JPWO2017170840A1 - Aggregate for refractory, method for producing the same, and refractory using the same - Google Patents

Abstract

Problem: In an amorphous refractory manufactured using a porous heat insulating aggregate having a crystalline phase of CaO.6Al2O3 (CA6), sufficient strength is ensured, and peeling and collapse are suppressed. Solution: The water absorption by the boiling method defined in JIS R 2205: 1992 is 50% to 100% and the bulk density is 0.40 g / cm 3 or more and 0 when sieving to a particle size of 3 mm or more and less than 6 mm. The fracture strength of the CA6 particles is improved by setting it to .60 g / cm3 or less, and when the refractory is produced using the CA6 particles, the area of the interface between the CA6 particles in the refractory and the matrix material is reduced. The bond strength is greatly increased and the strength of the refractory is improved.

Description

The present invention relates to a refractory aggregate that can be used in the field of refractories such as steel-related furnace materials, a manufacturing method thereof, and a refractory using the refractory. Furthermore, the present invention relates to an aggregate for refractories having long-term stability and a method for producing the same.

In the steel-related refractory field, which is one of the major fields of application of aggregates for refractories, the conventional furnace construction method using regular refractories is used to save labor for construction by mechanization in recent years and to save resources for repairs. For this reason, it has been converted to a furnace construction method using irregular refractories. In the construction method using an irregular refractory, there is a need for mass construction using a pressure pump.

On the other hand, reduction in recent years, has become a situation that must be addressed to CO ₂ emission reduction from environmental problems, by increasing the thermal insulation of the refractory used in the furnace or the like in steel-related, the CO ₂ emissions To be considered.

As a conventional heat insulating material used in the steel industry, a method of inserting a ceramic fiber between a refractory and a support to increase heat insulation has been the mainstream. The revision that refractory ceramic fiber (RCF) is added to “Management Class 2 Substance” of “Specified Chemical Substance (Class 2 Substance)” has been implemented. Development of high refractories is underway.

Patent Document 1 proposes to provide a refractory having excellent heat insulation properties by using CaO.6Al ₂ O ₃ (calcium hexaaluminate, hereinafter also referred to as CA6) as an aggregate for refractory. The proposed refractory aggregate is porous CA6 particles, has high heat insulation, excellent heat resistance and mechanical strength, and has high heat insulation without using ceramic fibers. It is promising as a material. The larger the pore volume per unit weight of the aggregate, the higher the heat insulation. The volume of pores per unit weight can be evaluated by a water absorption measurement method by boiling method defined in JIS R 2205: 1992 “Measurement method of apparent porosity, water absorption rate and specific gravity of refractory brick”.

In Patent Document 2, a refractory powder composition in which a porous heat insulating aggregate having a crystal phase of CaO.6Al ₂ O ₃ is blended in a coarse grain region, and an alumina raw material and alumina cement are blended in a fine grain region. And a heat insulating refractory containing construction water have been proposed, and can be used as a heat insulating material covering a skid pipe of a slab heating furnace, a soaking furnace, a support pipe that supports the slab pipe or the like.

PCT / WO00 / 30999 JP 2009-203090 A

As one of the construction methods for the amorphous refractory, a construction method is performed in which a material for an amorphous refractory mixed with castable and water containing aggregate for refractory and alumina cement is poured into a formwork. If the strength after construction is insufficient, the refractory will peel or collapse, resulting in an increase in CO ₂ emissions due to insufficient heat insulation and an increase in cost due to repair of the refractory. End up.

The refractory material using CA6 particles as an aggregate has a structure in which CA6 particles, which are porous bodies, are dispersed in a matrix portion made of surrounding alumina material and alumina cement. It is considered that the refractory is peeled off or collapsed when the fracture strength of the CA6 particles is insufficient or when the interface between the CA6 particles and the matrix is insufficient.

