JPH02217356A - Ceramic material for internal chill and production thereof - Google Patents

Abstract

PURPOSE:To improve stability of internal chill characteristics, heat (impact) resistance, cooling/heating cycle endurance, etc., by molding and burning a mixed powder of Al2O3 source raw material and TiO2 source raw material and cooling the burned material at a specific rate on the way to burning or during burning. CONSTITUTION:(i) Al2O3 source raw material containing <=96wt.% Al2O3 component, being 0-20wt.% in content of impurity consisting of SiO2 and/or Fe2O3 and having >=3mum average granule size is blended with (ii) TiO2 source raw material having <=3mum average granule size to provide a mixed powder. Then the mixed powder is molded and burned and then cooled from >=200 deg.C, preferably 350-1100 deg.C at a rate of 500 deg.C/Hr, preferably <=2000 deg.C/Hr to provide the title material containing >=65vol.% aluminum titanate as crystal phase and having >=10mum average granule size of the crystal and >=6X10<-3> breaking strain.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to ceramic materials used when hollow tubular ceramics are cast with molten metal such as aluminum or cast iron, and particularly to boat liners for gasoline engines, diesel engines, etc. , exhaust manifold liner, ceramic material for castings used in piston cavities, cylinder top plates, etc., and its manufacturing method.

(Prior Art) In recent years, environmental pollution caused by automobile exhaust gas has become an important social problem, and methods of removing harmful substances from automobile exhaust gas using catalysts have become the main method. Reducing the amount of precious metals used as catalysts, such as Pt and Rh, has become an issue due to resource and cost issues, and 4-valve engines, which have been on the rise in recent years, require catalyst purification by lowering the exhaust gas temperature. Deterioration in performance is a problem. One method to solve these problems has been proposed in the past: lining the inner surface of the exhaust system, such as the engine exhaust port, with a liner made of ceramic, which has excellent heat insulation properties, and raising the exhaust gas temperature due to its heat insulation effect. has been done.

Ceramic materials used for this purpose include:
A material with a low Young's modulus that can alleviate the large compressive stress caused by contraction of molten metal in the liner casting process is preferable, and the present inventors have previously developed a material with a low Young's modulus that contains 65% by volume or more of aluminum titanate as a crystalline phase. Developed a ceramic material for castings, published in Japanese Unexamined Patent Publication No. 63-236.
It has already been proposed as No. 759.

However, subsequent research revealed that some materials break during casting and others do not, even though the Young's modulus E is within the range of 50 to 2000 and 117 m''. However, since stable casting characteristics could not be ensured, there remained problems in its practical application.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and has excellent heat resistance, thermal shock resistance, heat insulation, cold and hot cycle durability, etc. This work was completed with the aim of creating a highly practical ceramic material for castings that is free from the risk of cracking even under compressive force, and a method for manufacturing the same.

(Means for Solving the Problems) As a result of repeated research in order to achieve the above-mentioned problems, the present inventor has found that the conventional Young's modulus is determined based on the relational expression between strain and stress in the elastic region of the material. However, in the case of ceramic materials for castings such as the present invention, the amount of deflection until the material actually breaks has an important meaning in determining whether or not cracks will occur. It was discovered that the properties of the material should be evaluated using the actual breaking strain calculated based on this.

The present invention has been completed based on the above findings, and is based on the first
The invention is characterized in that it contains 65% by volume or more of aluminum titanate as a crystal phase, the average grain size of the crystals is 10 μm or more, and the actual breaking strain is 6×10 −3 or more.

Note that the actual breaking strain is a dimensionless quantity defined by the following equation, and this definition will be used hereinafter in this specification.

Actual breaking strain = 4-point bending bending strength / Young's modulus determined from the amount of deflection of the sample until it breaks during the 4-point bending bending strength measurement.The second invention also uses aluminum titanate as the crystalline phase. Contains vol% or more, and the average grain size of its crystals is 10μ
m or more, and when the rare earth element is converted into an oxide, it is 0.
It is characterized in that the glass phase containing 5 to 16% by weight is 17% by volume or less, and the actual breaking strain is 6XlO-3 or more.

Further, the third invention relates to the method for producing the ceramic material for casting according to the first invention, and A1. A powder of a predetermined composition is formed by mixing a raw material with an AItos component of 96% by weight or less and an average particle size of 3 μm or more as an O, ifl raw material, and a raw material with an average particle size of 3 μm or less as a Ti01 source raw material. , fired at 200°C during and/or after firing.
It is characterized by cooling from the above temperature at a rate of 500° C./Hr or more.

