill bit. Alternatively, segregation may be advantageously used to produce designed variances such as cutting edges with different or varying asperital characteristics. For example, diamond particles within a given size distribution range may extend from approximately 5% of the nominal thickness of the superabrasive table to approximately 40% of the nominal thickness of the superabrasive table. As another alternative, agents may be used to prevent or reduce segregation of the particles prior to sintering. Glycerin is sometimes used to inhibit segregation of powders, as well as other means known in the art. However, such additional materials may not be desirable for cleanliness and material compatibility reasons.
A cobalt sintering agent or catalyst as known in the art was used in the fabrication of the exemplary PDC cutting element shown in FIGS. 5 and 6. Furthermore, the supporting substrate to which the photographed superabrasive table is sintered was constructed of a cemented tungsten carbide material, also well known and used within the art.
It should be further appreciated that although the present invention, as set forth herein, has been described and illustrated in the context of a cutting element having a superabrasive table bonded, or sintered, to an underlying relatively tough substrate which in turn may be secured to a drill bit, other types of cutting elements, such as freestanding or unsupported cutting elements comprising a volume of polycrystalline diamond or other superabrasive material may be fabricated which incorporate one or more aspects of the present invention in light of the preceding description and the drawings included herein.
This invention may be embodied in many forms without departing from the spirit of the invention disclosed herein. Therefore, the various embodiments disclosed herein are intended to be illustrative and not restrictive, and the scope of the appended claims are not to be unduly limited by the preceding description and drawings. Furthermore, all variations and combinations encompassed by the disclosed subject matter, or which are equivalent thereto, are therefore intended to be embraced by the following claims.

Superabrasive cutting element having an asperital cutting face and drill bit so equipped


A magnetic field position and orientation measurement system contains, confines and re-directs the magnetic field from one or more transmitters such that the fields are attenuated in areas outside of the operating volume in areas where metallic objects are commonly found. A thin barrier made of a highly permeable material such as ferrite or mumetal is placed on top of a conductive plate. The thickness of the permeable layer is from 0.01 inches to 0.25 inches while the conductive plate, preferably made of an aluminum alloy, may preferably be from 3/16 of an inch to 1/4 inch in thickness. On top of the permeable barrier, a rhombic three axis transmitter is placed. In the preferred embodiment, the transmitter consists of a PC board carrying the transmitter. PC boards having thicknesses varying from 0.03125-0.125 inches may be employed. Thus, the entire "stack" including the transmitter, the permeable barrier and the conductive plate may only be from 1/2 inch to 5/8 of an inch in thickness. The permeable barrier may have a flat, planar configuration. Alternatively, it may be made to resemble, in cross-section, a cake pan having a flat central region with uplifted peripheral edges. Alternatively, the permeable barrier may have a generally flat configuration with peripheral edges that taper outwardly from the top surface thereof to the bottom surface thereof with the taper making an angle with the bottom surface in the range of, preferably, 30.degree. to 85.degree..

The present invention relates to a magnetic position measurement system with field containment means. The concept of using transmitting and receiving components with electromagnetic coupling is well known with respect to biomechanics and medical diagnostics, wherein a sensor assembly is mounted on a point of interest and the position of the point is determined relative to a fixed transmitter. This information is then used by computing systems to precisely show the relative motions of the points in question, which, in the medical sense, allows instruments to be precisely located in a human body with respect to the body and each other. This allows new, advanced methods of surgery and diagnostics to be performed.
