A manufacturing method for controlling flatness of stainless steel by adjusting cold rolling heat dissipation

Abstract

The application discloses a manufacturing method for controlling flatness of stainless steel by adjusting cold rolling heat dissipation, comprising the following steps: (1) performing precision grinding and polishing on the roll of a rolling mill, and controlling the precision to be below 0.003 mu m; (2) cold rolling: adopting the rolling mill of step (1) to perform cold rolling on a stainless steel plate strip, adding 1-3 passes on the normal cold rolling process, dispersing heat generated during cold rolling through multiple cold rolling, controlling the cold rolling speed to be 80 m / min-100 m / min during the cold rolling process, controlling the nozzle distance to be L=26 mm, controlling the distance from the nozzle to the working roll to be within 140 mm, controlling the rotating angle of the spraying beam to be 170 DEG, controlling the spraying speed of the cooling liquid to be 25 m / s, controlling the temperature of the cooling liquid to be 20 DEG C, and regularly replacing the cooling liquid to improve the cooling efficiency of the cooling liquid. In this way, the stainless steel plate strip has good plate shape, and the plate shape change is small.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a manufacturing method for controlling the flatness of stainless steel by adjusting the heat dissipation during cold rolling. Background Technology

[0002] Cold-rolled steel sheet and strip are crucial products for steel enterprises, accounting for an increasingly larger proportion of total steel production. They are essential raw materials for production and daily life, and are widely used in various industries such as aerospace, automotive, home appliances, electrical engineering, and precision instrument manufacturing. Currently, my country has become the world's largest producer of cold-rolled equipment, and the scale of cold-rolled strip production has become an important indicator of a country's steel industry development level. However, in recent years, the demand for cold-rolled strip has reached saturation, and high-quality strip products are becoming increasingly competitive and attracting more attention. From the perspective of enterprises themselves, in order to improve their long-term competitiveness and secure a place in the high-quality sheet and strip market, they have successively increased their R&D efforts, striving to make my country's cold-rolled steel sheet and strip products internationalized and high-end.

[0003] Strip shape is a crucial indicator of cold-rolled strip quality, directly impacting its overall quality. Common strip shape control methods can eliminate some common non-high-order shape defects, but are insufficient to eliminate localized high-order waviness defects. During cold rolling, localized "hot spots" on the rolls frequently occur. These hot spots result from asymmetrical rolling loads or uneven temperature distribution across different parts of the roll body. These localized hot spots cause localized thermal bulges on the rolls, thus affecting strip quality. Controlling localized thermal bulges on the rolls and improving strip surface quality is crucial, especially in wide-band cold rolling mills.

[0004] Currently, widely used methods for controlling strip shape include roll tilting, support rolls, work roll bending, and special mills (such as CVC and HC mills). However, when local strip shape problems occur, these shape control methods can only reduce these deviations to a small extent and cannot solve the fundamental problem. Therefore, it is necessary to study a solution to address these issues. Summary of the Invention

[0005] In view of this, the present invention addresses the deficiencies of the prior art, and its main objective is to provide a manufacturing method for controlling the flatness of stainless steel by adjusting the heat dissipation during cold rolling. This method improves the local convective heat transfer of the work rolls and controls the temperature of the rolls, thereby greatly improving the shape of the cold-rolled stainless steel strip.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A manufacturing method for controlling the flatness of stainless steel by adjusting the heat dissipation during cold rolling includes the following steps:

[0008] (1) The rolling mill rolls are finely ground and polished, with the precision controlled below 0.003μm;

[0009] (2) Cold rolling: The stainless steel strip is cold rolled using the rolling mill in step (1). 1-3 passes are added to the normal cold rolling process. The heat generated during cold rolling is dispersed through multiple cold rolling processes. During the cold rolling process, the cold rolling speed is controlled at 80m / min-100m / min, the nozzle distance is controlled at L=26mm, the distance from the nozzle to the work roll is controlled within 140mm, the rotation angle of the spray beam is 170°, the coolant spray speed is 25m / s, the temperature of the coolant is controlled at 20℃, and the coolant is replaced regularly to improve the cooling efficiency of the coolant.

[0010] As a preferred embodiment, the mill is a 20-roll Senkimir mill with rolls having an outer diameter of 40 mm.

