Operation of Kelly Bars with Friction Lock

After assembling the kelly bars and aligning the drill rig over the borehole, the main hoist is lowered, allowing the kelly bars to descend into position due to their own weight. The rotary power head is then engaged for drilling operations. Once the drill bit has retrieved soil, it is reversed one to two turns to close the bucket door. The main hoist then lifts the kelly bars out of the hole to discharge the soil. As the kelly bars are lowered, when the shock absorber of the first section contacts the power head’s buffer, the power head supports the first section while the second and subsequent sections continue to drop under gravity. When the stop ring of the second section hits the upper end of the internal key on the first section, a slight impact sound is heard and the rig nods slightly (for example, with a 5x13 meter kelly bar, this occurs every 12 meters or so). The second section stops descending, and the third extends, with other sections following suit. When the bit reaches the bottom, the main hoist float function is activated, allowing rotation of the power head for drilling. After soil retrieval, the bucket door is reversed closed, and the main hoist and power head lift the kelly bars out of the hole. When the splash plate contacts the lower end of each kelly bar section, a similar nodding effect occurs.

 

Operation of Kelly Bars with Mechanical Lock

When the bit reaches the bottom (the descent process is the same as for friction lock kelly bars), the main hoist float is activated, and the power head applies pressure for drilling. Upon soil retrieval, the power head is lifted until it contacts the top shock absorber of the first kelly bar section. The main hoist is then put in float mode to slacken the wire rope. The power head is lifted another 30 cm while continuing to rotate forward to prevent the kelly bar from sliding down and damaging the power head. Once stopped, the power head is quickly reversed two turns to close the bucket door. Ensure the kelly bar is fully unlocked before releasing the float button and slowly reversing the power head while lifting the kelly bars until completely out of the hole.

When using mechanical lock kelly bars with a screw auger, during unlocking, note that after lifting the power head while rotating forward to the top of the first section, lift another 20-30 cm and reverse the power head 1-2 turns. Listen for the impact sound indicating unlocking, then lift. During lifting, the power head should reverse faster than when using a sampling bucket, but the main hoist should be slower to avoid soil falling between the screw blades and causing the innermost kelly bar section to relock. Maintain even speed for both functions to prevent locking. If a stuck pipe occurs, do not unlock mid-air; lower the kelly bars to the bottom and re-attempt unlocking.

 

Usage Precautions for Kelly Bars

Kelly bars and bits are only for drilling holes, not for moving or leveling soil at the construction site. Do not immerse the drill in liquid concrete, and only begin drilling when the bit touches the bottom. In sandy or gravel layers, be cautious not to advance too deeply, as this can cause hole shrinkage and result in major incidents like stuck drills. Select appropriate drill buckets based on geological conditions to improve efficiency and prevent major accidents.

 

Maintenance of Kelly Bars

Proper maintenance prevents premature wear and facilitates timely repair of damaged sections. For normal strata, initial inspection should occur 50-100 hours after equipment start-up for the fourth kelly bar section, and 100-150 hours later for the second and third sections. Routine checks are every 250-300 hours for the fourth section and every 400-500 hours for the second and third. Clean mud off the kelly bars daily and thoroughly clean them before maintenance.
 
Please note that in some contexts, particularly in oil drilling, "kelly bar" refers specifically to the topmost section of the drill string that extends through the derrick and is used for lifting and lowering the drill string. However, in the context provided here, the term "kelly bar" is being applied more broadly to refer to all sections of the drill string, which may not align with standard industry terminology.