JPH11347602A - Continuous rolling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the high effect of energy saving, high yield and high productivity by rolling materials which are cast with a continuous casting machine without heating. SOLUTION: This continuous rolling method is for manufacturing long size steel using the continuous casting machine 1 for casting billets and a rolling device 3 for rolling these billets and includes a conveying state of recuperating the heat of the billets by conveying the billets which are cut after casting to the rolling device 3 in a specified time along the conveying route where the upper surface and both sides of these billets are enclosed with heat insulating covers while insulating the heat and a rolling stage of rolling these cut billets without heating with the rolling device 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous rolling method. More particularly, the present invention relates to a continuous rolling method for continuously supplying a continuously cast billet to a rolling device at a high temperature to produce a long steel material such as a wire rod or a steel bar.

[0002]

2. Description of the Related Art Conventionally, a billet or a slab (hereinafter, also referred to as a material) cast by a continuous casting machine is transferred to a continuous casting apparatus and a rolling apparatus on a transfer line for the purpose of energy saving, high yield, and high productivity. A continuous rolling method using a directly connected device is known.

For example, as shown in FIG. 11, a continuous rolling device described in Japanese Patent Application Laid-Open No. 57-187102 includes a continuous casting machine 51, a cutting device 52, and a rolling device 54.
Are connected to each other by a transport line. Further, by installing an induction heating device or a heating furnace 53 in the middle of the transport line between the cutting device 52 and the rolling device 54 and raising only the material surface to a temperature necessary for rolling, energy saving and high energy saving are achieved. There are ways to achieve yield and high productivity.

[0004] When the material temperature required for rolling the material (for example, the surface temperature of the material) is insufficient (especially for a large-section slab such as a slab), a required corner is required during the transportation. 2. Description of the Related Art A method is widely used in which a material is reheated to a material temperature (surface temperature) required for rolling while securing a recuperation time and rolling is performed.

[0005] Here, the recuperation means keeping the material warm, and transferring the heat of the high temperature portion inside the material to the surface to return the material temperature (for example, the surface temperature) to a predetermined temperature or higher.

[0006]

However, in the conventional method described above, when a material such as a billet is manufactured by a continuous casting machine, the upper surface of the cast material, particularly the corner portion, is conveyed while the material is conveyed. The material is gradually cooled, and the material temperature required for rolling cannot be secured.

For this reason, it is necessary to provide a heating device for heating a corner portion of a material, such as an induction heating device, between the continuous casting device and the rolling device. This requires a huge amount of equipment when manufacturing billets with a plurality of strands. Moreover, temperature control for each billet is complicated and not economical. The temperature adjustment for each billet requires not only the average temperature of the cross-section but also the uniformity of the cross-section temperature of the material.

The present invention has been made to solve such a problem, and a high energy saving effect, a high yield, and a high productivity can be achieved by rolling a material cast from a continuous casting machine without heating. It is an object to provide a continuous rolling method.

[0009]

According to a first aspect of the present invention, there is provided a continuous rolling method for producing a long steel material using a continuous casting machine for casting a billet and a rolling device for rolling the billet. (A) a casting step of continuously casting a billet by the continuous casting machine; (b) a cutting step of cutting the billet to a predetermined size by a cutting device; (c) A conveying step of conveying the cut billet to a rolling device along a conveying path in which the upper surface and both side surfaces of the billet are surrounded by a heat insulating cover to a rolling device for a predetermined time while maintaining the temperature, and (d) And d) rolling the cut billet without heating by the rolling device.

At least at the front and rear surfaces of the cutting device, the average temperature of the cross section of the billet in the cutting device is 1100 ° C. or more, and the temperature difference between the surface temperature and the center temperature of the billet is within 50 ° C. It is preferable that the billet be reheated by disposing the heat retaining cover so as to be separated from the upper surface and side surfaces of the billet by a distance of about 300 mm or less.

