JPS58944B2 - continuous casting machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a connected casting machine, and more particularly to a belt caster, which is equipped with a casting wheel having an outer circumferential recess formed therein, and in which a part of the outer circumferential recess in the length direction is closed by an endless belt to form a mold. This invention relates to a slab cooling guide device that is disposed in a section where the slab that has come out of the mold is re-bent in a continuous casting machine.

Conventionally, a continuous casting machine for manufacturing continuous metal slabs has a casting wheel with a concave outer periphery, and an endless belt made of steel that runs in contact with a part of the outer circumference of the casting wheel in the longitudinal direction. A continuous casting machine, generally referred to as a belt caster, is equipped with a casting mold that forms a mold between the caster and the caster, injects molten metal into the mold, and pulls out the slab from the end of the belt that touches the outer periphery of the casting wheel. Are known.

In this type of casting machine, the mold is arcuate, so the slab that comes out of the mold is immediately reground and sent to the next process.

This re-bending is usually done by pulling out the cast piece from the mold by pinching it between pinch rollers arranged downstream of the mold.

Another method is to place a knife-shaped guide plate adjacent to the outlet of the mold as described in U.S. Pat. No. 3,659,643 in which a casting shoe is used instead of an endless belt. There is also a method that forcibly guides the cast slab to re-bend it.

Continuous casting machines of the above-mentioned type have so far been mainly used for producing metals with high thermal conductivity such as copper and aluminum.

However, in recent years, this type of continuous casting has tended to be used for continuous casting of metals with relatively low thermal conductivity, such as steel, and in this case, various problems basically arise due to the low thermal conductivity. However, it has not been fully put into practical use.

To elaborate on this point, when the metal to be cast has a high thermal conductivity of about 330 Kcal/mh°C, such as copper, the slab is pulled out from the mold outlet because heat dissipation takes place in a short time. By now, the inside has almost completely solidified, and there is no particular problem in bending it back.

However, when casting steel, for example, the thermal conductivity is as low as about 29 Kcal/mh°C, so the slab that comes out of the mold only has a solidified shell about 10 mm thinner than the surface, and the inside is in an unsolidified state. .

If bending is carried out under such conditions, distortion will occur in the thin solidified shell, causing surface cracks in the slab, resulting in what is called a breakout, an accident in which unsolidified molten metal flows out due to rupture of the solidified shell, and the casting You will have no choice but to interrupt your work.

Conventionally, in order to prevent breakout accidents, the slabs that came out of the mold were spray cooled using a spray nozzle, but breakout accidents still occurred.

Regarding this spray cooling, see US Pat. No. 3,623,535, although the problem faced is different.

Although breakout accidents caused by the above cracks on the surface of the slab must be avoided, another problem is internal cracks that occur during bending.

Although this does not directly lead to an accident, it does pose a quality problem, and if there is a large internal crack, the product cannot be passed on to the next process and will be scrapped as a defective product.

Therefore, in reality, it was necessary to compress these internal cracks using a rolling mill or the like before cutting and cooling the cast slab.

In other words, if internal cracks that occur during rebending can be minimized or completely eliminated, there will be no need for the process of crimping internal cracks, and belt casters will be used in the field of high-grade steel, where internal cracks are averse. can be expanded.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a slab cooling and guiding device in a continuous casting machine, which allows the rebending of the slab discharged from the mold to be carried out in such a way that surface cracks and breakouts caused by this occur with little occurrence. It is to provide.

According to the present invention, in a continuous casting machine, the slab cooling device has a wedge-shaped body portion inserted between the outer circumferential recess of the casting ring and the upper surface of the slab coming out of the mold with the tip thereof facing the mold outlet. and a guide device are obtained.

This wedge-shaped body has a gradually curved cooling and guiding surface which, in the inserted state, faces the upper side of the slab.

In connection with the cooling and guiding surface of this wedge-shaped body, a device is provided for applying a hydrostatic bearing and a water film flow between the cooling and guiding surface and the upper side of the slab.

In one embodiment, in connection with the tip of the wedge-shaped body:
A device is provided for ejecting a high-velocity coolant substantially along the upper surface of the slab between the tip of the wedge-shaped body and the mold outlet.

