Carbon wire heater and method for manufacturing a carbon wire heater

Abstract

This invention provides a carbon wire heater that uses a carbon wire heating element with low surface breakage and high flexibility. [Solution] The carbon wire heater 10 according to the present invention is a carbon wire heater in which a carbon wire heating element that generates heat when power is supplied is housed inside a glass member, wherein the carbon wire heating element W is formed by weaving together a plurality of carbon fiber bundles 1a, each made by bundling carbon single fibers 1, in a linear fashion, and the degree of graphitization of the carbon wire heating element is 0.2 or more and 0.6 or less.

Description

Technical Field

[0001] The present invention relates to a carbon wire heater, and particularly to a carbon wire heater having a carbon wire heating element with an adjusted graphitization degree and a method for manufacturing the carbon wire heater.

Background Art

[0002] Conventionally, a carbon wire heater in which a carbon wire heating element is enclosed in a glass tube has been known (Patent Document 1). The carbon wire heater described in this Patent Document 1 will be described based on FIGS. 4 to 6. The carbon wire heater 10 shown in FIG. 4 has a carbon wire heating element 12 and a long and small-diameter quartz glass tube 13 (also simply referred to as a glass tube 13) with both ends open for housing the carbon wire heating element 12. Larger-diameter glass tubes 14a and 14b are housed at both ends 13a and 13b of the glass tube 13, and a wire carbon material 20 is compression-housed inside the larger-diameter glass tubes 14a and 14b. Further, the outer ends of both ends 13a and 13b are sealed and closed by sealing terminal portions 18a and 18b.

[0003] The sealing terminal portions 18a and 18b have sealing members 15a and 15b made of cylindrical quartz glass, and one end of each is welded to both ends 13a and 13b of the glass tube 13. Connection lines 16a and 16b for supplying electric power to the carbon wire heating element 12 are disposed inside the sealing members 15a and 15b, and thermal expansion inclined portions 17a and 17b in which the coefficient of thermal expansion changes in the radial direction of the connection lines 16a and 16b are formed on a part of the outer peripheral surfaces of the connection lines 16a and 16b.

[0004] The sealing members 15a and 15b are cylindrical bodies formed with small-diameter portions 15a1 and 15b1, large-diameter portions 15a2 and 15b2, and rising portions 15a3 and 15b3 connecting the small-diameter portions 15a1 and 15b1 and the large-diameter portions 15a2 and 15b2. The inner surfaces of the small-diameter portions 15a1 and 15b1 are welded to the outer surfaces of the thermal expansion gradient portions 17a and 17b, and the end faces of the large-diameter portions 15a2 and 15b2 are welded to the end faces of both ends 13a and 13b of the large-diameter glass tube 13. This seals the inside of the glass tube 13.

[0005] The connecting wires 16a and 16b are made of Mo (molybdenum) or W (tungsten) rods. The ends of these connecting wires 16a and 16b are pointed so that they can be easily connected to the wire carbon material 20 that is compressed and housed inside the large-diameter glass tubes 14a and 14b.

[0006] Furthermore, in the heater shown in Figure 4, the carbon wire heating element 12 housed in the glass tube 13 uses carbon fibers with a diameter of 2 to 15 μm, for example, a fiber bundle 12a made by bundling about 3,000 to 3,500 single carbon fibers with a diameter of 7 μm, and about 8 such bundles are used to create a braided cord or woven shape with a diameter of about 2 mm, as shown in the side view of Figure 5 (the glass tube is shown in cross-section). In the above case, the braiding span of the wire is about 2 to 5 mm. As shown in Figure 6, in the carbon wire heating element 12, the inside of the fiber bundle 12a (carbon wire) woven into a braided or woven shape is hollow, and the core wire 19 of the carbon fiber bundle (carbon wire) is provided in this hollow.

[0007] Furthermore, Patent Document 2 indicates that carbon fibers (carbon wires) constituting a carbon wire heating element are heat-treated at a temperature of 2000°C or higher, preferably 2020°C or higher, to sufficiently graphitize the carbon fibers until they reach the crystalline structure, and the resulting graphitized carbon wires are cut to a length corresponding to a desired resistance value, stretched as a heating element within a predetermined quartz glass support member, connected to terminals, etc., and then sealed to assemble it as a heater. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-4526 [Patent Document 2] Japanese Patent Publication No. 2001-332373 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0009] By the way, conventional carbon wire heating elements, such as those shown in Patent Document 1, have the problem that because carbon fibers are used, the strength of the carbon wire heating element is weak, and fuzzing 12a1 occurs on the outer surface of the carbon wire heating element, which increases the resistance value and shortens the lifespan. Furthermore, conventional carbon wire heating elements had the problem that carbon (C), the main component of the carbon wire, and SiO, evaporated from the silica glass tube, reacted according to the following equation, causing gradual wire breakage. [Mathematics 1] SiO(s) + C(s) → Si(s) + CO(g)

