A control method for reducing the roll grinding amount of pinch rolls in front of a high-speed wire rod mill

Abstract

The present invention relates to the technical field of pinch roll control, and particularly to a control method for reducing the roll grinding amount of the pinch roll in front of the high-speed wire mill, including calculating the speed difference according to the average line speed of the rolling mill and the line speed after the lower roll of the pinch roll is worn; calculating the relative wear coefficient according to the wear amount and the theoretical wear coefficient; calculating the wear estimation coefficient according to the relative wear coefficient and the theoretical life of the new roll; calculating the wear estimation time according to the wear estimation coefficient and the relative wear coefficient; obtaining the estimated number of billets with wear according to the wear estimation time and the daily production number of billets; adjusting the roll diameter according to half of the first estimated number of billets with wear, and obtaining the new roll speed of the pinch roll according to the adjusted roll diameter. The present invention solves the problem of excessive wear of the pinch roll before rough rolling.

Description

Technical Field

[0001] The invention relates to the technical field of pinch roller control, and in particular to a control method for reducing the wear amount of pinch rollers in front of a high-speed wire machine. Background Art

[0002] In the production of high-speed wire rod, the steel billet is usually heated to about 900-1200℃ in a heating furnace, and then transported to the entrance of the rough rolling mill through the furnace roller. In order to help the mill bite the steel better, a front pinch roll is usually set in front of the rough rolling mill. This pinch roll generally has two speeds, of which the one that contacts the steel and lasts longer is the steel biting speed. According to the requirements, the steel biting speed is the same as the line speed of the 1# rolling mill.

[0003] There are two kinds of friction between the roller moving body of the pinch roller and the steel billet running on it, both of which are to provide the steel billet with forward power; one is static friction, at this time, the surface linear speed of the roller is the same as the forward speed of the steel billet. In this case, the roller wear is very small, but this situation is basically difficult to achieve. The other is dynamic friction, at this time, the surface linear speed of the roller is different from the forward speed of the steel billet. The pinch roller is driven by a motor controlled by a frequency converter, and the speed is reversed according to the linear speed and roller diameter; the speed of the steel billet is completely controlled by the 1# rolling mill after it bites into the 1# rolling mill. There is a linear speed difference △V between the two, which is equivalent to grinding between two pieces of metal at this speed. The larger the △V, the greater the wear in the same time.

[0004] The diameter of the pinch rollers before the rough rolling mill of a high-speed wire rod plant is 300MM, and the material is 45# steel; the daily production is 740 160MM square billets; the pinch rollers have been seriously worn for a long time. According to long-term tracking, generally after the new rollers are replaced, visible wear begins to be found 2 months later, and the wear grooves begin to become deeper after 4 months. At this time, the rollers need to be raised (otherwise it will cause production failures). The maximum wear reaches 20mm after 6 months, and the rollers must be replaced offline.

[0005] Roller wear has many effects on production: First, when the roller is worn and becomes shorter, the center of the billet will be lower than the No. 1 mill when it runs into the rolling mill, causing it to hit the lower roller of the No. 1 mill; second, the bulges on both sides of the groove marks caused by wear can easily cause secondary scratches on the billet, which in turn causes quality problems. Third, frequent replacement of rollers causes a waste of manpower and material resources. Fourth, the pinch roller loses its pinching function and cannot feed the billet into the No. 1 mill, causing production to stop. Summary of the invention

[0006] Aiming at the deficiencies of the existing algorithms, the present invention solves the problem of excessive wear of the pinch rolls before rough rolling.

[0007] The technical solution adopted by the present invention is as follows: A control method for reducing the roll grinding amount of the pinch roll in front of the high-speed wire rod mill includes the following steps:

[0008] Step 1: Calculate the speed difference according to the average speed of the rolling mill and the linear speed of the pinch roll after the new roll is worn.

[0009] Further, the calculation formula for the speed difference is:

[0010] △V = v - (D - 2x) * π * (d / S) (1)

[0011] Wherein, v is the average speed of the rolling mill, D is the diameter of the new roll, x is the wear amount of the new roll, d is the linear speed of the new roll, and S is the circumference of the new roll; the present invention only analyzes the wear of the lower roll, and the new roll mentioned in the text refers to the lower roll.

