JP2008224407A - Quality evaluation method for tubular refractory material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an individual quality evaluation method for product capable of simply and accurately evaluating the quality of a tubular refractory material with significant difference. <P>SOLUTION: A cylindrical test piece 8 is cut from the tubular refractory material and a seal members 9 are arranged and closely adhered to both end open parts of the cylindrical test piece 8 to hermetically close the inner hole 8a of the cylindrical test piece 8, while a gas is supplied to the inner hole 8a to raise the pressure in the inner hole 8a to predetermined pressure. The air passing amount of the cylindrical test piece 8 is measured under the predetermined pressure, and the quality of the tubular refractory material is evaluated, on the basis of the measured air passing amount. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating the quality of tubular refractories such as tubular nozzles used for continuous casting.

  Among tubular refractories, especially for continuous casting nozzles, the refractory has a single and independent functionality, and accidents such as damage due to defects or defects have serious consequences for operations. In the current evaluation items, accidents occur at a ratio of about 0.1% with respect to products, and in order to further reduce the accident rate, it is necessary to tighten the evaluation items.

  General tubular refractories such as nozzles for continuous casting are formed by hydrostatic pressing of earth, but the earth is kneaded mainly with binders such as oxide aggregates, graphite and phenolic resin. And a mixture of oxide aggregates + graphite + binding material, oxide aggregate + binding material, graphite + binding material composite, and oxide aggregate and graphite. It consists of a single unit.

  When manufacturing such a refractory material by molding the soil, the particle size and particle size of the soil depends on subtle differences such as the wet state of the soil, that is, the volatile content, external conditions during kneading, etc. Differences in the structure and physical characteristics such as the void size between them, which cause variations in quality between or within each lot of product soil lots, kneading lots, molding lots, etc. It becomes one of.

  On the other hand, in individual quality control in the refractory manufacturing process, individual quality evaluations made separately with the same soil to inspect and evaluate whether or not the quality according to the intended application is provided. In general, measurement of specific gravity, porosity, bending strength, compressive strength, etc. is performed with a small dedicated sample having an outer diameter of 130 mm, an inner diameter of 50 mm, and a height of about 120 mm. Since the molding conditions of the sample, such as filling and its management, molding pressure, and pressure distribution inside the sample during molding, are significantly different from those of the actual product nozzle, etc., such a method mainly evaluates the composition and state of the soil. Although it is possible, quality variation cannot be evaluated between lots such as molding lots or within lots.

  In order to grasp the product quality variation and manage the product, in the case of a tubular refractory, a destructive inspection may be specially performed on a test piece collected from the individual product. For example, in the case of a long nozzle that has open holes at both ends of a tubular refractory, add a length sufficient to collect the test piece, manufacture the product, and extract the excess length of the product. Then, a test piece is cut out from the portion into a shape for measuring various physical properties and shaped. Specifically, it is shaped into a columnar test piece, and the bulk specific gravity, the apparent porosity, and the bending strength are measured separately and evaluated as a value representative of the quality of the product.

  However, these quality evaluation methods have the following problems.

  1. In the measured values of specific gravity, porosity, and bending strength, there is no significant difference that causes defects or defects in the refractory with respect to troubles such as damage occurring at a rate of about 0.1%.

  2. In the process of cutting out the columnar test piece, external influences such as the application of external force to the test piece and the adhesion of powder at the time of cutting (including biting into the pores) cause variations in measured values.

  3. In the measurement of bending strength, the part that becomes the base point of the pressurization is local, and the pressurization is concentrated in a narrower local area due to subtle parallelism of the test piece, variation in surface accuracy, etc. In some cases, the measured values are not representative.

  4). Since the test piece is small, only the local quality of the part from which the test piece is collected is measured, and a wider range of defects cannot be detected, making it difficult to find defects as a product. (For example, the support span in the measurement of bending strength is generally about 50 to 100 mm.)

