JPH034511B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a silicon carbide composite with excellent dimensional accuracy and sliding properties, and in particular, the present invention relates to a method for producing a silicon carbide composite having excellent dimensional accuracy and sliding properties.
A porous silicon carbide sintered body formed into a desired shape and sintered with virtually no firing shrinkage, with synthetic resin filled in the open pores to provide excellent dimensional accuracy and sliding properties. The present invention relates to a method for producing a silicon carbide composite.

Silicon carbide generally has extremely excellent chemical and physical properties, and is used as wear-resistant materials such as mechanical seals and bearings, pump parts for highly corrosive solutions such as acids and alkalis, and seals for water pipes. It is a material that can be widely used as a corrosion-resistant material.

[Conventional technology]

By the way, silicon carbide sintered body has high hardness,
Although it has excellent wear resistance, it has poor self-lubricating properties.
In particular, when used as a mechanical component that is subject to abrasion phenomena such as mechanical seals and bearings, there has been a problem that the device lacks durability and reliability.

As a material to solve the above-mentioned problems, JP-A-Sho
No. 58-161982 discloses an invention related to a "ceramics composite in which a fluorine-containing polymer is bonded to ceramics," and the specification of the publication discloses a composite of a silicon carbide sintered body and a fluororesin. is listed.

However, the above-mentioned invention does not describe any characteristics of the silicon carbide sintered body suitable for compounding with a fluororesin.

[Problem that the invention seeks to solve]

A porous silicon carbide sintered body is used for the composite with the synthetic resin as described above. The conventionally known method for producing porous silicon carbide sintered bodies is as follows:
A recrystallization sintering method is generally known. However, in the recrystallization sintering method, coarse and fine silicon carbide particles are solidified with an organic binder, and this is fired at a recrystallization temperature range of 2000 to 2400°C to recrystallize the fine silicon carbide particles and exert a binding effect. This method combines coarse particles by sintering, and not only does it require an extremely high sintering temperature of 2,000 to 2,400°C, but since coarse particles are used as the starting material, the surface roughness is reduced. It is difficult to produce a sintered body with a high degree of dimensional accuracy and particularly high dimensional accuracy without special machining.

As described above, in the conventionally known method for manufacturing a porous silicon carbide sintered body, a porous silicon carbide sintered body that requires high dimensional accuracy can be manufactured easily and inexpensively without special machining. The method was unknown.

By the way, the present inventors have developed a sintering method different from the conventionally known sintering methods as described above, that is, sintering a green body formed into a desired shape without substantially causing firing shrinkage, and achieving dimensional accuracy. The purpose is to provide a method for manufacturing silicon carbide sintered bodies that require strength and strength at low cost without special machining, starting from fine silicon carbide powder that easily shrinks during firing. As a raw material, as a result of various research efforts to develop a sintering method that can suppress firing shrinkage caused by sintering, we have been able to control the impurity components contained in silicon carbide powder and sinter it within a specific atmosphere and temperature range. We discovered a new method for manufacturing high-strength silicon carbide sintered bodies with high surface precision without causing substantial firing shrinkage by sintering with No. 61-122165 states, "After forming silicon carbide powder with an average particle size of 5 μm or less into a green body, substantially shrinking the green body in a non-oxidizing atmosphere within a temperature range of 1700 to 2100°C. ``A method for producing a silicon carbide sintered body having an average bending strength of 7 Kg/mm ² or more, which is characterized by sintering without bending.''

However, the silicon carbide sintered body is a porous body, and it has been difficult to apply it particularly to applications requiring wear resistance or airtightness.

[Means for solving problems]

Therefore, with the aim of solving the above-mentioned problems, the present inventors conducted further research on the silicon carbide sintered body, and found that the open pores of the silicon carbide sintered body were filled with a synthetic resin. As a result, we have discovered that it is possible to manufacture silicon carbide composites with improved sliding properties and airtightness without compromising dimensional accuracy and surface accuracy.
The invention has been completed.

The present invention provides dimensional accuracy and accuracy in which a synthetic resin is filled into the open pores of a porous silicon carbide sintered body that is sintered without substantially shrinking and has a three-dimensional network structure of open pores. This is a method for producing a silicon carbide composite with excellent sliding properties.

The present invention will be explained in detail below.

