JP2572543B2 - Tool material for cordierite firing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordierite firing tool.

[0002]

2. Description of the Related Art Usually, ceramics, tiles and the like are fired by placing a work (a product to be fired) on a refractory shelf.
The firing tools used for refractory shelves are generally cordierite, SiC or the like. Cordierite is a material that is resistant to thermal shock due to its low coefficient of thermal expansion, is lightweight, and is relatively stable in an oxidizing and neutral atmosphere.

For example, Japanese Patent Application Laid-Open No. 1-133985 discloses a method of manufacturing a degreasing / firing setter having a side wall portion made of a ceramic sintered body and a bottom portion made of a ceramic porous sintered body. A mixture containing essentially (A) a sintering substance composed of an inorganic compound having an average particle size of 0.1 to 500 μm, (B) a sintering substance containing an ethylene-based polymer and (C) an organic peroxide. And the bottom is essentially composed of a mixture containing a sinterable substance consisting of the sinterable substance, an ethylene-based polymer, an organic peroxide and a pyrolytic foaming agent, and the side wall and the bottom are inserted. A method for producing a degreasing / sintering setter characterized by performing molding by crosslinking or crosslinking and foaming by an injection molding method or a two-color molding method, degreasing the resulting molded product, and then sintering. And before Cordierite as a sintering material is also described to the effect that can be used.

Japanese Patent Application Laid-Open No. 1-302703 discloses an electronic component in which at least a part of the surface of a sintered body constituting a substrate is covered with an electrofused spinel layer for preventing a reaction. A firing jig is disclosed, and the sintered body is any one of alumina, mullite, and cordierite refractories having a room temperature bending strength of 50 to 150 kgf / cm ^2. It is also described.

Further, Japanese Patent Application Laid-Open No. 2-68488 discloses that one surface is composed of a layer mainly composed of MgO (magnesia) having excellent corrosion resistance, and the other surface (rear surface) has a thermal shock resistance. 2MgO ・ 2Al ₂ O ₃・ 5SiO ₂ (Cordite)
Is composed of a layer mainly composed of
P comprising a composition continuously changed from a composition of gO.2Al ₂ O ₃ .5SiO _{2 to a} composition of MgO.
A functionally graded material suitable as a material for high-temperature jigs such as containers and setters used for heat treatment such as calcination and sintering of ZT and BaTiO ₃ ceramics is disclosed.

Further, Japanese Patent Publication No. 4-68256 discloses that Al ₂
O _{3 10 to} 82% by weight, SiO ₂ 14 to 54% by weight, Mg
A cordierite-based refractory containing 4 to 8% by weight of O as a main component, wherein a main crystal phase after firing is 10 to 40% of an andalusite mineral, 5 to 20% of an alumina mineral,
A cordierite refractory comprising 30% mullite mineral is disclosed.

[0007] Cordierite-based firing tools have a life span of hundreds of times before disposal. The damage pattern is firstly a phenomenon of deformation or breakage due to hot mechanical stress. This is due to factors such as the temperature conditions at which the firing tool is used, the shape of the firing tool, and the load on the workpiece. Cordierite is resistant to thermal shock, but is a mineral with a relatively low melting point. Since it is creep-deformed due to the weight of the work under a temperature condition of 1200 to 1300 ° C., two or more cordierites are usually reinforced by adding mullite. The cordierite sintering tool material is composed of minerals.

The second damage pattern is a phenomenon of cracking due to internal stress of the firing tool due to thermal expansion at the time of temperature rise and temperature decrease, such as the heating and cooling speed and the coefficient of thermal expansion of the tool. Is the quality characteristic. The cause of the remaining disposal is chipping or cracking due to handling.

However, since the firing tool material is subjected to a large number of heat histories as described above, its quality is not constant, and gradually changes with the number of uses, which is another factor that limits the number of uses. It is a big factor. Chipping or cracking due to handling is closely related to this quality change.

[0010]

The firing tool is heated to a high temperature in a furnace together with the workpiece. For this reason, the following phenomenon inevitably occurs in the firing tool material. First, there is a chemical reaction with a work or the like. A reaction by contact with the glaze applied to the work or its surface, or a gas phase reaction with an alkali component evaporating from the glaze or the like can be given.
In addition to these chemical reactions, the effect of temperature changes, such as repeated heating and cooling, on the firing tool is greater than expected, reducing the number of times the firing tool can be used in the form of quality deterioration due to residual expansion. . As mentioned above,
In order to improve durability, not only the initial product quality,
It is important to control quality changes.

The present inventors have paid attention to the fact that the quality change occurring when the firing tool material is used many times affects the durability, and studied means for chemically and physically stabilizing the tool. As a result, it was found that the low melting point component in the fine powder portion of the raw material mixture of the firing tool material not only promotes deterioration due to a chemical reaction with foreign components, but also forms a glass phase and raises the coefficient of thermal expansion of the fine powder bonding portion. . That is, when the glass phase exists in the fine powder bonding portion and the coefficient of thermal expansion is raised, a difference in thermal expansion between the hot particles and the coarse particles occurs, and a gap is formed at the grain boundary. In the cooling process, all of these gaps are not eliminated, and this appears as a form of residual expansion of the firing tool. Since the residual expansion generated in this manner is accompanied by embrittlement, the strength of the entire structure is deteriorated.