When conductive materials are present, which is often the case on, below, or near an operating table, they generate eddy current fields, which distort the received magnetic field waveform, which distorts the output of the system unless the system utilizes some distortion reducing or compensating technique. When permeable materials are present, they bend and otherwise distort the magnetic field, with effects similar to conductive materials. In a surgical theater, both conductive and permeable materials are present in substantial quantities. They are a major component of many operating tables, surrounding equipment such as carts and equipment, and are present in the movable spot lamps used to illuminate the surgical field. Many operating tables have many degrees of positional and angular freedom to allow optimal placement of the surgical field relative to the surgeon, and are designed to be extremely stable and sturdy while supporting a heavy human body. As a result of these requirements, the tables contain numerous mechanisms allowing fore, aft, up, down, sideways, roll, and tilt motions. These mechanisms are physically robust and typically fabricated from steel, so that they have substantial field distortion characteristics. Shapes may include screws, rack and pinion gears, or scissors type actuators. The table surface may be one piece, or may be divided into several sections, with each section capable of motion relative to the other sections, to allow a body to be flexed such that various stresses and relative anatomical positions are optimal for a particular surgical or diagnostic procedure. The installed bases of operating tables are extremely diverse in design, and as the tables are often in service for many decades, there are many vendors, with each vendor carrying a number of different operating table designs. This poses a significant problem for magnetic position tracking systems which are used in a critical surgical environment. The operating volume for the tracker is typically within the body which lies on top of the table. This means that the tracking system is operating in close proximity to the metallic structures on, under, and around the table. The magnetic fields are distorted by these structures, which may result in large errors in the reported magnetic sensor position. The large diversity in table designs makes it impossible to predict the severity of distortion experienced on a given table. This is an unacceptable condition for a surgical environment. Attempts to compensate for these degrading effects have been made with varying degrees of effectiveness.
One method already employed is to map the entire operating volume each time the system is used. This is very time consuming and expensive, as potentially thousands of points must be taken in a precise manner if the distortion is severe and the operating volume large. It is also unreliable since during a surgical or diagnostic procedure, the table geometry is often changed which changes the relation of the table metallic structures relative to the tracking system, thereby requiring a new map if errors cannot be tolerated. Instruments and diagnostic equipment are also introduced and removed from the vicinity of the tracking system, thus rendering a map ineffective. Also, for severe distortion, a map may become totally ineffective, as the system may, at two different physical sensor spatial points, determine the sensor to be at the same position. In this case, the output data is of minimal use.
Another known method commonly described in prior art is to use AC fields over a conductive ground plane. The ground plane attenuates the magnetic field below the plane to nearly zero, which has the benefit of making the system insensitive to metallic objects below the plane. In the case of a dipole transmitter, the "method of images" is used to compute the theoretical magnetic field vectors over the plane, which are then used to provide sensor position. This method has drawbacks. One is that near the ground plane, the magnetic field intensity is nearly zero, and the vector crossing angles are degraded, which seriously reduces system performance with respect to accuracy and noise. The net result is that the sensor must be kept a few inches above the plane. Also, the dipole must be located some distance from the ground plane in order to reduce signal losses and degraded vector crossing angles within the operating volume. For a 1 cubic foot volume, the bottom of the transmitter must be about 2 inches above the plane for acceptable performance. To compute the height at which a patient must be elevated if lying on the transmitter, the thickness of the transmitter must be added to this 2 inch figure. Transmitter size is determined by required signal level within the operating volume. Sensor coil size for minimally invasive surgical applications is about 1 mm.times.5 mm in cross-section, which is very small. The requirement for precise, low noise operation at the extreme edges of the volume requires that a relatively large magnetic field magnitude be present in order to induce sufficient signal in the small coils. Transmitter size is largely dictated by how much field it must output. Since the transmitter is typically a cube, to obtain sufficient signal within a 1 cubic foot volume with a small receiver coil, the practical transmitter dimensions are on the order of 2 inches per side. We can now see that the effective transmitter assembly in this prior art teaching, including the ground plane, is 4 inches thick. In a surgical environment, the patient must be elevated to levels which a surgeon may find uncomfortable. In addition, extra padding may become necessary if the patient must lie flat on the table. Both the transmitter and the padding must be secured to the table. In short, the configuration is cumbersome and may not allow the patient to be positioned in an optimal manner.
Placing the transmitter above the operating volume is not desirable as it will potentially interfere with the surgical field. Also, as the transmitter is placed further from the ground plane, and if the dimensions of the ground plane are fixed to be a square of about 18 inches on a side, the ground plane becomes ineffective at reducing the effects of metallic objects near the operating volume. The metal housings of the surgical lighting equipment will have a greater distorting effect in the upper portions of the operating volume, as they are closer to both the transmitter and receiver. Equipment used during the procedure, including the operating table, will cause potentially life threatening distortion, which is an unacceptable condition.
