JPH0437027B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF APPLICATION The present invention relates to a method for determining industrial-scale firing conditions for ceramic products. Specifically, the present invention relates to a method for immediately selecting industrial firing conditions by overcoming scale effect factors from laboratory-scale firing data for ceramic products. 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 producing ceramic products with a desired water absorption rate from obtained raw materials using industrial-scale firing furnaces, the so-called scale between laboratory firing data and industrial-scale firing conditions is known. The elucidation of the effect 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. Furthermore, given the current raw material supply situation, it is extremely difficult to constantly secure raw materials of the same quality, and each time the quality of raw materials changes, it is necessary to select complex firing conditions through trial and error on an industrial scale. Ta. 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 if any one of the maximum firing temperature, temperature increase rate, and temperature decrease rate is changed, similar complicated experiments on an industrial scale must be repeated. Also,
Laboratory data obtained using electric furnaces for new substrates is only for reference in terms of physical properties.When firing industrially in tunnel kilns, etc., the temperature rise rate and
It was necessary to conduct an industrial firing experiment by varying the temperature reduction rate and maximum temperature holding time. Means for Solving the Problems Therefore, the main object of the present invention is to overcome scale effect factors and immediately select industrial-scale firing conditions for ceramic products from simple laboratory-scale firing experiment data. The objective is to provide a method for determining the 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 present inventor has proposed that, in addition to isothermal firing after reaching the sintering temperature, industrial firing furnaces have a larger heat capacity and more complex thermal characteristics than laboratory-scale furnaces. The above-mentioned problems were solved by focusing on the fact that the firing conditions during the heating and cooling processes of the object greatly affect the firing effect. That is, the present inventor found a relational expression regarding the temperature, firing time, and degree of porcelain that is suitable for each firing stage described above, and determined industrial firing conditions by setting the sum of the degree of ceramization in each firing process as 100%. succeeded in doing so. Therefore, according to the present invention, from laboratory-scale data in which a ceramic product having a desired water absorption rate is obtained by firing ceramic raw materials at a plurality of ceramic forming temperatures (preferably three or more points), the formula lnt is obtained. =A/T+C (1) [Here, t is the maximum temperature firing holding time, T is the absolute temperature of the firing, and A and C are constants] to find the values of constants A and C; Ceramicization degree V ₁ (heating process firing), V ₂ (maximum temperature firing), V ₃ (temperature decreasing process firing), and degree of ceramification V
The following relational expressions (2), (3) and (4) showing (sum of all firing processes), Formula V ₂ =exp{-(C+X)}・t (2) Formula V ₁ (or V ₃ )= A/α・exp(−C) ・[exp(−X)/X ²・F(X)]X ₂ X ₁ , here F(X)=1−2! /X+3! /X ₂ − …(3) Formula V=V ₁ +V ₂ +V ₃ ≧1 (4) [Here, X=A/T, T is the absolute temperature of each temperature,
t is the maximum temperature firing holding time (minutes), α is the temperature increase or decrease rate (℃/min), X ₁ is the value of X of the absolute temperature at which firing starts in the above experimental data, and X ₂ is the maximum temperature firing temperature for ceramics. Value of X at power absolute temperature]
Provided is a method for determining industrial-scale firing conditions for a ceramic product having a desired water absorption rate, the method comprising selecting firing conditions from the following. In the above formula (4), when the ceramic degree is 100%, V = 1,
For example, if the degree of porcelain is set to 110% just in case, V=1.1 can be used. Normally,
V=V ₁ +V ₂ +V ₃ =1 is used. In addition, if a certain degree of error is allowed, the above equations (2) and (3)
etc. can be mathematically and simply approximated, and that case also naturally falls within the scope of the present invention. In this specification, absolute temperature means Kelvin temperature T, that is, T=Celsius temperature+273.15. Specific Embodiments of the Invention The present inventors believe that the above formulas (1), (2), (3) and (4), and especially formulas (2) and (3), hold true during firing during the production of ceramics. I discovered that. That is, the present invention is advantageously applied to ceramic materials such as porcelain (for example, water absorption rate of 1% or less), mortise material (for example, water absorption rate of 1 to 10%), and ceramic material (for example, water absorption rate of 10% or more). It has also been found that the present invention can 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 equations (2) and (3) above, it is generally easy to set the isothermal ceramic-forming 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. Below, it will be explained that formulas (1), (2), (3) and (4) in the present invention hold true in an industrial scale firing state. In other words, equation (1) is a type of Arrhenius equation, and is estimated by the inventor to be established in the firing of ceramic products related to the present invention. 1st
The data in the figure proves its establishment. Regarding equation (4), since under industrial firing conditions there is always a process of temperature rise - maximum temperature firing - temperature fall, the degree of ceramicization (V ₁ , V ₂ , V ₃ ) of each process is summed to 100%. It is clear that a degree of ceramicization is achieved. Therefore(4)
The formula holds true in the present invention. Equations (2) and (3) are equivalent to equation (1)
can be derived as follows, and since equations (2) and (3) do not include the firing scale factor,
It is clear that this holds true in the present invention. In equation (1), t is the time required to reach the melting point, and is a unique value determined by the material composition and temperature. Therefore, to distinguish it from t as a variable, it is rewritten as tv. Therefore, equation (1) becomes equation (A). 1n tv=A/T+C (A) Here, if we define the degree of melting V as a variable that indicates the degree of melting so that it takes a value of 1 when the melting point is reached, then assuming that the melting rate depends on the temperature, we can define it as φ
It can be summarized in (T) and expressed as equation (B). dv/dtφ(T) or V=∫φ(T)dt (B) Since φ(T) is constant in an isothermal state, V=φ(T)・t+B (C) When t=0, V=0, At the melting point (t=tv), V=1
Therefore, B=0, φ(T)・tv=1 From the relationship of equation (A), φ(T)=1/tv=exp{−(A/T+C)} (D) Therefore, from equation (C) V=exp{-(A/T+C)・t (2) Next, consider the process in which the temperature changes, such as the temperature increase/decrease process. Here, it is assumed that the temperature changes at a constant rate, and the rate is α (deg/min). t
If the absolute temperature when = 0 is To(K), then the temperature T(K)
can be expressed by equation (E). T=To+α・t (E) Assuming that equation (D) holds true even in the process of temperature change, equation (F) can be obtained by substituting into equation (B). V=∫exp{-(A/T+C)}dt (F) Considering the process of temperature change from T ₁ to T ₂ ,
Assuming that the time changes from t ₁ to t ₂ , the degree of melting at that time is V=∫t ₂ t ₁ exp{-(A/T+C)}dt (G) Here, if A/T=x, dt=- (A/α)x dx (H) Therefore, equation (G) is V=∫t ₂ t ₁ exp{-(x+C)}(-A/α)x ² dx =-A/αexp(-C)∫ x ₂ x ₁ exp (−x)/x ² dx (J) where x ₁ and x ₂ are the values of x at temperatures T ₁ and T ₂ . By repeatedly applying integrals by parts (3)
Get the formula. V=A/αexp(-C) [exp(-x)/x ² F(x)]x ₂ x ₁ (3) F(x)=1-2! /x+3! /x ² -... Example The embodiment of the present invention will be illustrated below with respect to the case of feldspathic porcelain having a water absorption rate of less than 1.0%. (1) Laboratory scale firing experiment Kaolin (22.4%) - Quartz (34.9%) by weight
%) - No addition of lime mainly composed of CaCO ₃ to the basic formulation of potassium feldspar (42.7%) or 2.5% of lime,
Four types of samples were prepared by adding 5% and 10%, respectively. For the experiment, clay with a moisture content of about 7% was prepared.
A disk shape of 30φ×4 mm was molded under constant pressure on the -axis, and this was used as a specimen. It was calcined at 1000°C and subjected to isothermal firing experiments. The firing experiment used two electric furnaces, one (EF1) was kept at 1000℃ and the other (EF2) was kept at the firing experiment temperature, and the specimen was heated at (EF1) - (EF2) -
(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. This laboratory data is shown in the table below. Furthermore, a graph of equation (1) based on the data is shown in FIG. Here, firing experiments were conducted on the four types of samples mentioned above, but in reality, it is sufficient to obtain data on the firing temperature and time at three points, for example, for one type of raw material for which firing conditions are to be determined.

