Hammer bit locking mechanism

Abstract

A hammer bit retainer system includes a hammer bit locking mechanism arranged and designed to prevent decoupling of a driver sub from a hammer casing. The hammer bit locking mechanism includes an expandable split ring which is disposed in the coupling between the driver sub and hammer casing. The hammer bit locking mechanism prevents axial movement of the driver sub relative to the hammer casing in at least one direction.

What is claimed is: 
     
         1 . A hammer bit locking mechanism, comprising:
 a driver sub adapted to receive and movably couple to a shank of a bit, the driver sub including a portion thereof having an outer surface with one or more grooves therein;   a hammer casing having a central bore and receiving the portion of the driver sub in the central bore; and   a locking device disposed between the hammer casing and the portion of the driver sub, the locking device including an inner surface with one or more grooves therein configured to engage the one or more grooves in the outer surface of the portion of the driver sub, the locking device arranged and designed to prevent axial movement of the driver sub relative to the hammer casing in at least one direction.   
     
     
         2 . The hammer bit locking mechanism of  claim 1 , wherein the locking device is disposed in a circumferential cavity defining the central bore of the hammer casing. 
     
     
         3 . The hammer bit locking mechanism of  claim 2 , wherein the locking device includes an outer surface thereof with one or more grooves therein configured to engage one or more corresponding grooves on an inner surface of the hammer casing. 
     
     
         4 . The hammer bit locking mechanism of  claim 1 , wherein engagement between the one or more grooves of the inner surface of the locking device and the one or more grooves of the outer surface of the driver sub prevent the driver sub from moving axially in one direction. 
     
     
         5 . The hammer bit locking mechanism of  claim 1 , wherein the hammer casing has an access window arranged and designed to permit access to the locking device. 
     
     
         6 . The hammer bit locking mechanism of  claim 5 , further comprising a lug disposed in the access window and positioned between end portions of the locking device. 
     
     
         7 . The hammer bit locking mechanism of  claim 1 , wherein the driver sub has a tapered outer profile along an axial length thereof, and wherein the tapered outer profile has an angle of between 5 degrees and 30 degrees relative to a central axis of the driver sub. 
     
     
         8 . A method of preventing decoupling of coupled components of a percussion hammer bit, the method comprising:
 inserting a locking device in a circumferential cavity positioned in a hammer casing;   expanding the locking device;   inserting at least a portion of a driver sub into a central bore of the hammer casing and through the expanded locking device; and   coupling the driver sub and the hammer casing such that one or more inner surface grooves of the locking device engage one or more outer surface grooves of the driver sub, thereby preventing axial movement between the driver sub and the hammer casing in at least one direction.   
     
     
         9 . The method of  claim 8 , wherein the locking device has one or more outer surface grooves configured to engage one or more corresponding inner surface grooves on the hammer casing. 
     
     
         10 . The method of  claim 8 , further comprising accessing the locking device through an access window in the hammer casing. 
     
     
         11 . The method of  claim 10 , further comprising installing a lug in the access window of the hammer casing, the lug arranged and designed to prevent the locking device from rotating. 
     
     
         12 . The method of  claim 8 , wherein expanding the locking device is facilitated by a tapered outer surface of the portion of the driver sub being inserted into the central bore of hammer casing and through the expanded locking device. 
     
     
         13 . A locking mechanism of a downhole tool, comprising:
 a first body adapted to receive and movably couple to a shank of a bit;   a second body having a central bore and receiving a portion of the first body in the central bore; and   a first split ring disposed between the second body and the portion of the first body, the first split ring including an inner surface with one or more grooves formed therein and an outer surface with one or more grooves formed thereon, the first split ring arranged and designed to prevent axial movement of the first body relative to the second body in at least one direction; and   a second split ring disposed radially within the first split ring, the second split ring including an outer surface with one or more grooves formed thereon, the one or more grooves of the second split ring configured to engage the one or more grooves in the inner surface of the first split ring.   
     
     
         14 . The locking mechanism of  claim 13 , wherein an axial length of the first split ring covered by the grooves formed on the inner surface thereof is between about 75% and about 100% of the axial length of the first split ring, or wherein an axial length of the second split ring covered by the grooves formed on the outer surface thereof is between about 75% and about 100% of the axial length of the second split ring. 
     
     
         15 . The locking mechanism of  claim 13 , wherein an axial length of the first split ring covered by the grooves formed on the inner surface thereof is between about 50% and about 75% of the axial length of the first split ring, or wherein an axial length of the second split ring covered by the grooves formed on the outer surface thereof is between about 50% and about 75% of the axial length of the second split ring. 
     
     
         16 . The locking mechanism of  claim 13 , wherein an axial length of the first split ring covered by the grooves formed on the inner surface thereof is between about 25% and about 50% of the axial length of the first split ring, or wherein an axial length of the second split ring covered by the grooves formed on the outer surface thereof is between about 25% and about 50% of the axial length of the second split ring. 
     
     
         17 . The locking mechanism of  claim 13 , wherein an axial length of the first split ring covered by the grooves formed on the inner surface thereof is between about 1% and about 25% of the axial length of the first split ring, or wherein an axial length of the second split ring covered by the grooves formed on the outer surface thereof is between about 1% and about 25% of the axial length of the second split ring. 
     
     
         18 . The locking mechanism of  claim 13 , wherein the downhole tool comprises a hammer bit. 
     
     
         19 . The locking mechanism of  claim 13 , wherein the first body comprises a driver sub. 
     
     
         20 . The locking mechanism of  claim 13 , wherein the second body comprises a hammer casing.