JPH0689775A - Manufacture of ceramic heater - Google Patents

Abstract

PURPOSE:To provide a ceramic heater having excellent durability and presenting good thermal efficiency by locating a heat emitting element precisely, reducing the thickness of a protection layer for the heat emitting element, and thereby lessening the temp. difference between the element and the surface of protection layer and also lessening thermal stresses. CONSTITUTION:A heat emitting element 12 is provided on the surface of the ceramic base 11. A protection layer 14 subjected to a sintering process is provided over the surface of this ceramic base 11. The protection layer 14 is ground into a specified thickness, and a ceramic heater is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic heater, and more particularly to a method for manufacturing a ceramic heater suitable for use in a glow plug of a diesel engine using a flame retardant fuel.

[0002]

2. Description of the Related Art Generally, a ceramic heater is used as a heating element in a glow plug of a diesel engine.
This ceramic heater has a structure in which a tungsten wire or the like is arranged as a heating element in the ceramic layer to protect the heating element. When this ceramic heater 3 is manufactured, as shown in FIG. 7, a heating element 1 made of a tungsten wire or the like is formed in a coil shape inside a ceramic powder 2 and is placed in a predetermined shape. Sintered at the temperature of.

[0003]

However, the above-mentioned general method for manufacturing a ceramic heater has a problem that it is difficult to form a ceramic heater having a heating element embedded in a predetermined shape. That is, when the coil-shaped heating element 1 is embedded in the ceramic powder 2 and sintered, the ceramic powder 2 moves and contracts by press molding and sintering.

As a result, as shown in FIGS. 8 (a) and 8 (b), the shape of the heating element 1 is deformed into an elliptical shape, the coil intervals are not uniform, and the heating element 1 is covered. The thickness of the ceramic layer (protective layer) that is being used will change. In this way, the front shape of the heating element 1 changes to an ellipse or the like,
The intermediate product of the ceramic heater, in which the intervals between the coils are non-uniform and the thickness of the ceramic layer covering the heating element 1 is changed, is ground in a subsequent finishing step, but the thickness of the ceramic layer covering the heating element 1 is increased. However, it is not possible to reduce the distance between the ceramic surface and the ceramic surface.

In the ceramic heater 3 having such a relatively thick ceramic layer, the temperature difference between the heating element 1 and the surface of the ceramic layer 3 becomes large, and a large thermal stress is generated, so that the ceramic heater 3 is easily damaged. There's a problem. This tendency is great especially in ceramic heaters used at high temperatures, and is a main cause of low reliability.

[0006]

The present invention has been made in order to solve the above-mentioned conventional problems, and comprises the steps of sintering ceramic powder to form a substrate, and attaching a heating element to the surface of the substrate. A step of covering the heating element with a ceramic powder of the same quality as the substrate, arranging a protective layer, hot pressing the substrate having the protective layer formed thereon, and grinding the sintered protective layer; Is a method for manufacturing a ceramic heater.

[0007] Preferably, the protective layer is formed by mixing a ceramic powder with a binder, and is formed by compacting. Further, the surface of the protective layer is covered with a ceramic powder which is difficult to sinter and has good fluidity, and hot press sintering is performed.

[0008]

EXAMPLE An example of a method for manufacturing a ceramic heater according to the present invention will be described below with reference to FIGS.
In FIG. 1, reference numeral 11 denotes a rod-shaped (round, plate-shaped, oval, etc.) substrate, which is formed by sintering a sinterable ceramic powder such as aluminum nitride, silicon nitride or alumina. (Substrate forming step).

A heating element 12 made of tungsten or the like is attached to the surface of the base 11 (step of attaching the heating element to the base). The heating element 12 is cut out in a zigzag shape or the like using a foil of tungsten, and attached by using an adhesive such as a silane-based adhesive. In addition, a method of winding a linear heating element in a coil shape is also used depending on the application. The shape of this heating element is determined by the distribution of the heating portion required as a heater. As the thin foil-shaped heating element, a tungsten foil having a thickness of about 0.02 to 0.20 mm is used.

Further, mark layers 13 made of a high melting point metal foil are wound around the both ends of the base 11 for a predetermined length. The mark layer 13 of the high melting point metal foil has a base 11 after the protective layer 14 described later is sintered.
It serves to prevent close contact with and to leave it as a centering position when the protective layer 14 is ground. The high melting point metal foil having a thickness of about 0.05 to 0.20 mm is used.

After the heating element 12 and the marking layer 13 are attached to the surface of the base 11 in this manner, the protective layer 14 is formed as shown in FIG. The protective layer 14 is formed by mixing, for example, a non-aqueous binder with a sinterable ceramic powder such as aluminum nitride having the same quality as the ceramic of the base 11, and the base 11 is placed in this mixture. Then, pressure is applied from the outer circumference of the base 11 so that a uniform external force acts (molding step).