[0010] On the other hand, in the case of a carbon wire heating element, such as the one shown in Patent Document 2, in which the carbon fibers are heat-treated to sufficiently graphitize them until they form the aforementioned crystalline structure, the resistance value decreases, and the heating efficiency as a heating element decreases. Furthermore, the flexibility of the carbon wire itself is lost, which presents a problem in that the degree of freedom in the shape of the carbon wire heating element is lost.

[0011] The inventors of the present invention diligently researched the appropriate degree of graphitization for a carbon wire heating element, rather than completely graphitizing the carbon fibers. As a result, we discovered that using a carbon wire heating element with a specific degree of graphitization results in fewer breaks on the surface of the carbon wire heating element and high flexibility, leading to the completion of the present invention.

[0012] The present invention was made to solve the above technical problems, and aims to provide a carbon wire heater that uses a carbon wire heating element with less breakage on the surface of the carbon wire heating element and high flexibility. [Means for solving the problem]

[0013] To achieve the above objective, the carbon wire heater according to the present invention is a carbon wire heater in which a carbon wire heating element that generates heat when power is supplied is housed inside a glass member, wherein the carbon wire heating element is formed by weaving together a plurality of carbon fiber bundles, each of which is a bundle of carbon single fibers, in a linear fashion, and the degree of graphitization of the carbon wire heating element is 0.2 or more and 0.6 or less.

[0014] Thus, because the degree of graphitization of the carbon wire heating element is between 0.2 and 0.6, the likelihood of wire breakage on the surface of the carbon wire heating element can be reduced, and its flexibility can be increased. As a result, in a carbon wire heater using this carbon wire heating element, it is possible to arrange the carbon wire heating elements in a complex shape, and the heater can have a long lifespan.

[0015] A method for manufacturing a carbon wire heater according to the present invention, made to achieve the above objective, is a method for manufacturing a carbon wire heater, characterized by comprising the steps of: heat-treating the carbon wire heating element so that its degree of graphitization is 0.2 or more and 0.6 or less; and housing the graphitized carbon wire heating element inside a glass member. [Effects of the Invention]

[0016] According to the present invention, it is possible to obtain a carbon wire heating element that is highly flexible and has few surface breaks, and a carbon wire heater with a complex shape and long lifespan can be obtained. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a schematic view showing a manufacturing apparatus for manufacturing a carbon wire heating element with adjusted graphitization degree. [Figure 2] Figure 2 is a side view showing an enlarged partial surface of a carbon wire heating element housed in a glass tube. [Figure 3] Figure 3(a) is a longitudinal sectional view showing an example of a carbon wire heater (an example not including a core wire), and (b) is a longitudinal sectional view showing another example of a carbon wire heater (an example including a core wire). [Figure 4] Figure 4 is a sectional view showing a conventional heater in which a carbon wire heating element is enclosed in a glass tube. [Figure 5] Figure 5 is a side view showing the configuration of the carbon wire heating element of the conventional heater in FIG. 4. [Figure 6] Figure 6 is a side view showing the core wire of the carbon wire heating element in FIG. 5.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the carbon wire heater according to the present invention will be described based on FIGS. 1 to 3. The carbon wire heater according to the present invention is a carbon wire heater in which a carbon wire heating element W that generates heat by power supply is housed inside a glass member, similar to a conventional carbon wire heater. In particular, the carbon wire heater according to the present invention is characterized in that the graphitization degree of the carbon wire heating element W is 0.2 or more and 0.6 or less. Therefore, since the configuration of the carbon wire heater itself is the same as that of the conventional one, a detailed description thereof will be omitted. Note that FIG. 3 corresponds to the I-I cross section of FIG. 4.

[0019] To make the graphitization degree of the above-described carbon wire heating element W 0.2 or more and 0.6 or less, as shown in FIG. 1, it is performed using a heat treatment furnace 20. Based on Figure 1, the graphitization of the carbon wire heating element W is explained as follows: The carbon wire heating element W, in which carbon fibers are woven, is placed in the heat treatment 20, and heat treatment is performed for about 10 hours at a temperature of 1900°C to 2350°C using the heater 21 in the furnace under a pressure of 0.1 Torr or less, to make the degree of graphitization of the carbon fibers 0.2 to 0.6. Furthermore, the degree of graphitization can be controlled by adjusting the heat treatment temperature.

