KR20180129447A - A manufacturing method for carbon heater - Google Patents

Abstract

The present invention relates to a method for manufacturing a carbon heater used in a heating device field such as an electric oven. According to the present invention, the method for manufacturing a carbon heater, including: a carbon composite composition mixing process, an extrusion process, a stabilization heat treatment process; and a carbonization heat treatment process is provided, thereby preventing insulation breakdown, sparks, and plasma in the carbon heater and providing the carbon heater with various mechanical and electrical characteristics.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a carbon heater,

The present invention relates to a method for producing a carbon heater for use as a heater for applying heat in the field of cooking appliances such as an oven, and a method for producing a carbon heater using a new carbon composite composition.

In recent years, ovens using a heater as a domestic or commercial cooking appliance have been widely used.

1 is a perspective view showing a general structure of an oven. Referring to Fig. 1, the oven 1 is provided with a cavity 2 in which food to be cooked is placed, a door 3 for selectively opening the cavity 2, And a plurality of heaters 6 for applying heat to the cavity 2 are mounted.

Particularly, the heater 6 is equipped with one or more heaters, and the heater 6 is protected by the cover 8 from the outside of the cavity. Further, in order to apply the electromagnetic wave heating method, a magnetron 4 is mounted outside the upper surface of the cavity 2. Electromagnetic waves generated from the magnetron 4 emit electromagnetic waves into an internal space of the cavity 2 through a predetermined waveguide and a heater. A sheath heater 5 is mounted on the upper side of the inner space of the cavity as required.

The operations of the heaters differ depending on the material of the heater, the heating method, and the like. Among the heaters, the carbon heater, which is generally used as the sheath heater 5 and the heater 6, is a grill heater that heats food inside the cavity 2 by a radiant heating method.

In the case of carbon heaters, carbon fibers (CFs) were conventionally used. Generally, carbon fiber refers to a fibrous carbon material having a carbon content of 90% or more.

Since the carbon fiber is made of a material called 'carbon', it has the microwave absorption characteristic of carbon itself. In addition, carbon fibers have inherent characteristics that the ratio of fiber length to fiber diameter is essentially very large due to the nature of the 'fiber'.

The inherent properties of such carbon fibers create some problems when using carbon fibers as a heating source in an oven.

First, as shown in Fig. 2, the carbon fibers are made of carbon filaments. However, the filaments have not only a diameter but also a spacing between filaments and filaments of several micrometers. Thus, under high electromagnetic fields, a high voltage is applied at very narrow distances (spacing) between the filaments. For example, when a voltage of 10 V is applied at an interval of 1 占 퐉, a high voltage of about 107 V / m is applied between filaments and filaments. In this case, the filaments are likely to cause dielectric breakdown and sometimes sparks.

The carbon heater includes a carbon fiber, a connector for applying electricity to the carbon fiber, a quartz tube containing the carbon fiber and the connector therein, and an assembly Unit). Further, the sealed gas maintains a vacuum atmosphere of about 10 ^-1 to 10 ^-2 torr. However, as described above, when a high voltage is applied between the filament and the filament, a plasma is generated due to an inert gas atmosphere under a high voltage even if insulation breakdown or sparking of filaments is not generated.

Conventionally, a shield member is provided between the carbon heater and the cabin to suppress the reaction of plasma or the like and the propagation of light due to the plasma to the cabin. However, since the shield member not only shields the plasma light but also partially blocks radiation emitted from the carbon heater, there is a problem that the radiation efficiency of the oven is greatly lowered.

Therefore, a new type of carbon heater which does not have a conventional fiber shape is required, and a manufacturing method for manufacturing a new type of carbon heater should also be developed.

On the other hand, Korean Patent Laid-Open Publication No. 10-2011-0109697 (October 10, 2011) discloses a related art related to the present invention.

An object of the present invention is to provide a carbon heater which does not generate dielectric breakdown, spark, and plasma even under a high voltage in a carbon heater.

It is another object of the present invention to provide a novel manufacturing method for manufacturing a new carbon heater.