Position determination depends on relative vector magnitudes from the x, y, and z coils. Distortion effects may again be removed by using a process such as mapping. As the magnitudes of the transmitted magnetic vectors from the x, y, and z coils become more similar, a given fixed amount of error in their determination will result in an increased error in position output. Again, considering the limiting case, if the magnitudes become equal then position determination is not possible. This combined effect of reduced angle of transmitted vector intersection and reduced difference in transmitted vector magnitudes is known to those skilled in the art as vector dilution. Use of a conductive ground plane under the transmitter will cause vector dilution. The severity of the vector dilution is increased as the transmitter becomes closer to the ground plane, and is also increased as the receiver becomes further from the transmitter. Vector dilution generally imposes a practical limit on how close the transmitter of a magnetic tracking system may be placed to a conductive ground plane. For a 1 cubic foot motion box, vector dilution approaches unacceptable levels if the transmitter is placed closer than 2 inches from an infinite extent conductive ground plane. Vector dilution is also present in non-dipole transmitter configurations, and the effects of its presence are similar.
The Following Prior Art is Known to Applicant
U.S. Pat. No. 4,849,692 to Blood discloses a method of eliminating eddy current distortion effects, which are generated by conductive objects, such as the stainless steel table surface, and in other objects having large surface areas. The distortion effects of permeable metals are not addressed by this system. This means that steel structures in, around, and under the operating region of the system will distort the received magnetic fields and degrade system performance. In addition, large, thick sheets of conductive metals such as Aluminum have eddy current decay times which can exceed 200 milliseconds. If the system uses 3 time division multiplexed transmit axes plus one period where all axes are off in order to compensate for the earth's field, as described in the preferred embodiment, this means that the update rate is 1/4*(200 mS)=1.25 Hz. This is unacceptably slow for many applications.
U.S. Pat. No. 5,767,669 to Hansen, et al. describes methods for eddy current field compensation without the need to compensate for the Earth's field effects. This system has no provision for reducing the effect of nearby permeable metals, nor does it address the drawback of requiring a slow update rate while operating near large, thick sheets of highly conductive metals.
U.S. Pat. No. 5,600,330 to Blood discloses a non-dipole loop transmitter-based magnetic tracking system. This system shows reduced sensitivity to small metallic objects in the operating volume, as the field from the smaller object will fall off as 1/r 3 with r being the received distance from that object, while the field from the larger transmitting loops will fall off as 1/r 2, which yields a reduced effect from the small metallic object. Large sheets of metal, however, can have an effective loop area larger than the magnetic transmitter loops, which diminishes this advantage in field fall off rate, which has the general effect of making the system quite sensitive to large metallic objects. Also, metallic objects parallel to and near the transmitter loops produce very large eddy current magnitudes which reduces the signal level within the operating volume. In order to reduce the effects of metallic objects near the transmitter in this system, the transmit coils must be placed some distance away from the ground plane in order to reduce signal loss, which occurs when a loop of wire gets close to a conducting ground plane parallel with the plane of the loop. In the case of the planar transmitter configuration in this system, a planar ground plane may be placed some distance below the transmit coils. For zero distance, the magnetic field reduction within the operating volume is nearly total, so one must find a compromise between effective transmitter thickness, defined as the total thickness of the transmit coils, ground plane, and spacing between them, and signal loss. Also, due to the fact that the ground plane eddy current loop area is large with respect to a single transmit coil area, there is an additional degrading effect as the sensor gets further from the transmitter. The ground plane current distribution is similar no matter which transmit coil is operating. This means that the ground plane eddy current field vectors will be similar also. Since the field at any point within the operating volume is the vector sum of transmit coil field minus ground plane eddy field, and the ground plane field effective radius is larger than the transmit coil radius, we can see that the further we get from the plane of the transmitter, the more the field is determined by the ground plane currents. The net effect is that the vectors from the 3 transmit coils are less distinct, which makes the system more sensitive to noise and metallic distortion, as the system uses differences in the vector magnitudes and directions to determine position. As these differences become small, a small change on one of the vectors can result in a large apparent change of receiver position.
