JPH0824005B2 - Electric insulating filling material and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric insulating filling material for a general-purpose sheathed heater, and in particular, an electric insulating filling material which is required to have a high filling property and is used in an intermediate temperature range and a high temperature range. The manufacturing method is related.

(Prior Art and Problems to be Solved by the Invention) Conventionally, magnesia has been used as an electrically insulating filling material for sheathed heaters because of its high thermal conductivity and appropriate hardness.

However, since crystal-grown magnesia is a prismatic or scaly non-spherical body, the following problems occur when it is used as an electrically insulating filling material for a sheathed heater. That is, (1) since the flowability of the magnesia powder is poor, the time required for filling is long, and the production efficiency of the sheathed heater is inevitably low. (2) It is impossible to obtain a high-density filled state only by the filling step. (3) In the above-mentioned prismatic or scaly magnesia powder, since the particles have particle edges, the inner wall of the metal pipe and the heating wire may be damaged during the filling and rolling process. was there.

As a method for solving this problem, heretofore, a method for producing spherical or substantially spherical magnesia powder by a mechanical method or a chemical method (JP-A-62-86604), or a spherical or substantially spherical magnesia powder has been used. It has been proposed that an electrically insulating filling material obtained by mixing powder and non-spherical magnesia powder is a material useful for industrial scale production in response to the above-mentioned technical problems (Japanese Patent Laid-Open No. 61-61160). −214389
issue).

On the other hand, the above-mentioned filling material made of magnesia easily absorbs moisture in a high-temperature and high-humidity environment and its insulating performance deteriorates. Therefore, careful handling is required. As a method for solving this, conventionally, after forming a coating layer of activated alumina on the surface of magnesia particles, a method of obtaining an α-alumina layer having excellent moisture resistance by heat treatment (JP-A-60-240005) There is.

Further, there has been a problem in the insulation performance of the electric insulation filling material from the viewpoint of the initial insulation resistance value and the insulation deterioration rate in the energization cycle test. As a method for solving this, conventionally, the chemical composition is improved, the packing density is increased, and the particles are spheroidized (JP-A-59-215690),
There is a method in which nickel oxide Ni ₂ O ₃ having a high oxygen content is added to improve the effect (JP-A-60-77305).

Each of the electrically insulating filling materials obtained by the above-mentioned conventional method is improved in terms of high-density filling performance, hygroscopicity, or insulation, as compared with conventional products, respectively.
An electrically insulating filling material in which all of these properties have been improved at the same time and a method for producing the same have not yet been invented.

Further, the operating temperature of the sheathed heater is gradually shifting from low temperature to high temperature at present, and therefore it is necessary to improve the insulation resistance value of the electrically insulating filling material during heating. .

The present invention has been made in view of the above-mentioned problems, and the purpose thereof is that all of high-density filling performance, moisture resistance, and insulation (especially thermal insulation resistance) are significantly improved. It is an object of the present invention to provide an electrically insulating filling material and a manufacturing method thereof.

(Means for Solving the Problems) The electrically insulating filling material of the present invention has been made in view of the problems and objects described above, and includes mullite (3Al ₂ O ₃
2SiO ₂ ) powder and a mixed powder surface of a magnesia powder composed of spherical, substantially spherical and non-spherical particles are coated with silicone oil, which is an electrically insulating filling material.

The electric insulating filling material of the present invention is the electric insulating filling material in which the magnesia powder is composed of 5% by weight or more of spherical or substantially spherical particles and the rest of non-spherical particles.

Furthermore, the electrically insulating filling material of the present invention, the addition amount of the mullite is 0.1 to 30 wt% with respect to the magnesia powder,
This is an electrically insulating filling material in which the amount of silicone oil added is 0.001 to 2% by weight based on the mixed powder of mullite and magnesia powder.

In addition, the method for producing an electrically insulating filling material of the present invention is a method in which a magnesia powder composed of spherical, substantially spherical and non-spherical particles is mixed with mullite (3Al ₂ O ₃ .2SiO ₂ ) powder, and then silicone powder is mixed with the mixed powder. A method for producing an electrically insulating filling material, comprising adding and mixing oil, and coating the surface of the mixed powder with silicone oil.

