JPH10232290A - Manufacturing method of ceramic bellows - Google Patents

Abstract

(57) [Problem] To provide a method for producing a bellows from ceramics. Conventionally, when a metal bellows is used at a high temperature, the withstand temperature is about 500 ° C. at the most. The use of the ceramic bellows of the present invention is advantageous because the creep amount is small even when used at about 1000 ° C. SOLUTION: A ceramic powder is filled between a corrugated graphite rod and a vinyl or rubber bag, which is then filled with CIP.
To make a ceramic molded body. Thereafter, the outer surface of the molded body is cut into a corrugated surface (a portion to be the outer surface of the completed bellows). A separately prepared mold having a corrugated inner surface is inserted into the molded body, and the two divided portions of the mold are welded in a vacuum. Thereafter, HIP processing is performed for each mold, and sintering of ceramics is performed. After sintering, the mold is removed and the graphite rod is extinguished by high temperature oxidation in air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ceramic bellows which can be used not only in the field of nuclear power such as a high temperature gas reactor and a fusion reactor but also in general industries using high temperature equipment, and a ceramic bellows manufactured by the method. It is about.

[0002]

[Prior art]

○ The HTGR is a nuclear fission reactor using helium gas as a coolant. The reactor is operated under high temperature and pressure,
The temperature and pressure of the helium gas at the reactor outlet are 900-95
It reaches 0 ° C and 4 MPa. Structural materials used under such high temperatures and pressures are mainly graphite materials near the core,
In the primary cooling system, a heat-resistant metal material is used.

[0003] There is a control rod in an apparatus constituting a nuclear reactor. This control rod is also exposed to high-temperature helium gas at about 900 to 950 ° C. during operation. In normal operation, the control rod moves slowly, but in the case of a reactor scram, the withdrawn control rod is rapidly inserted in a falling state.
At this time, the control rod collides with the bottom of the reactor, but a bellows is attached as a shock absorber below the control rod to reduce the impact force. The bellows currently attached use a heat-resistant alloy, but since the temperature of the bellows at the time of collision is high, deformation is likely to occur due to the collision force.

On the other hand, when hydrogen production is performed using nuclear energy (heat) of a high temperature gas reactor, the hydrogen production plant is installed outside the containment vessel, and is isolated between the reactor and the hydrogen production plant. A valve is provided. Helium gas of about 900 ° C. also flows through this isolation valve (currently under development), but it is desirable to use a valve provided with a bellows in order to maintain the airtightness of the valve. Valves that maintain airtightness with bellows are generally referred to as bellows valves, and this type of valve is currently available even if a heat-resistant alloy is used for the bellows material.
The operating temperature of 500 ° C. is considered to be the limit for long-term use.

[0005] In a fusion reactor, its structural members are exposed to a strong magnetic field due to its principle. If the pipe is installed in a place where a magnetic field is present, and if the material is metal, it receives a large electromagnetic force when the magnetic field fluctuates. It is disadvantageous to calculate strength. For future fusion reactors, we plan to use non-metallic materials as much as possible, not receive electromagnetic force and avoid activation, and the piping system there will be made of ceramics. At present, there is an outlook for pipes, but there is no production and use of bellows, so metal bellows will be used.

[0006] As described above for the high-temperature gas furnace, even if the bellows used at a high temperature is made of a heat-resistant alloy, the mechanical properties deteriorate at a high temperature at which creep occurs, and the Difficult to use. Therefore,
If a bellows is manufactured using ceramics such as SiC having excellent mechanical properties at a high temperature, it can be used at a high temperature for a long time. Regarding the “ceramic bellows” as the product and the “method of manufacturing bellows with ceramics” as the manufacturing method, no past technical information can be found, and no reference can be made to conventional technologies. Although the present invention discloses the "production method", it is for this reason that the use examples of the bellows at present for the high temperature gas reactor and the fusion reactor are described. The following method is known as a conventional manufacturing method.

A method of making a cylindrical block of SiC (silicon carbide) ceramics The powder of SiC necessary for making a cylindrical block is put into a cylindrical bag made of a rubber sheet or a vinyl sheet. The bag is sealed and put into a CIP (normal temperature isostatic press) chamber, and hydrostatic pressure is applied to mold. After molding, remove the rubber sheet or vinyl sheet. The formed cylindrical block is subjected to HIP (high-temperature isostatic pressing), and sintering is performed under high temperature and high hydrostatic pressure. As a preparatory work, a thin metal (with sintering temperature) is applied so that hydrostatic pressure is applied to the block. Cover the entire surface with softening metal). Seal welding is performed on metal seams, but welding is performed in a vacuum so that no air remains inside the block. In this state, it is subjected to HIP and sintered. After sintering, remove the block from the HIP and remove the metal covering. If necessary, this block is finished by grinding or the like to obtain a finished product.

