A method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill

Abstract

This invention discloses a method for controlling the dynamic bite and slippage of the strip at the entrance stand of a hot strip mill. The hot strip mill has a lower work roll and a lower support roll below the rolling center, and an upper work roll and an upper support roll above it. The method includes: the distance between the top of the lower work roll and the stand base plate is the elevation; a shim adjustment area is provided between the bottom of the lower support roll and the stand base plate; when replacing the support roll and calculating the shim, the elevation is raised by 2-10mm, allowing the strip head to bite tightly against the lower roll surface when entering the entrance stand; the roll diameter ranges from F1 to F3 (0-30mm), and from F4 to F7 (0-20mm), with all maximum roll diameters used in the F1 stand, followed by the F2 and F3 stands; the roll gap + impact bounce = exit thickness is set; all mechanical clearances are eliminated through zero-adjustment pre-pressure of the new roll; the clamping force of the pinch rolls is 5-20 kN, and the rotation speed of the pinch rolls is synchronized with the speed of the roller table. This invention can effectively reduce slippage during dynamic engagement of the inlet rack.

Description

Technical Field

[0001] This invention relates to the field of material supply control for finishing mills, specifically to a method for dynamic steel biting and slippage prevention at the entrance stand of a hot strip mill. Background Technology

[0002] The finishing mill is the core equipment of the entire main rolling line. Its operational stability directly affects the line's capacity utilization and quality improvement. The finishing mill consists of seven four-high mills, F1 to F7. Each mill is composed of upper and lower work rolls and upper and lower support rolls. In daily production rolling, slippage usually occurs at the entrance stands F1 and F2. This is mainly because the intermediate slab thickness of the incoming material is large in these two stands, and the relative reduction amount and reduction rate of these stands are much greater than those of the subsequent stands. In particular, the F1 stand is the first mill entering the line, and it is most prone to slippage due to fluctuations in incoming material thickness, incoming material head temperature, incoming material head shape, and head descaling water. At the same time, as the support rolls are used for a longer period, the slippage phenomenon will become more and more serious due to factors such as roll surface roughness and uneven wear of the roll diameter. The consequences of slippage are that the incoming material cannot be properly bitten into the scrap steel, or even if it is bitten in, the strip shape and dimensional accuracy will be abnormal, and the quality of the strip head cannot be guaranteed, resulting in significant losses. Slippage in the stands also has a fatal impact on the main drive shaft, gearbox, reducer, and large motor of the equipment.

[0003] Problems and Control Measures of Existing Technologies

[0004] The existing 2050 finishing mill is basically the same as the existing hot strip mills of domestic and foreign manufacturers. They are all four-high continuous rolling mills, with the support rolls passively driven by the work rolls. Therefore, based on our understanding, other manufacturers also frequently encounter the phenomenon of dynamic steel biting and slippage in the inlet stand. Regarding the slippage in the current 2050 hot strip mill, the causes and existing control measures are as follows:

[0005] 1. If the front stand of the finishing mill slips and has difficulty biting in or if scrap steel is found, the operator will reduce the thickness of the intermediate billet to maintain production and reduce the frequency of stand slippage. However, this cannot completely solve the problem of stand slippage, but can only relatively control and reduce the frequency of slippage. The method of thinning the intermediate billet will result in a long rolling rhythm for a single strip, which will affect the capacity utilization, affect the product compression ratio, and lead to substandard internal mechanical properties.

[0006] 2. If the entry stand of the finishing mill experiences slippage and difficulty in biting in or scrap steel, and the operator cannot eliminate the problem by thinning the intermediate billet, the number of descaling passes at the head of the incoming material will be reduced. Although this helps to control slippage, it will also reduce the surface quality of the strip head, causing the oxide scale to be pressed into the surface per unit length of the head, which will affect the product quality.

[0007] 3. If the entry stand of the finishing mill slips and has difficulty biting in or if scrap steel is found, the operator will reduce the load reduction of that stand. However, this method will also shift the overall load to the rear stand, causing the oxide film on the roll surface to peel off due to the increased load, resulting in surface quality problems of the strip steel.

