A method for preventing the bursting of pre-drilled holes in ribbed anchor bolts

Abstract

This invention relates to a method for preventing the bursting of grooves in the finished ribbed anchor bolt, comprising the following steps: Step 1: shutting down the spraying device of the roughing and intermediate rolling mills before production; Step 2: using the K1 roll of a Φ390 rolling mill for rolling, with an initial rolling temperature of 1050-1200℃, controlling the temperature of the continuously cast billet at 900-1000℃ during rolling, controlling the speed at which the continuously cast billet is fed into the rolling mill at 10-20 m / min, and controlling the number of feeds to within 3 times; after the start of rolling, temporarily shutting off the cooling water for the K1-K3 rolls; Step 3: controlling the height of the transverse ribs of the finished product according to the lower limit. This invention effectively avoids "grooving" or "piece falling off" of the rolls during continuous rolling production by adjusting the process parameters in the rolling process, which is beneficial to the stable production of ribbed anchor bolts.

Description

Technical Field

[0001] This invention relates to the field of anchor rod rebar rolling technology, specifically to a method for preventing the bursting of the finished hole groove in ribbed anchor rods. Background Technology

[0002] Threaded steel anchor bolts are support devices that utilize the mechanical interlocking between the threaded structure and the anchor body to reinforce rock, soil, or concrete structures. In recent years, threaded steel anchor bolts have become the mainstream choice for geotechnical anchoring engineering due to their advantages such as high strength, strong bonding performance, and good construction flexibility. Besides playing an important role in mine roadway support, threaded steel anchor bolts can also be used for high-strength, long-lasting roadway support in railway, hydropower, and other projects. Based on differences in processing technology and structure, threaded steel anchor bolts can be divided into ordinary threaded steel anchor bolts, fully threaded anchor bolts, threaded steel anchor bolts without longitudinal ribs, and fine-tooth ribbed anchor bolts. Ordinary threaded steel anchor bolts have a simple rolling process and low cost, but stress concentration occurs at the junction of transverse and longitudinal ribs, resulting in limited pull-out resistance. Threaded steel anchor bolts without longitudinal ribs retain only transverse thread ribs, offering good corrosion resistance and fatigue resistance, but poor initial bonding strength and construction flexibility. Fully threaded anchor bolts have uniform thread distribution, good construction flexibility, and strong shear resistance, but due to their larger thread spacing and shallower thread depth, they suffer from insufficient durability and fatigue resistance. Fine-tooth ribbed anchor bolts are made from ribbed steel bars, with fine, uniquely shaped ribs and strong bonding strength, forming a robust support structure in the formation. Compared to traditional threaded steel anchor bolts, they offer superior durability, strong bonding strength, and high tensile strength, enabling them to withstand high stress and deformation in the formation.

[0003] Fine-tooth ribbed anchor bolts, also known as ribbed anchor bolts, rely on the geometric precision and mechanical properties of their surface ribs (raised stripes) to directly determine the bond strength between the anchor bolt and the grout / soil / rock mass. Currently, the production of fine-tooth ribbed anchor bolts mainly relies on hot rolling forming—rolling steel billets into ribbed rods through high-temperature rolling. The roll die design and durability are key factors in controlling rib quality. However, during continuous rolling, localized material spalling (i.e., "groove bursting" or "piece falling off") often occurs on the roll surface due to the close rib spacing and extreme working conditions (high temperature, high stress, friction and wear). This not only leads to rib defects and dimensional deviations on the surface of the finished fine-tooth ribbed anchor bolt, severely reducing its physical properties, but also affects the smooth operation of the anchor bolt production process, and in severe cases, may even cause engineering safety hazards. Summary of the Invention

[0004] To address the technical problem of "groove bursting" or "piece falling off" that easily occurs when continuously rolling ribbed anchor bolts using hot rolling forming process, this invention provides a method to prevent groove bursting in the finished hole of ribbed anchor bolts. By adjusting the process parameters in the rolling process, "groove bursting" or "piece falling off" of the rolls during continuous rolling production can be effectively avoided, which is beneficial to the stable production of ribbed anchor bolts.

[0005] The technical solution of this invention is as follows:

[0006] A method for preventing the bursting of pre-drilled holes in ribbed anchor bolts includes the following steps:

[0007] Step 1: Shut down the spray system of the roughing and intermediate rolling mills before production begins;

[0008] Step 2: Use the K1 roll of the Φ390 rolling mill for rolling. The initial rolling temperature is 1050-1200℃ to prevent low-temperature grooving. During the rolling process, control the temperature of the continuous casting billet at 900-1000℃, control the speed at which the continuous casting billet is fed into the rolling mill at 10-20m / min, and control the number of feeding passes to 1-3. After the initial rolling, temporarily shut off the cooling water for the K1-K3 rolls.

[0009] Step 3: Control the height of the transverse ribs of the finished product according to the lower limit.

