CN111604697B

CN111604697B - Control method for transverse folding defect of thin-specification low-carbon steel

Info

Publication number: CN111604697B
Application number: CN202010481434.3A
Authority: CN
Inventors: 王野; 齐林雷; 李远旭; 姚广雷; 徐帅
Original assignee: Rizhao Baohua New Material Co Ltd
Current assignee: Rizhao Baohua New Material Co Ltd
Priority date: 2020-05-31
Filing date: 2020-05-31
Publication date: 2021-05-14
Anticipated expiration: 2040-05-31
Also published as: CN113118783B; CN111604697A; CN113118783A

Abstract

The invention discloses a method for controlling a transverse folding defect of thin low-carbon steel, which relates to the field of metallurgy and comprises the following steps of sequentially connecting: feeding, uncoiling, shearing, welding by a welding machine, leveling by a leveling machine, inlet loop, scale breaker, acid washing, rinsing, straightening and withdrawing, outlet loop, shearing and coiling. Compared with the prior art, the method can reduce the rate of change of the transverse folding defect and improve the yield.

Description

Control method for transverse folding defect of thin-specification low-carbon steel

Technical Field

The invention relates to the field of metallurgy, in particular to a method for controlling the transverse fracture defect of a thin-gauge 0.7-1.5mm low-carbon steel hot rolling raw material of a hot rolling production line in an acid pickling production line.

Background

With the progress of steel rolling technology and the development of hot rolling production lines, hot rolling of thin products is possible. The thickness specification of the hot rolled plate is expanded to 0.7-4.0 mm; the hot rolling raw material coil generates yield in the uncoiling process of an uncoiler of an acid pickling production line, and the surface generates a transverse folding defect vertical to the rolling direction.

The transverse folding defect of the hot-rolled coil is generated by the existence of a yield platform, and the plastic deformation of the strip steel is concentrated in a certain area, so that a strip-shaped deformation area is formed. In addition, the occurrence of the transverse rupture is influenced by many factors, such as the performance of the raw material coil, the shape of the plate, the coiling tension of the hot-rolled coil, the feeding temperature, the using mode of a reverse bending roller of an uncoiler of the pickling line, the uncoiling tension of the pickling line, the uncoiling speed and the like. With the successful development of a hot rolling production line, a hot rolling product with the thin specification of 0.8-1.5mm can be produced in a hot rolling mode. The thinner the raw material roll thickness specification is, the higher the probability of generating the transverse folding defect is, the more serious the defect degree is, and the outer ring transverse folding defect forms are different, so that the whole roll is wide and short linear shapes are arranged at two sides of the steel roll. Overall, the thin gauge has a rate of rejection of degradation due to a cross-fold defect of 3.5%; the cutting amount is increased at the head and the tail, and the yield of the strip steel is influenced by about 1.2 percent.

In the existing research, the discussion about the control of the transverse fracture defect aims at the raw material hot rolled coil with the thickness of more than 1.5 mm. The currently accepted control method in the industry is to reduce the coiling temperature of the hot rolled coil and improve the yield strength, thereby reducing the generation probability of uncoiling transverse folding defects, which is a very effective means for controlling transverse folding. However, the method is only limited to the raw material hot rolled coil with the thickness of more than 1.5mm, in the practical production, when the method is adopted for the hot rolled coil with the thickness of 0.7-1.5mm on the hot rolling production line, the strength of the produced hot rolled coil is higher than that of the hot rolled coil produced by the traditional process due to the process characteristics of the hot rolling production line, and if the coiling temperature of the whole hot rolled coil is reduced by adopting the traditional method, the strength is improved to reduce the transverse folding defect, so that the strength of the strip steel is increased, the elongation is reduced, and the product quality is sacrificed. Therefore, a method for controlling the transverse folding defect of the hot rolling raw material coil with the thickness specification less than or equal to 1.5mm produced by a hot rolling production line is urgently needed.

Disclosure of Invention

The technical task of the invention is to provide a control method for the transverse folding defect of thin low-carbon steel aiming at the defects of the prior art, effectively control the transverse folding of hot rolling raw material rolls with the thickness specification less than or equal to 1.5mm produced by a hot rolling production line, and simultaneously provide a control method for the angle of a reverse bending roll. The rate of change of the transverse folding defect is reduced, and the yield is improved.

