A Kelly bar is an essential element in hydraulic rotary drilling rigs, acting as a telescopic shaft that conveys both torque and crowd force from the rig to the drilling tool. This component is vital for achieving deep drilling, enabling the rig to penetrate greater depths. It plays a key role in numerous applications, such as foundation drilling, construction projects, and mining operations.

Kelly bars can be categorized into two primary types: friction kelly bars and interlocking kelly bars. Friction kelly bars derive their name from the frictional interaction between the rails of each segment. In contrast, interlocking kelly bars lack this frictional contact; instead, they feature drive ribs equipped with locking devices that enhance torque transfer to each section. Standard kelly bars are designed as fully lockable systems, incorporating a mechanical locking mechanism that connects each element to both the outer bar and the rotary drive.

Kelly bars play a vital role in the creation of boreholes using hydraulic rotary drilling rigs. They simultaneously transmit the torque from the rotary drive and the crowd pressure from the crowd system to the drilling tool. A kelly bar is comprised of multiple telescopic tubular sections featuring a system of drive keys and locking recesses welded onto their outer surfaces. Typically, standard kelly bars are equipped with six drive keys on each section. These tubular sections are crafted from high-tensile steel to achieve a balance of minimal weight and sufficient strength. Standard kelly bars are available as either friction kelly bars or fully interlocking kelly bars, compatible with various drilling rigs.

Kelly bars come with a range of standard features, including:

• Telescopic configurations that vary from 2 to 6 elements for applications in piling
• Depth capabilities that range from 10m to 110m
• Torque transfer capacities between 80kNm and 500kNm
• Choices of both interlocking and friction kelly bars
• High-grade seamless steel construction
• Six cams and drive ribs to enhance operational efficiency
• A top flange for connecting the kelly bar to a kelly swivel
• Upper and/or lower spring shock absorbers to improve stability
• A square kelly box for easy attachment of drilling tools
• A drive pipe that transmits torque and crowd force to the kelly bar

When choosing a kelly bar for a drilling rig, it is essential to focus on those made from high-quality steel with strong mechanical characteristics. Whether purchasing new or used kelly bars, look for products that come with origin and quality certifications to guarantee their reliability and longevity. Additionally, all kelly bars can feature a noise-damping system designed to reduce disruptive, high-frequency noise during operation. This system uses sound-absorbing materials on the outer section of the kelly bar, which are protected by steel plates.