Du Plooy, Dirk Jacobus (15 Pretorius Street, Noycedale, 1491 NIGEL, ZA)
| 1. | 1. A multiwing rotary boring bit comprising a bit body having a plurality of wings each of which is formed with a recess, and a cutting insert secured in each recess by a brazing operation, the bit body carrying integral projections arranged to hold the inserts in position in the recesses during the brazing operation. *& 2. |
| 2. | A boring bit according to claim 1 wherein the cutting inserts are formed with rebates therein and the projections are received in the rebates.*& 3. |
| 3. | A boring bit according to claim 2 wherein the projections and rebates are shaped such that the projections are received complementally in the rebates.*& 4. |
| 4. | A boring bit according to claim 2 or claim 3 wherein the projections extend into the recesses.*& 5. |
| 5. | A boring bit according to claim 4 wherein each projection extends in a forward direction into the associated recess and is spaced from a back wall of the recess, and the associated cutting insert includes a portion, located behind the rebate therein, which is located in the space between the projection and the back wall.*& 6. |
| 6. | A boring bit according to claim 5 wherein each projection is a rectangular, bladelike formation.*& 7. |
| 7. | A boring bit according to claim 6 wherein each projection has one face flush with a face of the associated cutting insert.*& 8. |
| 8. | A bit body for a multiwing rotary boring bit, the bit body having a plurality of wings each of which is formed with a recess to accommodate a cutting insert to be secured in the recess by a brazing operation, and the bit body carrying integral projections arranged to hold the inserts in position in the recess during the brazing operation.*& 9. |
| 9. | A bit body according to claim 8 wherein the projections are arranged to be received in rebates in the cutting inserts.*& 10. |
| 10. | A bit body according to claim 9 wherein the projections are shaped to be received complementally in the rebates.*& 11. |
| 11. | A bit body according to any one of claims 8 to 10 wherein the projections extend into the recesses.*& 12. |
| 12. | A bit body according to claim 11 wherein each projection extends in a forward direction into the associated recess and is spaced from a back wall of the recess.*& 13. |
| 13. | A bit body according to claim 12 wherein each projection is a rectangular, bladelike formation.*& 14. |
| 14. | A bit body according to claim 13 wherein each projection is arranged to have one face flush with a face of an associated cutting insert when the cutting insert is accommodated in an associated recess.*& 15. |
| 15. | A cutting insert for a multiwing boring bit, the cutting insert being shaped to be accommodated in a recess in a wing of a bit body according to any one of claims 8 to 14, the cutting insert having a rebate therein shaped to receive one of the integral projections of the bit body.*& 16. |
| 16. | A cutting insert according to claim 15 wherein the insert has opposite major surfaces and the rebate is of polygonal shape and formed in one of the major surfaces. |
In one particular application the invention is concerned with rotary boring bits with multiple wings or prongs, each supporting a hardmetal insert, such as are commonly used to bore holes in coal or. other soft rock. Typically such bits have a bit body with two or more angularly spaced and forwardly projecting wings or prongs. Towards its leading end each prong is recessed to accommodate a hardmetal insert of polygonal shape, each insert presenting a leading edge which carries out a cutting action as boring of a hole proceeds.
The inserts are secured to their respective prongs by brazing. In practice, during assembly of the bit, the braze components and inserts are placed in the respective recesses and the assembly is heated in an induction heater which melts the braze. On resolidification, the braze secures the insert in the recess.
A problem which has been encountered in this manufacturing process is that of holding the inserts in position in the recesses during transportation to the heating station and during the heating step itself. It has been the practice to address this problem using clips or other retainers to hold the inserts temporarily in position. Once the inserts are secured in position by the braze the retainers are-removed. Clearly the necessity to install retainers and then subsequently remove them increases the number of steps in the manufacturing process, reducing the efficiency of the process and increasing its cost.
SUMMARY OF THE INVENTION According to the invention there is provided a multi-wing rotary boring bit comprising a bit body having a plurality of wings each of which is formed with a recess, and a cutting insert secured in each recess by a brazing operation, the bit body carrying integral projections arranged to hold the inserts in position in the recesses during the brazing operation.
Typically the cutting inserts are formed with rebates therein and the projections are received, preferably complementally, in the rebates. The projections may extend into the recesses. In the preferred embodiment, each projection extends in a forward direction into the associated recess and is spaced from a back wall of the recess, and the associated cutting insert includes a portion, located behind the rebate therein, which is located in the space between the projection and the back wall. In this embodiment, each projection is a rectangular, blade-like formation and may have one face flush with a face of the associated cutting insert.
According to a second aspect of the invention there is provided a bit body for a multi-wing rotary boring bit, the bit body having a plurality of wings each of which is formed with a recess to accommodate a cutting insert to be secured in the recess by a brazing operation, and the bit body carrying integral projections arranged to hold the inserts in position in the recess during the brazing operation. As indicated above, the projections are preferably arranged to be received in rebates in the cutting inserts.
According to a third aspect of the invention there is provided a cutting insert for a multi-wing boring bit, the cutting insert being shaped to be accommodated in a recess in a wing of a bit body as summarized above, the cutting insert having a rebate therein shaped to receive one of the integral projections of the bit body. The insert may have opposite major surfaces and a rebate of polygonal shape formed in one of the major surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates, in an exploded perspective view, a rotary boring bit and cutting insert according to the invention; Figure 2 shows a pespective view of the assembled boring bit; and Figure 3 shows a cross-section at the line 3-3 in Figure 2.
DESCRIPTION OF PEFERRED EMBODIMENTS The drawings show a multi-wing rotary boring bit 10 which includes a steel bit body 12 and cutting inserts 14 typically of tungsten carbide or other hardmetal. The cutting inserts 14 are of polygonal shape and have forward or leading cutting edges 16.
The bit body 12 includes a pair of diametrically opposed prongs or wings 18 each of which is formed with a recess 20 to receive and accommodate one of the cutting inserts such that the leading cutting edge 16 of the insert projects a short distance forwardly beyond the leading extremity of the wing itself.
In accordance with the present invention, the bit 12 also includes, for each recess 20, an integral projection 22 which extends into the recess in a forward direction from the base 24 of the recess. As illustrated, each projection 22 is a rectangular, blade-like formation one face 26 of which is flush with the corresponding face 28 of the associated wing 18 and the other face 30 of which is spaced from the back wall 32 of the recess as indicated by the numeral 34.
The cutting inserts 14 are formed with recesses or rebates 36 complemental in shape to the projections 22.
To assemble the boring bit 10, each cutting insert is slid rearwardly relative to a wing 18, as indicated by the arrow 37, such that the associated projection 22 is received in the rebate 36 with a portion 38 of the insert, situated behind the rebate, locating in the space 34. It will be understood that appropriate braze components are also placed in each recess behind the cutting insert. In practice, the back wall 34 of the recess may carry ribs or other projections which serve to space the face 40 of the insert away from that wall, thereby creating room for the braze components.
The projections 22 are received complementally as snug fits in the rebates 36 and serve to locate the cutting inserts properly in the recesses 20.
Throughout transportation to the brazing station and during the brazing operation itself, the projections also hold the cutting inserts in the proper position and at the proper orientation. This avoids the need for installation of the conventionally used clips or other retainers.
It will be understood that in this specification, terms such as"forward", "leading","rearward"and the like are used with reference to the drilling direction, designated the forward direction as indicated by the arrow 42 in Figure 3.
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