Production process of high ductility cold rolled ribbed steel bar

Abstract

A production process of high ductility cold rolled ribbed steel bar, comprising the following steps: S1, the tail end of two adjacent rolls of raw materials is butt welded; resistance welding is used during butt welding, the heating time is 3s-60s, and the heating temperature is 600 DEG C-1000 DEG C; S2, the raw material is opened and descaled, and enters the rolling area after descaling; S3, the raw material entering the rolling area is first reduced in diameter, and the diameter reduction ratio of the diameter reduction is 0.66-0.97; S4, the steel bar after diameter reduction is formed and rolled at the same time, and the diameter reduction ratio of the forming rolling is 0.55-0.93; S5, the steel bar after forming rolling is heat treated at a temperature of 360-720 DEG C for 1-3s. The process can reduce the defective product rate, and effectively improve the product quality and production efficiency.

Description

Technical Field

[0001] This invention relates to the production of reinforcing bars, and particularly to a production process for high-ductility cold-rolled ribbed reinforcing bars, belonging to the field of cold-rolled reinforcing bar production technology. Background Technology

[0002] After more than a decade of rapid development, the production efficiency and product quality of high-ductility cold-rolled ribbed steel bars have significantly improved. Currently, it is possible to produce cold-rolled ribbed steel bars that meet the CRB600H standard. Early production processes for cold-rolled ribbed steel bars utilized the process disclosed in Chinese Patent No. 2011101148727 (Production Process of High-Ductility Cold-Rolled Ribbed Steel Bars). Through more than a decade of development and production practice, a wealth of experience has been accumulated in the production of cold-rolled steel bars. Production has gradually shifted from a relatively extensive method relying on manual experience for process adjustments to a more digitalized process. For example, regarding the reduction ratio in steel bar rolling, there are generally optimized reduction ratios for specific products (raw materials). For different diameter specifications of raw materials, production line speeds, and changes in the corresponding capacity per unit time, the output power of the induction heating equipment will also change accordingly. To adapt to the heating of steel bars with different diameters and operating speeds, the power formula for different diameters and operating speeds is first designed and embedded into the control system. During production, the corresponding formula power value can be called according to the actual measured speed value. This is an improvement over the cold rolling process more than ten years ago.

[0003] There are still areas for improvement in the existing steel bar production process. For example, analysis of long-term production data shows that under this heating power control method, the performance of the finished steel bars still fluctuates greatly, and even defective products may appear. The reason for this is that the existing control technology is based on the premise that the tensile strength of the raw materials is constant. However, due to uncontrollable factors such as the manufacturer, batch, and production process of the raw materials, the tensile strength of the incoming raw materials fluctuates greatly. Taking Q235, a commonly used raw material for cold-rolled ribbed steel bars, as an example, its original tensile strength range is 370-500 MPa (GBT_700- In practice, it was found that different tensile strength values ​​of raw materials require different heating temperatures (powers) to obtain qualified products during the processing. Generally, higher strength requires higher heating temperatures, and vice versa, to ensure that the final heat-treated product quality meets the standard requirements. However, the relationship between heating temperature (power) and tensile strength is not a simple linear one. Therefore, the current medium-frequency heating process does not consider the tensile strength of the raw steel bars, which is one of the reasons for the production of substandard products. After discovering the above problem, in order to overcome it, the applicant inspects each piece of raw material upon arrival at the factory and then divides them into different groups according to their strength. Based on the different strengths, the power of the medium-frequency heating is adjusted manually according to experience during production to reduce the probability of substandard products. However, this method increases the cost of raw material testing and management, and often requires a cycle of adjustment, testing, feedback, and readjustment based on human experience during production, which is time-consuming and highly dependent on human experience. Furthermore, after more than a decade of technological development, it has been found that the diameter reduction ratio and the welding process between two coils of steel bars can be better optimized. Therefore, in order to improve the yield and production efficiency of traditional cold-rolled steel bar production processes, further refinement and development are needed. Summary of the Invention

[0004] The purpose of this invention is to further optimize and develop the traditional cold-rolled ribbed steel bar process to improve yield and production efficiency.

