High yield strength mine hollow anchor rod and preparation method thereof

Abstract

The application belongs to the field of high-strength steel and the field of anchor rod supporting technology, and provides a high-yield strength mine hollow anchor rod and a preparation method thereof, wherein the high-yield strength mine hollow anchor rod comprises the following chemical components: the chemical components are as follows in terms of mass percentage: C: 0.4-0.5%, Si: 0.15-0.4%, Mn: 0.8-0.9%, Cr: 0.8-0.9%, P: ≤0.02%, S: ≤0.02%, Nb: 0.04-0.06%, V: 0.05-0.07%, Ti: 0.09-0.11%, Cu: 0.1-0.2%, Al: 0.2-0.3%, and the rest is Fe and inevitable impurities; the drill rod is of a hollow structure and is provided with a rod body left-hand thread on the surface, a drill bit is threadedly connected to one end of the drill rod, a tray is sleeved on the drill rod, the drill rod is connected with a connecting sleeve through thread cooperation, a right-hand thread is arranged in the connecting sleeve, a gushing stopper is arranged on one side of the tray, and the gushing stopper is made of rubber or plastic material; the yield strength of the application is significantly improved, the application is suitable for the demand of deep well supporting, the comprehensive performance is balanced and optimized, the supporting reliability is greatly improved, the production process is simplified and efficient, and the preparation cost is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the fields of high-strength steel and anchor bolt support technology, and particularly relates to a high yield strength hollow anchor bolt for mining and its preparation method. Background Technology

[0002] Coal is my country's primary energy source, accounting for approximately 58% of its primary energy structure, providing a stable energy guarantee for rapid socio-economic development. The vast majority of my country's coal mines are underground mines, and the smooth and stable operation of roadways, as essential passageways for underground mining, is fundamental to the safe and efficient operation of coal mines. Rock bolt support is the most common support method for coal mine roadways in my country, accounting for over 70% of the total roadway support. Hollow rock bolts, as core support components, essentially control discontinuous and uncoordinated expansion deformations such as surrounding rock delamination, sliding, tensile and shear cracks, maintaining the integrity and self-supporting capacity of the surrounding rock, and reducing the reduction in surrounding rock strength. They play a crucial role in the safe and efficient construction and production of mines.

[0003] Existing hollow anchor bolt technology has the following problems: Insufficient yield strength makes it difficult to meet the needs of deep well mining: As shallow and easily minable coal resources become increasingly depleted, deep well mining has become an inevitable trend. However, the yield strength of existing domestic anchor bolt materials is only 500-600MPa, and that of foreign materials is only 600-700MPa. Under the action of high surrounding rock stress in deep well roadways, they are prone to premature yield failure and cannot meet the strength requirements of deep well support.

[0004] Imbalance in overall performance, difficulty in achieving both plasticity and toughness: In existing technologies, to improve the strength grade of anchor bolts, it is necessary to significantly increase the content of precious alloying elements such as Mo, Ni, Nb, and rare earth elements. This not only leads to a significant decrease in the plasticity and toughness of the material, making the anchor bolts prone to damage when subjected to mining or impact pressure, but also significantly increases the material cost.

