A method for reducing high ridge and leakage of machine cleaning billet surface

Abstract

This invention discloses a method for reducing surface roughness and incomplete cleaning of machine-cleaned billets. The method categorizes the steel grades requiring machine-cleaned billets into four levels: FD, FC, FB, and FA, based on product surface requirements. The FD grade is for O5 automotive panels, the FC grade for appliance panels, the FB grade for high-strength steel series, and the FA grade for billets with fluctuating liquid surfaces during unsteady casting. For FD grade billets, a warm-billet machine cleaning process is used, with a billet temperature between 200℃ and 400℃, and preheating for 37-40 seconds before cleaning. For FC grade billets, a warm-billet machine cleaning process is used, with a billet temperature between 200℃ and 400℃, and preheating for 33-36 seconds before cleaning. For FB grade billets, a hot-billet machine cleaning process is used, with a billet temperature between 400℃ and 800℃, and preheating for 30-32 seconds before cleaning. This method can effectively eliminate surface defects such as porosity, cracks, slag inclusions, heavy scale, high edges, and leakage of cleaning fluid in cast billets, and the surface quality of cast billets is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting technology, and in particular, it is a method for reducing high edges and leakage on the surface of machine-cleaned billets. Background Technology

[0002] With the rapid development of my country's steel industry, customers have increasingly stringent requirements for product quality. In particular, high-quality and high-value-added products have become the main way for steel companies to improve economic efficiency. The rolling of these high-quality and high-value-added products places even stricter requirements on the surface quality of the billets. For example, quality defects such as surface cracks, pits, subcutaneous bubbles, and inclusions on the billet can, in mild cases, be inherited by the final product during subsequent rolling processes, affecting the surface quality of the product; in severe cases, they can lead to product downgrading and re-judgment, or even affect the smooth operation of production. Therefore, flame cleaning technology is needed to remove defects from the surface of the billets.

[0003] Flame cleaning machines (hereinafter referred to as machine cleaners) remove quality defects such as iron oxide scale, cracks, bubbles, and inclusions from the surface of continuously cast billets through the heat generated by the thermochemical oxidation reaction of burning oxygen and fuel gas. Compared with conventional manual cleaning, machine cleaning has the advantages of being labor-saving, environmentally friendly, and highly efficient in improving the surface quality of the billets. However, due to the influence of billet shape, billet temperature, machine cleaner burner, and equipment precision, phenomena such as high edges, heavy scale, slag flow, and incomplete cleaning frequently occur on the surface of the billets after flame cleaning. To ensure the surface quality of the billets, billets with abnormal surfaces after machine cleaning must be manually cleaned again, which increases time costs and incurs additional consumption of manpower and resources.

[0004] Current domestic and international research mainly focuses on the structural optimization and adjustment of machine cleaning equipment and online detection of billet surface quality. However, there are few reports on research into billet cleaning temperature, plate shape control, and equipment precision in combination with steel type to avoid the risk of abnormal billet surface quality after machine cleaning.

[0005] Chinese patent application CN 116559175 A discloses an online automatic grading method for the surface quality of machine-cleaned billets. This method uses detection devices installed on the four sides of the output roller conveyor to continuously acquire image data of the four sides of the billet, and uses a computer to automatically identify and count the number, size and location of inclusions and bubbles per unit area of ​​the billet to rate the surface quality of the billet, thereby improving the hot charging and hot delivery rate of the billet; however, it does not study how to ensure the surface quality of the billet after machine cleaning.

[0006] Chinese patent application CN 116698302 A discloses a device and method for detecting and alarming burner leaks on a flame cleaning machine. This method, through optimization of the gas guiding structure, gas guiding pipeline and sensor, can identify one or several burner devices that are leaking, detect the leaking gas, and issue an alarm through the human-machine interface to prevent equipment burn-out or fire accidents. However, it does not address the state of the machine-cleaned billet under different processes and operating conditions.

[0007] Chinese patent application CN 116603986 A discloses a flame cleaning burner adjustment mechanism for a continuous casting machine's robotic arm. This adjustment mechanism, in conjunction with a dedicated flame cleaning machine, enables the installation and configuration of multiple high-flow-rate cleaning burners, achieving automatic control at any angle, and efficiently cleaning single or localized defects on the surface of the cast billet. This invention does not address other processes involved in machine-cleaned cast billets.

