JPH10203828A - Melting optical glass and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for melting optical glass, capable of controlling at a desired temperature even a small amount of a glass and supplying the homogeneous glass. SOLUTION: This method for melting optical glass has a process of defoaming the molten glass in a vessel of a single body at a defoaming temperature, a process for removing a stria from the molten glass defoamed in the above vessel at a stria removing temperature, and a process of supplying the molten glass removed with the stria at a supplying temperature. The temperature for the defoaming, stria removing and supplying are set so as to become (defoaming temperature > stria removing temperature > supplying temperature).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for melting optical glass for batch melting optical glass and supplying homogeneous molten glass.

[0002]

2. Description of the Related Art Conventionally, as a technique for heating and melting optical glass, there is a technique disclosed in Japanese Patent Application Laid-Open No. 7-69648.
A melting furnace capable of continuously melting several to hundreds of kilometers of glass is described. 4 and 5 are a longitudinal sectional view and a plan view showing the melting furnace, as shown in FIGS.
The melting furnace includes a melting tank 21 for melting glass and a molten glass 2.
2 comprises a homogenizing tank 23 for agitating and homogenizing, and an outflow tank 24 for agitating the homogenized molten glass 22 and adjusting the outflow temperature. The melting tank 21 and the homogenizing tank 23 are connected by a connecting pipe 25. The homogenizing tank 23 and the outflow tank 24 are connected by a connecting pipe 26.

[0005] In the melting tank 1, an input section 28 for inputting glass raw material is formed by partitioning an end portion thereof by an input partition plate 27, and a plurality of partition plates 29 are provided in front of the glass input section 28. ing. The plurality of partition plates 29 are fixed to the bottom surface of the melting tank 21 such that the partition surfaces are perpendicular to the flow direction of the molten glass. Further, a plurality of partition plates 2
9, one side is fixed to the side of the melting tank 21, and a gap is alternately provided between the other side and the side of the melting tank 21. When flowing, the molten glass 22 is meandered to increase the convection time of the molten glass 22 in the melting tank 21, thereby preventing the bubbles from being mixed. Further, in the homogenizing tank 23 and the outflow tank 24, stirring devices 30 and 31 for stirring the internal molten glass 22 are provided, respectively. Further, the outflow tank 24 is provided with an outflow nozzle 32 for supplying the molten glass 22 therein to the outside.

[0004]

Problems to be Solved by the Invention Japanese Patent Application Laid-Open No. 7-69648
The problems of the publication are as follows. First, since there is no open / close door in each tank of this melting furnace, each tank needs to be filled with molten glass. Either a small amount of glass will flow out. Although the glass material is melted by heating, it is difficult to homogenize a small amount of molten glass of several kilograms in a homogenizing tank, depending on the capacity of each tank.

Secondly, in order to homogenize the molten glass, it is necessary to control the glass temperature in each tank, and it is necessary to pay close attention to the temperature gradient so that the glass raw material can be melted as uniformly as possible. For example, it is necessary to set the temperature higher in the defoaming step, and to set the temperature lower in the homogenizing tank. In a large continuous melting tank as in the prior art described above, the amount of glass is large and the glass flow is slow, so that it is possible to adjust the glass temperature by controlling the heaters of the individual tanks. However, when several kilograms of glass are melted, the heat capacity of the glass is so large that it is difficult to change the temperature of the glass to a desired temperature even when controlled by heaters in individual tanks.

The present invention has been made in view of the above-mentioned problems of the prior art, and a first object of the present invention is to control a desired temperature even with a small amount of glass and to supply a homogeneous glass. A second object is to provide a melting method for improving the yield of molten glass regardless of the amount of glass to be charged. A third object is to provide a melting device for improving the yield of molten glass regardless of the amount of glass to be charged.

[0007]

According to a first aspect of the present invention, there is provided a method for melting an optical glass by heating and melting the optical glass. A step of defoaming the molten glass in the defoaming temperature, a step of removing striae of the molten glass defoamed in the vessel at a striae removing temperature, and a step of removing the molten glass striae in the vessel. Supplying at a supply temperature, wherein the temperature relationship between the defoaming temperature, the striae removing temperature and the supply temperature is “defoaming temperature> striae removing temperature> supply temperature”.
So that

Further, the method for melting optical glass according to the second invention is the method for melting optical glass according to the first invention, wherein the step of supplying the molten glass includes the step of: The molten glass is agitated by the agitating means which moves so as not to come out of the liquid level with the liquid level.

Further, a melting apparatus for optical glass according to a third aspect of the present invention includes a container for housing the molten glass obtained by heating and melting the optical glass, a stirring means for stirring the molten glass in the container, and a container for stirring the molten glass. A driving means for moving between the bottom of the molten glass and the liquid level in the inside, and a control means for setting a moving distance for the stirring means to move between the bottom of the molten glass and the liquid level. Things.