[0005] The production process is complex and large-scale production is limited: higher strength anchor bolts require controlled rolling and cooling processes as well as subsequent heat treatment processes such as tempering and isothermal treatment in the bainite temperature zone. However, most rebar manufacturers do not have the conditions for online heat treatment, which leads to reduced production efficiency and a significant increase in preparation costs, which is not conducive to industrialized and large-scale production. Therefore, a high yield strength hollow anchor for mining and its preparation method are needed to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a high yield strength hollow anchor for mining and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a high yield strength hollow anchor bolt for mining, comprising the following chemical components: The chemical composition, by mass percentage, is as follows: C: 0.4-0.5%, Si: 0.15-0.4%, Mn: 0.8-0.9%, Cr: 0.8-0.9%, P: ≤0.02%, S: ≤0.02%, Nb: 0.04-0.06%, V: 0.05-0.07%, Ti: 0.09-0.11%, Cu: 0.1-0.2%, Al: 0.2-0.3%, with the remainder being Fe and unavoidable impurities; It also includes a drill rod, which is a hollow structure with a left-hand thread on its surface. A drill bit is threaded to one end of the drill rod, and a tray is fitted on the drill rod. A connecting sleeve is threaded to the drill rod, and a right-hand thread is provided inside the connecting sleeve. A grout stop plug is provided on one side of the tray. The grout stop plug is made of rubber or plastic. A nut is also threaded to the drill rod, and the nut cooperates with the tray to achieve locking and fixation. In terms of chemical composition design, carbon (C) enhances the strength of steel through solid solution strengthening while stabilizing austenite. A content range of 0.4-0.5% ensures strength while preventing deterioration of plasticity and weldability. Si (Si), as a deoxidizer, reduces oxide inclusions and promotes C enrichment into austenite through solid solution strengthening; a content of 0.15-0.4% avoids reducing the plasticity and weldability of the steel. Mn expands the austenite phase region, stabilizes austenite, improves hardenability, and lowers the Bs and Ms points; a moderate content of 0.8-0.9% can form a multiphase structure during air cooling while preventing intragranular segregation. Cr (Cr)... To enhance corrosion resistance, strength, hardenability, oxidation resistance, and wear resistance, a content of 0.8-0.9% ensures optimized performance. Strict control of P and S content (≤0.02%) avoids cold brittleness and hot brittleness, ensuring comprehensive material performance. Nb, V, and Ti, as strong carbide-forming elements, generate fine, dispersed carbides (nitrides) that inhibit austenite grain growth and recrystallization, playing a precipitation strengthening role. Cu refines grains and fixes N, improving aging resistance, corrosion resistance, and impact toughness. Al, as an auxiliary element, further optimizes material performance with a content of 0.2-0.3%. Structurally, the hollow drill rod, with its left-hand threaded design, facilitates assembly with components such as the right-hand threaded connecting sleeve and drill bit. These components work together to ensure the stability and reliability of the anchor bolt support. The drill bit is threadedly connected to the drill rod, allowing for easy disassembly and replacement, and suitable models can be selected based on different geological conditions. The tray, fitted onto the drill rod and secured with a nut, evenly distributes the support force to the surrounding rock surface, preventing localized stress concentration. The connecting sleeve, with its right-hand thread engaging the left-hand thread of the drill rod, allows for the splicing and extension of multiple drill rods to accommodate varying tunnel depths. The grout stopper, made of rubber or plastic, provides excellent sealing, preventing anchoring agent loss, ensuring anchoring effectiveness, and guaranteeing a firm bond between the anchor bolt and the surrounding rock.

[0008] A further technical solution is that the left-hand thread of the rod body and the right-hand thread inside the connecting sleeve have opposite directions of rotation, which cooperates to achieve an anti-loosening connection; The left-hand thread on the drill rod surface and the right-hand thread inside the connecting sleeve have opposite directions of rotation. The difference in thread rotation creates a reverse locking effect, which can effectively resist the risk of loosening caused by surrounding rock vibration and mining during the installation and use of the anchor bolt. This further strengthens the connection stability between the connecting sleeve and the drill rod, avoids the failure of the support structure due to loose component connections, and ensures that the anchor bolt maintains a reliable assembly state throughout the entire support cycle.

[0009] In a further technical solution, the drill bit width is greater than the drill rod diameter, and the drill bit has a drill hole for discharging the anchoring agent; The design of the drill bit width being greater than the drill rod diameter ensures that the diameter of the borehole is slightly larger than that of the drill rod, providing ample space for the anchoring agent to fill. This ensures that the anchoring agent can fully contact and solidify with the surrounding rock and the drill rod, improving the anchoring effect. The drill holes on the drill bit allow for timely removal of debris during drilling, preventing blockage and ensuring that the anchoring agent can be smoothly discharged from the central hole and evenly fill the borehole. This ensures that the anchor rod is firmly bonded to the surrounding rock, fully exerting its support function and avoiding insufficient support due to inadequate anchoring.

