JPH04138855A - Method for preheating flat nozzle for twin belt continuous casting - Google Patents

Abstract

PURPOSE:To execute a stable continuous casting operation by covering surroundings in the molten metal flowing end of a nozzle with the upper opening type vessel made of a fusible material with a molten metal introducing combustion gas from the upper end of a vertical penetrating gas flow passage in a stopper and blowing the gas to the molten metal flowing end at the upper end of the nozzle through a molten metal discharging hole in a tundish. CONSTITUTION:As preheat is executed by blowing the combustion gas into the flat nozzle 20 through inside of the stopper 13 closing the molten metal discharging hole in the tundish 10, the preheat can be continuously executed during supplying the molten metal into the tundish from a ladle, and the flat nozzle can be preheated just before casting. Further, since the surroundings in the molten metal flowing the end of the flat nozzle are covered with the upper opening type vessel 30 and moisture in discharged gas is not dewed by hitting the discharged gas flow to a mold wall, there is no danger of occurring of explosion caused by the moisture. Since the upper opening type vessel is made of the fusible material with the molten metal, there is no disturbance to the execution of the casting. By this method, the generation of spalling crack in the nozzle and the stickness of metal to the nozzle at the time of submerged casting, are prevented, and the stable twin belt continuous casting operation is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preheating a flat nozzle for twin-belt continuous casting before starting casting.

In the twin-belt continuous casting method, molten metal is injected between the walls of a movable mold, which consists of a pair of cooling belts arranged facing each other in parallel at intervals corresponding to a predetermined slab thickness. This is a continuous casting method in which casting is performed in synchronization with the drawing speed of , and is particularly suitable for casting slabs with a thickness of about 10 mm at high speed.

Conventionally, in order to manufacture thin metal sheets such as cold-rolled steel sheets using continuous casting, the mold is vibrated in the casting direction and the thickness is 100M.
The above slabs are cast, the surface of the resulting slabs is treated, and the slabs are heated to over 1,000 ℃ in a heating furnace, and then hot rolled in a hot strip mill consisting of a rough rolling mill row and a finishing rolling mill row. A hot strip with a thickness of several nanometers was prepared, and after hot-rolled plate annealing, pickling to remove surface scale, etc. were performed as necessary, cold rolling was performed.

If a twin-belt continuous casting method is applied in place of the conventional continuous casting method in such a thin metal sheet manufacturing process, slabs with a width of several 10 mm can be obtained, which is suitable for finishing hot rolling. Therefore, it is possible to omit the rough rolling step of hot rolling and the heating furnace therefor, and a significant improvement in production cost and productivity is expected.

In twin-belt continuous casting, molten metal is injected into a pair of cooling belts that are placed facing each other. However, because the opening distance between the cooling belts is as narrow as several tens of meters depending on the thickness of the slab, the injection nozzle is also a thin flat nozzle. is used.

At the start of casting, the molten metal flows from the tundish into the molten metal inlet of the flat nozzle, flows through the nozzle and flows out between the cooling belts, forming a pool. that time,
In order to prevent operational troubles such as thermal deformation due to molten metal flow, spalling cracks in the nozzle refractory due to thermal shock, and metal adhesion to the nozzle during immersion casting, it is necessary to preheat the flat nozzle until just before casting starts as much as possible. There is.

[Conventional technology]

Therefore, conventionally, a flat casting nozzle was attached to the lower part of the tap hole of the tundish, which opened and closed the tap hole using a sliding nozzle, and when the sliding nozzle was open,
A method has been used to preheat the flat nozzle by blowing a flow of combustion gas from the tap into the molten metal inlet end at the upper part of the nozzle, passing through the molten metal channel inside the nozzle, and discharging it from the molten metal outlet end at the lower part of the nozzle.

However, in the above-mentioned conventional method, the sliding nozzle must be closed before starting to supply molten metal from the ladle to the tundish, so it is necessary to close the sliding nozzle until the tundish is filled with molten metal to a predetermined level and ready to start casting. During this period, the flat nozzle was not preheated and could not be preheated until just before the start of casting.

In addition, COG gas containing CO+82 as the main component is generally used as combustion gas for preheating, but the gas flow discharged from the molten metal outlet end at the bottom of the flat nozzle contains moisture generated by the combustion of H2. This condensed on the cooling belt surface (mold wall), creating a risk of a hydrogen explosion during pouring.

[Problem to be solved by the invention]

The present invention solves the above-mentioned conventional problems, enables preheating to be carried out until just before the start of casting, and eliminates the risk of hydrogen bombing due to dew condensation even when preheating is performed with hydrogen-containing gas such as COG gas. The purpose is to provide a method for preheating a nozzle.

