JPH047078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a graphite resistance heating element reinforced with carbonaceous fibers.

Conventionally, the equipment used for high-temperature firing of various industrial materials such as carbon materials and ceramic materials is as follows:
Many high-temperature heating apparatuses are known, such as resistance furnaces, induction furnaces, arc furnaces, and plasma furnaces, among which resistance furnaces are widely used because their heating means are relatively simple.

By the way, in this resistance furnace, an electric current is normally passed through a tubular resistance heating element, and the workpiece is heated and fired using the Joule heat generated at the time. A graphite resistance heating element (hereinafter simply referred to as a graphite heater) is used in a gas atmosphere. This graphite heater does not melt or decompose during use, compared to heaters made from metal or ceramic materials.
It has the advantage of being resistant to melting and decomposition even in the high temperature range of 2000°C or higher, and is relatively inexpensive.

However, such a graphite heater also has a temperature of 2000℃.
In the above high temperature range, there are the following problems.

In other words, since graphite heaters are mainly composed of carbon, as is generally well known, carbon itself has a temperature of 3.3
11 ^-11 atm, 1.8×10 ^-7 atm at 25000〓 (2227℃),
It has a vapor pressure of 5.4×10 ^-5 atm at 3000〓 (2727℃) and 1.16×10 ^-2 g/cm ² at 2500K (2227℃).
It is also said that the carbon in hr evaporates.

For this reason, graphite heaters not only have durability problems due to evaporation of carbon, especially when used continuously for long periods of time, but also when the heater wears out due to evaporation.
Naturally, the electrical resistance value shifts relative to the depleted portion, further promoting the evaporation of carbon content.
Further, the wear and tear of the heater makes it difficult to maintain the set temperature during heating and firing, and furthermore, the local wear and tear of the heater causes a change in the predetermined temperature profile.

Therefore, how can a graphite heater used in a high temperature range of at least 2000°C reduce wear due to evaporation of carbon content, thereby maintaining a prescribed temperature and temperature profile during continuous heating and firing? This was an important technical issue to be solved today.

The present invention has been made to solve the above-mentioned technical problems in graphite heaters, and its configuration is as follows.

In other words, the fiber length cut into short fibers is 0.05~
1mm carbon fiber and/or fiber length 0.05-1mm
graphite fibers, granular carbonaceous material, and caking material are blended, molded and then fired, and the carbon fibers and/or
Alternatively, it is a graphite resistance heating element reinforced with carbonaceous fibers, which is characterized by containing 1 to 5% by weight of graphite fibers.

The structure of the present invention will be described in detail below. A conventional graphite heater mixes and kneads granular carbonaceous material and an appropriate amount of caking material to form a desired shape (for example,
In contrast, in the present invention, in addition to the granular carbonaceous material and the caking material, the carbonaceous material is cut into short fibers. The graphite heater is characterized by blending and kneading carbonaceous fibers, then molding and firing, and when such a graphite heater is used continuously for a long time, the carbonaceous fibers in the heater are in the form of granules. It acts as a kind of binder or shielding net for the carbonaceous material, suppressing depletion due to evaporation or scattering of carbon content, and this effect is particularly noticeable in high temperature ranges of 2000°C or higher.

In this case, carbonaceous fibers are ordinary carbon fibers or graphite fibers, that is, organic polymer fibers such as polyacrylonitrile fibers, cellulose fibers, and pitch fibers, which are oxidized by heat treatment in an oxidizing atmosphere such as air. It is then obtained by carbonization or graphitization in a high-temperature heating furnace in an inert atmosphere such as nitrogen gas, and this carbonaceous fiber fully exerts a binder or shielding effect on the granular carbonaceous material. In order to
It should be appropriately selected within the range of 0.05 to 1 mm, preferably 0.1 to 0.5 mm. The main reason for this is that when the fiber length is longer than 1 m, kneading with the granular carbonaceous material and caking agent described later tends to become uneven, and 0.05
If the length is too short than mm, the binder or shielding effect of the carbonaceous fibers cannot be sufficiently exerted.

In addition, the blending ratio of carbonaceous fiber is 1 to 5% by weight of the total amount (i.e., the total amount of carbonaceous fiber, granular fibrous material, and caking agent) for the same reason as above. At this time, in particular, the outer layer of the graphite heater is coated with a rich amount of carbon fiber (for example, 3 to 5
% by weight).

Next, the granular carbonaceous material in the present invention is usually coke with a particle size of 0.1 mm or less, and the caking agent is usually coal tar pitch, etc.
It is used in a range of 35% by weight.

The graphite heater of the present invention is manufactured from the above-mentioned carbonaceous fibers, granular carbonaceous material, and caking material by ordinary means, and since the manufacturing means are well known from general literature, the explanation here will be limited to the following: Although I will omit this, mold-inserting is easier than extrusion and can be expected to produce a uniform mixture, and re-impregnating the carbonaceous fiber with the binder after firing and before graphitization increases the reinforcing effect of the carbonaceous fibers. It is preferable.

As mentioned above, the graphite heater of the present invention has carbon fibers cut into short fibers interposed therein.
As a result, the wear and tear caused by evaporation of carbon content, which was a problem with conventional graphite heaters, especially in high-temperature regions of 2000°C or higher, is significantly suppressed, and as a result, the service life of graphite heaters is approximately 1.2 times longer than that of conventional products. It has the excellent effect of being able to be extended, and in addition, the change in temperature or temperature profile is small and can be maintained as specified for a long period of time. Furthermore, since the graphite heater according to the present invention is particularly effective at temperatures above 2000°C where carbon content is actively evaporated,
Of course, it is also applicable to types of resistance heating furnaces other than the above-mentioned Tammann furnaces, such as indirect heating furnaces, high frequency induction heating furnaces, etc.

The present invention will be specifically described below with reference to Examples. In the examples, the fiber diameter, fiber length, and carbon particle diameter are all shown as average values.

Example 1 (1) 3% by weight of carbon fibers with a fiber diameter of 7μ and a fiber length of 0.3mm,
Graphite obtained by blending and kneading 70% by weight of coke with a particle size of 0.1 mm or less and 27% by weight of coal tar pitch as a caking agent, molding under pressure, firing, and re-impregnating with coal tar pitch to graphitize. Practical tests were conducted on the heater at 2500℃ using a Tammann type resistance furnace. As a result, the lifespan of the graphite heater was extended by about 1.2 times compared to the conventional case without carbon fiber.

(2) About the graphite heater obtained above
In practical tests at 1300℃, the product's lifespan was only about 1.03 times longer than conventional products.

Example 2 3% by weight of graphite fibers with a fiber diameter of 6μ and a fiber length of 0.3mm,
It is obtained by blending and kneading 70% by weight of coke with a particle size of 0.1 mm or less and 27% by weight of coal tar pitch as a caking agent, pressurized and molded, and graphitized after firing (without re-impregnating with the caking agent). A practical test was conducted on the graphite heater at 2800℃ using a Tammann type resistance furnace.
As a result, the lifespan of the graphite heater was extended by about 1.15 times compared to the conventional case without carbon fiber.

Claims (1)

[Claims] 1 Carbon fibers cut into short fibers with a fiber length of 0.05 to 1 mm and/or graphite fibers with a fiber length of 0.05 to 1 mm, granular carbonaceous material, and a caking agent are blended, molded, and then fired. A graphite resistance heating element reinforced with carbonaceous fibers, characterized in that the carbon fibers and/or graphite fibers are contained in an amount of 1 to 5% by weight.