KR20010058258A - Apparatus for evaluating the crystallization characteristics of mold flux - Google Patents

Abstract

PURPOSE: A device for valuating crystallization feature of mold flux is provided to observe congelation and crystallization of mold flux generated under a temperature distribution similar to a real continuous molding condition and simultaneously measure a heat transfer rate through a copper foil and an interfacial thermal resistance between the mold flux and a mold. CONSTITUTION: A device for valuating crystallization feature of mold flux includes a furnace(10) for melting mold flux(100), a mold(20) receiving the mold flux, a plurality of thermocouples(P1,P2,P3,P4) mounted on the mold, and a data recording device(30) electrically connected to the thermocouples. The data recording device electrically connected to the thermocouples measures a heat transfer rate transferred to the mold through the mold flux and an interfacial thermal resistance between the mold flux and the mold.

Description

Apparatus for evaluating mold flux crystallization characteristics {APPARATUS FOR EVALUATING THE CRYSTALLIZATION CHARACTERISTICS OF MOLD FLUX}

The present invention relates to a test apparatus designed to simulate the solidification and crystallization behavior of a mold flux used for heat transfer control and improved lubricity during continuous casting of steel, in particular, in a mold flux under a temperature distribution similar to that of an actual continuous casting process. The present invention relates to an apparatus for evaluating a mold flux crystallization characteristic, which enables to quantitatively grasp the effect of the crystallization characteristic of the mold flux on the amount of heat by simultaneously measuring the amount of heat transfer through the copper plate while solidifying.

In general, the mold flux is an important subsidiary material having a role of controlling the amount of heat transfer from the solidification shell to the mold while reducing the friction force between the solidification shell and the copper mold in the continuous casting process of steel.

In recent years, as the casting speed is gradually increased in the continuous casting process of the integrated steelworks, the nonuniformity of the thickness of the initial solidification layer is increased, and thus, the occurrence of cracks in the longitudinal direction on the surface of the cast steel increases. Therefore, it is an important task to lower the heat transfer amount and to secure a uniform solidification shell by controlling the physical properties of the mold flux.

The greatest influence on the heat transfer through the mold flux during continuous casting is the solidification and crystallization behavior of the mold flux. That is, as shown in FIG. 1, the mold flux 100 completely dissolved at high temperature is sandwiched between the solidification shell 110 and the mold 120 in the form of a film and then solidified from the mold side having a low temperature from the glass 102. It is turned into crystalline 104. Since the mold flux 100 is reduced in volume as the phase transformation from the glassy 102 to the crystalline 104, the air gap due to the volume shrinkage between the copper (Cu) mold 120 and the crystalline 104 mold flux film ( air gap) 130 is generated, which causes a great disruption of heat transfer through the mold flux 100.

Therefore, for the high speed casting operation, the chemical composition of the mold flux 100, in particular, the basicity represented by CaO / SiO ₂ is adjusted to increase the ratio of crystal grains, thereby reducing the amount of heat transfer and suppressing the occurrence of surface cracks in the cast steel.

As described above, the crystallization behavior of the mold flux 100 has a great influence on the productivity of the continuous casting process and the quality of the cast, but the evaluation means and method thereof are not properly developed.

At present, the method for evaluating the crystallization characteristics of the mold flux in the mold flux manufacturer is to cool the liquid mold flux in a graphite crucible or pour it into a metal container such as iron or platinum, and then quench it and visually determine that there is much or little crystalline content. Stay on the level. However, this method has a big difference in the material and temperature distribution of the mold flux from the crystallization process of the mold flux in actual performance, and has a problem that the relationship between the crystallization behavior and the heat transfer amount cannot be investigated. It is difficult to actively use to improve quality and productivity through improvement.

