Method for rescuing yellow spot defect on surface of cold-rolled steel coil

Abstract

The invention belongs to the technical field of cold-rolled steel coils, and particularly discloses a cold-rolled steel coil surface yellow spot defect rescue method which comprises the following steps: when a steel coil has a yellow spot defect in the production process of a recoiling unit, an oiling machine of the recoiling unit is immediately turned off, and then the steel coil with the yellow spot defect produced by the recoiling unit is output. The method comprises the steps that firstly, a steel coil is conveyed into a bell-type furnace, hydrogen reduction annealing is conducted, then the steel coil obtained after annealing is completed is discharged from the bell-type furnace, the steel coil obtained after discharging is conveyed to a final cooling table to be cooled, the steel coil obtained after cooling is completed is conveyed to a temper mill unit to be rolled, and finally after rolling of a temper mill is completed, the steel coil is rewound through a recoiling machine. The invention aims to solve the problems of serious economic loss, storage cost increase and influence on long-term development of enterprises after the current steel coil has a yellow spot defect. The redox reaction is carried out on the steel coil, the yellow spot defect reacts into iron oxide, the iron oxide is reduced into iron through hydrogen, and therefore the yellow spot defect on the steel coil can be effectively eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of cold-rolled steel coils, and in particular to a method for rescuing yellow spot defects on the surface of a cold-rolled steel coil. Background Art

[0002] Cold-rolled steel coils play a vital role in modern industrial production and are widely used in many fields such as automobile manufacturing and home appliance production. In the production process of cold-rolled steel coils, after the flattening process, intermittent or continuous strip-shaped yellow spots appear in the middle of the steel coil, and the upper and lower surfaces have a light yellow or brownish yellow color, commonly known as yellow spot defects.

[0003] Through electron microscope scanning and energy spectrum analysis, the yellow spot defect is actually a rust defect. Once the yellow spot is formed, it cannot be wiped off with solvents, but it can be dissolved in dilute hydrochloric acid. Therefore, the yellow spot is actually a kind of "rust" produced after the steel coil is leveled. Unlike ordinary rust, its formation conditions and appearance are relatively special. It is a point-like diffusion type rust under insufficient oxidation conditions. The rust is caused by the potential difference on the surface of the steel coil after leveling. Under the joint action of residual leveling liquid, atmospheric moisture and oxygen, a series of iron oxides are formed by the galvanic cell reaction, which shows yellow-brown. The reaction mechanism is as follows:

[0004] Anode (Fe):Fe-2e - =Fe 2+

[0005] Cathode (impurity): O2+2H20+4e - =40H -

[0006] Overall reaction: 2Fe+O2+2H20=2Fe(OH)2

[0007] Fe(0H)2 will be further oxidized by O2 to generate FeOOH (yellow-brown).

[0008] Fe(0H)2+1 / 4O2=FeOOH+1 / 2H20

[0009] At present, when yellow spot defects appear on steel coils, they are usually sold at a lower quality grade, which greatly reduces their market value and severely compresses their profit margins, directly leading to serious economic losses. It is also possible that inventory will be piled up for a long time due to sales difficulties, increasing storage costs. If companies frequently encounter yellow spot defects on steel coils and carry out spot processing, it will affect the long-term development of the company. Summary of the invention

[0010] The purpose of the present invention is to provide a method for rescuing yellow spot defects on the surface of cold-rolled steel coils, so as to solve the problem that after the yellow spot defects appear on the steel coils, the quality grade is reduced for sale, resulting in a significant reduction in market value, serious economic losses, increased storage costs, and affecting the long-term development of the enterprise.

[0011] In order to achieve the above object, the basic scheme provided by the present invention is: a method for rescuing yellow spot defects on the surface of cold-rolled steel coils, comprising the following steps:

[0012] S1: When yellow spot defects appear on the steel coils during the production process of the rewinding unit, the oiling machine of the rewinding unit shall be immediately shut down;

[0013] S2: Output the steel coil with yellow spot defects in the rewinding unit;

[0014] S3: Weld 3-5 layers of the inner ring of the produced steel coil, at least 4 places, and the welding length of each place is 20-30mm; S4: Transport the steel coil to the bell-type furnace for hydrogen reduction annealing. When the heating temperature is below 460℃, heat slowly at a heating rate of 30-35℃ / h and a hydrogen blowing volume of 25m 3 / h; when the heating temperature is higher than 460℃, the heating speed is not limited, the insulation temperature of the bell-type furnace is 650-730℃, and the insulation time is 3-6h;

[0015] S5: taking the annealed steel coil out of the bell furnace;

[0016] S6: The steel coils are transported to the final cooling station for cooling after being taken out of the furnace. The cooling time is 18-24 hours, until the temperature of the steel coils is cooled to below 45°C;

[0017] S7: After cooling, the steel coil is transported to the leveling unit for rolling at a rolling speed of 500-650m / min and a rolling force of 1000-1500KN;

[0018] S8: After the flat-pass mill is finished, the steel coil is re-rolled, oiled and coiled by the re-coiler, and the coiling speed is 180-260m / min.

