JPH02197352A - Mold for continuous casting - Google Patents

Abstract

PURPOSE:To improve slow cooling ratio and to reduce longitudinal crack in shell by arranging multiple number of vent holes opening to the atmosphere between cooling water passage in a mold and surface of the mold and communicating the vent holes with header for supplying fluid as controllable to supplying rate. CONSTITUTION:Each vent hole 4 is communicated with the header 4 for supplying air, etc., and by allowing to flow the air into vent hole from there, control of delicate cooling capacity and cooling of coating layer 3 can be executed. The air is supplied to the supplying header 4a through a supplying rate controller. By this method, the developing ratio of the longitudinal crack of the cast slab can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting mold that has an improved slow cooling rate and is more effective in preventing longitudinal cracking of slabs.

[Conventional technology]

Generally, molds for continuous casting of steel are mainly made of copper or copper alloy. One of the reasons why copper is used as the main material is that it has high thermal conductivity, which includes the initial solidification of molten steel. This makes it suitable for rapid cooling, which is essential for forming slabs in molds.

In recent high-speed casting operations, in addition to relying on the thermal conductivity of the mold material itself, measures have also been taken to further improve the heat removal performance within the mold.

On the other hand, vertical cracks, which are one of the surface defects that occur in continuously cast slabs, have not completely disappeared, especially in the medium-coal steel region that involves δ→T transformation. The mechanism of vertical cracking is that during the process in which molten steel is cooled and a solidified shell is formed, the cooling rate is partially slowed down due to uneven thickness of the howder layer, which is a lubricant, and the shell layer becomes uneven.

At the same time, shrinkage occurs during solidification, and depending on the steel type, shrinkage due to transformation is also added, and tensile stress acts on the thin shell portion, resulting in vertical cracking.

Therefore, in order to prevent the occurrence of such vertical cracks, various slow cooling methods have already been proposed to prevent unevenness due to rapid cooling in the initial stage of solidification.

For example, (1) the inner surface of the mold may be made corrugated (Japanese Patent Laid-Open No. 53
-28027), providing narrow grooves in the casting direction on the inner surface (JP-A-61-92756), and (2) applying porous plating to the inner surface of the mold (JP-A-55-1566, 4).
No. 2, Copper No. 156643), (3) Method of embedding a metal heat resistance material in the upper part of the mold (Japanese Patent Application Laid-Open No. 1983 = 5 s,
No. 25).

[Problem to be solved by the invention]

However, in the method (1) above, powder adheres to the grooves and the function deteriorates early. In method (2), cracks occur in the coating due to expansion of air in the pores due to sealing of the pores by molten steel, and uniform control of cooling cannot be maintained as a result. For (3), the slow cooling rate is 10
%, and further improving the slow cooling rate requires increasing the thickness, leading to problems such as an increase in manufacturing costs.

The present invention has been made in view of these conventional problems, and aims to solve the above problems by providing ventilation holes in the copper plate of the mold.

[Means to solve the problem]

This invention provides, in a mold for a continuous casting machine, between a mold cooling channel provided in the mold and a mold surface that contacts molten steel.
The continuous casting mold is provided with a number of vent holes with at least one end open to the atmosphere, and the vent holes are communicated by a fluid supply header whose supply amount can be adjusted.

[Effect]

Since the present invention has the above structure, the slow cooling rate is significantly improved due to the large number of ventilation holes provided in the copper plate, and as a result, the incidence of vertical cracking in the slab (shell) can be significantly reduced. Ta. In addition, since one end of the vent is open to the atmosphere, it can handle the expansion of the air inside the vent, and by allowing fluid such as air to flow into the vent and changing its flow rate, subtle cooling can be achieved. The capacity can be adjusted, and problems such as cracks in the inner coating of the mold do not occur as in the past.

〔Example〕

Hereinafter, the present invention will be explained with reference to drawings, graphs, etc.

FIG. 1 is a longitudinal cross-sectional view of a mold according to the present invention, and FIG. 2 is a partially enlarged view of the cross section taken along the line 1--2 in FIG. In the figure, 1 is a copper plate forming a mold, and 2 is a mold cooling channel (water cooling hole) provided in this copper plate. 3 is molten steel 8 of copper plate 1
This is a coating layer provided to form ventilation holes 4 in the immediate vicinity of the contact surface.

The ventilation holes 4 in this embodiment are formed as follows.

That is, first, a large number of narrow grooves are formed along the steel casting direction by machining or other means on the side that will become the inner surface of the mold of the copper plate 1, and these narrow grooves are filled with wax and the surface is subjected to conductive treatment. , the coating layer 3 having a required thickness is formed by metal plating a copper plate. Thereafter, by heating and removing the wax, a cavity after removal, that is, a vent hole 4 is formed. Furthermore, each vent hole 4 communicates with a header 4a for supplying air, etc., and by flowing air into the vent hole from here, it is possible to finely adjust the cooling capacity and cool the coating layer 3. It has become. The supply ladder 4a is supplied with air via a supply cavity device (not shown).

