JPH1072255A - Low expansion ceramic ladle for nonferrous molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low expansion ceramic ladle capable of improving the productivity of a casting machine, etc., and the quality of castings as a ladle used for separating and feeding a nonferrous molten metal such as an Al alloy. SOLUTION: This ladle is made of an aluminum titanate sintered compact having a grain boundary phase made of Ti-Al-Si-O mixed crystals consisting of 9.4-12.2mol% Ti, 18.8-24.2mol% Al, 0.8-8.3mol% Si and the balance O and having 0-0.2% coefft. of linear expansion at the time of heating to 1,000 deg.C and $0.1% difference in the coefft. of linear expansion due to hysteresis at the time of cooling. The aluminum titanate sintered compact has high strength and superior thermal shock resistance because of its low thermal expandability and non-hysteresis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladle used for separating and supplying non-ferrous metal such as aluminum alloy.

[0002]

2. Description of the Related Art Ladles are generally used as containers for separating and supplying nonferrous molten metals such as aluminum alloys. In particular, die-casting machines use mechanically-operated ladles that pump molten metal and supply it into the plunger sleeve.These ladles are generally cast iron ladles, and when metal oxide powder is applied to prevent erosion by molten aluminum. There are many. However, such a coating agent has insufficient adhesive force, and is easily peeled when removing aluminum oxide and the like adhering to the surface, and the peeled portion is eroded by the molten aluminum to elute iron, etc. Affects quality. Therefore, frequent coating operations are required, but this will cause some hindrance to productivity. Furthermore, the high thermal conductivity of cast iron tends to lower the temperature of the molten metal, which also causes quality deterioration.

On the other hand, attempts have been made to convert the ladle material into ceramic. High thermal shock resistance and corrosion resistance are required, and there are already practical examples of silicon nitride or sialon. However, these have high manufacturing costs and tend to be expensive, making it difficult to exhibit the advantage of high durability. In addition, they have a relatively large thermal conductivity and may be insufficient in heat retention.

[0004] On the other hand, aluminum titanate ceramics have been tried for practical use. Originally, aluminum titanate is a ceramic that has a low coefficient of thermal expansion and is very resistant to thermal shock, and has a high melting point of 1850 ° C. and can withstand high temperatures. Further, the thermal conductivity is 1/5 to 1/10 that of silicon nitride, sialon and the like, and the heat retention effect as a ladle is large. However, the conventional aluminum titanate sintered body has a large hysteresis generated in the history of thermal expansion and contraction during heating and cooling, so that an aluminum titanate sintered body having high thermal shock resistance and sufficient strength and capable of withstanding practical use is obtained. It was very difficult. For example, it is possible to increase the strength and suppress the hysteresis with additives, but at the same time, the coefficient of thermal expansion is increased and the thermal shock resistance is reduced. On the other hand, strength is not greatly sacrificed for maintaining the thermal shock resistance. And hysteresis also appears greatly. With a low-strength ladle, problems such as breakage occur due to the rapid movement of the machine operation and the stress caused by the load.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ladle used for separating and supplying a non-ferrous metal such as an aluminum alloy, which is capable of improving the productivity of a casting machine and the like and improving the quality of a casting. An object of the present invention is to provide a ladle made of expandable ceramics.

[0006]

The low-expansion ceramic non-ferrous metal ladle according to the present invention comprises a sintered aluminum titanate which is a constituent material thereof, wherein the crystal grain boundary of the sintered body is titanium: 9.4 to 9.4. 12.2 mol%, aluminum:
18.8-24.2 mol%, silicon: 0.8-8.
Ti-Al-Si-O consisting of 3 mol%, the balance being oxygen
The objective was achieved by the fact that the alloy was composed of a system mixed crystal and had a linear expansion coefficient of 0 to 0.2% when heated at 1000 ° C. and a difference of 0.1% or less due to hysteresis upon cooling. .

