JPS636625Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an airtight ceramic heating element.

Many proposals have been made for ignition sources such as glow plugs and intake burners using ceramic heaters for the purpose of promoting ignition in various combustion heating devices or internal combustion engines. This kind of ceramic heater has a heating resistor pattern formed by a printing method in a ceramic body such as alumina or silicon nitride, or a heating resistor made of a high-melting point metal wire such as tungsten or molybdenum formed into a predetermined shape, and is embedded in the ceramic body to generate heat. By applying electricity from the leads that extend both ends of the resistor (pattern) to the outside, it generates joule heat and acts as a heater.Such a ceramic heater has a dense heat-generating resistor and is heat resistant. It is embedded in a ceramic body with a heat-resistant structure and is isolated from the outside air, making it less susceptible to oxidation and corrosion. It does not erode or deteriorate even in liquids or atmospheres where it cannot be used, and it has many features such as long life and quick temperature rise characteristics.

However, a ceramic heater with such excellent characteristics is held on a metal support to accelerate the startup of an internal heat engine.
In the glow plug G as shown in the figure, the ceramic body 1 constituting the ceramic heater and the metal holding fitting 2 that holds it are attached by brazing with a brazing material 3. In many cases, the holding fitting 2, to which the ceramic body 1 is attached by brazing, is further attached to the metal body 5 with brazing in an airtight manner in a high-temperature furnace. When brazing is performed, the strength of the metal holder 2 and main body 5 is significantly degraded, so the reality is that a high-frequency induction heating method must be used. However,
When high-frequency heating is performed to braze the holder 2 and the main body 5, only the metal holder 2 and the main body 5 are heated to a high temperature. Therefore, the ceramic body 1 that forms the heater, which is pre-attached to the holder 2 with the brazing material 3, is not heated but at a low temperature, and the brazing material 3 may melt or the ceramic body 1 and the ceramic body 1 may be held together. There was a risk that cracks or cracks would occur in the brazing material 3 due to the difference in thermal expansion with the tool 2.

Not only when performing brazing processing in this way,
When the heater generates heat or is present in a high temperature atmosphere, the ceramic body 1 and
In particular, the difference in thermal expansion with the holder 2 was the main cause of many problems. That is, ceramic body 1
One lead of the heating resistor (not shown) embedded in the holder 2 is brazed to the holder 2 for electrical connection, so if the brazing material 3 melts or cracks, the electrical Not only is there a risk of poor connection or disconnection, but also some oil and moisture from the fuel may enter the main body 5 from the outside through cracks or crevices in the brazing material 3. In particular, moisture that has entered the ceramic body 1 is likely to enter from the heating resistor and the boundary portion in contact with the heating resistor at the portion where the lead wire is led out from the ceramic body 1. For this reason, the moisture that has entered the ceramic body 1 is heated to a high temperature and undergoes rapid thermal expansion, causing cracks in the ceramic body 1, which may cause serious inconveniences such as damage to the ceramic heater. .

This product was developed in view of the above circumstances, and is characterized by being able to maintain airtightness even if cracks occur in the brazing material at the joint between the ceramic body and the metal holder. The aim is to provide a ceramic heater that

Hereinafter, embodiments of the present invention will be explained with reference to figures. Note that the same parts as in the conventional example are designated by the same reference numerals. Second
As shown in FIG. 3, which is an enlarged cross-sectional view of the envelope portion A in the figure, a ceramic body 1 having a heating resistor (not shown) embedded therein and constituting a heater is inserted into a cylindrical holder 2. The ceramic body 1 is fixed to the holder 2 by the presence of the brazing material 3, and the holder 2 is then heated and brazed to the main body 4 by a high frequency induction heating method or the like.

In this way, an organic sealing material P such as a synthetic resin is applied to the outer periphery of the part where the ceramic body 1 and the holder 2 are brazed, so that the holder 2
When the ceramic body 4 is brazed to the main body 4, even if minute cracks occur in the brazing material 3 used to braze the ceramic body 1 and the holder 2, the cracks are clogged. It turns out.