  On the other hand, in Patent Document 1, the test piece is made into a cylindrical shape that is easy to produce even with a brittle material, and as a load for destruction, pressure is applied uniformly to the inner surface of the cylindrical test piece in the circumferential direction. A method for measuring tensile strength by generating tensile stress is disclosed. And as a specific means of pressurization, a highly elastic body is disposed in the inner hole of the cylindrical test piece, a pressure plate is disposed on both end faces of the highly elastic body, and from both end faces of the highly elastic body. A method for applying pressure is disclosed. In addition, this Patent Document 1 also describes that there is a method of measuring tensile strength by applying gas pressure to the inside of a cylindrical test piece after press-contacting both ends of the cylindrical test piece with a sealing member and performing gas sealing. ing.

  However, all disclosed in Patent Document 1 are improvement plans related to the measurement of the strength of a cylindrical test piece, and as described above, the quality evaluation of a refractory cannot be accurately performed only by measuring the strength. Can not.

Thus, conventionally, there is no method that can easily and accurately evaluate the quality of tubular refractories, and establishment of a quality evaluation method based on a new standard has been desired.
Japanese Patent Laid-Open No. 11-64198

  An object of the present invention is to provide a quality evaluation method for individual products that can easily and accurately evaluate the quality of a tubular refractory with a significant difference.

  The inventor measured the air flow rate of a cylindrical test piece that had been subjected to the same soil, the same molding conditions, and the same firing conditions as a part of an individual product or the same product, so that the conventional quality evaluation method was used. The present invention has been found by finding that the variation in the structure of the refractory can be noticed significantly more than a certain specific gravity and porosity, and by finding a method that makes it possible to easily measure this air flow rate with a cylindrical specimen. Completed.

  Explaining why the ventilation rate is effective as a quality evaluation standard for refractories, first, when the soil particles are bonded with pressure, gaps are generated between the particles without completely adhering to each other. Due to this difference, a large or small difference occurs in the gap. When the gap is small, the adhesion area of the particles is large and the bonding strength is also high. On the other hand, when the gap is large, the adhesion area of the particles is small and the bonding force is also low. The size of this gap leads to the magnitude of the bonding force of the particles, resulting in a strength that is resistant to cracking and breaking, but the strength of bending and compression detects the size of the gap in terms of measurement accuracy. It is not an indicator. Further, the porosity only indicates the volume ratio of the pores in the test piece, and since the size of the pores cannot be evaluated, this is not an index for detecting the magnitude of the binding force. On the other hand, when gas is ventilated through the test piece, the pressure loss differs greatly depending on the size of the gap, and a large difference occurs in the amount of ventilation, which can be a strict indicator of the magnitude of the bonding force.

  That is, the present invention relates to a method for evaluating the quality of a tubular refractory, wherein both ends of a cylindrical test piece cut out from the tubular refractory or a cylindrical test piece simultaneously molded and fired in the same soil as the tubular refractory are used. The inner hole of the cylindrical test piece is sealed by placing a seal member in close contact with the open part, and gas is supplied to the inner hole of the cylindrical test piece to increase the pressure in the inner hole to a predetermined pressure. The airflow rate of the cylindrical test piece is measured below, and the quality of the tubular refractory is evaluated based on the measured airflow rate.

  In the present invention, after measuring the air flow rate of the cylindrical test piece, the pressure of the gas supplied to the inner hole of the cylindrical test piece is sequentially increased until the cylindrical test piece breaks, It is also possible to calculate the tensile strength of the cylindrical test piece from the pressure at the time of destruction, and to evaluate the quality of the tubular refractory based on the calculated tensile strength and the measured air flow rate.

  Conventionally, in a refractory used as a gas distribution channel, the amount of ventilation is sometimes used as a quality evaluation standard. However, the air flow rate in this case is used only for the purpose of evaluating the gas flow characteristics of the refractory, and is not used for product inspection of refractories other than that purpose. It has not been used as a normal quality evaluation method for inspection and sorting.

  Further, for the conventional measurement of the air flow rate, it is necessary to prepare a special test piece as shown in, for example, JIS-R2115. In this case, particularly in the case of a refractory product having a non-planar shape such as a cylindrical shape, it is difficult to collect a test piece from a part of the product. Therefore, the conventional measurement of air flow rate is adopted as an individual quality control method for industrially mass-produced refractories, especially tubular refractories, because it requires special test piece preparation and laborious measurement. It is difficult to do.