According to an aspect of the present invention, there is provided a method of manufacturing a carbon composite material, the method comprising: mixing a carbon composite material composition; An extrusion process; Stabilization heat treatment process; Carbonization heat treatment process; A method of manufacturing a carbon heater can be provided.

Preferably, the composition is a method for producing a carbon heater including a resin as a binder, a lubricant, and a base material for determining a specific resistance of the resistance heating body at a high temperature.

Preferably, the composition is a method for producing a carbon heater including a resin as a binder, a lubricant, a base material for determining a specific resistance of the resistance heating body at a high temperature, and a resistivity adjusting agent.

Particularly, the resin is a Novolac resin production method.

In particular, the lubricant is a graphite carbon heater.

Particularly, the base material is a silicon carbide (SiC) production method.

Also, the resistivity adjusting agent is a silicon oxide (SiO2).

Preferably, the extrusion process is performed at a speed of 100 to 180 at a speed of 10 to 120 rpm.

Preferably, the stabilization heat treatment process is performed at 270 to 320 ° C for 10 minutes to 2 hours.

Preferably, the carbonization heat treatment step includes a first carbonization heat treatment step of performing out-gassing at 600 to 1,000 ° C for 10 minutes to 2 hours.

Particularly, the carbonization heat treatment process includes a second and a third carbonization heat treatment process.

Also, the second carbonization heat treatment step is performed at 1,200 to 1,400 ° C for 10 minutes to 4 hours, and the third carbonization heat treatment step is performed at 1,500 to 1,700 ° C for 10 minutes to 4 hours.

The method of manufacturing a carbon heater of the present invention can produce a bulk carbon heater not in the form of a fiber unlike a carbon heater using a conventional carbon fiber, The local voltage concentration does not occur, and the dielectric breakdown, the spark and the plasma can be prevented originally.

Further, the carbon heater manufacturing method of the present invention can manufacture the carbon heater in various shapes, and thus it is possible to easily produce the carbon heater of the desired shape required for the oven of various sizes and shapes.

In addition, the carbon heater manufacturing method of the present invention can provide a carbon heater having various mechanical and electrical characteristics by changing the composition and the composition range of the raw material.

Meanwhile, the carbon heater manufacturing method of the present invention can control the electric characteristics of the carbon heater by controlling the carbonization heat treatment process even in the composition and composition range of the same raw material, thereby greatly improving the degree of freedom of the electrical design of the carbon heater.

1 is a perspective view showing a general structure of an electric oven.
2 is an enlarged view of the carbon fiber.
3 is a flowchart schematically showing a method of manufacturing a carbon heater using the carbon composite composition of the present invention.
Fig. 4 shows the result of DSC thermal analysis of raw materials made of novolak resin and silicon carbide.
5 is a microstructure photograph of the surface (a, c) and cross section (b, d) of the carbon composite composition after extrusion (a, b) and after stabilization heat treatment (c, d) of the present invention.
FIG. 6 is a graph showing the carbon microstructure of the carbon composite heat-generating body subjected to the second carbonization heat treatment step and (b) the carbon obtained through the third carbonization heat treatment step after the second carbonization heat treatment step, which were observed by a scanning electron microscope (SEM) This is a microstructure photograph of a cross section of a composite heating element.
7 is a photograph of a surface (a) and a cross section (b) of a stabilized heat-treated carbon composite material using the three-component carbon composite composition of Example 1 of the present invention.
8 is a photograph of a surface (a) and a cross section (b) of a stabilized heat-treated carbon composite material using the four-component carbon composite composition of Example 2 of the present invention.
9 is a view illustrating a carbon heater product made of a heating element using the composition of the present invention.
10 is a photograph showing a heating operation state of a carbon heater produced using the four-component carbon composite composition of Example 2 of the present invention.
11 shows the electric resistance value of the carbon heater according to the temperature of the third carbonization heat treatment process, which was produced using the four-component carbon composite composition of Example 3 of the present invention.
12 shows the thermal conductivity characteristics of the carbon heater according to the third carbonization heat treatment process temperature.

Hereinafter, a method of manufacturing a carbon heater according to a preferred embodiment of the present invention and a carbon heater manufactured by the method will be described in detail with reference to the drawings attached hereto.

It is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to inform.

