JP2005015246A - Porous silicon carbide-based sintered compact for sliding member and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily provide various kinds of products for a high quality sliding member keeping strength required as the sliding member of a seal ring or the like and having excellent sliding characteristic and free from crack or chipping. <P>SOLUTION: The porous silicon carbide-based sintered compact for the sliding member having silicon carbide as a main component, contains ≤11 wt.% aluminum compound, ≤15 wt.% rare earth element compound and ≤8 wt.% silicon oxide and has 20-40 μm average pore diameter and 13-18 vol.% porosity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５４】
【発明の効果】
以上のように、本発明によれば、炭化珪素を主成分とし、１１重量％以下のアルミニウム化合物と、１５重量％以下の希土類元素化合物と、８重量％以下の珪素酸化物とを含有し、平均気孔径２０〜４０μｍ、気孔率が１３〜１８体積％である多孔質炭化珪素質焼結体とすることにより、シールリング等の摺動部材としての必要強度を保持し、且つ、摺動特性に優れた摺動部材用各種製品を提供することができる。
【００５５】
又、上記製品の製造工程において、粉末成形体を焼成する工程の前に脱脂工程を追加し、その脱脂工程を経た粉末成形体の残炭率を０．５％〜３．０％の範囲に調整して焼成することにより、上記の特性を確保しつつも、クラックやカケの無い高品位の摺動部材用各種製品を容易に提供できる。
【図面の簡単な説明】
【図１】本発明の摺動部材用多孔質炭化珪素質焼結体を用いたメカニカルシールの基本構造を示した断面図である。
【符号の説明】
１：回転軸
２：ケーシング
３：密封端面
４：緩衝ゴム
５：シートリング
６：従動リング
７：パッキング
８：コイルスプリング
９：カラー
１０：セットスクリュー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous silicon carbide based sintered body for a sliding member such as a seal ring in a mechanical seal used as a shaft seal device such as a pump or a refrigerator.
[0002]
[Prior art]
As an example of a porous silicon carbide sintered body for a sliding member, a seal ring used for a mechanical seal is used.
[0003]
A mechanical seal is one of the shaft sealing devices of fluid equipment for the purpose of completely sealing the fluid of rotating parts of various machines. It consists of a driven ring that can move in the axial direction according to wear of the sealing end surface and a seat ring that does not move. Thus, it has a mechanism for buffering vibrations, and functions to limit fluid leakage at the sealed end surface substantially perpendicular to the axis of relative hostile rotation.
[0004]
As shown in FIG. 1, the basic structure is attached between a rotating shaft 1 and a casing 2, and a sealing end surface 3 having a sealing action is a pair of a seat ring 5 as a stationary member and a driven ring 6 as a rotating member. The contact surface forms a surface perpendicular to the shaft to provide a sealing action. The driven ring 6 is supported in a cushioning manner by the packing 7 and does not contact the rotating shaft 1.
[0005]
The collar 9 is fitted to the rotary shaft 1 and fixed to the rotary shaft 1 by a set screw 10. A coil spring 8 is interposed between the collar 9 and the packing 7. The driven ring 6 and the collar 9 are engaged with each other to prevent relative rotation therebetween, and the driven ring 6 can be moved in the axial direction.
[0006]
The side end surface of the seat ring 5 and the side end surface of the driven ring are both substantially perpendicular to the axis of the rotary shaft 1, and these surfaces are reduced in surface roughness by lapping to maintain a high degree of flatness. The sealed end face 3 is configured.
[0007]
The sealing fluid is in contact with the outer periphery of the sealed end surface 3 and the atmosphere is in contact with the inner periphery. The strength of the contact pressure of the sealed end surface is increased by the elastic force of the coil spring 8. The shock absorbing rubber 4 supports the seat ring 5 in a shock absorbing manner and prevents leakage between the driven ring 6 and the rotating shaft 1. The sealing end face 3 prevents leakage of the end faces of the seat ring 5 and the driven ring 6. When the rotary shaft 1 rotates, the collar 9 rotates with it. This collar 9 rotates the driven ring 6. Both the packing 7 and the coil spring 8 also rotate.