[0011] 300 from the top and side of the billet
When the billet arrives at least at the rolling device by disposing the heat retaining cover so as to be separated by a distance of about mm or less, and supplying the cut billet to the rolling device within about 3 minutes after cutting. It is preferable that the average temperature of the cross section of the billet is about 900 ° C. or more.

A continuous rolling method according to a fourth aspect of the present invention is a continuous rolling method for producing a long steel material using a continuous casting machine for casting a billet and a rolling device for rolling the billet. (A) a casting step of continuously casting billets by the continuous casting machine; and (b)
A cutting step of cutting the billet to a predetermined size by a cutting device, and (c) a rolling step of rolling the cut billet without heating by the rolling device, wherein the continuous casting machine includes a plurality of strands. By shifting the timing of the start of casting in each strand, and the timing of cutting the billet cast from the strand, the variation of the cross-sectional average temperature of each strand immediately before the rolling device is kept within ± 20 ° C. It is characterized by the following.

A continuous rolling method according to a fifth aspect of the present invention is a continuous rolling method for producing a long steel material using a continuous casting machine for casting a billet and a rolling device for rolling the billet. (A) a casting step of continuously casting billets by the continuous casting machine; and (b)
A cutting step of cutting the billet to a predetermined size by a cutting device, and (c) a rolling step of rolling the cut billet without heating by the rolling device, and reheating the cut billet. When the temperature difference between the billet surface temperature and the center temperature becomes about 50 ° C. or less, the billet surface temperature is continuously measured to determine whether or not rolling is possible without heating.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the continuous rolling method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart showing one embodiment of the continuous rolling method of the present invention, FIG. 2 is a cross-sectional explanatory view of a transfer line having a heat insulating cover used in the continuous rolling method of the present invention, and FIG. FIG. 4 is a cross-sectional explanatory view showing another embodiment of a transfer line having a heat retaining cover used in the present invention, FIG. 4 is a plan view of a continuous rolling device having a plurality of strands, and FIG. 5 shows a portion immediately after the continuous casting machine in FIG. FIG. 6 is a sectional explanatory view showing an unsolidified portion inside the billet of FIG. 5, FIG. 7 is a sectional view taken along line VII-VII of the billet of FIG. 6, and FIG. 8 is a line VIII-VIII of the billet of FIG. FIG. 9 is a cross-sectional view taken along line IX-IX of the billet of FIG. 6 and FIG. 10 is a surface temperature and cross-sectional average of the billet used to determine whether or not rolling is possible without heating in the continuous rolling method of the present invention. With temperature Is a graph showing the correlation.

As shown in FIG. 1, a continuous rolling method according to the present invention uses a continuous casting machine 1 for casting a billet and a rolling device 3 for rolling the billet, and uses a continuous material such as a wire or a bar. This is a continuous rolling method for producing a long steel material. Specifically, (a) the continuous casting machine 1
A casting process for continuously casting the billet; (b)
A cutting step of cutting the billet to a predetermined size by the cutting device 2; and (c) heating the cut billet at least on the upper surface and both side surfaces of the billet with an insulating cover 4,
24 (see FIGS. 2 to 3), a conveying step of recovering the billet by conveying the rolling sheet 3 to the rolling device 3 for a predetermined time while keeping the temperature along the conveying path surrounded by 24 (see FIGS. 2 to 3); And a rolling step of rolling by the rolling device 3 without heating. In FIGS. 2 and 3, reference numerals 5 and 25 denote transport rollers, and reference numerals 6 and 26 denote driving mechanisms such as motors.

For example, a billet B shown in FIGS.
When the drawing speed is 2.0 m / min or more, 900 ° C. or more that can be sufficiently rolled can be secured up to 180 seconds after cutting in the case of the drawing speed of 2.0 m / min or more.

On the other hand, the upper corner portion 42 is
Since it is lower by about 50 ° C., it is not suitable for rolling as it is.

