A method for controlling the dimensional accuracy of large-size cold-headed steel wire rod

Abstract

The invention discloses a control method for the dimensional accuracy of a large-size cold-headed steel wire rod, comprising S1, establishing a calculation model for the width of a rolled piece; S2, establishing a mathematical model for the influence of the starting rolling temperature, the temperature entering the finishing mill, the steel type and the hole type on the width expansion coefficient; S3, establishing a mathematical model for setting the height of the rolled piece and calculating the rolling speed; S4, calculating the elongation coefficient and the hole type fullness through step S3, and checking according to the dimensional accuracy, elongation coefficient and hole type fullness of the finished product; S5, according to the steel type and wire rod diameter required by the customer, using the mathematical model for the height of the rolled piece and the calculation of the rolling speed described in step S3 and the checking step S4 to debug the height of the rolled piece and the rolling speed of each rolling mill on the production line; S6, setting the debugged optimal height of the rolled piece and the rolling speed to the rolling mill of the production line. The invention can directly debug the wire rod size required by the user, reduce the cracking ratio of the cold-headed steel, and has the technical advantages of short debugging time and low production cost.

Description

Technical Field

[0001] The invention belongs to the technical field of metal wire rolling, and in particular relates to a method for controlling the dimensional accuracy of producing large-size cold-heading steel wire rods. Background Art

[0002] Large-size cold-forging steel wire rod is also called large-size cold-forging steel wire rod. The specifications are generally φ16.0mm~φ42.0mm. It is delivered in coils. The main steel type is cold-forging steel. It is widely used as the main raw material for the production of fasteners, standard parts such as bolts, nuts, screws, latches and special parts for automotive electrical equipment, and the market demand is huge.

[0003] When cold heading is used to produce fasteners and standard parts, the material deforms quickly, the amount of deformation is large, and the deformation is uneven. Therefore, high quality requirements are placed on the material. The material often suffers from problems such as cold heading cracking and dimensional accuracy that does not meet customer requirements.

[0004] The traditional method of producing cold heading steel wire rods and switching steel grades in a traditional steel rolling mill is to debug directly on the production line. During debugging, the height and rolling speed of each rolling mill are set according to the basic data of the basic steel grade close to the product specification. The "basic data" is provided by the equipment supplier or design company. After the machine is started, the height and rolling speed of each rolling mill are adjusted according to the finished product size required by the customer and the stacking and pulling conditions between the rolling mills. Finally, according to the finished product size, cold heading inspection results and the hole fullness of the intermediate rolling mill, it is determined whether the setting of the height and rolling speed of each rolling mill is reasonable. The "hole fullness" is obtained by manually measuring the width of the rolled piece through empirical observation or manual calculation. If it is unreasonable, the factory operator will increase and decrease the height and rolling speed of the rolled piece on the rolling mill again based on experience and re-inspect, which takes a long time and produces a large amount of waste and defective products, wasting raw materials.

[0005] The main reason is that the data provided by the equipment supplier or design company is for a single type of steel, which cannot cover the company's increasing demand for steel types and sizes in a few years or decades. The rolling temperature will also be adjusted according to the quality situation. The rolling speed, roll diameter, roll material, and wear of the hole type will affect the width of the rolled piece, which will lead to unstable production and product quality problems. The factory operators increase and decrease the height of the rolled piece and the rolling speed on the rolling mill based on experience and re-inspect it, which has a lot to do with the workers' technical level, and the process is cumbersome and takes a long time to check and inspect. Summary of the invention

[0006] Purpose of the invention: In view of the above technical problems, the present invention proposes a method for controlling the dimensional accuracy of large-size cold heading steel wire rods. First, by simulating the debugging method on the production line, by analyzing the various factors that affect the deformation of each rolling pass, the law of adjusting the size of the rolled piece and the rolling speed is found, and a simplified and practical rolling mathematical model is established. First, simulated rolling is performed in the rolling mathematical model, and then the optimal rolled piece height and rolling speed are set on each rolling mill of the production line. The present invention can directly debug the wire rod size required by the user, can ensure that the product accuracy meets the national standard C-level requirements, and can reduce the cracking ratio of cold heading steel. In addition, the present invention has the technical advantages of short debugging time and low production cost.

[0007] Technical means: In order to achieve the above technical objectives, the present invention adopts the following technical means:

[0008] A method for controlling the dimensional accuracy of a large-size cold-headed steel wire rod comprises the following steps:

[0009] S1. Establishing a model for calculating the width of rolled products

[0010] b=A+β*Δh (1)

[0011] In formula (1), b is the width of the rolled piece, mm; A is the original width of the rolled piece, mm; β is the width expansion coefficient;

[0012] Δh is the rolling mill reduction, mm;

[0013] S2. Establish a mathematical model for the influence of rolling start temperature, finishing mill temperature, steel type and pass type on the width expansion coefficient.

