JPS6231996Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to improvements in heating wires used to heat bimetallic instruments used in automobile instruments, particularly fuel gauges, coolant temperature gauges, oil pressure gauges, voltmeters, etc., as well as bimetallic devices used to adjust the voltage of these instrument circuits. be. Conventional bimetal heating wires have a structure in which a heating wire is coated with two to four layers of electrically insulating glass thread alternately wound horizontally in opposite directions, and a silicone resin paint is impregnated and baked on top of the coating. However, such conventional heating wires are no longer able to fully satisfy the strict quality characteristics and high reliability that have been required as automatic winding machines have been adopted in recent years. On the other hand, defects have also occurred in which the glass insulating layer breaks down during winding of the bimetal and during actual vehicle running, resulting in a short circuit between the heating wire and the bimetal. Furthermore, in order to improve flexibility, 2
Since a silicone resin paint with many functional groups is used as an impregnating and baking paint, when heated to around 200℃, a condensation reaction between Si-OH (silicon-hydroxyl) occurs and hydrocarbon gas is generated. This was also a cause of malfunction of the electrical contacts provided at the tip of the bimetal. Recently, a heating wire has been proposed in which aromatic polyamide fibers are wound horizontally around a heating wire instead of glass threads, the wire is impregnated and coated with a polyamide-imide or polyimide resin coating, and then cured by baking.
However, since such electric wires use organic fibers, there is a risk that, for example, if an abnormal current flows through a heating wire, as sometimes happens, the entire coating layer may carbonize, causing a short circuit. There is. Furthermore, when removing the coating layer with a wire brush or the like, fraying of the fibers, which is not seen in glass threads, is observed, impairing the workability of winding bimetal wires. The present invention is aimed at solving these problems, and as shown in the attached drawing, a first horizontally wound layer 2 in which electrically insulating glass thread is horizontally wound on a heating wire 1 is used.
A second horizontally wound layer 3 made of aromatic polyamide fibers horizontally wound is provided thereon, and an impregnated coated baked layer 4 obtained by impregnating and baking a polyamide-imide resin paint or a polyimide resin paint is further provided thereon. It is an electric wire. Here, the aromatic polyamide fibers include, for example, poly-m-phenylene isophthalamide or poly-p-phenylene terephthalamide. The present invention will be explained in more detail below. Generally, there is a certain limit to the thickness of the coating layer of a heating wire due to its nature, and the coating layer is usually provided with a thickness that is equal to or approximately half the diameter of the heating wire. If it is too thick, shear stress will act between the inner layer and outer layer of the coating during winding, causing layer peeling or surface cracking. On the other hand, if it is too thin, the desired insulation effect cannot be obtained. Therefore, also in the present invention, the thickness of the coating layer is preferably the same as or approximately half the diameter of the heating wire. In the present invention, the covering layer is composed of a horizontally wound layer of glass yarn and a horizontally wound layer of aromatic polyamide fiber,
The former constitutes the inner covering layer, and the latter constitutes the outer layer. The horizontally wound layer of glass yarn is directly coated on the heating wire, while the horizontally wound layer of aromatic polyamide fiber is wound around the heating wire via the horizontally wound layer of glass yarn. Furthermore, since the paint applied to the outer layer is impregnated into this outer layer, it is integrated with this outer layer to form an outer shell layer after baking. The coated and baked layers are shown as one separate layer. According to the present invention having such a configuration, first of all, by using the inner layer, which undergoes relatively little deformation during bimetal winding, as the first horizontally wound layer made of glass thread, the glass thread during bimetal winding is In addition, since the glass thread is in close contact with the heating wire, the excellent thermal conductivity of the glass thread is ensured and it can be used effectively. moreover,
Because the glass thread horizontally wound layer is interposed as an inner layer,
Even at temperatures exceeding 450°C during abnormal current flow, which is sometimes experienced, the entire surface of the insulation coating is prevented from becoming carbonized, thereby preventing short circuits. In a preferred embodiment of the present invention, the ratio of the thickness of the horizontally wound glass yarn layer to the thickness of the horizontally wound aromatic polyamide fiber layer is about 1:1 to about 3:1. Second, since aromatic polyamide fibers with excellent flexibility and bending resistance are used for the outer layer, which undergoes large deformation during bimetal winding, the elongation of the fibers alleviates the deformation stress experienced during bimetal winding. Due to the small friction coefficient of this aromatic polyamide fiber, breakdown of the insulation coating at the bimetal edge portion can be prevented. Thirdly, since polyamide-imide paint or polyimide paint is used as the baked insulation paint, it has good compatibility with the aromatic polyamide fiber that is the outer layer.
Therefore, impregnation becomes easy. Since polyamide-imide paints and polyimide paints are easily impregnated into layers made of aromatic polyamide fibers,
This paint also comes into contact with the inner layer of glass threads, which further strengthens the adhesion between the inner layer of glass threads and the outer layer of aromatic polyamide fibers, preventing them from peeling off. As a result, not only mechanical strength can be improved, but also thermal conductivity can be made uniform. The above paint also does not generate harmful gases to electrical contacts even at high operating temperatures of 250°C, and also contributes to improved slipperiness during high-speed winding. Next, the present invention will be further explained with reference to examples. Example 1 Electrical insulating glass thread (ECD 900) was wound horizontally around a nickel chrome heating wire with a diameter of 0.080 mm, and aromatic polyamide fiber (trade name "Nomex" by du Pont) was wound horizontally on top of it, and then A polyamide-imide resin paint was impregnated and baked on top of the wire to obtain a heating wire with a finished outer diameter of 0.243 mm, which is almost the same as the conventional product. The coating thickness was 0.082 mm, and the ratio of the thicknesses of the horizontally wound glass yarn layer and the horizontally wound aromatic polyamide fiber layer was approximately 1:1. The test results of various tests on this electric wire are shown in Table 1 below. For comparison, a heating wire (conventional product) obtained by baking the above heating wire with a conventional glass thread coated silicone resin paint, and a heating wire obtained by directly horizontally wrapping aromatic polyamide fibers on the above heating wire without using glass thread, and a polyamide A heating wire (reference product) obtained by impregnating and baking imide resin paint was also tested in the same manner, and the results are also shown in Table 1.