The present invention is to solve the conventional problems as described above, the object of which is to evaluate the mold flux crystallization characteristics and at the same time to quantitatively determine the relationship between the crystallization characteristics and the heat transfer amount, the same material as the continuous casting mold After making a test mold consisting of two long sides and two short sides, the thermocouple insertion holes having different depths were processed on the long side and the short side to observe solidification and crystallization of the mold flux under a temperature distribution similar to actual operating conditions. In addition, it is to provide a mold flux crystallization characteristics evaluation apparatus that can simultaneously measure the heat transfer through the copper plate and the interface thermal resistance between the copper plate and the mold flux.

1 is a schematic cross-sectional view of a mold flux film sandwiched between a copper plate and a slab during continuous casting of steel;

2 is an overall configuration diagram of a mold flux crystallization characteristic evaluation apparatus according to the present invention;

3 is a detailed view of a mold in a mold flux crystallization characteristic evaluation apparatus according to the present invention;

Figure 4 is a graph showing the temperature change of the mold copper plate and the mold flux in the evaluation of the mold flux crystallization characteristics using the apparatus according to the present invention;

5 is a graph showing a change in heat quantity during evaluation of mold flux crystallization characteristics using the apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

10 ..... melting furnace 12 ..... high frequency coil

15 ..... Nozzle 20 ..... Mold

22 ..... bottom plate 30 ..... data logger

40 ..... stopper 100 ... mold flux

110 ... solidified shell 120 ... mold

130 ... Clearance P1, P2, P3, P4 .... Thermocouple

In order to achieve the above object, the present invention, in the test apparatus manufactured to simulate the solidification and crystallization behavior of the mold flux used for heat transfer control and improved lubricity during continuous casting operation of steel, And a mold receiving a mold flux therefrom, wherein the mold is equipped with a plurality of thermocouples, and is equipped with a data recording device electrically connected to the thermocouple so as to solidify the molten mold flux in the mold while being transferred to the mold through the mold flux. And a mold flux crystallization characteristic evaluation apparatus, characterized in that it is configured to measure the calorific value and the interface thermal resistance between the mold flux and the mold.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

The mold flux solidification characteristic evaluation apparatus 1 according to the present invention is composed of a melting furnace 10 and a mold 20 as shown in FIG. 2 as a whole.

The melting furnace 10 includes a high frequency coil 12 as a heating means, and the mold 20 is equipped with a plurality of thermocouples P1, P2, P3, and P4, and the thermocouple P1 ( P2), P3, and P4 are electrically connected to a data recording device 30 made of a small computer to provide the temperature data signal measured by each of them as an electrical signal.

Then, the data recording device 30 is based on these temperature signals, as described below, the heat transfer amount and the mold flux transferred to the copper plate of the mold 20 through the mold flux in an environment similar to the actual performance operating conditions Simultaneously calculate the interfacial thermal resistance between the and copper plates, and based on this, the heat transfer control capability of the mold flux can be easily measured and evaluated.

The melting furnace 10 maintains a predetermined time at a predetermined temperature after dissolving the mold flux 100, and then rapidly melts the molten mold flux 100 by the operation of the stopper 40. Pours into). The mold flux 100 is charged into a melting furnace 10 made of graphite crucible and heated / dissolved by a high frequency induction current, and inserts a thermocouple P5 into the lower part of the melting furnace 10 to input the amount of power input at the temperature read here. Will be adjusted.

The stopper 40 is also made of graphite and is linearly driven in an air cylinder 50 manner for injection into the mold 20. The thermocouple P6 is also inserted into the stopper 40, where the measured temperature is compensated by the temperature of the molten mold flux 100 and recorded.

3 shows a part of the mold 20 in detail. The mold 20 has a box-shaped structure composed of a total of five plates, two long sides, two short sides, and a bottom one. The material of the long sides and the short sides 21 is the same as that of the mold. Cu), and the bottom surface 22 is made of stainless steel of 18% Ni-8% Cr having a lower heat transfer coefficient than copper (Cu).