The porous silicon carbide sintered body needs to be made of a silicon carbide sintered body that is sintered without being substantially shrunk. The reason is,
A silicon carbide sintered body that is shrunk during sintering is preferable in terms of strength and wear resistance, but the dimensions of a sintered body produced by a sintering method that involves shrinkage depend on the density of the formed body and the sintered body. Since it is greatly affected by the amount of shrinkage during sintering, it is necessary to uniformly cause shrinkage during sintering in order to produce a sintered body with excellent dimensional accuracy. By the way, in order to cause the above-mentioned contraction uniformly, it is important to obtain a formed body having a uniform density, but it is extremely difficult to obtain a formed body having such a uniform density. This is because it is difficult to produce a sintered body with excellent dimensional accuracy by causing firing shrinkage.

The sintering shrinkage rate of the silicon carbide sintered body sintered without substantially shrinking is advantageously 2% or less, and more preferably 1% or less.

The porous silicon carbide sintered body preferably has an average crystal grain size of 10 μm or less and an open porosity of 18 to 56% by volume. The average grain size of the crystals is 10 μm
The reason why the average grain size of the crystals is preferably less than 10 μm is because the surface roughness of the sintered body becomes large and the dimensional accuracy deteriorates. The reason why the open porosity is preferably 18 to 56% by volume is that if the open porosity is lower than 18% by volume, it is difficult to fill the synthetic resin. This is because if the amount is too high, the strength of the porous silicon carbide sintered body will be low and grains will easily separate.

The porous silicon carbide sintered body needs to have excellent dimensional accuracy, and is a silicon carbide sintered body having a three-dimensional network structure composed of silicon carbide crystals with an average aspect ratio of 5 or less. Preferably, it consists of a body.

The synthetic resins used in the present invention include acetal resin, nylon resin, polyethylene resin, polycarbonate resin, polybutylene terephthalate resin, styrene acrylonitrile resin,
Resins selected from polypropylene resins, polyurethane resins, polyphenylene sulfide resins, epoxy resins, silicone resins, and fluororesins can be used alone or in combination, and among them, acetal resins, nylon resins, polyethylene resins, Polybutylene terephthalate resin and fluororesin have excellent self-lubricating properties and can significantly improve sliding properties.

The silicon carbide composite obtained by the present invention is preferably one in which at least 10 parts by volume of the synthetic resin is filled with respect to 100 parts by volume of the open pores of the porous silicon carbide sintered body. The reason for this is that if the filling amount of the synthetic resin is less than 10 parts by volume, the effect of preventing the detachment of crystal grains from the silicon carbide sintered body will not be sufficient, and it will be difficult to improve the sliding properties. It is.

Next, a method of manufacturing a silicon carbide composite having excellent dimensional accuracy and sliding properties according to the present invention will be explained.

According to the present invention, silicon carbide powder having an average particle size of 5 μm or less is molded into a green body, and then the green body is sintered within a temperature range of 1700 to 2100°C without substantially shrinking to form a three-dimensional A silicon carbide composite with excellent dimensional accuracy and sliding properties is produced by producing a porous silicon carbide sintered body having open pores in a network structure, and then filling the open pores with a synthetic resin. can be manufactured.

The reason why silicon carbide powder with an average particle size of 5 μm or less is used is that silicon carbide with a particle size larger than 5 μm is preferable for suppressing firing shrinkage, but it reduces the number of bonding points between grains in the sintered body. This is because not only is it difficult to obtain a high-strength silicon carbide sintered body, but also the surface roughness is deteriorated.

By the way, the crystal system of silicon carbide has α type and β type.
There are two types: type and amorphous, and any of them or a mixture thereof can be used. Among them, β type is easy to obtain in fine powder form with a diameter of 5 μm or less, and is relatively easy to obtain. It can be advantageously used because a high-strength sintered body can be produced, and in particular, it is advantageous to use silicon carbide powder containing 50% by weight or more of β-type silicon carbide.

Advantageously, the silicon carbide powder has a total content of boron, aluminum and iron of 0.3% by weight or less in terms of elements. The reason for this is that if the total content of boron, aluminum and iron is more than 0.3% by weight in terms of elements, sintering will occur during sintering due to interaction with free carbon contained in silicon carbide powder. This is because it tends to shrink, making it difficult to manufacture a sintered body without causing substantial shrinkage.

