JPH03133555A - Method for continuously squeezing cast slab strand in continuous casting - Google Patents

Abstract

PURPOSE:To enable sqeezing work under condition of restricting the development of cutting waste cast slab to min. by obtaining the suitable casting velocity from the lapse of drawing time and the suitable arriving time to the squeezing work point of a strand in each block and executing the squeezing work while adjusting to the above velocity. CONSTITUTION:The interval from a casting start point into a mold 1 for continuous casting to arrival to the squeezing work point with anvils in a squeezing machine 2, is beforehand divided into plural blocks. The lapse of drawing time from the casting start time in the cast slab strand 3 corresponding to each block is tracked. Each suitable casting velocity in the cast slab strand 3 in each block is obtd. from this lapse of time and the suitable arriving time to the squeezing work point in the cast slab strand 3 in each block. The squeezing work is executed while adjusting to this suitable casting velocity. By this method, the development of deteriorated part in the quality can be restricted.

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention aims to improve the internal quality of high-grade wire/bar materials and thick plate materials where center segregation is a problem in continuous steel casting, and to The aim is to further reduce the amount of cut slabs that are generated during this process.

(Prior art) For improving the internal quality of the slab by applying forging near the solidified area of the slab strand pulled out of the continuous casting mold, for example, Japanese Patent Laid-Open No. 63-1
Reference is made to the forging method disclosed in Japanese Patent No. 83765.

(Problems to be Solved by the Invention) The technology disclosed in the above publication is based on the time it takes for the slab strand to reach the forging machine so that the unsolidified thickness at the forging point of the slab strand reaches a predetermined value. It is something to be adjusted.

Factors that influence the unsolidified thickness of the slab strand at the forging point include the steel type, slab size, casting speed, degree of heating of the molten steel, method of cooling the slab strand, or amount of cooling water. Among these, the degree of heating of the molten steel has a relatively small effect, and for cooling the slab strand, if the amount of cooling water is set depending on the casting speed based on the steel type and slab size, it can be used up to the forging machine. The unsolidified thickness of the strand can be controlled only by the casting speed corresponding to the arrival time of the strand. Conventionally, in such forging processing, the upper and lower limits of the arrival time t of the slab strand that can ensure good quality are respectively iQu+jq+, and the corresponding upper and lower limits of the casting speed V are V. , ■, 1, basically the casting speed V during operation is V, +≦V≦V
, u, but if you follow these processing instructions, the molten steel heating degree may deviate from the target value, or the speed may not be adjusted to the preset speed due to other disturbances such as a malfunction in the pouring system. As a result, the occurrence of cut-off slabs was unavoidable.

The purpose of this invention is to reduce as much as possible the cut-off slabs that conventionally occur under manual control by an operator when performing forging, which is advantageous for improving the internal quality of slabs obtained by continuous casting. be.

(Means for Solving the Problems) This invention applies a forging process to a region near the solidification completion point of a slab strand pulled out of a continuous casting mold using a pair of anvils sandwiching the strand on both sides in the thickness or width direction. In this process, the period from the casting start point of the continuous casting mold to the forging point with the anvil is divided in advance into multiple blocks, and the elapsed time for drawing out the slab strand corresponding to each block from the casting start point is calculated. The feature is that the appropriate casting speed for each slab strand in each block is determined by tracking and from this and the appropriate arrival time to the forging point, and the forging process of the slab strand is performed by adjusting to this appropriate casting speed. This is a continuous forging method for slab strands in continuous casting.

In this invention, the casting speed during continuous casting preferably satisfies the following conditions.

Note V=1/2 [(VK,,,) ff1l. + (
VKffll□) ,,,, IV: Casting speed (m/m
in) (VKssmx) ff1le: Upper limit value of the appropriate casting speed in any block k, minimum value when looking at V□, X through all blocks (m/min) (VKffilゎ)mat: Appropriate casting speed in any block k Maximum value (m/min) when the lower limit value V□1° is seen through all the blocks.Furthermore, in this invention, in the forging method having the above configuration,
When the casting speed of each block cannot be adjusted to within the appropriate range due to disturbances, this occurs when the casting speed is highest at the lower limit of the appropriate range and the length of the cut slab occurs when the casting speed is lowest at the upper limit of the appropriate range. It is preferable to compare the length of the cut slab and perform the forging process at a casting speed corresponding to whichever is smaller.

Furthermore, in the present invention, the elapsed time tracking area of the slab strand is an area excluding the initial stage of continuous casting, more preferably from at least the middle from the continuous casting mold to the forging point to the forging point. It is best to set the area up to

(Function) In order to guarantee the internal quality of continuously cast slabs, the elapsed time t (hereinafter simply referred to as solidification) from the start of continuous casting until the slab strand leaves the mold reaches the press installed downstream. It is necessary to control the casting speed so that the time (denoted as) j (+≦t≦jqu).

Here, the above t, l, and tqa are the lower limit and upper limit, respectively, of the coagulation time that can ensure stable quality.

In addition, in order to minimize the occurrence of cut-off slabs caused by fluctuations in casting conditions due to disturbances, it is necessary to take into consideration past history and adjust the casting speed to an appropriate casting speed over the entire length of the slab strand. .

