DE2046697C3 - Process for the production of electrical porcelain insulators coated with a semiconducting glaze - Google Patents

Description

The invention relates to a method for producing with a semiconducting glaze based on Sn / Sb coated porcelain electrical insulators.

Under the designation "semiconducting glaze mass" or "semiconducting glaze mixture" is a mass or mixture to understand, which is semiconducting in the fired state.

The surface resistance of a semiconducting glaze coating on a high voltage insulator is applied, should be in the range of 1 to Mti area unit. To make a semiconducting glaze coating with such a surface resistance, attempts have already been made to add various conductive metal oxides to conventional ceramic glaze mixtures. Namely

1. Semiconducting glaze mixtures,
which contain iron oxide as a conductive metal oxide

60

This glaze mixture can be applied to an electrical insulating body with a large wall thickness which must be fired in a reducing atmosphere. However, it is known that when using an electrical insulator coated with this glaze mixture in one heavily polluted atmosphere that is easily subjected to electrolytic corrosion- The The temperature coefficient of resistance is highly negative, making thermal instability likely is. Accordingly, an electrical insulator with such a semiconducting glaze mixture will fail essentially all of its surface area due to its thermal instability. The look this glaze is also disadvantageously black.

2. Semiconducting glaze mixtures,
which contain titanium oxide as a conductive metal oxide

When this glaze mixture is applied to a manufactured insulator body and in a reducing Atmosphere is fired, then the titanium oxide is reduced, and the surface resistance of the semiconducting glaze coating obtained is less than 100 mils / unit area. Titanium oxide glazes however, they are damaged by discharges, which is due to re-oxidation Conductivity losses of the titanium oxide occur. Furthermore, the manufacturing conditions, in particular the firing conditions are strictly adhered to, and the glazing process of the semiconducting glaze mixture is very complicated, which limits the technical production quite a lot. Hence this Glaze mix not commonly used.

3. Semiconducting glaze mixtures containing tin oxide

and antimony pentoxide as conductive metal oxides

contain

When this glaze mixture is applied to an insulator body, the semiconductive glaze coating has a high resistance to electrolytic corrosion, a low negative temperature coefficient of resistance and an adequate coefficient of thermal expansion. The coated surface is gray or white. This glaze mixture is therefore particularly suitable for the production of high-voltage insulators that require high mechanical strength. Examples of such semiconducting glaze mixtures are described in British patents 982,600, 1,098,958 (corresponding to US Pat. No. 3,368,026) and 1,112,765. In all of the processes described therein, a blue tin oxide, which is obtained by calcining a mixture of 99 to 95 mol percent SnO ₂ and 1 to 5 mol percent Sb ₂ O ₅ at temperatures of 1000 to 1200 C or by calcining a mixture of 99.5 to 95 mol percent SnO ₂ and 0.5 to 5 mole percent Sb ₂ O _{5 is obtained} at temperatures of 1200 to 1300 C, mixed with a conventional ceramic glaze mixture, and the mixture obtained is applied to the surface of a ceramic article and fired, whereby on the surface of the ceramic article a semiconducting glaze coating is obtained. However, these methods are only applicable to the firing of electrical insulators in an oxidizing atmosphere, but not to electrical insulators with a large wall thickness that have to be fired in a reducing atmosphere because the surface resistance of the semiconducting glaze coating obtained is more than 100 Ω / unit area and the surface expands considerably.

From the British patent specification 1 213 621 is finally

046

also borrowed an electrical insulator known, the is covered with a semiconducting glaze, which consists of an electrically conductive oxide that is coated with a conventional glaze mixture is coated, wherein the electrically conductive oxide consists of a mixture of s Antimony oxide and tin oxide, which contains 2.5 to 9 percent by weight of antimony.

