JPH05105462A - Method for molding molten glass - Google Patents

Abstract

PURPOSE:To improve mold releasability, to prevent burring and to obtain an optical element excellent in profile irregularity and dimensional accuracy by filling molten tin in a glass forming mold and then supplying molten glass while discharging the molten tin. CONSTITUTION:A mold 1 is heated to 300-700 deg.C, the outlet 3 is closed in a nonoxidizing atmosphere, and molten tin 5 is filled into the mold 1 from an inlet 2. A control stop valve 8 is provided close to the outflow orifice of a molten tin vessel 10 (molten glass vessel) to control the outflow of tin or glass from the vessel when the materials are not supplied. The mold is then heated by a heater, molten glass 11 is supplied, and the outlet 3 is simultaneously opened to discharge the molten tin 5. When the molten glass 11 is supplied into the mold, the glass is floated on the boundary of the molten tin 5 since glass is lower in sp.gr. than tin, and the glass level is kept horizontal. A pressure is exerted on the mold and the glass is uniformly filled in the mold by controlling the discharge of the molten tin 5 when the molten glass 11 is filled into the mold.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for shaping molten glass.

[0002]

2. Description of the Related Art Conventionally, as a method for molding glass that requires a precise shape such as an optical element, a preformed body prepared by pressing a glass mass in a softened state by heating and grinding it is ground and polished. The method of completion is common practice.

Particularly for elements having complicated shapes, grinding,
Since polishing is performed manually and takes time, a method such as a reheat press method or a direct press method is adopted as a simple process.

In the reheat press method, a preformed body prepared by cutting and grinding glass that has been melted and solidified in advance and prepared into a desired shape is prepared, and the preliminary molding is performed in a molding die having a highly accurate surface. In this method, the molded body is heated and pressed to be molded and completed.

In the direct press method, a molten glass flow that is supplied by being outflowed or extruded from an outflow orifice is cut into a required amount, placed in a molding die, and pressure-molded.

There is also a method in which a molten glass flow is sandwiched between molding dies and directly cut out and pressed and molded. Both reheat press method and direct press method, grinding,
It aims to facilitate the process by changing the molding by polishing to the pressing method.

Recently, a method has also been proposed in which a mold having a cavity is filled with molten glass under pressure and molded. For example, JP-A-49-81419 and JP-A-1-
As described in 249630, there is a method of filling molten glass into a cavity provided in a molding die while pressing it with a plunger and continuously molding the glass until the glass is solidified.

These methods do not require strict viscosity control of the molten glass and eliminate the extrusion of excess glass due to the molding die pressure to simplify the mold structure and device mechanism.

Since the molding temperature of glass is as high as 500 to 1200 ° C., the mold used for pressing or filling is generally made of heat-resistant steel. In the case of a steel mold, the mold surface is coated with a noble metal, the mold is divided into multiple parts, and slides are provided to promote mold separation.
Ceramic molds have also been proposed because of their excellent heat resistance.

[0010]

However, in the case of the reheat press method, it is necessary to cut out from the glass which has been melted and solidified in advance and grind it to prepare the preform into a desired shape. In order to finally obtain an optical element with excellent surface accuracy and dimensional accuracy, it is necessary to adjust the weight and surface roughness of the preform sufficiently, and it takes a lot of time and effort to produce the preform. ..

In the case of the direct press method, the labor of preparing a preform is unnecessary, but when cutting out the molten glass flow, there is a problem that the viscosity control of the glass flow is difficult. With the recent composition of optical glass, it is necessary to supply a glass flow having a low viscosity in order to prevent the devitrification phenomenon, but when the viscosity is low, folding may occur, resulting in defects or defective cutting.

When sandwiching with a molding die and cutting and press-molding, a method of eliminating defects occurring at the cut portion from the product part is adopted, but for stable molding, the glass flow must be highly viscous and severe. Since it needs to be managed, there is a problem of devitrification. In the case of the pressing method as described above, any excess glass material is required, and a mechanism for removing the excess glass extruded out of the mold is required, which makes the shape of the mold complicated. I will end up.

Unlike the pressing method, the method of press-filling the mold cavity with molten glass does not require strict viscosity control. Further, since neither a mechanism for removing the surplus glass nor a mold structure is required, there are advantages such as a simple structure of the device and the mold.

However, since the pressing method is compression of molten glass such as a plunger, the supplied molten glass is cooled and solidified by the runner having a diameter smaller than that in the cavity. Therefore, the pressing force is not transmitted to the entire mold, and it is impossible to manufacture a product having excellent accuracy and quality. If the pressing force does not act sufficiently stably, sink marks due to solidification shrinkage will occur when the molten glass is cooled. Further, there is a problem that a pressure mechanism such as a plunger that slides in the molten glass cannot operate stably for a long time due to corrosion resistance and wear resistance.

The mold used for forming the molten glass is made of steel, but its durability is insufficient for repeated use at a high temperature of 500 to 1200 ° C. Furthermore, it easily reacts with the glass during molding, resulting in poor mold release. In order to eliminate the bad mold release of the steel mold, there is a mold whose surface is coated with a noble metal, but abrasion and peeling occur, which also has a problem in durability.

When the mold is divided into multiple parts or slides are provided,
The shape of the mold becomes complicated. In the case of a ceramic mold, there is a problem that it is difficult to process and it is weak against impact, and while it has excellent heat resistance, it easily causes welding to the glass during molding, and its releasability is not improved.

According to the present invention, in a method of molding by filling molten glass under pressure with a molten glass, problems such as a pressure filling mechanism and mold releasability of mold are solved, and an excellent optical element is formed by a simple process. It is an object of the present invention to obtain a method for forming molten glass that can be used.

[0018]

The present invention utilizes the properties of molten tin such that tin has a melting point (232 ° C.) lower than the glass forming temperature, is less likely to react with molten glass, and has a larger specific gravity than molten glass. It is a thing.

The method of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a mold 1 used in the glass forming method of the present invention. The mold has a molten glass supply port 2 in the upper part, a discharge port 3 in the lower part, and a cavity 4 having a desired shape in the center through upper and lower runners. FIG. 2 is a view showing a cross section of the mold in another direction. In this example, a two-division or four-division type may be used. The mold can be manufactured by a method with a high processing accuracy that can obtain a desired shape. Also,
The material of the mold can be appropriately selected depending on the composition of the glass to be molded, such as steel or a steel coated with a noble metal.

As shown in FIG. 3, this mold is installed with the supply port 2 on the upper side and the discharge port 3 on the lower side. A molten tin bath 5 is connected to the upper supply port 3. A valve or the like for adjusting the discharge of the molten tin 6 is attached to the discharge port 3 at the bottom of the mold. A heater is attached to the molten tin tank 5 and the runner leading to the lower outlet 3 and below to keep the temperature as necessary.

As shown in FIG. 3, the discharge port 3 is closed and the mold 1 is filled with the molten tin 6 from the upper supply port 2. Since molten tin is very easily oxidized, it is necessary to fill and discharge it in a non-oxidizing atmosphere, for example, a nitrogen atmosphere. The filling method is performed by free fall in this example.

Although not explicitly shown in FIG. 3, an open / close control valve is provided in the vicinity of the outflow orifice of the bath in order to control the outflow of tin or glass from the molten tin bath or the molten glass bath at a time other than the time of supply, or Install a container, etc. on the upper part of the mold to receive the outflow of tin and glass. Next, the mold 1 is heated. The heating temperature varies depending on the glass to be molded, but is generally 300 to 700 ° C. The mold 1 may be heated before or after the molten tin 6 is filled.

As shown in FIG. 4, a mold 1 filled with molten tin.
The molten glass tank 10 is connected to the supply port 2 of the, and the molten glass 11 is supplied while the temperature is raised by the heater and at the same time, the discharge port 3
Is opened and the molten tin 6 is discharged. In the example of FIG. 4, the molten glass 11 is naturally dropped, and the molten tin 6 is discharged from the discharge port 3 by its own weight and the supply pressure of the molten glass 11. At this time, if the discharge of molten tin is controlled, pressure is applied to the mold, the glass is uniformly filled in the mold, and solidification shrinkage (sink) due to cooling can be compensated.

When the molten glass is fed into the mold, it has a smaller specific gravity than the molten tin, so that it floats at the interface of the molten tin and the liquid level of the glass is kept horizontal. Therefore, it is filled uniformly without causing folds and the like. Molten tin hardly reacts with the glass, and a small amount forms a thin film on the inner surface of the mold and remains.
It prevents the molten glass from reacting with the mold material and promotes mold release. It prevents the molten tin from entering the gap where the divided pieces of the mold come into contact with each other and forming burrs on the molded product. The molten tin bath, the molten glass bath, and the heaters installed near the die outlet prevent the molten tin and the molten glass from cooling and solidifying in the runner.

The molten glass is supplied and molten tin is discharged by
As shown in FIG. 4, it is possible to use the natural dropping of the molten glass or to pressurize the molten glass. In the example shown in FIG.
A gas pressure pressurizing device 7 is provided inside the molten glass tank 10, pressure is applied to the molten glass 11, and the opening / closing valve 8 adjusts the injection of the molten glass 11 into the mold 1. The pressure inside the mold 1 may be adjusted by the gas pressure pressurizing device 7 and the discharge amount adjusting device 9, and the glass may be filled and pressed to form the glass. When molded in the above steps, the molten glass comes into contact with the interface of tin in the mold, so that it does not react with the mold material and the mold releasability is good.

[0026]

As described above, according to the glass forming method of the present invention, the molten glass is filled while floating on the interface of the molten tin, so that the glass can be uniformly cast regardless of the viscosity of the glass. .. Therefore, even if the supplied glass has a low viscosity, defects such as folding do not occur. The molten tin is used to suppress the reaction between the glass and the mold, and the gap between the divided pieces of the mold is filled, so that the mold releasability is improved and burr is prevented from being generated in the molded product. By adjusting the discharge amount of molten tin and the supply pressure of molten glass, pressure can be applied to the mold to prevent sink marks.
In addition to an optical element that is excellent in surface transferability, reproducibility of details, and dimensional accuracy and requires high accuracy, it has an effect of being applicable to molding of artificial teeth and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a mold used in a molding method of the present invention.

FIG. 2 is a cross-sectional view showing an example of a mold used in the molding method of the present invention.

FIG. 3 is an explanatory diagram of a molding method of the present invention.

FIG. 4 is an explanatory diagram of a molding method of the present invention.

FIG. 5 is an explanatory diagram of a molding method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Supply port 3 Discharge port 4 Cavity 5 Molten tin tank 6 Molten tin 7 Gas pressure pressurizing device 8 Opening / closing valve 9 Emission control device 10 Molten glass tank 11 Molten glass

Claims (2)

[Claims] 1. A molten glass is filled in a glass molding mold having a cavity through which a supply port provided at an upper portion and a discharge port provided at a lower portion communicate with each other through a runner, and molten glass is supplied from the supply port of the mold. A method for forming molten glass, characterized in that molten tin is discharged from a discharge port at the same time that the molten glass is supplied. 2. The molten glass according to claim 1, wherein in the glass forming method, the mold is pressurized by adjusting the supply pressure of the molten glass or the discharge amount of the molten tin. Molding method.