Furthermore, the method for producing an electrically insulating filling material of the present invention is the method for producing an electrically insulating filling material, wherein the magnesia powder is composed of spherical or substantially spherical particles of 5% by weight or more and the remaining non-spherical particles.

Furthermore, the manufacturing method of the electrically insulating filling material of the present invention is the above manufacturing method, wherein the addition amount of the mullite is
This is a method for producing an electrically insulating filling material in which 0.1 to 30% by weight of magnesia powder and 0.001 to 2% by weight of silicone oil are added to the mixed powder of mullite and magnesia powder.

The present inventor uses a magnesia powder composed of spherical, substantially spherical and non-spherical particles having the above-mentioned high filling property as a base material, and has an effect of adding mullite powder exhibiting a high insulation resistance value at high temperature, water repellent property and fluidity. It was found that the high filling property, moisture resistance and insulating property of the electrical insulating filling material containing magnesia as a main component are remarkably improved by the interaction with the addition effect of silicone oil which gives the improvement of The invention has been completed. That is, in the state where any of the above-mentioned base material or additive is lacking, or the state where the water repellent property is not uniformly developed due to insufficient mixing operation, the initial high filling property and moisture resistance And it is difficult to obtain insulation.

Hereinafter, the electrically insulating filling material of the present invention and the method for producing the same will be described more specifically.

First, a magnesia powder composed of spherical, substantially spherical and non-spherical particles is prepared in advance as an electrically insulating filling material. The composition ratio is 5% by weight or more of spherical or substantially spherical particles, and the remaining non-spherical particles. It is preferably composed of particles. The reason is that if it is less than 5% by weight, the electrically insulating filling material consisting of only non-spherical particles and the physical properties (filling performance)
This is because there is no significant difference in.

Here, the spherical or substantially spherical magnesia particles used in the present invention mean particles including completely spherical particles and particles similar to spherical particles, and are composed of single crystals or polycrystals.

As a method of obtaining the spherical or substantially spherical magnesia particles, from a known mechanical or chemical manufacturing method,
It may be selected appropriately. For example, as a mechanical method, a method using a badge type mill to grind by utilizing collision between particles (Japanese Patent Laid-Open No. 59-215690), a method using a fluidized bed granulator and a rotary mixer, and a method using fire spraying ( JP 61-214389
No.), and as a chemical method, a commercially available non-spherical magnesia powder may be acid-treated or acid-treated and then alkali-treated (JP-A-62-38604). The spherical or substantially spherical body obtained by a method other than the above-mentioned manufacturing method can be used as the material of the present invention as long as it is a magnesia particle which can solve the above-mentioned technical problems.

The magnesia powder may have a purity of 90% by weight or more, and electromelted magnesia powder and / or sintered magnesia powder can be used.

Next, the magnesia powder previously prepared as the electrically insulating filling material is mixed with mullite (3Al ₂ O ₃ .2SiO ₂ ) powder, but as the mullite powder used as the improving agent of the insulating performance, preferably , Sillimanite group minerals (sillimanite, andalusite, and kyanite) are fired at high temperature to form mullite, or those synthesized from a mixture of kaolin group minerals and alumina are fired to form mullite. However, it is of course possible to use mullite obtained by a method other than this.

As the mullite, particularly, the alkaline component (Na ₂ O + K ₂ O) is 0.1% by weight or less, preferably 0.05% by weight or less, and the maximum particle size is 150 μm and 45 μm.
The following fine powders are preferably contained within 30%.

Further, the addition amount of this mullite is preferably 0.1 to 30% by weight with respect to the magnesia powder, from the viewpoint of insulating properties and properties originally required as a sheathed heater. That is, if the added amount is 0.1% by weight or less, it is difficult to obtain a sufficient effect on the insulation performance.
This is because if the content is more than 10% by weight, the thermal conductivity will decrease, and the performance of the sheath heater will deteriorate.

Next, silicone oil is added to and mixed with this mixed powder to uniformly coat the surface of the powder particles with silicone oil.The silicone oil used as the agent for improving the water repellent property and the fluidity is dimethyl-based. Its molecular structure is as follows.

