Intermediate frequency heating power control method in high ductility cold rolled steel bar production

Abstract

The high ductility cold rolled steel bar production in the intermediate frequency heating power control method, the high ductility cold rolled steel bar production only has one intermediate frequency heating process, the intermediate frequency heating equipment is located after the forming mill, the output power of the intermediate frequency heating equipment is output according to the following formula: In the formula, P is the intermediate frequency heating power, kilowatt; V is the production line speed, meter / second; A is the tensile strength of raw material, megapascal; D is the diameter of raw material, millimeter; the value range is 5-14; B is the compensation coefficient, the value range is 0.95-1.05. The method can obviously reduce the product performance unqualified caused by the improper heating power.

Description

Technical Field

[0001] This invention relates to the production of cold-rolled steel bars, and particularly to a method for controlling the medium-frequency heating power in the production of high-ductility cold-rolled steel bars, belonging to the field of cold-rolled steel bar production technology. Background Technology

[0002] High-ductility cold-rolled ribbed steel bars are produced from ordinary carbon steel coils through a multi-stage rolling process and online heat treatment, which improves the strength and ductility of the steel bars. Chinese Patent No. 2011101148727 (Production Process of High-Ductility Cold-Rolled Ribbed Steel Bars) is one of the earliest disclosed production processes for this type of steel bar. Current production technology can produce high-ductility cold-rolled ribbed steel bars that meet the CRB600H standard. Heat treatment after forming is an essential step in the production of high-ductility cold-rolled ribbed steel bars. The heat treatment process uses medium-frequency electromagnetic induction heating equipment. The production line's automated control system controls the output power of the medium-frequency electromagnetic induction heating equipment to change the heating temperature of the steel bars, thereby controlling the steel bar's performance. In the production of high-ductility ribbed steel bars, general production experience shows that the strength of the finished steel bars is inversely correlated with the heating temperature of the heat treatment process, and the plasticity index of the finished steel bars is generally inversely correlated with the strength index.

[0003] In the production process of high-ductility cold-rolled ribbed steel bars, the raw materials (products) have different diameter specifications, and the production line often needs to increase and decrease speed. When the diameter of the raw materials (products) and the speed change, while keeping the heating temperature constant, the output power of the induction heating equipment also changes due to the change in the production capacity per unit time. Current technology uses medium-frequency heating power. To adapt to the heating of steel bars under different product diameters and operating speeds, the existing heating power control method first designs a power formula for different product diameters and operating speeds and embeds it into the control system. During production, the corresponding formula power value is called according to the actual measured speed value.

[0004] Existing power control methods can ensure that steel bars operating at different speeds receive different power for heating, ultimately ensuring that each unit of steel bar receives essentially the same amount of energy and is heated to essentially the same temperature. However, analysis of long-term production data reveals significant fluctuations in the performance of finished steel bars under this heating power control method, sometimes even resulting in defective products. The reason for this is that existing control technologies assume a constant tensile strength in the raw materials. However, due to uncontrollable factors such as the manufacturer, batch, and production process, the tensile strength of incoming raw materials fluctuates considerably. For example, Q235, a commonly used raw material for cold-rolled ribbed steel bars, has an initial tensile strength range of 370-500 MPa (GBT_700-2006_Carbon Structural Steel). In practice, it has been found that different tensile strength values ​​require different heating temperatures (powers) to produce qualified products. Generally, higher strength requires higher heating temperatures, and vice versa, to ensure that the final heat-treated product meets 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 problems, in order to overcome them, the applicant inspected each raw material upon arrival at the factory, and then divided them into different groups according to their strength. Based on the different strengths, the power of the medium-frequency heating was adjusted manually according to experience during production to reduce the probability of unqualified products. However, this method increased the cost of raw material testing and management, and often required a cycle of adjustment, testing, feedback, and readjustment based on human experience during production. The adjustment time was long, the scrap rate was high during the adjustment period, and it was highly dependent on human experience. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems existing in the current production of high-ductility cold-rolled steel bars and to provide a method for controlling the medium-frequency heating power in the production of high-ductility cold-rolled steel bars.

[0006] To achieve the objectives of this invention, the following technical solution is adopted: a method for controlling the power of medium-frequency heating in the production of high-ductility cold-rolled steel bars. The production of high-ductility cold-rolled steel bars involves only one medium-frequency heating process. The medium-frequency heating equipment is located after the forming mill, and its output power is calculated according to the following formula:

[0007]

[0008] In the above formula: P---medium frequency heating power, kilowatts;

[0009] V --- Production line speed, meters per second;

[0010] A---Tensile strength of raw material, megapascals;

[0011] D---Product diameter, millimeters; value range 5-14;

[0012] B -- Compensation coefficient, with a value range of 0.95-1.05;

[0013] In the above formula, the dimensions are not included in the calculation.