U.S. Pat. No. 5,752,513 to Acker, et al. depicts a system which is a subset of the system described by Blood '330, and operation in all respects is identical with respect to non-dipole transmitter properties and metal sensitivity.
U.S. Pat. No. 5,550,091 to Fukuda, et al. depicts a system using a so-called "Helmholtz" arrangement to produce a controlled field within the operating volume. One disadvantage of this system is its bulk, requiring the operating volume to be surrounded by the "Helmholtz" coil assembly. A second disadvantage of this system is that, when placed upon a metallic object such as a steel table, the magnetic field from the transmit coils will be distorted inside of the operating volume.
U.S. Pat. No. 5,640,170 to Anderson discloses a method of positioning a dipole over a specially constructed spiral over a ground plane. The dipole transmitter in this system must be located over the center of the spiral ground plane assembly, which makes patient placement more difficult in a clinical setting, as this placement may interfere with the surgical field during certain procedures. The benefit of this method is that it is possible to locate the transmitter closer to the ground plane, and one does not need to use the "method of images" to solve for position, but the disadvantage of transmitter location over the spiral/ground plane assembly is very similar to the case of a ground plane only.
U.S. Pat. No. 5,198,768 to Keren depicts a surface coil array for use in NMR applications. The system does not determine position, and does not utilize any methods for reducing the effect of nearby metallic objects.
The present invention represents a radical departure from the prior art relating to such transmitting and receiving position and orientation devices insofar as it is capable of satisfying the requirement of insensitivity to metallic objects under and adjacent to the transmitter assembly without exhibiting the disadvantages of signal degradation.

Magnetic field permeable barrier for magnetic position measurement system


A method of treating metal-contaminated spent foundry sand, or other industrial waste, by combining the sand with a sulfite to produce insoluble metal sulfur oxide complexes that do not leach from the sand. The treated waste may also be processed to reducing xe2x80x9cclumping,xe2x80x9d thereby rendering the treated waste appropriate for use in another industrial process.

The present invention relates generally to methods of treating industrial waste, including spent foundry waste, and more particularly to a method of treating such waste to reduce the leachability of certain toxic metals and to process those wastes to make them suitable for use as a raw material.
Industrial wastes, such as spent foundry sands and slags, typically contain leachable or extractable metallic contaminants. These wastes are then classified as hazardous or non-hazardous, or toxic/non-toxic, depending on the levels of contaminants indicated by various leach modeling methods, including: 1) Toxicity Characteristic Leaching Procedure (TCLP; EPA method 1311, xe2x80x9cTest Methods for Evaluating Solid Waste, Physical/Chemical Methodsxe2x80x9d SW-846); 2) Synthetic Precipitation Leaching Procedure (SPLP; EPA Method 1312, xe2x80x9cTest Methods for Evaluating Solid Waste, Physical/Chemical Methodsxe2x80x9d SW-846); 3) Multiple Extraction Procedure (MEP; EPA method 1320, xe2x80x9cTest Methods for Evaluating Solid Waste, Physical/Chemical Methodsxe2x80x9d SW-846); and 4) Indiana Leaching Method, Neutral (Indiana NL; 329 Indiana Administrative Code 10-7-4(b)(3)(B)).
When the waste is hazardous or toxic, provisions exist for its disposal at a hazardous waste landfill. Because disposal in a hazardous waste landfill is expensive, hazardous or toxic waste is preferably treated to reduce the levels of contaminants to acceptable levels. The waste can then be disposed of at less expense in a non-hazardous waste landfill.
Although disposal of hazardous or toxic waste made non-hazardous or non-toxic by treatment is less costly than disposal of untreated toxic or hazardous waste, disposal of that waste is still relatively expensive. If the waste could be used in another industrial process, significant savings and environmental benefits could be achieved.
