JP4366685B2 - Method for firing ceramic honeycomb structure - Google Patents

Description

  The present invention relates to a firing method suitable for firing a ceramic honeycomb structure.

  Conventionally, after a ceramic clay obtained by mixing a cordierite forming raw material powder with a molding aid and / or a pore former is extruded to produce a honeycomb shaped ceramic molded body, a single furnace at a predetermined temperature, or The ceramic honeycomb structure was obtained by firing in a firing furnace such as a continuous furnace. In the above-mentioned firing, the method described in Patent Document 1 does not directly apply the formed body on the shelf board to prevent cracking and adhesion of the ceramic honeycomb structure. A method of placing on top and firing is described. In addition to the torch, a method of firing on a fired plate such as a heat resistant fiber is also known. In addition, in order to be able to fire a large number of honeycomb structured ceramic molded bodies in a single firing, the methods described in Patent Documents 2 and 3 form the molded body on the shelf so that the flow path direction of the ceramic molded body is approximately the direction of gravity. A method is disclosed in which a large number of slabs are placed, and a shelf is stacked via struts so that the compact is efficiently placed in a firing furnace and fired.

JP-A-62-202870 JP-A-1-246179 JP-A-1-215765

  The shelf plate for firing the honeycomb structure formed body is not described in the above-mentioned patent document, but it is necessary to hold the formed body by being exposed to high temperature while the honeycomb structure formed ceramic body is being fired. Therefore, a refractory material mainly composed of heat-resistant alumina, magnesia, mullite, silicon carbide or the like is appropriately selected and used. Among these, silicon carbide is expected to be advantageous in that it has high durability at high temperatures and high thermal conductivity, so that temperature rise and cooling can be performed quickly and firing time can be shortened.

  Therefore, the inventors put the molded body and the torch mainly on silicon carbide after placing the molded body on the torch so that the flow path direction of the ceramic molded body having the honeycomb structure is substantially the direction of gravity. It mounted on the shelf board used as a component, and also, the molded body was arrange | positioned in a baking furnace by stacking a shelf board, and it baked with the combustion heat from a burner. In the temperature raising process, each shelf board is also heated simultaneously with the molded body, and the shelf board mainly composed of silicon carbide having a higher thermal conductivity than the green body ceramic molded body, the temperature rises faster, The vicinity of the upper end surface of the molded body is locally heated from other portions by the radiant heat from the shelf board. However, since the lower end surface of the molded body is provided with a torch, the temperature is less likely to rise than the upper end surface, and cracks have occurred on the upper end surface of the locally heated molded body. This crack becomes more prominent as the outer diameter of the ceramic honeycomb structure becomes larger than 150 mm, so that there is a limit to the size of the ceramic honeycomb structure that can be manufactured.

  An object of the present invention is to use a shelf board mainly composed of silicon carbide in a firing furnace, and arrange and fire a honeycomb structure ceramic molded body. It is in providing the baking method which made it hard to generate | occur | produce a crack.

  In order to achieve the above object, a method for firing a ceramic honeycomb structure according to the present invention is a method in which a ceramic molded body having a honeycomb structure is placed on each of the multistage shelf boards and fired, and the shelf boards are carbonized. Silicon is the main component, the thermal conductivity of the shelf board is 10 W / m · K or more, and the space between the ceramic molded body and the shelf board located above the ceramic molded body is 10 to 200 mm. It is characterized by.

  In the present invention, since the shelf board is mainly composed of silicon carbide, the shelf board can be used for a long time, and the thermal conductivity of the shelf board is set to 10 W / m · K or more. Although the cooling time can be shortened, the molded body and the shelf positioned above the molded body can be used even if the shelf board mainly composed of silicon carbide is used. Since the space is set to 10 to 200 mm, it is possible to prevent cracks in the formed body of the honeycomb structure, to increase the number of pieces mounted in the firing furnace, and to improve the firing ability.

