JPH0454306A - Heat-resistant bolt - Google Patents

Abstract

PURPOSE:To prevent reduction of the tightening force of a bolt after a tempera ture rise by difference of a counter material by disposing yarn of integration of woven sheets consisting of warps and wefts of carbon fibers or carbon fiber- reinforced carbon composite material consisting of carbon fibers crossing each other along the shaft axis of the bolt, and setting the cross section in the verti cal direction to be as predetermined. CONSTITUTION:Phenol resin is impregnated in plain weave organization of polyachrylonitrile lone fibers, the organizations are put together in a die, and they are heated. The obtained matter is then baked in a vacuum furnace, it is put in mixed liquid of phenol resin and methanol, and it is pressurized and impregnated in vacuum to produce carbon fiber-reinforced composite material and a bolt is manufactured there of. In this case, the cross section in the vertical direction of the bolt shaft core is set at a value determined by an expression based on a root cross section of a screw, a differential expantsion coefficient to a counter material, tension resiliency coefficents for both, a temperature rise, etc. Elastic deformation or cutting differential expansion coefficient to the counter material to be tightened 4 eliminated, and a sufficient tightening force can be maintained after temperature rise.

Description

[Detailed description of the invention] Industrial fields of application The present invention is applicable to vacuum furnaces, non-oxidizing atmosphere furnaces, high temperature and high pressure press machines,
It is used for heat-resistant bolts that fasten parts of structures that are exposed to high temperatures in non-oxidizing atmospheres, such as space equipment.

BACKGROUND OF THE INVENTION Conventionally, the heating elements and internal structures of vacuum furnaces, atmospheric furnaces using nitrogen and argon, and high-temperature, high-pressure press machines used in the production of ceramic cemented carbide are made of heat-resistant materials. Bolts made of artificial graphite are used to fasten these, but they have low tensile strength and low impact strength, so they often break, and the fastening force is low.
It had caused an accident. However, recently, furnaces have become larger and the weight of each part has also increased, creating a demand for stronger bolt materials.

Carbon fiber-reinforced carbon composite materials (hereinafter referred to as CFRC), which have been developed in recent years to solve the above-mentioned problems, have remarkable tensile strength and impact strength of about 10 times and about 5 times that of artificial graphite. It is attracting attention as a high-performance bolt material that can withstand high temperatures.

Such CFRC can be applied to the surface of carbon fiber fabric or
After coating the surface of a real carbon fiber thread or a large number of carbon fibers arranged in a sheet shape with pitch or a thermosetting resin to serve as a carbon binder, and stacking the obtained sheets to form a laminate, This is heated and pressed to form a cured product, which is then fired at a temperature of 1000° C. or higher in a non-oxidizing atmosphere.

At that time, the resin thermally decomposes and gasifies into water, amine, charcoal (P:, hydrogen) and becomes porous Mm, so it is further immersed in the resin liquid, impregnated with vacuum pressure, etc., and fired. Repeating the process and making it more precise
67], the tensile coefficient of the CFRC bolts made in this way is smaller than the linear expansion coefficient of general artificial graphite. Therefore, as shown in Fig. 1, temporary 1a and 1b made of artificial graphite material are When the bolts 2 and nuts 3a and 3b are tightened and the temperature rises, the plate made of artificial graphite material tends to expand more than the CFRC bolt as the temperature rises in addition to the tensile load due to the tightening of the bolt. Tensile load is applied.

Therefore, even though the screws were initially fastened securely at room temperature, when the temperature rose and returned to room temperature, problems such as breakage or loosening occurred, making the fastening useless. CFRC bolts that prevent chipping due to delamination of material layers and bite into fragments, and take into account shear stress on threads, axial tensile force, and compressive force when tightening [Utility Model No. 63]
No. 49013] was not suitable for practical use because it caused breakage and plastic deformation due to tensile load due to thermal expansion due to temperature rise after fastening.

Problems to be Solved by the Invention The present invention is intended to solve such problems.The purpose of the present invention is to solve these problems by making it possible for the CFRC bolt to retain its strength even after the temperature rises without causing plastic deformation or breakage due to the difference in coefficient of expansion between the bolt and the mating material to which it is fastened. The object of the present invention is to provide a CFRC bolt that maintains sufficient fastening force.

