JPH0552671A - Compact for detecting heat history - Google Patents

Abstract

PURPOSE:To measure indicating temperature at high accuracy, and to strictly manage a baking process by forming a compact for detection out of a ceramic non-baked compact mainly composed of MgO of not less than a specified weight percentage. CONSTITUTION:A compact 10 for detecting heat history 10 is formed out of ceramic non-baked compact mainly composed of MgO of not less than 70wt%. More preferably, it is composed of a ceramic non-baked compact composed of combinations that fall in a range formed by points A(MgO100%), B(MgO90%, SiO210%), C(MgO70%, CaO30%) in a three-component structural diagram of SiO2. A chord part 12 in parallel to a disc body is formed by this compact 10, while the other arc part is defined as a surface 11 for measuring excellent circularity, while a recessed part 13 is formed on one side so as to discriminate the surface side from rear side, and the angular parts of the upper and lower surfaces are chamfered and are press-molded. The mold body 10 is baked along with a material to be baked, and the difference in the size after baking is measured, and a indicating temperature is determined based on a conversion table. Baking management in high temperature region of no more than 1700 deg.C can be carried out within the measurement accuracy of + or -2 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for detecting the thermal history in the firing process of ceramics and the like, and particularly in the firing of silicon carbide, silicon nitride, magnesia, alumina, etc. in a high temperature range exceeding 1700 ° C. The present invention relates to a heat history detection molded body.

[0002]

2. Description of the Related Art In the firing process of ceramics, the thermal history of the body to be fired changes depending on the temperature profile, the type of firing furnace, the settings in the furnace, and the like. That is, even if the firing temperature is the same, if the other conditions are different, the thermal history is different, and it is necessary to correctly detect this thermal history.

For example, the thermal history of a body to be fired has been detected using a Zegel cone as disclosed in Japanese Utility Model Laid-Open No. 56-29441. Zegel cones are provided with a plurality of triangular pyramids having different melting temperatures on a support, and after firing this Zegel cone together with the object to be fired, the thermal history of the triangular pyramids falls, It was supposed to detect. However, this method cannot be used for accurate detection, so that it is now less used.

Therefore, as disclosed in, for example, Japanese Unexamined Patent Publication No. 1-184388, an unfired ceramic body is used, and this body is fired together with the body to be fired, and then the dimensional change due to shrinkage is measured. By doing so, the thermal history has been detected. For example, a ring-shaped molded body 20 as shown in FIG. 3 or a sheet-shaped molded body 30 as shown in FIG. 4 was used.

When measuring such a dimensional change due to firing shrinkage, the dimensional change is expediently converted into a temperature, but this temperature does not represent an actual temperature but represents a thermal history. Therefore, in the present invention, it is referred to as an instruction temperature.

[0006]

However, the above-mentioned ceramic molded body for thermal history detection has a problem of Al ₂ O ₃ --Si.
Since it was made of a natural raw material containing O ₂ or SiO ₂ —MgO system as a main component and containing a large amount of impurities, the firing shrinkage ratio varied, and the accuracy of the detected indicated temperature was poor. In addition, in the high temperature region of 1700 ° C. or higher, there was no ceramic molded body whose thermal history was detected.

Further, in the ring shape shown in FIG. 3,
Since the volume is large, a large space is required in the firing furnace, and the sheet-like material shown in FIG. 4 has a problem that warpage occurs and the dimension cannot be measured correctly.

[0008]

Therefore, according to the present invention, a ceramic unfired compact containing 70% by weight or more of MgO as a main component, more preferably, a point A in the three-component composition diagram of MgO-CaO-SiO ₂ (MgO100, CaO0,
SiO ₂ 0), point B (MgO 90, CaO 0, SiO ₂
10), point C (MgO70, CaO30, SiO ₂ 0)
A ceramics unfired molded body having a composition within the range of is used as a thermal history detection molded body.

In the present invention, the reason why the composition is within the above range is that if the composition is out of this range, the composition is densified at 1700 ° C. In the present invention, the components other than the above three components may be included in a trace amount.

