JPH0741379B2 - Continuous casting lubrication method for wide and thin slabs - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of lubricating a space between a mold and a slab when continuously casting a wide and thin slab at a high speed.

(B) Conventional technology Conventionally, when manufacturing a slab by a continuous casting method,
The slab thickness is about 200 mm or more, and the operation is performed by immersion nozzle / powder lubrication. In recent years, for the purpose of simplifying the rolling process, attempts have been made to directly manufacture a slab that is considerably thinner than before by continuous casting. For example, when the slab thickness is 50 mm or less, the conventional immersion nozzle cannot be used, and even if a very thin flat nozzle is used, nozzle clogging easily occurs and stable large capacity continuous operation cannot be expected. . Further, as the thickness of the slab becomes thinner, high-speed casting becomes necessary from the viewpoint of productivity, and stable operation becomes more difficult.

Therefore, open hot water supply is indispensable for stable high-speed continuous casting of thin slabs. Therefore, the conventional powder lubrication cannot be performed, and the oil lubrication performed by the billet continuous casting is necessary.

With a billet with a small cross section, high-speed continuous casting of about 3.5 ^m / min is possible with oil lubrication, but for wide cast pieces, the bulging is at the center of the cast piece width, etc. The conventional method of pouring oil from above the meniscus has a high risk of lubrication failure. Furthermore, during high speed continuous casting, the shell thickness in the mold is generally thin,
The adhesion of the shell to the mold by bulging becomes even greater, and it is essential to ensure lubrication. A method of forcibly supplying the lubricant just below the meniscus is disclosed in, for example, Japanese Patent Laid-Open No.
-58960 publication. In this method, when the meniscus is below the supply hole due to fluctuations in the molten metal surface, there is a risk of seizure and breakout, and it is not possible to completely guarantee lubrication.

In order to stably operate high-speed casting of wide and thin slabs with open hot water supply, uniform lubrication in the slab width direction is required.Conventional oil can be poured from the upper part of the meniscus, or lubricant can be placed just below the meniscus. It is difficult to ensure sufficient lubrication only by the method of supplying.

(C) Problem to be Solved by the Invention The problem to be solved by the present invention is to perform high-speed casting of wide and thin slabs, ensure uniform lubrication in the slab width direction, and enable stable operation. To obtain a lubrication method.

(D) Means for Solving the Problem The continuous casting lubrication method for wide and thin slabs of the present invention, when continuously casting wide and thin slabs, has a boiling point from the top of the meniscus.
A first lubricant of 1500 ° C or less is supplied to gasify the first lubricant to prevent seizure between the mold and molten steel, and the melting point is 1000 ° C or less and the decomposition temperature is 1500 ° C or more from directly below the meniscus. The above problem is solved by means of forcibly supplying the second lubricant to liquid lubricate the space between the mold and the slab.

The first lubricant is an oil-based liquid lubricant, and the second lubricant is a boric acid lubricant.

The first lubricant is naturally dropped by a header provided on the upper part of the mold to be supplied to the upper part of the meniscus, and the second lubricant is supplied to a communication hole inside the mold at the lower part of the meniscus by a pump.

(E) Action In high-speed continuous casting of wide and thin slabs that require open lubrication, seizure prevention at the meniscus part, reduction of frictional force between the mold and slab below the meniscus, and lubrication
I found that I needed a point.

In addition, for the prevention of seizure of the meniscus (there is almost no problem of static pressure), gasification of the lubricant creates a clearance between the solidified shell of molten steel and the inner surface of the mold, so it is most effective in preventing seizure. effective. On the other hand, liquid lubrication is most effective in reducing the friction between the mold and the slab under the meniscus, and is advantageous in terms of heat removal. Gasification not only makes the lubrication unstable, but also causes poor heat extraction, which slows the growth of the solidified shell and increases the risk of breakout.

According to the results of experiments conducted by the inventors, it is clear that the supply position of the second lubricant below the meniscus should be within 100 mm below the meniscus. That is,
This is because the lubricating effect is maintained even if the casting speed increases and the risk area for seizure increases.

Further, in order to obtain a stable lubricating effect, it is preferable to set the supply position of the second lubricant in the following range according to the casting speed.

If the casting speed is 3 ^m / min or less, 100 mm below the meniscus 〃 3 to 5 ^m / min, 150 mm below the meniscus 〃 5 ^m / min or more, 200 mm below the meniscus, no seizure will occur. , More complete lubrication is ensured.

Based on the above basic facts, it is necessary to separate the lubricating function between the meniscus portion and the lower portion of the meniscus for lubrication between the mold and the slab during high-speed casting of wide and thin slabs. Two kinds of lubricants are also required, and if two kinds of lubricants are mixed, the performance may change, so it is necessary to supply from above. Therefore, the first lubricant poured from the upper part of the meniscus needs to be gasified when it comes into contact with molten steel. -Use boric acid molten salt, rapeseed oil, silicone oil, etc.).

