What are the Types of Threaded Extension Rods?

Table of Contents

A drill rod is a tool for connecting rock drill bits and matching them with rock drilling machinery, which is used for drilling in rock or rocky soil with rock drills and is widely used in rock drilling projects. It includes light drill rods and heavy drill rods. Threaded extension rods are one of the heavy drill rods. The choice of thread type is critical to the reliability and performance of the connection.

What is a threaded extension rod?

The threaded extension rod is a hollow circular or hollow hexagonal rod with connecting threads at both ends or one end of the rod. It is the main part of the threaded connection rock drill tool. It has the advantages of wide application range, fast drilling speed, small impact energy transfer loss, high rock drilling efficiency, easy realization of mechanized drilling, and improvement of rock drilling conditions.

The main thread form of the threaded extension rod

Corrugated thread (R thread)

The main thread structure form.

Characteristics are as follows:

A. After surface strengthening treatment such as carburizing, it has sufficient wear resistance.

B. The loss of energy transfer is small.

C. The loading and unloading are more convenient.

D. It can be processed by a special lathe, and the manufacturing cost is low.

Compound thread (HL thread)

Characteristics are as follows:

A. Large pressure area, high energy transfer efficiency.

B. Slow wear, large allowable wear amount, long service life.

C. Convenient loading and unloading.

Trapezoidal thread (T thread)

The characteristics are excellent application performance and long drilling life. It has gradually become the main threaded connection structure with drilling tools for medium and large cross-section threaded connections.

Types of threaded extension rods

Extension rod

extension rod

This is a threaded extension rod with the same nominal diameter of the thread and the hollow steel rod. The hollow steel does not need to be upset by hot forging, and the thread is directly formed by machining.

Light-weight extension rod

shank rod

This type of drill rod is a threaded extension rod with the nominal diameter of the thread larger than the hollow steel. During processing, the end of hollow steel must be forged and upset before threading. During drilling, the reduction in the weight of drill rod is beneficial to improve drilling efficiency.

Drifting and tunneling rod

MF rod

The drifting and tunneling rod is a threaded extension rod whose nominal diameter of the thread is greater than or equal to one end of hollow steel and equal to or less than the other end.

MF rod

MF rod

This is a circular or hexagonal threaded extension rod with an internal thread at one end and an external thread at the other end. Because it combines the coupling sleeve and the drill rod, it reduced the weight of the matching rock drilling tool, shortened the thread connection length, and reduced the impact energy loss at the thread connection, the connection, replacement, installation, and removal are more convenient, the drilling speed is accelerated, and the drilling efficiency is greatly improved.

Other structural threaded extension rods

It includes guide rods and tube rods. They are not commonly used, and no further introduction.

Application of threaded extension rod

Different thread types

Classification of threadNominal diameter applicableScope of application for rock drilling
Corrugated thread22、25、28、32、38Medium and small diameter rock holes
Trapezoidal thread38、45、51Medium and large diameter rock holes
Compound thread32、38、45Medium and large diameter rock holes
S threadMore than 51Large diameter rock holes

Different structures

With the rapid development of modern rock drilling machines, high-frequency, high-power hydraulic rock drilling equipment has also been significantly developed. The market demand for thread drilling tools with medium and large cross-sections has increased accordingly, which has also promoted the rapid development of threaded extension rods. Therefore, the selection of the appropriate type of threaded extension rod depends on the specific application requirements. Understanding the characteristics and applicable fields of each connection method will help you choose a suitable connection scheme to ensure the safety and performance of the equipment. When designing and selecting, manufacturers can develop or improve it through the material selection of threaded drill rods, hollow steel production process, brazing process, and other factors to ensure the reliability and safety of the connection. In the future, as technology advances, there may be more new types of threaded extension rods to meet the ever-changing engineering needs.

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