(Effect) Originally, the low thermal expansion and the high thermal shock resistance of aluminum titanate are caused by so-called microcracks, which are caused by extremely different expansion rates in the respective crystal axis directions. . Aluminum titanate has a very different coefficient of thermal expansion depending on the axial direction of the crystal.
While it has a large positive value of 10−6, 19.4 × 10−6, only the c-axis direction has a negative value of −2.6 × 10−6. Therefore, when this ceramic is sintered at a high temperature and then cooled, a large stress is generated at the interface between the two surfaces unless the crystal orientations of the bonded surfaces match each other. Cracks The existence form of the microcracks generated in this way largely governs the physical and mechanical properties of the sintered body, and the mechanical strength is greatly reduced as the microcracks increase. At this time, a phenomenon of thermal expansion hysteresis appears largely due to the opening / closing behavior of the microcracks. That is, during heating expansion, the microcracks show a very small expansion rate due to blockage of the microcracks. Then, at 600 to 400 ° C., it cannot withstand the stress, causes microcracks again, expands, and returns to the initial state. In other words, those having a large hysteresis are markedly closed by cracks during cooling, and are likely to be damaged by a thermal shock in an intermediate temperature range. As described above, conventionally, low thermal expansion and hysteresis coexist in an aluminum titanate sintered body, and high strength is a trade-off between the two properties.

[0008] Various improvements have been attempted so far, but none of them is satisfactory. For example, Fe as an additive
_Although it is possible to increase the strength with ₂ O ₃ , MgO or the like, the coefficient of thermal expansion also increases, and the thermal shock resistance decreases. On the other hand, in order to reduce the thermal expansion coefficient for maintaining the thermal shock resistance, it is necessary to introduce a large number of microcracks into the sintered body, and the strength has to be largely sacrificed. In addition, even if the expansion was low, there was hysteresis due to the above-mentioned factors, and breakage was liable to occur due to repeated thermal cycling. For example, when the temperature is cooled from 1200 ° C. to 500 ° C. and then heated rapidly again, it is inevitably damaged.

In view of the essential characteristics of such an aluminum titanate sintered body, the present invention combines low thermal expansion and non-hysteresis properties of the sintered body by controlling crack morphology and suppressing seizure. It is applied as a ladle material. That is, the composition of the grain boundary phase of the aluminum titanate sintered body is as follows: titanium: 9.4 to 12.2 mol%, aluminum:
18.8-24.2 mol%, silicon: 0.8-8.
Ti-Al-Si-O consisting of 3 mol%, the balance being oxygen
By comprising a system mixed crystal, the crystal growth is suppressed at the same time as the expansion anisotropy is relaxed, the generation of microcracks is minimized, and the microcracks have a property that seizure hardly occurs. It has high strength, low thermal expansion and excellent thermal shock resistance with a linear expansion rate of 0 to 0.2% when heated at 0 ° C and a difference in expansion rate due to hysteresis at cooling of 0.1% or less. Thus, a ladle comprising the aluminum titanate sintered body was obtained.

The grain boundary phase according to claim 1, Ti-Al-Si
The -O-based mixed crystal is used for other component systems such as Ti-A
l-Zr-O, Ti-Al-Mg-O, Ti-Al-F
This is because the e-O type or the like has a poor or insufficient crystal growth suppressing effect, resulting in hysteresis. This is considered to be because the crystal grows large and the sintering promoting component is concentrated at the grain boundaries, and a large number of microcracks that easily cause seizure when clogging occur. Ti-
The composition of the Al—Si—O-based mixed crystal was determined to be titanium: 9.4 to 1
2.2 mol%, aluminum: 18.8 to 24.2 m
ol%, silicon: 0.8 to 8.3 mol%, and the balance is composed of oxygen. If the silicon content is less than 0.8 mol%, the relaxation of the expansion anisotropy of the mother phase and the suppression of crystal growth are not sufficient. On the other hand, if it exceeds 8.3 mol%, the mullite phase becomes excessive and the low thermal expansion property is impaired. Although the ratio of titanium to aluminum is 1: 2, a slight excess of titanium is better. This is because excess Al ³ + may diffuse at a high temperature and promote crystal growth. The parent phase of the crystal is Al ₂ TiO ₅ , and similarly, a slight TiO ₂ excess composition is better and an Al ₂ O ₃ excess is not preferred.

