JPH0662335B2 - Casting ceramic material and manufacturing method thereof - Google Patents

Description

The present invention relates to a ceramic material used when a hollow tubular ceramic is cast with a molten metal such as aluminum or cast iron, especially a port liner for a gasoline engine, a diesel engine, or the like. The present invention relates to a heat insulating cast ceramic material used for an exhaust manifold liner, a piston cavity, a cylinder top plate and the like, and a method for manufacturing the same.

(Prior Art) In recent years, environmental pollution due to automobile exhaust has become an important social problem, and a method for removing harmful substances in automobile exhaust by a catalyst is mainly used. The precious metals such as Pt and Rh used as this catalyst have a problem of reducing their usage due to resource and cost problems. In addition, the catalyst purification performance due to the decrease in exhaust gas temperature in 4-valve engines has been increasing in recent years. Is a problem.

As one of the methods for solving these problems, it is possible to line the exhaust port of the engine and the inner surface of the exhaust manifold with a port liner made of a ceramic having a low Young's modulus, and to raise the exhaust gas temperature by the heat insulation effect.
It is proposed in Japanese Patent No. 759. The addition of rare earth elements to aluminum titanate, which is the object of the present invention, is disclosed in JP-B-57-3629 and JP-A-56-92164.

(Problems to be developed by the invention) However, in the material disclosed in Japanese Patent Laid-Open No. 63-236759, there is a problem that the strength deteriorates and breaks due to a cooling / heating cycle due to a change in exhaust gas temperature when used. was there.

Further, the inventions of JP-B-57-3629 and JP-A-56-92164 are both dense and have a low expansion by adding a predetermined amount of an oxide of Y, La or Ce to aluminum titanate. You have a sintered body. However, all of them have a high Young's modulus, and there is a problem that they cannot be used as cast-molding materials.

The present invention solves the conventional problems as described above, in addition to excellent heat resistance and thermal shock resistance and heat insulation, there is no risk of cracking due to the compressive force generated during casting, and the thermal cycle during use The present invention aims to provide a ceramic material for a low Young's modulus cast gurney that also has durability against the above and a manufacturing method thereof.

(Means for Solving the Problem) The ceramic material for cast iron of the present invention contains 65% by volume or more of aluminum titanate as a crystal phase, has an average grain size of 10 μm or more, and oxidizes rare earth elements. 20% by volume of glass phase containing 0.5 to 16% by weight
It is characterized in that it is a crystal of one or more kinds of rutile, corundum, and mullite, and Young's modulus is 50 to 2000 kgf / mm ² when it contains the following other components. .

Further, the manufacturing method of the ceramic material for cast iron of the present invention, as an Al ₂ O ₃ source material, the Al ₂ O ₃ component is 96 wt% or less,
A raw material having an average particle diameter of 3 μm or more, a raw material having an average particle diameter of 3 μm or less as a TiO ₂ source raw material, and a powder having a predetermined composition in which 1.8 wt% or less of a predetermined rare earth element are converted into oxides are molded, It is characterized by firing.

(Function) The coefficient of thermal expansion of the aluminum titanate crystal in each axial direction is
The a and b axes are positive and the c axis is negative, and the difference between them is very large.
Strain occurs at the grain boundaries. This distortion is not a serious problem in the conventional material composed of fine-grained crystals, but especially in the case of a material for cast iron that has a low Young's modulus by growing aluminum titanate crystals to an average of 10 μm or more. It was found that since the strain becomes extremely large, the intervals of the grain boundaries widen due to the cooling / heating cycle, and the strength deteriorates.

On the other hand, it was found that the addition of a trace amount of rare earth elements such as Y, Ce, La can prevent the strength deterioration due to the cooling / heating cycle. It is considered that this is because the added rare earth element aggregated in the grain boundary glass phase to improve the strength of the glass phase and the bonding force between the glass phase and the aluminum titanate crystal.

That is, the present invention has been completed on the basis of such knowledge, aluminum titanate having a predetermined crystal grain size as a main crystal phase, a predetermined amount of rare earth element in the grain boundary of the aluminum titanate crystal It has been found that a ceramic material having a structure containing a glass phase can contain the above-mentioned low Young's modulus, which is the object of the present invention, and also has a resistance to thermal cycling.