Furthermore, a fourth invention relates to a method for manufacturing the ceramic material for castings according to the second invention, and includes ^1xOs I
As the I raw material, a raw material with an Altos component of 96% by weight or less and an average particle size of 3tI■ or more, and as a ttozl raw material, a raw material with an average particle size of 3 μm or less, and a rare earth element of 1.8% in terms of oxide. A powder of a predetermined composition containing % by weight or less is molded and fired, and during and/or after firing 20%
It is characterized by cooling from a temperature of 0'C or higher at a rate of 500C/Hr or higher.

The configuration of each invention will be explained below.

First, in the first invention, the proportion of aluminum titanate in the crystal phase is set to 65% or more and the average grain size is set to 10 μm or more because, if these conditions are exceeded, the actual breaking strain is less than 6X10-3. This is because cranking occurs during casting. The reason why the actual breaking strain was set to be 6×10-” or more is because, as shown in the later examples, if the actual breaking strain is less than this value, cracks are likely to occur during casting. 10 x 10-' or more is preferable, and since ceramics come into contact with high-temperature molten metal during casting, the actual breaking strain is 6 x 1 even at high temperatures.
It is preferable that it is 0-3 or more.

The second invention is based on the first invention for the purpose of improving thermal cycle durability.
In this case, if the amount of glass phase exceeds 17% by volume, the actual breaking strain will be 6.
Since it becomes less than X10-", the amount of glass phase is
It was set to be 7% by volume or less. Furthermore, if the rare earth element in the glass phase is less than 0.5% by weight in terms of oxide, the deterioration rate of bending strength due to cooling and heating cycles will exceed 10%, and conversely
If the weight ratio exceeds %, the actual breaking strain will be less than 6×10-', so the rare earth element in the glass phase was adjusted to be within the range of 0.5 to 16% by weight in terms of oxide.

In addition, 1. In the material of the second invention, the porosity is 5%
If it is less than 35%, a sufficient heat insulating effect cannot be obtained, and if it exceeds 35%, the actual breaking strain may be out of the range of the present invention. Furthermore, the composition of the ceramic material is ^It (h 40-65% by weight, T
It is preferable to set iO*30 to 60% by weight, because with other compositions, it is difficult for the amount of crystals of aluminum titanate to exceed 65% by volume, and 5i01, MgO
It is preferable to contain at least 10% by weight or less of at least one of the following: , Fears in total, because if the content exceeds 10% by weight, the crystal content of aluminum titanate will be difficult to exceed 65% by volume, and the crystal grain size will be 10 μm or more. This is because the ceramic material of the present invention may not meet 2. Ox
It has a coefficient of thermal expansion of 1O-” (40 to 800°C) or less,
Suitable for port liners etc. that come into direct contact with high temperature exhaust gas.

Next, the reason for the numerical limitation in the third invention is as follows. Higher than 96% by weight of the refined material of the Al2O3 source raw material,
If the average particle size is 3 μm or more, ^1!0. Due to the low reactivity of the source material, there are many unreacted residues, and the actual breaking strain is 6X1.
If the average particle size of the raw material is 3μ, there is a risk of cracks occurring due to the casting.
If smaller than m, AI, 0. Regardless of the purity of the source material, the average particle size of aluminum titanate is 10 μm or less, and the actual breaking strain is less than 6X10-3. Furthermore, the impurities contained in the Altos R raw material are S
iOx 20%, Pe20.20%, or SiO□
If the total amount of Fe10H and Fe10H exceeds 20%, the crystal grain size of aluminum titanate will not exceed 65% and the crystal grain size will decrease lθμ.
Alto may not be greater than or equal to 0 for reasons greater than or equal to 0.
z Ifl raw material must have a purity of not more than 96% by weight and an average particle size of not less than 3 μm, preferably impurities are S
ing 0 to 20%, Peg's O to 20%, or the total amount of SiO□ and FeJz is preferably 0 to 20%.

Furthermore, if the average particle size of the Ti01 source material is larger than 3 μm, the actual breaking strain will be 6X 10- because unreacted residue will increase.
If it is less than ', there is a risk of cracks occurring due to the casting. Therefore, the TiO□ source material must have an average particle diameter of 3 ps or less.

In the third invention, the actual breaking strain of the material is increased by performing rapid cooling treatment during and/or after firing with a maximum cooling rate of 500°C/Hr from a temperature of 200°C or higher to 40°C. . Here, the quenching start temperature is less than 200℃ or the maximum cooling rate is 500℃/H.
If it is less than r, the actual breaking strain cannot be made sufficiently high. Preferably, the quenching start temperature is within the range of 350-1100°C, and the maximum cooling rate from the quenching start temperature is 2000°C.
℃/Hr, the actual breaking strain is 10 x 10
If the quenching start temperature exceeds 1100℃, the rate of improvement in the actual breaking strain will decrease, decomposition of aluminum titanate may occur, or if the product is large and has a complicated shape, quenching may cause There is a risk of damage when.