[0020] The degree of graphitization refers to a measure of the extent to which a non-graphitic structure has changed to a graphitic structure. It is measured using a Raman spectrometer and calculated from the ratio of the peak intensities of the G-band and D-band (peak intensity of the D-band / peak intensity of the G-band). Note that the D band is 1360cm -1 Those with a peak top nearby, the G band, are 1580cm. -1 It has a peak in the vicinity.

[0021] Incidentally, if the degree of graphitization is less than 0.2, the strength of the carbon wire heating element W is weak, and breakage (fraying) is likely to occur on the outer surface of the carbon wire heating element W, resulting in a shorter lifespan when used as a heater. On the other hand, if the degree of graphitization exceeds 0.6, the carbon wire heating element W becomes too rigid and loses its flexibility. Therefore, it is preferable that the degree of graphitization of the carbon wire heating element W is 0.2 or more and 0.6 or less.

[0022] Furthermore, the carbon wire heating element W will be described in more detail. The carbon wire heating element W is manufactured in the same way as conventional methods, by weaving together multiple bundles of carbon fiber bundles 1a, each made by bundling carbon single fibers 1, into a braided or cord-like shape, as shown in Figure 2(a) or Figure 2(b).

[0023] Furthermore, since this carbon wire heating element W is made by weaving together multiple fiber bundles (carbon fiber bundles) 1a of thin carbon single fibers 1, it is more flexible and has superior shape deformation adaptability compared to heating elements made of solid carbon material.

[0024] In the example shown in this embodiment, a carbon fiber bundle 1a consisting of 8 or 14 bundles is used. As shown in Figure 3(a), the carbon wire heating element W may be configured such that the inside of the 8 bundles of woven carbon fiber bundles 1a is hollow and does not contain the core wire of the carbon wire (carbon fiber bundle), or as shown in Figure 3(b), the inside of the 10 bundles of woven carbon fiber bundles 1a contains the core wire of the carbon wire (carbon fiber bundle) (4 bundles of core wire 1b are shown in the figure). Furthermore, it is preferable that the carbon wire heating element W does not have a core wire in its internal cavity. Because there is no core wire and therefore no current concentration on the core wire, the temperature of the core wire does not rise locally, which can lead to a longer lifespan for the carbon wire heating element W.

[0025] As described above, the carbon wire heating element W uses a carbon fiber bundle 1a made by weaving together multiple bundles (eight bundles in Figure 3(a)) of carbon fiber bundles 1a in a braided or cord-like manner with a diameter of approximately 2 mm. The carbon fiber bundle 1a consists of approximately 3500 single carbon fiber fibers with a diameter of 5 μm to 15 μm, for example, single carbon fiber fibers with a diameter of 9 μm.

[0026] Furthermore, it is desirable that the carbon wire heating element W as a whole consists of approximately 5,000 to 150,000 carbon fiber single fibers. For example, if one bundle of carbon fiber 1a is formed from 3,500 carbon fiber single fibers, it is desirable that the carbon wire heating element W be formed by weaving together 5 to 20 bundles of carbon fiber 1a. In the above case, the weaving span of the carbon wire heating element W is approximately 2 mm to 5 mm, and as shown in Figures 2(a) and (b), the weaving angle θ of the carbon fiber bundle 1a is set to a predetermined angle between 5° and 50°.

[0027] The carbon wire heating element W configured in this manner is heat-treated to achieve a graphitization degree of 0.2 to 0.6. In the carbon wire heater 10, when an electric current is passed through the carbon wire heating element W, which has a graphitization degree of 0.2 to 0.6, to generate heat, radiant heat is emitted from the glass tube 13 along the shape of the carbon wire heating element W (straight in this embodiment).

[0028] As described above, according to the embodiment of the carbon wire heater 10 of the present invention, the carbon wire heating element W housed in the glass tube 13 has a specific degree of graphitization, resulting in fewer breaks on the outer surface and high flexibility. Therefore, even if the glass tube 13 of the carbon wire heater 10 has a complex shape, the carbon wire heating element W can be housed inside it, further extending its lifespan.

