JP4461414B2

JP4461414B2 - Method for firing ceramic honeycomb structure

Info

Publication number: JP4461414B2
Application number: JP2002217617A
Authority: JP
Inventors: 修徳留
Original assignee: Hitachi Metals Ltd
Current assignee: Hitachi Metals Ltd
Priority date: 2002-07-26
Filing date: 2002-07-26
Publication date: 2010-05-12
Anticipated expiration: 2022-07-26
Also published as: JP2004059353A

Description

【０００１】
【発明の属する技術分野】
本発明は、セラミックハニカム構造体の焼成方法に関するものである。
【０００２】
【従来の技術】
従来、生素地のセラミックハニカム構造体を焼成してセラミックス製品を製造する方法として、ハニカム構造体のセル壁に生じる割れおよびセラミックハニカム構造体と棚板との付着を防止する方法として、棚板の上にトチと呼ばれる焼成台を乗せ、その上に生素地のセラミックハニカム構造体を載せて焼成する方法が知られている。ここで、トチとは、ハニカム構造体を例えば厚さ２０〜３０ｍｍになるように径方向に切断したもので、トチのハニカム構造の開口端面に生素地のセラミックハニカム構造体の開口端面が当接するように載置される。
【０００３】
以下、トチを用いた従来技術について詳述する。特公平２−４００１９号公報記載の発明では、生素地セラミックハニカム構造体の両開口端面にトチを当接させる技術が開示されており、生素地セラミックハニカム構造体端面での加熱による温度分布の不均一を原因とする切れの発生を防止でき、温度上昇が早く、温度分布が均一な焼成を可能とし、生産性を高くできるとしている。また特公平１−５４６３６号公報記載の発明では、外縁に面取りを施したトチを生素地のセラミックハニカム構造体に載置させる技術が開示されており、生素地ハニカム構造体の開口下端面の外縁部にトチと接触しない部分を設けることにより、生素地ハニカム構造体トチとの接触面で起こる摩擦抵抗力が軽減され、生素地ハニカム構造体の外縁部に特に多い切れの発生を防止できるとともに、生素地ハニカム構造体を充分均一に加熱することができ、また、昇温速度を高めることができるとしている。ここで、トチは生トチでも万年トチでも良いとされているが、生トチは一度しか使用できないため経済的でない。さらに、特開平７−２０８８７３号公報記載の発明では、凸形状のトチを焼成台として採用する技術が開示されており、焼成収縮する際、被焼成体の外縁部分のトチと被焼成体の接触面で摩擦抵抗力を無くすことができることによりクラックのないセラミックハニカム体の焼成が可能となるとともに、被焼成体はグラグラ揺れること無く安定して保持されるので、処理と取扱が容易になるとしている。
【０００４】
トチ以外の焼成台としては、特開平５−８５８３４号公報記載の発明では、生素地ハニカム構造体の開口端面を、主成分が耐熱性無機繊維からなり、嵩密度が１．００ｇ／ｃｍ^３以上のセラミック板の上に載せて焼成する方法が開示されており、焼成台の熱変形によるハニカム構造体のリブよれ、端面変形およびこれから発生する端面クラックを減少させ、焼成台の長寿命化を達成でき、ハニカム構造体の寸法上下差を減少することができるとしている。また、特開平６−８１７９７２号公報記載の発明では、結晶相の主成分の組成がコージェライト５５〜８５重量％、ムライト１５〜４５重量％からなる敷板を焼成台とする方法が開示されており、従来のトチ等の敷板に比べて、耐熱性が向上し、敷板の熱変形やシリカ成分の融出によるハニカム構造体下端面の変形、リブよれや、クラックの発生が抑止でき、さらにハニカム構造体下端面の変色を生じさせずに、生素地セラミックハニカム構造体を焼成することができるとしている。
