Friction bolt is a kind of very specialized support supplies, and it is an advanced material used for underground culvert roof and other engineering support.
Friction bolt is a new type of full-length anchor that actively reinforces surrounding rock. Its three-dimensional part is a high-strength steel pipe with a longitudinal slit. When installed in a hole smaller than the pipe diameter, it can be put presses immediately. The radial pressure is applied to the hole wall over the entire length and the frictional force preventing the surrounding rock from sliding down, plus the supporting force of the anchor tray pallet, so that the surrounding rock is in a three-way stress state and the rock formation is great. In the case of blasting vibration surrounding rock anchoring, the anchoring force is increased significantly in the later period. When the surrounding rock is displaced significantly, the rock bolt does not lose its supporting resistance. It has better characteristics than the expanded shell rock bolts.

Working principles of friction bolts
The friction bolt is installed in a borehole smaller than the pipe diameter. At this time, three forces will be applied to the surrounding rock. One is the radial pressure on the hole wall over the entire length of the friction bolt. One is friction to prevent the surrounding rock from sliding down, and the other is the supporting force of the friction bolt tray support plate. These three forces make the surrounding rock more stable.
Technical requirements for friction bolts
1. The surface of the friction bolts should be flat without serious strain and rust. Welds should be free of cracks, slag inclusions, and no burning through the pipe wall. The tray should be able to move freely on the pole. It is advisable that the retaining ring interface and the opening of the pipe slot are mutually offset from 170o to 190o.   
2. The pull-off force of the retaining ring weld is greater than or equal 80kN, the ultimate tensile strength of the rod is greater than or equal 110kN, the initial anchor force is greater than or equal 25kN / m, and the pallet bearing capacity is greater than or equal 65kN.
How to use pipe friction bolts

1. Determine the anchor hole position according to the design requirements, and drill the hole with a drilling rig.

2. Use compressed air to blow out the rock powder inside the hole.

3. Install the anchor plate on the rod body, and use an impact drill to drill the rock bolt into the hole.

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