The ceramic heater constructed as described above was actually applied to a glow plug as a starting promotion device for a diesel engine, and the amount of air leakage was measured each time the heater was used. The results are shown in FIG. In this case, glow plugs coated with either a thermosetting resin or a thermoplastic resin as the sealing material P showed almost the same tendency. However, the sealing material P applied to the joint by the brazing material 3 is partially melted or carbonized as a result of the heat generation of the ceramic heater or exposure to high temperatures of 600 to 1000°C in the pre-combustion chamber of the engine. A portion of carbon as an unburned component of the engine fuel enters into the cracks present in the brazing filler metal 3 and gradually exerts a sealing effect. Therefore, for structures such as glow plugs and intake burners using ceramic heaters, a brazing material 3 is used to join the ceramic body 1 and the metal holder 2.
By applying the sealing material P to the outer periphery of the filler metal 3, the amount of leakage can be reduced to almost zero at the beginning of engine startup, as is clear from the graph in Figure 4. Even if the sealing material P is burned out during engine operation, some of the carbon and unburned components of the fuel will remain intact. A portion of the carbon enters the crack and gradually exhibits sealing properties, achieving the effect of almost completely blocking the amount of leakage through the crack after 5 hours of operation. When installed in the engine in this manner, it is possible to provide the sealing effect by the sealing material P until immediately after the engine is started.

Furthermore, as shown in the graph of FIG. 5, in the case of a conventional glow plug in which the sealing material P is not applied to the outer circumferential portion of the brazing material 3 that joins the ceramic body 1 and the metal holder 2, the unburned fuel It takes 7.5 hours for some of the component carbon to enter the crack and gradually exhibit sealing properties, and the amount of air reeled during this time is large, which may cause the various problems mentioned above.

Incidentally, in the above embodiment, a case was described in which the sealing material was applied only to the outer circumference of the brazing material 3 that joins the ceramic body 1 and the holder 2 to provide a sealing effect, but in addition to this, the holder 2 It is sufficient to apply an organic substance as a sealant to the joint portion between the body 4 and the body 4, and more preferably, it is applied to the entire front half of the body 4 including the ceramic body 1 and the holder 2. One method of coating may be to dip the front half in a solution of synthetic resin, rubber, etc. at a predetermined concentration. Note that it is more effective if the thickness of the organic substance to be applied is 0.3 mm or more.

As described above, according to the present invention, an organic substance such as synthetic resin or rubber is applied to at least the joint between the ceramic body and the metal body of the ceramic heating element to provide initial sealing properties. It is possible to prevent oil, moisture, etc. from entering the heater, and therefore it is possible to extend the life of the heater without causing troubles due to these oils and moisture. In addition, by coating the front half of the main body including the ceramic body and the holder with an organic substance, the ceramic body or the ceramic body can be used as a heater when transporting the ceramic heating element or installing it in various devices. It is possible to provide a ceramic heater that has many effects, such as being able to prevent breakage of the ceramic body due to collision between the ceramic body and the metal body.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway view of a glow plug using a ceramic heater, FIG. 2 is a partially cutaway view of a glow plug as a ceramic heating element according to an embodiment of the present invention, and FIG. It is an enlarged cross-sectional view of only the envelope part A in the figure. FIG. 4 is a graph showing the amount of air leakage for each operating time when a glow plug in which a ceramic heater according to the present invention has a sealing property is attached to a diesel engine. FIG. 5 is a graph showing the amount of air leak for each operating time when a conventional glow plug using an untreated ceramic heater is installed in a diesel engine. 1: Ceramic body, 2: Holder, 3: Brazing material,
4: Main body.

Claims (1)

[Scope of utility model registration request] A ceramic heater comprising a heater having a heating resistor embedded in a ceramic body at the tip end and a holding mechanism and an energizing mechanism for the heater at the rear end, at least the ceramic body constituting the heater and the holding mechanism. An airtight ceramic heater characterized by having an organic substance coated on the joint with the metal body forming the heater.