JP2784068B2 - High temperature heating element using zirconia heating element - Google Patents

Description

The present invention relates to a high-temperature heating element using a zirconia heating element (ZrO2 heating element).

[Related Art] A zirconia heating element has been developed as a heating element that can be used up to about 2000 ° C. in an oxidizing atmosphere. The zirconia heating element has a negative temperature characteristic of resistance from 1200 ° C. to 1300 ° C., and has a very high resistance value. Therefore, when a zirconia heating element is used, the temperature at which the resistance value rapidly decreases (1200
(1500 ° C. to 1500 ° C.), the zirconia heating element is preheated to reduce the resistance value, and then energized.

When preheating the conventional zirconia heating element, the inside of the furnace 1 is divided into a heating space 1a and a preheating space 1b, 1b by heat insulating materials 2, 2 as shown in FIG. The bodies 3,3 are arranged, and the heating elements 4,4 for preheating are arranged in the preheating spaces 1b, 1b, and the zirconia heating elements 3,3 are preheated via the heat insulating materials 2,2. The heat insulating materials 2, 2 protect the preheating heating elements 4, 4 having a lower heat-resistant temperature than the zirconia heating elements 3, 3 from the heat generated by the zirconia heating elements 3, 3.

[Problems to be Solved by the Invention] When preheating is performed by the conventional structure, the preheating is performed through the heat insulating materials 2 and 2, so the heating efficiency is very poor. There is a problem of worsening. Further, since the inside of the furnace is provided in the heating space 1a and the preheating space 1b, there is a problem that the furnace has a double structure, the furnace becomes large, and the price of the furnace increases.

If a heating element having a higher heat-resistant temperature than the heating temperature of the zirconia heating elements 3, 3 is used as the heating element for preheating, preheating can be performed without having a double furnace structure. The provision is an obstacle to downsizing the furnace. Further, if the zirconia heating element and the preheating pulmonary tropics are simply provided side by side, there is a limit to an increase in heating efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-temperature heating element using a zirconia heating element that can minimize the space for arranging the zirconia heating element and the preheating heating element and improve the heating efficiency of the preheating heating element. Is to do.

[Means for Solving the Problems] In the invention of claim 1, in order to solve the above problems, a heating element housing for preheating is formed inside a zirconia heating element,
A preheating heating element that can be energized from room temperature is disposed in the preheating heating element housing in a state of being electrically insulated from the zirconia heating element.

The preheating heating element housing section is configured so as to enclose the preheating heating element in a substantially wrapping manner, and any shape that can efficiently transmit heat radiated from the preheating heating element to the zirconia heating element. For example, the hole may be a through-hole penetrating the zirconia heating element, a bottomed hole or a concave portion not penetrating the zirconia heating element, or a groove.

As the heating element for preheating, various known heating elements can be used. Examples of the heating element having a higher heat-resistant temperature than the zirconia heating element include a graphite heating element, a tungsten heating element, and a molybdenum heating element used in a non-oxidizing atmosphere.

When a heating element used in a non-oxidizing atmosphere is used as the heating element for preheating, the heating element for preheating is arranged in the gas shield tube. In this case, as in the second aspect of the present invention, the heating element housing for preheating can be configured to also serve as a gas shield tube that holds a non-oxidizing gas inside.

Also, a heating element having a heat-resistant temperature lower than the heating temperature of the zirconia heating element can be used as the heating element for preheating of the present invention if the heating element is cooled to a use temperature (heat-resistant temperature). In the invention according to claim 3, when a heat-resistant element whose heat-resistant temperature is lower than the heat-generation temperature of the zirconia heating element is used as the heating element for preheating,
The heating element for preheating is cooled by a gas flow. Heating elements that can be used by gas flow cooling include, for example, silicon carbide heating elements (SiC) and molybdenum silicide heating elements (M
oSi2) and lanthanum chromite heating element (LaCrO3).

[Operation] As described in the first aspect of the present invention, a preheating heating element storage section is provided inside the zirconia heating element, and the preheating heating element is stored in the storage section. Dissipated heat can be efficiently transmitted to the zirconia heating element surrounding the periphery of the preheating heating element, so that the heating efficiency can be improved and the response speed can be increased. As a result, preheating can be performed with a small amount of power. Also, compared to the case where the zirconia heating element and the heating element for preheating are arranged side by side,
When the high-temperature heating element of the present invention is used, the shape and size of the furnace can be made compact.