In this invention, the area from the continuous casting mold to the forging processing point of the forging press is divided in advance into multiple blocks, and the elapsed time from the casting start position of the slab strand corresponding to each block is tracked, and each block is Find the appropriate casting speed for each area so that the slab strand reaches the forging start point within a predetermined time, aggregate it for all blocks, and dynamically control it to achieve the optimal casting speed at that point. Therefore, there is no need for a large amount of cut-off slabs to be generated.

As shown in Figure 1, the length from the continuous casting mold 1 to the processing start point of the press machine 2! 9. Find the length of the block divided into any number! 4. When the coagulation time is [,], the allowable coagulation time jq between the remaining length l + 1*
+,t,. In order to fit within the upper limit of casting speed Vk+
nai and lower limit value Vkm+a as Vk, ax=cf!
+-1k)/(t, b) -mvh, n+n
=(*+-zh)/(tQo-h) - (2).

Upper limit value Vkmax and lower limit value Viyi of the above casting speed
If m is determined for each block and the appropriate casting speed range for the slab strand of each block is illustrated, for example, the second
It will look like the figure. Here, in order to ensure good quality over the entire length of the slab strand pulled out from the continuous casting mold, (Vk+nmx) ff1l++≧(Vk, a) rr
Fig. 2 above corresponds to this, but in this case, the casting speed V is (Vk+n1s) ff1a, ≦V≦(Vk+naj
By setting e+l+' (3), the internal quality of the slab is always maintained in a good state.

In order to ensure that the casting speed does not fall out of the appropriate range even with fluctuations due to external disturbances, it is preferable to take the middle value between the respective limit values of the casting speed as shown in the following equation.

V = 1/2 [(Vkm-z) 1lla + (
Vk, w) t+-j...(4) If the casting speed of the slab strand is set according to the above equation (4), the limit value of the casting speed of the continuous casting machine (Vu).

If it is within the range of V+), the limit value of quality improvement (V
Since the solidification time of the slab strand is within the range of t, l, and Lu even if it exceeds Vql), there is no quality problem at all. Compared to the case where it is applied, there is an advantage that the degree of freedom in adjustment is increased, and the frequency of occurrence of cut-off slabs can be extremely reduced.

When there are many disturbances in continuous casting, there are limits to manual adjustment, and when using conventional technology, there were problems such as the production of a large number of cut slabs if the control method was not appropriate, but this invention solves this problem. There is no joy at all.

Adjustment of the casting speed according to the present invention can be easily realized by using a device as shown in FIG. In the figure, number 3 is a slab strand, 4 is a roller apron, 5 is a pinch roll, 6 is a calculation device, and 7 is a control device.Based on the data obtained from each block, the calculation device 6 performs the above (3). , the casting speed {circle around (4)} is determined for each block, and the speed of the pinch rolls 5 is controlled by the control device 7 so as to achieve this casting speed.

Fig. 2 above shows an example in which the proper casting speed exists in the longitudinal direction, but if the disturbance is large, equation (3) is not satisfied and the condition shown in Fig. 4 is reached. There are cases where this happens. In such a case, it is inevitable that cut-off slabs will be generated, but it is more advantageous to collect the cut-off slabs into a portion in the longitudinal direction for later processing.

Therefore, in this invention, each limit value (Vk+naj tri., (Vkmla) a+ax
Calculate the cut-off slab lengths LRI and LI+2 from the following equations, adjust the casting speed to correspond to the shorter of the two, and perform forging.

a), V - (V k+naj ml+, the cut-off slab length LRI is (Vk+nax),, where ji- is the solidification time when continuous casting is continued, tq+≦t, -≦t qu The total number of blocks outside of m
Then, LR -m,・! ...(6). Here, l is the casting length per unit block.

b), V= (Vkffi+++) +ns, and for the cut-off slab length LI+2, do the same as above and let m2 be the total number of blocks outside of jq+≦jt-≦jqu, L*2=m2” (! -(8).The casting speed corresponding to the smaller cut-off length of the slab obtained from the above equations (6) and (8) is determined as the appropriate casting speed.

In addition, in this invention, since the arrival time of all blocks of the slab strand is always tracked and speed control is performed so that the entire length reaches the forging point within an appropriate time, especially the first block at the casting start point is The casting speed is always within the normal quality guaranteed speed range, i.e. vq, ≦V≦Vqu
will be limited to. The set speed in any area is determined to satisfy the appropriate range of all blocks, so when the entire area of the slab strand is measured,
The speed control range is inevitably limited to vq, ≦V≦V, and although it has the advantage of being able to follow even complex disturbances, the improvement in control responsiveness is small.
This may be insufficient from the viewpoint of reducing the amount of cut-off slabs generated. On the other hand, the degree of disturbance that occurs during actual operation can be predicted from past operation results, and by setting the maximum value of the disturbance, it is possible to
Sufficient control is possible by setting only the latter half as the control range.

