JPH054939B2 - - Google Patents

Description

[Detailed description of the invention]

Field of Application The present invention relates to a method for determining industrial standard firing conditions for ceramic products. Specifically, the present invention relates to a method for immediately selecting industrial firing conditions from laboratory-scale firing data for ceramic products by overcoming factors related to green bodies with different filling rates and scale effect factors. Conventional technology and problems In the production of ceramic products, in order to thermally efficiently obtain the desired physical properties and uniformity of the product, the optimum industrial Selection of firing temperature and firing time are extremely important factors. According to the prior art, when a ceramic product with a desired water absorption rate is manufactured from obtained raw materials using an industrial-scale firing furnace, the molding yield between laboratory firing data and industrial-scale firing conditions is Elucidation of the difference in the filling rate of the substrate and the so-called scale effect is
The issue remains virtually unresolved. Therefore, it has been necessary to determine industrial firing conditions by trial and error through trial firings on an industrial scale, depending on the quality of the raw materials, the performance of the furnace, the desired water absorption rate of the product, etc. In addition, given the recent raw material supply situation, it is extremely difficult to always secure raw materials of the same quality, and each time the quality of raw materials or the filling rate of the molding material changes, complicated firing conditions must be determined on an industrial scale by trial and error. It was then necessary to make a selection. For example, in the conventional technology, in order to determine the industrial firing conditions for ceramic products, it is necessary to assume an appropriate heating/cooling rate of the industrial furnace, and then fire at the highest temperature of 4 to 5 points for each heating rate/cooling rate. The materials were fired in an industrial furnace at different temperatures and times, and their water absorption rates were measured to estimate the firing time required to make ceramics. Therefore, even when changing any one of the maximum firing temperature, temperature increase rate, and temperature decrease rate, similar complicated experiments on an industrial scale must be repeated. In addition, laboratory data obtained using electric furnaces for new substrates is a process that can be used as a reference for physical properties.When firing industrially in a tunnel kiln, etc., the temperature rise rate, temperature fall rate, and maximum temperature holding time of the industrial furnace should be determined. It was necessary to conduct industrial firing experiments with various changes. Means for Solving the Problems Therefore, the main object of the present invention is to immediately select industrial-scale firing conditions by overcoming factors related to green bodies with different filling rates and scale effect factors from simple laboratory-scale firing experimental data. The object of the present invention is to provide a method for determining industrial firing conditions for ceramic products. Another main purpose is to provide a method for immediately selecting firing data necessary for designing a firing furnace installed in a ceramic product manufacturing line from laboratory-scale firing data, without having to rely on industrial-scale trial and error. It is to be. The inventor previously discovered that industrial firing furnaces have a large heat capacity and complex thermal characteristics compared to laboratory-scale furnaces, so in addition to isothermal firing after reaching the sintering temperature, focused on the fact that the firing conditions during the temperature rising and cooling processes of the fired product greatly affect the firing effect, and solved the above-mentioned problems when the filling rate of the green molded material is the same. That is, the present inventor found a relational expression regarding the temperature, firing time, and ceramizing temperature that is suitable for each of the above firing stages, and assuming that the sum of the degrees of ceramizing in each firing process is 100%,
We succeeded in determining industrial firing conditions. Furthermore, the present inventor has found that although Ai and Ci in the following formula (1) change when the filling rate of the green material in experimental firing and industrial firing differs, the Ai
It has been found that the values of and Ci are expressed by a linear relationship on a natural logarithmic scale, that is, by a linear equation, as shown in equations (2) and (3) below. Therefore, even if the filling rate of the green body changes due to changes in the dimensions of the green body or the particle size of the raw materials, the Ai of equation (1) can be determined from the experimental data.
Since the values of A and C corresponding to and Ci can be easily estimated, industrial firing conditions can be easily determined when the filling rate of the green material changes. Furthermore,
It has been found that the slopes of the graphs of the linear equations (2) and (3) tend to be similar to the same extent when the compositions of raw materials for ceramics are similar. Therefore, according to the present invention, a ceramic material having a desired water absorption rate can be obtained by firing a raw material formed from a raw material for ceramics at at least one filling rate at a plurality of ceramizing temperatures (preferably three or more points). From laboratory scale data to obtain the product, the formula Int=Ai/T+Ci (1) [where In is the natural logarithm symbol, t is the maximum temperature firing holding time, T is the absolute temperature of the firing, Ai and
Ci is a constant when the filling ratio of the green molding material is the same] Calculate the values of the constants Ai and Ci by formula (1) at the filling ratio of the green molding material fired on an industrial scale. A and C corresponding to Ai and Ci of
The formula is InA=-a ₁ ×Inr+b ₁ (2) In(-C)=-a ₂ ×Inr+b ₂ (3) [Here, r is the filling rate of the green material, and
a ₁ , b ₁ , a ₂ , b ₂ are constants that are constant depending on the raw materials for ceramics], and using the values of A and C _at this filling rate; process firing), V ₂ (maximum temperature firing), V ₃ (lowering temperature process firing), and degree of ceramification V