【０００５】
【発明が解決しようとする課題】
しかしながら、上述した従来技術に記載のいずれの焼成台を使用しても、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れが発生するという問題が完全には解消できなかった。特に、近年排ガス規制が厳しくなりつつあるディーゼルエンジンの排ガス浄化に用いられる様な、外径２００ｍｍ以上、長さ２００ｍｍ以上の大型セラミックハニカム構造体の場合、ハニカム構造体の自重が大きくなることから、ハニカム構造体が焼成収縮する際に、セラミックハニカム構造体と焼成台との当接面に発生する摩擦抵抗力が大きくなるため、セラミックハニカム構造体の開口端面に割れが発生し易いという問題があった。
【０００６】
本発明の課題は、セラミックハニカム構造体を焼成するにあたり、セラミックハニカム構造体の開口端面の外径が２００ｍｍ以上、長さが２００ｍｍ以上の大型品であっても、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れが生じないセラミックハニカム構造体の焼成方法を提供することにある。
【０００７】
【課題を解決するための手段】
本発明者は、セラミックハニカム構造体の開口端面と当接する焼成台を種々検討し、セラミックハニカム構造体の開口端面の外径と焼成台との関係について鋭意研究を行った。その結果、焼成台として耐熱性無機粉末を用いることにより、セラミックハニカム構造体の外径が２００ｍｍ以上、長さが２００ｍｍ以上の大型品であっても、焼成台との当接面であるセラミックハニカム構造体の開口端面に割れが発生しないセラミックハニカム構造体を得ることができるとの知見を得て、本発明に想到した。
【０００８】
具体的には、本発明は、外径が２００ｍｍ以上、長さが２００ｍｍ以上のセラミックハニカム構造体を焼成するにあたり、生素地のセラミックハニカム構造体の開口端面を平均粒径が０．１２ｍｍ〜０．３７ｍｍの耐熱性無機粉末により構成される厚さが５ｍｍ以上３０ｍｍ以下である焼成台の上に載せて焼成することを特徴とする。生素地のセラミックハニカム構造体の開口端面を平均粒径が０．１２ｍｍ〜０．３７ｍｍの耐熱性無機粉末により構成される厚さが５ｍｍ以上３０ｍｍ以下である焼成台の上に載せて焼成することにより、ハニカム構造体のセル壁で囲まれる流路の方向が概略重力方向に一致するため、焼成過程に於いてハニカム構造体が軟化してもセル壁の変形が発生しにくくなるのと共に、焼成過程においてセラミックハニカム構造体の膨張収縮が発生した際に、焼成台を構成する耐熱性無機粉末の個々の粒子の移動が可能であることから、セラミックハニカム構造体と耐熱性無機粉末との膨張収縮量の違いがあってもセラミックハニカム構造体当接面の耐熱性無機粉末がセラミックハニカム構造体の膨張収縮に伴い一部移動し、発生する摩擦抵抗力が緩和され、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れが発生しにくくなるからである。
【０００９】
本発明において耐熱性無機粉末の材質としては、コージェライト、ムライト、アルミナ、シリカ、炭化珪素、窒化珪素等の耐熱性の高い粉末、あるいはこれらの混合粉末が、焼成時の高温に曝されても変形しにくいことから適している。
