CPC E21B 10/5673 (2013.01) | 13 Claims |
1. A drillbit for percussion drilling, the drill bit comprising:
a drill bit body arranged to extend along an axis and having a front surface, the front surface including a first circular area surface arranged transverse and coaxially to the axis, a second area surface surrounding the first area, the second area surface extending at an angle in relation to a plane transverse to the axis, and a third area surface surrounding the second area surface, the third area surface is extending in an angle in relation to a plane transverse to the axis such that the front surface has a substantially convex shape, wherein the first circular area surface has a first radius (R1), the second area surface extends from a periphery of the first area surface to a second radius (R2) and the third area surface extends from a periphery of the second area surface to a third radius (R3), the first radius (R1) being within the range of 25 to 65% of the third radius (R3) and the second radius (R2) being within the range of 60 to 80% of the third radius (R3), wherein the third radius (R3) is within the range of 30 to 65 mm; and
a number (n) of buttons arranged in the second area surface and third area surface, the buttons each having a button body extending along an axis and having a length along a respective button body axis, each button body having a circular cross-sectional shape transverse to the button body axis, a rear end surface and a forward end surface, wherein the number of buttons arranged in the third area is within the range of 9 to 11, wherein the second area surface angle is within the range of 5 to 15°, the third area surface angle is within the range of 30 to 45° and the buttons are arranged in circular recesses extending substantially transverse from the second area surface and third area surface into the drill bit body, wherein the recesses have a radius corresponding to the button body radius (Rb) and a depth corresponding to the length L of the button body such that the button bodies are fitted within the drill bit body with the forward end surface exposed in the second area surface and third area surface.
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