[0010] Furthermore, in step one, the roughing and intermediate rolling mills include mills 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Mills 1-6 are roughing mills, and they are connected end-to-end to form a six-stand roughing section. Mills 7-12 are intermediate rolling mills, and they are connected end-to-end to form a six-stand intermediate section. A flying shear device can be installed between the six-stand roughing section and the six-stand intermediate section. The invention employs multiple rolling mills—a six-stand roughing mill and a six-stand intermediate mill—operating collaboratively to form a continuous rolling production line for producing ribbed anchor bolts. On one hand, the continuous casting billet production process eliminates the need for intermediate stops, significantly shortening the rolling cycle. On the other hand, each mill on the continuous rolling production line can be precisely controlled, and the cumulative reduction over 12 passes reduces the accumulation of errors per stand, accurately controlling the dimensional accuracy of the rolled piece. After shutting down the spraying devices of mills 1-12 before production, the entire continuous rolling production line forms a gradient insulation chain, which helps to reduce temperature fluctuations and improve the plastic stability of the material.

[0011] Furthermore, in step two, when rolling with the K1 roll of the Φ390 rolling mill, ordinary cooling water is used for cooling. The water pressure of ordinary cooling water is 6-8 kg, preferably 7 kg. High-pressure water used for controlled rolling and cooling is strictly prohibited. The roll material is preferably high-speed steel and / or semi-steel. Using ordinary cooling water reduces the cooling rate of the workpiece surface, narrows the temperature difference between the workpiece surface and interior, reduces residual stress on the workpiece surface and interior, and improves the quality stability of the finished rib anchor bolt. High-speed steel (HSS) is a tool steel containing high alloying elements such as tungsten (W), molybdenum (Mo), chromium (Cr), and vanadium (V), characterized by high hardness, high wear resistance, and high heat resistance. Rolls made of high-speed steel can maintain high hardness during high-temperature rolling, ensuring that the rolls can still effectively bite into the workpiece at high temperatures, avoiding roll gap misalignment caused by thermal softening. The high rigidity of high-speed steel also reduces rolling force fluctuations and suppresses surface defects, including slotting. Semi-steel is a hypereutectoid cast steel with extremely high carbon content (1.4%-2.4%). This type of high-carbon cast steel actually falls into the category of cast iron, hence the common name "semi-steel." Semi-steel is a ferroalloy material with high strength, good wear resistance, and good corrosion resistance. Its main components are iron with small amounts of carbon, manganese, and other elements. Semi-steel possesses good mechanical properties and resistance to thermal fatigue; rolls made from semi-steel exhibit lower thermal stress. Furthermore, rolls made from semi-steel have a moderate modulus of elasticity, providing good deformation compatibility and reducing fluctuations in transverse rib height.

[0012] Furthermore, in step two, cooling water is used to cool the looper. The flow rate of the looper cooling water is appropriately reduced, controlled at 20-35 m³ / h, to ensure cooling effectiveness. During the cooling process, it is important to prevent the cooling water from splashing onto the red-hot steel. The complex geometry of the fine-toothed rib structure of the rib anchor rod makes it prone to becoming a point of thermal stress concentration. Using a small flow rate of cooling water to cool the looper allows for a more gradual temperature change, avoiding thermal stress concentration in critical components such as the looper due to sudden cooling, thereby reducing the risk of cracks or deformation. Controlling the flow rate of the looper cooling water within the range of 20-35 m³ / h not only meets the cooling requirements of critical components such as the looper but also stabilizes the working temperature of the rolls, preventing a decrease in surface hardness due to overheating, thus reducing the accelerated wear of the rib anchor rods due to softening during rolling. If the cooling water splashes onto the red-hot steel surface, it may cause thickening of the steel oxide scale or micro-cracks. Such defects will increase the risk of damage to the rolls during rolling. Localized pressure (especially in the contact area of ​​the fine ribs) can cause scratches, chipping, or bursting of the roll surface. When the mill is shut down for more than 2 hours due to reasons such as changing the type of continuously cast billet, waiting for gas, or peak-avoidance production, the CP2 control system notifies the pump room to shut down all cooling tower fans and control the temperature of the ordinary cooling water at 25-35℃. After shutting down the cooling tower fans, the active heat dissipation capacity of the cooling tower is reduced, making the temperature of the ordinary cooling water higher than normal. On the one hand, this can prevent the temperature difference between the surface and core of the roll from being too large due to the excessively cold ordinary cooling water after the mill is shut down, thereby reducing the concentration of thermal stress and reducing the risk of micro-cracks in the rib anchor rods. On the other hand, controlling the temperature of the ordinary cooling water at 25-35℃ can not only prevent the temperature of the roll from dropping to the brittle range of the material, which could lead to brittle fracture or spalling of the rib anchor rods, but the relatively mild cooling environment can also help to slowly release residual stress and maintain the stability of the roll shape. When the mill restarts, the roll temperature can reach the steady-state rolling temperature more quickly, preventing thermo-mechanical fatigue damage to the rib anchor bolts and protecting the rib anchor bolt structure.

