Method for testing melting performance of casting powder

Abstract

The invention provides a casting powder melting performance testing method. The casting powder melting performance testing method comprises the following steps: (1) selecting a heating furnace capable of simulating unidirectional heating of a crystallizer on site as a casting powder melting performance testing furnace; (2) selecting a porcelain boat with good thermal shock property and small reaction with the casting powder as a casting powder melting property test crucible, placing the casting powder in the porcelain boat, and carrying out unidirectional heating at a furnace mouth of a casting powder melting property test furnace; (3) after the porcelain boat and the casting powder in the porcelain boat are completely cooled, the casting powder in the porcelain boat is taken out and screened with a 20-mesh sieve, the weight of powder slag under the 20-mesh sieve is G1, the weight of picked-out liquid slag is G2, and the balance is the weight G3 of a sintering part; (4) calculating the sintering index T1 of the casting powder according to the formula T1 = G3 / t * Q * (G1 + G2 + G3) * 100%; calculating the melting rate index T2 of the casting powder according to the formula: T2 = t * Q * G2 / (G1 + G2 + G3) * 100%; the ignition loss index T3 is equal to t * Q * [20-(G1 + G2 + G3)] / 20 * 100%, t is the heating and melting time of the casting powder in the porcelain boat, and Q is the initial weight of the casting powder in the porcelain boat.

Description

Technical Field

[0001] The present invention relates to the related technology of auxiliary materials for steelmaking continuous casting, and particularly relates to a method for testing the melting performance of mold powder. Background Art

[0002] Continuous casting mold powder is a powdery or small granular steelmaking auxiliary material, which is used to cover the surface of molten steel in the continuous casting mold. Under the high temperature action of the molten steel, the mold powder presents a solid-liquid two-layer state. The molten layer is adjacent to the molten steel, and above the molten layer, the mold powder still remains in the original granular or powdery state, so as to play a good heat insulation and heat preservation role to prevent the surface of the molten steel from solidifying. Under the action of the periodic vibration of the mold, the molten layer will continuously flow into the gap between the copper plate of the mold and the primary shell of the molten steel, lubricating the relative movement between the shell and the copper plate, so as to ensure good surface quality of the cast billet. In addition, the molten layer also has the function of absorbing non-metallic inclusions floating in the molten steel and purifying the molten steel. The mold powder film flowing into the gap between the copper plate of the mold and the shell is usually only 1-2 mm. The side close to the copper plate is solid, and the side close to the shell is still liquid. The liquid phase plays a lubricating role, and the solid phase can well control the cooling capacity of the copper plate of the mold on the shell, so as to adjust the cooling rate of the molten steel and achieve the role of controlling heat transfer. Therefore, the mold powder is the last process technology for controlling the surface quality of the cast billet in the steelmaking process. The mold powder with unsuitable performance will cause surface defects such as slag inclusion and crack in the cast billet, and even cause the shell to tear and lead to a breakout accident in severe cases. Therefore, the mold powder is an important means to ensure the smooth progress of the continuous casting process and the surface quality of the cast billet.

[0003] Generally, the mold powder is mainly based on the CaO-SiO2 binary system, and is externally added with fluxes such as CaF2, Na2O, Li2O, etc. Its main function is to reduce the melting point and viscosity of the CaO-SiO2 binary system. In addition, a small amount of components such as Al2O3, MgO, MnO, Fe2O3, etc. are also added to achieve suitable metallurgical properties. Since the melting point of the mold powder is about 400 °C lower than the temperature of the molten steel, in order to control the slow melting of the relatively low-melting mold powder on the surface of the molten steel, a certain amount of carbonaceous material must be added. The carbonaceous material has a very high melting point and can effectively prevent the aggregation of mold powder droplets, thus delaying the melting of the mold powder. Generally, the mold powder on the molten steel surface in the mold is divided into three-layer structures from top to bottom: powder slag layer, sintered layer and liquid slag layer. The mold powder with good melting performance has a suitable liquid slag layer thickness (8-15 mm), an underdeveloped sintered layer, and the powder slag layer has good heat preservation performance, and there is no or less slag ring / slag bar formed near the meniscus. These service performances can only be tested after the finished mold powder is applied on site. There is no good method for analyzing the melting performance in the mold powder industry laboratory, and only the type and ratio of the carbonaceous material can be determined by experience, which seriously affects the uncertainty of the use effect of the mold powder on site and the research and development progress of new mold powder.

