JPH039065B2 - - Google Patents

Description

[Detailed description of the invention]

<Purpose of the Invention> Industrial Application Field The present invention relates to a method for preventing cracking and peeling of monolithic refractories, and more specifically, to monolithic refractories used for pouring construction of iron making troughs, steelmaking ladles, continuous casting tundishes, etc. Relates to methods for preventing cracking and peeling of refractories. Conventional technology Monolithic refractories used in pour-in construction have traditionally been used as lining refractories for various containers that receive hot metal and molten steel, such as ladles, but pour-in construction not only saves labor but also requires skilled workers. Since it is not necessary, its range of use is expanding. However, although the poured material is a uniformly constructed object, peeling damage to some extent always occurs during operation. As a solution to this problem, for example, in Japanese Patent Application Laid-Open No. 59-92975, by mixing coarse aggregate (30 to 100 mmφ) with a smaller thermal expansion coefficient than the base material to the basic pouring material for ladle, the entire construction body is The expansion coefficient of the material is reduced, thermal stress is reduced, and peeling is prevented. However, although this method can prevent peeling due to simple thermal stress, it has the disadvantage that it cannot prevent structural spalling due to slag penetration. That is, when pouring materials widely used in various types of containers for pig iron and steel making come into direct contact with molten metal or slag, thermal stress is generated due to a rapid temperature gradient, causing cracks in the pouring materials. In addition, as a particular effect of slag, the slag penetrates into the poured material, creating a substance with physical properties different from those of the base material, and stress is generated due to the difference in thermal expansion with the base material, causing cracks and peeling. (So-called structural spalling). When these cracks and peeling occur, not only can the refractory not be used effectively, but it also becomes difficult to determine the end of use, which also poses a safety problem. Problems to be Solved by the Invention The present invention aims to solve these problems, and specifically, it aims to solve the problems caused by thermal stress, slag infiltration, and oversintering of the working surface due to the temperature gradient inside the construction body. The purpose of this study is to provide a method for preventing cracking and peeling of monolithic refractories due to structural spalling. <Structure of the Invention> Means for Solving the Problems and Their Effects The present invention provides for the use of coarse cast refractory material having a grain size of 30 to 100 mm and a modulus of elasticity greater than the modulus of elasticity of the cast refractory material. It is characterized by containing 10 to 50% by weight of aggregate. Hereinafter, the structure of these means and their operation will be further explained with reference to the drawings. Figures 1a and 1b are models of crack generation in poured material, where a is a state where no stress is generated,
b is an explanatory diagram showing the state where stress is generated, Fig. 2 is a graph showing the temperature gradient of the poured material in a steady state, and Fig. 3 is a graph showing the temperature gradient of the poured material when coarse aggregate is mixed in the poured material. It is an explanatory diagram showing a model,
FIG. 4 is a graph showing the stress generated in the poured material and coarse aggregate. The biggest problem with pouring materials used in various containers for molten metal in pig iron and steel manufacturing is peeling. Until now, drying,
It is explained that cracks occur when the strength changes during heating, and a weak layer is formed on the back side, or that the difference in physical properties between the sintered layer and the unsintered layer near the operating surface is the cause of crack generation and peeling. There is. However, the mechanism by which the pouring material peels off has not yet been clarified. According to the inventor's experiments, the timing and circumstances of occurrence of peeling are as follows. (1) Peeling occurs after 10 charges or more of use. (2) Blisters occur on the surface of the pouring material, which burst and form peeling. (3) All cracks that cause delamination are parallel to the operating plane. As mentioned in (1) above, peeling occurs after 10 charges or more of use, so it is thought that cracks occur during use rather than when the container is drying, and the cracks expand. In addition, since the blistering phenomenon (2) progresses slowly over several charges, it is difficult to imagine that rapid thermal shock during refractory is the cause of peeling. Based on these facts, it is presumed that the cause of the crack generation is a change in physical properties due to a steady temperature gradient in the poured material. Therefore, we devised the following model to examine the crack generation mechanism. As shown in Figure 1a, substances 1 with different physical properties
It is assumed that 2 and 2 are joined in a layered manner and no stress is generated between them. Also, for the sake of simplicity, it is assumed that there are no external constraints on the expansion. This model corresponds to the case where shrinkage cracks appear in the poured material after drying. The shrinkage crack is about 2.5m according to observation of the actual pot.
It occurs at intervals. From the state where no stress is generated in these two substances, the temperature of each substance is t ₁ and
Consider the case when t becomes ₂ . Assuming that the stresses acting on substances 1 and 2 are σ ₁ and σ ₂ , there is no external force acting on them, so if the cross-sectional areas are A ₁ and A _2, respectively, (1)
The formula holds true. σ ₁ A ₁ +σ ₂ A ₂ =0 (1) The amount of strain is the same because there is expansion due to thermal expansion and stress, and the two materials are joined. Therefore, the strain is ε=σ ₁ /E ₁ +α ₁ t ₁ =σ ₂ /E ₂ +α ₂ t ₂ (2). From the above, σ ₁ =E ₁ (α ₂ t ₂ −α ₁ t ₁ )/1+A ₁ E ₁ /A ₂ E ₂ ...(3) σ ₂ =E ₂ (α ₂ t ₂ −α ₁ t ₁ ) /1+A ₂ E ₂ /A ₁ E ₁ =σ ₁ A ₁ /
A ₂ ...(4). Note α ₁ and α ₂ : Coefficient of linear expansion of substances 1 and 2 E ₁ and E ₂ : Modulus of elasticity of substances 1 and 2 The temperature gradient of the poured material is as shown in Figure 2 in a steady state. Peeling occurs in actual pots with a thickness of 20 to 50 mm. Furthermore, cracks in the pouring material after using the actual pot extend from the working surface to the back. According to the results of preliminary experiments in the casting tundish, this crack formation area is approximately 50 mm from the operating surface. Therefore,
A ₁ =A ₂ , and |σ ₁ |=|σ ₂ |. In addition, the poured material was separated at 50 mm from the working surface side, and 2
If we consider it as two layers consisting of substances 1 and 2, the second
From the figure, the average temperature is t ₁ = 1500℃ and t ₂ = 1300℃. Since α ₁ t ₁ and α ₂ t ₂ in equations (3) and (4) correspond to the strain after alteration of materials 1 and 2,
It is necessary to consider the hot linear expansion coefficient and residual expansion of The hot linear expansion coefficient of the poured material is 4.7 in actual value.
×10 ^-6 (1/℃). Therefore, α ₁ t ₁ and α ₂ t ₂ are α ₁ t ₁ =4.7×10 ^-6 ×1500+0.037=0.044 α ₂ t ₂ =4.7×10 ^-6 ×1300+0.006=0.012 where 0.037 and 0.006 is 1500℃ and 1300℃
This is the residual expansion after heating. Table 1 shows the physical properties of the poured material.

