Patent Application
20200102793
The invention pertains to a roof drill bit, as well as a roof drill bit body and a cutting insert (i.e., hard insert) for use in a roof drill bit, that has a typical use of drilling boreholes in mine roofs. More particularly, the invention pertains to a roof drill bit, as well as a roof drill bit body and a hard insert for use in a roof drill bit, that exhibits an improvement in the performance of drilling boreholes in a roof bolting operation due to an improvement in drilling debris evacuation and hard cutting insert retention.
Expansion of an underground mine (e.g., a coal mine) requires digging a tunnel that initially has an unsupported roof. To provide support for the roof, an operator will drill boreholes using a roof drill bit, wherein the boreholes can extend from about two feet to twenty feet into the earth strata. The roof drill bit attaches to a drill steel, which connects to a rotary driver. The rotary driver powers the roof drill bit to drill the boreholes. The operator then affixes roof bolts within the boreholes and a roof support (e.g., a roof panel) connects to the roof bolts to support the roof of the underground mine.
As one can appreciate, the drilling operation generates drilling debris. It is important to remove this drilling debris from the vicinity of the borehole. One typical way to remove or evacuate drilling debris from the vicinity of the borehole is to exert a vacuum at dust ports in the roof drill bit body. Under the vacuum, drilling debris passes through the dust ports and through a bore of a hollow drill steel into a debris collector. The debris collector is away from the borehole.
Although earlier roof drill bits, which utilize a vacuum to evacuate drilling debris, operate in a satisfactory fashion, there remains a need to improve upon the operation of the roof drill bit. More specifically, there is need to need to provide an improved roof drill bit that exhibits an improvement in the evacuation of drilling debris.
Roof drill bits operate at high rotational speeds. For example, a typical rotational speed is 650 rpm (revolutions per minute). When operating at such speeds, typically the drilling debris does not directly enter the dust port, but travels about the circumference of the roof drill bit prior to entering a dust port. In other words, the drilling debris does not directly enter the dust port closest to the point of engagement generating the drilling debris. Instead, the drilling debris travels about the circumference of the roof drill bit body prior to entry into a dust port that is not the dust port closest to the point of engagement. Significant disadvantages result from the inability of earlier roof drill bits to evacuate drilling debris directly through the dust ports.
One such disadvantage is excessive abrasive wear on the surface of the drill bit body. The drilling debris exhibits abrasive characteristics so that as the roof drill bit rotates at high speeds, drilling debris between the earth strata defining the borehole and the roof drill bit body abrades the roof drill bit body. Such abrasion reduces the underlying support for the hard insert, which over time may result in a premature removal of the roof drill bit from service, i.e., a reduction in the expected useful tool life. Thus, it would be highly desirable to provide an improved roof drill bit that provides for an improvement in the evacuation of drilling debris under the influence of the vacuum at the dust ports.
Another significant disadvantage associated with the inability of earlier roof drill bits to evacuate drilling debris directly through the dust ports is an increase in the tendency of the roof drill bit to become stuck once the roof drill bit ceases operation. The presence of drilling debris between the roof drill bit and the earth strata defining the borehole can make removal of the roof drill bit-drill steel assembly difficult. The drilling debris actually can frictionally hold or retain the roof drill bit within the borehole. Thus, upon cessation of the rotation of the roof drill bit, an attempt by the operator to remove the roof drill bit-drill steel assembly may encounter problems. For example, the operator may be unable to remove the entire roof drill bit-drill steel assembly without great difficulty. As another example, during an attempt to remove the roof drill bit-drill steel assembly from the borehole, the drill steel may disengage from the roof drill bit. The result is that the roof drill bit remains stuck in the borehole. As one can appreciate, these difficulties decrease the overall production efficiency of the mining operation. Thus, they would be highly desirable to provide an improved roof drill bit that better evacuates drilling debris so as to reduce or eliminate drilling debris retained between the earth strata defining the borehole and the roof drill bit.
In one aspect, the invention is a roof drill bit comprising an elongate bit body having an axial forward end. The bit body includes at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface. A hard insert is affixed to the bit body at the axial forward end thereof. The hard insert includes a plurality of leading cutting edges for cutting the earth strata. The at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.