[0014] β=β1*a*d*e (2)

[0015] In formula (2), β is the expansion coefficient; a is the temperature coefficient; d is the steel type coefficient; e is the hole type coefficient;

[0016] S3, establishing a mathematical model for setting the height of the rolled piece and calculating the rolling speed;

[0017] The set rolling piece height is obtained from the basic data of the basic steel grade;

[0018] The rolling speed is calculated in reverse rolling order. First, the rolling speed V of the finished rolling mill is set according to the equipment capacity of the factory. 成品 , and then according to formula (8), let V 成品 V n , calculate the rolling speed of the previous rolling mill:

[0019]

[0020] In formula (8): V n-1is the rolling speed of the previous rolling mill, m / s; V n is the rolling speed of a rolling mill, m / s; R n is the speed coefficient, calculated according to formula (9),

[0021] R n =Uc*K1 (9)

[0022] In formula (9): Uc is the elongation coefficient, K1 is the tension coefficient, K1 = 0.970 ~ 1.030;

[0023]

[0024] In formula (10):

[0025] F n is the cross-sectional area of ​​the rolled product of a rolling mill, mm 2 ;

[0026] F n-1 is the cross-sectional area of ​​the rolled piece of the previous rolling mill, mm 2 ;

[0027] The cross-sectional area F of the rolled piece is calculated according to formula (11):

[0028]

[0029] In formula (11): F is the cross-sectional area of ​​the rolled piece, mm 2 ; F1 is the hole area, which is equal to the sum of the upper and lower groove areas of the hole, mm 2 ; H1 is the hole depth, mm; W1 is the hole width, mm; H1 and W1 data are from the hole drawing; s is the roll gap, mm; ψ is the area correction coefficient, ψ=0.987~1.000;

[0030] The hole filling degree ω is obtained by formula (12):

[0031]

[0032] The same method is used to infer the rolling speed of all rolling mills in the upstream stand.

[0033] S4. The elongation coefficient and hole fullness calculated in step S3 are checked according to the dimensional accuracy, elongation coefficient and hole fullness of the finished product, and the following three conditions are met at the same time:

[0034] Condition 1: The dimensional accuracy of the finished product meets the requirements of the customer or the provisions of the national standard;

[0035] If the finished product size does not meet the customer's requirements or national standards, increase or decrease the height of the rolled product on each rolling mill in reverse rolling order until a product that meets the requirements is debugged;

[0036] Condition 2: The extension coefficients of each unit are allocated in order from large to small, and the extension coefficients within the unit are evenly distributed.

[0037] Condition 3: The hole filling degree is reasonable. The hole filling degree of the elliptical hole is 86-92%, the hole filling degree of the round hole is 92-98%, and the hole filling degree of the finished hole is 97.8-99.9%;

[0038] S5, according to the steel type and wire rod diameter required by the customer, use the mathematical model of the rolling height and the rolling speed calculation described in step S3 and the verification step of step S4 to debug the rolling height and rolling speed of each rolling mill on the production line;

[0039] S6. Set the debugged optimal rolling piece height and rolling speed on each rolling mill in the production line.

[0040] In step S3, the basic data is provided by the equipment supplier or design company;

[0041] If the equipment supplier or design company does not provide basic data, first input an arbitrary value of the height of the rolled piece starting from the first rolling mill. After input, calculate the elongation coefficient and hole fill rate through step S3 to see whether the calculation result meets the conditions 2 and 3 in step S2. If not, simulate the factory debugging method to increase or decrease the height of the rolled piece on the first rolling mill until the required result is produced.

[0042] When switching steel types, first input the conditional parameters of the reproduced steel type into the rolling mathematical model described in step S3, that is, the size of the billet, the specification of the product, the rolling temperature and the steel type, and then input the basic data of the rolled piece height, that is, the basic rolled piece height. Then, based on the calculation results, check whether the basic rolled piece height setting of each rolling mill is reasonable. If it is unreasonable, increase or decrease the rolled piece height of each rolling mill until the best result is selected.

[0043] In step S2, the mathematical model of the temperature coefficient a is established according to formula (5):

[0044] a=θ a *(T0-T1)+1 (5)

[0045] In formula (5): θ a is the influence value of 1℃ temperature change on the width expansion coefficient; T0 is the reference temperature, ℃, which is equal to 1000℃ for the start rolling temperature and 890℃ for the temperature entering the finishing mill; T1 is the actual temperature, ℃;

[0046] The effect of 1°C temperature change on the expansion coefficient θ a Calculated using formula (4),

[0047]

[0048] In formula (4), β1' is the expansion coefficient after temperature change.

[0049] In step S2, the mathematical model of the steel grade coefficient d is obtained by formula (6),

[0050] d=β2' / β1 (6)

[0051] In formula (6), d is the steel type coefficient; β2' is the width expansion coefficient after the steel type changes; β1 is the base width expansion coefficient of the rolling mill.

[0052] In step S2, the mathematical model of the hole coefficient e is established according to formula (7):

[0053]

[0054] In formula (7), β3' is the actual expansion coefficient.

[0055] The steel types are divided into two categories according to the tensile strength of the product: carbon cold heading steel with a tensile strength of less than 495 MPa, and alloy cold heading steel with a tensile strength of ≥495 MPa.

[0056] Step S4, the elongation coefficient in the second condition is divided into the following types according to different rolling mills:

[0057] The elongation coefficient of the roughing mill is between 1.25 and 1.45;

[0058] The elongation coefficient between the intermediate rolling mill groups is between 1.20 and 1.40;

[0059] The elongation coefficient of the pre-finishing mill is between 1.15 and 1.35;

[0060] The elongation coefficient of the finishing mill is between 1.05 and 1.25.

[0061] Beneficial effects:

[0062] Compared with the prior art, the present invention has the following technical advantages:

[0063] 1. The present invention simulates rolling in a rolling model according to the type of cold heading steel and the rolling temperature. When it is found that the setting of the height of the rolled piece and the rolling speed is unreasonable, that is, the product size does not meet the customer's requirements, and the elongation coefficient and the hole fill rate verification fail, the height of the rolled piece can be adjusted in the rolling model until a satisfactory result is output, and then the calculated height of the rolled piece and the rolling speed are set on each rolling mill of the production line, which saves the debugging time of the production line and improves the output.