First, a manufacturing method for manufacturing a carbon heater according to the present invention will be described.

FIG. 3 is a view for explaining a method for manufacturing a carbon heater according to the present invention, which comprises mixing a raw material (hereinafter referred to as carbon composite composition, composition or raw material) made of a carbon composite composition, an extrusion process, a stabilizing heat treatment process, .

First, the manufacturing method of the present invention starts from the step (S 100) of uniformly mixing the raw materials. In the method of mixing the raw materials, the raw materials having desired components and composition ranges are prepared, and then the raw materials are mixed for a sufficient time by using a mill. In the present invention, they are mixed for 2 hours using an attrition mill, but the present invention is not limited thereto. Also in the pulverizer, a ball mill, a crushing mill, a pin mill, as well as a jet mill, a vibrating mill, a colloid mill and the like may be used.

The raw material used in the present invention is a carbon composite composition comprising a resin as a binder, a lubricant, and a base material for determining a specific resistance of the resistance heating body at a high temperature.

Further, in the present invention, a carbon composite material composition containing a resin as a binder, a lubricant, a base material for determining a specific resistance of the resistance heating body at a high temperature, and a resistivity adjusting agent may be used as a raw material.

First, the binder is a component added for mechanical bonding between the powders at a relatively low temperature before the inorganic powders serving as a heating element of the carbon heater are bonded by diffusion at a high temperature. The binder in the present invention also functions as a source of carbon, which is the main component of the carbon heater, which is the final product.

In the present invention, as one embodiment of the binder, Novolac resin, which is a kind of phenol resin having excellent heat resistance, is used. Novolac resin is one of the phenolic resins produced by the reaction of phenol and formaldehyde, and is made when the catalyst is acid (Acid). However, it is not necessarily limited to a phenol resin, particularly a novolak resin, as a binder. Specifically, in addition to novolak resin, a resol resin among phenol resins is also possible. Further, in addition to the phenol resin, an organic resin that can be used as a binder generally responsible for an adhesive function, such as acrylic resin, is all possible.

More specifically, the Novolac resin can be obtained by reacting phenol with formaldehyde at a compounding molar ratio of 0.5 to 1.0 using an acidic catalyst such as sulfuric acid, hydrochloric acid, or the like. Since the condensation reaction takes place rapidly in the presence of an acidic catalyst, a large number of phenol nuclei are linked by a methylene group, and therefore, it is a thermoplastic resin itself and has a property of not curing without a curing agent. Cured by condensation curing or thermosetting, usually mixed with hexamine and cured by heating. However, as will be described in detail in the extrusion process, the present inventors have confirmed that the novolak resin in the present invention has an advantageous effect that a curing agent is not required in the extrusion process and the stabilization heat treatment process.

The present invention also includes silicon carbide (SiC) as a base material for determining the resistivity of the heating element in the carbon heater, which is the final product.

Silicon carbide is characterized by lower electrical resistivity and relatively higher electrical conductivity and thermal conductivity than inorganic powder of other components. The electrical properties of the base material are fundamental properties that must be provided for use as a heating element in a carbon heater. Also, the thermal conductivity is also important because, when the thermal conductivity is low, the operating temperature when used as the carbon heater is extremely high, which is about 1,200 ° C., so if the heat is not smoothly discharged around the heater, the heating element may break.

In addition, the raw material of the carbon composite composition of the present invention contains graphite as a lubricant. The lubricant is used to reduce the friction between the raw material and the die when the raw material is extruded.

Generally, since carbon is used as a main material, graphite, carbon black, and activated carbon, which are lubricants containing carbon as a main material, can be used.

On the other hand, in the present invention, in addition to graphite as a lubricant and a carbon source, another function of graphite was confirmed. As described above, it is known that the novolak resin used as a binder in the present invention is not cured by itself. The process such as simply raising the temperature can not cure the novolak resin. Therefore, in order to cure the novolak resin, a separate curing agent (for example, a curing agent such as hexamine) must be included.

If a resol resin is used as a binder among other phenolic resins, a separate curing agent is unnecessary. This is because the resol resin can be thermally cured without a separate curing agent.