[0010] A further technical solution is that the hollow anchor has a yield strength Rel≥800MPa, tensile strength Rm≥1000MPa, elongation after fracture A≥18%, and impact energy AKv≥80J at 20℃. With a yield strength ≥800MPa and tensile strength ≥1000MPa, the anchor bolts can withstand the high surrounding rock stress in deep well tunnels, effectively avoiding premature yield failure and meeting the strength requirements of deep well mining. With an elongation after fracture ≥18% and an impact energy AKv ≥80J at 20℃, the anchor bolts have good plasticity and impact toughness, can adapt to the continuous deformation of the surrounding rock, resist the instantaneous impact force brought by mining and rockburst, avoid brittle fracture of the anchor bolts, and improve the safety and stability of the support.

[0011] A further technical solution is that the outer diameter of the drill rod is 20-25mm, the wall thickness is 4-6mm, and the straightness of the drill rod is ≤2mm / m; The drill pipe's outer diameter of 20-25mm and wall thickness of 4-6mm achieve a balance between strength and lightness. While ensuring sufficient strength and rigidity to withstand the stress of the surrounding rock, it also takes into account the lightweight nature of the hollow structure, facilitating the transportation, handling, and downhole installation of the anchor bolts. The requirement of drill pipe straightness ≤2mm / m ensures that the anchor bolts can fit tightly against the borehole wall during installation, avoiding uneven stress caused by drill pipe bending, ensuring that the support force is evenly transmitted to the surrounding rock, and further improving the overall support effect.

[0012] A method for preparing a high-yield-strength hollow anchor bolt for mining, applicable to any of the high-yield-strength hollow anchor bolts described above, includes the following steps: S1. Smelting: The ingredients are prepared according to the chemical composition ratio, and then smelted in a converter and refined in an LF furnace; S2, Continuous casting: The refined molten steel is continuously cast into billets to obtain cast billets; S3. Rolled bar stock: Round bars are obtained by heating and holding the cast billet at a certain temperature. S4. Pipe threading: After heating the round bar, the pipe threading process is carried out by hot threading to obtain a hollow tube body (i.e., the base blank of the drill rod). S5. Extrusion Full Thread: After the tube is inserted, the hollow tube body is directly extruded to form a left-hand thread on the rod body. After air cooling to room temperature, the drill rod is obtained as a finished product. Then, the drill bit, connecting sleeve, grout stop plug, tray, and nut are assembled to obtain a complete product. Smelting and refining in an LF furnace according to specific chemical composition ratios ensures the purity and uniformity of the molten steel, laying the foundation for subsequent product performance. The continuously cast billets provide high-quality raw materials for the rolling process. The design of rolling bars, threading tubes, and extruding fully threaded rods enables the gradual formation of hollow, left-hand threaded drill rods from solid bars. The process of directly extruding fully threaded rods after threading tubes and air-cooling eliminates the need for additional controlled cooling and subsequent heat treatment processes, simplifying the production process, improving production efficiency, reducing production costs, and ensuring the formation of the required multiphase refined microstructure, guaranteeing the overall performance of the anchor bolts meets standards. In the finished product assembly stage, a complete support system is formed by rationally matching components such as drill bits, connecting sleeves, grout plugs, trays, and nuts, meeting the actual needs of mine support.

[0013] In a further technical solution, S3, the billet heating temperature is 1180~1200℃, the holding time is 0.5~2 hours, the initial rolling temperature is 1150~1180℃, and the final rolling temperature is 1050~1100℃. The billet heating temperature is controlled at 1180-1200℃, and the holding time is 0.5-2 hours. This ensures that the billet is fully heated, eliminates internal structural stress, and achieves a homogenized structure. It also prevents structural defects from occurring during subsequent rolling due to insufficient heating. The parameters of 1150-1180℃ for the initial rolling temperature and 1050-1100℃ for the final rolling temperature provide suitable temperature conditions for phase transformation during the subsequent cooling process. This facilitates the formation of a refined microstructure of bainite, martensite, and retained austenite during air cooling, ensuring that the anchor bolt possesses both high yield strength and good plasticity and toughness.