[0011] As a preferred embodiment, in step (2), the rolling force is controlled under certain rolling conditions, and the steps are as follows:

[0012] (2.1) Determine the original plate crown based on the thickness H and tolerance Δ of the raw material;

[0013] (2.2) Calculate the roll stiffness coefficient K R Thermal convexity Y t Based on the original roll crown, the relationship between rolling force and plate thickness is established:

[0014] P=K R (Δ / H) h i +K R (Y t +w) (1)

[0015] (1) In the formula, h i —Thickness of the workpiece in the i-th pass; w —Original roll profile crown;

[0016] (2.3) The thickness h of the finished product n Determine the rolling pressure p n Under the condition of satisfying various constraints, according to Δh n Requires a rolling pressure p to achieve a good plate shape. n－1 The amount of pressure applied in each pass is determined by recursion in this way.

[0017] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0018] By controlling the precision of the rolls to below 0.003μm, and coordinating with the control of cold rolling speed, nozzle distance, nozzle-to-work roll distance, spray beam rotation angle, coolant spray speed, and coolant temperature, stainless steel strip achieves excellent shape, making it suitable for high-end, precision, and advanced products with stringent shape requirements. Furthermore, the strip exhibits stable temperature resistance, with minimal shape change after high-temperature baking. This invention expands the deep processing industrial chain of cold-rolled strip, enabling the expansion and reduction of cold-rolled resources. Additionally, products manufactured using this process can be used in automobile manufacturing, electrical products, locomotives, aerospace, precision instruments, and canned food, reducing the impact of residual stress on the product.

[0019] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0020] Figure 1 This is a graph showing the variation of roll temperature and rolling speed in a preferred embodiment of the present invention.

[0021] Figure 2 This is a graph showing the change in velocity and temperature of the coolant when the nozzle spacing is different in a preferred embodiment of the present invention.

[0022] Figure 3 This is a graph showing the change in axial length versus temperature when the nozzle spacing is different in a preferred embodiment of the present invention.

[0023] Figure 4 This is a curve showing the change between the viscosity of the coolant and the surface heat transfer coefficient in a preferred embodiment of the present invention.

[0024] Figure 5 This is a curve showing the change in coolant viscosity versus temperature in a preferred embodiment of the present invention;

[0025] Figure 6 This is a graph showing the variation of the nozzle-to-roll surface distance and the surface heat transfer coefficient in a preferred embodiment of the present invention.

[0026] Figure 7 This is a schematic diagram of the angle of the nozzle centerline in a preferred embodiment of the present invention;

[0027] Figure 8 This is a curve showing the variation of nozzle beam angle and surface heat transfer coefficient in a preferred embodiment of the present invention.

[0028] Figure 9 This is a graph showing the variation of coolant injection velocity and surface heat transfer coefficient in a preferred embodiment of the present invention.

[0029] Figure 10This is a curve showing the change in coolant temperature and surface heat transfer coefficient in a preferred embodiment of the present invention. Detailed Implementation

[0030] This invention discloses a manufacturing method for controlling the flatness of stainless steel by adjusting the heat dissipation during cold rolling, comprising the following steps:

[0031] (1) The rolls of the rolling mill are finely ground and polished, with the precision controlled below 0.003μm; the rolling mill is a twenty-roll Senkimir rolling mill, and the outer diameter of the rolls is 40mm.

[0032] (2) Cold rolling: The stainless steel strip is cold rolled using the rolling mill in step (1). 1-3 passes are added to the normal cold rolling process. Through multiple cold rolling passes, the heat generated during cold rolling is dispersed. During the cold rolling process, the cold rolling speed is controlled at 80m / min-100m / min. This controls the rate of heat generation, prevents the temperature of the rolls from getting too high, and ensures a certain production efficiency. The nozzle distance is controlled at L=26mm, the distance from the nozzle to the work roll is controlled within 140mm, the spray beam rotation angle is 170°, the coolant spray speed is 25m / s, the coolant temperature is controlled at 20℃, and the coolant is replaced regularly to improve the cooling efficiency of the coolant.

[0033] Based on the thermal expansion of the rolls, the pressure and rolling passes are adjusted by monitoring the plate shape to maintain the flatness of the plate. In order to achieve a good plate shape, in step (2), the rolling force is controlled under certain rolling conditions. The steps are as follows:

[0034] (2.1) Determine the original plate crown based on the thickness H and tolerance Δ of the raw material;

[0035] (2.2) Calculate the roll stiffness coefficient K R Thermal convexity Y t Based on the original roll crown, the relationship between rolling force and plate thickness is established:

[0036] P=K R (Δ / H) h i +K R (Y t +w) (1)

[0037] (1) In the formula, h i —Thickness of the workpiece in the i-th pass; w —Original roll profile crown;

[0038] (2.3) The thickness h of the finished product n Determine the rolling pressure p n Under the condition of satisfying various constraints, according to Δh n Requires a rolling pressure p to achieve a good plate shape. n－1 The amount of pressure applied in each pass is determined by recursion in this way.

