1. Field of the Invention
The invention relates generally to improvements in roof drilling systems used in the industry, mining and construction fields.
2. Description of the Prior Art
Polycrystalline diamond (PCD) has become widely used in making cutting tool inserts. PCD materials are formed of fine diamond powder sintered by intercrystalline synthesis technology into a predetermined layer or shape; and such PCD layers are usually bonded to a substrate of “precemented” tungsten carbide to form a polycrystalline diamond compact (PDC) or insert (e.g. cutting element). The term “high density ceramic” (HDC) is sometimes used to refer to a mining tool having an insert with a PCD layer. The term “chemical vapor deposition” (CVD) is a form of pure PCD used for inserts, and “thermally stable product” (TSP) is another form of pure diamond that can be bonded to a carbide substrate or directly to a steel bit body using new vacuum furnace techniques by GE and Sandia Laboratories. Still other superhard surfacing and layered materials, such as “advanced diamond composite (ADC)” and “nitride” compositions of titanium (TiN) and carbon (C2N2), are gaining acceptance in the mining field. All such superabrasive or superhard materials—PCD, TSP, CVD, ADC and nitride compositions are applicable to the present invention, and the terms “PCD” and “PCD” shall be considered inclusive of all.
Drag bits are one class of drill bits used in rotary drilling operations. Drag bits have PCD or like cutting elements which act to cut or shear the earth material. The action of some flushing medium (fluid drilling mud, water, a compressed air or vacuum system) is important in all types of drilling operations to cool the cutting elements and to flush or transport cuttings away from the cutting site to prevent accumulation of debris. The cooling action is particularly important in the use of PCD cutters to prevent carbon transformation of the diamond material at about 1250° F.
The prior art is replete with various cutting element designs directed by a desire to form structurally stronger, tougher and more wear-resistant and fracture-resistant tools. It is well-known for example, that superabrasive (PCD) cutting elements can fail caused by the fact that the materials comprising the superabrasive portion, or diamond table, and the substrate have different coefficients of thermal expansion, elastic moduli and bulk compressibilities. Thus the table and substrate materials of a PCD wafer shrink at different rates during cooling after formation and the diamond table tends to be in residually stressed tension while the substrate material tends to be in residually stressed compression when subjected to cutting loads during drilling operations which may result in fracturing of the cutting element. My prior U.S. Pat. No. 6,374,932 addressed these heat management problems, and other prior art attempts to find solutions.
My prior U.S. Pat. Nos. 5,180,022; 5,303,787 and 5,383,526 disclose substantial improvements in HCD roof drill bits using PCD cutting elements constructed in a non-coring arrangement, and also teach novel drilling methods that greatly accelerated the speed of drilling action as well as substantially reduced bit breakage and change-over downtime. These prior HCD non-coring drill bits are capable of drilling over 100-300 holes of 4 foot depth for a roof bolting matrix with a single bit and in shorter times with less thrust than the standard carbide bits in certain hard rock or sandstone formations of 22,000-28,000 psi compressive strength. Although these prior HCD bits drilled through such earth structures, it was discovered that some drill bits might plug in drilling through mud seams and other soft shale or broken earth formations and PCD cutting inserts may even shatter in working through stratus of extremely hard or fractured earth conditions. My U.S. Pat. No. 5,535,839 discloses another HCD roof drill bit designed to operate more efficiently in broken and muddy earth formations. It should be noted that in some metal/non-metal mining, and particularly in tunnel construction there is frequently extremely hard rock formations in the compressive strength range of 25,000 to 50,000 together with seams of other mud, shale and the like. My prior PCD bits are capable of achieving some success in these conditions, but drilling speeds are slow and fracturing of drill steel, couplers and drill bits frequently occurs.
The invention is embodied in a heavy duty hard rock drill tool comprising a high fatigue resistant high alloy steel bit body having a working head portion with PCD cutter inserts, and an enlarged shank portion constructed and arranged to obviate breakage from torsion forces exerted thereon during drilling operations in earth formations including, hard rock structures with a compressive strength as high 50,000 psi, and non-PCD reamer/coupler means to compensate for bore hole rifling. The invention further involves the method of forming a roof bolting matrix in hard/soft rock formations using PCD wafers on a high alloy steel body having heavy duty square shank mounting means.
It is the principal object of the present invention to provide a hard rock boring tool with an improved heavy duty high alloy steel body and mounting shank that will extend the useful life of the tool.
