Method for reducing degraded products in roll changing of a skin pass mill of a hot galvanizing production line

Abstract

The present application relates to a kind of hot galvanizing production line finishing machine roll replacement reduces the method of degraded product, belong to hot galvanizing continuous production process technical field.The technical scheme is: according to the following steps to operate: step one: reduce process section one and process section two strip speed;Step two: when strip weld reaches finishing machine outlet, process section two strip speed reduces to 0 m / min;Step three: replace finishing machine work roll, and flushing is carried out to the work roll after replacement;Step four: after finishing machine work roll flushing is completed, process section two speed strip starts to run with the minimum strip running speed specified by finishing machine, tension leveler and roll coater, when finishing machine, tension leveler and roll coater start finishing, tension leveling and roll coating, process section two strip speed is gradually increased, and intermediate looper is released, until process section one and process section two restore normal production speed.The beneficial effects of the present application are: it can reduce the degraded product of strip due to not finishing when finishing machine roll replacement.

Description

Technical Field

[0001] This invention relates to a method for reducing downgraded products by changing rollers on a hot-dip galvanizing production line, belonging to the technical field of continuous hot-dip galvanizing production process in the metallurgical industry. Background Technology

[0002] The hot-dip galvanizing production line includes hot-dip galvanizing, finishing, tension leveling and roll coating processes. Hot-dip galvanizing is the first process, while finishing, tension leveling and roll coating are the second process. An intermediate loop is set up before finishing to store the strip steel continuously fed from the first process, so that the production line can run continuously without stopping.

[0003] The finishing machine has the functions of stretching strip steel, improving strip shape and flatness, improving the adhesion of paint film on strip steel, and eliminating yield plateau.

[0004] During the continuous hot-dip galvanizing process, due to changes in steel grade, strip width, and rolling mileage of the work rolls, it is often necessary to replace the work rolls of the finishing mill. The roll replacement is done without stopping the machine, and the second stage of the process runs at a speed of 60m / min. This results in a large number of downgraded products being generated during the roll replacement process, reducing the product qualification rate and increasing production costs.

[0005] During continuous production, the straightening machine and the roll coating machine are always online, performing straightening and passivation treatments on the strip according to the control plan. If the second stage of the process stops, both the straightening machine and the roll coating machine automatically open to prevent wear on the roll system from the strip. Therefore, in the current continuous production process of the hot-dip galvanizing unit, the second stage of the process involves roll changes without stopping the machine. Each roll change takes approximately 90-120 seconds, resulting in 150 meters of unfinished and downgraded strip. Simultaneously, the large amount of oil on the surface of the new work rolls during hoisting further increases the amount of downgraded strip. Because the unfinished portion and oil-contaminated strip are too long, the flying shear at the exit section cannot remove them, requiring the exit section to cut smaller coils. However, the smallest coil cut at the exit section is 3 tons, leading to a significant waste of high-quality strip. Downgraded strip severely impacts the product yield and increases production costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for reducing downgraded products when changing rolls on a hot-dip galvanizing production line, which can reduce downgraded products caused by the strip steel not being finished during roll changes, thus solving the problems existing in the background art.

[0007] The technical solution of this invention is:

[0008] A method for reducing downgraded products by changing rolls on a hot-dip galvanizing production line finishing machine includes a hot-dip galvanizing process, a finishing process, a tension leveling process, and a roll coating process. The hot-dip galvanizing process is a single process stage, while the finishing, tension leveling, and roll coating processes are two separate processes. An intermediate looper is set up before the finishing process to store the strip steel continuously fed from the first process stage. When changing rolls on the finishing machine of the hot-dip galvanizing production line, the following steps are followed:

[0009] Step 1: Reduce the strip speed of process 1 and process 2 to ensure that the storage capacity of the intermediate looper is sufficient to meet the time required for the finishing mill to stop and change rolls. At the same time, it is also necessary to ensure the quality of hot-dip galvanizing of the strip in process 1.

[0010] Step 2: When the strip weld reaches the exit of the finishing machine, the strip speed of the second process section is reduced to 0m / min, and at the same time, the finishing machine, tension leveler and roll coating machine of the second process section stop finishing, tension leveling and roll coating.

[0011] Step 3: Replace the work roll of the finishing machine and rinse the replaced work roll to clean its surface.

[0012] Step 4: After the finishing machine's work rolls are washed, the strip steel in the second process section begins to run at the minimum strip steel running speed specified by the finishing machine, tension leveler, and roll coater. When the finishing machine, tension leveler, and roll coater begin finishing, tension leveling, and roll coating, the strip steel speed in the second process section is gradually increased, and the intermediate looper is unloaded until the first and second processes return to normal production speed.

[0013] Step one: The strip speed in the first process section is reduced to above 80 m / min, and the strip speed in the second process section is reduced to below 60 m / min. The reduction of the strip speed in the first process section to above 80 m / min is due to two reasons: firstly, if the speed in the first process section drops below 80 m / min, the zinc coating quality on the strip surface is poor, and it is necessary to maintain a speed above 80 m / min in the first process section; secondly, sufficient time must be allowed for roll changing. The length of the intermediate looper is typically 420 meters, and the time for changing rolls on the entire machine is approximately 2 minutes, rinsing the work rolls takes about 1 minute, leaving about 1 minute for handling unexpected events.

