Method for preventing slab from being frozen after breakout of continuous casting machine

Abstract

A method for preventing a slab from being frozen after breakout of a continuous casting machine. The method comprises: providing a breakout button, and forcibly executing breakout control; and respectively improving control over the position of a fan-shaped section (2), control over the drawing speed, control over a cooling loop of secondary cooling water, control over the opening of holding rollers, and control over a target force of the holding rollers. By increasing an opening value of the fan-shaped section, the volume in a tail slab is increased, the problem of steel overflow is solved, and the slab drawing resistance is reduced by 20-40%; by controlling the slab drawing speed and the flow of secondary cooling water, the cooling strength for the slab and a breakout point is increased by 30-50%; by controlling automatic opening of the holding rollers to prevent an excessive holding force from squeezing the slab, the majority of molten steel overflows can be reduced; and by increasing the target force of the holding rollers and increasing friction force between the rollers and the slab, a guarantee is provided for drawing out the slab, and the time taken for urgent repair of an apparatus after breakout is reduced, thereby saving on costs and increasing the operation rate of a casting machine.

Description

A method for preventing billet freezing after steel leakage in continuous casting machine Technical Field

[0001] The present invention relates to the technical field of continuous casting, in particular to a method for preventing billets from freezing after steel leakage from a continuous casting machine. Background Art

[0002] Steel leakage in a continuous casting machine refers to the phenomenon that during the casting process, the solidification of the billet shell is not good or the billet shell is broken or leaked due to other external forces, causing the internal molten steel to flow out. Steel leakage is a serious accident in continuous casting production. Severe steel leakage accidents not only affect the normal production of the continuous casting machine, but also cause frozen billets due to inability to pull, reduce the operating rate of the casting machine, and cause significant equipment losses. Steel leakage accidents can be divided into various types according to the time and location of occurrence on the casting machine, such as steel leakage at the beginning of casting, steel leakage during casting, steel leakage at the corner of the billet, steel leakage inside or outside the arc of the billet, etc. After steel leakage occurs, the casting machine will control the corresponding equipment in the tail billet discharge mode to pull the billet out of the fan-shaped segment. During this period, the casting machine's supporting rollers, fan-shaped segments, and secondary cooling water will act according to the tail billet tracking control sequence to complete the tail billet discharge.

[0003] During the breakout process on today's continuous casting machines, the segments open sequentially based on the tail billet tracking value until the actual thickness at the mold outlet is reached (this thickness varies depending on the casting machine type). The support rollers open sequentially based on the tail billet tracking value, and the secondary cooling water closes sequentially based on the tail billet tracking value. Once the tail billet is tracked to the last segment, the casting machine's tail billet is discharged. According to recent experience, when a breakout occurs on a casting machine, production operators activate the machine. If the breakout is minor, the casting machine is able to pull the billet out. However, if the breakout is significant, due to factors such as delayed detection, the casting machine often cannot pull the billet out, resulting in a serious continuous casting frozen billet accident. Even if the billet is pulled out, the large amount of liquid steel in segments 0-6 has not cooled and solidified in time. Due to the squeezing effect of the segments, the liquid steel overflows onto the segments again, causing serious damage to segments 0-6 and increasing the time required to handle the breakout accident. Addressing these issues is urgent.

[0004] Chinese patent publication number CN101332499A discloses a method for predicting and controlling steel breakout in slab continuous casting, comprising the following steps: a. capturing typical temperature characteristics: determining the typical temperature characteristics of each thermocouple based on the mold parameters and the installation position of the thermocouple in the mold; b. determining the steel breakout probability: determining the steel breakout probability of each thermocouple based on the typical temperature characteristics of adjacent thermocouples, while taking into account the steel breakout temperature transfer and temperature anomaly distribution characteristics; c. controlling the casting speed: stopping casting when the thermocouple steel breakout probability reaches 95%. However, the patent's dynamic monitoring and tracking of temperature changes will cause control lag due to temperature lag, resulting in steel breakout accidents.

