Prevention method for surface defects of 430 stainless steel

Abstract

The invention belongs to the technical field of stainless steel surface processes, and particularly relates to a 430 stainless steel surface defect prevention method which comprises the following steps: (1) adjusting the pressure of a side guide head part according to the thickness of a steel belt; (2) adding a program to enable the coiling tension to identify the coiling weight; (3) the rigidity precision of the pinch roll is improved; (4) additionally arranging vertical wheels on the working side and the transmission side of the side guide; (5) pre-treating the new wrapper roller by adopting a roller ironing process after the new wrapper roller is put on a machine; (6) a welding rod made of a 1Cr13 material cannot be used, and a W-shaped staggered welding process is adopted between welding beads; (7) the head CT precision in the coiling process is precisely controlled by adjusting the heat conduction coefficient of each cooling section and the target temperature of the cooling section; (8) controlling the roll gap of the wrapper roll to display the actually measured deviation; (9) the blocked water nozzle is found in time, and the water nozzle with the small flow is still replaced after manual dredging; and (10) a powder wear-resistant lining plate is adopted as the lining plate. According to the method, the surface defect problems of pinch roll scratches and wrapper roll marks are reduced, and the product percent of pass is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel surface processing, and in particular relates to a method for preventing surface defects of 430 stainless steel. Background Art

[0002] Among the surface defects of 430 steel, defects caused by coiling machines account for more than 70%, which are mainly reflected in the scratches of pinch rollers and the marks of auxiliary coiling rollers. Domestic 430 steel manufacturers have made positive improvements in the surface quality of 430 steel, such as the side water blowing flow of pinch rollers before coiling, pressure control, improvement of auxiliary coiling roller accuracy, and the addition of spare pressure tanks. Although these have played a positive role in improving the surface quality of 430 steel, they are also applicable to the 2250 line. However, the characteristics of 430 steel such as heat fatigue resistance are not enough, and surface defects still exist. The main reasons for the scratches of pinch rollers are as follows: (1) At present, the domestic coiling side guide uses a liner side guide. The head pressure of the coiling side guide is small. After the strip bites into the pinch roller, the strip cannot be quickly centered. The strip is wrapped around the head of the reel for several turns and seriously deviates from the center of the reel. After the side guide is completely closed, friction occurs between the strip and the side guide. In addition, the liner is prone to point contact. The side guide is subjected to large force and sparks. The sparks of the side guide are brought to the surface of the pinch roller to form scratches; (2) The reel speed fluctuates greatly with the change of coiling weight. With the same tension and different coiling weight, the reel speed will be different after finishing and polishing. The change of reel speed will cause scratches.

[0003] The main reasons for the roller marks on the winding roller are as follows: (1) Regular welds are imprinted on the steel plate surface due to adhesives on the surface of the winding roller or uneven hardness of the winding roller surface; (2) The precision of the winding roller is not up to standard, especially the horizontal precision of the winding roller is not up to standard, resulting in a pull-out defect in the 6-10 turns of the steel coil head; (3) The roller surface of the winding roller is not evenly cooled, and the high-temperature strip steel causes annealing of the roller surface and causes adhesion. Summary of the invention