[0014] Step 3: The rinsing time of the replaced work roll should be controlled within 2 minutes. The work roll is rinsed because the oil stains generated during the hoisting and grinding process of the work roll contaminate the surface of the strip steel, affecting product quality and producing downgraded products.

[0015] Step four: The minimum strip running speed specified for the finishing machine, tension leveler, and roll coating machine is 30m / min.

[0016] The beneficial effects of this invention are:

[0017] (1) The present invention utilizes the function of intermediate looper to store strip steel, so that the strip steel in the second process section is not continuously running during the roll changing process, thereby reducing the generation of unfinished strip steel;

[0018] (2) The tension leveler and roller coating machine stop tension leveling and roller coating during the roller changing process of the finishing machine to reduce the generation of downgraded products that do not meet the process requirements;

[0019] (3) By rinsing the replaced work roll, the oil stains on the surface of the work roll are prevented from being imprinted on the strip steel, thus avoiding the generation of downgraded products. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the two-stage process;

[0021] Figure 2 This is a schematic diagram of the roller change process in the second stage of the finishing machine.

[0022] Figure 3 This is a layout diagram of the roller changing system for the finishing mill;

[0023] Figure 4 for Figure 1 Top view of the strip steel;

[0024] In the diagram: 1. Intermediate looper, 2. Directional roller, 3. Correcting roller, 4. Weld inspection, 5. Tension roller #6, 6. Tension measuring roller, 7. Bending roller, 8. Support roller, 9. Working roller, 10. Anti-wrinkle roller, 11. Tension roller #7, 12. Tension leveler, 13. Roller coating machine, 14. Strip steel, 15. Weld magnification, 16. Roll receiving trolley, 17. Spare roller trolley, 18. Weld, 19. Pusher device. Detailed Implementation

[0025] The invention will be further described below with reference to the accompanying drawings and examples.

[0026] See attached document Figure 1-4 A method for reducing downgraded products by changing rolls on a hot-dip galvanizing production line finishing machine includes a hot-dip galvanizing process, a finishing process, a tension leveling process, and a roll coating process. The hot-dip galvanizing process is a single process stage, while the finishing, tension leveling, and roll coating processes are two separate processes. An intermediate looper is provided before the finishing process to store the strip steel continuously fed from the first process stage. The method is characterized by the following steps during roll changing on the finishing machine of the hot-dip galvanizing production line:

[0027] Step 1: Reduce the strip speed of process 1 and process 2 to ensure that the storage capacity of the intermediate looper is sufficient to meet the time required for the finishing mill to stop and change rolls. At the same time, it is also necessary to ensure the quality of hot-dip galvanizing of the strip in process 1.

[0028] Step 2: When the strip weld reaches the exit of the finishing machine, the strip speed of the second process section is reduced to 0m / min, and at the same time, the finishing machine, tension leveler and roll coating machine of the second process section stop finishing, tension leveling and roll coating.

[0029] Step 3: Replace the work roll of the finishing machine and clean the replaced work roll, rinsing the surface of the work roll clean.

[0030] Step 4: After the finishing machine's work rolls are washed, the strip steel in the second process section begins to run at the minimum strip steel running speed specified by the finishing machine, tension leveler, and roll coater. When the finishing machine, tension leveler, and roll coater begin finishing, tension leveling, and roll coating, the strip steel speed in the second process section is gradually increased, and the intermediate looper is unloaded until the first and second processes return to normal production speed.

[0031] In this embodiment, as shown in the appendix Figure 1 As shown, the second stage of the process, in sequence according to the strip running direction, includes an intermediate looper 1, a steering roller 2, a straightening roller 3, a weld inspection machine 4, a No. 6 tension roller 5, a tension measuring roller 6, a bending roller 7, a finishing mill, an anti-wrinkle roller 10, a No. 7 tension roller 11, a tension leveler 12, a No. 6 tension roller 5, a tension measuring roller 6, a steering roller 2, and a roll coating machine 13. The weld inspection provides strip tracking for the finishing mill's roll changing. The finishing mill's stop-roll changing utilizes the strip storage capacity of the intermediate looper 1. When the strip to be changed reaches the weld seam of the strip at the intermediate looper 1 weld inspection machine 4, the weld seam is stopped at the finishing mill, and then the stop-roll changing procedure is run. After the roll changing is completed, the unfinished portion is cut off at the exit section flying shear to reduce the generation of downgraded products.