[0013] Furthermore, in step two, rolling is performed using a multi-unit collaborative operation. The K1 roll of the Φ390 mill is only the core roll of the finishing section; in actual rolling, 1-20 Φ390 mill stands can be used in collaborative operation as needed. Using a multi-unit collaborative operation not only significantly shortens the total rolling time for a single anchor bolt, enabling continuous high-speed production, but also avoids production line shutdowns due to roll changes or maintenance on some mills by rotating multiple units, ensuring production continuity. Multi-unit collaborative operation also prevents a single roll from bearing high loads for extended periods, reducing roll wear rate and extending roll service life while preventing temperature accumulation due to continuous operation.

[0014] Furthermore, in step two, the continuously cast billet is a cylindrical steel material with a length of 1-1.5 meters and a diameter of 22 millimeters. The surface of the billet is free of severe iron oxide scale or defects. A length of 1-1.5 meters facilitates clamping and pushing, reducing jamming or positioning deviations caused by excessive billet length, and ensuring continuous feeding rhythm of the rolling mill. Limiting the billet diameter to 22 millimeters allows for more uniform heating, avoiding excessive core-to-surface temperature differences due to excessive cross-section, suppressing residual stress concentration in the fine-tooth rib area, and improving the fatigue resistance of the rib anchors. This invention feeds the billet into the rolling mill at a low speed of 10-20 m / min, avoiding failure to bite the billet or jamming due to excessive feeding speed. During the feeding process, the stability of the billet as it passes through each pass is observed (e.g., whether deviation or vibration occurs). After rolling, use calipers to measure key dimensions such as diameter, ovality, and rib height of the rolled continuous casting billet, and observe whether there is any misalignment of ribs in the rolled continuous casting billet.

[0015] Furthermore, in step two, the standard roll gap is controlled within 1-3 mm, preferably 2 mm. Controlling the standard roll gap to 2 mm ensures that the roll pattern is fully pressed into the steel surface, avoiding insufficient rib height or pitch deviation caused by an excessively large roll gap. Adjusting the roll gap consistency on both sides of all rolling mills and aligning the guides with the roll groove prevents the continuous casting billet from developing a sickle-like bend and uneven head deformation (or experiencing temperature differences) during rolling, which could lead to uneven deformation and potential groove bursting when the billet head bites into the K1 roll.

[0016] Furthermore, in step two, after the start of rolling, when the heads of the first, second, and third continuously cast billets pass through the mill, the cooling water for the K1 roll of mill #20, the K2 roll of mill #19, and the K3 roll of mill #18 is temporarily shut off for 1-2 seconds. During high-temperature rolling, the rolls accumulate heat. If they suddenly come into contact with low-temperature cooling water, the roll surface will experience extreme thermal stress due to rapid cooling, causing micro-cracks on the roll surface to expand, ultimately leading to roll breakage or spalling. Temporarily shutting off the cooling water prevents the sudden drop in roll surface temperature from causing a huge impact on the roll, leading to roll breakage and slippage, and avoids localized shrinkage and deformation of the roll, affecting the matching degree between the groove and the workpiece, and causing uneven rib depth. Temporarily shutting off the cooling water also maintains the stability of the roll dimensions, ensuring uniform thread formation.

[0017] Furthermore, in step three, the height of the transverse ribs in the finished product is 0-0.1 mm, preferably 0.05-0.1 mm, and the inclination angle of the transverse ribs is 60º in the die design. First, a 60º inclination angle in the die design helps balance the rolling force and reduces rib height fluctuations caused by uneven stress on the rolled piece. Second, a 60º inclination angle in the die design allows the metal to flow evenly along the roll groove during rolling, avoiding metal accumulation or surface tearing of the rolled piece due to excessive inclination angle. Third, a 60º inclination angle in the die design makes alignment easier during roll regrinding and roll changing, reducing downtime caused by die misalignment and ensuring production continuity. A shallow groove design with a transverse rib height ≤ 0.1 mm reduces local pressure on the rolls, and combined with the optimized force component at a 60º inclination angle, it reduces wear on the groove edges and extends the roll's service life.

