JPS62170336A - Composite material consisting of graphite and metal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a composite material made of graphite and metal used for parts of various types of equipment.

(Prior art and its problems) Generally, metals and graphite have significantly different thermal expansion coefficients from each other. For example, the coefficient of linear expansion of steel is 13 to 18X 10
``6, whereas the linear expansion coefficient of graphite is 2~5X1
0'. Generally, the range in which the coefficient of thermal expansion does not pose a practical problem in brazing or diffusion bonding is when the difference in the coefficient of linear expansion between the two is smaller than 1×10″G.

For this reason, when metal and graphite are joined by brazing or diffusion bonding, the shrinkage rate of the metal is greater during the cooling process after joining, resulting in a dimensional difference between the two and a large residual stress. may destroy graphite.

As an example, when a cylindrical graphite 2 is applied to the outside of a cup-shaped or vibe-shaped metal material 1 made of chromium copper, as shown in FIG. Diffusion bonding (or hard brazing) via 3
Assume that In this case, if the dimensions of each part are set so that the outer surface of metal material 1 is in close contact with the inner surface of graphite 2 in the high temperature state during bonding, metal material 1 will be relative to graphite 2 during the cooling process after bonding. to shrink. Since the metal material 1 contracts not only in the radial direction but also in the axial direction, the graphite 2 bonded to the metal material 1 receives a force that causes it to bend in the axial direction. For this reason, cranks may occur at the ends 2a, 2b of the graphite 2, or cracks may develop, leading to destruction.

Therefore, research on composite materials made of metal and graphite is currently limited to simple test pieces such as joining small cylinders or rectangular parallelepipeds, research on the reactivity of graphite and metal, or research on the difference in thermal expansion coefficient. Research was only being carried out on very small parts where this would not be a problem.

On the other hand, mechanical fastening by shrink fitting or cold fitting, which has been conventionally often applied to pipe-shaped materials, has not been able to provide sufficient fastening strength, partly due to the low strength of graphite.

Another possibility is to bond metal and graphite with adhesive, but bonding using adhesive has the disadvantage of poor heat resistance, and furthermore, when used in a vacuum or special atmosphere, gas is generated from the adhesive. becomes a problem.

[Means for solving problems]

The present invention involves bonding a graphite outer cylinder to the outside of a metal inner cylinder by high-temperature bonding means such as diffusion bonding or hard brazing, and forming tapered or curved corners at both ends of the graphite outer cylinder. It is a composite material made of graphite and metal that is characterized by its chamfered edges.

[Effect]

If no measures are taken at the end of the graphite outer cylinder, depending on the material combination, shape, size, etc., the end of the graphite outer cylinder may be damaged during the cooling process after joining due to the difference in thermal expansion between the two. However, according to the present invention, the occurrence of cracks can be prevented by chamfering both end corners of the graphite outer cylinder into a tapered or curved shape.

The graphite outer tube and the metal inner tube of the above composite material are joined together by high-temperature bonding such as hard brazing or diffusion bonding, so the bonding strength is higher and heat resistant compared to mechanical fastening such as shrink fitting or cold fitting. There is. Furthermore, compared to bonding using adhesives, the heat resistance is far superior, and there is no risk of gas release in a vacuum atmosphere.

〔Example〕

In the example shown in FIG. 1, the composite material 5 includes an outer tube 6 made of graphite and an inner tube 7 made of metal inserted into the outer tube 6 of graphite. The graphite outer cylinder 6 has a cylindrical shape or a ring shape with both ends open.

In this embodiment, the metal inner cylinder 7 is cup-shaped with one end open. This metal inner cylinder 7 is made of a metal having a larger coefficient of thermal expansion than graphite, such as copper, nickel, titanium, steel, or an alloy thereof. The metal inner cylinder 7 is not limited to a cup shape, and may be, for example, a vibrator shape with both ends open.

The graphite outer tube 6 and the metal inner tube 7 are bonded to each other via a bonding material 9 by a bonding means performed at high temperature such as diffusion bonding or hard brazing. Binding material 9
is, for example, a cylindrical nickel or titanium foil, but any suitable hard soldering material may be used. The thickness of the bonding material 9 is, for example, about several tens of microns.

The inner diameter of the graphite outer cylinder 6, the outer diameter of the metal inner cylinder 7, and each dimension of the bonding material 9 are determined based on the coefficient of thermal expansion of each material so that each part can be tightly attached to each other when heated to the bonding temperature. Let me know in advance.

The corners of both ends 6a and 6b of the graphite outer cylinder 6 are each tapered chamfered over the entire circumference.

In the composite material 5 having the above structure, the bonding material 9 is set in the metal inner tube 7, inserted into the graphite outer tube 6, and then heated to the bonding temperature. The diameter of the metal inner cylinder 7 is relatively expanded by heating, and it is diffusion bonded (or hard brazed) to the graphite outer cylinder 6 via the bonding material 9.
joined by.

The graphite outer cylinder 6 joined to the metal inner cylinder 7 in this way is subjected to forces in the radial direction, axial direction, etc. due to the difference in coefficient of thermal expansion with the gold mud during the cooling process after joining. Here, if the graphite outer cylinder 6 does not take any measures at both ends as in the conventional case (see Fig. 4), if there is a large difference in the coefficient of thermal expansion in the axial direction, both ends of the graphite outer cylinder 6 Cracks may occur in the parts. However, the graphite outer cylinder 6 of this embodiment has both ends 6a, 6
By chamfering b in advance into a tapered shape, it is possible to prevent cracks from forming during the cooling process and from propagating cracks leading to breakage.