[0012] Step 2: Calculate the relative wear coefficient according to the wear amount and the theoretical wear coefficient; calculate the estimated wear coefficient according to the relative wear coefficient and the theoretical life of the new roll; calculate the estimated wear time according to the estimated wear coefficient and the relative wear coefficient; obtain the estimated number of billets worn according to the estimated wear time and the daily production number of billets.

[0013] Further, the calculation formula for the relative wear coefficient is:

[0014] a i = A / x i , i = 1 - A (2)

[0015] Wherein, A is the theoretical wear coefficient, x i is the wear amount, and i is an integer;

[0016] Further, the calculation formula for the estimated wear coefficient is:

[0017] b i = T / sum(a i ) (3)

[0018] Wherein, T is the theoretical life of the new roll, in days; a i is the relative wear coefficient;

[0019] Further, the calculation formula for the estimated wear time is:

[0020] t i = a i * b i (4)

[0021] Wherein, a i is the relative wear coefficient; b i is the estimated wear coefficient, in days;

[0022] Further, the calculation formula for the estimated number of billets worn is:

[0023] C i = t i * c(5)

[0024] Wherein, t i is the wear estimation time, in days; c is the number of billets produced per day;

[0025] Step 3: Adjust the roll diameter according to half of the number of the first worn billets estimated, and obtain the new roll speed of the pinch roll according to the adjusted roll diameter.

[0026] Advantages of the present invention:

[0027] 1. Reduce the amount of roll wear of the pinch roll in front of the roughing mill, and reduce the consumption of manpower and material resources caused by replacing the rolls.

[0028] 2. Reduce problems such as the quality risks caused by the billet not being bitten in due to roll wear, hitting the lower roll of the No. 1 rolling mill, and the wear groove scratching the billet.

[0029] 3. The service life of the lower roll of the pinch roll in front of the mill can be increased from the original 6 months to more than one year. Description of the Drawings

[0030] Figure 1 is the flowchart of the control method for reducing the roll grinding amount of the pinch roll in front of the high-speed wire mill of the present invention;

[0031] Figure 2 is the schematic diagram of the working principle of the pinch roll of the present invention;

[0032] Figure 3 is the schematic diagram of the degree of roll wear of the present invention;

[0033] Figure 4 is the PLC control flowchart in a certain actual production process. Specific Embodiments

[0034] The present invention will be further described below with reference to the drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, so it only shows the components related to the present invention.

[0035] Such as Figure 2The figure shows a schematic diagram of the working principle of pinch rolls. The pinch rolls in the figure are the upper and lower rolls for pinching steel. The red-hot steel comes out of the heating furnace and is transported to the 2# hot inspection area through the discharge roller table. At this time, the speed of the discharge roller table, including the speed of the pinch rolls, changes from high speed to low speed to prepare for the upcoming biting into the rolling mill. When the head of the billet reaches the pinch rolls, the upper roll of the pinch rolls descends under the control of the solenoid valve. The upper roll is a free roll, and the lower roll is a driving roll. For each billet, there is a sliding friction between the roll and the billet for about 120 seconds (taking a certain rolling mill producing a 5.5 specification as an example) (because it is impossible to make the linear speed of the roll surface exactly equal to the actual speed of the billet). Therefore, the main reason for the wear of the rolls comes from the sliding friction in this stage. In actual production applications, the lower roll always shows relatively deep wear, and the longest online time does not exceed 180 days. The pinch rolls pinch the red-hot steel and send it into the 1# rolling mill for rolling at the same speed as the 1# rolling mill. At this speed, the impact of the billet on the rolls is minimized, and it can also help the billet bite in smoothly.

[0036] The pinch rolls are divided into an upper roll and a lower roll. The lower roll is fixed and driven by a motor and a speed reducer. The upper roll is a free roll and can be lifted and lowered by two cylinders. When lifted, the billet only receives the reaction force of the sliding friction when passing through. When lowered, it will greatly increase the friction force between the upper and lower metal contact surfaces. Through this friction force, the pinch rolls can easily send the billet into the 1# rolling mill for rolling. Currently, there are also technologies to increase the roll life by changing the roll material. For example: chromium-based tungsten nickel molybdenum high wear-resistant alloy steel. However, the cost pressure of the rolls with changed material is very high. In addition, there are those with surface coatings and laser cladding, and the effects are not particularly good. Sometimes, due to the relatively long time required to change the rolls, the running rolls are also repaired by electric welding surfacing. Among the above methods, except for the overall material change, the other several methods all have significant quality risks.

