Rock drilling tool

Abstract

The present invention relates to a rock drilling element for percussive drilling that is designed to reduce the stress usually developed on a thread joint when the shock wave transmits from a slender portion to a thicker part. The rock drilling element has an elongated body comprising a first portion and a second portion. The first portion has a female or male thread intended to be connected to a drill rod or a drill tube. The first portion has an outer diameter approximately equal to the major diameter of said thread. The second portion has a male or female thread intended to be connected to a drill bit or a guide tube. The second portion forms a guide portion for radial guiding in a hole being drilled. The length of the first portion is at least 500 mm, such that the thread joint is moved away from an unfavorable reflection area. Furthermore, the present invention relates to a drill string and a method of transferring impact energy in a drill string.

1 . A rock drilling element for use in percussive top hammer drilling having an elongated body comprising a first portion and a second portion, said first portion having a female or male thread intended to be connected to a drill rod or a drill tube,
 wherein the first portion has an outer diameter approximately equal to the major diameter of said thread,   wherein the second portion has a male or female thread intended to be connected to a drill bit or a guide tube, said second portion forming a guide portion for radial guiding in a hole being drilled, and   wherein the length of the first portion is at least 500 mm.   
   
   
       2 . The rock drilling element according to  claim 1 , wherein the outer diameter of the first portion is 90-110% of the major diameter of the thread that is associated with said first portion. 
   
   
       3 . The rock drilling element according to  claim 1 , wherein the outer diameter of the second portion is 105-250% of the outer diameter of the first portion. 
   
   
       4 . The rock drilling element according to  claim 1 , wherein the cross sectional area of the second portion is maximum 250% of the cross sectional area of the first portion. 
   
   
       5 . The rock drilling element according to  claim 1 , wherein the second portion has external splines. 
   
   
       6 . The rock drilling element according to  claim 1 , wherein the first and/or the second portion consist of multiple components friction welded to each other. 
   
   
       7 . A drill string for percussive rock drilling comprising a drill bit, one or more extension rods or extension tubes, wherein the drill string further comprises a rock drilling element as defined in  claim 1 . 
   
   
       8 . A method for transferring impact energy from a top hammer unit to a drill bit, which unit has a piston that provides shock waves, each shock wave having a length, the method comprising the steps of:
 providing a drill string comprising one or more extension rods or extension tubes, a rock drilling element as defined in  claim 1 , and a drill bit or one or more guide tubes connected to a drill bit,   connecting an end of said rock drilling element facing towards the piston via a thread joint to an extension rod or an extension tube,   accelerating the piston,   impacting an end of the drill string to create the shock wave,   allowing more than half of the shock wave to pass the thread joint before any reflected wave is allowed to be created, and   rotating and impacting said drill bit against a rock material for making a hole therein.