JPS6172989A - Ceramic roller and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to rollers for roller hearth kilns.

Conventional technology and its problems A roller hearth kiln is a type of continuous heat treatment furnace that has a desired temperature distribution in the length direction of the furnace. Heat-resistant rollers are installed in parallel on the hearth, and the Format in which the material to be heat treated moves above: %Formula %Tunnel furnaces have been widely used as firing furnaces for ceramic products that require heat treatment at temperatures of 10°C or higher.

However, in a tunnel furnace, a metal-like truck made of firebrick to provide heat resistance is used to move the objects to be fired, so a lot of thermal energy is wasted. Also,
Some small-sized furnaces move the objects to be fired by moving heat-resistant plates with pushers, but this is not economical because the heat-resistant plates are severely damaged and accidents occur frequently.

On the other hand, the roller hearth kiln described above has the advantage of greatly improving thermal efficiency and shortening heat treatment time because the heat capacity of the members required to move the object to be fired is extremely small. , has become popular in recent years.

Currently, rollers made of stainless steel, heat-resistant alloys, ceramics, porcelain, alumina, etc. are used as rollers for roller hearth kilns. However, for metal rollers, the temperature is less than 1000"C, and for ceramic or porcelain rollers, it is 100"C or less.
Its use is limited to furnaces with temperatures below 250°C, and alumina rollers are only used for extremely small tests, and there is a large limit to the heat treatment temperature. Furthermore, these rollers are limited in the load that can be applied to each roller, and there is a limit to the firing ff1ffi per volume, so they are only used for heat treatment of lightweight materials fired at low temperatures, such as tiles and tableware. .

However, with the future spread of ceramic products, especially so-called advanced ceramics, it is thought that energy saving and speeding up of the heat treatment process will become increasingly important. For this reason, rollers for roller hearth kilns must have high mechanical strength, excellent corrosion resistance against fugitive evaporation from heat sources and heat-treated materials, high toughness at high temperatures, and resistance to fracture due to creep. difficult things,
A material that satisfies the requirements of high thermal shock resistance, excellent durability, and low heat dissipation is desired.

Means for Solving the Problems In view of the shortcomings of the prior art, the present inventor developed a 1200'CI
In order to develop rollers for roller hearth kilns that can be heat-treated at a high temperature of 1,300 to 1,600 degrees Celsius, have excellent durability, can withstand high loads, are suitable for mass production, can save energy, and can speed up production. As a result of repeated research,
A pulp-like roller made of a specific mullite sintered body is
We have discovered that this requirement can be met, and have completed the present invention based on this knowledge.

Namely, Glt of the present invention, 1) Total amount of AGi203 and SiO2 97. o wt% iX, fi) CaQO, 218
1% or less, 1 person 1. :iii) Na2O and 'CfK
The total amount of 2O is 10.2% by weight or less, and AQ203/S i O2 (molar ratio) -1.30 to 1.
85. Ceramic roller for roller hearth kiln made of sintered body mainly composed of mullite crystals with bulk density of 2.96 g/cm3 or more and composition after sintering AQ203
and 5i02 total amount 97.0 weight fn% or more, 1t
) CaO 0.2mm% or less, and iii) Total amount of Na20 and K2O 0.21ffi% or less F, AQ2
03/3102 (Characterized by pulverizing and/or dispersing the raw materials prepared so that the molar ratio is 1.30 to 1.85, forming them into a vibrator shape, and firing at 1500 to 1750"C. Relates to the manufacturing method of ceramic rollers for roller hearth kilns.

The sintered body mainly composed of mullite crystals in the present invention is not limited to a sintered body consisting only of mullite solid solution, but has a small amount of amorphous matrix present at grain boundaries and alumina crystals (α-AQ203). It is sufficient that the sintered body contains 10% by volume or less of mullite crystals, and specifically, it satisfies the following conditions.

a) Al2203/S i 02 <molar ratio) is within the range of 1.30 to 1,85.

A9203/S! If 02 is less than 1.30, the amount of mullite crystal phase decreases and the amount of 8102 or amorphous phase increases, resulting in a decrease in high temperature creep and a decrease in corrosion resistance, resulting in poor durability. On the other hand, AQ 20
3/S i○2 exceeding 1.85 is unsuitable because the amount of AQ 203 crystal phase increases in addition to the mullite crystal phase, resulting in a decrease in high temperature strength, toughness, and durability. .

b) Al2203 and HiS l 02 (7) The total weight is 97.0% or more.