[0037] As Figure 3 is a schematic diagram of the wear degree of the rolls, which is divided into no wear, 10 mm wear, and 20 mm wear. When the rolls are worn, the linear speed of the roll surface will decrease. Because the electrical control program is fixed and only mechanically converts the given linear speed into the target speed of the motor through the calculation of the reduction ratio and the roll diameter, the actual linear speed of the roll surface cannot be obtained, and only the closed-loop control of the speed is performed.

[0038] As Figure 1 shown is a control method for reducing the roll grinding amount of the pinch rolls in front of the high-speed wire mill, including:

[0039] Step 1: Calculate the speed difference according to the average linear speed of the rolling mill and the linear speed of the new rolls of the pinch rolls after wear;

[0040] The calculation formula for the speed difference is:

[0041] △V = v - (D - 2x) * π * (d / S) (1);

[0042] Among them, v is the average rolling speed of the rolling mill, D is the diameter of the new roll, x is the wear amount of the new roll, d is the linear speed of the new roll, and S is the circumference of the new roll;

[0043] Table 1 shows the production data of a certain rolling mill. Calculate the relationship between the roll wear amount x and the difference △V between the roll linear speed and the linear speed of the No. 1 rolling mill. The diameter of the new roll D = 300 mm, the average linear speed v of the No. 1 rolling mill at the production site is 120 mm / s for the 5.5 specification billets produced daily at the production site, the number of billets produced daily c = 740 pieces, the circumference of the new roll S = 942 mm, the initial linear speed of the new roll is the same as that of the No. 1 rolling mill at 120 mm / s. Calculate the rotational speed of the roll d / S = 120 / 942 = 0.12739 rps; the wear amount is x, then the roll diameter reduction value is 2x. According to formula (1), the speed difference △V = 0.8x (mm / s) is calculated. That is, when the wear amount is 1 mm, △V = 0.8 mm / s; when the wear amount is 10 mm, △V = 8 mm / s; when the wear amount is 20 mm, △V = 16 mm / s.

[0044] Table 1: Production data of a certain rolling mill

[0045]

[0046]

[0047] Step 2: Calculate the wear relative coefficient according to the wear amount and the theoretical wear coefficient; calculate the wear estimation coefficient according to the wear relative coefficient and the theoretical life of the new roll; calculate the wear estimation time according to the wear estimation coefficient and the wear relative coefficient; obtain the estimated number of worn billets according to the wear estimation time and the number of billets produced daily;

[0048] Furthermore, the formula for calculating the wear relative coefficient is:

[0049] a i = A / x i , i = 1 - A;

[0050] Among them, A is the theoretical wear coefficient, x i is the wear amount, and i is an integer;

[0051] The formula for calculating the wear estimation coefficient is:

[0052] b i = T / sum(a i );

[0053] Among them, T is the theoretical life of the new roll in days; a i is the wear relative coefficient;

[0054] The formula for calculating the wear estimation time is:

[0055] t i = a i * b i ;

[0056] wherein, a i is the relative wear coefficient; b i is the wear estimation coefficient, unit: day;

[0057] Furthermore, the calculation formula for the number of billets with wear estimation is:

[0058] C i = t i * c;

[0059] wherein, t i is the wear estimation time, unit: day; c is the number of billets produced per day;

[0060] Table 2 is the estimation model of wear amount designed based on the data calculated in Table 1. The actual production situation is that the wear is 20 mm after 180 days of using a new roll. Then the theoretical wear coefficient A = 20, and the theoretical life T of the new roll = 180 days; calculate the wear estimation coefficient b i = 180 / 72 = 2.5 days. Thus, according to the model, it takes t 1 = 50 days for the new roll to start wearing 1 mm, which is consistent with the obvious wear marks after 2 months during on-site maintenance; the number of billets C 1 = 50 * 740 = 37000 billets are required for the production wear estimation when starting to wear 1 mm.

[0061] Table 2: Estimation Model of Wear Amount

[0062]

[0063]

[0064] Step 3: Adjust the roll diameter according to half of the number of billets with the first wear estimation, and obtain the new roll speed of the pinch roll according to the adjusted roll diameter.