In contrast, the present invention relates to a process of the type described above, which is characterized in that a mixture of 85 to 94 mol percent, calculated as SnO ,, at least one tin component from the group SnO ₂ and H ₂ SnO ₃ and 6 to 15 is used mole percent, calculated as Sb ₂ O _5, at least one antimony component from the group Sb, Sb ₂ O ₃ and Sb ₂ O ₅ at a tempera-, ₅ calcining temperature from 1000 to 1300 ⁰ C in an oxidizing atmosphere, pulverizing the calcinkirte mixture, 25 to 45 percent by weight of the pulverized mixture mixed with 55 to 75 percent by weight of a conventional ceramic glaze mixture, the mixture ^{obtained melts at a temperature of 1200 to 1400 0} C in an oxidizing atmosphere, the melt obtained pulverized, not less than 70 percent by weight of the fried material obtained with not more than 30 percent by weight of at least one material from the group consisting of clay, kaolin, bentonite and conventional r mixed ceramic glaze mixtures, the mixture obtained is applied to an insulator body and this is fired in a conventional reducing atmosphere.

In this way a semiconducting glaze mass can be produced, which can easily be converted to an electrical Insulator with a large wall thickness, which must be fired in a reducing atmosphere, is applicable.

Products with such good properties can be manufactured using the state-of-the-art processes, z. British patents 1,213,621 and 982,600 cannot be obtained.

Thus, according to the present invention, there becomes a calcined material of tin oxide and antimony oxide and powdered and pulverized a conventional ceramic glaze mixture. The mixture is melted to make a fried material. The fritted material and a conventional one ceramic glaze mix are pulverized and mixed again. In this way particles, in which the electrically conductive oxides with a frit with a conventional ceramic glaze composition are coated. Therefore, even if a manufactured insulator body, which is glazed with the semiconducting glaze mixture, fired in a reducing atmosphere the firing atmosphere is closed off for each of the particles by the covering frit layer, and the electrically conductive oxide in the central part of the particles is from the reducing Atmosphere not affected. In this way, a semiconducting glaze mass came to be produced easily on an electrical insulator with a large wall thickness, which is in a reducing atmosphere must be fired, can be applied. It has been impossible until now by the conventional method. Even with electrical insulators with a large wall thickness, the electrical properties can be significantly improved according to the invention.

The invention is to be explained in more detail below with reference to the drawings.

Figures IA and 1B are flow sheets illustrating that conventional methods of manufacturing electrical insulators using conventional ones Compare semiconducting glaze mixtures with the method according to the invention, which the semiconducting glaze mixes used;

F i g. Fig. 2 is a graph showing the relationship between the ratio of the tin component to the Antimony component and the properties of the coating from the semiconducting glaze mixture after application to an electrical insulator body and firing in a reducing Atmosphere shows;

F i g. Fig. 3 is a diagram showing the relationship between the burning conditions in the deep frying process and the properties of the semiconducting glaze coating after application shows an electrical insulator body and burning in a reducing atmosphere;

Fig. 4 is a graph showing the relationship between the mixing ratio of the electric conductive oxide to the conventional ceramic glaze mixture and the properties of the coating from the semiconducting glaze after application to an electrical insulator body and firing shows in a reducing atmosphere;

F i g. 5 is a front view, partly in cross section shown, a solid core insulator with a semiconducting glaze coating according to the invention is provided.

FIG. 1A shows a conventional method for manufacturing insulators, while FIG. 1B shows the method according to the invention. In the method of Fig. 1B, at least one of tin oxides such as tin oxide (SnO ₂ ) and metatannic acid (H ₂ SnO,) is used in an amount of 85 to 94 mole percent calculated as SnO ₂ . with at least one of antimony oxides such as metallic antimony (Sb), antimony trioxide (Sb ₂ O ₃ ) and antimony pentoxide (Sb ₂ O ₅ ) in an amount of 6 to 15 mole percent calculated as Sb ₂ O ₅ . mixed. The resulting mixture is calcined in air or in an oxidizing atmosphere at a temperature of HMK) to 1300 ° C. (this step will hereinafter be referred to as the calcining process). It is then pulverized. 25 to 45% by weight of the powder obtained is 55 to 75 percent by weight of a conventional ceramic glaze mixture for insulators. The latter consists of the commonly used glaze materials. Such as feldspar, dolomite, talc, calcite, kaolin, clay and quartz sand. The mixture obtained is at temperatures of 1200 to 1400 C in air or in an oxide (This stage will hereinafter be referred to as the deep-fried material.) Not less than 70 percent by weight of this fried material and not more than 30 percent by weight of at least one of clay, kaolin, bentonite or conventional glaze mixture pulverized and using a T drum mixed into a semiconducting glaze mass. This mass is suitable for application to an insulator body with a large wall thickness, which must be fired in a reducing atmosphere. If this mass is applied to the surface of a manufactured insulating body by a conventional method, for example a spray or immersion

process, is applied and the glazed insulator body in a for firing porcelain bodies The usual reducing atmosphere is fired, then a semiconducting glaze coating with a Surface resistance from 1 to 100 ΜΩ / unit area and a gray or white color is formed on the surface of the insulator body.