Although it is desirable that the total amount of AQ203 and SiO2 be large, it is not necessarily economical. Also, ZrO2, TiO2
, Cr2O3, Y2O2, and the like cause some deterioration in the quality of the roller, but they have effects such as promoting sintering and improving toughness. Therefore, components other than AQ203 and 3i02 containing these components are permissible as long as they are less than 3%. However, if the total amount of A+1203 and 5I02 is less than 97%, it is not preferable because corrosion resistance to flying evaporates from the heat source or the object to be treated decreases, and high-temperature creep decreases.

C) The content of CaO shall be 0.2% by weight or less.

If the CaO content increases, it is thought that a Ca0-AQ203SiO2-based compound will be formed, which is not preferable because creep rupture increases at high temperatures. Therefore, the CaO content must be 0.2% by weight or less, preferably 0.1% by weight or less, and more preferably 0.05% by weight or less.

d) Na2O and K2O77) Total content m c, 0.
The content shall be 2% by weight or less.

If the content of Na2O and K2O increases, Na2O or/and K2O A Q 203-3I02 type compounds will be formed and the quality, life, etc. will decrease, so the content of these should be 0.2% by weight or less, preferably 0. .1!
1! f11% or less.

e) The key density shall be 2.960/C■3 or more.

If the bulk density is less than 2.960/CI3, corrosion resistance and mechanical strength will decrease, so the bulk density is
It is necessary to set it to 2.960/c+a3 or more, preferably 3.960/c+a3 or more. OOQ/Cl should be 113 or more.

As a starting material for manufacturing the roller of the present invention, Teha, A
Q20s/S! 02=1.30 to 1.85, and Na
It is desirable to use raw materials that contain less than the specified amount of 2O, K2O, and CaO, or that only less than the specified amount remains after firing, and in which the active ingredients are uniformly distributed.

These are not limited to those in which mullite crystals are formed in advance, but may be a mixture of alumina and silica or a compound of alumina or/and silicate in which mullite crystals are formed in the firing process. Starting materials that can be used in the present invention include, for example, specific surface areas of 2 to 20 m2.
/q of easily sinterable low soda alumina and high-purity silica or quartz; this mixture is heated to 1300-1450℃.
For example, raw materials prepared by baking to synthesize mullite, and raw materials prepared from a solution of AQ and Si compounds by a coprecipitation method, a roasting method, etc.

In the present invention, first, the raw material has an average particle size (measured by a sedimentation method based on Stokes' law or a light transmission method) of usually 2 μm.
It is pulverized and dispersed to a particle size of 1.5 μm or less, preferably 1.5 μm or less, and more preferably 0.5 to 1.0 μm. BE
The specific surface area measured by the T method is preferably 2 to 15 m2/Q. It is efficient to perform this grinding and dispersion process wet, and ball milling with grinding media made of agate, alumina, zirconia, etc. using a mill lined with rubber, resin, alumina, etc. good. As the pulverizer, a ball mill, vibration mill, attrition mill, centrifugal mill, etc. can be used, and pulverization and dispersion can be performed at the same time. When using a fine powder raw material of about 2 μm or less, the pulverization step can be omitted, but it is necessary to sufficiently disperse the raw material to obtain a raw material in which the components are distributed as uniformly as possible.

The pulverized and/or dispersed raw material is then molded into a desired shape in a molding step. As the molding method, methods used for ordinary ceramic products can be applied, and for example, the following method is used for molding.

In CIP (hydrostatic pressing), a granulated powder (mainly by spray drying method) is prepared by adding several percent of a molding aid such as PVA to the above raw materials and molded. The molding pressure is 0
．． A pressure of about 5 to 2 tons/ClO2 is preferred. In the case of extrusion molding, methylcellulose, dextrin, P
A pasty molding aid with high caking properties, such as VA, is kneaded with the raw material to be treated, and the mixture is molded using an extruder. In the case of the cast molding method, the raw material to be treated is in the form of a slurry, and the viscosity is 30 to 30.
00 cp, molded using a mold such as a plaster mold, and dried after molding to form a molded body. These compacts are made into shapes with additional dimensions larger than the desired roller dimensions based on firing shrinkage during the firing process.

The molded body is then fired at a temperature of 1500-1750°C in an open atmosphere. The firing temperature depends on the type of raw material, the components of the molded body, the sintering activity of the molded body, etc., but in the case of pressureless sintering, it is preferably 1550 to 1750°C,
The temperature is preferably 1550 to 1700°C. If the sintering temperature is lower than 1500°C, the desired density cannot be obtained, and if the sintering temperature is higher than 1750°C, it is not economical and the crystal grain size becomes too coarse, resulting in a decrease in strength and density. This is undesirable because deformation tends to occur during the firing process.