[Table] As is clear from the results in Table 1, the heating wire according to the present invention has excellent heat resistance, mechanical strength, and good winding properties, and has extremely high practical value. In particular, when compared to the reference product, glass thread is wound horizontally around the heating wire as a base layer, so in addition to effectively exhibiting its excellent insulation and thermal conductivity, the coating is easy to peel off. And there is less fraying. In addition, since the glass thread layer is on the inner layer and is relatively thin compared to conventional products, it can withstand severe bending of the bimetal edge during bimetal winding, and also resists deformation of the bimetal itself when bimetal is activated. . Furthermore, since the amount of expensive aromatic polyamide fiber used is smaller than that of the reference product, it also has the economical effect of being able to be manufactured at low cost. Example 2 In this example, Example 1 was repeated, but a heating wire with a diameter of 0.10 mm was used, and for comparison, glass thread wound in a single layer or in multiple layers, and a surface treatment paint were used. We obtained products using silicone resin and products wrapped in multiple layers of aromatic polyamide fiber, and evaluated their characteristics. The results are summarized in Table 2. From the results shown in the same table, it can be seen that the heating wire according to the present invention is excellent in both dielectric breakdown voltage and wear resistance. Note that for practical purposes, wear resistance is sufficient for about 5 to 10 times.

[Table] Example 3 Three types of heating electric wires shown in Table 3 were obtained in the same manner as in Example 1, and using these, a temperature rise characteristic test and an overcurrent characteristic test were conducted in the following manner.

[Table] Test conditions A Temperature rise characteristic test Winding resistance 86Ω Voltage value DC8V Current value 94mA Current conduction time 2 minutes B Overcurrent characteristic test Winding resistance value 86Ω Voltage and current value DC18V, 210mA Current conduction time 2 minutes Temperature rise characteristic test It measures the temperature change of the sample when electricity is applied, and the results are shown graphically in Figure 2.
In the figure, curve A shows the test results of the conventional product, curve B shows the test results of the invented product, and curve C shows the test results of the reference product. As can be seen from the graph, the temperature rise characteristics of the product of the present invention are inferior to the conventional product coated only with glass fiber, but are superior to the reference product. On the other hand, the overcurrent characteristic test measures the insulation resistance between the heating wire and the bimetal after 2 minutes of energization, and the results are shown in Table 4 below.

[Table] As can be seen from the results in Table 4, the heating wire of the reference product made of double horizontally wound aromatic polyamide fibers was 4.
Two of the samples caught fire in 20 to 30 seconds, and the remaining two
The heat resistance of the sample was also very low, with the coating layer turning black and carbonized after 2 minutes of energization, and the insulation resistance becoming almost zero. The conventional sample, which was a double glass fiber horizontally wound heating wire, did not carbonize, but did turn yellow.
The reason why the insulation resistance values of these conventional products are low in all samples is because the silicone resin paint is impregnated and baked, which gasifies due to heat, and the glass coating layer is unable to follow the thermal deformation of the bimetal. Conceivable. The reason why this product has high insulation resistance is that even if the aromatic polyamide fiber coating layer is carbonized,
This is thought to be because the remaining glass fiber coating layer can maintain insulation. As described above, the product of the present invention has much better heat resistance than the reference product, and can maintain its insulation properties even when abnormal current flows.

[Brief explanation of drawings]

Fig. 1 is an enlarged perspective view showing a partially destroyed heating wire according to the present invention, and Fig. 2 is a graph showing the temperature rise characteristics of the product of the present invention when energized, along with those of conventional products and reference products. . In FIG. 1, 1: heating wire, 3: second horizontally wound layer, 2: first horizontally wound layer, 4: impregnated coating baking layer.

Claims (1)

[Claims for Utility Model Registration] (1) A heating wire, a first horizontally wound layer made of electrically insulating glass thread that directly covers the heating wire, and an aromatic polyamide fiber that covers the first horizontally wound layer. and an impregnated and baked layer of polyamide-imide resin paint or polyimide resin paint obtained by impregnating and baking the second horizontally wound layer. heating wire. (2) The heat-generating electric wire for a bimetal automotive instrument as claimed in claim 1, wherein the ratio of the thickness of the first horizontally wound layer to the second horizontally wound layer is 1:1 to 3:1.