DE1596943C3 - Process for producing an alumina-silicate glass with a relatively high alumina content and a glass object made from this glass - Google Patents

Description

SiO ₂ 51-63

Al ₂ O ₃ 15-22

CaO + MgO expressed as

equivalent amount of CaO 10-22

total alkali metal oxide expressed as an equivalent amount
Na ₂ O 7-14

and the decadic logarithm of the poise viscosity of the glass at the liquidus temperature (Equilibrium temperature between molten glass and its primary crystals) is at least 3.4.

2. The method according to claim 1, characterized in that a mixture is used whose alkali-aluminum-silicate mineral 55 to 90Gew.-% and its oxide and / or carbonate and / or aluminum silicate of calcium and / or magnesium 45 to 10 % By weight of the total weight of the batch ingredients, minus the weight of CO _{2 of} the possible carbonate content of the calcium and / or magnesium.

3. The method according to claim 1, characterized in that a mixture is used whose alkali aluminum silicate mineral 75 to 90 wt .-% and its oxide and / or carbonate and / or aluminum silicate of calcium and / or magnesium 25 to 10 wt. -% of the total weight of the batch ingredients, minus the weight of CO _{2 of} the possible carbonate content of the calcium and / or magnesium.

4. The method according to claim 1, characterized in that a mixture is used whose alkali aluminum silicate mineral 80 to 90 wt .-% and its oxide and / or carbonate and / or aluminum silicate of calcium and / or magnesium 20 to 10 wt. -% of the total weight of the batch ingredients, minus the weight of CO _{2 of} the possible carbonate content of the calcium and / or magnesium.

5. The method according to any one of claims 1 to 4, characterized in that the alkali-aluminum-silicate mineral selected from feldspar, nepheline syenite, aplite and their mixtures will.

6. The method according to any one of claims 1 to 5, characterized in that the oxide and / or Calcium and / or magnesium carbonate from high calcium limestone, dolomite limestone and their mixtures is selected.

7. The method according to any one of claims 1 to 6,

characterized in that a glass of the following composition is produced in% by weight:

SiO ₂ 54-63

Al ₂ O ₃ 17-22

CaO + MgO expressed as

equivalent amount of CaO 10-22

Na ₂ O + K ₂ O expressed as

equivalent amount of Na ₂ O 8-13,

where the decadic logarithm of the viscosity of the glass given in poise at the liquidus temperature is at least 4.

8. Glass article, characterized in that ^: at least its inner part consists of the glass composition according to claim 1 or claim 7.,

9. Glass object according to claim 8, characterized in that its surface layer is through Exchange of alkali ions is placed under compressive stress.

10. Glass article according to claim 9, characterized in that the alkali ions and sodium Are potassium.

The present invention relates to a method for producing an alumina-silicate glass with a relatively high alumina content with the aim of obtaining a melt which can be cooled quickly and is therefore suitable for machine processing, as well as a glass object made from this glass. Normally, traditional soda-lime-silicate glasses already _{contain a small amount of alumina (aluminum oxide Al 2} O ₃ ), as some of the materials in the batch used to manufacture these glasses contain a small amount of aluminum oxide. _{In general, however, the Al 2} O ₃ content of commercially available soda-lime glasses rarely exceeds 10% by weight. Only glasses with an Al ₂ O ₃ content of around 20% by weight are referred to as alumina-silicate glasses. However, these glasses are more difficult to melt and work with than conventional soda-lime glasses. Glasses with an Al ₂ O ₃ content of around 20% by weight are therefore preferably used as special glasses.

Feldspars, representatives of feldspar or feldspar-rich rocks such as nepheline syenite, aplite etc. are generally used as the starting material for the incorporation of Al ₂ O ₃ in alumina-silicate glasses. For example, nepheline syenite has been used as a batch component in the manufacture of container glass. This is described in US Pat. No. 25,496, according to which this component is quite insignificant compared to the total batch, so that the aluminum oxide content of the glasses is substantially less than 3% by weight.