In the case where another resin such as an acrylic resin is used as the binder, the binder may be cured by using a curing agent or by using heat curing or photo curing if necessary. If photocuring is used, a photoinitiator may be further included, and various additives may be included.

In the present invention, it is not known what kind of mechanism is used yet. However, when the graphite is contained in the carbon composite composition to which the curing agent of the present invention is not added, the carbon composite composition itself is hardened after the extrusion process without addition of the curing agent. . Therefore, the carbon composite raw material of the present invention may perform the function of the lubricant and the curing agent simultaneously with the graphite without requiring a separate curing agent depending on the kind of the binder. Of course, when a binder of another component is used depending on the component of the binder, the curing agent may be necessarily included in the carbon composite composition together with the binder.

In addition, the carbon composite composition as a raw material of the present invention may include a resistivity adjusting agent for controlling the resistivity of the heating element in the carbon heater, which is the final product, if necessary.

The resistivity adjusting agent performs the function of raising or lowering the resistivity of the heating element of the carbon heater. In the present invention, a silicon carbide having a relatively low resistivity is used as the base material, and therefore, a material capable of raising the resistivity is mainly used as the resistivity adjusting agent.

Typically, oxides generated by phonons (or lattice vibrations) without electrical conduction by electrons are typically known as materials with high resistivity. In the present invention, silicon oxide (SiO ₂ ) or aluminum oxide (Al ₂ O 3) was used as a resistivity adjusting agent.

However, the silicon oxide is more preferable as the resistivity adjusting agent than the aluminum oxide because the melting point of the silicon oxide is lower than that of the aluminum oxide, so that the control (increase) of the resistivity of the carbon heater can be more easily controlled to be.

Next, in the manufacturing method of the present invention, a step (S 200) of extruding using a uniform raw material is performed.

The extrusion process in the present invention is carried out at a temperature of 100 to 180 DEG C at a speed of 10 to 120 rpm. If the extrusion temperature is lower than 100 캜, the viscosity of the binder is high and it is difficult to bond with the ceramic powder, and the mechanical stability of the extrudate after extrusion is reduced. On the other hand, if the extrusion temperature is higher than 180 ° C, the binder reacts with graphite to initiate curing, which forms a polymer network, so that the extrudate becomes too hard to be extruded.

In the present invention, an injection process using a mold may be applied instead of the extrusion process.

The principle of the extrusion process is that the polymer components are melted in the screw extruder and then advanced along the screw channel and then extruded through the die at the end of the extruder by the high pressure formed at the end of the screw. Therefore, while the extrusion process has an advantage of high productivity, the density, strength, surface roughness, or linearity of the product are less favorable than the injection process.

In contrast, in the injection process, the polymer material or the polymer-containing raw material is transferred to the front side of the cylinder while the polymer component is melted. When the transfer is finished, the polymer or polymer component melt transferred to the screw or plunger is passed through the nozzle at the end of the cylinder It uses a way to let it flow into the mold. Therefore, the injection process is advantageous in that the shape is designed according to the mold design, the density and the strength of the product, and the surface roughness are superior to the extrusion process.

FIG. 4 is a DSC thermal analysis result showing a curing reaction which occurs when a raw material composed of noble-lock resin and silicon carbide, which is one embodiment of the present invention, is heated.

As shown in FIG. 4, when the content of the resin increases in the carbon composite composition as a raw material, the initiation temperature, peak temperature, and termination temperature at which the curing reaction occurs are increased. Therefore, the upper limit of the extrusion temperature in the present invention is determined to be around 180 DEG C, which is the curing initiation temperature of the resin used as the binder in the present invention.

According to the manufacturing method of the present invention, the stabilization heat treatment step (S 300) is performed after the extrusion step. The stabilization heat treatment process (S 300) is a heat treatment process for inducing a bond structure of carbon and oxygen in the binder. As a result of the stabilization heat treatment process, the binder is cured so that the extruded carbon composite composition maintains the extruded shape and secures mechanical stability.

In the stabilization heat treatment process, the viscosity of the binder is lowered firstly as the process temperature is increased, so that a densification process is performed to fill the gap between the ceramic powders. After the stabilization heat treatment process, the hardening reaction is completed and the extruded shape is stably maintained .