During the calcination process, the antimony component is doped into the tin component, to develop electrical conductivity. If the calcination temperature is in air or in a oxidizing atmosphere is lower than 1000 C, then the antimony component can be converted into the tin component not be completely doped into it, and if the glaze, which this calcined material contains, is applied to a previously manufactured insulator body, then the properties of the semiconducting glaze coating is unstable. If the calcination temperature is higher than 1300 ° C, then the antimony component rapidly volatilizes, and a desired tin component cannot be used which is doped with the antimony component. so that when applying the glaze which this calcined material contains, on an insulator body, the surface resistance of the semiconducting Glaze coating is more than 100 M U / unit area. It is therefore necessary that the calcination process is carried out at a temperature of 1000 to 13OCKFC in an oxidizing atmosphere. Furthermore, when the calcination process is carried out in a reducing atmosphere, for example in the presence is made of gaseous carbon monoxide or of gaseous hydrogen, then will at temperatures of more than about 1000 C the tin component to metallic tin, which volatilized, reduced, so that neither with the Antimony component doped tin component can be obtained. Conversely, at temperatures below 1000 "C the antimony component is not completely doped into the tin component so that the desired glaze growth cannot be obtained even in this case. Hence the calcination process should be carried out in an oxidizing atmosphere.

If a semiconducting glaze mixture is made from less than 70 percent by weight of the fried material and no more than 30 percent by weight of at least one of clay, kaolin, bentonite or a conventional ceramic glaze mixture, then the viscosity of the resulting semiconducting glaze mixture can be more easily controlled. Furthermore, the workability of the glaze mixture is compared to one made from the fried material aHein. improved. Finally, the semiconducting glaze coating has an excellent surface condition. ie. there are only very few needle sticks. These phenomena become more significant when the amount of the above clay, kaolin. Bentonite or the conventional ceramic glaze mixture increases. However, if this amount is more than 30% by weight, the surface resistance of the resulting semiconducting glaze coating increases rapidly and exceeds 100 MU / unit area. Although the semiconducting glaze compound made from the fried material alone has a somewhat reduced workability, it can still be used. Accordingly, the amount of the materials clay, kaolin, bentonite or the other conventional ceramic glass mixture is preferably not more than 30 percent by weight.
The invention is illustrated in the examples.

example 1

SnO ₂ and Sb ₂ O ₅ were mixed in the ratio shown in Table 1. The resulting mixture was calcined in air in an electric furnace at 1200 ° C. for 2 hours. The calcined material was pulverized to a particle size of 0.044 mm. 30% by weight of the powder obtained and 70% by weight of a conventional ceramic

The glaze mixture was mixed together and melted in air at 1300 C to prepare a fried material. 97% by weight of the obtained refined material and 3% by weight of kaolin were mixed and pulverized by means of a drum to a particle size of 0.044 mm, whereby a semiconductive glaze was obtained. The mass was applied to a previously prepared insulator body, and the glazed insulator body was fired in a reducing atmosphere at a firing temperature of 1260 ° C. and a maximum carbon monoxide gas concentration of 6.1%. Thus, there was obtained an insulator fired body exhibiting a surface condition and surface resistance as shown in FIG. 2 is shown.

From Fig. 2, it can be seen that if the Sb ₂ O ₅ content is less than 6 mole percent, bubbles are formed on the surface of the semiconducting glaze coating. If the proportion is more than 15 mol%, the surface resistance of the semiconducting glaze coating is higher than 100 MU / unit area, and the aimed properties cannot be obtained.

