JP2008273800A - Glass flow path and method for manufacturing optical glass molded body using the flow path - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease generation of striae or devitrification in a glass flow path that normally has a tendency of an increase in the flow speed near the center, by equalizing the flow speed, and thereby, to provide a flow path for easily obtaining a high-quality glass block of a recent high refractive index glass or a low temperature softening glass the molding conditions of which are extremely difficult to determine. <P>SOLUTION: The flow path to be connected to a molten glass tank to allow the molten glass to flow is segmented into a plurality of portions by one or more partition plates disposed almost perpendicular to the out-flow direction of the molten glass, wherein the partition plate has a plurality of holes to allow the glass flow to pass through. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a technique for producing a predetermined amount of optical glass block.

  In recent years, in the field of optical devices such as digital cameras and projectors, there has been a demand for miniaturization and weight reduction, and accordingly, there is an increasing demand for aspheric lenses that can reduce the number of lenses used.

In general, the lenses constituting the optical system generally include a spherical lens and an aspheric lens. Many spherical lenses are manufactured by grinding and polishing a glass molded product obtained by reheat press molding a glass material. On the other hand, an aspheric lens is a method in which a heat-softened preform is press-molded with a mold having a high-precision molding surface, and the shape of the high-precision molding surface of the mold is transferred to a preform material, that is, It is mainly produced by precision press molding.

  As a precision press-molding preform, a spherical, elliptical or flat glass molded body (glass gob) is often used. These materials are melted in a melting apparatus such as a crucible and then melted in a melting apparatus. It can be manufactured by allowing it to flow out from a connected nozzle or the like onto a mold, forming it into plate-like glass or rod-like glass, and further cold-working them. Further, in recent years, molten glass flowing out from a flow path such as a nozzle is cut by a shear or separated by using surface tension, and flows down (drops) onto, for example, a porous mold that ejects gas, and then floats. A technique for adjusting the glass gob to an appropriate size and shape by molding is used. However, in the former case, traces of cutting by the shear may remain on the glass gob, so in recent years the latter is often used.

In any of the above means, when glass is caused to flow out of the flow path, in order to control the temperature and flow rate of the glass flow, or to prevent defects such as striae and devitrification occurring during molding, Various shapes have been devised for the nozzle. In recent years, various methods have been devised to cope with the increase in the liquid phase temperature and / or the decrease in the viscosity accompanying the increase in the refractive index of the optical glass, or the decrease in the viscosity associated with the softening at a low temperature. The current situation is not enough.

  In Patent Document 1, the diameter of the outlet is made larger than the diameter of the channel main body, for example, the molten glass outlet at the end of the channel is opened in a tapered shape so that the molten glass flow is longer than the channel outlet. Nozzles are described that can be held for a period of time to delay the timing of glass flow.

  In Patent Document 2, when molten glass starts to flow from a melting apparatus, passes through a pipe, and flows out from an outlet, the flow velocity distribution is made uniform by adding a constriction inside, and the modified glass in which the components are volatilized is disclosed. A method is described that suppresses retention and prevents striae. In addition, it is described that the temperature of the throttle portion is controlled to be higher than that other than the throttle portion in order to prevent the flow rate from being reduced due to the throttle.

  Patent Document 3 describes a method in which a resistance member is provided inside a flow path to reduce the flow velocity of the glass flow flowing through the center of the cross section of the flow path and increase the maximum weight of the glass gob that can be obtained.

JP-A-10-36123 JP 2003-306334 A JP-A-8-26737

However, the above conventional methods have the following problems.

In general, when molten glass is flowed out of a melting tank through a flow path and molded with a molding die, temperature control is performed by reducing the temperature from the melting tank to the outlet to a temperature suitable for molding. It is necessary to lower the molten glass temperature. Here, for example, striae derived from the volatilization of the glass component may occur after the outflow, but in this case, it is necessary to cope with this by lowering the flow path control temperature. However, the molten glass flow is a flow of a highly viscous fluid that goes from the high temperature side to the low temperature side, and the temperature inside the nozzle is low near the inner wall surface and high near the center of gravity of the cross section. Further, the flow velocity distribution is low near the inner wall surface and is high near the center of gravity of the cross section.

When control based on nozzle temperature measurement is performed, the measured temperature in the flow path represents the glass temperature in the vicinity of the inner wall surface almost accurately. The temperature of the passing glass stream) is a low temperature. Therefore, in glass with a high liquidus temperature, the flow path temperature (the glass temperature near the inner wall of the flow path) drops to the temperature at which crystals grow, the so-called devitrification temperature, before the glass flow center drops to a temperature at which no volatilization occurs. This may cause devitrification.

In the flow path described in Patent Document 1, since the outlet is tapered and the inner diameter is increased, the temperature difference and the flow velocity difference between the inner wall surface and the glass flow center are increased, and the above-described tendency is more prominent. Become.