5 is a microstructure photograph of the surface (a, c) and cross section (b, d) of the carbon composite composition after extrusion (a, b) and after stabilization heat treatment (c, d).

The microstructure of the carbon composite composition after extrusion shows that the ceramic powder is coated with a binder resin, and the binder resin fills the gap between the powder without relatively large voids. However, the cross-sectional microstructure shows a somewhat faceted shape in part because the temperature during the mixing process or extrusion process is not high enough to cause the binder to flow and the binder is not sufficiently coated with some ceramic powders to be.

On the other hand, after the stabilization heat treatment, the microstructure shows a larger surface irregularity than the microstructure after extrusion. In addition, the cross-sectional microstructure shows roundness in most areas after stabilization heat treatment. This is because not only the curing reaction of the binder during the stabilization heat treatment but also the viscosity of the binder decreases as the temperature rises, so that the binder in which the fluidity of the ceramic powder is increased is coated and the binder between the ceramic powders is filled up by the binder. Due to the densification process caused by the stabilization heat treatment process, fine shrinkage occurs on the surface to cause fine irregularities on the surface, and the shape of the particles in the cross-sectional microstructure is more curved than the particles after the extrusion process I have.

Meanwhile, the stabilization heat treatment process in the present invention is performed at a temperature of 270 to 320 ° C in the air for 10 minutes to 2 hours. In particular, the lower limit value of the process temperature is determined by the thermal property of the binder. As shown in FIG. 4, the crystallization completion temperature of the Novalock resin as a binder in the embodiment of the present invention is about 270 ° C. Therefore, if the stabilizing heat treatment process is performed at a temperature lower than 270 ° C, the curing of the binder can not be guaranteed. On the other hand, although the upper limit of the stabilization heat treatment temperature is not technically limited, it is preferable not to raise the temperature to an excessively high temperature in terms of energy.

The rate of temperature rise in the stabilization heat treatment process is preferably 1 to 10 占 폚 / min. From the viewpoint of microstructure, the slower the heating rate is, the slower the temperature is, the slower the process time is, the longer the process time per unit process is, and the productivity is greatly decreased. On the other hand, when the temperature increase rate is higher than 10 ° C / min, the reaction time is not sufficient, resulting in defects in the final microstructure and durability.

Next, the cured carbon composite composition is subjected to a carbonization heat treatment process (S 400). In the carbonization heat treatment process, outgassing of the volatile components among the constituent components of the carbon composite composition is first performed, and then carbonization of most of the remaining components is performed to form an active ingredient of the carbon heater resistor, . To this end, the carbonization heat treatment process of the present invention includes a first carbonization heat treatment process and a second carbonization heat treatment process.

First, the first carbonization heat treatment step is performed in an inert gas atmosphere such as nitrogen at a relatively low temperature of 600-1,000 DEG C for 10 minutes to 2 hours compared with the subsequent second carbonization heat treatment step, and the other components And other components other than carbon which may be present in impurities contained in components other than the binder among the components of the composition.

After the first heat treatment carbonization process, a second carbonization heat treatment process is performed. In the second carbonization heat treatment step, the components of the carbon composite composition remaining after the outgassing step are carbonized, and are carried out at a temperature of 1,200 to 1,400 ° C for 10 minutes to 4 hours under an inert gas atmosphere such as nitrogen. When the temperature of the second carbonization heat treatment step is lower than 1,200 ° C, there is a problem that the carbonization of the components is incomplete and the electric conductivity of the heating element of the carbon electrode is lowered. On the other hand, when the temperature of the second carbonization heat treatment step is higher than 1,400 ° C, the vaporization of the "-CC-" structure caused by the binder material or the like occurs too much, and the yield of the heating element of the carbon electrode is greatly lowered do.

In addition, the carbonization heat treatment process may be integrated into a single carbonization heat treatment process without being divided into the first carbonization heat treatment process and the second carbonization heat treatment process in order to improve the productivity. In this case, adjustment of other process conditions such as changing the temperature raising rate for smooth outgassing can also be performed.