[0032] See attached document Figure 2-4 Taking DX51D+Z strips with a thickness of 0.58mm and a width of 1400mm and DX52D+Z strips with a thickness of 0.78mm and a width of 1600mm as examples, roll changing is performed after the strip width is increased to prevent uneven printing on the finishing machine. The specific operating steps are as follows:

[0033] 1) Determine the number of the work roll 9' to be replaced, input the diameter of the new work roll 9' into the HIM screen, then open the roller shutter door on the operating side of the finishing machine, and drive the roller receiving trolley 16 on the operating side into the frame. Lock the roller receiving trolley 16 on the operating side using the hydraulic lock, open the roller changing door on the drive side of the finishing machine, and finally select the stop roller changing program, tension leveler, automatic input program of roller coating machine, and work roll cleaning program in the HIM screen;

[0034] 2) When the DX52D+Z strip 14 requiring roll changing reaches the intermediate looper 1, the speed of the first process stage is reduced by 80 m / min. This is to prevent the intermediate looper 1 from becoming fully loaded due to excessive speed in the first process stage, thus causing the first process stage to stop. When the weld inspection 4 detects the weld 18 between strip 14 and 14', the speed of the second process stage is reduced to 60 m / min. When weld 18 reaches the finishing mill, the speed of the second process stage is rapidly reduced to 0 m / min. The intermediate looper 1's capacity to store strip 14 is used to stop the second process stage for roll changing. At the same time, the tension leveler 12 and the roll coating machine 13 are turned on during the second stage stop. Figure 2 The positions of the strip straightening machine and the finishing machine are designed to prevent wear on the strip straightening machine 12 and the roll coating machine 13.

[0035] 3) Start the roll changing program; the entire machine's work rolls open quickly, such as... Figure 2 At the position of the finishing machine, the new working roll 9' is fully opened with its diameter introduced into the working roll 9. At the same time, the hydraulic lock of the working roll 9 is opened, and the trolley device 19 pushes the new working roll 9' on the transmission side spare roll trolley 17 into the finishing machine frame, pushing out the old working roll 9 and pushing it into the operating side receiving roll trolley 16. At the same time, the new working roll 9' enters the frame, the hydraulic lock of the new working roll 9' is closed, the trolley device 19 retracts to its original position, the hydraulic lock of the operating side receiving roll trolley 16 is automatically opened, and the operating side receiving roll trolley 16 is manually moved away from the frame.

[0036] 4) After the new work roll 9' enters the frame, the roll gap closing operation begins. First, the finishing machine is quickly opened and reset, then the finishing machine roll gap is calibrated, followed by the ready operation. Then, the finishing machine roll gap is opened to the middle position. At the same time, the work roll cleaning program is automatically started to rinse the work roll 9' for 1 minute to prevent oil stains generated during hoisting and grinding from contaminating the strip surface and causing downgraded products.

[0037] 5) After rinsing, the second stage of the process runs at a speed of 30m / min. At the same time, the straightening machine 12 and the roller coating machine 13 in the second stage of the process are put into operation according to the production control plan and then the finishing machine is closed.

[0038] 6) After closing the finishing mill, click the rolling start button to start rolling. Adjust tension roller 5 (6#) and tension roller 11 (7#) to ensure the tension at the inlet and outlet of the finishing mill. At the same time, adjust the rolling force. Then, adjust the finishing mill to constant elongation mode. After the parameters are adjusted, increase the speed of the second process stage and release the intermediate looper. The speed of the first process stage is restored and the mill is operated at the normal production speed.

[0039] 7) During the roll changing process, at most 20 meters of strip steel will be produced that is not smooth and has surface quality defects. The 20 meters of defective strip steel can be cut off by flying shear at the exit section. By taking the above steps, downgraded products can be avoided.

Claims

1. A method for reducing downgraded products in roll changing of a skin pass mill in a hot-dip galvanizing production line, comprising a hot-dip galvanizing process, a skin pass process, a tension leveler process and a roll coating process, the hot-dip galvanizing process being a first process section, the skin pass process, the tension leveler process and the roll coating process being a second process section, and an intermediate loop being arranged before the skin pass process to store the strip steel continuously delivered from the first process section, characterized in that: When the finishing mill of the hot-dip galvanizing production line is changed, the following steps are taken: ​ Step 1: Reduce the speed of the strip in the process 1 and process 2 to ensure that the intermediate loop can store enough strip to meet the time required for changing the finishing mill, and also ensure the quality of the hot-dip galvanizing of the strip in the process 1; the speed of the strip in the process 1 is reduced to above 80 m / min, and the speed of the strip in the process 2 is reduced to below 60 m / min; Step 2: When the weld of the strip reaches the outlet of the finishing mill, the speed of the strip in the process 2 is reduced to 0 m / min, and the finishing mill, the tension leveler and the roll coater in the process 2 are stopped; Step 3: Change the work roll of the finishing mill, and flush the changed work roll to clean the surface of the work roll; the flushing time of the changed work roll is controlled within 2 minutes to prevent the oil dirt produced in the hoisting and grinding process from polluting the surface of the strip and producing downgraded products; Step 4: After the work roll of the finishing mill is flushed, the strip in the process 2 starts to run at the minimum speed specified by the finishing mill, the tension leveler and the roll coater, and when the finishing mill, the tension leveler and the roll coater start to finish, level and coat, the speed of the strip in the process 2 is gradually increased, and the intermediate loop is released until the process 1 and the process 2 return to the normal production speed; the minimum speed specified by the finishing mill, the tension leveler and the roll coater is 30 m / min.

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