JPS59131577A - Silicon carbide material and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon carbide material particularly useful as sliding parts such as mechanical seals and plain bearing rings, and a method for producing the same.

In recent years, many ceramics have been developed and put into practical use as high-temperature structural materials, but those made of silicon carbide have high strength at high temperatures and little strength deterioration, and are resistant to thermal shock. It has many advantages such as excellent wear resistance, light weight, and excellent corrosion resistance.In terms of manufacturing technology, the invention of the pressureless sintering method has made it easy to produce high quality products. Now that it can be manufactured, it is being developed for a wide range of applications, including gas turbine parts, automobile engine parts, mechanical seals, and various bearings.

The above-mentioned pressureless molding method is disclosed in Japanese Patent Application Laid-Open No. 50-78609,
In particular, as disclosed in JP-A No. 51-1.48 Vi 2, etc.
In terms of boron and/or aluminum, 0.0% is added as a sintering aid to silicon carbide fine powder (with a μI of 11 or less).
2 to 2% of boron, aluminum and/or their compounds, and 0.2 to 4% of carbon and/or carbonizable organic material, both in the form of submicron fine powder, are uniformly mixed. This is a method in which easily sinterable powder, which is a mixture of powders, is molded and then sintered without pressure. This manufacturing method is intended for manufacturing structural materials that place emphasis on strength, heat resistance, and oxidation resistance, especially at high temperatures, and is sufficiently excellent in that respect. However, when silicon carbide materials manufactured using this method are used as N-moving parts such as mechanical seals and brain bearings, under conditions of insufficient lubrication, the coefficient of friction becomes extremely high, causing the sliding material to wear out quickly. It has the disadvantage that it can be damaged or damaged, and it is also prone to wear and crank.

As a result of repeated research aimed at solving the above-mentioned drawbacks of silicon carbide materials, the present inventors found that carbon powder as a sintering aid was added to the raw materials for the pressureless sintering method. Apart from this, we have found that the coefficient of friction of silicon carbide sintered bodies can be lowered by adding carbon powder that can act as a lubricant.

The present invention is based on the above knowledge and consists of two inventions. (However, in the case of compounds, the value converted to boron or aluminum) In a silicon carbide material that is a sintered body with the remainder essentially consisting of silicon carbide and free carbon, the carbon phase exposed surface with a diameter of 5 μto or more This is an invention of a silicon carbide material with a low coefficient of friction, which occupies 1.5 to 45% of the total surface of a sintered body.

The second aspect of the present invention relates to a method for producing a silicon carbide material according to the first aspect of the present invention, which comprises 0.2 to 2% by weight of submicron powder consisting of boron or aluminum alone or a compound (with the exception that the compound 0.2 to 4% by weight of submicron powder made of carbon or carbonizable organic material (value converted to carbon in the case of carbonizable organic material), average particle size 5 A sinterable powder mixture consisting essentially of 1 to 31% by weight of ~50 μm carbon powder and 7 μm silicon carbide powder is molded, and the resulting molded product is sintered by heating in a non-oxidizing atmosphere. It is characterized by causing

The silicon carbide material according to the present invention consists of two phases, a silicon carbide phase and a carbon phase, whereas conventional silicon carbide materials have a single phase of silicon carbide. The carbon phase that appears on the surface acts as a lubricant. Of course, the part of the surface made of silicon carbide has a high degree of wear resistance, so the silicon carbide material of the present invention has both lubricity and wear resistance, making it extremely suitable for sliding parts. It is something. The higher the ratio of the carbon phase exposed surface to the total surface area of the sintered body, the better the lubricity will be, but since the deterioration of other physical properties cannot be ignored, it is generally desirable that the ratio does not exceed 45%. The silicon carbide material of the present invention in which a carbon phase coexists is slightly inferior in heat resistance and oxidation resistance compared to conventional products consisting only of a silicon carbide phase, but it does not normally exceed 400°C. It exhibits sufficient durability under the conditions of use for sliding parts such as mechanical seals.

Next, a method for producing the silicon carbide material according to the second aspect of the present invention will be explained.

The submicron powders of silicon carbide, boron (or its compounds), aluminum (or its compounds), carbon, or carbonizable organic materials used as raw materials are the same as those used in conventional manufacturing methods. You don't need anything special to use it. In addition to being used alone, boron and aluminum may be used in the form of a compound, and either boron or aluminum may be used alone or both may be used in combination.

Examples of suitable boron and aluminum compounds include boron carbide, boron nitride, boron phosphide, aluminum boride, and the like. The carbonizable organic material is preferably one that dissolves in various solvents and decomposes at high temperatures to produce carbon, with a high carbon yield. Specific examples thereof include phenol resin, furan resin, polyphenylene resin, There is also coal tar pitch.

In the manufacturing method of the present invention, in addition to the above-mentioned raw materials, carbon powder having an average particle size of 5 to 50 μm is used. This carbon powder has a different particle size from the submicron carbon powder used as a sintering aid, and cannot be used as a sintering aid. Its role is to form a carbon phase by uniformly distributing it in the product while substantially maintaining the above particle size, and a part of it is exposed on the surface of the product to perform a lubricating action. Setting the average particle size to 5 to 507 zm is an important requirement in order to exhibit a lubricating effect without substantially impairing the physical properties of the product, and if the average particle size is 57 zm or less, the lubricating effect is insufficient. On the other hand, if it exceeds 50 μm, the sintering of silicon carbide is inhibited and the sintered body has poor airtightness, making it particularly unusable as a mechanical seal sliding part. Particularly preferred as this carbon powder are spherical particles of artificial graphite and natural graphite, especially those with a particle size of 10
~SO7zm.

The mixing ratio of the following sintering raw materials is as follows.

