JPH0320590A - Melt container - Google Patents

Abstract

PURPOSE:To keep a melt in a predetermined temperature region by providing an electrode part on at least part of an outer surface part of a container body formed with a conductive ceramics, and applying voltage across the metal melt and the electrode part to drive a current in the thickness direction of the container body for heating of the container body. CONSTITUTION:A melt holding furnace 1 comprises a container body 12 having a holding space for holding a 3-6kg steel melt and an electrode part 14. The container body 12 is formed with a conductive ceramics. The iron steel melt is melted to about 1550 deg.C and is transferred into the holding space 10. Further, a conductive wire 26 is connected to a power supply and a conductor wire 30 which is fixed to a rod-shaped electrode part 16 with a band 28 is connected to the power supply. Additionally, a thermocouple 20 is set to a control device. In this situation, a predetermined voltage (about 120V) is applied between the electrode part 14 and the electrode part 16 to drive a current (50A) in the thickness direction of the container body 12. Thus, the entire of the container body 12 is gradually heated to keep the melt in a predetermined temperature region.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a molten metal holding container.

[Prior Art] Molten metal holding containers, for example, molten metal holding furnaces, have been used to maintain high temperature molten metal melted in a melting furnace in a predetermined temperature range before sending it to a subsequent process.

This molten metal holding furnace is made of iron! l8! A refractory layer made of a refractory material is lined with the furnace shell to form a holding space, and a coil is embedded in the refractory layer.

In use, the high-temperature molten lagoon melted in the melting furnace is temporarily held in the holding space of the molten metal holding furnace, and in that state, a high frequency current is passed through the coil to generate a secondary induced S current in the molten metal.
This resistance heat maintains the melt lagoon within a predetermined temperature range.

[Problems to be Solved by the Invention] The present invention provides a molten metal holding container that adopts a method different from the above-described molten metal holding furnace, that is, a molten metal holding container whose entire container body is made of conductive ceramics. The task is to do so.

[Means for Solving the Problems] The present inventor has spent many years intensively researching a heating device that is immersed in molten metal to heat the molten metal.

As a result, we have recently developed an hO heating device for immersion in molten metal, which consists of a cylindrical heating element made of conductive ceramics and a rod-shaped electrode section mounted on the inner periphery of the heating element. This heating device applies a voltage between a rod-shaped electrode portion and the molten metal to flow a current in the thickness direction of the heating element, thereby causing the conductive ceramic of the heating element to generate heat.

As a result of further research into such a heating device, the present inventor found that the inner circumference of the cylindrical heating element has a higher calorific value per unit volume. The reason is presumed to be as follows. That is, in FIG. 6, the heating element Q is considered to be formed from a large number of shell layers (R1 to Rn) divided in the thickness direction.

Here, the thickness of each shell layer (Rl to Rn> is ΔY, the specific resistance value of the material forming the heating element Q is ρ, and the heating element Q
The resistance Rn of each shell layer is basically expressed by the formula (1>) since the electric current flows in the thickness direction from the inside to the outside.

Rn=(ρ-ΔY)/(2π-Yn-father)=(1) Therefore, it is considered that the smaller the radius Yn of the inner shell layer, the higher the resistance.

Further, the total resistance can be obtained by integrating the equation (1) from the inner diameter Yi to the outer diameter To.

R- (ρ/2π father) ・Qn (To/Y i )
- (2) The present inventor further advanced this knowledge and completed the molten metal holding container of the present invention in order to effectively utilize the inner circumferential portion of the cylindrical heating element which has a high calorific value. .

That is, the molten metal holding container according to the present invention includes a bottomed container body that has a holding space for holding molten metal and is entirely made of conductive ceramics, and a container that is provided on at least a part of the outer surface of the container body. It is characterized by having a structure in which a voltage is applied between the molten metal and the electrode part to flow a current in the thickness direction of the container body, thereby causing the container body to generate heat.

The volume of the holding space can be set as necessary for small, medium, or large containers, taking into account the strength of the container body, etc., but generally the molten steel is 1 to 50 kg, especially 3 to 6 kg. The volume can be set to a capacity that can be held.

