JPS6057196B2 - Manufacturing method of spiral ceramic heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic heating element having a cylindrical, columnar or similar shape, and particularly provides a ceramic heating element having the above shape that can be rapidly heated repeatedly.

Conventionally known columnar ceramic heating elements include one that has a ceramic core with a resistive coating on the front and a ceramic protective outer layer (Utility Model Application Publication No. 51-96638); After forming an inorganic conductive material pattern on one side of the sheet, the pattern is placed outside and the opposite side (non-patterned side) is wrapped around a pipe with both opposing end surfaces brought together to form a cylindrical shape, and then another green sheet is wrapped around it. There is one made by baking it as a protective outer shell (Japanese Patent Publication No. 51-22659).

These rod-shaped or cylindrical ceramic heating elements differ from previous ones in that the resistive coating is protected by a ceramic outer layer.
Compared to uncoated, synthetic resin coated, enamel coated, etc., the heat resistance of the resistive coating itself and prevention of changes in resistance value over time are improved. However, if repeated rapid heating is still required, for example when used as a rod-shaped ceramic heating element for a glow plug in a diesel engine, ring cracking may occur at the boundary between the heating part and the rod holding part (non-heating part). It has the disadvantage of being easy to use. The object of the present invention is to provide a ceramic heating element having a cylindrical, columnar or similar shape and a method for manufacturing the same, which eliminates this drawback.

That is, the present invention has a resistive coating formed on the inside of the ceramic green sheet in one or more turns from the outer circumferential edge of a spiral-shaped ceramic body obtained by winding and firing a ceramic green sheet in a spiral shape, and The spiral ceramic heating element is characterized in that the thickness of the central ceramic spiral from the inner surface of the resistive coating to the center of the spiral is greater than the thickness of the protective outer layer of the resistive coating. Furthermore, the present invention also provides a novel method for manufacturing the spiral ceramic heating element.

That is, the method for manufacturing the spiral ceramic heating element of the present invention involves forming an inorganic conductive material film pattern on a portion of one surface of a ceramic green sheet, and starting from one side of the margin area and forming the inorganic conductive material film pattern on the inner side. It is characterized in that the ceramic green sheet is rolled up in a spiral shape and fired. The present invention will be explained in detail below.

The spiral-shaped ceramic heating element of the present invention is a spiral-shaped ceramic body 1 in which a ceramic green sheet is rolled up and fired in a spiral shape.
has a main body structure, and has a resistive coating 3 between the spiral layers.

At this time, the resistive coating is formed between the spiral layers from the outer peripheral end of the spiral layer toward the center of one or more turns, preferably the first or second turn. Inside this resistive coating, a central ceramic spiral without a resistive coating between layers exists up to the central edge of the spiral. According to the invention, the thickness of the central ceramic spiral is greater than the thickness of the protective outer skin layer of the resistive coating. In one embodiment of the present invention, the spiral ceramic body is formed by winding up a ceramic green sheet. In addition, the resistive coating is formed on a part of one side of the ceramic green sheet as a resistive coating pattern (arbitrary shape) using a known method such as metallization paste before winding up, and the resistive coating is placed on the inside of the green sheet and It is formed by winding up the green sheet in a spiral shape starting from one side of the green sheet on the side of the margin where the resistive coating is not present. Therefore, making the thickness of the central ceramic spiral larger than the thickness of the protective outer layer means that the number of turns of the central ceramic spiral is 2.
This can be easily achieved by making it more than a roll. The thickness of the protective outer skin layer herein refers to the thickness of the protective outer skin layer (one layer) directly between a certain one layer of the resistive coating, and in the above embodiment, corresponds to the thickness of the spiral sheet. However, it is not necessarily excluded that the protective outer layer, which is the outermost periphery of the spiral, may be machined to make it thinner as necessary, and the edge of the ceramic green sheet at the outer edge of the spiral may be tapered or the tip may be cut thinly and diagonally. It is also preferable to remove the spiral outer peripheral end stage. Ceramic green sheets to be formed and fired into spirals according to the present invention include known ones, such as ones containing alumina with 1% magnesia, 1% calcia and 2% silica as a solvent, ones made of beryllia, 96% alumina, There are those having a composition of 2% silica and 2% dolomite, those having a composition of 99.5% alumina and 0.5% magnesia, and forsterite.

Particularly preferably, silica, calcia, and magnesia are mixed in a ratio of 90 to 94% alumina and the remainder as a solvent in a ratio of 3 to 6:0.
Added at a ratio of 5-2:0.5-2. Ceramic green sheets are made by blending the above powder materials, then pulverizing and mixing them, adding an organic binder diluted with a known organic solvent to form a slurry, and forming the sheets into sheets using known methods (e.g. extrusion molding method, doctor blade method, etc.). It is obtained by evaporating the solvent, usually by slow heating. As shown in Fig. 2, an inorganic conductive material film, such as a paste film mainly composed of tungsten, is formed on a part of the surface of the green sheet obtained in this way by a known method (when fired, it forms a resistive film). Become).

