Friction kelly bar

The kelly bar assembly is composed of drill rod, guide frame, lifter and other components (some kelly bar assemblies also include casing). The rotary drilling rod is a tubular structure that is used between the rotary drilling rig and the rotary drilling bit to transmit torque, axial pressure and other loads. It is a telescopic structure along the common axis and is composed of several sections of steel pipes of different diameters and rods made of internal and external keys. The rotary drilling rod is mainly divided into two structural forms: friction kelly bar and machine lock kelly bar.

Friction kelly bar refers to the kelly bar that transmits axial pressure between each layer of rods through friction when the rotary drilling rig is drilling. Each section of the kelly bar is composed of a seamless steel pipe and internal and external drive keys welded thereon. There are two types of external drive keys: three-key type and six-key type, and there is no pressurized lock platform in the middle of the external drive key. The friction kelly bar has the characteristics of simple operation and large drilling depth. It is mainly suitable for construction in soft strata, such as clay, silt, silty soil, artificial backfill soil and strata containing some pebbles and gravel.

The interlocking kelly bar refers to the kelly bar that transmits pressure between the layers of rods through the pressure-bearing lock block when the rotary drilling rig is drilling. Each section of the kelly bar is composed of a seamless steel pipe and an inner and outer drive key welded thereon. There are two types of outer drive keys: three-key type and six-key type, and there are two, three or four pressure locks in the middle of the outer drive key. When the inner drive key of the kelly bar rotates to the pressure lock of the outer drive key, the downward pressure generated by the pressure cylinder of the power head is directly transmitted to the drill tool. The operation of the interlocking kelly bar is relatively complicated, and the drilling depth is relatively shallow, but the interlocking kelly bar can transmit a large pressure through the pressure point, and can be used for drilling in rock formations, such as strongly weathered, medium weathered, and slightly weathered rock formations.

As an important working part of the rotary drilling rig, improper disassembly or installation of the rotary drilling rod will not only affect the construction efficiency, but may also damage the rotary drilling drill. Therefore, before assembling the rotary drilling rod, it is necessary to confirm that there is no debris in the tube body of each section of the kelly bar to prevent poor assembly or jamming. After each section of drill pipe is assembled, a tensile test should be conducted on the drill pipe along the drilling direction to observe the expansion and contraction of the drill pipe. If abnormal expansion and contraction is found, assembly shall not be carried out, and the abnormal parts shall be clearly marked and dismantled for inspection. Assembly can only be continued after the abnormal situation is resolved.