さらには、耐熱性無機粉末が、焼成して得られるセラミックハニカム構造体と同系統の材質であると、焼成台とセラミックハニカム構造体との熱膨張係数差が小さくなり、焼成台とセラミックハニカム構造体との当接面に生じる摩擦抵抗力の緩和効果が大きくなるため、好ましい。ここで、同系統の材質であるとは、例えば、焼成して得られるセラミックハニカム構造体がコージェライトを主成分とする場合は、耐熱性無機粉末もコージェライトを主成分とすることを意味する。ここで、耐熱性無機粉末は、その全量が焼成して得られるセラミックハニカム構造体と同系統の材質である必要は必ずしもなく、少なくとも１０質量％以上が焼成して得られるセラミックハニカム構造体と同系統の材質であれば、焼成台とセラミックハニカム構造体との当接面に生じる摩擦抵抗力が緩和されるため、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れが発生しにくくなる。
【００１０】
また、本発明において、前記耐熱性無機粉末の平均粒径が０．１２ｍｍ以上０．３７ｍｍ以下であることが好ましい。耐熱性無機粉末の平均粒径が０．１２ｍｍ未満であると、微細な粉末であることから焼成炉内部のガス流により粉末が周囲に拡散してしまうこともあるため、焼成台としての機能を果さなくなる場合もあるからである。一方、耐熱性無機粉末の平均粒径が０．３７ｍｍを超える場合、耐熱性無機粉末個々の粒子の移動抵抗が大きくなり焼成台である耐熱性無機粉末とセラミックハニカム構造体との当接面に生じる摩擦抵抗力の緩和が不十分となるため、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れを発生させることもあるからである。耐熱性無機粉末の平均粒径は、上記の理由から、０．１２ｍｍ以上、０．２ｍｍ以下がより好ましい範囲である。本発明において、焼成台を構成する耐熱性無機粉末の粒子形状が、略球形状のように丸みを帯びていることがより望ましい。粒子形状が、略球形状のように丸みを帯びていることにより、略球形状粉末の転がり作用により、耐熱性無機粉末の個々の粒子の移動がより容易になり、耐熱性無機粉末で構成される焼成台とセラミックハニカム構造体との当接面に生じる摩擦抵抗力をより小さくできるため、焼成台との当接面であるセラミックハニカム構造体の開口端面の割れ防止により有効に作用するからである。
【００１１】
また、本発明においては、耐熱性無機粉末で構成される焼成台の厚さを１ｍｍ以上、５０ｍｍ以下とすることが望ましい。焼成台の厚さが１ｍｍ未満であると、耐熱性無機粉末の下に敷かれる棚板の種類によっては、耐熱性無機粉末の一部が棚板との界面で化学反応を起こし耐熱性無機粉末が棚板に固着する場合もあるため、セラミックハニカム構造体と耐熱性無機粉末との当接面に生じる摩擦抵抗力の緩和が不十分となり、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に割れが発生する場合もあるからである。一方、焼成台の厚さが５０ｍｍを超えると、セラミックハニカム構造体の長さに対する焼成台の厚さが無視できなくなり、生素地セラミックハニカム構造体の焼成炉内への搭載量が減少するため製造コストが上昇するという悪影響が発生するからである。なお、耐熱性無機粉末で構成される焼成台の厚さは、上記の理由から、５ｍｍ以上３０ｍｍ以下がより好ましい範囲である。
【００１２】
【発明の実施の形態】
以下、本発明を実施の形態により説明する。
予めコージェライト組成に配合したセラミック原料粉末、成形助剤、および添加剤を混合、混練、押出成形、乾燥して生素地のハニカム構造体を得た。一方、別途焼成台を構成するための耐熱性無機粉末として、平均粒径が０．４ｍｍ、０．３７ｍｍ、０．２ｍｍ、０．１２ｍｍ、０．０２ｍｍ、０．００８ｍｍ、０．００５ｍｍのコージェライト粉末、および平均粒径が０．１２ｍｍのムライト粉末、平均粒径が０．１２ｍｍのアルミナ粉末、平均粒径が０．１２ｍｍのシリカ粉末をそれぞれ用意した。また、平均粒径０．１２ｍｍのコージェライト粉末、平均粒径０．１２ｍｍのムライト粉末、平均粒径０．１２ｍｍのアルミナ粉末を表２に示す配合比で混合して、これらが混合された耐熱性無機粉末を準備した。