JPS6037597B2 - Sea heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheathed heater, and in particular, an object of the present invention is to provide a sheathed heater whose insulation resistance value is less likely to deteriorate even when left in a high temperature and humid atmosphere, and which has a long life.

Generally, as shown in Fig. 1, a heating wire 2 with terminal rods 1 at both ends is inserted into a metal pipe 3, and this metal pipe 3 is filled with electrical insulating powder 4 such as magnesia. Accordingly, both ends of the metal pipe 3 are sealed with heat-resistant resin 5 or glass.

Since the electrical insulating powder 4 such as magnesia has hygroscopicity,
When a sheathed heater is left in a humid atmosphere, the insulation resistance value decreases.

For this reason, it has been proposed to add silicone resin to the electrically insulating powder 4 or to completely seal both ends of the metal pipe 3 with glass. However, when the electrical insulating powder 4 to which silicone resin is added is used, there is a drawback that it cannot be used at high temperatures of 500 degrees or higher because the silicone resin has a heat resistance temperature of about 450 degrees. On the other hand, a sheathed heater completely sealed with glass had a drawback in that when an external force was applied to the terminal bar 1, the glass would crack, the sealing effect would be lost, and the insulation resistance of the sheathed heater would decrease. For the above electrical insulating powder, the present inventors have improved the airtightness of the sheathed heater by using a mixture of glass powder whose main components are Ca0, &03, and Si02 in the secondary electrical insulating powder. I discovered that it is possible.

However, when this electrical insulating powder is used at high temperatures, Ca and Si elements, which are component elements of the glass powder, react with the heating wire, resulting in a shortened lifespan of the heating wire.

As a result of further study on electrical insulating powder, the present inventors found that glass powder, Nj○, Coo, W03, C
By using a mixture of at least one kind of oxide selected from the group of u○, Ga203, Sn02, and Fe203, the reaction between the glass component and the heating wire can be suppressed, and a sheathed heater with a long heating wire life can be obtained. I got the conclusion. Examples of the present invention will be described below.

First, 31% by weight of calcium oxide, 39% by weight of boron oxide, and 3% by weight of silicon oxide were mixed, and this was heated to 1400°C.
After melting it, it was crushed to create glass powder.

Next, Ni○, Coo. W03, Cu○, Ga203,
At least one kind of oxide selected from the group of Sn02 and Fe203 and the above-mentioned glass powder were added to magnesia powder to prepare electrical insulating powder 4.

Note that the particle size of the oxide was 5 microns or less. Next, as the metal pipe 3, NCF2P (product name Incoloy 8
00), and a type 1 nichrome wire was used as the heating wire 2.

This heating wire 2 is made into a coil shape, terminal rods 1 are connected to both ends, and after this is inserted into the metal pipe 3, each metal pipe 3 is filled with the electrical insulation powder 4 prepared in advance, and compressed and reduced. After passing through the steps of seating and annealing, both ends of the metal pipe 3 were simply sealed with heat-resistant resin 5, and sample numbers 4, 6, 7, 8, 9, and 6.6 ribs in outer diameter and 500 ribs in length were prepared. 10, 12
, 13 14, 15, 1017, 181 ku 20, 21
, 22, 23, 25, 26, 28, 29, 31, and 32 sheathed heaters were created. In addition, the bran bran mentioned above is 11000
0, and also served as the melting treatment of the glass powder. Further, the amount of glass powder added, the type of oxide, and the amount of the oxide added to the electrically insulating powder 4 of these sheathed heaters were as shown in Table 1. For comparison, sample number 1 is a conventional sheath heater using only magnesia powder as an electrical insulating powder, and sample numbers 2, 3, 5, and 2 are electrical insulating powders in which the above-mentioned glass powder is added to magnesia powder. 11, 24
, 27, and 30 conventional sheathed heaters were created. In addition,
In the sheathed heaters of each sample number, the resin 5 does not completely seal both ends of the metal pipe 3, but is used to ensure an insulating distance between the terminal bar 1 and the metal pipe 3.
Each of the sheathed heaters with sample numbers 1 to 32 was left in a humid atmosphere with a temperature of 40oo and a relative humidity of 95%, and
Insulation resistance values were measured in the greenhouse after 1 day and 14 days.
In addition, the metal pipe surface temperature was 800q○, and the O
Intermittent energization was performed with N and OFF for 10 minutes, and the intermittent energization cycle until the heating wire 2 was disconnected was measured. The results of these measurements are shown in Table 1. Table 1 When examining the disconnection life based on Table 1, sample numbers 4, 6, 7, 8, 9, 10, and 1, which are examples of the present invention, are shown.
314, 15, 101819 20, 21, 22, 23
The sheathed heaters of 2F2028 and 29 are several times longer than the conventional sheathed heaters of sample numbers 2, 3, 5, 11, 24, 27, and 30, which are made using electrically insulating powder with only glass powder added. Sample number 1, which is a subordinate example,
It has the same degree of strength as that of the sheathed heater.