[0004] In the prior art, Chinese patent documents with application numbers 03117824.3, 200610131650.5, 201310413314.X, and 201410187290.5 focus on the production method of finished mold powder for reducing the sinterability of mold powder; the Chinese patent document with application number 200410089438.8 mainly introduces the measurement method of the liquid slag layer, sintered layer, and powder slag layer of on-site mold powder; the Chinese patent document with application number 200810233073.X introduces a method in the laboratory to measure the sintering temperature of mold powder by measuring the temperature at the sudden change of air pressure difference after passing through the sintered layer of mold powder in a closed environment. The Chinese patent document with publication number 114674704A introduces a device and method for testing the melting rate of mold powder for a continuous casting mold based on the copper bath method. A copper block is arranged in a graphite crucible, and the copper block is heated and melted to form a copper bath. The mold powder is melted and flows out from the slag outlet after being heated by the copper bath. The melting rate of the mold powder is calculated by the amount of molten slag flowing out. This method is greatly affected by the viscosity and surface tension of the molten slag of the mold powder and cannot well evaluate the true situation of the sintering performance of the mold powder. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above deficiencies of the prior art and provide a method for testing the melting and use performance of mold powder that can simulate and evaluate the melting and use performance of mold powder in a laboratory before the on-site use of finished mold powder, and reduce the test cost caused by the on-site application link of mold powder.

[0006] The technical problem to be solved can be implemented by the following technical solutions.

[0007] A method for testing the melting performance of mold powder, characterized by including the following steps:

[0008] (1) Select a heating furnace that can simulate the unidirectional heating of an on-site continuous casting mold as a testing furnace for the melting performance of mold powder;

[0009] (2) Select a porcelain boat with good thermal shock resistance and small reaction with mold powder as a crucible for testing the melting performance of mold powder, and place the mold powder in the porcelain boat and perform unidirectional heating at the furnace mouth of the testing furnace for the melting performance of mold powder;

[0010] (3) After the porcelain boat and the mold powder in it are completely cooled, take out the mold powder in the porcelain boat and screen it with a 20-mesh sieve. Take the weight of the material passing through the 20-mesh sieve as the weight G1 of the powder slag, pick out the weight of the liquid slag as G2, and the rest is the weight G3 of the sintered part;

[0011] (4) Calculate the sintering index T1 of the measured mold powder: T1 = G3 / t * Q * (G1 + G2 + G3) * 100%; the melting rate index T2 = t * Q * G2 / (G1 + G2 + G3) * 100%; calculate the loss-on-ignition index T3 = t * Q * [20 - (G1 + G2 + G3)] / 20 * 100%, where t is the heating and melting time of the mold powder in the porcelain boat, and Q is the initial weight of the mold powder in the porcelain boat.

[0012] Among them, in step (2), the heating time of the to-be-tested finished mold powder in the porcelain boat ends when the surface layer of the mold powder in the porcelain boat is completely melted into a spherical liquid droplet.

[0013] Furthermore, the heating furnace is built with refractory materials, and the furnace opening is provided at the upper part of the furnace body.

[0014] Preferably, the heating element of the heating furnace is a silicon carbide rod, and the maximum heating temperature is 1400 °C.

[0015] Furthermore, when heating unidirectionally, the heating rate of the heating furnace is 15 - 20 °C / min, keep the temperature constant at 1350 °C ± 15 °C, and the constant temperature time is more than 30 minutes.

[0016] Preferably, the heating time for every 15 - 20 grams of the to-be-tested finished mold powder is 3 - 7 minutes.

[0017] Preferably, in step (3), the porcelain boat is placed on a closed refractory brick for cooling.

