TWI655292B - Method of setting annealing time for steel coil - Google Patents

Abstract

The invention provides a method for setting an annealing cycle of a steel coil, wherein the temperature of different positions of the steel coil is calculated by an algorithm, and the annealing cycle of the steel coil is determined according to the obtained cold spot temperature and the thermal equivalent area. The set annealing cycle saves the processing time of the annealing process and avoids unnecessary energy waste.

Description

Method for setting the annealing cycle of steel coil

The present invention relates to a method for setting an annealing cycle of a steel coil, and more particularly to a method for setting an annealing cycle of a steel coil according to a furnace temperature of the annealing furnace.

The Batch Annealing process is one of the annealing methods of cold-rolled steel coils. However, the annealing process of the sealed box tends to cause uneven temperature distribution at various points inside the coil. Therefore, the cold spot (temperature) of the steel coil during the annealing process is controlled. The lowest point) and the temperature change of the hot spot (the highest temperature point) are important factors in determining the quality of the coil after annealing.

The annealing cycle of the conventional package annealing process is empirically set, lacks flexibility for different production conditions, and cannot be adjusted for the characteristics of different annealing furnaces. In general, the annealing cycle of the conventional package annealing process is performed by stepwise heating according to the weight of the steel coil. However, this setting method often has a lighter weight of the steel coil but a longer length. The situation of time annealing, thus often causing waste of energy.

In view of this, it is not necessary to provide a method for setting the annealing cycle of the steel coil, which is reasonable for the characteristics of different annealing furnaces and the weight of the steel coil. Annealing cycle.

One aspect of the present invention provides a method of setting an annealing cycle of a steel coil by calculating a temperature at a plurality of locations of the steel coil to obtain a cold spot temperature and a thermal equivalent area of the steel coil. Then, by adjusting the preset value of the annealing cycle so that the cold spot temperature is greater than the cold spot temperature set value, and the thermal equivalent area is greater than the thermal equivalent area threshold, the preset period of the annealing cycle is set to be the annealing period of the coil.

According to an aspect of the present invention, a method of setting an annealing cycle of a steel coil is provided. The method includes providing the size and thermal conductivity of the steel coil, as well as providing an annealing cycle preset value and furnace temperature for the annealing process. Next, the time step is set and the algorithm is used to calculate a plurality of temperatures at a plurality of locations of the steel coil.

Then, the cold spot temperature and the cold spot temperature set value of the steel coil are compared, wherein the cold spot temperature of the steel coil is the minimum of the above temperatures. When the cold spot temperature is less than the cold spot temperature set value, the preset value of the annealing cycle is extended; when the cold spot temperature is greater than or equal to the cold spot temperature set value, the thermal equivalent area of the coil is calculated. The thermal equivalent area is the integrated area of the cold spot temperature and the preset value of the annealing cycle.

Next, the above-described thermal equivalent area and thermal equivalent area threshold are compared. When the thermal equivalent area is less than the thermal equivalent area threshold, the annealing period preset value is extended; when the thermal equivalent area is greater than or equal to the thermal equivalent area threshold, the annealing period setting step is performed to set the annealing period preset value It is an annealing cycle.

According to an embodiment of the invention, the step of setting the time step further comprises performing a determining step, wherein the determining step calculates the algorithm by using a finite difference method to determine whether the algorithm converges. When the time step makes the algorithm divergence, the time step is adjusted until the algorithm converges; when the time step makes the algorithm converge, the time step is used to calculate the temperature of the coil.

According to an embodiment of the invention, the algorithm is a heat transfer equation of a steel coil.

According to an embodiment of the invention, the position of the steel coil is defined by a two-dimensional coordinate.

According to an embodiment of the invention, the cold spot temperature set point and the hot equivalent area threshold are defined by a standard steel coil, wherein the standard steel coil has predetermined mechanical properties.

According to an embodiment of the invention, the annealing process includes a preheating step and a heating step, and the heating step heats the furnace temperature to a preset temperature.

According to an embodiment of the invention, after the heating step, the annealing process further comprises a temperature holding step, wherein the furnace temperature of the temperature holding step is the predetermined temperature.