Another important object of the invention is to provide a boring tool of high tensile strength with super abrasive cutter elements in which the problem of bit failure due to drilling torque is obviated.
Another object is to provide a method for producing clean bore holes in a roof bolting matrix.
Still another object is to provide a method for obviating premature tool failure in hard/soft rock drilling.
Still another object is to provide a method for operating super hard surfaced cutter elements on a heavy duty high alloy steel body permitting drilling at optimum speed and thrust in hard/soft rock structures.
Still another object is to provide an HCD bit using PCD cutting elements and an optimum supporting body, that accommodates torsional stress, and drills faster in extremely hard/soft rock structures.
Other objects and features will become more apparent hereinafter.
In the accompanying drawings which form a part of this specification, and wherein like numerals refer to like parts wherever they occur:
The present invention relates to improvements in rotary drag bits, particularly roof drill bits for boring and drilling operations in metal/non-metal mining and construction, and to methods for carrying out such metal/non-metal mining operations. The following definitions will be useful for a fuller understanding of the scope of the invention disclosed:
“Metal/non-metal mine” or “metal/non-metal mining” is used herein as a generic or comprehensive term to mean any type of underground mine or tunnel and encompasses ore mining, hard rock mining and coal mining operations.
“High-fatigue resistant” and/or “high alloy” are used herein with reference to the material strength of steel having a tensile strength in the range of 209,000 to 211,000 psi (typically 209,500 to 210,000 for 4340 steel) and a fatigue yield strength in the range of 135,000 to 145,000 psi (typically 141,000 psi for 4340 steel).
“Hard/soft rock” is used to designate earth formations that are extremely difficult to bore, as found in metal/non-metal mines, and include dense rock structures with a compressive strength in the upper range of 25,000 to 50,000 psi.
“Heavy duty” is used with reference to any drill tool that has a connecting shank of proportionately larger dimension as contrasted with prior drill tools with ½ inch or smaller shanks.
“Multitude” or “multitudinous” is used with reference to the drilling of roof bore holes or the like to indicate an extremely extensive number of holes and/or amount of drilling length (depth) far in excess of a scant few such holes or short length drilling capability of the prior art.
The bit coupler or mounting adapter 123,
The coring-type drill bit 110 of
In operation, the earth boring bit will be assembled on the drilling machine and be rotationally driven into the ground, wall or roof structure and the resulting cuttings should be flushed outwardly by the drilling fluids to clean the bore-hole B. The reamer/bit seat coupler 123 follows into the bore-hole and acts as a secondary drill bit to assure a smoother bore wall. Thus, the reamer/bit seat is especially valuable in roof bolting operations to assure that the hole for roof bolts is relatively smooth and clean so that installation of resin and roof bolts is facilitated.
As defined, hard/soft rock designates earthen formations that include solid hard rock sections HR having a high compressive strength in the range of 25,000 to 50,000 psi, and may include interspersed strata of fractured rock or shale F and mud seams M. Such earthen formations have heretofore been extremely difficult to drill into with prior state of the art drill bits. It is desirable to drill roof bore holes BH as quickly as possible to achieve optimum work production, and to that end optimum drilling parameters of thrust and drilling speeds are mandated. However, the density or compressive strength of any type of earth formation, which includes ores, hard/soft rock, coal, shale, mud, etc. may call for different drilling parameters and even different drill bit construction or configuration, as seen with reference to the prior art tools of
The essence of the present roof drilling invention resides, in part, in the more rugged design of the drill bit inserts, but also in providing a wider range of larger size bits that have a high fatigue resistant and high alloy steel body coupled to reamer/coupler means and operative to rapidly drill an increased amount of bore holes at faster drilling speeds in hard/soft rock formation including hard rock strata of the greatest density.