As a result of intensive studies to solve the above problems, the present inventor has produced a refractory using crushed CA6 particles having a low bulk density while maintaining a high porosity. Obtaining knowledge that the area of the interface between the CA6 particles and the matrix material is large and the bonding strength is strong and the strength of the refractory is improved, the present invention has been completed.

Moreover, in the manufacture of CA6 particles, the present inventor can easily obtain crushed CA6 particles having a low bulk density by adding an appropriate amount of borax to the raw material, and manufactured a refractory using these CA6 particles. In some cases, the inventors have obtained knowledge that the breaking strength is improved, and have reached the present invention.

That is, in the present invention, when the crystal phase is CA6 and the particle size is sieved to 3 mm or more and less than 6 mm, the water absorption by the boiling method defined in JIS R 2205: 1992 is 50% or more and 100% or less, And an aggregate for a refractory material having a bulk density of 0.40 g / cm ³ or more and 0.60 g / cm ³ or less, preferably 0.02 mass% or more and 0.4 mass% or less of boron. It is related with the aggregate for amorphous refractories contained.

The present invention also relates to a refractory using alumina cement as a binder using the refractory aggregate.

Furthermore, the present invention is a method for producing an aggregate for a refractory obtained by mixing an aggregate raw material containing a calcia raw material and an alumina raw material with water, followed by molding and firing at 1000 ° C. to 1700 ° C. The present invention also relates to a method for producing a refractory aggregate characterized by adding borax to a raw material. This manufacturing method is preferably a method for manufacturing an aggregate for refractory, wherein the amount of borax added to the aggregate material is 0.1% by mass or more and 4.0% by mass or less.

According to the present invention, in the aggregate for a refractory having a crystal phase of CA6, when the crushed CA6 particles having a low bulk density and a high porosity are maintained, the CA6 particles and the matrix substance in the refractory The area of the interface is large and the bonding strength becomes strong, so that the strength of the refractory can be improved.

FIG. 1 shows the results of X-ray diffraction analysis of CA6 particles, which are examples of the present invention, in comparison with comparative examples.

Hereinafter, the present invention will be described in detail.

In the production of CA6 particles, a molar ratio of CaO and Al ₂ O ₃ of calcium aluminate finally synthesized by mixing or mixing and grinding borax in addition to aggregate raw materials such as calcia raw material and alumina raw material. Is prepared by blending so that the component ratio is approximately 1: 6, kneading with water, molding, and firing at a temperature of 1000 ° C. to 1700 ° C., and pulverizing with a pulverizer Is preferred.

The calcia raw material, powdered limestone or burnt lime or _{CaO · Al 2 O 3 (CA} ), CaO · 2Al 2 O 3 (CA2), 12CaO · 7Al 2 O 3 (C12A7), 3CaO · Al 2 O 3 ( C3A) or the like can be used, and these raw materials may be used in combination.

As the alumina raw material, alumina (Al ₂ O ₃ ), gibbsite (Al (OH) ₃ ), boehmite (AlO (OH)) and the like can be used, and these raw materials may be used in combination. Absent. However, it is known that it is advantageous to use gibbsite, which is a hydrate of aluminum, in order to synthesize porous CA6 particles. By using an alumina raw material containing gibbsite, a porous structure in which the primary crystals of scaly CA6 are aggregated is easily obtained, which is preferable.

In order to develop higher heat insulation, it is effective to synthesize a porous body of CA6 having more pores. Therefore, it is preferable to add a pore-forming agent to the raw material. For example, by adding a flammable substance to the raw material as a pore-forming agent, the pore-forming agent is combusted and vaporized during firing, voids are formed in the synthesized CA6 particles, and CA6 particles with many pores are formed. As the pore-forming agent, starch (corn starch), polyvinyl alcohol, methyl cellulose, acrylic resin, latex and the like can be used. Of these, starch (corn starch) is preferably used because it is relatively inexpensive and can form a gap of several tens of μm.