[0008]
Since the seat ring 5 does not rotate, the sealing end surface 3 becomes a meeting surface of the relatively rotating surfaces and prevents leakage of the sealing fluid while the rotating shaft 1 is rotating. As the sealed end face 3 is worn due to friction, the driven ring 6 is pushed toward the seat ring 5 and the tight contact of the sealed end face 3 is maintained. The buffer rubber 4 and the packing 5 reduce the transmission of vibration of the rotary shaft 1 to the sealed end surface 3.
[0009]
Although the mechanical seal is formed by the above structure, the above-described seat ring 5 and driven ring 6 are generally called a seal ring.
[0010]
The seal ring members used here are mainly carbon materials, cemented carbides, silicon carbide sintered bodies, and alumina sintered bodies. In recent years, they have high hardness, high corrosion resistance, and sliding. The number of cases using a silicon carbide sintered body having a small friction coefficient and excellent smoothness is increasing.
[0011]
Moreover, in order to further improve the sliding characteristics among the silicon carbide based sintered bodies, in the manufacturing process of the dense silicon carbide based sintered body, independent pores having an average pore diameter of 10 to 40 μm or 50 to 500 μm are formed. As a sintering aid for obtaining a silicon carbide sintered body, it is disclosed that a porous silicon carbide sintered body having a volume of 13% by volume or less is used as a seal ring member. This is mainly by solid phase sintering using boron carbide and carbon.
[0012]
In addition, as a method for producing this porous silicon carbide sintered body, pores are generated by adding high molecular organic compounds such as spherical polystyrene beads into the raw material and decomposing them in the firing stage. Etc. are disclosed (see Patent Document 1 and Patent Document 2).
[0013]
[Patent Document 1]
US Pat. No. 5,834,387 specification
[Patent Document 2]
Japanese Patent Publication No. 05-69066 [0015]
[Problems to be solved by the invention]
The above-mentioned porous silicon carbide sintered body known as the prior art means that the necessary strength as a seal ring member in a mechanical seal is ensured. In most cases, the rate is set to 13% by volume or less, but in order to further improve the sliding characteristics as a seal ring member, it is necessary to set the porosity in the silicon carbide sintered body to be high. desired.
[0016]
However, when the porosity is set high in the silicon carbide sintered body mainly composed of solid phase sintering, the strength reduction is remarkably confirmed. As a result, the silicon carbide sintered body exceeding the porosity of 13 volume% is obtained. Is considered impractical. Therefore, a method for substantially producing a seal ring member having a porosity in the silicon carbide based sintered body exceeding 13% by volume has not been found.
[0017]
In addition, as a method for producing a porous silicon carbide sintered body, a macromolecular organic compound such as a spherical polystyrene bead is added to a raw material, and these are decomposed in a firing stage to generate pores. However, in order to generate pores with a porosity exceeding 13% by volume in the silicon carbide sintered body, it is necessary to add a considerable amount of a high molecular organic compound. There was a problem that the product cracked and the product value was substantially lost.
[0018]
The present invention has been made in view of the above-described problems, and its purpose is to maintain the necessary strength as a sliding member such as a seal ring, to have excellent sliding characteristics and to be free from cracks and chips. An object is to easily provide a silicon carbide sintered body for a moving member.
[0019]
[Means for Solving the Problems]
The present invention contains silicon carbide as a main component, contains 11 wt% or less of an aluminum compound, 15 wt% or less of a rare earth element compound, and 8 wt% or less of a silicon oxide, and has an average pore diameter of 20 to 40 µm, A porous silicon carbide sintered body for a sliding member is configured with a porosity of 13 to 18% by volume.
[0020]
Further, as a method for producing the porous silicon carbide sintered body for the sliding member, a raw material obtained by adding and mixing each of the above components, an organic substance for forming pores, and a molding aid is formed into a predetermined shape and degreased. The residual charcoal rate is adjusted to a range of 0.5 to 3.0% by the process and then fired.
