EP3595406A1

EP3595406A1 - Ceramic heater

Info

Publication number: EP3595406A1
Application number: EP19185691.3A
Authority: EP
Inventors: Yusuke Makino; Atsutoshi Sugiyama; Yuya HIGASHIDE
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2018-07-12
Filing date: 2019-07-11
Publication date: 2020-01-15
Anticipated expiration: 2039-07-11
Also published as: ES2911664T3; CN110719653A; EP3595406B1; CN110719653B; JP2020009704A; JP6860277B2

Abstract

[Objective] To assuredly ground a ceramic heater to the outside via a metal flange which is joined by an insulating material.

[Means for Solution] A ceramic heater includes: a heater body that is made of ceramic, has a tubular shape, and extends in an axial direction; and a flange that is made of a metal, has an annular shape, and is fitted onto the heater body. A ground wire is connected to the flange. The flange has a recess-shaped portion which includes a side portion that has a cylindrical shape and extends in the axial direction, and a bottom portion that is continuous with the side portion and is curved so as to have a radius reduced in a radial direction. The recess-shaped portion is filled with an insulating material, and is joined to the heater body via the insulating material. The flange further has an extension portion that is continuous with the bottom portion, extends toward an end side in the axial direction, and is directly exposed to water.

Description

[Technical Field]

The present disclosure relates to a ceramic heater for use, for example, in a warm water washing toilet seat, an electric water heater, and a 24-hour bath.

[Background Art]

In general, a warm water washing toilet seat includes a heat exchange unit having a ceramic heater, and a heat exchanger constituted by a container made of resin. The ceramic heater is used for heating washing water in the heat exchanger.
In general, a heat exchange unit (heat exchanger) having a resinous container is used for a warm water washing toilet seat. The heat exchange unit has a tubular ceramic heater mounted thereto in order to heat washing water in the heat exchanger.
As this type of ceramic heater, a ceramic heater, in which an annular metal flange is fitted onto a cylindrical ceramic heater body and the heater body and the flange are joined to each other via glass, is known (see, for example, Patent Document 1).

[Prior Art Document]

[Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2017-069083

[Summary of the Invention]

[Problems to be Solved by the Invention]

In order to prevent an accident in which a heater portion is exposed to water to cause electric leakage due to, for example, a crack being generated in the surface of the ceramic heater, a ground wire is connected to a metal flange to ground the heater to the outside. However, glass for joining the flange has insulating properties. Therefore, as shown in FIG. 6, when the flange is covered by glass up to the outer surface, the outer surface of the flange may not be exposed to water. In this case, since the flange and water do not contact with each other, the heater may not be grounded to the outside.

[Means for Solving the Problems]

A ceramic heater according to one aspect of the present disclosure includes: a heater body that is made of ceramic, has a tubular shape, and extends in an axial direction; and a flange that is made of a metal, has an annular shape, and is fitted onto the heater body. A ground wire is connected to the flange. The flange has a recess-shaped portion which includes a side portion that has a cylindrical shape and extends in the axial direction, and a bottom portion that is continuous with the side portion and is curved so as to have a radius which reduces in a radial direction. The recess-shaped portion is filled with an insulating material, and is joined to the heater body via the insulating material. The flange further has an extension portion that is continuous with the bottom portion, and extends toward an end side in the axial direction, wherein the extension portion is adapted to be directly exposed to water.
The ceramic heater having such a structure can be assuredly grounded to the outside via the ground wire by the extension portion being directly exposed to water.
Furthermore, in the ceramic heater according to one aspect of the present disclosure, the extension portion may protrude beyond the insulating material toward the end side in the axial direction.
In the ceramic heater having such a structure, the extension portion protrudes beyond the insulating material toward the end side in the axial direction, whereby the extension portion can be easily exposed to water.
Furthermore, in the ceramic heater according to one aspect of the present disclosure, the insulating material may be formed from glass.
For the ceramic heater having such a structure, a process step of joining the flange can be simplified.
Furthermore, in the ceramic heater according to one aspect of the present disclosure, the extension portion may protrude in a length of 0.5 mm or more from an outer surface of the bottom portion.
In the ceramic heater having such a structure, since the extension portion protrudes in a length of 0.5 mm or more from the outer surface of the bottom potion, the extension portion can be easily exposed to water.