[0018] The mold powder melting property testing method adopting the above technical solution is simple to operate, can better simulate the conditions of unidirectionally heating the mold powder on the liquid steel surface of the continuous casting mold on site, can quickly obtain the powder ratio, sintering rate and liquid slag melting rate of the mold powder in each test, can well evaluate the melting properties (such as loss-on-ignition index, sintering index, melting rate index, etc.) of the mold powder before on-site application, and provides reliable technical support for the on-site use of the mold powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the melting property testing furnace in the testing method of the present invention;

[0020] Figure 2 It is a top view of the melting property testing porcelain boat in the testing method of the present invention;

[0021] Figure 3 For Figure 2 side view;

[0022] In the figure: 1 - furnace mouth cover; 2 - heating element; 3 - temperature control thermocouple; 4 - adiabatic refractory brick; 5 - furnace lining. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Considering that the melting and usability of the mold powder directly affect the operation behavior of the finished mold powder on the molten steel surface in the mold, the mold powder with inappropriate melting and usability directly causes serious slag rings and well-developed sintered layers of the mold powder on the molten steel surface in the mold, affects the uniformity of the inflow of the liquid slag of the mold powder, and causes accidents such as temperature fluctuations, longitudinal cracks, and leakage of molten steel on the copper plate of the mold. The present invention provides a method for testing the melting performance of the mold powder.

[0024] The technical solution of the present invention is as follows:

[0025] 1) Fabrication of a unidirectional heating melting performance test furnace for the mold powder.

[0026] Refer to Figure 1 , the heating element 2 is made of silicon carbide rod, the maximum heating temperature is 1400 °C, and a heating gap of 100 mm * 50 mm is exposed in the center of the furnace mouth (the heating gap will be covered with a heat-insulating furnace mouth cover 1 before the official test), and it is separated by heat-insulating refractory bricks 4 around to simulate the unidirectional heating of the mold powder in the on-site mold. The furnace temperature is controlled at 1350 °C. The lower part and the surrounding of the furnace body are built with a furnace lining 5, the upper part is heat-insulating refractory bricks 4, there is a furnace mouth starting from the middle position of the upper part, and the heating element 2 is arranged at the lower end of the furnace mouth; the furnace mouth is used to place a porcelain boat. A temperature control thermocouple 3 is also arranged in the furnace.

[0027] 2) Select a porcelain boat with good thermal shock resistance, small reaction with the mold powder, and low cost as the crucible for testing the melting performance of the mold powder. Refer to Figure 2 and Figure 3 . There are two reasons for selecting the porcelain boat: good resistance to rapid cooling and heating, and fast heat transfer.

[0028] 3) Heat the unidirectional heating melting performance test furnace for the mold powder according to the programmed temperature rise, the heating rate is 15 - 20 °C / min, keep the temperature constant at 1350 °C ± 15 °C, and the constant temperature time is more than 30 minutes.

[0029] 4) Before the official test, first weigh the weight of the porcelain boat for testing the melting performance and record it (the purpose is to facilitate the calculation in the subsequent steps when the mold powder adheres to the porcelain boat), weigh 15 - 20 grams of the finished mold powder to be tested and put it into the porcelain boat for testing the melting performance, open the furnace mouth cover, use a clamp to place the porcelain boat filled with the mold powder at the Figure 1 unidirectional heating furnace mouth in, start timing, observe the melting condition of the mold powder in the porcelain boat, and when the surface layer of the mold powder in the porcelain boat is completely melted into spherical liquid droplets, record the melting time, take down the porcelain boat and place it on the airtight refractory brick to cool. The sintering performance of the mold powder is an important index affecting the normal on-site use of the mold powder. Through the equipment and method provided by the present invention, the process of different mold powders melting into liquid slag and the evaluation of the sintering performance of the mold powder can be quickly observed.

[0030] 5) After the porcelain boat and the flux in it are completely cooled, take out the flux in the porcelain boat and screen it with a 20-mesh sieve. Record the weight of the powder residue passing through the 20-mesh sieve as G1, pick out and record the weight of the liquid slag as G2, and the rest is the weight of the sintered part and record it as G3.

[0031] 6) Calculate the sintering index T1 of the measured flux: T1 = G3 / (t * Q * (G1 + G2 + G3)) * 100%; the melting rate index T2 = t * Q * G2 / (G1 + G2 + G3) * 100%; calculate the loss-on-ignition index T3 = t * Q * [20 - (G1 + G2 + G3)] / 20 * 100%, where t is the heating and melting time of the flux in the porcelain boat, and Q is the initial weight of the flux in the porcelain boat.

[0032] The following are more specific embodiments.