When a flow path having a restriction as in Patent Document 2 is used, there is an effect of uniforming the flow velocity distribution of the glass flow, but a high temperature glass flow near the center of gravity of the cross section of the flow channel is taken out. Sometimes it is difficult to prevent striae from volatilization. If the control temperature is lowered to suppress volatilization, devitrification is likely to occur and grow immediately, thereby blocking the flow path of the throttle portion, and the outflow itself is likely to stop. In the example, in order to suppress the flow rate drop due to the restriction, the temperature of the restriction part is set to a temperature higher than that other than the restriction part, and it is clear that this is not a method suitable for the production of high refractive index glass in recent years. .

The flow path described in Patent Document 3 delays the flow rate of the molten glass at the center by a resistance member provided at the center of the inside, and the velocity distribution of the outflow rate is made uniform, but the heat capacity In a small resistance member mainly composed of a small noble metal, the glass flow center temperature immediately becomes high. Therefore, the effect of lowering the glass flow center temperature cannot be obtained, and there is no effect of suppressing striae derived from volatilization. Further, as shown in FIG. 3 in Patent Document 3, it is necessary to fix the resistance member using a support member, and it is extremely difficult to process the glass outlet channel mainly containing a noble metal such as platinum.

Further, in claim 4 of Patent Document 3, a plurality of channels are provided at the bottom of the crucible, and tip portions of the plurality of channels are connected to each other to form one channel port. However, the high temperature glass flow is generated at the center of each of the plurality of flow paths, and the effect of lowering the glass flow center temperature flowing down cannot be obtained. Applying such a complicated structure makes it very difficult to change the structure to adapt to the temperature, viscosity, wetting, density, and fluid pressure of the glass, which also complicates the flow rate and temperature distribution. However, a simpler structure was sought.

  In the present invention, the occurrence of striae and devitrification is usually reduced by averaging the flow velocity in the glass flow path where the flow velocity near the center tends to increase. As a result, the present invention provides a flow path for obtaining a glass lump of recent high refractive glass or low temperature softened glass which is very difficult to select molding conditions easily and with high quality. It is another object of the present invention to provide a flow path that enables simple and short-distance control even in conventional glass, and that can reduce the size of the apparatus.

The present inventors partition the flow path using a partition plate having a plurality of holes, and in some cases limit the area of the holes to a predetermined value in relation to the flow velocity, thereby averaging the temperature / flow velocity distribution. In addition to the above, the inventors have found that a desired temperature / flow velocity distribution can be obtained, and as a result, disadvantages such as striae can be suppressed, and the above problems have been solved.

A first configuration of the present invention is a flow path that is connected to a molten glass tank and allows molten glass to flow out, and is partitioned into a plurality of parts by one or more partition plates that are installed substantially perpendicular to the flowing direction of the molten glass. The partition plate is provided with a plurality of holes for allowing glass flow to pass therethrough.

According to a second configuration of the present invention, the plurality of holes provided in the partition plate have a smaller area as the distance from the center of gravity of the channel cross section is larger. is there.

In the third configuration of the present invention, at the partition plate installation position, a flow velocity at the center of the channel cross section when there is no partition plate is a, and b is a flow velocity at a position r away from the center of gravity of the channel cross section in the radial direction. B × c = a × d, where c is the cross-sectional area of the center hole of the partition plate to be installed, and d is the cross-sectional area of the hole located at a distance r from the center of the partition plate in the radial direction. The flow path of the configuration 2 is provided with a hole through which the glass flow passes so that the above is established.

According to a fourth aspect of the present invention, there is provided a glass molded body comprising melting a glass raw material in a melting tank and flowing a molten glass flow into a molding die through a nozzle connected to the melting tank. It is a manufacturing method of this, Comprising: It is the said manufacturing method including the process of averaging the temperature distribution in a flow path by allowing molten glass to pass through the flow path of the said structures 1-3.

  Hereinafter, the flow path of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. .

In the present invention, the “flow path” is connected to a melting tank for melting and / or holding molten glass, and the entire flow path and flow path through which the glass flow passes when the molten glass flows out into a mold (for example, a mold). It is a concept that includes an exit. That is, it is a concept that encompasses so-called pipes, orifices, and nozzles. The “flow path cross-sectional center of gravity” means, for example, the center when the cross section perpendicular to the outflow direction of the flow path is a circle or an ellipse, and the flow path cross-sectional center of gravity at the partition plate installation position is the partition plate at that position. This means the center of gravity of the cross section of the flow channel when there is no channel.

Normally, the temperature control of the flow path is also heated by various methods, but the temperature distribution of the molten glass flowing through the flow path is greatly influenced by the flow velocity in the flow path, and the cross-section of the flow path with the fastest flow velocity The vicinity near the center of gravity (the center in the cross-section direction when the channel cross section is substantially circular) is the highest, and the vicinity near the inner wall surface with the slowest flow velocity is the lowest. As described above, in the present invention, a partition plate is installed in the flow path to temporarily block the glass flow, or to slow down the flow velocity, thereby reducing the gap due to the temperature distribution and the position of the flow velocity. is there.

FIG. 1 is an example showing the flow path of the present invention. As shown in FIG. 1, the partition plate 1 is preferably in contact with the inner wall of the flow path 2. However, the installation method is not particularly limited, and it may be installed by welding, or it may be a fitting type by performing a process such as providing a groove on the inner wall of the flow path. If it is a built-in type, the partition plate can be appropriately changed depending on the type of glass to be melted. In addition, it is preferable that the partition plate is installed substantially vertically.