[0008] Chinese patent application CN 2755441 Y discloses a machine cleaning burner for preventing groove defects in slabs. This burner greatly reduces machine cleaning groove defects in slabs caused by excessive gaps between the shoe blocks by setting a knife-shaped airflow wall on the side wall of the shoe block. However, it does not cover other process parameters in detail.

[0009] The paper, "Application of Flame Cleaning Machine in Slab Continuous Casting Production" (Continuous Casting, March 2012, No. 2, pp. 38-41), provides a comprehensive analysis of the technical parameters, equipment composition, energy consumption, working principle, and application results of the flame cleaning machine used in Benxi Steel's continuous casting process. However, it does not address the state of the machine-cleaned slab under different processes and operating conditions. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a method for reducing the high edge and missing cleaning on the surface of machine-cleaned billets, so as to effectively improve the surface quality of machine-cleaned billets.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: the steel grades of the billets requiring machine cleaning are classified into four grades according to the surface requirements of different products: FD, FC, FB, and FA. The FD grade is for O5 automotive panels, the FC grade is for home appliance panels, the FB grade is for high-strength steel series, and the FA grade is for billets with fluctuating liquid surface under unsteady pouring conditions.

[0012] The FD grade billet is subjected to warm billet cleaning treatment, with a billet temperature of 200℃≤billet temperature<400℃, and preheating for 37s~40s before cleaning treatment;

[0013] The FC surface grade billet is subjected to warm billet cleaning treatment, with a billet temperature of 200℃≤billet temperature<400℃, and preheating for 33s~36s before cleaning treatment;

[0014] The FB surface grade billet is subjected to hot billet cleaning treatment, with a billet temperature of 400℃≤billet temperature<800℃, and preheating for 30s~32s before cleaning treatment;

[0015] The FA surface grade billet is subjected to a cooling and cleaning process, with the billet temperature controlled at <200℃, and preheated for 37s to 40s before the cleaning process.

[0016] Furthermore, for the FD surface grade ingots, the preheating oxygen pressure is 0.26MPa~0.28MPa, and 0.22MPa < cleaning oxygen pressure ≤0.24MPa; for the FC surface grade ingots, the preheating oxygen pressure is 0.26MPa~0.28MPa, and 0.22MPa < cleaning oxygen pressure ≤0.24MPa; for the FB surface grade ingots, the preheating oxygen pressure is 0.26MPa~0.28MPa, and 0.20MPa < cleaning oxygen pressure ≤0.22MPa; for the FA surface grade ingots, the preheating oxygen pressure is 0.26MPa~0.28MPa, and 0.22MPa < cleaning oxygen pressure ≤0.24MPa.

[0017] Furthermore, the FD surface grade casting billet is cleaned using a four-sided cleaning method, with a cleaning depth of 3.7mm to 4.0mm on the upper and lower surfaces and a cleaning depth of 3.3mm to 3.5mm on the two narrow sides;

[0018] The FC surface grade billet is cleaned using a four-sided cleaning method, with a cleaning depth of 3.3mm to 3.5mm on the upper and lower surfaces and a cleaning depth of 2.7mm to 3.0mm on the two narrow sides.

[0019] The FB surface grade casting billet is cleaned using a four-sided cleaning method, with a cleaning depth of 2.7mm to 3.0mm on the upper and lower surfaces and a cleaning depth of 2.7mm to 3.0mm on the two narrow sides.

[0020] The FA surface grade billet is cleaned using a two-sided cleaning method, cleaning both the upper and lower surfaces. For billets with liquid level fluctuations > 20 mm, deep cleaning is performed, with a cleaning depth of 4.0 mm < cleaning depth of both upper and lower surfaces ≤ 4.5 mm. For billets with liquid level fluctuations 10 mm < liquid level fluctuations ≤ 20 mm, cleaning depth of 3.3 mm < cleaning depth ≤ 4.0 mm. For billets with liquid level fluctuations 5 mm ≤ liquid level fluctuations ≤ 10 mm, shallow cleaning is performed, with a cleaning depth of 2.3 mm ≤ cleaning depth ≤ 3.3 mm.

[0021] Furthermore, the cleaning speed during machine cleaning is calculated according to formula (Ⅰ).

[0022] (I),

[0023] In the formula, T: billet temperature, °C; F: oxygen pressure, MPa; D: cleaning depth, mm.