Some wastes have physical characteristics that enable them to be used in other industrial processes. For example, addition of pozzolanic coal ash to portland cement mixtures allows the derived concrete to obtain a much greater compressive and shear strength than concretes derived from portland cements alone. More specifically, addition of pozzolanic fly ash to portland cement is essential in obtaining compressive and shear strengths required for construction of certain articles. Furthermore, several states currently allow the use of foundry wastes as alternate raw materials.
However, many states require the levels of contaminants in foundry sands, slags and other industrial waste to be below certain levels prior to their reuse. Therefore, if they are present above those levels, the leachable and extractable metallic contaminants must first be chemically stabilized before the industrial waste can be utilized in another process.
Typical methods of treating industrial waste include adding to the waste either a phosphate compound in combination with a metal oxide and water or Portland cement (and/or cement kiln dust, quicklime, pozzolanic fly/bottom ash, etc.) and water. These methods result in the waste becoming substantially solid and typically add at least ten percent by weight of other non-useful materials to the waste. Because of the need for subsequent crushing to form aggregate, these methods destroy the useful characteristics of wastes as substitute aggregate. For example, the particle size and shape distribution of foundry sands would be detrimentally altered after being treated by these methods. Moreover, although some prior art methods treat industrial waste with only a phosphate-containing compound, no steps are taken to retain or recover the particle size and shape distribution of the waste so it can be used in other industrial processes.
There is therefore a need for an economical method to treat industrial wastes such as foundry sands or slags. Specifically, there is a need for a method of treating industrial wastes that leave their useful particle shapes and size distributions unchanged so the wastes may be recycled as raw materials useful in other industrial processes.
Briefly describing one aspect of the present invention, there is provided a method of treating waste contaminated with leachable metallic contaminants by combining the waste with a sulfite such as calcium sulfite. The previously leachable metal contaminants are then complexed as insoluble metal sulfur oxides, and the material is safe for use as a raw material.
In another aspect of the invention, industrial wastes such as foundry sand or slag containing metallic contaminants is treated by first reducing the size of the sand or slag xe2x80x9cclumpsxe2x80x9d or xe2x80x9cchunksxe2x80x9d until the sand or slag is returned to a particle size that is about the same as the size of the sand or slag particles before it was contaminated. The particles are then combined with a reactant effective for converting the metallic contaminants to a non-leachable form, and the product thus formed is useful as a substitute raw material in the production of, for example, concrete. In a preferred embodiment of this second aspect of the invention, the reactant is comprised of a sulfite such as calcium sulfite.
One object of the present invention is to provide a method for recycling industrial waste, including foundry sands and slags.
Further objects and advantages will be apparent from the following description.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein, being contemplated as would normally occur to one skilled in the art to which the invention relates.
The present invention relates to a method for reducing leachable levels of metallic contaminants such as antimony, arsenic, barium, beryllium, cadmium, chromium, lead, selenium, silver, nickel, iron, manganese, magnesium, aluminum, bismuth, copper, thallium, and zinc in industrial wastes, and particularly in foundry sands and crushed slags. In the most preferred embodiments the sizes and shapes of the sand or slag particles are returned to the size and shape distributions inherent to those materials before they became wastes. One advantage of the inventive method is that it provides treated wastes that are in a condition such that they are useable as raw materials in other industrial processes.
In one aspect of the present invention, the grain structure and size distribution of typical spent foundry sands are restored or retained to make that material useful as a fine aggregate when added to cement to form concrete. The grain structure allows the use of less portland cement in a concrete mix, while affording an equally strong or stronger end product. The cost reduction obtained by using less raw material, and the added strength imparted by the grain structure, are significant. Thus, foundry sands and crushed slags can be processed so as to make them eminently suitable for use as an aggregate, raw material, or fill material. Ready-mix concrete, brick and block, mortar, bricks, concrete blocks, etc., may all benefit from the inclusion of waste foundry sand that has been processed according to the present invention. Asphalt used in roadways, parking lots, etc., can benefit structurally from the inclusion of processed slag. Moreover, the inventive treatment may be utilized to make wastes more suitable for other uses where certain jurisdictions allow environmentally benign wastes to be used in manners other than as an industrial raw material.
