JPH07252726A - Method for graphitization of low-density carbon fiber molded form - Google Patents

Abstract

PURPOSE:To provide a method for graphitization of low-density carbon fiber molded form, designed to obtain a product less apt to deform and excellent in producibility and quality, etc. CONSTITUTION:Carbon fiber molded forms each <=1.0g/cm<3> in density are put into graphite vessels 1 which are, in turn, embedded in packing coke 2 and then subjected to graphitization treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for graphitizing a low density carbon fiber molded body.

[0002]

2. Description of the Related Art A low-density carbon fiber molding is used as a precursor of a carbon fiber heat insulating material or a carbon fiber-carbon composite material (C / C composite material), and is graphitized to obtain a C / C composite material. Is getting In this graphitization treatment, a resistance heating type furnace, an induction heating type furnace, etc. are usually used.

[0003]

However, in the conventional graphitization treatment, the efficiency of filling in the furnace is low, and particularly when treating a product having a cylindrical shape, the efficiency is low,
It was not possible to process a large amount. And the inefficiency directly affects the cost, which is a big problem. or,
In order to solve such a problem, even if an attempt is made to use an Acheson furnace that is often used for graphitizing electrode materials, artificial graphite materials, etc., because of high electric resistance, it is difficult to energize and self-heat. , Causing abnormal heat generation,
The product is likely to have uneven processing temperature, the product is prone to creep cracking or deformation due to the furnace pressure (due to the packing coke weight), and the air to be leaked into the product tends to oxidize and exhaust the product to be processed. It was difficult to realize such problems as impurities in the packing coke, etc., tended to increase the amount of contaminants in the product.

[0004]

Therefore, as a result of earnest studies, the inventors of the present invention put an appropriate carbon fiber molded body in a container made of a graphite material instead of simply performing the graphitization treatment in an Acheson furnace. Moreover, it was found that such a problem could be solved by embedding in packing coke and performing graphitization treatment,
The present invention has been reached. That is, an object of the present invention is to provide a method capable of inexpensively mass-producing a high-quality carbon fiber heat insulating material and a C / C composite material, and an object of the present invention is to provide a carbon fiber having a density of 1.0 g / cm ³ or less. This is easily achieved by a method for graphitizing a low-density carbon fiber molded body, which is characterized in that the molded body is placed in a container made of a graphite material, embedded in packing coke, and then graphitized. The present invention will be described in more detail below.

The carbon fiber molded body used in the present invention is mainly composed of carbon fibers and is not particularly limited as long as it is generally used as a raw material such as a C / C composite material, and its density is 1.0 g / cm. ³ or less, more preferably 0.5 g
/ Cm ³ or less. If the density exceeds 1.0 g / cm ³ , the possibility of causing problems such as deformation becomes small, and thus the value of using the method of the present invention is small. In the graphitization treatment of the present invention, the low-density carbon fiber molded body to be heat-treated is placed in a graphite case for treatment. The size (outer size) of the graphite case (Fig. 1) is usually determined by L
Is ~ 2.5 m, W is 0.2-1 m, preferably 0.2-
In the range of 0.5 m, H has a size of ˜1.8 m. The graphite case does not necessarily have to be an integral body, and may be made by appropriately combining graphite plates having an appropriate size. However, in this case, it is desirable to enhance the sealing property in order to keep the shape of the graphite case and further to reduce the oxidation consumption of the molded body housed inside. It is preferable to assemble by a drop lid method or the like.

The thickness of the graphite case or the graphite plate for assembling the graphite case is a balance between the handling weight, the load weight and the easiness of heat generation. When the thickness is large, the weight of the graphite case itself becomes large, which makes it difficult to put the graphite case in and out of the furnace, and the amount of the molded body accommodated in the case becomes small. On the other hand, if the thickness is small, the case may be broken due to the weight of the molded body contained in the case or the weight of the packing course. Therefore 10
It is desirable that the thickness is in the range of -100 mm, preferably 20-50 mm. The electrical resistivity of the graphite material used for the graphite case is 3000 μΩ · cm or less, preferably 150
It is desirable that it is 0 μΩ · cm or less from the viewpoint of heat generation.

