JPS6040153B2 - sheath heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Shih Tzu heater, and particularly relates to insulation properties that deteriorate with use of the Shih Tzu heater.

The insulation characteristics of the Shih Tzu heater are determined by the length of the heat generating part, the outer diameter of the Shih Tzu heater, and the properties of the electrically insulating powder filled in the Shih Tzu heater, based on the configuration of the Shih Tzu heater shown in FIG.

In FIG. 1, 1 is a metal protection tube, 2 is an electric heating element, 3 is a terminal, and 4 is an electric insulating powder.

Reference numeral 5 indicates a sealing section made of various types of glass or silicone rubber, and reference numerals 6 and 7 indicate connection sections between the electric heating element and the terminal.

Magnesium oxide (Mg0) has been used as an electrically insulating powder because it has good electrical insulation properties even at high temperatures and good thermal conductivity. but,
These electrical insulating powders have a high hygroscopic property, and when exposed to air for a long period of time, the insulating powders absorb moisture, and this moisture causes a decrease in insulation resistance. Therefore, in order to prevent the electric insulating powder from absorbing a large amount of water, the ends of the sheathed heater were sealed with various types of glass or silicone rubber 5 to provide a sealed structure. This makes it possible to prevent the insulation properties from deteriorating even if the product is not used for a long time and is exposed to the air or submerged in water. A sheathed heater that uses silicone rubber as a sealant can be used when the surface temperature of the sheathed heater is up to 400 oo. At temperatures higher than this, the temperature of the sealing part will also increase, and the silicone rubber will oxidize, making the sealing no longer possible. The agent no longer functions. On the other hand, with a glass-sealed sheathed heater, oxidation of the glass does not occur, and it can be used even if the surface temperature of the sheathed heater is raised to a high temperature such as 800 oo.
It could be used as a high temperature sheathed heater.

However, a new problem has arisen in that as the sheathed heater is used at high temperatures, its insulation properties gradually deteriorate.

The present invention aims to prevent the phenomenon that insulation resistance deteriorates over time, which occurs when a hermetically sealed sheathed heater is used at high temperatures.

Conventionally, it has been thought that the electrical resistance of electrically insulating powder in a sheathed heater is due to moisture absorbed into the powder.

For this reason, in order to reduce the moisture content in the sheathed heater when the sheathed heater is used at high temperatures, methods have been proposed to reduce the moisture content of the gas sealed in the sheathed heater, that is, the humidity of the gas. However, as described later in the present invention, the water absorbed by the electrical insulating powder is
Even if heated at 10,000 ℃, it is impossible to completely remove the moisture, and some moisture will inevitably remain.

Compared to this residual moisture, the amount of moisture held by the gas in the sheathed heater is a small amount, and even if a sheathed heater is manufactured by sealing dry air, the insulation resistance deteriorates as the heater is used. . The present invention proposes a method completely different from the above-mentioned methods for dealing with the phenomenon of deterioration of insulation properties that occurs when a sheathed heater is used at high temperatures.

It is believed that the electrical resistance of electrically insulating powder varies greatly depending on not only the moisture absorbed by the powder but also the total pressure of the gas surrounding the powder.

It is known as the Wa starvation theory that the electrical resistance of an oxide is usually related to the partial pressure of oxygen existing around the oxide. However, the present inventors found that the electrical resistance of the Mn powder used as an electrically insulating powder at temperatures below 900°C is not limited to the pressure of not only oxygen but also inert gases such as nitrogen, helium, neon, argon, krypton, xenon, and radon. It was found that there was a large variation depending on Wayanagi's theory is related to electronic conduction such as holes and electrons in oxides, and the phenomenon discovered by the present inventors is thought to be related to ionic conduction by hydroxyl groups on the surface of Mg○, so it is assumed that only oxygen It was thought that the electrical resistance would change due to the presence of other gases. Hereinafter, the causes of the deterioration phenomenon of insulation resistance will be described, and examples of the present invention will be shown.

'1' Cause of insulation resistance deterioration Figure 2 shows a cross-sectional view of a sheathed heater whose both ends are sealed with glass.

Reference numeral 8 designates a metal protection tube with open ends at both ends made of carbon steel, fusen steel, etc., and 9 designates an electric heating element, which is usually made of a metal heating element such as nichrome wire, iron chrome wire, or molybdenum wire.

As is clear from FIG. 2, the electric heating element must be maneuverable because the heating element may be wound into a coil or the sheathed heater may be bent. For this reason, metal wires are used as electric heating elements. 10 is a terminal, 11 is an electrically insulating powder, and 8 to 11 are the same as 1 to 4 in FIG.

12 is a sealing part made of glass or the like for hermetically sealing the sheathed heater, and 13 and 14 are joint parts between the electric heating element and the terminal.