[0004] The purpose of the invention is to provide a method for preventing surface defects of 430 stainless steel, so as to solve the problems of scratches and roller marks on the surface of 430 stainless steel.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: A method for preventing surface defects of 430 stainless steel, comprising the following contents: (1) According to the thickness of the steel strip, adjust the pressure of the side guide head; the thicker the strip, the greater the pressure of the side guide head. The pressure of the side guide head is the set pressure of the side guide belt body * coefficient. The greater the pressure of the side guide head, the faster the side guide head moves. In order to quickly clamp the head of the strip and avoid the tower shape, let the strip roll in the center of the reel. There is a gap of 30mm on each side between the strip and the side guide before the strip enters the side guide. After the strip bites into the pinch roller, the side guide is quickly closed. Only when the side guide and the strip have a certain contact force can the side guide reach or find the set pressure. The set pressure on the control system is the parameter sent by the process control machine. After the side guide contacts the strip on site, the pressure sensor will collect the pressure. The closer the actual pressure collected on site on the control system is to the set pressure, the better; (2) Add a program to make the winding tension identify the winding weight and stabilize the winding speed; different winding weights require different winding tensions. The winding weight is divided into three levels through the program, and different winding weights correspond to different winding tensions to stabilize the winding speed; (3) Improve the stiffness and accuracy of the pinch roller. The specific contents are as follows: <1> Before leaving the factory, each time the pin hole sleeve is replaced, the platform is put on for elevation inspection; <2> Add a gasket under the pinch roller bearing seat to adjust the pinch roller stiffness. For every 1mm gasket added, the pressure can be reduced by about 16kn. <3> Adjust the eccentric pin according to the roller gap deviation before zeroing, and the roller gap deviation on both sides of the working side and the transmission side 0.2; (4) Additional wheels are added on the working side and transmission side of the side guide to convert the sliding friction between the strip and the side guide into rolling friction, thus reducing the generation of sparks between the side guide and the strip; (5) After the new auxiliary roll is put on the machine, it is pre-treated by the hot roll process. High-temperature stainless steel above 780 degrees is not rolled within 48 hours, and specifications with strength above T500 are not rolled within 48 hours; (6) Improve the surface surfacing process of the winding roller. Do not use 1Cr13 welding rods. Use W-shaped staggered welding process between welds to improve the hardness of the winding roller surface. (7) By adjusting the heat transfer coefficient of each cooling section and the target temperature of the cooling section, the head CT accuracy during the coiling process is precisely controlled; the heat transfer coefficient is adjusted from 0.9 to 1.1, the temperature sensitive system is adjusted from 0.3 to 0.16, and the target temperature and head temperature are adjusted with a difference of 10 degrees; (8) Control the measured deviation of the roll gap of the auxiliary roll, select automatic zero adjustment, manually press and test for a second time, and then manually correct the roll gap control method. This method can accurately control the deviation between the display of the auxiliary roll and the actual measurement on site; (9) Timely find the blocked water nozzles, replace the ones with small flow after manual unblocking, and control the uniformity of cooling water in the full width direction of the auxiliary roll; (10)The liner adopts a powder wear-resistant liner. When the strip steel contacts the liner, friction occurs. There is no adhesion on the liner, and the wear presents as powdery iron filings, which will not press on the surface of the steel plate.

[0006] Preferably, in the above (1), when H ≤ 2.0 mm, the pressure at the side guide head is 1.23 * the set pressure; when 2.0 < H ≤ 3.4, the pressure at the side guide head is 1.2 * the set pressure; when 3.4 < H ≤ 4.0, the pressure at the side guide head is 1.15 * the set pressure; when 4.0 < H ≤ 5.0, the pressure at the side guide head is 1.16 * the set pressure; when 5.0 < H ≤ 6.5, the pressure at the side guide head is 1.1 * the set pressure; when 6.5 < H ≤ 8, the pressure at the side guide head is 0.9 * the set pressure; when 8.0 < H, the pressure at the side guide head is 1 * the set pressure, where H is the thickness of the steel strip and the unit of the set pressure is kn.

[0007] Preferably, in the above (2), it also includes an accurate alarm function for the coiling tension screen. The program design alarm is divided into 4 segments. When the coiler speed - the speed of the lower pinch roll is less than 0, a yellow tension alarm is generated on the screen. When the coiler speed - the speed of the lower pinch roll is within the range of 0 - 0.8 m / s, the screen shows green indicating the normal range. When the coiler speed - the speed of the lower pinch roll is within the range of 0.8 - 1.2 m / s, the screen shows pink to prompt the operator to intervene to reduce the coiling tension. When the coiler speed - the speed of the lower pinch roll is greater than 1.2 m / s, the screen shows red to prompt that immediate intervention is required, and failure to intervene will result in surface scratch defects.

[0008] Preferably, in the above (2), it also includes an optimized production scheduling structure. Coils with similar weights are scheduled for production together. The coil weights are divided into three grades, namely below 18 tons, 18 - 23 tons, and above 23 tons. Coils with the same grade of weight are scheduled for production together, avoiding frequent switching of the required coiling tension by the system due to different weights, which affects work efficiency and increases energy consumption.

[0009] Preferably, in the above (4), there are 5 vertical wheels on both the working side and the driving side. The radial force Fr of the vertical wheel is 50000 N, the axial force Fa is 10000 N, the circumferential force Ft is 50000 N, the journal diameter d1 is 55 mm, the rotational speed n is 1000 r / min, the designed life Lh' is 2000 h, the acting point distance L is 200 mm, the distance L1 between Fr and bearing 1 is 100 mm, the distance La between Fr and the axis line is 100 mm, the temperature coefficient ft is 1, the lubrication method Grease is oil lubrication, the bearing type is tapered roller bearing, the bearing inner diameter d is 55 mm, and the basic static load rating Co is 270000 N.