[0005] Summary of the Invention

[0006] The present invention provides a method for avoiding freezing of billets after steel leakage in a continuous casting machine. In order to prevent accidents of freezing of billets due to steel leakage caused by untimely steel leakage detection, a steel leakage button is added, and steel leakage control is enforced. By increasing the opening value of the fan segment, the volume of the tail slab is increased, the problem of steel overflow is effectively solved, and the resistance to billet drawing is reduced. By controlling the billet drawing speed and the flow rate of the second cooling water, the cooling intensity of the slab and the steel leakage point is increased. By controlling the automatic opening of the supporting roller to prevent the slab from being squeezed by excessive supporting force, most of the molten steel overflow can be reduced. By increasing the target force of the supporting roller, the friction between the roller and the slab is increased, which provides a guarantee for pulling out the slab, reduces the time for emergency repair of equipment after steel leakage, saves costs, and improves the operation rate of the casting machine.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preventing frozen billets after steel breakout in a continuous casting machine comprises the following steps:

[0009] 1) Activate the steel leakage button;

[0010] 2) Segment control:

[0011] (1) Segment position control: Segments 1 to 3 are opened to a thickness 10 to 40 mm greater than the mold thickness, and segments 4 to 15 are opened to the mold thickness;

[0012] (2) Casting speed control: Control the casting speed to 0.8-1.1 m / min;

[0013] (3) Secondary cooling water circuit control: The control valves of the 1st to 6th cooling circuits of the secondary cooling water in the sector are opened 70-100℅ to supply water;

[0014] (4) Holding roller opening control: When the tail billet position tracking value of segments 1 to 3 is 0 to 500 mm, holding rollers 1 to 3 are lifted. When the tail billet position tracking value of segments 4 to 15 is the metallurgical length of the corresponding holding roller from the actual distance to the crystallizer ± 500 mm, the corresponding holding roller is automatically opened.

[0015] (5) Holding roller target force control: Control the target force of the holding roller at 100% to 150%;

[0016] 3) When the tracking value of the tail position of the casting billet is greater than the metallurgical length of the sector 0 entrance from the crystallizer ±500mm, the equipment starts the next action;

[0017] (1) Segment position control: Segments 4 to 15 are opened sequentially to a size 10 to 40 mm greater than the mold thickness;

[0018] (2) Casting speed control: After activating the steel leakage button for 3 minutes, the casting speed is controlled to increase to 1.1-1.3 m / min;

[0019] (3) Secondary cooling water circuit control: The secondary cooling water circuit of the fan-shaped segment remains open until the tail billet of the casting strand is pulled out of the corresponding fan-shaped segment, and then the secondary cooling water circuit of the previous fan-shaped segment is automatically closed;

[0020] (4) Holding roller opening control: Holding rollers No. 1 to 3 are kept lifted up. When the position tracking value of the tail billet of the sector segments 4 to 15 is ±500 mm from the actual metallurgical length of the holding roller of the corresponding sector to the crystallizer, the holding roller of the corresponding sector segment is automatically opened until the tail billet is completely pulled out of the sector segment, thus ending the entire leakage and tail billet discharge process.

[0021] Furthermore, the cooling positions of the 1st to 2nd cooling circuits of the second cooling water in the sector segment are the foot roller area, the cooling positions of the 3rd to 6th cooling circuits of the second cooling water in the sector segment are sector 0, and the cooling positions of the 7th to 20th cooling circuits of the second cooling water in the sector segment are sector 1 to 15.

[0022] Furthermore, the acceleration of the ramp section of the casting speed in step 2) is 4 to 8 m / min. 2 .

[0023] Furthermore, when the tracking value of the tail position of the casting strand is greater than the metallurgical length of the secondary cooling water circuit corresponding to the sector, the secondary cooling water circuit of the corresponding sector and the secondary cooling water circuit of the previous sector are automatically closed.

[0024] Furthermore, the segment 0 is located at the front end of the sector.

[0025] Furthermore, the tracking value of the tail position of the casting strand is the length of the slab pulled out by the straightening machine.

[0026] Furthermore, the steel leakage button is installed in the central control room, and the machine side and the central control room are interlocked for operation.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) Add a steel leakage button to enforce steel leakage control and prevent steel leakage and frozen billet accidents caused by untimely steel leakage detection.

[0029] 2) By increasing the opening value of the fan segment, the volume of the tail slab is increased, effectively solving the problem of steel overflow and reducing the casting resistance by 20-40%;

[0030] 3) By controlling the casting speed and the secondary cooling water flow rate, the cooling intensity of the slab and the breakout point is increased by 30-50%;

[0031] 4) By controlling the automatic opening of the holding roller to prevent excessive holding force from squeezing the slab, most of the molten steel overflow can be reduced. By increasing the target force of the holding roller, the friction between the roller and the slab is increased, providing a guarantee for pulling out the slab;

[0032] 5) Reduce the time for equipment repair after steel leakage, save costs and improve the operation rate of the casting machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic diagram of the process flow of the present invention.

