JPH0791108B2 - Method for manufacturing silicon carbide sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to, for example, production of a silicon carbide sintered body used as a sliding material for mechanical seals, bearings, heat-resistant jigs for heat treatment, and other various mechanical parts. Regarding the method.

(Prior Art) Generally, the SiC sintered body of the above example has heat resistance and high strength,
Since it has excellent wear resistance, it is used as various mechanical parts such as mechanical seals, bearings, heat treatment jigs.

However, since the above-mentioned SiC sintered body has high strength and high hardness, it is relatively difficult to process it.Therefore, it is desired that the SiC sintered body be molded into a shape close to the final shape and fired. There is.

Conventionally, as the above-mentioned SiC molding method, there are, for example, a casting molding method, an extrusion molding method, an injection molding method, and a dry die molding method using a uniaxial press.

However, in the above-mentioned cast molding method, due to the use of a stone mold, not only good dimensional accuracy cannot be obtained due to mold wear, but there is a problem that mass productivity is poor.

Further, the above-mentioned extrusion molding method has an advantage that it is suitable for molding a long product having a specific shape such as a pipe shape, a rod shape, and a honeycomb shape, but has a problem that it is difficult to mold a product having a complicated shape.

Furthermore, while the injection molding method described above is suitable for molding complex shaped products and is excellent in mass productivity, the mold parts are extremely expensive, and when molding SiC powder as abrasive grains, the mold deteriorates. However, there is a problem that the molding cost is significantly increased.

Furthermore, while the dry die molding method using a single-axis press has the advantages of excellent mass productivity and low molding cost, it is inferior in uniform formability with a die press, making it difficult to press-form complex shaped products. Therefore, conventionally, the SiC granulated powder was once press-molded into a simple shape by the dry die molding method, and the green body (molded body when the powder was molded) was used with a lathe or a milling machine before the firing. Although a method of firing after mechanical processing is used, there is a problem that the number of steps increases because a mechanical processing step from a simple molded body is essential.

In order to solve such a problem, a method of containing a liquid as a pressure transmission medium in the SiC granulated powder is conceivable, and as an example, when impregnated with a so-called water binder such as a polyvinyl alcohol aqueous solution, a large amount is obtained. Due to water absorption and dissolution of the phenolic resin, which is the sintering aid included, it is difficult to bleed air during molding, and a so-called blistering phenomenon occurs in which large bubbles are generated on the surface of the molded body, and as a result, sufficient sintering density
Unable to obtain SiC sintered body, for example, sintered density is 2.95g
There was a problem of less than / cm ³ (92%).

It is presumed that this is because boron B as a sintering aid is oxidized by the aqueous polyvinyl alcohol solution during impregnation, resulting in insufficient sintering.

On the other hand, in the case of producing an alumina Al ₂ O ₃ sintered body, it is possible to plasticize the alumina powder by impregnating a small amount of water, and thus plasticizing the alumina powder.
As shown in the following table, as compared with C, wear resistance, heat resistance, and thermal conductivity are all poor, and there are problems in characteristics.

(Object of the Invention) This invention mixes three components of SiC powder, a sintering aid and a molding aid (polyethylene glycol) in a dry granulation process, and a lubrication action up to the compression molding process (reduction of friction between powders). To reduce friction between powder and mold), shape retention (retention of molding strength), pressure propagation between powders, and 5 to 15 parts by weight of oil on the surface of the dried and granulated particles. By adding it, compression molding can be performed as it is without any long-time roasting process, and a complex shaped product can be obtained by mold molding using a uniaxial press at room temperature. It is intended to provide a method for manufacturing a sintered body.

(Structure of the Invention) The present invention comprises a step of mixing a silicon carbide powder with a sintering aid and a molding aid made of polyethylene glycol to dry granulate, and 5 to 5 parts of oil on the surface of the dry granulated granule. 15 parts by weight of impregnated silicon carbide, a step of compression-molding the treated powder after the impregnation of added oil with flow at room temperature, and a step of firing the compression-molded body molded by the step It is characterized in that it is a method for producing a bound body.

(Effect of the Invention) According to the present invention, since the three components of the SiC powder, the sintering aid and the forming aid (polyethylene glycol) are mixed in the above dry granulation process, the lubricating action up to the compression forming process ( The effects of reducing friction between powders and friction between powders and dies), shape retention (retention of molding strength), and pressure propagation between powders are achieved.

In addition, since the surface of the dry granulated porous hollow silicon carbide granulated particles is impregnated with oil, boron B (or a boron compound) used as a sintering aid is oxidized by the added oil. In addition, as described above, even if oil is added, the flowability of the granulated powder is not impaired, uniform filling in the mold can be ensured, and addition at the time of pressure compression is added. There is an effect that plastic fluidization by oil can be expressed.

As a result, a complex shaped product can be obtained by press molding using a uniaxial press at room temperature, and one-molding by die molding becomes possible, which has the effect of achieving high productivity.

Moreover, in the impregnation step of adding oil, 5 to 15 parts by weight of oil is added to the surface of the dried and granulated particles, so that the roasting step, which takes a long time, can be completely eliminated, and compression molding can be performed as it is. Therefore, there is an effect that the manufacturing time can be shortened.