The heat can be restored by keeping the heat at least on the upper surface and the side surfaces for about 30 seconds or more by the heat insulating covers 4 and 24 during the transportation. As a result, the billet B immediately before the rolling device 3 has a temperature (900 ° C.) or higher at which uniform rolling can be sufficiently performed substantially uniformly.
Rolling is possible without heating.

In the present invention, the structure of the heat insulating cover is not particularly limited, and various forms can be adopted. For example, the heat retaining cover 24 shown in FIG.
A heat insulating material 27 made of ceramic fiber is disposed inside the upper cover 28 and the side guide 29 so as to face the upper surface and both side surfaces of the billet B. The side guide 29 is formed with a convex portion 29a to prevent rattling of the billet B in the width direction. Further, a water cooling box 30 is provided outside the side guide 29 to prevent the side guide 29 from being thermally deformed.

Further, a heat insulating cover may be provided on the truck by a truck type.

Next, as shown in FIG. 4, when the continuous casting machine 1 is provided with a plurality of strands 7, in order to eliminate variations in the material temperature for rolling without heating between the respective strands 7, In the casting step and the cutting step, the timing of the start of casting in each strand 7 is shifted, and the cutting timing of the billet cast from the strand 7 is shifted, so that the average cross section of each strand 7 immediately before the rolling device 3 is obtained. The temperature variation is kept within ± 20 ° C., and thereafter, the non-heating rolling step is performed. In this case, in order to perform rolling without heating, the material may be reheated by using the heat retaining cover as described above, or may be reheated by another method.

In the conventional continuous rolling method, a heating device is provided between the continuous casting machine and the rolling device. The heating device is used in response to a continuous casting operation variation, for example, a material temperature variation caused by a casting speed variation. Can be supplied to the rolling mill at a predetermined temperature by heating, but when supplying to the rolling mill without heating as in the present invention, the fluctuation of the material temperature is reduced as much as possible by another means. There is a need.

As shown in FIG. 4, a general billet casting machine is provided with a plurality of strands 7, and is provided with a cutting device 2 for each strand 7, and cuts a material into a predetermined length. To a common rolling device 3.

If the material is cut at the same timing in each of the strands 7 and is conveyed to the rolling device 3 at the same timing, the preceding material is rolled immediately before the rolling device 3. It will wait until it finishes.

For example, when the rolling pitch is 30 seconds and there are four strands, a maximum of about 90 seconds must be waited, and the rolling temperature may drop by about 30 ° C.

Therefore, in the continuous rolling method of the present embodiment, it is possible to eliminate the variation in the average temperature of the cross section of the billet when rolling without heating by shifting the timing of starting casting by at least the rolling pitch time in each strand. it can.

Further, as a preferable method for equalizing the temperature of the material for rolling without heating, at least the average sectional temperature of the billet in the cutting device 2 is 1100.
℃ or more, so that the temperature difference between the surface temperature and the center temperature of the billet is within 50 ℃, at least 300mm or less distance from the upper and side surfaces of the billet on the front and rear surfaces of the cutting device 2. The billet may be reheated by arranging the heat retaining covers 4 and 24 on the billet.

That is, the continuous casting machine is a method of continuously producing a material of a predetermined size while cooling a molten steel material sequentially from the surface. Then, the central part of the material may be solidified.

More specifically, as shown in FIG. 5, in the continuous casting machine 1, the molten steel M is poured into the primary cooling mold 11 for each strand, and the surface of the billet B (or slab) is solidified. At the same time, the billet B is continuously cooled by being gradually cooled by a water cooling unit 12 for secondary cooling and drawn out by a roller 13 so as to have a predetermined sectional shape. The billet B continuously cast is cut into a predetermined length by the cutting device 2.

