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Understanding Kelly Bar Types in Rotary Drilling Rigs

august 7, 2025

1. What Is a Kelly Bar?

A Kelly bar is a key component of a rotary drilling rig, used to transmit torque and crowd force from the rig’s rotary drive to the drilling tool. It enables the rig to reach deep drilling depths while maintaining high torque.

2. Types of Kelly Bars

? Interlocking Kelly Bar

Provides high torque transmission
Ideal for hard soil and rock layers
Better vertical rigidity and depth control

? Friction Kelly Bar

Lighter and more economical
Suitable for soft to medium soil
Faster drilling speed

3. Common Specifications

Tip	Sections	Max Drilling Depth	Torque Capacity
Interlocking	3–6	Up to 90 m	High
Friction	3–5	Up to 60 m	Medium

4. Application Scenarios

High-rise building foundations
Bridge pile foundations
Infrastructure and civil engineering projects

5. Maintenance Tips

Lubricate locking mechanisms regularly
Avoid over-torqueing in rocky ground
Inspect for wear at section joints