[0018] Furthermore, in step three, the strength grade of the finished product is any one of 335MPa, 400MPa, 500MPa, and 600MPa. If different strength grades of finished products need to be produced, they are produced in descending order of strength grade to match the different cooling rate requirements of the water temperature and the finished products of different strength grades. Different strength grades of ribbed anchor bolts have different cooling rate requirements. Using higher temperature cooling water to slowly cool the finished products of lower strength grades can avoid overcooling and the accumulation of residual stress; using lower temperature cooling water to rapidly cool the finished products of higher strength grades can improve strength and toughness through phase transformation strengthening.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention provides a method for preventing the bursting of the finished hole in a ribbed anchor bolt. By shutting down the spray system of the roughing and intermediate rolling mills before production and temporarily shutting down the cooling water of rolls K1-K3 after rolling begins, a stable high-temperature rolling environment is created, ensuring the continuously cast billet is in its optimal plastic state and reducing phase transformation stress caused by sudden temperature changes. By controlling the temperature of the continuously cast billet at 900-1000℃ and the initial rolling temperature at 1050-1200℃, a thermodynamic equilibrium system is established, effectively avoiding brittle fracture caused by low-temperature rolling. By using the K1 roll of a Φ390 rolling mill and controlling the speed at which the continuously cast billet is fed into the mill at 10-20 m / min, and limiting the number of passes to less than 3, the cumulative strain energy is reduced, and the work hardening effect is also minimized. By controlling the transverse rib height of the finished product according to the lower limit, the surface stress distribution of the finished product becomes more uniform. Finite element analysis shows that the maximum principal stress can be reduced by 25-30 MPa, fundamentally eliminating the risk of bursting caused by stress concentration. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0022] Example 1

[0023] A method for preventing the pre-drilled holes of MG600X(Z)Φ22 ribbed anchor bolts includes the following steps:

[0024] Step 1: Before production, confirm that the cooling water temperature is 25-35℃, and shut down all the spray devices of the roughing and intermediate rolling mills. The roughing and intermediate rolling mills include mills 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Mills 1-6 are the roughing mills, and they are connected end-to-end to form a six-stand roughing section. Mills 7-12 are the intermediate rolling mills, and they are connected end-to-end to form a six-stand intermediate section. A flying shear device is installed between the six-stand roughing section and the six-stand intermediate section. After the continuously cast billet is fed, it undergoes heating in a heating furnace, high-pressure water descaling, rough rolling in a six-stand roughing mill, flying shearing of the head and tail, and intermediate rolling in a six-stand intermediate mill. This invention utilizes multiple rolling mills operating in a coordinated manner in a six-stand roughing and intermediate mill to form a continuous rolling production line for producing ribbed anchor bolts. On one hand, the continuous casting billet production process eliminates the need for intermediate stops, significantly shortening the rolling cycle. On the other hand, each mill on the continuous rolling production line can be precisely controlled, and the cumulative reduction over 12 passes reduces the accumulation of errors per stand, accurately controlling the dimensional accuracy of the rolled piece. After shutting down the spraying devices of mills 1-12 before production, the entire continuous rolling production line forms a gradient insulation chain, which helps to reduce temperature fluctuations and improve the plastic stability of the material.

[0025] Step 2: Use the K1 roll of the Φ390 rolling mill for rolling. The initial rolling temperature is 1050-1200℃ to prevent low-temperature grooving. During the rolling process, control the temperature of the continuous casting billet at 900-1000℃, control the speed at which the continuous casting billet is fed into the rolling mill at 10-20m / min, and control the number of feeding times to two. After the initial rolling, temporarily shut off the cooling water of the K1 roll to K3 roll.

[0026] When rolling with the K1 rolls of a Φ390 rolling mill, ordinary cooling water with a pressure of 7 kg is used. The use of high-pressure water for controlled rolling and cooling is strictly prohibited. The rolls are made of high-speed steel. Using ordinary cooling water reduces the cooling rate of the workpiece surface, minimizes the temperature difference between the workpiece surface and interior, reduces residual stress on both the surface and interior of the workpiece, and improves the quality stability of the finished ribbed anchor bolts. High-speed steel (HSS) is a tool steel containing high alloying elements such as tungsten (W), molybdenum (Mo), chromium (Cr), and vanadium (V), characterized by high hardness, high wear resistance, and high heat resistance. Rolls made of high-speed steel can maintain high hardness during high-temperature rolling, ensuring that the rolls can effectively bite into the workpiece at high temperatures, avoiding roll gap misalignment caused by thermal softening. The high rigidity of high-speed steel also reduces rolling force fluctuations and suppresses surface defects, including slotting. Semi-steel is a hypereutectoid cast steel with extremely high carbon content (1.4%-2.4%). This type of high-carbon cast steel actually falls into the category of cast iron, hence the common name "semi-steel." Semi-steel is a ferroalloy material with high strength, good wear resistance, and good corrosion resistance. Its main components are iron with small amounts of carbon, manganese, and other elements. Semi-steel possesses good mechanical properties and resistance to thermal fatigue; rolls made from semi-steel exhibit lower thermal stress. Furthermore, rolls made from semi-steel have a moderate modulus of elasticity, providing good deformation compatibility and reducing fluctuations in transverse rib height.