On the other hand, when examining the insulation resistance value at room temperature in a humid atmosphere, the insulation resistance value hardly decreases if the amount of oxide added is 1% by weight or less. Therefore, it is preferable that the amount of the oxide added is in the range of 0.1 to 1% by weight, and the amount of the glass powder added is in the range of 0.5 to 3% by weight.

In other words, if the amount of glass powder added is 0.5% by weight or less, the ability to suppress the hygroscopicity of the electrical insulating powder is insufficient, and the insulation resistance value decreases in a short period of time as in the sheathed heaters of sample numbers 1 and 2. Therefore, it cannot be put to practical use.

In addition, if the amount of glass powder added is more than 3% by weight, the glass powder component will have a negative effect on the heating wire 2, and a large difference in coefficient of thermal expansion will appear during cooling after heat treatment, causing many cracks. Like the sheathed heaters of sample numbers 30, 31, and 32, the disconnection life is significantly shortened. On the other hand, when the amount of oxide added is 0.1% by weight or less, the ability to suppress the reaction between the glass powder component and the heating wire is insufficient, and the disconnection life is not extended as in the sheathed heater of sample number 12.

Furthermore, if the amount of oxide added is 10% by weight or more, hygroscopicity of the oxide appears and the insulation resistance value decreases as in the case of the sheathed heater of sample number 17. In this way, Ni○,
Coo, W03, Cu○, Ga203, Sn02, Fe
It has been revealed that the oxide of No. 203 suppresses the reaction between the glass powder and the heating wire, extending its life.

Note that the above oxides may be mixed at the stage of creating the glass powder.

For example, a glass is created by blending 2% by weight of calcium oxide, 6% by weight of boron oxide, 15% by weight of silicon oxide, and 5% by weight of nickel oxide and melting at 1350 qo.
Even if this glass is crushed to create a glass powder to which nickel oxide is added, and this glass powder is added to magnesia powder to create the electrical insulating powder 4, the same effect as in the above embodiment can be obtained. Moreover, although the case where magnesia powder was used as the base material of the electrically insulating powder 4 was described in the above embodiment, other alumina powder or silica powder may be used.

As is clear from the above description, according to the present invention, Ni〇・C.

〇, W〇3, Cu〇・Ga2〇3, Sn〇2, Fe2Q
By using electrical insulating powder to which at least one oxide selected from the group of oxides and glass powder whose main components are calcium oxide, boron oxide, and silicon oxide are added, it can be used at high temperatures without the need for complete insulating. It is possible to provide a sheathed heater that can withstand use in a humid atmosphere and has a high insulation resistance value even when left in a humid atmosphere.

[Brief explanation of drawings]

The figure is a cross-sectional view of a typical sheathed heater. 2...Heating wire, 3...Metal pipe, 4
...Electrical insulating powder.

Claims (1)

[Claims] 1 In a sheathed heater formed by inserting a heating wire into a metal pipe and filling it with electrically insulating powder, the electrically insulating powder may include NiO, CoO, WO_3, CuO, G
at least one oxide selected from the group of a_2O_3, SnO_2, and Fe_2O_3; and CaO, B_2O_
3. A sheathed heater using a glass powder containing SiO_2 as a main component.