On the other hand, the inventors of the present invention confirmed that, even when the same carbon composite composition is used, the electrical properties of the carbon heater as the final product can be changed through the carbon heater manufacturing method of the present invention.

In particular, in order to reduce the amount of electric power used in the heater under the condition of being used as a carbon heater, it is necessary to raise the electric resistance of the heater heating element to a certain level within the specification.

Therefore, the present inventors have succeeded in oxidizing or vaporizing a part of the "-CC-" structure resulting from the binder material or the like around the silicon carbide as the base material or by melting (melting) the silicon oxide (SiO 2) And melted to reduce the cross-sectional area of electrons passing through the silicon oxide by coating the silicon carbide as a base material. Through this, the mean free path of electrons was shortened by decreasing the electron collision time, so that the electric conductivity of the heater heating body was reduced and the electric resistance was increased.

To this end, the inventors of the present invention have found that the melting point (1,600 ° C) of the silicon oxide is not higher than the melting point of a metal oxide having a high specific resistivity such as aluminum oxide (Al 2 O 3, 2,072 ° C) or zirconium oxide (ZrO 2, 2,715 ° C) And a third carbonization heat treatment step was added after the second carbonization heat treatment step.

In the third carbonization heat treatment step of the present invention, the electrical conductivity and the electrical resistivity are increased, and the mechanical strength, which is a condition to be satisfied by the heater heating body, is greatly improved. This is because some of the fused silicon oxides fill voids or defects, especially between the ceramic powders present on the surface, to remove surface defects which are a major cause of brittle fracture in the ceramic material.

In addition, the third carbonization heat treatment process in the present invention causes a change in the thermal conductivity of the carbon heater. This is due to the change in the composition and microstructure in the composition for the heater heater due to the molten silicon oxide

The third carbonization heat treatment process in the present invention is performed at a temperature of 1,500 to 1,700 DEG C for 10 minutes to 4 hours under an inert gas atmosphere such as nitrogen.

When the temperature of the third carbonization heat treatment step is lower than 1,500 ° C, vaporization of the "-C-C-" structure caused by the binder material or the like occurs too much, and the yield of the heating element of the carbon electrode is lowered. In addition, when the temperature of the third carbonization heat treatment process is lower than 1,500 ° C., the thermal conductivity of the carbon electrode is too low, which can not transmit the high heat of the carbon electrode to the surroundings during heating, resulting in disconnection.

On the other hand, when the temperature of the third carbonization heat treatment step is higher than 1,700 DEG C, the molten silicon oxide reacts with the "-C-C- " structure resulting from the binder material or the like and is converted into silicon carbide. As a result, the proportion of molten silicon oxide coating the silicon carbide is reduced and the resistivity is rather reduced.

6 is a cross-sectional view of a carbon composite heating element subjected to the second carbonization heat treatment step (a) or the second carbonization heat treatment step to the third carbonization heat treatment step (b) by a scanning electron microscope (SEM) to be.

The carbon composite heating element (a), which has been subjected to the second carbonization heat treatment step, has a microstructure in which a " -C-C- "structure derived from a binder resin surrounds silicon carbide or silicon oxide having a size of 20 to 40 mu m. Since the bonding strength of the "-CC-" structure to the silicon carbide or silicon oxide is weaker than the bonding strength of the silicon carbide or silicon oxide itself, the surface of the silicon carbide or silicon oxide in the microstructure showing the fracture surface of the carbon composite It is observed relatively smoothly.

On the other hand, the carbon composite heat generating element (b) which has been subjected to the third carbonization heat treatment step is formed by melting or melting a part or a plurality of silicon oxides to coat the surrounding silicon carbide, - "are oxidized or have vaporized microstructure. When the molten silicon oxide is coated with the surrounding silicon carbide, the bonding force between the molten silicon oxide and the silicon carbide is much stronger than the bonding force between the conventional " -CC- "structure and the silicon carbide or silicon oxide, As a result, in the microstructure of the fracture surface of the carbon composite, the silicon oxide fused and coated on the surface of the silicon carbide remains in a fine shape like the residue.

Thus, the microstructure observation results are in good agreement with the expectation that the melting of the silicon oxide in the third carbonization heat treatment process will occur in the present invention.

