JPH0778676A - Cartridge heater - Google Patents

Abstract

PURPOSE:To secure the safety with a cartridge heater by allowing its heat emitting body itself to sense any failure in heating in the case a cause of partial heating is generated, and thereupon controlling the fed current. CONSTITUTION:A metal pipe 1 is equipped in the center of its inside with a self-controlled heat emitting body 3 in powder form which controls heat emission through a great increment of its own resistance when the temp. exceeds the Curey point. and the gap between this heat emitting body 3 and the inside of the metal pipe 1 is filed with an electrically insulative powder 4. An electrode 5 is embedded in the heat emitting body 3, and one end thereof is protruded to outside of the pipe 1, and its open end is sealed by a seal plate 2 and with a sealing material of glass 6 and insulative material 7. Even though a cause of partial heating is generated in the heater, the heat emitting body's own resistance increases greatly to restrict the current flowing when the temp. of the part with temperature running exceeds the Curie point of the body 3, and thereby the heat emission is self-controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cartridge heater used as an underwater heating heater for raising the temperature of a mold.

[0002]

2. Description of the Related Art In a conventional cartridge heater of this type, a cylindrical insulating core wound with a heating wire is inserted into a metal pipe whose one end is sealed, and an electrically insulating powder is filled around the insulating core, and the other end is filled. The lead wire is led out from the opening.

This heater accelerates the temperature rise of the mold,
Since it is used as an underwater heater, it is usually used in a state where the surface power density of the heater is extremely high. Therefore, if abnormal heating occurs, it is burnt or broken, which is dangerous for safety.

As an invention for preventing this abnormal heating, for example, as shown in FIG. 4, a heat sensitive wire 11 having a melting point lower than that of the heat generating wire 10 is connected in series with the heat generating wire 10 in the metal pipe 1 and installed. Sometimes, the one that melts the heat sensitive wire 11 is open to the public. (For example, Japanese Patent Laid-Open No. 59-56386) A method of detecting temperature by installing a thermocouple in a cartridge heater has also been disclosed. (For example, 59
-2089)

[0005]

In the case where the heat-sensitive wire 11 having a low melting point is used for preventing abnormal heating as described above, since the heat-sensitive wire 11 is embedded in the electrically insulating powder 4,
Even if it melts during abnormal heating, the electrically insulating powder 4 may maintain the original shape while covering the heat-sensitive wire 11, and there is a drawback that the effect of cutting off the current cannot be fully exerted.

In the case where the thermocouple is installed inside the metal pipe, the performance greatly depends on the position where the thermocouple is installed when used as an underwater heater, for example.

For example, if the thermocouple is located below the water surface when a part of the underwater heater is exposed above the water surface due to a decrease in the amount of water, abnormal heating cannot be detected, the exposed portion becomes an abnormal heating state, and burnout occurs. Or wire breakage occurs. Such a drawback becomes more remarkable as the cartridge heater becomes longer.

[0008]

The present invention has been made to solve the above-mentioned drawbacks. In the first aspect of the invention, when the temperature exceeds the Curie point at the inner center of the metal pipe, the present invention itself Control the heat generation by significantly increasing the resistance of
That is, positive resistance-temperature characteristic (hereinafter referred to as PTC characteristic)
With a powdery self-regulating heating element having
An electrically insulating powder is filled between the self-control heating element and the inside of the metal pipe, and an electrode is embedded in the self-control heating element, and one end of the electrode is projected to the outside of the metal pipe.

According to the second aspect of the invention, the self-regulating heating element is formed into a bobbin shape and disposed in a metal pipe, which is compressed from the outside of the metal pipe to be crushed into a powder form. Is.

Further, in the third aspect of the invention, there are two or more electrodes embedded in the self-regulating heating element, and one end of each of the electrodes is projected outside the metal pipe.

[0011]

When the cartridge heater is used for heating a mold or the like, if a partial cause of heating occurs, when the temperature of that portion exceeds the Curie point, the resistance of the cartridge itself increases remarkably. Limit and self-control fever. When used as an underwater heater such as a water heater, water is heated by the heat generated by the self-control heating element itself,
When the water evaporates and the heater is exposed, the temperature of the exposed part rises, the self-controlled heating element detects this temperature rise and the specific resistance of itself increases, limiting the energizing current to keep a safe temperature. Hold.

In the case of the second aspect of the invention, the conventional equipment can be used as it is for manufacturing the cartridge heater.

Further, in the case of the third aspect of the invention, one self-controlled heating element is in a state equivalent to a case where a plurality of self-controlled heating elements are respectively connected in parallel, and an economic effect can be measured.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

In the figure, 1 is a metal pipe, one end of which is sealed with a sealing plate 2 made of the same material. Reference numeral 3 denotes a self-controlled heating element made of a semiconductor such as ceramics, which has a PTC characteristic and is disposed in a powder form at the center of the metal pipe 1. An electrically insulating powder 4 made of magnesia oxide or the like is filled between the inner surface of the metal pipe 1 and the self-control heating element 3. Reference numeral 5 denotes an electrode, which is composed of two or more (two in the figure), one end of which is embedded in a part of the self-control heating element 3, and the other end of which is projected in parallel to the outside of the metal pipe 1. A sealing material 6 seals the other end of the metal pipe 1, and melts the glass and then cools it to seal the end of the metal pipe 1 to prevent moisture absorption. An insulating material 7 made of silicon rubber or the like is attached to the outside of the sealing material 6 and serves to increase the creepage insulation distance at the end of the metal pipe 1.