[0064] 2. The present invention can check whether the height of the rolled product and the rolling speed setting of each rolling mill are reasonable according to the calculated elongation coefficient and hole filling degree, thereby avoiding rolling problems such as ears and torsion caused by excessive or insufficient hole filling degree during machine debugging, or serious steel piling due to improper rolling speed setting, resulting in process accidents or cold heading cracked products, thereby saving raw materials and reducing production costs.

[0065] 3. The present invention can directly adjust the wire rod diameter size required by the user, can improve the dimensional accuracy of the product, can reduce the cracking ratio of cold heading steel, and improve product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 The steel rolling process layout diagram of the present invention;

[0067] Figure 2 This is a schematic diagram of the classification of steel grades according to average tensile strength in the present invention;

[0068] Figure 3 It is the main interface of the dimensional accuracy control system of the large-size cold heading steel of the present invention;

[0069] Figure 4 The present invention is a flow chart of a method for controlling the dimensional accuracy of a large-size cold-headed steel wire rod. DETAILED DESCRIPTION

[0070] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can have a clearer understanding of the technical solution of the present invention.

[0071] The present invention provides a method for controlling the dimensional accuracy of a large-size cold-headed steel wire rod, and the improvement idea is as follows:

[0072] (1) Starting from the causes of dimensional fluctuations and quality defects, by studying the deformation laws of various specifications and steel grades between various racks, the present invention establishes a large-size cold heading steel dimensional accuracy control system, accurately calculates the parameters of various specifications, various steel grades, and various racks, and guides on-site control of the material shape size and rolling speed of each pass, thereby ensuring the dimensional accuracy of the finished product, reducing rolling defects, and reducing the cracking ratio of large-size cold heading steel.

[0073] (2) The process factors that affect the dimensional accuracy of wire rods include: steel type, temperature, tension, hole shape, roll material and processing accuracy, wear of hole grooves and guides, etc. Equipment factors include: rolling mill frame stiffness, rolling mill adjustment accuracy, roll and roll system stiffness, and rolling mill electronic control level. Since there are many types of cold heading steel, to establish a dimensional accuracy control system for large-size cold heading steel, it is necessary to first classify the steel types, then establish a mathematical model for the effects of the starting temperature and the temperature of the finishing mill on the width expansion, and improve the effects of tension, hole shape, roll material and processing accuracy, hole grooves, etc. Cold heading steel is divided into two categories: carbon steel and alloy steel according to the average tensile strength of each steel type. See Figure 2 "Classification of steel grades according to average tensile strength". The material size and rolling speed of each pass are calculated for the two types of steel.

[0074] Technical Solution

[0075] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0076] (1) Prepare basic process table

[0077] The basic rolling process table includes parameters such as the workpiece height, workpiece width, hole width, hole filling degree, roll gap, elongation coefficient, workpiece cross-sectional area, rolling speed, etc. for each pass. All data in the table are automatically associated using formulas.

[0078] (2) Classification of cold heading steel

[0079] Since there are many types of steel in the large-size cold heading steel production line, it is a lot of work to establish a mathematical model for each type of steel and it is of little significance for actual production guidance. Therefore, it is necessary to simplify the system model and divide it into two types of steel: alloy cold heading steel and carbon cold heading steel, with the 15CrNiCu steel type with a tensile strength of 495MPa as the dividing line. Carbon cold heading steel includes: 8A, ML08AL, 10A, 15A, 18A, 22A, 10B21, and the ML08AL with the largest production volume is selected as the research object; alloy cold heading steel includes: 15CrNiCu, 51B20, 35K, 45K, ML40Cr, SCM440, SCM435, and the ML40Cr with the largest production volume is selected as the research object.

[0080] (3) Calculation of rolled product width

[0081] The environment for the development of this system is a factory model. The purpose is to analyze the relationship between the reduction and width, while considering the influence of steel type and temperature on the state of each pass of the rolled piece. Therefore, the absolute width expansion coefficient is used to calculate the rolled piece width b:

[0082] b=A+β*Δh, where: b is the width of the rolled piece, mm; A is the original width of the rolled piece, mm; β is the width expansion coefficient; Δh is the reduction of the rolling mill, mm;

[0083] There are many factors that affect the expansion coefficient. The key to establishing a mathematical model is to simplify the calculation. First, the expansion coefficient β1 of the reference steel grade at the reference temperature must be calculated. Taking ML08AL as the reference steel grade and the rolling temperature of 1000℃, a=1, d=1, e=1, so β=β1. Measure the size of the rolled piece of each stand and calculate β1 according to b=A+β*Δh. Since the steel grade and temperature factors must be considered, the temperature coefficient and steel grade coefficient must be multiplied.

[0084] β=β1*a*d*e In the formula: β is the expansion coefficient; a is the temperature coefficient; d is the steel type coefficient; e is the hole type coefficient;

[0085] When the height and temperature of each rolling mill remain unchanged, the width of each rolling mill is measured again by changing to ML40Cr steel. β2' is still calculated according to the calculation method of β1. β2' divided by β1 is equal to the steel grade coefficient d value of alloy steel. The temperature coefficient is calculated again according to the same principle, and the data is locked after entering the system. When developing the system, an interface for inputting the hole correction coefficient e can be reserved to facilitate users to calibrate the system.