As shown in FIGS. 6 to 9, immediately after leaving the mold 11, a large amount of the unsolidified portion B ₁ still melted remains in the center of the billet B. , it solidified but less solidified portion B ₂ is, the number of solidified portion B ₂ as withdrawing the billet B, and so that solidification is completed immediately before the cutting device 2.

If the billet having unsolidified portions is cut, there is a problem that molten steel starts to flow. Conversely, if the solidification is completed by cooling too quickly, the temperature of the billet becomes too low. There is a problem that can not be. Therefore, in order to obtain a higher temperature billet after cutting, the billet may be solidified immediately before cutting.

Conventionally, as a method of obtaining a high-temperature material with a continuous casting machine, a method using air-water cooling for secondary cooling (Japanese Patent Application Laid-Open No. 58-209457) or by controlling secondary cooling water. Method for controlling solidification completion point
No. 5-5166).

However, according to the conventional method, although the average temperature of the material can be ensured, the difference between the internal temperature and the surface temperature of the material sometimes reaches 300 ° C. or more at the time of solidification completion, and the material arrives at the rolling mill. Even at this point, the temperature may reach 200 ° C. or higher.

However, if the surface temperature and the internal temperature are made uniform by cooling over time, the average temperature decreases. Also, if rolling is performed as it is because the average temperature is high, the surface temperature is low and cracks are generated on the surface during rolling, so conventionally, the material temperature is made uniform by a heating device or the temperature is raised. Needed.

Therefore, the present inventors utilize the cutting time, install heat insulation covers on the front and rear surfaces of the cutting device for uniformizing the temperature of the material, and use the reheating of the material to obtain an average. It has been found that both the temperature and the temperature difference between the inside and the surface of the material can be satisfied. This heat insulating cover is similar to the heat insulating covers 4 and 24 shown in FIGS. 2 and 3 and is 300 mm or less from the upper and lower surfaces and both side surfaces of the billet B in order to at least recover the upper corner portion 42 of the billet B. For example, by disposing the heat insulating cover 24 covered with the heat insulating material 27 shown in FIG. 3 so that the billet B can be sufficiently reheated, at least the general required temperature of the material dimensions can be obtained. It has been found that a cross-sectional average temperature of 1100 ° C. or more and a temperature difference of 50 ° C. between the inside of the material and the surface can be achieved. Of course, the average cross-sectional temperature of 1100 ° C. is a temperature that can be sufficiently achieved by a conventionally known continuous casting technique.

Further, as described in Japanese Patent Publication No. 60-35225, a plurality of ventilation blocking plates may be rotatably mounted on the upper inside of the heat insulating cover like goodwill.

Further, at least 3 mm from the top and side surfaces of the billet B so that rolling can be suitably performed without heating.
By disposing the heat retaining covers 4 and 24 so as to be separated by a distance of about 00 mm or less, and supplying the cut billet B to the rolling device 3 within about 3 minutes after cutting, at least the rolling device 3 When the billet B arrives at a temperature of 900
It is preferable that the temperature is about not lower than about ° C.

Here, the reason why the heating time is set within about 3 minutes after cutting is that if it takes more time than 3 minutes, a heating device is required as in the related art.

In this case as well, the heat insulating covers 4, 24 (see FIGS. 2 and 3) or other forms of the heat insulating cover may be employed as described above.

Of course, if the transport distance is long, FIG.
Billet B in addition to the heat insulating covers 4 and 24
A lower heat insulating cover that covers the lower side of the vehicle may be installed.

Further, after the casting step and the cutting step, the cut billet is re-heated so that the internal temperature can be predicted from the surface temperature of the cast billet, and the temperature difference between the billet surface temperature and the center temperature. When the temperature is within about 50 ° C., the surface temperature of the billet is continuously measured to determine whether or not rolling is possible without heating. If rolling is possible, the above-mentioned rolling step without heating is performed. In this case, in order to perform rolling without heating, the material may be reheated by using the heat retaining cover as described above, or may be reheated by another method.