[0019] The beneficial effects of the present invention are as follows: (1) when yellow spot defects appear on steel coils during the production process of the rewinding unit, shutting down the oiling machine of the rewinding unit can prevent the oiling from further aggravating the yellow spot defects. If the oiling continues, the yellow spot may be mixed with the oil, making the defects more difficult to handle;

[0020] (2) By welding the inner ring of the output steel coil, the inner ring of the steel coil can be made more solid and not easy to loosen during the subsequent transportation and handling process;

[0021] (3) Through hydrogen reduction annealing, the yellow spot defects on the surface of the steel coil can be effectively removed. Under specific temperature and time conditions, hydrogen can react with impurities such as oxides in the yellow spot, reducing it to substances that are easy to remove, thereby restoring the surface quality of the steel coil;

[0022] (4) Cooling in the final cooling station can make the internal structure of the steel coil more stable, avoiding stress concentration and deformation caused by excessive cooling;

[0023] (5) Temper rolling can further improve the surface quality and shape of the steel coil, making the steel coil smoother and smoother, and improving the appearance quality and performance of the product;

[0024] (6) Re-coiling can make the size of the steel coil more in line with customer requirements and improve the applicability of the product. Oiling can provide protection for the steel coil to prevent it from rusting and contamination during storage and transportation. The appropriate coiling speed can ensure that the steel coil is tightly coiled for easy storage and transportation.

[0025] In summary, the steel coil undergoes an oxidation-reduction reaction, causing the yellow spot defect (FeOOH) to react into iron oxide, and the iron oxide reduces Fe under the action of hydrogen, thereby effectively eliminating the yellow spot defect on the steel coil, avoiding the steel coil from being sold at a lower quality grade due to the yellow spot defect, and reducing economic losses.

[0026] Scheme 2 is the preferred option of the basic scheme. In S2, the steel coils with yellow spot defects are produced as a whole roll. Producing the steel coils as a whole roll is convenient for loading out of the furnace, avoiding multiple handling and placement of small rolls after splitting, thereby reducing labor intensity.

[0027] Option 3 is the preferred basic option. In S2, the detection light source lens of the EPC correction system in the rewinding unit is inspected and wiped to control the misalignment defect of the steel coil to less than 5 mm. Controlling the misalignment defect to less than 5 mm can prevent the overflow edge of the steel coil from softening during the annealing process, causing the edge folding.

[0028] Scheme 4 is the preferred basic scheme. In S4, the amount of hydrogen is increased during the high temperature insulation stage of the bell furnace, and the hydrogen blowing amount is 30-35m 3 / h, the hydrogen blowing time is 2-4h; the amount of hydrogen is increased during the high-temperature insulation stage of the bell-type furnace to facilitate the further reduction of Fe by the iron oxide under the action of hydrogen, thereby completely reducing the iron oxide.

[0029] Scheme 5 is the preferred basic scheme. In S4, the temperature of the charge chamber in the bell-type furnace is controlled to 550-580°C, the original heating hood is removed and replaced with a cooling hood; when the temperature of the bell-type furnace charge chamber is less than 550, the insulation effect of the charge chamber is poor, which reduces the complete reduction of the steel coil; when the temperature of the bell-type furnace charge chamber is greater than 580, bonding line defects are likely to appear in the charge chamber.

[0030] Scheme 6: This is the preferred basic scheme. In S5, when the bell-type furnace load is less than 45t, the furnace outlet temperature is 50°C.

[0031] When the bell-type furnace has a loading capacity of 45-70t, the outlet temperature is 80℃;

[0032] When the charging capacity of the bell-type furnace is greater than 70t, the discharge temperature is 90-100℃; there is a deviation between the discharge temperature and the actual temperature of the steel coil, and the smaller the tonnage, the greater the deviation. Controlling the charging capacity and discharge temperature can prevent secondary oxidation of the steel coil after discharge.