[0014] In a further technical solution, in S4, the temperature of the round bar in the heating furnace soaking section is 1225℃, the holding time is extended by 40 minutes, the tube threading equipment adopts TT-LD-200-1200 hot processing equipment, and the wall thickness of the hollow tube body (drill rod base blank) is controlled by the mold during tube threading. Increasing the temperature of the round bar to 1225℃ in the soaking zone of the heating furnace and extending the holding time by 40 minutes effectively eliminates micro-cracks inside the bar. High-temperature oxidation causes these micro-cracks to detach, reducing the scrap rate. Using TT-LD-200-1200 hot-working equipment for hot-threading, combined with mold control of the wall thickness, ensures uniform wall thickness and dimensional accuracy of the hollow tube (drill rod base blank), preventing stress concentration in the anchor rod due to uneven wall thickness. This provides a reliable guarantee for subsequent extrusion of the rod's left-hand thread and the stability of the finished product's performance. During the threading process, precise control of the drill rod's wall thickness using molds ensures that the finished drill rod's wall thickness meets the design requirement of 4-6mm, further enhancing the structural stability of the anchor rod.

[0015] In a further technical solution, in S4, the tube insertion start temperature is 1100℃ and the tube insertion end temperature is >1050℃; In S5, the extrusion forming of the left-hand thread of the rod ends at a temperature >1000℃, and after air cooling, a multiphase refined structure of bainite, martensite, and retained austenite is formed; The tube threading process begins at 1100℃ and ends at >1050℃, while the left-hand threading of the extruded rod ends at >1000℃. This temperature control ensures that the hollow tube remains at a high temperature after threading and extruding the full thread, allowing for the natural formation of a refined microstructure consisting of bainite, martensite, and retained austenite during air cooling. Bainite and martensite, as hard phases, guarantee the material's high strength, while retained austenite enhances the material's ductility and toughness through a phase transformation-induced plasticity effect. This eliminates the need for additional heat treatment processes, simplifying the production process and reducing equipment investment and production costs.