On the other hand, the second lubricant used immediately below the meniscus needs to be present as a liquid between the mold and the slab,
A material that does not gasify even at 1500 ° C (for example, boric acid-based lubricant) is required. In addition, the melting point must be 1000 ° C. or lower in order to maintain sufficient liquid lubrication.

If the melting point is 1000 ° C or higher, the lubricant supplied from just below the meniscus is difficult to melt, and there is a risk that the lubricant will not exert its lubricating effect. The surface of the slab is about 1300 ° C, but it is necessary to quickly melt it in order to have a lubricating effect in high-speed casting. If it does not melt, most of it remains as powder or solid, and the frictional force increases, resulting in poor lubrication.

At a decomposition temperature of 1500 ° C or less, depending on the amount of medium, for example, a violent vaporization phenomenon occurs, gas is generated in the meniscus, causing boiling, and further breaking the solidified shell to cause breakout. There is also a nature.

(F) Example An example of a continuous casting lubrication method for wide and thin cast pieces according to the present invention will be described with reference to FIG.

Molten steel 11 is injected into the mold 1 from the nozzle 2. The first lubricant 4 spontaneously drops from the header 3 from above the meniscus, and becomes the vaporized lubricant 5. The second lubricant 9 is supplied from the tank 8 by the pump 7 to the communication hole 12 inside the mold provided directly below the meniscus of the mold 1 through the pipe 6.

In the wide thin slab 13 drawn out from the mold 1, the unsolidified molten steel remains inside the solidified shell 10.

The continuous casting lubrication method of a wide thin cast piece of the present invention is a method of continuously casting a wide thin cast piece, in which the first lubricant 4 having a boiling point of 1500 ° C. or less is supplied from the upper part of the meniscus 14 to form the first lubricant. To prevent seizure between the mold 1 and the molten steel 11 and to forcibly supply the second lubricant 9 having a melting point of 1000 ° C or lower and a decomposition temperature of 1500 ° C or higher from immediately below the meniscus 14. And liquid lubricates the space between the mold 1 and the slab 13.

Next, a specific example in which the lubrication method of the present invention is actually carried out will be described.

A single-point straightening continuous casting machine with a bending radius of 10 m is used to cast wide thin slabs with a slab size of 50 mm thick and 1800 mm wide at a casting speed.
High speed continuous casting was performed at 7 ^m / min. Open hot water was supplied from the steel types shown in Table 1, and as the lubricant, only conventional oil casting was used for the first strand, and the first and second lubricants according to the method of the present invention were used for the second strand. Repseed oil was used as the first lubricant. As the second lubricant, a boric acid-based lubricant of the type shown in Table 2 was used.

The supply position of the second lubricant was 170 mm below the meniscus.

The first circulating agent was supplied by spontaneous falling from the header 3. Second
The lubricant was supplied under pressure up to 2 kg / cm ² by the pump 7.

The Cu plate temperature was measured on both strands, and the restraint condition in the mold is shown in Fig. 2 in comparison with the conventional method. It can be seen that, in the second strand using the method of the present invention, no constraint occurs and good mold lubrication is achieved.

FIG. 3 shows the amount of heat removed from the mold. It was found that the second strand using the method of the present invention had a larger amount of heat removed and liquid lubrication was ensured.

(G) Effect According to the lubrication method of the present invention, the lubrication between the slab and the mold is ensured, and the constrained continuous casting of wide and thin slabs can be stably operated.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a casting mold for wide and thin cast pieces to which the lubricating method of the present invention is applied, and FIG. 2 is a graph showing a comparison of breakout occurrence rates. FIG. 3 is a graph showing a comparison of heat removal amounts. 1: Mold, 2: Nozzle, 3: Header, 4: First lubricant, 5: Vaporized lubricant, 6: Pipe, 7: Pump, 8: Tank, 9: Second lubricant, 11: Molten steel, 12: Mold inner surface communication hole, 13: slab, 14: meniscus, 10: solidified shell.

Claims (3)

[Claims] 1. When continuously casting wide and thin slabs, a first lubricant having a boiling point of 1500 ° C. or less is supplied from the upper part of the meniscus to gasify the first lubricant and burn the mold and molten steel. Wide width characterized by preventing sticking and forcibly supplying a second lubricant with a melting point of 1000 ° C or less and a decomposition temperature of 1500 ° C or more from the bottom of the meniscus to perform liquid lubrication between the mold and the slab. Lubrication method for continuous casting of thin slabs. 2. The lubricating method according to claim 1, wherein the first lubricant is an oil-based liquid lubricant, and the second lubricant is a boric acid lubricant. 3. The first lubricant is naturally dropped by a header provided on the upper part of the mold and supplied to the upper part of the meniscus, and
The lubrication method according to claim 1, wherein the second lubricant is supplied to a communication hole in the inner surface of the mold below the meniscus by a pump.