The method for setting an annealing cycle of the steel coil according to the present invention is to calculate the temperature of the steel coil at different positions by an algorithm, and determine the annealing cycle of the steel coil according to the obtained cold spot temperature and the thermal equivalent area. The set annealing cycle saves process time and avoids wasted energy.

100‧‧‧ method

110‧‧‧Provide the size and thermal conductivity of the coil

120‧‧‧Provide the preset value of the annealing cycle of the annealing process and the furnace temperature of the annealing furnace

130‧‧‧Steps for setting the time step and calculating the temperature of the coil using the algorithm

140‧‧‧Steps on whether the cold spot temperature is greater than or equal to the cold spot temperature setting

145‧‧‧Steps to extend the preset value of the annealing cycle

150‧‧‧Steps on whether the thermal equivalent area is greater than or equal to the thermal equivalent area threshold

160‧‧‧Experimenting the annealing cycle

201/203/205/207/209‧‧‧Measurement points

501‧‧ points

The above and other objects, features, advantages and embodiments of the present invention will become more <RTIgt; <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; Flowchart of the setting method.

2A is a schematic view showing the configuration of an annealing test of a steel coil according to an embodiment of the present invention.

2B is a graph showing the relationship between the temperature measured at different positions in FIG. 2A and the annealing time according to an embodiment of the present invention.

Fig. 3 is a graph showing the relationship between the steel coils of different weights according to Example 1 and Comparative Example 1 and the temperature equalization step time.

Fig. 4 is a graph showing the relationship between the steel coils of different weights according to Example 2 and Comparative Example 1 and the temperature equalization step time.

Fig. 5 is a graph showing the relationship between the steel coils of different weights according to Example 3 and Comparative Example 1 and the temperature equalization step time.

In view of the above, the present invention provides a method for setting an annealing cycle of a steel coil by calculating a temperature at a plurality of locations of the steel coil to obtain a cold spot temperature and a thermal equivalent area of the steel coil. Then, by adjusting the preset value of the annealing cycle so that the cold spot temperature is greater than the cold spot temperature set value, and the thermal equivalent area is greater than the thermal equivalent area threshold, the preset period of the annealing cycle is set to be the annealing period of the coil.

Please refer to FIG. 1 , which is a flow chart showing a method 100 of setting an annealing cycle of a steel coil according to an embodiment of the invention. First, take the steps 110, providing the size and thermal conductivity of the coil. In one embodiment, the size of the coil includes the inner radius, outer radius, and width of the coil. In another embodiment, the density of the steel coil can be obtained using the size and weight of the steel coil. In one embodiment, the radial equivalent thermal conductivity of the coil can be obtained by utilizing the heat transfer coefficient of the coil and the heat transfer coefficient of the shielding gas used.

Next, the method 100 proceeds to step 120 to provide a predetermined value of the annealing cycle of the annealing process and the furnace temperature of the annealing furnace. In one embodiment, the annealing process includes a preheating step and a heating step, wherein the heating step heats the furnace temperature of the annealing furnace to a preset temperature. In this embodiment, after the heating step, the temperature holding step may be selectively performed to maintain the furnace temperature at the preset temperature for a period of time (in other words, the annealing period minus the time required for the preheating step and the heating step) The time after the temperature is the progress of the temperature holding step).

The method 100 then proceeds to step 130, sets the time steps, and uses the algorithm to calculate the temperature of the coil. In one embodiment, the algorithm is a heat transfer equation for a coil, and the algorithm can be, for example, shown in equation (1). The algorithm of equation (1) considers only the radial and axial heat transfer in the coil, and assumes that the initial temperatures of the coil and the shielding gas are ambient temperatures. In this embodiment, the position of the coil is defined by a two-dimensional coordinate (i.e., a two-dimensional coordinate formed by the radial and axial directions of the steel coil). In an embodiment, the algorithm is calculated using a finite difference method.

In formula (1), T is temperature; r and z are radial and axial coordinates, respectively; λ _s is the heat transfer coefficient of the coil; λ _r is the radial equivalent heat transfer coefficient of the coil; ρ is the coil Density; C _p is the heat capacity of the coil; t is the time step. In an embodiment, the radial equivalent heat transfer coefficient of the steel coil can be obtained by the following formula (2).