When the preheating heating element housing is used as a gas shield tube as in the second aspect of the present invention, a gas shield tube becomes unnecessary, and the size of the preheating heating element housing is reduced to reduce the size of the high-temperature heating element. Can be achieved.

Furthermore, if the heating element for preheating is cooled by a gas flow as in the invention of claim 3, a heating element having a heat resistant temperature lower than that of the zirconia heating element can be used as the heating element for preheating. .

Embodiment An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a zirconia heating element formed in a cylindrical shape, and a through hole 11 extending in the axial direction constitutes a heating element housing recess for preheating. Annular electrode fixing portions 12 and 13 are formed at both ends of the zirconia heating element 10, and ring-shaped electrodes 14 and 15 are fixed to the electrode fixing portions 12 and 13, respectively. The electrodes 14 and 15 are connected to a power supply device 16 that outputs AC power.

A heating element 17 for preheating is inserted into the through hole 11. In the present embodiment, the heat-generating element 17 for preheating uses a heat-resistant temperature higher than the heat-generating temperature (about 2000 ° C.) of the zirconia heat-generating element. Specifically, as the heating element 17 for preheating, magnesium oxide (Mg
A heating element having a structure in which a graphite heating element 19 formed in a spiral shape is disposed in a gas shield tube 18 made of O). The opening of the gas shield tube 18 is sealed with a sealing body 20 made of a heat-resistant insulating material whose main material is zirconia fiber, and the graphite heating element 19 penetrates the sealing body 20 and enters the gas shield tube 18. Has been inserted.

Both ends in the axial direction of the gas shield tube 18 are integrated with the zirconia heating element 10 via insulating spacers 21 and 22 made of a heat-resistant insulating material whose main material is zirconia fiber. Reference numeral 23 denotes a terminal block to which the terminal portions 19a and 19b of the graphite heating element 19 are fixed, and the terminal block 23 also functions to keep the gas shield tube 18 airtight. Current-carrying electrodes 24a and 24b are fixed to the terminal portions 19a and 19b of the graphite heating element 19,
The current-carrying electrodes 24a and 24b are connected to a power supply device 25 for a preheating heating element that outputs AC power.

In order to generate heat from the high-temperature heating element, first, power is supplied to the graphite heating element 19 from the preheating heating element power supply device 25, and the graphite heating element 19 is heated to 1300 to 1500 ° C., and the zirconia heating element is heated.
Preheat 10 to a temperature where the resistance drops. Then power supply
Electric power is supplied to the zirconia heating element 10 from 16 to cause the zirconia heating element 10 to generate heat at about 2000 ° C. or more. After the energization of the zirconia heating element 10 is started, the energization of the graphite heating element 19 is stopped.

FIG. 2 shows another embodiment of the present invention. The same parts as those in the embodiment of FIG. 1 are denoted by the same reference numerals as those in the embodiment of FIG. The present embodiment differs from the embodiment of FIG. 1 in that a preheating heating element housing formed in the zirconia heating element 110 is used as a gas shield tube. In FIG. 2, inside the zirconia heating element 110, a bottomed hole 111 which is open at one end side in the axial direction is formed as a heating element housing section for preheating. A sealing body 120 made of a heat-resistant insulating material is inserted into the opening end of the hole 111, and the graphite heating element 19 is inserted into the hole 111 through the sealing body 120. A heat-resistant hermetic seal 26 is arranged between one end face of the zirconia heating element 110 and the terminal block 23.