[0086] (4) Area calculation

[0087] The strip area of ​​each pass is equal to the hole area plus the roll gap area. The hole area can be calculated according to the calculus method, first calculate the area when the hole is 100% full, and then subtract the excess hole area. The roll gap area is equal to the width of the rolled piece multiplied by the roll gap height, that is:

[0088] F s =b*sIn the formula: F s — area of ​​rolled product at the roll gap b — width of rolled product s — roll gap;

[0089] In actual production, the edge of the rolled piece usually has a transition arc, so the final calculation needs to be completed on-site measurement, and CAD is used for mapping and verification of the deviation coefficient. The deviation coefficient is usually between 0 and 1.3%. The calculation result multiplied by the deviation coefficient can obtain the accurate cross-sectional area of ​​the red steel section.

[0090] (5) Speed ​​coefficient R n and speed calculation

[0091] In order to ensure that all steel grades and specifications can be rolled stably, the size and speed parameters of each stand need to be adjusted on the basis of equal continuous rolling constants. Before the rolled piece enters the finishing mill, the continuous rolling constant of the last stand of the intermediate rolling mill (or pre-finishing mill) is used as the benchmark, and the tension coefficients between the stands of the roughing and intermediate rolling mills are allocated in reverse rolling order. According to the formula

[0092] R n=Uc*K1In the formula: Uc is the elongation coefficient, K1 is the tension coefficient, K1=0.970~1.030.

[0093] The tension coefficient of the roughing mill is about 1.02 to 1.03;

[0094] The tension between the intermediate rolling mills is about 1.01 to 1.02;

[0095] The tension coefficient of the pre-finishing mill is about 1.00 to 1.02;

[0096] The tension coefficient of the finishing mill is about 1.00 to 1.02;

[0097] The tension coefficient between units is approximately 0.97 to 1.01.

[0098] Calculate the speed factor R n Value, based on the line speed of the finished rack and the speed factor R n According to the formula:

[0099]

[0100] In the formula: V n-1 is the rolling speed of the previous rolling mill, m / s; V n is the rolling speed of a rolling mill, m / s; R n is the speed coefficient;

[0101] Calculate the linear speed of the previous stand, and use the same method to reversely calculate the linear speeds of all rolling mills.

[0102] (6) Establish system database

[0103] Establish a database based on the logical relationship required by the system. The database can be developed using programming languages ​​such as Excel, Visual Basic, and Visual C++. See the main interface. Figure 3 .

[0104] After selecting five parameters: billet size → specification → steel type → rolling temperature → finishing temperature, the rolling process table is automatically generated, and the rolled piece size, hole fill and elongation coefficient, rolling speed and other data are automatically calculated. If the calculation result does not meet the process requirements, the height of the rolled piece can be adjusted, and the system will automatically complete a new round of calculations. If the calculation result meets the process requirements, it can be set on the rolling mill and the electronic control system to organize production. If satisfactory requirements are not met, it means that the hole needs to be optimized or the system parameters need to be calibrated.

[0105] A method for controlling the dimensional accuracy of a large-size cold-headed steel wire rod comprises the following steps, see Figure 4 As shown:

[0106] S1. Establish the rolling model of cold heading steel production line

[0107] S11. Establish a mathematical model for calculating the width of rolled products

[0108] A mathematical model for calculating the width of the rolled piece is established, and the absolute width expansion coefficient is used to calculate the width b of the rolled piece.

[0109] b=A+β*Δh (1)

[0110] In formula (1):

[0111] b is the width of the rolled piece, mm;

[0112] A is the original width of the rolled piece, mm;

[0113] β is the broadening coefficient;

[0114] Δh is the amount of reduction, mm;

[0115] S12, establishing a mathematical model of the effects of rolling start temperature, temperature entering the finishing mill, steel type and pass type on the width expansion coefficient;

[0116] The broadening coefficient is calculated according to formula (2):

[0117] β=β1*a*d*e (2)

[0118] In formula (2), β is the width expansion coefficient; β1 is the base width expansion coefficient of the rolling mill; a is the temperature coefficient; d is the steel type coefficient; e is the hole type coefficient;

[0119] In step S12, the mathematical model of the rolling mill reference width expansion coefficient β1 is established by the following method:

[0120] Taking ML08AL cold heading steel as the reference steel grade, the starting rolling temperature is 1000℃, the finishing rolling temperature is 890℃, the original width and the width of the rolled piece are measured, and the formula (3) is used to calculate:

[0121] β1=(bA) / Δh (3)

[0122] In formula (3):

[0123] b is the width of the rolled piece, mm;

[0124] A is the original width of the rolled piece, mm;

[0125] Δh is the amount of reduction, mm;

[0126] In step S12, the mathematical model of the temperature coefficient a is established in the following manner:

[0127] Taking ML08AL cold heading steel as the reference steel grade, the starting rolling temperature is 1000℃, the finishing rolling temperature is 890℃, the temperature coefficient a is set to 1.0, the steel grade coefficient d is set to 1.0, and the hole type coefficient e is set to 1.0. When the height of the rolled piece remains unchanged, the starting rolling temperature and the finishing rolling temperature are increased by 50℃, and the width of the rolled piece is re-measured. The width expansion coefficient β1' after the temperature change is calculated according to formula (3), and then the influence value θ of the temperature change of 1℃ on the width expansion coefficient can be calculated by formula (4). a ,

[0128]

[0129] In formula (4):

[0130] θ a is the effect of 1℃ temperature change on the expansion coefficient;

[0131] β1' is the expansion coefficient after temperature change;

[0132] β1 is the reference expansion coefficient.