[0016] Further technical solutions: S2 yields a billet size of 150×150mm, and S3 yields a round bar with a diameter of 20-30mm; Before threading the tube, forging defects (such as protrusions, misalignments, etc.) on the surface of the round bar are detected and repaired to avoid outward bending during threading. The setting of 150×150mm billet size and 20-30mm diameter round bar provides a reasonable machining allowance for subsequent tube forming into hollow tube bodies (drill rod base blanks) with an outer diameter of 20-25mm and a wall thickness of 4-6mm, ensuring forming accuracy. Before tube forming, the forging defects on the surface of the round bar (such as protrusions, misalignment, etc.) are detected and repaired, which can promptly address surface problems and avoid outward bending caused by surface defects during tube forming. This ensures the surface quality and structural integrity of the hollow tube body, thereby improving the performance reliability and service life of the finished drill rod and the overall anchor rod.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention significantly improves yield strength, making it suitable for deep well support requirements: By rationally controlling the proportions of alloying elements such as C, Mn, and Si, combined with the precipitation strengthening effect of microalloying elements such as Nb, V, and Ti, and by optimizing rolling temperature parameters and air cooling process, the anchor bolt forms a refined microstructure of bainite, martensite, and retained austenite under air cooling. Bainite and martensite act as hard phases, and the solid solution strengthening effect of C, Mn, Si, and Cu elements further supplements the strength. Ultimately, the yield strength of the anchor bolt is ≥800MPa and the tensile strength is ≥1000MPa, effectively solving the problem of insufficient yield strength of existing anchor bolts, which makes it difficult to withstand the high surrounding rock stress in deep well tunnels, and fully meeting the support strength requirements of deep well mining. This invention achieves comprehensive performance balance and optimization, significantly improving support reliability: While ensuring high yield strength, by controlling the C content and rationally combining alloy element ratios, and utilizing the transformation-induced plasticity effect of retained austenite, the anchor bolt achieves an elongation at break ≥18% and an impact energy AKv ≥80J at 20℃, exhibiting excellent plasticity and impact toughness. This effectively solves the problem of insufficient plasticity and toughness in some existing high-strength anchor bolts, making them susceptible to damage from mining and rock bursts. Simultaneously, the addition of Cr and Cu elements enhances the anchor bolt's corrosion resistance and wear resistance, extending its service life and ensuring long-term stable support in complex mining environments. The coordinated design of various structural components further improves the stability and reliability of the support system. This invention simplifies and improves the production process, significantly reducing manufacturing costs. Through reasonable composition design and process optimization, the required multiphase refined microstructure can be obtained in the post-rolling air-cooled state without additional controlled cooling and subsequent heat treatment processes. This effectively solves the problems of complex production processes and high equipment requirements in existing high-strength anchor bolt production. At the same time, it eliminates the need to add excessive amounts of expensive alloying elements, reducing raw material costs. Furthermore, it clarifies key process details such as pipe insertion methods, equipment, and wall thickness control, ensuring process reproducibility, improving production efficiency, meeting the needs of industrial-scale production, and significantly reducing the cost of support material preparation and the overall cost of mine support.

[0018] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall assembly structure of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the drill pipe of the present invention; Figure 3 This is a partially enlarged structural diagram of the left-hand thread on the rod body of the present invention; Figure 4 This is a cross-sectional structural diagram of the connecting sleeve of the present invention; Figure 5This is a schematic diagram of the assembly structure of the slurry stop plug and the tray of the present invention; Figure 6 This is a schematic diagram of the right-hand thread of the present invention; Figure 7 This is a flowchart of the preparation process of the present invention; Figure 8 This is a metallographic diagram of the hollow anchor rod obtained in Embodiment 1 of the present invention; Figure 9 The table below shows the chemical composition and mass percentage of the cast billets in Examples 1 and 2 of this invention. Figure 10 The table shows the mechanical properties of the hollow anchor bolts in Embodiments 1 and 2 of this invention.

[0020] In the diagram: 1. Drill bit; 2. Drill rod; 3. Left-hand thread on the rod body; 4. Connecting sleeve; 5. Sewer plug; 6. Tray; 7. Nut; 8. Right-hand thread. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments.

[0022] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0023] Example 1

[0024] like Figure 1-10 As shown, this invention provides a high yield strength hollow anchor bolt for mining and its preparation method, covering all core technical features.

[0025] In this embodiment, the chemical composition of the hollow anchor rod, by mass percentage, is: C: 0.42%, Si: 0.18%, Mn: 0.83%, Cr: 0.84%, P: 0.007%, S: 0.009%, Nb: 0.042%, V: 0.064%, Ti: 0.108%, Cu: 0.1%, Al: 0.25%, with the remainder being Fe and unavoidable impurities.

[0026] The preparation process follows the corresponding process requirements: first, the billets are smelted in a converter and refined in an LF furnace, then continuously cast to obtain 150×150mm square billets; after the billets are stacked and cooled to room temperature, they are heated to 1185℃ and held for 1.5 hours, then rolled at 1160℃ for the first rolling and 1050℃ for the final rolling, followed by air cooling to obtain round bars with a diameter of 25mm; after inspection and repair of forging defects such as protrusions and misalignments on the surface of the round bars, they are held at 1225℃ in the soaking section of the heating furnace for 40 minutes, using TT-LD-200-1200 heat exchangers. The processing equipment starts hot threading at 1100℃ and ends at >1050℃. The wall thickness is controlled by the mold. The long oval tube of φ25×1000mm is heated and threaded into a steel tube of φ25×7mm. After threading, the tube is directly extruded with full thread. The extrusion ends at >1000℃. It is then air-cooled to room temperature to form a complex microstructure of bainite, martensite and retained austenite. No controlled cooling treatment or subsequent heat treatment is required. Finally, a drill rod 2 with an outer diameter of 25mm, a wall thickness of 5mm and a straightness of ≤2mm / m is obtained.