By the way, cordierite has an advantage of low coefficient of thermal expansion, but 2MgO-2Al ₂ O ₃ -5SiO
_It has a relatively low softening point because it has the composition of ₂ , and is easily made of glass when other components are contained. However, cordierite is inherently low in melting point, and research has been conducted to prevent softening deformation during manufacturing [for example,
H. RASCH, Some effects of temporary liquid phases,
firing conditions and raw materials, cfi / Ber.DKG68
(1991) No. 7 / 8p338], almost no consideration has been given to the effect of using a glass phase. When cordierite is heated and reacted with alkali such as Na ₂ O and K ₂ O from the chemical composition, it easily forms a silica glass phase,
Even MgO, which should originally constitute cordierite, melts into the glass phase. The glass phase thus formed has a higher coefficient of thermal expansion than the original cordierite, and has the disadvantage of further increasing the coefficient of thermal expansion beyond the transition temperature (by Naruse:
Glass Engineering p262). MgO, which should have been added to lower the coefficient of thermal expansion, acts in the direction of producing glass, and changes to one that gives a bad effect in terms of thermal expansion.
Therefore, it is necessary to limit the content of impurities in order to suppress the generation of a glass phase. Alkali is, of course, an impurity, but Fe ₂ O ₃
Is mentioned. Fe ₂ O ₃ has a relatively high content in refractory raw materials, and when Fe ₂ O ₃ is reduced to FeO, a lower melting point is formed between Al ₂ O ₃ and SiO _2. Generate substances with Therefore, Fe ₂ O ₃ , FeO
Must also be limited. In addition, MgO, which is a main component of cordierite, should be included in the restriction because it affects the formation of glass as described above.

Accordingly, an object of the present invention is to improve the thermal shock resistance, improve the volume stability against repeated use of heating and cooling for multiple uses, suppress deterioration in quality, and extend the number of service life. An object of the present invention is to provide a cordierite firing tool material.

[0014]

That is, the present invention provides a cordierite of 20 to 80% by weight and a mullite + clay of 80 to 80% by weight.
Particle size distribution of the raw material mixture in a range of 30 to 65% by weight of particles having a particle size of 0.3 to 3mm and particles of a particle size of 35 to 70% by weight having a particle size of less than 0.3mm containing 20% by weight. The total amount of Na ₂ O and K ₂ O contained in the fine powder portion composed of particles having a particle size of less than 0.3 mm is 0.7% by weight or less, and Al ₂ The present invention relates to a cordierite-based firing tool material having a weight ratio of O ₃ / (Fe ₂ O ₃ × MgO) of 8.0 or more.

[0015]

According to the present invention, in a cordierite firing tool material, impurities in a fine powder portion having a particle size of less than 0.3 mm are divided into two groups of Na ₂ O, K ₂ O, MgO, and Fe ₂ O _3. By separately defining the content, the generation amount of the glass phase is reduced, and the coefficient of thermal expansion is reduced.
This effect can be expected not only to improve the thermal shock resistance, but also to increase the volume stability against repeated heating and cooling due to repeated use, and to suppress quality deterioration.

As a specific method, the total amount of Na ₂ O and K ₂ O contained in the fine powder portion composed of particles having a particle size of less than 0.3 mm is set to 0.7% by weight or less, and Al ₂ O ₃ / ( Fe ₂ O ₃
× MgO) The object can be achieved by restricting the value of the weight ratio to 8.0 or more.

The amount of mineral cordierite is between 20 and 80% by weight, preferably between 30 and 70% by weight. If the amount of cordierite is less than 20% by weight, the effect of adding cordierite is too small to contribute to lowering the overall thermal expansion. As described above, cordierite refractories usually use mullite as a countermeasure against creep, so that the upper limit of the cordierite content is about 80% by weight. For the same reason, the total amount of mullite and clay is 20
８０80% by weight, preferably 30-70% by weight. Therefore, when these components are represented by compositions, they are approximately MgO3 to 1
1 wt%, Al ₂ O ₃ 40~60 wt%, SiO _2. 35 to
It becomes 50% by weight.

As the cordierite used in the present invention, the theoretical ratio of 2MgO-2Al ₂ O ₃ -5SiO ₂ is ideal, but the allowable range is 10% by weight or more of MgO, and Al ₂ O ₃
There 30-40 wt%, SiO ₂ 45 to 55% by weight is one measure. Mullite can be applied widely, and its Al ₂ O ₃ value is 50 to 75% by weight, and SiO ₂ value is 25 to 5%.
0% by weight is a standard, and either a fired product or an electrofused product may be used. Furthermore, clay can be widely used as long as it is plastic and has good moldability, such as natural Kibushi clay, ball clay, and processed elutriated clay. In order to further improve the creep resistance, the clay can be partially replaced with calcined alumina. However, what is important in common among these raw materials is that there are few impurities such as Na ₂ O, K ₂ O and Fe ₂ O ₃ . Preferably Na ₂ O and K ₂ O
Is less than 0.7% and Fe ₂ O ₃ is less than 1.0%.

