JPS6230793Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a substantially flat heating wire with self-regulating properties.

A resistor made of rubber or plastic is placed between two or three parallel conductors (electrodes), and a heating wire is used as the heating member to generate heat by applying a voltage between the conductor electrodes. There is.

FIG. 1 shows a conventional heating wire, in which electrodes 1 and 1 are connected by a resistor 2 formed by an extruded layer of semiconducting material, and the surface of the resistor 2 is covered with an insulating coating 3. , a protective sheath 4 is provided on the outside of the insulation coating 3.

The resistor 2 of this heating wire has a positive temperature coefficient of resistance, and the resistance value increases as the temperature rises.
At a temperature above a predetermined temperature, the resistance increases, so the current flow is suppressed and a self-control characteristic is provided.

The heating portion of this heating wire is formed of a flat rubber/plastic conductor (resistor) having a substantially uniform thickness in the width direction.

When the resistor 2 and the electrode portion 1 are energized, a current flows inside the resistor 2 in the width direction from the electrode 1 of the heating wire toward the opposing electrode 1 as shown in FIG.

The characteristics of the temperature (T) and resistance value (R) of this resistor 2 are constant, as shown in curve A in Figure 3, where the horizontal axis represents the temperature T and the vertical axis represents the resistance value R. When the temperature is reached, the resistance value increases and reaches the saturation value.

Now, when voltage is applied to this heating wire, an inrush current flows because the resistance value is initially small. Because the electrodes 1, 1 at both ends through which this current flows are shaped as dissipating surfaces that are not heated, the horizontal axis represents the interelectrode position d, and the vertical axis represents the temperature T.
A temperature distribution between the electrodes as shown by curve B in the figure is formed. When current is applied while the temperature in the middle is relatively high, the resistance increases according to the temperature-resistance characteristic, and although the current is the same everywhere between electrodes 1 and 1, the resistance increases in the middle part. It is also difficult to rapidly dissipate the heat, resulting in the intermediate portion becoming increasingly overheated.

In FIG. 5, which is displayed similarly to FIG. 4, the intermediate portions of the electrodes 1 and 1 rise with the passage of time as shown by arrows in the order of curves a-b-c. Along with this, the potential distribution also rises as shown by curves e, f, and g in FIG. 6, where the horizontal axis represents the interelectrode position d and the vertical axis represents the voltage E.

In this way, there is a possibility that the intermediate portion between the electrodes 1 and 1 will be repeatedly overheated locally when electricity is applied.

In addition, there is a drawback that the electric field is higher in the middle part and becomes concentrated, increasing the possibility of local partial destruction or electrical deterioration.

An object of the present invention is to provide a heating wire that eliminates the above-mentioned drawbacks, can heat uniformly, and has a long stable life.

Usually, as a means to reduce the temperature rise at the intermediate portion between the electrodes of the heating wire and prevent a local increase in resistance, measures such as reducing resistance or improving heat dissipation can be considered. For resistors with the same specific resistance, the resistance can be lowered by increasing the cross-sectional area, and by increasing the volume, the heat capacity increases, which slows down the rate of temperature rise.
Since the heat dissipation surface becomes larger, the temperature can be averaged.

Furthermore, even if a conductive member is placed inside the resistor at a position intermediate between the electrodes, the temperature can be averaged.

The heating wire of the present invention is formed in such a way that the temperature is increased by connecting multiple electrodes through a resistor and energizing them, and as the resistance value increases, the current flowing is suppressed at a predetermined temperature or higher. The resistor has self-control characteristics and is provided with means for reducing the resistance at an intermediate position between the electrodes of the resistor.

Hereinafter, an embodiment of the heating wire of the present invention will be described with reference to FIG. 7, with the same parts as those in the prior art being designated by the same reference numerals and explanations of the same parts being omitted.

Between the electrodes 1 and 1, a resistor 2 as a semiconductive layer is formed by extrusion molding a material in which carbon is blended or polymerized with a plastic material such as crosslinked polyethylene, crosslinked polyolefin, fluororesin, or Teflon.

As shown in the figure, the resistor 2 is extruded so that the middle part between the electrodes 1 is thicker and the area near the electrode 1 is thinner.

By making this middle part thicker, the resistance of this part is lowered, and the resistance does not suddenly increase when electricity is applied, and the electric field is not concentrated, so that only the center part is not heated.

Furthermore, since the heat capacity increases and heat dissipation improves, it becomes possible to even out the initial temperature distribution.

FIG. 8 shows another embodiment. The difference from the above embodiment is that in the above embodiment, the thickness of the resistor 2 in the intermediate portion is increased, whereas in this embodiment, the thickness of the resistor 2 is not increased, and the thickness of the resistor 2 is increased. The copper strip 5 is made uniform and the resistor 2 in the middle part has a built-in copper strip 5, which can lower the resistance and increase the heat capacity to increase the effect, and has the same effect as the above embodiment. has.

In this case, the copper strip 5 does not need to be connected to a power source or the like. Further, although each of the above embodiments has been described with reference to the case of two conductors, the same effect can be obtained even if three conductors are arranged in parallel.

In order to lower the resistance of the intermediate portion, it is conceivable to use a high resistance material near the power supply 1 and form the intermediate portion using a resistive material, but this is difficult and impractical in terms of manufacturing.

Since the heating wires of both embodiments are formed in this way, it is possible to average the temperature rise in the width direction when voltage is applied, and sudden changes in resistance are avoided, so heating is concentrated in the middle part. A long-term stable life of the heating wire can be obtained without any damage.

As described above, the heating wire of the present invention has the effect of uniformly heating and having a long and stable life.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional heating wire, and Figure 2 is a cross-sectional view of a conventional heating wire.
Fig. 3 is an explanatory diagram of the relationship between temperature and resistance when the heating wire of Fig. 1 is energized;
Figures 6 to 6 show the relationship between the interelectrode position, temperature, and potential distribution. Figure 4 is an illustration of temperature distribution at the initial stage of energization, Figure 5 is an illustration of temperature changing over time, and Figure 6 is an illustration of temperature distribution over time. FIG. 7 is a sectional view of one embodiment of the heating wire of the present invention, and FIG. 8 is a sectional view of another embodiment of the heating wire of the present invention. 1: Electrode, 2: Resistor, 3: Insulating coating, 4: Protective sheath, 5: Copper strip.

Claims (1)

[Scope of utility model registration request] A heating wire with self-control characteristics that is formed by connecting multiple electrodes through a resistor and applying current to increase the temperature and suppress the current flowing above a predetermined temperature as the resistance value increases. In,
A heating wire characterized in that the heating wire is provided with means for reducing the resistance at an intermediate position between the electrodes of the resistor.