[0034] In the figure: 1. Crystallizer 2. Sector 3. Secondary spray cooling 4. Straightening machine 5. Section 0 6. Slab DETAILED DESCRIPTION

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0036] FIG1 is a process flow chart of the present invention. Molten steel flows from a crystallizer 1 into a sector 2. The sector 2 is divided into segments 0 to 15 from top to bottom. The sector 2 is subjected to secondary spray cooling 3. The cooled slab 6 is pulled out by a straightening machine 4. The present invention provides a method for preventing frozen slabs after steel leakage in a continuous casting machine, characterized by comprising the following steps:

[0037] 1) Activate the steel leakage button, which is installed in the central control room and can be chained operated both at the machine side and in the central control room.

[0038] 2) Segment 2 parameter control, specifically including segment 2 position control, casting speed control, secondary cooling water circuit control, holding roller opening control, and holding roller target force control:

[0039] (1) Segment 2 position control: The thickness of the mold 1 is 242.5 mm. Segments 1 to 3 of segment 2 are opened to 260 mm, and segments 4 to 15 of segment 2 are opened to 242.5 mm. The billet bulges under the action of the static pressure of the molten steel, increasing the volume of the slab 6 and effectively solving the problem of steel overflow. It also prevents the liquid steel from leaking onto the segment 2 under the action of the squeezing of the segment 2 when the billet moves downward, thereby increasing the damage to the equipment. This reduces the amount of steel wrapped around the rollers and reduces the billet drawing resistance by 20 to 40%.

[0040] (2) Casting speed control: Control the casting speed to 1.0m / min, and the acceleration of the slope section of the casting speed is 6m / min 2 ;

[0041] (3) Secondary cooling water circuit control: Under the condition of no steel leakage, the target flow rate of the secondary cooling water circuit of sector 2 is given according to the casting speed table, see Table 1:

[0042] Table 1

[0043] Loop 1 to Loop 20 are the 1st to 20th cooling loops for the secondary cooling water in sector 2. The control valves of Loop 1 to Loop 6 are opened 100% to supply water. The target flow rate of the secondary cooling water in Loop 7 to Loop 20 is still given according to the nearest speed on the speed table, increasing the cooling intensity of slab 6 and the breakout point by 30%.

[0044] (4) Holding roller opening control: When the tail position tracking value of segments 1 to 3 of sector 2 is 0 mm, holding rollers 1 to 3 are lifted to prevent excessive holding force from squeezing the slab 6 and reduce most of the overflowing molten steel. When the tail position tracking value of segments 4 to 15 of sector 2 is ±500 mm of the actual metallurgical length of the holding roller of the corresponding segment from the crystallizer 1, the holding roller of the corresponding sector 2 is automatically opened. The holding rollers are opened one by one according to the tail tracking value, as shown in Table 2:

[0045] Table 2

[0046] (5) Control of target force of holding roller: Increase target force of holding roller and control target force of holding roller at 120% to compensate torque and improve drawing torque. Due to steel leakage, the steel billet adheres to the main body of sector 2, resulting in excessive resistance and insufficient straightening torque. Increase target force of holding roller, thereby increasing friction between roller and slab 6 and providing guarantee for pulling out slab 6.

[0047] 3) The slab 6 is gradually pulled out by the straightening machine 4. The pulled-out length is the position tracking value of the tail of the strand. When the position tracking value of the tail of the strand is greater than the metallurgical length of the distance between the entrance of segment 0 and the mold 1 by ±500mm, the equipment starts the next step of the segment 2 position control, pulling speed control, secondary cooling water circuit control and holding roller opening control.

[0048] (1) Segment 2 position control: Segments 4 to 15 of segment 2 are opened to 260 mm in sequence. When the tracking values ​​of the tail billet position of the four segments of segment 2 are greater than the actual metallurgical length of the distance between the inlet of segment 0 and the crystallizer 1 by ±500 mm and the actual metallurgical length of the outlet of segment 0 and the crystallizer 1 by ±500 mm, the four segments of segment 2 are opened to 260 mm. Similarly, when the metallurgical lengths of segments 5 to 15 correspond to the metallurgical lengths of segments 1 to 11, and the tracking values ​​of the tail billet of the mainstream after the breakout are greater than the values ​​in Table 3, the segments are opened to 260 mm in sequence.

[0049] Table 3

[0050] Increasing the opening value of sector 2 effectively solves the problem of large billet pulling resistance after breakout and difficulty in pulling the billet out of sector 2.

[0051] (2) Pulling speed control: After activating the steel leakage button for 3 minutes, the pulling speed of the slab 6 is controlled to 1.2m / min;

[0052] (3) Secondary cooling water circuit control: The secondary cooling water circuit of segment 2 remains open until the tail billet of the strand is pulled out of the corresponding segment 2, then the secondary cooling water circuit of the previous segment 2 is automatically closed. The secondary cooling water circuit corresponding to segment 2 is closed as shown in Table 4.