An inert gas such as nitrogen or argon may be introduced into the graphite case in order to reduce oxidation consumption of the molded body contained therein and the amount of impurities after the heat treatment. In this case, the packing coke outside the furnace is introduced from the graphite case. A method of feeding gas through the graphite pipe guided above is preferable. An example of the structure of the Acheson furnace used in the present invention is shown as an embodiment of the present invention. As an explanatory diagram, the state seen from above the furnace is shown in FIG.
FIG. 4 shows a state cut along a cross section orthogonal to the energization direction. The size of the Acheson furnace is generally 10 to 25 in length.
m, the width is 1.2 to 2.5 m, and the depth is 1.2 to 2 m, and the graphite case 1 containing the molded body is arranged therein.

It is necessary to arrange the graphite cases at intervals in the furnace length direction. An energization gap is created by this gap and the energization resistance is adjusted to ensure the energization efficiency of the furnace, that is, the heat generation efficiency. The gap is usually adjusted within the range of 10 to 100 cm, and it is desirable to provide at least 5 or more locations. However, if the number is increased, the size of the graphite case is inevitably reduced, and a low density carbon fiber molded body to be housed in the graphite case. There is a restriction on the size of. Since the shape of the furnace is an oblong rectangle, the length L of the graphite case is usually aligned with the lengthwise direction of the furnace. However, due to the above circumstances, the L of the graphite case is limited. It is desirable to arrange the graphite cases in the furnace width direction at intervals.

That is, the main heating surface of the graphite case in the furnace is a surface parallel to the energization direction, but it is possible to disperse the heating surface by disposing a plurality of graphite cases in the width direction of the furnace. Desirable to enhance sex. In this case, if the adjacent graphite cases are too close to each other, the heat generating surfaces will be close to each other, and the temperature of that portion becomes relatively high.
A spacing of 30 cm is desirable. General furnace width,
Due to the arrangement of a plurality of graphite cases and the need to provide an interval between them, W of the graphite case is limited. There are no conditions such as length direction and width direction for the depth direction of the furnace. A graphite case with a height of H, H, which is full of the furnace depth, may be placed. You can stack them without taking them. However, the total height is completely at least 30c in the packing coke 2.
It is necessary to have a thickness of at least m in order to protect the graphite case and the internal molded body from oxidation consumption. In the figure, 3 is a furnace wall, 4 is a current-carrying terminal, and 5 is a hearth.

When arranging the graphite case, a graphite member (a plate, a round bar, etc.) other than the graphite case may be properly arranged for adjusting the electric current path and the heating surface. For example, since the upper surface and side surfaces of the furnace radiate heat, the temperature tends to be lower than that in the central part of the furnace. To prevent this, the top surface of the graphite case,
It is effective to arrange a graphite plate or the like on the side surface on the furnace wall side. The low-density carbon fiber molded body can be graphitized by the above-mentioned method, but it is desirable to measure the temperature in the furnace in order to adjust the processing temperature more accurately. As this method, an inert gas-sealed graphite pipe 6 is introduced from the outer surface of the graphite case in the furnace onto the packing coke outside the furnace.
A general method is to laterally heat the outer surface of the graphite case with a radiation thermometer.

Generally, the heat generated on the plane parallel to the energization direction of the graphite case is early and the heat generated on the vertical plane is delayed as compared with the parallel plane. Therefore, the temperatures at these two points are measured, and the temperature of the parallel plane is the target. When the temperature approaches the processing temperature, the energization amount is adjusted to maintain the processing temperature. Then, during this time, if the temperature of the vertical surface catches up with the processing temperature and the energization is stopped, the entire surface can be processed at a uniform temperature. Hereinafter, the present invention will be described using examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded.

[0012]

【Example】

(Example 1) Phenolic resin (Gunei Kagaku PL-221) was added to defibrated carbon fiber (Mitsubishi Kasei Dilead K-521).
After impregnation with 1), the molded body obtained by hot plate pressing is fired to 1000 ° C. in a retort type external heating type firing furnace,
00 × 1000mm, thickness 52mm, average density 0.19
A low-density carbon fiber molded body of 5 g / cm ² was obtained. This low-density carbon fiber molded body has an inner size of 315 ^W x 1650 ^L x 1190
^H mm 40 mm thick graphite plate (electrical resistivity 740 μΩ
cm)) 6 pieces in a graphite case
I prepared the case. This graphite case is used as shown in Fig.
In an Acheson furnace of 800 mm, furnace width 1200 mm, furnace depth 1300 mm, 7 rows were arranged in the furnace length direction and 2 rows were arranged in the furnace width direction. The graphite case spacing was 430 mm in the energizing direction and 80 mm in the direction perpendicular to the energizing direction.