The dimensions of the roller depend on the width of the kiln, the shape of the material to be heat treated,
It is determined by the weight n applied per area, the operating temperature, etc., but the outer diameter is 15 to 5 Qia + φ, outer diameter / inner diameter = 1.2 to 1
．． 5. The length/outer diameter is preferably about -25 to 80. The inner surface is not necessarily limited to being a circle, but
The outer surface is preferably a perfect circle with an accuracy within ±0.51.

Effects of the Invention The roller for a roller hearth kiln of the present invention has the following excellent characteristics.

1. 5i, which is generally considered to be a high-temperature, high-strength ceramic
Compared to 3Nz, SiC, etc., it is stable in a high temperature open atmosphere.

2. Low thermal conductivity, less heat dissipation to the metal driving parts at both ends of the roller, economical, and high thermal efficiency.

3. It exhibits high resistance to contamination by vaporized substances at high temperatures from heat sources and heat-treated materials, and can be used for a long period of time.

4. Has thermal shock resistance that can withstand rapid temperature changes.

It has a lower elastic modulus than ceramics such as 5, S f3Nt 1S fC, A+2203, deforms appropriately especially at high temperatures, and is a flexible structure that is less susceptible to stress concentration.

6. Mullite crystals are acicular with a high aspect ratio, forming a silky structure, having high toughness and being resistant to creep rupture.

The roller for a roller hearth kiln of the present invention has the above-mentioned excellent properties, so it can be subjected to high temperature heat treatment.
It has excellent durability, can withstand high loads, and is useful as a roller for roller hearth skills that is suitable for mass production.

Example The present invention will be explained in more detail below based on Examples.

Example] Average particle size is 0.7 μm, specific surface area is 8 m2/I is 99.9
5% AQ203 and 99.9% Si with average particle size 1.5 μm
Blend 3 kg of O2 so that A+12ch/Sf○2=1.34, add 1% CMG to 91% A Q 203
The powder was pulverized and dispersed in a 48-hour system using a manufactured ball mill and pulverizing media to obtain an average particle size of 0.7 μm, and then spray-dried to obtain 2.5 kg of powder for molding.

This powder was formed into a pipe shape by CIP at a pressure of 1.5 tons/cm2 and fired at 1680'C for 3 hours.

Example 2 Using the same raw materials as Example 1, AQ203/5tO2-1,
After adding 0.14% of precipitated calcium carbonate in terms of CaO, the mixture was calcined at 1650° C. for 3 hours in the same manner as in Example 1.

Example 3 A+2203/8102- using the same raw materials as 1
3ka compounded to give a specific surface area of 1.62, and a specific surface area of 10
After adding 2.5% of 99.9% ZrO2 fine powder with a m2/g average particle size of 0.4 μm, it was crushed and dispersed using a reinforced zirconia ball mill and crushing media in a 48-hour process to obtain an average particle size of 0. .55 μm. The subsequent steps were the same as in Example 1, and firing was performed at 1630° C. for 5 hours.

Example 4 AQ203/S! 02-1.801A (2203 and Si
30% by weight of fine powder of fused mullite with a total of O2 f199.2% and A+1203 of Example 1 and S! 02 to Al22
03/S! 70 mixed so that 02=1.55
Raw materials consisting of 99.5% by weight are wet processed into a resin mill.
Using AQ20s media, the particles were crushed and dispersed by vibration to an average particle size of 1.1 μm in 12 hours.

A small amount of surfactant was added to this slurry to reduce the viscosity to 250.
C1), applying a pressure of 2 kll/C12, casting into a plaster mold, drying, and baking at 1650°C for 3 hours.

Example 5 0.3% Y203 and feldspar [main component
Na, K)20-AQ203 ・6SiOa) as Na2
After adding and blending O+K2O to 0.1%, the powder was pulverized to an average particle size of 0.6 μm in the same manner as in Example 3, treated and molded in the same manner, and fired at 1590° C. for 6 hours.

Example 6 40% by weight of mullite of Example 4 and 99.9% of alumina
%S! 02 and AQ 203 /S! 02 =1.
0.05% by weight (calculated as CaO) of precipitated calcium carbonate was added to a raw material consisting of 60% by weight of powder mixed so as to have a concentration of 80% by weight, and the mixture was fired in the same manner as in Example 4 at a firing temperature of 1720°C for 2 hours.