[Brief Description of the Drawings]

[FIG. 1A] Front view of a ceramic heater according to an embodiment of the present invention.
[FIG. 1B] Partial cross-sectional viewaccording to the embodiment of the present invention, which partial cross-sectional view is obtained by a flange and a glass portion of the ceramic heater being cut along the axial direction.
[FIG. 2] Plan view as viewed through the glass portion of the ceramic heater according to the embodiment.
[FIG. 3] Development of a heater pattern layer side of a ceramic layer of the ceramic heater, according to the embodiment.
[FIG. 4A] Plan view of the flange of the ceramic heater according to the embodiment.
[FIG. 4B] Cross-sectional view taken along A-A in FIG. 4A.
[FIG. 5] Enlarged cross-sectional view of a main portion obtained by the flange and the glass portion of the ceramic heater being cut along the axial direction, according to the embodiment.
[FIG. 6] Enlarged cross-sectional view of a main portion obtained by a flange and a glass portion of a ceramic heater being cut along the axial direction, according to conventional art.
[FIG. 7] Enlarged cross-sectional view of a main portion obtained by the flange and the glass portion of the ceramic heater being cut along the axial direction, according to the embodiment.
[FIGS. 8A to 8F] Views illustrating a method for producing the ceramic heater according to the embodiment.

[Modes for Carrying Out the Invention]

