JPS61238452A - Detection of joint of ingot in continuous casting - Google Patents

Abstract

PURPOSE:To detect a joint with good accuracy, to decrease the crop quantity at the joint and to improve yield by measuring continuously the temp. of a solidified ingot and detecting the part below the set temp. as the joint. CONSTITUTION:A molten steel 3 in a ladle 2 is cast via a tundish 4 into a casting mold 6 and the formed ingot 8 is cut to a prescribed length by a cutter 16 via a guide roll group 10, leveling rolls 12 and pinch rolls 14. A surface thermometer 18 measures continuously the surface temp. of the ingot 8 and feeds a signal via a temp. converter 20 to a joint detector 22. The temp. decreases sharply at the joint and since the lower limit temp. is preliminarily set in the detector 22, the detector discriminates the joint when the surface temp. decreases to the lower temp. or below and outputs a signal to a lower limit alarm which in turn emits a signal to that effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for detecting joints in slabs in continuous casting, and particularly relates to a highly accurate detection method and is used in the field of continuous casting.

[Conventional technology]

Initially, continuous casting was interrupted every time a tandish was replaced, and a new work was started from the start of casting, but in recent years, tandishes that were no longer unusable were replaced with new tundishes during casting. Subsequently, pouring into molds began to be performed.

Furthermore, when switching to a different steel type, so-called continuous casting is performed continuously without any new work.

When replacing the tundish mentioned above, the components of the molten steel before and after replacement mix in the unsolidified part of the slab, and this mixed part does not have the desired composition, so it must be cut and removed. .

In continuous continuous casting of different types of molten steel, JP-A-57-25
In order to prevent mixing of the first molten steel and the second molten steel, 256 proposes a method in which a cooling member is immersed in the molten steel in the mold to form a barrier layer. It is necessary to remove it.

Traditionally, the location of the seam in the slab that needs to be cut and removed is known by tracking on a process computer. That is, starting from the signal input by the operator when replacing the tundish, the pulses of the pulse generator of the measuring roll that rotates as the slab advances are counted, and the casting length is calculated based on this. From the casting length, the movement of the slab joint from the mold to the cutting device was determined.

In the conventional seam grasping method as described above, the calculation start timing based on the start of movement of the slab due to a deviation in the input timing of the operator, or an error in the movement length of the slab due to measurement error of the measuring roll, etc. There was a drawback that the position of the seam could not be accurately determined. Therefore, in the conventional method, ±3001III is required for seam detection.
There was an error of about I, and when cutting and removing the seam, an extra length of about 300++ m was added before and after the seam and was cut and removed, which caused a problem of lower yield.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method for detecting joints in slabs in continuous casting that can accurately detect joints in slabs, reduce cut and removed parts, and improve yield. be.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, in a method for detecting joints in slabs caused by replacing a tundish in continuous casting or by continuously casting different steel types, the temperature of the solidified slab is continuously measured, and the portions below a set temperature are detected as joints. This is a method for detecting joints in slabs during continuous casting.

During tundish replacement or continuous continuous casting of different steel types, the drawing of the slab is temporarily stopped, so the molten steel is supercooled in the mold, and the temperature at the seam is lower than that of the slab that has already been pulled downward from the mold. do. Next, when new molten steel is injected, the temperature rises and the temperature of the slab returns to normal.

Replacing the tundish is an operation that has a great impact on improving the productivity of continuous casting, and it is done quickly because it is related to the solidification of the slab, but it takes several minutes, and during this time the cooling rate in the mold is high, so it takes a considerable amount of time. A drop in temperature is inevitable.

We continuously measured the surface temperature of the slab at the roll exit end of the continuous casting machine, and found that the temperature at the joint of the slab when replacing the tundish was approximately 500°C, compared to the normal temperature before and after the joint. was 700 to 800°C, and there was a temperature difference of 200 to 300°C between the two. When this is illustrated, it becomes as shown in Fig. 1, and the seam can be clearly recognized.

In addition, in continuous continuous casting, not only the drawing of the slab is temporarily stopped, but also a cooling member is put into the mold, which causes the molten steel to be significantly supercooled in the mold, and the joint of the slab at the exit end of the rolls. The temperature was about 200-300°C, and there was a large temperature difference of 400-600°C between the front and rear normal parts.

The present inventors focused on the temperature difference between the joint of the slab and the normal portion before and after the joint, as described above, and were able to accurately detect the joint using this.

〔Example〕

The details of the present invention will be explained by examples. The outline of the continuous casting machine and the apparatus used in the present invention will be explained with reference to FIG. The molten steel 3 in the ladle 2 is poured into the mold 6 via the tundish 4, and the formed slab 8 is passed through the guide roll u1m41! After passing through i-rows 1 and 12 and pinch rolls 14, it is cut into a predetermined length by a cutting device 16. As a device used in the present invention, a surface thermometer 18 is installed above the slab 8 on the upstream side of the cutting device 16. A temperature converter 20 that converts the signal into temperature and a seam detection device 22 to which the signal is input are provided.

The installation location of the surface thermometer 18 is preferably as close to the upstream side of the cutting device 16 as possible, but is not particularly limited. Also, the type of surface thermometer does not matter.

For detection, the surface temperature of the slab 8 is continuously measured with a surface thermometer 18 and a signal is sent to a seam detector 22 via a temperature converter 20. During continuous measurement, the temperature of the seam drops rapidly as shown in Figure 3, and the seam detection device 22 has a lower limit temperature set in advance, so when the surface temperature falls below the lower limit temperature, it is determined to be a seam and an output is sent to the lower limit alarm bud. This will issue an alarm to that effect, or output to a joint display device to display a mark to that effect at the joint of the slab. Note that the lower limit temperature is appropriately set depending on the steel type, slab dimensions, etc.

In the present invention, as mentioned above, the temperature drop at the seam is extremely large compared to the front and rear slabs, so the detection accuracy is extremely good because the large temperature difference is used for detection.
It is about 0m. The conventional detection accuracy is about ±300 nm, and the seam crop is 60 nm as a margin before and after the conventional method.
However, according to the method of the present invention, the margin is about 1100a+, and the yield can be significantly improved.

〔Effect of the invention〕

The present invention makes it possible to detect seams with good accuracy by continuously measuring the temperature of a solidified slab and comparing it with the set temperature, which reduces the amount of seam cropping and improves yield. I was able to give it to you.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the change in slab temperature during continuous measurement.
FIG. 2 is a sectional view of a continuous casting machine showing the arrangement of devices used in the present invention, and FIG. 3 is a diagram showing the relationship between the surface temperature of the slab and the output of the seam detection device in the present invention. 4... Tandishu 6... Mold 8... Slab 16... Cutting device 18... Surface thermometer 20... Temperature conversion word 22... Seam detection device

Claims (1)

[Claims] (1) A method for detecting joints in slabs caused by replacing tundishes in continuous casting or continuously pouring different steel types, characterized in that the temperature of the solidified slab is continuously measured and the portions below a set temperature are detected as joints. A method for detecting joints in slabs during continuous casting.