The manufacturing method of the sheathed heater is as follows. An iron chrome wire as an electric heating element 9 with terminals attached to both ends was placed in a metal protection tube 8 made of fusen steel so as not to come into contact with the protection tube, and then heated to 900°C in advance as an electrical insulating powder 1. The furnace was filled with magnesia Mg0 that had been heated and dried to a packing density of 2.8.

In addition, the length of the heat generating part was set to 40 mm. Here, the length of the heat generating part is the length occupied by the heat generating wire in the sheathed heater, and is the length from 6 to 7 in FIG. 1, and the length from 13 to 14 in FIG. 2. When it is necessary to bend the sheathed heater, after bending it, it is heated in air to 900 qo, and after air cooling, the entrance part of the sheathed heater is sealed with molten glass. The gas sealed in the sheathed heater manufactured in this way was air at an atmospheric pressure of 20 oo.

This sheathed heater was used in the tests shown below.

This sheathed heater has a metal protection tube surface temperature of 800CO.
Figure 3 shows the change over time in the insulation resistance of the sheathed heater when energized so that the current is applied, and Figure 4 shows the change over time in the pressure of the gas sealed in the sheathed heater.

From Figures 3 and 4, the initial 28
It can be seen that the pressure of the enclosed gas, which was 0.000 Hg, has decreased, and that the insulation resistance has also decreased, and that there is a correlation between the two.

Further, Table 1 shows the results of gas analysis of the gas in the sheathed heater at points c and d in FIG. Table 1 Analysis of gases Metal oxides and nitrides were detected when the surface of the iron-chromium wire used as an electric heating element was analyzed using an X-ray microanalyzer.

From these results, it was found that during use, the oxygen and nitrogen in the enclosed air react with the heating element and are lost as oxides and nitrides, resulting in a reduced pressure state. . Next, one sealed part of the sheathed heater was opened and a prototype was made that served as a gas inlet and a suction port.

While applying electricity so that the surface temperature of the metal protective tube of this sheathed heater reached 800℃, various gases were introduced from the gas inlet (hereinafter referred to as 800qo).
At this time, the gas pressure and insulation resistance were measured. The results are shown in FIG. Figure 5 shows the insulation resistance R when a sheathed heater with a heat generating part length of 40 arcs is used at 800qo.
The relationship between 40800 (MQ) and the gas pressure P800 (Yanagi Hg) in the sheathed heater at 800°C is shown.

In Fig. 5, 0 is air, ● is oxygen, △ is nitrogen, and × is argon. From this, the insulation resistance of the sheathed heater R408
00 and the pressure P800 of the gas in the sheathed heater, there was a relationship expressed by the formula {1}, and the higher the pressure, the higher the insulation resistance.

R40800 (MQ) 〇.

95 no P800 (costal Hg),. , {1) It was also found that the insulation resistance is determined by the total pressure of the gas in the sheathed heater, regardless of the type of gas, such as air, oxygen, nitrogen, inert gas such as helium, etc.

Based on the above results, the cause of the deterioration of the insulation resistance of the sheathed heater was considered to be as follows. While using a sheathed heater, a reaction occurs between the electric heating element and the oxygen and nitrogen in the enclosed air, creating metal oxides and nitrides.

Oxygen and nitrogen in the enclosed air 4 are consumed, and in the sheathed heater, only argon, which is present in the air at about 0.9%, exists as a gas, and the pressure is reduced. As a result of this reduced pressure state, the insulation resistance decreased as shown in FIG. Due to the causes of deterioration of insulation resistance as described above, it can be seen that in order to improve the insulation characteristics of the sheathed heater, it is necessary to prevent a reduced pressure state within the sheathed heater.

In an insulation test for a sheathed heater, it is generally required that the insulation resistance be at least IMO during use, regardless of its shape.

From FIG. 5, in this sheathed heater, when used at 800o0, it is sufficient to have a gas pressure of about 0111 side Hg. However, if gases such as oxygen or nitrogen that react with the heating element metal are sealed in the sheathed heater, these gases will be consumed while the sheathed heater is being used, making it difficult to use these gases. It is.

Even if a sheathed heater is used, it is necessary to use an inert gas in order to maintain a stable gas state without reacting with the heating element metal. In other words, when using a sheathed heater at 800 qo, the partial pressure of the inert gas as the enclosed gas is 800 qo.
00, if Hg or more exists on the 111 side, the insulation resistance is IM
It is better than Q.

Further, even if oxygen or nitrogen is present in the sealed gas, if the partial pressure of the inert gas is 111 skin Hg or more at 800° C., it is possible to prevent the insulation resistance from becoming less than IMO.

Traditionally, 20qC, 1 atm, 76 mHg
When air is sealed at a pressure of It just has to happen. In other words, in the conventional method of enclosing air, the pressure of the inert gas is insufficient. To prevent insulation deterioration of the sheathed heater, use an inert gas alone or a mixture of air, oxygen, nitrogen, and an inert gas as the sealed gas, and keep the pressure of the inert gas at 11% at 800°C.
Must be 1 willow Hg or more.