After the graphite case was installed, packing coke was filled and the graphite case was covered to a height of 550 mm from the upper surface. A graphite pipe having an inner diameter of 20 mm was attached to each graphite case so that N ₂ gas could be poured from outside the packing course. In addition, a graphite pipe sealed with N ₂ gas was introduced from the end faces parallel to and perpendicular to the energization direction of the graphite case installed in the center of the furnace, and the outer surface temperature of the graphite case could be measured with a radiation thermometer. After completion of the above-mentioned set, first, 2 Hr was aerated at a rate of 2 l / min, N ₂ was aerated in the graphite case, and then N ₂ was stopped to start the energization of the furnace. The temperature of the plane parallel to the energization direction of the graphite case reached 2500 ° C. 59 hours after the start of energization, so the applied power was reduced, and after 21 hours, the energization was stopped when the temperature of the vertical plane reached 2460 ° C. From 3 hours before the stop of energization,
N ₂ was again bubbled into the graphite case at a rate of 0.5 l / min, and cooling was continued thereafter, and the flow was continued until the product was taken out after 8 days. After cooling the furnace, the packing coke was removed, the graphite case was taken out, and the carbon fiber molded body inside was taken out.

The obtained carbon fiber molded body showed no abnormal appearance except that a part of carbon-like carbon was adhered to it.
Almost no oxidative consumption was observed. Further, the thickness of the molded body was reduced by an average of 1.8% due to graphitization shrinkage, but there was no warpage or deformation. The ash content of the molded body was 287 ppm on average.

[0015]

Comparative Example 1 1500 × 10 obtained in the same manner as in Example 1
00 mm, thickness 52 mm, average density 0.196 g / cm
Six low density carbon fiber moldings of ³ , 1500 x 1000
It was installed in the Acheson furnace as shown in FIG. 6 in such a manner that two graphite plates having a thickness of 40 mm and a thickness of 40 mm were sandwiched from both sides. 7 products such as extruded carbon plates were arranged around the product. After the whole was embedded in a packing coke, it was electrically heated according to a conventional method, and after cooling, the molded body 8 was taken out. The heat treatment temperature estimated from the X-ray bending index (d00 ₂ ) of the molded product was 2550 ° C. In the obtained molded body, the thickness was reduced by 5.6% on average, and the portion in contact with the packing coke was remarkably oxidized and consumed, and the inner portion was partially eroded by about 200 mm. The ash content was 1230 ppm on average (9: graphite plate).

[0016]

EFFECTS OF THE INVENTION The present invention can provide a method for graphitizing a low-density carbon fiber molded body which is resistant to deformation and is excellent in productivity and quality.

[Brief description of drawings]

FIG. 1 is an explanatory view of a container made of a graphite material used in the present invention.

FIG. 2 is an explanatory view of a container made of a graphite material used in the present invention.

FIG. 3 is an explanatory view showing a state where the method of the present invention is carried out using an Atchison furnace.

FIG. 4 is an explanatory view showing a state in which the method of the present invention is carried out using an Acheson furnace, which is cut along a cross section orthogonal to the current-carrying direction.

FIG. 5 is an explanatory view showing a state of the Acheson furnace used in the examples of the present invention (a state viewed from the furnace top surface direction and the furnace cross-sectional direction).

FIG. 6 is an explanatory view showing the state of the Acheson furnace used in the examples of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryo Yashima Shima 122-1 Ogasawara, Kushigata-cho, Nakakoma-gun, Yamanashi Toyo Carbon Co., Ltd. Yamanashi factory

Claims (1)

[Claims] 1. A low-density carbon fiber molded product characterized by containing a carbon fiber molded product having a density of 1.0 g / cm ³ or less in a container made of a graphite material, embedding it in packing coke, and then subjecting it to graphitization treatment. Graphitization treatment method.