Some of the alumina content comes from the alumina contamination of that used in the batch Sand.

The TJS-PS 25 81 638 concerns the production of pane glass. Aplit is also included in the batch.

However, the batch contains large amounts of sand and Na ₂ O ash, and the total weight of the limestone and dolomite exceeds that of the aplite. As a result, the aluminum oxide content of the finished glass is only 3.04%.

The glasses described in the publications mentioned are therefore not alumina-silicate glasses.
In French patent 13 29 124 or

3 4

the South African patent 62/2353 is described in US-PS 33 80 818. According to the invention can

given that sodium aluminum silicate glasses contain little - the mixture: alkali feldspar, such as soda

must contain at least 5% by weight of aluminum oxide, feldspar, potassium feldspar and their mixtures, sodium

after undergoing treatment to exchange tron-orthoclase and -anorthoclase, nephelinsyehit,

Sodium ions in the surface layer against 5 nepheline, aplite and lithium spar, such as spodumene and

Potassium ions have been subjected to a petalite.

Improved strength against bending and breaking stress. The advantages obtained by the method according to the invention for the stressing, the advantages achieved essentially even after glass manufacture are essentially based on considerable abrasion of the glass surface, on the one hand on the possible direct behavior. This sodium-aluminum-silicate twist of widespread minerals or glass consists of at least 5% by weight Na ₂ O, stones as batch components and, on the other hand, at least 5 % by weight Al ₂ O ₃ , with SiO ₂ as the remainder, as well the extremely comparable glass-forming constituents achieved through the special selection of the claimed up to about 15% by weight of other areas of the composition, depending on the circumstances. It is furthermore the short cooling times of the glasses which make them suitable for the 'that glasses in which either the production of glassware using auto-' the content of Na ₂ O or Al ₂ O _{3 is} greater than approximately matic machines .
25% by weight, for ordinary too little. Should the glass be ion-exchanged, have chemical resistance and / or become too difficult to melt one alkali ion by another alkali to be of practical interest or smaller ions. In addition, however, these gauges have to be exchanged, so the initial MoI publication should not provide any information as to whether the content of the alkali ion to be exchanged in the glass of these glasses for the manufacture of glassware is significantly less, e.g. less than 75% Mole use of automatically operating machines to be the content of the alkali ion that is to be replaced, and whether they are suitable. The small amounts required for this if the glass and the goods made from it have cooling times. 25 later not be subjected to an ion exchange,

Commonly known soda-lime-silicate batches the glass is said to contain sodium, although too

for the manufacture of glass containers start at about potassium can be contained, so the weight

80O ⁰ C to melt. Long after the start of melting, the sodium / potassium ratio is less than 1: 1 and is

and even after the batch is the desired preferably at 0.75: 1.

Has reached the maximum temperature which is necessary for complete 30 The mixture of the for the fusion according to the invention and reacting to form molten drive used batch can be lesser amounts Glass is required, there is a considerable gas - other, also coloring metal oxides have. the development takes place, whereby a relatively long refining total amount of these other materials in the Process and thus relatively long cooling times. Batch mixing is a maximum of 5% by weight. in the are required. 35 with regard to the fact that in the inventive

It is the object of the present invention to provide a batch-using alkaline aluminum process for the production of an alumina-silicate glass nium-silicate-minerals and all alkaline-earth-aluminum create, with the glassware using silicate minerals commonly known iron oxide impurities Automatically working machines included, so that the glass produced is colored and glasses can be created, 40 is and therefore not suitable as flint glass, that is the much shorter cooling times than known methods according to the invention more for production Soda-lime-silicate glasses have and are therefore suitable for colored glasses and glass objects machine processing are suitable. suitable.

According to the invention, this object is achieved by a supplement to the prior art, the method mentioned at the beginning, which thereby refers 45 GB-PS 7 14 004, in which a glass is characterized for the fact that glass is described from a mixture of glass fibers, the 40 is melted, in which an alkali-aluminum up to 60% SiO ₂ , 4 to 18% Al ₂ O ₃ , 15 to 22% CaO, silicate mineral and at least one oxide and / or 4 to 12% MgO, 10 to 15 % Na ₂ O, up to 6% B ₂ O ₃ carbonate and / or aluminum silicate of calcium and 0.5 to 6% TiO ₂ and in which the total and / or magnesium contains such an amount of SiO ₂ and Al ₂ O ₃ in the range from 50 to 65% so that the glass has the following composition and the total content of CaO and MgO in the range in% by weight: from 20 to 30%. The special selection of here

51 b "63 areas claimed and the areas that can be achieved thereby

Q .. -,. 22 important advantages in terms of lower cooling

VO "'expresses" ak " ^{55 times and the} use of widespread mines

S CaO. 10 to 22 ^ralies . ^{are not in this} publication

7 to 14 "STSUß the verb according to the invention

. Glaziers with useful processing properties and the decadic logarithm of the 60 poise is to be observed as an additional rule, given viscosity of the glass at the liquidus temperature, that is the decadic logarithm of the in poise (Equilibrium temperature between the molten viscosity of the glass in the case of the liquidus temptation Glass and its primary crystals) min- erature, which is known to be the equilibrium temperature test 3.4 is. rature between molten glass and its pri-For all glass according to the invention is therefore the 65 mary crystals, at least 3.4. Through this Viscosity at the liquidus temperature considerably results in glasses with excellent processing properties than most other glasses. Glass properties on automatic machines. Already with similar viscosity behavior are z. B. in US-PS 33 80 818 it is pointed out

that glasses with low viscosity values are not suitable for further processing at the liquidus temperature suitable on automatic machines.

The glasses produced by the process according to the invention have cooling times which are considerably below the cooling times of the known soda-lime-silicate glasses, because they have an average cooling time of 96 seconds. The term "cooling time" is used as a measure of the processing properties of the glass compared to other glasses. The “cooling time” is the period in which the viscosity of the glass increases from 10 ³ to 10 ⁴ poise, ie the glass moves from a processable plastic state to a dimensionally stable state in which it no longer sags.

Further preferred embodiments of the invention can be found in the attached subclaims will.

The invention also relates to a glass object which is characterized in that at least its inner part consists of the composition recited in claim 1 or claim 7. Preferably is the surface layer of the glass object by exchanging alkali ions underneath Compressive stress set. The alkali ions sodium and potassium are used in particular.

During the past 25 years glasses with ever shorter cooling times have been developed, with cooling times reduced from about 108 to 96 seconds while speeds of automatic machines have increased accordingly. With the method according to the invention Manufactured glasses thus represent a continuation of this development, so that now the There is a desire to develop new machines with even higher speeds. Two of the novel Glass compositions have already been used for the manufacture of bottles, and it was possible to from one of these glass compositions on a single machine 500 glass containers at one temperature to shape, which was 66 ° lower than the temperature for well-known soda-lime-silicate glass. In the work done for experimental purposes, 500 containers were made in the following manner.

A glass was made from a glass melting tank provided with a known zirconium lining one batch with the following components melted:

Feldspar (1) 603.0 kg

Raw dolomite limestone (2) 236.0 kg

Arsenic trioxide (3) 1.81 kg

Saltpetre (4) ....... 1.81 kg

Sodium antimonate (5) 1.11 kg

(1) The feldspar had the following analysis in% by weight:

(2) The raw dolomite limestone resulted in the following analysis in% by weight:

SiO ₂ .
Al ₂ O ₃
CaO.
MgO

68

18.9
1.6
0.1

Na ₂ O 6.7

K ₂ O 4.7

Iron, expressed as Fe ₂ O ₃ 0.07

P ₂ O ₅ 0.0004

Chromium expressed as Cr ₂ O ₃ 0.0004.

SiO ₂

Al ₂ O ₃

Fe ₂ O ₃

P ₂ O ₅

SO ₃

CaO

MgO

Remainder of CO _{2 from} the carbonate.

0.5

0.1

0.072

0.023

0.04

30.4

21.5

(3) and (5) were used as refining agents and (4) as oxidizing agents.