[0008]

The conventional bellows is made of metal, and even if a heat-resistant alloy is used, there is a problem that long-term use at a high temperature that causes creep is limited. . Thus, the present invention has solved this problem by manufacturing a bellows from ceramics that exhibit superior mechanical properties at higher temperatures than a heat-resistant alloy.

[0009]

Hereinafter, one method of manufacturing the bellows of the present invention from ceramics will be described. A round rod made of graphite having a wavy surface as shown in FIG. 1 (hereinafter referred to as a graphite core) is cut out with a lathe. Leave the center hole of the end face left by lathe work. As shown in FIG. 2, a graphite core is placed in a cylindrical bag made of a rubber sheet or a vinyl sheet, and the surroundings are filled with ceramic powder as a raw material. After filling, the cylindrical bag is sealed. When sealing, put both ends of the graphite core out of the bag. This part is a part to be gripped by a chuck or a part into which a center is inserted when lathing is performed later. As shown in FIG. 3, the filler formed in the step is put into CIP as it is, hardened by applying high hydrostatic pressure, and formed into a block. The bag is peeled off from the block-shaped compact after the CIP treatment, and the lathe is used to cut off the bellows so that the thickness of the bellows remains. FIG. 4 shows the state of the compact after shaving. A mold that can be separated into two as shown in FIG. 5 is prepared. This mold has a wavy inner surface, and is made to have a size that fits the molded product obtained in the step. The molded body is put in this mold, and the seam split into two is sealed and welded in a vacuum. FIG. 6 shows the state after welding. The molded body closed by the mold is subjected to HIP, and the ceramic is sintered under high temperature and high pressure of argon gas. Since the mold is made of a material that softens at the sintering temperature, the hydrostatic pressure is uniformly applied to the molded body. FIG. 7 shows a state of sintering by HIP. After the HIP treatment, the seal welding portion of the mold is scraped off with a razor to separate the mold. Thereafter, holes are drilled from both end surfaces of the graphite core. This hole is for easily performing air oxidation of the graphite core in the next step.
FIG. 8 shows a bellows with a perforated graphite core. The bellows with the graphite core is placed in an electric furnace and gradually heated in air to oxidize the graphite core. At the end of the oxidation, a small amount of ash remains and is removed to complete the bellows fabrication. The finished product is shown in FIG.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The ceramic bellows manufactured according to the present invention and the metal bellows are compared in strength at high temperature.

[0011] External force (pull, pressure) applied to the bellows
The relationship between the stress and the generated stress is shown in the following equation (the source of the equation is JIS
B8243 P79). Refer to FIG. 10 for the symbols related to the dimension display in the formula.

[0012]

(Equation 1) Here, σ: stress generated in the bellows E: Young's modulus of the material of the bellows t: thickness of the bellows plate δ: elongation of the bellows b: 1/2 of the pitch of the bellows wave h: height of the bellows wave N : Twice the wave number of the bellows P: pressure applied to the bellows The comparison is made of the difference between ceramics and metal, that is, the difference in material, so equation (1) is simplified. First, it is assumed that no pressure is applied (therefore, the second term of the equation (1) becomes zero), and that elongation is applied by pulling, and that the dimensions of the bellows are the same for both ceramics and metals. (Thus, the t, b, h associations and the constant 1.5, excluding δ, can be comprehensively replaced by K). The simplified equation is as follows.

[0013]

(Equation 2) (2) By transforming the equation

[0014]

(Equation 3) Here, mechanical properties of, for example, SiC (silicon carbide) ceramics will be described. The generated stress that can be used safely, that is, the allowable stress, is that the fracture stress at about 900 ° C. is 350 MPa even when sintered under normal pressure.
It is estimated to be about 117 MPa. Young's modulus is 400MP
a.

On the other hand, in the case of metal, the heat-resistant alloy used is Hastelloy XR (Ni-based heat-resistant alloy, the composition of which is Cr: 2
0.5-23.0%, Mo: 8-10%, Fe: 17-
20%, Co: 0.5-2.5%, W: 0.2-1.0
%, The remaining Ni) at about 900 ° C. and 10,000
The stress at which creep rupture occurs in 0 hours is about 9 MPa, and if 2/3 times the stress is defined as the allowable stress, it will be about 6 MPa.
The Young's modulus is 140 GPa.

That is, the allowable stress of SiC (silicon carbide) can be increased by about 20 times (117/6 = 19.5) compared to Hastelloy XR, and the Young's modulus can be increased by about 3 times (400/140 = 2.9).
It is.

