RU2579043C2 - Method for toughening of glass - Google Patents

Abstract

FIELD: glass.

SUBSTANCE: invention relates to methods for thermally hardening of polished glass and the combined method may be used for the manufacture of constructional optics. Invention consists in that in the first step is carried out in an ion exchange strengthened glass melt of potassium nitrate to obtain a compressive stress layer depth of 30-85 microns, then glass is etched in a solution of hydrofluoric acid and sulfuric acid to a depth of 5-15 microns. Removal of the surface layer of ion exchange fractured glass to a depth of 10-15 microns does not affect the optical characteristics of products and increase the strength at centrally symmetric bending 1.5-2 times. Along with the static strength and significantly increased dynamic strength composite materials with the impact different types of indenters (balloon bird).

EFFECT: technical result of the invention is to increase the strength of large parts of complex geometry derived from toughened glass, while maintaining high optical performance.

2 cl, 3 tbl, 4 ex

Description

The invention relates to methods for hardening thermally polished glass of industrial composition by a combined method and can be used for the manufacture, for example, of structural optics.

A known method of hardening (UK patent No. 1082064, C1M, 1967), in which glass samples before hardening by ion exchange in a molten potassium nitrate (KNO ₃ ) are subjected to preliminary etching to remove the surface defective layer, then kept in vacuum at a temperature of 300-350 ° C after which the glass is subjected to ion exchange treatment in a molten potassium nitrate.

The disadvantage of this method is the high complexity of the manufacture of samples, the manifestation of structural defects of glass (etching to a depth of 30-100 microns), therefore, it has not received industrial distribution.

Closest to the proposed method is the invention according to the author's certificate of the USSR No. 649672, C03C 21/00, 1979, (prototype), in which, in order to increase the hardening efficiency and thermal stability, the glass is etched in a solution of hydrofluoric acid to a depth of 100 μm, then the hydrated layer is removed by treatment in a melt of fluoroborates of alkali metals and hardened in a melt of potassium nitrate.

The disadvantages of this method are the large number of processing steps (extra ion-exchange bath), the aggressiveness of melts containing fluoroborates in relation to the bath material, the manifestation of glass structure defects during deep etching and when processing glass in fluoroborate melts, which makes it impossible to use it when hardening full-scale glasses for composite materials.

The objective of the present invention is to develop a method of hardening, which allows to increase the strength of ion-exchange glasses while maintaining high optical characteristics in order to obtain large-sized products of complex geometry.

This is achieved by the fact that at the first stage, ion-exchange hardening of the glass is carried out in a potassium nitrate melt with regenerating additives to obtain a layer of compressive stresses with a depth of 30-85 μm, then the glass is etched in a solution of hydrofluoric and sulfuric acids to a depth of 5-15 μm. Removing the fractured surface layer of ion-exchange glasses to a depth of 10-15 μm does not affect the optical characteristics of the products and increases the strength under central-symmetric bending by 1.5-2 times (table 1).

Table 1 The strength of samples hardened by ion exchange (h = 65 μm) + etching in a mixture of acids HF + H ₂ SO ₄ (h = 10-12 μm) Protective coating, microns Strength, MPa Without cover 1360 (660-2110) 0.02 1550 (910-2340) 0,03 1520 (830-2240) 0.05 2060 (1720-2390)

The test results show that the combined method of glass hardening allows to obtain high strengths on the samples both with and without coating, while maintaining the optical characteristics of the original glass. The application of a protective coating reduces the dispersion of particular strength values, which increases the reliability of composite materials from them in operation and allows the use of toughened glass both for internal power units and for the outer glasses of structural engineering products.

Along with static strength, the dynamic strength of composite materials when impacted by different types of indenters is also significantly increased, which allows to reduce the weight of products and increase operational properties at a lower cost for their production.

Example 1

Composite material (triplex) for windshields of automobile glazing is made of thermally polished glass with a thickness of 2.5 and 1.3 mm, glued with a polyvinyl butyral film (PVB) 0.76 mm thick. Dynamic strength tests are carried out by dropping a steel hardened ball weighing 227 g into the middle of a 300 × 300 mm sample or an automobile windshield from the side of the outer surface. The results of the destruction of the composite material by a ball from a height of, for example, 6 m are estimated by the size of the fragments in accordance with GOST 27903-88 (Safety glass for cars, tractors and agricultural machines). The authors tested triplexes 300 × 300 × 4.5 mm in size when hit with a ball from a height of 9 m. The results of comparative tests are shown in Table 2 (outer glass - glass 2.5 mm thick).

table 2 Type of hardening Nature of destruction Outer glass, H = 2.5 mm Inner glass, H = 1.3 mm ion exchange (35 μm) + 5 μm etching ion exchange, layer depth 35-40 microns Both glasses are intact ion exchange (35 μm) + 5 μm etching ion exchange, layer depth 35-40 microns Both glasses are intact Without hardening Without hardening 2 glasses are destroyed ion exchange, layer depth 35 μm ion exchange, layer depth 35-40 microns 2 glasses are destroyed ion exchange (35 μm) + 5 μm etching Without hardening Outer glass - whole, inner - broken

The strength of satellite samples hardened at a temperature of 460 ° C for 24 hours with centrally symmetric bending (CSI) was: Initial samples - 150 (90-230) MPa;

Samples hardened by ion exchange - 670 (440-920) MPa;

Samples hardened by ion exchange + etching to a depth of 5 μm, - 1330 (600-2150) MPa.

It can be seen that etching one ion-exchange glass to a depth of 5 μm allows one to obtain a composite material that remains intact when hit by a ball even from a height of 9 m, while when testing standard compositions conducted in accordance with GOST 27903-88, the samples were destroyed

Example 2

For structural optics of complex geometry, a composite material is made of three glasses 3 mm thick glued with a polyurethane film. The glass is hardened by the ion exchange method over a long-term regime until a layer of compressive stresses of 75-80 microns and their maximum values of 250-300 MPa are reached. Next, the model of the structural optics product is glued in an autoclave so that the ends of the product are covered with a polyurethane film, and then etched in a solution of hydrofluoric and sulfuric acids to a depth of 10-12 microns. Thus, the etching process takes place only on the outer glass. Models of products were subjected to dynamic tests (bird strike weighing 1.8 kg at different speeds).

Dynamic tests showed that a composite material based on ion-exchange glasses can withstand a bird at a speed of 400-450 km / h at full rear strength (whole glass), while a block etched from the outside withstood a bird at a speed of 700 km / h while maintaining all the glasses of the composite material. The optical characteristics of a block processed by the proposed technology are identical to the characteristics of a composite material based on glasses strengthened by ion exchange.

Example 3

For structural optics of complex geometry, a composite material is made of three glasses 3 mm thick glued with a polyurethane film. The glass is hardened by the ion exchange method over a long-term regime until a layer of compressive stresses of 80-85 microns and their maximum values of 250-320 MPa are reached. Next, the mock-up of the product of structural optics is glued in an autoclave so that the ends of the product are closed with a polyurethane film, and then etched in a solution of hydrofluoric and sulfuric acids to a depth of 15 μm. Models of products were subjected to dynamic tests (bird strike weighing 1.8 kg at various speeds) and passed the tests.

Example 4

Composite material (triplex) for windshields of automobile glazing is made of thermally polished glass with a thickness of 3 ± 0.5 and 1.5 ± 0.5 mm glued with a polyvinyl butyral film (PVB) 0.76 mm thick. Tests for dynamic strength are carried out according to example 1. The results of comparative tests are shown in table 3 (outer glass - glass 3 mm thick).

Based on the above examples, we can conclude that the proposed combined method of hardening allows to increase the static and dynamic strength of both glass billets and composite materials from them by 1.5-2 times while maintaining the optical characteristics.

Information sources

1. UK patent No. 1082064, CL C1M, 1967.

2. Copyright certificate of the USSR, No. 649672, cl. C03C 21/00, 1979.

Claims (2)

1. A method of hardening glass, including etching in an aqueous solution containing hydrofluoric acid, ion-exchange hardening in a molten potassium nitrate, characterized in that the glass for the composite material is hardened by ion exchange to obtain a layer of compressive stresses with a thickness of 30-85 μm with its subsequent etching to a depth of 5-15 microns. 2. The method according to p. 1, characterized in that for a composite material based on 3 glasses, each glass is hardened by ion exchange to obtain a layer of compressive stresses with a thickness of 70-85 μm, then they are glued into a glass block, and then the external glasses are etched onto depth of 10-15 microns.