The molten glass had a liquidus temperature of 1230 ° C, and the temperature at a viscosity of 10 poise was * 1127 ⁰ C. The glass analysis gave the following values in wt .-%:

SiO ₂ 56.4

AUO ₃ 15.6

CaO 11.6

MgO 6.9

Na ₂ O 5.5

K ₂ O 3.7

As, O ₃ 0.25

Sb ₂ O ₃ 0.23

Fe ₂ O ₃ 0.09.

To make this glass, the oven was preheated to 732 ° C, then the main burn nozzles ignited. The batch was charged at a rate of 90.7 kg / h, so that after about 3 hours the Bath height was 15.24 cm. Refilling of the mixture was then omitted until it was filled The batch was completely melted. Only then did it mix again at a rate of about 68 kg / h filled. The molten glass was taken out at a rate of 31.8 kg / h.

Finally, the desired glass height of about 28 cm was reached in the molten bath. Then the feed station was switched to automatic control. By measuring radiation, it was found that the glass in the molten bath had a temperature of 1496 ° C. The glass temperature in the working tank was 1260 ° C and in the tank of the loading station 1204 ° C, while the glass gob flowing out of the opening was at a temperature of 1199 ° C. Devitrification took place when the glass current reached by cooling in 1188 ^0C. The take-off speed was reduced to 22.7 kg / h, as a result of which the glass flowing out set itself to a temperature of 1210 ° C. When the blanks were formed, however, the glass hardened too quickly, so that the blanks could not be reshaped.

Both temperature values were instead of the expected liquidus temperature of 1230 ° C and the temperature at a viscosity of 10 ⁴ poise of 1127 ° C 126o ⁰ C and 1 107 ⁰ C. It was assumed that these errors could be eliminated by a stronger heating of the blank molds, but Finally, the glass composition was better changed. To do this, the vat was emptied until only 15.24 cm of molten glass remained in the vat.

A new batch of the following ingredients was added to the vat at a rate of approximately 136 kg / h given while. Glass was peeled off at 40.8 kg / h until the desired glass height was reached.

Components

Weight
(kg)

Feldspar (1)

Raw dolomite limestone (2)

Arsenic Trioxide (3)

Saltpeter (4)

Sodium Antimonate (5)

high calcite limestone (6)

603.0
118.0
1.81
1.81
1.81
111.0

(6) This limestone had the following composition in% by weight:

CaO 55.3

MgO 0.4

SiO ₂ 0.4

Al ₂ O ₃ 0.04

Fe ₂ O ₃ 0.046

SO ₃ 0.03

P ₂ O ₅ 0.008

Cr ₂ O ₃ ■ 0.004

Remainder CO ₂ .

The composition of the glass melted from these materials in% by weight is as follows:

SiO ₂ 56.3

Al ₂ O ₃ x 15.6

CaO 14.8

Na ₂ O 5.5

K ₂ O 3.7

MgO 3.5

As ₂ O ₃ 0.25

Sb ₂ O ₃ 0.023

Fe ₂ O ₃ 0.08.

First the take-off speed was reduced to 34 kg / h and then the temperatures in the feed tub and in the working tub were reduced, while finally the take-off speed was set to about 11.3 kg / h in order to improve the refining of the glass. After a pretty good purification had taken place, the production of the 500 model container at a purification temperature of 1260 ° G, a sump temperature of 1221 ⁰ C and a glass stream temperature of 1193 ° C was started. 4 bottles were produced per minute and remained satisfactory as long as the blank molds were heated. However, the peeled glass did not have the composition of the modified composition mentioned above. Rather, it was between this and the first composition. The liquidus temperature of the peeled glass was 1235 ° C, which is sufficient to form a gob without devitrification.

The following table shows the chemical resistance of the glass, with the specific Test trials, however, do not constitute an absolute economic benchmark and are therefore not definitive can be equated with the chemical resistance of glassware in use. Nevertheless, the following applies: the lower the specified numerical value for a type of glass, the greater the probability that that the glass products made from it are more resistant to the respective liquids are than a type of glass that receives a higher value in the test.