At this time, as described above, the inorganic conductive material film is formed on one side of the green sheet, and the film is spirally wound so as to be wound inside the sheet. This measure effectively prevents damage to the paste film due to cutting and winding operations due to the paste film being stretched during winding, and therefore also increases the durability of the resistive film after firing. In this case, as in the above-mentioned known method, winding the ceramic green sheet so that the resistance film is formed on the outside may cause tensile stress and expansion in the inorganic conductive material film, such as the paste film, during winding. It has become clear from the present invention that the resistive coating after firing has a drawback that there is a high probability of wire breakage. As illustrated in the developed view (FIG. 3), this paste film is formed from one end (outer peripheral edge) of the surface of one green sheet to just the required length and width and in an arbitrary pattern.

A preferred embodiment of the present invention is a pattern in which a large number of resistor circuits are formed in parallel approximately S parallel to the outer peripheral edge, and both ends are connected in parallel with each other through lead portions (in this pattern, the entire resistive film circuit is It is formed parallel to the spiral axis, is less affected by deformation due to spiral winding, and can withstand use even if some unit resistor coatings are broken). Further, it is preferable to leave an appropriate margin near the spiral outer peripheral end 0 to protect the resistive coating. In a preferred embodiment of the invention, the resistive coating is formed on a portion of the length of the spiral heater and on one end thereof.

For example, when used as a heater for a glow plug for a diesel engine, one end side is preferable, and in the case of a Tammann tube, the central part is preferably used as the heat generating part. In this case, the developed green sheet has, for example, as shown in Figure 3.
The inorganic conductive material film pattern is formed near the lower half of one of the sides perpendicular to the outer periphery on the outer periphery end side (0 side). This is wound up from the spiral inner starting point 1 so that the resistive coating is on the inside to obtain the spiral ceramic heater shown in FIGS. 1 and 2. Note that the lead portion 4 can be led to the non-heat generating end of the spiral ceramic heating element at an appropriate interval and used as a terminal 8.

The advantages of the present invention are particularly apparent when a part of the heating element is used as a heat generating part and when rapid heating is required.

That is, in the spiral ceramic heating element of the present invention, the heating portion is located at the outer periphery of the spiral and at one end of the spiral. When a heat generating part is rapidly heated, only the heat generating part tries to thermally expand, but the non-heat generating part stays at a low temperature. Therefore, tensile stress acts on the non-heat generating portion side. In known columnar or cylindrical ceramic heaters, this tensile stress acts directly on the low-temperature part and is not buffered anywhere, so ring-shaped fracture is inevitable. This is because ceramics are strong against compressive stress but weak against tensile stress. In the spiral heating element of the present invention, it is presumed that this tensile stress is partially buffered as stress between the spiral layers. That is, the thermal expansion force counteracts the restraining force exerted by one spiral layer and the adjacent layer, but the bonding force between the layers is slightly different from that of the sheet itself and is therefore weak, resulting in a considerable concentration of stress between the layers. As a result, it is presumed that a ceramic heating element that can withstand rapid heat due to its spiral shape can be obtained. In the present invention, the thickness of the central ceramic spiral (corresponding to the green sheet margin) of the spiral ceramic heating element is equal to the thickness of the resistive coating protective outer layer (for example, in the embodiment shown in FIG. (equivalent to).

In this case, the spiral-wound ceramic heating element of the present invention can best withstand rapid heating. This is clearly seen from the fact that Comparative Examples 1 and 2 are inferior to Example 1 in repeated rapid heating resistance, as shown in Table 1. The reason for this is thought to be as follows. That is, due to the rapid heating of the heat generating part, compressive stress is first generated in the ceramic body (high temperature part) near the heat generating part, and tensile stress is generated in the ceramic body (low temperature part) that is not close to the heat generating part. For this reason, in the case of Comparative Example 1 or Comparative Example 2, which has a heat generating part inside the spiral, thermal expansion occurs deep inside the spiral, and tensile stress is generated at the outer periphery.
Due to the low tensile strength of the ceramic body, it is prone to breakage. On the other hand, when the heat generating part is arranged on the outer periphery as in Example 1,
Although tensile stress is generated deep inside, it is thought that this tensile stress is relaxed between the layers of the relevant portion (the central ceramic spiral) and is thus prevented from breaking. For this reason, two or more turns of the central ceramic spiral are required. Of course, since the interlayers of the spiral are also sintered, the spacing between the layers is not expanded like in a spiral spring, but the bonding force between the layers is weaker than the bonding force within the layers, based on their formation history, so the stress is similar to that of a spiral spring. distribution can be assumed. In this respect, it is thought that a different effect will be produced than when the heating element is placed deep inside the spiral. In short, arranging the heat generating part in the middle or deep part of the spiral does not fully exhibit the effect of the spiral structure. Therefore, in the present invention, the heat generating part is formed on the outer periphery of the spiral ceramic body and at the center. The spiral of the ceramic body is required to have a sufficient thickness or number of turns to disperse and buffer tensile stress.