In the above structure, the manufacturing method will be described. A bobbin-shaped self-controlled heating element 3 having a plurality of holes for inserting electrodes is prepared in advance, and the electrode 5 is inserted into the hole of the heating element 3. This is arranged in the central portion of the metal pipe 1 whose one end is sealed by the sealing plate 2, and the electrically insulating powder 4 is filled between the heating element 3 and the inner surface of the metal pipe 1.

Next, the metal pipe 1 is compressed from the outside to crush the bobbin of the self-controlled heating element 3 to improve the electrical contact between the electrode 5 and the self-controlled heating element 3 and, at the same time, the self-controlled heating element 3 itself. Make good electrical contact. After that, the open end of the metal pipe 1 is sequentially sealed with the glass sealing material 6 and the insulating material 7, and the manufacturing is completed.

According to the above construction, when a voltage is applied to the self-controlled heating element 3 between the electrodes 5 and 5, a current according to the internal resistance flows, Joule heat is generated according to Joule's law, and the metal pipe 1 Dissipates heat from the outer wall surface of.

When heating is performed, the metal pipe 1 is heated by the heat generated by the self-regulating heating element 3, and the heat is radiated from the outer surface of the metal pipe 1 to raise the temperature of the object to be heated. When a cause of heating occurs and the temperature at that portion exceeds the Curie point, the resistance of the device itself significantly increases to limit the flowing current and self-control heat generation. See also FIG.
When this cartridge heater is used for heating water in the water heater 8 as shown in FIG.
Since they are arranged in parallel, it is the same as connecting a plurality of self-controlling heating elements 3 in parallel between the plurality of electrodes 5, so if the Curie point is set appropriately, the self Even when a part of the control heating element 3 is exposed to water 9 and is energized, the part immersed in the underwater part is
Since it continues to be cooled by, a large amount of Joule heat is generated and water is efficiently heated. On the other hand, the exposed part becomes high resistance when it exceeds the Curie point, the amount of heat generation is suppressed, and it is prevented from reaching a dangerous temperature, and wasteful heat radiation released into the air is suppressed, and both safety and energy saving are achieved. To be realized at the same time.

Next, FIG. 3 shows another embodiment of the present invention. The difference from FIG. 1 is that the electrode 5 is projected outward from both ends of the metal pipe 1, and the openings at both ends of the metal pipe 1 are opened. It is sealed with a glass sealing material 6 and an insulating material 7 such as silicon rubber.

Also in this embodiment, the function of the self-regulating heating element 3 is the same as that shown in FIG. 1, and it is suitable for use in, for example, temperature rise and control of a mold and the like.

[0023]

As described above, according to the present invention, the powdery self-controlling heating element having the PTC characteristic is disposed in the inner central portion of the metal pipe 1, and the heating element and the inner surface of the metal pipe. Since I filled the electric insulation powder between
Even if the heater causes a partial heating, the self-control heating element itself detects this abnormal heating and limits the flowing current, and self-controls the heat generation, so that safety and energy saving can be realized at the same time.

When the self-regulating heating element is formed into a bobbin shape and is inserted into the metal pipe and then the metal pipe is compressed and crushed, the conventional equipment can be used as it is in the production. Furthermore, when the number of electrodes embedded in the self-controlled heating element is two or more, the state becomes equivalent to connecting a plurality of self-controlled heating elements in parallel with one self-controlled heating element, which is economically effective. It can be measured.

[Brief description of drawings]

FIG. 1 is a sectional view of a cartridge heater according to the present invention.

FIG. 2 is a cross-sectional view when the heater is used as an underwater heating heater.

FIG. 3 is a sectional view of another embodiment of the heater.

FIG. 4 is a sectional view of a conventional cartridge heater.

[Explanation of symbols]

 1 Metal Pipe 3 Self-Controlled Heating Element 4 Electrical Insulation Powder 5 Electrode

Claims (3)

[Claims] 1. A powdery self-controlling heating element (3) is disposed in the center of the inside of the metal pipe (1) to control the heat generation by significantly increasing the resistance of the metal pipe when the temperature exceeds the Curie point. At the same time, an electrically insulating powder (4) is filled between the self-regulating heating element (3) and the inner surface of the metal pipe (1), and an electrode (5) is placed in the self-controlling heating element (3).
A cartridge heater in which one end is embedded and one end thereof is projected to the outside of the metal pipe (1). 2. A self-regulating heating element (3) is formed into a bobbin shape and disposed in the inner central part of the metal pipe (1), which is compressed from the outside of the metal pipe (1) and crushed to obtain powder. The cartridge heater according to claim 1, which is formed into a shape. 3. A cartridge heater according to claim 1, wherein there are two or more electrodes (5) embedded in the self-regulating heating element (3), and one end of each of these electrodes is projected outside the metal pipe (1).