In addition, when the content of boron, aluminum, and iron in the silicon carbide powder is within the above range, a carbonaceous substance can be added to make the starting material contain 5% by weight or less of free carbon.
The free carbon has the effect of suppressing the coarsening of crystal grains, and by making it present in the starting raw material, it is possible to make the crystal grain size of the sintered body uniform and obtain a sintered body with relatively high strength. can. The reason why the free carbon content is set to 5% by weight or less is that if it is more than 5% by weight, excessive carbon will exist between the silicon carbide powder particles, which will significantly inhibit the bonding between the particles. This is because the strength of the sintered body deteriorates.

The carbonaceous material may be any material that allows carbon to be present at the start of sintering, such as various organic materials such as phenolic resin, lignin sulfonate, polyvinyl alcohol, cornstarch, sugar, coal tar pitch, and alginate. Alternatively, pyrolytic carbon such as carbon black or acetylene black can be advantageously used.

The silicon carbide powder has a total content of boron, aluminum, and iron of 0.3 in terms of elements.
When the content exceeds 0.6% by weight, it is advantageous that the content of carbonaceous substances and free carbon is 0.6% by weight or less in terms of fixed carbon content. The reason is that when the total content of boron, aluminum and iron exceeds 0.3% by weight in terms of elements, the content of carbonaceous substances and free carbon exceeds 0.6% by weight in terms of fixed carbon content. As I explained earlier, if there are many,
This is because the interaction between boron, aluminum, or iron and carbon tends to cause sintering shrinkage during sintering, making it difficult to obtain a sintered body without substantial shrinkage. In addition, if the contents of boron, aluminum, and iron are too large, they will deteriorate the physical properties of the sintered body, so it is desirable that the contents be as low as possible, and the total content should be 2
% by weight or less.

The resulting body is fired within a temperature range of 1700-2100°C. The reason for this is that if the temperature is lower than 1700°C, it is difficult to sufficiently develop the bonds that connect the grains, making it impossible to obtain a sintered body with high strength, whereas if the temperature is higher than 2100°C, once the Among the nets that have grown, those that are smaller than a certain size become constricted or, in severe cases, disappear, resulting in a decrease in strength, and some particles become coarser, causing the surface to become rougher. This is because the roughness deteriorates.

The resulting shaped body is fired in a non-oxidizing atmosphere without substantial shrinkage. The reason for this is that shrinkage during sintering is preferable for improving the strength of the sintered body, but generally speaking, the amount of shrinkage during sintering has a large effect on the density of the formed body, so it is necessary to generate uniform shrinkage. In order to achieve this, it is important to obtain a green body with a uniform density. However, it is extremely difficult to obtain a green body with such a uniform density, so it is necessary to sinter a sintered body with extremely high dimensional accuracy. This is because it is difficult to manufacture by causing shrinkage.

In addition, in order to obtain a sintered body with high dimensional accuracy as described above, the firing shrinkage rate when sintering without substantially shrinking is preferably 2% or less, particularly 1% or less. is more suitable.

In addition, the formed body has a gas partial pressure of at least one of CO or N ₂ in the atmosphere of 100 Pa for at least 10 minutes within a temperature range of 1700 to 2100°C.
It is advantageous that the firing is carried out in an atmosphere maintained above. The reason for this is that by increasing the partial pressure of at least one of CO or _N2 in the atmosphere to 100 Pa or higher for at least 10 minutes within the above temperature range, the growth of the nets can be promoted and the sintering of silicon carbide can be accelerated. This is because shrinkage during firing can be effectively suppressed.

According to the present invention, it is advantageous to charge the green body into a heat-resistant container in which the firing atmosphere can be controlled and fire it. The reason why it is advantageous to charge the silicon carbide in a heat-resistant container and fire it while controlling the firing atmosphere is because it can promote the bonding between adjacent silicon carbide crystals and the growth of nets. be. The reason why bonding between adjacent silicon carbide crystals and the growth of nets can be promoted by charging the formed body into a heat-resistant container and firing while controlling the firing atmosphere as described above is because the carbonization This is thought to be because movement of silicon carbide between silicon particles by evaporation-recondensation and/or surface diffusion can be promoted.

