JPH0787114B2 - Sheath heater - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sheathed heater in which a heating wire is arranged in a metallic tubular sheath (protective tube) and an insulating material is filled.

<Problems to be Solved by Conventional Techniques and Inventions> Conventionally, in the sheathed heater, the sheath is completely sealed in order to prevent electric shock or leakage during use under high temperature and high humidity conditions. There is.

However, in the sheathed heater with the sheath sealed,
Especially when used at high temperature, the heating wire is likely to break,
Moreover, when the heating wire is broken, the sheath may be broken, and the sparks generated at that time may be scattered to cause an accident such as a burn or a fire.

The destruction of the sheath in the sheathed heater is considered to occur due to the following mechanism.

When the heat generating line generates heat, an oxidative reaction occurs and oxygen in the sheath is consumed to reduce the pressure inside the sheath.

Further, an oxide film is formed on the surface of the heating wire by the above-mentioned oxidation. In a normal heating wire, this oxide film serves as a protective layer having a sufficient film thickness to improve the durability of the heating wire. However, if you are sealing the sheath,
Since the oxygen in the sheath is insufficient, a complete oxide film is not formed on the surface of the heating wire.

Therefore, when the inside of the sheath is in a decompressed state, the nitrogen remaining in the sheath is diffused and consumed in the heating wire, and the decompressed state in the sheath is further promoted to reach the vacuum state.

When the inside of the sheath is in a vacuum state, as described above, the heating wire with an incomplete oxide film loses its oxide film by evaporation at every heat generation, and then gradually becomes thin due to evaporation of the metal as a constituent material. , It becomes easy to break the wire at various places.

Further, the evaporated metal lowers the insulating property of the insulating material, and in combination with the lowering of the insulating property due to long-term use, the insulating material is in a state of easily causing dielectric breakdown.

Therefore, when the heating wire is broken, the insulating material between the heating wire and the sheath is dielectrically broken down, causing a short circuit to generate a spark, and the heat melts and breaks the sheath.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sheathed heater that does not cause an accident such as a burn or a fire due to scattering of sparks when the heating wire is broken.

<Means for Solving the Problems> In order to solve the above problems, the sheathed heater according to the present invention is provided with a weak point at which at least one portion of a heating wire is rapidly disconnected due to aging, and the weak point of the sheath is provided at the weak point. It is characterized in that an annular reinforcing layer having insulation and heat resistance is provided on the inner peripheral surface or the outer peripheral surface of the corresponding portion.

Further, another sheathed heater of the present invention is characterized in that at least one position of the heating wire is provided with a weak point that is quickly disconnected due to a change with time, and a sheath is provided on the outside of a portion corresponding to the weak point. I am trying.

<Operation> In the sheathed heater of the present invention having the above-mentioned configuration, the insulating and heat-resistant annular reinforcing layer reinforces a portion of the sheath corresponding to the weak point,
Prevents breakage of the sheath when a wire break occurs at the weak point. Further, when a cover is provided on the outer side of the sheath, this cover prevents sparks from scattering when the sheath breaks.

<Example> Hereinafter, the sheathed heater of the present invention will be described with reference to the drawings illustrating an example.

First, the embodiment of FIGS. 1A to 1C will be described.

As shown in these drawings, the sheathed heater A of this embodiment is configured by arranging a heating wire 2 spirally wound in a tubular sheath 1 and filling an insulating material 3 therein. There is.

Both ends of the sheath 1 have low melting point glass 4, 4 and sealing resin
It is sealed at 5, 5.

Further, electrode rods 6,6 electrically connecting the inside and outside of the sheath 1 are inserted through the glass 4,4 and the sealing resin 5,5, and the electrode rods 6,6 project into the sheath 1. Heated wire 2 at the tip
Both ends of are connected.

The heating wire 2 includes a main body portion 20 that is spirally wound, and a small-diameter portion 21 that is provided near one end of the main body portion 20 and that serves as a weak point that breaks quickly due to aging.

The small-diameter portion 21 has a higher resistance value than the other portions of the heating wire 2 and has a higher temperature than other portions during heat generation, so that the diameter is small from the beginning, and therefore due to the change over time, The exothermic wire 2 is consumed before the other parts of the exothermic wire 2, and breaks quickly.
Therefore, the breakage point of the heating wire 2 is specified in the small-diameter portion 21.

Since the spiral main body portion 20 is placed close to the sheath 1 to improve the thermal efficiency of the sheathed heater A, it is shown in FIG.
As shown in, the coil is wound into a coil diameter slightly smaller than the inner diameter of the sheath 1.

An annular reinforcing layer 11 having insulation and heat resistance is provided on the inner peripheral surface of the portion of the sheath 1 corresponding to the small diameter portion 21.

As the reinforcing layer 11, a tubular insulator having an outer diameter corresponding to the inner diameter of the sheath 1 is preferably used because it has excellent insulation and heat resistance, is inexpensive, and is easy to handle.

The reinforcing layer 11 may be provided on the outer peripheral surface of the portion of the sheath 1 corresponding to the small diameter portion 21, as shown in FIGS. 2 (a) and 2 (b).

As the reinforcing layer 11 in the case of the figure, a tubular insulator having an inner diameter corresponding to the outer diameter of the sheath 1 is preferably used.

Further, as the weak point of the heating wire 2, instead of the small diameter portion 21, as shown in FIG. 3, a spiral dense portion 22 in which the spiral winding is denser than that of the main body portion 20 is adopted. You can also

Since the spiral dense portion 22 has a higher temperature than other portions of the heating wire 2 during heat generation, it is consumed earlier than the other portions of the heating wire 2 due to a change with time, and breaks quickly.

Further, as the weak point, it is also possible to adopt one in which the composition of the alloy forming the heating wire 2 is partially changed to facilitate breakage.

In addition, there is a risk that uniform heat generation may not be achieved due to a difference in heat capacity between the portion of the sheath 1 where the reinforcing layer 11 is provided and the other portion, due to the difference in heat capacity. Further, when the sheath 1 is red-hot, there is a possibility that a difference in color development may occur in the portion where the reinforcing layer 11 is provided due to the temperature difference. Therefore, in the embodiment described above, a weak point such as the small diameter portion 21 is provided at one end portion of the heating wire 2, and
The reinforcing layer 11 is provided on one end portion of the sheath 1 to make the heat generation as uniform as possible and to make the difference in color development inconspicuous.

The sheath 1, the heating wire 2 and the insulating material 3 may be made of the same materials as conventional ones.

For example, as the sheath 1, a tubular body made of various metal materials such as stainless steel, copper, and a corrosion resistant heat resistant alloy can be used.

A nichrome wire is preferably used as the heating wire 2.

As the insulating material 3, powder of an insulating metal oxide such as magnesium oxide (magnesia) is preferably used.

In the embodiment described above, the insulating property of the insulator,
The heat-resistant annular reinforcing layer 11 reinforces the portion of the sheath 1 corresponding to the weak point of the heating wire 2. Therefore, when the heating wire 2 is broken at the weak point, the sheath 1 is prevented from being broken, and there is no risk of causing an accident such as a burn or a fire.

Next, the embodiment shown in FIGS. 4A and 4B will be described.

As shown in these figures, in the sheathed heater A of this embodiment, instead of the reinforcing layer 11, the sheath 1 is provided outside the portion corresponding to the small-diameter portion 21 and the above-mentioned portion is provided over the entire circumference. A cylindrical cover 12 for covering is provided.

The cover 12 is formed in a cylindrical shape having an inner diameter larger than the outer diameter of the sheath 1, is supported by a plurality of spacers 13, 13, ... And is arranged concentrically with the sheath 1.

As the cover 12, a material having excellent heat resistance such as metal and ceramics is preferably used.

The cover 12 is formed of the sheath 1 as in the above embodiment.
The portion corresponding to the small diameter portion 21 may not be covered over the entire circumference, but may be a portion of the portion corresponding to the small diameter portion 21 as shown in FIG. 5, for example.

The cover 12 shown in the figure is effective for preventing sparks from scattering and falling downward when the sheathed heater A is used in a ceiling-mounted heater shown in FIGS. 6 (a) and 6 (b), for example. Can be used for

The above-mentioned heater is provided with brackets 9 and 9 for supporting the sheathed heater A suspended from the ceiling surface R, and this bracket.
It is provided with a reflection plate 7 arranged above the sheathed heater A supported by 9, 9 for reflecting heat rays downward. Then, as shown in FIG.
With the cover 12 positioned downward,
If attached to 9,9, even if the sheath 1 is broken due to the disconnection of the heating wire 2, it is possible to prevent sparks from scattering and falling downward.