In addition to water repellency, this silicone oil improves the fluidity of the filling material, so its viscosity is important,
Viscosity (25 ℃) 10-100cs, Specific gravity (25 ℃) 0.930-0.970,
And the viscosity temperature coefficient is preferably in the range of 0.54 to 0.60.

Furthermore, the amount of the silicone oil added is preferably 0.001 to 2% by weight based on the mixed powder of the mullite and magnesia powder, from the viewpoint of water repellency, fluidity and insulation. That is, when the addition amount is 0.001% by weight or less, it is difficult to obtain a sufficient effect on water repellency and fluidity, and when the addition amount is 2% by weight or more, the fluidity of the powder at room temperature is significantly reduced and the thermal decomposition at high temperature is performed. This is because the deterioration of the insulation resistance value due to the carbon that is generated during the treatment is significant.

By adding the silicone oil described above, it is possible to prevent moisture absorption of the filling material containing magnesia as a main component at around room temperature, and it itself is used as a filling material for sheathed heaters, and after being heated to a high temperature during the manufacture of sheathed heaters, it is filled with an inorganic material. A SiO ₂ film is formed on the surface of the object. Therefore, even after the decomposition of the organic matter contained in the silicone oil,
Since the moisture resistance of the filling material is not lost due to the formation of this SiO ₂ film, the use of the filling material prepared by adding this silicone oil causes an extremely low change in the electrical insulation resistance value at the initial stage and after the current application cycle. It is possible to provide a typical sheath heater.

(Example) As a main component of the electrical insulating filling material, 70% by weight of ore-based electro-fused magnesia powder and 30% by weight of seawater-based sintered magnesia powder were mixed to obtain a magnesia powder. Its chemical composition is shown in Table 1 below. Incidentally, this magnesia powder is composed of 20% by weight of spherical or substantially spherical particles by grinding treatment and 80% by weight of untreated non-spherical particles,
Furthermore, the maximum particle size is 355 μm, the packing density is 2.40 g / cm ³ , and the fluidity is 180 sec / 100 g.

Subsequently, the following electrically insulating filling materials were prepared from the prepared electro-fused magnesia powder.

A ... Kyanite powder was calcined at about 1650 ° C. for 1 hour to form mullite, and 2.0% by weight of mullite powder pulverized to a particle size of 150 μm or less was added to the above-mentioned electro-fused magnesia powder and mixed, and further mixed. Prepared by adding 0.03% by weight of dimethyl silicone oil to the powder and mixing B ... Kyanite powder was burned at about 1650 ° C. for 1 hour to make mullite, and 2.0% by weight of mullite powder was crushed to a particle size of 150 μm or less. Prepared by adding and mixing the above-mentioned fused magnesia powder C ... prepared by mixing 0.03% by weight of dimethyl silicone oil with the above fused magnesia powder D ... only by the above fused magnesia powder What was prepared For each of these four types of electrical insulation filling materials A, B, C, and D, the packing density and fluidity were measured. The results are shown in Table 2 below. In addition, for this measurement
Boeh Model AP901122 Tap Density Measuring Device (ASTM.D.3477
Was used).

As is clear from Table 2, the electrically insulating filling material of the present invention does not impair the filling property of the base material even by the addition treatment, as compared with the conventional electrically insulating filling material.

Next, each of these four types of electrical insulation filling materials A, B, C, and D, with a heating wire (Nichrome wire, trade name "Nichrome 5"), outer diameter 7.5 mm, wall thickness 0.5 mm, length 700 mm Was filled in the gap with the metal pipe (NCF2P, trade name "Incoloy 800"), and after undergoing the steps of rolling reduction and annealing, both ends of the metal pipe were sealed with low melting point glass. In this way, samples A, B, C, and D each having an outer diameter of 6.5 mm, a heater total length of 785 mm, and an effective heat generation length of 585 mm were prepared.

Next, the following energization cycle test was carried out using each of these samples. That is, the thermal insulation resistance value was measured under the conditions of power density of 10 W / cm ² , metal pipe surface temperature of about 900 ° C., (20 minutes energization-10 minutes rest) / cycle. The results are shown in FIG.