[0033] Option seven is the preferred basic option. In S7, the medium temperature in the leveling liquid mixed liquid tank, raw liquid tank and desalted water tank in the leveling unit is 30-50°C; the medium temperature of the leveling liquid mixed liquid tank, raw liquid tank and desalted water tank is controlled to 30-50°C to reduce the residual black ash. When the medium temperature is greater than 50°C, the medium components are easy to volatilize. When the medium temperature is less than 30°C, the additives contained in the medium are easy to precipitate and settle at the bottom of the box, affecting the cleaning effect of the medium.

[0034] Option 8, which is the preferred option of Option 7, is to spray the media in the leveling liquid mixed liquid tank, raw liquid tank and desalted water tank in the leveling unit in a fan-shaped overlapping manner to 50-100mm in front of the roller gap; and to spray the various media of the leveling unit in a fan-shaped overlapping manner onto the steel coil, so as to facilitate the uniform spraying of various media on the strip, thereby increasing the cleaning effect of the strip surface.

[0035] Option nine is the preferred basic option. In S7, the angle of the nozzle of the blowing device in the leveling unit is 40°-65°, and the blowing pressure of the blowing device is above 0.4 bar. The angle of the nozzle of the blowing device and the blowing pressure are set to facilitate achieving the best effect of blowing the leveling liquid. When the blowing angle is less than 40°, the leveling liquid on the surface of the strip is not effectively purged. When the blowing angle is greater than 65°, the leveling liquid remaining on the surface of the strip splashes, causing leveling liquid spot defects. When the blowing pressure is less than 0.4 bar, the leveling liquid on the surface of the strip is prone to unclean cleaning. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below through specific embodiments:

[0037] Example 1

[0038] A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil comprises the following steps:

[0039] S1: When yellow spot defects appear on the steel coils during the production process of the rewinding unit, the oiling machine of the rewinding unit shall be immediately shut down;

[0040] S2: The steel coils with yellow spot defects produced by the rewinding unit are output as a whole, and the detection light source lens of the EPC correction system in the rewinding unit is inspected and wiped to control the steel coil misalignment defect to less than 5mm;

[0041] S3: Weld the three layers of the inner ring of the produced steel coil at least 4 places, and the welding length of each place is 20mm;

[0042] S4: The steel coil is transported to the bell-type furnace for hydrogen reduction annealing. When the heating temperature is below 460°C, it is slowly heated at a heating rate of 30°C / h and a hydrogen blowing volume of 25m 3 / h; when the heating temperature is higher than 460℃, the heating speed is not limited, the insulation temperature of the bell-type furnace is 650℃, the insulation time is 3h, and the hydrogen volume is increased during the high-temperature insulation stage of the bell-type furnace, and the hydrogen blowing volume is 30m 3 / h, hydrogen blowing time is 2h, when the bell-type furnace charge chamber temperature cools to 550℃, remove the original heating hood and replace it with a cooling hood;

[0043] S5: The annealed steel coil is taken out of the bell furnace. When the bell furnace is loaded with less than 45 tons, the temperature is 50°C; when the bell furnace is loaded with 45 tons, the temperature is 80°C; when the bell furnace is loaded with more than 70 tons, the temperature is 90°C;

[0044] S6: The steel coils are transported to the final cooling station for cooling after being taken out of the furnace. The cooling time is 18 hours, until the temperature of the steel coils is cooled to below 45°C;

[0045] S7: After cooling, the steel coil is transported to the leveling unit for rolling. The rolling speed is 500m / min, the rolling force is 1000KN, the medium temperature in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling unit is 30°C, the angle of the nozzle of the purging device in the leveling unit is 40°, the purging pressure is above 0.4bar, and the medium in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling unit is sprayed in a fan-shaped state to 50㎜ in front of the roll gap (the fan-shaped state means that the shape of each medium when sprayed is similar to a fan-shaped, and the overlap means that the sprayed medium does not act alone when it reaches the surface of the strip, but is superimposed on each other);

[0046] S8: After the rolling of the flat-pass mill is completed, the steel coil is re-rolled, oiled and coiled by the re-coiler at a coiling speed of 180m / min.

[0047] Through the above rescue method, the weld was found to be detached, there was a slight yellow spot defect in the middle of the steel coil, which was not fully restored, and there was a leveling liquid spot defect on the 20m edge of the head of the steel coil. The overall rescue rate reached 99.5%.