Here, assuming that the number of waves of the bellows is the same in SiC (silicon carbide) and in the case of Hastelloy XR, and that the shape and dimensions are the same, Equation (3) is used to obtain σ, E, K, and σ in the case of Hastelloy XR. If N and δ are each 1, SiC
Δ of (silicon carbide) is 20 for σ, 3 for E, 1, N for K
Substituting 1 into gives 6.7. That is, the bellows made of SiC (silicon carbide) at a high temperature (about 900 ° C.) is 6.7 compared with the bellows made of Hastelloy XR.
Double elongation can be tolerated. This point is a feature of the present invention and should be emphasized as an operational effect.

[0018]

【Example】

・ The ceramic raw material powder is made of SiC and the graphite core is made of fine-grained isotropic graphite.

A mold is made of molybdenum, and the seal welding of the mold is electron beam welding.

Means for Solving the Problems A method for producing a bellows by the processes of (1) to (4) was carried out.

The ceramic raw material powder is SiC,
The graphite core is made of fine-grained isotropic graphite, and without using a mold,
HIP is applied, but without pressure but with temperature. That is, none of the above-mentioned steps is performed, and no pressure is applied in the step. A method for producing bellows in this way was performed.

With this method, as shown in FIG. 11, the thickness of the bellows curve portion was increased to obtain a bellows in which the concentration of stress was reduced.

[0022]

Conventionally, when a metal bellows is used at a high temperature, the withstand temperature is at most about 500 ° C. On the other hand, when the ceramic bellows of the present invention is used, even when used at about 1000 ° C., the creep amount is small, which is advantageous.

That is, the conventional metal bellows is 900
When used at a high temperature of about ℃, a creep phenomenon occurs, and the bellows must be designed with a low allowable stress. On the other hand, in the bellows using SiC (silicon carbide) of the present invention, a large allowable stress can be obtained, and at about 900 ° C., almost no creep occurs.

[Brief description of the drawings]

FIG. 1 is a view showing a graphite round bar having a wavy surface.

FIG. 2 is a diagram showing that a graphite core is placed in a cylindrical bag made of a rubber sheet or a vinyl sheet, and ceramic powder as a raw material is filled around the core.

FIG. 3 is a view showing that the obtained filler is put into CIP as it is, hardened by applying a high hydrostatic pressure, and formed into a block. .

FIG. 4 is a diagram showing a state of a molded body that is obtained by removing a bag from a block-shaped molded body that has been subjected to the CIP process, and then shaving the lamination so that a portion of the bellows thickness remains.

FIG. 5 is a view showing a mold that can be split into two and has a wavy inner surface, and has a size that fits the molded product obtained in the process of FIG. 4;

FIG. 6 is a diagram showing a state after welding in which a seam split into two pieces is seal-welded in a vacuum.

FIG. 7 is a diagram showing a state in which a molded body closed by a mold is subjected to HIP and sintering of ceramics is performed under high temperature and high pressure of argon gas.

FIG. 8 is a view showing a bellows with a graphite core obtained by drilling holes from both end surfaces of a graphite core by shaving off a seal welding portion of the die after HIP processing, separating the die, and drilling.

FIG. 9 is a view showing a completed bellows obtained by placing a bellows with a graphite core in an electric furnace and heating to burn off the graphite core.

FIG. 10 is a view showing a wavy surface shape of the bellows of the present invention.

FIG. 11 is a view showing a bellows having a thicker wavy portion on a wavy surface according to the present invention.

[Explanation of symbols]

r: inner radius of the wave portion, t: thickness of the bellows plate, b: 1/2 of the pitch of the wave of the bellows, h: height of the wave of the bellows.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FIF16J 3/04 C04B 35/64 302Z

Claims (3)

[Claims] Claims 1. A ceramic powder is filled between a graphite core having a wavy surface and a bag made of rubber or vinyl, and the bag is sealed. Then, the surface of the molded body is cut into a wave shape, the two-part mold having the wavy shape is fitted into the molded body, the two parts are welded in a vacuum, and the whole mold is subjected to high-temperature isostatic pressing to fire ceramics. A method for producing ceramic bellows, comprising sintering, sintering, removing the mold, and extinguishing the graphite core by oxidation in air. 2. The ceramic powder is SiC, the graphite core is fine isotropic graphite, the mold is made of molybdenum, the mold is welded by electron beam welding, and the sintering is in an argon gas atmosphere. The method for producing a ceramic bellows according to claim 1, which is performed. 3. A ceramic bellows manufactured by the method according to claim 1 or 2, wherein a thickness of a curved portion of the bellows is increased.