For comparison, a typical amber glass containers served with a liquidus temperature of 1038 ⁰ C and temperatures at viscosities of 10 ^2, 10 ³ and 10 ⁴ poise of 1466 ° C, 1196 ⁰ C and 763 ⁰ C. The percentage of Na ₂ O, which in the chemical

ίο tests resolved using H ₂ O and N / 50 H ₂ So _{4 were} 0.027 and 0.032, respectively.

The tests to determine chemical resistance were carried out by crushing glass, allowing the glass to pass through a No. 40 sieve and being retained by a No. 50 sieve. Exactly 10 g of crushed glass sample were placed in a 200-ml Erlenmeyer borosilicate flask previously at least 24 hours was aged at least 9O ⁰ C with the aggressive liquid. Exactly 50 ml of the aggressive liquid, either purified water or 0.02 NH ₂ SO ₄ aqueous solution, were added. After the flask with a Einlochgummistopfen which was equipped with a 30.5 cm long chemically resistant glass tubes was stoppered, it was immersed in a water bath at 9O ⁰ C (within 0.02 ⁰ C) 4.Stunden long. Then the container and its contents were cooled by overflowing water on the outside of the container. Exactly 40 ml of the aqueous extraction medium in the container was transferred to another container.

If the aggressive medium was water, the transferred solution was titrated with 0.02 NH ₂ SO ₄ to an excess of 1 ml by using two drops of a methyl red indicator which were added before the start of the titration. Then the contents of the container were boiled with stirring. This was repeated three times to remove the dissolved gases. The solution was then titrated to the end point with 0.02 N NaOH with methyl red. The percentage of Na ₂ O was determined by multiplying the difference in volume in ml of the acid and base used in the two titrations by a factor of 0.00775.

If, on the other hand, the aggressive medium was sulfuric acid, two drops of methyl red indicator solution were added to the cooled solution of the aggressive medium and the acid was then titrated to the end point with 0.02 N NaOH. _{The percentage of Na 2} O removed from the aggressive medium was calculated by multiplying the difference between the number of ml of NaOH solution _{equivalent to 50 ml of 0.02 NH 2} SO ₄ and the number of ml of the NaOH solution determined with a factor of 0.0062.

The glasses produced by the process according to the invention can be improved in their strength properties in an outstanding manner by means of suitable ion exchange treatments. In order to demonstrate these properties, the following tests were carried out: All 19 glass samples from the examples in Table I were immersed _{in molten KNO 3.} The potassium nitrate was held at 393 ° C for 20 hours. This preliminary experiment showed increased ion exchange, with the percentage RO (CaO + MgO) decreasing.

609 582/173

ίο

Table I.

(All components in% by weight)