[0010] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1)Identify the coiling weight through the coiling tension. After the finishing mill casts off the steel, the reel speed remains unchanged to avoid the generation of scratches. (2)Adjust the pressure at the head of the side guide through the strip thickness to achieve rapid centering of the strip. Combine with the vertical wheels to change the sliding friction between the strip and the side guide into rolling friction, reduce the generation of sparks between the side guide and the strip, and avoid the formation of scratches on the surface of the pinch roll. (3)Vertical wheels are added on both the working side and the driving side. The friction between the strip and the side guide is rolling friction, and there is almost no spark. (4)Do not coil high-temperature steel above 780 degrees within 48 hours to prevent the surface annealing from reducing the hardness, not generating adhesives, and avoiding the coiling roll mark defect. Combine with controlling the uniformity of the coiling roll cooling water in the full-width direction to prevent the coiling roll surface from annealing due to the high-temperature strip and causing adhesion. (5)By replacing the electrode material and optimizing the welding process, improve the hardness of the coiling roll surface to avoid the regular weld bead marks on the steel plate surface caused by uneven hardness. (6)The CT stability at the head of the thick gauge has a great influence on the coiling shape appearance and the coiling roll marks. By adjusting the heat transfer coefficient of each cooling section and the target temperature of the cooling section, accurately control the CT accuracy during coiling to prevent the strip from slipping between the strip and the coiling roll during the head coiling process and reduce the roll marks. (7)By controlling the measured deviation of the coiling roll gap display, avoid the slipping caused by the too large coiling roll gap, and at the same time prevent the large impact on the coiling roll caused by the too small coiling roll gap and resulting in adhesion. Specific implementation method

[0011] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0012] A method for preventing surface defects of 430 stainless steel includes the following content: (1)Adjust the pressure at the head of the side guide according to the strip thickness. The thicker the strip, the greater the pressure required at the head of the side guide. The pressure at the head of the side guide is the set pressure of the side guide strip body * coefficient. The greater the pressure at the head of the side guide, the faster the action speed of the head of the side guide. In order to quickly clamp the head of the strip and not appear tower shape, let the strip coil at the center position of the reel. There is a 30mm gap on each side between the strip and the side guide before the strip enters the side guide. After the strip bites into the pinch roll, the side guide quickly closes. Only when there is a certain contact force between the side guide and the strip can the side guide reach or find the set pressure. The set pressure on the control system is the parameter sent by the process control machine. The pressure sensor will collect the pressure after the side guide and the strip contact on site. The closer the actual pressure collected on site to the set pressure on the control system, the better. When 3.4 < H ≤ 4.0, the pressure at the head of the side guide is 1.15 * the set pressure, where H is the strip thickness. (2) Add a program to make the winding tension identify the winding weight and stabilize the reel speed; different winding weights require different winding tensions. The winding weight is divided into three levels through the program. Different winding weights correspond to different winding tensions to stabilize the reel speed; the winding tension screen has an accurate alarm function. The program is designed to have an alarm divided into 4 sections. When the reel speed - the lower pinch roller speed is less than 0, the screen generates a yellow tension alarm. When the reel speed - the lower pinch roller speed is within the range of 0-0.8m / s, the screen displays green to indicate the normal range. When the reel speed is - When the speed of the lower pinch roller is within the range of 0.8-1.2m / s, the screen displays a pink prompt that the operator needs to intervene to reduce the roll tension. When the roll speed - the speed of the lower pinch roller is greater than 1.2m / s, the screen displays a red prompt that immediate intervention is required. Failure to intervene will cause surface scratch defects. Optimize the production scheduling structure, and schedule production of rolls with similar weights. The roll weight is divided into three levels, namely, below 18 tons, 18-23 tons, and above 23 tons. The rolls in the same weight level are scheduled together. The winding tension settings at different stages are shown in Table 1.

