Right-handed rock anchor bolt adopts the design of right spiral rib and one-way right screw thread, reinforced pitch and anchor bolt connection internal thread can be directly and effectively coordinated, it has the following advantages: simple connection and anchoring, strong adhesion, safety and reliability, etc. It is mainly used in underground rail track support engineering of coal mine, for ensuring smooth underground railway safety and coal mine construction industry. Except for low strength and poor safety of domestic old type rock anchor bolt, there are also higher strength and high tensile rock anchor bolt being developed.
Rock Anchor Bolt Production Line – Equipment Introduction
Here is a sample of small steel mill for rock anchor bolt production. Steel Mill adopts all rolling system, the air and gas – double heat furnace, use steel billet as raw material, with alternate arrangement of 6 roughing mills, and finishing mill group in all 6 high rigidity of short stress mills , and setting controlled cooling after rolling equipment, which is 120 m x 10 m step cooling equipment.
High Strength Rock Anchor Bolt Production
Here are list of difficulties and aspects in combination equipments in small steel mills for anchor bolt production:
- High strength rock anchor bolt steel has high-performance requirements. The raw material composition of steel rebar cannot reach the required yield strength and elongation, so it needs to be controlled in rolling process and heat treatment after rolling. The finished rock anchor bolt yield strength requires high carbon content, but it will lead to poor elongation. There are clear requirements for elongation in the standard, which requires post-rolling heat treatment. However, there is no post-rolling heat treatment equipment in small steel mills.
- The difficulty of rolling process development lies in the fact that steel rebar produced needs to be directly fitted with nuts, which means its size has to meet the deviation of standard requirements, and the threads on both sides should be exactly on the same spiral line. Therefore, groove width, expansion angle and radius of the base circle should be reasonable in the design of the threading process, and the cross rib spacing and included angle of the finished hole should be precise in both the design and processing.
- The middle and finishing mill groups without vertical roll rolling of continuous rolling production line, which requires torsion rolling; The second flow balance of rolled pieces cannot be controlled accurately, and the end – end difference will occur. The steelhead and tail have an extra part basically, which influence finished production rate.
- High processing precision is required for of finished rock anchor bolt products rolling groove; consistent transverse rib spacing between upper and lower rollers; consistent transverse rib spacing between the same roll; the actual pitch spacing of rolled products shall be consistent with the target value, and the design value of the transverse rib spacing shall be taken into account of impacting of sliding forward, cold shrinkage and others.
- Rolling mill, reducer quality ensures the upper and lower roll speed synchronization, no axial movement for rolling mill.
In order to solve the above problems completely before test run production of rock anchor bolt rebar, marking threads similar to right-handed rock anchor bolt steel transverse ribs were selected for test verification during production, so as to shorten the process development period and improve the success rate.
Design of Rock Anchor Bolt
- According to the use characteristics and dimensions of high strength rock anchor bolt steel, the design ideas of finished pass and finished front pass are determined:
- The finished product’s inner diameter height and width of free expansion surface shall meet the standard requirements; transverse rib filling degree is guaranteed on the premise, width of free expansion surface is as close as possible to the lower limit of the standard;
- Accurately measure the influence of forwarding sliding and cold shrinkage of Kl under certain conditions, and make corresponding data compensation during design, control the spacing deviation of transverse ribs within 0.2mm after the steel bar is cooled;
- Determine the diameter of Kl rolls of different specifications and the number of transverse ribs processed according to the front slip value, outlet speed of rolled pieces, the distance between transverse ribs and adjustment form to ensure the alignment effect and accuracy;
- Adjust the angle of the axis of the transverse rib, which can directly fit with the nut of the same specification under the condition of the horizontal rib alignment.
Rock Anchor Bolt Grades and Mechanical Properties
|Grade MG335||Yield Strength(MPa)||Tensile Strength(MPa)||Elongation(%)|
|Not Less Than|
The proper calculation method of cross-rib alignment is determined through calculation and selection, so as the relationship between cross-rib phase error distance and adjustment parameters, the accurate rib alignment is realized through empirical data compensation, and the accuracy of roll turning and cross-rib machining is improved to create conditions for the successful manufacture of the high-strength rock anchor bolt.