The cover 12 may hinder the uniform heating of the sheathed heater A, and is conspicuous. Therefore, in the embodiment described above, the small-diameter portion 21 serving as the weak point is provided at one end portion of the heating wire 2. And cover 12
Is provided at one end of the sheath 1 to make the heat generation as uniform as possible and to make the cover 12 inconspicuous.

As a weak point of the heating wire 2 in the sheathed heater A of the above embodiment, the composition of the spiral dense portion 22 shown in FIG. 3 and the alloy forming the heating wire 2 is partially changed instead of the small diameter portion 21. Needless to say, it is also possible to adopt a device that is easy to break.

As the sheath 1, the heating wire 2 and the insulating material 3, the same material as the conventional one can be used as in the previous embodiment.

As described above, in the sheathed heater A of the embodiment provided with the cover 12, even if a spark is generated when the sheath 1 is broken due to the breakage of the heating wire 2, the cover 12 causes the sparks to scatter. As it is prevented, there is no danger of causing an accident such as a burn or a fire.

In addition, the sheathed heater A of each embodiment described above is
Although all of them are formed in a linear shape, the sheathed heater of the present invention can be formed in an appropriate shape such as a hairpin shape or a ring shape having a single or plural bent portions as in the conventional case.

The sheath 1 is not limited to a simple tubular one, and a tubular body having a spiral or flat radiating fin can be used.

In each embodiment, the weak point of the heating wire 2 such as the small-diameter portion 21 is provided at one location of one end of the heating wire 2, and the reinforcing layer 11 and the cover 12 correspond to the weak points. It was provided at one place on one end of 1.
The weak point, the reinforcing layer, and the cover may be provided at two or more locations.

The weak points and the positions of the reinforcing layer 11 and the cover 12 corresponding thereto are not limited to the end portions of the heating wire 2 and the sheath 1, and may be provided in the middle of the respective members.

In addition, various design changes can be made without changing the gist of the present invention.

<Effects of the Invention> The sheathed heater of the present invention is configured as described above, and the annular reinforcing layer having insulation and heat resistance reinforces the portion of the sheath corresponding to the weak point,
Prevents breakage of the sheath when a wire break occurs at the weak point. Further, when a cover is provided on the outer side of the sheath, this cover prevents sparks from scattering when the sheath breaks. Therefore, the sheathed heater of the present invention has no risk of causing an accident such as a burn or a fire when the heating wire is broken.

[Brief description of drawings]

1 (a) to 1 (c) are views showing a first embodiment of a sheathed heater of the present invention, in which FIG. 1 (a) is a longitudinal sectional view thereof.
FIG. 2B is an enlarged cross-sectional view showing a main part, FIG. 2C is a cross-sectional view of the main part, and FIGS. 2A and 2B show a second embodiment of the sheath heater of the present invention. It is a figure, the figure (a) is the longitudinal cross-sectional view, the figure (b) is a cross-sectional view showing the principal part, and 3rd figure.
FIG. 4 is an enlarged sectional view showing a modified example of the weak point of the heating wire, FIGS. 4 (a) and 4 (b) are views showing a third embodiment of the sheathed heater of the present invention, and FIG. FIG. 6B is a longitudinal sectional view, FIG. 5B is a transverse sectional view showing a main part, FIG. 5 is a transverse sectional view showing a modified example of the cover, and FIG. Cross-sectional view showing an example, No. 6
Figure (b) is a side view of the heater. A: Sheath heater, 1 ... Sheath, 11 ... Reinforcing layer, 12 ... Cover, 2 ... Exothermic wire, 3 ... Insulating material, 21 ... Weak point (small diameter portion), 22 ... Weak point (Spiral dense part).

Claims (2)

[Claims] 1. A sheathed heater (A) in which a heating wire (2) is arranged in a metallic tubular sheath (1) and is filled with an insulating material (3), and at least one portion of the heating wire (2) is provided. Is provided with weak points (21) and (22) that are quickly disconnected due to aging, and the sheath (1) has an insulating property on the inner peripheral surface or outer peripheral surface of the portion corresponding to the weak points (21) (22). A sheathed heater (A), which is provided with a heat-resistant annular reinforcing layer (11). 2. A sheathed heater (A) in which a heating wire (2) is arranged in a metallic tubular sheath (1) and is filled with an insulating material (3), at least one location of the heating wire (2). In addition, the weak points (21) and (22) that are disconnected rapidly due to changes with time are provided, and the cover (12) is provided on the outer side of the sheath (1) at the location corresponding to the weak points (21) and (22). Characteristic sheathed heater (A).