[0013] Table 1 Winding tension settings at different stages

[0014] (3) Improve the stiffness and accuracy of the pinch roller. The specific contents are as follows: <1> Before leaving the factory, each time the pin hole sleeve is replaced, the platform is put on for elevation inspection; <2> Add a gasket under the pinch roller bearing seat to adjust the pinch roller stiffness. For every 1mm gasket added, the pressure can be reduced by about 16kn. <3> Adjust the eccentric pin according to the roller gap deviation before zeroing, and the roller gap deviation on both sides of the working side and the transmission side 0.2; (4) Five vertical wheels are added on the working side and transmission side of the side guide. The radial force of the vertical wheel is Fr = 50000N, the axial force is Fa = 10000N, the circumferential force is Ft = 50000N, the journal diameter is d1 = 55mm, the speed is n = 1000r / min, the design life is Lh' = 2000h, the action point distance is L = 200mm, the distance between Fr and bearing 1 is L1 = 100mm, the distance between Fr and the axis centerline is La = 100mm, the temperature coefficient is ft = 1, the lubrication method is Grease = oil lubrication, the bearing type is a tapered roller bearing, the bearing inner diameter is d = 55mm, the basic rated static load is Co = 270000N, the sliding friction between the strip and the side guide is changed to rolling friction, and the spark generation between the side guide and the strip is reduced; (5) After the new auxiliary roll is put on the machine, it is pre-treated by the hot roll process. High-temperature stainless steel above 780 degrees is not rolled within 48 hours, and specifications with strength above T500 are not rolled within 48 hours; (6) Improve the surface surfacing process of the winding roller, use 3Cr13Mn welding rod, the surface hardness of which can reach HRC60, and adopt W-shaped staggered welding process between welds to improve the surface hardness of the winding roller; (7) By adjusting the heat transfer coefficient of each cooling section and the target temperature of the cooling section, the head CT accuracy during the coiling process is precisely controlled; the heat transfer coefficient is adjusted from 0.9 to 1.1, the temperature sensitive system is adjusted from 0.3 to 0.16, and the target temperature and head temperature are adjusted with a difference of 10 degrees; (8) Control the measured deviation of the roll gap of the auxiliary roll, select automatic zero adjustment, manually press and test for a second time, and then manually correct the roll gap control method. This method can accurately control the deviation between the display of the auxiliary roll and the actual measurement on site; (9) Timely find the blocked water nozzles, replace the ones with small flow after manual unblocking, and control the uniformity of cooling water in the full width direction of the auxiliary roll; (10) The lining plate adopts powder wear-resistant lining plate. Friction is generated when the strip steel contacts the lining plate. The lining plate is not bonded and the wear and tear will show powdery iron chips, which will not be pressed on the surface of the steel plate.

[0015] Before using this method, the maximum deviation between the auxiliary winding roller display and the actual measurement was 3.0mm. After using this method, the deviation was reduced to 0.6mm. Set wheels were added to the working side and the transmission side. There was rolling friction between the strip and the side guide. There was almost no spark observed on site.

[0016] After using this method, the surface defects of the 430 coil caused by the pinch roller and auxiliary roller of the coiler were reduced from 1.79% to 1.12%, which improved the qualified rate and reduced the cost, which was much lower than the average unqualified rate of 1.55% of its peers.