[0024] The design concept of this invention is as follows: If the surface of the machine-cleaned billet has surface quality defects such as cracks, high edges, incomplete cleaning, slag flow, and heavy scale, these defects will continue to expand in the next rolling process, seriously affecting the surface quality of the product. This invention, based on the machine cleaning equipment and considering the different surface requirements of various steel grades, establishes a set of cleaning rules for machine-cleaned billets. It differentiates cleaning based on four surface grades: FD, FC, FB, and FA. The aim is to reduce high edges and incomplete cleaning defects on the machine-cleaned billet surface through optimization and reasonable control of machine cleaning speed, temperature, billet shape, and burner precision, thereby further ensuring product surface quality.

[0025] The beneficial effects of adopting the above technical solution are as follows: This invention classifies the steel grades and categories requiring machine cleaning into four surface grades: FD, FC, FB, and FA, based on their applications and types. This establishes a grading rule for machine-cleaned billets, effectively eliminating surface defects such as porosity, cracks, inclusions, heavy scale, high edges, and incomplete cleaning. The surface quality of the billets after machine cleaning is significantly improved. Using this method, the proportion of hot-rolled and cold-rolled strip steel downgraded due to inclusions, cracks, and peeling scale decreased from 3.8% to 0.86%, resulting in a qualitative leap in product surface quality and earning high praise from customers. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 This is a picture of the surface of the O5 plate after machine cleaning, obtained by conventional methods;

[0028] Figure 2 This is a surface image of O5 steel strip obtained using conventional methods;

[0029] Figure 3 This is a real image of the surface of the O5 plate after machine cleaning obtained in Embodiment 1 of the present invention;

[0030] Figure 4 This is a real-world image of the O5 strip steel obtained in Embodiment 1 of the present invention. Detailed Implementation

[0031] The method for reducing the surface high edge and leakage of the machine-cleaned billet adopts the following process steps: (1) Classify the product surface requirements: According to the different surface requirements of the product, the grades are divided into four grades: FD, FC, FB and FA; the FD grade is the O5 automotive panel with the highest surface requirements, the FC grade is the home appliance panel with higher surface requirements, the FB grade is the high-strength steel series, and the FA grade is the billet with liquid surface fluctuation under unsteady pouring.

[0032] (2) Machine cleaning treatment: After the continuous casting process is cut off, the billets are stacked and cooled slowly. To prevent the top layer of billets from buckling, the billets are pressed and stacked. The billet shape is good and there is no buckling phenomenon. From the time the billets are cut off to the time before machine cleaning treatment, they are cooled slowly. The cooling time should ensure the temperature requirements of the machine cleaning treatment process as described below. During the machine cleaning treatment of billets, the surface cleaning state of billets varies depending on the steel grade and temperature. The machine cleaning treatment process of each grade of billet is as follows:

[0033] The FD product surface grade casting billet is preheated for 37-40 seconds at an oxygen pressure of 0.26-0.28 MPa. Then, a warm billet cleaning process is performed, with the billet temperature between 200°C and 400°C and the oxygen pressure between 0.22 MPa and 0.24 MPa. The cleaning mode is four-sided cleaning, with the cleaning depth on the upper and lower surfaces being 3.7-4.0 mm and the cleaning depth on the two narrow sides being 3.3-3.5 mm.

[0034] The surface grade of the FC product billet is as follows: First, it is preheated for 33s to 36s with a preheating oxygen pressure of 0.26MPa to 0.28MPa; then, it is cleaned by a warm billet cleaning machine, with the billet temperature between 200℃ and 400℃ and the oxygen pressure between 0.22MPa and 0.24MPa; the cleaning mode adopts four-sided cleaning, with the cleaning depth of the upper and lower surfaces being 3.3mm to 3.5mm and the cleaning depth of the two narrow sides being 2.7mm to 3.0mm.

[0035] The surface grade casting billet of the FB product is preheated for 30-32 seconds at an oxygen pressure of 0.26-0.28 MPa. Then, a hot billet cleaning process is performed, with the billet temperature between 400°C and 800°C and the oxygen pressure between 0.20 MPa and 0.22 MPa. The cleaning mode is four-sided cleaning, with a cleaning depth of 2.7-3.0 mm on the upper and lower surfaces and 2.7-3.0 mm on the two narrow sides.

