KR20020050434A - Method of in-line rolling for strip casting - Google Patents

Abstract

PURPOSE: A continuous hot rolling method in a strip casting machine is provided to smoothly proceed rolling operation by controlling a roll gap and a rolling speed of a rolling mill during the initial rolling, thereby preventing skewness of a strip. CONSTITUTION: In a method for continuously manufacturing an ultra thin strip by supplying thin steel billet cast in a strip casting machine to a rolling mill through a looper as controlling a threading speed, the continuous hot rolling method in the strip casting machine comprises the steps of measuring a thickness of an initial thin steel billet cast in the strip casting machine; measuring rolling loads of driving and working sides of rolling rolls as reducing roll gaps of the driving and working sides of the rolling rolls that are in the rolling waiting state when a thickness of the steel billet is constantly maintained; adjusting the roll gaps of the driving and working sides so that a rolling load difference between the driving and working sides of the rolling rolls is a certain value or less when rolling loads measured start to be increased; and performing rolling by reducing the rolling rolls to a target roll gap as maintaining the state that the rolling load difference between the driving and working sides of the rolling rolls is a certain value or less.

Description

Continuous hot rolling method in sheet casting machine {Method of in-line rolling for strip casting}

The present invention relates to a method of hot rolling continuously in the sheet casting process, more specifically in the sheet casting machine to control the roll gap and the rolling speed of the rolling mill in the early stage of rolling to prevent the running of the judge to smoothly proceed the rolling operation It relates to a continuous hot rolling method of.

In general, the manufacturing method of the strip (STRIP) is to manufacture the slab by the continuous casting method through the molten steel through the tundish, the continuous casting method of manufacturing the slab into a thin plate through rolling and finishing work, and the molten steel directly to the rotating twin-roll casting roll There is a twin roll type sheet casting method for casting a thin plate directly without the rolling and finishing work of the slab through the casting roll. Currently, the latter twin roll sheet metal casting method can directly cast thin plates without going through several processes of continuous casting method, which can reduce the cost in terms of cost, and can reduce the manufacturing process of sheet metal. There is much research going on.

In particular, in recent years it is possible to improve the quality of the sheet through the composite process of sheet casting and hot rolling to perform hot rolling in 1-2 stands in succession to the twin-roll type sheet casting process as shown in Figure 1 can be made in the conventional general method Much research has been made on obtaining ultra-thin hot rolled sheets of about 1.2 mm or less. As a technique for manufacturing a thin plate by hot rolling continuously in a thin plate casting process, there are Japanese Patent Application Laid-Open Nos. 08-252652, 08-300107, and 09-194947, which are hot rolling conditions such as rolling temperature. The main focus is to improve the quality of steel sheet by controlling the

As described above, there is an advantage in that a hot rolled sheet having a thin thickness that cannot be obtained by a conventional process can be manufactured through a continuous hot rolling technique in twin roll type sheet casting, but it must be solved when hot rolling is performed following the sheet casting process. Many problems arise. One of these problems is meandering of the plate when hot rolling is performed following the sheet casting process.

In the sheet casting and hot rolling composite process, problems such as edge damage, fracture, and downtime of the plate produced by meandering of the rolled plate occur. There are many reasons for the judged line to occur, but in most cases it is due to the nonuniformity of the rolling reduction in the width direction. Both width directions of the rolling roll are named as the driving side and the working side, respectively, the driving side means one side of the roll to which the driving device for rotating the roll is connected, and the other side is the working side because the driving device for rotating the roll is not connected. do. On the driving side and the working side of the rolling roll, there are installed pressing devices for independently adjusting the roll gap by moving up and down independently.If there is a difference in the roll gap between the driving side and the working side, the rolling rate is different and the plate is lowered toward the smaller rolling rate. It will bend and this will cause meandering. Consider this in more detail as follows.

According to the rolling theory, the mass speed of rolling speed, rolling speed of rolling mill and rolling speed of rolling mill should be constant and therefore satisfy the following equation.