[0039] The rate of cold rolling directly affects the heat generated during cold rolling, which in turn determines the temperature of the rolls. Furthermore, the drastic temperature fluctuations make it difficult to maintain stable sheet shape control. Maintaining the roll temperature below 55℃ minimizes changes in roll thermal crown. Figure 1 As shown, the temperature of the rolls increases with the increase of speed. For every 50 m / min increase in the initial rolling speed, the temperature will increase by an average of 5.6℃. By controlling the cold rolling speed at around 80 m / min-100 m / min, the temperature can be controlled at 50℃-60℃.

[0040] When the nozzle spacing is different, the intensity of the interaction between the jets during the flow process varies, resulting in different flow rates reaching the roll surface. For example... Figure 2 As shown, when the nozzle distance L = 26 mm, the cross-interference between the jets is significantly stronger than when L = 52 mm. Therefore, the flow rate of liquid reaching the impact zone per unit time is greater, resulting in a better cooling effect than when L = 52 mm. Furthermore, as the coolant velocity increases, the cooling effect of nozzle distance L = 26 mm is more significant than that of L = 52 mm. When the velocity is less than 20 m / s, the average temperature of the cooling zone is nearly 1°C lower when the nozzle distance L = 26 mm is less than that when L = 52 mm. However, when the velocity is greater than 20 m / s, the cooling effect of nozzle distance 26 mm becomes significantly stronger than that of distance 52 mm, with an average temperature difference of about 2°C. Therefore, the distance between nozzles has a significant impact on the temperature change of the roll in segmented cooling control.

[0041] Due to the interference between the jets, the wall jet zone and the upward spray formation zone between the two jets are compressed, and the direct impact zone of the jets becomes larger. Therefore, the difference in nozzle distance will affect the uniformity of coolant spraying in the transverse direction of the roll. Figure 3 It can be seen that when the nozzle distance L=26mm, the cooling in the transverse direction of the roll is more uniform, and the temperature difference is about 1.1℃. Therefore, when the local temperature of the work roll needs to be reduced rapidly to reduce the impact of roll crown on the sheet shape, the spraying scheme with a smaller nozzle distance L responds quickly to local thermal crown.

[0042] Different coolant viscosities result in varying intermolecular binding forces between fluid molecules, leading to significant differences in their heat transfer capabilities. For example... Figure 4 As shown, when the viscosity of the coolant increases from 0.001 Pa·s to 0.002 Pa·s, the average heat transfer coefficient of the working roller surface decreases significantly from 7046 W / m² due to the increased intermolecular viscosity. 2 The K) decreased to 4336 (W / m 2The viscosity of the coolant decreases almost linearly (kPa·s). However, when the viscosity of the coolant reaches 0.002 Pa·s, the viscosity of the fluid increases, and the binding force between the fluid's micro-molecules becomes very strong. Under the same flow rate, it becomes very difficult for the flow to develop into a turbulent state. At this point, the cooling efficiency of the coolant will decrease very slowly.

[0043] like Figure 5 As shown, for every 0.0005 Pa·s increase in viscosity from 0.001 Pa·s, the temperature of the rolls in the spray zone drops by approximately 1.3°C. Therefore, regularly checking the quality of the coolant is essential to improve cooling efficiency and avoid adverse effects on strip production.

[0044] The distance from the nozzle to the roll and the rotation angle of the spray beam directly affect the heat exchange of the cold rolling system. Different distances between the nozzle and the roll surface result in different direct spray areas, varying impacts of the coolant on the roll surface, and consequently, differences in the heat transfer coefficient of the roll surface. Figure 6 As shown, when the distance is less than 140mm, the average heat transfer coefficient of the work roll surface does not change significantly with increasing distance; when the distance exceeds 140mm-150mm, the velocity of the liquid sprayed onto the roll decreases significantly, the convection effect deteriorates, and its heat transfer capacity decreases significantly; when the distance exceeds 150mm and continues to increase, the average heat transfer coefficient of the work roll surface decreases slowly with increasing distance. Therefore, the distance from the nozzle to the work roll should be controlled within 140mm.