[0008] 4. If the entry stand of the finishing mill experiences slippage and difficulty in biting in or scrap steel, the operator may adjust other process parameters after adjusting the relevant measures, such as increasing the temperature of the strip head, increasing the strip threading speed, and reducing the cooling water of the rolls, because the effect is not obvious. However, these measures are all done after the fact and it is difficult to find a solution to the slippage of the entry stand from the source.

[0009] Therefore, if the entry stand of the finishing mill experiences slippage and difficulty in biting in or scrap steel, and the relevant operators are able to adjust and implement measures in a timely manner, uncertain slippage may still occur. In the end, the machine must be stopped to replace the support rolls or work rolls, which will disrupt the rolling line maintenance and roll replacement cycle, and its impact will be even greater.

[0010] The hot continuous rolling mill in question refers to the finishing F1 stand. The main issue is that the F1 stand frequently experiences unexplained slippage when the intermediate billet enters the finishing continuous rolling mill. Once this slippage occurs, it can lead to minor issues like errors in strip dynamic tracking, resulting in strip size and shape quality problems. In severe cases, discrepancies between dynamic tracking and actual strip quality can cause serious scrap accidents. This phenomenon severely disrupts normal production line operations, significantly impacting output, quality, cost, and safety. It is necessary to identify the causes and control methods for the stand's slippage to ensure the safe and smooth operation of the production line. Summary of the Invention

[0011] Therefore, the technical problem to be solved by the present invention is to provide a method for controlling the dynamic steel biting and slippage of the inlet stand of a hot strip mill.

[0012] By analyzing the causes of slippage at the entrance stand of Baosteel's 2050 hot strip mill over the years and repeatedly seeking control solutions in field practice, this invention combines theoretical analysis of stand slippage with control of the workpiece biting into the rolls, considering various actual operating conditions. The aim is to ultimately find a method to control and resolve dynamic biting slippage at the entrance stand from its source, thus addressing a series of existing slippage problems. The technical solution of this invention is as follows:

[0013] A method for controlling dynamic bite slippage at the entrance stand of a hot strip mill, the entrance stand including an F1 stand and an F2 stand, wherein a lower work roll and a lower support roll are arranged sequentially below the rolling center of the hot strip mill, and an upper work roll and an upper support roll are arranged sequentially above the rolling center; the method includes the following:

[0014] The distance between the top of the lower working roll and the bottom plate of the frame is the elevation; a pad adjustment area is provided between the bottom of the lower support roll and the bottom plate of the frame. When replacing the support roll and calculating the pad, the elevation is raised by 2-10mm so that the strip head bites tightly against the lower roll surface when entering the inlet frame.

[0015] Within the support roller replacement cycle, before replacing the support roller, confirm the actual roller diameter range of each frame's working rollers to determine the matching support roller diameter and pad thickness for this cycle, ensuring the usable range of the corresponding frame's actual working rollers within this cycle. The maximum roller diameter is the factory-issued new roller diameter, and the minimum roller diameter refers to the scrap roller diameter of the corresponding frame. Within one cycle after replacing the support roller, work rollers F1 to F3 should be based on the current maximum roller diameter, minus 0 to 30 mm; work rollers F4 to F7 should be based on the current maximum roller diameter, minus 0 to 20 mm. Frames within this roller diameter range can be used. In the next replacement cycle, the roller diameter after wear and re-grinding in the previous cycle is the current maximum roller diameter. Within one cycle after replacing the support roller, work rollers F1 to F3 should be based on the current maximum roller diameter, minus 0 to 30 mm; work rollers F4 to F7 should be based on the current maximum roller diameter, minus 0 to 20 mm. This continues until the working rollers are worn down to a diameter smaller than the scrap roller diameter. Meanwhile, within this cycle, relatively large roller diameters within the range of F1 to F3 will be used on the F1 frame, followed by the F2 and F3 frames.

[0016] Roll gap setting: Roll gap setting + impact bounce = exit thickness; All mechanical clearances are eliminated through zero-adjustment preload of the new roll;

[0017] The strip is conveyed into the rolling mill by the rotational force of the roller conveyor and the rotational friction of the strip surface. The clamping force of the pinch rollers is 5 to 20 kN. At the same time, the rotational speed of the pinch rollers is matched and synchronized with the speed of the roller conveyor.