In such a case, the tracking area of the slab strand should be set to an area excluding the initial stage of casting start, more preferably from the midpoint between the casting start point and the forging start point to the forging start point. By setting the area as the measurement target area, the responsiveness of casting speed control can be improved and the amount of cut-off slabs generated can be minimized. Fifth
The figure is a graph showing the range of suitable casting speed for each block. In Figure 5, the time required for speed adjustment for blocks near the forging point is shorter, but the speed adjustment range is correspondingly expanded, and in the case of normal disturbances in actual operation, the control target is the area at the initial stage of casting. Even if it is removed, the speed adjustment range is widened, so sufficient control is possible. Although the target area for speed control varies depending on the type of continuous casting machine and the type of steel, it is generally desirable to set the area to 172 to 1/4 of the length from the continuous casting mold to the forging point.

(Example) All blocks of a continuous cast strand are set as the control target area, and while continuous casting is performed under the conditions shown below, forging is performed near the solidification completion point of the continuous cast strand, and the occurrence of cut-off slabs at that time. investigated.

Operating conditions Slab size: Thickness 270mm, width 340mm Distance from the mold to the press ffi+: 20m Continuous casting machine casting speed limit v ll: I, 2m/min v, : 0.3m/min Proper solidification Time t + :22.2m1nto :23.
0m1n tu : 23.8 mi mouth proper casting speed v , + : 0.84 m/mi mouth v q
o: 0.87 m/min v qu: 0.90 m/min Disturbance: Appropriate casting speed v, o: (When casting was performed at 187 m/min, due to a malfunction in the pouring system, a speed pattern as shown in Figure 6 was created. Length n per unit block: 0.5 m As a result, according to the present invention, no cut-off slabs were produced even in the speed pattern shown in Fig. 6, but with manual control, the adjustment operation was not possible. It took a lot of effort, and about 1.5m of cut slabs were generated.

Next, when continuous casting is performed under the same operating conditions as above with the continuous casting strand control target area in the range of 10 m to 20 m downstream of the continuous casting mold, as a disturbance during casting,
Casting speed V was reduced to 0.87 m/mi due to inappropriate molten steel temperature.
The occurrence of cut-off slabs was investigated when casting was performed for 3.3 minutes at 0.6 m/min from n to a casting length of about 2 m. As a result, the cut-off length of the slab was 2.4 m, which was approximately 3.8 m longer than the cut-off length of 6.2 m that would have occurred if all blocks of the continuous casting strand were to be controlled.
It was confirmed that the degree of damage could be reduced.

(Effects of the Invention) According to the present invention, even if a complex casting pattern as shown in FIG. 7 is formed depending on the operating conditions, the casting speed is adjusted to suit the casting pattern and the parts that are of poor quality are cut off. It is possible to perform forging processing that minimizes the generation of slabs.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the forging process according to the present invention, Fig. 2 is a graph showing changes in casting speed in each partitioned block, and Fig. 3 is a continuous casting apparatus suitable for carrying out the present invention. The schematic diagram, Figures 4 and 5 are graphs showing changes in casting speed in each divided block, and Figures 6 and 7 are graphs showing the relationship between elapsed time during continuous casting and casting speed. be. l...Mold for continuous casting 2...Forging machine 3...
Slab strand 4...Roller apron 5...
Pinch roll 6...Arithmetic device 7...Control device Figure 1 @ Figure 2 Frog 80. Figure 4 Block Δθ Figure 3 @ Figure 5 % Frog 8 price drop

Claims (1)

[Claims] 1. For forging the area near the solidification completion point of a slab strand pulled out of a continuous casting mold using a pair of reciprocating anvils that sandwich the strand on both sides in the thickness or width direction. , the period from the casting start point of the continuous casting mold to the forging point with the anvil is divided in advance into multiple blocks, and the elapsed time for drawing out the slab strand corresponding to each block from the casting start point is tracked. Then, from this elapsed time and the appropriate arrival time for the slab strands in each block to reach the forging point, the appropriate casting speed for each slab strand in each block is determined, and the forging process is performed while adjusting to this appropriate casting speed. A continuous forging method for slab strands in continuous casting. 2. The method according to claim 1, wherein the appropriate casting speed satisfies the following conditions. Note V=1/2 {(V_K_m_a_x)_m_i_n+(
V_K_m_i_n)_m_a_x}V: Casting speed (m
/min) (V_K_m_a_x)_m_i_n: The minimum value (m/min) of the upper limit value of the appropriate casting speed in any block k, V_K_m_a_x, when looking at all blocks (m/min) (V_K_m_i_n)_m_a_x: The lower limit value of the appropriate casting speed in any block k Maximum value of V_K_m_i_n for all blocks (m/min) 3. In the method according to claim 1, when the casting speed of the slab strand of each block cannot be adjusted to within the appropriate range due to disturbance, the lower limit value of the appropriate range is set. Compare the length of the cut-off slab produced when the casting speed is the highest and the length of the cut-off slab produced when the casting speed is the lowest at the upper limit of the appropriate range, and then set the casting speed corresponding to the smaller one and press forging. A continuous forging method for slab strands in continuous casting, characterized by performing machining. 4. Claim 1, wherein the tracking area of elapsed time for drawing the slab strand is an area excluding the initial stage of continuous casting.
Method described.