The following relational expressions (4), (5) and (6) indicating (sum of all firing processes), Formula V ₂ =exp{-(C+X)}・t (4) Formula V ₁ (or V ₃ ) = A/α・exp(-C) × [exp(-X)/X ²・F(X)] ^X2/X1 here F(X)=1-2! /X+3! /X ² −… (5) Formula V=V ₁ +V ₂ +V ₃ ≧1 (6) [Here, X=A/T, T is the absolute temperature of each temperature, and T is the maximum temperature firing holding time (minutes) , α is the temperature increase or decrease rate (°C/min), X ₁ is the value of X of the absolute firing start temperature in the above experimental data, and X ₂ is the value of characterized by selecting firing conditions from
A method is provided for determining industrial scale firing conditions for a ceramic product having a desired water absorption rate for different filling rates of green bodies. In the above method, laboratory data obtained by firing green bodies experimentally molded at multiple points (preferably 3 or more points) of filling rates at multiple points of ceramizing temperature is obtained in advance. , An accurate method is to determine the values of A in equation (2) and C in equation (3) at the filling rate r of a molded green body to be fired on an industrial scale from this data. In the case of a firing experiment of a green body molded at a filling rate at one point rather than at multiple points, estimation can be made as follows, for example. If there is firing experiment data for raw materials with similar compositions for ceramics, use formula (2) and formula for raw materials with similar compositions.
The slopes of the graphs in (3) tend to be of similar slope, and the values of a ₁ and a 2 in equations (2) and ( ₃ ) are in the range of 1.2 to 2.0 and typically 1.4 to 1.8, respectively. Therefore, from the slope of the graph, the above
By setting the values of a ₁ and a ₂ to values within the range of 1.2 to 2.0, the values of A in equation (2) and C in equation (3) can be approximately determined. In addition, in the case of industrially firing a green body with a filling rate close to that of the green body in a laboratory-scale firing experiment, the formula
Let the values of a ₁ in (2) and a ₂ in equation (3) be
A of formula (2) is set to 1.6, which is the average value of 1.4 to 1.8.
It is also possible to approximate the value of C in equation (3). In addition, the values of b ₁ and b ₂ in formulas (2) and (3) are
It is obtained by substituting the known values of Ai, Ci, and r. In addition, in the above formula (6), the degree of ceramics is set to 100%.
For example, if the degree of porcelain is set to 110% just in case, V=1.1. Usually, V=V ₁ +V ₂ +V ₃ =
1 is used. Note that if a certain degree of error is allowed, it is possible to mathematically simplify and approximate the above equations (4), (5), etc., and this case also naturally falls within the scope of the present invention. Specific Embodiments of the Invention The present inventor has discovered that the above formulas (1), (2), (3)...(6), and especially formulas (2)...(5) are effective in firing during the production of ceramics. I found out that it works. That is, the present invention is advantageously applied to ceramic materials such as porcelain (for example, water absorption of 1% or less), mortise (for example, water absorption of 1 to 10%), and porcelain (for example, water absorption of 10% or more). It has been found that the present invention can also be advantageously applied to ceramic raw materials containing MgO, FeO ₃ and/or Li ₂ O, which may cause slight variations in firing conditions, within the usual range of addition amounts. Furthermore, it has been known that the addition of a small amount of lime to ceramic raw materials slightly lowers the ceraminization temperature; Its behavior remained unknown. Therefore, it has been particularly difficult to estimate the industrial firing conditions for raw materials containing lime. The present inventor has found that the present invention can be advantageously applied when the amount of lime as CaCO ₃ is within about 3% by weight of the ceramic raw material. Here, lime usually refers to natural or processed raw materials whose main components are CaCO ₃ , CaO and/or Ca(OH) _{2 ,} etc., and in a broad sense, it is mainly removed by calcination.
Refers to the raw material that produces CaO. In the above equations (4) and (5), it is generally easy to set the ceramic-forming isothermal firing temperature and the heating rate and cooling rate of the furnace based on the raw materials, desired product water absorption rate, characteristics of the industrial furnace, etc. can do. It is generally advantageous to determine from the above equation the firing time required for maximum temperature firing in an industrial scale kiln by presetting these temperature conditions. However, if the maximum temperature firing time and the like are set in advance as necessary, it is of course possible to find other corresponding firing conditions from the above equation. Examples The embodiments of the present invention will be illustrated below with respect to the case of feldspathic porcelain with a water absorption rate of less than 1.0%. (1) Laboratory-scale firing experiment The raw materials used for preparing the base material were imported kaolin, Indopotassium feldspar, Indian silica, and Chinese soda feldspar.
Each was ground individually, and the average particle size of potassium feldspar and soda feldspar was adjusted to about 17 microns. No. 1 potassium feldspar type (22.4% kaolin, quartz) by wet mixing
34.9%, potassium feldspar 42.7%,) and soda feldspar type
No.2 (24.5% kaolin, 34.7% quartz, soda feldspar
40.7%) were prepared, and the amounts (molar ratios) of alkaline components were made equal.
These were granulated by adding water to a water content of approximately 7%, and uniaxial constant pressure molding was performed by changing the molding pressure in three levels to obtain a specimen of 30φ×4 mm. For the sample name, enter the approximate value of the filling rate in parentheses, for example
Shown as No.1 (69). Before subjecting to isothermal experiments
Calcined at 1000℃. The firing experiment uses two electric machines, one (FE1) is kept at 1000℃ and the other (EF2) is kept at the firing experiment temperature, and the specimen is heated at EF1-EF2.
- This was done by replacing it with EF1. In this way, data on firing temperature and firing time were obtained for each of the three points to obtain a porcelain product with a water absorption rate of less than 1.0% for each sample. A graph of equation (1) based on this data is shown in FIG. Note that the filling rate of the above-mentioned green material is shown in Table 1.

