JPS6049695B2 - How to heat thick plate slabs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thick slab heating method for uniformly heating steel materials such as slabs and blooms charged in double rows into a heating furnace.

Recently, demand for controlled rolling materials has increased,
There has been an increasing demand for uniform heating of steel materials such as slabs or blue steel.

Controlled rolling material at target extraction temperature (900
By uniformly heating the material at temperatures around 10,000° C. to 10,000° C., it is possible to reduce the amount of titanium, niobium, etc. added in component system design or material design, making it possible to greatly rationalize the material. However, the degree of uniform heating required in heating the controlled rolling material needs to be suppressed to 200C to 40C or less as a temperature deviation within the slab, which is determined by the difference between the maximum value and the minimum value of the temperature within the slab. Moreover, the amount exceeding the target extraction temperature,
That is, the amount of overshoot usually needs to be suppressed to 20° C. or less. As shown in Fig. 1, the temperature deviation within the slab that occurs in commonly used rolling heating furnaces such as walking beam furnaces and pusher furnaces has the following Ξ element (in Fig. 1, slab 3 is ).

(1) Temperature deviation within the slab 3 in the thickness direction (for example, temperature difference between B and F, usually B>C>F).

(2) So-called skid marks where the slab temperature at the part connecting to the skid 2 that supports the slab 3 is lower than the slab temperature at other positions (for example, the average temperature difference between C and D or between the (C>D) (3) Furnace temperature distribution in the furnace width direction,
Temperature deviation in the slab in the furnace width direction (for example, between A-B and A'
-B, whichever is larger, or the temperature difference between E-F and E'-F, whichever is larger, A>B
, , A'>B or E>F, , E'>F) The temperature deviation within the slab is such that uniform heating in the furnace width direction is achieved during the furnace time that ensures a predetermined productivity.

In normal heating, about 15 to 20°C in the above (1)
In (2) above, the temperature is about 20 to 30°C, and in (3) above, it is about 30 to 40°C. That is, the difference between the highest temperature point within the slab and the lowest temperature point within the slab is approximately 50°C. The present invention relates to the temperature deviation shown in (3) above, and assuming that the temperature deviations occurring in (1) and (2) above are unavoidable, the temperature deviation due to (3) above is It is necessary to keep the temperature below about 15°C. Second
The figure shows slabs 3a and 3b for thick plate rolling, which are shorter than hot strip slabs that are transferred in parallel in two rows of charging, for example.
FIG. When slabs 3a and 3b charged in double rows are heated in a rolling heating furnace equipped with a conventional axial burner 4, the furnace temperature in the width direction of the furnace is as shown in FIG. However, the vicinity of the longitudinal ends of the slabs 3a, 3b, that is, the furnace side wall 1a and the vicinity 6a of the facing surface of the slabs 3a, 3b, are easily heated due to the relationship with the furnace shape, and therefore the temperature deviation within the slab in the furnace width direction is The result is as shown in FIG. Figure 4 shows that the temperature deviation within the slab in the width direction of the oven is approximately 30°C, as shown by line A or line (A is the slab surface temperature, and line is the center temperature in the thickness direction of the slab). And in the vicinity of the facing surface 6a of the slabs 3a and 3b, the amount of overshoot with respect to the target average extraction temperature C is about 35
℃, and the above requirements cannot be satisfied. conventionally,
For areas where the amount of overshoot exceeded a predetermined value, processing such as cutting off the slab was taken, resulting in a decrease in yield. To solve this problem, as shown in FIG. 5, in order to lower the furnace temperature near the furnace side wall 1a and near the facing surfaces 6a of the slabs 3a and 3b, an axial burner 4a is installed.
, 4b, by distributing the flame temperature as shown in Figure 6, or by setting the furnace temperature lower and extending the furnace time. A method was adopted to reduce the internal temperature deviation.
However, with the first two methods, the temperature deviation within the slab could be improved to about 20°C by suppressing and uniformizing the heating at the longitudinal ends of the slabs 3a and 3b;
It was difficult to achieve temperature 3 of 0 to 15°C or lower. In the last method, for example, as shown in Figure 7, by increasing the heating time in the furnace, the temperature deviation in the longitudinal direction of the slab became smaller (however, the furnace temperature remained constant at 1020°C in both the furnace length and width directions). 4, assuming that the slab extraction temperature is 950°C.
However, this method had drawbacks such as lower productivity and lower fuel consumption due to long heating times. For this reason, with conventional methods, it is not possible to reduce the temperature deviation within the slab in the width direction of the furnace, and this has been countered by increasing the amount of alloy added or increasing the allowable temperature deviation within the slab, but this increases production costs. There were flaws. In addition, in a component system in which titanium, niobium, etc. are added, in order to obtain the precipitation effect and the effect of microstructural refinement during rolling, and to obtain a fine microstructure during heating, it is necessary to add titanium, niobium, etc. Since partial solid solution of the elements is desired, it is undesirable for any part of the slab to rise much above the target extraction temperature during heating.

