JPH0554236B2 - - Google Patents

Description

[Detailed description of the invention]

[0001]

FIELD OF THE INVENTION The present invention relates to a silicon carbide resistance heating element, and more particularly to a method for producing a resistance heating element that has a coil shape that has a wide range of applications, is oxidation resistant, and does not deteriorate in strength at high temperatures.

[0002]

[Prior Art] Graphite heating elements processed from graphite materials as heating elements for high-temperature electric furnaces are used in various industrial furnaces because of their excellent heat resistance, thermal shock resistance, and corrosion resistance.

[0003] However, since graphite begins to oxidize at about 500°C in air or in an atmosphere where water vapor is present, it cannot be used in an oxidizing atmosphere, which has the disadvantage that the range of application is limited.

[0004] Conventionally, as a heating element that can be used in air at temperatures below 1600°C, a silicon carbide heating element is known, which is made by kneading and firing silicon carbide powder, a binder, and a sintering aid. ing.

【0005】

[Problems to be Solved by the Invention] However, when this silicon carbide heating element is used in a high-temperature furnace, it cannot absorb the stress generated inside the heating element and tends to crack or creep. However, there were problems such as the inability to suppress oxidative consumption, severe thermal deformation, and vibration during heat generation, which caused poor fixation in the furnace.

[0006] In view of the current situation, the present inventor has repeatedly researched on silicon carbide resistance heating elements and found that the coil shape of the silicon carbide resistance heating element has a hollow structure composed of silicon carbide hollow linear bodies. This increases elasticity and flexibility, prevents the heating element from being improperly fixed in the furnace due to vibrations, eliminates cracks in the heating element caused by stress generated inside the heating element, and prevents the heating element from cracking due to stress generated inside the heating element. It was discovered that oxidative consumption of the resistance heating element can be prevented by flowing an inert gas through the heating element.

[0007] The present invention aims to improve the manufacturing method for efficiently manufacturing a coil-shaped resistance heating element made of such a hollow linear body.

[0008]

[Means for Solving the Problems] That is, the present invention is a method for manufacturing a resistance heating element, which comprises the following steps, and includes the following steps: A first step in which a mixture of two or more types is used as a raw material, is shaped into a coil-shaped flocculent body, and is heated and fired.The coil-shaped article obtained in the first step is reacted with silicon monoxide to form a core. a second step of converting the coiled material into silicon carbide while leaving behind the core portion obtained in the second step;
The third step is to oxidize and remove the carbon part of the core. ” is the gist.

[0009] Coke as a starting material used in the present invention refers to pitch coke, petroleum coke, etc., and carbon black includes channel black, furnace black, lamp black, thermal black, etc. The graphite powder uses natural graphite such as phosphorous graphite, earthy graphite, and other types of graphite and artificial graphite. As the pitch, coal tar pitch, petroleum pitch, etc. are used. As the fibrous material, carbon fiber, silicon carbide fiber, etc. are used. As the synthetic resin, thermosetting resins such as phenolic resin and furan resin, thermoplastic resins such as polyamide and polyimide, and other various polymeric substances are used.

[0010] One or more of the above mixtures are uniformly kneaded using a pressurized and heated kneader.
The blended starting materials are made into a linear body using an extrusion molding machine, and then wound around a core and fixed in a coil shape.

[0011] The molded body thus obtained is 200
Infusible in air at temperatures between ℃ and 300℃. Next, 700℃～
It is carbonized by heating and firing at 2300°C, preferably 1000°C to 1200°C.

[0012] The carbonized coiled material is reacted with silicon monoxide gas to be converted into silicon carbide, leaving the core as an unreacted carbon portion.

[0013] To convert the carbonized coiled material into silicon carbide, in a silicon monoxide gas atmosphere, 1700
It is preferable to carry out heating to a temperature range of .degree. C. to 2300.degree. Here, silicon monoxide gas can be generated by heating a mixture of silicon powder and silicon dioxide powder, or a mixture of carbon powder and silicon dioxide powder to 1400°C to 2300°C.

[0014] When the processing temperature is 1700°C or lower, silicon monoxide gas preferentially reacts with carbon monoxide gas in the atmosphere to produce fine fibrous silicon carbide whiskers, which grow on the carbon surface. No silicon carbide conversion occurs inside the coiled body. On the other hand, if the treatment temperature exceeds 2300°C, the layer converted to silicon carbide will begin to decompose, which is not preferable.

[0015] Obtaining a coil-shaped resistance heating element made of a silicon carbide hollow linear body is achieved by oxidizing and removing the carbon portion of a silicon carbide coil having an unreacted carbon portion in the core. be done.

[0016] As a method of oxidation removal, 600% in air
If the coiled material is left at a temperature of 1500°C to 1500°C, the silicon carbide material obtained by the conversion method is porous and has the same porosity as the carbon material before being converted to silicon carbide. Therefore, the carbon part of the core selectively reacts with the diffused air and is oxidized and removed.

[0017] A coil-shaped resistance heating element made of a hollow linear body made of silicon carbide is heated by flowing an inert gas such as helium, argon, or nitrogen into the hollow part.
Even when used in air at high temperatures of around 2000℃, inert gas easily flows out from the hollow part through the porous thick-walled silicon carbide part to the surface of the heating element. It has the function of forming a film barrier and suppressing the oxidative wear and tear of the silicon carbide layer on the surface.

[0018] In addition, by flowing various gas bodies into the hollow part of the resistance heating element made of a silicon carbide hollow linear body, the gas body at the required temperature can be easily and accurately obtained, which can be used in many ways. The range of applications can be expanded to Generally, the manufacturing method of silicon carbide heating element is as follows:
It was not possible to manufacture products with complex shapes, and post-processing was extremely difficult due to the high hardness of silicon carbide itself. However, a coiled silicon carbide resistance heating element can be easily manufactured by the above manufacturing method.