Hereinafter, the present invention will be described in more detail by way of examples through various embodiments. The following examples are merely illustrative of the present invention in order to more clearly illustrate the present invention, and the present invention is not limited thereto.

Example  One

First, a ternary carbon composite composition was prepared by adding 74 wt.% (Hereinafter referred to as%), 23%, and 3% of graphite as a lubricant to silicon carbide (SiC) as a binder,

The prepared three-component composition was uniformly mixed through a raw material mixing process using a crusher for 1 to 4 hours, extruded at 120 to 160 ° C, and stabilized at 280 to 300 ° C. The first carbonization heat treatment process and the second carbonization heat treatment process were performed for one hour at the temperatures of 800 ° C. and 1,400 ° C. for the outgassing and carbonization, and the heating element made of the carbonized heat treated carbon composite was processed by the final carbon heater, The properties were evaluated.

7 shows the surface and cross-section of the three-component carbon composite material after the stabilization heat treatment process. As shown in FIG. 7, the carbon composite material composed of the three-component composition has excellent macroscopic mechanical stability and shows almost no defects on the surface. It is also seen that the silicon carbide is uniformly distributed by the binder even in the cross-section microstructure of the carbon composite material, without segregation, aggromeration, or macropores.

A carbon heater was manufactured using the three-component composition of Example 1, and electrical characteristics were evaluated. At an applied voltage of 115 V, the electric resistance of the carbon heater was measured to be about 4 to 5 OMEGA.

Example  2

Among the inorganic powder components, 62%, 12%, 23% and 20% of graphite as a lubricant were added to an inorganic powder further containing silicon oxide (SiO2) as a resistivity modifier based on silicon carbide (SiC) 3% by weight of a carbon black composite composition was prepared.

The prepared four-component compositions were uniformly mixed with each other under the same conditions as in Example 1, and then extruded through a raw material mixing step. Thereafter, after the stabilization heat treatment, the first carbonization heat treatment and the second carbonization heat treatment, Carbon heaters were used to evaluate electrical properties.

Fig. 8 shows the surface and cross section of the carbon composite material of the four-component system after the stabilization heat treatment process. As shown in Fig. 8, the carbon composite material composed of the four-component composition has excellent macroscopic mechanical stability as in the case of the carbon composite material composed of the three-component composition in Example 1, . It is also seen that the silicon carbide is uniformly distributed in the cross-sectional microstructure of the carbon composite material without segregation, agglomeration, or macropores. In particular, it was confirmed that silicon carbide and silicon oxides were uniformly dispersed without macroscopic / micro segregation.

9 is a view illustrating a carbon heater product made of a heating element 11 using the composition of the present invention. The actual carbon heater includes a heating element 11 and a connector 14 for supplying power from the outside while supporting the heating element 11. A metal wire 15 for supplying electricity to the heating element from the outside, a metal piece 16, an outer electrode 17, an insulator 18 And a terminal terminal 19 are also included.

10 shows a heating state of a carbon heater made of a heating element using the four component composition of Example 2. Fig. Since the carbon heater according to the present invention does not use carbon fiber, the heating state is stably maintained without generating sparks and plasma due to dielectric breakdown. On the other hand, the heating element made of the four component composition of Example 2 had a saturation resistance of about 13? At an applied voltage of 115 V, and the output was measured at about 950 W.

Example  3

First, an inorganic powder containing silicon oxide (SiO2) as a resistivity modifier based on silicon carbide (SiC), graphite as a lubricant, and graphite as a binder were mixed in an amount of 56 to 59%, 15 to 18 %, 23%, and 3% of the composition were prepared.

The prepared four-component compositions were uniformly mixed under the same conditions as in Example 1 until the second carbonization heat treatment process, and then extruded and then subjected to a stabilization heat treatment process, a first carbonization heat treatment process and a second carbonization heat treatment process . Next, the carbon composite material compositions were further subjected to a third carbonization heat treatment process in a temperature range of 1,500 to 1,900 ° C. Subsequently, the carbon composite heater elements composed of the four-component carbon composite composition of the composition range in which the third carbonization heat treatment process was performed were processed with a final carbon heater to evaluate electrical characteristics.