The technical scheme for solving the technical problem is as follows: a control method for the transverse folding defect of thin-specification low-carbon steel is characterized by comprising the following steps: the process comprises the following steps of sequentially connecting: feeding, uncoiling, shearing, welding by a welding machine, flattening by a flattening machine, looping at an inlet, crushing by a scale breaker, pickling, rinsing, straightening and withdrawing, looping at an outlet, shearing and coiling; in the feeding procedure, the feeding temperature of the raw material roll is controlled to be less than or equal to 45 ℃; the anti-bending roll is arranged at the rear part of the uncoiler used in the uncoiling process, the wrap angle theta of the anti-bending roll is 35-55 degrees, and the uncoiling speed is over 600 m/min.

And an oiling process is added between the outlet loop and the shearing process.

The raw material roll is stored for more than 5 days when the thickness is 0.7-1.2mm, and is stored for more than 4 days when the thickness is 1.2-1.5 mm.

The working roll of the descaler is made of tungsten carbide, and the period of the working roll is set to 6000-6500 km.

The coiling temperature of the head and the tail of the strip in the hot rolling production process of the raw material coil is 580-600 ℃.

A first tension roller set is arranged between the welding process of the welding machine and the leveling process of the whole machine, a second tension roller set is arranged between the inlet loop and the scale breaker process, a third tension roller set is arranged between the scale breaker and the acid washing process, and a fourth tension roller set is arranged at two ends of the pulling and straightening process.

The roller diameter of the tension roller group is 1200-1250 mm, and the roller surface abrasion of the tension roller is less than 2.0 mm.

Compared with the prior art, the invention has the following outstanding beneficial effects:

1. a control method of the wrap angle of the reverse bending roll of the uncoiler of the pickling production line is provided, and the application period of the reverse bending roll is standardized;

2. the rate of change of the transverse folding defect is reduced, and the yield is improved;

3. the rate of judging the transverse fold of the strip steel with the thickness less than or equal to 1.5mm is reduced from 3.5 percent to less than 0.5 percent; the yield is improved by 0.5 percent.

Drawings

Fig. 1 is a schematic structural view of the present invention.

FIG. 2 is a schematic view of the wrap angle of the recurved roll of the present invention.

Detailed Description

The invention is further described with reference to the drawings and the detailed description.

The process comprises the following steps: feeding → uncoiling → shearing → welding → leveling machine leveling → inlet loop → descaler → acid cleaning → rinsing → straightening → outlet loop → shearing → coiling.

Wherein, between the outlet loop and the shearing process, an oiling process can be added according to the production purpose.

The above process steps can be performed by the existing metallurgical machinery capable of realizing the above steps, and can also be optimized to perform specialized production by a special production line, wherein the production line is shown in fig. 1 and comprises an uncoiler 1, an inlet shear 2, a welding machine 3, a temper mill 4, an inlet loop 5, a scale breaker 6, an acid washing section 7, a rinsing section 8, a tension leveler 9, an outlet loop 10, an outlet shear 12 and a coiler 13 which are connected in sequence. An oiling machine 11 is then added between the outlet loop 10 and the outlet shears 12 as the case may be, and then the oiling or no-oiling process is performed depending on the end product conditions.

The present invention specifically controls the above-described steps, and the parts not mentioned are not described in detail since they are consistent with the prior art.

1. Feeding process

(1) Controlling the feeding temperature of the raw material roll

The feeding temperature of the raw material roll is controlled to be less than or equal to 45 DEG C

(2) Controlling storage time in stock repository

Compared with the prior art, the storage time of the thin-specification low-carbon steel in the raw material warehouse is prolonged. The metal or alloy is kept for a period of time at a certain temperature, the strength is gradually increased, and the elongation is gradually reduced. The invention utilizes the effect of the aging of the strip steel, prolongs the feeding time of the strip steel, considers the strength and the elongation rate in two ways, reasonably improves the yield strength of the raw materials and reduces the probability of generating transverse wrinkles. Specifically, the strip steel with the thickness of 0.7-1.2mm needs to be stored for more than 5 days, and the strip steel with the thickness of 1.2-1.5mm needs to be stored for more than 4 days.

And the online production can be realized only if the temperature and the storage time of the raw material roll meet the requirements.

The feeding can be realized by adopting a walking beam.

