JPH01212272A - High-alumina insulator for ignition plug - Google Patents

Abstract

PURPOSE:To provide the subject insulator which is low in sintering temp., is less deformed, is inexpensive and has excellent mass productivity by compounding fine particles of alumina as an essential component and specific 3 kinds of oxides as an auxiliary component at prescribed ratios and calcining and sintering the mixture. CONSTITUTION:(A) 85-97.5wt.% fine particles of the alumina as the essential component and the auxiliary component consisting of (B) 0.5-15wt.% >=1 kinds selected from SiO2, MgO, CaO, BaO, ZnO, and SrO, (C) 0.55-9wt.% B2O3, and (D) 0.3-6wt.% >=1 kinds selected from TiO2, HfO2, ZrO2, NiO, Cr2O3, CaF2, and As2O3 are compounded. The resulted powder raw material is then molded and the molding is calcined and sintered, by which the high-alumina insulator for an ignition plug is produced. The glassy material formed in the initial calcination stage is thereby phase-split to increase the high-temp. viscosity and to restrain the movement of the sintered particles of the alumina; therefore, the generation of bending, warpage, etc., in the calcination is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an insulator for a spark plug used in an internal combustion engine.

(Prior Art) In recent years, as the output of internal combustion engines for automobiles has increased, the area occupied by intake and exhaust valves in the combustion chamber of the internal combustion engine has been expanding. Therefore, spark plugs that ignite the air-fuel mixture need to be made smaller, and the combustion temperature inside the combustion chamber is also rising due to supercharging devices such as turbochargers, so spark plugs have high heat resistance. High alumina insulators have come to be commonly used due to the high performance requirements.

(Problem to be Solved by the Invention) However, in the conventional insulators described above, in the case of insulators made of high alumina, most of them are made of alumina 85 to 9
Since it is an oxide that is sintered at a high temperature with 5% by weight of SiO, 1Mgo, and CaO as the balance, the sintering temperature is 1,600℃ or higher, and it can be fired at a lower firing temperature and in a shorter time. something is required. On the other hand, by adding -BBO, to the above components, the strength,
It has excellent chemical corrosion resistance and electrical insulation, and the sintering temperature is 5θ~ lower than before! Insulators that can be heated to temperatures as low as 00°C have been proposed, but due to the glassy properties of 5iOL* MgO, CaO, etc., when attempting to manufacture long insulators with a narrower diameter, the insulators bend during firing. This has the disadvantage of producing products with low dimensional accuracy.

Therefore, the present invention aims to improve the drawbacks of the above-mentioned conventional products by lowering the firing temperature and suppressing deformations such as bending and warping during firing.

(Means for solving the problem) For this purpose, the main component is 85 to 37.5% by weight of alumina fine particles, and the remaining subcomponent is sio.

0.5 to 15% by weight of MgO, Cab, BaO + ZnO, SrO alone or a combination of two or more components and 0.5% by weight of BO.
55 to 9% by weight, and 0.3 to 9% of at least one component of TiOzs3HfO*ZrOtN1ps Cr, O, t CL a-F+As
It is made by firing and sintering a powder raw material containing 6% by weight.

(Function) With the above configuration, the vitreous substance generated in the initial firing stage undergoes phase separation, increasing high temperature viscosity and restricting the movement of the alumina sintered particles, thereby preventing bending, warping, etc. during firing. The occurrence of deformation can be suppressed.

(Example) This occurrence will be further explained using an example. First, aluminum hydroxide is calcined at t, ooo℃, and the resulting Al, LO
A sample with J purity of 99.3% by weight or more is wet-milled to have a particle size of 2.5μ or less, and 90% by weight of A1
It was taken as the main component of j. To this, S iO,s M g O
s Ca O * B a Ox Z n 0s Subcomponent containing SrO alone or in combination of two or more components, 1 and B
5 as a subcomponent and 2, and further T t O, t Hf O
z * Z r O, L + N t Oe Crz
At least one component of Os t Ca F, L*A S, and L O3 was used as a subcomponent 3, and this was weighed and prepared as shown in the attached table, wet-mixed for about 10 hours using an alumina ball, and then methyl cellulose was added as a binder. was added in an amount of about 2% by weight based on the dry raw materials, and groove-mixing was performed for about 1 hour. - On the other hand, for the subcomponents, each component is dry-processed.
The mixture was mixed using an alumina ball, kept at the specified temperature for 1 hour in an electric furnace, and then taken out of the furnace and rapidly cooled using stainless steel rollers.