[0048] Example 2

[0049] A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil comprises the following steps:

[0050] S1: When yellow spot defects appear on the steel coils during the production process of the rewinding unit, the oiling machine of the rewinding unit shall be immediately shut down;

[0051] S2: The steel coils with yellow spot defects produced by the rewinding unit are output as a whole, and the detection light source lens of the EPC correction system in the rewinding unit is inspected and wiped to control the steel coil misalignment defect to less than 5mm;

[0052] S3: Weld the 4 layers of the inner ring of the produced steel coil at least 4 places, and the welding length of each place is 25mm;

[0053] S4: The steel coil is transported to the bell-type furnace for hydrogen reduction annealing. When the heating temperature is below 460°C, it is slowly heated at a heating rate of 33°C / h and a hydrogen blowing volume of 25m 3 / h; when the heating temperature is higher than 460℃, the heating speed is not limited, the insulation temperature of the bell-type furnace is 690℃, the insulation time is 5h, and the hydrogen volume is increased during the high-temperature insulation stage of the bell-type furnace, and the hydrogen blowing volume is 33m 3 / h, hydrogen blowing time is 3h, wait for the bell-type furnace charge chamber temperature to cool to 570℃, remove the original heating hood and replace it with a cooling hood;

[0054] S5: The annealed steel coil is taken out of the bell furnace. When the bell furnace is loaded with less than 45 tons, the temperature is 50°C; when the bell furnace is loaded with 60 tons, the temperature is 80°C; when the bell furnace is loaded with more than 70 tons, the temperature is 95°C;

[0055] S6: The steel coils are transported to the final cooling station for cooling after being taken out of the furnace. The cooling time is 21 hours, until the temperature of the steel coils is cooled to below 45°C;

[0056] S7: After cooling, the steel coil is transported to the leveling mill for rolling. The rolling speed is 600m / min, the rolling force is 1300KN, the medium temperature in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling mill is 40°C, the angle of the nozzle of the purging device in the leveling mill is 50°, the purging pressure is above 0.4bar, and the medium in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling mill is sprayed in a fan-shaped state to 80㎜ in front of the roll gap (the fan-shaped state means that the shape of each medium when sprayed is similar to a fan-shaped, and the overlap means that the sprayed medium does not act alone when it reaches the surface of the strip, but is superimposed on each other);

[0057] S8: After the rolling of the flat-pass mill is completed, the steel coil is re-rolled, oiled and coiled by the re-coiler at a coiling speed of 230m / min.

[0058] Through the above rescue method, there is no detachment in the weld, the yellow spot defect has been fully restored, the performance of the steel coil is normal, no black spots appear, the surface blowing effect of the steel coil is good, and the overall rescue rate reaches 100%.

[0059] Example 3

[0060] A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil comprises the following steps:

[0061] S1: When yellow spot defects appear on the steel coils during the production process of the rewinding unit, the oiling machine of the rewinding unit shall be immediately shut down;

[0062] S2: The steel coils with yellow spot defects produced by the rewinding unit are output as a whole, and the detection light source lens of the EPC correction system in the rewinding unit is inspected and wiped to control the steel coil misalignment defect to less than 5mm;

[0063] S3: Weld the 5 layers of the inner ring of the produced steel coil, at least 4 places, and the welding length of each place is 30mm;

[0064] S4: The steel coil is transported to the bell-type furnace for hydrogen reduction annealing. When the heating temperature is below 460°C, it is slowly heated at a heating rate of 35°C / h and a hydrogen blowing volume of 25m 3 / h; when the heating temperature is higher than 460℃, the heating speed is not limited, the insulation temperature of the bell-type furnace is 730℃, the insulation time is 6h, and the hydrogen volume is increased during the high-temperature insulation stage of the bell-type furnace, and the hydrogen blowing volume is 35m 3 / h, hydrogen blowing time is 4h, wait for the bell-type furnace charge chamber temperature to cool to 580℃, remove the original heating hood and replace it with a cooling hood;

[0065] S5: The annealed steel coil is taken out of the bell furnace. When the bell furnace is loaded with less than 45 tons, the temperature is 50°C; when the bell furnace is loaded with 70 tons, the temperature is 80°C; when the bell furnace is loaded with more than 70 tons, the temperature is 100°C;

[0066] S6: The steel coils are transported to the final cooling station for cooling after being taken out of the furnace. The cooling time is 24 hours, until the temperature of the steel coils is cooled to below 45°C;