At 800°C, the pressure on the 111 side Hg corresponds to a pressure of 31 sides Hg at 20q0 according to the gas equation of state.

Since the gas is sealed at a room temperature of about 20° C., when filling the sheathed heater with gas, it is necessary to ensure that the inert gas has a partial pressure of Hg or higher on the 31 side. The above was a case where a sheathed heater with a heat generating part length of 40 mm was used at 80,000 mm.

The insulation resistance of a sheathed heater also changes depending on the temperature at which it is used.

In other words, this is because the electrical resistance of the filled M mosquitoes changes depending on the temperature. The insulation resistance of a sheathed heater must be IMO or higher regardless of the temperature at which it is used.

A sheathed heater with a heat generating part length of 40 mm is used, and the pressure of argon in the sheathed heater is set to 760 Hg at each temperature.
Keep the operating temperature constant at 10 Hg and 1 Hg, and set the operating temperature to 65.
FIG. 6 shows the change in insulation resistance R4 when changing from 0o to 850o.

When the operating temperature is a°C, the horizontal axis in Figure 6 is the absolute temperature T.
= 1/T, the reciprocal of 2730a〇. At this time, the common logarithm lo of insulation resistance is expressed as 40. It can be seen that a good linear relationship can be obtained between a and 1/T. Figure 7 shows *argon pressure Pa and insulation resistance R at each operating temperature a°C from Figure 6.
40. Indicates the relationship with a.

At this time, it can be seen that the insulation resistance is proportional to Pa in the range of 650 to 850 degrees as in FIG. Figure 6,
From Figure 7, from 650°C to 85000, the electrical conduction of Mg○ has one activation energy and is based on the same electrical conduction formula, and this activation energy is 2.7 eV, and this electrical conduction property is It was found that the resistance is related to the pressure Pa of the gas surrounding Mg○, and that the resistance is proportional to the pressure Pa. This property was the same for other gases such as air, oxygen, nitrogen, helium, neon, xenon, krypton, and radon. From this, when a sheathed heater with a heat generating part length of 40° is used at a temperature of a°C, the insulation resistance of the sheathed heater can be expressed as follows based on equation [1}.

R40-a (MQ) = 0-095 x CX Pa (costal Hg
)
'2} In the formula, k is Borckmann's constant, and c is a proportionality constant.

According to the data in FIG. 6, c = 2.14 x 10-ne, and by substituting the Borckmann constant k = 8.62 x 105 eV'deg into equation (2), equation '3' is obtained. R40-a:2
05 x 10-14 x ZoPa (side Hg) e
``3'' or higher was for the sheathed heater used in this test, which had a heat generating part with a length of 40 skins.

There is a difference between the length of the heat generating part of the sheathed heater and the insulation resistance.
There is an inversely proportional relationship.

In other words, the longer the sheathed heater, the lower the insulation resistance.
Insulation resistance (R) using a sheathed heater with the length of the heat generating part at a temperature of c. a is given by the t4-formula based on the 40-skin sheathed heater.

R-a=R4QaX etc. 0...(4'R40.
Since a is given as a glue formula, the '5} formula is obtained.

R. a=82oXm13×years old;
Xp (Ryojoshuang) .-■ To use a sheathed heater with a length of the heat generating part at a degree Celsius and to make the insulation resistance more than IMO, set R〆.a=IMO in formula '3'. By substituting (6-), a gas pressure greater than the pressure expressed by equation ★ must exist in the sheathed heater at a degree Celsius.

Pa (willow Hg) = 1-49 x 1bi 4X〆 (skin)
- Shigei Hishimine) ... ■ At room temperature 20:00, using the gas equation of state, the pressure and force of the gas is required to be greater than the pressure P20 at 2 and 0 expressed by the '7} formula.

In other words, a sheathed heater with a length of heat generating part of
In order to maintain insulation resistance of IMO or higher even after use at There is. P2o (Yanagi Hg) = Sehogaku x Buddha 9
×・pi 4
Examples of the present invention are shown below.

The sheathed heater shown in Figure 2 was made.

A metal protection tube made of fusen steel with a wall thickness of 0.2 mm and an iron chrome wire were used for the electric heating element.

The electrical insulating powder contains 40
Mesh to 375 mesh furnace-fired magnesia (Mya) was filled to a packing density of 2.8. Further M
In order to remove moisture contained in g○, it was heated at 900o○ and cooled in air. After once discharging the gas in the sheathed heater using a vacuum pump, various gases were injected at various pressures at 2000° C., and the sheathed heater was hermetically closed using glass as a sealant. Example 1 Outer diameter 7 skin,
I made a sheathed heater with a heat generating part length of 40cm.