Referring now to
The drilling tool system DT of the invention includes a drill bit body section BS with a head portion 214 and a shank portion 216 connected to a reamer/coupler section RS that couples the drilling tool system to the end of a tubular drive steel column 219. The head portion 214 has a pair of PCD cutter inserts 220 comprising full circle discs of PCD layer 221a increased in thickness from about 0.250 inches to a thickness of 0.290 inches to thereby obviate compression fracturing. These PCD layers are bonded to a tungsten carbide substrate 221b and constructed and arranged on the steel body head portion 214 in a typical way, as by brazing. Also, as typical of my prior PCD tools, the PCD wafers have wear faces 222 mounted to face in the direction of rotation and preferably angularly mounted at preselected negative rake and skew angles to produce optimum slicing action into the hard/soft rock formation during drilling. The cutter inserts 220 are positioned in slightly spaced relation at the axial center of the drill bit to thereby form a coring-type bit and achieve a larger diameter bore hole BH for the size of PCD wafers used. The size of bore holes formed by tools of the present invention are larger than heretofore—in the range of about 1⅛ inch to 2 inches although some features of the invention may render the smaller 1 1/16 inch boring tool an acceptable substitute in some hard/soft rock drilling. It should be noted that these larger sized PCD wafers have a larger diameter providing a cutting edge 224 with a wider and more efficient curvature. The lower side 226 of each wafer 220 is seated against a complementary shoulder 227 on the steel body to thereby form an opposing resistance to the compressive drilling forces exerted against these cutting insert wafers at the cutting edges 222.
The shank portion 216 of the drill bit section is enlarged from ½ inch to about ⅝ inch as a preferred change of about 25% in the generally acceptable range of 9/16 to ¾ inches. This larger ⅝ inch shank has a substantially square cross-sectional configuration and is referred to as a heavy duty square shank for reference. The shank 216 has typical water flutes 218 on opposite sides for channeling flushing fluids for cooling and cleaning debris from the cutter inserts 220. The shank 216 is cross-bored at 217 to be cross-pinned to the reamer/coupler R5 and form a unitary drilling and reaming construction, as will be described.
An important feature is the use of a high fatigue resistant steel to form the drill bit body 214 including, shank 216 and the reamer/coupler RS—and even the drilling drive steel 219. Such high fatigue resistant steel will be more expensive, but testing has now established that superior performance of the present drilling system will more than justify the expense. The high fatigue resistant steel should have a tensile strength in the range of 175,000 to 225,000 psi and a yield strength in the range of 135,000 to 145,000 psi. For instance a preferred high nickel/chromium (NiCr) steel identified as 4340 heat treated to about Rc 40-45 has a tensile strength of about 200,000 psi and a yield strength of about 141,000 psi. In actual testing, the drilling system of the invention showed an improvement performance 18.3 times better than prior PCD tools and is 1873 times better than carbide tools in drilling hard sandstone.
Referring particularly to
As indicated, a feature of the invention is to construct the reamer/coupler RS using the same high fatigue resistant, high alloy steel as used for the drill bit body 214, 216. The high nickel/chromium 4340 steel previously described is substantially stronger than prior high carbon steels, such as 4140, and permits the use of thinner reamer tubing which provides a larger central chamber 250 to accommodate the larger square shank 216 of the invention.
The roof drill tool DT and method of the present invention are designed to drill thousands of feet of bore holes BH in hard/soft rock formations having hard rock strata with a density in the range of 25,000 to 50,000 psi and withstand high thrust forces as well as torsion stresses as when drilling in broken earth formations. A typical New Fletcher roof bolting machine has a maximum thrust pressure of about 5000 pounds or 1550 psi gauge setting, and drilling systems of the invention can operate at maximum thrust pressures and high and rotational speeds to achieve the highest production performance without failure. In the past the PCD tools could only work at 3500 pounds or 1100 psi gauge settings—and could still be expected to fail in hard rock environments.
In operation therefore, the drilling tool DT is secured to the reamer/coupler RS with the shank 216 nested within the central cavity 250 and being cross-pinned together by bolt 217A or the like which permit disassembly in case of excessive wear upon and need for replacement of the reamer section RS.
This drilling system is then assembled on the end of the drive steel 219 for drilling. Roof bolt holes are generally formed by engagement of the cutter inserts 220 against the face of the roof R at the designated bolt hole location. Vertical drilling upwardly into the rock or the roof structure takes place under the maximum drill speeds and thrust pressures possible, which in the past has generally been at about three-fourths of the machine potential, i.e. about 3750 pounds. The present drill system permits drilling operations at maximum thrust of 5000 pounds. At such speeds there is still a potential for rifling in the bore hole BH. This is illustrated in
From the foregoing it will be seen that substantial advances have been made by the present drilling system and method in the field of roof bolting matrix in metal/non-metal mining.
When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The Terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
It is now apparent that the objects and advantages of the present invention over the prior art have been fully met. Changes and modifications of the disclosed forms and methods of the invention will become apparent to those skilled in the metal/non-metal mining field and related arts, and the invention is only limited to the scope of the appended claims.