When corn starch is used as the pore-forming agent, the amount added is preferably 5% by mass or more and 50% by mass or less in the total raw material. When the amount added is less than 5% by mass, a sufficient effect as a pore-forming agent cannot be obtained. When the amount added exceeds 50% by mass, the volume of pores becomes too large, and sufficient mechanical strength as an aggregate for refractory is obtained. This is because it can not be obtained and also causes an increase in cost.

In the method for producing an aggregate for a refractory according to the present invention, preferably the aggregate raw material is borax (Na₂B₄O ₅(OH)₄・ 8H₂O) is added. By adding borax, it acts as a flux during firing, promotes material diffusion of various raw materials through the formed liquid phase, suppresses unreacted raw material residue, and bonds between primary crystals of scale-like CA6 And the strength of the CA6 particles is increased.

The amount of borax added to the aggregate raw material is preferably 0.1% by mass or more and 4.0% by mass or less. If the added amount is less than 0.1% by mass, the effect of improving the strength is not sufficiently obtained. If the added amount is more than 4.0% by mass, sintering due to the progress of sintering occurs, and pores per unit weight of the aggregate This is because the sufficient volume of heat insulation cannot be obtained.

The method of mixing raw materials such as calcia raw material, alumina raw material, pore former, borax, etc. is not particularly limited, and each material is blended in a predetermined ratio, and a V-type blender, a corn blender, It is possible to mix uniformly using a mixer such as a Nauter mixer, a bread mixer, and an omni mixer. The mixing time is not particularly limited, and has an optimum value depending on the mixer, but is preferably 5 minutes or more, and more preferably 15 minutes or more. There is no upper limit for the mixing time.

In the method for producing an aggregate for a refractory according to the present invention, it is preferable that a mixed raw material containing a calcia raw material and an alumina raw material is mixed with water, molded, put into a firing furnace, and fired at 1000 ° C to 1700 ° C. When the firing temperature is lower than 1000 ° C., the firing becomes insufficient, and unreacted raw materials remain, causing insufficient strength as a refractory and poor stability when used at high temperatures. On the other hand, if the firing temperature is made higher than 1700 ° C., the facility becomes large, while the physical properties of the CA6 particles are almost the same as those calcined at 1700 ° C. As the firing method, facilities such as an electric furnace, a shuttle kiln, a rotary kiln can be used.

In the method for producing an aggregate for refractory according to the present invention, the fired CA6 fired product is pulverized to an appropriate particle size by a pulverizer. The pulverizer to be used is not limited, but pulverizers such as a ball mill, a hammer mill, a vibration mill, a tower mill, a roller mill, and a jet mill are preferable.

When this inventor grind | pulverizes to the target particle size using the CA6 baking products manufactured by adding borax, it is easy to obtain the crushed CA6 particle | grains with a low bulk density, and using this CA6 particle | grains It has been found that when a refractory is produced, the area of the interface between the CA6 particles in the refractory and the matrix material is large and the bonding strength is increased, thereby improving the strength of the refractory.

By increasing the mechanical strength of the calcined product of CA6, wear on the fracture surface during pulverization is suppressed, and it is considered that crushed CA6 particles having a low bulk density can be produced after pulverization. The amount of boron contained in the aggregate for the irregular refractory of CA6 particles is preferably 0.02% by mass or more and 0.4% by mass or less. If the amount is less than 0.02% by mass, the effect of improving the strength is hardly obtained. If the amount is more than 0.4% by mass, sintering due to the progress of sintering occurs, and the pore volume per unit weight of the aggregate is small. It is because it is difficult to obtain sufficient heat insulation by reducing.

If CA6 particles having a low bulk density are simply produced, this can be achieved, for example, by increasing the amount of pore-forming agent and increasing the pore volume of the CA6 particles. Since the mechanical strength is impaired, the strength of the refractory when used in an aggregate for refractory is impaired. Therefore, it is necessary to improve the strength of the refractory material by reducing the bulk density while keeping the volume of pores per unit weight of the aggregate within a certain range.