As mentioned above, surface cracking of slabs, which is the cause of breakouts, is caused by the fact that steel has low thermal conductivity, so when the slab is pulled out of the mold, only a relatively thin solidified shell is formed on the surface. It is produced by bending a slab of thin solidified shell.

It was observed that this breakout occurred from the surface of the casting wheel side of the slab, which was subjected to tensile strain during resurfacing.

In this regard, in the continuous casting machine to which the present invention relates,
When the slab comes out of the mold and is bent back, the slab tries to move upward together with the casting wheel, but the pinch roller installed in front of the mold outlet counters this upward movement and bends the slab laterally. Since the slab tries to be pulled out in the horizontal direction, the part of the slab that is about to leave the casting wheel ends up having an upwardly curved shape.

It is thought that this curvature generates excessive tensile stress on the surface of the slab on the casting wheel side, that is, on the upper surface of the slab, and the thin solidified shell cannot withstand this and breaks, resulting in surface cracking of the slab and breakout.

Therefore, it is expected that breakout can be prevented if the slab can be gradually straightened without forming such a curved portion in the slab that comes out of the mold.

As a guide device for this purpose, it is conceivable to insert a knife-shaped guide plate, such as the one disclosed in US Pat. , the tip of the guide plate and its guide surface wear out quickly, making it impractical.

In the cooling and guiding device of the present invention, the body portion is wedge-shaped, and the guide surface of the wedge-shaped body portion is gradually curved. A device that applies hydrostatic bearings was installed.

Therefore, the cooling and guiding device of the present invention can apply its guide surface to the slab from a position close to its mold outlet due to the wedge-shaped shape of the body, and also has a gradually curved guide surface. Because of its shape, the slab can be straightened gradually, and the slab that comes out of the mold does not have the above-mentioned curvature, and surface cracking can be almost completely prevented. Since the static pressure bearing between the parts generates a force for straightening the slab without direct contact, wear on the guide surface can also be prevented.

Regarding internal cracks in the slab, a position close to the surface of the slab on the casting wheel side, that is, the upper surface of the slab, for example, approximately 8 to 1
It was observed that it was observed within a range of 5 mm.

That is, internal cracks in the slab occurred not at locations that were subjected to compressive stress during bending, but at locations that were subject to tensile stress.

It has been found that this internal cracking can be greatly reduced by strongly cooling the surface of the slab on the casting wheel side, that is, the upper surface of the slab, before completing the rebending of the slab that comes out of the mold, and that a healthy slab can be obtained. did.

The reason why internal cracks are reduced by this strong cooling is thought to be as follows after various studies.

First of all, regarding the cause of internal cracks, the slab that comes out of the mold not only has a liquid phase part that has not completely solidified inside, but also a part that is changing from a liquid phase to a solid phase, that is, the liquidus line (15
There should be a portion that reaches the solidus line (around 1470°C for ordinary steel).

In this state, the material has no strength at all, and in ordinary steel, the material strength is close to 0 at temperatures above 1360°C.

Therefore, when tensile stress is applied to the region from the liquidus line to the solidus line, cracks, that is, initial internal cracks, occur.

If a crack occurs in a sealed environment, that is, a cavity is created, this part becomes a vacuum, and the surrounding unsolidified or semi-solidified hot water enters this part and attempts to fill the cavity.

However, if the cavity is long, it will not be completely filled and cracks will still remain.

It is thought that internal cracks in the slab occur in this way on the side of the slab that receives tensile stress.

Based on this assumption, it is thought that if the length of the initial internal crack can be shortened, it will be possible to completely fill with unsolidified molten metal and eliminate the void.

According to the concept of the present invention, if the surface of the casting wheel side of the slab that has come out of the mold is strongly cooled before the slab re-milling is completed, the distance between the solidus line and the liquidus line in the slab will be shortened, and the tensile strength will increase. Stress also reduces the length of the initial internal crack or cavity that develops in this area.

Therefore, it can be seen that internal cracks in the slab as a product are reduced.

In the cooling and guiding device of the present invention, in addition to the configuration in which the slab is gradually re-bent as described above, in addition to the configuration in which the slab is gradually re-bent as described above, the cooling and guiding device of the wedge-shaped body part is A device is provided for applying a high velocity water film between the sides.

It has been demonstrated that high-velocity water film cooling (water film cooling) has significantly higher cooling capacity than, for example, spray cooling.

In spray cooling, even if the spray pressure is increased, the pressure reaching the surface of the slab is attenuated, and the vapor film that forms on the surface of the hot slab is not removed, and this vapor film acts as an insulator, limiting the cooling capacity. occurs.

On the other hand, in high-speed water film cooling, the static pressure of the coolant is applied to the surface of the slab, and the steam film is carried away by the cooling water flow, resulting in a large cooling capacity.

In the present invention, the high-speed water film causes the upper surface of the slab to be strongly cooled before the slab is fully bent after being removed from the mold, thereby reducing internal cracks in the slab.

In addition, in the cooling and guiding device of the present invention, a device is provided on the upper surface of the slab between the tip of the wedge-shaped body and the mold outlet for applying a high-speed coolant jet along this surface. .

The cooling action of this high-velocity coolant jet can further reduce internal slab cracking, similar to that discussed above in connection with high-velocity water film cooling.

This is because a sufficient cooling effect can be obtained by acting with a high-speed coolant jet flow in a narrow space surrounded by the slab, wedge-shaped body, and belt.

Preferred embodiments of the present invention will be described with reference to the drawings.
Reference numeral 1 indicates a continuous casting machine, and the continuous casting machine 1 has an outer circumferential recess 2.
A casting ring 3 is provided, and a portion of the outer peripheral recess 2 in the length direction is closed by an endless belt 4 to form a mold 5.

The casting wheel 3 rotates in the direction indicated by the arrow around the shaft 6, and at the same time, the belt 4 that closes the outer peripheral recess 5 of the casting wheel 3 moves in synchronism.

The belt 4 runs around an upper belt guide roller 7 , a lower belt guide roller 8 , and a belt tension roller 9 as well as around the outer circumference of the casting wheel 3 .

A tundish 10 is located above the casting wheel 3, and a nozzle 11 at the bottom of the tundish is connected from the tandish 10.
Molten steel 12 is injected into the mold 5 through.

The injected molten steel 12 is supported by a belt section that contacts the outer periphery of the casting wheel and is cooled by a coolant, preferably water, which is flowed behind this belt section by a device not shown.

The inner surface of the molten steel 12 in contact with the outer peripheral recess 2 of the casting wheel 3 is also cooled by the cooling water flowing through the outer portion of the casting wheel 3.

The injected molten steel 12 is cooled in this way and gradually becomes a solidified shell 13.
(See FIG. 3) and while increasing its thickness, it is pulled out as a slab 14 from the outlet 15 of the mold 5 by a pinch roller 16.

Pinch roller 16 is held by frame 17.

Between the outlet 15 of the mold 5 and the pinch row 216 is located a slab resurfacing section incorporating a cooling and guiding device 18 according to the invention, which can be more clearly illustrated in FIGS. 2 and 3.

The cooling and guiding device 18 has a wedge-shaped body 19, which has a tip 21 between the outer circumferential recess 2 of the casting ring 3 and the upper surface 20 of the slab 14 emerging from the mold 5. It is inserted facing the exit 15.

As shown, the wedge-shaped body portion 19 has a gradually curved cooling and guiding surface 22, and in the inserted state, the cooling and guiding surface faces the upper surface 20 of the slab.

The wedge-shaped body part 19 is fixed to a guide frame 23 attached to the frame 17 holding the pinch roller 16 by suitable fixing means (not shown) so that it can be raised and lowered relative to the guide frame 23 when the fixing means is removed. , installed.

A guide roller 24 is attached to the lower part of the wedge-shaped body portion 19 for engaging the upper surface 20 of the slab and setting a gap G between this and the cooling and guiding surface 22 .

The gap G can be adjusted by changing the diameter of the guide roller 24 or by changing the position of the rotating shaft.

Beneath the wedge-shaped bodies 1 to 9 are slabs 14 produced from the mold 5.
Straightening rollers 26 that engage the lower surface 25 and re-curve the slab in cooperation with the cooling and guiding device 18 are arranged at approximately equal intervals.
A spray nozzle 27 for cooling is provided.