Therefore, it is not possible to use a heating method that uniformizes the temperature distribution inside the slab during extraction by heating a slab with such a component system using a heat pattern that has an overshoot, resulting in a monotonically increasing temperature distribution in the furnace length direction. It is necessary to heat for a long time with a heat pattern of 7 to improve the uniformity of heating. Of course, it is practically impossible to heat for such a long time that productivity is completely ignored. For example, if the target extraction temperature is 950℃ and the heating time is about 23 minutes, even if the furnace temperature is uniform across the width of the furnace, as shown in Figure 11. There is a temperature difference of about 50°C in the longitudinal direction of the slab. In such a state, it is necessary to use a component system that is insensitive to the heating temperature, which has the disadvantage that the merits of rationalizing the addition of alloying elements are reduced. The present invention was made in order to solve the above-mentioned drawbacks, and an object of the present invention is to provide a method for uniformly heating thick plate slabs charged in double rows without reducing productivity.

The present invention has been made to achieve the above object, and provides a heating furnace in which slabs are charged in double rows, including a plurality of partition walls extending in the furnace length direction above and/or below each slab end. The present invention provides a method of uniformly heating the slab by installing the furnace vertically to divide the inside of the furnace into a plurality of sections, and adjusting the furnace temperature and radiant heat in the plurality of sections.

FIG. 8 shows an embodiment of the present invention, in which slabs 3a, 3b
FIG.

In the figure, the longitudinal direction of the partition walls 7a to 7d is the slab 3a.
, 3b, its upper end is fixed to the ceiling 1b of the furnace wall 1, and its lower end hangs down to a predetermined height from the surface of the slabs 3a, 3b. Accordingly, the heating furnace is divided into five sections A by partition walls 7a to 7d. The furnace temperature of sections A, C, and E is determined by the partition walls 7a to 7d.
As shown in Figure 9, the shadows created by the central section B,
The temperature will be lower than that of D, and the thermal radiation will also be smaller. Therefore, the temperature rise at both ends of the slabs 3a, 3b is suppressed, and the surface temperature of the slabs in the longitudinal direction is made uniform as shown in FIG. Note that line A is the target extraction temperature of 950°C.
According to the embodiment of the present invention, under heating conditions such as a target extraction temperature of 950°C, a furnace temperature of about 1020°C, and a heating temperature of about 230 minutes, the difference in furnace temperature between the central part and the end of the slab is about 70°C. At that time, the temperature deviation in the longitudinal direction of the slab becomes the minimum, about 1
It was 5°C.

Next, in the above embodiment, in order to further uniformly heat the slab, a case will be considered in which the combustion amount of the axial flow burners 4a, 4c, and 4e in the sections outside the partition wall (FIG. 8A, C, and E) is reduced.

FIG. 11 shows the temperature distribution during extraction in the longitudinal direction of the slab when no partition wall is provided in the longitudinal direction of the furnace.