[Table] Regarding the above table and attached Figure 1,
The scope of application of the invention in the case of lime addition will be discussed.
In FIG. 1, when 2.5% lime is added, the graph shows the same slope and moves toward the lower temperature side compared to when no lime is added. That is, when fired under the same conditions, adding 2.5% lime lowers the porcelain temperature by about 60°C. When the amount of lime added is increased to 5% or 10%, the slope of the straight line increases, and minute changes in temperature and time have a large effect on the degree of porcelain formation. Therefore, in the case of adding lime in the present invention, the critical value for the addition amount is approximately 3% as CaCO ₃ . Adding a large amount of lime contributes little to lowering the porcelain temperature,
The time required for porcelain formation changes greatly depending on minute changes in temperature. That is, it can be seen that the slope of the graph straight line is steep, making firing management difficult. (2) Selection of firing conditions in an industrial firing furnace (in the case of 2.5% lime added) From the table above and the graph in attached Figure 1, for ceramic raw materials with no lime added or with lime added less than about 3% by weight, It can be seen that the present invention is realized.
As an example, the raw material (1) above with a lime content of 2.5% by weight as CaCO ₃ is heated to a water absorption rate of 1.0 in an industrial kiln.
Find the conditions for firing to a porcelain quality of less than %.
Therefore, based on the laboratory data for obtaining porcelain with a water absorption rate of less than 1.0%, the temperature of the maximum temperature firing process for porcelain formation was set at 12000℃, and from the thermal characteristics of the industrial firing furnace, it was set at 1200℃.
The heating rate (α) to 5°C/min and 1200°C
Set the cooling rate (α) to 20°C/min. Calculating A and C in equation (1) from the corresponding graph in Figure 1 (the graph with 2.5% lime added), A=6.597 C=-41.27 From equation (3), the degree of porcelain in the temperature rising process V ₁ To calculate, V ₁ = 6.597/5×exp(41.27) [exp(-X)/X ²・F(X
)] 6.597/1200+273/6.597/1000+273=0.187 In the same way, the degree of porcelain V ₃ during the cooling process is calculated from equation (3): V ₃ =0.047 The degree of porcelain V ₂ during the firing process at the highest temperature is calculated using equation (4). V=
1, V ₂ =1-0.187-0.047=0.766 Therefore, the holding time for the maximum temperature firing is t=25.8 (minutes) from equation (2). 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 1200°C.
The material may be transported and heated to 1200°C, transported and fired for 26 minutes at an average temperature of 1200°C, and then transported and taken out with the furnace temperature decreasing rate at 20°C/min. Note that although the firing of a porcelain product with a water absorption rate of less than 1.0% has been exemplified above, firing conditions are similarly required for the firing of a ceramic product. That is, a porcelain raw material is molded in the same manner as in Example (1) above, calcined at, for example, about 1000°C, and then subjected to experimental conditions (e.g., 1150°C) to obtain a desired water absorption rate (e.g., 13%). A firing experiment is performed at three points (before and after). Using this laboratory data, industrial firing conditions can be determined by setting the maximum pottery firing temperature to, for example, 1150°C, as in (2) of the above example. Functions and Effects As described above, in the present invention, the temperature suitable for each firing stage in an industrial firing furnace for ceramic products;
Relational equation for firing time and degree of ceramification [Eq.
(2), (3), (4)] were found. Therefore, industrial firing conditions for ceramic products having a desired water absorption rate can be obtained immediately by combining these relational expressions from relatively simple laboratory data without the need for industrial experiments based on trial and error. It will be done.

[Brief explanation of drawings]

Figure 1 shows the laboratory data of porcelain raw materials with no added lime and with added lime added to produce porcelain with a water absorption rate of less than 1.0%, with the vertical axis logt (minutes) and the horizontal axis 1/T×
This is a graph plotted at ¹⁰⁴ . t... Ceramicization degree temperature firing time, T... Ceramicization absolute temperature, (--○--)... No lime content added, (-●-
)
...2.5% lime content added, (--△--)...5% lime content added, (-▲-)...10% lime content added.

Claims (1)

[Claims] 1. From laboratory-scale data obtained by firing raw materials for ceramics at a plurality of ceramizing temperatures to obtain a ceramic product having a desired water absorption rate, the formula lnt=A/T+C (1) [ Here, t is the maximum temperature firing holding time, T is the Kelvin temperature of the firing, and A and C are constants] to find the values of constants A and C; Ceramicization degree V ₁ (temperature raising process firing), V ₂ (maximum temperature firing), V ₃ (lowering temperature firing), and degree of ceramification V
The following relational expressions (2), (3) showing (sum of all firing processes),
and (4), formula V ₂ =exp{-(C+X)}・t (2) formula V ₁ (or V ₃ )=A/α・exp(−C)・[exp(−X)/X ²・F(X)〕X ₂ X ₁ , here F(X)=1-2! /X+3! /X ² − …(3) Formula V=V ₁ +V ₂ +V ₃ ≧1 (4) [Here, X=A/T, T is the Kelvin 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,
1. A method for determining industrial-scale firing conditions for a ceramic product having a desired water absorption rate, the method comprising selecting firing conditions from the value of . 2 From laboratory-scale data, a ceramic product with a desired water absorption rate is obtained by firing a raw material for ceramics containing 3% by weight or less of lime as CaCO ₃ at multiple ceramizing temperatures, using the formula lnt=A. /T+C (1) [Here, t is the maximum temperature firing holding time, T is the Kelvin temperature of the firing, and A and C are constants] to find the values of constants A and C; Ceramicization degree V ₁ ( The following relational expressions (2) and (3) showing the temperature increasing process firing), V ₂ (maximum temperature firing), V ₃ (temperature decreasing process firing), and porcelain degree V (sum of all firing processes),
(4), Formula V ₂ = exp {-(C+X)}・t (2) Formula V ₁ (or V ₃ )=A/α・exp(-C) ・[exp(-X)/X ²・F (X)〕X ₂ X ₁ , here F(X)=1-2! /X+3! /X ² − …(3) Formula V=V ₁ +V ₂ +V ₃ ≧1 (4) [Here, X=A/T, T is the Kelvin 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,
1. A method for determining industrial-scale firing conditions for a ceramic product containing lime and having a desired water absorption rate, the method comprising selecting firing conditions based on the value of .