Means for Solving the Problems In order to solve this problem, the present invention consists of accumulating mending sheets made of warps and wefts made of carbon fibers, or by stacking carbon fiber sheets with carbon fibers arranged in one direction. It is made of carbon fiber-reinforced carbon composite material (CFRC) made by stacking the carbon fibers in alternating directions so that they are perpendicular to each other, and the threads made of carbon fibers parallel to the sheet surface are arranged in the fine direction of the bolt. The cross-sectional area in the direction perpendicular to the core direction satisfies equation (1).

However, A1 = cross-sectional area of the thread root of the CFRC bolt
- A2 = Surface M where the nut or washer contacts the m connection
aJ C = Difference between linear expansion coefficient of CFRC bolt and linear expansion coefficient of the object fastened with it/' Et = Tensile elastic modulus of CFRC bolt /- 22 = Compressive elastic modulus of the object fastened with CFRC bolt
σ1 = Tensile strength of CFRC klr/dG = Tightening force T = Temperature rise °C β = 0.7 to 2.5 coefficient The carbon fiber used in the CFRC may be either carbon fiber or graphitic carbon fiber. Also, any of acrylonitrile-based, rayon-based, pitch-based, lignin-based, or thermosetting If resin-based carbon fibers can be used.

Sheets made of carbon fibers used in the present invention include woven fabrics, knitted fabrics, nonwoven fabrics, and brippure rugs in which many long fibers are arranged in parallel.

The preferred procedure for CFRC used in bolts is to impregnate carbon fiber material with phenol resin, cut it to fit the mold, and stack dozens to hundreds of sheets to produce 100 kIr/-.
Carbon fiber-reinforced WMF and composite materials are produced by the above pressurization and heating at 120°C to 200°C. This is fired at about 1000° C. in a vacuum or in a non-oxidizing atmosphere such as nitrogen gas or argon gas, and then impregnated with pitch, phenol*a, and furan resin. This firing and impregnation process is repeated several times, and depending on the application, the temperature is raised to 2000°C or higher to graphitize. Generally CFRC
The mechanical properties and coefficient of linear expansion vary depending on the material manufacturing method. The coefficient of linear expansion in the direction perpendicular to the carbon fiber sheet is almost the same as that of general carbon materials, 5 to 6 x 10-'/''K.
However, in the direction of carbon fiber, 1.5 xlo-'
/"K is smaller than artificial graphite, I!I Mechanical strength is weaker in the direction of lamination of fiber sheets than in general carbon materials. High-temperature bolts made of CFRC have their axial direction aligned with the direction of carbon fibers. This is desirable because the tensile strength required for bolts can be increased by making them the same.In other words, in order to utilize the high tensile strength of CFRC when made into bolts, it is better to use artificial graphite in the direction of carbon fiber, which has a linear expansion coefficient of CFRC. A direction smaller than that will be used.

On the other hand, the linear expansion coefficients of artificial graphite and CFRC change depending on the temperature, and an example is shown in Table 1.Next, to describe the present invention in detail, as shown in FIG. , 3b, plates 1a, l made of heat-resistant material
The force required to fix the plates 1a and lb in the state in which the plates 1a and 1b are fastened is G in the above equation (1). CFRC has a small linear expansion coefficient and is a heat-resistant material (plates 1a, lb)! ! If the coefficient of expansion is large, as the temperature increases, the CFRC bolt will
The contact surface A2 of the nut causes the CFRC to expand beyond its own thermal expansion. On the other hand, the thermal expansion of the heat-resistant material itself is restricted by the bolts and nuts of CFRC, and does not expand sufficiently. Therefore, in addition to the fastening force G, CFRC is subjected to the force of the expansion difference between CFRC and the heat-resistant material, and the CFRC's tensile strength is Based on the elastic modulus and the compressive elastic modulus of the heat-resistant material, the strength of the bolt is required to be able to remain within the elastic deformation. Also, Natsu's contact surface A
If 2 is large, the force applied to the bolt will be large.

It is best to follow equation (1) in consideration of each factor.

If β is less than 0.7, the bolt will break. t, CFRC
The variation in tensile strength may be ±50% with respect to the average value, and it is uneconomical to make β too large, so a range of 0.7 to 2.5 is appropriate.

Effect With the above configuration, it is possible to prevent MA damage on the bolt due to the difference in thermal expansion caused by the combination of different materials by selecting the cross-sectional area of the bolt in consideration of elastic modulus and strength. These bolts have made it possible to firmly fasten structures used in high-temperature conditions.

Example Examples of the present invention will be described below.