[0029] In the above embodiment, Figure 3(a) shows the case where there are 8 fiber bundles 1a constituting the carbon wire heating element W, but the number of fiber bundles 1a to be woven is not limited. Also, in the above embodiment, the carbon wire heating element W (and the glass tube housing it) was described as being linear, but it is not limited to this, and may be rectangular or curved, for example. [Examples]

[0030] Next, the carbon wire heater of the present invention will be further described based on examples. (Example 1) First, a carbon wire heating element with a diameter of approximately 2.5 mm (a total of 42,000 carbon fiber single fibers) was created by weaving together 12 bundles of carbon fiber bundles, each consisting of 3,500 carbon fiber single fibers with a diameter of 9 μm. The weaving angle was set to 30°. The carbon wire heating element prepared as described above was heat-treated in a heat treatment furnace under reduced pressure (0.01 Torr) at a temperature of 1900°C for 10 hours. The degree of graphitization of the obtained carbon wire heating element was measured using a laser Raman spectrometer. The degree of graphitization was 0.2. The degree of graphitization was calculated using the following formula. Graphitization degree = D-band peak intensity / G-band peak intensity

[0031] Furthermore, when a specific area (1.5 mm × 1.5 mm) of the outer surface of the obtained carbon wire heating element was photographed under a microscope and the amount of wire breakage in that area was measured, 40 carbon single fibers were found to be broken (frayed). The flexibility of the obtained carbon wire heating element was confirmed by manually inserting the carbon wire heating element into a U-shape created by bending a glass pipe with an inner diameter of Φ2.6 mm and a total length of 100 mm to a radius of curvature of R8 (8 mm), and then pulling it out from the other end. The carbon wire heating element was found to be flexible, with minimal resistance during insertion, and could be easily inserted. (It could be pulled out from the other end within 10 seconds.)

[0032] (Example 2) The heat treatment temperature was set to 2350°C, and the same heat treatment, graphitization degree measurement, and evaluation of the amount of wire breakage and flexibility of the carbon wire heating element were performed as in Example 1. As a result, the degree of graphitization was 0.6. The number of broken wires on the surface of the carbon wire heating element was 30. The flexibility of the obtained carbon wire heating element was confirmed by manually inserting the carbon wire heating element into a glass pipe with an inner diameter of Φ2.6 mm and a total length of 100 mm, which was bent to create a U-shape with a radius of R8, and pulling it out from one end of the pipe. The resistance during insertion was greater than in Example 1, but it was possible to pull it out from the other end without using any tools.

[0033] (Comparative Example 1) The heat treatment temperature was set to 1700°C, and the same heat treatment, graphitization degree measurement, and evaluation of the amount of wire breakage on the outer surface of the carbon wire heating element and its flexibility were performed as in Example 1. As a result, the degree of graphitization was 0.1. The number of broken wires on the surface of the carbon wire heating element was 100. The flexibility of the obtained carbon wire heating element was confirmed by manually inserting the carbon wire heating element into a U-shape created by bending a glass pipe with an inner diameter of Φ2.6 mm and a total length of 100 mm at an R8 curve, and then pulling it out from the other end. The carbon wire heating element was found to be flexible, with minimal resistance during insertion, and could be easily inserted. (It could be pulled out from the other end within 10 seconds.)

[0034] (Comparative Example 2) The heat treatment temperature was set to 2500°C, and the same heat treatment, graphitization degree measurement, and evaluation of the amount of wire breakage and flexibility of the carbon wire heating element were performed as in Example 1. As a result, the degree of graphitization was 0.7. The number of broken wires on the surface of the carbon wire heating element was 10. The flexibility of the obtained carbon wire heating element was tested by manually inserting the carbon wire heating element into a glass pipe with an inner diameter of Φ2.6 mm and a total length of 100 mm, which was bent to create a U-shape with a radius of R8, and pulling it out from one end of the pipe. As a result, the carbon wire heating element W became hard and lost its flexibility, resulting in increased resistance during insertion and making it impossible to pull it out from the other end.

[0035] Based on the results of the above embodiments, it was confirmed that the carbon wire heater of the present invention has higher flexibility of the carbon wire heating element than conventional heaters, reduces the number of disconnections on the outer surface of the carbon wire heating element, can accommodate complex shapes of carbon wire heaters, and extends the lifespan. [Explanation of Symbols]

[0036] 1 carbon single fiber 1a Fiber bundle of carbon single fibers (carbon fiber bundle) W carbon wire heating element 10 Carbon Wire Heaters 13 Glass tubes

Claims

1. A carbon wire heater in which a carbon wire heating element that generates heat when power is supplied is housed inside a glass member, wherein the carbon wire heating element is formed by weaving together a plurality of carbon fiber bundles, each bundled with a single carbon fiber, in a linear fashion, and the degree of graphitization of the carbon wire heating element is 0.2 or more and 0.6 or less.

2. A method for manufacturing a carbon wire heater as described in claim 1, A step of heat-treating the carbon wire heating element so that its degree of graphitization is 0.2 or more and 0.6 or less, A method for manufacturing a carbon wire heater, characterized by including the step of housing the graphitized carbon wire heating element inside a glass member.

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