A core barrel is a special drilling tool that cuts an annular groove, allowing the rock core to be broken by a percussion hammer or auger.
Due to different welded cutting rings, core barrels are classified into four types: CB-I, CB-II, CB-III, and CB-IV. For relatively hard bedrock formations, large boulder layers, and hard permafrost layers, direct drilling with augers or rotary drilling bits is difficult. It requires core barrel annular bits in combination with augers and sand bailers. They are divided into core-retaining annular core barrels and non-core-retaining annular core barrels. According to different formations, they are further divided into pick-type annular bits for drilling weathered bedrock and permafrost, and roller cone annular core barrels for drilling hard bedrock. Structural features and principles of the core-retaining annular core barrel: The bucket body consists of an inner tube and an outer tube. Main cutting teeth are welded on the outer tube, and secondary cutting teeth are welded on the inner tube. A hinge plate is installed at the lower end of the inner tube to support the core. During drilling, the rock core pushes the hinge plate open and enters the tube. When the drill is lifted, the hinge plate returns to a horizontal position by its own weight, sealing the core inside the inner tube and bringing it out of the hole. Structural features and working principle of the non-core-retaining annular core barrel: Cutting teeth are directly welded to the lower part of the drill barrel. During drilling, the core barrel first drills the formation into an annular shape, leaving a cylindrical core. Then an auger is lowered to break the cylindrical core into fragments, which are then removed with a sand bailer.
Operating precautions: When the barrel is full, the drill can be lifted. Lifting must be done at a slow speed because the bit has inner cutting edges. The non-core-retaining bit may also retrieve cores or large boulders; if it fails to do so, it is normal, as its main purpose is to create a free face for subsequent drilling with a sand bailer or auger.