[Relationship]

V _o = V _i / (1-RR) = a × V _r / (1-RR)

Where V _o : Rolling mill exit thickness

V _i : Roll thickness of rolling mill

RR: Rolling down rate (= (side plate thickness-side plate thickness) / side plate thickness)

a: constant according to rolling conditions (determined by the position of the neutral point)

V _r : Rotational linear velocity of rolling roll

In the rolling mill, in general, since the roll diameters of the working side and the driving side are the same, the linear linear speeds of the rolling rolls of the driving side and the working side are the same, and the rolling conditions are almost the same as the working side and the driving side. a will be the same and the plate speed on the exit side of the rolling mill is determined by the reduction ratio. If the rolling rate is different between the driving side and the working side, the rolling plate of the rolling mill with the higher rolling rate is faster and the rolling speed of the rolling mill with the smaller rolling rate is slower. Bent.

Representative techniques for solving the problem of judge execution in the hot rolling process subsequent to such thin sheet casting are Japanese Patent Laid-Open Nos. 8-294715 and 9-19748.

In Japanese Patent Laid-Open No. 8-294715, a tension control device for a strip made of a braid roll or pinch roll is provided between a strip continuous casting machine and a hot rolling mill or between a hot rolling mill and a heat treatment furnace. It is a technique of preventing the meandering of the strip by detecting the plate position of the strip at the entrance side and using the detected value to guide the strip to the center.

In Japanese Patent Laid-Open No. 9-19748, when a continuous casting of thin cast steel pieces using a cooling drum is loaded into a rolling mill, the tension of the thin cast steel in front of the rolling mill is adjusted to a range of 0.3-1.5 kgf / mm 2 and loaded into the rolling mill. This is a technique to prevent meandering of the strip.

These prior arts use steering units to ensure proper tension on the plate and to position the cast pieces in the center of the width direction, which is effective when rolling starts and reaches a steady state, but rolling starts. It is difficult to make an effect in the section that increases the amount of reduction. That is, when the steady state is reached in the sheet casting and hot rolling composite process, the state becomes almost the same as in the conventional batch rolling line, and thus, the problem related to the judge line can be solved by applying the batch rolling line. However, at the start of rolling, there are many differences between the sheet casting and the hot rolling composite process and the conventional batch rolling line, and in the case of the problem of judge execution in the sheet casting and the hot rolling composite process, the rolling is mainly started.

The problem at the beginning of rolling in the thin sheet casting and hot rolling composite process is that the method of starting rolling with the roll gap of the rolling mill set as a target value before rolling starting like a conventional batch rolling line cannot be applied. In other words, in the process of sheet casting and hot rolling, the rolling process does not start rolling with the start of casting, but starts rolling while reducing the roll gap of the rolling mill in the situation where the casting is started and the rolled steel passes through the rolling mill at high speed. The situation is different. The thin plate casting process is a process of manufacturing a thin plate using molten steel, so there is a special casting start sequence to prevent leakage of molten steel at the start of casting, and as a result, as shown in FIG. The steady state in which the plate of the target thickness is cast is reached. Therefore, if rolling starts from the transition region where a sudden change in plate thickness occurs, the rolling mill is damaged by overload, so the rolling must start rolling after the initial thickness of the thin slab reaches a constant thickness, that is, reaches a steady state.

At the start of casting, the roll gap of the rolling mill is kept to have a roll gap wide enough to prevent rolling in the thickness transition region of the sheet cast slab, and the roll gap is reduced to roll to the target thickness at the end of the transition region. At this time, the rolling reduction of the driving side and the working side is changed due to the variation in the thickness direction of the thin plate cast plate and the difference in the speed of change of the roll gap between the driving side and the working side of the rolling mill, thereby severely meandering the plate. As described above, in the continuous hot rolling of the sheet casting machine, there is a high possibility of meandering at the start of rolling, but the above-described prior art cannot solve the situation, and thus a new technique is required.