[0053] Table 4

[0054] (4) Holding roller opening control: Holding rollers No. 1 to 3 are kept lifted up. When the position tracking value of the tail billet of segments 4 to 15 of sector 2 is ±500 mm of the actual metallurgical length of the holding roller of the corresponding segment from the crystallizer 1, the holding roller of the corresponding sector 2 is automatically opened until the tail billet is completely pulled out of sector 2, thus ending the entire leakage and tail billet discharge process.

[0055] This improved method reduces equipment repair time after breakouts by 8 to 23 hours. Assuming 50 workers, 16 hours per person, and a cost of 25 yuan per hour, this occurs approximately four times per year on a two-machine, three-stream system. This reduces labor costs by approximately 80,000 yuan, reduces the number of premature segment 2 production lines by approximately 12 units, and increases segment 2 service life. Based on the annual cost of spare parts and maintenance labor costs for segment 2 repairs due to molten steel overflow and burning of segment 2 driven rollers, the cost of repairs is approximately 1.2 million yuan, and the cost of maintenance labor is approximately 60,000 yuan. This improves caster availability, and by reducing breakout handling time by approximately 50 hours per year, it can produce an additional 50 heats of 180 tons each, generating approximately 4.5 million yuan in indirect benefits.

[0056] The above embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A method for preventing freezing of billets after steel leakage in a continuous casting machine, characterized in that: The following steps are involved: 1) Activate the steel leakage button; 2) Sector control: (1) Segment position control: Segments 1 to 3 are opened to a size 10 to 40 mm greater than the mold thickness, and segments 4 to 15 are opened to the mold thickness; (2) Casting speed control: Control the casting speed to 0.8-1.1 m / min; (3) Secondary cooling water cooling circuit control: The control valves of the 1st to 6th cooling circuits of the secondary cooling water of the fan-shaped segment are opened by 70-100℅ to supply water; (4) Holding roller opening control: When the tail position tracking value of segments 1 to 3 is 0 to 500 mm, holding rollers 1 to 3 are lifted; when the tail position tracking value of segments 4 to 15 is ±500 mm of the actual metallurgical length of the corresponding holding roller from the crystallizer, the corresponding holding roller is automatically opened; (5) Holding roller target force control: Control the holding roller target force at 100% to 150%; 3) When the tracking value of the tail position of the casting billet is greater than the metallurgical length of the sector 0 entrance from the crystallizer ±500mm, the equipment starts the next action; (1) Segment position control: Segments 4 to 15 are opened sequentially to a size 10 to 40 mm greater than the mold thickness; (2) Casting speed control: After activating the leakage button for 3 minutes, the casting speed is controlled to increase to 1.1-1.3 m / min; (3) Secondary cooling water circuit control: The secondary cooling water circuit of the fan-shaped segment remains open until the tail billet of the casting strand is pulled out of the corresponding fan-shaped segment, and then the secondary cooling water circuit of the previous fan-shaped segment is automatically closed; (4) Holding roller opening control: Holding rollers 1 to 3 are kept lifted up. When the position tracking value of the tail billet of the casting strand of segments 4 to 15 is ±500 mm of the actual metallurgical length of the holding roller of the corresponding segment from the crystallizer, the holding roller of the corresponding segment is automatically opened until the tail billet is completely pulled out of the segment, thus ending the entire leakage and tail billet discharge process.

2. A method for preventing freezing of billets after steel leakage in a continuous casting machine according to claim 1, characterized in that: The cooling positions of the 1st to 2nd cooling circuits of the secondary cooling water of the fan-shaped segment are the foot roll area, the cooling positions of the 3rd to 6th cooling circuits of the secondary cooling water of the fan-shaped segment are the fan-shaped segment 0, and the cooling positions of the 7th to 20th cooling circuits of the secondary cooling water of the fan-shaped segment are the fan-shaped segments 1 to 15.

3. A method for preventing freezing of billets after steel leakage in a continuous casting machine according to claim 1, characterized in that: The acceleration of the ramp section of the billet drawing speed in step 2) is 4 to 8 m / min. 2 .

4. A method for preventing freezing of billets after steel leakage in a continuous casting machine according to claim 1, characterized in that: When the tracking value of the tail position of the casting strand is greater than the metallurgical length of the secondary cooling water circuit corresponding to the fan-shaped segment, the corresponding secondary cooling water circuit of the fan-shaped segment and the secondary cooling water circuit of the previous fan-shaped segment are automatically closed.

5. The method for preventing freezing of billets after steel leakage in a continuous casting machine according to claim 1, characterized in that: The steel leakage button is installed in the central control room, and the machine side and the central control room are interlocked for operation.

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