[0045] like Figure 7 As shown, the angle between the nozzle centerline and the horizontal line is defined as the selection angle of the spray beam. The rotation angle of the spray beam affects the position of the nozzle and the work roll in direct spray. Different positions result in different impact pressures on the roll surface, leading to significant differences in the boundary layer and thus greatly affecting the heat transfer coefficient. Figure 8 As shown, the attenuation is greatest when the spray beam rotates at an angle of 165°; when the spray beam rotates at an angle of 170°, the average heat transfer coefficient of the work roller surface reaches its maximum value of 8294 (W / m²). 2 When the angle is greater than 170°, the average heat transfer coefficient of the work roll surface begins to decrease. At nozzle tilt angles of 160° and 180°, the average heat transfer coefficient of the work roll surface is similar, approximately 7000 (W / m²). 2 Therefore, 170° is considered the optimal choice when designing the rotation angle of the spray beam.

[0046] Heat exchange is achieved by spraying coolant onto the roll surface through nozzles. Therefore, different nozzle pressures result in different liquid flow rates; higher pressure leads to higher flow rates, and thus, a larger volume of coolant is sprayed per unit time. Consequently, the cooling rate of the coolant significantly affects the heat exchange between the coolant and the roll. Figure 9 As shown, when the coolant velocity increases from 10 m / s to 25 m / s, the Reynolds number of the fluid increases with the increase in velocity, the flow rate obtained by the roll surface per unit time increases, the turbulence tendency of the fluid intensifies, and therefore the heat transfer capacity is enhanced, and the heat transfer coefficient increases accordingly from 3634 (W / m). 2 The K) increased to 7046 (W / m 2 When the velocity increases from 25 m / s to 30 m / s, the heat transfer coefficient does not change much and remains stable at 7000 (W / m). 2 The flow rate is around 0.05 kJ / L; because as the flow rate continues to increase, the resistance experienced by the fluid increases more than the increase in flow rate, and at this point, the effect of increasing the flow rate on the heat transfer coefficient gradually decreases.

[0047] Whenever the coolant injection speed increases by 5 m / s, the temperature of the corresponding injection zone rolls drops by approximately 1.1°C.

[0048] The temperature of the rolling mill rolls varies during operation, thus requiring coolants of varying temperatures. The temperature of the coolant significantly impacts cooling efficiency. Under certain conditions, the lower the coolant temperature, the higher the cooling efficiency and the greater the corresponding heat transfer coefficient. For example... Figure 10 As shown, when the temperature increases from 20℃ to 25℃, the viscosity of the coolant increases rapidly due to the temperature rise, resulting in a significant change in the average heat transfer coefficient of the working roller surface, from 7686 (W / m²). 2 .K) decreased to 7046 (W / m 2 When the temperature increases from 26℃ to 29℃, the viscosity of the coolant does not change significantly, and the work roll viscosity decreases slowly with increasing coolant temperature. When the coolant temperature exceeds 29℃, the average heat transfer coefficient of the roll surface decreases slowly as the temperature difference between the roll and the coolant decreases. Therefore, it can be seen that at low temperatures, decreasing the temperature has a more significant effect on increasing the heat transfer coefficient, while at higher temperatures, the effect of decreasing the temperature on the heat transfer coefficient gradually decreases.

[0049] In experiments, there are often multiple factors and variables. If every variable of each factor were obtained experimentally, the total number of experiments would increase exponentially. For such complex experiments, orthogonal experiments are an effective method. The patterns show that within a small range of variation, the distance between the nozzle and the roll has little effect on the convective heat transfer coefficient. In actual production, the inclination angle of the spray beam is generally fixed; only the temperature, velocity, and viscosity of the coolant and the temperature of the roll vary. Therefore, orthogonal experimental analysis is conducted on these four variables. Three representative experimental conditions are selected from these four factors according to L9(3)... 4 Orthogonal array arrangement of experiments:

[0050] L9(3 4 Orthogonal array

[0051]

[0052] The coolant temperature, velocity, viscosity, and roll temperature are divided into three levels, and the level values ​​for each factor are shown in the table below:

[0053] Rank values ​​of each factor

[0054]

[0055] The rightmost end of the orthogonal experimental table uses heat flux density values ​​to represent the performance of the experiment. The table shows the sum of the rank of each factor and the range obtained from the sum of the rank of each factor. The ranges of the four factors are then sorted from largest to smallest, as shown in the table below.