The fact that the amount of rare earth elements added in the fourth invention is 1.8% by weight or less in terms of oxides also reduces the actual breaking strain to 6X10-
``This is to raise the level even higher than that.

To produce the ceramic material of the present invention, first, alumina, calcined bauxite, purified rutile, crude rutile, anatase titanium, ilmenite, red red ferrite, fused magnesium, magnesite, fused spinel, kaolin, quartz, fused From silica and certain rare earth elements, etc.
Chemical composition is 40-65% by weight of AhOs, TiOx
30-60%, StO, MgO, Pt403
The raw materials are selected so that the total content of at least one of the following is 10% or less. At this time, a material containing 96% by weight or less of O3 component and an average particle size of 3μ or more layer is used as the AlxOs source material, and a material with an average particle size of 3μ as the TiOzlll material is used.
It is necessary to mix with m or less raw materials. Rare earth elements added to improve thermal cycle durability can also be added in the form of nitrates, oxides, and other compounds, but in order to obtain a sufficient effect with a trace amount of addition, it is necessary to Rare earth elements that are preferably uniformly dispersed using raw materials include Y, La, Ce, Dy, and Nd.
etc. are economically preferable. La, Dy,
Nd has the same effect as Y.

To this, 0.1 to 1.0% of a deflocculant selected from water glass, polycarboxylic acid ammonium salt, amines, sodium pyrophosphate, etc. is added, and further PVA, MC, CMC,
A binder selected from acrylates and the like is used in a range of 1.0-5.
Add 0% and thoroughly mix and stir with 15-40% water using a trommel, bond mill, etc. to make 200-1000 cp.
Adjust the viscosity of the slurry. Such a slurry is formed into a cylindrical or port liner shape by a casting method, and then dried and fired. As a result, a heat-resistant product containing 65% or more of aluminum titanate as a crystal phase, and 17% or less of a glass phase containing 0.5 to 16% of the rare earth element in terms of oxide when rare earth elements are added. An aluminum titanate sintered body having excellent properties, thermal shock resistance, heat insulation properties, and cold/hot cycle durability can be obtained, but it may also contain one or more crystals among rutile, corundum, and mullite as other crystal phases. .

In the present invention, the firing conditions are, for example, 145
0 to 1650°C, preferably tsoo to 1600°C
Contrary to conventional wisdom, the average particle size of aluminum titanate crystals was 10 μm by film-containing for ~16 hours.
Let it grow until it reaches the above level. Furthermore, during and/or after firing, 200°C or more, preferably 350°C
When cooling from a temperature above to 40℃, the maximum cooling rate should be 500℃/Hr or more, preferably 2000℃/Hr.
This rapid cooling treatment can be carried out by cooling in a furnace, air cooling with a blower, or dropping into water, and the treatment can be repeated two or more times.

This makes it possible to obtain a material with an actual breaking strain of 10 This is presumed to be due to the extremely small micro-crank inside the acid aluminum sintered body increasing within a range that hardly reduces the strength.

Ceramic materials with such high actual breaking strain can shrink together with the metal material when the undulating metal material contracts, and in particular, conventional high-strength, low actual breaking strain ceramics break due to stress concentration. Even with such a complicated shape, cranking does not occur.Therefore, not only cylindrical port liners but also two ports on the cylinder side for 4-pulp engines as shown in Figures 1 and 2 (
2) and is also suitable for a complex-shaped port liner (3) having a single exhaust port (1) on the exhaust manifold side or an exhaust manifold liner (4) as shown in FIG. Furthermore, the microcranks in this sintered body lower the thermal conductivity, and a sufficient heat insulating effect can be achieved even if the porosity is relatively small.

Since aluminum titanate has a melting point of over 1700℃, there are no particular restrictions on the molten metal used for casting, and it is applicable to castings made of gray cast iron, spheroidal graphite cast iron, white cast iron, aluminum alloy, copper alloy, magnesium alloy, and zinc alloy. can.

In addition, by having a small amount of rare earth elements present in the glass phase, the grain boundary glass phase is firmly bonded to aluminum titanate, and the cold and heat durability is improved without impairing the above-mentioned properties suitable for castings with high breaking strain. You can obtain materials that have both

Examples of the present invention are shown below.

(Example) Using the Altos source material shown in Table 1 below and the TiO2 source material shown in Table 2 as main raw materials, tests N[L1 to N[113] shown in Table 3 and shown in Table 4 were used as main raw materials. The raw materials were mixed to have the compositions of N114 to N128, and poured into a mold to create a test piece (5) in the form of a bifurcated elliptical cylinder with a wall thickness of 4 mm as shown in Figure 5. Baked under the conditions listed in Tables 3 and 4,
Various properties were measured for the obtained fired body.

