JP5110539B2 - FeO resistant coating material - Google Patents

Description

  The present invention relates to a fire resistance such as a ceramic fiber block or a ceramic fiber molded body for a skid post applied to a heating furnace, a soaking furnace, a heat treatment furnace, a furnace lid, a cover, etc. used in steelmaking, steel making, rolling processes, etc. The present invention relates to a FeO-resistant coating material applied to the surface of a ceramic fiber heat insulating material.

  In recent years, ceramic fibers have been used for the purpose of energy saving and heat insulation of various kiln facilities such as a heating furnace. Ceramic fiber not only has low thermal conductivity, but also has a light weight and low bulk specific gravity, so it has advantages such as excellent thermal inertia, lowering furnace temperature, and shorter heating time, and compression lamination of ceramic fiber blankets. A ceramic fiber block in which a material or a ceramic fiber blanket is folded and integrated with a mounting bracket is employed as a main lining at a portion that does not come into contact with molten metal. Moreover, the ceramic fiber molded object is used as a heat insulating material for skid posts.

  However, although these heat insulating materials made of ceramic fibers have the excellent characteristics as described above, they are inferior in erosion resistance to FeO produced when a steel slab is heated, and are low melting point materials. There is a problem that the generation of firelite or the like promotes melting, shrinkage, and sintering, thereby reducing the heat insulation thickness, causing joint opening, and lowering the heat insulation.

  In order to solve such a problem, a coating material applied on the surface of the ceramic fiber heat insulating material by a spray gun or the like is used. For example, Patent Document 1 discloses a ceramic fiber containing a refractory aggregate powder containing alumina, silica powder having an α-quartz crystal form, boric acid, and a plasticizer-containing synthetic resin emulsion in a predetermined ratio. A coating material is disclosed. In this coating material, the main aggregate is alumina (70% or more), the aggregate other than alumina (0 to 30%) is spinel, magnesia, silica, silicon carbide, silicon nitride, and other refractories usually used for refractories. Substance is being used. Patent Document 2 discloses a method in which a ceramic fiber-containing spray material is sprayed on the surface of a ceramic fiber, and a coating material containing alumina is further applied to the construction surface. Furthermore, Patent Document 3 contains a crystalline fiber, an inorganic binder, an organic binder, and alumina powder as essential components, and the total of the crystalline fiber and the alumina powder is 90% by mass or more for the total firing. A furnace scale resistant coating material is disclosed.

  However, as the operation becomes severe, the amount of FeO generated from the steel slab increases, and when the operation temperature rises, the coating material mainly composed of alumina has FeO resistance even when spinel is added as described above. Is insufficient. In addition, in the conventional coating material as described above, a liquid phase is likely to occur between the heat, and during use, the coating material applied to the surface of the ceramic fiber heat-insulating material shrinks, causing cracks and peeling, thereby causing the ceramic fiber. There is a problem that the heat insulating material is eroded by FeO, and troubles such as a decrease in the heat insulating material thickness and a decrease in heat insulating property due to joint opening occur frequently. Furthermore, since the conventional coating material has a large residual shrinkage when cooled in the cold, it may be peeled off from the ceramic fiber heat insulating material during cooling, and there is a problem in durability.

By the way, as an amorphous refractory for molten metal container lining having a different technical field from the coating material for coating the surface of the ceramic fiber heat insulating material, an alumina / spinel amorphous refractory is known. the spinel made a MgO · Al ₂ O ₃ as a main component contains 50 to 95 wt%, the balance being mainly composed of Al ₂ O _3, molten iron removal flow lump material having excellent FeO resistance have been described . However, since the above-mentioned alumina-spinel amorphous refractory mainly uses relatively large particles (several mm or more) as an aggregate, it is difficult to produce an alumina-rich secondary spinel, as will be described later. -The peelability is insufficient.

Japanese Examined Patent Publication No. 63-56194 JP 2000-283656 A JP 2004-168565 A JP 59-128271 A

  In the present invention, in order to prevent erosion of the ceramic fiber heat insulating material applied to a heating furnace or the like by FeO, the coating material coated on the surface has FeO resistance, suppression of hot shrinkage, and suppression of residual shrinkage. In addition to providing excellent resistance to FeO, a coating material excellent in crack resistance, peelability and the like is provided.

