DE2004234C - Hardenable, hydrolytically improved glass for the manufacture of electrical insulating components - Google Patents

Description

The invention relates to glass compositions which are intended for the production of electrical insulating components, for example hardened glass insulators.

Glasses for electrical insulation purposes generally contain lead oxide. Because of this PbO content, such insulating glasses are relatively heavy, expensive and unsuitable for hardening (generating a compressive prestress in the surface). In addition, the use of lead glass for direct voltage insulators, for example, is avoided because at high field strengths and temperatures it can very easily lead to lead precipitation ("lead trees"), which destroys the insulating body.

For high-voltage insulators, e.g. cap insulators made of glass, alkali-lime-silicate glasses are often used, in which the ratio of the alkalis Na and K to one another is chosen so that a minimum of the loss factor is achieved. For these glasses it is generally in the range of 30 times 10 [high] -3 at 50 Hz; the dielectric constant is around 7, the T [deep] k [deep] 100 value (small Rho = 10 [high] 8 large omega times cm) at 200 to 250 ° C.

The loss factor of the known insulating glass is, however, still undesirably high for many purposes, and the T [low] k [low] 100 value is too low. Overall, glasses with a higher insulating capacity are required today.

Another disadvantage of the known insulating glasses is their relatively low chemical, in particular hydrolytic, resistance. The glasses known for this are in the 4th hydrolytic class.

The hardening of such glasses has become of particular importance for the development of modern glass insulators; by generating a compressive prestress in the glass surface, the mechanical strength of the insulators can be considerably improved. Many of the known insulating glasses have a coefficient of thermal expansion that is too low and a modulus of elasticity that is too low to be optimally hardened.

The aim of the present invention are new glass compositions for the production of glass insulators which do not have the disadvantages of the glass compositions previously used for this purpose and in particular have the following properties:

1. High coefficient of thermal expansion and high modulus of elasticity, so that the glasses can be hardened optimally;

2. high transformation temperatures (Tg values); this property is also an important prerequisite for hardening, because this is the only way to maintain the high superficial compressive stresses during operation;

3. improved electrical insulation properties;

4. good chemical resistance; the new glasses should fall into a better class than hydrolytic class 4 (mostly outdoor use);

5. high devitrification resistance (important and necessary for automatic production).

In addition, the glasses should have such a favorable toughness behavior that they can be melted, refined and processed fully automatically at relatively low temperatures.

It has now been found that these conditions can be fully met by glasses with the following composition range in percent by weight:

SiO [deep] 2 57.4 to 66.5

B [deep] 2O [deep] 3 2.5 to 10.7

Al [deep] 2O [deep] 3 5.0 to 7.6

Na [deep] 2O 3.5-5.0

K [low] 2O 13.0 to 16.7

BaO 2.0 to 5.0

CaO 2.0 to 4.0

MgO 0.0 to 2.0

It has been shown that the glasses have a high coefficient of thermal expansion> 88 times 10 [high] -7 / ° C and an electrical insulation capacity T [low] k [low] 100> 300 ° C.

The table contains five exemplary embodiments in percent by weight from the aforementioned composition range, together with the property values.

All glasses according to the invention can be refined either with a maximum of 0.10 percent by weight As [deep] 2O [deep] 3 or with a maximum of 0.15 percent by weight Na [deep] 2O as sulfate, with the simultaneous introduction of 0.70 percent by weight Na [deep] ] 2O or 0.70 percent by weight K [deep] 2O as nitrate.

The glasses according to the invention can be melted between 1440 and 1470 ° C; the refining temperature is 1480 ° C. The processing temperatures when using an automatic press are between 1100 and 1200 ° C and the cooling temperatures for the manufactured articles between 560 and 580 ° C. The cooling time depends on the wall thickness of the article. In general, ½ to 2 hours is sufficient.

Embodiment 1

Required raw material quantities for 100 kg calculated glass: 49.00 kg sand, 3.80 kg rasorite, 26.20 kg potassium feldspar, 0.34 kg sodium sulfate, 1.90 kg sodium nitrate, 4.94 kg soda, 15.00 kg potash, 5.40 kg of lime, 6.50 kg of barium carbonate.

Embodiment 4

Required raw material quantities for 100 kg calculated glass: 43.00 kg sand, 11.00 kg rasorite, 26.20 kg potassium feldspar, 0.34 kg sodium sulfate, 0.80 kg soda, 1.50 kg potassium nitrate, 18.96 kg potash, 7.20 kg lime, 3.90 kg barium carbonate.

Claims (4)

1. Hardenable, hydrolytically improved glass for the production of electrical insulating components, characterized by the following composition range in percent by weight: SiO [deep] 2 57.4 to 66.5 B [deep] 2O [deep] 3 2.5 to 10.7 Al [deep] 2O [deep] 3 5.0 to 7.6 Na [deep] 2O 3.5-5.0 K [low] 2O 13.0 to 16.7 BaO 2.0 to 5.0 CaO 2.0 to 4.0 MgO 0.0 to 2.0 2. Glass according to claim 1, characterized by the following composition in percent by weight: 66.5 SiO [deep] 2 2.5 B [deep] 2O [deep] 3 5.0 Al [deep] 2O [deep] 3 5.0 Na [deep] 2O 13.0 K [deep] 2O 5.0 BaO 3.0 CaO 3. Glass according to claim 1, characterized by the following composition in percent by weight 60.0 SiO [deep] 2 5.6 B [deep] 2O [deep] 3 7.0 Al [deep] 2O [deep] 3 3.7 Na [deep] 2O 16.7 K [deep] 2O 2.0 BaO 3.0 CaO 2.0 MgO 4. Glass according to claim 1, characterized by the following composition in percent by weight: 57.4 SiO [deep] 2 10.7 B [deep] 2O [deep] 3 5.0 Al [deep] 2O [deep] 3 3.5 Na [deep] 2O 16.4 K [deep] 2O 5.0 BaO 2.0 CaO