[0014] Furthermore, the tensile strength of the raw material is obtained by direct testing of the raw material.

[0015] 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 tensile strength of the raw material 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 tensile strength of the corresponding raw material is obtained from the rolling mill motor current corresponding to the product diameter and production speed in the mapping relationship database A.

[0016] Furthermore, 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 current value is obtained through linear relationship.

[0017] 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. 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.

[0018] Furthermore, when the sum of the two pressure sensors is not collected in the mapping relationship database B, the 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.

[0019] The positive and beneficial technical effects of this invention are as follows: The method of this invention establishes the relationship between the tensile strength of raw materials, production speed, product diameter and the power of medium frequency heating equipment, which can be directly and easily applied to the production of high ductility cold-rolled steel bars. After use, it has been found that it can significantly reduce the product performance defects caused by unsuitable heating power, greatly improve the yield rate, and overcome many problems caused by relying on manual experience. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the rolling force measuring device of the present invention. Detailed Implementation

[0021] 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.

[0022] The markings in the diagram are 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 corresponding pressure sensors.

[0023] The method for controlling the power of medium-frequency heating in the production of high-ductility cold-rolled steel bars: The production of high-ductility cold-rolled steel bars involves only one medium-frequency heating process. The medium-frequency heating equipment is located after the forming mill, and its output power is calculated according to the following formula:

[0024]

[0025] In the above formula: P---medium frequency heating power, kilowatts;

[0026] V --- Production line speed, meters per second;

[0027] A---Tensile strength of raw material, megapascals;

[0028] D---Product diameter, millimeters; value range 5-14;

[0029] B: Compensation coefficient, with a value range of 0.95-1.05;

[0030] In the above formula, the dimensions are not included in the calculation.

[0031] Furthermore, the tensile strength of the raw material is obtained through direct testing of the raw material. This method requires testing the tensile strength of each or every batch of material rolls.

[0032] 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.

[0033] Table 1 below provides an example of a mapping relational database A.

[0034]

[0035] Table 1

[0036] The rebar diameter in Table 1 corresponds to the product diameter. When producing products with a diameter of 6-14mm, the raw material diameter is typically 2mm larger than the rebar diameter. Table 1 is also derived 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 such cases, 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.

[0037] When calculating heating power in this way, only the current value of the rolling mill motor needs to be collected. For example, when the diameter of the product steel bar is 6mm (the diameter of the raw material is 8mm), the production speed is 900m / min, the current of the rolling mill motor is collected as 600A, and the corresponding tensile strength of the steel bar is 470MPa; when the diameter of the product steel bar is 10mm (the diameter of the raw material is 12mm), the production speed is 450m / min, the current of the rolling mill motor is collected as 395A, and the corresponding tensile strength of the steel bar is 440MPa.

[0038] 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.

[0039] Table 1 is merely an example of a 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 mapping database A, it should be determined according to the corresponding production line.

[0040] 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 1 The 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 sensor readings. When calculating the medium-frequency heating power, the sum of the two pressure sensor readings 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 sensor readings in the mapping database B, the two pressure values ​​adjacent to the collected sum of the two pressure sensor readings are selected from the mapping database, and the raw material tensile strength corresponding to the sum of the two pressure sensor readings is obtained through a linear relationship. When using this method, each product specification corresponds to a specific raw material diameter. In the production of products with diameters between 5 and 14 mm, except for the 5 mm product which uses a raw material diameter of 6.5 mm, the raw material diameter for other specifications is 2 mm 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 is the same when producing the same specification of product at different times. The reduction ratios on the first rolling mill are as follows: 0.7 for 5 mm products; 0.8 for 6 mm products; 0.85 for 8 mm products; 0.83 for 10 mm products; 0.9 for 12 mm products; and 0.92 for 14 mm products. The same reduction ratio is used when mapping the tensile strength of the raw material corresponding to the rolling mill current. The reduction ratio refers to the cross-sectional area after rolling divided by the cross-sectional area before rolling.

[0041] 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.

[0042]

[0043] 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 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. The data in Table 2 is obtained under the aforementioned reduction ratio. When the reduction ratio of the first rolling mill changes, the mapping 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.

[0044] 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.

[0045] 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.

[0046] Table 2 is just an example.