[0005] To achieve the objective of this invention, the following technical solution is adopted: a production process for high-ductility cold-rolled ribbed steel bars, the production process comprising the following steps:

[0006] S1. After unpacking and tidying up the ends of the steel bars, weld the ends of two adjacent rolls of raw materials together. Resistance welding is used for welding, with a heating time of 3s-60s and a heating temperature of 600℃-1000℃.

[0007] S3. Unwind the coil, descale and dephosphorize the raw material, and then it enters the rolling area;

[0008] S4. The coil entering the rolling zone is subjected to diameter reduction rolling, and the diameter reduction ratio is 0.66-0.97.

[0009] S5. The steel bars that have undergone diameter reduction rolling are simultaneously shaped and rolled, with a diameter reduction ratio of 0.55-0.93.

[0010] S6. After forming and rolling, the steel bars are heat-treated at 360-720℃ for 1-3 seconds; the heat treatment equipment adopts medium-frequency electromagnetic induction heating equipment, and the output power of the medium-frequency electromagnetic induction heating equipment is output according to the following formula:

[0011] ;

[0012] In the above formula: P---medium frequency heating power, kilowatts;

[0013] V --- Production line speed, meters per second;

[0014] A---Tensile strength of raw material, megapascals;

[0015] D---Diameter of raw material, millimeters; value range 5-14;

[0016] B -- Compensation coefficient, with a value range of 0.95-1.05;

[0017] In the above formula, the dimensions are not included in the calculation.

[0018] Furthermore, the diameter of the produced products is 5-14mm. Products with a diameter of 5mm are produced using raw materials with a diameter of 6.5mm, while other raw materials have a diameter 2mm larger than the product diameter.

[0019] Furthermore, the tensile strength of the raw material is obtained by direct testing of the raw material.

[0020] Furthermore, the tensile strength of the raw material is obtained by the following method: In production, a correspondence is established between product diameter, production speed, raw material tensile strength, and rolling mill motor current. The raw material tensile strength is obtained by testing the raw material, forming a mapping relationship database A of product diameter, production speed, raw material tensile strength, and rolling mill motor current. When calculating the medium-frequency heating power, the corresponding tensile strength of the raw material is obtained from the rolling mill motor current corresponding to the product diameter and production speed in the mapping relationship database A.

[0021] Furthermore, when no rolling mill motor current value is collected in the mapping relationship database A, two current values ​​that are adjacent to the collected rolling mill motor current value are selected in the mapping relationship database A, and the tensile strength of the raw material corresponding to the collected rolling mill current value is obtained through linear relationship.

[0022] Furthermore, the tensile strength of the raw material is obtained through a rolling force measuring device: the rolling force measuring device is installed on the first rolling mill and includes two pressure sensors installed on the mill stand. Two bearing seats at both ends of the lower roll shaft press on one pressure sensor respectively. The pressure sensors are connected to a controller. During production, a mapping relationship database B is formed by establishing a correspondence between the product diameter, the tensile strength of the raw material, and the sum of the two pressure sensors. When calculating the medium-frequency heating power, the sum of the two pressure sensors is collected, and the tensile strength of the raw material is obtained through the mapping relationship database B.

[0023] Furthermore, when the sum of the two pressure sensors is not collected in the mapping relationship database B, two pressure values ​​that are adjacent to the sum of the two collected pressure sensors are selected in the mapping relationship database between the tensile strength of the raw material and the sum of the two pressure sensors, and the tensile strength of the raw material corresponding to the sum of the two pressure sensors is obtained through linear relationship.

