Fault Phenomenon: XCMG XR550 rotary drilling rig during deep hole operation, the Kelly bar safety lock pin does not engage properly.

Troubleshooting Process:
– Checked mechanical structure: anti-drop pin stuck in retracted position.
– Checked hydraulic cylinder: small hydraulic cylinder for pin drive internal leakage.
– Checked sensor: pin position sensor false reading.
– Checked mud: dried mud obstructing pin movement.

Root Cause: Mud entered the anti-drop device and dried, preventing the mechanical pin from engaging under spring force.

Required Parts: Thoroughly clean anti-drop device, replace damaged seals.