[0027] Cooling water is used to cool the looper. The flow rate of the looper cooling water should be controlled at 20-35 m³ / h to ensure cooling effect. During the cooling process, it is important to prevent the cooling water from splashing onto the red steel. The complex geometry of the fine toothed rib structure of the rib anchor rod makes it prone to becoming a point of thermal stress concentration. Using a small flow rate of cooling water to cool the looper can make the temperature change of the looper more gradual, avoiding thermal stress concentration in critical components such as the looper due to sudden cooling, thereby reducing the risk of cracks or deformation. Controlling the flow rate of the looper cooling water within the range of 20-35 m³ / h can not only meet the cooling needs of critical components such as the looper, but also stabilize the working temperature of the rolls, avoiding a decrease in surface hardness due to overheating, thereby reducing the accelerated wear of the rib anchor rods due to softening during rolling. If the cooling water splashes onto the surface of the red steel, it may cause the steel oxide scale to thicken or microcracks. Such defects will increase the local pressure on the rolls during rolling. Especially in the contact area of ​​the fine tooth ribs, this can lead to scratches, chipping, or bursting of the roll surface. When the mill is shut down for more than 2 hours due to reasons such as changing the type of continuous casting billet, waiting for gas, or peak-avoidance production, the CP2 control system notifies the water pump room to shut down all cooling tower fans and control the temperature of the ordinary cooling water at 25-35℃. After shutting down the cooling tower fans, the active heat dissipation capacity of the cooling tower is reduced, making the temperature of the ordinary cooling water higher than normal. On the one hand, this can prevent the temperature difference between the surface and the core of the roll from being too large due to the excessive cooling of the ordinary cooling water after the mill is shut down, thereby reducing the concentration of thermal stress and reducing the risk of micro-cracks in the rib anchor rods. On the other hand, controlling the temperature of the ordinary cooling water at 25-35℃ can not only prevent the temperature of the roll from dropping to the brittle range of the material, which could lead to brittle fracture or spalling of the rib anchor rods, but the relatively mild cooling environment can also help to slowly release residual stress and maintain the stability of the roll shape. When the mill restarts, the roll temperature can reach the steady-state rolling temperature more quickly, preventing thermo-mechanical fatigue damage to the rib anchor bolts and protecting the rib anchor bolt structure.

[0028] Rolling is performed using a multi-unit collaborative operation. The K1 roll of the Φ390 mill is only the core roll of the finishing section; in actual rolling, 20 Φ390 mill stands are used in collaborative operation. Using a multi-unit collaborative operation not only significantly shortens the total rolling time for a single anchor bolt, enabling continuous high-speed production, but also avoids production line shutdowns due to roll changes or maintenance on some mills by rotating multiple units, ensuring production continuity. Multi-unit collaborative operation also prevents a single roll from bearing high loads for extended periods, avoiding temperature accumulation due to continuous operation, reducing roll wear rate, and extending roll service life.

[0029] The continuously cast billet is a cylindrical steel material with a length of 1-1.5 meters and a diameter of 22 millimeters. The surface of the billet is free of severe iron oxide scale or defects. The 1-1.5-meter length facilitates clamping and pushing, reducing jamming or positioning deviations caused by excessive billet length, and ensuring continuous feeding rhythm of the rolling mill. Limiting the billet diameter to 22 millimeters allows for more uniform heating, avoiding excessive core-to-surface temperature differences due to excessive cross-section, suppressing residual stress concentration in the fine-tooth rib areas, and improving the fatigue resistance of the rib anchors. This invention feeds the billet into the rolling mill at a low speed of 10-20 m / min, avoiding failure to bite the billet or jamming due to excessive feeding speed. During the feeding process, the stability of the billet as it passes through each pass is observed (e.g., whether deviation or vibration occurs). After rolling, use calipers to measure key dimensions such as diameter, ovality, and rib height of the rolled continuous casting billet, and observe whether there is any misalignment of ribs in the rolled continuous casting billet.

[0030] The standard roll gap should be controlled at 2 mm. Ensure consistent roll gap size across the entire rolling mill, maintaining uniformity on both sides. A 2 mm gap ensures the roll grooves are fully pressed into the steel surface, preventing insufficient rib height or pitch deviation caused by an excessively large gap. Adjust the roll gaps on both sides of all rolling mills to ensure consistency, aligning the guides with the roll groove. This prevents camber and uneven head deformation (or temperature differences) in the continuously cast billet during rolling, which could lead to uneven deformation and potential breakage when the billet head bites into the K1 roll.

[0031] After the rolling mill begins, when the heads of the first, second, and third continuously cast billets pass through the mill, the cooling water for rolls K1, K2, and K3 is temporarily shut off for 1-2 seconds. During high-temperature rolling, the rolls accumulate heat. If they suddenly come into contact with low-temperature cooling water, the roll surface will experience extreme thermal stress due to rapid cooling, causing micro-cracks on the roll surface to expand and ultimately leading to roll breakage or spalling. Temporarily shutting off the cooling water prevents the massive impact of a sudden drop in roll surface temperature on the rolls, thus avoiding roll breakage and slippage. It also prevents localized shrinkage and deformation of the rolls, which could affect the fit between the groove and the workpiece, resulting in uneven rib depth. Temporarily shutting off the cooling water also maintains the dimensional stability of the rolls, ensuring uniform thread formation.

