Guide adapter

Abstract

A guide adapter for guiding a drill bit during percussion drilling is arranged between the drill bit and an elongated drill string extending along an axis. The guide adapter includes a sleeve shaped adapter body including a forward end with a first coupling arranged for connecting the guide adapter to the drill bit, and a rear end with a second coupling arranged for connecting the guide adapter to the drill string. A plurality of guiding elements extend substantially radially in relation to the axis from the adapter body. The guiding elements extend along 60% or less of the adapter body length and are arranged in the rear end. The guiding elements in the rear end have an extension in the radial direction substantially equal to a first radius of the drill bit and curved, straight or stepwise reduced radial extension towards the forward end.

1 . A guide adapter for guiding a drill bit during percussion drilling, said guide adapter being intended to be arranged between the drill bit and an elongated drill string extending along an axis, said drill bit having a first radius transverse to the axis, said guide adapter comprising:
 a sleeve shaped adapter body arranged to extend along the axis and including a forward end with a first coupling arranged for connecting the guide adapter to the drill bit, and a rear end with a second coupling arranged for connecting the guide adapter to the drill string; and   a plurality of guiding elements extending substantially radially in relation to the axis from the sleeve shaped adapter body, wherein the guiding elements extend along 60% or less of a body length of the adaptor along the axis and are arranged in the rear end of the adapter body, said guiding elements in the rear end has having an extension in a radial direction from the axis substantially equal to said first radius and a curved, straight or stepwise reduced radial extension towards the forward end along the axis.   
     
     
         2 . The guide adapter according to  claim 1 , wherein the plurality of guiding elements comprises at least five guiding elements having substantially identical shape and dimension. 
     
     
         3 . The guide adapter according to  claim 1 , wherein the guiding elements are substantially straight and extend parallel to the axis along the sleeve shaped adapter body. 
     
     
         4 . The guide adapter according to  claim 1 , wherein the guiding elements, in a plane transverse to the axis, have a base arranged towards the sleeve shaped adapter body, said guiding elements having a tapered shape in the radial direction from the axis and being ended by an outer end surface. 
     
     
         5 . The guide adapter according to  claim 4 , wherein the outer end surface is shaped like a circular arc with a radius corresponding to the radius from the axis to the outer end surface. 
     
     
         6 . The guide adapter according to  claim 4 , wherein at least an area of the outer end surface of at least one guiding element is covered by a hard layer. 
     
     
         7 . The guide adapter according to  claim 4 , wherein the hard layer is applied on the outer end surfaces along all of the guiding elements along the axis. 
     
     
         8 . The guide adapter according to  claim 1 , wherein each of the guiding elements includes a rear end surface, the rear end surface of at least one guiding element being covered by a rear end surface hard layer. 
     
     
         9 . The guide adapter according to  claim 1 , wherein the guiding elements in the rear end has an extension in the radial direction from the axis of about 94-96% of said first radius, and a radial extension in the forward end of the guiding elements of about 89-91% of said first radius. 
     
     
         10 . The guide adapter according to  claim 9 , wherein a wear indicator is arranged in the outer end surface of at least one of the guiding elements to indicate when the guide adapter is worn out and needs to be replaced. 
     
     
         11 . The guide adapter according to  claim 10 , wherein the wear indicator is a notch, recess or cut out portion arranged in the top end surface, said notch, recess or cut out portion having a depth selected such that when the guide adapter is worn out, the notch is no longer visible in the top end surface. 
     
     
         12 . The guide adapter according to  claim 10 , wherein the distance from the axis to the wear indicator is within the range of 80-99% of the guiding element extension in radial direction from the axis in the rear end of the guide adapter. 
     
     
         13 . The guide adapter according to  claim 1 , wherein the guiding elements extend along 50% or less of the adapter body length along the axis. 
     
     
         14 . The guide adapter according to  claim 1 , wherein the radial extension of the plurality of guiding elements decrease in the direction from the rear end towards the forward end such that the plurality of guiding elements have a convex shape along axis the axis, or a substantially straight shape angled in relation to the axis along the axis. 
     
     
         15 . A drill arrangement for percussion drilling comprising:
 a drill string extending along an axis;   a drill bit having a first radius transverse to the axis; and a   guide adapter according to  claim 1  arranged between the drill string and the drill bit arranged to reduce the risk for deviation.