That is, in the method for melting optical glass according to the first invention, the molten glass in a single container is defoamed at a defoaming temperature, and the molten glass defoamed in the container is removed at a striae temperature removing temperature. And the molten glass that has been striae-removed in the container is supplied at a supply temperature. Here, the stria temperature is set lower than the defoaming temperature and higher than the supply temperature.

Further, in the optical glass melting method according to the second invention, when the molten glass is supplied, the molten glass is moved between the bottom of the molten glass and the liquid level in the container so as not to come out of the liquid level. The molten glass is stirred by the stirring means.

Further, in the optical glass melting apparatus according to the third invention, the moving distance of the stirring means for moving between the bottom of the molten glass housed in the container and the liquid level is set by the control means. The molten glass is stirred by moving the stirring means by the driving means.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] First, a step of defoaming molten glass;
The step of removing the defoamed molten glass from the striae and the step of supplying the molten glass from which the stroma has been removed will be briefly described. When the optical glass is preliminarily melted in another furnace and the solidified glass cullet is melted again, the glass components are decomposed and bubbles are generated. The bubbles absorb gas components inside the molten glass and cause striae in the molten glass. Therefore, when melting the glass, it is necessary to remove (defoam) the bubbles in the first step. There are two methods for removing the bubbles. One method is to raise the temperature of the molten glass to lower the viscosity of the glass, and to remove the bubbles by making them easier to float. Second, as shown in FIG. 2, once the temperature is increased to reduce the gas component (bubble generation area a) to lower the solubility of the molten glass, and then the temperature is lowered to allow the bubbles to be melted into the glass again. (Resolution solubility range b).

Next, the heterogeneous region of the molten glass is decomposed by stirring to remove striae. In this step, if the amount of gas components in the molten glass is large, bubbles are generated by the impact of stirring, so that it is necessary to reduce the amount of gas components.

Then, the molten glass is supplied to the outside. In this step, if the temperature is too high, volatilization occurs from the surface of the molten glass, a heterogeneous region is generated, and striae are generated. . Hereinafter, an example of a method and an apparatus for melting optical glass will be described.

An embodiment of the present invention will be described with reference to FIGS. 2 schematically shows an optical glass melting device, FIG. 2 (a) is a plan view, FIG. 2 (b) is a front view, and FIG. 3 is a cross-sectional view showing the optical glass melting device.

The optical glass is heated and melted to form a molten glass 10
As shown in FIG. 2 (a), the melting crucible 1 as a container for accommodating has a cross-sectional shape in which tangents of circles having different diameters are connected. The volume of the melting crucible 1 is about 30
00 cc, and the actual melting amount of the glass housed in the melting crucible 1 is about 2500 cc. Further, although the melting crucible 1 is entirely made of platinum, it is preferable to use reinforced platinum in which zirconia is dispersed.

The shaft 2a of the stirring blade 2 as stirring means is provided at the center of the different circle having the larger diameter. The stirring blade 2 is provided with two blades provided at the tip of the shaft 2a, and the two blades are attached to the shaft 2a at an angle of about 45 ° in the opposite direction. The shaft 2a of the stirring blade 2 is connected to a stirring motor 3 provided in the upper part of the apparatus, and the stirring blade 2 is rotatable at 30 to 200 rpm by driving the stirring motor 3. The stirring blade 2 is made of platinum as in the melting crucible 1, but it is preferable to use reinforced platinum in which zirconia is dispersed. The stirring motor 3 is provided on a stirring blade drive actuator 4 as a driving means of the stirring means. The stirring blade drive actuator 4 moves the stirring blade 2 up and down via the stirring motor 3 and the shaft 2a, and can move the stirring blade 2 between the bottom of the molten glass 10 (the bottom surface of the melting crucible 1) and the liquid surface. I have to. The start point, the end point, and the moving speed of the up and down movement of the stirring blade 2 can be arbitrarily set by a servo motor (not shown) as a control means. This moving speed can be set in the range of 20 to 100 mm / sec.

A supply nozzle 5 is provided below the smaller center of the different circles. The diameter of the supply nozzle 4 depends on the amount of glass supplied from the melting crucible 1,
About 3 mm to 10 mm is used. Above the supply nozzle 5, a plunger 6 that can move up and down on the axis of the supply nozzle 5 is provided. The tip 6a of the plunger 6 has a spherical shape whose diameter is larger than the diameter of the supply nozzle 5, and the downward movement of the plunger 6 securely closes the opening of the supply nozzle 5 on the melting crucible 1 side. Is prevented from flowing out to the supply nozzle 5. A plunger drive actuator 7 for moving the plunger 6 up and down to supply and stop the molten glass 10 is provided on and above the axis of the plunger 6. The plunger drive actuator 7 is driven by a servomotor in the same manner as the stirring blade drive actuator 4, so that the moving speed of the plunger 6 and the start and end positions of the vertical movement of the tip 6a of the plunger 6 can be set arbitrarily. ing. With this setting, the moving distance and the moving speed of the plunger 6 in the vertical movement can be changed, and the supply amount of the molten glass 1 can be arbitrarily set.