The container body is made of conductive ceramics. Conductive ceramics are electrically conductive in the operating temperature range. The type of conductive ceramics and their blending ratio are determined not only by their heat generation properties but also by their resistance to metal melting, thermal shock resistance,
It is necessary to select the material in consideration of various factors such as oxidation resistance, corrosion resistance, aging resistance, etc., and it can be selected from among oxide-based, nitride-based, boride-based, etc. As conductive ceramics, it is desirable to have a high specific resistance value in order to secure the required calorific value because the resistance of molten metal is low, and in this case, the specific resistance value should be 10 cm or more at around 1500 ° C. In particular, one having a specific resistance value of 200 Ωcm or more, especially about 360 Ωcm, can be used. Note that the specific resistance value of the conductive ceramic can be changed by blending a non-conductive ceramic or a 111 conductive ceramic with the conductive ceramic and adjusting the blending ratio.

When heating molten steel, magnesia (MgO) and zirconia (ZrOz) are used as conductive ceramics.
>, alumina (A52203), a mixture of magnesia and zirconia, and a mixture of magnesia, zirconia, and alumina can be used. Here, magnesia usually does not have electrical conductivity at around room temperature, but takes on the required electrical conductivity at around 1,500 to 1,650° C., which is the heating temperature range of molten steel.

When a mixture of magnesia and zirconia is used as the conductive ceramic, the blending ratio is appropriately selected taking into consideration the required resistance value, etc.
Magnesia is preferably 60 to 100%, particularly preferably 85 to 95%, zirconia is preferably O to 40%, particularly 5 to 25%, alumina is preferably O to 40%, particularly 2.5 to 15%, calcia (Cab) , one or more materials mainly containing chromia, beryllia, toria, ceria,
It can also be blended in a content of 30 to 60% or more. In order to reduce the amount of ceramics, carbon powder, graphite, etc. may be added to suitably contain the carbon amount, for example, 1 to 5% by weight.

Furthermore, depending on the melting point of the metal, conductive ceramics such as silicon carbide (SiC), lanthanum chromate (LaCr03), and beryllium mide (B
ed), thorium oxide (ThO2), molybdenum silicide (MoSi2), and titanium nitride (TiN),
Materials containing titanium carbide (TiC) or the like as a main component can also be used.

For reference, the relationship between the operating temperature and specific resistance of conductive ceramics is shown in FIGS. 4 and 5.

In addition, in the case of molten steel, the target value of the specific resistance value of the ceramic is preferably 200 Ωcm or more in the operating temperature range.

The particle size of the conductive ceramic may affect the resistance value, so the maximum particle size is preferably about 1 to 5 mm, particularly about 1.5 to 3 mm. The main reason for this is that if the particle size is too large, the current tends to become uneven.

Note that it is also possible to adjust the heat generation characteristics between the lower and upper parts by changing the particle size or the type of conductive ceramic between the lower and upper parts of the container body. It is also possible to divide the container body in the thickness direction and change the particle size between the inner layer and the outer layer, or change the type of conductive ceramic to make the heat generation characteristics different. In this case, the inner layer that comes into direct contact with the molten metal can be made of a material that has good erosion resistance against the molten metal and a high electrical resistance value. Since the outer layer, which does not come into contact with the molten metal, does not need to be given as much consideration as the inner layer in terms of corrosion resistance to the molten metal, the degree of freedom in selecting the type of conductive ceramic and the proportion of the conductive ceramic can be expanded. In this case, an intermediate layer made of carbon, a molten low-melting point metal, or the like can be interposed between the inner layer and the outer layer to ensure electrical contact between the inner layer and the outer layer.

The container body according to the present invention can be manufactured, for example, as follows. That is, after thoroughly pulverizing and mixing the raw ceramic powder with a ball mill, vibration mill, etc. and adjusting it to a predetermined composition,
A slurry made by mixing raw ceramic powder and water is poured into a mold cavity and formed into a container shape to obtain a container body.The container body is then heated to a predetermined temperature and sintered. implement. Prior to the sintering process, a curing process and a drying process are performed if necessary. Note that in a certain shaping process, vibration or shaping can be performed while applying vibration to the mold.

In the molten metal holding container according to the present invention, the electrode portion is for passing electricity through the container body, and is provided on the entire or part of the outer surface of the container body.

The material of the electrode part is selected in consideration of electrical conductivity, heat transfer coefficient, etc. In this case, the heat transfer coefficient can be reduced in order to increase the electrical conductivity and reduce heat transfer loss.