In the above, the thickness of the long side and the short side 21 part is set to the thickness of the long side and the short side 21 part in the range of 10 to 40 mm in order to adjust the surface temperature to between 300 and 350 ° C. which is the surface temperature of the copper plate during the continuous casting operation. The long side and short side 21 may be cooled by air or water cooling.

And, as shown in Figure 3, the long side and short side 21 is a hole for thermocouple insertion (hole) is processed. The hole has two deep and shallow pairs, and the heat transfer amount is obtained from the difference between the temperatures T1 and T2 of the thermocouples P1 and P2 inserted into the two holes by the following equation. do.

Q = k (T1-T2) / (d1-d2)

Where Q: heat transfer amount (Wm ^-2 ), k: thermal conductivity (Wm ^-1 K ^-1 )

T1, T2: Thermocouple measurement temperature (K), d1, d2: Depth of the hole where the thermocouple is inserted

Further, as shown in FIG. 3, a plurality of holes penetrating the long side and short side 21 plates are processed as required, and the inside of the mold flux 100 and the surface temperature T3 (T4) during solidification by the thermocouples P3 and P3. Measure The internal temperature (T4) of the mold flux (100) is used to predict the crystal phase of the mold flux (100) generated after solidification, and between the mold flux (100) and the copper plate from the surface temperature (T3) of the mold flux (100). The interfacial thermal resistance is obtained by the following equation.

R _INT = (T3-T _Cu ) / Q

Q: Heat quantity (Wm ^-2 )

T _Cu : Copper plate surface temperature (K) on mold flux (100) side

Here, since the copper plate surface temperature T _Cu of the mold flux 100 side cannot be measured directly, the measured temperature T1 and T2 of the copper plate and the depths d1 and d2 are used, and the temperature distribution of the long and short sides of the copper plate is linear. It is assumed that it is an enemy.

In addition, the purpose of this apparatus is to observe the crystallization behavior of the mold flux 100 under a temperature distribution similar to the actual performance conditions, so that the maximum attained temperatures of the long and short side 21 plates during the test are the copper surface temperature during the actual performance. The thickness of the long side and short side 21 plates is set to be similar to, depending on the amount of mold flux 100 used for the test.

Referring to the operation and effects of the present invention configured as described above are as follows.

First, a suitable amount of the mold flux 100 is charged into the melting furnace 10 made of the graphite crucible of FIG. 2, and then the mold flux 100 is dissolved by a high frequency heating method. Then, the temperature of the molten mold flux 100 is determined from the temperature of the thermocouples P5 and P6 inserted into the lower part of the melting furnace 10 and the stopper 40 and maintained at a desired temperature for a predetermined time. When the molten mold flux 100 reaches a state of complete melting and component homogenization, the stopper 40 is vertically lifted by the air cylinder 50 to lift the molten mold flux 100 through the nozzle 15 through the melting furnace 10. Inject into the mold 20 located at the bottom.

After injection into the mold, the temperature change of the mold copper plate and the mold flux 100 is measured by thermocouples P1, P2, P3, and P4 until the complete solidification and crystallization ends. ) And the interface thermal resistance value between the copper plate.

Therefore, the heat transfer amount transmitted to the copper plate through the mold flux 100 and the interface heat between the mold flux 100 and the copper plate through the mold flux crystallization characteristic evaluation apparatus 1 according to the present invention in an environment similar to the actual operating conditions. By simultaneously measuring the resistance, the effect of easily measuring / evaluating the heat transfer control capability of the mold flux 100 can be obtained.

(Example)

The mold flux crystallization characteristic evaluation apparatus 1 produced by the present invention was used to test two types of mold fluxes 100 used in the actual performance process. Physical properties including the chemical composition of the test target mold flux 100 are shown in Table 1, the general test conditions are shown in Table 2, and the test results are shown in FIGS. 4 and 5.