[0021]
As described above, while maintaining the strength required as a sliding member such as a seal ring in a mechanical seal, it has excellent sliding characteristics, and has a high-quality porous structure free from chipping and firing cracks during product handling. A silicon carbide sintered body can be supplied.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0023]
FIG. 1 shows the basic structure of a mechanical seal, which is one of the shaft seal devices of fluid equipment for the purpose of completely sealing the fluid of rotating parts of various machines. The seat ring 5 and the driven ring 6 are described, and both are collectively called a seal ring.
[0024]
In the present invention, as a result of various studies to solve the above-described problems in the seal ring, silicon carbide is a main component as a silicon carbide sintered body forming the seal ring, the aluminum compound is 11% by weight or less, a rare earth element compound Even in a silicon carbide sintered body having a porosity of more than 13% by volume by containing 15% by weight or less and silicon oxide by 8% by weight or less, and setting the average pore diameter of the pores within a range of 20 to 40 μm It was found that 200 MPa, which is a necessary strength standard for the ring, can be maintained.
[0025]
This utilizes the fact that by using the above-mentioned sintering aid for silicon carbide, liquid phase sintering mainly results in a reduction in the sintering temperature and the effect of improving the strength.
[0026]
By setting the strength improvement effect and the average pore diameter in the range of 20 to 40 μm, it becomes possible to set a high porosity exceeding 13 volume%, and at the same time, reducing frictional force when sliding the seal ring and lubricating liquid This promotes the lubrication effect and improves the sliding characteristics.
[0027]
For example, if the aluminum compound, rare earth element compound, or silicon oxide used as a sintering aid for obtaining a silicon carbide-based sintered body exceeds the above range, a liquid phase is often generated in the sintering stage and decomposed. Since the evaporation becomes intense, there arises a problem that the strength is reduced due to the generation of fine pores and the molded shape cannot be maintained.
[0028]
On the other hand, if the aforementioned components are very small, the liquid phase is not sufficiently generated and the densification is impaired, leading to a decrease in strength.
[0029]
Accordingly, the sintering aid is preferably in the range of 1 to 6% by weight of aluminum compound, 1 to 10% by weight of rare earth element compound, and 0.1 to 5.0% by weight of silicon oxide.
[0030]
As impurities other than these components, metals such as iron and titanium or compounds thereof, carbon, and the like can be raised. However, these impurities cause densification inhibition and strength reduction, so the content should be 2% by weight or less. preferable.
[0031]
As for the pores, if the average pore diameter is less than 20 μm, the lubricating effect of the lubricating liquid is reduced, and if it exceeds 40 μm, the required strength cannot be maintained.
[0032]
Further, when the porosity is 13% by volume or less, the sliding property tends to be inferior, and when it is 18% by volume or more, the strength may be lowered, and it is preferably in the range of 14 to 17% by volume. .
[0033]
The average pore diameter explained here was obtained by taking a metal micrograph or SEM photograph of the mirror-finished surface of the sintered body, and after determining pores due to organic matter decomposition on the photograph, measuring the diameter of each pore and calculating the average value. The porosity is obtained by calculating the ratio of the theoretical density in the above-mentioned sintered body composition and the bulk density of the obtained sintered body.
[0034]
On the other hand, in order to obtain a silicon carbide sintered body having a porosity exceeding 13% by volume, it is necessary to make a silicon carbide powder to which an organic substance such as a pore material or a binder is added. When this powder is simply molded and fired, There was a problem that the product was cracked and chipped, and the product value was substantially lost.
[0035]
In order to solve this problem, a silicon carbide powder to which an organic substance such as a pore material and a binder is added is molded, and then a degreasing step is added, and the residual carbon ratio of the powder molded body obtained in the degreasing step is set to 0.5 to 3 By sintering after adjusting to the range of 0.0% by weight, the sintered body has excellent sliding properties while maintaining the required strength as a sliding member while exceeding the porosity of 13% by volume, and the product. It has been found that a porous silicon carbide sintered body free from burrs and firing cracks during handling can be obtained.