In the formula (2), c is the thickness of the slit; d is the thickness of the coil; and λ _g is the heat transfer coefficient of the shielding gas.

In this embodiment, the initial condition of the above equation (1) of the heat conduction equation is set by the following formula (3), and the boundary conditions are in accordance with the following formulas (4) to (7).

In formula (3), T(r,z) is the temperature at different positions in the coil; T ₀ is the initial temperature of the coil; R _i and R _o are the inner and outer radii of the coil; W ₁ is The width of the coil.

In equations (4) to (7), h ₀ , h _i , h _b and h _t are the convective heat exchange coefficients of the outer, inner, lower and upper surfaces of the coil, respectively. , , and The radiant heat flux density of the outer surface, the inner surface, the lower surface and the upper surface of the steel coil respectively; T _g is the furnace temperature.

In an embodiment, step 130 may optionally include a step of determining the time step. In a specific example, the determining step calculates the above algorithm using the finite difference method to determine whether the time step converges. In this embodiment, when the time step provided by step 130 causes the algorithm to diverge, the time step must be adjusted, and then the calculation is performed until the selected time step causes the algorithm to receive When converge, this time step is utilized and the algorithm is used to calculate the temperature at each location in the coil.

Next, step 140 is performed to compare the cold spot temperature and the cold spot temperature set value of the coil to determine whether the cold spot temperature is greater than or equal to the cold spot temperature set value. The cold spot temperature as described in the specification of the present invention is defined as the minimum of the temperatures of all the positions of the above-mentioned steel coil. In one embodiment, the cold spot temperature set point is determined by a standard steel coil, wherein the standard steel coil refers to a steel coil having a desired mechanical property (ie, predetermined mechanical properties). In this embodiment, the cold spot temperature of the standard steel coil is defined as the cold spot temperature set point.

When the cold spot temperature is lower than the cold spot temperature set value, as shown in FIG. 1, along the arrow of "NO", step 145 is performed to extend the preset value of the annealing cycle. Then, step 120 and step 130 are repeated to recalculate the temperature of each position of the coil, and then step 140 is performed until the obtained cold spot temperature is greater than or equal to the cold spot temperature set value. The thermal equivalent area is calculated when the cold spot temperature is greater than or equal to the cold spot temperature set point. The "thermal equivalent area" as used in the specification of the present invention means the integral area of the relationship between the cold spot temperature and the annealing time at a preset value of the annealing cycle.

Then, the method 100 proceeds to step 150 to compare the thermal equivalent area and the thermal equivalent area threshold to determine whether the thermal equivalent area is greater than or equal to the thermal equivalent area threshold. In one embodiment, the thermal equivalent area threshold value is the thermal equivalent area calculated by the relationship between the cold spot temperature and the annealing time in the annealing cycle of the standard steel coil as the thermal equivalent area threshold value.

When the thermal equivalent area is less than the thermal equivalent area threshold, proceed to step 145 along the "No" arrow shown in Figure 1, extending the annealing cycle. Set the value. Then, step 120 to step 140 are repeated to calculate the temperature of each position of the coil, and the cold spot temperature is obtained, and then step 150 is repeated until the obtained thermal equivalent area is greater than or equal to the thermal equivalent area threshold. Then, step 160 is performed to perform an annealing cycle setting step to satisfy conditions such as (1) the cold spot temperature of the steel coil is greater than or equal to the cold spot temperature setting value, and (2) the thermal equivalent area is greater than or equal to the thermal equivalent area threshold value. The preset value of the annealing cycle is set to the annealing cycle of the coil, which saves process time and avoids unnecessary energy waste.

The following examples are used to illustrate the application of the present invention, and are not intended to limit the present invention. Those skilled in the art can make various changes without departing from the spirit and scope of the present invention. Retouching.