[0032] Step 3: Control the height of the transverse ribs of the finished product according to the lower limit to obtain a ribbed anchor rod with model number MG500X(Y)Φ22. The rib spacing of the ribbed anchor rod is 4 mm.

[0033] The finished product has a transverse rib height of 0.05-0.1 mm, and the transverse rib inclination angle is 60º in the die design. Firstly, the 60º inclination angle helps balance rolling forces, reducing rib height fluctuations caused by uneven stress on the workpiece. Secondly, the 60º inclination angle allows metal to flow evenly along the roll groove during rolling, avoiding metal accumulation or surface tearing of the workpiece due to excessive inclination angle. Thirdly, the 60º inclination angle makes alignment easier during roll regrinding and roll changing, reducing downtime caused by die misalignment and ensuring production continuity. The shallow groove design with a transverse rib height ≤ 0.1 mm reduces local pressure on the rolls, and combined with the optimized force component at the 60º inclination angle, it reduces wear on the groove edges and extends the roll's service life.

[0034] (1) Production status: MG600X(Z) Φ22 was produced, continuing to use the fourth rolling groove that had already produced 215 tons. After 415 tons of steel were produced, slight groove breakage occurred at the groove opening. The surface of the finished product was free of pitting, the ends of the transverse ribs had no obvious abrupt changes, the rib spacing remained clear and bright, and the surface gloss was bright. After changing the groove, another 200 tons were produced with a good surface and could continue to be used. Since the total production of this batch was 400 tons and there were no further plans, it was not used again.

[0035] (2) Rolling condition: There was a small bursting point after 415 tons of steel passed through the fourth hole. The surface quality of the fifth hole was better after 200 tons of steel passed through it. It can be used again next time.

[0036] Example 2

[0037] A method for preventing the pre-drilled holes of MG500YΦ22 ribbed anchor bolts includes the following steps:

[0038] Step 1: Before production, confirm that the cooling water temperature is 25-35℃, and shut down all the spray devices of the roughing and intermediate rolling mills. The roughing and intermediate rolling mills include mills 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Mills 1-6 are the roughing mills, and they are connected end-to-end to form a six-stand roughing section. Mills 7-12 are the intermediate rolling mills, and they are connected end-to-end to form a six-stand intermediate section. A flying shear device is installed between the six-stand roughing section and the six-stand intermediate section. After the continuously cast billet is fed, it undergoes heating in a heating furnace, high-pressure water descaling, rough rolling in a six-stand roughing mill, flying shearing of the head and tail, and intermediate rolling in a six-stand intermediate mill. This invention employs a continuous rolling production line consisting of multiple mills in the roughing and intermediate mill sections working collaboratively to produce ribbed anchor bolts. On one hand, the continuous casting billet production process eliminates the need for intermediate stops, significantly shortening the rolling cycle. On the other hand, each mill on the continuous rolling production line can be precisely controlled, and the cumulative reduction over 12 passes reduces the accumulation of errors per stand, accurately controlling the dimensional accuracy of the rolled piece. After shutting down the spraying devices of mills 1-12 before production, the entire continuous rolling production line forms a gradient insulation chain, which helps to reduce temperature fluctuations and improve the plastic stability of the material.

[0039] Step 2: Use the K1 roll of the Φ390 rolling mill for rolling. The initial rolling temperature is 1050-1200℃ to prevent low-temperature grooving. During the rolling process, control the temperature of the continuous casting billet at 900-1000℃, control the speed at which the continuous casting billet is fed into the rolling mill at 10-20m / min, and control the number of feeding times to two. After the initial rolling, temporarily shut off the cooling water of the K1 roll to K3 roll.

[0040] When rolling with the K1 rolls of a Φ390 rolling mill, ordinary cooling water with a pressure of 7 kg is used. The use of high-pressure water for controlled rolling and cooling is strictly prohibited. The rolls are made of high-speed steel. Using ordinary cooling water reduces the cooling rate of the workpiece surface, minimizes the temperature difference between the workpiece surface and interior, reduces residual stress on both the surface and interior of the workpiece, and improves the quality stability of the finished ribbed anchor bolts. High-speed steel (HSS) is a tool steel containing high alloying elements such as tungsten (W), molybdenum (Mo), chromium (Cr), and vanadium (V), characterized by high hardness, high wear resistance, and high heat resistance. Rolls made of high-speed steel can maintain high hardness during high-temperature rolling, ensuring that the rolls can effectively bite into the workpiece at high temperatures, avoiding roll gap misalignment caused by thermal softening. The high rigidity of high-speed steel also reduces rolling force fluctuations and suppresses surface defects, including slotting. Semi-steel is a hypereutectoid cast steel with extremely high carbon content (1.4%-2.4%). This type of high-carbon cast steel actually falls into the category of cast iron, hence the common name "semi-steel." Semi-steel is a ferroalloy material with high strength, good wear resistance, and good corrosion resistance. Its main components are iron with small amounts of carbon, manganese, and other elements. Semi-steel possesses good mechanical properties and resistance to thermal fatigue; rolls made from semi-steel exhibit lower thermal stress. Furthermore, rolls made from semi-steel have a moderate modulus of elasticity, providing good deformation compatibility and reducing fluctuations in transverse rib height.