[0018] Currently, the calculation of the pad thickness is based on the roller diameter of the frame support roller plus the roller diameter of the working roller provided in this cycle. The required pad thickness is determined by rounding rules and is also determined in conjunction with the standard specifications of the pads configured on site.

[0019] The entry stand has seven identical stands, the first called F1 and the seventh F7. The maximum new roll diameter for F1-F3 is 850mm, and the scrap roll diameter is 765mm. The maximum new roll diameter for F4-F7 is 765mm, and the scrap roll diameter is 685mm. The continuous rolling mill unit has seven stands, F1-F7. The roll diameter range for F1-F3 is 0-30mm, and for F4-F7 it is 0-20mm. This means that after the support roll diameter used in this cycle is determined, the maximum to minimum working roll diameter to be matched is within the range of 0-30mm and 0-20mm. For example, the maximum new working roll diameter for F1-F3 is 850mm, and according to the allowable usage range of 0-30mm, the roll diameter range used in this cycle is 850-820mm. After a period of use, the work rolls will wear down. The maximum diameter of the work rolls is 840mm. Adjustments are made to the support rolls with shims, but the working roll diameter still falls within the 0-30mm range. Since the maximum diameter of all work rolls on this frame is only 840mm, and the allowable range is 0-30mm, the working roll diameter range for this frame is 840-810mm. After another cycle of use, due to wear, the maximum working roll diameter may become 830mm. During the next support roll replacement cycle, the range will be 0-30mm, meaning the maximum usable diameter will be 830mm - 30mm = 800mm, and the range will be 830-800mm. This continues until the diameter drops below 765mm, at which point the rolls are scrapped. The scrapping diameter range is clearly defined: for F1-3, the maximum new roll diameter is 850mm, and the scrapping diameter is 765mm. For F4-7, the maximum new roll diameter is 765mm, and the scrapping diameter is 685mm.

[0020] The working roll diameters of the seven stands F1 to F7 vary with the tonnage of the strip being rolled, and each roll needs to be re-ground on a grinding machine. Therefore, the so-called maximum working roll diameter also changes dynamically (the maximum working roll diameter mentioned in the text refers to the new roll from the manufacturer, which is 850mm, and the minimum working roll diameter refers to the scrapped roll diameter, which is 765mm).

[0021] Production line process specifications: The replacement cycle for support rollers is generally controlled at around one month, for example, 20-40 days. Before replacing support rollers, it is necessary to confirm the actual roller diameter range of the work rollers for each stand to determine the matching support roller diameter and backing plate thickness for this cycle, ensuring that the actual work rollers of the corresponding stand are within the usable range within this cycle. The work roller diameters of the seven stands F1 to F7 vary with the tonnage of the rolled strip and require grinding on a grinding machine each time. Therefore, the so-called maximum work roller diameter also changes dynamically (the maximum work roller diameter mentioned in the text refers to the new roller from the manufacturer, 850mm, and the minimum work roller diameter refers to the scrapped roller diameter, 765mm). After replacing the support rollers, within one cycle, work rollers F1 to F3 are adjusted to their current maximum diameter, minus 0 to 30 mm. Work rollers 4 to F7 are adjusted to their current maximum diameter, minus 0 to 20 mm. Frames within this roller diameter range can be used. At the same time, within this cycle, the relatively larger roller diameters within the F1 to F3 range are used on frame F1, followed by frames F2 and F3.

[0022] The roll gap is set according to the finished strip thickness and stand load distribution, based on the springback equation in rolling mill technology. The stand zero-adjustment accuracy is 1500 tons for the upper and lower work rolls (F1-F3) and 1000 tons for F4-F7. The existing process involves statically pressing to 300 tons after replacing the work rolls, then dynamically pressing to 1500 tons for stands F1-3 and 1000 tons for stands F4-7. The springback amount is calculated automatically by computer based on process parameters such as the hardness and specifications of the rolled product. The work roll replacement cycle is generally once per planned roll (maximum mileage less than 120 km, mainly determined by the planned structure and process). The support roll replacement cycle is approximately two months (about 1 million tons) for F1-3 and one month (about 500,000 tons) for F4-7.