In this case, as is clear from the figure, the maximum temperature deviation within the slab is almost dominated by the temperature deviation in the longitudinal direction of the slab, with a temperature deviation in the longitudinal direction of approximately 40°C and a temperature deviation in the thickness direction of approximately 10'C.
= approximately 50°C. Now, as shown in Fig. 12, in the case of the shortest slab with partition walls installed at intervals exactly equal to the length of the slab, there is almost no temperature deviation in the longitudinal direction of the slab and the maximum temperature deviation. about 10°C
can be suppressed to Here, ko is the upper surface temperature of the slab, nu is the temperature at the center of the slab, and ru is the target extraction temperature. These are all data when the target extraction temperature was 950°C, the heating time was 23 minutes, and the slab thickness was 22 degrees. On the other hand, slabs other than the shortest slab as shown in FIG. 12 are paired. The top and bottom parts of the slab protrude outside the partition wall, and unless the burner is fired in the compartment corresponding to this protrusion, the coldest spot will occur within this protrusion. This coldest point temperature is a function of the length of the protruding part, as shown in FIG. 13, and the longer the protruding part, the lower the temperature. To solve this problem, as shown in Figure 8, burner combustion may be performed in the section corresponding to this protruding section, but in this case, the combustion amount in the end heating section is controlled more than the burner in the central heating section. The use of a burner with a low lower limit constitutes one preferred embodiment of the present invention. In other words, for a slab with a protrusion length of 800 mm,
When the combustion amount of the burner was changed, in order to make the temperature distribution in the protruding part almost flat, the combustion amount in the protruding part was reduced by a large width than the combustion amount between the pair of partition walls.
I found that it is best to set it to around %. The temperature distribution during extraction at this time is as shown in FIG. However, the amount of combustion refers to the amount of combustion input per unit volume for each compartment. Of course, the appropriate combustion amount of the protruding part is a function of the length of the protruding part, and when there is no protruding part, there is no need to burn it,
If the protruding portion is long, it is necessary to increase the amount of combustion. However, if the protruding part is less than 1.3 TrL, the combustion amount in this part must be kept to 50% or less of the combustion amount between the pair of partition walls, otherwise the temperature at the end will rise too much. It is necessary to lower the amount of combustion compared to the other sections. Various methods can be considered to make the amount of combustion in the protruding section variable and smaller than in other sections. For example, it is possible to ignite and extinguish the roof burner or control the amount of fuel input, but this requires a large number of burners to be controlled. This is too inappropriate for actual operation. Therefore, it is preferable to use a large burner, such as an axial flow burner, with a low lower limit for combustion amount control. Next, we will discuss the effect of the partition wall when the height of the partition wall is changed, that is, the distance between the bottom end of the partition wall and the top surface of the slab in the upper zone, and the distance between the top end of the partition wall and the bottom surface of the slab in the bottom zone.

In order to reduce the temperature deviation in the longitudinal direction of the slab as much as possible, it is preferable to configure the height of the partition wall to be variable so that it can always be set at an appropriate value. Figures 15A and 15b show an embodiment of the present invention in which the height of the partition wall is variable. The figure shows that the partition walls 4f to 41 that partition the upper furnace chamber are suspended and supported so that they can be raised and lowered by a chain 8 connected to a hoisting mechanism installed outside the furnace. This heating furnace is equipped with a roof burner 10, a side burner 11, and an axial burner 12. The movable partition walls 4f to 41 are suspended in the furnace by a chain 8 via a hook 13, and the chain 8 is wound around a sprocket 14. The rotation shaft 15 of the sprocket 14 is connected to the motor sprocket 16
The movable partition walls 4f to 41 are moved up and down by being connected to a motor 17 via a motor 17, and the sprocket 14 is rotated by the drive of the monitor 17, and the chain 8 is let out or reeled in. Note that a guide 18 is provided to prevent or reduce leakage of the furnace atmosphere gas from the sliding portions of the partition walls 4f to 41 and to guide the movement up and down. 1
Reference numeral 9 is a hearth, and opening and letter C indicate the charging and extraction directions of the slabs 3a and 3b, respectively.