Under actual operation, the temperature of the material such as the billet naturally fluctuates due to troubles in the equipment of the continuous casting machine and the rolling device and the operation, and so on. It is necessary to judge whether or not rolling can be continuously measured by a gauge.

However, the thermometer can measure the surface temperature of the material, and cannot measure the internal temperature. Therefore, neither the average temperature nor the temperature difference between the inside and the surface can be measured (in particular, immediately before cutting, immediately after cooling, immediately after cooling). The surface is not necessarily appropriate to represent the average temperature of the cross section).

Therefore, the present inventors previously calculated the temperature of the material, summarized the relationship between the temperature difference between the surface temperature and the average temperature, and decided whether or not rolling was possible. Judgment sites are a place where the material before cutting has not sufficiently regained heat (before cutting by the shear), a place immediately after cutting, and a temperature difference between the surface temperature and the center temperature where the cut material has sufficiently regained heat. As a result of performing the test at three places where it is considered that the temperature was within approximately 50 ° C. (after cutting and immediately before the rolling device), the best judgment result was obtained after cutting and immediately before the rolling device. Met. The reasons are as follows: (1) In measuring the temperature, as a certain material is conveyed, the scale attached to the material surface is removed and the measurement error is reduced. (2) When the temperature difference between the internal temperature and the surface temperature is large, And that a stable measurement result cannot be obtained due to a change in the surface temperature during the measurement.

Taking the cross-sectional average temperature as an example, the relationship between the surface temperature and the cross-sectional average temperature is as shown in the graph of FIG. The billet temperature calculation in FIG. 10 is obtained by solving a difference of Fourier's heat conduction equation by a computer. In FIG. 10, I is before cutting, II is
Is a graph immediately after cutting, and III is a graph immediately before rolling.

When determining whether or not rolling is possible using the graph of FIG. 10, first, the surface temperature of the billet is measured with a thermometer.
Before cutting (line I), immediately after cutting (line II), or immediately before rolling (line III), it is checked whether or not the corresponding cross-sectional average temperature has reached the directly transportable temperature t ₀ . Direct delivery temperature t
A billet of ₀ or more is rolled so that it can be directly sent.

The test numbers were 85, 95 and 90 before cutting, immediately after cutting and immediately before rolling, respectively.

Among them, some of the materials judged to be directly transportable have defective materials such as corner cracks. At this time, the defect rate X (direct delivery rate) is the number of test pieces N and the number of defective pieces n
Than,

[0049]

(Equation 1)

Is represented by

The determination as to whether or not rolling was possible was made based on the product defect rate X of the rolled material determined to be rollable at each measurement point. The evaluation results are as shown in Table 1. Although the defect rate X includes factors other than the material temperature of several percent, they are ignored here.

[0052]

[Table 1]

As is clear from Table 1, the defect rate X is the lowest immediately before the rolling mill. The place immediately before the rolling device is a place where the heat has sufficiently recovered, and by measuring the temperature at this place, the internal temperature can be sufficiently predicted from the surface temperature of the cast billet, and whether or not rolling is possible when rolling without heating can be determined. It can be done easily.

[0054]

According to the first aspect of the present invention, there is provided a method of directly connecting a continuous casting apparatus and a rolling apparatus by a transport line and continuously rolling a billet cast by a continuous casting machine without heating. Thereby, higher energy saving effect, higher yield, and higher productivity can be achieved as compared with the conventional continuous rolling method.

According to the fourth aspect of the invention, it is possible to eliminate variations in the average temperature of the cross section of the billet when rolling without heating.

Further, according to the fifth aspect of the present invention, the internal temperature can be sufficiently predicted from the surface temperature of the cast billet, and it is possible to easily determine whether or not rolling is possible when rolling without heating.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of the continuous rolling method of the present invention.

FIG. 2 is an explanatory sectional view of a transfer line having a heat insulating cover used in the continuous rolling method of the present invention.