[0133] The mathematical model of temperature coefficient a is established according to formula (5):

[0134] a=θ a *(T0-T1)+1 (5)

[0135] In formula (5):

[0136] a is the temperature coefficient;

[0137] θ a is the effect of 1℃ temperature change on the expansion coefficient;

[0138] T0 is the reference temperature, °C,

[0139] T0 is used for the start rolling temperature equal to 1000℃, and for the temperature entering the finishing mill equal to 890℃;

[0140] T1 is the actual temperature, °C;

[0141] In step S12, the mathematical model of the steel grade coefficient d is established in the following way:

[0142] The steel types are divided into two categories according to the tensile strength of the product: carbon cold heading steel with a tensile strength of less than 495MPa, and alloy cold heading steel with a tensile strength of ≥495MPa. Carbon cold heading steel includes the following 7 grades: 8A, ML08AL, 10A, 15A, 18A, 22A, and 10B21; alloy cold heading steel includes the following 7 grades: 15CrNiCu, 51B20, 35K, 45K, ML40Cr, SCM440, and SCM435.

[0143] Taking ML08AL cold heading steel as the reference steel grade, the starting rolling temperature is 1000℃, the temperature entering the finishing mill is set to 890℃, the temperature coefficient a is equal to 1.0, the steel grade coefficient d is equal to 1.0, and the hole type coefficient e is equal to 1.0. When the height of the rolled piece remains unchanged, it is replaced with ML40Cr cold heading steel, and the width of the rolled piece of each rolling mill is re-measured. The width expansion coefficient β2' after the steel grade change is calculated, and the mathematical model of the steel grade coefficient d is established according to formula (6).

[0144] d=β2' / β1 (6)

[0145] In formula (6):

[0146] d is the steel type coefficient;

[0147] β2' is the width expansion coefficient after the steel grade changes;

[0148] β1 is the reference expansion coefficient.

[0149] In step S12, the mathematical model of the hole coefficient e is established according to formula (7):

[0150]

[0151] In formula (7), β3' is the actual width expansion coefficient of the rolling mill.

[0152] In the initial stage of establishing the model, the hole coefficient e can be set to a constant of 1.0;

[0153] S13. Establish a mathematical model for setting the height of the rolled piece and calculating the rolling speed

[0154] The mathematical model is established through factory research. Before the factory is started, its design company will provide the height and rolling speed of the rolled piece of basic steel grades of common specifications at a fixed rolling temperature. This parameter is the basic data for factory debugging. The present invention is to establish a mathematical model for inputting the height of the rolled piece and automatically calculating the rolling speed, and then input the height of the rolled piece in the basic data into the mathematical model for debugging. According to the calculation results of the elongation coefficient and the hole filling degree, the height and rolling speed of the rolled piece of each specification, each steel grade, and at different rolling temperatures are optimized, and the finished product size is guaranteed to meet customer requirements.

[0155] The specific steps are:

[0156] (1) Calculate the size of the rolled piece

[0157] The size of the rolled product refers to the height and width of the rolled product of each rolling mill. The height of the rolled product is obtained by setting the debugging method of the simulated production line, and the width of the rolled product is obtained by formula (1).

[0158] (2) Calculate rolling speed

[0159] The rolling speed is calculated in reverse rolling order. First, the rolling speed V of the finished rolling mill is set according to the equipment capacity of the factory. 成品 , and then according to formula (8), let V 成品 V n , calculate the rolling speed of the previous rolling mill:

[0160]

[0161] In formula (8): V n-1 is the rolling speed of the previous rolling mill, m / s; V n is the rolling speed of a rolling mill, m / s; R n is the speed coefficient;

[0162] The same method is used to infer the rolling speeds of all rolling mills in the upstream rack.

[0163] The speed factor R n According to formula (9),

[0164] R n =Uc*K1 (9)

[0165] In formula (9): Uc is the elongation coefficient, K1 is the tension coefficient, K1 = 0.970 ~ 1.030.

[0166] The tension coefficient of the roughing mill is about 1.02 to 1.03;

[0167] The tension between the intermediate rolling mills is about 1.01 to 1.02;

[0168] The tension coefficient of the pre-finishing mill is about 1.00 to 1.02;

[0169] The tension coefficient of the finishing mill is about 1.00 to 1.02;

[0170] The tension coefficient between units is approximately 0.97 to 1.01.

[0171] The elongation coefficient Uc is calculated according to formula (10):

[0172]

[0173] In formula (10):

[0174] F n is the cross-sectional area of ​​the rolled product of a rolling mill, mm 2 ;

[0175] F n-1 is the cross-sectional area of ​​the rolled piece of the previous rolling mill, mm 2 .

[0176] The cross-sectional area F of the rolled piece is calculated according to formula (11):

[0177]

[0178] In formula (11): F is the cross-sectional area of ​​the rolled piece, mm 2 ; F1 is the hole area, which is equal to the sum of the upper and lower groove areas of the hole, mm 2 , is the data obtained by CAD measurement during hole design; H1 is the hole depth, mm, W1 is the hole width, mm, H1 and W1 data come from the hole drawings, and the original data is provided by the design companies or equipment suppliers of each factory; s is the roll gap, mm, and its value is equal to the height of the rolled piece minus 2 times the hole depth; ψ is the area correction coefficient, ψ=0.987~1.000, and its value can be set to 1.000 first. After the first calculation of the model is completed, draw the contour of the rolled piece in the CAD software, and the measurement result of the contour area divided by the calculated area of ​​the mathematical model is the ψ value;

[0179] S2. According to the steel type and wire rod diameter required by the customer, the rolling model is used to debug the rolling height of each rolling mill on the production line and automatically calculate the rolling speed.