The height of the partition walls 4f to 41 can be detected by a method such as detecting the rotation angle of the sprocket 14, and its value is determined by the furnace temperature distribution in the furnace width direction, the temperature inside the furnace or in the longitudinal direction of the slab at the time of extraction. Adjust so that the temperature deviation inside the slab is small while checking the distribution. FIG. 16 shows another embodiment of the present invention, in which movable partition walls 4j to 4m are further provided at the bottom of the embodiment shown in FIG. 15, in which the partition wall is provided at the top. The same parts are given the same reference numerals and their explanation will be omitted. In the figure, the lifting cylinder 20 is the lower partition wall 4.
A guide 21 is provided adjacent to the partition wall. In addition, 22 is an arm, 23 is a fulcrum, and 24 is a hearth. If the distance between the furnace side walls 1a, 1b and the ends 3a, 3b of the slab changes, the effect of the partition wall will naturally change; distance)〉(slab 3a
, 3b), and the center of the furnace is approximately
If the partition walls 4f to 4m are provided so that Uniform heating is possible without much change in effectiveness. In this case, as in the above example, if a burner with a lower combustion rate control lower limit is used in the end heating section than the burner in the center heating section, the heating becomes even more effective.111) Good! not.
Usually, the length of the slab charged into the heating furnace varies depending on the operation.

In order to uniformly heat the slabs from the minimum length to the maximum length in a heating furnace where two rows of slabs are charged, partition walls 4f: to 4m are fixed in the furnace width direction as shown in FIG.
When installing individual slabs, install them according to the furnace insertion position of the minimum length slabs 3c and 3d, and for longer slabs 3e and 3f, change the height of the partition walls 4f to 4m or adjust the combustion amount in the burner. It is desirable to make adjustments by

In addition, when using long slabs 3e and 3f, the partition wall 4f~
The desirable installation position of 4 m varies depending on the burner type, arrangement, etc., but in a normal heating furnace, the minimum length slab 3c, 3
It is desirable for each partition wall 4f to 4m to be 0 to 1 m closer to the slab center than the position in the furnace of d, and F-M in the figure.
indicates the desired installation range. Of course, in order to increase the effect of partition walls, if space or engineering permits, install multiple partition walls in the width direction of the furnace.
Depending on the length of the slab, it is desirable to move a suitable partition wall vertically or across the furnace width. FIGS. 18A and 18B show still another embodiment of the present invention, which includes a device for charging and conveying copper materials to be heated so that the longitudinal centers of all the steel materials to be heated are approximately coincident, and a device for charging and conveying copper materials to be heated, and a plurality of pairs of partition walls extending in the longitudinal direction of the furnace at intervals equal to or slightly shorter than the length of the shortest steel material therein, and with their centers substantially coinciding with the longitudinal center of the steel material to be heated; A heating furnace capable of uniform heating is shown in which a section of the furnace including the top or bottom part of the steel material to be heated has a burner with a lower combustion rate control lower limit than other sections.

In the figure, the steel material 25 to be heated is charged into the heating furnace from the N side of the preheating zone, but before that, a positioning sensor 26 and a conveyance/positioning roller 27 are used to ensure that the longitudinal center of the steel material 25 is is adjusted to match q or q″.

Q and q'' are the centers of a pair of partition walls, which will be described later.
The positioning sensor 26 may be of any type, but for example, a phototube type sensor is simple. The steel material 25 to be heated charged into the heating furnace is transported to a pre-heating zone N1, a heating zone 0, and a soaking zone P using a transportation mechanism such as a walking beam or rollers so that its center almost coincides with q or q''. , and then extracted from the furnace after being heated to a predetermined temperature. Only the skid vibe 28 in the case of the walking beam type is shown in the figure. The partition walls 29 are in pairs (e.g. -s'') The interval is equal to or slightly shorter than the length of the shortest steel material of the heated steel material 25.

In other words, if the length of the shortest steel material is t, then r-r'' and s
-s'' distance r-bi, s-s'' is r-bikuT, s-s''
The partition wall and furnace wall are paired (w-R.l in the figure).
5s''-w'') and the paired partition walls (beam s in the figure), there is a burner 30 with a low combustion rate limit, and between the pair of partition walls (beam s'' in the figure -S''), a normal burner 31 is arranged.