In addition, this inventor has discovered that CA6 particle | grains of a desired water absorption rate (porosity) and a bulk density are easy to be obtained when it grind | pulverizes using the CA6 baking products manufactured by adding borax. However, the effect of the present invention can be realized if there is a pulverization method other than borax that adds an additive that increases the hardness while maintaining the same water absorption rate or obtains a desired bulk density.

As a measure of the pore volume per unit weight of the aggregate, it can be evaluated by the water absorption measurement method by the boiling method defined in JIS R 2205: 1992. As a result of examining the range of the water absorption and bulk density of the CA6 particles necessary for obtaining sufficient strength as a refractory by the present inventor, JIS R 2205: 1992 when sieving to a particle size of 3 mm or more and less than 6 mm. Strength and heat insulation as a refractory when the water absorption by the boiling method as defined in the above is 50% to 100% and the bulk density is in the range of 0.40 g / cm ^{3 to} 0.60 g / cm ³ It was found that the balance of sex is excellent. If the water absorption is lower than 50%, the pore volume is small and the heat insulation is low, and if the water absorption is higher than 100%, the strength of the CA6 particles is low and the strength of the refractory is low. Similarly, when the bulk density is lower than 0.40 g / cm ³ , the strength of the refractory is weakened, and when the bulk density is higher than 0.60 g / cm ³ , the heat insulating property is lowered.

The amorphous heat-insulating refractory according to the present invention has a crystal phase of CA6, and has a water absorption rate of 50% or more and 100% by the boiling method defined in JIS R 2205: 1992 when the particle size is sieved to 3 mm or more and less than 6 mm A predetermined amount of water is added to a castable containing a refractory aggregate having a bulk density of 0.40 g / cm ³ or more and 0.60 g / cm ³ or less and alumina cement, and kneaded. Is cast into a formwork.

For example, a castable containing 40 to 70% by mass of CA6 particles of the present invention, 40 to 60% by mass of alumina cement, and 0 to 10% by mass of alumina fine powder having a particle size of less than 45 μm is used. When the blending amount of the CA6 particles is more than 70% by mass, the strength as a refractory is insufficient, and when it is less than 40% by mass, sufficient heat insulation cannot be obtained. Moreover, when there are more compounding quantities of an alumina cement than 60 mass%, sufficient heat insulation is not acquired, and when it is less than 40 mass%, the intensity | strength as a refractory is insufficient. Alumina fine powder having a particle size of less than 45 μm becomes a matrix component of a heat-resistant refractory by reaction with alumina cement, and the strength is improved as compared with the case where alumina fine powder is not blended. No further improvement in strength.

The mixing method of each material in the method for manufacturing an amorphous heat-resistant refractory according to the present invention is not particularly limited, but according to a normal method for manufacturing an amorphous refractory, each constituent raw material has a predetermined ratio. And blending uniformly using a mixer such as a ball mill, a V-type blender, a cone blender, a nauter mixer, a bread mixer, and an omni mixer.

In the construction of the amorphous heat-resistant refractory according to the present invention, a predetermined amount of water is added to the castable and blended and kneaded. The amount of water to be added is preferably 40 to 60% by mass based on the total amount of castable. If the amount is less than 40% by mass, sufficient fluidity cannot be ensured, resulting in poor construction. If the amount is more than 60% by mass, the strength is lowered due to a decrease in the density of the refractory.

Hereinafter, the present invention will be further described based on examples.
[Examples 1-5, Comparative Examples 1-3]

Calcium carbonate or calcium hydroxide as a calcia raw material, aluminum hydroxide as an alumina raw material, corn starch as a pore-forming agent, borax as an additive, were weighed to the formulation shown in Table 1, and then mixed using a Nauta mixer . In addition, the ratio of the calcia raw material and the alumina raw material shown in Table 1 is set to be CaO · 6Al ₂ O ₃ .