Perform rolling. This subcomponent melt is wet-pulverized using an alumina pole for about 50 hours to obtain a particle size of 2.5 μm or less.

After mixing the binder, all slurries were degassed for about 10 minutes, and then dried in a constant temperature bath kept at about 100° C. while being gently stirred. This dry lump was further crushed to obtain a test powder with a particle size of 150 to 350 μm.

This test powder was put into a mold and pressed at 600 kg/cIIi' to obtain a square prism molded product of 7XIOX70mm. This rectangular prism molded body was heated at a rate of 300° C./hr and held at a predetermined temperature for 1 hour to obtain a sintered body. The degree of sintering of this sintered body is determined by calculating the degree of sintering at each temperature using the Archimedes method, with the time when the apparent specific gravity no longer changes as 100%. The amount of deformation was measured. The results are shown in FIG. Each number in the figure indicates the number of an example. In this figure, the conventional one is t, so
Although complete sintering occurs at a temperature of 1,000°C to 1,200°C, the glassy phase generated at the grain boundary phase between alumina grains in the initial sintering stage initiates sintering. The sintered body becomes viscous, and the alumina crystal grains move easily and are significantly deformed by the weight of the sintered body. On the other hand, the examples of the present invention showed sinterability equal to or better than the conventional products, and in particular, N009 showed sinterability of 1
．． Sintering is completed at 500°C. Further, the amount of deformation during the sintering stage shown in FIG. 2 can be reduced to 1/2 or less of that of conventional products. As shown in FIG. 3, in the initial stage, the subcomponent, 1 is the subcomponent, and B of 2 is 0. (A) Due to the action of L, subcomponents, and 3, extremely fine particles (C
) are formed by phase separation, and these phase separation particles (C) are
Depending on the component system, 5iO1* Ba5s CaO or multiple components, or T iOL + Z r O back.

It is considered that NiO is dispersed in the glassy material (A) to increase its viscosity and suppress deformation.

Furthermore, those using subcomponents 1 to 3 and subcomponents prepared by dissolving them and alumina in advance (No. 9.10.12.1)
3.14) (see Table 1) also has the same effect of suppressing deformation.

(Effects of the invention) As described above, by lowering the sintering temperature and reducing the amount of deformation, the yield of the product can be improved, the cost can be reduced, and mass production is possible. It is particularly useful as an insulator for small spark plugs.

[Brief explanation of the drawing]

FIG. 1 shows the sintering achievement rate with respect to the firing temperature of Examples including the conventional example, and FIG. 2 shows the amount of deformation with respect to the same firing temperature. FIG. 3 is a schematic diagram of the composition. Patent Applicant Agent Patent Attorney Fujiki Sanko Yakiniku #Ambient Temperature

Claims (3)

[Claims] (1) The main component is 85 to 37.5% by weight of alumina fine particles, and the remaining subcomponents are SiO_2, MgO, Ca-O, B.
0.5 to 15% by weight of aO, ZnO, SrO alone or in combination of two or more components, 0.55 to 9% by weight of B_2O_3, and further TiO_2, Hf-O_2, ZrO_2,
NiO, Cr_2O_3, Ca-F_2, As_2O_
An alumina insulator for a spark plug, which is obtained by firing and sintering a powder raw material containing 0.3 to 6% by weight of at least one of the following components. (2) 900 to 1,500 subcomponents constituting the remainder above.
After melting at ℃, the particle size is reduced to 2.5 μm by crushing.
A high alumina insulator for a spark plug according to claim (1) as follows. (3) 0.15 to 3% of alumina fine particles, which are the main component,
The high alumina insulator for a spark plug according to claim 1 or 2, wherein the high alumina insulator is dissolved in an amount of 5 to 30% by weight based on the remaining subcomponents.