[0047] Example of controlling the output power of a medium-frequency heating device using the method of the present invention (using the manufacturing process of Chinese Patent No. 2011101148727):

[0048] When producing φ6mm products (using 8mm raw materials), with a production speed of 900 m / min and a raw material strength of 400 MPa, the power input of the medium-frequency heating furnace should be approximately 1230 kW.

[0049] When producing φ6mm products (using 8mm raw materials), with a production speed of 900 m / min and a raw material strength of 450 MPa, the power input of the medium-frequency heating furnace should be approximately 1383 KW.

[0050] Heating power can be obtained using this method for products with diameters ranging from 5 to 14 mm. For example, when producing a φ12 mm product (using 14 mm raw material), at a production speed of 250 m / min and a raw material strength of 430 MPa, the calculated power required for the medium-frequency induction furnace is approximately 1304 kW. Similarly, when producing a φ10 mm product (using 12 mm raw material), at a production speed of 450 m / min and a raw material strength of 440 MPa, the calculated power required for the medium-frequency induction furnace is approximately 1737 kW. Here, φ refers to the product diameter D.

[0051] In the above calculations, B is set to 1. 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, it can be adjusted between 0.95 and 1.05.

[0052] 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.

[0053] 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.

[0054] Production testing has shown that this method is applicable to current steel reinforcement raw materials such as Q235, Q215, and HPB300.

[0055] 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 method for controlling the power of intermediate frequency heating in the production of high-ductility cold-rolled steel bars, said production of high-ductility cold-rolled steel bars having only one intermediate frequency heating process, the intermediate frequency heating equipment being located after the forming mill, characterized in that: The output power of the intermediate frequency heating equipment is output according to the following formula: ​ ； In the formula, P is the intermediate frequency heating power, kilowatt; V is the production line speed, meter / second; A is the tensile strength of the raw material, mega pascal (MPa); D is the product diameter, millimeter; B is the compensation coefficient, and the value range is 0.95-1.05; and the dimension is not involved in the calculation. The tensile strength of the raw material is obtained by directly testing the raw material. The tensile strength of the raw material is obtained by the following method: in production, the corresponding relationship among the product diameter, the production speed, the tensile strength of the raw material and the rolling mill motor current is established, the tensile strength of the raw material in production is obtained by testing the raw material, the mapping relationship database A of the product diameter, the production speed, the tensile strength of the raw material and the rolling mill motor current is formed, and the tensile strength of the raw material corresponding to the rolling mill motor current of the product diameter and the production speed in the mapping relationship database A is obtained through the rolling mill motor current when the intermediate frequency heating power is calculated. When the rolling mill motor current value is not collected in the mapping relationship database A, the tensile strength of the raw material corresponding to the collected rolling mill motor current value is obtained through linear relationship by selecting two current values adjacent to the collected rolling mill motor current value in the mapping relationship database A. The tensile strength of the raw material is obtained through the rolling force measuring device: the rolling force measuring device is installed on the first rolling mill, and includes two pressure sensors installed on the rolling mill frame, two bearing seats at the two ends of the lower roller shaft are respectively pressed on one pressure sensor, and the pressure sensor is connected to the controller; in production, the corresponding relationship among the product diameter, the tensile strength of the raw material and the sum of the two pressure sensors is established, the mapping relationship database B of the product diameter, the tensile strength of the raw material and the sum of the two pressure sensors is formed, and the sum of the two pressure sensors is collected when the intermediate frequency heating power is calculated, and the tensile strength of the raw material is obtained through the mapping relationship database B. When the sum of the two pressure sensors is not collected in the mapping relationship database B, the tensile strength of the raw material corresponding to the sum of the two pressure sensors is obtained through linear relationship by selecting two pressure values adjacent to the collected sum of the two pressure sensors in the mapping relationship database B of the tensile strength of the raw material and the sum of the two pressure sensors.

2. The method of controlling the power of the medium frequency heating in the production of high-ductility cold rolled steel bars according to claim 1, characterized in that: ​ 3. The method of controlling the power of the medium frequency heating in the production of high-ductility cold rolled steel bars according to claim 1, characterized in that: ​ 4. The method for controlling the intermediate frequency heating power in the production of high-ductility cold rolled steel bars according to claim 3, characterized in that: ​ 5. The method for controlling the power of the medium frequency heating in the production of high-ductility cold rolled steel bars according to claim 1, characterized in that: ​ 6. The method of controlling the medium frequency heating power in the production of high-ductility cold rolled steel bars according to claim 5, characterized in that: ​

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