[0036] The surface grade castings for the FA products are preheated for 37-40 seconds at an oxygen pressure of 0.26-0.28 MPa. Then, a mechanical cleaning process is performed, with the casting temperature controlled below 200°C and the oxygen pressure between 0.22 MPa and 0.24 MPa. The cleaning process involves cleaning both the upper and lower surfaces. For castings with liquid level fluctuations >20 mm, deep cleaning is performed, with a cleaning depth between 4.0 mm and 4.5 mm for both surfaces. For castings with liquid level fluctuations between 10 mm and 20 mm, the cleaning depth between 3.3 mm and 4.0 mm is required. For castings with liquid level fluctuations between 5 mm and 10 mm, shallow cleaning is performed, with a cleaning depth between 2.3 mm and 3.3 mm.

[0037] During the machine cleaning process of billet casting, the combustion media of the burners are blast furnace gas and oxygen. During this process, the pore channels through which the combustion media flow through the burners are easily blocked, directly affecting the combustion media pressure and causing unstable flame quality in the burner orifices. Therefore, a long, elliptical slit structure is adopted for the burners, with dimensions of 1.8mm–2.0mm for the major axis and 1.0mm–1.2mm for the minor axis, replacing the existing needle-like pore structure to reduce the probability of burner blockage during machine cleaning of billet casting. The burner blockage rate has been reduced from 26% to 3.9%, and the surface quality of the billet after machine cleaning has been significantly improved. Burners are replaced regularly for offline inspection and maintenance. The number of billet pieces cleaned by the upper and side burners is guaranteed to not exceed 2000 pieces, and the number of billet pieces cleaned by the lower burner is guaranteed to not exceed 1500 pieces.

[0038] During the billet cleaning process, the cleaning speed is closely related to the billet temperature, cleaning depth, billet type, and medium pressure. Considering the influence of the above parameters, the cleaning speed during billet cleaning is calculated according to formula (I).

[0039]

[0040] In the formula, T: billet temperature, °C; F: oxygen pressure, MPa; D: cleaning depth, mm.

[0041] During the slow cooling process of warm billets or slowly cooled billets, pressing and stacking the billets is used to prevent the top layer of billets from being stuck, resulting in poor billet shape during machine cleaning, incomplete burner closure, and affecting burner opening rate.

[0042] Example 1: The method for reducing high edges and missing cleaning on the surface of machine-cleaned billets is as follows.

[0043] Eight O5 plate billets were selected for machine cleaning. After the O5 plate billets were cut off the production line, they were stacked and slow cooled. To ensure that the O5 plate billets were cleaned at a warm temperature, the slow cooling time for the eight O5 plate billets from the time they were cut off the production line to the time before machine cleaning was 30 to 36 hours. The temperatures of the eight billets were measured to be 230, 200, 260, 350, 390, 300, 360 and 240℃, respectively.

[0044] The O5 plate billets requiring machine cleaning are transported to the machine cleaning roller conveyor for preheating. The preheating oxygen pressure is 0.28 MPa, and the preheating time is 40 seconds. After preheating, the O5 plate billets are cleaned under an oxygen pressure of 0.24 MPa. A four-sided cleaning mode is adopted, with the upper and lower surfaces plus the left and right narrow sides. The cleaning depth of the upper and lower surfaces is 4 mm, and the cleaning depth of the left and right narrow sides is 3.5 mm. The machine cleaning speeds of the eight billets are 10 m / min, 10 m / min, 10 m / min, 10.5 m / min, 11 m / min, 10.5 m / min, 10.5 m / min, and 10 m / min, respectively.

[0045] The gas flow passage through the burner is an elongated elliptical shape with a major axis length of 2.0 mm and a minor axis length of 1.2 mm. The burner pipeline is unobstructed. The number of cleaned casting billets on the upper and side burners is 2000, and the number of cleaned casting billets on the lower burner is no more than 1500. After the machine cleaning process, there is no leakage at the burner opening.

[0046] After the above-mentioned cleaning process, the preheating pit molten pool is well formed, and the upper and lower surfaces and left and right sides of the billet are flat and smooth, without high edges or incomplete cleaning. Figure 1 This is a picture of the surface of the O5 plate after machine cleaning, obtained by conventional methods. Figure 2 This is a surface image of O5 steel strip obtained using conventional methods; Figure 3 These are actual surface images of the same batch of cast billets after machine cleaning according to this embodiment. Figure 4 This is a photograph of the surface appearance of the O5 strip steel obtained after machine cleaning in this embodiment; by Figure 1-4 As can be seen, the method effectively eliminates surface defects and improves the surface quality of the billet, resulting in a significant improvement in the surface quality of the O5 plate and strip steel.

[0047] Example 2: The method for reducing high edges and missing cleaning on the surface of machine-cleaned billets is as follows.