<Materials used>
Calcium carbonate: manufactured by Funao Mine stern limestone calcium hydroxide: manufactured by Joto Sangyo Aluminum hydroxide: manufactured by Sumitomo Chemical C301N
Cornstarch: Y-3P made by Nippon Cornstarch
Borax: Dehybor made by Wako Pure Chemical Industries

The mixed raw material was formed into about φ20 mm or less with a bread granulator, put into an alumina container, and baked at a temperature shown in Table 1 in an electric furnace (atmosphere). Thereafter, the calcined product of CA6 obtained by cooling was pulverized with a roller mill to produce an aggregate for an amorphous refractory having CA6 as a crystal phase. The boron content of the aggregate of the obtained CA6 particles was measured by ICP (Inductively Coupled Plasma) emission analysis. Further, the obtained aggregate of CA6 particles was sieved to a particle size of 3 mm or more and less than 6 mm, and the water absorption, bulk density, and aggregate load resistance were measured. The results are shown in Table 1.

<Water absorption measurement method>
Measured by a water absorption measurement method by a boiling method defined in JIS R 2205: 1992 “Measurement method of apparent porosity / water absorption / specific gravity of refractory brick”. Since the water absorption rate of the aggregate has a negative correlation with the thermal conductivity of the refractory produced using the aggregate, the water absorption rate for obtaining a refractory with a sufficiently low thermal conductivity is over 50%. ), Less than 50% was evaluated as x (failed).

<Bulk density measurement method>
After the aggregate of CA6 particles obtained in a glass bottle with an internal volume of 15.8 cm ³ is accumulated until it overflows from the mouth of the glass bottle, the aggregate overflowing from the mouth of the glass bottle is tapped several times (falling from a height of 1 cm). The bulk density was determined by dividing the weight increment of the glass bottle by the internal volume.

<Aggregate load resistance measurement method>
Place one 3-6 mm CA6 particle aggregate on a horizontal surface plate and push the CA6 particle aggregate with a load measuring instrument with a surface parallel to the surface plate until the aggregate is destroyed. The load was the aggregate load capacity. Here, as a pass / fail judgment criterion for the aggregate load-bearing capacity, 10N or more was evaluated as ◯ (pass), and less than 10N was determined as x (fail).

From Examples 1 to 5 in Table 1, it can be seen that the aggregate load resistance is as high as 10 N or more when the boron content is in the range of 0.02 to 0.4 mass%. On the other hand, when CA6 particles were produced without adding borax, the aggregate load resistance was lower than 10N because the number of pores increased as the water absorption rate exceeded 100%. In addition, when the boron content exceeds 0.4 mass% as in Comparative Example 2, the aggregate load resistance is as high as 66.3 N, but the water absorption is a low value of 50% or less, which is disadvantageous as a heat insulating property. It is thought that it becomes. Although the aggregate of CA6 particles of Comparative Example 3 contains 0.02% by mass or more of boron and has pores with a water absorption rate of 50% or more, the bulk density is 0.6 g / cm ³ or more. It shows a high value. This is presumably because the firing temperature was low and the effect of boron addition was insufficient, making it difficult to obtain crushed CA6 particles when the CA6 fired product was pulverized.

Table 1 shows the X-ray diffraction analysis evaluation results of the aggregates of CA6 particles of Examples 1 to 5 and Comparative Examples 1 to 3, and X-ray diffraction of the aggregates of CA6 particles of Examples 1, 3 and Comparative Example 3 The spectrum is shown in FIG. As in Examples 1 to 5 and Comparative Examples 1 and 2, when the firing temperature is 1450 ° C., almost single-phase CA6 is formed regardless of whether calcium carbonate or calcium hydroxide is used as the calcia raw material. I understand that On the other hand, from Comparative Example 3, when the firing temperature is lower than 1000 ° C., a large amount of unreacted raw material Al ₂ O ₃ and CaO and reaction intermediate CaO · 2Al ₂ O ₃ (CA2) remain, and firing is performed. It can be seen that the temperature is too low.