[Table] The data shown in Table 2 was obtained from the obtained data shown in FIG. These are the vertical axis InA or In(-c)
FIG. 2 shows a plot with respect to the horizontal axis Inr (r=filling rate). The filling rate means bulk density (according to Archimedes method) ÷ true density (according to pycnometer method) x 100%.

[Table] In Figure 2, the graph straight line (A or In
-C are clearly shown to have similar slopes. (2) Selection of firing conditions in an industrial firing furnace The conditions for forming the No. 1 raw material above into a green body with a filling rate of 68% and firing it into a porcelain material with a water absorption rate of less than 1.0% in an industrial firing furnace were determined. demand. Here, from the laboratory data to obtain the above-mentioned porcelain material with a water absorption rate of less than 1.0%, the temperature of the maximum temperature firing process for porcelain formation is set to 1250°C, and the temperature increase rate α to 1250°C is determined from the thermal characteristics of the industrial firing furnace.
5℃/min and cooling rate α from 1250℃ is 20
Set to °C/min. A and C in equations (2) and (3) at a filling rate of 68% are determined from the corresponding graphs in Figures 1 and 2. A = 5.707, C = -33.25 From equation (5), the temperature increase process Calculating the degree of porcelain V ₁ , V ₁ = (5.707) / 5 × exp (33.25) [exp (−
^X ₎ ^/ _{_ _} degree V ₂ in equation (6) =
1, _V2 =1-0.113-0.028=0.859 Therefore, the holding time for the maximum temperature firing is t=58.5 (minutes) from equation (4). In other words, in the case of this industrial firing furnace, the heating rate of the furnace is 5°C/min, and the heating rate is 1250°C.
It is sufficient to transport and heat the product to a temperature of 1250°C, transport and bake it for 59 minutes at an average temperature of 1250°C, and then transport and take it out with the temperature decreasing rate of the furnace being 20°C/min. Functions and Effects As described above, in the present invention, the relational expression for the temperature, firing time, and degree of ceramicization that is suitable for each firing stage in an industrial firing furnace for ceramic products when the filling rate of the green molding material is different [Equation ( 1)-(6)] were found. Therefore, without the need for industrial experiments based on trial and error, if the filling rate of the molded material differs from the laboratory data by a combination of these relational expressions from relatively simple laboratory data, it can be immediately calculated. Industrial firing conditions for ceramic products with desired water absorption are obtained.