[0027] The finished product structure is configured as follows: the drill rod 2 has a left-hand thread 3 on its surface, and one end is threaded to the drill bit 1. The drill bit 1 is wider than the diameter of the drill rod 2 and has an anchoring agent discharge hole. A tray 6 is fitted on the drill rod 2, and the threaded engagement is achieved through a connecting sleeve 4 with a right-hand thread 8. A rubber grout stop plug 5 is installed on one side of the tray 6. A nut 7 is threaded on the drill rod 2 and engages with the tray 6 to lock it in place. The mechanical properties of the anchor rod, as tested, are: yield strength 812 MPa, tensile strength 1140 MPa, elongation after fracture 19.5%, and impact energy at 20℃ 82 J. The testing standards are GB / T228.1 (tensile) and GB / T229 (impact).

[0028] Example 2

[0029] The difference between this embodiment and Embodiment 1 is that the proportion of some chemical components, the size of the round bar and the finished drill rod are adjusted within the corresponding range, while the remaining process features and structural configurations are the same as in Embodiment 1.

[0030] In this embodiment, the chemical composition of the hollow anchor rod, by mass percentage, is: C: 0.45%, Si: 0.39%, Mn: 0.88%, Cr: 0.89%, P: 0.008%, S: 0.005%, Nb: 0.058%, V: 0.055%, Ti: 0.097%, Cu: 0.15%, Al: 0.28%, with the remainder being Fe and unavoidable impurities.

[0031] During the preparation process, the parameters such as billet heating, heat preservation, initial rolling and final rolling temperatures were the same as in Example 1. The diameter of the rolled round bar was 30 mm. The tube threading was carried out using the same TT-LD-200-1200 equipment, hot threading method and die thickness control process as in Example 1. The tube threading start temperature was 1100℃, the end temperature was >1050℃, the extrusion full thread end temperature was >1000℃, and after air cooling, a multiphase refined structure of bainite, martensite and retained austenite was formed, and finally a drill rod 2 with an outer diameter of 22 mm, a wall thickness of 4.5 mm and a straightness of ≤2 mm / m was obtained.

[0032] The finished product structure is configured as follows: the left-hand thread 3 on the rod body and the right-hand thread 8 on the connecting sleeve 4 have opposite directions of rotation. The assembly method of the drill bit 1, tray 6, grout stop plug 5, and nut 7 is the same as in Example 1. The mechanical properties of the anchor bolt, as tested, are: yield strength 841 MPa, tensile strength 1180 MPa, elongation after fracture 18.7%, and impact energy at 20°C 91 J. The testing standards are the same as in Example 1, making it suitable for deep mine support scenarios with different size requirements.

[0033] This invention achieves a comprehensive improvement in the overall performance of hollow anchor bolts through scientific chemical composition ratios, optimized manufacturing processes, and rational structural design. In terms of chemical composition, it eliminates the need for excessive amounts of expensive alloying elements; by controlling the proportions of conventional elements and precisely adding micro-alloying elements, it reduces costs while ensuring performance. In terms of manufacturing processes, it eliminates controlled cooling and subsequent heat treatment steps, simplifying the process, improving efficiency, and adapting to large-scale industrial production. In terms of structural design, the drill bit 1, drill rod 2, left-hand threaded rod body 3, connecting sleeve 4, grout stop plug 5, tray 6, nut 7, and right-hand threaded rod 8 work together to ensure support reliability. The final product possesses high yield strength, high tensile strength, good plasticity and toughness, and corrosion resistance, making it particularly suitable for deep mine support. It can significantly improve the safety level of mine support, reduce support costs, and solve many pain points of existing technologies.