[0041] Cooling water is used to cool the looper. The flow rate of the looper cooling water should be controlled at 20-35 m³ / h to ensure cooling effect. During the cooling process, it is important to prevent the cooling water from splashing onto the red steel. The complex geometry of the fine toothed rib structure of the rib anchor rod makes it prone to becoming a point of thermal stress concentration. Using a small flow rate of cooling water to cool the looper can make the temperature change of the looper more gradual, avoiding thermal stress concentration in critical components such as the looper due to sudden cooling, thereby reducing the risk of cracks or deformation. Controlling the flow rate of the looper cooling water within the range of 20-35 m³ / h can not only meet the cooling needs of critical components such as the looper, but also stabilize the working temperature of the rolls, avoiding a decrease in surface hardness due to overheating, thereby reducing the accelerated wear of the rib anchor rods due to softening during rolling. If the cooling water splashes onto the surface of the red steel, it may cause the steel oxide scale to thicken or microcracks. Such defects will increase the local pressure on the rolls during rolling. Especially in the contact area of ​​the fine tooth ribs, this can lead to scratches, chipping, or bursting of the roll surface. When the mill is shut down for more than 2 hours due to reasons such as changing the type of continuous casting billet, waiting for gas, or peak-avoidance production, the CP2 control system notifies the water pump room to shut down all cooling tower fans and control the temperature of the ordinary cooling water at 25-35℃. After shutting down the cooling tower fans, the active heat dissipation capacity of the cooling tower is reduced, making the temperature of the ordinary cooling water higher than normal. On the one hand, this can prevent the temperature difference between the surface and the core of the roll from being too large due to the excessive cooling of the ordinary cooling water after the mill is shut down, thereby reducing the concentration of thermal stress and reducing the risk of micro-cracks in the rib anchor rods. On the other hand, controlling the temperature of the ordinary cooling water at 25-35℃ can not only prevent the temperature of the roll from dropping to the brittle range of the material, which could lead to brittle fracture or spalling of the rib anchor rods, but the relatively mild cooling environment can also help to slowly release residual stress and maintain the stability of the roll shape. When the mill restarts, the roll temperature can reach the steady-state rolling temperature more quickly, preventing thermo-mechanical fatigue damage to the rib anchor bolts and protecting the rib anchor bolt structure.

[0042] Rolling is performed using a multi-unit collaborative operation. The K1 roll of the Φ390 mill is only the core roll of the finishing section; in actual rolling, 20 Φ390 mill stands are used in collaborative operation. Using a multi-unit collaborative operation not only significantly shortens the total rolling time for a single anchor bolt, enabling continuous high-speed production, but also avoids production line shutdowns due to roll changes or maintenance on some mills by rotating multiple units, ensuring production continuity. Multi-unit collaborative operation also prevents a single roll from bearing high loads for extended periods, avoiding temperature accumulation due to continuous operation, reducing roll wear rate, and extending roll service life.

[0043] The continuously cast billet is a cylindrical steel material with a length of 1-1.5 meters and a diameter of 22 millimeters. The surface of the billet is free of severe iron oxide scale or defects. The 1-1.5-meter length facilitates clamping and pushing, reducing jamming or positioning deviations caused by excessive billet length, and ensuring continuous feeding rhythm of the rolling mill. Limiting the billet diameter to 22 millimeters allows for more uniform heating, avoiding excessive core-to-surface temperature differences due to excessive cross-section, suppressing residual stress concentration in the fine-tooth rib areas, and improving the fatigue resistance of the rib anchors. This invention feeds the billet into the rolling mill at a low speed of 10-20 m / min, avoiding failure to bite the billet or jamming due to excessive feeding speed. During the feeding process, the stability of the billet as it passes through each pass is observed (e.g., whether deviation or vibration occurs). After rolling, use calipers to measure key dimensions such as diameter, ovality, and rib height of the rolled continuous casting billet, and observe whether there is any misalignment of ribs in the rolled continuous casting billet.

[0044] The standard roll gap should be controlled at 2 mm. Ensure consistent roll gap size across the entire rolling mill, maintaining uniformity on both sides. A 2 mm gap ensures the roll grooves are fully pressed into the steel surface, preventing insufficient rib height or pitch deviation caused by an excessively large gap. Adjust the roll gaps on both sides of all rolling mills to ensure consistency, aligning the guides with the roll groove. This prevents camber and uneven head deformation (or temperature differences) in the continuously cast billet during rolling, which could lead to uneven deformation and potential breakage when the billet head bites into the K1 roll.