[0023] Abnormal bouncing is generally ignored. Even if a rack has abnormal bouncing, the target value for the finished rack export is guaranteed after seven racks.

[0024] The strip is fed into the rolling mill by roller conveyor, which relies on the rotational force of the roller conveyor and the rotational friction of the strip surface. The general process specifies that the roller conveyor feeds the strip at a speed of 1 meter / second. The clamping force of the pinch rollers is 5 to 20 kN. At the same time, the rotational speed of the pinch rollers is matched and synchronized with the speed of the roller conveyor.

[0025] When the strip head bites into the inlet frame, the kinetic energy is affected by the different shapes of the strip head at that time, resulting in different vertical and horizontal components of force, which will cause changes in the biting conditions and ultimately lead to slippage.

[0026] The main consideration was to improve the bite angle of the strip entering the inlet stand. Before entering, the strip head needs to be cut off by a flying shear. However, since most of the cut heads are slightly upturned, if the rolling center line is too low, the slightly upturned head will be pressed down by the upper roller and then fed into the roll gap at the moment of biting into the stand. This can easily cause bite difficulties and slippage. Therefore, when replacing the support roller calculation plate, the elevation was specifically raised by a certain distance. This solves the problem of poor bite due to the upturned head, allowing the strip head to bite close to the lower roller surface when entering the inlet stand. This bite condition is much better than the bite condition when the elevation is too low, ensuring favorable bite at the inlet stand and preventing bite slippage.

[0027] Based on the bite angle conditions of the hot strip mill rolls, we analyzed the causes of slippage. Therefore, we made adjustments to the use of work roll diameters at the entrance stands. The current production line defines the entrance stands as two stands, F1 and F2. Based on years of experience with stand slippage, the first entrance stand has the highest probability of slippage. Therefore, we made new regulations for the use of grinding roll diameters. Currently, the roll diameter range for F1 to 3 is 0 to 30 mm, and the roll diameter range for F4 to 7 is 0 to 20 mm. All the largest roll diameters are used in the F1 stand, followed by the F2 and F3 stands. The larger work roll diameter is also the most advantageous from the bite angle theory, and can also minimize the probability of slippage at the entrance stand.

[0028] The roll gap setting is based on the bounce equation in the rolling mill principle. The principle is to set the exit thickness requirement according to the frame. The preset roll gap is the set roll gap + impact bounce = exit thickness. The premise is that all mechanical gaps are eliminated by zero adjustment and pre-pressure of the new roll. If the zero adjustment is inaccurate, there may be mechanical gaps that should be eliminated but are not eliminated, which will be superimposed on the set roll gap value and ultimately produce an exit thickness deviation.

[0029] This step places higher demands on the roll gap setting of the entry stand. If the roll gap is incorrectly set, the strip will experience a sudden change in bounce at the moment of biting, leading to an abnormal actual roll bite angle and slippage. Therefore, the zero-adjustment accuracy of the stand is crucial. If the zero-adjustment rolling force and zero-adjustment accuracy exceed the standard, it is considered a functional malfunction and must be addressed promptly. Furthermore, inaccurate roll gap setting is related to the service life and wear of the support rolls, so the replacement cycle must be clearly defined to reduce slippage caused by dynamic anomalies. Inaccurate roll gap setting mainly refers to the zero-adjustment required when new rolls are installed in the stand according to process specifications. This involves using a certain pre-pressure to compact all gaps between stands, ensuring the correctness of the pre-set embedded roll gap before strip rolling. When the strip enters the upper and lower rolls, the impact bounce is within the pre-calculated range, taking into account the pre-calculated embedded roll gap to avoid abnormal changes in the roll gap during bite due to unforeseen errors, which could lead to slippage.

[0030] To ensure the strip enters the inlet frame with sufficient kinetic energy, the main factor affecting the strip's gripping force is severe wear of the inlet frame guide plates. This wear can cause the strip to become stuck in the grooves of the excessively worn guide plates, increasing running resistance and resulting in insufficient kinetic energy. Additionally, the pushing force of the strip before it grips the frame is also influenced by the clamping force of the conveyor rollers and descaling pinch rollers. Insufficient pushing force from either of these sources will affect the inlet frame's gripping kinetic energy, leading to slippage during the gripping process. This places higher demands on equipment precision management. If strip slippage during gripping is caused by abnormal wear or precision degradation, it indicates a management failure. Before entering the inlet frame, the pushing force of the conveyor rollers alone is insufficient for normal gripping; the strip needs to be simultaneously gripped by the descaling pinch rollers before being fed into the frame to facilitate proper gripping and minimize slippage.

