Characteristics and processing method of self-drilling hollow anchor bar thread

Self-drilling anchor system is an advanced anchorage system, which can directly perform drilling and grouting functions in loose soil and broken rocks. It includes a continuous wave-thread hollow bar and other accessories. Self-drilling anchor system can be used as micropile and soil nail, it’s a fast and efficient geotechnical anchoring solution.

The thread shape of hollow bar is very similar to ribbed reinforcement, with large pitch and deep teeth. Its surface thread can not only bond with cement, provide good adhesion and friction resistance, but also can be arbitrarily extended.
External thread of hollow bar needs to be processed by three-axis thread rolling machine. As the raw material, the hollow bar is easy to be elliptical, flat and even cracked in two-axis rolling machine. The thread processed by three-axis rolling machine has good forming and high precision, which can meet the demand of drilling construction.

There are two types of hollow bar thread. One is R thread according to ISO10208 standard, the other is T thread which can provide more support force. T-thread has a larger bonding area with concrete due to its deeper teeth. Generally, the adhesive friction force of T thread bar is double than R in the same type. T thread self drilling anchor bolt is more used as micropile on a variety of occasions.

Two methods are usually used to process hollow bar, cold rolling and temperature control rolling. Cold rolling of the thread can improve the steel grain structure and increase its yield stress. And temperature control rolling can change the mechanical properties of hollow bar according to the needs of different engineering applications. It can more effectively ensure the microstructure of hollow bar and make the grains smaller. Generally suitable for occasions with higher elongation requirements to meet the needs of more customers.

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