[0034] Working principle and usage process of this invention: Raw material smelting and refining: Raw materials are proportioned according to the set chemical composition ratio. Iron ore, scrap steel and other raw materials are put into the converter for smelting to remove impurities from the raw materials. Then the molten steel is sent to the LF furnace for refining to further improve the purity and composition uniformity of the molten steel and ensure that the quality of the molten steel meets the requirements of subsequent processing. Continuous casting: Refined and qualified molten steel is poured into a continuous casting machine and produced into a square billet with a size of 150×150mm through the continuous casting process. After the billets are stacked, they are naturally cooled to room temperature for use, ensuring that the billet structure is stable and there is no internal stress concentration. Rolled bars: The cooled billet is fed into a heating furnace and heated to 1180-1200℃, and held for 0.5-2 hours to ensure that the billet is fully heated and the structure is homogenized; then the heated billet is conveyed to the rolling mill and rolling is started at an initial rolling temperature of 1150-1180℃, and the final rolling temperature is controlled at 1050-1100℃. After rolling, the billet is air-cooled to obtain round bars with a diameter of 20-30mm. Round bar pretreatment: The surface quality of the rolled round bars is inspected to promptly identify and repair surface defects such as protrusions and misalignments left by forging; then the round bars are sent into a heating furnace and held at a soaking temperature of 1225℃ for 40 minutes to eliminate micro-cracks inside the round bars and reduce the scrap rate in subsequent processing. Piping process: Using TT-LD-200-1200 hot working equipment, the pre-treated round bar is hot-piped at an initial temperature of 1100℃. The wall thickness of the hollow tube (the base blank of drill rod 2) is precisely controlled by the mold. The temperature is maintained at >1050℃ at the end of the pipe-piercing process to obtain a hollow tube that meets the dimensional requirements. Extrusion of full thread and cooling: After the tube is inserted, when the temperature of the hollow tube body is >1050℃, it is directly extruded to form the left-hand thread 3 of the rod body. The temperature at the end of the extrusion is >1000℃. Then the hollow tube body with the left-hand thread 3 of the rod body is naturally air-cooled to room temperature. During the air-cooling process, a multiphase refined structure of bainite, martensite and retained austenite is formed to obtain the hollow anchor drill rod 2. Assembly and molding: The drill bit 1 is installed at one end of the hollow anchor drill rod 2 by means of threaded connection. The tray 6 and nut 7 are sequentially fitted on the drill rod 2. The connecting sleeve 4 with right-hand thread 8 is tightly fitted with the left-hand thread 3 of the drill rod body. Finally, the rubber or plastic grout stop plug 5 is installed on one side of the tray 6 to complete the overall preparation of the high yield strength mining hollow anchor rod. Support Application: After drilling in the mine roadway, the prepared hollow anchor rods are inserted into the borehole. The anchoring agent is discharged through the drill hole on the drill bit 1. The anchoring agent is evenly filled and cured in the duct, so that the anchor rod is firmly bonded to the surrounding rock. The right-hand thread 8 of the connecting sleeve 4 and the left-hand thread 3 of the drill rod 2 are used to realize the splicing of multiple rods. The anchor rod is fixed by locking the tray 6 with the nut 7. The drill rod 2, with its high yield strength, good plasticity and toughness and other comprehensive properties, effectively controls the delamination, sliding and crack propagation of the surrounding rock, maintains the integrity and self-supporting capacity of the surrounding rock, and realizes reliable support for the mine roadway.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high yield strength hollow anchor bolt for mining, characterized in that, Includes the following chemical components: The chemical composition, by mass percentage, is as follows: C: 0.4-0.5%, Si: 0.15-0.4%, Mn: 0.8-0.9%, Cr: 0.8-0.9%, P: ≤0.02%, S: ≤0.02%, Nb: 0.04-0.06%, V: 0.05-0.07%, Ti: 0.09-0.11%, Cu: 0.1-0.2%, Al: 0.2-0.3%, with the remainder being Fe and unavoidable impurities; It also includes a drill rod (2), which is a hollow structure and has a left-hand thread (3) on its surface. A drill bit (1) is threaded to one end of the drill rod (2). A tray (6) is fitted on the drill rod (2). A connecting sleeve (4) is threaded to the drill rod (2). A right-hand thread (8) is provided inside the connecting sleeve (4). A grout stopper (5) is provided on one side of the tray (6). The grout stopper (5) is made of rubber or plastic. A nut (7) is also threaded to the drill rod (2). The nut (7) and the tray (6) cooperate to lock and fix it.

