Thread joint for a drill string for percussive rock-drilling

1. A screw joint for a drill run or drill string for percussion rock drilling, comprising male and female screw threads ( 5 , 9 ) on the elements ( 1 , 2 ) to be joined together to form a drill string, wherein the male thread ( 5 ) and the female thread ( 9 ) have a trapezoidal shape and a slight conical inclination along the length of the threads, wherein the flanks of said threads define approximately a same angle with the centre line of the threads,

wherein the flank angles (α, β) between the flanks of the threads and the line ( 13 ; 12 ) that is tangential with the apices ( 5 c ; 9 c ) of the threads ( 5 ; 9 ) is smaller than 45°.

2. The screw joint according to claim 1 , wherein the slight conical inclination along the length of the threads extends to the distal end of the male thread.

3. The screw joint according to claim 1 , wherein a cone angle of the conical inclination is smaller than 7°.

4. The screw joint according to claim 3 , wherein the cone angle is about 4°.

5. A drill rod for percussion rock drilling, wherein the drill rod in one end is provided with a male thread ( 5 ) and in its other end with a female thread ( 9 ), which male and female threads have a trapezoidal shape and a conical inclination along the length of the threads, wherein the flanks of said threads define approximately a same angle with the center line of the threads,

wherein the flank angles (α, β) between the flanks of the threads and the line ( 13 ; 12 ) that is tangential with the apices ( 5 c ; 9 c ) of the threads ( 5 ; 9 ) is smaller than 45°.

6. The drill rod according to claim 5 , wherein a cone angle of the conical inclination is smaller than 7°.

7. The drill rod according to claim 6 , wherein the cone angle of the threads is about 4°.