The gas sealed in the sheathed heater is air as in the conventional example, and inert gas such as helium, neon, argon, krypton, xenon, radon, etc. in the present invention.
The sample was sealed to give a reading of 0.0 and 76 mHg. FIG. 8 shows the change in insulation resistance over time when the sheathed heater 15 containing air and the sheathed heater 16 containing xenon were used at 80,000. With conventional air-filled sheathed heaters, the amount becomes below IMO after about 2 feeding hours,
It can be seen that after about 40 hours, it remains constant at about 0.8 MQ.

On the other hand, it can be seen that the sheathed heater 16 of the present invention in which xenon as an inert gas is sealed remains at about HMO even after 10M hours and does not change much. Table 2 lists air, helium as an inert gas, neon, argon,
Krypton, xenon, radon at 20qo is 76m
This figure shows the insulation resistance after 1 hour and after 10 feeding hours when a sheathed heater sealed at a pressure of 80,000 g is used.

Table 2 Insulation resistance values of sheathed heaters using various gases From Table 2, it can be seen that the sheathed heaters filled with inert gas show almost no deterioration in insulation resistance and are higher than IMO.

Example 2 A sheathed heater having the same shape as in Example 1 was used, and an inert gas was used as the sealed gas, and the sealed gas was sealed at various pressures of 20 oo.

As a conventional example, a sheathed heater sealed with air at 76 mHg in 2000 was used at 15, a sheathed heater sealed at 760 Hg in 2000 using argon as the inert gas of the present invention, and 17 in which air was sealed at 100 mHg. 18, 31 side H
Figure 9 shows the change in insulation resistance over time when these sheathed heaters were used at 800 qo. It can be seen that in a sheathed heater filled with only inert gas, the insulation resistance value changes depending on the sealed pressure, but does not change over time.

Insulation resistance after 10 heating hours derived from Figure 9 R40.80
The relationship between the pressure P20 at 0 and the pressure P20 of the enclosed argon at 2000 is shown in FIG. It can be seen from FIG. 10 that there is a relationship expressed by equation {8). R40800 (MQ) Ni〇, 18 no P20 (costal Hg),. , (8) From this, in order to make the insulation resistance value higher than IMO, the argon pressure should be 20o
It turns out that it is best to keep the skin Hg above 31 at o.

This relationship between insulation resistance and gas pressure is similar to that for other inert gases,
The same is true for helium, neon, krypton, xenon, and radon; if an inert gas is filled at 20 oo and 31 Hg or more, the insulation resistance of the sheathed heater will be at least IMO and will not change over time. In addition, the sealing pressure is 1 atm, 760
It may be lower than rib Hg.

Example 3 A sheathed heater having the same shape as in Example 1 was used, and a mixed gas of various compositions of inert gas and air was used as the gas sealed in the sheathed heater, and the gas pressure was 2000 ml as the total pressure. It was sealed to give a pressure of 76 m.Hg.

The first result is when krypton is used as an inert gas.
Shown in Figure 1. A conventional example is a sheathed heater 15 that contains air, and a sheathed heater that uses a mixed gas of air and krypton at a volume ratio of 1:1, 21, and a 10:1 sheathed heater.
22 uses a mixed gas of 30:1, 23 uses a 30:1 mixed gas, and 24 uses a 80:1 mixed gas. It shows the change in insulation resistance over time when used at 800qo.

When using a mixture of inert gas and air, unlike in Examples 1 and 2 where only inert gas was used,
Changes in insulation resistance occur over time. However, after about 4 hours of feeding, the insulation resistance becomes almost constant. This is because the oxygen and nitrogen in the mixed gas react with the heating element and become oxides and nitrides, so only inert gas remains in the sheathed heater, and the pressure is reduced compared to when it was first used. This is because Since the insulation resistance of a sheathed heater is determined by the total pressure of the gas in the sheathed heater, it is thought that the insulation resistance after about 4 feeding hours is determined by the pressure of the inert gas remaining in the sheathed heater.

20 of the inert gas in this mixture of inert gas and air
The partial pressure at q0 is shown in Table 3. Table 3 The total pressure of the inert gas in the gas mixture is approximately 20% oxygen and 79% nitrogen by volume percentage.
, contains about 0.9% argon.

Therefore, the partial pressure of the inert gas in the gas mixture is the sum of the partial pressures of argon and nitrogen. The total pressure P20 (in Hg) of the inert gas in the gas mixture shown in Table 3 at 2000
) and the insulation resistance R4 after 10 legs using a sheathed heater using the mixed gas shown in Figure 11 at 800oo.
The relationship with 0800 (MQ) is shown in Figure 12. From this, it can be seen that even if a mixed gas of inert gas and air is used and sealed at 2000 Hg and 760 Hg, the same relationship expressed by the shelf type as in FIG. 10 is obtained.

Therefore, in this case as well, the total partial pressure of the inert gas is 20
When the temperature is 31 Hg or more at ℃, the insulation resistance remains IM even after aging.
It can be seen that the value is O or more. In this example, krypton was used as the inert gas, but other gases such as helium, neon, argon, quinocene, and radon could also be used.