As is clear from FIG. 1, the sample A prepared using the electrically insulating filling material of the present invention (that is, the one prepared by adding mullite and silicone oil) is the filling material prepared by adding only mullite. Compared with the sample B prepared by using the sample B, the sample C prepared by using the filler material prepared by adding only the silicone oil, and the sample D prepared by using the conventional filler material composed only of the electro-melting magnesia, Had a high insulation resistance and showed a very high value with little insulation deterioration even after 2000 cycles. Also, from the results of Samples B and C, it is clear that the material properties of the present invention are exerted by the interaction of two types of additives, mullite and silicone oil.

In this example, as the main component of the electrically insulating filling material, a mixed powder of fused magnesia and sintered magnesia was used, but instead of this, fused magnesia powder alone or sintered magnesia alone, It has been found that there is a tendency similar to that of the above-mentioned embodiment and that it can be used in the present invention.

In addition, the main component magnesia used in this example was 96.0 to 97.0% by weight of extremely high purity, but instead of this, the purity of the magnesia powder used was 90%.
If it is at least% by weight, there is a tendency similar to that in the above example,
It has been found that it can be used in the present invention.

Furthermore, as a mullite additive, other than the kyanite used in the above examples, a calcined product of andalusite and sillimanite, and a mullite powder selected from calcined products synthesized from a mixture of kaolin group minerals with alumina. It has been found that there is a similar tendency by using, and it can be used in the present invention.

(Operation / Effect) As described above, according to the electrically insulating filling material of the present invention and the method for producing the same, the magnesia is composed of spherical, substantially spherical and non-spherical particles with magnesia having a high thermal conductivity as a main component. Mullite, which has excellent insulating properties when heated, is added to the surface of the mixed particles, and silicone oil that has water repellency and improves fluidity is added to the surface of the base material. Easily provide excellent electrical insulation filling material with significantly improved filling performance, moisture resistance and insulation of electrical insulation filling material mainly composed of magnesia due to interaction by shape and addition effect of the additive It is possible.

That is, according to the electrically insulating filling material and the method for producing the same of the present invention, (1) there is no damage to the metal, the pipe, and the heating wire in the manufacturing process of the sheathed heater, and high filling density is possible, and (2) long-term It is possible to easily provide an electrically insulating filling material that does not deteriorate in quality due to moisture absorption even when it is stored, and has an excellent insulation resistance value at the initial stage and after a current cycle. (3) Furthermore, magnesia, which is the main component, 90 purity
Since it can be used if it is at least wt%, it is an excellent invention that has many operational effects such as the use of inexpensive ore-based raw materials and the provision of filling materials that are inexpensive.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a thermal insulation resistance value and an energization cycle in a sheathed heater made using the electrically insulating filling material of the present invention and a sheathed heater made using a conventional electrically insulating filling material. Is.

Claims (2)

[Claims] 1. An electrically insulating filling material in which the mixed powder surface of mullite (3Al ₂ O ₃ .2SiO ₂ ) powder and magnesia powder composed of spherical, substantially spherical and non-spherical particles is coated with silicone oil. And the magnesia powder is 5
% Or more spherical or substantially spherical particles, and the remaining non-spherical particles, the addition amount of the mullite is 0.1 to 30% by weight of the magnesia powder, the addition amount of the silicone oil is mullite and magnesia. 0.001 to 2% by weight based on the mixed powder with the powder, the silicone oil has a viscosity (25 ° C) of 10 to 100cs and a specific gravity (25 ° C) of 0.9.
An electrically insulating filling material characterized by having a viscosity temperature coefficient of 30 to 0.970 and a viscosity temperature coefficient of 0.54 to 0.60. 2. A magnesia powder composed of spherical or substantially spherical particles of 5% by weight or more and the remaining non-spherical particles, and 0.1 to 30% by weight of mullite (3Al ₂ O ₃ .2SiO ₂₎ based on the magnesia powder. ) After mixing the powders, add 0.001 to the mixed powder of mullite and magnesia powder.
~ 2% by weight, viscosity (25 ℃) 10-100cs, specific gravity (25 ℃)
A method for producing an electrically insulating filling material, comprising adding and mixing silicone oil having a viscosity temperature coefficient of 0.54 to 0.60 with a viscosity coefficient of 0.930 to 0.970 and coating the surface of the mixed powder with the silicone oil.