[0180] The dimensional accuracy of cold heading steel products usually complies with GB / T 14981. According to the standard, the dimensional accuracy of hot rolled wire rods is divided into three levels: A, B, and C, with C being the highest level. General products are delivered according to B-level accuracy, high-end products are delivered according to C-level accuracy, and special products will have special requirements for the control range of product dimensions based on C-level accuracy.

[0181] The size of the rolled product refers to the height and width of the rolled product of each rolling mill. The height of the rolled product is obtained by setting the debugging method of the simulation factory. The specific situation is as follows:

[0182] (1) Factory debugging method:

[0183] The traditional method of producing cold heading steel wire rods and switching steel grades in a traditional steel rolling mill is to debug directly on the production line. During debugging, the height and rolling speed of each rolling mill are set according to the basic data of the basic steel grade close to the product specification. The "basic data" is provided by the equipment supplier or design company. After the machine is started, the height and rolling speed of each rolling mill are adjusted according to the finished product size required by the customer and the stacking and pulling conditions between the rolling mills. Finally, according to the finished product size, cold heading inspection results and the hole fullness of the intermediate rolling mill, it is determined whether the setting of the height and rolling speed of each rolling mill is reasonable. The "hole fullness" is obtained by manually measuring the width of the rolled piece through empirical observation or manual calculation. If it is unreasonable, the factory operator will increase and decrease the height and rolling speed of the rolled piece on the rolling mill again based on experience and re-inspect, which takes a long time and produces a large amount of waste and defective products, wasting raw materials.

[0184] The main reason is that the data provided by the equipment supplier or design company is for a single type of steel, which cannot cover the company's increasing demand for steel types and sizes in a few years or decades. The rolling temperature will also be adjusted according to the quality situation. The rolling speed, roll diameter, roll material, and wear of the hole type will affect the width of the rolled piece, which will lead to unstable production and product quality problems. The factory operators increase and decrease the height of the rolled piece and the rolling speed on the rolling mill based on experience and re-inspect it, which has a lot to do with the workers' technical level, and the process is cumbersome and takes a long time to check and inspect.

[0185] (2) In view of the above problems, a rolling model is established. First, input the conditional parameters: input the size of the steel billet, select the specification and steel type, and input the rolling temperature. Then input the height of the rolled piece, that is, input the basic data of the basic steel type into the rolling model. If the equipment supplier or design company does not provide basic data, you can first input any value of the height of the rolled piece starting from the first rolling mill. After input, the rolling model automatically calculates the elongation coefficient and the hole fill degree to see whether the calculation result meets the conditions 2 and 3 in step S2. If not, the simulation factory debugging method is used to increase or decrease the height of the rolled piece on the first rolling mill until the required result is produced. Continue to produce the height of the rolled piece to the downstream frame in the same way until the last rolling mill, that is, the finished product rolling mill, should pay attention to the fact that the finished product rolling mill must meet the conditions 2 and 3 in step S2 on the basis of meeting the conditions 1, that is, the dimensional accuracy of the finished product meets the requirements of the customer or the provisions of the national standard. If the finished product size is not met, continue to simulate the factory debugging method, first increase or decrease the height of the rolled product of the finished product rolling mill, and then reverse the rolling order and adjust the height of the rolled product toward the upstream frame until the finished product rolling mill meets conditions one, two, and three in step S2, and other rolling mills meet conditions two and three in step S2.

[0186] (3) When switching steel types, first input the conditional parameters of the reproducible steel type into the rolling model, i.e., the size of the billet, the specification of the product, the rolling temperature, and the steel type. Then input the basic data of the height of the rolled piece. Then, based on the calculation results, check whether the height setting of the rolled piece of each rolling mill is reasonable. If it is unreasonable, it is necessary to increase or decrease the height of the rolled piece of each rolling mill until the best result is selected.

[0187] The verification of the rolled piece size is based on the dimensional accuracy, elongation coefficient and hole filling of the finished product, and the following three conditions should be met:

[0188] Condition 1: The dimensional accuracy of the finished product meets the requirements of the customer or the provisions of the national standard.

[0189] If the finished product size does not meet the requirements, the height of the rolled piece on each rolling mill should be increased or decreased in the reverse rolling order until a product that meets the requirements is debugged.

[0190] Condition 2: The extension coefficients of each unit are allocated in order from large to small, and the extension coefficients within the unit are evenly distributed.

[0191] The elongation coefficient of the roughing mill is between 1.25 and 1.45;

[0192] The elongation coefficient between the intermediate rolling mill groups is between 1.20 and 1.40;

[0193] The elongation coefficient of the pre-finishing mill is between 1.15 and 1.35;

[0194] The elongation coefficient of the finishing mill is between 1.05 and 1.25;

[0195] Condition three: The hole filling degree is reasonable. The hole filling degree of the elliptical hole is 86-92%, the hole filling degree of the round hole is 92-98%, and the hole filling degree of the finished hole is 97.8-99.9%.