Aluminum titanate as a parent phase is synthesized from titanium oxide such as rutile, anatase or brookite and aluminum oxide such as corundum. The finer the particles, the more preferable it is 1 μm or less. Grain boundary phase T
The i-Al-Si-O-based mixed crystal is synthesized from the same aluminum titanate composition and Si compound as the parent phase, but the average particle diameter needs to be finer.
It is 0.1 μm or less. Examples of the Si compound include colloidal silica, ethyl silicate, mullite, amorphous silica, and clays.
Is highly dispersed, a Ti-Al-Si-O-based mixed crystal can be formed.

In the second aspect, the linear expansion coefficient at the time of heating at 1000 ° C. is set to 0 to 0.2%. If it exceeds 2%, the thermal shock resistance is poor. The reason why the difference in expansion rate due to hysteresis during cooling is 0.1% or less is that if it exceeds 0.1%, damage due to thermal shock is likely to occur in an intermediate temperature range. Hereinafter, the present invention will be described specifically with reference to examples.

[0013]

Example 1 An aluminum titanate powder serving as a mother phase synthesized from an Al ₂ O ₃ .TiO ₂ mixture having a molar ratio of 1: 1 was added to
A mixture of Al ₂ O ₃ and TiO ₂ having a molar ratio of 1: 1 and additional components (kaolinite in the material of the present invention, ZrO ₂ , M
gO, Fe ₂ O ₃ ), a powder to be a grain boundary phase was added, an organic binder and a deflocculant were added, and the mixture was mixed by a ball mill, and the resulting slurry was poured into a gypsum mold and molded. The obtained molded body is dried and then dried at 1550 ° C. in an electric furnace.
Was fired.

[0014]

[Table 1]

Table 1 shows the composition of the grain boundary phase, bending strength, coefficient of thermal expansion and hysteresis of the material of the present invention and the comparative material. FIG. 1 shows the thermal expansion and contraction curves of a typical material of the present invention and a comparative material. The material of the present invention has extremely small occurrence of hysteresis while maintaining high strength and low expansion property with respect to the comparative material. (See Table 1 and FIG. 1) Since the strength is high and the expansion characteristics are excellent, it is possible to sufficiently withstand the stress applied to the ladle due to the rapid movement of the mechanical operation and the weight of the molten metal.

[0016]

Embodiment 2 FIG. 2 shows an example of a ladle product using the sintered body of the present invention. The ceramic ladle is generally provided with a metal mechanical mounting portion and is used by being fixed with bolts or the like. In particular, a conventional low-strength aluminum titanate requires a careful fixing method. On the other hand, the sintered body of the present invention can be used as a ceramic integrated product as shown in FIG. Also, the fixing structure can be simplified even when a metal mechanical mounting portion is involved.

[0017]

Embodiment 3 With a 1.0 kg robot ladder attached to a company A die-casting machine, the ladder of the present invention has a high durability of 9 months or more, and maintenance such as a work for applying a ladder protection material is almost unnecessary. In addition, the temperature after holding the aluminum alloy for 20 seconds showed a heat retaining effect of + 5 ° C. with respect to the conventional cast iron ladle, and the quality of the cast product was improved.

[0018]

According to the present invention, as is clear from the examples, the aluminum titanate sintered body having high strength and excellent thermal shock resistance due to the coexistence of low thermal expansion and non-hysteresis of the sintered body. Laddle consisting of:

[Brief description of the drawings]

FIG. 1 is a chart showing the thermal expansion / shrinkage curves of a typical material of the present invention and a comparative material.

FIG. 2 shows an example of a ladle product using the sintered body of the present invention.

Claims (2)

[Claims] 1. The composition of a crystal grain boundary phase of a sintered body: titanium: 9.4 to 12.2 mol%;
8 to 24.2 mol%, silicon: 0.8 to 8.3 mol
A low-expansion ceramic non-ferrous metal ladder comprising an aluminum titanate sintered body composed of a Ti-Al-Si-O-based mixed crystal composed of 1% and the balance being oxygen. 2. The linear expansion coefficient at the time of heating at 1000 ° C. is 0.
A low-expansion ceramic comprising the aluminum titanate sintered body according to claim 1, wherein the difference in linear expansion coefficient due to hysteresis upon cooling is 0.1% or less. Ladle for quality non-ferrous metal.