| 摘要 |
<p>An air operated down-the-hole drill comprising a backhead for the connection of a drill to a source of compressed air, a wear sleeve secured to the backhead and a chuck adapted to retain a drill bit secured to the opposite end of the wear sleeve. There is within the wear sleeve an inner cylinder with a valve seat at one (inner) end of the cylinder having a valve stem extending into the cylinder and a piston within the cylinder reciprocable therein from one position where the valve stem engages in a bore in the piston to a second position where a stem on the piston enters a bearing located in the cylinder and strikes a drill bit held within the chuck. The dimensions of the piston are such that the ratio of the piston head area is in the range 9.9/9.95 to 1, the ratio of the piston head length to the piston stem length is in the range 1.5/1.52 to 1, the ratio of the piston head diameter to the piston stem diameter is in the range 1.4/1.43 to 1 and the ratio of the piston stem length to the length of the piston stem within the bearing at the point at which the piston strikes the drill bit is 1.4/1.45 to 1.</p> |