Naturally, the difference in thermal expansion coefficient also appears in the radial direction. However, when the diameter of the graphite outer cylinder 6 is small, for example, on the order of several to several tens of meters, the graphite outer cylinder 6 can maintain a relatively stable bonded state to the metal inner cylinder 7 without taking any special measures. However, if the diameter of the graphite outer cylinder 6 is relatively large and the difference in the coefficient of thermal expansion in the radial direction with respect to the metal inner cylinder 7 becomes a problem, it is desirable to take the following measures.

That is, as shown in FIG. 2, the inner surface 7 of the metal inner cylinder 7
Make a tapered. This tapered inner surface 7a has a presser member 1 made of graphite or a material with a thermal expansion coefficient equivalent to graphite.
0 is inserted. The holding member 10 has a truncated conical shape, and its outer surface is tapered to match the tapered inner surface 7a.

As shown in Fig. 2, the metal inner cylinder 7 is attached to the graphite outer cylinder 6 at room temperature.
Then, the bonding material 9, the pressing member 10, etc. are placed in the cera 1 and heated to the bonding temperature. Due to this heating, the outer diameter and inner diameter of the metal inner cylinder 7 relatively expand, so by applying an appropriate load to the presser member 10 from the direction of arrow F, the presser member 1
Press 0 all the way in.

By heating the presser member 10 to the bonding temperature while pressing it in this manner, the graphite outer tube 6 and the metal inner tube 7 are bonded via the bonding material 9 by diffusion bonding (or hard brazing). When the presser member 10 is cooled while continuing to apply a load, the presser member 10 maintains the fitted state without being pushed out from the metal inner cylinder 7.

In this way, the metal inner cylinder 7 is prevented from shrinking by the internal presser member 10, and is returned to room temperature with its diameter expanded, causing a kind of plastic deformation during the cooling process, so that even if the presser member 10 is removed, the metal inner cylinder 7 is prevented from shrinking. The inner cylinder 7 remains expanded in diameter.

Therefore, it is possible to prevent excessive force from being generated in the peeling direction at the joint surface between the graphite outer cylinder 6 and the metal inner cylinder 7. The holding member 10 is usually removed by an appropriate method after cooling, but if there is no particular problem, it may be left inserted without being removed.

The composite material 5 described above has higher heat resistance and bonding strength than mechanical fitting such as simple shrink fitting or cold fitting. Moreover, unlike the case where adhesives are used, no pollutants are released, so it can be used, for example, in the following applications.

Graphite has an excellent heat resistance of about 2500° C. in a non-oxidizing atmosphere, so by cooling the inside of the metal inner cylinder 7 by an appropriate means, it exhibits excellent high temperature heat resistance. Moreover, because the mechanical bonding strength between the graphite outer @ 6 and the metal inner cylinder 7 is high, it can be used in vibration components such as mechanical seals and bearings under conditions where conventional adhesives and shrink fitting could not be used due to the strength. Is possible. In this case, a suitable material for the metal inner cylinder 7 is a steel-based metal. Graphite is self-lubricating and has low frictional resistance, so it can be used as an oil-free bearing.

Moreover, the composite material 5 obtained by the above method has high heat resistance and does not release pollutant gas even at high temperatures, so for example
When carbon is used as a ta generation target or a sputtering target, it can be used at a higher temperature than before. The target for X-ray generation is used in a vacuum and is heated to high temperatures by irradiation with electron beams, so heat resistance is required, and bonding without contamination in a vacuum atmosphere is required. The material is suitable for this type of application. In this case, the metal inner tube 7 is made of, for example, a copper alloy.

In addition, as shown in FIG. 3, both ends 6a and 6b of graphite
Even if the graphite edges 5a and 5b are chamfered into a curved shape, it is possible to prevent cracks from occurring at the ends 5a and 5b of the graphite, as in the above embodiment.

〔Effect of the invention〕

According to the present invention, when a graphite outer cylinder and a metal inner cylinder having different coefficients of thermal expansion are joined to each other by high-temperature bonding such as diffusion bonding or hard brazing, damage to the graphite can be prevented. Furthermore, the composite material of the present invention is heat resistant and there is no fear of gas release into the atmosphere.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a composite material showing one embodiment of the present invention;
The figure is a cross-sectional view when a presser member is used in the manufacturing process of the composite material shown in FIG. 1, FIG. 3 is a cross-sectional view of a composite material showing another embodiment of the present invention, and FIG. 4 is a conventional FIG. 2 is a cross-sectional view illustrating a composite material. 5... Composite material, 6... Graphite outer cylinder, 5a, 6b...
Both ends, 7... Metal inner cylinder, 9... Binding material. Applicant's agent Patent attorney Takehiko Suzue Figure 2-1 Figure 3 Figure 4

Claims (1)

[Claims] A graphite outer cylinder is bonded to the outside of the metal inner cylinder by high-temperature bonding means such as diffusion bonding or hard brazing, and the corners of both ends of the graphite outer cylinder are chamfered into a tapered or curved shape. A composite material made of graphite and metal that is characterized by: