JPH07106438B2 - Metal melt container with heating part - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molten metal container that holds a molten metal at high temperature such as steel and has a heating unit that heats the molten metal.

The molten metal container having the heating unit according to the present invention can be used when heating the molten metal held in the tundish used in the continuous casting method to adjust the temperature of the molten metal.

[Prior Art] In a metal melting factory or the like, a molten metal may be held in the container body until it is processed in the next step.
However, there is a problem that the molten metal in the container body is cooled. For example,
In the continuous casting method, a molten steel of, for example, about 1400 to 1600 ° C is temporarily received from a ladle in a tundish, and the molten metal is injected into a water-cooled mold from a tundish discharge port to be cooled and solidified,
After the secondary cooling by the spray band, the cooled and solidified portion is pulled by a pinch roll and cut into a predetermined length, thereby manufacturing a slab, a billet and the like. In the above continuous casting method, the quality of the manufactured product is improved and the yield is also improved as compared with the slabbing method. However, in recent years, steel products have been required to have higher quality. Therefore, continuous casting methods have been earnestly developed to improve the quality of steel products.

By the way, in the continuous casting method, the temperature of the molten steel is apt to be lowered in the tundish because the molten steel is primarily received by the tundish. Especially when performing continuous casting
The temperature of the molten metal is several to several tens at the end of casting compared to the beginning of casting.
Decrease about ℃. Here, the injection temperature of the molten metal injected into the water-cooled mold has a considerable influence on the quality of the manufactured product even if it fluctuates by several to several tens of degrees. Therefore, it is not preferable in terms of quality control that the temperature of the molten steel is lowered in the tundish.

Therefore, in recent years, in order to adjust the temperature of the molten steel in the tundish, an electrode is immersed in the molten metal in the tundish, and an electric current is directly applied to the molten metal in the tundish to heat the molten metal itself by Joule heat. ing. However, in this case, since the electric resistivity of the molten metal is small, a considerably large amount of current is required. There is also provided a device for inductively heating the molten metal in the tundish. There is also provided a device in which a plasma torch is installed above the tundish to plasma-heat the molten metal in the tundish.

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and an object thereof is to melt a metal melt held in a container body by causing a heating element made of a conductive ceramic to generate heat. In order to provide a metal molten metal container having a heating part for heating.

[Means for Solving Problems] A molten metal container having a heating unit according to the present invention includes a container body for holding the molten metal, and an electrode portion and an electrode portion inside which is immersed in the molten metal held in the container body. At least one heater device made of a conductive ceramic heating element covering the heating element, and applying a voltage between the electrode part and the molten metal to energize the heating element to generate heat. It is what
The number of heater devices is appropriately set, but may be one, two, or more.

Specific examples of conductive ceramics include zirconia (Zr
O ₂ ), a mixture of zirconia and magnesia, silicon carbide (SiC), lanthanum chromate (LaCrO ₃ ), molybdenum silicide (MoSi ₂ ), titanium nitride (TiN), titanium carbide (TiC), etc. Things can be used. However, the conductive ceramic materials should be selected in consideration of the heating temperature of the molten metal, the acidity of the place where the heater device is used, the reducing atmosphere, the heat resistance of the ceramics, and the impact resistance of the ceramics at high temperatures. is there.

When the heat generation is mainly composed of zirconia, stabilizers such as calcium oxide (CaO), magnesia (MgO), yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb)
₂ O ₃ ) and scandium oxide (Sc ₂ O ₃ ) are added in the range of several% to several tens%, and it is desirable to use stabilized zirconia or metastable zirconia that avoids transition. By doing so, expansion accompanying the transition can be avoided, and distortion of the heating element can be suppressed. It is desirable that the conductive ceramic material forming the heating element does not change the resistance value of the heating element even if the temperature changes, or exhibits a positive property that the resistance value increases. When the temperature rises in this way, the resistance value of the conductive ceramic increases, and when the heating element has a high temperature portion, the resistance value of the high temperature portion increases. Therefore, an electric current flows through a portion having a temperature lower than that of the high temperature portion, and therefore, it is convenient to cause the entire heating element to generate heat uniformly. If the conductive ceramic has the negative property that the resistance value decreases as the temperature rises, when the heating element has a high temperature portion, the resistance value of the high temperature portion becomes low. Therefore, it becomes difficult for the current to flow in a portion having a temperature lower than that in the high temperature portion, and the current easily flows in the high temperature portion. Therefore, the temperature of the high-temperature portion becomes higher and higher, which causes uneven heat generation of the heating element, which is not desirable.

The total resistance R (Ω) of the heating element is influenced by the specific resistance value ρ (Ωcm) of the conductive ceramics, the wall thickness t (cm) of the heating element, and the area S (cm ² ) of the heating element, and therefore its shape. Is affected by the wall thickness and so on, and R = (ρ · t) / S. The specific resistance value ρ of conductive ceramics is 1 to 5 × 10 ³ (Ωcm)
Something can be adopted.

The specific resistance value of the heating element can be changed by blending conductive ceramics with non-conductive ceramics and adjusting the blending ratio.

The heating element, after molding the conductive ceramic powder into a predetermined shape, or after molding a mixed powder of the conductive ceramic powder and the non-conductive ceramic powder into a predetermined shape,
It is formed by heating to a predetermined temperature and sintering. For example, the raw material ceramic powder is prepared by thoroughly pulverizing and mixing the ceramic powder with a ball mill, a vibration mill or the like. Then, the raw material ceramic powder is pressure-molded to form a compact. Then, if necessary, a drying process is performed, and heating is performed at a high temperature to sinter. For the pressure molding, known means such as a press pressing method, a hydrostatic pressing method, a hot pressing method can be adopted. Sintering is in a non-oxidizing atmosphere,
It is preferable to perform it in an inert atmosphere or high vacuum.

The electrode part needs to have a melting temperature higher than the temperature of the molten metal so as not to be melted by the heat of the molten metal. Further, it is desirable that the electrode portion has a heat transfer coefficient as large as possible. Therefore, it is desirable that the electrode portion is made of carbon. Also, a conductive ceramic having a low electric resistance can be used as the electrode portion. In such a case, it is also possible to integrally mold the electrode portion and the heating element and fire them as they are. The heater device can be formed of a plate-shaped electrode portion and a layered or plate-shaped heating element that covers the electrode portion, as shown in Examples described later. Further, the heater device can be formed of a rod-shaped electrode portion and a heating element that covers the electrode portion. Further, the heater device can be formed from a plate-shaped electrode portion and a heating element having a trapezoidal cross section that covers the electrode portion from both sides.

In the molten metal container according to the present invention, a sensor such as a γ-ray level meter for detecting the stored amount of the molten metal held in the container body is provided, and the current to the heating element is controlled according to the signal of the sensor. It is also possible to provide a control device for this. With this configuration, the amount of current flowing to the heating element is controlled according to the amount of change in the molten metal held in the container body, so that the temperature of the molten metal can be adjusted more accurately.

[Embodiment] A first embodiment in which a molten metal container having a heating unit according to the present invention is applied to a tundish apparatus used in a continuous casting method for steel will be described.

First, a continuous casting apparatus used in the continuous casting method will be described. This continuous casting apparatus, as shown in FIG. 5, includes a tundish 1 as a container body for holding a molten steel,
A water-cooled mold 2 arranged below the tundish 1,
It is composed of a secondary cooling spray zone 3, a pinch roll 4, and a straightening roll 5. The tundish 1 has a capacity for holding the molten metal for about 5 tons.

The first heater device 6 and the second heater device 9 used in this embodiment are shown in FIG. The first heater device 6 includes a layered heating element 7 containing zirconia and magnesia as main components, and a plate-shaped electrode portion 8 formed of carbon in contact with the layered heating element 7.
It consists of and. Here, the layered heating element 7 has a width l1
The length is about 1 m, the length l2 is about 1 m, and the wall thickness t1 is about 5 cm. The planar electrode portion 8 is divided by an insulator 70 and an insulator 71 made of alumina, and is divided into three parts, an electrode body 72, an electrode body 73, and an electrode body 74. Terminals 75, 76, and 77 project from the electrode body 72, the electrode body 73, and the electrode body 74, respectively.

The second heater device 9 has substantially the same configuration as the first heater device 6, and is formed of a layered heating element 10 containing zirconia and magnesia as main components, and carbon in contact with the layered heating element 10. It is composed of a plate-shaped electrode portion 11. Here, the layered heating element 10 has a width of about 1 m, a length of about 1 m, and a wall thickness of about 5 cm. The plate-shaped electrode portion 11 is divided by an insulator 110 and an insulator 111, and is divided into three parts, an electrode body 112, an electrode body 113, and an electrode body 114. Terminals 115, 116, and 117 project from the electrode body 112, the electrode body 113, and the electrode body 114, respectively. An insulating film 8a made of a mixture of alumina and magnesia as an electrically insulating material is provided on a portion of the plate-shaped electrode portion 8 and the plate-shaped electrode portion 11 which is not in contact with the layered heating element 7 and the layered heating element 10. , 11a
Are covered.

Next, the case of continuous casting will be described. First, as shown in FIG. 1, in the first heater device 6, the terminals 75 and
77 is connected to an AC power source, and a current of 100 to 600 A is passed between the electrode body 72 and the electrode body 74 through the layered heat generating body 7, whereby the heat generating body 7 generates heat, and thus the heat generating body 7 is generated. Preheat.
Similarly, in the second heater device 9, the terminals 115 and 1
17 is connected to an AC power source, a current of 100 to 600 A is caused to flow between the electrode body 112 and the electrode body 114 through the layered heat generating body 10, whereby the heat generating body 10 generates heat and thus the heat generating body 10 is Preheat.

With the heater device 6 and the heater device 9 preheated in this way, the heater device 6 and the heater device 9 are placed in the molten steel of high temperature of about 1400 to 1600 ° C. which is transferred from the ladle 30 and is held in the tundish 1. Soak. A plan view of the immersed state is shown in FIG. As shown in FIG. 6, the heater device 6 and the heater device 9 are arranged in the tundish 1 so as to be substantially parallel to each other along the longitudinal direction of the tundish 1. In this case, since the molten metal transferred from the ladle flows in the direction of arrow X toward the discharge port 10 as shown in FIG. 6, the flowing molten metal does not directly contact the heater device 6 and the heater device 9. Therefore, damage to the heater devices 6 and 9 can be prevented as much as possible.

As shown in FIG. 7, the heater device 6 is arranged so that the molten metal flowing in the direction of the arrow X toward the discharge port 10 directly contacts the heater device 6.
Also, the heater device 9 may be arranged substantially in parallel.
By doing so, the molten metal flowing toward the discharge port 10 directly hits the heater device 6, which is advantageous for improving the effect of heating the molten metal in the tundish 1. In the case shown in FIG. 7, the molten metal transferred from the ladle between the lower part of the heater device 6 and the bottom wall of the tundish 1 flows toward the discharge port 10a.

The heater devices 6 and 9 before the molten metal is immersed as described above.
By preheating, the rapid heating of the heating element 7 and the heating element 10 can be prevented. Therefore, the occurrence of cracks in the layered heating element 7 and the layered heating element 10 can be suppressed as much as possible. Further, the above-mentioned preheating can ensure the conductivity of the heating element 7 and the heating element 10 containing zirconia as a main component. When the heating element 7 and the heating element 10 are cracked, the molten metal and the plate-shaped electrode portion 8 and the plate-shaped electrode portion 11 are directly connected to each other, and the heat generation amount of the heating element 7 and the heating element 10 is small. Therefore, the heater devices 6 and 9 cannot be effectively used.

With the heater devices 6 and 9 immersed as described above,
As shown in FIG. 2, the terminals 76 and 116 are connected to an AC power source, and a voltage of 100 to 600 V is applied between the terminals 76 and 116. As a result, an electric current is passed between the layered heating element 7 of the heater device 6 and the layered heating element 10 of the heater device 9 through the molten metal held in the tundish 1. Current amount is 200-400A
It is a degree. At this time, the heat generating element 7 and the heat generating element 10 containing zirconia as a main component generate heat at a high temperature. Therefore, the molten metal held in the tundish 1 is heated to about 1 to 30 ° C.
The temperature is raised and the temperature is adjusted.

In this embodiment, the heating element 7 of the heater device 6 and the heater device 9
Since the molten metal is heated by the heat generation amount of the heating element 10, compared with the case where the molten metal is heated by the Joule heat generated in the molten metal itself by directly supplying an electric current to the molten metal, which has been conventionally provided,
The amount of current required is small, and therefore its electrical control is easy to perform.

Further, in the present embodiment, since the heating elements 7 and 10 are layered, the surface area is large, that is, the heat radiation area can be increased, and it is possible to suppress the heat from being accumulated in the heating elements 7 and 10 as much as possible. Therefore, it is advantageous for suppressing cracks and damages due to heat of the heating elements 7 and 10. Therefore, in this embodiment, the heat-resistant temperature of the heat-generating body 7 and the heat-generating body 10 may be low. Therefore, the types of conductive ceramic materials forming the heat-generating body 7 and the heat-generating body 10 can be expanded to those having a low heat-resistant temperature. it can.

FIG. 3 schematically shows the temperature distribution in the cross section of the heating elements 7 and 10. As shown in FIG. 3, in the heating elements 7 and 10, the maximum temperature (Tmax) is reached at the electrode portions 8 and 11 side,
The temperature gradually decreases toward the surface A that contacts the electrode portions 8 and 11 and the surface B that contacts the molten metal. In this case, in order to prevent melting of the heating elements 7 and 10, the maximum temperature (Tmax)
It is necessary to set the temperature lower than the melting temperature of the conductive ceramics forming the heating elements 7 and 10.

The molten metal whose temperature is adjusted in the tundish 1 as described above is discharged from the discharge port 10a of the tundish 1, and the mold 2
After being cooled and solidified, it is further cooled by jetting cooling water from the spray zone 3 and cooled and solidified is pulled downward by a pinch roll 4. After that, it is cut into a predetermined length by a cutter.

As described above, in the present embodiment, the temperature of the molten metal held in the tundish 1 can be adjusted by heating the molten metal held in the tundish 1 by the heater device 6 and the heater device 9, so that the temperature of the molten metal held in the tundish 1 can be secured at an appropriate value. This is advantageous in improving the quality of products such as blooms and billets produced by the continuous casting method.

In the above-mentioned examples, the heating elements 7 and 10 had an area of 1 m ² and a thickness of 5 cm, but the layered heating elements 7 and 10 can be thinned to have an area of 1 m ² and a thickness of 1 cm. When the thickness is reduced, heat can be suppressed from being accumulated in the heating elements 7 and 10, but if the temperature of the molten metal is high, it is easily melted by the heat of the molten metal and the life is shortened. Therefore, in order to suppress melting loss, the heating element 7 may have an area of 1 m ² and a thickness of 3 cm. Further, the layered heating element 7 has an area of 3 m ² and a thickness of 5
It can also be cm.

Since the heater devices 6 and 9 are thin and plate-shaped, when the tundish 1 has a small volume, as shown in FIG.
Since the heater device 6 has to be held in contact with the inner wall of the tundish 1, heat transfer loss to the tundish 1 side is likely to occur.

(Second Embodiment) FIG. 8 and FIG. 9 (A) showing the second embodiment of the present invention.
This will be described with reference to (B) and (C). This embodiment is also applied to the tundish device used in the continuous steel casting method. The heater device 12 used in this embodiment is immersed in the molten metal held in the tundish 1 as the container body, as in the case of the first embodiment. This heater device
The electrode 12 is formed of an electrode portion 13 formed of carbon, and a heating element 14 mainly composed of zirconia and magnesia, which is coated on both surfaces of the electrode portion 13 in the thickness direction. As shown in FIG. 9, the heating element 14 according to the second embodiment has a height h of 50 cm.
The long side l3 is about 85 cm, and the short side l4 is about 60 cm. The heating element 14 according to the second embodiment secures a heat radiation area while
The strength of the heating element 14 can be secured. Since the heat radiation area can be secured, the amount of heat transferred to the molten metal can be secured while suppressing the heat buildup and lowering the internal temperature of the heating element 14.

Further, as shown in FIG. 8, the molten metal moved from the ladle into the tundish 1 toward the discharge port 10 is directly heated by the heater device 12.
Since the heater device 12 can be arranged so as to hit, the heat transfer efficiency from the heater device 12 to the molten metal can be improved accordingly.

Moreover, even if the volume of the tundish 1 is small,
Since it is not necessary to bring the heater device 12 into contact with the inner wall of the tundish 1, heat of the heater device 12 can be prevented from being transferred to the tundish 1 side, and heat transfer loss can be reduced.

Also in the case of this embodiment, the heating element of the surface of the electrode portion 13
A portion not in contact with 14 is covered with an insulating film made of a mixture of alumina and magnesia.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. This embodiment is also applied to the tundish device used in the continuous steel casting method. In the present embodiment, the heater device 15 is composed of the electrode portion 16 and the heating element 17 covered by the electrode portion 16. Then, on the bottom wall of the tundish 1 as the container body, weirs 1a and 1b are formed so as to be located on both sides of one heater device 15. The weirs 1a and 1b facilitate convection in the molten metal heated by the heater device 15, thereby facilitating floating of impurities in the molten metal.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. This embodiment is also applied to the tundish device used in the continuous steel casting method. The heater device 18 used in this embodiment is composed of a rod-shaped carbon electrode part 19 and a cap-type heating element 20. The heater device 21 is
The rod-shaped carbon electrode part 22 and the cap-type heating element 23
It is formed by. The heating elements 20 and 23 are of a cap type, and female threads are formed on the inner peripheral portion thereof.
It is attached by screwing into the male threads of the tips of 9 and 22. Also in this case, a portion of the surfaces of the electrode portions 19 and 22 that does not come into contact with the heating elements 20 and 23 is covered with an insulating film made of a mixture of alumina and magnesia.

[Effect of the Invention] According to the molten metal container having the heating unit according to the present invention, the molten metal held in the container body can be heated by the heat generated by the conductive ceramics, and therefore the temperature of the molten metal is adjusted. be able to. Therefore, when the molten metal container having the heating unit according to the present invention is applied to the tundish apparatus used in the continuous casting method, the quality of the product manufactured by the continuous casting method can be improved.

[Brief description of drawings]

The drawings show respective embodiments of a metal melt container having a heating portion according to the present invention, FIG. 1 is a perspective view of a first heater device showing a preheating state of the first embodiment, and FIG. FIG. 4 is a schematic perspective view of a state where electricity is supplied between the heater device and the second heater device, FIG. 3 is a graph schematically showing a temperature distribution in a cross section of a heating element, and FIG. FIG. 5 is a schematic plan view of the apparatus immersed, FIG. 5 is a schematic sectional view of the apparatus used in the continuous casting method, FIG. 6 is a plan view of the heater apparatus immersed in the molten metal, and FIG. The figure is a plan view of the heater device immersed in the molten metal. 8 and 9 (A) (B) (C) show a second embodiment of the metal melt container according to the present invention, and FIG. 8 is a plan view of the heater device immersed in the melt. FIG. 9 (A) is a cross-sectional view of the heater device, FIG. 9 (B) is a side view of the heater device, and FIG. 9 (C) is a perspective view of the heater device. FIG. 10 shows a third embodiment of the molten metal container according to the present invention, and is a schematic cross-sectional view of a main part of a state where the heater device is immersed in the molten metal. FIG. 11 shows a fourth embodiment of the molten metal container according to the present invention, and is a schematic cross-sectional view of the heater device immersed in the molten metal. In the figure, 1 is a tundish (container body), 6 is a first heater device, 7 is a layered heating element, 8 is a plate-shaped electrode portion, and 9 is a second.
Heater device, 10 is a layered heating element, 11 is a plate electrode part, 12 is a heater device, 13 is an electrode part, 14 is a heating element, 15 is a heating device, 18 is a heater device, 18 is a heating device, 19 is an electrode part, and 20 is heating. A body, 21 is a heater device, 22 is an electrode part, and 23 is a heating element.

Claims (6)

[Claims] 1. A container main body for holding a molten metal, at least one of which is comprised of an electrode part immersed in the molten metal held by the container main body and a heating element made of conductive ceramics for covering the electrode part. A metal melt container having a heating unit, comprising: a heater device, wherein a voltage is applied between the electrode portion and the metal melt to energize the heating element to generate heat. 2. A molten metal container having a heating unit according to claim 1, wherein the heater device comprises a plate-shaped electrode portion and a layered or plate-shaped heating element that covers the electrode portion. 3. A metal melt container having a heating part according to claim 1, wherein the heater device comprises a rod-shaped electrode part and a heating element covering the electrode part. 4. A metal melt container having a heating part according to claim 1, wherein the heater device comprises a plate-shaped electrode part and a heating element which covers the electrode part from both sides in the thickness direction. 5. A molten metal container having a heating portion according to claim 1, wherein the electrode portion is made of carbon or silicon carbide. 6. The container body is a tundish used in a continuous casting method, and has a discharge port for temporarily storing the molten metal injected from above and discharging the molten metal. Molten metal container with the described heating part