2. Uncoiling process

(1) Control of the counter-bending rolls of an unwinder

When the strip steel is uncoiled under the action of tension, the hot rolled strip steel with a certain thickness continuously receives the action of bending moment in the process of bending to flattening, the bending moment is continuously increased along with the uncoiling of the strip steel, the fiber rate of the surface layer of the strip steel reaches the upper yield strength and is rapidly softened in a local narrow area where the maximum bending moment acts, the fiber rate flows on the stress level of the lower yield strength, and at the moment, if the fiber stress of the surface layer of the strip steel in the adjacent area can exceed the threshold of the upper yield strength, the area where the yield flows expands to two sides, and the strip steel is smoothly uncoiled. If the fiber stress of the surface layer of the strip steel in the adjacent area cannot exceed the threshold of the upper yield strength, the area where the yield flows is limited to the initial part, and the deformed part is bent, namely, the transverse bending defect is generated. The uncoiler is provided with the reverse bending roller, so that the strip steel generates reverse bending deformation, and when the algebraic sum of the internal stress of the strip steel and the stress generated by the reverse bending roller for bending the strip steel is greater than the upper yield strength and the generated deformation exceeds the yield extension area, the transverse bending can be avoided. Meanwhile, the reverse bending roller is pressed against the strip steel, so that the strip steel can be guaranteed to be stably deformed layer by layer in the uncoiling process, and transverse folding defects can be caused due to nonuniform deformation between layers.

In the prior art, the control of the reverse bending roll comprises two modes:

position control: the pressing position of the reverse bending roller is adjusted along with the diameter change in the uncoiling process. According to the relative relation between the outer diameter of the steel coil and the extension of the hydraulic cylinder, the anti-bending roller automatically adjusts the extension position according to the coil diameter.

Pressure control: and (3) according to the pressure generated by the hydraulic cylinder on the strip steel, keeping the pressure of the hydraulic cylinder at a set value, and automatically adjusting the position of the reverse bending roller.

However, in practice, in the case of thin gauge strip steel, the hot rolled coil tends to yield more at the head and tail than at the middle during uncoiling, and therefore, neither constant position control nor constant pressure can be improved.

The present invention therefore proposes a wrap angle control concept. As shown in fig. 2, the reverse bending roll 14 is arranged at the upper rear part of a winding drum 15 of the uncoiler 1, and the wrap angle theta is an angle formed by a median line of an arc surface of a contact part of the reverse bending roll 14 and the strip steel 16 and a tangent line of the strip steel 15 and the strip steel 16. The wrap angle is constant, the strip steel can be uniformly deformed in the process of pressing down the reverse bending roll, and the probability of generating transverse folding defects is reduced. When the position of the anti-bending roller is set to have a wrap angle of 35-55 degrees, the transverse fold defects can be reduced.

The low-carbon steel has different thickness specifications, and the control angle of the reverse bending roll has corresponding optimized values, as shown in the following table:

thickness (mm)	Wrap angle
		0.7～1.2mm	45～46゜
1.2～1.5mm	44～45゜
		＞1.5mm	40～43゜

The specific control method of the angle of the reverse bending roller can be various, and a person skilled in the art can set the extending position by using the variables of the specific model of the uncoiler, the diameter specification and the thickness specification of the steel coil.

(2) Increase the uncoiling tension and the uncoiling speed of the hot-rolled coil

On the basis of the wrap angle control of the reverse bending roll, the combination of increasing the uncoiling tension and the uncoiling speed of the hot-rolled coil can ensure uniform deformation so as to reduce the probability of generating transverse fold line defects.

The uncoiling maximum speed designed by the production line is 800 m/min; the uncoiling tension is designed to be 30 KN.

The actual uncoiling speed is set according to the thickness specification: for low-carbon steel with the thickness of more than or equal to 0.7mm and less than or equal to 1.2mm, the uncoiling speed must be kept above 700m/min in the uncoiling process; for 1.2mm_＜The thickness of the low-carbon steel is less than or equal to 1.5mm, and the uncoiling speed must be kept above 600m/min in the uncoiling process;

as shown in the table below, the uncoiling tension range is selected according to the width and thickness specifications, and strip steel with the thickness not more than 1.5mm under the condition allowed by the conditions in the production process is uncoiled by adopting the maximum tension.

(3) The cycle requirement of the reverse bending roll is as follows:

because the wrap angle control of the reverse bending roll is increased, and the uncoiling tension and the uncoiling speed of the hot-rolled coil are improved, compared with the reverse bending roll in the prior art, the abrasion of the reverse bending roll is more serious, the pressure of strip steel in the uncoiling process is unstable, the transverse fold defect is easily generated, and the plate shape defect is caused. The material of the reverse bending roller of the invention requires the reverse bending roller made of tungsten carbide, and has high hardness and good wear resistance. Meanwhile, the service cycle is shortened from 5 months to 2-3 months, and can not exceed 3 months.