Furthermore, since an expensive mold like the conventional injection molding method is not required and a machining process from a simple molded body is also unnecessary, a SiC sintered body can be manufactured at low cost and the above-mentioned added oil is used. Is easier to dewax than resins such as PVA, and has the effect of shortening the firing process time.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

The drawing shows the manufacturing method of the SiC sintered body. In the mixing step 1 in Fig. 1, α-SiC (hexagonal and rhombohedral high temperature polytype SiC) powder with an average particle size of about 0.7 μm is used. With respect to 100 parts by weight, 0.5 parts by weight of boron B as a sintering aid, 15 parts by weight of phenol resin as a carbon source, and polyethylene glycol [-(-CH ₂ -CH ₂ -O as a molding aid.
-) N-] is mixed by 5 parts by weight. Methanol (CH ₃ OH) was used as the mixed solvent, and the ball mill (ball mil) was used.
l) Wet mix by mixing means.

Next, in a drying step 2, the above-mentioned mixed material is dried with a spray dryer to obtain granulated powder.

Next, in the impregnation step 3, oil is added and impregnated on the surface of the granulated particles after dry granulation to obtain a treated powder.

The addition impregnation method is preferably a method of stirring while granulating powder is sprayed with oil, or a method of impregnating a liquid obtained by diluting oil with a solvent and then evaporating the solvent.

The treated powder thus obtained has a porous hollow particle structure shown in FIG. 4, and has a particle structure capable of ensuring a uniform packing property without impairing the flowability as a granulated powder. Has become.

And as the added oil, liquid paraffin (CnH ₂ n + 2),
Naphthenic (CnH ₂ n), olefinic mineral oils, or fatty acids known as vegetable oils and animal oils (R-COOH, fats and oils)
5 to 15 parts by weight (15 to 45% by volume) of the additive oil is added to 100 parts by weight of the granulated powder, preferably 6 to 8 parts by weight.

Next, in the molding step 4, the treated powder after the impregnation with the added oil is placed on the lower punch 6 shown in FIG.
And a uniaxial press molding (cold plastic molding) at room temperature by a pressure press of the upper punch 8 to obtain a press molded body 9.

Here, the surface pressure by uniaxial press molding is, for example, 500 to 200.
Set to 0kg / cm ² .

Next, in the firing step 5, the above-mentioned press molded body 9 is
Firing at 00 ° C. produced a SiC sintered body 10 as shown in FIG.

According to the production method of this example, a large amount of paraffin oil as an additive oil and a molding surface pressure were made different, and as a comparative example, a large amount of PVA 10% aqueous solution was added in place of the above-mentioned added oil was produced. The following table shows the results obtained by measuring the moldability, the sintered density, the shrinkage rate of the portion a in FIG. 3, and the shrinkage rate of the portion b in FIG.

As is clear from the above table, the SiC sintered bodies manufactured based on the manufacturing method of the above-described example showed good results in both formability and sintered density.

That is, since the three components of the SiC powder, the sintering aid and the molding aid (polyethylene glycol) were mixed in the above-mentioned dry granulation process, the lubricating action up to the compression molding process (friction reduction between powder and powder and gold) There is an effect that the friction with the mold can be reduced), the shape-retaining property (retention of the molding strength), and the pressure-propagating action between the powders can be exhibited.

In addition, since a predetermined amount (5 to 15 parts by weight) of liquid paraffin, naphthenic or olefinic mineral oil or degreasing acid was added to the surface of the granulated particles dried and granulated in the drying step 2 in FIG. 1 in the next step 3. Boron B used as a sintering aid is not oxidized by this added oil, and the flowability of the granulated powder can be maintained even if oil is added as described above. At the same time, this added oil acts as a pressure transmission medium, the pressure transmission is promoted, the uniform filling property in the mold can be secured, and it is shown that the oil is molded to a uniform density.

As a result, by press molding using a uniaxial press at room temperature, for example, a complex-shaped product as shown in FIG. 3 can be obtained, and one-molding by die molding becomes possible, and high productivity can be achieved. There is an effect that can be done.

Moreover, in the impregnation step of adding oil, 5 to 15 parts by weight of oil is added to the surface of the dried and granulated particles, so that the roasting step, which takes a long time, can be completely eliminated, and compression molding can be performed as it is. Therefore, there is an effect that the manufacturing time can be shortened.

In addition, since an expensive mold like the conventional injection molding method is not necessary at all, and no machining process from a simple molded body is required, an effect that a SiC sintered body can be manufactured at low cost is obtained. In addition, since the above-mentioned added oil is easier to dewax as compared with the resin such as PVA, there is an effect that the time of the firing step 5 can be shortened.

[Brief description of drawings]

The drawings show one embodiment of the present invention, FIG. 1 is a process diagram showing a method for manufacturing a silicon carbide sintered body, FIG. 2 is an explanatory view at the time of press molding, and FIG. 3 is an example of a silicon carbide sintered body. FIG. 4 is a diagram showing a particle structure of treated powder obtained by impregnating granulated particles of silicon carbide with oil. 2 ... Drying step 3 ... Impregnation step 4 ... Molding step 5 ... Firing step 9 ... Press-molded body 10 ... SiC sintered body

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Claims (1)

[Claims] 1. A step of mixing silicon carbide powder with a sintering aid and a molding aid made of polyethylene glycol to dry granulate, and adding 5 to 15 parts by weight of oil to the surface of the dry granulated particles. Manufacture of a silicon carbide sintered body, which comprises a step of impregnating, a step of compression-molding the treated powder after impregnating the added oil at room temperature with flow, and a step of firing the compression-molded body molded by the step Method.