Example 7 A sintered body was produced in the same manner as in Example 5 using AQ 203 /S f 02-1 and 47 nom 5ite powder synthesized by a thermal decomposition method from a solution of AQ and a Si compound.

Comparative Example 1 A fired body was produced in the same manner as in Example 1, except that AQ 203 /S i 02 to 1.18 and the crushing time was 24 hours.

Comparative Example 2 The mullite of Example 4, 99.6% alumina powder, kaolin (main component A+1203・28!02・2H20) and feldspar were blended to give A+2203/5iO3-1,27, and after pulverization, After dehydration and drying, a thickener was added to the dough to form a clay, extrusion molding was performed, and the mixture was fired at 1700° C. for 3 hours.

Comparative Example 3 Zr021.5%, fvlool, 3% and Fe203
The powder was pulverized in the same manner as in Example 1, except that 0.3% was added, and then molded and fired in the same manner as in Comparative Example 2.

Comparative Example 4 Using the same raw materials as Comparative Example 2, AQ203/5iO2=1.
A fired body was produced in the same manner as in Comparative Example 2, except that the composition was blended so as to be 47%.

Comparative Example 5 A fired body was produced in the same manner as in Example 1, except that AQ 203/SiO2-1,47 was used and feldspar was blended so that the total amount of Na2O and K2O was 0.24%. .

Comparative Example 6 By changing the blending ratio, TeA 0203/S i 02-1.
A fired body was manufactured by the same method as in Comparative Example 2 except that the temperature was changed to 78.

Comparative Example 7 99.95% AQ203 and 9 with different particle sizes from Example 1
9.9%S i 02 trA Q 203/5iO
z-1.78, pulverized so that the average particle size after pulverization was 2.1 μm, and baked at 1760°C for 1
A fired body was produced in the same manner as in Example 1 except that the firing was carried out for a longer time.

Comparative Example 8 The mullite used in Example 4 was ground for 120 hours using a 97% AQ203 mill and grinding media, and thereafter a fired body was produced in the same manner as in Example 1. - Test Example Accelerated life tests and durability tests were conducted on the pipe-shaped fired bodies manufactured according to the above Examples and Comparative Examples. The composition and bulk density of the fired body are shown in Table 1, and the test results are shown in Table 2. The test method is as shown below.

0 Accelerated Life Test: Using a pipe with an outer diameter of 21φ1fl, an inner diameter of 16φ■, and a length of 450am as a sample, the distance between the supports is l! A fulcrum is provided at t300IllIl, and the furnace temperature between these points is 1400℃ or 146℃.
The sample was maintained at 0° C., and the sample was placed so that both ends were located outside the furnace. A load was applied to the center of the sample, and the time until the pipe broke was measured. Note that the pipe was rotated half a rotation every 5 minutes. Table 2 shows the load in terms of stress per unit area, which was based on the following calculation formula.

D: outer diameter, d: inner diameter This test condition is estimated to be 3 to 6 times the load applied to one roller in a practical kiln, and it is predicted that the life in a practical kiln will be 10 times longer.

Therefore, a life of 100 minutes or more allows use at higher temperatures or higher loads.

0 durability test: 1,500 hours inside a heavy oil-burning ceramic firing furnace during operation
``Cc) Insert a pipe sample with an outer diameter of 21φl, an inner diameter of 16φ11, and a length of 15011ffi into the atmosphere, hold it for one month, then take it out indoors and measure its bending strength based on the previous formula. (Span: 100mm) Strength before test It is expressed as an intensity ratio percentage.

From Table 2, the rollers for the roller hearth kiln of the present invention are as follows:
It is clear that it can withstand use under high loads at high temperatures and has high strength even after long-term use.

(U top)

Claims (1)

[Claims] [1] i) Total amount of Al_2O_3 and SiO_2 97
．． 0 weight % or more, ii) CaO 0.2 weight % or less, and iii) the total amount of Na_2O and K_2O 0.2 weight %
The following is true, and Al_2O_3/Si〇_2 (molar ratio)=1.
30 to 1.85 and a bulk density of 2.96 g/cm^3 or more. [2] The components after sintering are i) a total amount of Al_2O_3 and SiO_2 of 97.0% by weight or more, ii) a total amount of CaO of 0.2% by weight or less, and iii) a total amount of Na_2O and K_2O of 0.2% by weight
The following is true, and Al_2O_3/SiO_2 (molar ratio)=1.
After pulverizing and/or dispersing the raw materials mixed so that the particle size is 30 to 1.85, it is formed into a pipe shape and
A method for manufacturing a ceramic roller for a roller hearth kiln, which is characterized by firing at 50°C.