Next, each fired body was filled with casting sand and then cast with aluminum to create a metal-ceramic composite with an aluminum wall thickness of 7 mm. After removing the casting sand, it was visually confirmed whether or not cracks had occurred in the test piece. The results are shown in Tables 3 and 4.

In Table 4, in the thermal cycle test, as shown in FIG. 6, a thermal cycle of holding at room temperature for 10 minutes and holding at 900° C. for 20 minutes was repeated 50 times, and the deterioration rate of bending strength was measured before and after the cycle. Further, the amounts of aluminum titanate and glass phase were calculated as volume % determined from the respective area ratios in the 88M photograph. Furthermore, the amount of rare earth elements in the glass phase was measured using BOX analysis using a transmission electron microscope. For the materials of the present invention and comparative examples, electron micrographs of the fired products and the fired products after the rapid cooling treatment are shown in Figure 8 (a) and (
From Figures 8(a) and 8(b) shown in b), there is no major change in the crystal structure due to the quenching treatment, and no change in strength is expected due to the quenching treatment.Also, the quenching start temperature of the quenching treatment conditions was changed. FIG. 7(a) shows the change in the actual breaking strain when the cooling rate of the quenching treatment conditions was changed, and FIG. 7(b) shows the change in the actual breaking strain when the cooling rate of the quenching treatment conditions was changed.

Table 1 Table 3 Rotation Table 2 Table 3 Inner 2) 4A2) 4th reaping 1) (Effects of the invention) As is clear from the above explanation, the ceramic material for castings and the manufacturing method thereof of the present invention If the actual breaking strain is 6X
It is possible to obtain a novel ceramic material for castings having a particle diameter of 10-3 or more. This material has excellent heat resistance, thermal shock resistance, and heat insulation properties, and is highly practical as it does not cause any risk of cranking due to the compressive force generated during casting. It is suitable as a material for various liners of exhaust systems, including Therefore, the present invention greatly contributes to the development of industry as a ceramic material for castings and a method for producing the same that solves the conventional problems.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a boat liner for a 4-pulp engine.
Figure 2 is a cross-sectional view of the boat liner after being cast into the engine head, Figure 3 is a cross-sectional view of the exhaust manifold liner after being cast, Figure 4 is a graph showing an example of the schedule for rapid cooling treatment conditions, Figure 5 (a) is a vertical sectional view of the test piece used in the casting test, FIG. 5(b) is a horizontal sectional view thereof, FIG. 6 is a graph showing the schedule of the cooling and heating cycle in the evaluation method of the present invention, and FIG. 7 (a)
7(b) is a graph showing the change in the actual breaking strain when changing the quenching start temperature of the quenching treatment condition, and FIG. FIG. 8(a) is a photograph substituted for a drawing showing the crystal structure of a fired body subjected to a quenching treatment after firing, and FIG. 8(b) is a photograph substituted for a drawing showing the crystal structure of a fired body of a comparative example.

Claims (1)

[Claims] 1. Contains 65% by volume or more of aluminum titanate as a crystal phase, and the average grain size of the crystals is 10 μm or more;
A ceramic material for casting, characterized by having an actual breaking strain of 6×10^-^3 or more. 2. A glass phase containing 65 volumes or more of aluminum titanate as a crystalline phase, the average grain size of the crystals being 10 μm or more, and 0.5 to 16% by weight of rare earth elements in terms of oxides. A ceramic material for castings, characterized in that the actual breaking strain is 6×10^-^3 or more, and the actual breaking strain is 6×10^-^3 or more. 3. Molding powder of a predetermined composition by mixing a raw material with an Al_2O_3 component of 96% by weight or less and an average particle size of 3 μm or more as an Al_2O_3 source raw material, and a raw material with an average particle size of 3 μm or less as a TiO_2 source raw material. , fired, and heated to 50°C from a temperature of 200°C or higher during and/or after firing.
A method for manufacturing a ceramic material for casting, characterized by cooling at a rate of 0° C./Hr or more. 4. As the Al_2O_3 source raw material, a raw material with an Al_2O_3 component of 96% by weight or less and an average particle size of 3 μm or more, and as a TiO_2 source raw material, a raw material with an average particle size of 3 μm or less, and rare earth elements converted into oxides. A powder of a predetermined composition containing 1.8% by weight or less is molded and fired, and heated from a temperature of 200°C or higher to 500°C during and/or after firing.
A method for producing a ceramic material for casting, characterized by cooling at a rate of Hr or more.