[Means to solve the problem]

According to the present invention, with a flat casting nozzle attached to the lower part of the tap of a tundish whose tap opening is opened and closed by lifting and lowering a stopper, a flow of combustion gas is blown from the molten metal inflow end at the top of the nozzle. , a method of preheating the flat nozzle by passing the molten metal through a flow path inside the nozzle and discharging it from the outflow end at the bottom of the nozzle, using a stopper with a gas flow path running vertically inside as the stopper, and discharging the molten metal from the outflow end of the nozzle. Cover the molten metal outlet end with an upwardly open container of molten metal soluble material to prevent the exhaust gas flow from directly spouting sideways and downwards, and with the stopper lowered and the tundish outlet closed, open the stopper. This is achieved by a method of preheating a flat nozzle for twin-belt continuous casting, which is characterized by introducing combustion gas from the upper end of the longitudinal gas flow and blowing it into the molten metal inflow end at the upper end of the nozzle through the outlet of the tundish.

[Effect]

In the method of the present invention, preheating is performed by blowing combustion gas into the flat nozzle through the inside of the stopper that closes the outlet of the tundish, so that the preheating continues even while the molten metal is being supplied from the ladle to the tundish. The flat nozzle can be preheated until just before the start of casting.

In addition, the upper open type container prevents exhaust gas from spewing out sideways and downwards around the molten metal outflow end of the flat nozzle.
There is no risk of water explosion because the exhaust gas flow hits the mold wall and moisture in the exhaust gas does not condense on the mold wall.

Since the top-opening container is made of molten metal soluble material,
Since it is melted by the molten metal flow at the start of casting, it does not interfere with casting. In other words, since the container only needs to act as a barrier to the exhaust gas flow, its wall thickness can be made quite thin.For example, if it is made of an iron plate with a thickness of about 1 inch, the initial flow of molten metal at the start of casting can be made. Dissolves almost instantly.

In the following, the invention will be explained in more detail by means of examples with reference to the accompanying drawings.

〔Example〕

FIG. 1 shows an example of the arrangement of a chamber for preheating a flat nozzle for double-belt continuous casting according to the present invention.

The outlet 11 of the tandish 10 has a gas flow path 1 inside.
2 is opened and closed by raising and lowering a stopper 13 that runs through it.

This figure shows a state in which the stopper 13 is lowered to the lowest position, the tap outlet 11 is closed, and a certain amount of molten metal M has been supplied into the tundish 10. In this state, the upper part of the stopper 13 protrudes upward from the lid 14 of the tundish L10.

After the flat nozzle 20 is preheated by gas burner heating from the lower end, the top-opening type container 30 made of iron plate with a thickness of 1 mm is connected to the hook part 21 of the flat nozzle 20 using a chain 31.
With the molten metal flowing around the edge a at the bottom,
The tundish 10 is attached to the lower part of the tap opening 11, and the molten metal outlet end is inserted into a mold made up of a pair of cooling belts 40.

Combustion gas such as COG gas introduced from the upper end of the vertical gas flow path 12 of the stopper 13 as shown by the arrow flows out from the lower end of the stopper 20, near the outlet 11 where the temperature is high due to the heat of the molten metal M. It ignites and burns like flame F, and is blown into the molten metal inlet end 22 of the flat nozzle 20.
The molten metal passes through the molten metal channel 23 and is discharged from the molten metal outlet end 24 as shown by arrow E.

Exhaust gas stream E is blocked in its lateral and downward path by vessel 30 and is thus discharged upwardly as shown, avoiding impingement on cooling belt (mold wall) 40.

While performing preheating as described above, molten metal continues to be supplied from a ladle (not shown) to the tundish 10, and when the molten metal level in the tundish 10 reaches a predetermined level, the introduction I of combustion gas is stopped, and the stopper 13 is closed. Casting is started by raising the tap and opening the tap 11.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to preheat the casting nozzle until just before the start of casting while preventing dew condensation on the surface of the cooling belt. Prevents gold adhesion and enables stable twin-belt continuous casting operations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an example of the arrangement for carrying out the preheating method of the present invention. DESCRIPTION OF SYMBOLS 10... Tandishu 11... Outlet, 12... Vertical gas flow path, 13... Stopper 14... Lid, 20... Flat nozzle, 21... Hook, 22... Molten metal inflow end, 23... Molten metal flow path, 24... Molten metal outflow end, 30... Upper open type container, 31... Chain, 40... Cooling belt, M... Molten metal, ■. ...Introduced combustion gas, F...Flame, E...Exhaust gas flow.

Claims (1)

[Claims] 1. Open and close the tap by raising and lowering the stopper. With the flat nozzle for casting installed at the bottom of the tap of the tundish, a flow of combustion gas is blown from the molten metal inflow end at the top of the nozzle to open and close the molten metal flow path inside the nozzle. In the method of preheating the flat nozzle by passing the molten metal through the nozzle and discharging it from the molten metal outlet end at the bottom of the nozzle, a stopper having a vertical gas passage therein is used as the stopper, so that the exhaust gas flow from the molten metal outlet end of the nozzle is directly horizontal. Then, the area around the outflow end of the molten metal is covered with an upwardly open container of molten metal soluble material to prevent the molten metal from spouting downward, and the stopper is lowered to close the outlet of the tundish, and combustion starts from the upper end of the gas flow through the stopper. A method for preheating a flat nozzle for twin-belt continuous casting, characterized by introducing gas and blowing it into the molten metal inflow end at the upper end of the nozzle through the outlet of a tundish.