In another aspect, the invention is a roof drill bit body that comprises an elongate bit body having an axial forward end. The bit body has a peripheral surface and contains a central bore. The bit body includes at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface. The bit body further includes at least three debris ports in the peripheral surface communicating with the central bore, and each one of the debris ports has an axial forward edge, and the axial forward edge of each debris port is spaced a different distance away from the axial forward end of the bit body. A hard insert is affixed to the bit body at the axial forward end thereof. The hard insert presents at least three discrete leading cutting edges for cutting the earth strata. The at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.
In still another aspect, the invention is a roof drill bit body that comprises an elongate bit body having an axial forward end. The elongate drill bit body has a longitudinal axis. The axial forward end is defined at least in part by a discrete first axial forward surface that is generally perpendicular to the longitudinal axis and a discrete second axial forward surface that is generally perpendicular to the longitudinal axis. The first axial forward surface is axially spaced apart from the second axial forward surface. The bit body includes at least one helical twisted surface terminating at a dust port and a feeder ledge proximate the at least one helical twisted surface. A hard insert is affixed to the axial forward end of the drill bit body so as to form a joint between the hard insert and the bit body. The joint is defined at least in part by the second axial forward surface. The at least one helical twisted surface and the feeder ledge enhance the flow of debris into the dust port.
While various embodiments of the invention are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention.
Referring to
The preferred method to make the roof drill bit body 22 is cold-forming. As will become apparent from the discussion hereinafter, using cold-forming techniques to make the roof drill bit body 22 result in a number of advantages that improve the overall performance of the roof drill bit itself. For example, U.S. Pat. No. 6,915,867 B2 to Bise (assigned to Kennametal Inc. of Latrobe, Pa.) discloses a roof drill bit body made via cold-forming techniques. Although the preferred manufacturing technique is cold-forming, there should be an appreciation that powder metallurgical techniques are also suitable to make the roof drill bit body 22. Powder metallurgical techniques provide the opportunity to employ a wide variety of materials for the manufacture of the roof drill bit body. This is in contrast to manufacturing processes that require machining or extensive machining.
There should be an appreciation that the cutting insert of the invention, as well as the cutting assembly of the invention, can operate in a number of different applications. The cutting insert, which has internal coolant delivery, is for use in the removal of material from a workpiece. In this respect, the cutting insert is for use in a material removal operation, wherein there is enhanced delivery of cryogenic coolant to the entire cutting insert to diminish excessive heat at the interface between the cutting insert and the workpiece (i.e., the insert-chip interface).
The enhanced delivery of coolant to the insert-chip interface leads to certain advantages. For example, enhanced delivery of coolant to the insert-chip interface results in reduced tool wear and increased tool life. Further, enhanced flow of coolant to the insert-chip interface leads to better evacuation of chips from the vicinity of the interface with a consequent reduction in the potential to re-cut a chip.
The description herein of specific applications should not be a limitation on the scope and extent of the use of the cutting insert.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
Throughout the text and the claims, use of the word “about” in relation to a range of values (e.g., “about 22 to 35 wt %”) is intended to modify both the high and low values recited, and reflects the penumbra of variation associated with measurement, significant figures, and interchangeability, all as understood by a person having ordinary skill in the art to which this invention pertains.
For purposes of this specification (other than in the operating examples), unless otherwise indicated, all numbers expressing quantities and ranges of ingredients, process conditions, etc are to be understood as modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired results sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, as used in this specification and the appended claims, the singular forms “a”, “an” and “the” are intended to include plural referents, unless expressly and unequivocally limited to one referent.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements including that found in the measuring instrument. Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, i.e., a range having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.
In the following specification and the claims, a number of terms are referenced that have the following meanings.
The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
Furthermore, as used herein, the term “cryogenic coolant” refers to a super cooled coolant, such as liquid nitrogen, and the like, that is cooled to a temperature of approximately −321 degrees Fahrenheit.
Referring back to
Each debris port 38 is generally circular having a diameter, D, equal to about 0.375 inches (about 0.95 cm) near the axial rearward edge thereof. Each debris port 38 is slightly offset a distance, E, equal to about 0.082 inches (about 2.08 millimeters [mm]) from the centerline F-F of each helical twisted surface 36. The center of the debris port 38 is spaced a distance, X, equal to about 0.939 inches (about 2.38 cm) from the axial rearward end 26 of the bit body 22. The debris ports 38 are in communication with the central, longitudinal bore 28 to permit evacuation of the drilling debris, including larger size pieces of debris, under the influence of a vacuum in dry drilling. The roof drill bit 20 is also useful for wet drilling.