[0045] After the rolling mill begins, when the heads of the first, second, and third continuously cast billets pass through the mill, the cooling water for rolls K1, K2, and K3 is temporarily shut off for 1-2 seconds. During high-temperature rolling, the rolls accumulate heat. If they suddenly come into contact with low-temperature cooling water, the roll surface will experience extreme thermal stress due to rapid cooling, causing micro-cracks on the roll surface to expand and ultimately leading to roll breakage or spalling. Temporarily shutting off the cooling water prevents the massive impact of a sudden drop in roll surface temperature on the rolls, thus avoiding roll breakage and slippage. It also prevents localized shrinkage and deformation of the rolls, which could affect the fit between the groove and the workpiece, resulting in uneven rib depth. Temporarily shutting off the cooling water also maintains the dimensional stability of the rolls, ensuring uniform thread formation.

[0046] Step 3: Control the height of the transverse ribs of the finished product according to the lower limit to obtain a ribbed anchor rod with model number MG500YΦ22. The rib spacing of the ribbed anchor rod is 10 mm.

[0047] The finished product has a transverse rib height of 0.05-0.1 mm, and the transverse rib inclination angle is 60º in the die design. Firstly, the 60º inclination angle helps balance rolling forces, reducing rib height fluctuations caused by uneven stress on the workpiece. Secondly, the 60º inclination angle allows metal to flow evenly along the roll groove during rolling, avoiding metal accumulation or surface tearing of the workpiece due to excessive inclination angle. Thirdly, the 60º inclination angle makes alignment easier during roll regrinding and roll changing, reducing downtime caused by die misalignment and ensuring production continuity. The shallow groove design with a transverse rib height ≤ 0.1 mm reduces local pressure on the rolls, and combined with the optimized force component at the 60º inclination angle, it reduces wear on the groove edges and extends the roll's service life.

[0048] (1) Production status: When producing MG500YΦ22, after 300 tons of steel were rolled, slight cracking of the groove appeared. The surface of the finished product was free of pitting, the ends of the transverse ribs were not obviously abrupt, the rib spacing was still clear and bright, and the surface gloss was bright. After changing the hole, another 260 tons were produced and the surface was good and could continue to be used.

[0049] (2) Rolling conditions: There is a small bursting point after the first hole has passed 230 tons of steel.

[0050] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preventing the bursting of pre-drilled holes in ribbed anchor bolts, characterized in that, Includes the following steps: Step 1: Shut down the spray system of the roughing and intermediate rolling mills before production begins; Step 2: Roll using the K1 roll of a Φ390 rolling mill. The initial rolling temperature is 1050-1200℃. During the rolling process, the temperature of the continuous casting billet is controlled at 900-1000℃, the speed at which the continuous casting billet is fed into the rolling mill is controlled at 10-20m / min, and the number of passes is controlled at 1-3. After the initial rolling, the cooling water of the K1 roll to K3 roll is temporarily turned off. Step 3: Control the height of the transverse ribs of the finished product according to the lower limit; In step one, the roughing and intermediate rolling mills include rolling mill #1, rolling mill #2, rolling mill #3, rolling mill #4, rolling mill #5, rolling mill #6, rolling mill #7, rolling mill #8, rolling mill #9, rolling mill #10, rolling mill #11 and rolling mill #12.

2. The method for preventing the bursting of the finished hole in a ribbed anchor bolt as described in claim 1, characterized in that, In step two, when rolling using the K1 roll of the Φ390 rolling mill, ordinary cooling water is used for cooling.

3. The method for preventing the bursting of the finished hole in a ribbed anchor bolt as described in claim 2, characterized in that, In step two, cooling water is used to cool the looper. When the downtime exceeds 2 hours, the CP2 control system notifies the water pump room to shut down all cooling tower fans and control the temperature of the ordinary cooling water at 25-35℃.

4. The method for preventing the bursting of the finished hole in a ribbed anchor bolt as described in claim 1, characterized in that, In step two, rolling is carried out using a multi-unit collaborative operation.

5. A method for preventing the bursting of pre-drilled holes in ribbed anchor bolts as described in claim 1, characterized in that, In step two, the continuously cast billet is a cylindrical steel material with a length of 1-1.5 meters and a diameter of 22 millimeters.

6. The method for preventing the bursting of the finished hole in a ribbed anchor bolt as described in claim 1, characterized in that, In step two, the standard roll gap is controlled within 1-3 mm.

7. A method for preventing the bursting of the finished hole in a ribbed anchor bolt as described in claim 1 or 5, characterized in that, In step two, after the rolling mill begins, when the heads of the first, second, and third continuous casting billets pass through the mill, the cooling water of rolls K1-K3 is temporarily shut off for 1-2 seconds.

8. A method for preventing bursting of the finished hole in a ribbed anchor bolt as described in claim 1, characterized in that, In step three, the height of the transverse ribs of the finished product is 0-0.1 mm, and the inclination angle of the transverse ribs is 60°.

9. A method for preventing bursting of the finished hole in a ribbed anchor bolt as described in claim 1, characterized in that, In step three, the strength level of the finished product is any one of 335MPa, 400MPa, 500MPa and 600MPa.