そして、図１及び図２に示すように、これら各耐熱性無機粉末５をハニカム構造体の焼成棚板４上に載せてヘラ等で平坦に一定厚さ６とした焼成台２の上に前記生素地のハニカム構造体１を載せ、バッチ式焼成炉による焼成を行った。一方、本発明に対する比較例の焼成台として、コージェライト生素地のハニカム構造体からなる厚さ１０ｍｍのトチ、焼成済みのコージェライト質のハニカム構造体からなる厚さ１０ｍｍのトチ、シリカ・アルミナ質の耐熱性無機繊維板をそれぞれ用意し、これら焼成台の上に前記生素地のハニカム構造成形体の開口端面を載せて配置し、バッチ式焼成炉による焼成を行った。焼成は１４００℃で行い、セル壁の厚さが０．３ｍｍ、セルピッチが１．４６ｍｍのセル構造を有する直径φ３００ｍｍ、長さ４００ｍｍのコージェライト質セラミックハニカム構造体を得た。焼成後、セラミックハニカム構造体の焼成台に接触している開口端面について割れの目視検査を実施し、セルが２ヶ所以上連続して切断しているものを割れと判定した。開口端面の割れ発生率は、焼成台との当接面であるセラミックハニカム構造体の開口端面について割れが認められた焼成体数の、同条件で試験を実施した焼成体数に対する比率として求めた。
【００１３】
焼成台の種類と割れ発生率との関係を、表１および表２に示す。
【００１４】
【表１】

【００１５】
【表２】

【００１６】
表１から、焼成台としてトチ、および耐熱性無機繊維板を用いた比較例１〜３対し、耐熱性無機粉末を用いた実施例１〜９では割れ発生率が実使用上問題無い範囲である２０％以下であることがわかる。割れ発生率は、耐熱性無機粉末の厚さが１ｍｍ以上５０ｍｍ以下であるとさらに低く、さらには耐熱性無機粉末の厚さが５ｍｍ以上であるとより低いことが判る。また、耐熱性無機粉末の平均粒径が０．００８ｍｍ以上０．３７ｍｍ以下であると割れ発生率が低く、さらには耐熱性無機粉末の平均粒径が０．０２ｍｍ以上０．２ｍｍ以下であるとより低いことが判る。また、耐熱性無機粉末の材質については、実施例１〜４においてコージェライト、ムライト、アルミナ、シリカのいずれを用いた場合でも割れ発生率は、０〜２．５％であったが、なかでもセラミックハニカム構造体と同系統の材質の粉末であるコージェライトを用いた実施例１では、割れ発生率が最も低いことがわかる。さらには、表２から、耐熱性無機粉末を混合して作成した焼成台の場合では、セラミックハニカム構造体と同系統の材質の粉末であるコージェライトを１０質量％以上含む焼成台を用いることが、割れの低減に有効であることが判る。
【００１７】
以上の結果より、生素地のセラミックハニカム構造体の開口端面を耐熱性無機粉末の上に載せる焼成方法は、焼成台とセラミックハニカム構造体との当接面であるハニカム構造体の開口端面に発生する割れの低減に有効であることが判る。
【００１８】
以上、本発明につき、実施の形態をもとに説明したが、本発明はこれに限定されず、技術思想の範囲で応用可能である。
【００１９】
【発明の効果】
以上詳細に説明のとおり、本発明のセラミックハニカム構造体の焼成方法は、耐熱性無機粉末を焼成台として用いることにより、焼成台とセラミックハニカム構造体との当接面であるセラミックハニカム構造体の開口端面に生じる摩擦抵抗力が緩和され、大型のセラミックハニカム構造体であっても、ハニカム構造体の開口端面に割れを発生させることなく良品を得ることができる。
【図面の簡単な説明】
【図１】本発明に係わるセラミックハニカム構造体の開口端面を耐熱性無機粉末に載せた焼成方法を示す図である。
【図２】本発明に係わる耐熱性無機粉末により構成される焼成台を示す図である。
【符号の説明】
１セラミックハニカム構造体
２焼成台
３当接面
４棚板
５耐熱性無機粉末
６耐熱性無機粉末の厚さ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for firing a ceramic honeycomb structure.