example No. 3 4th 5 6th 7th 8th 9 10 1 2 composition
the oxides 58.29 60.96 *) 58.76 *) 58.26 61.56 51.84 55.04 *) 51.94 *) SiO ₂ 61.22 57.94 15.97 17.40 14.15 15.98 17.40 20.12 20.38 18.87 Al ₂ O ₃ 16.57 16.34 13.03 9.22 10.60 10.02 7.04 15.01 10.06 13.38 CaO 11.67 14.30 3.19 1.63 3.18 6.22 3.55 0.08 0.00 1.68 MgO 0.04 1.33 6.14 6.26 8.59 6.14 6.26 8.59 9.56 9.45 Na ₂ O 6.11 5.96 3.32 4.24 4.24 3.32 3.95 4.29 4.50 4.30 K ₂ O 4.08 4.00 0.06 0.11 0.08 0.06 0.11 0.07 0.06 0.10 Fe ₂ O ₃ 0.07 0.11 1193 1190 1149 1213 1207 1202 1171 1157 Liquid temp. ⁰ C 1230 1204 3.73 4.39 3.88 3.69 4.31 3.41 4.18 3.72 Log. d. viscosity
at the liquidus temp. 4.12 3.61 Log. d. viscosity
for ⁰ C 1538 - 1510 1568 1665 1493 1613 1490 2 1695 1545 1410 1543 1385 1435 1532 1369 1477 1366 2.5 1545 1410 1307 1424 1285 1327 1421 1268 1363 1268 3 1427 1304 1157 1243 1135 1171 1249 1121 1196 1121 4th 1249 1152 1049 1119 1027 1060 1127 1018 1074 1018 5 1119 1046 971 1024 946 977 1030 941 982 941 .6 1021 968 908 950 884 914 955 879 909 879 7th 947 908 875 911 851 880 916 846 870 846 7.65 906 877 62 61 67 63 58 66 64 64 Cooling time in sec. 62 61 77.8 72.3 **) 83.1 **) 71.2 69.6 **) 88.6 **) 85.2 **) 86.9 **) κ ■ 10 ⁴ (0-300 ° C) ² ) 73.7 76.7 **) Batch components
(Wt .-%) 85 90 85 85 90 85 90 85 Feldspar 90 85 7.5 5 3.75 - - 15th 90 85 Calcium-lime 10 11.25 7.5 5 11.25 15th 10 - 10 3.75 Dolomite lime - 3.75 Chem. Resistance
(% Na ₂ O dissolved) - 0.003 - - 0.003 - 0.006 - '· H ₂ O 0.003 -. 0.053 0.057 0.13 n / 50 H ₂ SO ₄ 0.037

Table I (continued) Example no.
11th 12th 13th 14th 15th 16 • 1665 12th 18th 19th 11th 1519 composition
the oxides 54.38 51.79 *) 54.26 *) 51.80 54.80 61.76 *) 1399 17th 62.12 *) 61.82 SiO ₂ 21.00 20.12 20.65 20.12 21.29 18.15 1221 17.53 18.15 Al ₂ O ₃ 9.58 12.01 8.00 10.51 6.12 9.72 1099 55.43 8.36 5.84 CaO 0.61 3.11 2.47 4.63 4.08 1.11 1007 15.38 1.50 3.85 MgO 9.76 8.59 9.86 8.59 9.09 8.53 938 16.04 9.73 9.44 Na ₂ O 4.53 4.29 4.53 4.29 4.55 0.59 901 4.25 0.59 0.59 K ₂ O 0.06 0.08 0.06 0.06 0.07 0.17 62 8.35 0.16 0.18 Fe ₂ O ₃ 1113 1143 1088 1180 1127 1149 70.3 0.42 1160 1204 Liquidustem. ⁰ C 4.68 3.80 4.92 3.49 4.55 4.56 0.13 4.43 4.19 Log. d. Viscosity ■
at the liquidus temp 90 1141 Log. d. viscosity
for ⁰ C 1624 1488 - 1463 1574 10 3.4 - 1684 ■ 2 1485 1363 1493 1349 1449 1530 1530 2.5 1371 1266 1377 1254 1349 1413 1404 1410 3 1199 1119 1202 1116 1193 1299 1221 1232 4th 1077 1016 1080 1016 1080 1210 1093 1104 5 985 938 988 938 993 1080 999 1013 6th 911 878 918 880 927 985 926 941 7th 871 846 880 849 890 918 886 902 7.65 68 65.5 67 64 61 866 66 62 Cooling time in sec. 86.6 **) 86 **) 85.7 **) 84.3 **) 71.4 838 73.2 70.0 _K. 10 ^ (0-30O ⁰ C) ² ) 62 Batch components
(Wt .-%) 90 85 90 85 90 46.7 90 90 Feldspar 7.5 7.5 5 3.75 - 5 - Calcium-lime 2.5 7.5 5 11.25 10 80 5 10 Dolomite lime 10 10

Chem. Resistance
(% Na ₂ O dissolved)

H ₂ O -. - 0.006 - 0.005 0.004 0.007 0.003 0.004

n / 50 H ₂ SO ₄ - ■ - 0.11 - 0.16 0.055 0.13 0.036 0.051

♦♦ SAS-AASE ^{from the Ge} ™ ^e * «*» * ·

*) Fiber devitrified.