[0010]

EXAMPLES Examples of the present invention will be described below.

As shown in FIGS. 1 (a) and 1 (b), the thermal history detecting molded body 10 of the present invention comprises a chord portion 12 parallel to the disc body.
12 is formed, and the remaining circular arc portions are the measurement surfaces 11 and 11 having excellent roundness. Further, a concave portion 13 is formed on one surface by marking such as dots or alphabets for distinguishing the front side and the back side, and chamfers 14 are provided at upper and lower corners.

Further, the molded body 10 contains 70% by weight or more of MgO as a main component and contains CaO, SiO _{2 and the} like, and in detail, MgO ₂ --CaO--S shown in FIG.
As shown in the io ₂ ternary composition diagram, point A (MgO 10
_{0, CaO0, SiO 2 0)} , point B (MgO90, Ca
O0, SiO ₂ 10), point C (MgO70, CaO3)
0, SiO ₂ 0) and the composition within the range
It is an unsintered compact formed by press molding while controlling the particle size of the raw material powder, the green density of the compact, and the like very strictly. Then, as will be described later, the firing temperature is changed under a certain condition, the dimension of the molded body 10 after firing is measured, and the relationship between the dimension and the firing temperature is prepared as a conversion table. afterwards,
When firing is performed under different conditions, the molded body 10 is fired together with the body to be fired, and the dimensional change after firing is measured, so that the indicated temperature can be obtained from the conversion table.

As described above, the indicated temperature is not an actual temperature but a thermal history for convenience. That is, if the heat history detecting molded body of the present invention is used, the heat history itself can be managed by obtaining the indicated temperature even when the firing conditions are different.

The molded product of the present invention can be used in various firing atmospheres, but when used in a non-oxidizing atmosphere, it is better to perform calcination to remove the binder.

Further, the molded body 10 of the present invention comprises the chord portion 1
Since it has 2 and 12, it has a smaller area than the conventional example shown in FIG. 2 and does not require a large space in the firing furnace. The string portions 12 and 12 do not have to be parallel to each other, and may be formed at only one place. Furthermore, since the molded product 10 of the present invention is a press-molded product having a wall thickness of about 3 to 10 mm, warpage does not occur,
Further, at the time of dimension measurement, as shown in FIG. 1A, a low constant pressure micrometer may be used to measure between the arcuate measurement surfaces 11, 11 and the same diameter D can be accurately measured even if the measurement position is deviated.

Further, the shape of the molded body 10 of the present invention can be various as long as it is a simple shape having a uniform density.

Example 1 Purified MgO raw material having a purity of 99.9% or more was added with CaO and S.
iO ₂ was added to obtain the composition shown in Table 1 and FIG.
Composition No. 1 is dry pulverized with a jet mill and has a composition N
o. After 2 is wet pulverized with alumina balls and subjected to particle size analysis by a laser light scattering method to obtain an average particle size of 2.0 ±
The range was 0.1 μm. In addition, composition analysis was performed by a fluorescent X-ray analysis method. 11% by weight of a wax-based binder was added to and mixed with this raw material powder, and spray-dried to obtain granules with good fluidity. The granules were placed in an air-conditioned molding chamber as shown in FIGS. Press-molding into the shape shown in Fig. 1, but at this time, the green density of the molded body is 1.400 ± 0.00
Within the range of 5 g / cm ³ , a heat history detecting molding of the present invention was obtained.

These molded bodies were treated at 1700 ° C. for 2 hours,
Firing was performed under two kinds of conditions of 1900 ° C. for 2 hours. The results are shown in Table 2. The composition ratios in Table 2 are compounding ratios, but the analysis values are shown in parentheses.

[0019]

[Table 1]

[0020]

[Table 2]

It is apparent from Tables 1 and 2 that No. 1 outside the range connecting the points A, B and C. Nos. 6, 7, and 8 were densified at 1700 ° C. and could not be used in the intended high temperature range.

On the other hand, No. 10 within the range connecting points A, B and C In Examples 1 to 5 of the present invention, the shrinking process was in the range of 1700 ° C. or higher, and it was found that it can be used in a high temperature range. However, No. 1 is MgO
Other components were not included at all, and did not shrink even at 1900 ° C. Therefore, it can be used in a temperature range higher than 1900 ° C. On the other hand, No. Since No. ₂ was crushed with alumina balls, it contained minute amounts of SiO ₂ and Al ₂ O ₃ , contracted in the range of 1700 to 1900 ° C., and was usable in this temperature range.

Experimental Example 2 In the same manner as in Experimental Example 1, No. 1 in Table 1 was used. With the composition of 2,
A heat history detecting molded body 10 having a diameter D of 22.300 mm was prepared. This molded body 10 was heated in an oxidizing atmosphere at a temperature rising rate of 200 ° C./hour using a firing furnace that was rigorously controlled and calibrated.
It was held at the maximum firing temperature for 2 hours, fired at a temperature lowering rate of 300 ° C./hour, and degreased at 350 ° C. for 1 hour. The dimensions of the molded body 10 after firing were measured at 20 ° C. with a low constant pressure micrometer.

The firing temperature (instructed temperature) was variously changed, and the firing of 20 molded bodies 10 was repeated three times. The results are shown in Table 3 and FIG.

Further, from the dimensional variation (3σ) at each temperature and the dimensional change amount (tangent slope) per 1 ° C. at that temperature, the detection accuracy of the indicated temperature = ± dimensional variation / per 1 ° C. The detection accuracy (3σ) of the indicated temperature was calculated from the dimensional change amount. As a result, as shown in Table 3, in the range of 1700 to 1900 ° C, the detection accuracy of the indicated temperature could be within ± 2 ° C.

Further, although Table 3 shows the dimensions of the molded body for each indicated temperature of 50 ° C., a conversion table for the dimensions of the molded body and the indicated temperature can be obtained by measuring the dimensions for each of the more detailed indicated temperatures. Can be

[0027]

[Table 3]

Further, in the above embodiment, in order to obtain the heat history detecting molded body 10, the grain size of the raw material is 2.0 ± 0.1 μm,
The green density of the molded body was 1.400 ± 0.005 g / cm ³ , but the green density is not limited to this value and can be variously changed. Normally, the particle size is controlled at ± 0.2 μm, and the raw density is ± 0.01 g
By suppressing the variation within the range of / cm ³ , it was possible to make the detection accuracy of the indicated temperature ± 2 ° C.

[0029]

As described above, according to the present invention, 70% by weight
The above MgO as a main component, especially MgO-CaO-Si
In the ternary composition diagram of the O _2, the point A (MgO100, C
aO0, SiO ₂ 0), point B (MgO90, CaO0,
SiO ₂ 10), point C (MgO70, CaO30, Si
By using a ceramics unfired molded body having a composition within the range connecting O ₂ 0) as the thermal history detection molded body, the measurement accuracy of the indicated temperature can be made extremely accurate to within ± 2 ° C. Even if the temperature changes, the firing process can be strictly controlled, and an excellent sintered body can be obtained. Further, it is possible to enable firing control particularly in a high temperature range of 1700 ° C. or less.

[Brief description of drawings]

FIG. 1 (a) is a plan view showing a heat history detection molded body according to an embodiment of the present invention, and FIG. 1 (b) is a sectional view taken along line XX in FIG. 1 (a).

FIG. 2 is a three-component composition diagram showing the composition range of the molded article for heat history detection of the present invention.

FIG. 3 is a perspective view showing a conventional molded body for heat history detection.

FIG. 4 is a perspective view showing a conventional heat history detection molded body.

FIG. 5 is a graph showing the relationship between the firing shrinkage rate and the indicated temperature in the heat history detection molded body of the present invention.

[Explanation of symbols]

 10 ... Mold for thermal history detection 11 ... Measurement surface 12 ... Chord portion 13 ... Recessed portion 14 ... Chamfer

Claims (1)

[Claims] 1. A molded article for thermal history detection, comprising a ceramic unfired molded article containing 70% by weight or more of MgO as a main component.