It has therefore been found to be preferable.

the tin component in amounts of 85 to 94 mol percent, calculated as SnO _2, and the antimony component in amounts of 6 to 15 mol percent, calculated as Sb ₂ O ₅ . Especially in the case of the tin component from 88 to 92 mole percent (as SnO ₂ )

and the antimony component of 8 to 12 mol% (as Sb ₂ O ₅ ), the surface of the obtained semiconductive glaze coating is good. and a stable surface resistance is obtained.

see table 1

SnO ₂ Sb ₂ O ₅

Mole percent

99T97J95 T93
1 I 3 I 5 I 7

Example 2

A mixture of 92 mole percent SnO ₂ and 8 mole percent Sb ₂ O ₅ was calcined in air in an electric furnace at 1100 ^° C. for 2 hours. The calcined material was pulverized to a particle size of less than 0.044 mm. 35 weight percent de

The powder obtained was 65% by weight of a conventional ceramic glaze mixture mixed. The resulting mixture was subjected to the next deep-frying processes.

In one of these processes, the mixtures were fired in air in an electric furnace at 1000, 1100, 1200, 1300, 1400 or 1500 ^° C. for 2 hours. In another of these processes, the mixtures were fired for 2 hours in a reduced atmosphere with a concentration of gaseous carbon monoxide of 3% at 1100, 1200, 1300 and 1400 ° C, respectively.

Each of 95% by weight of the obtained fried materials and 5% by weight of a conventional glaze mixture were mixed and pulverized by means of a drum, whereby ten semiconducting glazes were obtained. The individual glazes were applied to a previously prepared insulator body, and the glazed insulator was ^{subjected to a conventional firing process in a reduced atmosphere at a firing temperature of 1280 °} C. and a maximum carbon monoxide concentration of 6.4%, whereby a fired insulator body was obtained. The surface resistances of the fired insulator bodies are shown in FIG. 3 shown.

From Fig. 3 it can be seen that if the firing temperature in the deep-frying process in an air atmosphere is less than 1200 ^° C. or more than 1400 ^° C., then the surface resistance is more than 100 M12 units of area. Accordingly, such temperature ranges are not preferable. It was further found that. if the frying process is fired in a reducing atmosphere, the surface resistance is always more than 1000 MU area unit. Accordingly, firing in a reducing atmosphere is not preferable.

Example 3.

A mixture of 90 mole percent SNQ ₂ and 10 mole percent Sb ₂ O ₅ was calcined for 2 hours in air in an electric furnace at 1200 ⁰ C. The resulting calcined material was pulverized to a particle size of less than 0.044 mm. The powder obtained was mixed with a conventional ceramic glaze mixture in the weight ratio shown in Table 2. The mixtures obtained were subjected to Frittierungsverfahren, the mixtures were melted for 2 hours in air in an electric furnace at 1400 'C ^1. In this way, fried materials were obtained. Each fried material was pulverized to a particle size of less than 0.044 mm using a drum, thereby obtaining a semiconducting glaze.

The individual semiconducting glaze masses were applied to a previously produced insulating body. The glazed insulator bodies were in a reduced atmosphere at a firing temperature of 1280'C and a maximum carbon monoxide concentration of 6.4% a conventional burning subjected, whereby fired insulator bodies were resounded. In Fig. 4 are the surface resistances the fired insulator body shown. From Fig. 4 it can be seen that the surface resistances are higher than 100 m above sea level, area unit, if not the electrically conductive oxide and the conventional ceramic glaze mixture in quantities from 25 to 45 percent by weight or from 55 to 75 percent by weight is used. A semiconducting one Glaze mixing outside of these ranges is therefore not preferable.

Electrically conductive oxide

Conventional
ceramic
Glaze mixture ....

15th 20th Table 2 25th 30th 35 40 45 50 85 80 75 70 65 60 55 50 10 Weight percent 90

