DE1596922A1 - Process for the production of glass objects with increased mechanical strength - Google Patents

Description

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N.V. Philips'Gloeilampenfabrieken, Eindhoven / Holland

"Process for the manufacture of glass objects increased

mechanical strength "

The invention relates to a method for the production of glass objects of increased mechanical strength, which also retained after severe damage, and items made by this process.

In a known method of this type, one starts from a glass of the alkali aluminum silicate type within a specific composition area and exchanges the alkali ions in a surface layer of the glass for alkali ions with a larger ion radius. This exchange takes place in that the glass objects are brought into contact with a molten salt or salt mixture with these alkali ions at a temperature which is at least 75 ^° C. below the relaxation temperature of the glass. As a result of this exchange, e.g. B. of lithium ions against sodium ions or sodium ions against potassium ions, the network in a surface layer of the object is deformed in such a way that the layer is subject to compressive stress. This has the consequence that the strength of the glass in terms of

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Tensile load increases and is maintained even after severe damage to the surface, e.g. B. if the item with rotating sandpaper is brought into contact.

The mentioned composition area in percent by weight is as follows:

: 35 to 75, where up to about 25 percent by weight of the SiO _{2 can be} replaced by TiO ₂ ,

between (27.6 - 0.3 ΓSiO ₂ - TiO ₂ I) and 36 percent by weight, whereby up to 35 percent by weight of the ₂ O can be replaced by B _{2 O ^,}

Na ₂ O: 10-48 percent by weight, whereby up to 25 percent by weight of the Na ₂ O can be replaced by alkaline earth _{oxide and the Na 2} O can be replaced equimolecularly by Li ₂ O.

Within this composition range, the glasses are generally as a result of their change in viscosity Function of temperature not particularly interesting from a technological point of view. In particular, they are not suitable for processing than flat glasses, all the more because there is often a tendency to crystallize, especially under the circumstances under which the flat glass is drawn.

The invention creates a number of types of glass, the viscosity of which as a function of temperature is that they can be drawn excellently in the form of flat glass or tubular glass while they move comfortably through Let bubbles deform. Indeed, the composition field according to the invention represents a selection from that the aforementioned known area.

1U9H 17 / D234

The method according to the invention, in which in the usual manner manufactured articles of alkali aluminum silicate glass at a temperature which is at least 75 ° C lower than the lowest relaxation temperature of the glass in contact with the melt of a salt or a salt mixture which contains alkali ions with a larger ionic radius than the alkali ions in the glass characterized in that the objects are made from a type of glass whose composition is within of the following area is in percent by weight:

SiO ₂ 50 - 70 HgO 2 - 7th Al ₂ O ₃ 10 - 25th Na ₂ O 10 - 20th Li ₂ O < 1 nhanet with particularly ho!

to prefer the composition within the following range in percent by weight:

SiO ₂ 50 - 60 MgO 2 - 5th Al ₂ O ₃ 20th - 25th Na ₂ O 15th - 20th Li ₂ O <1

The invention is illustrated in more detail by means of the following examples where the temperatures used are defined as follows:

ORIGINAL INSPECTED 109817/0234

159R92Z

The lowest relaxation temperature is the temperature at which the viscosity is 10 'poise. The highest relaxation temperature is the temperature at which the viscosity is 10 ¹ ^ 'poise. The softening temperature is the temperature at which the viscosity is 10 '.

The tests specified in the table were carried out with rods of the specified composition with a diameter of 3 mm and a length of 80 mm. These rods were kept in contact with the aforementioned molten salt in the manner described. The strength vi ^r _D ) was measured in a three-point bending test with a support distance of 60 mm on rods which were given standard damage by contact with rotating sandpaper for a few seconds. The strength of the untreated glass after the standard damage was 5 to 7 kg / mm.

TABEL

- (wt.%) 1 400 579 2 400 560 3 400 604 4th 400 560 SiO ₂ ) 66.8 64 614 57.4 64 589 54.8 64 638 64.3 64 590 MgO
Al ₂ O ₃ Molten salt 3.8
14.6 65 870 6.5
16.3 65 797 3.1
23.2 75 876 5.4
13.7 60 814 Na ₂ O Temp. ⁰ C 14.8 19.8 18.8 16.6 Time (hours) KNO, KNO ₃ KNO ₃ KNO ₃ 7 _D (kg / mm) 475 475 475 475 LOT ⁰ C 6th 6th 4th 6th HOT ⁰ C 45 55 65 50 Softening temp. ⁰ C

Claims

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Claims (3)

-5- 1596B22 claims: 1. A process for the production of glass objects of increased mechanical strength, whereby objects made from alkali aluminum silicate glass in the usual way are brought into contact with a melt of a salt or a salt mixture ^{at a temperature which is at least 75 ° C. lower than the lowest stress-relieving temperature of the glass,} contains the alkali ions with a larger ionic radius than the alkali ions in the glass, characterized in that the objects are made from a glass whose composition is within the following range in percent by weight: SiO ₂ 50 - 70 MgO 2 - 7th Al ₂ O ₃ 10 - 25th Na ₂ O 10 - 20th Li ₂ O <1 2. The method according to claim 1, characterized in that the composition of the glass is within the following range in percent by weight: SiO ₂ 50 - 60 MgO 2 _ 5 Al ₂ O ₃ 20 - 25th Na ₂ O 15 - 20th Li ₂ O < 1 3. Articles made by the method of claim 1 or 2. ORIGINAL INSPECTED 109817/02 3A