  In the measurement of specific gravity and porosity, which is a conventional quality evaluation method, the measured values are within a narrow range that is much narrower than the control standard, and for each individual product, between soil lots, between kneading lots, between molding lots, and dried. In addition, it was not possible to evaluate or select the quality between the firing lots, especially the density of the structure and the bonding state. However, according to the present invention, the measurement of the air flow rate varies between individual products and between the lots. Can be detected as a significant difference in measured values, whereby the quality of the tubular refractory can be accurately evaluated.

  That is, variations in the quality of the tubular refractory can be realized, and the degree can be clearly grasped. And by using it for evaluation and selection of products, troubles such as breakage at the usage site of tubular refractory products can be remarkably reduced. Furthermore, it can be used for evaluation and management of various manufacturing processes, and can contribute to improvement of manufacturing technology.

  In addition, it is not necessary to prepare and measure specially shaped test pieces that require complicated and advanced techniques as in the conventional measurement of air flow, and individual quality can be easily grasped and measured by each measurer. The variation due to the difference in the measurement technology level can be reduced, and the measurement efficiency and measurement cost can be greatly improved.

  As one form of the quality evaluation method of the tubular refractory according to the present invention, there are the following steps.

  1. Designing a tubular refractory product with a length that allows a cylindrical specimen for quality evaluation to be taken.

  2. Molding, drying, firing, and perimeter shaping of individual tubular refractory products including cylindrical specimens.

  3. Cutting a cylindrical specimen from a predetermined length position of the tubular refractory product.

  4). Measuring the inner and outer diameters and heights of the cylindrical specimen, and calculating the inner hole area and average thickness of the cylindrical specimen.

  5. A step of sealing the inner hole of the cylindrical test piece so as not to leak gas by placing a lid (seal member) with a sealing material on the open ends of the cylindrical test piece and pressurizing and sticking them.

  6). Supplying gas at a predetermined pressure to the inner hole of the sealed cylindrical test piece via the lid (seal member);

  7. Measuring the air flow under the predetermined pressure;

  8). After measuring the air flow rate, successively increase the pressure of the gas supplied to the inner hole of the same cylindrical specimen until the cylindrical specimen breaks, and measure the pressure when the cylindrical specimen breaks. Step.

  9. Calculating the tensile strength of the cylindrical specimen from the pressure when the cylindrical specimen is broken.

  10. The step of evaluating the quality of individual tubular refractory products based on the value of air flow rate and tensile strength, selecting the tubular refractory products, and grasping the quality variation of each lot.

  The cylindrical test piece for quality evaluation is not cut out from a tubular refractory product, but may be a cylindrical test piece that is simultaneously molded and fired in the same soil as the tubular refractory product. Good. Further, the measurement of the tensile strength of the cylindrical test piece may be performed by the method described in Patent Document 1 after removing the cylindrical test piece after measuring the air flow rate.

  Hereinafter, the best mode of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing an example of a continuous casting long nozzle in a tubular refractory.

  The long nozzle 1 for continuous casting has a cylindrical shape with both ends (upper and lower ends) open. At the lower end (molten steel discharge side) of the long nozzle 1 for continuous casting, a portion 2 (length L1) for collecting a cylindrical specimen is added to a predetermined product body 3 (length L). ing.

  In order to obtain such a nozzle, as shown in FIG. 2, a metal core bar 5 is disposed in a portion corresponding to the inner hole 4 (see FIG. 1) which is a molten steel flow path, and a space 6 is formed outside thereof. A rubber mold 7 is attached, and the space 6 is filled with a soil that has been kneaded in advance to adjust the volatile content, and is pressed and molded from the entire outer periphery of the mold 7 in a sealed state. The molded body taken out from the mold is shaped into a predetermined product shape by processing such as grinding of the outer periphery and cutting of the lower end after the drying process and firing process. Measure strength.

  FIG. 3 is a cross-sectional view showing a method for measuring the air flow rate and tensile strength of a cylindrical test piece.

  Prior to the measurement, the inner and outer diameters and heights of the cylindrical test pieces are measured in order to convert the obtained measurement values into the aeration amount per unit area, per unit length, and tensile strength per unit cross-sectional area.

  Next, as shown in FIG. 3, both ends of the cylindrical test piece 8 are arranged up and down, and lids 9 and 9 provided with a sealing material 9a are arranged at the upper and lower end open portions, and are pressed and brought into close contact with the cylinder. The inner hole 8a of the shape test piece 8 is sealed to prevent gas from leaking.

  For fixing the cylindrical test piece 8 including the lids 9 and 9, a base 10a and a head 10b of an Amsler tester generally used for measuring the compressive strength or the like of the refractory can be used.

  Next, gas is supplied at a predetermined pressure from a nozzle 11 installed through the lid 9 into the inner hole 8a of the cylindrical test piece 8 in a sealed state. The gas may be air, and the pressurization is stopped at a predetermined pressure, and the amount of ventilation under the pressure is measured. That is, the passage amount of air per unit time flowing out through the cylindrical test piece 8 under a predetermined pressure is measured, and divided by the area of the inner hole 8a to obtain the ventilation amount per unit area.

  What is necessary is just to set the pressure at the time of this measurement to the appropriate value which can express the variation notably for every individual material.

After measuring the air flow rate, the gas pressure is gradually increased until the cylindrical test piece breaks, and the maximum tensile strength σ of the cylindrical test piece is obtained from the pressure P when the breakage occurs. That is, the maximum tensile strength σ of the cylindrical test piece is generated inside the cylindrical test piece. When the pressure when fractured is P, the inner diameter of the cylindrical test piece is r, and the outer diameter is R, the following equation is obtained. Is calculated by
σ = (r × r + R × R) ÷ (R × R−r × r) × P

  The measured values of the air flow and tensile strength obtained as described above are used as a standard for selecting individual products and products for each lot. That is, when the air flow rate and the tensile strength do not conform to a predetermined management standard, or when they show an abnormal tendency, they are arranged for each lot element, and individual products are selected on the basis thereof.

  In this example, the results of measuring the air flow rate and the tensile strength by the method of the present invention were collected from the same product by a conventional method as a comparative example for a long nozzle for continuous casting having an inner hole open at both ends. It shows with the result of having measured the apparent porosity and bending strength about the test piece.

  As a factor causing fluctuations in the structure of the refractory, there is a wet state of the soil, that is, a volatile content. In this embodiment, in the soil kneading process, a plurality of soil soil lots in which the content of volatile components in the soil soil is continuously changed are prepared, and then the soil soil of each lot is processed in a normal process. Products finished up to the process were prepared, and the above items were measured for each.

  Here, the reference value α mass% of the volatile content is a product-specific value that varies for each type of product depending on the use of the refractory product, and in this example, the reference value α mass of the adopted product. %, The degree of filling failure was continuously increased, that is, the degree of tissue failure was continuously increased.

  The measurement conditions of the examples are as follows.

  The cylindrical test piece was obtained by cutting one side (lower end side in use) of the product in a state after dimensions and the outer peripheral machining step of a long nozzle for continuous casting having inner holes open at both ends. The cylindrical test piece has an outer diameter of 130 mm, an inner diameter of 80 mm, and a height of 100 mm. Air at a pressure of 0.098 MPa is supplied to the inner hole of the cylindrical test piece, and the amount of air passing per unit time flowing out through the cylindrical test piece under this pressure is measured. To obtain the air flow per unit area.

  After measuring the air flow rate, the gas pressure was gradually increased until the cylindrical test piece was broken, and the maximum tensile strength of the cylindrical test piece was determined from the pressure at the time of the breakage in the manner described above.

  The measurement conditions of the comparative example are as follows.

  The test piece was cut out from the main body near the portion where the cylindrical test piece for the example was obtained, and the surface was polished. The shape of the test piece was a rectangular parallelepiped of 20 mm × 20 mm × 80 mm.

  The apparent porosity was measured in accordance with JIS R2205, and the bending strength was measured by a so-called three-point bending test method in which the support span was 50 mm and the center was pressurized in accordance with the method of JIS R2213.

  FIG. 4 shows the measurement results of the air permeability and the apparent porosity with respect to the volatile content of the soil, and FIG. 5 shows the measurement results of the tensile strength and the bending strength.

  As the volatile content of the soil becomes lower than about α-0.15% by mass, the air flow rate is remarkably increased, and the tensile strength is remarkably reduced. This shows that the lower limit of the volatile content for maintaining the soundness of the refractory structure of the product is up to about α-0.15 mass%.

  On the other hand, the apparent porosity, which is a comparative example, shows a tendency to increase almost linearly in a range of about 3% from 14.7% to 18.0%, and the bending strength is 8.5 MPa to It shows a tendency to decrease almost linearly in the range of about 1 MPa of 7.5 MPa, and none of the measured values show a significant change, and the change is within a narrow range that is well within the normal control range. Stays on.

  As described above, according to the method of the present invention, it is possible to clearly estimate the quality of the structure of the refractory product, or it is possible to select the product based on the volatile content for each kneading lot of the clay. I understand that.

  In this Example 2, the results of measuring the air flow rate and the tensile strength by the method of the present invention for the long nozzle for continuous casting having the inner holes opened at both ends of Example 1 described above are the results of various steps in the production of the product. The quality of the finished product that is fed back to the management is kept within the specified control range, and the product outside the specified control range is removed by sorting, and about 3000 pieces of steel are continuously cast for about half a year. The results used over time are shown.

  For the product according to this example, the trouble associated with destruction of the refractory was “zero”, that is, there was no trouble. In the result of using the same product according to the conventional management method immediately before using the product according to the present embodiment, the trouble of cracking or cracking and breakage was about 0.5%, whereas the remarkable improvement effect was 0%. Admitted.

  The method of the present invention can be used for the inspection, evaluation, and quality control of the structure of tubular refractories used as building materials and the like as well as tubular refractories used in steel making processes such as long nozzles for continuous casting.

It is sectional drawing which shows the example of the long nozzle for continuous casting among tubular refractories. It is sectional drawing which shows the manufacturing method of the long nozzle for continuous casting of FIG. It is sectional drawing which shows the measuring method of the air flow rate and tensile strength of the cylindrical test piece in this invention. The measurement results of aeration volume and apparent porosity with respect to the volatile content of soil are shown. FIG. 5 shows the measurement results of tensile strength and bending strength with respect to the volatile content of yes earth.

Explanation of symbols

1 Long nozzle for continuous casting (tubular refractory)
2 Part for collecting cylindrical test piece 3 Product body 4 Inner hole of long nozzle for continuous casting 5 Metal core rod 6 Space 7 Mold 8 Cylindrical test piece 9 Lid (seal member)
9a Sealing material 10a Pedestal of Amsler testing machine 10b Head of Amsler testing machine

Claims (2)

  In the method for evaluating the quality of a tubular refractory, a sealing member is attached to both ends of a cylindrical specimen cut from the tubular refractory or a cylindrical specimen that is simultaneously molded and fired in the same soil as the tubular refractory. The inner hole of the cylindrical test piece is sealed by arranging and closely contacting, and gas is supplied to the inner hole of the cylindrical test piece to increase the pressure in the inner hole to a predetermined pressure. Under the predetermined pressure, the cylindrical test piece A method for evaluating the quality of a tubular refractory, in which the amount of aeration is measured and the quality of the tubular refractory is evaluated by the measured amount of ventilation.   After measuring the air flow rate of the cylindrical test piece, the pressure of the gas supplied to the inner hole of the cylindrical test piece is sequentially increased until the cylindrical test piece breaks, and from the pressure when the cylindrical test piece breaks to the cylinder The method for evaluating the quality of a tubular refractory according to claim 1, wherein the tensile strength of the shape test piece is calculated, and the quality of the tubular refractory is evaluated based on the calculated tensile strength and the measured air flow rate.

Images