Example 1 300gr/polyacrylonitrile carbon long fiber
CD plain weave fabric [manufactured by Toho Rayon ■] is impregnated with 50% phenolic resin [manufactured by Sumitomo Durdret Co., Ltd.], and
120 sheets were cut to a size of x200/11, stacked, placed in a mold, and heated in a hobtoburette at 100 kr/cd at 170°C. Then in a vacuum furnace for 20
Baked at 00℃, and the baked product is coated with phenolic resin 50℃.
%, put it in a solution of 50% methanol and evacuate it, then 10
Pressure impregnation was carried out with kIr/ali. Firing and impregnation were repeated five times to produce a carbon fiber-reinforced carbon composite material having a thickness of 30 m/m, a length of 2001/m, and a width of 200 Il/l.

The tensile strength of CFRC made in this way is 1500k.
g/-, the tensile modulus is 6 X 10' kl/d, and the linear expansion coefficient is 1.5 X 10-'/''K, 1 at 300°C.
It was 2.1 x 10-'/'K at 300°C. Also,
The compressive elastic modulus of the artificial graphite (Niseasy MGY) that is to be fastened with this CFRC bolt is 1xtO
'to! r/J, linear expansion coefficient 4300℃te 4.5 xl
o-', 1300"Cte 5.4xIQ-". A plate having a length of 100 m/m, a thickness of 2411/m and a width of 24 m/m was cut from this CFRC material in the male direction. In formula n (1), A2 = nut, contact area
7,1-C = Difference in linear expansion coefficient between CPRC and artificial graphite 3.3 xlO-'/''KE, = Longitudinal elastic modulus of FRC 6 x10' kIr/ad E2 = Compressive elasticity gA1 of artificial graphite!! 1x10'*/
ai σ> = Tensile strength of CFRC 1500 bet/- G = Load applied to bolt 3500 + r T - Temperature 1300℃ β = 1 When A1 is 3.89 csi, the length from this plate on a lathe 10 (ill/11, M-27 pitch 3.0s/m outer diameter 2711#e, valley) diameter 23.75
A coarse thread with a circular cross section of n/n, Tanino [1ff4.4d] was made. And 40m made of artificial graphite (MGY>)
3500m by stacking two boards of /m and fastening them with CFRC bolts and square nuts of 32II/11 on one side.
The temperature was raised to 1300'C by applying a load of 1000°C, and the temperature was maintained for 2 hours until the temperature reached room temperature. When I inspected the bolts, I found no signs of stretching or breaking.

Example 1 CFRC material shown in Example 1 with length in the fiber direction 10
0-/-T, thickness 201/Il, width 201/11] [
wo (IJ Absolutely M-20, pitch 2.5, valley diameter 17.2
A bolt with a coarse thread of 94 mm was made, and two plates made of artificial graphite shown in Example 1 with a thickness of 40 m/s were
A tightening force of 20 with a nut of thickness 15 Il/l with one side of m
We concluded the deal for 00kr.

And if the temperature rises to 1500℃, the bolt will break.

Effects of the Invention From the above explanation, according to the present invention, the bolt does not undergo plastic deformation or breakage due to the difference in expansion coefficient between the CFRC bolt and the mating material to be fastened, and sufficient fastening force is maintained even after the temperature rises. can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a state of fastening with bolts and nuts. la, lb...plate, 2...bolt, 3a, 3b...
・Natsuto. 1.1. /& 4L Agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. A woven sheet consisting of warps and wefts made of carbon fibers is accumulated, or sheets in which carbon fibers are arranged in one direction are accumulated by alternating the directions so that the carbon fibers are perpendicular to each other. The carbon fiber reinforced carbon composite material (CFRC) is made by arranging carbon fiber threads parallel to the sheet surface in the axial direction of the bolt, so that the cross-sectional area in the direction perpendicular to the bolt axial direction is ( 1) A bolt that satisfies the formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) However, A_1 = Cross-sectional area of the thread valley of the CFRC bolt cm^2 A_2 = Area where the nut or washer contacts the fastener cm^2 C= Difference between linear expansion coefficient of CFRC bolt and linear expansion coefficient of the object fastened with it/K゜E_1=tensile elastic modulus of CFRC bolt kg/cm^
2 E_2 = Compressive elastic modulus of the material to be fastened with CFRC bolts kg/cm^2 σ_1 = Tensile strength of CFRC kg/cm^2 G = Tightening force kg T = Temperature rise °C β = 0.7 to 2.5 coefficient