The pedestal portion 32 includes a trio of pedestal lobes 40 wherein each lobe 40 is defined between each pair of the scalloped surfaces 36. The axial forward end 24 presents a discrete first axial forward surface 41 and a discrete second axial forward surface 43.
Each pedestal lobe 40 has a distal peripheral edge 42 adjacent a feeder ledge 44, and a leading edge 46 near a leading peripheral surface 48. The feeder ledge 44 of the pedestal portion 32 enhances the flow of debris along the helical twisted surface 36 and into a respective debris port 38, while providing for excellent strength and assisting the drill bit body 22 to resist failure during stalling of the roof drill bit 20.
The roof drill bit body 22 further contains a lobed socket 50 in the axial forward end 24 thereof. The lobed socket 50 presents a trio of generally radial socket lobes equally spaced apart about 180 degrees. As clearly shown in the drawings, a bottom second axial forward surface of the lobed socket 50 is generally parallel to a peripheral first axial forward surface of the axial forward end 24 of the drill bit body 22. As described hereinafter, the configuration of the lobed socket 50 corresponds to the configuration of a lobed projection that depends from the bottom surface of a hard insert.
The roof drill bit 40 further includes a hard insert 56 that presents three discrete leading cutting edges. However, there may be more or less than three discrete leading cutting edges, depending upon the application.
The hard insert 56 is preferably (but not necessarily) a single monolithic member formed by powder metallurgical techniques from a hard material such a cemented (e.g., cobalt) tungsten carbide alloy wherein a powder mixture is pressed into a green compact and then sintered to form a substantially fully dense part. Applicants contemplate that the hard insert also could be made by injection molding techniques. The preferred grade of cemented tungsten carbide for the hard insert (i.e., Grade 1) contains about 6.0 weight percent cobalt (the balance essentially tungsten carbide) and has a tungsten carbide grain size of about 1-8 micrometers and a Rockwell A hardness of about 89.9.
The hard insert 56 has a top surface 58 with a central area 60 surrounding the center point, G, (see
When the hard insert 56 is affixed to the drill bit body 22, the leading surface 66 of each first lobe 64 is disposed at a rake angle, H, (see
Each lobe 64 further includes a distal peripheral surface 74. The leading surface 66 intersects the relief surface 70 at the upper portion thereof so as to form a generally straight leading cutting edge 76 at the intersection thereof. The leading surface 66 intersects the distal peripheral surface 74 to form a generally straight side clearance cutting edge 78 at the intersection thereof. While the leading cutting edge 76 presents a generally straight geometry, applicants contemplate that the leading cutting edge may take on a different configuration such as, for example, an arcuate configuration in either or both the vertical and horizontal directions.
The hard insert 56 has a lobed projection 80, which has a trio of projection lobes spaced apart about one hundred twenty degrees, that depends away from the bottom surface 62 of the hard insert. Lobed projection 80 has a side surface 84 and a bottom surface 86. The bottom surface 62 of the hard insert has a shoulder 88 that surrounds the lobed projection 80 and is generally parallel to the bottom surface 62. Each one of the projection lobes has a general radial orientation so that its central longitudinal axis passes through the geometric center of the hard insert (i.e., the point on the hard insert that lies along the central longitudinal axis A-A of the roof drill bit 20 when the hard insert is affixed to the bit body).
Referring back to the geometry of the leading and side cutting edges, while these cutting edges are generally straight and perform in an acceptable fashion, other geometries for these cutting edges are acceptable for use. For example, the following patent documents disclose suitable geometries for these cutting edges: U.S. Pat. No. 4,787,464 to Ojanen, U.S. Pat. No. 5,172,775 to Sheirer et al., U.S. Pat. No. 5,184,689 to Sheirer et al., U.S. Pat. No. 5,429,199 to Sheirer et al., and U.S. Pat. No. 5,467,837 to Miller et al.