[0002]
[Prior art]
Conventionally, as a method for producing a ceramic product by firing a ceramic honeycomb structure of a green body, as a method for preventing cracks generated on the cell walls of the honeycomb structure and adhesion between the ceramic honeycomb structure and the shelf, There is known a method in which a firing base called a torch is placed on top and a ceramic honeycomb structure as a raw material is placed thereon and fired. Here, the torch is a honeycomb structure obtained by cutting the honeycomb structure in a radial direction so as to have a thickness of 20 to 30 mm, for example, and the opening end face of the raw ceramic honeycomb structure abuts on the opening end face of the honeycomb structure. Is placed as follows.
[0003]
Hereinafter, the prior art using the torch will be described in detail. In the invention described in Japanese Patent Publication No. 2-40019, a technique is disclosed in which a torch is brought into contact with both opening end faces of a green ceramic honeycomb structure, and temperature distribution due to heating at the end face of the green ceramic honeycomb structure is not disclosed. It is said that the occurrence of cutting due to uniformity can be prevented, the temperature rises quickly, baking with a uniform temperature distribution is possible, and productivity can be increased. In addition, in the invention described in Japanese Patent Publication No. 1-54636, a technique is disclosed in which a torch having a chamfered outer edge is placed on a ceramic honeycomb structure of the green body, and the outer edge of the lower end surface of the opening of the green body honeycomb structure is disclosed. By providing a portion that does not come into contact with the torch, the frictional resistance generated at the contact surface with the green honeycomb structure torch is reduced, and the occurrence of particularly many cuts at the outer edge of the green honeycomb structure can be prevented, It is said that the green substrate honeycomb structure can be heated sufficiently uniformly and the rate of temperature rise can be increased. Here, it is said that the tochi can be a raw tochi or a perennial tochi, but the raw tochi can only be used once and is not economical. Furthermore, in the invention described in Japanese Patent Application Laid-Open No. 7-208873, a technique is disclosed in which a convex torch is used as a firing table. When firing shrinkage, the contact between the torch of the outer edge portion of the fired body and the fired body is disclosed. By eliminating the frictional resistance on the surface, it becomes possible to fire the ceramic honeycomb body without cracks, and because the fired body is stably held without shaking, the processing and handling are easy. .
[0004]
As a firing table other than the torch, in the invention described in JP-A-5-85834, the open end face of the green body honeycomb structure is mainly composed of heat-resistant inorganic fibers, and the bulk density is 1.00 g / cm ³ or more. A method of firing on a ceramic plate is disclosed, and the ribs of the honeycomb structure due to thermal deformation of the firing table, end surface deformation and end surface cracks generated therefrom are reduced, and the life of the firing table is extended. In other words, the difference in size of the honeycomb structure can be reduced. Further, in the invention described in Japanese Patent Laid-Open No. 6-817972, a method is disclosed in which a base plate comprising 55 to 85% by weight of cordierite and 15 to 45% by weight of mullite is used as a firing table. Compared with conventional floor plates such as tochi, heat resistance is improved, deformation of the bottom surface of the honeycomb structure due to thermal deformation of the floor plate and melting of the silica component, rib twisting, and generation of cracks can be suppressed. The raw ceramic honeycomb structure can be fired without causing discoloration of the lower end surface of the body.
[0005]
[Problems to be solved by the invention]
However, even if any of the firing tables described in the above-mentioned prior art is used, there is a problem that cracks occur at the opening end surface of the ceramic honeycomb structure, which is a contact surface between the firing table and the ceramic honeycomb structure. Could not be resolved. In particular, in the case of a large ceramic honeycomb structure having an outer diameter of 200 mm or more and a length of 200 mm or more, as used for exhaust gas purification of diesel engines whose exhaust gas regulations are becoming stricter in recent years, the self-weight of the honeycomb structure is increased, When the honeycomb structure is fired and contracted, the frictional resistance generated on the contact surface between the ceramic honeycomb structure and the firing table is increased, so that there is a problem that the opening end face of the ceramic honeycomb structure is likely to be cracked. It was.
