Backreaming tool

• US 20040089473A1
• Filed: 02/24/2003
• Published: 05/13/2004
• Est. Priority Date: 04/26/2000
• Status: Abandoned Application

• Current Assignee: Allan George Kayes
• Original Assignee: Allan George Kayes
• Inventors: Kayes, Allan George
• Application Number:
  US10/258,755
• Publication Number:
  US 20040089473A1
• Time in Patent Office: Days
• US Class Current: 175/19
• CPC Class Codes: E21B 4/145 of the self propelled-type, e.g. with a reverse mode to retract the device from the hole
• CPC Class Codes: E21B 7/28 Enlarging drilled holes, e.g. by counterboring

Abstract

The invention provides a backreaming tool for expanding a pilot bore produced by a drill string, comprising a pneumatic perCussion hammer (1) in combination with a drill string, the drill string being rotatable and reversible through the pilot bore to effect backreaming by the pneumatic perCussion hammer. The pneumatic percussion hammer is longitudinally adjustable relative to the drill string. The arrangement is such that the compressed air supply to the working cylinder of the hammer is cut off when the hammer is longitudinally close to the end of the drill string, then restored as the hammer becomes more distant from the drill string.

Claims

1. A backreaming tool for expanding a pilot bore produced by a drill string, comprising a pneumatic percussion hammer (1) in combination with a drill string, the drill string being rotatable and reversible through the pilot bore to effect backreaming by the pneumatic percussion hammer;

wherein the pneumatic percussion hammer has a first end (3) adjacent the forward end of the drill string, and a second end (2) remote from the drill string, a compressed air inlet pipe (8) which passes through the first end and into a working cylinder (6) of the hammer, whereby the working cylinder is capable of reciprocating and exerting hammer blows on an internal end surface of the hammer at the first end;

wherein the compressed air inlet pipe (8) is connected to the forward end of the drill string, for supply of compressed air through the drill string into the air inlet pipe, and the compressed air inlet pipe is connected to the pneumatic percussion hammer in longitudinally slidable manner and in rotatably fixed manner, whereby the pneumatic percussion hammer is longitudinally adjustable relative to the drill string but is rotatable in accordance with rotation of the drill string;

and wherein the position of the air inlet pipe (8) relative to the working cylinder (6) is such that the compressed air supply to the working cylinder is cut off when the hammer is longitudinally close to the end of the drill string, then restored as the hammer becomes more distant from the drill string, so as to prevent hammer blows falling on the forward end of the drill string. A shock damping device between the hammer and the drill string may also be employed to further ensure that the hammer blows do not strike the drill string.

2. A backreaming tool according to claim 1, also comprising shock damping means between the hammer and the drill string.

3. A backreaming tool according to claim 1 or 2, wherein the pneumatic percussion hammer has a flat-faced head at its second end (2).

4. A method of expanding a pilot bore which has been produced by a drill string, which comprises connecting a pneumatic percussion hammer (1) to the forward end of the drill string, supplying compressed air through the drill string to the pneumatic percussion hammer and reversing the drill string through the bore while rotating the drill string, so as to effect backreaming of the pilot bore by the pneumatic percussion hammer;

wherein the supply of compressed air actuates the pneumatic percussion hammer so as to create hammer blows towards the drill string; and

wherein the compressed air supply to the pneumatic percussion hammer is cut off when the hammer is longitudinally close to the end of the drill string, then restored as the hammer becomes more distant from the drill string, so as to prevent hammer blows falling on the forward end of the drill string.