On the other hand, a crucible heater 8 is provided on the outer periphery of the melting crucible 1 so that the melting temperature can be increased to a maximum temperature of 1600 ° C. The crucible heater 8 is preferably made of a ceramic heater, particularly made of molybdenum disilicide. Further, a nozzle heater 9 is provided on an outer peripheral portion of the supply nozzle 5. The crucible heater 8 and the nozzle heater 9 can be controlled individually, and the melting temperature of the melting crucible 1 and the supply nozzle 9 can be controlled independently. Nozzle heater 9
It is desirable to use a ceramic heater or a high-frequency heater having a high heating rate as in the melting crucible 1. A heat insulating material 11 is provided around the melting crucible 1.

Next, a method of melting the optical glass using the melting device will be described. In the present embodiment, a case where SK-based glass is used as the optical glass for melting will be described.

With the supply nozzle 5 closed by the tip 6 a of the plunger 6, about 2500 cc of the glass block made of the above glass material is put into the melting crucible 1, and heated and melted by the crucible heater 8. The temperature pattern at this time is 13
The temperature is raised to 00 ° C. in 1.5 hours, the temperature is maintained at 1300 ° C. for 3 hours, and a defoaming process for floating bubbles generated in the molten glass 10 is performed.

After the defoaming treatment, the temperature is lowered from 1300 ° C. to 1200 ° C. in 30 minutes. Then, while maintaining the temperature at 1200 ° C., the stirring motor 3 is rotated at a rotation speed of 60 rpm to stir the molten glass 10. Simultaneously with this stirring, the stirring blade driving actuator 4 moves the stirring blade 2 up and down within a range of 5 mm above the bottom surface of the melting crucible 1 and 20 mm below the liquid level of the molten glass 10 at a vertical movement speed of 40 mm / sec. A striae removing process is performed. This stirring condition was performed for 4 hours. After that, the stirring temperature was kept at 1150 without stopping the stirring.
The temperature is lowered to 30 ° C. in 30 minutes, and this 1150 ° C. is maintained for 30 minutes.

After the holding, the nozzle heater 9 is heated to 1040 ° C., and the molten glass 10 in the melting crucible 1 is supplied to the supply nozzle 9.
Supply processing is performed. The supply of the molten glass 10 is performed by moving the plunger 6 closing the supply nozzle 5 by 4 mm at 2 mm / sec by the plunger drive actuator 7.
m, and waited for 5 seconds after the rise, and then lowered at a rate of 2 mm / sec to supply about 4 g of the molten glass 10 from the supply nozzle 5 to the outside of the melting crucible 1. Then, in accordance with the decrease of the molten glass 10 in the melting crucible 1, the vertical movement distance of the stirring blade 2 is reduced so as to maintain a distance of 20 mm from the liquid surface of the molten glass, and the stirring is performed when the vertical movement distance becomes zero. The stirring speed of the blades 2 was set to 20 rpm, and all of them were supplied.

Here, the moving range of the vertical movement of the stirring blade 2 is set to a position 5 mm above the bottom surface of the melting crucible 1 from a position 20 mm below the liquid level of the molten glass 10. This is because if the liquid comes out of the liquid surface of the molten glass 10, air is entrained by the stirring blades 2 and bubbles are regenerated in the molten glass 10. Further, regardless of the amount of the molten glass 10 in the melting crucible 1, the stirring blade 2 stirs the vicinity of the liquid level of the molten glass 10, so that the entire molten glass 10 can be homogenized.

In the embodiment of the present invention, the input amount is 2000
The yield was 90% with a heterogeneous amount of 200 cc. In the present embodiment, the defoaming temperature is set to 1300 ° C., but at a temperature higher than this, the glass component volatilizes a lot, and the optical characteristics change largely. At a temperature lower than that, bubbles can completely rise. Did not. The reason why the striae treatment was set to 1200 ° C. was that bubbles were regenerated by stirring at a temperature higher than that, and stria could not be removed at a temperature lower than that because the glass viscosity was high and the glass flow did not occur due to stirring. is there. Furthermore, the reason why the supply temperature was set to 1150 ° C. is that at a temperature higher than this, the glass component volatilizes a lot and a stria occurs on the surface layer, and at a temperature lower than that, the viscosity is high and 4 g
This is because a small amount of glass could not be supplied.