[0006]
An object of the present invention is to sinter a ceramic honeycomb structure, even if the ceramic honeycomb structure has a large size having an opening end face of 200 mm or more and a length of 200 mm or more. Another object of the present invention is to provide a method for firing a ceramic honeycomb structure in which cracks are not generated in the opening end face of the ceramic honeycomb structure, which is a contact surface of the ceramic honeycomb structure.
[0007]
[Means for Solving the Problems]
The present inventor has studied various firing tables that come into contact with the opening end face of the ceramic honeycomb structure, and conducted intensive research on the relationship between the outer diameter of the opening end face of the ceramic honeycomb structure and the firing table. As a result, by using a heat-resistant inorganic powder as a firing table, even if the ceramic honeycomb structure has a large outer diameter of 200 mm or more and a length of 200 mm or more, the ceramic honeycomb that is a contact surface with the firing table The inventors have obtained the knowledge that a ceramic honeycomb structure in which cracks are not generated on the opening end face of the structure can be obtained, and have arrived at the present invention.
[0008]
Specifically, in the present invention, when firing a ceramic honeycomb structure having an outer diameter of 200 mm or more and a length of 200 mm or more , the average particle diameter of the open end face of the raw ceramic honeycomb structure is 0.12 mm to 0 mm. It is characterized by being mounted on a baking table having a thickness of 5 mm or more and 30 mm or less, which is composed of a 37 mm heat-resistant inorganic powder, and baking. The opening end face of the ceramic honeycomb structure of the green body is placed on a firing table having a thickness of 5 mm or more and 30 mm or less and composed of a heat-resistant inorganic powder having an average particle size of 0.12 mm to 0.37 mm and firing. As a result, the direction of the flow path surrounded by the cell walls of the honeycomb structure coincides approximately with the direction of gravity, so that even if the honeycomb structure softens during the firing process, the cell wall is less likely to be deformed and fired. When expansion and contraction of the ceramic honeycomb structure occurs during the process, the individual particles of the heat-resistant inorganic powder constituting the firing table can be moved, so the expansion and contraction of the ceramic honeycomb structure and the heat-resistant inorganic powder Even if there is a difference in the amount, the heat-resistant inorganic powder on the ceramic honeycomb structure contact surface partly moves as the ceramic honeycomb structure expands and contracts, and the generated frictional resistance is relaxed. It is, because cracks firing table and the opening end face of the ceramic honeycomb structure which is the contact surface of the ceramic honeycomb structure is less likely to occur.
[0009]
In the present invention, as the material of the heat-resistant inorganic powder, a highly heat-resistant powder such as cordierite, mullite, alumina, silica, silicon carbide, silicon nitride, or a mixed powder thereof may be exposed to a high temperature during firing. Suitable because it is difficult to deform.
Furthermore, when the heat-resistant inorganic powder is made of the same material as the ceramic honeycomb structure obtained by firing, the difference in thermal expansion coefficient between the firing table and the ceramic honeycomb structure is reduced, and the firing table and the ceramic honeycomb structure are reduced. This is preferable because the effect of alleviating the frictional resistance generated on the contact surface with the body is increased. Here, the material of the same system means that, for example, when the ceramic honeycomb structure obtained by firing has cordierite as a main component, the heat-resistant inorganic powder also has cordierite as a main component. . Here, the heat-resistant inorganic powder is not necessarily made of the same material as the ceramic honeycomb structure obtained by firing, and at least 10% by mass or more is the same as the ceramic honeycomb structure obtained by firing. If the material of the system is used, the frictional resistance generated on the contact surface between the firing table and the ceramic honeycomb structure is relieved, so the opening of the ceramic honeycomb structure that is the contact surface between the firing table and the ceramic honeycomb structure is reduced. Cracks are less likely to occur on the end face.