[0031] Sufficient kinetic energy can be guaranteed by the hot rolling process itself. However, due to various uncontrollable factors, the change in kinetic energy may not meet the requirements for steel biting, resulting in slippage. The speed at which the strip enters the inlet stand is not a fixed value. It changes continuously according to the different requirements of the rolled product, such as the steel grade, specifications, and mechanical properties. Currently, this is achieved automatically by the L2 computer and the L1 control system. The descaling and pinching roll pressure is also automatically set according to the different product thickness and width specifications. What we need to pay attention to is that the computer setting may be affected by other working conditions, resulting in the failure to meet the required biting conditions. In actual abnormal processes, we can also check and compare the computer setting with the actual curve stored in the basic automation register.

[0032] According to a method for controlling the dynamic steel biting and slippage of the inlet stand of a hot continuous rolling mill according to the present invention, it is preferable to raise the elevation by 5-10mm.

[0033] Preferably, during the replacement cycle of the support rollers, the relatively large roller diameters in the range of F1 to F3 are used on the F1 frame, followed by the F2 and F3 frames.

[0034] According to a method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill, preferably, in the roll gap setting, H0 = H + P / K, where H0 is the actual exit thickness, H is the set roll gap, P is the rolling force, and K is the mill stiffness coefficient.

[0035] According to a method for controlling dynamic steel biting and slippage at the entrance stand of a hot strip mill, the method preferably further includes the following: during dynamic shearing of the strip in operation, the shearing speed of the flying shear is greater than the running speed of the strip; and the shearing speed of the flying shear is corrected every 3-8 days.

[0036] Regarding the relationship between the shape of the strip head after shearing and slippage during bite entry, years of experience have revealed a significant correlation. Because our production line dynamically shears the incoming strip during operation, a mismatch between the roller conveyor speed and the flying shear's shearing speed directly impacts the shape of the strip head after shearing. If the flying shear's shearing speed is lower than its operating speed at the moment of shearing, the shear will carry the strip head along with it during its return to the waiting position after shearing. This results in the aforementioned upward-curving shape of most strip heads after shearing, which is detrimental to the strip's bite entry into the inlet frame and increases the likelihood of slippage. Therefore, we adjust and verify the flying shear's shearing speed weekly to ensure the shearing head does not hit the blade and to maintain a relatively flat head shape after shearing. The primary consideration is to provide the best possible head shape to facilitate bite entry into the inlet frame. If the mismatch between the dynamic roller conveyor speed and the dynamic shearing speed causes external factors to lead to the strip head curving or bumping, the result is a more favorable outcome.

[0037] The shearing speed does not affect slippage and does not participate in the bite speed, but it will affect the shape of the strip head after shearing, causing it to curl upwards or downwards, thus affecting the bite conditions. Furthermore, the shearing speed is 1–1.25 m / s. The shearing speed is determined by the process based on the shearing accuracy of the strip head and tail, and is generally matched with the roller conveyor speed of 1–1.25 m / s.

[0038] According to a method for controlling dynamic steel biting and slippage at the entrance stand of a hot strip mill, the method preferably further includes controlling the temperature of the strip head and the temperature of the billet in the heating furnace to be as consistent as possible.

[0039] Furthermore, the strip head refers to the first 8%-15% of the strip's length.

[0040] Temperature control at the head of the strip is primarily based on the fact that the head of the strip experiences significant heat dissipation and a large temperature drop. Additionally, different furnaces have varying heating temperatures for the strip billet. Therefore, it's desirable for the head temperature to be as consistent as possible with the middle of the billet. Our process control aims to keep the head temperature 0-30 degrees Celsius higher than the target temperature. However, this isn't the primary factor; in actual production, adjusting the head shearing amount can help maintain this, while also considering the yield rate. Currently, the longest billet in our production line furnaces is controlled within 11.5 meters, and the head temperature is generally controlled within 1-1.5 meters.