45

Example 4

A mixture of 90 mole percent SnO ₂ and 10 mole percent Sb ₂ O was calcined in air in an electric furnace at 1200 C for 2 hours. The calcined material was pulverized to a particle size of less than 0.044 mm. 35 percent by weight of the powder obtained was mixed with 65 percent by weight of a conventional ceramic glaze with a molar composition of 0.40 KNaO. 0.30 CaO, 0.30 MgD. 0.75 Al ₂ O ₃ and 6.00 SiO ₂ mixed. The resulting mixture was fired in air in an electric furnace at 1250 "C for 2 hours, thereby obtaining a fried material. This was then pulverized to a particle size of less than 0.044 mm. 90% by weight of the powdered fried material and 10% by weight of the above ceramic Glaze mixtures were mixed with one another using a drum and with the addition of WasseT, the amount of water added being such that the water content was 42 percent by weight. In this way, a semiconducting glaze mass was produced. 5-K V post-insulator body, as shown in Fig. F, applied. The maximum core diameter after firing was 80 mm. The thickness of the glaze layer was 0.30 to 0.33 mm. The other part 2 of the insulator body was Glazed with a conventional, slightly gray, non-conductive glaze. Then the outer periphery was 3 the lower end sandblasted. The be in the above way

to acted insulator body was in a conventional reducing atmosphere at a firing temperature of 1260 C and a maximum carbon monoxide concentration of 6.6% burned.

The surface resistance of the semiconducting GIa surcoat after firing was within one Range from 11.0 to 14.8 M12 / area unit. Tue ( Surface had a good appearance and a light gray color.

A metallic fitting was then cemented onto the outer circumference 3. It became the corona initial voltage test accomplished. The voltage observed was about 45 KV.

Example 5

Semiconducting glass masses according to Table 3 were produced. These crowds were on the entire surface of the suspension insulator body door high-voltage lines with a diameter of mm applied. The thickness of the glaze layer was 0.27 to 0.32 mm. The glazed insulator body were in a conventional reduced atmosphere at a firing temperature of 1290 ° C and burned with a maximum carbon monoxide concentration of 5.8%. After the firing was finished cemented the cap and needle onto the fired insulator body. It became the surface

resistance, the surface condition and the resistance to voltage in the contaminated state are determined. The results obtained are also shown in Table 3. The test was carried out as follows: The sample was contaminated to a level of contamination. in terms of a salt deposition density of 0.21 mg / cm ² , whereupon an artificial mist was formed and the maximum stress that the pattern withstood without occurrence of skip or failure due to thermal instability was determined.

As can be seen from Table 3, the suspension insulator fired according to the invention has a 30% higher voltage resistance per unit than a traditional hanging insulator that comes with a semiconducting glaze is coated. the EiseinIlI) oxide and which is burned in a reducing atmosphere.

Table 3

Manufacturing conditions of the semiconducting glaze

Combination of electrically conductive oxides

SnO ₂

H ₂ SnO,

Sb ... "

Sb ₂ O ₅

Sb ₂ O,

Mixing ratio of electrically conductive oxides (mol percent, calculated value)

SnO ₂

Sb ₂ O ₅

Calcination conditions (at air temperature (C) in an electric furnace) ..

Time (hours)

Particle size of powdered calcined material (mm)

Ceramic glaze mixture for the production of the fried material (molar Composition)

KNaO

CaO

MgO

AI ₂ O ₃

SiO ₂

Mixing ratio of the calcined material to the ceramic glaze mixture in the manufacture of the fried material (Weight percent)

calcined material

ceramic glaze mixture

88 12

1150

OJO 0.50 0.20 0.60 5.00

35 65

According to the invention (d) (b) (C) ♦ + 88 88 88 12th 12th 12th 1150 1150 1150 2 2 2 0.044 0.044 0.044 0.35 0.30 0.35 0.45 0.50 0.45 OJO 0.20 0.20 0.65 0.60 0.65 5.0!) 5.00 5.00 35 35 35 65 65 65

Conventional method

Iron (III) oxide, titanium dioxide and chromium oxide

Fe ₂ O ₃ : 60 / TiO ₂ : 25 /
Cr ₂ O _3: 15

not calcined

The symbol 4 indicates the oxide used.

continuation

Manufacturing conditions of the semiconducting glaze

Firing conditions in the deep-frying process (in air in an electric oven)

Temperature ( ⁰ C)

Time (hours)

Particle size of powdered material (mm)

Offset for the production of the semiconducting glaze mass (percent by weight)

fried material

kaolin

volume

Bentonite

Properties of the suspension insulators

Surface resistance (M Ü / area unit)

Surface condition color

Status

Withstand voltage in the contaminated state per unit (KV)