Further, as a method for producing a ceramic material having this crystal structure, by using a coarse grain Al ₂ O ₃ source raw material and fine grain TiO ₂ source raw material and a predetermined amount of rare earth element, a crystal phase suitable as the above material Aluminum titanate as 65
Contains more than volume%, the average grain size of the crystal is more than 10μm, Young's modulus is 50 ~ 2000kgf / mm ² , compressive strength is 5 ~ 40k
It is possible to obtain a ceramic material for cast bodies having a gf / mm ² and a porosity of 5 to 35%.

The reasons for limiting the respective constituents and the preferable ranges of the ceramic material of the present invention are as follows. Aluminum titanate 65% by volume or more, the average grain size of the crystal is 10
The reason why the value is limited to μm or more is that if the respective values are less than 65% by volume and less than 10 μm, the Young's modulus exceeds 2000 kgf / mm ² and cracks occur during casting. Also,
When the amount of glass phase exceeds 20% by volume, Young's modulus is 2000 kgf /
Since it exceeds mm ² , the amount of the glass phase is set to 20% by volume or less. Further, if the rare earth element in the glass phase is less than 0.5% by weight in terms of oxide, the deterioration rate of the bending strength due to the cooling / heating cycle exceeds 10%. If the deterioration rate of the transverse strength exceeds 10%, the ceramic may be damaged in the thermal cycle durability test of the product encased in metal, so 10% is considered as the upper limit of the deterioration rate and the lower limit of the rare earth element is set.
It was 0.5% by weight. On the other hand, when the rare earth element in the glass phase exceeds 16% by weight in terms of oxide, the Young's modulus is 2000 kgf /
Since it exceeds mm ² , cracks occur during casting, so the upper limit of rare earth was set to 16% by weight. From the above,
The content of rare earth elements in the glass phase was limited to 0.5 to 16% by weight.

Further, the preferable range is for the following reason. Compressive strength is 5
If it has a bending strength of less than 0.2 kgf / mm ² and / or a bending strength of less than 0.2 kgf / mm ² , it may be deformed during casting, causing handling problems, and whether the compressive strength exceeds 40 kgf / mm ² . If the bending strength exceeds 2.0 kgf / mm ² , the Young's modulus is 2000.
It may exceed kgf / mm ² . Further, if the porosity is less than 5%, a sufficient heat insulating effect cannot be obtained, and if the porosity exceeds 35%, the strength and Young's modulus may be out of the numerical range of the present invention.
It is most preferable that the Young's modulus in particular 50~200kgf / mm ^2, the rare earth elements of the glass phase is more than 10 wt% in terms of oxide Young's modulus exceeds the 200 kgf / mm ^2. Furthermore, the composition of the ceramic material is preferably Al ₂ O ₃ 40 to 65% by weight and TiO ₂ 30 to 60% by weight, because the crystal amount of aluminum titanate is less than 65% by volume in other compositions. Further, it is preferable that the total content of at least one of SiO ₂ , MgO and Fe ₂ O ₃ is 10% by weight or less.
This is because when the amount exceeds 5% by weight, the crystal amount of aluminum titanate is unlikely to be 65% by volume or more, and the crystal grain size may not be 10 μm or more. Furthermore, the ceramic material of the present invention has a thermal expansion coefficient of 2.0 × 10 ⁻⁶ (40 to 800 ° C.) or less, and a thermal conductivity of 0.8 to 5.0 × 10 ⁻³ cal / cm · sec · ° C. Suitable for port liners that come into direct contact with hot exhaust gas.

Next, in the manufacturing method of the present invention, Al ₂ O ₃ source material and T
The reasons for limiting the iO ₂ source material are as follows. Al ₂ O ₃
If the purity of the source material is higher than 96% and the average particle size is 3 μm or more, the reactivity of the Al ₂ O ₃ source material is low, so there are many unreacted residues, and the Young's modulus is higher than 2000 kgf / mm ^2. There is a risk of cracks due to cast metal. When the average particle size of the Al ₂ O ₃ source material is smaller than 3 μm, the average particle size of aluminum titanate is 10 μm or less regardless of the purity of the Al ₂ O ₃ source material, and the Young's modulus exceeds 2000 kgf / mm ² . Will end up. Furthermore, if the impurities contained in the Al ₂ O ₃ source material exceed 20% by weight of SiO _{2 and} 20% of Fe ₂ O ₃ or the total amount of SiO ₂ and Fe ₂ O ₃ is 20% by weight, aluminum titanate crystals are crystallized. Is 65%
In some cases, the crystal grain size does not exceed 10 μm. From the above, the Al ₂ O ₃ source raw material must have a purity of 96% or less by weight% and an average particle size of 3 μm or more, and preferably the amount of impurities is SiO ₂ 0 to 20% and Fe ₂ O ₃ 0 to 0. 20% or SiO
It is preferable that the total of ₂ and Fe ₂ O ₃ is 0 to 20%.