As a result of diligent research and development focusing on spinel and MgO raw materials excellent in FeO resistance, the present inventors have formed a liquid phase at a high temperature, and due to shrinkage, spinel (MgO · Al ₂ O ₃ ) Although it is a raw material inferior in crack resistance, surprisingly, by using a spinel of 1 mm or less and alumina of 1 mm or less in combination at a predetermined concentration, an alumina-rich secondary spinel is generated, and the expansion causes a high temperature. The present inventors completed the present invention by finding that the shrinkage and residual shrinkage of the resin were suppressed and the crack resistance and peelability were significantly improved.
The gist of the present invention is as follows.

(1) A FeO-resistant coating material applied to the surface of a fire-resistant ceramic fiber heat insulating material. As an aggregate, 17.6 to 60% by mass of spinel having a particle size of 1 mm or less and a particle size of 1 mm or less 20 to 60% by mass of alumina, 5 to 30% by mass of crystalline fiber, and colloidal silica , and 25 to 60% by mass of water as an outer coating. Wood.
(2) The coating material according to (1), wherein the contained spinel and alumina all have a particle size of 1 mm or less .
(3) The coating material according to (1) or (2), wherein the crystalline fiber is a mullite crystalline fiber.

  A spinel that is excellent in FeO resistance but inferior in crack resistance due to shrinkage at high temperature produces an alumina-rich secondary spinel when used in combination with alumina as in the present invention, and its expansion suppresses shrinkage at high temperature. Thus, it is possible to obtain a FeO-resistant coating material with significantly improved crack resistance and excellent FeO resistance and crack / peeling resistance. Therefore, according to the present invention, the lifetime of the ceramic fiber block and the like can be extended, and stable operation is possible.

FIG. 1 is a graph showing a change in thermal expansion coefficient of the coating material of Example 1 according to a thermal expansion test. FIG. 2 is a graph showing a change in thermal expansion coefficient of the coating material of Comparative Example 1 by a thermal expansion test. FIG. 3 is a graph showing changes in the coefficient of thermal expansion of the coating material of Comparative Example 2 according to the thermal expansion test.

  The FeO-resistant coating material of the present invention will be further described below with reference to preferred embodiments.

The present invention is a FeO-resistant coating material applied to the surface of a refractory ceramic fiber heat insulating material, and contains, as an aggregate, a spinel having a particle diameter of 1 mm or less and an alumina having a particle diameter of 1 mm or less, Further, it contains crystalline fiber and colloidal silica. The ceramic fiber is an artificial inorganic fiber mainly composed of alumina (Al ₂ O ₃ ) and silica (SiO ₂ ), and has different heat resistance depending on the content of the alumina component. Crystalline fibers having an alumina content of 70% or more are also referred to as alumina fibers (including mullite fibers), and have particularly high heat resistance. The coating material according to the present invention can be applied to any of the common ceramic fibers by using these alumina and silica as main components.

  In the FeO resistant coating material of the present invention, spinel and alumina are used in combination in order to utilize the FeO resistance of the spinel and to form a coating layer having excellent crack resistance and peelability. Preferably, spinel having a particle size of 1 mm or less is contained in an amount of 20 to 60% by mass, more preferably 20 to 50% by mass, and alumina having a particle size of 1 mm or less is preferably 20 to 60% by mass, more preferably 20 to 50% by mass. %contains. The effect of using spinel and alumina in combination can be confirmed, for example, from the contents described in the following examples and comparative examples. That is, when measuring the thermal expansion coefficient curve when the temperature is increased from room temperature to 1400 ° C. at a rate of 4 ° C./min, and then the thermal expansion curve when the temperature is decreased to room temperature at a cooling rate of 4 ° C./min. In the case of a coating material containing only one of spinel or alumina as an aggregate, even if the particle diameter is 1 mm or less, FIG. 2 (aggregate is only alumina) or FIG. 3 (aggregate is only spinel) As is apparent from the above, since shrinkage is once performed at a high temperature of a predetermined temperature or higher, it can be understood that the remaining shrinkage after the heat history is large due to further shrinkage when cooling from such high temperature to cold. On the other hand, in the case of a coating material using both a spinel having a particle size of 1 mm or less and an alumina having a particle size of 1 mm or less, it is confirmed from FIG. Since it turns into expansion and shrinkage at high temperature hardly occurs, shrinkage occurs when it is cooled in the cold after that, but it can be seen that the residual shrinkage after the thermal history is much smaller than in the case of FIG. 2 or FIG.