[Brief explanation of the drawing]

Figure 1 shows feldspar-based porcelain raw material with a water absorption rate of 1.0%.
The vertical axis t is the laboratory data fired to a porcelain quality of less than
(minutes) (logarithmic scale), and the horizontal axis is 1/T (K ^-1 ). FIG. 2 is a graph in which InA (formula 2) or In(-C) (formula 3) is plotted on the vertical axis and the filling rate Inr is plotted on the horizontal axis based on the data in FIG. t... Ceramicizing constant temperature firing time, T... Ceramicizing absolute temperature, r... Filling rate, No. 1 and No. 2
... Sample number, 65-71 ... Approximate value of filling rate.

Claims (1)

[Claims] 1. A laboratory-scale method for obtaining a ceramic product having a desired water absorption rate by firing a raw material formed from a raw material for ceramics at at least one filling rate at a plurality of ceramizing temperatures. From the data, the formula Int=Ai/T+Ci (1) [where In is the natural logarithm symbol, t is the maximum temperature firing holding time, T is the absolute temperature of the firing, Ai and
Ci is a constant when the filling ratio of the green molding material is the same] Calculate the values of the constants Ai and Ci by formula (1) at the filling ratio of the green molding material fired on an industrial scale. A and C corresponding to Ai and Ci of
The formula is InA=-a ₁ ×Inr+b ₁ (2) In(-C)=-a ₂ ×Inr+b ₂ (3) [where r is the filling rate of the green material, and
a ₁ , b ₁ , a ₂ , b ₂ are constants that are constant depending on the raw materials for ceramics], and using the values of A and C at this filling rate _; process firing), V ₂ (maximum temperature firing), V ₃ (lowering temperature process firing), and degree of ceramification V
The following relational expressions (4), (5) and (6) indicating (sum of all firing processes), Formula V ₂ =exp{-(C+X)}・t (4) Formula V ₁ (or V ₃ ) = A/α・exp(-C) × [exp(-X)/X ²・F(X)] ^X2/X1 here F(X)=1-2! /X+3! /X ² −… (5) Formula V=V ₁ +V ₂ +V ₃ ≧1 (6) [Here, X=A/T, T is the absolute temperature of each temperature, and T is the maximum temperature firing holding time (minutes) , α is the temperature increase or decrease rate (°C/min), X ₁ is the value of X of the absolute firing start temperature in the above experimental data, and X ₂ is the value of characterized by selecting firing conditions from
A method for determining industrial standard firing conditions for ceramic products having a desired water absorption rate when the filling ratio of the green molding material is different. 2. From laboratory data obtained by firing green blanks experimentally formed at multiple filling rates at multiple ceramizing temperatures, we found that , A in equation (2)
and the determining method according to claim 1, which determines the numerical value of C in formula (3). 3. From the slopes of the graphs of equations (2) and (3) in the firing experiment data for ceramic raw materials with similar compositions, the values of a ₁ and a ₂ are set to 1.2 to 1.2, respectively.
The determining method according to claim 1, wherein the values of A in equation (2) and C in equation (3) are approximately determined by setting the values to be within the range of 2.0. 4. When industrially firing a green body with a filling rate close to the filling rate of the green body in a laboratory-scale firing experiment, the values of a ₁ in equation (2) and a ₂ in equation (3) are each set to 1.6.
The determination method according to claim 1, wherein the numerical values of A in equation (2) and C in equation (3) are approximately obtained by setting .