However, in general, the higher the conductivity of conductive materials, the higher the heat transfer rate. The apparent degree of heat transfer of the electrode portion can be reduced while ensuring the required conductivity of the electrode portion by appropriately combining materials with small . Further, the electrode portion can also be formed of conductive ceramics with low electrical resistance. In this case, the electrode portion and the container body may be integrally formed.

In addition, when equipping the container body with the electrode part, means such as tightening of a band, bolting, screwing, fitting, etc. can be adopted, for example.

[Example] A first example in which a molten metal holding container according to the present invention is applied to a crucible type molten metal holding furnace will be described with reference to FIGS. 1 and 2.

(Configuration of Embodiment) This molten metal holding furnace 1 includes a bottomed container body 12 having a holding space 10 for holding 3 to 6 kilograms of molten steel, and an electrode portion 14 provided on the outer surface of the container body 12. The container body 12 is entirely made of conductive ceramics.In other words, the container body 12 is made of 90% magnesia, 5% zirconia, 5% alumina, and 5% alumina by weight. It is made of mixed ceramics containing impurities.A rod-shaped electrode part 16 and a thermocouple holding tube 18 are inserted into the holding space 10 of the container body 12 via a stand (not shown).The rod-shaped electrode part 16 is made of carbon The thermocouple holding tube 18 has a thermocouple 2 for measuring the temperature of the molten metal.
0 is inserted.

The N-pole portion 14 is formed by laminating many layers of carbon paver. The electrode section 14 is provided on the outer surface of the container body 12 via a stainless steel tightening band 22 and covered with a heat insulating member 24 . Note that the heat insulating member 24 is omitted in FIG. Here, the electrode part 14 and the container body 1
The tip of a conductive wire 26 is inserted between the two. The tightening band 22 is formed of a band main body 22a and a tightening tool 22b. The heat insulating member 24 is formed by laminating many layers of alumina ceramic vapor.

By the way, the total resistance R (Ω) of the container main body 12 is basically determined by the specific resistance value ρ (Ωcm) of the conductive ceramic forming the container body 12, the wall thickness t (cm) of the container body 12, and the container body. It is determined by the area 3 (cm2) of 12.

The container body 12 of the melt holding furnace 1 of this example was manufactured as follows. That is, an adjustment step in which raw ceramic powder is adjusted to a predetermined blending ratio and then water is added to form a slurry;
A molding process in which the slurry is poured into a mold cavity and molded into a container shape, a drying process in which the container-shaped molded body is removed from the mold, cured, and further dried at 150°C for a predetermined time, and the dried molded body is heated at 1650°C. A sintering process of heating and sintering for a predetermined period of time was performed in order. Note that the maximum particle size of the raw ceramic powder used in the adjustment step was about 3 mm.

In using the above-mentioned melting and holding furnace 1, first,
The flame of a burner is applied to the inner surface of the container body 12 to preheat the inner surface of the container body 12 to about 700° C. to 1000° C. The above-mentioned preheating makes it possible to ensure the conductivity of the container body 12, which becomes conductive only in a high temperature range because the main component is magnesia.

Then, melt the steel (carbon steel) in advance in a high frequency furnace to 1550
The high temperature molten metal is melted at a temperature of about
It is transferred and held in the holding space 10 of. Thereafter, the conducting wire 26 is connected to a power source, the conducting wire 30 fixed to the rod-shaped electrode portion 16 with a band 28 is connected to the power source, and the thermocouple 20 is connected to the power source.
Set in the control device.

In this state, a predetermined voltage (approximately 120 V) is applied between the electrode part 14 and the electrode part 16, and a current (50 A) is caused to flow in the thickness direction of the container 12.

As a result, the entire container body 12 gradually generates heat (heat generation at
6 KW>, the carbon steel molten metal (10 kg>) held in the holding space 10 is gradually heated from all around, and the molten metal is maintained within a predetermined temperature range.

In this embodiment, a conductive heating layer made of carbon powder may be interposed at the boundary between the container main cover 12 and the electrode portion 14. The conductive heating layer functions as a current diffusion layer and a thermal expansion RLI layer, so it increases the electrical contact between the container body 12 and the electrode section 14 as well as the thermal contact. This is advantageous in suppressing local overheating.

(Effects of Example) In this example, the molten metal can be maintained within a predetermined temperature range using the calorific value of the container body 120. Further, since the entire container body 12 is heated, the molten metal is heated from the periphery of the entire molten metal, which is advantageous in uniformly heating the entire molten metal.