Example 4 A sheathed heater having the same shape as in Example 1 was used.

In Example 3, a mixture of inert gas and air was sealed at a pressure of 76 mHg at 2,000 mm, but this example shows a case where the pressure of the gas mixture was changed. A gas mixture of neon and air at a volume ratio of 1:1 was used as an inert gas, and this gas mixture was sealed in a sheathed heater at various pressures of 2,000 ℃.

25,100 sheathed heaters sealed with 76 tons of Hg
The one encapsulated with skin Hg is 26, the one encapsulated with 62 willow Hg is 27, and the one encapsulated with 10 foot Hg is 28.

These sheathed heaters and the conventional 20qo 760h
FIG. 13 shows the change in insulation resistance over time when 15 g and 15 in which air was sealed were used at 800 oo. After 4 hours, it begins to show a certain insulation resistance.

This is due to the same reason as stated in the third embodiment. Table 4 shows the total partial pressure of the inert gas at 2000 when the mixed gas is sealed at each pressure. , △
Total pressure of inert gas P20 (side H) at 20 o'clock in Table 4
g) and the insulation resistance R408 after 100 hours in Figure 13.
00(MQ) is shown in FIG.

From this, it can be seen that the same [8i formula] relationship as in Examples 2 and 3 holds. Also, even if a sheathed heater is used at 80,000, in order to make the insulation resistance more than IMO,
It can also be seen that the partial pressure of the inert gas in the mixed gas needs to be at least 31 Hg at 20°C. To use a 1:1 mixture of air and neon by volume, 66 at 20:00.
It is sufficient to seal the mixed gas at a pressure higher than side Hg, and there is no need to seal the mixed gas at a pressure higher than 1 atm, 760 Hg. In this example, the case of neon was described, but
The same was true for other inert gases, helium, argon, krypton, xenon, and radon.

Example 5 Using a sheathed heater having the same shape as in Example 1, a mixed gas of nitrogen and an inert gas was sealed at 20 qo and a pressure of 76 kHg.

A sheathed heater filled with a 1:1 volume ratio of nitrogen and radon as an inert gas is 29, 30 is a 10:1 sheathed heater, 31 is a 30:1 sheath heater, 50 :32 is the one using 1.
These sheathed heaters and conventional air are heated at 20o
Sheathed heater sealed at 76 degrees Hg at o 1 5 to 8
FIG. 15 shows the change in insulation resistance over time when used at 0000.

Inert gas pressure P at 20o0 in each sheathed heater
20 (costal Hg) and 100 hours obtained from Figure 15, 8
Insulation resistance R4 after using a sheathed heater at 00oo
The relationship with 0800 (MO) is shown in FIG.

From this, the insulation resistance of the sheathed heater and the partial pressure of the inert gas at 20 qo are determined by the same formula '8 as in Examples 2, 3, and 4.
It can be seen that the relationship 1 is established.

In addition, in order to make the insulation resistance after aging equal to or higher than IMO, the partial pressure of the inert gas sealed at 2000 must be set to 31 side Hg.
It turns out that the above is necessary. The reason why the insulation resistance changes over time during use of the sheathed heater is thought to be due to the reaction between the metal heating element and nitrogen and the formation of a metal compound, as shown in Examples 3 and 4. It will be done.

Similar results were obtained using other inert gases, helium, neon, argon, krypton, and xenon. Example 6 Using a sheathed heater having the same shape as in Example 1, a mixed gas of oxygen and an inert gas was sealed at a pressure of 760 skin Hg at 20q○.

The results were the same as in Example 5. Although the time for the insulation resistance to change is only slightly faster, the insulation resistance after 10 field hours when used at 80000 and the pressure of the inert gas in the sheathed heater at 20qo are as shown in Figure 16. The same results were obtained for the relationship. From this, even when a mixed gas of oxygen and inert gas is sealed, as long as the partial pressure of the inert gas is set to be higher than 31 side Hg at 2000, the insulation resistance will remain at IMO even after aging. It turns out that the above is true. Example 7 A sheathed heater having the same shape as in Example 1 was used.

Examples 1 to 6 were heated at 20°C in a sheathed heater at 31°C.
It has been found that if an inert gas is present at a pressure higher than skin Hg, the insulation resistance of the sheathed heater will remain higher than IMO even after aging. Air contains 0.9% argon by volume, and it is thought that it is possible to make a sheathed heater with good insulation properties even if only air is used.

At this time, in order to make the pressure of argon as an inert gas higher than 31 Hg at 20°C, in the sheathed heater, 200
At 0, it is necessary to fill the air with a pressure of 350 m²Hg, or 4.6 atm. At 2000, a sheathed heater sealed with air at a pressure of 350 mHg was installed at a pressure of 33,170 mHg.
34 is the one filled with air at a pressure of 2.2 g (2.2 atm).