In one aspect of the invention, the size of the waste is first reduced prior to being combined with a reactant. Slags are generally reduced in size for subsequent use as alternate raw material prior to application of the reactant. If the size of the slag is not reduced prior to treatment, only certain surfaces of the slag will be in contact with the reactant. This reduces the efficacy of the treatment, and reduces the chances that the slag will be accepted for beneficial use under applicable rules and laws. Slags tend to be glassy, and will shatter readily upon application of suitable forces such as those generated by aggregate crushers, hammer mills, or pug mills. This generates a range of particle sizes which must then be screened in order to separate out the most useful size distributions. Larger particles can be reprocessed until a suitable size is obtained.
Chemically bonded sands must be processed in such a fashion as to reduce the agglomeration back to its original size distribution, without damaging the beneficial aspect of the grain structure. The types of bonding agents added to the sands in preparation of cores or molds are engineered to be broken up into chunks by application of moderate force, such as is found on a typical shakeout table. Placing core pieces in a tumbling device similar to a concrete mixer, or a mill of some type will provide the necessary force to break down the agents bonding the sand grains together. When this processing step is performed in conjunction with addition of a chemical oxidizer such as hydrogen peroxide, the chemical bonding agents are further broken down prior to stabilization of the metallic contaminants. Heat is also effective in breaking down chemical bonding agents.
Sands containing a bentonite/coal dust (e.g., greensand) or other bonding agent which is used to form molds by compression do not require a particle size reduction step and are treated by addition of a reactant. However, as bentonite colors the greensand, the sand may require removal of the bonding agent by a washing step to meet the material specifications of the end user. For example, for a facility that prepares colored paver tiles or manufactures concrete products such as cisterns or septic tanks, the coloration imparted by the bond agent may be of no importance. If coloration is important, the washing step is easily accomplished by backflushing the sand with water. The washing step can occur prior to, or subsequent to, treatment. This process can be performed in a tank or other suitable apparatus.
After any required size reduction step, the sands or slags are treated with a reactant to render any toxic metal unleachable from the material. On one preferred embodiment the reactant is a phosphoric acid or phosphate oxide. In another preferred embodiment the reactant is an orthophosphoric acid or a polyphosphoric acid, including metaphosphoric acids, and their monosubstituted or polysubstituted salts such as sodium, ammonium or calcium phosphates (especially calcium phosphate in the triple-superphosphate form). The phosphate oxide is preferably phosphorus pentoxide. Furthermore, the phosphoric acid or phosphate oxide is preferably present in an aqueous solution.
In another embodiment of the invention, the reactant is typically comprised of organic or inorganic sulfides, sulfates, sulfites or bisulfites. Other agents that may be combined with the reactant include sulfuric acid, nitric acids, aluminum oxides, and oxides of tungsten such as tungstic acid.
Furthermore, heat or chemical oxidizers such as peroxides or permanganates may be used to remove organic bonding agents from chemically bonded sands. Moreover, certain agents may be added to adjust the final pH of the treated materials when pH considerations are necessary. For example, when the treated waste is to be used as a structural fill material, the treatment should be carried out at a substantially neutral pH as acidic or basic media may destroy clays and influence the transport of metals in groundwater or surface water systems. The pH-adjusting agents include, but are not limited to, the disubstituted or trisubstituted salts of phosphoric acid, such as disodium phosphate, diammonium phosphate and trisodium phosphate.
In the most preferred embodiment, the waste foundry sand is treated with calcium sulfite. For most foundry sands or slags, about 5% to 25% by weight dried calcium sulfite is sufficient to treat the waste material, although lesser or greater amounts may be required for a particular waste.
Treating the foundry sand with a reactant converts the metallic contaminants to a non-leachable form. For example, treatment of foundry sand or slag containing metallic contaminants with a phosphoric acid or phosphate oxide converts the metallic contaminants to an insoluble form in water or acid media. Treatment with a sulfite converts the metallic contaminants to an insoluble metal sulfur oxide complex, which does not leach from the treated material.