[0036]
Therefore, a degreasing step is added before the step of firing the powder compact, and the residual carbon ratio of the powder compact after the degreasing step is adjusted to a range of 0.5 to 3.0% by weight and fired. It is an important feature, and if the residual carbon ratio is set in the above range, it prevents the rapid volume expansion due to gasification of organic substances decomposed in the degreasing process while maintaining the minimum strength that maintains the shape of the powder compact. The effect is obtained, and a high-quality sliding member free from cracks and chips can be easily provided.
[0037]
As a means for adjusting the residual carbon ratio to the above-mentioned range, it is effective to define the maximum holding temperature, the temperature rising time to the maximum holding temperature, and the furnace atmosphere as the degreasing conditions of the powder compact.
[0038]
For example, when the residual carbon ratio of the powder molded body obtained through the degreasing process is less than 0.5% by weight, the strength of the powder molded body becomes low, so that the product shape cannot be maintained, or chipping occurs during handling. There is a high possibility of doing.
[0039]
In addition, when the residual carbon ratio exceeds 3.0% by weight, when the added organic matter is decomposed in the subsequent firing step, cracks due to rapid volume expansion due to gasification occur, This leads to a significant reduction in yield.
[0040]
The residual carbon ratio described here is calculated by calculating the weight loss ratio obtained by subtracting the weight after degreasing from the weight of the powder molded body produced to obtain the porous silicon carbide sintered body described above. It is a value subtracted from the addition ratio of the organic compound for forming binders and pores.
[0041]
Hereinafter, the manufacturing method of the porous silicon carbide sintered body for sliding members of the present invention will be described.
[0042]
First, alumina carbide, yttria powder and water are mixed into a silicon carbide powder containing a small amount of silica as a starting material to form a slurry, and then fine acrylic beads are added to the slurry as a binder and a pore material, mixed and then spray-dried. This produces granulated powder.
[0043]
After forming this granulated powder into a predetermined shape and entering a vacuum degreasing furnace, the temperature is raised from 450 to 650 ° C. in a nitrogen atmosphere in 10 to 40 hours, and holding at 450 to 650 ° C. for 2 to 10 hours. Cool naturally.
[0044]
Here, the powder compact adjusted to a residual carbon ratio in the range of 0.5 to 3.0 wt% was further fired at a temperature of 1800 to 1900 ° C. in an argon atmosphere in a vacuum furnace, and the obtained sintered body was predetermined. A sliding member such as a seal ring is produced by processing into a shape.
[0045]
The sliding member produced by the above manufacturing method has a porosity of more than 13% by volume, maintains a required strength standard of 200 MPa, and has a high quality with excellent sliding characteristics without cracks and chips. Can be a thing.
[0046]
【Example】
(Experimental example 1)
The proportion of alumina powder, yttria powder, 122% water, 0.3% by weight ammonia water and 84% by weight as a dispersing agent with respect to 100% by weight of silicon carbide powder containing 1% by weight silica. % Urethane balls were put into a ball mill and then mixed for 48 hours to form a slurry. A granulated powder is obtained by adding 8% by weight of a binder mainly composed of an acrylic resin and acrylic beads having an average particle diameter of 23 μm, 38 μm and 69 μm as pore materials to the slurry in the proportions shown in Table 1, followed by spray drying. Was made. This granulated powder is molded into a predetermined shape at a pressure of 1 ton / cm ² , heated to 450 to 650 ° C. in a nitrogen atmosphere in a vacuum degreasing furnace in 5 to 60 hours, and then 2 to 10 at 450 to 650 ° C. The remaining carbon ratio was calculated by measuring the weight loss after degreasing under the condition of holding for a time and then naturally cooling. Next, the porosity, average pore diameter, bending strength, cracks, chips and deformation of the sintered body obtained by firing the degreased powder compact in a vacuum furnace at 1800 to 1900 ° C. in an argon atmosphere And the like were evaluated. The results are shown in Table 1, and comparative examples of solid-phase sintered bodies using boron carbide and carbon as sintering aids are also shown in Table 1.
