| 摘要 |
PCT No. PCT/SE91/00841 Sec. 371 Date Sep. 27, 1993 Sec. 102(e) Date Sep. 27, 1993 PCT Filed Dec. 6, 1991 PCT Pub. No. WO92/11436 PCT Pub. Date Jul. 9, 1992.The present invention related to a drill bit (10) for rock drilling, preferably a down-the-hole drill bit, said drill bit (10) including a head (11) and a shaft (12), said head (11) defining a cutting face (14) that carries a number of hard material button inserts (15) having end portions extending outwardly of said cutting face (14), means (16,17) for transporting flushing medium from the free end (13) of the shaft (12) to the cutting face (14) of the head (11), said means for transporting flushing medium including a central passage (16) extending from the free end (13) of the shaft (12) and terminating in the head (11) short of the cutting face (14) and at least one branch passage (17) emanating from the central passage (16) and emerging in the cutting facc (14). In the field of down-the-hole drill bits big volumes of flushing medium, normally compressed air, are used since the flushing medium is also activating the down-the-hole hammer. Those big volumes provide erosion of the cutting face since the flushing medium has a very high speed when passing the front face of the drill bit. Said erosion creates problems when so much material, usually steel, of the cutting face had been eroded away that the button inserts are lost before they are worn out. The idea of the present invention is to decrease the velocity of the flushing medium before reaching the cutting face (14) of the drill bit (10). This is done by increasing the cross-sectional area of the branch passage (17) along a certain length (L) of said branch passage (17). |