Coil temperature

First, the steel coil is placed in an annealing furnace in the arrangement of FIG. 2A, an annealing test is performed, and the temperatures of the points 201, 203, 205, 207, and 209 are measured by thermocouples, respectively, wherein the point 201 is within the center of the coil. At the wall, point 203 is near the outer wall of the top surface of the coil, point 205 is at the center of the center of the coil, point 207 is at the outer wall of the center of the coil, and point 209 is the temperature of the furnace of the annealing furnace. The relationship between the temperature measured at each point and the annealing time is shown in Fig. 2B. It can be seen from Fig. 2B that the temperature curve of point 207 is similar to that of point 209, that is, the temperature of point 207 is close to the furnace temperature, so point 207 is steel. The hot spot of the roll (the point with the highest temperature), and the temperature curves of points 201, 203, and 205 are similar, wherein the temperature rise rate of point 205 is the slowest, so point 205 is the cold spot of the steel coil (the point with the lowest temperature).

The experiment of temperature measurement at each point above was repeated three times and The measured temperatures of points 201 to 207 are compared with the temperatures calculated using the above algorithm of the present invention, as shown in Table 1 below. The results in Table 1 show that the error between the temperature value of each point calculated by the algorithm and the actual measured temperature value does not exceed 1.30%. In other words, the algorithm used in the present invention calculates the temperature at different locations of the coil to have a relatively high accuracy.

Example 1 and Comparative Example 1

Embodiment 1 performs an annealing process for steel coils having different weights of only the difference in width, and sets a preheating step and a heating step for the same time. Next, an annealing cycle of steel coils of different widths (different weights) is obtained according to the above-described annealing cycle setting method, wherein the cold spot temperature setting value is 610 ° C, and the thermal equivalent area threshold value is 70,000. Since the annealing process includes the preheating step, the heating step, and the time of the homogenization step, the difference between the steel coils of different weights is only the time of the soaking step under the conditions of the same preheating step time and the heating step time. The preheating step time and the heating step time of Example 1 were 1 hour and 5 hours, respectively.

Please refer to FIG. 3 , which is a graph showing the relationship between the steel coils of different weights according to Example 1 and Comparative Example 1 and the temperature equalization step time. Comparative Example 1 is a method for setting an annealing cycle of a package annealing process according to a rule of thumb. To perform the annealing process. It can be seen from the results of FIG. 3 that the average temperature step time obtained in Example 1 increases as the weight of the steel coil increases, that is, the temperature equalization step time is positively correlated with the steel coil weight, and Comparative Example 1 has more weight. Lighter coils have longer temperature equalization steps. In comparison, the method of Comparative Example 1 is likely to cause more energy waste.

Examples 2 and 3

Example 2 is similar to Example 1, except that the time for fixing the preheating step and the heating step is 1 hour and 5 hours, respectively, but the weight difference of the steel coil of Example 2 includes the difference in width and thickness. Please refer to FIG. 4 , which is a graph showing the relationship between the steel coils of different weights according to Example 2 and Comparative Example 1 and the temperature equalization step time. It can be seen from Fig. 4 that the average temperature step time of the three different weight steel coils of Example 2 is not positively related to the weight, which may be due to the difference in thickness of the steel coils, or the steel coil is retreating. The configuration position in the stove is different.

The preheating step time and the heating step time of Example 3 were based on the furnace temperatures of different annealing furnaces used in practice, and the annealing cycles were estimated for steel coils of different weights. Please refer to FIG. 5 , which is a graph showing the relationship between the steel coils of different weights according to Example 3 and Comparative Example 1 and the temperature equalization step time. As can be seen from Fig. 5, the soaking step time of the point 501 is much smaller than the set value used for the steel coil of the same weight in Comparative Example 1, mainly because the furnace temperature of the annealing furnace is subjected to a heating step for a long time. Only after the set cold point temperature setting value is reached, the cold spot temperature of the steel coil can be made greater than or equal to the cold spot temperature set value after the short-time soaking step, and the thermal equivalent area is greater than or Equal to the thermal equivalent area threshold.

Since the embodiment 3 is directed to different annealing furnaces, the characteristics of the annealing furnaces will cause the difference between the preheating step time and the heating step time required for the annealing furnace to reach the set temperature, so that the temperature of the coil is different, and thus the influence is The time required for the thermal step.