[0041] Controlling the strip head temperature is crucial for ensuring proper bite without slippage. Reducing descaling passes and increasing the temperature during the process can lead to various quality problems on the strip head surface. Even if slippage is controlled, the resulting quality issues are a case of penny-wise and pound-foolish, an undesirable approach. Therefore, I have higher requirements for slab head temperature control in the furnace to ensure that the strip does not slip due to excessively low temperature when biting into the inlet stand. Even if a low head temperature is detected, the water usage can only be adjusted in the roughing zone; descaling in the finishing zone cannot be arbitrarily reduced. The key is balancing slippage and strip head surface quality. In actual production, if continuous slippage occurs due to other factors, it may be necessary to temporarily resolve this abnormal continuous slippage by reducing the head descaling water usage, sacrificing some quality. However, this situation can be quickly resolved by adjusting the process temperature.

[0042] The requirements vary depending on the product specifications. In addition, the distance from the furnace to the finishing mill bite line is 600 meters, and the process is greatly affected by the working conditions. Generally, the higher the temperature, the smoother the bite, and vice versa. Reducing the amount of descaling water is a last resort method for immediate and temporary control and adjustment. Temperature control is mainly carried out in the heating furnace, while on the rolling line, the temperature drop is mainly controlled by controlling the speed and water consumption.

[0043] Beneficial effects

[0044] 1) The present invention provides a method for controlling dynamic bite slippage of the inlet stand of a hot strip mill. Without changing the structure of the peripheral equipment of the mill, the method mainly optimizes and improves the process control and equipment precision control based on the causes of slippage, which can minimize the occurrence of dynamic bite slippage of the inlet stand.

[0045] 2) The present invention provides a method for controlling the dynamic strip bite slippage of the inlet stand of a hot strip mill. This method does not increase the workload of the operators. It only requires the calculation and pre-adjustment of the inlet stand elevation before the replacement of the unit support rolls to optimize and improve the strip bite conditions and control the abnormal slippage caused by the failure to meet the bite conditions.

[0046] 3) The present invention provides a method for controlling the dynamic strip bite slippage of the inlet stand of a hot strip mill. By analyzing the strip bite conditions, it is clear which factors affect the bite. Through the analysis of these conditions before, during and after the process, and by taking practical and feasible improvement methods, the slippage problem caused by the inlet stand bite can be further controlled.

[0047] 4) This invention provides a method for controlling dynamic bite slippage at the entrance stand of a hot strip mill. After implementation, this method has largely solved the problem of bite slippage at the entrance stand. This patented technology analyzes and controls the bite conditions based on the stand's bite conditions, considering factors such as the shape of the workpiece head, resistance, and clamping force to improve the roll bite angle and reduce dynamic bite slippage. It has significant applicability and can be widely adopted for similar hot strip mill production lines. It generates considerable economic benefits in terms of accident control, cost savings, and safety risk management. Attached Figure Description

[0048] Figure 1 This is the process flow diagram for 2050 hot rolling.

[0049] Figure 2 This is a diagram of the actual production strip steel buckle.

[0050] Figure 3 This is the ideal strip bite diagram.

[0051] Figure 4 This is a diagram illustrating the difficulty in biting into the steel strip.

[0052] Figure 5 Diagram showing the snap-in state of the steel buckle.

[0053] Figure 6 Schematic diagram of the slightly upturned head of the strip being bitten in.

[0054] Figure 7 A schematic diagram of abnormal bouncing of the roll gap when the strip bites in.

[0055] Figure 8 Schematic diagram of the guide plate biting into the strip on one side.

[0056] Figure 9 Schematic diagram of strip feeding into the bite roll. Detailed Implementation

[0057] A method for controlling dynamic bite and slippage at the inlet stand of a hot strip mill, wherein the lower work roll and the lower support roll are arranged sequentially below the rolling center of the hot strip mill, and the upper work roll and the upper support roll are arranged sequentially above the rolling center (see...). Figure 3 The method includes:

[0058] The distance between the top of the lower working roller and the base plate of the frame is the elevation; a pad adjustment area is provided between the bottom of the lower support roller and the base plate of the frame (see...). Figure 5 When replacing the support roller calculation pad, raise the elevation by 2-10mm so that the strip head bites into the lower roller surface when entering the inlet frame;

[0059] Within each support roll replacement cycle, after confirming the reference roll diameter value, the applicable range of the roll diameter is as follows: F1 to F3 roll diameter wear range 0 to 30 mm, F4 to F7 roll diameter wear range 0 to 20 mm; all the largest roll diameters are used in the F1 frame, followed by the F2 and F3 frames.