[0048] Five appliance sheet billets were selected for machine cleaning. After the appliance sheet billets were cut off the production line, they were stacked and slow cooled. To ensure that the appliance sheet billets were cleaned while still warm, the slow cooling time for the five appliance sheet billets from the time they were cut off the production line to the time before machine cleaning was 30 to 36 hours. The temperatures of the five billets were measured to be 200, 250, 360, 370 and 230℃, respectively.

[0049] The appliance board billets requiring machine cleaning are transported to the machine cleaning roller conveyor for preheating. The preheating oxygen pressure is 0.26 MPa, and the preheating time is 35 seconds. After preheating, the appliance board billets are cleaned under an oxygen pressure of 0.23 MPa. A four-sided cleaning mode is adopted, consisting of the upper and lower surfaces plus the narrow left and right sides. The cleaning depth of the upper and lower surfaces is 3.5 mm, and the cleaning depth of the narrow left and right sides is 3 mm. The machine cleaning speeds for the five billets are 9.5 m / min, 9.5 m / min, 10 m / min, 10.5 m / min, and 9.5 m / min, respectively.

[0050] The gas flow passage through the burner is an elongated elliptical shape with a major axis length of 1.8 mm and a minor axis length of 1.2 mm. The burner pipeline is unobstructed and free of blockages. After the machine cleaning process, there is no leakage at the burner opening.

[0051] After the above-mentioned cleaning process, the preheating pit molten pool is well formed, and the upper and lower surfaces and left and right sides of the billet are flat and smooth, without high edges or incomplete cleaning.

[0052] Example 3: The method for reducing high edges and missing cleaning on the surface of machine-cleaned billets is as follows.

[0053] Six high-strength steel billets were selected for machine cleaning. After the high-strength steel billets were cut off the production line, they were stacked. To ensure the cleaning of hot billets, the six high-strength steel billets were stacked for no more than 10 hours from the time they were cut off the production line to the time they were machine cleaned. The temperatures of the six billets were measured at 500, 650, 400, 700, 660, and 780℃ respectively.

[0054] The high-strength steel billets requiring machine cleaning are transported to the machine cleaning roller conveyor for preheating. The preheating oxygen pressure is 0.27 MPa, and the preheating time is 30 seconds. After preheating, the high-strength steel billets are cleaned under an oxygen pressure of 0.22 MPa. A four-sided cleaning mode is adopted, with the upper and lower surfaces plus the narrow left and right sides. The cleaning depth of the upper and lower surfaces is 3 mm, and the cleaning depth of the narrow left and right sides is 3 mm. The machine cleaning speeds of the six billets are 11.5 m / min, 12 m / min, 11.5 m / min, 12.5 m / min, 12 m / min, and 13 m / min, respectively.

[0055] The gas flow passage through the burner is an elongated elliptical shape with a major axis length of 1.9 mm and a minor axis length of 1.0 mm. The burner pipeline is unobstructed and free from blockages. After the machine cleaning process, there is no leakage at the burner opening.

[0056] After the above-mentioned cleaning process, the preheating pit molten pool is well formed, and the upper and lower surfaces and left and right sides of the billet are flat and smooth, without high edges or incomplete cleaning.

[0057] Example 4: The method for reducing high edges and missing cleaning on the surface of machine-cleaned billets is as follows.

[0058] Ten molten surface fluctuating billets were selected for machine cleaning. After the molten surface fluctuating billets were cut off the production line, they were stacked and slowly cooled. The molten surface fluctuating billets were then cleaned. The stacked and slowly cooled 10 molten surface fluctuating billets from the time they were cut off the production line to the time they were machine cleaned for more than 60 hours. The temperatures of the 10 billets were measured at 50, 30, 20, 100, 40, 80, 120, 180, 30, and 190℃.

[0059] The surface-fluid slabs requiring machine cleaning are transported to the machine cleaning roller conveyor for preheating at an oxygen pressure of 0.28 MPa for 40 seconds. After preheating, the surface-fluid slabs are cleaned at an oxygen pressure of 0.24 MPa. The surface fluctuation values ​​of the 10 surface-fluid slabs are 8 mm, 10 mm, 6 mm, 12 mm, 9 mm, 23 mm, 16 mm, 7 mm, 15 mm, and 20 mm, respectively. The surface-fluid slabs are cleaned on both the upper and lower surfaces. The cleaning depths of the 10 slabs are 2.6 mm, 3.3 mm, 2.4 mm, 3.5 mm, 3.0 mm, 4.5 mm, 3.4 mm, 2.5 mm, 3.6 mm, and 4.0 mm, respectively. The machine cleaning speeds of the 10 slabs are 9 m / min, 9 m / min, 9 m / min, 10 m / min, 9 m / min, 9 m / min, 10 m / min, 10 m / min, 9 m / min, and 10.5 m / min, respectively.