[0024] The positive and beneficial technical effects of this invention are: the process of this invention can reduce the defect rate and effectively improve product quality and production efficiency. Attached Figure Description

[0025] Figure 1 It is a rolling force testing device. Detailed Implementation

[0026] To more fully explain the implementation of the present invention, implementation examples are provided. These implementation examples are merely illustrative of the present invention and do not limit the scope of the present invention.

[0027] First of all Figure 1 The markings in the diagram are explained as follows: 1: Rolling mill stand; 2: Lower roll bearing housing; 3: Pressure sensor A; 4: Pressure sensor B; 5: Rebar; 6: Upper roll bearing housing. The rolling mill stand in the diagram is also commonly referred to as the rolling mill archway. Figure 1 The weight of the two lower roller bearings rests entirely on the pressure sensor.

[0028] After years of development, the cold-rolled steel bar process has established a relatively suitable process for specific product specifications. Each product specification corresponds to a specific raw material diameter. In the production of 5-14mm products, except for the 5mm product which uses a 6.5mm diameter raw material, the raw material diameter for other specifications is 2mm larger than the product diameter. In actual production, each specification of product has a fixed reduction ratio on the first rolling mill. The reduction ratio on the first rolling mill remains the same regardless of the production time of that specification. The reduction ratios on the first rolling mill are as follows: 0.7 for 5mm products; 0.8 for 6mm products; 0.85 for 8mm products; 0.83 for 10mm products; 0.9 for 12mm products; and 0.92 for 14mm products. The reduction ratio refers to the cross-sectional area after rolling divided by the cross-sectional area before rolling. In the following examples, the data in mapping relationship databases A and B are obtained based on the aforementioned corresponding raw material specifications and reduction ratios. In certain special circumstances, such as when a certain specification of raw material is unavailable, larger specification raw materials can be used as substitutes. In such cases, this method can still be used to create a mapping database for the corresponding specification of raw material. Similarly, when the reduction ratio of the first rolling mill changes, this method can still be used to create a mapping database for the corresponding reduction ratio.

[0029] A production process for high-ductility cold-rolled ribbed steel bars, the production process comprising the following steps:

[0030] S1. After unpacking and tidying up the ends of the steel bars, weld the ends of two adjacent rolls of raw material together. Resistance welding is used for welding, with a heating time of 3s-60s and a heating temperature of 600℃-1000℃. Production time has proven that this type of welded joint is strong, has virtually no impact on the rolling mill, and the finished steel bars produced at the welded joint meet the requirements.

[0031] S3. Unwind the coil, descale and dephosphorize the raw material, and then it enters the rolling area; the dephosphorization equipment and process are all existing technologies;

[0032] S4. The coils entering the rolling zone first undergo a reduction rolling process with a reduction ratio of 0.66-0.97. This reduction ratio is achievable in cold-rolled steel bar production and is not the same as the reduction ratio corresponding to a specific specification in actual production. For example, when producing 5mm products, the first reduction ratio can be 0.66. The following mapping relationship databases A and B are obtained with a reduction ratio of 0.66, and their database relationships are suitable for use when producing 5mm products with a reduction ratio of 0.66.

[0033] S5. The steel bars after the reduction rolling are simultaneously etched during forming rolling. The reduction ratio of forming rolling is 0.55-0.93. The reduction ratio of forming rolling also refers to the reduction ratio that can be achieved in the production of cold-rolled steel bars. The specific value is determined according to the raw material specifications, product specifications, and the reduction ratio of the reduction rolling.

[0034] S6. After forming and rolling, the steel bars are heat-treated at 360-720℃ for 1-3 seconds; the heat treatment equipment adopts medium-frequency electromagnetic induction heating equipment, and the output power of the medium-frequency heating equipment is output according to the following formula:

[0035] ;

[0036] In the above formula (power calculation formula): P---medium frequency heating power, kilowatts;

[0037] V --- Production line speed, meters per second;

[0038] A---Tensile strength of raw material, megapascals;

[0039] D---Diameter of raw material, millimeters; value range 5-14;

[0040] B -- Compensation coefficient, with a value range of 0.95-1.05;

[0041] In the above formula, the dimensions are not included in the calculation.