[0060] Roll gap setting: Roll gap setting + impact bounce = exit thickness; All mechanical clearances are eliminated through zero-adjustment preload of the new roll;

[0061] The strip is conveyed into the rolling mill by the rotational force of the roller conveyor and the rotational friction of the strip surface. The clamping force of the pinch rollers is 5 to 20 kN. At the same time, the rotational speed of the pinch rollers is matched and synchronized with the speed of the roller conveyor.

[0062] Currently, the calculation of the pad thickness is based on the roller diameter of the frame support roller plus the roller diameter of the working roller provided in this cycle. The required pad thickness is determined by rounding rules and is also determined in conjunction with the standard specifications of the pads configured on site.

[0063] The process of this invention is as follows:

[0064] 001-Replacement of support roller diameter pad calculation and adjustment: F1 lower support roller diameter is 1515.68mm, theoretically calculated pad thickness is 57.16mm, actual added pad thickness is 65mm (considering the slippage factor of the inlet frame, it is 7.9mm more than the calculation), F1 working roller diameter is 820~850mm.

[0065] 002-Rolled strip steel plan 118772600100, steel tapping mark AP1056E5, steel grade specification \1277*3.99, furnace tapping temperature 1230 degrees, hardness group 01.

[0066] 003 - The roll numbers and diameters of the seven-stand work rolls during production according to this plan are as follows:

[0067] Table of finishing mill roll diameters and roll numbers for F1 to F7

[0068] F1 F2 F3 F4 F5 F6 F7 upper roller number 6605 6110 6525 9001 5512 5501 5523 Lower roller number 6606 6111 6115 9561 5513 5898 5525 upper roller diameter 834.21 795.88 795.95 707.66 729.97 714.11 753.32 Lower roller diameter 833.96 795.76 796.11 707.61 729.75 714.31 753.24

[0069] 004-Rolling Plan Finishing Roller F1~F7 Roll Gap Setting Parameters:

[0070] Finishing mill F1 to F7 parameter settings

[0071] frame thickness Roller gap Rolling force Compression ratio (%) speed Inlet temperature F1 24.61 23.94 24320 44.5 1.43 985 F2 14.15 13.62 22740 42.5 2.48 957 F3 9.65 9.19 18652 31.8 3.75 952 F4 6.81 6.18 15941 29.5 5.39 946 F5 5.15 4.36 13255 24.2 7.22 939 F6 4.14 3.9 11215 19.7 9.14 929 F7 3.61 3.99 8235 12.7 10.66 919

[0072] Figure 2 In actual production, it is generally difficult to ensure that the head of the hot strip is in an ideal straight state. The warped head has a direct impact on whether the dynamic biting of the inlet frame is smooth, and it is also a key factor causing abnormal slippage when the inlet frame bites the strip.

[0073] Figure 3 In actual production, the desired state of the rolled piece is that it is perfectly aligned with the rolling centerline, with a straight head shape and an optimal bite angle, minimizing the probability of slippage during dynamic bite.

[0074] Figure 4 In actual production, due to the low rolling centerline, the head of the workpiece contacts the upper work roll first, and the upper roll presses against the head of the workpiece to bite it in, which easily causes slippage. This state has the highest probability of slippage in actual production.

[0075] Figure 5 In actual production, to facilitate workpiece biting and reduce slippage as shown in Figure-4, we manually raise the rolling centerline by 5-10mm when changing the support rolls. This ensures that the workpiece head contacts the lower roll first upon biting, minimizing slippage.

[0076] Figure 6 In actual production, when the elevation is fixed and cannot be adjusted, we try to control the head of the rolled piece to be slightly raised after the flying shear cuts it. This is also conducive to the bite of the rolled piece and can relatively reduce the occurrence of dynamic bite slippage.