In the present embodiment, the case where SK-based glass is used has been described. Even with SF-based glass, homogeneous glass was obtained with a yield of 80% or more. At least 400cc by changing the vertical movement distance of the stirring blade 2
Was possible.

In the embodiment of the present invention, the defoaming temperature is set to 1300 ° C. However, as long as the volatilization of the molten glass 10 does not increase and bubbles in the molten glass 10 float,
Not limited to this temperature. In addition, the striae removing temperature is set to 1200 ° C.
However, the temperature is not limited to this temperature as long as bubbles are not generated again by stirring and a glass flow as shown by an arrow 15 in FIG. 2B is generated by stirring. Further, the supply temperature of the molten glass 10 was 1150 ° C.
The temperature is not limited to this temperature as long as the volatilization from the surface of 0 is small and the viscosity is such that a small amount of molten glass 10 can be supplied.

According to the embodiment of the present invention, a homogeneous region of the molten glass 10 of 80% or more can be obtained in the range of several liters to several tens of liters regardless of the amount of glass. Also,
Even if the amount of the molten glass 10 in the melting crucible 1 is reduced by supplying the molten glass 10 from the inside of the melting crucible 1 to the outside, the moving amount of the stirring blade 2 according to the reduced amount (the descending amount of the liquid level) , It is possible to supply a homogeneous molten glass 10 without bubbles and striae to the end.

The technical idea having the following configuration is derived from the specific embodiment. (1) In a method for melting an optical glass by heating and melting the optical glass in a melting crucible to form a molten glass, a step of defoaming the molten glass at a defoaming temperature of a predetermined temperature pattern, and A step of removing striae at a striae removing temperature of a predetermined temperature pattern while stirring by a movable stirring means, and a step of supplying the molten glass having a striae removed at a supply temperature of a predetermined temperature pattern while stirring by the stirring means. When,
Is performed in a single melting crucible, and the temperature relationship among the defoaming temperature, the striae removing temperature and the supply temperature is as follows: defoaming temperature> striae removing temperature> supply temperature. Method.

(2) In the step of removing striae and the step of supplying, the stirring means controls the upward movement position according to the amount of the supplied molten glass, and causes the stirring means to stir only in the molten glass. The method for melting an optical glass according to the configuration (1), wherein

According to the constitution (1), a homogeneous molten glass can be obtained, and according to the constitution (2), even if the molten glass in the melting crucible decreases, the homogeneous molten glass can be supplied. .

[0033]

According to the method for melting optical glass of claim 1 of the present invention, it is possible to obtain a homogeneous molten glass having no change in optical characteristics and no mixing of bubbles and the like.

According to the optical glass melting method of the second aspect of the present invention, even if the molten glass in the container is reduced, the molten glass is always stirred at a position below the liquid level in the molten glass. And a homogeneous molten glass can be supplied.

Further, according to the optical glass melting apparatus of the third aspect of the present invention, a homogeneous molten glass can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between temperature and solubility of molten glass.

FIG. 2 schematically shows a melting apparatus according to an embodiment of the present invention, wherein FIG. 2 (a) is a plan view and FIG. 2 (b) is a cross-sectional view.

FIG. 3 is a sectional view showing a melting apparatus according to the embodiment of the present invention.

FIG. 4 is a longitudinal sectional view showing a conventional melting device.

FIG. 5 is a plan view showing a conventional melting device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 melting crucible 2 stirring blade 3 stirring motor 4 stirring blade driving actuator 5 supply nozzle 6 plunger 7 plunger driving actuator 8 crucible heater 9 nozzle heater

Claims (3)

[Claims] 1. A method for melting an optical glass by heating and melting an optical glass to form a molten glass, comprising: a step of defoaming molten glass in a single container at a defoaming temperature; and a step of defoaming the molten glass in the container. And a step of supplying at a supply temperature the molten glass striae-removed in the container at a supply temperature, the defoaming temperature, the stria-removal temperature and the supply. A method for melting optical glass, wherein a temperature relationship of temperature is defoaming temperature> striae removing temperature> supply temperature. 2. In the step of supplying the molten glass, the molten glass is stirred by a stirring means that moves between the bottom of the molten glass in the container and the liquid level so as not to come out of the liquid level. The method for melting optical glass according to claim 1, wherein: 3. A container for accommodating molten glass obtained by heating and melting optical glass; a stirring means for stirring the molten glass in the container; and a stirring means for moving the stirring means between the bottom of the molten glass in the container and the liquid level. An optical glass melting apparatus, comprising: a driving means for moving; and a control means for setting a moving distance by which the stirring means moves between a bottom portion of the molten glass and a liquid surface.