[0010]
Moreover, in this invention, it is preferable that the average particle diameter of the said heat resistant inorganic powder is 0.12 mm or more and 0.37 mm or less. If the average particle size of the heat-resistant inorganic powder is less than 0.12 mm , the powder may diffuse to the surroundings due to the gas flow inside the firing furnace because it is a fine powder. This is because there are cases where it will not be completed. On the other hand, when the average particle size of the heat-resistant inorganic powder exceeds 0.37 mm, the movement resistance of the individual particles of the heat-resistant inorganic powder increases, and the contact surface between the heat-resistant inorganic powder that is the firing table and the ceramic honeycomb structure is increased. This is because relaxation of the generated frictional resistance is insufficient, and cracks may occur in the opening end surface of the ceramic honeycomb structure, which is the contact surface between the firing table and the ceramic honeycomb structure. The average particle size of the heat-resistant inorganic powder is more preferably 0.12 mm or more and 0.2 mm or less for the above reason. In the present invention, it is more desirable that the particle shape of the heat-resistant inorganic powder constituting the firing table is round like a substantially spherical shape. Due to the round shape of the particles, such as a substantially spherical shape, the rolling action of the substantially spherical powder facilitates the movement of individual particles of the heat-resistant inorganic powder, and is composed of the heat-resistant inorganic powder. Because the frictional resistance generated on the contact surface between the firing table and the ceramic honeycomb structure can be reduced, it effectively works to prevent cracking of the opening end surface of the ceramic honeycomb structure that is the contact surface with the firing table. is there.
[0011]
Moreover, in this invention, it is desirable that the thickness of the baking stand comprised with a heat resistant inorganic powder shall be 1 mm or more and 50 mm or less. When the thickness of the baking table is less than 1 mm, depending on the type of shelf plate laid under the heat-resistant inorganic powder, a part of the heat-resistant inorganic powder causes a chemical reaction at the interface with the shelf plate. May adhere to the shelf board, so that the frictional resistance generated on the contact surface between the ceramic honeycomb structure and the heat-resistant inorganic powder is not sufficiently relaxed, and the contact surface between the firing table and the ceramic honeycomb structure is insufficient. This is because cracks may occur on the opening end face of a certain ceramic honeycomb structure. On the other hand, if the thickness of the firing table exceeds 50 mm, the thickness of the firing table relative to the length of the ceramic honeycomb structure cannot be ignored, and the amount of green ceramic honeycomb structure mounted in the firing furnace is reduced. This is because the adverse effect of increasing costs occurs. In addition, the thickness of the baking stand comprised with a heat resistant inorganic powder is a range with more preferable 5 mm or more and 30 mm or less from said reason.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to embodiments.
The raw material honeycomb structure was obtained by mixing, kneading, extrusion molding, and drying ceramic raw material powder, molding aid, and additive previously blended in the cordierite composition. On the other hand, cordierite having an average particle size of 0.4 mm, 0.37 mm, 0.2 mm, 0.12 mm, 0.02 mm, 0.008 mm, and 0.005 mm as a heat-resistant inorganic powder for separately constituting a firing table. A powder, a mullite powder having an average particle diameter of 0.12 mm, an alumina powder having an average particle diameter of 0.12 mm, and a silica powder having an average particle diameter of 0.12 mm were prepared. Further, a cordierite powder having an average particle size of 0.12 mm, a mullite powder having an average particle size of 0.12 mm, and an alumina powder having an average particle size of 0.12 mm were mixed at a blending ratio shown in Table 2, and the heat resistance was mixed. Inorganic powder was prepared. Then, as shown in FIGS. 1 and 2, each of these heat-resistant inorganic powders 5 is placed on a firing shelf board 4 of the honeycomb structure, and flat on the firing table 2 having a constant thickness 6 with a spatula or the like. The raw honeycomb structure 1 was placed and fired in a batch-type firing furnace. On the other hand, as a firing table of a comparative example for the present invention, a 10 mm thick torch composed of a cordierite raw honeycomb structure, a 10 mm thick torch composed of a fired cordierite honeycomb structure, silica-alumina Each of the heat-resistant inorganic fiber boards was prepared, and the open end face of the green body honeycomb structure formed body was placed on the firing table and fired in a batch-type firing furnace. Firing was performed at 1400 ° C. to obtain a cordierite ceramic honeycomb structure having a cell structure with a cell wall thickness of 0.3 mm and a cell pitch of 1.46 mm and a diameter of 300 mm and a length of 400 mm. After firing, the open end face of the ceramic honeycomb structure in contact with the firing table was visually inspected for cracks, and those in which the cells were continuously cut at two or more locations were determined to be cracks. The crack occurrence rate of the open end face was determined as a ratio of the number of fired bodies in which cracks were observed on the open end face of the ceramic honeycomb structure, which is the contact surface with the firing stand, to the number of fired bodies that were tested under the same conditions. .