[0196] The hole filling degree ω is obtained by formula (12):

[0197]

[0198] In formula (12):

[0199] ω is the hole filling degree;

[0200] b is the width of the rolled piece, mm;

[0201] W1 is the hole width, mm.

[0202] The rolling speed is automatically calculated by the rolling model after the rolling speed of the finished rolling mill is input according to the step S13.

[0203] S3. Set the adjusted rolling height and rolling speed on each rolling mill in the production line to produce products that meet customer requirements.

[0204] In step S2, after the best rolling piece size is selected based on the three factors of finished product size accuracy, elongation coefficient and hole fill, the rolling model will automatically calculate the rolling speed. The rolling piece height and rolling speed are set on each rolling mill of the production line, and the start rolling temperature and the temperature of the finishing mill are adjusted according to the process requirements to produce products that meet customer requirements. The adjustment process can usually be completed within 1 to 2 steel bars.

[0205] 1. Establish a dimensional accuracy control system

[0206] 1. First, classify all cold heading steel products and prepare the basic process table according to the technical plan.

[0207] 2. Taking ML08AL, which has the largest production and sales volume, as the benchmark, measure the dimensions of the rolled products of each rolling mill under the process conditions of the benchmark starting rolling temperature and the benchmark finishing rolling temperature. The free parking method can be used to measure with a caliper, a clamp, or a ruler, or a mobile profilometer can be used for online measurement.

[0208] 3. According to the technical plan, a program for calculating the width and cross-sectional area of ​​the rolled product is compiled. The actual cross-sectional area of ​​the rolled product is measured using the actual measurement results and CAD software. The area correction coefficient ψ is added to the system for correction, and then the elongation coefficient Uc and speed coefficient R are compiled. n and rolling speed calculation procedure.

[0209] 2. Embodiment

[0210] 1. A company uses 140mm small square billets to roll large-size cold heading steel wire rods. After the precision control system is established, it is found through analysis that the overfilling of the 4# and 6# holes of the rough rolling unit is too large, both above 98%. When producing alloy cold heading steel, ears are prone to occur, resulting in increased cold heading cracking. Therefore, the height of the rolled product of 1# and 2# rolling mills was reduced from 98mm and 116mm to 95mm and 110mm respectively. However, the torsion problem of the rolled product between 1# and 3# rolling mills was aggravated, and there were more problems of corner wrinkles. The parameters of 1#, 2#, 4# and 6# hole types were modified. The bottom size of the groove of 1# hole type was reduced from 148mm to 143mm; the bottom size of the groove of 2# hole type was reduced from 97mm to 96mm; the radius size of 4# round hole type was changed from R45mm to R46mm; the radius size of 6# round hole type was changed from R34mm to R34.5mm; the size of the rolled product of each rolling mill was recalculated, and the rolling defects were eliminated.

[0211] 2. Analysis found that the filling degree of the 12# and 14# rolling mills when rolling different specifications and different types of steel is quite different. Taking φ28mm as an example, when producing alloy steel, the filling degree of the original hole type of the 12# rolling mill is above 98.9%, and cold heading cracking is often caused by ears on the rolled piece. By increasing the width of the 12# hole type from 35.56mm to 36.88mm, adjusting the rolled piece size and rolling speed of the 11# and 12# rolling mills, the filling degree of the 12# hole type dropped to 95.4%. The same specification of the finishing mill uses two sets of rolled piece sizes and rolling speeds according to the steel type. The surface quality of the finished product is normal, and the proportion of cold heading cracking is significantly reduced. When the rolling speed of the φ28mm finished product is 9.00m / s, the rolled piece size and rolling speed of the carbon steel and alloy steel of the intermediate rolling mill group are shown in Table 1:

[0212] Table 1 Size of rolled product and rolling speed of the rolling mill group for two steel grades with diameter 28 mm

[0213]

[0214] 3. Analysis of φ16.0mm~φ18.0mm specifications 15# and 16# rolling mills found that the fullness of 15# elliptical hole type was only 84.0%, and the fullness of 16# round hole type was only 89%, which was lower than the process standard, indicating that the original hole type design was too large. Through hole type optimization, the width of 15# hole type was reduced from 39.19mm to 37.71mm, and the width of 16# hole type was reduced from 23.38mm to 22.58mm. Then the rolled piece size and rolling speed of 13#~16# rolling mills were adjusted. The fullness of 15# elliptical hole type reached 88.4%, and the fullness of 16# round hole type reached 92.16%, which met the process standard, improved the stability of the rolling process, reduced the head and tail trimming of the finished product by 1~2 turns, improved the yield rate, and reduced the production cost.

[0215] According to the present invention, large-size cold-forging steel wire rods can be produced, rolling defects can be reduced, cold-forging cracking rate can be lowered, and dimensional accuracy of products can be improved, and the quality can fully meet customer requirements. At the same time, the enterprise's product qualification rate, yield rate and equipment operation rate are improved, and production costs are reduced.