Here, a heating furnace with a pre-heating zone N, a heating zone 0, and a soaking zone P is illustrated, but the shape of the furnace may be box-shaped, and
There is no need for row charging, and single row or other double row charging may be used. The only difference is the number of paired partition walls depending on the number of charging rows. Regarding the length of the partition wall in the furnace length direction, it is preferable that the partition wall be long as long as it does not cause problems in terms of equipment. Note that the partition wall does not necessarily need to be provided along the entire length of the furnace, and may be installed only in the soaking zone or in the soaking zone and heating zone where it is most effective. There is no particular limit to the thickness of the partition wall, but it is preferable that the partition wall be thin.
It can also be constructed of reticulated metal ceramics. Furthermore, it is possible to carry out the process regardless of the type of furnace, whether it is a walking beam furnace or a Buscher furnace.

In addition, the burner installed in the rolling heating furnace may be a half burner instead of an axial burner, and even in the case of a side burner, the same can be achieved by making a hole in the partition wall only in the area that is exposed to fire. effect can be achieved. Although the present invention relates to a heating method for making the slab temperature uniform, the following heating method is also possible. In other words, for materials where the amount of overshoot is not a problem, in order to make the material of the product uniform and to reduce waste firing, the slab between the extraction from the heating furnace and the exit from the final rolling mill is determined based on past operational experience or theoretical analysis. Considering the temperature drop due to heat radiation in the longitudinal direction, calculate the necessary temperature distribution in the longitudinal direction of the slab at the time of extraction from the heating furnace so that the temperature in the longitudinal direction of the steel material at the exit side of the optimal rolling mill is uniform. Adjust the height of the partition wall, burner combustion rate, etc. to achieve this temperature distribution.
As described above, according to the method of the present invention, it is possible to actively and intentionally create a temperature distribution in the longitudinal direction of the slab. As is clear from the above explanation, according to the present invention, it is possible to uniformly heat the temperature in the longitudinal direction of the slab without reducing productivity, and furthermore, the temperature rise at both ends of the slab in the longitudinal direction can be suppressed. Since the amount of fuel input to the burner is reduced, it also contributes to energy conservation, and its implementation has a large effect.

[Brief explanation of the drawing]

Figures 1, 2, and 5 are cross-sectional views showing an example of a conventional heating furnace, and Figures 3, 4, 6, and 7 illustrate the temperature in the width direction of a conventional slab furnace, respectively. longitudinal temperature,
A diagram showing temperature in the oven width direction and temperature deviation with respect to heating time, FIG. 8 is a sectional view of an embodiment of the present invention, FIG.
Figure 0 is a diagram showing the temperature in the width direction of the furnace and the temperature in the longitudinal direction of the slab according to the embodiment of the present invention, and Figures 11 and 12 are diagrams showing the longitudinal direction of the slab during extraction when there is no partition wall and when there is a partition wall. Diagrams showing temperature distribution, FIGS. 13 and 14 are diagrams showing the relationship between the protrusion part and the coldest point temperature and the relationship between the protrusion part temperature distribution according to the embodiment of the present invention, respectively, and FIG. In other embodiments, -a is its cross-sectional view, b is a(7)
16 is a sectional view of still another embodiment of the present invention, FIG. 17 is a sectional view showing the setting range of the furnace wall of the present invention, and FIGS. 18A and b are sectional views of still another embodiment of the present invention. FIG. 7 is a cross-sectional view of yet another embodiment. ') 3a, 3b...Slab, 7a to 7d, 4f
~4m...Partition wall.

Claims (1)

[Claims] 1. In a heating furnace in which slabs are charged in double rows, a plurality of partition walls extending in the furnace length direction are vertically provided above and/or below the ends of each slab to divide the inside of the furnace into a plurality of sections. A method for heating a slab, characterized by uniformly heating the slab by adjusting the furnace temperature within the section.