In the present invention, in the sheet casting and hot rolling composite process, the rolling process is prevented from occurring from the moment when the rolling starts to increase until the steady state is reached, and the rolling process can be performed smoothly. To provide a rolling method, the object is.

1 is a schematic diagram showing the overall configuration of a thin plate casting and hot rolling composite process

2 is a graph showing the change in thickness of the thin cast steel cast over time

Figure 3 is a rolling mill control flowchart at the start of rolling in accordance with the present invention

Explanation of symbols on the main parts of the drawings

1 .... casting roll 2 .... molten steel paste

3 .... sheet steel 4 .... first pinch roll

5 .... Looper 6 .... 2nd Pinch Roll

7 .... rolling mill 8 .... third pinch roll

9 .... Coiler

In the continuous hot rolling method of the thin plate casting machine of the present invention for achieving the above object, in the method for continuously manufacturing ultra-thin thin plate by supplying the thin cast steel cast in the thin plate casting machine through a looper while adjusting the plate speed ,

Measuring the thickness of the initial thin cast steel cast in the sheet caster,

Measuring the rolling load of the driving side and the working side of the rolling roll while reducing the roll gap between the driving side and the working side of the rolling roll in the rolling standby state when the thickness of the cast steel becomes a constant thickness,

Adjusting the roll gap of the driving side or the working side when the rolling load starts to increase so that the difference in rolling load between the driving side and the working side of the rolling roll is less than or equal to a predetermined value; and

And rolling the reduced rolling roll to the target roll gap while maintaining the difference between the rolling load of the driving roll and the working side of the rolling roll below a predetermined value.

Hereinafter, the present invention will be described in detail.

In the present invention, in order to efficiently solve the meandering problem of the plate at the start of rolling in the process of sheet casting and hot rolling, by controlling the roll gap at the beginning of rolling, rolling reduction is started by the same amount of rolling on the driving side and the working side of the rolling roll. Is to prevent meandering. Furthermore, the rolling gap is kept at a low speed at the start of rolling so that the roll gaps of the driving side and the working side of the rolling rolls become equal, and then rolling at a normal speed to prevent the judged stroke as much as possible.

A representative example of a thin sheet casting-continuous rolling apparatus to which the present invention is applied is shown in FIG. 1. A looper 5 capable of forming a loop is provided between two casting rolls 1 and a rolling mill 7 installed in parallel, and the first pinch roll 4 and the second pinch at the front and rear ends of the looper 5. Install the roll (6). The coiler 9 of the rear end of the rolling mill 7 is comprised similarly to a normal rolling line. The role of the looper 5 is to compensate for the difference between the casting speed and the rolling speed of the cast 3 in the sheet casting machine.

When casting is started in the sheet casting machine, as shown in FIG. 2, the thickness of the cast steel passes through a transition state, and at this time, rolling cannot be performed, so that the roll gap of the rolling mill 7 is sufficiently widened. Rolling starts when the cast steel produced by the sheet casting machine reaches a steady state through a transition state. In order to start rolling, the roll gap of the rolling mill is reduced.In this case, the roll gap change of the driving side and the working side that is independently lowered does not occur at the same speed, and if the roll gap decreases faster on one side, the roll gap reduced quickly starts rolling first. As a result, meandering occurs in the plate, and the fast-moving slabs are sharply inclined. To prevent this, it is necessary to control the roll gap of the working side and the driving side to be reduced at the same speed. To this end, the roll gap reduction speed is very slow and there are a lot of difficulties. In addition, although the roll gap of the working side and the driving side decreases together, if the thickness of the cast steel produced in the sheet casting apparatus is different from the working side and the driving side, the thick side first starts rolling and meandering occurs.