[0033] Examples 1 - 4:

[0034] Weigh 20 grams each of finished fluxes of different grades, namely flux A, flux B, flux C, and flux D, and place them in a flux melting property test furnace with programmed heating, and keep the temperature constant at 1350 °C for half an hour to 1 hour. First, weigh the empty porcelain boat and record it. Put 15 - 20 grams of the finished flux to be tested into the melting property test porcelain boat, open the furnace lid, and use tongs to place the porcelain boat filled with the flux on Figure 1 the one-way heating furnace opening, start timing, observe the melting condition of the flux in the porcelain boat. When the surface flux in the porcelain boat is completely melted into spherical liquid droplets, record the melting time, take down the porcelain boat and place it on the airtight refractory brick to cool. After the porcelain boat is cooled, take out the flux in the porcelain boat and screen it with a 20-mesh sieve. Record the weight of the powder residue passing through the 20-mesh sieve as G1, pick out and record the weight of the liquid slag as G2, and the rest is the weight of the sintered part and record it as G3. Repeat the above steps to measure the melting properties of flux A, flux B, flux C, and flux D in turn. Record the corresponding weights G1, G2, and G3 in Table 1 respectively, and calculate the sintering index T1, melting rate index T2, and loss-on-ignition index T3 of the flux according to the formulas T1 = G3 / (t * Q * (G1 + G2 + G3)) * 100%, T2 = t * Q * G2 / (G1 + G2 + G3) * 100, T3 = t * Q * [20 - (G1 + G2 + G3)] / 20 * 100%, where t is the heating and melting time of the flux in the porcelain boat, and Q is the initial weight of the flux in the porcelain boat.

[0035] The following Table 1 is the test record of the melting properties of different fluxes.

[0036] Table 1:

[0037]

[0038] The laboratory test method for the melting performance of the mold powder provided by the present invention can well evaluate the melting and service performance (sintering index, melting rate index and loss-on-ignition index) of the mold powder through simulating the on-site unidirectional heating method, can evaluate the sintering performance and melting rate of different mold powders, and provides good technical support for the research and improvement of the on-site application and melting performance of the mold powder.

Claims

1. A method for testing the melting performance of a mold powder, characterized in that, It includes the following steps: (1) Select a heating furnace that can simulate the unidirectional heating of the on-site crystallizer as the testing furnace for the melting performance of the mold powder; (2) Select a porcelain boat with good thermal shock resistance and little reaction with the mold powder as the crucible for testing the melting performance of the mold powder. Place the mold powder in the porcelain boat and conduct unidirectional heating at the furnace mouth of the testing furnace for the melting performance of the mold powder; (3) After the porcelain boat and the mold powder in it are completely cooled, take out the mold powder in the porcelain boat and sieve it with a 20-mesh sieve. The weight of the powder residue passing through the 20-mesh sieve is G1, the weight of the picked liquid slag is G2, and the rest is the weight of the sintered part G3; (4) Calculate the sintering index T1 of the measured mold powder = G3 / t * Q * (G1 + G2 + G3) * 100%; Calculate the melting rate index T2 of the measured mold powder = t * Q * G2 / (G1 + G2 + G3) * 100%; Calculate the loss-on-ignition index T3 = t * Q * [20 - (G1 + G2 + G3)] / 20 * 100%; Wherein, t is the heating and melting time of the mold powder in the porcelain boat, and Q is the initial weight of the mold powder in the porcelain boat.

2. The method for testing the melting performance of the mold powder according to claim 1, characterized in that, In step (2), the heating time of the to-be-tested finished mold powder in the porcelain boat ends when the surface layer of the mold powder in the porcelain boat is completely melted into spherical liquid droplets.

3. The method for testing the melting performance of the mold powder according to claim 1, characterized in that, The heating furnace is built with refractory materials, and the furnace mouth is opened at the upper part of the furnace body.

4. The method for testing the melting performance of the mold powder according to claim 1 or 3, characterized in that, The heating element of the heating furnace is a silicon carbide rod, and the maximum heating temperature is 1400 °C.

5. The testing method for the melting performance of the mold powder according to claim 1, characterized in that When heating unidirectionally, the heating rate of the heating furnace is 15 - 20 °C / min, keep the temperature constant at 1350 °C ± 15 °C, and the constant temperature time is more than 30 minutes.

6. The testing method for the melting performance of the mold powder according to claim 1, 2 or 5, characterized in that, The heating time for every 15 - 20 grams of the to-be-tested finished mold powder is 3 - 7 minutes.

7. The testing method for the melting property of the mold powder according to claim 1, characterized in that, In step (3), the porcelain boat is placed on a closed refractory brick for cooling.

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