[0019] Also, cut out from graphite block,
Although it is possible to make a heating element by making a slit or cutting it into a spiral shape and converting it into silicon carbide through a silicification reaction, it is also possible to make a heating element by cutting out a coil shape made of a hollow wire from a graphite block. However, by using the above manufacturing method, it is possible to efficiently manufacture a coiled silicon carbide resistance heating element. Therefore, the above manufacturing method is suitable for industrial production.

[0020] The coil-shaped resistance heating element made of the silicon carbide hollow wire body obtained in this way has a stress absorption ability that does not work with other shaped heating elements due to the coil elasticity, and it has the ability to absorb stress in the furnace due to vibration etc. This prevents the heating element from being improperly fixed, eliminates cracks in the heating element caused by stress generated inside the heating element, and provides flexibility in the design of the furnace. In addition, silicon carbide resistance heating elements are different from silicon carbide sintered bodies that contain sintering aids.
It is a reactive sintered body composed only of silicon carbide, and does not contain low-melting point oxides that would form a liquid phase during high-temperature use, so it does not cause rapid strength deterioration or creep at high temperatures. do not have. Furthermore, inert gas is flowed into the hollow part of the silicon carbide resistance heating element.
It is possible to prevent oxidative consumption of the coiled resistance heating element, and it can be used as a heating element in air up to 2300°C, which is the decomposition temperature of silicon carbide.

[0021]

[Function] In the method for manufacturing a resistance heating element according to the present invention, silicon monoxide gas is diffused and permeated into the carbonaceous coiled material obtained in the first step to convert the carbonaceous coiled material into silicon carbide. Since the silicon carbide method is used, the silicon carbide retains its shape in the first step, and there is no need for post-processing. A coil-shaped resistance heating element made of a silicon carbide hollow linear body can be easily produced by oxidizing and removing the carbon portion of a silicon carbide coil having an unreacted carbon portion in the core. can do.

【0022】

[Examples] Next, the present invention will be specifically explained using examples.

[0023] Example 1 15 parts of petroleum coke, 45 parts of lamp black, 28 parts of artificial graphite powder, 2 parts of earthy graphite powder, and 49 parts by weight of coal tar pitch per 100 parts of resol type phenolic resin 10 parts as carbon aggregate. was placed in a kneader using a combination of two Z-type mixing blades and mixed for 150 minutes. During mixing, the carbon aggregate and coal tar pitch were first thoroughly mixed at room temperature, then heated to 170°C and mixed for 120 minutes. The obtained mixture was fed to an extrusion molding machine and extruded at an extrusion temperature of 150°C into a linear body with a diameter of 3 mmφ.
It was wound into a coil shape as shown in Fig. 1 around a mmφ graphite core. This was made infusible in air at 200°C for 24 hours, and then heated to 2000°C at a heating rate of about 300°C/hr to obtain a carbonaceous coiled material. The obtained carbonaceous coiled material was placed in a sealed graphite container to avoid contact with 2 kg of a mixed molded product of silicon powder and silicon dioxide powder (molar ratio 1.0), heated to 1950°C, and held at this temperature for 30 minutes. did. As a result of this treatment, a coiled product was obtained in which the cross section of the linear body was converted into β-type silicon carbide while the carbon portion remained in the core as shown in FIG. This was placed in a furnace in an air atmosphere at 800°C to oxidize and remove the carbon portion of the core, yielding a coil-shaped resistance heating element made of a silicon carbide hollow linear body as shown in FIG. The power supply terminal portion of the heating element was treated with aluminum metallic. While flowing argon gas at 0.51/min into the hollow part of the heating element obtained, it was heated to 1900℃ in air.
Although it was used 30 times, there was hardly any change in the electrical resistance of the heating element or any cracks or thermal deformation.

【0024】

Effects of the Invention As explained above, the manufacturing method of the present invention increases elasticity and flexibility, prevents the heating element from being improperly fixed in the furnace due to vibrations, etc., and reduces the stress generated inside the heating element. We have developed a resistance heating element in the form of a coil with a hollow interior that eliminates the cracks that occur in the heating element and prevents the resistance heating element from being consumed by oxidation, without the need for post-processing and without size restrictions. It can be easily manufactured and can achieve efficient production, making it an extremely important contribution to industry.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view showing a carbonaceous coiled material heat-treated in a manufacturing method according to the present invention.

FIG. 2 is a schematic sectional view showing a cross-section of a linear body of a coil-shaped product that is being manufactured in the manufacturing method of the present invention, and shows a state in which the periphery is made of silicon carbide while leaving a carbon portion in the core.

FIG. 3 is a schematic cross-sectional view showing a linear body forming a coiled silicon carbide resistance heating element obtained by oxidizing and removing the carbon portion of the core in the manufacturing method of the present invention.

[Explanation of symbols]

1 Coiled resistance heating element 2 carbon 3 Silicon carbide material 4 Hollow part.

Claims (1)

[Claims] 1. A method for manufacturing a resistance heating element, comprising the following steps. The first step is to use one or a mixture of two or more of coke, carbon black, graphite powder, pitch, fibrous materials, and synthetic resin as raw materials, shape it into a coil-shaped cotton body, and heat and bake it. a second step of reacting the coil-shaped material obtained by the step with silicon monoxide to form silicon carbide while leaving the core; heating the substance in an oxidizing atmosphere,
The third step is to oxidize and remove the carbon part of the core.