[Examples 6 to 10, Comparative Examples 4 to 6]
The aggregates of CA6 particles obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were reduced to a particle size of 3 mm or more and less than 6 mm (coarse particles), 1 mm or more and less than 3 mm (medium particles), and a particle size of less than 1 mm (fine particles). What was sieved, alumina fine powder with an average particle diameter of 2 μm, and alumina cement were weighed into the formulation shown in Table 2, a predetermined amount of water was added and mixed using a universal mixer, and then a 40 mm × 40 mm × 160 mm mold Poured into a frame, cured at a temperature of 20 ° C., de-framed, and then dried at 110 ° C. for 24 hours to obtain a refractory using CA6 particles as an aggregate.

<Materials used>
Alumina fine powder: AL-170, manufactured by Showa Denko
Alumina cement: Denka high alumina cement super

Assuming actual furnace use conditions of the refractory, the bending strength after the obtained refractory was heat-treated at 1400 ° C. using an electric furnace was measured. The results are shown in Table 2.

<Measurement method of bending strength>
Measured by the method described in JIS R 2553: 1992 “Strength Test Method for Castable Refractories”. Here, as a pass / fail judgment criterion for bending strength, 1.5 MPa or more was evaluated as ◯ (passed), and less than 1.5 MPa was determined as x (failed).

From Examples 6 to 10 in Table 2, it can be seen that the refractories manufactured using the aggregates of CA6 particles of Examples 1 to 5 have a bending strength as high as 1.5 MPa or more. On the other hand, in the case of the refractory of Comparative Example 4 using the aggregate of CA6 particles of Comparative Example 1 to which no borax was added, the bending strength was a value lower than 1.5 MPa. Moreover, in the case of the refractory of Comparative Example 5 manufactured using the aggregate of CA6 particles of Comparative Example 2 having a boron content exceeding 0.5 mass%, although the bending strength is as high as 2.5 MPa, Thus, the water absorption rate of Comparative Example 2 is a low value of 50% or less, which is considered to be disadvantageous as a heat insulating property. In the case of the refractory of Comparative Example 6 manufactured using the aggregate of CA6 particles of Comparative Example 3, the bending strength was lower than 1.5 MPa even though the aggregate load resistance was 10 N or more. When the water absorption rate of the aggregate of CA6 particles is 50% or more and the bulk density is higher than 0.60 g / cm ³ as in Comparative Example 3, crushed CA6 particles are not obtained, and the refractory material is obtained. In this case, it is considered that the area of the interface between the matrix material and the CA6 particles is small, the bond strength is weakened, and the strength of the refractory is weakened.

When an appropriate amount of borax is added to the raw material in the production of CA6 particles, the breaking strength of the CA6 particles is improved, and when the pulverized product is pulverized to the target particle size using the CA6 calcined product produced by adding borax. In addition, crushed CA6 particles having a low bulk density can be produced. When a refractory is produced using these CA6 particles, the area of the interface between the CA6 particles in the refractory and the matrix substance is large, and the binding force is large. Strengthens and improves refractory strength. Therefore, the present invention is extremely useful industrially.

Claims (5)

When the crystal phase is CaO.6Al ₂ O ₃ and the particle size is sieved to 3 mm or more and less than 6 mm, the water absorption rate by the boiling method defined in JIS R 2205: 1992 is 50% or more and 100% or less, and An aggregate for refractory, characterized by having a bulk density of 0.40 g / cm ³ or more and 0.60 g / cm ³ or less. The aggregate for refractories according to claim 1, comprising 0.02 mass% or more and 0.4 mass% or less of boron. A refractory comprising the refractory aggregate according to claim 1 or 2 as an aggregate and alumina cement as a binder. The method for producing an aggregate for a refractory according to claim 2, obtained by mixing an aggregate raw material containing a calcia raw material and an alumina raw material with water, followed by molding and firing at 1000 ° C to 1700 ° C. The method for producing an aggregate for refractory according to claim 2, wherein borax is added to the refractory.   The method for producing an aggregate for a refractory according to claim 4, wherein an amount of borax added to the aggregate material is 0.1 mass% or more and 4.0 mass% or less.

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