[0047]
From Table 1, first, in order to obtain a porosity exceeding 13% by volume, it is necessary to add 8% by weight or more of the acrylic beads used as the pore material, and at the same time, when the addition amount is in the range of 10% by weight or less. It can be seen that the required strength for the seal ring member exceeds 200 MPa.
[0048]
On the contrary, when the amount of the acrylic beads added exceeds 12% by weight, a decrease in strength is remarkably confirmed as the porosity increases. It can be seen that the required strength as a seal ring product cannot be maintained as in the case of 19 solid-phase sintered body.
[0049]
Similarly to the above, the average pore diameter is confirmed to decrease in strength in the range exceeding 40 μm.
[0050]
In addition, Sample No. 2 in which the aluminum compound and rare earth element compound which are sintering aid components are out of the scope of the present invention. 17 and 18, it can be seen that the strength decreases due to the generation of fine pores and the deformation accompanying the decomposition and evaporation of the liquid phase component occurs, and the practical value as a seal ring product is lost.
[0051]
On the other hand, sample No. 1-16, when looking at the relationship between the remaining charcoal rate and appearance, in the range below the remaining charcoal rate of 0.5%, it is not possible to secure the minimum strength that can maintain the shape as a powder molded body, so abnormal appearance such as cracks Is confirmed. Moreover, in the range exceeding 3.0% of residual charcoal, the appearance abnormality, such as a crack accompanying rapid volume expansion by the gasification at the time of organic substance decomposition | disassembly, is confirmed.
[0052]
As described above, acrylic beads having an average particle size of 38 μm are added to a silicon carbide raw material containing 11% by weight or less of an aluminum compound, 15% by weight or less of a rare earth element compound, and 8% by weight or less of a silicon oxide as a sintering aid. A powder molded body added by weight% is prepared, the powder molded body is degreased, adjusted to a residual carbon ratio of 0.5 to 3.0%, and then fired, so that the average pore diameter is in the range of 20 to 40 μm. It is confirmed that a high-quality porous silicon carbide sintered body that retains a strength of 200 MPa or more while having a porosity exceeding 13% by volume, is excellent in sliding characteristics, and has no cracks or chips is obtained. did it.
[0053]
[Table 1]

[0054]
【The invention's effect】
As described above, according to the present invention, silicon carbide is the main component, containing 11 wt% or less of an aluminum compound, 15 wt% or less of a rare earth element compound, and 8 wt% or less of a silicon oxide, By using a porous silicon carbide sintered body having an average pore diameter of 20 to 40 μm and a porosity of 13 to 18% by volume, the required strength as a sliding member such as a seal ring is maintained, and sliding characteristics are maintained. It is possible to provide various products for sliding members which are excellent in the above.
[0055]
Moreover, in the manufacturing process of the above product, a degreasing step is added before the step of firing the powder compact, and the residual carbon ratio of the powder compact after the degreasing step is in the range of 0.5% to 3.0%. By adjusting and firing, various products for high-quality sliding members free from cracks and chips can be easily provided while ensuring the above characteristics.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a basic structure of a mechanical seal using a porous silicon carbide sintered body for a sliding member according to the present invention.
[Explanation of symbols]
1: Rotating shaft 2: Casing 3: Sealing end surface 4: Buffer rubber 5: Seat ring 6: Driven ring 7: Packing 8: Coil spring 9: Collar 10: Set screw

Claims (2)

Containing silicon carbide as a main component, containing 11% by weight or less of an aluminum compound, 15% by weight or less of a rare earth element compound, and 8% by weight or less of silicon oxide, having an average pore diameter of 20 to 40 μm and a porosity of 13 A porous silicon carbide sintered body for a sliding member, characterized in that it is -18% by volume. It is a manufacturing method of the porous silicon carbide sintered body for sliding members of Claim 1, Comprising: The said each component, the organic substance for forming a pore, and the raw material which added and mixed the shaping | molding adjuvant in the predetermined shape A method for producing a porous silicon carbide sintered body for a sliding member, comprising molding and adjusting a residual carbon ratio in a range of 0.5 to 3.0% by a degreasing step and then firing.

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