3. Leveling procedure

In the traditional process technical route: feeding → uncoiling → shearing → welding → inlet loop → descaler → acid washing → rinsing → leveling → straightening → outlet loop → oiling/not oiling → shearing → coiling.

The leveling in the traditional process aims at leveling the surface after scale breaking and acid pickling, and the yield is not obviously improved.

In fact, after the strip steel is reversely bent and deformed by the reverse bending roller 14 of the uncoiler, the stable deformation can be attenuated along with the forward process of a production line, the thickness of the traditional strip steel is thicker, so that the deformation attenuation cannot cause excessive transverse folding, the subsequent flattening and straightening processes can be effectively corrected, but for low-carbon steel hot rolling raw materials with the thin specification of 0.7-1.5mm, the attenuation of the deformation is more obvious, and the low-carbon steel hot rolling raw materials are easy to yield in the repeated bending process of a roll system to generate transverse folding lines, so that the later correction failure is caused. Therefore, the invention puts the leveling procedure behind the welding machine equipment, adds the leveling machine at the position, and can keep the benign uniform deformation effect caused by reverse bending under the matching of the wrap angle theta of the reverse bending roller, eliminate the inherent yield platform of the strip steel, match the tension of the tension roller, reduce the following procedures of the hot-rolled strip steel coil, and ensure that the strip steel is repeatedly bent to have the transverse bending defect when passing through the roller system, thereby ensuring that the effect is stable and continuous without secondary leveling.

4. Scale breaking procedure

When the working roll of the scale breaker is seriously worn, the seriously worn position of the working roll of the scale breaker can be unevenly deformed when the strip steel is bent by the scale breaker, and the worn shape of the scale breaker can generate a transverse folding defect on the surface of the strip steel. The transverse folding defect generated by the scale breaker is characterized in that the transverse position of the strip steel is fixed and corresponds to the abrasion position of a working roll of the scale breaker, and the full length of the whole roll of the strip steel exists.

In order to reduce the probability of the cross-folding of the working roller of the scale breaker, the working roller of the scale breaker is made of tungsten carbide, so that the wear resistance of the working roller of the scale breaker can be improved, and the period is prolonged.

Setting the grinding period of the working roller: usually, the period of the working roll of the descaler made of common materials is 1100-1400km, and the period of the working roll of the descaler made of tungsten carbide is set at 6000-6500 km.

5. Production line tension roller system parameter control

(1) Roller diameter of tension roller

The tension roll is a roll system for establishing tension on a production line, is also called a tension roll set (S roll), and is specifically set as follows: a first tension roller set is arranged between the welding machine 3 and the leveling machine 4, a second tension roller set is arranged between the inlet loop 5 and the scale breaker 6, a third tension roller set is arranged between the scale breaker 6 and the pickling section 7, and a fourth tension roller set is arranged at two ends of the withdrawal and straightening machine 9.

The roll diameter of a tension roll of the pickling production line influences the transverse folding of thin-specification strip steel, the roll diameter of the tension roll is small, the curvature is large, the strip steel is easy to yield in the process of winding the tension roll, the transverse folding is particularly obvious for the strip steel with the thickness less than or equal to 1.0mm, and the probability of transverse folding is higher. Therefore, the roller diameter of the tension roller is controlled to be 1200-1250 mm.

(2) Wear of roller surface of tension roller

The middle part or the edge part of the S roller is greatly abraded, so that the stress on the upper surface and the lower surface of the strip steel is uneven when the strip steel passes through the S roller, the stress balance cannot be achieved, and the surface of the strip steel is subjected to yielding to generate the transverse folding defect. Therefore, the surface wear of the tension roller is not less than 2.0mm for the acid pickling line for producing the thin hot rolled coil, and the tension roller needs to be replaced. That is to say, the roller surface abrasion of the production line tension roller is controlled to be less than 2.0 mm.

6. Concerning control in the production of rolls of stock

The coiling temperature of the head and the tail of the hot-rolled coil is reduced in the hot rolling production process of the raw material coil.

In the traditional production process, the normal coiling temperature of the low-carbon steel is controlled to be 680-720 ℃. The preferable scheme of the raw material coil in the process is that in the production of the raw material coil, the coiling temperature of the head and the tail of the strip is controlled to be 580-600 ℃ in a way of strongly cooling the head and the tail of the strip, so as to improve the strength of the head and the tail of the strip.