Further, in the TiO ₂ source material, if the average particle size is larger than 3 μm, unreacted residue increases, Young's modulus exceeds 2000 kgf / mm ^2, and there is a risk of cracking due to cast aluminum. Therefore, the TiO ₂ source material must have an average particle size of 3 μm or less.

The addition amount of rare earth elements such as Y, La, and Ce is 1.8 wt% or less, so that Young's modulus is 2000 kgf / mm ² or less, and more preferably
If it is less than 0.3% by weight, the Young's modulus can be 200 kgf / mm ² or less.

(Example) In order to produce the ceramic material of the present invention, first, alumina, calcined bauxite, refined rutile, crude rutile, anatase type titanium, ilmenite, ferrite red iron oxide,
Al ₂ O ₃ 40-65%, TiO ₂ 30-60% by weight% in chemical composition from fused magnesium, magnesite, fused spinel, kaolin, quartz, fused silica and certain rare earth elements.
And at least one of SiO ₂ , MgO, and Fe ₂ O ₃ is 10 in total.
The raw materials are selected so as to be less than or equal to%.

At this time, it is necessary to mix a raw material having an Al ₂ O ₃ component of 96% by weight or less and an average particle diameter of 3 μm or more as an Al ₂ O ₃ source raw material with a raw material having an average particle diameter of 3 μm or less as a TiO ₂ source raw material. .

Further, the rare earth element can be added in the form of nitrate, oxide, or other compound, but it is preferable to uniformly disperse it by using a fine particle raw material in order to obtain the effect by adding a trace amount.

Peptizer selected from water glass, ammonium polycarboxylate, amines, sodium pyrophosphate, etc.
0.1 to 1.0% added, and further added 1.0 to 5.0% binder selected from PVA, MC, CMC, acrylate, etc., 15 to 40%
Mix well with water using a trommel, pot mill, etc. to prepare a slurry having a viscosity of 200 to 1000 cp. Such a slurry is formed into a cylindrical shape or a port liner shape by a pouring method, and then dried and fired.
As a result, containing 65 or more aluminum titanate as a crystal phase, heat resistance, thermal shock resistance containing 20% or less of a glass phase containing 0.5 to 16% by converting a rare earth element into an oxide,
Although an aluminum titanate sintered body having excellent heat insulating properties and cold cycle durability can be obtained, other crystalline phase may include one or more crystals of rutile, corundum and mullite. In the present invention, the conditions for this firing are, for example, 1450 to 1650 ° C, preferably 1500 to 1600 ° C.
By setting the time to about 1 to 16 hours, the crystals of aluminum titanate are sufficiently grown until the average grain size becomes 10 μm or more. As a result, the Young's modulus is 50 to 2000 kgf / mm
² , preferably 5-40kgf / mm ² compressive strength, 0.2 bending strength
It can have physical properties of ~ 2.0 kgf / mm ² and porosity of 5-35%. Such a low Young's modulus ceramic material can shrink together with the metal material when the cast metal material shrinks, and in particular, the conventional high-strength high Young's modulus ceramic is likely to be destroyed due to stress concentration. No cracks occur even in complicated shapes.

Therefore, not only the cylindrical type port liner but also the four-valve engine has two ports 2 on the cylinder side and a single exhaust port 1 on the exhaust manifold side as shown in FIGS. It is also suitable for a shaped port liner 3 or an exhaust manifold liner as shown in FIG. In addition, the thermal conductivity becomes low due to the microcracks in the sintered body, and a sufficient heat insulating effect is exhibited even if the porosity is relatively small.

Since aluminum titanate has a melting point of 1700 ° C or higher, there is no particular limitation on the molten metal for casting, and it can be applied to cast iron made of gray cast iron, spheroidal graphite cast iron, white cast iron, aluminum alloy, copper alloy, magnesium alloy, zinc alloy. .

In addition, the presence of a trace amount of rare earth elements in the glass phase causes the grain boundary glass phase to be strongly bonded to aluminum titanate, and the thermal cycle durability without impairing the properties suitable for the above-mentioned low Young's modulus cast iron. A material having both properties is obtained.

Hereinafter, an actual example will be described.