A ceramic heater and a method for producing the ceramic heater according to one embodiment of the present invention will be described below with reference to FIG. 1 to FIG. 8.
A ceramic heater 11 according to the present embodiment is, for example, used for heating washing water in a heat exchanger of a heat exchange unit in a warm water washing toilet seat.
As shown in FIG. 1 and FIG. 2, the ceramic heater 11 includes a cylindrical ceramic heater body 13, and an annular metal flange 15 which is fitted onto the heater body 13. The heater body 13 includes a ceramic tube 17, and a ceramic layer 19 that covers almost the entirety of the outer circumference of the ceramic tube 17. In the present embodiment, the ceramic tube 17 is set so as to have an outer diameter of 10 mm, an inner diameter of 8 mm, and a length of 65 mm, and the ceramic layer 19 is set so as to have a thickness of 0.5 mm and a length of 60 mm. The ceramic layer 19 does not fully cover the outer circumference of the ceramic tube 17. Therefore, an outer circumferential surface 14 of the heater body 13 has a groove 21 formed so as to extend along the axial direction and have, for example, a width of 1 mm and a depth of 0.5 mm.
The ceramic tube 17 and the ceramic layer 19 of the heater body 13 are formed from, for example, alumina. The alumina has a thermal expansion coefficient in a range of 50×10^-7/K to 90×10^-7/K, and the alumina according to the present embodiment has a thermal expansion coefficient of 70×10^-7/K (30°C to 380°C) .
As shown in FIG. 3, a heater pattern layer 22 having a meandering pattern shape, and a pair of internal terminals 23 are formed on the inner circumferential surface (the surface on the ceramic tube 17 side) of the ceramic layer 19 or inside the ceramic layer 19. The internal terminals 23 are electrically connected, through a not-illustrated via conductor or the like, to external terminals 25 (see FIG. 1) disposed at end portions, on the outer circumferential surface, of the ceramic layer 19.
As shown in FIG. 4, the flange 15 is, for example, an annular member formed from a metal such as stainless steel, and, in the flange 15, the center portion of a plate material is bent toward a first surface S1 side to form a recess (cup shape). More specifically, the flange 15 of the present embodiment is, for example, formed by a plate material having a thickness of 1 mm being bent. A hole 27 is formed, at the center portion of the plate material, so as to penetrate through the first surface S1 that is an inner surface and a second surface S2 that is an outer surface. In the present embodiment, the inner diameter of a recess-shaped portion 16 on the opening side (that is, the upper side in FIG. 4B) is set as, for example, 16 mm. Meanwhile, the inner diameter of the recess-shaped portion 16 on the bottom side (that is, the lower side in FIG. 4B), that is, the inner diameter of the hole 27 is set as, for example, 12 mm. Furthermore, a ground wire 34 (see FIG. 1) is connected at the opening of the recess-shaped portion 16 to ground the ceramic heater to the outside.
The entire height H1 (the up-down direction in FIG. 4B) of the flange 15 is, for example, 6 mm. The flange 15 includes a bottom portion 29 which is curved with a radius r (for example, 1.5 mm), a cylindrical side portion 31 that extends upward (in the axial direction) from the bottom portion 29, and an extension portion 32 that extends downward (in the axial direction) from the bottom portion 29. That is, the flange 15 has the recess-shaped portion 16 which includes: the cylindrical side portion 31 that extends in the axial direction; and the bottom portion 29 that is continuous with the side portion 31 and is curved so as to reduce the diameter in the radial direction. The flange 15 further includes the extension portion 32 that is continuous with the bottom portion 29, extends toward the end side in the axial direction, and is directly exposed to water.
For example, a height H2 from the outer surface, on the end side, of the bottom portion 29 to a lower end of the extension portion 32 is 1.5 mm, and a height H3 from the outer surface, on the end side, of the bottom portion 29 to the upper end of the opening is 4.5 mm. The radius r represents a radius on the cross-section taken along the axial direction.
The thermal expansion coefficient of the metal of the flange 15 has a value in a range of 100×10^-7/K to 200×10^-7/K. For example, when the flange 15 is formed from SUS304 (main component is Fe, Ni, Cr), the thermal expansion coefficient is 178×10^-7/K (30°C to 380°C), and, when the flange 15 is formed from SUS430 (main component is Fe, Cr), the thermal expansion coefficient is 110×10^-7/K (30°C to 380°C).
In the present embodiment, as shown in FIG. 5, in the recess-shaped portion 16 of the flange 15, a space surrounded by the outer circumferential surface 14 of the heater body 13 and the first surface S1 that is the inner surface of the flange 15 is a glass-accumulated portion 35 which is filled with glass 33. In FIG. 1 and FIG. 2, the glass 33 portion is indicated by hatching.
A first end represents the upper end in FIG. 3, and a second end represents the lower end in FIG. 3. Furthermore, the first end of a wiring portion disposed between paired wiring portions when the ceramic sheet 19 is viewed in the thickness direction is connected via a connection portion to the first end of an adjacent wiring portion, and the second end of the wiring portion disposed therebetween is connected via the connection portion to the second end of an adjacent wiring portion.
The glass-accumulated portion 35 is filled with the glass 33 up to 1/3 or more of a height H4 of the glass-accumulated portion 35, and the heater body 13 and the recess-shaped portion 16 of the flange 15 are welded and bonded to each other via the glass 33.
As the glass 33, for example, Na₂O·Al₂O₃·B₂O₃·SiO₂ based glass, that is, Al₂O₃·B₂O₃·SiO₂ based glass (borosilicate glass) is used. For example, the thermal expansion coefficient of the glass 33 has a value in a range of 50×10^-7/K to 90×10^-7/K (30°C to 380°C), and is 62×10^-7/K (30°C to 380°C) in the present embodiment.
As shown in FIG. 7 which is an enlarged view of FIG. 5, a gap 39 that has a size of, for example, about 0.1 mm to 1.0 mm is formed between an inner surface 28 of the hole 27 disposed on the bottom portion 29 side of the recess-shaped portion 16, and the outer circumferential surface 14 of the heater body 13. In the present embodiment, the dimension Y of the gap 39 is set to be about 0.3 mm to 0.5 mm. A part of the glass 33 with which the glass-accumulated portion 35 on the first surface S1 side is filled, flows into the gap 39 in the axial direction along the outer circumferential surface 14 of the heater body 13.
In the case of the flange 15 shown in FIG. 7, the extension portion 32 is formed so as to extend downward (in the axial direction) from the bottom portion 29 of the flange 15 and include the circumferential edge of the hole 27 on the second surface S2 side. In other words, the extension portion 32 extends downward from the bottom portion 29. The extension portion 32 of the present embodiment is formed by the lower end of the bottom portion 29 being bent.
In the ceramic heater 11 of the present embodiment, since the extension portion 32 having such a structure is disposed on the second surface S2 side, the flange 15 protrudes toward the end side beyond a region in which the glass 33 flows along the axial direction. Thus, the extension portion 32 is not covered by the glass 33, and is assuredly exposed to water, whereby the ceramic heater can be assuredly grounded via the ground wire 34 to the outside.
Next, a method for producing the ceramic heater 11 of the present embodiment will be described with reference to FIG. 8.
Firstly, as shown in FIG. 8A, a cylindrical ceramic tube 17 made of an alumina-based material is preliminarily baked.
As shown in FIG. 8B, a metal such as tungsten having a high melting point is printed on the surface of a ceramic sheet 51 made of an alumina-based material, or inside the stacked sheets. Thus, a pattern 53 which forms the heater pattern layer 22, the internal terminals 23, and the external terminals 25 at a later stage is formed.
Next, ceramic paste (alumina paste) is applied to the one side surface of the ceramic sheet 51, and, as shown in FIG. 8C, the ceramic sheet 51 is wound around and adhered to the outer circumferential surface of the ceramic tube 17, and the ceramic sheet 51 and the ceramic tube 17 are integrally baked. Thereafter, the external terminals 25 are nickel-plated to form the heater body 13.
Next, a plate material formed from stainless steel is press-molded to form the flange 15 which is cup-shaped. Thereafter, the flange 15 is fitted onto the heater body 13 at a predetermined mounting position, as shown in FIG. 8D. In this state, the heater body 13 and the flange 15 are supported by a not-illustrated tool.
A glass material formed from borosilicate glass is press-molded so as to be ring-shaped, and the obtained product is calcined at 640°C for 30 minutes to produce a calcined glass material 55. As shown in FIG. 8E, the ring-shaped glass material 55 having been calcined is disposed in the glass-accumulated portion 35 between the heater body 13 and the flange 15.
Next, the obtained product in this state is put into a continuous furnace for baking, to adhere the heater body 13 and the flange 15 by the glass. Specifically, the obtained product is heated in the continuous furnace in a reducing atmosphere (for example, N₂+5%H₂) at a welding temperature (1015°C) for a predetermined period of time, to fuse the calcined glass material 55. Thereafter, the calcined glass material 55 is cooled to room temperature (for example, 25°C) and solidified, whereby the heater body 13 and the flange 15 are welded and fixed via the glass 33, to complete the ceramic heater 11.