Claims

1. A method for preventing surface defects of 430 stainless steel, characterized in that: It includes the following: (1) According to the thickness of the steel strip, adjust the pressure of the side guide head; the thicker the strip, the greater the pressure of the side guide head. The pressure of the side guide head is the set pressure of the side guide belt body * coefficient. The greater the pressure of the side guide head, the faster the side guide head moves. In order to quickly clamp the head of the strip and avoid the tower shape, let the strip roll in the center of the reel. There is a gap of 30mm on each side between the strip and the side guide before the strip enters the side guide. After the strip bites into the pinch roller, the side guide is quickly closed. Only when the side guide and the strip have a certain contact force can the side guide reach or find the set pressure. The set pressure on the control system is the parameter sent by the process control machine. After the side guide contacts the strip on site, the pressure sensor will collect the pressure. The closer the actual pressure collected on site on the control system is to the set pressure, the better; (2) Add a program to make the winding tension identify the winding weight and stabilize the winding speed; different winding weights require different winding tensions. The winding weight is divided into three levels through the program, and different winding weights correspond to different winding tensions to stabilize the winding speed; (3) Improve the stiffness and accuracy of the pinch roller. The specific contents are as follows: <1> Before leaving the factory, each time the pin hole sleeve is replaced, the platform is put on for elevation inspection; <2> Add a gasket under the pinch roller bearing seat to adjust the pinch roller stiffness. For every 1mm gasket added, the pressure can be reduced by about 16kn. <3> Adjust the eccentric pin according to the roller gap deviation before zeroing, and the roller gap deviation on both sides of the working side and the transmission side 0.2; (4) Additional wheels are added on the working side and transmission side of the side guide to convert the sliding friction between the strip and the side guide into rolling friction, thus reducing the generation of sparks between the side guide and the strip; (5) After the new auxiliary roll is put on the machine, it is pre-treated by the hot roll process. High-temperature stainless steel above 780 degrees is not rolled within 48 hours, and specifications with strength above T500 are not rolled within 48 hours; (6) Improve the surface surfacing process of the winding roller. Do not use 1Cr13 welding rods. Use W-shaped staggered welding process between welds to improve the hardness of the winding roller surface. (7) By adjusting the heat transfer coefficient of each cooling section and the target temperature of the cooling section, the head CT accuracy during the coiling process is precisely controlled; the heat transfer coefficient is adjusted from 0.9 to 1.1, the temperature sensitive system is adjusted from 0.3 to 0.16, and the target temperature and head temperature are adjusted with a difference of 10 degrees; (8) Control the measured deviation of the roll gap of the auxiliary roll, select automatic zero adjustment, manually press and test for a second time, and then manually correct the roll gap control method. This method can accurately control the deviation between the display of the auxiliary roll and the actual measurement on site; (9) Timely find the blocked water nozzles, replace the ones with small flow after manual unblocking, and control the uniformity of cooling water in the full width direction of the auxiliary roll; (10) The lining plate adopts powder wear-resistant lining plate. Friction is generated when the strip steel contacts the lining plate. The lining plate is not bonded and the wear and tear will show powdery iron chips, which will not be pressed on the surface of the steel plate.

2. A method for preventing surface defects of 430 stainless steel according to claim 1, characterized in that: In (1), when H ≤ 2.0 mm, the side guide head pressure is 1.23 * set pressure; when 2.0 < H ≤ 3.4, the side guide head pressure is 1.2 * set pressure; when 3.4 < H ≤ 4.0, the side guide head pressure is 1.15 * set pressure; when 4.0 < H ≤ 5.0, the side guide head pressure is 1.16 * set pressure; when 5.0 < H ≤ 6.5, the side guide head pressure is 1.1 * set pressure; when 6.5 < H ≤ 8, the side guide head pressure is 0.9 * set pressure; when 8.0 < H, the side guide head pressure is 1 * set pressure, where H is the steel strip thickness and the unit of set pressure is kn.

3. A method for preventing surface defects of 430 stainless steel according to any one of claims 1 or 2, characterized in that: In (2), it also includes the precise alarm function for the coiling tension screen. The program design alarm is divided into 4 segments. When the coiler speed - the speed of the lower pinch roll is less than 0, a yellow tension alarm is generated on the screen; when the coiler speed - the speed of the lower pinch roll is within the range of 0 - 0.8 m / s, the green color on the screen indicates the normal range; When the coiler speed - the speed of the lower pinch roll is within the range of 0.8 - 1.2 m / s, the pink color on the screen prompts the operator to intervene to reduce the coiling tension; when the coiler speed - the speed of the lower pinch roll is greater than 1.2 m / s, the red color on the screen prompts that immediate intervention is necessary, and if not intervened, surface scarring defects will occur.

4. A method for preventing surface defects of 430 stainless steel according to claim 3, characterized in that: In (2), it also includes optimizing the production scheduling structure. Coils with similar weights are scheduled for production together. The coil weights are divided into three grades, namely below 18 tons, 18 - 23 tons, and above 23 tons. Coils with the same grade of weight are scheduled for production together to avoid the system frequently switching the required coiling tension due to different weights, which affects work efficiency and increases energy consumption.

5. A method for preventing surface defects of 430 stainless steel according to claim 4, characterized in that: In (4), there are 5 vertical wheels on both the working side and the drive side. The radial force Fr of the vertical wheel is 50000 N, the axial force Fa is 10000 N, the circumferential force Ft is 50000 N, the journal diameter d1 is 55 mm, the rotational speed n is 1000 r / min, the designed life Lh' is 2000 h, the acting point distance L is 200 mm, the distance L1 between Fr and bearing 1 is 100 mm, the distance La between Fr and the axis line is 100 mm, the temperature coefficient ft is 1, the lubrication method Grease is oil lubrication, the bearing type is tapered roller bearing, the bearing inner diameter d is 55 mm, and the basic static load rating Co is 270000 N.

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