Here, the reason why the thermal conductivity of the shelf board is set to 10 W / m · K or more is to quickly transmit the combustion heat from the burner to the ceramic molded body, thereby shortening the time for firing. In addition, the space between the molded body and the shelf positioned above the molded body is 10 to 200 mm. If the space is less than 10 mm, the upper surface of the molded body is locally overheated by radiant heat from the shelf on the molded body. This is because the temperature difference between the upper surface of the formed body and other portions becomes large, and cracks occur on the upper surface of the honeycomb structure after firing. On the other hand, if the space between the molded body and the shelf located above the molded body exceeds 200 mm, the number of molded bodies placed in the firing furnace is reduced and the firing ability is reduced.
From the above viewpoint, the space between the molded body and the shelf plate located above the molded body is preferably 20 to 80 mm.

  In this invention, it is preferable that the 4-point bending strength in 1400 degreeC of the said shelf board is 30 Mpa or more. In general, since the cordierite ceramic honeycomb structure is fired at 1380 to 1430 ° C., if the four-point bending strength at 1400 ° C. is 30 MPa or more, the deformation of the shelf board during firing is reduced as much as possible. It is because it can be used over.

  In the present invention, the ceramic honeycomb structure is preferably a large honeycomb structure having an outer diameter of 150 mm or more. This is due to the following reason. When the ceramic honeycomb structure is a large honeycomb structure having an outer diameter of 150 mm or more, it is difficult to raise the temperature of the entire honeycomb structure, and cracks on the upper end face are likely to occur. However, by adopting the firing method of the present invention, a large honeycomb structure having an outer diameter of 150 mm or more has a great effect of suppressing the occurrence of cracks on the upper end face of the honeycomb structure. For the same reason, the higher the porosity of the honeycomb structure having a porosity of 60% or more, the greater the effect of suppressing the occurrence of cracks on the upper end face of the honeycomb structure.

  According to the method for firing the honeycomb structure of the present invention, local overheating of the upper surface of the molded body due to radiant heat from the shelf on the molded body is reduced, and the temperature difference between the vicinity of the upper end surface of the molded body and other portions. Thus, after firing, cracking and deformation of the upper end face of the honeycomb structure can be reduced, and firing ability can be improved.

Next, embodiments will be described in detail.
1A and 1B show a firing furnace 30 in the embodiment, in which FIG. 1A is a schematic cross-sectional view thereof, and FIG. 1 (a) and 1 (b), the firing furnace 30 is arranged in a zigzag manner up and down with a furnace body 31, a plurality of carriages 32 inserted into the furnace body 31, and between the carriages 32. Combustion burners 33a and 33b. The combustion burner 33a (black mark on the inner circle of the double circle) is attached to the furnace body 31 on the back side of the carriage and blows out flames toward the front, and the combustion burner 33a (marked in Marunouchi) is on the front side of the carriage. It is attached to the furnace body 31 and the flame is blown out in the back direction. By preventing the burner flame from directly hitting the molded body 1 by the combustion burners 33a and 33b arranged in a staggered manner, the molded body 1 into the firing furnace 30 without arranging a burner direct fire prevention wall. The loading quantity is increased. On each carriage 32, a shelf set 20 including a plurality of shelf boards 21 and support posts 22 that support each shelf board 21 is provided. As shown in FIG. 2, the ceramic structure 1 having a honeycomb structure has a torch 23 having a thickness of 10 mm that is obtained by slicing the same base material as the formed body between the shelf boards 21. The shelf board 21 is made of ceramics containing 90% by mass or more of silicon carbide, has a thermal conductivity of 17 W / m · K, a 4-point bending strength at 1400 ° C. of 30 MPa, a porosity of 10%, and a thickness of 20 mm. I used one. A space (H) is provided in the upper surface 1 a of the molded body 1 and the shelf plate 21 positioned above the molded body 1. Moreover, the support | pillar 22 for stacking a shelf board was comprised with the ceramic containing 890 mass% or more of silicon carbide similar to a shelf board.