In order to prevent such meandering, the present inventors have been looking for a way to adjust the roll gap between the driving side and the working side of the rolling roll in consideration of the difference in thickness of the cast steel, and the rolling load reflects the reduction ratio. It was noted that by detecting the thickness difference of the bias and adjusting the roll gap based on the bias, the meandering can be prevented. In the rolling mill, the rolling load reflects the reduction ratio, and therefore, the same rolling load means that the reduction ratio is the same. If the working side of the rolling roll starts rolling first, the rolling load on the working side increases and the rolling load on the driving side hardly increases.

According to the present invention, when the thickness of the initial thin slab reaches a steady state in a thin sheet casting machine, the roll gap of the driving side and the working side of the rolling roll is gradually reduced independently and the rolling load of the rolling side and the working side of the rolling roll is measured. do. At this time, while maintaining the difference of the measured rolling load below a predetermined value, the roll gap of the driving side and the working side of the rolling roll is reduced to the target roll gap. According to the present invention, it is recommended that the difference between the rolling load on the driving side and the working side of the rolling roll be 2-10 tons.

If one rolling load increases by 2-10 ton while reducing the roll gap while measuring the rolling loads of the driving and working sides of the rolling rolls, it is judged as the start of rolling and the rolling load increases until both rolling loads are equal. The roll gap is not reduced and only the roll gap on the side where the rolling load is not increased is reduced. If the rolling loads on both sides are equal, the roll gaps on both sides are reduced simultaneously, and if the rolling loads on both sides are 2-10 tons, the roll gap on the side with the higher rolling load is maintained while the rolling load is the same until the rolling load is the same as before. Only reduces. By repeating the above process until the target roll gap, rolling can be performed while minimizing meandering. At this time, if the rolling load is in the same state on both the driving side and the working side, but the roll gap is different, this means that the thickness of the cast steel produced in the sheet casting apparatus is different from the driving side and the working side. In this case, the gap of the casting roll of the sheet casting apparatus Adjust the thickness of the cast so that it is the same. In this case, the reason for maintaining and reducing the roll gap based on the difference in rolling load difference by more than 2-10 tons is based on the noise of the rolling load measuring device and the rolling roll gap during rolling. If it is not the difference between the actual rolling loads due to changing inertia, etc., wrong control will be performed. For example, it can be recognized that a rolling load of 2 tons is applied to one side even though the actual reduction has not started due to noise, etc. Severe deviations can cause damage to equipment. On the other hand, if the difference is more than 10 tons, the difference in rolling reduction becomes too large, and the meandering occurs severely while controlling the rolling loads on both sides to be the same.

By the way, even when adjusting a roll gap by such a method, meandering may arise if it turns to one side of the rolling mill of a slab at the time of actual rolling. If the rolled plate is biased to one side, even if the reduction ratios are the same on both sides, the rolling load on the side on which the plate is biased is large and the rolling load on the opposite side is reduced. Therefore, if one side begins to roll down at the beginning of rolling, the first side that starts rolling keeps the roll gap and reduces the roll gap on the opposite side, but meandering occurs until both sides have the same load, and the faster the rolling speed, the worse the meandering. . At this time, the rolling plate is biased toward the smaller rolling rate by the meandering, whereby the rolling load of the smaller rolling reduction is larger than the larger rolling reduction. Due to this plate deflection, the rolling load of the smaller rolling rate is larger. Therefore, if the roll gap control is carried out as mentioned above, the roll gap of the smaller rolling rate is maintained and the roll gap of the larger rolling rate is further reduced. As a result, the difference in rolling reduction becomes more severe and the meandering becomes more severe, resulting in rolling accidents such as plate folding and plate breaking.