Chemical composition (mass%) CaO SiO ₂ Na ₂ O F 30% 29% 15% 7% Physical properties Solidification Temperature (Celsius) Softening Temperature (Celsius) Viscosity at 1300 degrees 1129 degrees 1000 degrees 0.72poise

Injection Mold Flux Mold Flux Melting Temperature Retention time after melting Specimen size after solidification 400 grams 1300 degrees 20 minutes Width: 50mm Thickness: 40mm Height: 80mm

As shown in Fig. 4, the temperature (Tcu) of the copper plate is rapidly increased after the injection of the molten mold flux 100, indicating a maximum temperature in the range of 300-350 ° C. This value is in good agreement with the surface temperature of the copper plate during actual performance of the test. It can be seen that the temperature distribution conditions given in Fig. 11 are similar to those of actual performance.

Based on the temperature data in FIG. 4, the heat transfer amount Q and the interfacial thermal resistance R are calculated and shown in FIG. 5. In FIG. 5, after about 3 seconds have passed after the injection of the molten mold flux 100, the heat transfer amount indicates a maximum value, and then rapidly decreases, and after about 30 seconds, the decrease trend becomes smooth. The change in heat transfer amount corresponds to the change in interfacial thermal resistance. In other words, immediately after the injection of the molten mold flux 100, since the mold flux 100 has not yet crystallized, the interface thermal resistance does not occur, but the interface thermal resistance rapidly increases with time, and the interface thermal resistance increases after about 30 seconds. This time point is exactly the same as the time when the heat trend decreases.

From this fact, it is determined that the crystallization of the mold flux 100 under this experimental condition is completed after a large amount of 30 seconds after the injection of the molten mold flux 100.

As described above, if the mold flux 100 crystallization characteristic evaluation apparatus according to the present invention is utilized, the amount of heat transferred to the copper plate through the mold flux 100 and the mold flux 100 in an environment similar to the actual performance conditions of operation. Since the interface thermal resistance between the and the copper plate can be easily measured / evaluated at the same time, the physical properties of the mold flux 100 can be improved, thereby improving the productivity of the continuous casting industry and improving the quality of the cast steel.

Claims (4)

In a test apparatus manufactured to simulate the solidification and crystallization behavior of the mold flux 100 used for heat transfer control and improved lubricity during continuous casting operation of steel, A melting furnace 10 for dissolving the mold flux 100 and a mold 20 receiving the mold flux 100 therefrom, wherein the mold 20 includes a plurality of thermocouples P1, P2, P3, P4 And a data recording device 30 electrically connected to the thermocouples P1, P2, P3, and P4 to solidify the molten mold flux 100 in the mold 20 and to mold flux 100. Mold flux crystallization characteristics evaluation apparatus, characterized in that configured to measure the amount of heat transfer to the mold (20) and the interface thermal resistance between the mold flux (100) and the mold (20) through. The method of claim 1, wherein the molten mold flux 100 in the melting furnace 10 is injected into the mold 20 through the nozzle 15, the nozzle 15 is vertically moved up and down by the air cylinder 50 Mold flux crystallization characteristics evaluation apparatus characterized in that the opening and closing is made by the stopper (40). According to claim 1, In order to measure the long side and short side (21) temperature of the copper plate constituting the mold 20, two deep and shallow pairs of holes in the thermocouple for measuring the temperature (T1) (T2) ( P1) and P2 are mounted, and a plurality of through holes are formed to thermocouple P3 and P4 for measuring the inside and the surface temperatures T3 and T4 of the mold flux 100 during the solidification of the mold flux 100. Mold flux crystallization characteristics evaluation apparatus characterized in that the mounting. The thickness of the long side and short side 21 portions of the mold is set so as to adjust the surface temperature Tcu between 300 and 350 ° C. which is the surface temperature of the copper plate during the continuous casting operation. An apparatus for evaluating mold flux crystallization characteristics, characterized in that the thickness is in the range of 10 to 40 mm and the long and short sides are cooled by air or water cooling.