[0077] Figure 7 In actual production, under the condition that other conditions remain unchanged, if the mill is not zero-adjusted properly due to inaccurate roll gap or other reasons, the roll gap will exhibit abnormal bounce at the moment the workpiece bites in. That is, the normal bounce is S0, the abnormal bounce is S1, and S1 is much larger than S0. In this case, slippage will generally occur.

[0078] Figure 8 In actual production, it is generally difficult for the incoming rolled parts to run on the conveyor roller table to exit the line. The rolled parts will basically stick to one side of the guide plate when entering the inlet frame. If the guide plate liner is severely worn, the kinetic energy of the rolled parts biting and feeding will increase due to the increased resistance caused by the wear on one side, which will also cause slippage.

[0079] Figure 9 In actual production, a large part of the kinetic energy of the incoming rolled piece during the biting process depends on the clamping force of the pinch rolls. However, if the descaling pinch rolls fail to clamp the rolled piece tightly for other reasons, the feeding kinetic energy will be greatly reduced, and slippage will occur during biting.

Claims

1. A method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill, the inlet stand comprising an F1 stand and an F2 stand, characterized in that: The hot strip mill has a lower work roll and a lower support roll arranged in sequence below the rolling center, and an upper work roll and an upper support roll arranged in sequence above the rolling center; the method includes: The distance between the top of the lower working roll and the bottom plate of the frame is the elevation; a pad adjustment area is provided between the bottom of the lower support roll and the bottom plate of the frame. When replacing the support roll and calculating the pad, the elevation is raised by 2-10mm so that the strip head bites tightly against the lower roll surface when entering the inlet frame. Within the support roller replacement cycle, before replacing the support rollers, confirm the actual roller diameter range of each frame's work rollers to determine the matching support roller diameter and pad thickness for this cycle, ensuring the usable range of the corresponding frame's actual work rollers within this cycle. The maximum roller diameter is the factory-issued new roller diameter, and the minimum roller diameter refers to the scrap roller diameter of the corresponding frame. Within one cycle after replacing the support rollers, work rollers F1 to F3 should be based on the current maximum roller diameter minus 0 to 30 mm, and work rollers F4 to F7 should be based on the current maximum roller diameter minus 0 to 20 mm. Frames within this roller diameter range can be used. In the next replacement cycle, the roller diameter after wear and re-grinding in the previous cycle is the current maximum roller diameter. Within one cycle after replacing the support rollers, work rollers F1 to F3 should be based on the current maximum roller diameter minus 0 to 30 mm, and work rollers F4 to F7 should be based on the current maximum roller diameter minus 0 to 20 mm, until the work rollers are worn down to a diameter smaller than the scrap roller diameter. Roll gap setting: Roll gap setting + impact bounce = exit thickness; All mechanical clearances are eliminated through zero-adjustment preload of the new roll; The strip is conveyed into the rolling mill by the rotational force of the roller conveyor and the rotational friction of the strip surface. The clamping force of the pinch rollers is 5 to 20 kN. At the same time, the rotational speed of the pinch rollers is matched and synchronized with the speed of the roller conveyor.

2. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 1, characterized in that: Raise the elevation by 5-10mm.

3. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 1, characterized in that: During the replacement cycle of the support rollers, the relatively large roller diameters in the range of F1 to F3 are used on the F1 frame, followed by the F2 and F3 frames.

4. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 1, characterized in that: In the roll gap setting, H0 = H + P / K, where H0 is the actual exit thickness, H is the set roll gap, P is the rolling force, and K is the mill stiffness coefficient.

5. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 1, characterized in that: The method also includes that when the strip is dynamically sheared during operation, the shearing speed of the flying shear is greater than the running speed of the strip; and the shearing speed of the flying shear is corrected every 3-8 days.

6. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 5, characterized in that: Shearing speed: 1–1.25 m / s.

7. The method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 1, characterized in that: The method also includes controlling the temperature at the head of the strip in the heating furnace to be as consistent as possible with the temperature in the middle of the billet.

8. A method for controlling dynamic steel biting and slippage at the inlet stand of a hot strip mill according to claim 7, characterized in that: The term "strip head" refers to the first 8%-15% of the strip's length.

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