When phosphoric acid is used, the sands or slags are preferably sprayed with an aqueous solution of orthophosphoric acid. The solution must be of a suitable molarity and amount to completely coat the surface of all particles being treated, and to react with the leachable metallic contaminants present in the waste sands and additional materials. The solution strength and addition rate must be experimentally determined. The strength and quantity of the solution added will depend on the selection of reactant, the chemical makeup of the waste, waste porosity, the quantity of waste and the level of contaminants in the waste. The concentration and quantity of solution added can be determined by one of skill in the art by performing one or more of the appropriate leaching tests described above. Typically, an aqueous orthophosphoric acid solution comprising 0.1-5% phosphate by weight is used.
When calcium sulfite is used, the sulfite is first preferably dried before being combined with the waste material, although the sulfite may be added while wet. A small amount of thiosulfate or other sulfate inhibitor is preferably added with the sulfite to prevent formation of the sulfate.
Further as to the calcium sulfite embodiment, calcium sulfite is generated as a sludge in the exhaust gas desulfurization process stemming from use of coal as a fuel source. The exhaust gases are funneled through a slurry of calcium carbonate in water. Through a substitution reaction in an oxygen poor atmosphere, calcium sulfite is formed rather than calcium sulfate.
Atmospheric oxygen will naturally change the sulfite to sulfate, but addition of an oxidation inhibitor during the sludge generation process keeps this from happening. In the preferred embodiments, a small amount of thiosulfates are added as the inhibitor. In other embodiments, other oxidation inhibiting compounds may be used. Adding the inhibitor significantly improves performance however, because the sulfate form is not as useful in terms of reacting with metals to form insoluble metal sulfur oxide complexes.
The dewatered calcium sulfite sludge is then dried, and is ready to be added to a toxic waste and the mixture either disposed of or used as an alternate raw material. Drying is not essential to preparation of the treatment material, but it does facilitate handling and storage at the treating facility. If necessary, the wet sludge could be added to a waste, and the treatment would still be effected.
The sulfite embodiment proceeds by forming an insoluble metal sulfur oxide complex when soluble forms of toxic metals that are present in the waste go into solution. These insoluble complexes prevent leaching of the toxic metals from the waste.
Reference will now be made to a specific example using the processes described above. It is to be understood that the example is provided to more completely describe preferred embodiments and that no limitation to the scope of the invention is intended thereby.

Sulfite treatment of spent industrial wastes


The extendible building post includes a telescoping hydraulic cylinder integrated within a construction member externally configured and dimensioned essentially identically to a conventional building construction member, e.g., a four-by-four or six-by-six length of lumber, or alternatively a plastic column. The hydraulic system may be formed of stock plastic pipe and fittings, and may use water as the working fluid. The device may include insulation and a heating system to prevent freezing when used in such an environment, with certain types of insulation also providing additional rigidity for the hydraulic assembly.

1. Field of the Invention
The present invention relates generally to building structural components. More specifically, the present invention comprises various embodiments of an extendible post that may be used in building construction, with the post including a hydraulic strut mechanism integrated therewith.
2. Description of the Related Art
Many people are requesting and demanding additional comfort and convenience features in their homes today. In many instances, such features are not merely conveniences, but are necessities for providing assistance to those who live in such homes. Examples of such are residential wheelchair lifts and elevators, serving the needs of physically handicapped and/or infirm residents.
In the past, the needs of such residents have been handled by providing wheelchair ramps for access from the exterior of the home, and through other ground floor accommodations. In some instances, chair lifts have been installed along existing stairway runs for access to higher floors. Generally speaking, however, access, particularly to the higher levels of residences, has been relatively limited by the lack of economical means for lifting a person from one floor or level to the next. Conventional residential lifting devices tend to be complex and expensive, comprising elevator systems utilizing self-contained hydraulic power packs and/or electric motors. Not only is the initial purchase price of such devices relatively high, but the installation is labor intensive and accordingly costly.
Thus, an extendible building post solving the aforementioned problems is desired.