  A plurality of compacts 1 shown in FIG. 2 were placed on each shelf 21 using the firing furnace 30 in FIG. 1, heated to 1400 ° C., and fired for a total firing time of 196 hours. The molded body 1 is obtained by extruding and drying a ceramic clay obtained by mixing and kneading a molding aid, a pore-forming agent, water and the like with a cordierite forming raw material such as kaolin, talc, silica, and alumina. The outer diameter was 290 mm and the total length was 350 mm. The fired honeycomb structure had a partition wall thickness of 0.32 mm, a partition wall pitch of 1.62 mm, and a porosity of 65%.

  In this firing, the space (H) between the molded body 1 and the shelf plate 21 positioned above the molded body 1 is changed, cracks generated on the upper surface 10a of the honeycomb structure 10 after firing, The firing ability was evaluated from the number of loading stages of the compact 1. In addition, the crack which generate | occur | produced in the upper surface 10a of the honeycomb structure 10 after baking is less than 5% per lot ((double-circle)), 5-10% (1) per lot ((circle)), and more than 10% per 1 lot (*) ). Moreover, the firing capacity of the molded body 1 is that the number of stages of the molded body 1 that can be placed on the shelf assembly 20 per carriage at an effective height in the furnace of 2350 mm is 5 (段), 4 is (◯), 3 Was evaluated as (×). Here, the height of the column can be obtained by the following calculation formula. Column height = (molded body length 350 mm + thickness 10 mm + space H) × stage number + (shelf thickness 20 mm) × (stage number + 1). The results are shown in Table 1.

  From Table 1, in the example of the present invention in which the space (H) between the formed body 1 and the shelf board 21 positioned above the formed body 1 is 10 to 200 mm, cracking of the upper surface 10a of the honeycomb structure 10 after firing is generated. As can be seen from the figure, the firing ability is also ensured. Moreover, if the space (H) between the molded body 1 and the shelf plate 21 located above the molded body 1 is 20 to 80 mm, both crack generation and evaluation of the firing ability are (◎), which is more excellent. I understand.

  On the other hand, as a comparative example, a similar experiment was performed using a shelf plate having a thickness of 20 mm mainly composed of mullite. The shelf board mainly composed of mullite had a thermal conductivity of 1.6 W / m · K, a 1400 ° C. four-point bending strength of 10 MPa, and a porosity of 15%. Using this shelf board, similarly to the example, a honeycomb structure formed body having an outer diameter of 290 mm and a length of 350 mm was used, and a space (H between the formed body 1 and the shelf board 21 positioned above the formed body 1 (H ) Was 40 mm, and the same experiment was conducted. In this comparative example, since a mullite plate having a low thermal conductivity was used, the firing time was long and 240 hours were required.

The baking furnace 30 in embodiment of this invention is shown, (a) is the schematic cross section, (b) is the arrow A enlarged view in (a). In embodiment of this invention, it is the side view which has mounted the molded object 1 in the shelf group 20 which combined several shelf boards 21. FIG.

Explanation of symbols

1: green body (molded body)
10: Ceramic honeycomb structure (honeycomb structure)
DESCRIPTION OF SYMBOLS 1a, 10a: Upper surface 1b, 10b: Lower surface 20: Shelf set 21: Shelf board 22: Strut 23: Tochi 30: Firing furnace 31: Furnace body 32: Carriage 33a, 33b: Combustion burner H: Space

Claims (2)

A method of firing a ceramic molded body having a honeycomb structure on each of a plurality of shelves, wherein the shelves are composed mainly of silicon carbide, and the thermal conductivity of the shelves is 10 W / m · K or more. A method for firing a ceramic honeycomb structure, wherein a space between the ceramic molded body and the shelf plate located above the ceramic molded body is 10 to 200 mm. The method for firing a ceramic honeycomb structure according to claim 1, wherein the four-point bending strength at 1400 ° C of the shelf board is 30 MPa or more.

Images