  For this reason, the present inventors speculate that spinel with a particle size of 1 mm or less and alumina with a particle size of 1 mm or less react to form an alumina-rich secondary spinel, and its expansion suppresses thermal shrinkage at high temperatures. It is thought that this is because residual shrinkage is suppressed, and as a result, it is assumed that cracking is prevented. At this time, if the spinel particle size is larger than 1 mm or the alumina particle size is larger than 1 mm, secondary spinel is hardly generated even if spinel and alumina are used in combination, shrinkage cannot be suppressed, and cracking occurs. It becomes easy. In addition, even if spinel or alumina having a particle size exceeding 1 mm is mixed, if both a spinel having a particle size of 1 mm or less and an alumina having a particle size of 1 mm or less exist, it is considered that an alumina-rich secondary spinel is generated. The present invention can be applied. However, if the application to the surface of the refractory ceramic fiber heat insulating material is premised on the spraying work, if the particle size of the spinel or alumina contained as the aggregate exceeds 1 mm, the work with the spray gun or the like may not be possible. Therefore, it is preferable to use almost all spinel and alumina having a particle diameter of 1 mm or less. Further, when removing spinel or alumina having a particle diameter of more than 1 mm, a sieve may be used. The particle diameters of spinel and alumina both indicate the particle diameter obtained by a laser diffraction / scattering measurement method.

  Of these, α-alumina having high thermal stability is preferably used as alumina. On the other hand, various types of alumina / magnesium spinels are used as the spinel, including a theoretical composition spinel, an alumina rich spinel with more alumina than the theoretical composition spinel, and a magnesia rich spinel with more magnesia than the theoretical composition spinel. The spinel used in the present invention preferably has an MgO content of 5% by mass to 35% by mass. If the content of MgO is less than 5% by mass, the composition of alumina approaches and secondary spinel is difficult to be generated. On the other hand, when the content of MgO exceeds 35% by mass, hydration occurs due to reaction with water added as described later, and cracks due to digestion are likely to occur.

  The crystalline fiber is for suppressing cracking during curing and drying, and for increasing the bonding strength with the surface of the ceramic fiber heat insulating material used for the coating material. Preferably, the alumina fiber or alumina content is 72. It is preferable to use mullite crystalline fiber having a mass of at least%. The concentration range of the crystalline fiber is preferably 5 to 40% by mass. If the amount is less than 5% by mass, the effect of increasing the bonding force cannot be expected. On the other hand, if the amount exceeds 40% by mass, the crystalline fibers are difficult to uniformly disperse in the coating material. More preferably, it is 7-30 mass% from a viewpoint of bonding strength and uniform dispersion. Further, the crystalline fiber has a strong reaction with the scale, and when it exceeds 30% by mass, the FeO resistance is extremely lowered. Furthermore, since the crystalline fiber hardly expands, the thermal expansion coefficient decreases as the amount added increases, which is a preferable direction, but the FeO resistance deteriorates. % Is preferable, and 7 to 30% by mass is more preferable. In addition, since the amorphous fiber has low heat resistance, it shrinks at a high temperature to generate a crack, and easily reacts with the scale, so that it is inferior in crack resistance / peeling resistance and FeO resistance.

  Colloidal silica is a binder and may be used in a general blending ratio, but the concentration range is, for example, 5 to 30% by mass, preferably 10 to 25% by mass. When the amount is less than 5% by mass, the adhesiveness is lowered. When the amount is more than 30% by mass, a large amount of hot liquid phase is generated, not only the heat resistance is lowered, but also the shrinkage is increased.

  Although there is no restriction | limiting in particular about the method of apply | coating the FeO-resistant coating material of this invention to a ceramic fiber heat insulating material, Generally, the method of applying to a ceramic fiber heat insulating material with a spray gun etc. is employ | adopted. At this time, water is added to the FeO-resistant coating material of the present invention so that the viscosity is usually about 8000 to 20000 cP, and the construction thickness is about 0.5 to 10 mm. It is preferable to do this. When the construction thickness is thinner than this, the effect of the FeO-resistant coating material is not sufficient. On the other hand, when the construction thickness is thicker than this, there is a risk that it will fall without being able to withstand its own weight. The amount of water added (outer coating) is usually 25 to 60% by mass. Furthermore, the FeO-resistant ceramic fiber coating material of the present invention includes, in addition to the above components, if necessary, in order to prevent sag during spraying or application and to improve adhesion, an organic binder such as CMC (carboxymethylcellulose) or PVA (polyvinyl alcohol) etc. can be mix | blended, refractory materials, such as bentonite, can be mix | blended, and trace control agents, such as surfactant, can be mix | blended, and storage stability etc. can be improved. However, these additional components are desirably 8% by mass or less of the FeO resistant coating material so as not to impair the FeO resistance.

