Patent Application
20140360790
The invention pertains generally to an excavating tool such as, for example, a rotary drill bit useful for drilling through various earth strata. More specifically, the invention pertains to a rotary drill bit with a cutting insert such as, for example, a roof drill bit useful for drilling bore holes in an underground mine.
The expansion of an underground mine, such as for example, a coal mine, requires digging a tunnel. Initially, this tunnel has an unsupported roof. In order to support and stabilize the roof in an underground tunnel, bore holes are drilled in the roof, i.e., earth strata. The apparatus used to drill these holes typically comprises a drill with a long shaft, i.e., drill steel, attached to the drill. A roof drill bit is detachably mounted to the drill steel at the distal end thereof. In certain roof drill bits, a hard cutting insert is mounted on a body of the roof drill bit.
A hard cutting insert for use in a roof drill bit is typically formed of cemented tungsten carbide and can be secured by brazing the insert within a slot formed within a top working surface of the body of the roof drill bit. Tungsten carbide is a costly material and cutting inserts are expensive to manufacture. Thus, it is important that the hard cutting insert be securely held in the slot of the roof drill bit so as not to become dislodged during use. Therefore, it is important to use a technique to produce an effective braze joint between the bit body and the hard cutting insert so as to provide a more durable tool having an increased useful life.
Because tungsten carbide is a costly material and cutting inserts are expensive to manufacture, it is also important that care be taken not to damage the hard cutting insert prior to being used, e.g. during shipping, while installing the hard cutting insert, and/or prior to the operation of the roof drill bit containing the hard cutting insert. Heretofore, hard cutting inserts have been damaged in one or more of these situations resulting in the hard cutting insert being defective and not suitable for use or having a shortened useful cutting life.
There is a need for improved roof drilling bits that overcome disadvantages, limitations and shortcomings of known roof drilling bits. It would also be desirable to provide an improved roof drill bit that has a longer useful life. It would also be desirable to provide a hard cutting insert that is not damaged prior to being used for a cutting operation.
An aspect of the present invention is to provide rotary drill bit for engaging an earth strata material that includes an elongate drill bit body having an axial forward end and an axial rearward end, wherein the drill bit body contains a slot at the forward end. The rotary drill bit also includes an edge protector received in the slot of the drill bit body, the edge protector including: a first side having a first bottom edge and a first top edge; a second side opposed to the first side, the second side having a second bottom edge and a second top edge; and a bottom portion adjoining the first bottom edge of the first side and the second bottom edge of the second side. The rotary drill bit also includes a cutting insert having an elongate insert body rotatable about a central axis, the elongate insert body having a pair of symmetrical halves symmetrical about the central axis, each symmetrical half including: a leading face; a top surface; and a cutting edge formed between the leading face and the top surface. The cutting insert is received in the edge protector such that the cutting edge is recessed below one of the first top edge of the first side or the second top edge of the second side.
Another aspect of the present invention is to provide an edge protector assembly for a rotary drill bit includes a shim having a first side having a first bottom edge and a first top edge, a second side having a second bottom edge and a second top edge, and a bottom portion adjoining the first bottom edge of the first side and the second bottom edge of the second side. The edge protector assembly also includes a cutting insert having a leading face, a top surface, and a cutting edge formed between the leading face and the top surface. The cutting insert is received in the shim such that the cutting edge is recessed below one of the first top edge of the first side or the second top edge of the second side.
A further aspect of the present invention is to provide an edge protector for a roof drill bit cutting insert having at least one cutting edge, the edge protector including a first side having a first bottom edge and a first top edge, a second side having a second bottom edge and a second top edge, and a bottom portion adjoining the first bottom edge of the first side and the second bottom edge of the second side. The first side, the second side and the bottom portion are configured for receiving the cutting insert such that the at least one cutting edge is recessed below the first top edge of the first side or recessed below the second top edge of the second side.
These and various other features and advantages will be apparent from a reading of the following detailed description.
The following description is for purposes of illustrating various aspects of the invention only and not for purposes of limiting the scope of the invention.
Referring to the drawings,
The roof drill bit assembly 10 also includes a cutting insert 22 (or rotary drill bit insert). The cutting insert 22 is made from, for example, a cemented tungsten carbide that is a mixture of cobalt and tungsten carbide. Other super hard, wear resistant materials such as polycrystalline diamond, ceramics, or cermet may be used as a supplement and/or substitute. For example chromium carbide-coated metals and other cermets where titanium carbide or vanadium carbide is added to tungsten carbide may be candidates for inserts materials in accordance to aspects of the invention. Alternate ceramics for such applications include aluminum-based, silicon based, zirconium-based and glass varieties. Still other insert materials alternatives include cubic refractory, transition metal carbides or any other known or subsequently developed material(s) harder than the base material. Also coatings of the inserts such as PVD or CVD coatings can be used.