*) λ is the average coefficient of linear thermal expansion per ° C.

On the basis of this preliminary test, 7 samples with particularly preferred glass compositions were selected for detailed study. These glasses were compositions of 90% feldspar or nepheline syenite and 10% mixed calcium dolomite lime. The ion exchange was not performed as in the preliminary test at 393 ⁰ C, but at 454 ° C and 566 ° C in molten KNO. ₃ The test times were 15 minutes and 1 hour. It was found that greater surface compressive stresses were obtained at the higher temperatures. In addition, a higher penetration depth could be determined at the higher temperatures.

In view of these results, the glass composition of example 15 selected for further experiments. The particular purpose of these experiments consisted in the relationship between the depth and magnitude of the compressive stress and the time and the

Determine temperature. The following times were used during these experiments: '/ 4 ⁿ > Va h, 1 h, 2 h and 4 h. The temperatures were 538, 566, 593, 621 and 677 ° C. These temperatures were chosen because temperatures above and below the lower relaxation temperature of the glass (621 ° C) were desirable. In contrast to the results obtained at the lower temperature intervals, the magnitude of the resulting compressive stress appeared to decrease as the exchange temperatures increased. In general, the depth of the compressive surface layer was proportional to the square root of time. "The depth also increased as the temperature increased until the glass appeared to flow and took in the larger potassium ion. The depth of the compressive surface layer in µ and the The size of the compressive stress in 1000 kg / cm ² is given in Table II:

table II μ ^{1 and} ₂ hours μ 1 hour μ 2 hours μ 4 hours μ Temp. '/,.Lesson 1.83 *) thousand 2.11 *) thousand 2.39 *) thousand 3.52 *) thousand 4.78 *) thousand 1.48 kg / cm ² 3.37 kg / cm ² 5.06 kg / cm ² 5.62 kg / cm ² 6.33 ^U C kg / cm ² 2.11 *) 0.98 2.67 *) 1.62 4.22 *) 2.60 5.62 *) 2.53 7.03 *) 538 1.83 2.11 1.55 2.53 1.34 3.52 1.83 4.22 1.90 6.05 566 1.05 1.76 1.20 2.81 1.34 2.32 5.84 2.45 7.03 1.34 2.46 1.05 2.46 1.12 4.78 1.27 6.68 1.12 9.14 593 1.27 ' 2.11 1.34 5.62 3.78 0.77 1.34 1.83 0.84 0.70 0.42 0.63 621 0.77 0.21 0.14 Nothing Nothing 677 0.21

*) Exchange in the KNOj charge bath; all others were exchanged in a eutectic mixture of 32.8% by weight NaC and 67.2% by weight K ₂ SO ₄ .

From the results of these experiments that the best exchange conditions for the glass sample 19 538-566 ° C for _^3/4 hour passed shows.

Finally, various types of glass produced according to the invention in Table I were subjected to an ion exchange with potassium nitrate at 455 and 566 ° C. for 15 minutes and 60 minutes. In addition, a glass produced from a batch of 90% by weight of feldspar and 10% by weight of MgO was subjected to ion exchange with potassium nitrate at 566 ° C. for 60 minutes. This glass had a surface layer under compressive stress of 98 μ. The 25 cm long rods drawn from the glass in the molten state had a flexural strength of 5610 kg / cm ² after the ion exchange. After abrasion with a sandblast, the rods still had a flexural strength or a modulus of rupture of 1800 kg / cm ² .

Claims (1)

Patent claims: 1. A method for producing an alumina-silicate glass with a relatively high alumina content the aim of obtaining a melt that can be cooled down quickly and therefore for a machine Processing is suitable, characterized in that the glass consists of a Mixture is melted into which an alkali-aluminum-silicate mineral and at least one Oxide and / or carbonate and / or aluminum silicate of calcium and / or magnesium in is introduced in such an amount that the glass has the following composition in percent by weight having: