Abstract: A drill string for top hammer drilling includes a drill bit, a set of central rod members for transferring impact energy to the drill bit, and a set of tubular members surrounding the rod members for transferring rotation to the drill bit. The rod members define a first internal channel for conducting flushing medium. The drill bit defines a second internal channel which extends rearwardly and penetrates a rear end of the drill bit to communicate with the first channel. The drill bit further includes a transverse channel disposed in an intermediate section of the drill bit and which is connected to the second channel. The transverse channel penetrates an envelope surface of the drill bit for conducting flushing medium out of the drill bit and into an enlarged space defined between the drill bit and the tubular member.

Abstract: A drill string element for use in top hammer percussive drilling comprises first and second tubes coupled together by a cylindrical thread, and at least one impact-transmitting ord slidably disposed in the tubes. The rod(s) includes abutments which engage restrictions formed at remote ends of the tubes whereby the rod(s) can be removed only by unscrewing the tubes from one another. Remote ends of the tubes define male and female conical threads which enable the element to be connected to similar elements in the forming of a drill string. The conical threads are easier to unscrew than the cylindrical threads to avoid an accidental separation of the tubes of each element when that element is being unscrewed from another element.

Abstract: A drill bit for use in a drill string comprising a set of a plurality of central rod members and a set of a plurality of tubular members surrounding said rod members. The drill bit is provided with a longitudinally extending flushing channel which communicates with an annular space between the rod members and the tubular members via a transverse passage. The flushing channel comprises at least two end passages terminating in the bit front. The cross section area of each of the end passages is smaller than the overall cross section area of the portion of the flushing channel located between the end passages and the transverse passage.