Claims

1. A method for controlling the dimensional accuracy of large-size cold-headed steel wire rod, characterized in that: The following steps are involved: S1. Establishing a model for calculating the width of rolled products b=A+β*Δh (1) In formula (1), b is the width of the rolled piece, mm; A is the original width of the rolled piece, mm; β is the width expansion coefficient; Δh is the rolling mill reduction, mm; S2. Establish a mathematical model for the influence of rolling start temperature, finishing mill temperature, steel type and pass type on the width expansion coefficient. β=β1*a*d*e (2) In formula (2), β1 is the base width coefficient of the rolling mill; a is the temperature coefficient; d is the steel type coefficient; e is the hole type coefficient; S3, establishing a mathematical model for setting the height of the rolled piece and calculating the rolling speed; The set rolling piece height is obtained from the basic data of the basic steel grade; The rolling speed is calculated in reverse rolling order. First, the rolling speed V of the finished rolling mill is set according to the equipment capacity of the factory. 成品 , and then according to formula (8), let V 成品 V n , calculate the rolling speed of the previous rolling mill: In formula (8): V n-1 is the rolling speed of the previous rolling mill, m / s; V n is the rolling speed of a rolling mill, m / s; R n is the speed coefficient, calculated according to formula (9), R n =Uc*K1 (9) In formula (9): Uc is the elongation coefficient, K1 is the tension coefficient, K1 = 0.970 ~ 1.030; In formula (10): F n is the cross-sectional area of ​​the rolled product of a rolling mill, mm 2 ; F n-1 is the cross-sectional area of ​​the rolled piece of the previous rolling mill, mm 2 ; The cross-sectional area F of the rolled piece is calculated according to formula (11): In formula (11): F is the cross-sectional area of ​​the rolled piece, mm 2 ; F1 is the hole area, which is equal to the sum of the upper and lower groove areas of the hole, mm 2 ; H1 is the hole depth, mm; W1 is the hole width, mm; H1 and W1 data are from the hole drawing; s is the roll gap, mm; ψ is the area correction coefficient, ψ=0.987~1.000; The hole filling degree ω is obtained by formula (12): The same method is used to infer the rolling speed of all rolling mills in the upstream stand. S4. The elongation coefficient and hole fullness calculated in step S3 are checked according to the dimensional accuracy, elongation coefficient and hole fullness of the finished product, and the following three conditions are met at the same time: Condition 1: The dimensional accuracy of the finished product meets the requirements of the customer or the provisions of the national standard; If the finished product size does not meet the customer's requirements or national standards, increase or decrease the height of the rolled product on each rolling mill in reverse rolling order until a product that meets the requirements is debugged; Condition 2: The extension coefficients of each unit are allocated in order from large to small, and the extension coefficients within the unit are evenly distributed. Condition 3: The hole filling degree is reasonable. The hole filling degree of the elliptical hole is 86-92%, the hole filling degree of the round hole is 92-98%, and the hole filling degree of the finished hole is 97.8-99.9%; S5, according to the steel type and wire rod diameter required by the customer, use the mathematical model of the rolling height and the rolling speed calculation described in step S3 and the verification step of step S4 to debug the rolling height and rolling speed of each rolling mill on the production line; S6. Set the debugged optimal rolling piece height and rolling speed on each rolling mill in the production line.

2. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1 is characterized in that: In step S3, the basic data is provided by the equipment supplier or design company; If the equipment supplier or design company does not provide basic data, first input an arbitrary value of the height of the rolled piece starting from the first rolling mill. After input, calculate the elongation coefficient and hole fill rate through step S3 to see whether the calculation result meets the conditions 2 and 3 in step S2. If not, simulate the factory debugging method to increase or decrease the height of the rolled piece on the first rolling mill until the required result is produced.

3. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1 is characterized in that: When switching steel types, first input the conditional parameters of the reproduced steel type, i.e., the size of the billet, the specification of the product, the rolling temperature and the steel type, into the mathematical model for setting the workpiece height and calculating the rolling speed as described in step S3, and then input the basic data of the workpiece height, i.e., the basic workpiece height. Then, based on the calculation results, check whether the basic workpiece height setting of each rolling mill is reasonable. If it is unreasonable, increase or decrease the workpiece height of each rolling mill until the best result is selected.

4. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1 is characterized in that: In step S2, the mathematical model of the temperature coefficient a is established according to formula (5): a=θ a *(T0-T1)+1 (5) In formula (5): θ a is the influence value of 1℃ temperature change on the width expansion coefficient; T0 is the reference temperature, ℃, which is equal to 1000℃ for the start rolling temperature and 890℃ for the temperature entering the finishing mill; T1 is the actual temperature, ℃; The effect of 1°C temperature change on the expansion coefficient θ a Calculated using formula (4), In formula (4), β1' is the expansion coefficient after temperature change.

5. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1 is characterized in that: In step S2, the mathematical model of the steel grade coefficient d is obtained by formula (6), d＝β2' / β1 (6) In formula (6), d is the steel type coefficient; β2' is the width expansion coefficient after the steel type changes.

6. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1, characterized in that: In step S2, the mathematical model of the hole coefficient e is established according to formula (7): In formula (7), β3' is the actual expansion coefficient.

7. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 3 is characterized in that: The steel types are divided into two categories according to the tensile strength of the product: carbon cold heading steel with a tensile strength of less than 495 MPa, and alloy cold heading steel with a tensile strength of ≥495 MPa.

8. The method for controlling the dimensional accuracy of large-size cold-headed steel wire rod according to claim 1, characterized in that: Step S4, the elongation coefficient in the second condition is divided into the following types according to different rolling mills: The elongation coefficient of the roughing mill is between 1.25 and 1.45; The elongation coefficient between the intermediate rolling mill groups is between 1.20 and 1.40; The elongation coefficient of the pre-finishing mill is between 1.15 and 1.35; The elongation coefficient of the finishing mill is between 1.05 and 1.25.

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