The substrate 11 thus coated with the thick protective layer 14 is hot-press sintered (sintering step). In this case, as shown in FIGS. 3 (a) and 3 (b), the protective layer
It is preferable to fill the periphery of 14 with a ceramic powder 15 that is more difficult to sinter than the ceramic powder on which the substrate 11 such as boron nitride is formed and has good fluidity as a pressurizing material and perform hot press sintering. At this time, since the ceramic powder 15 is not sintered by hot press sintering, excellent fluidity is not impaired. Therefore, the ceramic powder 15 propagates the uniaxial pressing pressure P of hot press sintering to the protective layer 14 and the base 11 in a form close to the hydrostatic pressure, and the deformation of the base 11 can be minimized.

After the completion of the sintering process, the ceramic powder 15 as a pressurizing material is removed, and as shown in FIG. 4, the base material 16, the heating element 12, the refractory metal foil 13 and the base material 16 having the protective layer 14 are removed. It is formed. In this base material 16, the deformation of the base 11 and the heating element 12 is small, and the protective layer 14 is formed as a dense ceramic material having no continuous pores. The end portion of the base material 16 manufactured in this way is first ground. Specifically, as shown in FIG. 5, after the protective layer 14 ′ on the outer periphery of the mark layer 13 made of a high melting point metal foil is ground, the mark layer 13 is peeled off to expose the end portion of the base 11. . Then, the protective layer 14 is ground to have a predetermined thickness t while performing centering using the exposed end of the base 11 (grinding step).
As a result, the ceramic heater 17 is manufactured as shown in FIG.

In this case, the thickness of the protective layer t, specifically, the distance between the heating element 12 and the surface of the protective layer 14 is ground to be about 0.2 to 0.6 mm. When the ceramic heater 17 manufactured in this manner is used at a relatively high temperature of, for example, 1000 ° C. or higher, when the protective layer 14 is formed of aluminum nitride, a silicon carbide film formed by a vapor phase method is further formed on the surface thereof. It is preferably formed. That is, there is a problem that the protective layer 14 is oxidized at such a high temperature. Such a silicon carbide film is excellent in oxidation resistance and corrosion resistance, and therefore the oxidation resistance and corrosion resistance of the protective layer 14 can be improved.

[0015]

The method of manufacturing a ceramic heater according to the present invention comprises the steps of sintering ceramic powder to form a base, attaching a heating element to the surface of the base, and heating the heating element with a ceramic powder of the same quality as the base. It comprises a step of covering and disposing a protective layer, hot pressing and sintering the substrate on which the protective layer is formed, and a step of grinding the sintered protective layer.

Therefore, it is possible to manufacture a predetermined ceramic heater in which the heating element is not deformed and the distance between the protective layer surfaces is small. As a result, the temperature difference between the heating element and the surface of the protective layer is reduced, and therefore the thermal stress is reduced, and the durability of the ceramic heater is reduced. Further, in order to grind the protective layer to a predetermined thickness, the thickness of the protective layer on the heating element can be accurately ensured while confirming the position of the heating element arranged on the base with the mark layer,
A highly efficient ceramic heater can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a step of providing a heating element and a marking layer on a substrate in one example of the present invention.

FIG. 2 is an explanatory diagram of a protective layer forming step.

3A and 3B are explanatory views of a process of sintering the protective layer while applying pressure.

FIG. 4 is an explanatory diagram of a sintering process.

FIG. 5 is an explanatory diagram of a grinding process.

FIG. 6 is an explanatory diagram of a ceramic heater.

FIG. 7 is an explanatory view of a manufacturing process of a conventional ceramic heater.

8A is a side view of a ceramic heater manufactured by a conventional manufacturing method, and FIG. 8B is a front view of the same.

[Explanation of symbols]

1, 12 Heating element 2 Ceramic 3, 17 Ceramic heater 11 Base material 13 Mark layer 14 Protective layer 15 Ceramic powder 16 Base material.

Claims (3)

[Claims] 1. A step of forming a base by sintering ceramic powder, a step of mounting a heating element on the surface of the base, a heating layer is covered with a ceramic powder of the same quality as the base, and a protective layer is arranged to protect the heating element. A method of manufacturing a ceramic heater, comprising: a step of hot-press sintering a substrate having a layer formed thereon; and a step of grinding a sintered protective layer. 2. The method for producing a ceramic heater according to claim 1, wherein the surface of the protective layer is hard to sinter and is covered with a ceramic powder having a good fluidity and then hot press-sintered. 3. A step of forming a base by sintering ceramic powder, a step of mounting a heating element on the surface of the base, a step of forming a mark layer at an end of the base, and a step of forming the base with a ceramic powder of the same quality as the base. A method of manufacturing a ceramic heater, comprising: a step of coating a heating element with a protective layer; hot-sintering a substrate having the protective layer formed thereon; and a step of grinding the sintered protective layer.