The conventional example with air sealed at 760 Hg is 15,
Figure 17 shows the change in insulation resistance over time when these sheathed heaters were used at 80,000. From now on, 800
Even after 100 hours at 00, 350 Hg at 2000
It can be seen that the insulation resistance of the sheathed heater 33 in which air is enclosed is IMO.

However, when the sheathed heater is sealed at a pressure of 350 Hg at 2000° C. and the temperature rises to 800° C., the air pressure in the sheathed heater increases to 1280 Hg, or 17 atm. The pressure resistance of the glass used as the sealant is approximately 8 atmospheres, and the pressure exceeds this pressure resistance. For this reason, when using a sheathed heater filled with air at 2000 and 350 Hg, when used in a completely stationary state,
Only about 1 out of 1 hard sheathed heaters can be used at 800oo, and the remaining 9 or if the sheathed heater is subjected to a little vibration, the glass used as a sealant may crack or break again. It was scattered. For this reason, a sheathed heater in which high-pressure air is sealed in a sheathed heater to improve insulation resistance must be used in a static state without vibrations, and is not very useful industrially. On the other hand, 80,000
Even if the temperature is raised to 1, in order to maintain the air pressure of 8 atmospheres, which is the withstand pressure of the glass, it is necessary to seal in air at a ratio of 170 Hg at 2000 mm.When using this sheathed heater 34 at 800 mm, The insulation resistance became below IMO after aging.

In the sheathed heaters of the present invention described in Examples 1 to 6, the pressure inside did not increase much even at 800 qo, and the sheathed heaters 16, 17, 21, and 2 that showed the maximum pressure
Even at 2, 23, 24, 25, 29, 30, 31, and 32, the pressure is about 2800 Hg, that is, 3.7 atmospheres, which is within a sufficient range compared to the pressure resistance of glass as a sealant.

In addition, in the sheathed heaters 18, 19, 26, and 27, 8
Even at 00oo, the pressure of the gas inside the sheathed heater is 76 tons of Hg, less than 1 atm, which is also within the range of glass pressure resistance.

Example 8 A sheathed heater having the same shape as in Example 1 was used.

We investigated the effect on the insulation resistance of the sheathed heater by changing the amount of moisture contained in the gas sealed in the sheathed heater. As the gas, a mixed gas of air and argon at a volume ratio of 1:1 was used, and the mixture was sealed at 20° C. and a pressure of 760 Hg. At this time, the partial pressure of each component gas is 300 Hg for nitrogen, 76 for oxygen
Willow Hg, argon 384 side Hg. The amount of water in the gas was adjusted by passing the mixed gas through water, and the Karl Fischer method was used for quantitative determination. FIG. 18 shows the relationship between the moisture content of the gas lccK used and the insulation resistance of the sheathed heater after using the sheathed heater using gases with various moisture contents at 80,000 for 10 intervals.

From this, it can be seen that when the amount of water in the gas LCC is 17 grams or less, it has no effect on the insulation resistance.

Also, with 2000, it was not possible to contain more than 17 grams of water in LCC gas. This is probably because the vapor pressure of water at 20 oo is 17.5 Hg. This shows that using a gas saturated with water has no significant effect on insulation resistance. During the sheathed heater,
It is filled with Mg0 at a packing density of 2.8.

The true specific gravity of Mg○ is 3.65. From this, the lcc in the sheathed heater is filled with 2.8 cc of Mg0, and the volume of Mg0 at this time is 0.77 cc. 0 left
．． 23 cc will be occupied by the sealed gas. When Mg○ in a sheathed heater is soaked in dehydrated methanol and the amount of water contained in Mg carp is determined from the amount of water increased in the methanol4, it is found that approximately 100 mg of water is contained in Mg01. I found out that From this, the moisture contained in Mg0 in the sheathed heater LCC is 100 x 2.8 =
280 French g, moisture due to gas saturated with water 17 x 0.2
There will be 3=3.9 Buddhas g.

It can be seen that the amount of moisture contained in Mg○ is greater than that introduced by the enclosed gas. For the above reasons, it was thought that the amount of moisture in the enclosed gas did not significantly affect the insulation properties of the sheathed heater.

Example 9 The insulation resistance of a sheathed heater must be greater than or equal to IMO, regardless of its shape.

In Examples 1 to 8, fusen steel with a wall thickness of 0.2 ribs was used as the metal protective tube, and a sheathed heater with an outer diameter of 7 ribs and a heat generating part length of 40 mm was used. The outer diameter of the sheathed heater is also thought to affect insulation resistance. In this example, the wall thickness is 0.
．． Using a 2-rail non-ferrous metal protection pipe, the length of the heat generating part is 4.
A sheathed heater was prototyped with a temperature of 0c and the outer diameter changed.