In order to solve this problem, the present invention was able to prevent meandering as a result of reducing the rolling gap after reducing the rolling speed at the start of rolling at a low speed, that is, 10 m / min or less. If the rolling speed is slowed down to 10 m / min or less at the beginning of rolling, the degree of meandering until the roll gaps on both sides are equally reduced when one side is first pressed down, and hardly any plate deflection occurs. In addition, the tendency to cause slight plate gap is easily resolved by the tension generated by the second pinch roll 6 and the third pinch roll 8 in FIG. Even if the rolling speed is reduced at the beginning of the rolling, the casting speed of the sheet casting machine, which is determined by the plate thickness, the cooling capacity, and the roll separation force of the casting roll, cannot be reduced. Therefore, in order to eliminate the stacking of the cast pieces due to the difference between the rolling speed and the casting speed, the looper 5 is installed, and the tension generated by the looper's operation is transmitted to the sheet casting device at the front end of the looper to prevent plate breakage from occurring. In order to install the first pinch roll (4).

If the rolling speed is slowed to 10 m / min or less and then roll rolling is performed by using the aforementioned rolling load, rolling can start without judgment. While reducing the roll gap for rolling initiation, the loop formed in the looper is eliminated by increasing the rolling speed after reaching the target roll gap. After that, if the rolling speed is synchronized so that the casting speed and the rolling speed of the rolling mill are the same, the composite sheet casting and hot rolling can be normally performed. The hot rolling method according to the present invention is shown in FIG.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Referring to FIG. 3, the rolling operation was performed for the case of rolling by controlling the driving side and the working side of the rolling roll, and the operation results were examined. Table 1 shows the results. A typical control method in Table 1 is a method of controlling the position of the rolling mill roll gap so as to be the target roll gap with the rolling mill entry speed equal to the casting speed.

Condition Mail order Remarks Conventional Control Method Meandering terrible Stop working by meandering Only roll gap control using rolling load Meandering is terrible If it is biased to one side of the rolling mill of the cast steel, meandering occurs at the beginning of rolling, meandering continues and operation stops. Reduced rolling speed only A little bit of meandering Meander recovery after meandering Method of the invention Almost no meandering in normal operation

As can be seen from Table 1, it was found that meandering does not occur when the rolling speed is reduced while controlling the roll gap according to the present invention.

As described above, the present invention is a judge that can occur in the hot rolling process after sheet casting by preventing the judge row, in particular the judge row at the beginning of rolling by the rolling mill control method in the sheet casting and hot rolling composite process The thin plate manufacturing process can be performed more stably and productivity can be prevented by preventing the deterioration of the thin plate due to the row and the interruption of operation.

Claims (4)

In the method for continuously manufacturing ultra-thin sheet by supplying the thin cast slab cast in the sheet casting machine to the rolling mill while adjusting the plate speed through the looper, Measuring the thickness of the initial thin cast steel cast in the sheet caster, Measuring the rolling load of the driving side and the working side of the rolling roll while reducing the roll gap between the driving side and the working side of the rolling roll in the rolling standby state when the thickness of the cast steel becomes a constant thickness, Adjusting the roll gap of the driving side or the working side when the rolling load to be measured begins to increase so that the difference in the rolling loads between the driving side and the working side of the rolling roll is equal to or less than a predetermined value; and And rolling the reduced rolling roll to a target roll gap while maintaining the difference between the rolling load on the driving side and the working side of the rolling roll to a predetermined value or less. 2. The continuous hot rolling in a sheet casting machine as claimed in claim 1, wherein when the initial thin cast piece has a predetermined thickness and starts rolling, the rolling speed is lowered to 10 m / min or less until the rolling roll gap becomes a target roll gap. Rolling method. The rolling roll of the rolling roll side according to claim 1 or 2, wherein the rolling gap on the rolling roll side is unchanged when one rolling load reaches 2 to 10 tons while reducing the roll gap between the driving side and the working side of the rolling roll. The roll gap is reduced so that the load is within the range of 2 to 10 tons, and then, when the rolling loads on the driving side and the working side of the rolling roll are the same, the rolling gap is adjusted to the target roll gap. 4. The thin plate according to claim 3, wherein after the gap of the rolling roll is used as a target gap roll, the rolling speed is increased to remove the loop from the looper, and then the rolling speed is synchronized so that the casting speed matches the entrance speed of the rolling mill. Continuous hot rolling method in casting machine.