In this embodiment, it is possible to ensure that the molten metal in the container main suspension 12 remains stationary, and inclusions can be easily floated to the surface of the molten metal. In this regard, in conventional molten metal holding furnaces in which a high-frequency current is passed through a coil, the molten metal is actively stirred due to the secondary induced current flowing through the molten metal. This is different from the case where it does not float to the surface and cannot be separated from the molten metal. If a highly clean molten metal whose temperature is precisely controlled in the container body 12 and whose inclusions have been removed is used in the subsequent process, it is advantageous to improve the quality of the product.

Furthermore, if the container main suspension 12 is preheated before charging the molten metal into the holding space 10, it is possible to prevent the container body 12 from rapidly heating when the molten metal is directly charged into the holding space 10. The occurrence of cracks in the container body 12 can be suppressed as much as possible.

[Other Examples] A second example in which the molten metal holding container according to the present invention is applied to a molten metal holding furnace will be described with reference to FIG. 3.

This molten metal holding furnace 4 is formed of a bottomed container 42 having a holding space 40 for holding molten metal, and a cylindrical electrode portion 44 provided over almost the entire outer surface of the container body 42. There is. The container body 42 is entirely made of conductive ceramics. That is, the container body 42 is made of a mixed ceramic containing unavoidable impurities such as 90% magnesia, 5% zirconia, and 5% alumina by weight. A ring-shaped flange portion 42a is formed on the upper surface of the container body 42 to avoid contact between the molten metal and the electrode portion 44. The electrode portion 44 is made of a mixture of alumina and graphite.

A threaded portion 42c is formed on the outer surface of the container body 42. A threaded portion 44C is also formed on the inner surface of the electrode portion 44. The container body 42 and the electrode part 44 are temporarily assembled by screwing the threaded part 44c and the threaded part 42c together. Further, expanded graphite is interposed between the outer surface of the container main body 42 and the inner surface of the electrode section 44. When the container main body 12 generates heat and rises in temperature during use, the expanded graphite expands, and therefore the degree of contact between the container main body 12 and the electrode section 44 can be further improved.

Furthermore, as shown in FIG. 3, a rod-shaped electrode portion 46 is inserted into the holding space 40 of the container body 42 via a stand (not shown). The rod-shaped electrode portion 46 is formed of a carbon cord rod. In this embodiment, the conducting wire 48 is fixed to the outer surface of the electrode section 46 with a band 50, the conducting wire 52 is fixed to the outer surface of the electrode section 44 with the band 54, and the conducting wire 48 on the electrode section 46 side and the conducting wire 48 on the electrode section 44 side are fixed. The conductive wire 52 is connected to a power source and electricity is applied between the electrode portion 46 and the electrode portion 44 to cause current to flow in the thickness direction of the container body 42 and cause the container body 42 to generate heat.

In this second embodiment as well, since the entire container body 42 is made of conductive ceramics, basically the same effects as in the first embodiment can be obtained, which is advantageous in uniformly heating the molten metal.

[Effects of the Invention] According to the wetting and holding container according to the present invention, the melt can be maintained within a predetermined temperature range using the calorific value of the container body.

Further, according to the molten metal holding container according to the present invention, since the entire container body is made of conductive ceramics, the entire container body generates heat, which is advantageous for uniformly heating the molten metal. Using the molten metal whose temperature has been adjusted in the container body in a subsequent process is advantageous in improving the quality of products manufactured in the subsequent process.

[Brief explanation of the drawing]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a perspective view of the molten metal holding furnace in a heated state with the heat insulating member omitted, and FIG. 2 is a plan view of the same. It is. FIG. 3 is a sectional view of a molten metal holding furnace showing a second embodiment of the present invention. FIGS. 4 and 5 are graphs showing the relationship between the operating temperature and specific resistance value of each material. FIG. 6 is a perspective view showing the concept of dividing a conventional heating element in the thickness direction. In the figure, 10 is a holding space, 12 is a container main body, 14 is an electrode section, 40 is a holding space, 42 is a container main body, and 44 is an electrode section.

Claims (1)

[Claims] (1) It is formed of a bottomed container body having a holding space for holding molten metal and made entirely of conductive ceramics, and an electrode part equipped on at least a part of the outer surface of the container body, A molten metal holding container characterized in that a voltage is applied between the molten metal and the electrode portion to flow a current in the thickness direction of the container body, thereby causing the container body to generate heat.