[0056] Orthogonal experimental table

[0057]

[0058] When the coolant temperature is 23℃, the convective heat transfer value is greater than that at 26℃ and 29℃; when the cooling rate is 25m / s, the convective heat transfer value is significantly greater than that at 15m / s and 20m / s; when the coolant viscosity is 0.001Pa·s, the convective heat transfer value is greater than that at 0.0015Pa·s and 0.002Pa·s; furthermore, a higher roll temperature significantly enhances the heat transfer coefficient between the roll and the coolant. Therefore, it can be seen that single-factor analysis can only obtain the optimal value for each factor, but the magnitude of each factor's influence on convective heat transfer cannot be shown. In the orthogonal experiment, the range of each column ranks the influence of each factor on the experimental index. A larger range indicates that the factor is more active, and its change has a greater impact on the results than other factors. It can be seen that the influence of the four factors on convective heat transfer is ranked as follows: the roll temperature has the greatest influence, followed by the coolant viscosity, and the coolant temperature has the least influence. The influence of the coolant velocity lies between that of the coolant viscosity and temperature. The viscosity of the coolant and the temperature of the rolls have almost equal effects on the convective heat transfer capacity.

[0059] In terms of improving the heat transfer coefficient, the viscosity of the coolant itself has the greatest potential. When the temperature of the roll increases, under the same conditions, the cooling effect of the coolant will be enhanced, making it easier for the roll to reach a stable state sooner and improving rolling efficiency. The spraying speed also has a significant impact on the heat transfer coefficient; as the spraying speed increases, the flow rate per unit time increases, resulting in a better cooling effect. However, due to objective limitations, the spraying speed cannot be increased indefinitely, and the viscosity of the coolant cannot be decreased indefinitely. Therefore, adjustments must be made through the coordination of various factors. When the viscosity of the coolant is fixed, convective heat transfer can be increased by increasing the speed and the flow rate per unit time.

[0060] The effects of coolant properties, spray beam rotation angle, and distance between the nozzle and the work roll on the convective heat transfer coefficient were described above, and the optimal values ​​for each factor were obtained. Using orthogonal experiments, the degree of influence and ranking of the four factors—coolant temperature, coolant velocity, coolant viscosity, and roll temperature—on the heat transfer coefficient were determined.

[0061] The following embodiments are used to verify the beneficial effects of the present invention:

[0062] Flatness data before and after process optimization: (taking 0.15mm 316Li as an example)

[0063]

[0064] Before process optimization, the flatness was basically between 0.45-0.75mm. After process optimization, the flatness was basically stable at 0.2-0.25mm, and the board shape improvement effect was good.

[0065] A 130mm*70mm sample was prepared by punching and baked at 220℃ for 45 minutes. The difference in flatness before and after baking was measured (taking 0.15mm 316Li as an example).

[0066]

[0067] Baking at 220℃ for 45 minutes, the difference in flatness before and after baking is basically less than or equal to 0.05mm, indicating that the plate shape is stable and the stress is relatively uniform.

[0068] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A manufacturing method of controlling flatness of stainless steel by adjusting cold rolling heat dissipation, characterized by: It includes the following steps: (1) The rolling mill rolls are finely ground and polished, with the precision controlled below 0.003μm; (2) Cold rolling: The stainless steel strip is cold rolled using the rolling mill in step (1). 1-3 passes are added to the normal cold rolling process. The heat generated during cold rolling is dispersed through multiple cold rolling processes. During the cold rolling process, the cold rolling speed is controlled at 80m / min-100m / min, the nozzle distance is controlled at L=26mm, the distance from the nozzle to the work roll is controlled within 140mm, the rotation angle of the spray beam is 170°, the coolant spray speed is 25m / s, the temperature of the coolant is controlled at 20℃, and the coolant is replaced regularly to improve the cooling efficiency of the coolant.

2. A method of manufacturing stainless steel with controlled flatness by adjusting the cold rolling and heat dissipation according to claim 1, characterized in that: The mill is a 20-roll Senkimir mill, with the outer diameter of the rolls being 40 mm.

3. The method of claim 1, wherein the method further comprises: adjusting the cold rolling to control flatness of the stainless steel sheet. In step (2), the rolling force is controlled under certain rolling conditions, and the steps are as follows: (2.1) Determine the original plate crown based on the thickness H and tolerance Δ of the raw material; (2.2) Calculate the roll stiffness coefficient K R , thermal crown Y t , according to the original roll type crown, the relationship between the rolling force and the plate thickness is established: P=K R (Δ / H ) h i +K R (Y t +w)(1) (1) where h i — thickness of the i-pass rolled piece; w— original roll profile crown; (2.3) the rolling pressure p is determined from the finished thickness h n n , under the condition that various constraints are satisfied, the rolling pressure p is determined from Δh n n－1 , and the rolling reduction amount of each pass is determined by recursion.​​

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