Spray nozzles 30, 31 for cooling the side end surfaces 28, 29 of the slab 14 are arranged in the lateral direction (
(See Figure 4).

The straightening roller 26 is fixed on a support frame 32, which supports the hydraulic piston device 3 around an axis 33.
4, which allows the correction roller 26 to be attached and detached.

In connection with the cooling and guiding surface 22 of the wedge-shaped body 19, a hydrostatic bearing is provided between the cooling and guiding surface 22 and the top surface 20 of the slab, and a reservoir device for applying a high-velocity water film flow. (See Figure 5).

For hydrostatic bearings and high-velocity water film application devices, a plurality of grooves 35 are formed in the cooling and guiding surface 22 .

Each groove 35 communicates via a small hole or slit 36 with a header chamber 37 formed in the wedge-shaped body 19 .

The header chamber 37 is supplied with coolant, preferably water, in a controlled manner via a channel 38 from an external supply device, not shown.

The installation of the header chamber 37 is preferable in that the coolant supplied from the outside is temporarily brought into a static pressure state so that the coolant at a stable pressure can be ejected into the grooves 35 .

If there is no header chamber 37, pressure fluctuations of the coolant applied to the upper surface 20 of the slab tend to be large, making it difficult to obtain a stable hydrostatic bearing action.

The cooling and guiding device 18 further includes a wedge-shaped body 19
In conjunction with the tip 21 of the mold outlet 15, a device is provided for ejecting a high-velocity coolant onto the upper surface 20 of the slab between this tip 21 and the mold outlet 15, essentially along this surface.

The coolant ejection device consists of a plurality of small holes or slits 39 that open at one end into the header chamber 37 and at the other end at the body tip 21.

The slab 14 that has come out of the mold 5 has to be re-bent, but at that time, the slab surface on the casting wheel side, ie, the top surface 20 of the slab, is subjected to tensile stress, and the slab surface on the opposite side, ie, the bottom surface 25 of the slab, is subjected to compressive stress. As mentioned above, is added.

The slab 14 that has come out of the mold 5 is re-bent, with its underside 25 being sprayed by a spray nozzle 27, and its side end faces 28, 29 being sprayed by spray nozzles 30, 31.

This method is the same as the conventional one.

This is because no tensile stress acts on the slab material near these parts, and breakouts and internal cracks do not occur, so there is no need for strong cooling, and spray nozzles can be easily arranged in terms of space. It is.

As mentioned above, the problem is the smooth guiding and strong cooling of the casting wheel side surface 20 of the slab 14 coming out of the mold 5.

In the present invention, it is difficult to install a cooling device at the mold outlet 1.
Extremely effective guidance and strong cooling in the vicinity of the cooling and guiding device 18 is made possible.

The wedge-shaped body 19 of the cooling and guiding device 18 according to the invention allows its guiding surface 22 to be applied to the slab from the point already shown in FIG. 2, close to the mold outlet 15. Therefore, since the cooling and guiding surface 22 of the wedge-shaped body portion 19 has a gradually curved shape, it should be noted that the slab can be straightened gradually between 8 and 0 in FIG. .

Still associated with the cooling and guiding surface 22, a hydrostatic bearing and a device for applying a high-velocity water film flow are provided between the surface 22 and the top surface 20 of the slab.

That is, the coolant is supplied in a controlled manner from an external supply device (not shown), is made static pressure in the header chamber 37, is injected into the groove 35 through the small hole or slit 36, and is sprayed onto the upper surface of the slab. It flows through the gap G between 20 and the cooling and guiding surface 22 as indicated by the arrow n, resulting in a hydrostatic bearing effect and a water film cooling effect.

Due to this hydrostatic bearing action, the guide surface 22 generates a force to straighten the slab 14 every time it comes into contact with it, so the slab can be guided extremely smoothly without wearing out the guide surface 22. can.

Regarding the cooling of the upper surface 20 of the slab 14 undergoing re-bending,
As described above, the portion between b and c of the upper surface 20 is strongly cooled by high-speed water film cooling.

