Drill bit for a down-the-hole drill
The invention concerns a drill bit, intended to be used with a down-the-hole drill and comprising a drill head ( 2 ) with a front surface provided with drill pins ( 3 ) and a shaft ( 4 ), whereby the shaft is narrower than the drill head and intended to be inserted in a manner that allows axial sliding into the end of a drill chuck that is a component of a down-the-hole drill and which shaft has a rear end part ( 6 ) that is somewhat thickened with a plane striking surface ( 7 ) against which a hammer piston ( 8 ) that is a component of the down-the-hole hammer drill is arranged to impact, that the drill head when viewed along its axial direction has a cylinder-shaped forward part ( 20 ) provided with cuttings channels ( 22 ), a rear cylinder-shaped part ( 21 ) that is located for the reception of drill cuttings at the same level or somewhat below the bottom ( 25 ) of the cuttings channels, whereby the diameter (D 1 ) of the forward part is greater than the diameter (D 2 ) of the rear part. In a drill bit that has high performance and a long useful life, and that is furthermore well-suited to be used for directed drilling, the cylinder-shaped forward part ( 20 ) of the drill head ( 2 ) has an axial length (L 3 ) from the main plane of the front surface to a shoulder plane ( 26 ) located between the drill head ( 2 ) and the shaft ( 4 ) that is greater than the axial length (L 4 ) of the cylinder-shaped rear part ( 21 ) of the drill head.
1. A drill bit, intended to be used with a down-the-hole drill and comprising a drill head with a front surface provided with drill pins and a shaft, whereby the shaft is narrower than the drill head and intended to be inserted in a manner that allows axial sliding into the end of a drill chuck that is a component of a down-the-hole drill and which shaft has a rear end part that is somewhat thickened with a plane striking surface against which a hammer piston that is a component of the down-the-hole hammer drill is arranged to impact, the drill head when viewed along an axial direction thereof has a cylinder-shaped forward part provided with cuttings channels to lead away drill cuttings, a rear cylinder-shaped part that is located for the reception of drill cuttings at the same level or somewhat below the bottom of the cuttings channel, whereby the diameter of the forward part is greater than the diameter of the rear part, and the cylinder-shaped forward part and the cylinder-shaped rear part of the drill head have respective axial lengths, whereby the cylinder-shaped rear part terminates at a shoulder impact surface facing a forward end surface of the drill chuck, wherein the axial length of the cylinder-shaped forward part of the drill head is greater than the axial length of the cylinder-shaped rear part of the drill head, and wherein the shoulder impact surface of the cylinder-shaped rear part is held abutted to an outer edge of the chuck.
2. The drill bit according to claim 1 , whereby the total axial length of the drill head has been selected so as to be always less than the axial length of the shaft calculated from the shoulder impact surface to an end surface or the striking surface of the shaft.
3. The drill bit according to claim 1 , whereby the ratio of axial lengths of the forward part and the rear part of the drill head lies in the interval 2-4.
4. The drill bit according to claim 1 , whereby the ratio between the diameter of the forward part and the diameter of the rear part of the drill head lies in the interval 1-1.25.
5. The drill bit according to claim 1 , whereby the ratio between the total axial length of the drill head and the axial length of the shaft from the shoulder to the end surface, is always less than 0.3.
6. The drill bit according to claim 1 , whereby the greatest diameter of the shaft forms an imaginary cylinder that extends forwards towards the front surface of the drill head and intersects at least some drill pins that are located centrally in the front surface, mainly in a centre or in the vicinity of a central part of an active crushing surface of the pins.
7. The drill bit according to claim 1 , whereby the ratio of axial lengths of the forward part and the rear part of the drill head is 3.
8. The drill bit according to claim 1 , whereby the ratio between the diameter of the forward part and the diameter of the rear part of the drill head is 1.05.
9. The drill bit according to claim 1 , whereby the ratio between the total axial length of the drill head and the axial length of the shaft from the shoulder to the end surface, is always less than 0.15.
10. The drill bit according to claim 1 , wherein the forward part is angled and the rear part is levelled with respect to an axis of the drill shaft.
11. The drill bit according to claim 1 , wherein there is a step on a sidewall of the drill head between the forward part and the rear part.