As the heat-resistant container, materials such as graphite and silicon carbide, and materials having functions equivalent to these materials can be advantageously used.

Furthermore, it is advantageous to control the volatilization rate of silicon carbide to 5% by weight or less during firing by charging the formed body into a heat-resistant container in which the firing atmosphere can be controlled and firing it.

Advantageously, the product form has a density of 45 to 80% by volume. The reason for this is that if the density of the formed body is lower than 45% by volume, there will be fewer points of contact between the silicon carbide particles, which will inevitably result in fewer bonding points, making it difficult to obtain a high-strength sintered body. , on the other hand, because formed forms with higher than 80 volume % are difficult to manufacture.

Also, in the temperature increase process up to 1700℃ mentioned above,
By maintaining the total gas partial pressure of CO and _N2 in the atmosphere at 100Pa or less at 1500℃ or higher for at least 30 minutes, the nets between silicon carbide particles are uniformly generated and bonded firmly. be able to.

According to the present invention, the open pores of the porous silicon carbide sintered body are filled with a synthetic resin. The reason for this is that by filling the open pores of the porous silicon carbide sintered body with synthetic resin, detachment of crystal grains from the porous silicon carbide sintered body can be prevented, and sliding This is because the characteristics can be significantly improved.

Methods for filling the synthetic resin into the pores of the porous body include heating the resin to melt it and impregnating it, dissolving the resin in a solvent and impregnating it, and impregnating the resin in a monomer state and then turning it into a polymer. Alternatively, a method of dispersing a finely divided resin in a dispersion medium, impregnating a porous body with this dispersion, drying, and then baking the resin at the melting temperature of the resin can be applied.

According to the present invention, it is advantageous to fill at least 10 parts by volume of the synthetic resin into 100 parts by volume of open pores of the porous silicon carbide sintered body. The reason for this is that if the amount of synthetic resin filled is less than 10 parts by volume, the effect of preventing the detachment of crystal particles from the silicon carbide sintered body is insufficient, and it is difficult to improve wear resistance. It is.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 The silicon carbide powder used as a starting material consisted of 94.6% by weight of β-type crystals and the remainder substantially of 2H-type crystals, and contained 0.29% by weight of free carbon, 0.17% by weight of oxygen, 0.03% by weight of iron, It mainly contained 0.03% by weight of aluminum, had an average particle size of 0.28 μm, and no boron was detected.

5 parts by weight of polyvinyl alcohol and 300 parts by weight of water are blended with 100 parts by weight of the silicon carbide powder,
The mixture was mixed in a ball mill for 5 hours and then dried.

An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal mold at a pressure of 3000 kg/cm ² . The dimensions of this generated feature are 250mm x 250mm x 30mm
The density was 2.0 g/cm ³ (62% by volume).

The formed body was placed in a graphite crucible and fired in a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. The temperature was raised to 2000°C at a rate of 450°C/hour and held at the maximum temperature of 2000°C for 10 minutes. CO gas partial pressure during sintering ranges from room temperature to 1700℃
is 80Pa or less, 300±50Pa at higher temperatures than 1700℃
The argon gas flow rate was appropriately adjusted and controlled so that it was within the range of .

The density of the obtained sintered body was 2.05 g/cm ³ , the open porosity was 36% by volume, and the crystal structure was observed with a scanning electron microscope, and the average aspect ratio was
It has a three-dimensional structure in which 2.5 silicon carbide plate crystals are intricately intertwined in multiple directions, and the linear shrinkage rate of the formed shape is 0.25 ± 0.02% in any direction.
Within the range of , the dimensional accuracy of the sintered body was within ±0.05 mm. Also, the average bending strength of this sintered body is 18.5
It showed an extremely high value of Kg/mm ² .

After processing this sintered body into a ring shape with an outer diameter of 30 mm, an inner diameter of 15 mm, and a thickness of 5 mm, the average grain size was 0.26μ.
The composite was impregnated by immersing it in suspension water in which 60% by weight of polytetrafluoroethylene fine particles (m) were dispersed under vacuum, and then baked at a temperature of 380 to 400°C to obtain a composite.
The amount of polytetrafluoroethylene filled in this composite was 0.85 g, and its proportion in the voids of the sintered body was 50.1% by volume.