[0013]
Tables 1 and 2 show the relationship between the type of firing table and the crack generation rate.
[0014]
[Table 1]

[0015]
[Table 2]

[0016]
From Table 1, as compared with Comparative Examples 1 to 3 using a torch and a heat resistant inorganic fiber board as a firing table, in Examples 1 to 9 using a heat resistant inorganic powder, the crack occurrence rate is in a range where there is no problem in actual use. It turns out that it is 20% or less. It can be seen that the crack generation rate is lower when the thickness of the heat-resistant inorganic powder is 1 mm or more and 50 mm or less, and is further lower when the thickness of the heat-resistant inorganic powder is 5 mm or more. When the average particle size of the heat-resistant inorganic powder is 0.008 mm or more and 0.37 mm or less, the crack occurrence rate is low, and further, the average particle size of the heat-resistant inorganic powder is 0.02 mm or more and 0.2 mm or less. It turns out that it is lower. As for the material of the heat-resistant inorganic powder, the crack occurrence rate was 0 to 2.5% regardless of whether cordierite, mullite, alumina, or silica was used in Examples 1-4 . In Example 1 using cordierite, which is a powder of the same material as the ceramic honeycomb structure, it can be seen that the crack occurrence rate is the lowest. Furthermore, from Table 2, in the case of a firing table prepared by mixing heat-resistant inorganic powder, a firing table containing 10% by mass or more of cordierite, which is a powder of the same material as the ceramic honeycomb structure, is used. It can be seen that this is effective in reducing cracks.
[0017]
Based on the above results, the firing method of placing the open end face of the raw ceramic honeycomb structure on the heat-resistant inorganic powder occurs on the open end face of the honeycomb structure, which is the contact surface between the firing stand and the ceramic honeycomb structure. It can be seen that this is effective in reducing cracking.
[0018]
As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to this, It can apply in the range of technical thought.
[0019]
【The invention's effect】
As described above in detail, the method for firing a ceramic honeycomb structure of the present invention uses a heat-resistant inorganic powder as a firing table, thereby allowing the ceramic honeycomb structure to be a contact surface between the firing table and the ceramic honeycomb structure. The frictional resistance generated on the opening end face is alleviated, and even a large ceramic honeycomb structure can be obtained without causing cracks on the opening end face of the honeycomb structure.
[Brief description of the drawings]
FIG. 1 is a view showing a firing method in which an opening end face of a ceramic honeycomb structure according to the present invention is placed on a heat-resistant inorganic powder.
FIG. 2 is a view showing a firing table composed of a heat-resistant inorganic powder according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic honeycomb structure 2 Firing stand 3 Contact surface 4 Shelf board 5 Heat resistant inorganic powder 6 Thickness of heat resistant inorganic powder

Claims

When firing a ceramic honeycomb structure having an outer diameter of 200 mm or more and a length of 200 mm or more, the open end face of the raw ceramic honeycomb structure is composed of a heat-resistant inorganic powder having an average particle diameter of 0.12 mm to 0.37 mm A method for firing a ceramic honeycomb structure, comprising firing on a firing table having a thickness of 5 mm to 30 mm .

2. The method for firing a ceramic honeycomb structure according to claim 1, wherein the heat-resistant inorganic powder is made of the same material as the ceramic honeycomb structure obtained by firing at least 10% by mass or more .