In the cordierite firing tool material of the present invention, the definition of the impurity component should be made in the fine powder portion of the raw material mixture having particles having a particle diameter of less than 0.3 mm. The reason is that the large particles having a particle diameter of 0.3 mm or more have a small specific surface area and are relatively stable, so that the progress of the reaction is slow in the sintering process and heating conditions during use,
This is because particles having a particle size of less than 0.3 mm have a rapid increase in activity, so that the reaction proceeds rapidly, and therefore a glass phase is easily formed.

N has the greatest effect on the formation of the glass phase.
These are alkaline components such as a ₂ O and K ₂ O, and the upper limit of the total amount is 0.7%. If the total amount is more than this, glass is easily formed.

Al ₂ O ₃ is a component that suppresses the formation of a glass phase, while it is a component that contributes to the formation of MgO and Fe ₂ O ₃ glass. From this, Al ₂ O ₃ and MgO
And the ratio of Fe ₂ O ₃ , that is, Al ₂ O ₃ / (MgO × Fe ₂
The value of the O ₃ ) weight ratio can be used as another measure for suppressing the formation of the glass phase. This value must be at least 8.0, and if it is less than this, the amount of glass produced increases,
The coefficient of thermal expansion increases.

The maximum particle size of the raw material used is preferably up to 3 mm. If it is larger than this, the absolute length affected by the difference in thermal expansion becomes large, so that cracks at the grain boundaries tend to occur.

In producing the cordierite-based firing tool material of the present invention, a general molding aid such as PVA, sodium alginate, sodium lignin / sulfonate, or CMC is added to the raw material mixture in an amount of 0 to 4 depending on the shape. 0.1 to 3.0 parts by weight, preferably 0.5 to 2.0 parts by weight and water 3 to 8 parts by weight, preferably 4 to 6 parts by weight, and kneaded,
It is molded into a predetermined shape at a molding pressure of 30 to 100 MPa, dried and fired at 1250 to 1400 ° C. At this time, the particle size distribution of the raw material mixture is as follows.
If it is set in the range of 70% by weight, molding is easy. If the amount of particles having a particle size of less than 0.3 mm is less than 35% by weight, it is too coarse, resulting in insufficient strength of the molded body. The firing temperature is 125
If the temperature is lower than 0 ° C., the strength becomes insufficient, and if the temperature is higher than 1400 ° C., the generation amount of the glass phase rapidly increases, which is not preferable.

[0024]

The present invention will be described below in more detail with reference to examples of the present invention. Example Using a raw material having a chemical composition shown in Table 1 below, a raw material mixture was prepared in a mixing ratio shown in Table 2 below. Table 2 also shows the overall composition of the raw material mixture and the composition of the fine powder portion composed of particles having a particle size of less than 0.3 mm. Next, 1.5 parts by weight of lignin-sulfonate and 5 parts by weight of water were added and kneaded with 100 parts by weight of the raw material mixture as a molding aid, and the mixture was kneaded at a molding pressure of 50 MPa and 160 mm ×
It was formed into a shape of 40 mm × 15 mm. After drying the obtained molded body at 100 ° C. for 12 hours, it was fired at 1350 ° C. for 2 hours to obtain a specimen. Table 2 also shows various properties of the obtained specimen.

[0025]

[Table 1]

[0026]

[Table 2]

[0027] In Table 2, the bending strength is JIS 2213
This is a value measured by a -78 three-point bending test. The elastic modulus is a value measured by a sound wave method. Further, the coefficient of thermal expansion is a value measured by the non-contact measurement method of JIS 2207-76. Further, the residual expansion rate after 400 times is a value measured by a caliper, and the bending strength after 400 times is a value measured by a three-point bending test.

[0028]

In the cordierite-based firing tool for firing ceramics and the like according to the present invention, impurities in the fine powder portion composed of particles smaller than 0.3 mm in particle size are Na ₂ O and K ₂ O.
By defining the content in two groups, that is, MgO and Fe ₂ O ₃ , the generation amount of the glass phase was reduced, and the coefficient of thermal expansion was reduced. This effect not only improved the thermal shock resistance, but also increased the volume stability against repeated heating and cooling due to multiple uses, suppressed quality deterioration, and increased the number of service life.

Claims (1)

(57) [Claims] 1. A composition comprising 20 to 80% by weight of cordierite and 80 to 20% by weight of mullite + clay, 30 to 65% by weight of particles having a particle size of 0.3 to 3 mm, and 0.3 to 0.3% by weight.
In a cordierite-based firing tool having a particle size distribution of a raw material mixture within a range of 35 to 70% by weight of particles having a particle size of less than 3 mm, Na ₂ O and K ₂ O contained in a fine powder portion composed of particles having a particle size of less than 0.3 mm are used. A cordierite-based sintering tool material characterized in that the total amount is 0.7% by weight or less and the weight ratio of Al ₂ O ₃ / (Fe ₂ O ₃ × MgO) is 8.0 or more. .