[Description of Reference Numerals]

11:: ceramic heater
13:: heater body
15:: flange
16:: recess-shaped portion
27:: hole
33:: glass
35:: glass-accumulated potion

S1:: first surface
S2:: second surface

Claims

A ceramic heater (11) comprising:
a heater body (13) that is made of ceramic, has a tubular shape, and extends in an axial direction; and

a flange (15) that is made of a metal, has an annular shape, and is fitted onto the heater body (13), wherein

a ground wire (34) is connected to the flange (15),

the flange (15) has a recess-shaped portion (16) which includes a side portion (31) that has a cylindrical shape and extends in the axial direction, and a bottom portion (29) that is continuous with the side portion (31) and is curved so as to have a radius which reduces in a radial direction,

the recess-shaped portion (16) is filled with an insulating material (33), and is joined to the heater body (13) via the insulating material (33), and

the flange (15) further has an extension portion (32) that is continuous with the bottom portion (29), and extends toward an end side in the axial direction, wherein the extension portion (32) is adapted to be directly exposed to water.
The ceramic heater (11) according to claim 1, wherein the extension portion (32) protrudes beyond the insulating material (33) toward the end side in the axial direction.
The ceramic heater (11) according to claim 1 or claim 2, wherein the insulating material (33) is formed from glass.
The ceramic heater (11) according to any one of claims 1 to 3, wherein the extension portion (32) protrudes in a length of 0.5 mm or more from an outer surface of the bottom portion (29).