The manufacturing method, Mg0 used, etc. are the same as in Example 1.
As the gas sealed in the sheathed heater, a mixed gas of air and helium as an inert gas with a volume ratio of 1:1 was used, and the gas was sealed at a pressure of 76 mHg at 20 oo. 1st
Figure 9 shows the sheathed heater used in this way.
The relationship between the insulation resistance after 10 cycles and the outer diameter when used at 0oo is shown. This shows that even if the outer diameter of the sheathed heater is changed, the insulation resistance value does not change much. It can be expected that as the outer diameter increases, the distance between the metal heating element and the metal protection tube increases, and the insulation resistance also increases. However, as the outer diameter increases, the surface area of the metal protection tube of the sheathed heater increases, and the surface temperature of the metal protection tube increases to 800 oo.
The metal heating element must generate a large amount of heat in order to maintain
Therefore, the temperature near the heating element is higher than that of a sheathed heater with a small outer diameter.

As the temperature increases, the electrical resistance of Mg○ decreases. In this way, as the outer diameter increases, there are factors that increase the insulation resistance and factors that decrease it, and they work in a complementary manner, so that even if the outer diameter of the sheathed heater apparently increases,
It was thought that the value of insulation resistance did not change much. Example 10 In Examples 1 to 9, a sheathed heater with a heat generating part length of 40 kg was used, and if an inert gas was present at a pressure of 31 qHg or more in the sealed gas at 20 qo, the sheathed heater was heated to 80,000 qo. It has become clear that the insulation resistance exceeds IMO even after long-term use.

However, it was expected that the insulation resistance would decrease as the length of the heat generating part increased. In this example, a sheathed heater was prototyped in which the length of the heat generating part on the outer diameter 7 side was changed.

The manufacturing method is the same as in Example 1. Figure 20 shows the relationship between the insulation resistance after 10 hours and the length of the heat generating part when a sheathed heater with argon sealed at various pressures of 2,000 was used at 80,000 by changing the length of the heat generating part. . As shown in FIGS. 8 and 9 in Examples 1 and 2, the insulation resistance of the sheathed heater did not change much over time.

Curve 35 in Fig. 20 shows a sheathed heater in which argon is sealed at 30 mHg and the length of the heat generating part is changed.
This is the case when argon was filled at 1 mHg and the length of the heat generating part was changed.

Here is the heating part. 3*Length is the length occupied by the heating wire in the sheathed heater, and is the length from 6 to 7 in Figure 1, and the length from 13 to 14 in Figure 2. 20th
From the figure, it can be seen that the length of the heat generating part and the insulation resistance are in an inversely proportional relationship. Insulation resistance R40 after 100 hours of use at 80,000 for a twin sheathed heater with a heat generating part length of 40 cm.
．． There was a relationship between 800 (MQ) and the pressure P20 (°C) of the inert gas sealed at 20qo (8' formula) described in Example 2. R40,800 (MQ) Ni〇,18 NoP20 (Yanagi Hg)... (8) From Figure 20, when the pressure of the sealed gas is kept constant, there is an inversely proportional relationship between the length of the heat generating part and the insulation resistance R〆.800. (9
} can be expressed by the formula.

Rso-8oo=R4o-8ooX etc...■【8}
The dish type is obtained by the equation and the side equation.

Rso. 800 (MQ)=〇. 18X-type" x no p2o (
伽Hg) ・・・
(1) The length of the heating part is 80,000.
If the insulation resistance after 10 field hours is IMO, ** is the working formula Rso. Substituting 800 (MO) = 1 (
11) Obtain the formula.

P2o〈skin Hg)=(phrase saibou)2=.

o・9×〆{e' (skin). ...(11)
From Figure 20, the relationship between the length (skin) of the heat generating part of the sheathed heater when the insulation resistance becomes IMO and the pressure P20 (side Hg) of the argon sealed in 2000 is determined and plotted. It is shown in Figure 21. FIG. 21 also shows the relationship with part 2. From this, it can be seen that P20 and So2 are in a proportional relationship and agree well with equation (11). Also, by substituting a=80000 into equation (7), (1
1) From the obtained formula, it can be seen that formula '7} is valid. From the above, the sheathed heater with the length of the heat generating part is 8
To use at 0000, P20 (side Hg) = 20 o'clock
The insulation resistance of the sheathed heater changes over time by filling an inert gas at a pressure higher than that calculated by 0.019 x 2, or by filling a mixed gas with a partial pressure of the inert gas higher than that. However, I was able to achieve better results than IMO. This was also true for other inert gases such as helium, neon, krypton, xenon, and radon.

Example 11 Examples 1 to 10 were about a sheathed heater used in 80,000.

However, sheathed heaters are used at a variety of temperatures. Further, the insulation resistance must be IMO or higher regardless of the temperature at which it is used. The length of the heat generating part as a conventional example is 40 cM, 2
000 sealed air heater, 65000
, 70,000, the insulation resistance was good, being about 50 MQ, about 50 MQ, about 100% MO, which was higher than IMO even after aging.