Preferably, the portion between a and b of the upper surface 20 of the slab directs the cooling water at a higher speed than the small hole or slit 39 provided at the tip 21 of the wedge-shaped body portion 19 toward the mold outlet 15, that is, the point a. It is cooled by ejecting it in the direction of arrow m almost along the upper surface 20 of the slab.

The cooling capacity of these cooling means can be easily achieved by changing the flow rate W of the coolant flowing on the upper surface 20 of the slab.

That is, when the magnitude of the cooling capacity is expressed by the heat transfer coefficient α, the following relational expression holds true regarding the cooling means.

αKcal/m2h℃=2900×W0.85(1+0
．． 014θW) Here, W is the cooling water flow rate (m/s) θW is the cooling water temperature (°C) Therefore, the heat transfer coefficient α is determined by the cooling water temperature and flow velocity, so if the water temperature is constant, it is a function only of the flow velocity. It is required as.

Generally, the heat transfer coefficient α of spray cooling using cooling means such as spray nozzles 27, 30, 31 is 2000 to 30.
It is known that 00Kcal/m2h°C is the limit.

In contrast, according to the cooling means according to the present invention, the flow rate W of the cooling water passing through the small holes or slits 36 and 39 is reduced to 2 m/
s, it can be reduced to 6700 Kcal/m2h°C.

FIG. 6 shows the improvement result of the α value of the cooling method according to the present invention.

In the figure, a, b, and c are a, b of FIG. c indicates the point at which the slab 14 passes through, the solid line W2 represents the cooling capacity of the cooling method of the present invention for the upper surface 22 of the slab 14 that has come out of the mold 5, and the two-dot chain line W2' represents the cooling capacity of the conventional cooling method for the upper surface 22 of the slab 14 that has come out of the mold 5. Indicates the cooling capacity of spray cooling.

The solid line W3 represents the cooling capacity of the known cooling means for the outer surface of the casting wheel of the slab in the mold 5, and the broken line B1 represents the cooling capacity of the known cooling means for the belt side surface of the slab in the mold 5. B2 indicates the cooling capacity of spray cooling on the lower surface 25 of the slab 14 coming out of the mold 5 for reference.

The effect of strong cooling according to the present invention will be clear from the above discussion.

To reiterate the important point, referring to FIGS. 7 and 8, the cause of internal cracking in the slab is the slab 14 that has come out of the mold 5.
If the upper surface 20 is insufficiently cooled, the distance D1 (Fig. 7) between the solidus line and the liquidus line remains relatively long and it receives tensile stress due to rebending, resulting in the length of the initial internal crack that occurs. This is thought to be due to the fact that the temperature is so long that the surrounding unsolidified hot water cannot be completely filled.

When the upper surface 20 of the slab is strongly cooled according to the present invention, the distance between the solidus line and the liquidus line becomes D2, as shown in FIG. 8, and the length of the initial internal crack that occurs also becomes shorter. Internal cracks can be greatly reduced.

Note that the gap G between the cooling and guide surface 22 and the upper surface 20 of the slab is determined from the viewpoints of effective cooling and smooth guidance of the slab and reduction of the coolant flow rate.
Preferably about 0.2-3 mm, more preferably about 0.5
It was found to be ~2.0 mm.

Furthermore, in Japanese Patent Publication No. 52-23326, it is stated that the straightening curve of the slab coming out of the mold is such that the separation point (corresponding to point a in Figure 2) from the casting ring outer circumference recess is below the casting ring outer circumference recess. It is located upstream of the dead center, and the height of the straightening completion point of the slab (approximately equivalent to point C in Fig. 2) is below the bottom dead center of the outer circumferential recess of the casting ring. A technical idea has been disclosed in which the straightening speed is slowed to minimize surface cracks and internal cracks in the slab while ensuring a sufficient feeder effect.

According to this concept, the wedge-shaped body 19 according to the invention comprises:
Preferably, the slab separation point a of the casting ring outer circumferential recess 2 is located upstream of the casting ring outer circumferential recess bottom dead center, and the height of the straightening completion point C of the slab is higher than the casting ring outer circumferential recess bottom dead center. It is positioned below the point.

As a result, the slab can be reground more smoothly, and surface cracks or breakouts of the slab and internal cracks in the slab can be more effectively prevented.