Cutting insert 22 has a cutting insert body, generally designated as 24, that has a top surface generally designated as 26, a bottom surface generally designated as 28, and opposite end surfaces generally designated as 32 and 34. The cutting insert body 24 is structured and arranged into two opposite symmetric connected portions, i.e. a pair of symmetrical halves, which are symmetric about the central axis A-A. One symmetric portion includes a leading face 40 and a cutting edge 50 formed between the leading face 40 and the top surface 26. In one aspect, the top surface 26 includes a primary relief surface 44. In another aspect, the top surface 26 also includes a secondary relief surface 46 wherein the primary relief surface 44 and the secondary relief surface 46 are contiguous and non-coplanar. It will be appreciated that each symmetric portion is generally the same and only one symmetric portion will be described in detail herein.
The rotary drill bit or roof drill bit assembly 10 also includes an edge protector, generally designated as 60, configured to be received in the transverse slot 18 of the drill bit body 12. The edge protector 60 includes a first side 62 having a first bottom edge 64 and a first top edge 66. The edge protector 60 also includes a second side 68 generally opposed to and/or parallel to the first side 60. The second side 68 includes a second bottom edge 70 and a second top edge 72. The edge protector 60 also includes a bottom portion 74 adjoining or connecting the first bottom edge 64 of the first side 62 and the second bottom edge 70 of the second side 68.
In accordance with an aspect of the invention, the cutting insert 22 is configured to be received in the edge protector 60 such that the cutting edge 50 is recessed below one of the first top edge 66 of the first side 62 or the second top edge 72 of the second side 68. As shown, for example, in
Advantageously, the described and illustrated configuration of the cutting edge 50 with respect to the first top edge 66 of the first side 62 provides for the first top edge 66 to protect the cutting edge 50 to prevent, for example, chipping or other damage to the cutting edge 50 prior to being used, e.g. during shipping, while installing the hard cutting insert 22, and/or prior to the operation of the roof drill bit 10 containing the hard cutting insert 22.
It will be appreciated that the other symmetric portion of the cutting insert 22 can include a second cutting edge 51 (see
The edge protector 60 is positioned within the transverse slot 18 and the insert 22 is positioned in the edge protector 60. In one aspect, the edge protector 60 is affixed to the slot 18 of the drill bit body 12. In another aspect, the cutting insert 22 is affixed to the edge protector 60. The cutting insert 22 and the edge protector 60 may be affixed to each other first and then affixed to the slot 18, or all may be affixed to one another at generally the same time. They may be affixed as described by, for example, attaching mechanically or otherwise, via brazing or gluing using conventional compositions and techniques known to those skilled in the art. To assist in, for example, affixing these components by brazing, the first side 62, second side 68 and/or the bottom portion 74 can include a plurality of perforations 76 formed therein. The perforations can be of various shapes and sizes and aid in allowing the braze material to flow efficiently in relation to the cutting insert 22, the edge protector 60 and the slot 18 to provide for a better attachment of these components to each other.
In another aspect of the invention, the edge protector 60 is formed of a material having a hardness value that is less than a hardness value of the cutting insert 22. As described, the cutting insert is made of a relatively hard material such as, for example, cemented tungsten carbide. The edge protector 60 is made with a material such as, for example, copper, steel, aluminum, brass, triclad, or any iron based material that is less hard in comparison to the cutting insert 22 material. Advantageously, by selecting the relative hardness of the edge protector 60 and the cutting insert 22 as described, the edge protector 60 will provide the desired shielding or protection for the cutting edges 50 and 51 while allowing for the roof drill bit 10 to be put directly into operation without the need to remove the edge protector 60 because the edge protector 60 will wear relatively quickly during operation of the roof drill bit 10 to expose or unshield the cutting edges 50 and 51 so that they may perform the desired cutting operation.
In another aspect, the edge protector 60 may also be configured such that other parts of the cutting insert 22 are shielded or protected. For example, as illustrated in
In another aspect, the edge protector 60 also may be in the form of a shim that also provides and includes the edge protection benefits as described herein. In one aspect, the shim helps the flow of braze to fully and uniformly cover the cutting insert 22 and transverse cutting slot 18. The shim also helps to provide a uniform gap between the cutting insert 22 and the transverse cutting slot 18.
Whereas particular aspects of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