11 shows the resistance of the carbon heater according to the temperature of the third carbonization heat treatment process (PN, GP, SC and SO in FIG. 10 denote novolak resin, graphite, silicon carbide and silicon oxide, respectively).

The embodiments in which the third carbonization heat treatment step was performed at 1,500 to 1,700 ° C showed that the third carbonization heat treatment step was not performed or that the electrical resistivity was greatly increased as compared with the embodiments in which the third carbonization heat treatment step was performed at 1,800-1,900 ° C Able to know.

This result means that the resistance and the output of the carbon heater can be easily controlled through the addition of the third carbonization heat treatment step in the present invention even in the carbon composite composition having the same composition and composition range. This can significantly increase the degree of freedom of the electrical design of the carbon heater by using only the process parameters, which is very useful for practical purposes.

12 shows the thermal conductivity characteristics of the carbon heater according to the third carbonization heat treatment process temperature.

The thermal conductivity of the carbon heater of the present invention increases as the temperature of the third carbonization heat treatment process increases beyond 1,400 ° C, but after 1700 ° C, the thermal conductivity tends to be stabilized or slightly decreased.

The silicon oxide having a low thermal conductivity becomes unstable as the third heat treatment temperature is increased, and as a result, the silicon oxide is transferred to the surrounding carbon contained in the composition and phase-transformed into silicon carbide having a high thermal conductivity. As the ratio of silicon carbide with high thermal conductivity increases, the macroscopic thermal conductivity of the carbon heating element increases.

Even if the third heat treatment temperature is further increased, since the phase transition has already been almost completed at around 1,600 DEG C, the thermal conductivity of the carbon heating element is measured to be substantially unchanged or slightly decreased even when heated to a higher temperature.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the invention is not limited to the disclosed exemplary embodiments. It is obvious that a transformation can be made. Although the embodiments of the present invention have been described in detail above, the effects of the present invention are not explicitly described and described, but it is needless to say that the effects that can be predicted by the configurations should also be recognized.

1: Oven 2: Cavity
3: Door 4: Magnetron
5: Sheath heater 6: Heater
11: Heating element 12: tube
14: connector 15: metal wire
16: metal piece 17: outer electrode
18: insulator 19: terminal terminal
S 100: mixing step S 200: extrusion step
S 300: stabilization heat treatment process S 400: carbonization heat treatment process

Claims (12)

Carbon composite composition;
An extrusion process;
Stabilization heat treatment process;
Carbonization heat treatment process; Of the carbon heater.
The method according to claim 1,
Wherein the composition comprises a phenol resin as a binder, a lubricant, and a base material for determining a specific resistance of the resistance heating body at a high temperature.
The method according to claim 1,
Wherein the composition comprises a phenol resin as a binder, a lubricant, a base material for determining a specific resistance of the resistance heating body at a high temperature, and a resistivity adjusting agent.
The method according to claim 2 or 3,
Wherein the phenol resin is a Novolac resin.
The method according to claim 2 or 3,
Wherein the base material is silicon carbide (SiC).
The method according to claim 2 or 3,
Wherein the lubricant is graphite.
The method of claim 3,
Wherein the resistivity adjusting agent is silicon oxide (SiO ₂ ).
The method according to claim 1,
Wherein the extrusion process is performed at a temperature of 100 to 180 DEG C at a rate of 10 to 120 rpm.
The method according to claim 1,
Wherein the stabilizing heat treatment process is performed at 260 to 300 ° C for 10 minutes to 2 hours.
The method according to claim 1,
Wherein the carbonization heat treatment step includes a first carbonization heat treatment step of performing out-gassing at 600-1,000 DEG C for 10 minutes to 2 hours.
The method according to claim 1,
Wherein the carbonization heat treatment step includes a second and a third carbonization heat treatment step.
12. The method of claim 11,
Wherein the second carbonization heat treatment step is performed at 1,200 to 1,400 ° C for 10 minutes to 4 hours and the third carbonization heat treatment step is performed at 1,500 to 1,700 ° C for 10 minutes to 4 hours.

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