[0042] Using the above formula to control the power of the medium-frequency heating equipment, the heating temperature of the steel bars is within the range of 360-720℃.

[0043] The tensile strength of the raw material is obtained through direct testing. This method requires testing the tensile strength of each or every batch of material rolls.

[0044] Furthermore, the tensile strength of the raw material is obtained through the following method: During production, a correspondence is established between product diameter, production speed, raw material tensile strength, and mill motor current. The raw material tensile strength is obtained through testing the raw materials, forming a mapping database A of product diameter, production speed, raw material tensile strength, and mill motor current. When calculating the medium-frequency heating power, the corresponding mill motor current in mapping database A for that product diameter and production speed is used. The tensile strength of the raw material is then obtained from the mill motor current. When no mill motor current value is collected in mapping database A, two current values ​​adjacent to the collected mill motor current value are selected in mapping database A, and the tensile strength of the raw material corresponding to the collected mill motor current value is obtained through a linear relationship. The production line mills adopt a driven mill configuration; the forming mill is connected to the mill motor, while other mills are not driven by a power source.

[0045] Table 1 below illustrates an example of a mapping relational database A:

[0046]

[0047] Table 1

[0048] The rebar diameter in Table 1 is the same as the product diameter. During production, the raw material diameter is usually 2mm larger than the rebar diameter, and Table 1 is also based on this 2mm difference. In some special cases, such as when a certain specification of raw material is unavailable, larger specification raw materials can be used as substitutes. In this case, the mapping relationship between the product diameter, rolling mill current, raw material strength, and production speed for the corresponding specification of raw material can still be established using this method. This method is applied to a specific production line, i.e., the mapping relationship database A is obtained on that production line. This method is applicable to that production line during production adjustments. When calculating the heating power using this method, only the rolling mill motor current value needs to be collected. For example, when the product rebar diameter is 6mm (raw material diameter is 8mm), the production speed is 900m / min, and the collected rolling mill motor current is 600A, the corresponding rebar tensile strength is 470MPa; when the product rebar diameter is 10mm (raw material diameter is 12mm), the production speed is 450m / min, and the collected rolling mill motor current is 395A, the corresponding rebar tensile strength is 440MPa.

[0049] When the product rebar diameter is 12mm (raw material diameter 14mm), the mill motor current is 482.5A. The table above does not show the corresponding tensile strength of the rebar. Therefore, the corresponding tensile strength is calculated as 445MPa using a linear relationship. It's important to note that this linear relationship method is approximate and does not mean that the mill motor current and the tensile strength of the rebar are linearly related. When there is sufficient data in the database, the difference between two adjacent current values ​​is very small, and this method can approximate the true value as closely as possible.

[0050] Table 1 is merely an example of the mapping database A. For steel bars corresponding to specific specifications, a production line typically has one or more corresponding production speeds; these speeds are not infinitely divisible. When using the mapping database A, it should be determined according to the corresponding production line. The rolling mill motors on the production line are installed on the forming rolling mill; other rolling mills do not have drive motors.

[0051] The tensile strength of the raw material is obtained through Figure 1 The rolling force measuring device shown is installed on the first rolling mill and includes two pressure sensors mounted on the mill stand 1. Figure 1The two pressure sensors are pressure sensor A3 and pressure sensor B4. Two bearing seats at both ends of the lower roll shaft press against one of the pressure sensors, as shown in Figure 4. The pressure sensors are connected to the controller. During production, a mapping database B is formed by establishing a correspondence between product diameter, raw material tensile strength, and the sum of the two pressure sensors. When calculating the medium-frequency heating power, the sum of the two pressure sensors is collected, and the tensile strength of the raw material is obtained through the mapping database B. When the raw material tensile strength does not match the sum of the two pressure sensors in the mapping database B, the two pressure values ​​adjacent to the collected sum of the two pressure sensors are selected from the mapping database, and the raw material tensile strength corresponding to the sum of the two pressure sensors is obtained through a linear relationship. Using this method, each product specification has a corresponding raw material diameter specification. In the production of products with a diameter of 5-14mm, except for the 5mm product which uses a raw material diameter of 6.5mm, the raw material diameter for other specifications is 2mm larger than the product diameter.

[0052]

[0053] Table 2 provides an example of the mapping relationship database B. The rolling pressure in Table 2 is the sum of the pressure from the two pressure sensors.

[0054] The mapping database B is relatively simplified, but requires the installation of pressure sensors on the rolling mill. The rebar diameter in Table 2 is the same as the product diameter. During production, the raw material diameter for products with diameters between 6mm and 14mm is typically 2mm larger than the rebar diameter. Table 2 is also obtained under the condition that the raw material diameter is 2mm larger than the product diameter. In some special cases, such as when a certain specification of raw material is unavailable, larger specification raw materials can be used as substitutes. In this case, the mapping relationship between product diameter, rolling pressure, and raw material strength under the corresponding specification of raw material can still be established using this method. When the reduction ratio of the first rolling mill changes, the mapping relationship database under the corresponding reduction ratio can still be established using this method. This method is used on a specific production line, i.e., mapping database B is obtained on that production line, and this method is applicable to that production line during production adjustments.

[0055] When using the mapping database B, the corresponding tensile strength of the steel bar can be directly obtained from the bar diameter and rolling pressure. For example, if the raw material diameter is 10mm and the rolling pressure is 20 tons, the corresponding tensile strength of the steel bar is 460MPa.

[0056] If the diameter of the raw material is 8mm and the rolling pressure is 10.75, and there is no corresponding data in Table 2, then the tensile strength of the steel bar is obtained by linear relationship processing as 447.5Mpa.

[0057] Table 2 is just an example; the actual mapping relationship in database B contains much richer data. Specific Implementation Example 1:

[0059] Using 10mm diameter Q235 coils as raw material, products with an 8mm diameter are produced at a speed of 750 m / min. A single-stage reduction mill is used, and the forming mill reduces the diameter while simultaneously scoring. The forming mill is an active mill, with the rolling motor mounted on it. After uncoiling, butt welding, descaling, reduction rolling, and forming mill, the material enters the medium-frequency heating equipment. According to the mapping relationship database A, the tensile strength of the raw material is 430MPa. Based on the power calculation formula, B is taken as 1, resulting in an output power of approximately 1884KW for the medium-frequency electromagnetic coil heating equipment, with a heating temperature of around 450℃.

[0060] Using 14mm diameter Q235 wire rod as raw material, a 12mm diameter product is produced. The first rolling mill has a reduction ratio of 0.9, a rolling pressure of 25 tons, and a production speed of 250 meters per minute. Through a mapping database, the corresponding tensile strength of the reinforcing steel is determined to be 460 MPa. Based on the power calculation formula, with B set to 1, the output power of the medium-frequency electromagnetic coil heating equipment is approximately 1395 kW, and the heating temperature is around 650℃.

[0061] In the above calculations, a B value of 1 is generally sufficient to ensure that the product performance is up to standard. If further control and optimization of the product's performance indicators are required, the value can be adjusted between 0.95 and 1.05.

[0062] In actual production, a certain specification of raw material usually corresponds to several different production speeds, so the production speed as a variable does not take infinite values ​​in application.

[0063] After testing this method on the production line, the steel bars produced under normal operation of each process on the production line met the required performance targets, and the scrap rate was significantly reduced.

[0064] Production testing has shown that this method is applicable to current steel reinforcement raw materials such as Q235, Q215, and HPB300.

