JPH06552U - Electric heating type immersion nozzle for continuous casting - Google Patents

Abstract

(57) [Summary] [Purpose] Prevents nozzle clogging of continuous casting immersion nozzles. [Structure] In a nozzle refractory body 1, a sheet-like energization heating resistor 2 extending from an upper portion of the body 1 to a portion below a molten steel outlet 4 is provided.
To bury. Direct current is applied to the heating resistor 2 to generate heat,
The temperature of the nozzle refractory body 1 is increased. Prevents clogging of nozzles and non-metallic inclusions due to temperature drop of molten steel, eliminating nozzle clogging.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an electric heating type immersion nozzle for continuous casting capable of preventing nozzle clogging.

[0002]

[Prior art]

 Along with the progress of continuous casting technology, we have started casting one after another by changing the ladle with the aim of further improving productivity. For this reason, the pouring time per pouring nozzle becomes long, and nozzle clogging due to impurities in the molten metal poses a problem. Furthermore, in order to promote the equiaxed crystallization of the slab, it is necessary to lower the temperature of the molten metal as much as possible, but at this time, the immersion nozzle is blocked by the metal, and the degree of superheat of the molten metal must be increased. It was

Therefore, for example, nozzle heating by induction heating as disclosed in Japanese Patent Laid-Open No. 59-202143 has been used to solve the above problems. However, in order to heat the nozzle by induction heating, a water-cooling coil and a high-frequency power source are required, which is not only a large-scale installation, but also a water-cooling coil is required in the immediate vicinity of the molten metal, and if the coil seal breaks. There is a danger of steam explosion, which hinders industrialization.

Further, nozzle heating by direct energization to the nozzle as disclosed in the publications of JP-A-63-56349, JP-A-63-56350 and JP-A-63-56351 is disclosed. ing. However, when electricity is directly applied to the nozzle, a current path is generated in the molten metal inside the nozzle because the metal melt inside the nozzle has a higher electric conductivity. In this case, the molten metal in the nozzle may or may not be filled due to the molten metal flow inside the nozzle, so that the current path in the molten metal may also occur in the horizontal direction, which not only complicates but also becomes unstable in terms of time and heating efficiency. There was a problem above. In addition, it is not possible to obtain the optimum nozzle temperature distribution to prevent nozzle clogging, and increasing the amount of heat generation increases the amount of melt damage to the outer wall of the nozzle due to the molten metal, leading to a reduction in nozzle life and a continuous hindrance to casting. was there.

[0005]

[Problems to be solved by the device]

 The present invention not only solves the above problems and can suppress the adhesion of metal and non-metallic inclusions to the inner wall of the nozzle with relatively simple equipment, but preferably controls the temperature distribution of the nozzle. By doing so, it is an object of the present invention to provide a submerged nozzle for continuous casting, in which melt damage of the outer wall of the nozzle due to the molten metal is not promoted even by nozzle heating.

[0006]

[Means for Solving the Problems]

 Means for Solving the Problems The present invention for achieving the above object provides an electric heating type immersion casting nozzle for continuous casting, which has an appropriate width in the nozzle refractory body from the upper portion of the nozzle refractory body to the lower portion of the molten steel outlet. The sheet-like energization heating resistors are paired in the vertical direction, the lower ends are connected and buried, and the energization terminals are attached to the portions of the energization heating resistors that are opposite to each other near the upper ends. It is an electric heating type immersion nozzle for continuous casting.

In the present invention, it is preferable to embed an energization heat-generating antibody having a different heat generation distribution in the height direction of the nozzle refractory body.

[0008]

[Action]

 The continuous casting dipping nozzle of the present invention has a sheet-like heating resistor inside the nozzle refractory body, and is heated from the inside of the nozzle refractory body by applying a DC voltage thereto. Since the heat generation amount Q is determined by the current value I and the electric resistance R of the heating element as described later, the heat generation amount of the entire nozzle adjusts the current value I.

Further, preferably, the distribution of the heat generation amount is controlled by increasing the electric resistance R of the heating resistor at a position where a large amount of heat generation is required and decreasing the electric resistance R at a position where a small amount of heat generation is desired. You can As described above, the nozzle refractory body is internally heated by passing a direct current through the conductive sheet heating element in the continuous casting immersion nozzle of the present invention. The heat generation amount Q at this time is estimated as Q = IR ² from the flowing current value I and the electric resistance R of the conductive heating element.

In order to reduce the deposits in the nozzle refractory body, it is desirable that the temperature of the inner wall of the nozzle be uniform, but if the nozzle refractory body is immersed in the molten metal, As shown schematically in FIG. 2, the heat flow is such that the heat held by the molten metal 7 in the mold 9 from the lower end of the nozzle refractory body 1 of the continuous casting immersion nozzle attached to the lower part of the tundish 8. Movement occurs and heat is dissipated into the atmosphere. Therefore, the temperature of the molten metal 7 passing through the nozzle refractory body 1 is lowered, and the temperature is lower than that of the surrounding molten metal 7 in the lower portion of the nozzle refractory body 1, which promotes adhesion of metal and non-metallic inclusions. Will be. In addition, 5 shows a heat transfer direction, 6 shows a mold powder.