FIG. 3 is an explanatory cross-sectional view showing another embodiment of a transfer line having a heat insulating cover used in the continuous rolling method of the present invention.

FIG. 4 is a plan view of a continuous rolling device having a plurality of strands.

FIG. 5 is a partially enlarged front view showing a portion immediately after the continuous casting machine in FIG. 4;

6 is an explanatory sectional view showing an unsolidified portion inside the billet of FIG. 5;

FIG. 7 is a sectional view taken along line VII-VII of the billet of FIG. 6;

FIG. 8 is a sectional view taken along line VIII-VIII of the billet of FIG. 6;

FIG. 9 is a sectional view taken along line IX-IX of the billet of FIG. 6;

FIG. 10 is a graph showing a correlation between a surface temperature of a billet and an average temperature of a cross section used for determining whether or not rolling can be performed without heating in the continuous rolling method of the present invention.

FIG. 11 is a flowchart of a conventional continuous rolling method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Cutting device 3 Rolling device B Billet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyasu Hayashibe 1 Nitsutsu-Hachimancho, Chikko Minato, Sakai City, Osaka Prefecture (72) Within the Inventor Takashi Yamamuro 1-Nitsutsu Yawatacho, Sakai City, Osaka Nitsutsu-Osaka Engineering Co., Ltd.

Claims (5)

[Claims] 1. A continuous casting machine for casting a billet and a rolling device for rolling the billet,
A continuous rolling method for producing a long steel material,
(A) a casting step of continuously casting a billet by the continuous casting machine; (b) a cutting step of cutting the billet into a predetermined size by a cutting device; and (c) converting the cut billet to the billet. A transporting step of recovering the billet by transporting the billet to the rolling device for a predetermined time while maintaining the temperature along a transporting path surrounded by a heat insulating cover on the upper surface and both side surfaces of the billet; A rolling step of rolling without heating by a rolling device. 2. The front and rear surfaces of the cutting device such that the average temperature of the cross section of the billet in the cutting device is at least 1100 ° C. and the temperature difference between the surface temperature and the center temperature of the billet is within 50 ° C. 2. The continuous rolling method according to claim 1, wherein the heat retaining cover is disposed so as to be separated from an upper surface and side surfaces of the billet by a distance of about 300 mm or less, so that the billet is reheated. 3. 30 minutes from the top and side surfaces of the billet.
When the billet arrives at least at the rolling device by arranging the heat retaining cover so as to be separated by a distance of about 0 mm or less, and supplying the cut billet to the rolling device within about 3 minutes after cutting. 3. The continuous rolling method according to claim 1, wherein the average temperature of the cross section of the billet is about 900 ° C. or more. 4. A continuous casting machine for casting a billet and a rolling device for rolling the billet,
A continuous rolling method for producing a long steel material,
(A) a casting step of continuously casting a billet by the continuous casting machine; (b) a cutting step of cutting the billet to a predetermined size by a cutting device; and (c) rolling the cut billet by the rolling. And a rolling step of rolling without heating by the apparatus, wherein the continuous casting machine includes a plurality of strands, and shifts the timing of starting casting in each strand, and shifts the cutting timing of a billet cast from the strand. A continuous rolling method whereby the variation of the cross-sectional average temperature of each strand immediately before the rolling device is within ± 20 ° C. 5. A continuous casting machine for casting a billet and a rolling device for rolling the billet,
A continuous rolling method for producing a long steel material,
(A) a casting step of continuously casting a billet by the continuous casting machine; (b) a cutting step of cutting the billet to a predetermined size by a cutting device; and (c) rolling the cut billet by the rolling. A rolling step in which the billet is re-heated by a device, and the temperature difference between the surface temperature and the center temperature of the billet is 5%.
A continuous rolling method in which the surface temperature of the billet is continuously measured when the temperature falls within about 0 ° C., and it is determined whether or not rolling is possible without heating.