According to the above embodiment, the present invention can calculate the temperature of different positions of the steel coil by an algorithm, and determine the annealing period of the steel coil according to the obtained cold spot temperature and the thermal equivalent area. Since the method provided by the invention can set the annealing cycle of the annealing process according to the furnace temperature of different annealing furnaces and the characteristics of the steel coil, the setting of the annealing cycle can be standardized, and the requirements of various annealing furnaces and steel coils can be satisfied, thereby avoiding the conventional knowledge. Relying on the defects caused by the rule of thumb, the method of setting the annealing cycle of the present invention can save process time and avoid unnecessary waste of energy.

While the invention has been described above in terms of several embodiments, it is not intended to limit the scope of the invention, and the invention may be practiced in various embodiments without departing from the spirit and scope of the invention. The scope of protection of the present invention is defined by the scope of the appended claims.

Claims (6)

A method for setting an annealing cycle of a steel coil, comprising: providing a size of a steel coil and a heat transfer coefficient; providing an annealing cycle preset value of one annealing cycle and a furnace temperature; setting a time step and using a calculation The method calculates a plurality of temperatures of the steel coil, wherein the temperatures are respectively a temperature of a plurality of locations of the steel coil, and the algorithm is a heat conduction equation of the steel coil, the heat conduction equation is: Where T is temperature, r and z are radial and axial coordinates, λ _{s is} the heat transfer coefficient of the coil, λ _{r is} the radial equivalent heat transfer coefficient of the coil, and ρ is the density of the coil, C _{p is} the heat capacity of the coil, t is the time step, and the formula for obtaining the radial equivalent heat transfer coefficient of the coil is: Where c is the thickness of the gap, d is the thickness of the coil, and λ _g is the heat transfer coefficient of a shielding gas; the formula for setting the initial condition of the heat conduction equation is: Where T(r,z) is the temperature at different locations in the coil, T _{0 is} the initial temperature of the coil, R _i and R _o are the inner and outer radii of the coil, respectively, and W _{1 is} the coil Width; a cold spot temperature and a cold spot temperature set value of the steel coil, wherein the cold spot temperature is a minimum value of the temperature, the cold spot temperature set value is determined by a standard steel coil, The standard steel coil refers to a steel coil having a predetermined mechanical property that meets the requirements; when the cold spot temperature is less than the cold temperature setting value, the preset value of the annealing cycle is extended; and when the cold spot temperature is greater than or equal to When the cold spot temperature is set, a thermal equivalent area is calculated, wherein the hot equivalent area is an integral area of the cold spot temperature and a preset value of the annealing cycle; and the thermal equivalent area and a thermal equivalent area threshold are compared, Wherein the thermal equivalent area threshold value is the thermal equivalent area calculated by the relationship between the cold spot temperature and the annealing time in the annealing cycle of the standard steel coil as a thermal equivalent area threshold value; when the thermal equivalent area is smaller than When the thermal equivalent area threshold is The anneal cycle preset value; and when the area is greater than or equal to the thermal equivalent of the thermal equivalent threshold area, performing an annealing period setting step to the annealing cycle set as the default value of the anneal cycle. The method for setting an annealing cycle of a steel coil according to claim 1, wherein the step of setting the time step further comprises performing a determining step, wherein the determining step calculates the algorithm by using a finite difference method. To determine whether the algorithm converges, when the time step makes the algorithm diverge, adjust the time step until the algorithm converges; when the time step makes the algorithm converge, use the time step calculation The temperatures of the coil. The method for setting an annealing cycle of a steel coil according to claim 1 or 2, wherein the boundary condition of the heat conduction equation conforms to the following formula: Where h ₀ , h _i , h _b and h _t are the convective heat exchange coefficients of the outer surface, the inner surface, the lower surface and the upper surface of the steel coil, respectively. , , and The radiant heat flux density of the outer surface, the inner surface, the lower surface and the upper surface of the steel coil, respectively, T _{g is} the furnace temperature. The method for setting an annealing cycle of a steel coil according to claim 1, wherein the initial temperature of the steel coil and the shielding gas is an ambient temperature. The method for setting an annealing cycle of a steel coil according to claim 1, wherein the annealing process comprises a preheating step and a heating step, and the heating step heats the furnace temperature to a predetermined temperature. The method for setting an annealing cycle of a steel coil according to claim 6 is characterized in that after the heating step, the annealing process further comprises a temperature holding step, wherein the furnace temperature of the temperature holding step is the preset temperature.