Referring to the assembled roof drill bit 20, it is typical that the hard insert 56 is brazed to the axial forward end 24 of the bit body 22. More specifically, the lobed projection 80 depending from the bottom surface 62 of the hard insert 56, has a corresponding geometry with, and thus is received within, the lobed socket 50 contained in the axial forward end 26 of the bit body 22. There is geometric correspondence between the shape of the lobed socket 50 and the shape of the lobed projection 80, whereby the projection 80 is received within the socket 50 so as to ensure that the hard insert is correctly positioned with respect to the drill bit body 22. There is a braze joint between the surface of the drill bit body at the axial forward end thereof and the rearward surface of the hard insert wherein the braze joint includes the surfaces defining the projection on the hard insert and the socket in the drill bit body, as well as the shoulder of the hard insert and the peripheral surface of the bit body that surrounds the socket, i.e., the axial forward most surface.
The preferred braze alloy is HI-TEMP 548 braze alloy manufactured and sold by Handy & Harmon, Inc., 859 Third Avenue, New York, N.Y. 10022. HI-TEMP 548 braze alloy is composed of 55+/−1.0 weight percent copper, 6+/−0.5 weight percent nickel, 4+/−0.5 weight percent manganese, 0.5+/−0.05 weight percent silicon, and the balance zinc with 0.50 weight percent maximum on total impurities. Additional information on HI-TEMP 548 braze alloy may be found in Handy & Harmon Technical Data Sheet D-74 available from Handy & Harmon, Inc.
When in the assembled condition, the radially outward portion of the leading cutting edge 76 of each lobe 64 extends forward of the leading peripheral surface 48 of its corresponding pedestal lobe 40. This distance decreases as the leading cutting edge 76 moves in a radial inward direction. Furthermore, for each lobe 64 the side clearance cutting edge 78 extends a distance in a radial outward direction past the distal peripheral surface 44 of its corresponding pedestal lobe 40.
Referring to
Each one of the leading cutting edges 76 begins at a point that is a distance, K, (
In operation, the roof drill bit 20 rotates and impinges against the earth strata so that the leading cutting edges 76 contact the earth strata so as to cut a borehole and the side clearance cutting edges 78 cut the side clearance for the borehole. The circle cut by the hard insert is about 1.024 inches (about 2.6 cm) in diameter. Although optimum parameters depend upon the specific circumstance, typical rotational speeds range between about 450 to about 650 revolutions per minute (rpm) and typical thrusts range between about 1000 and 3000 pounds.
The drilling operation generates debris and dust particulates. In certain applications the higher penetration rates associated with the roof drill bit generates larger-sized debris that has the potential to clog the roof drill bit. The debris, and especially the larger-sized debris, needs to be handled and removed from the borehole so as to not interfere with the drilling operation. In the roof drill bit 20, the debris smoothly moves over the leading surfaces 66 of each one of the lobes 64 and directly into the corresponding debris port 38. By providing the trio of debris ports 38, the roof drill bit 20 provides a way for the debris to quickly and efficiently be removed from the vicinity of the drilling. The removal of debris, and especially larger size debris, is enhanced by the configuration of the helical twisted surface 36, the feeder ledge 44 and the offset and axial location of the debris port 38. The consequence is that the debris generated by the drilling (and especially larger-sized debris) does not interfere with the efficiency of the overall drilling operation.
Because these three discrete leading cutting edges 76 have a generally radial orientation, the roof drill bit 20 exhibits excellent balance so as to continue to steadily advance with little, and possibly no, wobble, i.e., side-to-side movement. While the generally radial orientation of the leading cutting edges appears to provide the above-described advantage, applicants would expect that the roof drill bit would still exhibit improved performance even if the hard insert would have leading cutting edges that would not have a generally radial orientation.
In addition, the hard insert 56 covers the entire axial forward end 24 (including the axial forward most surface) of the drill bit body 22. By providing coverage of the axial forward end 24 of the drill bit body 22 the hard insert 56 protects the braze joint between the hard insert and the drill bit body from erosion so as to maintain the integrity of the braze joint. This is especially true for the portion of the braze joint defined by the bottom surface and side surface of the lobed socket of the bit body and the corresponding surfaces of the hard insert since the braze joint is actually within a volume of the bit body protected by the hard insert.
The patents and other documents identified herein are hereby incorporated by reference herein. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or a practice of the invention disclosed herein. It is intended that the specification and examples are illustrative only and are not intended to be limiting on the scope of the invention. The true scope and spirit of the invention is indicated by the following claims.