Therefore, by embedding the sheet-like heat generating resistor 2 having a heat generation amount distribution due to the change in thickness as shown in FIG. 1 in the nozzle refractory body 1, heat from the lower end of the nozzle refractory 1 to the upper side can be increased. By lowering the movement, the temperature drop at the lower end of the nozzle refractory 1 is suppressed, and the adhesion of metal or non-metallic inclusions is prevented. The distribution of the heat generation amount can be adjusted by the electric resistance value of the heat generating element. For example, in the central part of the nozzle where a large amount of heat is required due to large heat dissipation, the cross-sectional area of the sheet heating element 2 is reduced to reduce the electric The resistance should be increased and the amount of heat generated should be increased. The heating resistor 2 can be inserted into the nozzle refractory body 1 by embedding graphite or the like before manufacturing (pressing) the nozzle.

[0012]

【Example】

 Using the immersion nozzle for continuous casting of the present invention, a continuous casting experiment was performed on molten steel containing Ti-containing stainless steel (Fe-17% Cr-0.2% Ti) for three consecutive times (80 ton ladle x 3 ch). The shape and dimensions of the heating element inside the used nozzle body are schematically shown in FIGS. 1 (a) and 1 (b).

That is, as shown in FIGS. 1 (a) and 1 (b), the sheet-like energization heating resistors 2 extending from the upper part of the nozzle refractory body 1 to below the pair of molten steel outlets 4 are arranged vertically. It is also embedded with the lower end connected. Further, current-carrying terminals 10 are provided near the upper ends of the current-carrying heating resistors 2 at positions facing each other, one of which is connected to the + side and the other of which is connected to the-side DC power supply. As for the thickness of the sheet-like energization heating resistor 2, the thickness is reduced to 2 mm in the upper part where a large amount of heat is required and the thickness of the lower part where the amount of heat may be reduced gradually increases from 2 mm to 4 mm. The bottom of the molten steel outlet 4 is 4 mm.

In this case, as the sheet-like energization heating resistor 2, one made of alumina graphite is used, and a DC voltage of 30 V is applied between A and B of the pair of energization terminals 10 during preheating of the tundish. A current was passed in the direction indicated by arrow 3. As a comparative example, an experiment was conducted using a conventional continuous casting immersion nozzle having the same size and shape and having no heating element. In this equipment, the stopper opening of the tundish is controlled so that the level of the mold surface is constant.Therefore, if the amount of deposits on the inner wall of the nozzle increases, the opening of the stopper increases, so the amount of deposits on the nozzle increases. Can be evaluated by changing the stopper opening.

FIG. 3 shows the change in the stopper opening when the conventional nozzle is used for comparison with the case of using the nozzle of the present invention by casting length. As is apparent from FIG. 3, the use of the nozzle of the present invention reduces the amount of deposits on the nozzle and reduces the change in the stopper opening. Furthermore, when the nozzles used after the triple casting were collected, cut at a vertical plane including the center axis, and the thickness of the metal and non-metallic inclusions adhering to the nozzle was measured, the amount of adhering substances on the nozzle Is less than 1/2 of that of the comparative nozzle, which is in agreement with the change in stopper opening shown in FIG. Also, when the deposits increase on the nozzle refractory body and the nozzle clogging worsens, the flow inside the mold becomes unstable, which promotes the entrainment of mold flux, and part of the deposits on the nozzle refractory body during casting. It is known that peeling occurs and this is trapped on the surface layer of the slab, resulting in product defects.

Therefore, the surface defect index of the hot-rolled sheet due to defects in the surface layer of the slab when the nozzle of the present invention is used and when the conventional nozzle is used for comparison is shown in FIG. From FIG. 4, by using the nozzle of the present invention, product defects were reduced, and not only productivity was improved but also product quality was improved.

[0017]

[Effect of device]

 By using the immersion nozzle for continuous casting according to the present invention, it is possible to suppress clogging of the nozzle while suppressing the amount of melt damage on the outer wall of the nozzle, and to increase the number of continuous casting continuously, thus improving productivity. To be done. Further, the fluctuation of the molten metal flow in the mold due to the nozzle clogging becomes small, so that the product quality can be improved.

[Brief description of drawings]

1 is a sectional view showing a structure of the present invention, (a) is a vertical sectional view, and (b) is a sectional view taken along line CC 'of FIG.

FIG. 2 is a schematic view showing a heat flow around a normal immersion nozzle.

FIG. 3 is a line graph showing changes in stopper opening change according to the present invention and a conventional example.

FIG. 4 is a graph showing a defect occurrence ratio of the present invention and a conventional hot-rolled sheet.

[Explanation of symbols]

 1 Nozzle refractory body 2 Electric heating resistor 3 Direction of current 4 Molten metal discharge port 5 Heat transfer direction 6 Mold powder 7 Molten metal 8 Tundish 9 Mold 10 Conductive terminal

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[Procedure amendment]

[Submission date] July 30, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (2)

[Scope of utility model registration request] 1. An electric heating exothermic dipping nozzle for continuous casting, wherein a sheet-like electric heating resistor having an appropriate width extending from an upper portion of the nozzle refractory body to a lower portion of the molten steel outlet is provided in the nozzle refractory body. Immersion for continuous casting of electric heating type, characterized in that they are buried in a pair in the same direction with the lower ends connected, and the electric terminals are attached to the electric heating resistors at positions facing each other near the upper ends of the electric heating resistors. nozzle. 2. The immersion nozzle for continuous casting according to claim 1, wherein an energization heating resistor having a different calorific value distribution in the height direction of the nozzle refractory body is embedded.