[0060] The gas flow passage through the burner is an elongated elliptical shape with a major axis length of 2.0 mm and a minor axis length of 1.2 mm. The burner pipeline is unobstructed and free from blockages. After the machine cleaning process, there is no leakage at the burner opening.

[0061] After the above-mentioned cleaning process, the upper and lower surfaces and left and right sides of the billet are flat and smooth, without high edges or incomplete cleaning.

Claims

1. A method for reducing the high ridge and leakage of the machine-cast billet surface, characterized in that: The steel grades for billets requiring machine cleaning are classified into four grades: FD, FC, FB, and FA, based on the surface requirements of different products. The FD grade is for O5 automotive panels, the FC grade is for appliance panels, the FC grade is for high-strength steel series, and the FA grade is for billets with fluctuating liquid surface under unsteady pouring conditions. The FD grade billet is subjected to warm billet cleaning treatment, with a billet temperature of 200℃≤billet temperature<400℃, and preheating for 37s~40s before cleaning treatment; The FC surface grade billet is subjected to warm billet cleaning treatment, with a billet temperature of 200℃≤billet temperature<400℃, and preheating for 33s~36s before cleaning treatment; The FB surface grade billet is subjected to hot billet cleaning treatment, with a billet temperature of 400℃≤billet temperature<800℃, and preheating for 30s~32s before cleaning treatment; The FA surface grade billet is subjected to a cooling and cleaning process, with the billet temperature controlled at <200℃, and preheated for 37s to 40s before the cleaning process. The cleaning speed during machine cleaning is calculated according to formula (Ⅰ). V = 1.2T 1.5 × F × (1 / D 2 ) (I), In the formula, T: billet temperature, °C; F: oxygen pressure, MPa; D: cleaning depth, mm.

2. The method of reducing high ridge and missing cleaning of a billet surface according to claim 1, wherein: The FD surface grade ingots have a preheating oxygen pressure of 0.26 MPa to 0.28 MPa and a cleaning oxygen pressure of 0.22 MPa to 0.24 MPa; the FC surface grade ingots have a preheating oxygen pressure of 0.26 MPa to 0.28 MPa, where 0.22 MPa < cleaning oxygen pressure ≤ 0.24 MPa; the FB surface grade ingots have a preheating oxygen pressure of 0.26 MPa to 0.28 MPa, where 0.20 MPa < cleaning oxygen pressure ≤ 0.22 MPa; and the FA surface grade ingots have a preheating oxygen pressure of 0.26 MPa to 0.28 MPa, where 0.22 MPa < cleaning oxygen pressure ≤ 0.24 MPa.

3. The method of reducing high ridge and missing cleaning of a billet surface of claim 1, wherein: The FD surface grade slab is cleaned using a four-sided cleaning method, with a cleaning depth of 3.7mm to 4.0mm on the upper and lower surfaces and a cleaning depth of 3.3mm to 3.5mm on the two narrow sides. The FC surface grade billet is cleaned using a four-sided cleaning method, with a cleaning depth of 0.33mm to 3.5mm on the upper and lower surfaces and a cleaning depth of 2.7mm to 3.0mm on the two narrow sides. The FB surface grade casting billet is cleaned using a four-sided cleaning method, with a cleaning depth of 2.7mm to 3.0mm on the upper and lower surfaces and a cleaning depth of 2.7mm to 3.0mm on the two narrow sides. The FA surface grade billet is cleaned using a two-sided cleaning method, cleaning both the upper and lower surfaces. For billets with liquid level fluctuations > 20 mm, deep cleaning is performed, with a cleaning depth of 4.0 mm < cleaning depth of both upper and lower surfaces ≤ 4.5 mm. For billets with liquid level fluctuations 10 mm < liquid level fluctuations ≤ 20 mm, cleaning depth of 3.3 mm < cleaning depth ≤ 4.0 mm. For billets with liquid level fluctuations 5 mm ≤ liquid level fluctuations ≤ 10 mm, shallow cleaning is performed, with a cleaning depth of 2.3 mm ≤ cleaning depth ≤ 3.3 mm.

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