[Table] From Table 1, 1500℃ and 1300℃ of poured material
The elastic modulus after heat treatment is 6×10 ⁴ Kgf/cm ²
and 2×10 ⁴ Kgf/cm ² . Expression (3)
Substituting into σ ₁ =6×10 ⁴ (0.044−0.012)/1+6×10 ⁴ /2×10 ⁴
=480 (Kgf/cm ² ). This σ ₁ is the shear force at the boundary between substances 1 and 2 rewritten as the force on cross section A ₁ . Therefore, the strength of shear acting on the boundary between substances 1 and 2 is, assuming that the range of shrinkage cracks is 2.5 m (observed value of actual pot) τ = 480 (Kgf/cm ² ) x 250 cm x 5 cm/250 cm ×250cm/
2 ≒ 20 (Kgf/cm ² ). (250cm; pouring height, 250cm/2; range where shrinkage cracks exist and shear force acts) The shear strength of refractories in hot conditions cannot be measured, so it is estimated from the values in Table 1. Ordinary compression tests on refractories result in failure due to shear force. The shear strength is 1/2 of the compressive strength because it is a compressive force in only one direction. The compressive strengths after treatment at 1500° C. in Table 1 are 241 Kgf/cm ² and 205 Kgf/cm ² , and the larger value is taken as 241 Kgf/cm ² . Therefore, the shear strength is approximately 120 Kgf/cm ² .
Here, the ratio of the strength at room temperature and at hot temperature is 10:1 by analogy with the results of hot bending measurements. Therefore, the hot shear strength is estimated to be 12 Kgf/cm ² . From the above, there is a possibility that the poured material will crack due to the above shearing force. Therefore, as a solution to the above problem, (1) Add coarse aggregate of 30 mm or more. (2) Coarse aggregate should be in the range of 10% to 50%. (3) Mix coarse aggregate with a higher modulus of elasticity than the base material pouring material. The problem is solved by performing steps 1 to 3 above. Next, consider the case where coarse aggregate is mixed into the pouring material. It is assumed that the above-mentioned shearing force of 20 Kgf/cm ² is acting on the boundary. Let V ₁ and V ₂ be the volume fractions of the pouring material and coarse aggregate, respectively. Furthermore, if σ ₁ is the stress generated in the poured material at the boundary and σ ₂ is the stress generated in the coarse aggregate at the boundary, then from the balance of forces at the boundary, σ ₁ V ₁ + σ ₂ V ₂ =P (P=20Kgf/cm ² )...(5). Here, since the strain inside the poured material is equal, in the same way as formulas (3) and (4) were derived, σ ₁ = E ₁ P/E ₁ V ₁ + E ₂ V ₂ ...(6) σ ₂ = E ₂ P / E ₁ V ₁ + E ₂ V ₂ = E ₂ /E ₁ σ ₁ ...(7) (E ₁ : Elastic modulus of poured material, E ₂ : Elastic modulus of coarse aggregate). E ₁ = 6×10 ⁴ , E ₂ = 56×10 ⁴ (test value) In the case of 30% coarse aggregate mix in this experiment, V ₁ = 0.82, V ₂ =
Since it is 0.18, σ ₁ =8Kgf/cm ² and σ ₂ =75Kgf/cm ² . Coarse aggregate has a higher elastic modulus than pouring material, so when stress is applied to the entire pouring material, the stress is concentrated on the coarse aggregate. If the hot shear strength of coarse aggregate is estimated in the same way as above, it is approximately 55 kgf/cm ² . Therefore, although the strength of the poured material is lower than that of coarse aggregate, it is thought that the coarse aggregate will be destroyed preferentially and no cracks will occur in the poured material. Figure 4 shows the stress generated in the refractory with respect to the mixing ratio of coarse aggregate. In addition, indicates the stress generated in the poured material and the stress generated in the brick aggregate. As the amount of coarse aggregate added increases, the stress generated in the poured material becomes smaller. As a result, when the amount of coarse aggregate exceeds a certain level, cracks will no longer form in the poured material. Assuming that the hot shear strength of the poured material is 12 Kgf/cm ² above, the range in which cracks do not appear in the poured material is when 11% or more of coarse aggregate is mixed. As the content of brick coarse aggregate increases, the stress decreases. Shear strength 55Kgf/cm ²
If 35% or more of coarse aggregate is added, cracks will not form in the coarse aggregate. Inside the actual poured material, there are parts where the coarse aggregate is dense and parts where it is sparse, and in the dense parts, neither the poured material nor the coarse aggregate will crack.
It is expected that cracks will appear in both areas in the sparse areas. As a result, the cracks do not connect as a whole;
It is thought that this will not lead to peeling. Furthermore, it is conceivable that the elastic modulus of the pouring material containing the coarse aggregate decreases due to the destruction of the coarse aggregate, and as a result, stress decreases and cracks do not form in the pouring material. Further, the coarse aggregate needs to have a higher elastic modulus than the pouring material, and its blending amount needs to be 10% or more. However, if the blending amount exceeds 50%, it becomes difficult to form a continuous structure in the pouring material, causing strength deterioration. Therefore, the appropriate amount of coarse aggregate is 10 to 50%. Examples Examples will be described below. On top of the permanent lining bricks on the side walls of the ladle (250 tons) used at the Mizushima 2 Steel Mill, a pouring material made of the following monolithic refractory material mixed with 30-40% coarse aggregate with a diameter of 30-60 mm was placed. Lining was performed using a core, and after removing the core, the lining was dried with a gas burner. The elastic modulus of the monolithic refractory material and coarse aggregate is as shown in Table 1, and in all cases, no damage due to cracks or peeling of the lining layer was observed, and the materials could be used stably.

[Table] <Effects of the Invention> As explained above, the present invention includes coarse aggregate having a particle size of 30 to 100 mm and a modulus of elasticity greater than that of the previous cast refractory material in an amorphous cast refractory material. A method for preventing cracking and peeling of monolithic refractories characterized by blending ~50% by weight, wherein the method of the present invention prevents cracks and peeling caused by thermal stress, particularly cracks caused by structural spalling due to slag penetration. Peeling was also completely prevented, allowing stable use of the pouring material. As a concrete effect, as a result of actual pot tests at our company's Mizushima No. 2 Steel Works, it was found that there was an advantage of about 20 yen/ton compared to ordinary brick construction pots, and it was possible to reduce costs by 140 million yen per year.

[Brief explanation of the drawing]

Figures 1a and 1b are models of crack generation in poured material, where a is a state where no stress is generated,
b is an explanatory diagram showing a state where stress is generated, the second
The figure is a graph showing the temperature gradient of the poured material in a steady state, Figure 3 is an explanatory diagram showing a model when coarse aggregate is mixed with the poured material, and Figure 4 is the stress generated in the poured material and coarse aggregate. This is a graph showing. Code 1... Substance 1, 2... Substance 2, 3... Substance 3 (brick coarse aggregate), 4... Interface between Substances 1 and 2.

Claims (1)

[Claims] 1 Particle size of 30~
A method for preventing cracking and peeling of monolithic refractories, which comprises blending 10 to 50% by weight of coarse aggregate whose elastic modulus is larger than that of the poured refractory material at a diameter of 100 mm.