2. The high yield strength hollow anchor bolt for mining according to claim 1, characterized in that, The left-hand thread (3) on the rod body and the right-hand thread (8) inside the connecting sleeve (4) have opposite directions of rotation, which cooperate to achieve an anti-loosening connection.

3. The high yield strength hollow anchor bolt for mining according to claim 1, characterized in that, The drill bit (1) is wider than the diameter of the drill rod (2), and the drill bit (1) has a hole for the discharge of the anchoring agent.

4. The high yield strength hollow anchor bolt for mining according to claim 1, characterized in that, The hollow anchor has a yield strength Rel≥800MPa, tensile strength Rm≥1000MPa, elongation after fracture A≥18%, and impact energy AKv≥80J at 20℃.

5. The high yield strength hollow anchor bolt for mining according to claim 1, characterized in that, The drill rod (2) has an outer diameter of 20-25mm, a wall thickness of 4-6mm, and a straightness of ≤2mm / m.

6. A method for preparing a high-yield-strength hollow anchor bolt for mining, applicable to the high-yield-strength hollow anchor bolt described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Smelting: The ingredients are prepared according to the chemical composition ratio, and then smelted in a converter and refined in an LF furnace; S2. Continuous casting: The refined molten steel is continuously cast into billets to obtain billets; S3. Rolled bar stock: Round bars are obtained by heating and holding the cast billet at a certain temperature. S4. Piping: After heating the round bar, the hollow tube is pierced by hot piercing to obtain a hollow tube. S5. Extrusion of full thread: After passing through the tube, the hollow tube body is directly extruded to form a left-hand thread (3) on the rod body. After air cooling to room temperature, the drill rod (2) is obtained. Then, the drill bit (1), connecting sleeve (4), grout stop plug (5), tray (6), and nut (7) are assembled to obtain the complete product.

7. The method for preparing high-yield-strength hollow anchor bolts for mining according to claim 6, characterized in that, In S3, the billet heating temperature is 1180~1200℃, the holding time is 0.5~2 hours, the initial rolling temperature is 1150~1180℃, and the final rolling temperature is 1050~1100℃.

8. The method for preparing high-yield-strength hollow anchor bolts for mining according to claim 6, characterized in that, In S4, the temperature of the round bar in the heating furnace soaking section is 1225℃, and the holding time is extended by 40 minutes. The tube threading equipment adopts TT-LD-200-1200 heat treatment equipment, and the wall thickness of the hollow tube is controlled by the mold during tube threading.

9. The method for preparing a high-yield-strength hollow anchor bolt for mining according to claim 6, characterized in that, In S4, the initial temperature for tube insertion is 1100℃, and the final temperature for tube insertion is >1050℃. In S5, the rod body is extruded to form a left-hand thread (3) at a temperature >1000℃. After air cooling, a multiphase refined structure of bainite, martensite, and retained austenite is formed.

10. The method for preparing a high-yield-strength hollow anchor bolt for mining according to claim 6, characterized in that, The billet size obtained by S2 is 150×150mm, and the diameter of the round bar obtained by S3 is 20-30mm. Before threading the tube, forging defects on the surface of the round bar are inspected and repaired to prevent outward bending during threading.

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