RU2356858C2 - Method for glass sheet bending - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention is related to industry of construction materials, in particular to manufacture of bent glass sheets. Sheet stock is placed on previously heated solid mold and inserted into furnace heated up to bending temperature. As stock is curved accordingly, mold with stock is withdrawn from furnace. Stock is withdrawn from mold onto heat insulated substrate with the purpose to carry out semi-hardening of bent stock under conditions of natural air convection.

EFFECT: improved quality of bent small-size products from thin glass sheet by optical and geometric parametres.

2 cl, 1 ex, 1 tbl

Description

The invention relates to the building materials industry, in particular to the field of manufacture of curved glass, and can be used in the glass industry to obtain bent small-sized products from thin sheet glass, used, for example, for glazing the scales of aircraft devices and other vehicles.

A known method of molding sheet glass, including placing a flat billet on a preheated form, heating, bending, moving it into the annealing chamber using a pneumatic shuffler, followed by annealing, according to USSR copyright certificate No. 461904, class. C03B 23/26, 1975.

The disadvantage of this method is that it does not allow to obtain bent products with a given surface curvature and high optical performance due to curvature and damage to their surface during the operation of moving to the annealing chamber using a pneumatic shifter. This disadvantage is especially evident when molding thin small-sized blanks. In addition, the known method does not provide an increase in the mechanical strength of bent blanks, as it involves an annealing operation after their bending.

Closest to the invention is a method of molding sheet glass, comprising placing a sheet of glass blanks on a preheated heat-insulated, for example, asbestos or chalk coating, a solid metal form, introducing it into a furnace heated to a glass molting temperature, and when the workpiece reaches the desired geometry, the shape is removed from a furnace for half-hardening a bent billet in conditions of natural air convection, according to the author's certificate of the USSR No. 20136, class. C03B 23/02, 1967.

The known method does not allow to obtain bent products with a given surface curvature and high optical performance, since when cooling a bent workpiece on a mold in conditions of natural air convection, the workpiece surfaces are in different thermal conditions, the upper surface of the workpiece cools much faster than the lower, since the last in contact with the surface of a thermally insulated solid metal form. In view of this, the geometric parameters of the bent workpiece deviate from those obtained during bending. In addition, a mold coated with a heat insulating material, such as asbestos or chalk coating, does not provide molding of the workpieces without damaging their surface from the always existing defects of the forming surface that are formed during the manufacture of such molds. After several bending cycles, due to the different coefficients of thermal expansion of the metal form and the heat-insulating coating, as well as due to the different coefficients of their thermal conductivity, the heat-insulating coating is destroyed. Since the solid metal form has a large heat capacity, a large period of time is required for its cooling and extraction of the bent workpiece from it. For the same reason, a large period of time is required to heat the mold to the glass bending temperature. All this leads to a low productivity of the bending process and at the same time to a small degree of half-hardening of the resulting products.

The objective of the invention is to improve the quality of bent small-sized products from thin sheet glass by optical and geometric indicators.

To achieve the objective of the invention, a method for molding sheet glass is provided, comprising placing the glass preform on a preheated continuous mold, introducing it into a furnace heated to a molding temperature, and when the preform reaches a predetermined curvature, removing the mold from the furnace for half-quenching of the bent preform under conditions of natural air convection, characterized in that after removing the mold from the furnace, the preform is removed from the mold by turning the mold on a thermally insulated substrate, stvlyaetsya out of shape.

Moreover, the solid form is made of quartz ceramics containing at least 99.9% of silicon dioxide.

The proposed method allows to obtain bent small-sized products from thin sheet glass with higher optical and geometric parameters compared to the known method. This is due to the fact that the half-hardening of the bent workpiece is carried out out of shape on a thermally insulated substrate, while the same conditions are created for the rapid cooling of both surfaces of the workpiece in conditions of natural air convection. Under these conditions, the curvature of the surface of the bent workpiece obtained on the form is retained, while at the same time a greater degree of its half-hardening is achieved, and hence a higher strength compared to the known method. Removing the bent workpiece from the mold by turning the mold on a thermally insulated substrate after removing the mold from the furnace can significantly increase the productivity of the bending process.

The implementation of a continuous form of quartz ceramics containing at least 99.9% of silicon dioxide, allows to obtain bent blanks with high optical performance. The specified quartz ceramic has low thermal conductivity of 0.5-1.0 W / m ² × ° C in the temperature range of 50-1000 ° C and thermal expansion coefficient of 0-6 × 10 ^-7 deg ^-1 . This allows you to use a solid form with a temperature difference from room temperature to glass bending temperature (600-700 ° C) for a long time (1000 cycles or more) without changing both its geometric parameters and the purity of the forming surface.

The proposed method is as follows.

A glass blank with predetermined geometric dimensions is placed on a preheated continuous mold with a given curvature of the forming surface and made of quartz ceramics containing at least 99.9% silicon dioxide. A mold with a preform placed in it is introduced into a furnace heated to a milling temperature, and when the preform reaches a predetermined curvature of the forming surface of the mold, the latter is taken out of the furnace and a bent preform is removed from it by turning it onto a substrate insulated with, for example, asbestos or fiberglass, and placed on a solid mold the next glass blank and the bending cycle are repeated in the described sequence.

Example. It is necessary to obtain bent blanks from thin sheet glass with a thickness of 1.2 mm with a cylindrical radius of curvature of 58 mm, a length of 60 mm and a deflection arrow of 7 mm. The blanks are intended for the manufacture of glazing products for aircraft instrument scales.

Use flat glass blanks with a thickness of 1.2 mm and with geometric dimensions of 48 × 60 mm. A mold made of quartz ceramic containing 99.9% silicon dioxide with a thermal conductivity of 0.5-1.0 W / m ² × ° C in the temperature range of 50-1000 ° C and with a coefficient of thermal expansion of 0-6 × 10 is used ^-7 deg ^-1 . The radius of curvature of the forming surface of the mold is 58 mm, the length of the generatrix is 250 mm, the deflection arrow is 10 mm. The softening temperature of the glass is 610 ± 5 ° C.

From the furnace heated to a temperature of 640 ± 5 ° C, the solid form located in it is removed and 3 flat glass blanks are placed on its forming surface and the solid form is introduced into the furnace. All these operations are carried out for 40 seconds. The furnace is heated to a temperature of 640 ± 5 ° C for 7 minutes and maintained at this temperature for 12 minutes for the workpieces to take the specified curvature of the forming surface of the mold under its own weight. The mold is taken out of the furnace and bent blanks are removed from it by turning the mold on a metal table, heat-insulated with 6 layers of KT-11 fiberglass, for cooling in natural air convection to room temperature. These operations are carried out for 25 seconds. Thus, the bending cycle is carried out for 20 minutes 5 seconds. The following 3 flat blanks are placed on the forming surface of the mold and the mold is introduced into the oven. Next, the operations of heating, bending and cooling the bent blanks are repeated in the sequence described above.

After cooling the bent blanks for 15 minutes to room temperature, they are transferred to the enlightenment area to obtain glazing products for aircraft instrument scales.

According to an example, a batch of bent blanks in an amount of 150 pieces was obtained.

For comparison, a batch of bent blanks with the same geometric parameters was obtained by a known method.

Comparative data of the results are shown in the table.

No. p / p Name of parameters Results The proposed method Known method one Minimum strength, kgf / mm ² 8.2 5,4 2 Average strength, kgf / mm ² 19.2 11.1 3 Hardening stresses in the edge region of the workpieces, nm / cm 130-150 70-90 four Hardening stresses in the central region of the workpieces, nm / cm 70-90 10-20 5 Deviation from a given surface curvature, mm 0.1-0.2 0.9-1.2 6 Inadmissible optical distortions on the surface of the workpieces,% 3 75

From the above data it is seen that the proposed method allows to obtain bent small-sized blanks from thin sheet glass with high geometric and optical parameters that meet the requirements for glazing products of instrument scales of aircraft and other vehicles. In addition, the proposed method provides the preparation of workpieces with higher rates of quenching stresses and strength due to the fact that the half-hardening of bent workpieces is carried out out of shape on a thermally insulated substrate.

Information sources

1. USSR author's certificate No. 461904, cl. C03B 23/26, 1975.

2. USSR Copyright Certificate No. 201603, cl. C03B 23/02, 1967.

Claims (2)

1. The method of molding sheet glass, including placing the glass preform on a preheated solid form, introducing it into a furnace heated to a bending temperature, and when the preform reaches a predetermined curvature, removing the mold from the furnace for half-quenching the bent preform under conditions of natural air convection, characterized in that after removing the mold from the furnace, the workpiece is removed from the mold onto a thermally insulated substrate, while half-hardening is carried out outside the mold. 2. The method according to claim 1, characterized in that the solid form is made of quartz ceramics containing at least 99.9% silicon dioxide.