FIG. 3 shows still another embodiment of the present invention. The present embodiment is an embodiment in which a heating element having a heat-resistant temperature lower than the heating temperature of the zirconia heating element 10 is used as the heating element for preheating. In the present embodiment, a silicon carbide heating element (operating temperature: 1500 to 1600 ° C.) is used as the preheating heating element 117, and after the zirconia heating element 10 starts to generate heat, the preheating heating element is used.
117 is gas flow cooled. Therefore, in the present embodiment, a cylindrical gas shield tube 27 made of magnesium oxide (MgO) and having both ends opened is held inside the through-hole 11 via the insulating spacers 121 and 122. Inside the gas shield tube 27, a heating element 117 for preheating is disposed via sealing bodies 28 and 29 having cooling gas inlets and outlets 28a and 29a. Gas shield tube 2
The gas supplied into 7 is preferably an inert gas, and in this embodiment, an argon gas is used. When the high-temperature heating element of the present embodiment generates heat, first, power is supplied from the power supply device 25 to the preheating heating element 117 to heat the heating element to 1500 to 1600 ° C., and the heat causes the zirconia heating element 10 to be heated. Preheat. After that, when the power supply 16 starts energizing the zirconia heating element 10, the cooling gas is supplied into the gas shield tube 27 simultaneously with or after energization. The gas flows in the flow path shown by the arrow in the figure, and cools the preheating heating element 117 to a temperature equal to or lower than the allowable temperature limit. The flow rate and flow rate of the cooling gas are appropriately selected according to the heat-resistant temperature of the heating element used for the heating element 117 for preheating.

In the embodiment shown in FIG. 1 to FIG. 3, each part is exaggerated to some extent for the sake of explanation, and the length is also drawn short. For example, when the high-temperature heating element of the embodiment of FIG. 1 is actually used in a furnace, it is used in a configuration as shown in FIG. In FIG. 4, 30 is a furnace, 31 is a heat insulating material, 32 and
33 is a support frame.

[Effect of the Invention] According to the invention of claim 1, since the preheating heating element housing is provided inside the zirconia heating element and the preheating heating element is housed in the housing, the heating element for preheating is provided. Can be efficiently transmitted to the zirconia heating element surrounding the periphery of the preheating heating element, so that the heating efficiency can be improved and the response speed can be increased. As a result, preheating can be performed with a small amount of power. Further, compared with the case where the zirconia heating element and the preheating heating element are arranged side by side, the use of the high-temperature heating element of the present invention has an advantage that the shape and size of the furnace can be reduced.

According to the second aspect of the present invention, since the preheating heating element housing portion is used as a gas shield tube, a gas shield tube is not required, and the size of the preheating heating element housing portion is reduced to reduce the shape of the high-temperature heating element. There is an advantage that the size can be reduced.

Further, according to the third aspect of the present invention, the heating element for preheating is cooled by the gas flow, so that there is an advantage that a heating element having a heat resistant temperature lower than the heating temperature of the zirconia heating element can be used as the heating element for preheating. .

[Brief description of the drawings]

1 to 3 are schematic cross-sectional views showing an embodiment of a high-temperature heating element of the present invention, respectively. FIG. 4 is a schematic cross-sectional view of a case where the high-temperature heating element of the embodiment of FIG. 1 is applied to a furnace. FIG. 5 is a schematic sectional view of a conventional furnace for explaining a conventional preheating method. 1 Furnace 2,2 Heat insulation 3,10,110 Zirconia heating element 4,17,117 Heating element for preheating, 11 ... Through hole (heating element housing for preheating), 111 Bottom hole (heating element housing for preheating), 14,15 …… electrode, 16,25 …… power supply device, 18,27…
... Gas shield tube, 19 ... Graphite heating element, 20,28,29,120 ...
... sealing bodies, 21, 22, 121, 122 ... insulating spacers.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-50-156736 (JP, A) JP-A-63-48789 (JP, A) JP-A-2-210784 (JP, A) JP-A-2- 210785 (JP, A) Japanese Utility Model Showa 61-33392 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 3/62 H05B 3/14

Claims (3)

(57) [Claims] 1. A state in which a heating element housing for preheating is formed inside a zirconia heating element, and a heating element for preheating which can be energized from room temperature is electrically insulated from the zirconia heating element in the heating element housing for preheating. A high-temperature heating element using a zirconia heating element, wherein the zirconia heating element is arranged in a high temperature heating element. 2. The heating element for preheating comprises a heating element used in a non-oxidizing atmosphere, and the housing for the heating element for preheating also serves as a gas shield tube for holding a non-oxidizing gas therein. A high-temperature heating element using the zirconia heating element according to claim 1. 3. The preheating element according to claim 1, wherein said preheating element has a heat-resistant temperature lower than that of said zirconia heating element, and said preheating element is gas-flow cooled below said heat-resistant temperature. A high-temperature heating element using the described zirconia heating element.