A summary of the effects of the present invention has already been described, but they can be summarized as follows.

(a) In the present invention, by applying a hydrostatic bearing type cooling and guiding device to the surface of the casting wheel side of the slab coming out of the mold, it is possible to prevent breakout accidents caused by bending of the slab, which existed in the past. .

(b) The high-speed water film flow flowing through the hydrostatic bearing portion of the cooling and guiding device enables far superior cold strength and reduces internal cracks in the slab.

Therefore, the quality of the slab as a product can be made high.

(c) Since the body of the cooling and guiding device is wedge-shaped, it can be placed close to the mold outlet, thereby providing more effective cooling and guiding.

(d) The slab can be strongly cooled immediately after exiting the mold by the high-speed coolant jet flow from the tip of the wedge-shaped body of the cooling and guide device, thereby further reducing internal cracks in the slab.

(e) Straightening and cooling of slabs using the cooling and guiding device of the present invention can be performed extremely easily.

(f) The completion of the present invention has opened the way for this type of continuous casting machine, which was conventionally used for continuous casting of copper and aluminum in bundles, to be fully put to practical use in the production of steel slabs. The characteristics of the type as a high-speed casting machine could be utilized for casting steel.

[Brief explanation of drawings]

FIG. 1 is a partially sectional front view of a continuous casting machine incorporating an embodiment of a cooling and guiding device according to the present invention. FIG. 2 is an enlarged partial cross-sectional view of the cooling and guide device of the continuous casting machine of FIG. 1 and related parts thereof. Figure 3 shows a larger enlargement of the cooling and guide device and related parts of the continuous casting machine in Figure 1, and Figure 2 shows the structure of the wedge-shaped body, the flow of the coolant, and the solidification state inside the slab. This is a similar diagram. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. FIG. 5 is a plan view of the wedge-shaped body section viewed from the direction of the line ■--■ in FIG. 4. FIG. FIG. 6 is a diagram comparing the heat transfer coefficient when a slab released from a mold is cooled by conventional spray cooling and when it is cooled by the cooling means of the present invention. FIG. 7 is a cross-sectional view of a slab portion showing internal cracks that are thought to occur inside the slab when the slab emerging from the mold is bent while being cooled by conventional spray cooling. FIG. 8 is a diagram similar to FIG. 6, showing internal cracks that are thought to occur inside the slab when the slab released from the mold is bent while being cooled by the cooling means of the present invention. . DESCRIPTION OF SYMBOLS 1... Continuous casting machine, 2... Outer periphery recess, 3... Casting wheel, 4... Belt, 5... Mold, 14... Slab,
19... Wedge-shaped body part, 20... Top surface of slab, 22...
...Guide surface, 35...Groove, 36...Small hole.

Claims (1)

[Claims] 1. A continuous casting machine in which a mold is formed by abutting an endless belt on the outer periphery of a casting ring having a peripheral recess, and molten metal is injected into the mold to continuously draw out slabs, A slab cooling and guiding device having a wedge-shaped body is provided between the outer circumferential recess of the casting ring and the upper surface of the slab coming out of the mold, and the wedge-shaped body gradually approaches the upper surface of the slab. Continuous casting machine, characterized in that it has cooling and guiding surfaces of curved shape, said cooling and guiding surfaces being provided with hydrostatic bearings and a device for applying a water film flow. 2. The device that applies the hydrostatic bearing and the water film flow consists of a groove used in the cooling and guide surface and a small hole that opens into the groove and spouts high-speed cooling water toward the slab. A continuous casting machine according to claim 1, characterized in that: 3. The wedge-shaped body part is provided with a guide roller that rotatably contacts the upper surface of the slab, and the cooling of the wedge-shaped body part and the gap between the guide surface and the upper surface of the slab are positioned by the guide roller. A continuous casting machine according to claim 2, characterized in that: 4. The gap between the cooling and guide surface and the top surface of the slab is 0.
4. The continuous casting machine according to claim 3, wherein the continuous casting machine is set at a distance of 2 to 3 mm. 5. The continuous casting machine according to claim 1, further comprising a device at the tip of the wedge-shaped body portion for spouting a high-speed coolant jet toward the mold outlet side.