[0065] The number of billets with the first wear estimation for adjusting the roll diameter C 1 = half of 37000. When the actual number of billets reaches C 1 / 2 = 18500, make the first adjustment x 1 / 2 = 0.5 mm for the wear amount of 1 mm, then the speed difference = 0.8x 1 / 2 = 0.4 mm / s, and adjust the speed of the pinch roll to 120 + 0.4 = 120.4 mm / s through PLC control;

[0066] When the actual number of billets reaches 37000, make the second adjustment x 2 / 2 = 1mm, then the speed difference = 0.8x 2 / 2 = 0.8mm / s, then the speed of the pinch roll is adjusted to 120 + 0.8 = 120.8mm / s through PLC control;

[0067] When the actual number of billets reaches 55500, the third adjustment is made for the wear amount of 3mm x 3 / 2 = 1.5mm, then the speed difference = 0.8x 3 / 2 = 1.2mm / s, then the speed of the pinch roll is adjusted to 120 + 1.2 = 121.2mm / s through PLC control;

[0068] And so on. When the total number of billets reaches the set value (for example, 133117 pieces), a new roll is replaced.

[0069] In a certain actual production, the adjustment period of the actual number of billets is 20000 pieces (not the theoretical calculation of 18500 pieces). This is mainly to prevent excessive correction of the speed of the pinch roll. Every 20000 pieces, the set roll diameter of the roll is reduced by 1mm (equivalent to a wear radius of 0.5mm). In this way, the speed difference △V between the roll speed and the linear speed of the rolling mill is always controlled within 0.8mm / s, which can greatly reduce the wear amount of the roll; verified according to reducing 1mm roll diameter for every 20000 pieces of steel, after rolling 300000 pieces of steel, the actual wear of the new roll is reduced by 15mm in roll diameter, that is, the wear degree of the roll is only 7.5mm, which is much less than the original wear of 20mm when rolling 133200 pieces of steel, indicating that the method of the present invention is basically consistent with the actual production adjustment value.

[0070] Figure 4 It is the PLC control flowchart in a certain actual production process. Whenever a new roll of the pinch roll is replaced, the number of steel pieces passing through is cleared, and then the actual number of steel pieces passing through is re-counted through the tracking signal of the rolling mill. The count value is set as y. When y is less than 20000, the roll diameter of the pinch roll is set to the initial roll diameter of 300mm, and then for every increase of 20000 pieces, the set roll diameter is reduced by 1mm. When the count value reaches 300000 pieces, the set roll diameter no longer decreases, and an alarm is output to prompt the maintenance personnel that the life of the pinch roll has expired and needs to be replaced.

[0071] In actual production, it is set to 20000 pieces for the speed adjustment of the pinch roll. This value can be further optimized according to the actual situation on site, as long as the set roll diameter of the roll is infinitely close to the actual roll diameter, so as to achieve that the linear speed difference △V is within the controllable range, and then control the roll from wearing too fast.

[0072] Based on the above-mentioned ideal embodiments of the present invention as inspiration, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A control method for reducing the roll grinding amount of the pinch roll in front of the high-speed wire mill, characterized in that, it includes the following steps: Step 1: Calculate the speed difference according to the average line speed of the rolling mill and the line speed of the pinch roll after the new roll is worn; The calculation formula for the speed difference is: △V = v - (D - 2x) * π * (d / S) (1) where, v is the average line speed of the rolling mill, D is the diameter of the new roll, x is the wear amount of the new roll, d is the line speed of the new roll, and S is the circumference of the new roll; Step 2: Calculate the wear relative coefficient according to the wear amount and the theoretical wear coefficient; calculate the wear estimation coefficient according to the wear relative coefficient and the theoretical life of the new roll; calculate the wear estimation time according to the wear estimation coefficient and the wear relative coefficient; obtain the wear estimation billet number according to the wear estimation time and the daily production billet number; The calculation formula for the wear relative coefficient is: a i = A / x i , i = 1 - A(2) where A is the theoretical wear coefficient, x i is the wear amount, and i is an integer; The calculation formula for the wear estimation coefficient is: b i = T / sum(a i ) (3) Among them, T is the theoretical life of the new roll, in days; a i is the relative wear coefficient; The calculation formula for the wear estimation time is: t i = a i * b i (4) Among them, a i is the relative wear coefficient; b i is the wear estimation coefficient, with the unit of day; The calculation formula for the wear estimation billet number is: C i = t i * c(5) where t i is the wear estimation time in days; c is the number of billets produced per day; Step 3: Adjust the roll diameter according to half of the first wear estimation billet number, and obtain the new roll speed of the pinch roll according to the adjusted roll diameter.

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