[0065] After a detailed description of the embodiments of the present invention, those skilled in the art will clearly understand that various changes and modifications can be made without departing from the scope and spirit of the above-mentioned patent applications. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention, and the present invention is not limited to the embodiments of the examples given in the specification.

Claims

1. A process for producing high ductility cold rolled ribbed steel bars characterized by The production process includes the following steps: S1. After unpacking and tidying up the ends of the steel bars, weld the ends of two adjacent rolls of raw materials together. Resistance welding is used for welding, with a heating time of 3s-60s and a heating temperature of 600℃-1000℃. S2. Unwind the coil, descale the raw material, and then it enters the rolling area; S3. The raw material entering the rolling zone is first subjected to diameter reduction rolling, and the diameter reduction ratio of the diameter reduction rolling is 0.66-0.97; S4. The steel bars that have undergone diameter reduction rolling are simultaneously shaped and rolled, with a diameter reduction ratio of 0.55-0.

93. S5. After forming and rolling, the steel bars are heat-treated at 360-720℃ for 1-3 seconds; the heat treatment equipment adopts medium-frequency electromagnetic induction heating equipment, and the output power of the medium-frequency electromagnetic induction heating equipment is output according to the following formula: ； In the above formula: P---medium frequency heating power, kilowatts; V --- Production line speed, meters per second; A---Tensile strength of raw material, megapascals; D---Product diameter, millimeters; value range 5-14; B---Compensation coefficient, with a value range of 0.95-1.05; In the above formula, the dimensions are not included in the calculation.

2. The process for producing high ductility cold rolled ribbed steel bar as claimed in claim 1 wherein: The production process described above produces products with a diameter of 5-14mm. Products with a diameter of 5mm are produced using raw materials with a diameter of 6.5mm, while other raw materials have a diameter 2mm larger than the product diameter.

3. The production process of high-ductility cold-rolled ribbed steel bars according to claim 1, characterized in that: The tensile strength of the raw material is obtained by direct testing of the raw material.

4. The process as claimed in claim 1, wherein the process is characterized by: The tensile strength of the raw material is obtained by the following method: In production, a correspondence is established between product diameter, production speed, raw material tensile strength, and rolling mill motor current. The tensile strength of the raw material in production is obtained by testing the raw material, forming a mapping relationship database A of product diameter, production speed, raw material tensile strength, and rolling mill motor current. When calculating the medium frequency heating power, the corresponding rolling mill motor current at the product diameter and production speed in the mapping relationship database A is used to obtain the tensile strength of the corresponding raw material through the rolling mill motor current.

5. The production process of high-ductility cold-rolled ribbed steel bars according to claim 4, characterized in that: When no rolling mill motor current value is collected in the mapping database A, two current values ​​that are adjacent to the collected rolling mill motor current value are selected in the mapping database A, and the tensile strength of the raw material corresponding to the collected rolling mill motor current value is obtained through linear relationship.

6. The production process of high-ductility cold-rolled ribbed steel bars according to claim 1, characterized in that: The tensile strength of the raw material is obtained through a rolling force measuring device: the rolling force measuring device is installed on the first rolling mill and includes two pressure sensors installed on the mill stand. Two bearing seats at both ends of the lower roll shaft press on one pressure sensor respectively. The pressure sensors are connected to a controller. In production, a mapping relationship database B is formed by establishing a correspondence between the product diameter, the tensile strength of the raw material, and the sum of the two pressure sensors. When calculating the medium frequency heating power, the sum of the two pressure sensors is collected, and the tensile strength of the raw material is obtained through the mapping relationship database B.

7. The process for producing high ductility cold rolled ribbed steel bars as claimed in claim 6 wherein: When the sum of the two pressure sensors is not collected in the mapping relationship database B, select two pressure values adjacent to the sum of the two pressure sensors collected in the mapping relationship database B of the raw material tensile strength and the sum of the two pressure sensors, and obtain the raw material tensile strength corresponding to the sum of the two pressure sensors through linear relationship.

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