The above structure and effects of the present invention will become clearer from the following Examples and Comparative Examples. Examples are described below.

Example 1 Alumina with 1% each of magnesia and calcia (hereinafter referred to as weight%)
) and 2% silica were mixed, wet-pulverized for 7 (turns) in a ball mill, and then dehydrated and dried.

This powder/powder contains 3% isobutyl methacrylate.
Nitrocellulose 1%, dioctyl phthalate 0.5%
Further, trichlorethylene and n-butanol were added and mixed in a ball mill to form a slurry. This slurry was degassed under reduced pressure and poured out onto a flat plate to obtain a green sheet with a thickness of 0.3 mm. After the solution has evaporated, this green sheet is cut into a rectangle with a width of 30 m as shown in Figure 1, and a heating resistor pattern and a heating resistor pattern are inscribed on the right side of one surface using metallizing ink mainly composed of tungsten. A lead portion was formed. Thereafter, the green sheet was spirally rolled up starting from the left side edge 1 and with the pattern on the inside of the sheet. At this time, the green sheet was rolled up while applying a solvent to the opposite side of the pattern. In this way, a firing spiral was obtained with five ceramic spirals in the center and one spiral in the pattern portion. This spiral was slowly heated to remove organic matter, and then fired at 1550° C. for 13 hours in a hydrogen atmosphere to obtain a spiral ceramic heating element having an outer diameter of 5.2 mφ, an inner diameter of 2 wfmφ, a total length of 30 wn, and a heating part length of 1''. Note that a terminal was separately formed at the tip of the lead part using gold paste. The rapid heating characteristics of this heating element were as shown in Table 1.

That is, Example 1 had a higher limit temperature than Comparative Examples 1 and 2, and could withstand repeated rapid heating over 100 times. Comparative Example 1 A spiral ceramic heating element was manufactured in the same manner as in Example 1, except that the heating element resistor pattern was provided at the center of the green sheet (in the middle layer of the spiral) as shown in FIG.

The comparative rapid heating test results are shown in Table 1. Comparative Example 2 A spiral ceramic heating element was manufactured in the same manner as in Example 1, except that the heat generating part resistor pattern was formed on the green sheet on the opposite side from Example 1, as shown in FIG.

The comparative rapid heating test results are shown in Table 1. Example 2 A ceramic green sheet with a thickness of 0.6 Tfr1n was made in the same manner as in Example 1, and had a length of 30 h, an outer diameter of 10 i, and an inner diameter of 90 m, the number of turns of the resistor pattern part was 1 turn, and the number of turns of the ceramic spiral in the center was 8 turns. A type cylindrical heating element was obtained.

However, the resistor pattern was formed at the center of the cylinder with a length of 100wn. This product can be used as a Tammann tube and has particularly excellent rapid heating properties.

[Brief explanation of the drawing]

FIG. 1 shows a side view of one embodiment of the invention. FIG. 2 shows an enlarged sectional view of the heat generating portion of the heat generating element shown in FIG. 1 (hatching is omitted). FIG. 3 shows a developed view of the ceramic green sheet of the embodiment shown in FIGS. 1 and 2. FIGS. 4 and 5 show developed views of Comparative Examples 1 and 2, respectively. 1... Spiral shaped ceramic body, 2...
・Ceramic green sheet, 3... Resistance heating element pattern, 4... Lead part, 5... Center margin, 6, 7... Heat generating part, 8... ...Resistive heating element protective outer skin layer, 9...Central ceramic spiral, I...Start end edge on spiral center side, 0...
・End point edge on the outer circumference of the spiral, W...Upward arrow of the spiral.

Claims (1)

[Scope of Claims] 1. A spiral-shaped ceramic body obtained by spirally winding and firing a ceramic green sheet, which has a resistive coating formed on the inside of the ceramic green sheet in one or more spirals from the outer peripheral end, and the resistor A spiral ceramic heating element characterized in that the thickness of the central ceramic spiral from the inner surface of the coating to the center of the spiral is greater than the thickness of the protective outer layer of the resistive coating. 2. The spiral ceramic heating element according to claim 1, wherein the resistive coating is formed over the entire length of the spiral heating element or a portion thereof. 3 Form an inorganic conductive material film pattern on a part of one surface of the ceramic green sheet, and wind up the ceramic green sheet in a spiral shape starting from one side on the margin side and with the inorganic conductive material film pattern on the inside. A method for manufacturing a spiral ceramic heating element characterized by firing. 4. The method for manufacturing a spiral ceramic heating element according to claim 3, wherein the blank space forming a central spiral has at least two turns. 5. The spiral-shaped ceramic according to claim 3 or 4, wherein the inorganic conductive material film pattern is formed on one surface of the ceramic green sheet to have a length of one or more turns from the outer peripheral edge of the spiral. Method of manufacturing heating elements.