When this composite was subjected to a dry sliding test on stainless steel (SUS304) using the ring-on-ring method in which the composite was slid at a sliding speed of 500 mm/sec and an end face load of 10 Kgf/cm ² was applied, the friction coefficient was 0.15. ~
0.22, wear coefficient is 3.1×10 ^-4 mm/Km・(Kgf/cm ² )
It was recognized that the material had extremely excellent sliding properties.

Note that the wear coefficient (K) is a value determined by the following functional formula.

K=h/PVT K: Wear coefficient (mm/Km・(Kgf/cm ² )) h: Wear depth (mm) T: Sliding time (sec) P: End face load (Kgf/cm ² ) V: Sliding speed (Km/sec) Comparative example 1 A sliding test was performed in the same manner as in Example 1, but without compounding polytetrafluoroethylene, and the friction coefficient was 0.5 to 0.7, and the wear coefficient was 2.3 × ^10-1
(mm/Km・(Kgf/cm ² )).

Example 2 A sintered body was obtained in the same manner as in Example 1, except that the molding pressure was changed to 40 Kg/cm ² .

The density of the obtained sintered body was 1.76g/cm ³ , the open porosity was 55% by volume, and the linear shrinkage of the formed body was within the range of 0.36±0.03% in any direction. The dimensional accuracy of the body was within ±0.08 mm.
Furthermore, the average bending strength of this sintered body was extremely high at 720 Kg/mm ² .

Next, this sintered body has an outer diameter of 30 mm, an inner diameter of 15 mm,
After processing it into a ring shape with a thickness of 5 mm, it was impregnated with heated and melted polyacetal resin to produce a composite. The proportion of the polyacetal resin filled in this composite in the voids of the sintered body was 98% by volume.

When the sliding properties of this composite were measured in the same manner as in Example 1, the friction coefficient was 0.18 to 0.25, and the wear coefficient was 6.2×10 ^-4 mm/Km・(Kgf/cm ² ), which was excellent. It was recognized that the material had sliding properties.

Example 3 In the same manner as in Example 1, a composite was obtained by heating and melting a nylon resin, a polycarbonate resin, a polybutylene terephthalate resin, and an epoxy resin and impregnating them into a porous body.

It was found that all of the obtained composites had excellent sliding properties.

Example 4 Same as Example 1, but using polyethylene resin,
A styrene acrylonitrile resin, a polyphenylene sulfide resin, and a silicone resin were dissolved in benzene and impregnated into a porous body to obtain a composite.

It was found that all of the obtained composites had excellent sliding properties.

〔Effect of the invention〕

As mentioned above, the silicon carbide composite obtained by the present invention has extremely excellent dimensional accuracy and sliding properties, and is suitable for special machining of wear-resistant parts that require dimensional accuracy such as mechanical seals and bearings. It is extremely useful industrially as it can be manufactured without any additional treatment.

Claims (1)

[Claims] 1. After molding silicon carbide powder with an average particle size of 5 μm or less into a green body, CO or N ₂ in the atmosphere is heated for at least 10 minutes within a temperature range of 1700 to 2100°C.
A porous sintered body having open pores with a three-dimensional network structure is produced by sintering without substantially shrinking in an atmosphere in which the partial pressure of at least one of the gases is maintained at 100 Pa or more, and then the open pores are sintered without substantially shrinking. A method for producing a silicon carbide composite with excellent dimensional accuracy and sliding properties, characterized by filling pores with a synthetic resin. 2. The manufacturing method according to claim 1, wherein the silicon carbide powder has a total content of boron, aluminum, and iron of 0.3% by weight or less in terms of elements. 3 The silicon carbide powder has a total content of boron, aluminum, and iron exceeding 0.3% by weight and 2.0% by weight or less in terms of elements, and a content of carbonaceous substances in terms of fixed carbon content. 0.6% by weight
The manufacturing method according to claim 1, which is as follows. 4. The manufacturing method according to any one of claims 1 to 3, wherein the porous silicon carbide sintered body has a shrinkage rate of 2% or less during sintering. 5. The manufacturing method according to any one of claims 1 to 4, wherein at least 10 parts by volume of the synthetic resin are filled into 100 parts by volume of open pores of the porous silicon carbide sintered body.