However, even if used at 650qo, 70000, if the length of the heat generating part is 4m, the temperature will change over time after approximately 9○, 0.9M.
0, and cannot be used at 70,000. 6500 again
Even at zero operating temperature, in a 28-hour product in which six heat-generating parts each having a length of 4 m are arranged in parallel, the insulation resistance changes over time and becomes approximately 0.8 MQ, making it unusable. 8500 again
When used at 0, the insulation resistance of a sheathed heater with a heat generating part length of 40 cm was 0.19 after changing over time. From this, even when the operating temperature during heating is low, when the length of the heat generating portion is long, the insulation resistance decreases below the IMO.

When using a sheathed heater with a heat generating part length of cm at a degree Celsius, in order to maintain the insulation resistance at or above IMO even after changes over time, it is necessary to
It was necessary to seal in an inert gas at a pressure higher than the gas pressure given by the equation at 0qo. Outer diameter: 7 ribs, length of heating part: 4
Using 0 arc, 4 m, and 25 m sheathed heaters, argon was sealed as an inert gas at 20oC and at various pressures, and 650
Table 5 shows the insulation resistance after 10 cycles when used at temperatures of 0, 700 o'clock, 800 o'clock, and 850 o'clock.

It also shows the pressure at 2000 ℃ of the enclosed inert gas necessary to make the insulation resistance calculated by the formula {7->IMO or higher.

The x mark in the table indicates that the insulation resistance is less than IMO. From this, it can be seen that when the inert gas is filled in at a pressure higher than the pressure calculated by the formula '7}, the insulation resistance is higher than the IMO.

From this, it can be seen that formula (7) is valid.Table 5:
Operating temperature, length of heat generating part, 20℃ of enclosed inert gas
The insulation resistance (R) after 100 hours of use with different pressures at
Table 6: Pressure (P) of minimum required inert gas at 20°C to achieve MO or more: Example 1. From 5.7. The insulation resistance R of the saw heater shown in 100 hours of use, the pressure of the inert gas in the sealed gas at 20°C, and (7)
Table 6 shows the insulation resistance of the sheathed heaters shown in Examples 1 to 5 and 7 after 100 hours of use. and the pressure of the inert gas sealed in 2000 and the required pressure of the inert gas calculated from the formula '7}.

From this Table 6, it can be seen that if the inert gas is sealed at a pressure higher than the pressure calculated using formula '7}, the insulation resistance will remain I even after changing over time.
It can be seen that it is above MO.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a sheathed heater that is not hermetically sealed, Figure 2 is a cross-sectional view of a sheathed heater that is hermetically sealed, Figure 3 is a relationship diagram showing the change in insulation resistance of a conventional sheathed heater over time, and Figure 4 The figure is a relationship diagram showing the change in gas pressure in the sheathed heater over time, and Figure 5 is a relationship diagram between gas pressure and insulation resistance when various gases are injected into the sheathed heater at each pressure. Figure 6 is a relationship diagram showing the change in insulation resistance when argon is injected into the sheathed heater at various pressures and the temperature is changed. Figure 7 is a relationship diagram showing the change in insulation resistance when argon is injected into the sheathed heater at various temperatures. Relationship diagram between pressure and insulation resistance, Fig. 8, Fig. 9, Fig. 11, Fig. 13, Fig. 15,
Figure 17 is a relationship diagram showing the change in insulation resistance over time when the inert gas of the present invention is sealed in a sheathed heater. Figure 18 is a diagram showing the relationship between the pressure of the inert gas sealed in the sheathed heater and insulation resistance after changes over time, Figure 18 is a diagram showing the relationship between moisture in the gas sealed in the sheathed heater and insulation resistance, and Figure 19 is the outer diameter of the sheathed heater. Figure 20 is a diagram showing the relationship between the length of the heat generating part of the sheathed heater and insulation resistance when the pressure of the inert gas sealed at 2,000 ℃ is changed, and Figure 21 is a diagram showing the relationship between insulation resistance and insulation resistance.
The figure shows the relationship between the length of the heat generating part and the pressure of the enclosed inert gas at 2000 ℃ when the insulation resistance of the sheathed heater becomes IMO. 8... Metal protection tube, 9... Electric heating element, 11...
Electrical insulation powder. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21

Claims (1)

[Claims] 1. A Shih Tzu heater consisting of an airtightly closed metal protection tube, an electric heating element provided in the protection tube, electrical insulating powder filled between the electric heating element and the protection tube, and a gas sealed in the protection tube. When the length of the heat generating part is 1 cm and the surface temperature of the metal protective tube is a degree Celsius when the Shih Tzu heater is energized and used, 20
At °C (4.37×10^2^6)/(273+a)×l
^2×exp(-(6.26×10^4)/((273
+a))) Helium, neon,
A Shih Tzu heater characterized by the presence of at least one inert gas among argon, krypton, xenon, and radon.