(I have to do with the connection

1350

100 0 0 0

5-

Gray

Well

16.5 Flashover at 17.0KV

(b) (C) 1350 1350 2 0.044 0.044 80 SO 0 20th 20th 0 0 0 32 42 26 40 easy easy Gray Gray Well Well 16.0 16.0 Over Over shi ow blow at at 16.5 KV 16.5 KV

(d)

1350

0.044

95
0
0

Conventional method

15 26

Gray
Well

16.5
Over aa
at
17.0KV

electrically conductive oxide: 25%, ceramic glaze mixture:

KNaO 0.30

CaO 0.20

MgO 0.50 75%

AUO ₃ 0.65

SiO ₇ ! 5.00i

18 39

black
Well

12.0

Failure due to reason
thermal instability
at 12.5 KV

The raw materials clay, kaolinite and bentonite used in the experiments in Table 3 had the chemical compositions given in Table 4 below.

The ceramic glaze with a molar composition of 0.2 to 0.5 KNaO. 0.2 to 0.6 CaO. less than 0.3 MgO, 0.5 to 0.9 Al ₂ O ₃ and 4.0 to 9.0 SiO ₂ are preferably used in the invention.

Table 4

Chemical compositions (percent by weight) of the raw materials used in Example 5

Loss on ignition.

SiO ₂

Al ₂ O.,

Fe ₂ O ₃

CaO

MgO

K ₂ O

Well, O

total

volume Kaolinite 14.16 11.20 48.76 50.56 31.50 33.80 1.42 0.50 0.29 0.04 0.16 0.08 0.70 2.70 track 0.90 99.97 99.88

Bcnlojiil

6.06

69.85

12.86

1.83

4.48

0.58

2.01

1.06

98.71

In the above example 4 it was described that the semiconducting glaze mixture according to the invention is applied to the upper part of the post-insulator body and that a conventional non-conductive glaze mixture is applied to the other part 2 of this insulator body, but the semiconducting glaze mixture can also be applied according to the invention the entire surface of the post line insulator bodies and the suspension insulators are applied. The composition according to the invention can also be applied additionally to a conventional non-conductive glaze layer.

With the invention, the disadvantages of the known isolators and the like can be completely eliminated.

According to the invention, it is possible to manufacture high-performance suspension insulators with an excellent semiconducting glaze coating on a large scale of the obtained isolators improved. Hence can the overhead lines can also be used for heavier pollution. After all, they own insulators obtained a nice gray or white appearance

In addition 5 sheets of drawings

Claims (3)

Patent claims: * 1. Process for the production of electrical porcelain insulators coated with a semiconducting glaze based on Sn / Sb, characterized in that a mixture of 85 to 94 mol percent, calculated as SnO ₂ , of at least one tin component from the SnO _{2 group} and H ₂ SnO ₃ and 6 to 15 mol percent, calculated as Sb ₂ O ₅ , at least one antimony component from the group Sb, Sb ₂ O ₃ and Sb ₂ O ₅ at a temperature of 1000 to 1300 ⁰ C in an oxidizing atmosphere calcined, the calcined mixture pulverisiei t, 25 the resultant mixture is mixed to 45 percent by weight of the pulverized mixture with 55 to 75 weight percent of a conventional ceramic Glasurmisdiung, at a temperature of 1200 to 1400 ° C in an oxidizing atmosphere to melt the ER zo preserved Melt pulverized, not less than 70 percent by weight of the fried material obtained with not more than 30 percent by weight of at least one material from the group of clay, K aolin, bentonite and conventional ceramic 2s glaze mixtures are mixed, the mixture obtained is applied to an insulator body and this is fired in a conventional reducing atmosphere. 2. The method according to claim 1, characterized in that a mixture of 88 to 92 mol percent, calculated as SnO ₂ , at least one tin component from the group SnO ₂ and H ₂ SnO ₁ and 8 to 12 mol percent, calculated as Sb ₂ O ₅ . at least one antimony component from the group consisting of Sb. Sb ₂ O ₃ and Sb ₂ O _{5 is} calcined. 3. The method according to claim 1 or 2, characterized in that a mixture of SnO ₂ and Sb ₂ O _{5 is} calcined. 40