The specific operation of controlling the head and tail temperature of the cold strip steel is as follows: the distance between the head and the tail of the ESP hot-rolled coil is detected by a strip steel tracking system, the head of the hot-rolled coil is 50 meters, the tail of the hot-rolled coil is 30 meters, the opening degree of a regulating valve is controlled by increasing the injection amount and pressure of a nozzle of a layer cooling area, and the coiling temperature of the head and the tail of the ESP hot-rolled coil is reduced.

In the optimization scheme, the following control modes can be added

(1) Reducing the stagger degree of the scale breaker

The stagger degree of all thickness specifications in traditional production is in the range of 50-55 mm. The stagger degree of the scale breaker is reduced to 20-40mm, so that the deformation curvature of the strip steel is reduced, the tension of the scale breaker is increased, and the elongation of the scale breaker is ensured to be unchanged.

(2) Elongation setting of scale breaker

The elongation percentage range of the scale breaker in the traditional production is 0.8-1.2%, the elongation percentage of the scale breaker can be reduced to 0.4-0.8%, the reduced elongation percentage is increased to the elongation percentage of a temper mill, and the total elongation percentage of the strip steel is ensured to be unchanged.

The following are the various control parameters of the specific embodiment: the parameters not mentioned in the table are according to the parameter ranges and methods described in the above control modes.

In addition, in order to compare the technical effects of the prior art and the present invention, three control groups were also set:

in comparison group 1, the process is a conventional process, namely: feeding → uncoiling → shearing → welding → inlet loop → descaler → acid washing → rinsing → leveling → straightening → outlet loop → oiling/not oiling → shearing → coiling. The uncoiler reverse bending roller is controlled by adopting position control, the relative relation between the external diameter of the steel coil and the extension of the hydraulic cylinder is-0.2952 x +1276.2, and the extension position of the reverse bending roller is automatically adjusted according to the size of the coil diameter. The remaining parameters were the same as in example 1.

In comparison group 2, the process was a conventional process, the parameters of example 1 were used for setting, the reverse bending roll was wrap angle controlled, and the wrap angle degree was 45 °.

Control 3 was set in the procedure of example 1, but the position control in control 1 was used for the uncoiler reverse bending control. The remaining parameters were the same as in example 1.

The results show that the judgment rate of the transverse fold lines of each example is less than 0.5 percent, and the judgment rates of the control groups are respectively as follows: 3.5%, 2.4%, 1.8%, which are significantly different from the group of example 1.

It should be noted that while the invention has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various obvious changes can be made therein without departing from the spirit and scope of the invention.

Claims

1. A control method for the transverse folding defect of thin-specification low-carbon steel is characterized by comprising the following steps: the process comprises the following steps of sequentially connecting: feeding, uncoiling, shearing, welding by a welding machine, flattening by a flattening machine, looping at an inlet, crushing by a scale breaker, pickling, rinsing, straightening and withdrawing, looping at an outlet, shearing and coiling; in the feeding procedure, the feeding temperature of the raw material roll is controlled to be less than or equal to 45 ℃; the anti-bending roll is arranged at the rear part of the uncoiler used in the uncoiling process, the wrap angle theta of the anti-bending roll is 35-55 degrees, and the uncoiling speed is over 600 m/min; the thin specification is 0.7-1.5mm thickness specification.

2. The method for controlling the transverse rupture defect of the thin gauge low carbon steel according to claim 1, characterized by comprising the following steps: and an oiling process is added between the outlet loop and the shearing process.

3. The method for controlling the transverse rupture defect of the thin gauge low carbon steel according to claim 1, characterized by comprising the following steps: the coiling temperature of the head and the tail of the strip in the hot rolling production process of the raw material coil is 580-600 ℃.

4. The method for controlling the transverse rupture defect of the thin gauge low carbon steel according to claim 1, characterized by comprising the following steps: a first tension roller set is arranged between the welding process of the welding machine and the leveling process of the whole machine, a second tension roller set is arranged between the inlet loop and the scale breaker process, a third tension roller set is arranged between the scale breaker and the acid washing process, and a fourth tension roller set is arranged at two ends of the pulling and straightening process.

5. The method for controlling the transverse rupture defect of the thin gauge low carbon steel according to claim 4, wherein the method comprises the following steps: the roller diameter of the first tension roller group and the second tension roller group is 1200-1250 mm, and the roller surface abrasion of the tension rollers is less than 2.0 mm.