8 is molten steel poured into the mold from a tundish (not shown) through an immersion nozzle 9, and 6 indicates a meniscus of the molten steel. 7 is a powder as a lubricant supplied onto the meniscus 6 to lubricate between the coating layer 3, the molten steel 8, and the shell 5 whose surface has begun to solidify. This is to facilitate pulling out in the f direction.

Regarding the arrangement range of the ventilation holes 4, as shown in FIG. Taking this into account, it is sufficient to form it at a depth of about 300 mm from the upper end of the mold, that is, the copper plate 1, but it may be formed over the entire length to the lower end of the mold.

FIG. 3 shows the state of mold heat transfer in the present invention, and when the slow cooling rate of poured molten steel is calculated, it can be expressed by the following equation (1).

In addition, each character in the figure shows the following meaning.

α: Heat transfer coefficient between molten steel and coating surface α3: Heat transfer coefficient of vent hole α8: Heat transfer coefficient between cooling water and mold θ5: Molten steel temperature θp: Temperature of mold coating surface θ8: Temperature of coating side of vent hole θ, temperature on the copper plate side of the double inverted pore θC: temperature on the cooling water side of the copper plate 6W: cooling water temperature d,: coating thickness da: ventilation hole thickness do: copper plate thickness λp: coating thermal conductivity λC: copper plate thermal conductivity q- □ (θ5-θ8) αS λ, α3 λ0 α8 da 1 α5 λ, λ.

α However, q: Reduced amount of heat removed when using the mold invented by Niki 9 to the amount of heat removed per unit area △9/q: Slow cooling rate Figure 4 shows the amount of heat removed from the mold and the longitudinal crack score. By making the amount of heat removed less than 70X10'kcaj2/n (h, it is possible to significantly reduce the conventional vertical crack rating. In this case, 90X], O'kcaβ/r
If a slow cooling rate of 20% is achieved based on the amount of heat removed by rrh, it becomes possible to reduce the vertical crack occurrence level to 1.5 or less. Incidentally, when the slow cooling rate is 20%, the dimensions to be taken in the structure shown in FIG. 2 can be determined by equation (1).

Note that it is effective to provide the vent hole in the mold (copper plate) anywhere from just below the surface of the mold on the molten steel side to the water cooling section. However, in reality, the distance from the surface of the mold (copper plate) is 0.1 to 1. It is desirable to provide it in the range of 0mm. This is because if the diameter is less than 0.1, the ventilation holes will be damaged due to abrasion of the mold surface and static iron pressure. Furthermore, the effect of slow cooling by the ventilation holes decreases as the ventilation holes move away from the surface of the mold (copper plate). Therefore, a range within l + ntn is preferable. Further, the ventilation hole may penetrate from the upper part of the mold (copper plate) to the lower part, but it is sufficient if at least one end is opened to the atmosphere. This ensures that problems will not arise if the mold temperature increases and the gas in the vent expands. Further, by flowing air or the like through the ventilation hole, α8 changes, making it possible to delicately control the cooling capacity and cooling the coating layer 3. The fluid flowing through the vents is generally a gas such as air, but it may also be a liquid.

The shape and dimensions of the vent hole 4 shown in FIG. b
=0.5. P=1. mm, dp=0.1mm
(The vent hole was open at the top of the mold, and air of lXl 0-6Nnf/S was flowed through the vent hole, which was 300 mm deep from the top.) The mold was used for casting, and the vertical crack rating was compared with the conventional one. The resulting graph is shown in Figure 4. In the figure, the white circles indicate the case of the conventional mold structure, and the black circles indicate the case of the mold according to the present invention, and it was possible to reduce the occurrence of vertical cracks by about 50%. Additionally, the lifespan of the coating layer was extended two to three times compared to when no air was allowed to flow through the vents.

〔Effect of the invention〕

As explained above, according to the present invention, there is no possibility of powder adhering to the vertical inner grooves or the groove shape cannot be maintained due to wear during use, resulting in non-uniform cooling conditions, as is the case with conventional examples. It can respond to the expansion of air inside the vents, and has a delicate control function for cooling performance.
By significantly improving the slow cooling rate, we were able to significantly reduce box cracking of the shell.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a mold according to the present invention, Fig. 2 is an enlarged cross-sectional view taken along the line ■-■ in Fig. 1, Fig. 3 is a conceptual diagram showing the state of mold heat transfer in the present invention, and Fig. 4 is a cross-sectional view of the mold according to the present invention. It is a graph comparing the relationship between the amount of heat removed from the mold and the vertical crack score between the present invention and a conventional example. 1...Mold (copper plate), 2...Mold cooling channel, 4...Vent hole, 4a...Fluid supply header, 8... ... Molten steel.

Claims (1)

[Claims] (1) In a mold for a continuous casting machine, a large number of ventilation holes with at least one end open to the atmosphere are provided between the mold cooling channel provided in the mold and the mold surface that comes into contact with the molten steel, and the ventilation holes are A mold for continuous casting, characterized in that the mold is connected by a fluid supply header whose supply amount can be adjusted.