RU2365540C2 - Method for sagging of sheet glass - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to sagging of sheet glass and may be used to produce bent products from glass with opening. Glass workpiece is installed and heated up to softening temperature. Glass is sagged first under gravity and then under vacuum action. Prior to workpiece installation on mold cut is done along contour of removed central part of workpiece. After final sagging, workpiece is extracted from mold and is cooled under conditions of natural air convection. Mechanical effect is applied along contour of removed central part of workpiece.

EFFECT: higher strength of bent products from glass with opening in their central part.

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Description

The invention relates to the building materials industry, in particular to glass, and in particular to molding flat glass, and can be used to produce bent glass products with a hole intended for glazing various kinds of devices and installations, for example electric grills.

For glazing the upper part of the electric grill, round bent glass with a spherical curvature of the surface is used, which has a circular hole in its central part to accommodate a heating element with a fan in it.

A known method of molding sheet glass, including placing the preform on the mold, heating it to a softening temperature of the glass, molting the preform, cooling and then separating the removed edge portion from it by cutting with repeated annealing of the trimmed preform according to US patent No. 3278287, cl. POPs 23/02 (NKI 65-103), 1966.

The known method can be used to separate the removed edge part from the workpiece and cannot be used when it is necessary to separate its removable central part from the workpiece, that is, to obtain a bent workpiece with an opening. In addition, the workpiece after separation of the removed edge part must be repeatedly annealed, which requires additional costs in the manufacture of products.

Closest to the proposed method is a method of molding sheet glass, including placing the preform on the mold, heating it to a softening temperature of the glass, initial molding of the preform under its own weight, final molding under vacuum, separation of the removed edge of the preform by mechanical action and cooling according to US patent No. 3552941, class POPs 23/02 (NKI 65-67), 1971. In this case, the removal of the removed edge part of the preform is carried out in the furnace at the time of the beginning of exposure to vacuum by mechanical pressing of the softened preform with a metal ring-shaped element, and the bent preform is cooled by annealing it.

The known method can also be used when it is necessary to separate its removable edge part from the workpiece, and cannot be used when it is necessary to separate its removable central part from the workpiece, that is, to obtain a bent workpiece with an opening. In addition, the implementation of the separation of the removed edge part of the preform in the furnace space at a glass softening temperature requires a special device for moving the metal ring-shaped element. Carrying out annealing of the bent workpiece does not provide an increase in its strength compared to flat sheet glass used for bending.

An object of the present invention is to provide bent glass products with a hole in their central part.

To achieve the objective of the invention, a method for molding sheet glass is provided, including placing a preform on a mold, heating it to a softening temperature of the glass, initial molding of the preform under its own weight, final molding under vacuum, separation of the removed part of the preform by mechanical action and cooling, characterized in that Before placing the workpiece on the mold, an incision is made along the contour of the removed central part of the workpiece, and after the final bending the billet is removed from the mold, moreover, mechanical action is applied along the contour of the removed central part of the billet, while cooling is carried out under conditions of natural air convection from the moment the billet is removed from the mold.

The proposed method allows to obtain bent products with a hole in their central part. This is explained by the fact that when the bent workpiece is removed from the mold, it cools under conditions of natural air convection, while the edge part cools faster than the central one. In this regard, tensile stresses are created in the cut along the contour of the removed central part of the workpiece, which, with a small mechanical impact along the contour of the removed central part of the workpiece, leads to separation of the central part from the workpiece. In this case, mechanical action is carried out by tapping with a solid object, for example, a ceramic or metal rod, along the contour of the removed central part of the workpiece. The resulting bent products with a hole in their central part have greater strength compared to flat sheet glass used for bending. This is due to the fact that when the workpiece is cooled in conditions of natural air convection from the moment it is removed from the mold, compressive stresses are created on its surface, which increase the strength of the workpiece.

The method is carried out in the following sequence.

On the surface of the glass preform, with the given geometric dimensions, an incision is made along the contour of the removed central part of the preform using a diamond glass cutter. After that, the workpiece is placed on a mold with a given curvature of the forming surface located in the furnace, heated to the softening temperature of the glass. The workpiece is heated to a glass softening temperature at the rate of 1 minute per 1 mm of its thickness. The furnace is kept at the softening temperature of the glass to bend it under its own weight. Then carry out the final bending under the influence of vacuum. The billet is removed from the furnace using, for example, a thermally insulated vacuum rod and placed on a metal table, thermally insulated with asbestos or fiberglass. After that, they have a mechanical effect along the contour of the removed central part of the workpiece by tapping with a ceramic or metal rod along the notch line. After separation of the removed central part from the workpiece, it is transferred to a ceramic stand for cooling to room temperature. Then, the sharp edges of the workpiece along the contour of the hole are dulled with a diamond tool and the resulting bent product with the hole is transferred to the electric grill assembly area.

Example. It is necessary to obtain a glass product intended for glazing the upper part of the electric grill. The product should have a ring-shaped shape with a spherical curvature of the surface with a radius of curvature of 245 mm, a generatrix length of 82 mm, an outer diameter of 314 mm, an inner diameter of 190 mm and a thickness of 5 mm.

Use sheet glass of industrial composition according to GOST III-2001, 5 mm thick with a softening temperature of 600 ± 5 ° C. Cut a round glass blank with a diameter of 325 mm and dull its sharp edges with a diamond tool. An incision is made on the surface of the workpiece in its central part using a diamond glass cutter along a circle with a radius of 95 mm relative to the geometric center of the workpiece. A mold made of cast iron with a spherical curvature of the forming surface with a radius of 245 mm and a diameter of 335 mm is used.

The form is placed in an oven and heated to a temperature of 600 ± 5 ° C. After holding the oven for 30 minutes at the indicated temperature, the glass blank is placed on the mold using a thermally insulated vacuum rod. Heat the workpiece to a temperature of 600 ± 5 ° C for 5 minutes and maintain at this temperature for 10 minutes for the initial bending of the workpiece under its own weight. Then carry out the final molding under the influence of vacuum of 0.9 atmospheres for 1.5 minutes. The billet is removed from the furnace using a thermally insulated vacuum rod and placed on a metal table, thermally insulated with sheet asbestos, 10 mm thick. This operation is carried out for 15 seconds. Then tap with a metal rod 20 mm long and 4 mm in diameter along the contour of the removed central part of the workpiece, that is, along a notch line, until the central part is separated from the workpiece. The indicated moment occurs after 25 seconds. The blank is placed on a ceramic stand, and its removable central part is placed in a container for cullet. After cooling the bent workpiece with the hole, its sharp edges in the resulting hole are dulled with a diamond tool and transferred to the electric grill assembly area.

According to the described example, a batch of products with a hole in their central part in the amount of 120 pieces was obtained. The reproducibility of the results of the proposed method was 90%. In addition, the average strength of the obtained products with a hole is 1.6 times higher than that of flat sheet glass used for bending.

Information sources

1. US patent No. 3278287, CL. СО3В 23/02 (NKI 65-103), 1966.

2. US Patent No. 3552941, cl. СО3В 23/02 (NKI 65-67), 1971.

Claims (1)

A method of molding sheet glass, including placing a preform on a mold, heating it to a glass softening temperature, initial molding of a preform under its own weight, final molding under vacuum, separating the removed part of the preform by mechanical action and cooling, characterized in that before placing the preform on the mold an incision is made along the contour of the removed central part of the workpiece, and after final bending, the workpiece is removed from the mold, moreover, mechanically impact is applied along the contour removable central portion of the preform, wherein the cooling is carried out in conditions of natural air convection from the time of extraction of the preform shape.