Examples Tests shown in Table ₃ using Al ₂ O ₃ source materials shown in Table 1 below and TiO ₂ source materials shown in Table ₂ as main materials.
Raw materials were prepared so as to have compositions of Nos. 1 to 35, and the mixture was poured into a mold to prepare an elliptic cylindrical test piece having a wall thickness of 3 mm, a long diameter of 64 mm, and a short diameter of 36 mm. Each test piece was fired under the conditions shown in Table 3, and various characteristics of the obtained fired body were measured.

Next, after filling each of the fired bodies with sand, a cast body made of aluminum was prepared to produce a metal-ceramic composite body having an aluminum wall thickness of 7 mm. After removing the casting sand, it was confirmed whether the test piece had cracks. The results are shown in Table 3.

In Table 3, the thermal cycle test shows 5 thermal cycle cycles of room temperature for 10 minutes and 900 ° C for 20 minutes, as shown in Figure 4 for the thermal cycle schedule and actual sample temperature.
The deterioration rate of the bending strength before and after repeating 0 times was measured.
The amount of aluminum titanate and glass phase is SE
The volume percentage was calculated from the area ratio of each M photograph. Furthermore, the amount of rare earth elements in the glass phase was measured using EDX analysis with a transmission electron microscope.

In addition, regarding the materials of the present invention and the comparative example, in order to make it easier to confirm the change due to the thermal cycle, an electron micrograph of the calcined material and the calcined material after the above thermal cycle test up to 600 cycles is shown in FIG. 5 (a). , (b) and FIGS. 6 (a), (b), respectively. That is, FIGS. 5 (a) and 5 (b) show the crystal structures of the fired body of the present invention before and after the cooling / heating cycle, and FIGS.
The crystal structures of the fired body of the comparative example of (b) before and after the cooling / heating cycle are shown, respectively. 5 (a), (b) and 6 (a), (b)
Therefore, in the material of the comparative example, the intervals of the grain boundaries are widened by the heat cycle, but in the material of the present invention, no remarkable difference is observed before and after the heat cycle test.

From the results shown in Table 3, it can be seen that the ceramic materials obtained in the examples of the present invention have no cracks caused by the cast metal and are less deteriorated by the thermal cycle test than the comparative examples.

(Effects of the Invention) As is clear from the above description, according to the ceramic material for cast iron of the present invention and the method for manufacturing the same, a predetermined coarse grain Al ₂ O ₃ source raw material, fine grain TiO ₂ source raw material, and rare earth are provided. By using an element, the crystal phase contains aluminum titanate at 65% by volume or more, and the average grain size of the crystal is 10 μm.
As described above, it is possible to obtain a crystal structure containing 20% by volume or less of a glass phase containing 0.5 to 16% by weight of a rare earth element as an oxide, and as a result, the Young's modulus is low, and the heat resistance, thermal shock resistance and heat insulation are low. It is possible to obtain a ceramic material for cast iron which is excellent in properties, has no possibility of cracks due to the compressive force generated during casting, and has both heat and cold cycle durability.

[Brief description of drawings]

FIG. 1 is a perspective view of a port liner for a 4-valve engine, FIG. 2 is a cross-sectional view of the port liner after being cast into the engine head, FIG. 3 is a cross-sectional view of the exhaust manifold liner after being cast in, and FIG. 5 (a) and 5 (b) are SEM photographs showing the crystal structures of the fired body of the present invention before and after the cooling / heating cycle, and FIG. 6 (a) and 6 (a), respectively. (b) is an SEM photograph showing the crystal structure of the fired body of the comparative example before and after the thermal cycle.

Claims (2)

[Claims] 1. An aluminum titanate as a crystal phase is contained in an amount of 65% by volume or more, the average grain size of the crystal is 10 μm or more, and the rare earth element is converted into an oxide in an amount of 0.5 to 16% by weight.
If the glass phase contained is 20% by volume or less, and if it contains other components, it is a crystal of at least one of rutile, corundum, and mullite, and the Young's modulus is 50 to 2000 kg.
A ceramic material for cast bodies characterized by having f / mm ² . Wherein Al as ₂ O ₃ source material, Al ₂ O ₃ component is 96 wt%
In the following, a raw material having an average particle diameter of 3 μm or more, a raw material having an average particle diameter of 3 μm or less as a TiO ₂ source material, and a powder having a predetermined composition in which 1.8 wt% or less of a predetermined rare earth element are converted into oxides A method for producing a ceramic raw material for cast dolls, which comprises molding and firing.