JPH0789513B2 - Sheath heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is a sheath in which a heating wire wound in a spiral shape is arranged in a metallic tubular sheath (protective tube) and is filled with an insulating material. It is about heaters.

<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.

On the other hand, in order to increase the heat efficiency of the sheath heater, the heating wire is arranged in a state in which the coil diameter of the spiral is set slightly smaller than the inner diameter of the sheath and is extremely close to the sheath.

For this reason, when the heating wire is broken, the insulating material between the closely arranged heating wire and the sheath in the vicinity of the broken wire causes dielectric breakdown, causing a short circuit and sparks, and the heat causes the sheath to melt and break. It is.

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 in which the sheath is not likely to be broken when the heating wire is broken.

<Means for Solving the Problems> In order to solve the above problems, a sheathed heater according to the present invention has a radial center of the sheath which is parallel to the longitudinal direction of the sheath at at least one position of the spiral heating wire. It is characterized in that a straight line portion that passes through the section is provided, and a weak point that is abruptly broken due to aging is provided in the middle of this straight line portion.

<Operation> In the sheathed heater of the present invention having the above-described configuration, the weak point provided on the heating wire is consumed earlier than the other parts of the heating wire due to a change with time, and the wire breaks quickly, so The breaking point of the line is specified at the weak point. Since this weak point is provided in the straight line portion of the heat generation line passing through the radial center of the sheath and a sufficient insulation distance can be secured between the weak point and the inner peripheral surface of the sheath, disconnection occurs. In this case, the sheath is prevented from being broken due to dielectric breakdown.

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

As shown in FIG. 1, the sheathed heater A of this embodiment
Is a heating wire 2 spirally wound inside a tubular sheath 1.
Is arranged and the insulating material 3 is filled.

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 that electrically proliferate inside and outside the sheath 1 are inserted through the glass 4,4 and the sealing resin 5,5. The heating wire 2 is attached to the protruding tip.
Both ends of are connected.

The heating wire 2 includes a body portion 20 that is spirally wound, and a straight portion 21 that is provided near one end of the body portion 20.

The spiral main body portion 20 is placed close to the sheath 1 to increase the thermal efficiency of the sheathed heater A, and therefore the spiral main body portion 20 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.

As shown in FIG. 2 (a), the linear portion 21 is arranged parallel to the longitudinal direction of the sheath 1 and, as shown in FIG. 2 (b), in order to prevent short circuit with the sheath 1. , Is arranged at the center of the sheath 1 in the radial direction. Further, a thin portion 22 as a weak point is provided at a substantially central portion in the longitudinal direction of the straight portion 21.

The small-diameter portion 22 has a higher resistance value than the other portions of the heating wire 2 and has a higher temperature than other portions when generating heat. 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 22.

The dimensions of the sheath 1 and the heating wire 2 are not particularly limited, but the inner peripheral surface of the sheath 1 and the small-diameter portion 22 of the heating wire 2 are separated by 2 mm or more in the radial direction of the sheath 1. It is preferable. If the distance between the two is less than 2 mm, the straight part 2
Although 1 is arranged at the center of the sheath 1 in the radial direction, the insulation distance between the small-diameter portion 22 and the inner peripheral surface of the sheath 1 is insufficient. It may be destroyed.

Since the small-diameter portion 22 is arranged at the center in the radial direction of the sheath 1 as described above, in order to separate the small-diameter portion 22 and the inner peripheral surface of the sheath 1 in the radial direction by 2 mm or more, So that the difference between the outer diameter of the diameter portion 22 and the inner diameter of the sheath 1 is 4 mm or more,
The outer diameter of the small diameter portion 22 and the inner diameter of the sheath 1 may be set.

As described above, the straight portion 21 and the main body portion 20 have different distances to the sheath 1.
At the time of heat generation, a temperature difference may occur due to a difference in heat transfer efficiency, and uniform heat generation may not be performed. Further, when the sheath 1 is red-heated, there is a possibility that a difference in color development may occur in the portion corresponding to the straight line portion 21 due to the temperature difference. Therefore, in this embodiment, the straight line portion 21 is provided at one end portion of the heating wire 2 so as 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 sheathed heater A of this embodiment having the above structure, the small-diameter portion 22 specified as the disconnection point of the heating wire is used.
However, the sheath 1 is arranged at the center in the radial direction where a sufficient insulation distance can be maintained between the sheath 1 and the inner peripheral surface. Therefore, when the wire breakage occurs in the small-diameter portion 22, the sheath 1 is prevented from being broken due to dielectric breakdown, and there is no risk of causing an accident such as a burn or a fire.

The sheathed heater A can be used in a ceiling-mounted heater as shown in FIGS. 3 (a) and 3 (b), for example.

This heater is provided with brackets 9 and 9 for supporting the sheathed heater A suspended from a ceiling surface R, and a heat ray arranged below the sheathed heater A supported by the brackets 9 and 9 to lower the heat rays. And a reflection plate 7 for reflecting the light. In addition, in the above heater, even if the sheath 1 is destroyed when the heating wire 2 is broken, in order to prevent the spark generated at that time from falling downward, The saucer 8 shown by the chain double-dashed line in the figure
It can also be arranged below the small-diameter portion of the heating wire 2 described above.

The sheathed heater A of the embodiment described above was formed in a linear shape, but the sheathed heater of the present invention is
Similarly to the prior art, it can be formed into an appropriate shape such as a hairpin shape or a ring shape having a single or a plurality of bent portions.

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 the illustrated embodiment, the straight line portion 21 of the heating wire 2 is provided at one location of one end of the heating wire 2, but the straight portion may be provided at two or more locations of the heating wire.

The position of the straight line portion 21 is not limited to the end of the heat generating wire 2, and a straight line portion may be provided in the middle of the heat generating wire.

The weak point of the heating wire 2 is not limited to the small-diameter portion 22. For example, the weak point of the heating wire 2 may be changed by partially changing the composition of the alloy forming the heating wire 2. it can.

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 weak point specified as the breakage point of the heating wire is arranged on the straight line portion passing through the radial center of the sheath. Therefore, a sufficient insulation distance can be secured between the sheath and the inner peripheral surface of the sheath, and when the wire breaks at the weak point, the sheath is prevented from being broken by dielectric breakdown. Therefore, the sheathed heater of the present invention is
When the heating wire is broken, there is no risk of causing an accident such as a burn or a fire.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the sheathed heater of the present invention, FIG. 2 (a) is an enlarged sectional view showing an essential part of the above embodiment, and FIG. 2 (b) is a cross section of the essential part. Side view, FIG. 3 (a)
Is a cross-sectional view showing an example of a heater using the sheathed heater of the above embodiment, and FIG. 3 (b) is a side view of the heater. A: Sheath heater, 1 ... Sheath, 2 ... Heating wire, 3 ... Insulation material, 21 ... Straight portion, 22 ... Weak point (small diameter portion).

Claims (1)

[Claims] 1. A sheathed heater (A) in which a spirally wound heating wire (2) is arranged in a metallic tubular sheath (1) and an insulating material (3) is filled in the sheathed heater (A). A straight line portion (21) parallel to the longitudinal direction of the sheath (1) and passing through the radial center of the sheath (1) is provided at at least one position of the line (2), and the straight line portion (21) is in the middle thereof. The sheathed heater (A) is characterized in that a weak point (22) is provided to quickly disconnect the wire due to changes over time.