[Examples 1-5 , Examples 7-9, Reference Examples , Comparative Examples 1-7]
Coating materials according to Examples 1 to 5, 7 to 9, and Reference Examples and Comparative Examples 1 to 7 were prepared with the materials and blends shown in Table 2 using the aggregates described in Table 1 below. . In addition, Table 2 shows various characteristics of the coating materials obtained in Examples , Reference Examples, and Comparative Examples.

  Each coating material prepared above is kneaded with water, poured into a casting frame, cured at room temperature for 24 hours, and then a test coating sample of 100 × 100 × thickness 10 (mm) was prepared, and cracks generated on the surface The presence or absence was confirmed visually. Moreover, the test coating sample was baked at 1400 ° C. for 3 hours, and the presence or absence of cracks generated on the surface was observed. Further, as an evaluation of FeO resistance, a disc-shaped FeO of 25 mmφ was placed on the test coating sample and fired at 1400 ° C. for 3 hours in that state, and the reaction discoloration diameter formed by the reaction with FeO was measured. . Then, in Comparative Example 1, the average length of the two points that reacted with FeO and spread in a circular shape was defined as 100, and the average length of the reaction discoloration diameter of each sample was displayed as the reaction discoloration ratio. Furthermore, a thermal expansion test up to 1400 ° C. was carried out using a test sample of 20 × 20 × 70 mm in length, and the residual line change when cooled to room temperature was measured (both the heating rate and the cooling rate were both 4 ° C / min). The residual line change rate was determined by the ratio (shrinkage amount) of shrinkage from the sample length after heating to 1400 ° C. and cooling to room temperature based on the sample length before heating. The results are shown in Table 2. Moreover, about the case of Example 1 and Comparative Examples 1 and 2, the change of the thermal expansion coefficient by a thermal expansion test is shown in FIGS. 1-3, respectively.

Comparative Example 1 is a case of using conventional alumina alone. It can be seen that cracks are generated, the residual line change rate is large, and the FeO resistance is poor. Comparative Example 2 was a case where spinel was used alone, but the residual shrinkage was large, cracking occurred after firing, and FeO resistance was poor. Comparative Examples 3 and 4 are cases in which magnesia and alumina are used in combination, but it is considered that cracks were generated by digestion of magnesia. In Comparative Examples 5 and 6, since spinel or alumina having a particle size larger than 1 mm was used, secondary spinel was hardly generated, and it was considered that shrinkage could not be suppressed and cracking occurred. In Comparative Example 7, since amorphous fibers were used, the FeO resistance was inferior and cracks also occurred. On the other hand, the coating materials of Examples 1 to 5 and 7 to 9 are suppressed in shrinkage at a high temperature by using spinel and alumina in combination, have little residual shrinkage, do not generate cracks, and have FeO resistance. It turns out that it is excellent.

  In addition, the coating materials obtained in Examples 1 and 2 and Comparative Example 1 were applied to a hot rolled heating furnace ceiling block (using ceramic fiber with a heat-resistant temperature of 1600 ° C) at A Steel Works to a thickness of 2 mm using a spray gun. As a result, in the in-furnace inspection after 4 months, the coating material of Comparative Example 1 reacted with FeO and cracks were generated and peeled off, but the coating materials of Examples 1 and 2 showed a reaction with FeO. Neither crack nor peeling was generated.

Claims (3)

A FeO-resistant coating material applied to the surface of a refractory ceramic fiber heat insulating material, comprising 17.6 to 60% by mass of spinel having a particle diameter of 1 mm or less and alumina having a particle diameter of 1 mm or less as an aggregate. A coating material comprising 20 to 60% by mass , further containing 5 to 30% by mass of crystalline fiber and colloidal silica, and containing 25 to 60% by mass of water as an outer shell . 2. The coating material according to claim 1, wherein the spinel and alumina contained each have a particle size of 1 mm or less.   The coating material according to claim 1, wherein the crystalline fiber is a mullite crystalline fiber.

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