[0067] S7: After cooling, the steel coil is transported to the leveling unit for rolling. The rolling speed is 650m / min, the rolling force is 1500KN, the medium temperature in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling unit is 50°C, the angle of the nozzle of the purging device in the leveling unit is 65°, the purging pressure is above 0.4bar, and the medium in the leveling liquid mixed liquid tank, the raw liquid tank and the desalted water tank in the leveling unit is sprayed in a fan-shaped state to 100㎜ in front of the roll gap (the fan-shaped state means that the shape of each medium when sprayed is similar to a fan-shaped, and the overlap means that the sprayed medium does not act alone when reaching the surface of the strip, but is superimposed on each other);

[0068] S8: After the rolling of the flat-pass mill is completed, the steel coil is re-rolled, oiled and coiled by the re-coiler at a coiling speed of 260m / min.

[0069] Through the above rescue method, there is no weld detachment phenomenon, black spots appear on the steel coils adhered with anti-rust oil, the yellow spot defects have been fully restored, the leveling liquid spots on the steel heads and tails of the steel coils have increased, the cleaning effect is poor, and the overall rescue rate reaches 99.8%.

[0070] In summary, the steel coil is subjected to reduction annealing by the above method, so that the yellow spot defect (FeOOH) reacts into iron oxide, and the iron oxide reduces Fe under the action of hydrogen. Example 2 can completely eliminate the yellow spot defect, and there is no detachment phenomenon in the weld, and no black spots appear. The performance of the steel coil and the cleanliness of the surface plate can be effectively guaranteed, which does not affect the later use of the steel coil, thereby reducing the economic losses of the enterprise.

[0071] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil, characterized in that: The following steps are involved: S1: When yellow spot defects appear on the steel coils during the production process of the rewinding unit, the oiling machine of the rewinding unit shall be immediately shut down; S2: Output the steel coil with yellow spot defects in the rewinding unit; S3: Weld 3-5 layers of the inner ring of the produced steel coil, at least 4 places, and the welding length of each place is 20-30mm; S4: The steel coil is transported to the bell-type furnace for hydrogen reduction annealing. When the heating temperature is below 460°C, it is slowly heated at a heating rate of 30-35°C / h and the hydrogen blowing volume is 25m 3 / h; when the heating temperature is higher than 460℃, the heating speed is not limited, the insulation temperature of the bell-type furnace is 650-730℃, and the insulation time is 3-6h; S5: taking the annealed steel coil out of the bell furnace; S6: The steel coils are transported to the final cooling station for cooling after being taken out of the furnace. The cooling time is 18-24 hours, until the temperature of the steel coils is cooled to below 45°C; S7: After cooling, the steel coil is transported to the leveling unit for rolling at a rolling speed of 500-650m / min and a rolling force of 1000-1500KN; S8: After the flat-pass mill is finished, the steel coil is re-rolled, oiled and coiled by the re-coiler, and the coiling speed is 180-260m / min.

2. A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that ,In S2, the steel coil with yellow spot defects is produced as a whole roll.

3. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S2, the detection light source lens of the EPC correction system in the rewinding unit is inspected and wiped to control the misalignment defect of the steel coil to less than 5mm.

4. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S4, the amount of hydrogen is increased during the high temperature insulation stage of the bell furnace, and the hydrogen blowing amount is 30-35m 3 / h, hydrogen blowing time is 2-4h.

5. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S4, the temperature of the charge chamber in the bell-type furnace is controlled to 550-580°C, and the original heating hood is removed and replaced with a cooling hood.

6. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S5, when the bell-type furnace load is less than 45t, the furnace outlet temperature is 50℃; When the bell-type furnace has a loading capacity of 45-70t, the outlet temperature is 80℃; When the bell-type furnace loading capacity is greater than 70t, the furnace outlet temperature is 90-100℃.

7. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S7, the medium temperature in the leveling liquid mixed liquid tank, raw liquid tank and desalted water tank in the leveling unit is 30-50℃.

8. A method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 7, characterized in that: The media in the leveling liquid mixed liquid tank, raw liquid tank and desalted water tank in the leveling unit are sprayed in a fan-shaped overlapping manner to 50-100mm in front of the roller gap.

9. The method for rescuing yellow spot defects on the surface of a cold-rolled steel coil according to claim 1, characterized in that: In S7, the angle of the nozzle of the blowing device in the leveling unit is 40°-65°, and the blowing pressure of the blowing device is above 0.4 bar.