Characteristics and Thread Processing Method of Hollow Bar of Self-drilling Rock Bolt

The self-drilling anchor bolt system is composed of a hollow anchor bar, coupler, nut, drill bit, plate, and centralizer. It can combine drilling, grouting, and anchoring in one process. The self-drilling anchor bolt system is safe, efficient, and convenient. It is suitable for broken rock, loose soil, and geological conditions where is difficult to drill holes. It helps to ensure the anchoring effect in complex ground conditions and achieve the best construction result.

It is an advanced anchoring system that can directly realize drilling and grouting functions in loose soil layers and broken rock layers, consisting of a continuous full-threaded hollow bolt body, a sacrificial drill bit, a coupler, a flat or domed plate, a hex or domed nut, a centralizer, and other accessories. Self-drilling anchor systems can be used as micro piles and soil nails and are a fast and efficient solution for geotechnical anchoring.

Thread Processing Methods

The thread shape of the hollow bolt body is very similar to the thread of the steel rib. The thread pitch is large and the teeth are deep. The surface thread of the connection can not only bond with the cement, but also provide good adhesion and friction resistance, and can be extended at will.

The external thread of the hollow bolt body needs to be processed by a three-axis thread rolling machine. Because the raw material is a hollow steel pipe, the two-axis rolling machine is prone to the problems of oval, flattening, and even cracking of the hollow bolt body. Therefore, a three-axis thread rolling machine is used. The processing thread has good forming and high precision, which can meet the needs of drilling construction.

Thread Types

There are two kinds of threads on the surface of the hollow bolt body, one is the R-type thread that conforms to the ISO10208 standard, and the other is the T-type thread that can provide greater support force. Generally, the adhesion friction force of the same type of T-thread is more than twice that of the R-type, and the T-thread anchor is more used in the application of micro piles.

Two methods are used to process the hollow bolt body, cold rolling, and temperature-controlled rolling. Cold-rolled threads are rolled to improve the grain structure of the steel and increase the yield strength. The temperature-controlled rolling can be changed according to the different needs of the application scenarios. The mechanical properties of the hollow bolt body and temperature-controlled rolling can more effectively ensure the metallographic structure and finer grains of the rod body. It is suitable for occasions with high elongation requirements and meets more customer needs.

Features and Advantages

1. Self-drilling anchor bolt system, which combines drilling, grouting, and anchoring together, is suitable for broken rock and conditions which are difficult to drill holes. Casing pipe is omitted in construction, which greatly improves construction efficiency.

2. Self-drilling anchor bolt system has a rich variety of drill bits, and the drill bit can be selected according to the properties of rock and soil, which can improve the drilling efficiency.

3. Self-drilling anchor bolt system can fill cracks, consolidate rock mass and soil layer through pressure grouting, and has good grouting spreading radius and reliable anchoring quality.

4. The hollow anchor bar can be cut arbitrarily and lengthened by the coupler. Therefore, the self-drilling anchor bolt is suitable for construction in a narrow space that large equipment cannot enter.