(2) 20.2 to 2% by weight of submicron powder consisting of boron or aluminum alone or a compound (however, in the case of a compound, the value is converted to boron or aluminum). 2
When using 91 of the second aspect, the total amount should be within the above range.

If the blending ratio is less than 0.2%, sintering will not proceed sufficiently.
This results in a sintered body with poor airtightness. Further, even if the amount exceeds 2%, no problems will immediately occur, but there will be no effect by increasing the amount. The most preferred blending ratio is 1.0-2.0%
It is.

■ 7 micron powder consisting of carbon or carbonizable organic material 20.2 to 4% (carbon equivalent value in case of carbonizable organic material). When the blending ratio is less than 0.2%, sintering does not proceed sufficiently, resulting in a sintered body with poor airtightness. Further, even if the amount exceeds 4%, no problems will occur immediately, but there will be no effect by increasing the amount. Particularly preferred blending ratio is 1.5
~3.0%.

■ Carbon powder with an average particle size of 5 to 50 μm: 1 to 31% by weight
. Preferably 2 to 20% by weight. When the amount is too large, sintering is inhibited as in the case where the particle size is too large.When it is less than 1%, the required amount of carbon phase exposed surface cannot be formed.

■Silicon carbide submicron powder: The remainder of the above ingredients.

In addition to the above-mentioned sintering raw materials, binders such as stearic acid, polyvinyl alcohol, phenolic resin, acrylic resin, etc. can be used to facilitate molding and give the molded body before sintering the strength necessary for handling. .

Each of the raw materials from ■ to ■ is mixed uniformly using a ball mill, etc.
Further, silicon carbide and molding binder are added and mixed, and then molded into a desired shape. Molding can be done by using various molding methods depending on the molded shape, such as press molding or rubber press at room temperature, hot extrusion molding or injection molding by adding a slightly large amount of molding bindu. .

The compact is sintered in a vacuum or in a non-oxidizing atmosphere such as nitrogen gas. The sintering temperature is usually 1900 to 23
00°C is required. It is desirable that the sintering treatment be carried out until the theoretical density ratio of the sintered body reaches 95% or more; if it is less than 95%, the airtightness will be insufficient, and the strength will be low and highly variable.

As described above, according to the manufacturing method of the present invention, the conventional pressureless sintering method for manufacturing silicon carbide materials can be used as is, and carbon powder with an average particle size of 5 to 50 μm can be added to the raw material. , it is possible to easily produce a silicon carbide material with good lubricity.

The present invention will be explained below with reference to Examples. The theoretical density ratio is expressed as a percentage of the measured density to the theoretical density of the sintered body, and the theoretical density was measured by crushing the sintered body and using an air comparison method.

In addition, the carbon phase exposed surface area ratio is the ratio of the carbon phase exposed surface with a diameter of 5/J, lf1 or more on the surface of the sintered body (
%) means an image analysis device manufactured by Nihon Regulator Co., Ltd.
This is a value measured using Luzex 450.

Example 1 1.5% by weight of fine boron carbide powder with an average particle size of 0.4), 5.6% by weight of novolac type 7-el resin, 1% by weight of stearic acid, and the remainder having an average particle size of 0.4% by weight. A raw material mixture consisting of 3 μm silicon carbide powder is mixed in a wet ball mill using acetone as a dispersion medium, and then the average particle size is 15 μm.
The carbon powder of a was added in an amount of 5% based on the weight of the raw material mixture and mixed again, then dried and pulverized.

The combined powder was formed into a ring having an inner diameter of 44 τnm, a top diameter of 66 mm, and a thickness of 10 mm under a pressure of 1.5 ton/am'', and was sintered by heating to 2100° C. in vacuum.

The obtained sintered body had a theoretical density ratio of 95% and a carbon phase exposed surface area ratio of about 7%.

On the other hand, a control product manufactured in the same manner as above without the addition of carbon powder with an average particle size of 15 μm1 had a theoretical density ratio of 9.
8%, and was a single-phase substance consisting essentially of silicon carbide.

Next, the above two types of sintered bodies were subjected to a sliding test in hot water at 100°C. The test conditions were: hydraulic pressure 1. O
KB/cm2 (:, rotation speed 3600 rpm, PV value (
Surface pressure x circumferential speed) 78 KB/c+o''-m/sec, test time was 100 hours, and carbon impregnated with Fe/Fel resin was used as the mating material. The test results are shown in Table 1.

Table 1 Sample Average coefficient of friction Sample wear Amount Wear of mating material Invention product 0.08 0.1μm 0.3
NoJ11° control product 0.18. 1.1μmo13μ
m.

Agent Patent Attorney Oboro Itai

Claims (2)

[Claims] (1) One or more substances selected from the group consisting of simple substances and compounds of boron or aluminum in a total amount of 0.
In a silicon carbide material that is a sintered body containing 2 to 2% by weight (value calculated as boron or aluminum in the case of a compound), with the remainder consisting essentially of silicon carbide and free carbon, the diameter is 5/Jln. A silicon carbide material characterized in that the carbon phase exposed surface occupies 1.5 to 45% of the total surface of the sintered body. (2) 0.2 to 2% by weight of No. 7 micron powder consisting of boron or aluminum alone or a compound (however, in the case of a compound, the value is converted to boron or aluminum),
0.2 to 4% by weight of submicron powder consisting of carbon or carbonizable materials (however, carbonizable (in the case of geometry, the value converted to carbon), carbon powder with an average particle size of 5 to S01ihI forming a sinterable powder mixture consisting essentially of 1 to 31% by weight and submicron powder of silicon carbide;
A method for producing a silicon carbide material, which comprises heating and sintering the obtained molded product in a non-oxidizing atmosphere.