The material of the partition plate 1 is not particularly limited, but it is necessary to have both heat resistance and strength sufficient to withstand the thermal load and pressure load of the molten glass flow. Therefore, it is preferable to use a known platinum alloy, a reinforced platinum alloy in which a reinforcing material is dispersed, or a gold-containing reinforced platinum alloy with improved wettability.

The entire periphery of the partition plate is preferably in contact with the inner wall of the flow path. This is because if there is a gap between the periphery of the partition plate and the inner wall of the flow path, the effect of holding the partition plate is reduced and deformation is likely to occur. In addition, it is difficult to make precise adjustments between the holes provided in the partition plate described later and the flow velocity.

The partition plate is preferably provided with a plurality of holes for passing the molten glass flow. This is because when only one wide hole is provided as a hole for passing the molten glass flow, a new irregular temperature distribution is generated in a series of glass flows passing through the hole, and a new flow velocity bias is generated. It is because it becomes easy to produce. On the other hand, if only one narrow hole is provided, the blocking effect of the glass flow becomes excessive and the averaging of the temperature distribution can be promoted, but the flow of the glass flow deteriorates, so that devitrification is avoided. There is a fear that it will occur. Moreover, since the outflow rate is significantly reduced, it is not realistic from the viewpoint of productivity. Therefore, for these reasons, the cross-sectional area of the hole provided in the partition plate is preferably 10% or more, more preferably 20% or more, most preferably 30% or more, preferably 90% of the flow-path cross-sectional area. Hereinafter, it is more preferably 85% or less, and most preferably 80% or less.

The plurality of holes provided in the partition plate preferably have a smaller area as the distance from the center of gravity of the cross section of the flow path increases. That is, when the cross section of the flow path is substantially circular, the hole near the center of the circle is large and becomes smaller as the distance from the center increases.

As described above, the flow velocity of the glass flow flowing through the flow path becomes smaller as the vicinity of the flow path cross-sectional center of gravity becomes the earliest and approaches the flow path inner wall. On the other hand, the average flow velocity of the fluid flowing in the circular pipe also depends on the cross-sectional area of the flow channel, and the average flow velocity of the glass flow increases as the cross-sectional area of the flow channel decreases. In the present invention, since it is desired to average the flow velocity in the entire flow path, the flow velocity in the vicinity of the inner wall may be relatively increased as compared with the vicinity of the flow path center.

Since the partition plate of the present invention is provided with a plurality of holes, assuming that each hole is a small flow path, the flow rate is smaller when the glass flow is made to pass through the smaller holes than when the larger holes are passed. The effect of keeping large is great. Therefore, by passing the glass flow near the center of the flow path with a large flow velocity through a relatively large hole and passing the glass flow near the inner wall with a small flow velocity through the small hole, the gap in the flow velocity in the flow path that originally existed is relaxed, It becomes possible to realize a more uniform flow velocity distribution.

Specifically, when determining the size of the hole of the partition plate, it is preferable to determine as follows. When the flow rate at the flow path position where the partition plate is to be installed has a flow velocity at the flow path cross-section center of gravity when there is no partition plate, and the flow speed at a position r away from the flow path cross-section center of gravity in the radial direction is b, The relationship when the cross-sectional area of the hole at the center of the partition plate is c and the cross-sectional area of the hole at a position r away from the center of the partition plate in the radial direction is d is b × c = a × d. It is preferable to provide a hole. By providing the partition plate having such a relationship, the flow velocity distribution in the flow channel can be averaged, and disadvantages such as striae and devitrification are less likely to occur.

A plurality of the partition plates of the present invention may be installed in one flow path. In particular, since the glass flow that has passed through the partition plate also tends to generate a new flow velocity distribution as it passes through the flow path, it is possible to further promote the averaging of the flow velocity distribution by providing partition plates at a plurality of locations. it can.

The installation position of the partition plate is not particularly limited, but each position is determined in consideration of the thermal conductivity, heat capacity, flow path diameter, flow rate, desired temperature / temperature distribution, and the like of the glass. Although it naturally depends on the total length of the flow path, if it is too upstream, a new flow velocity distribution is likely to be generated even if the flow velocity distribution is once averaged, and it is difficult to obtain the effect expected in the present invention. Therefore, it is preferable to have one or more of the partition plates in a range of 50% downstream of the entire flow path, more preferably 45% downstream, and most preferably 40% downstream. Moreover, depending on the case, you may provide in the lowest end (namely, flow-path exit) of a flow path.

The flow path of the present invention does not hinder heating and / or cooling by the flow path itself and / or external addition means. As the heating of the channel itself, a known heating method by directly energizing the channel can be used, and as an external addition means, a known method such as a gas burner, an electric heater, infrared radiation, high frequency heating or the like can be used. You may use suitably. Further, by covering the vicinity of the glass outlet with a ring burner or the like and keeping it warm, defects such as devitrification and striae can be further suppressed.

The glass forming means using the flow path of the present invention is not particularly limited. As optical glass molding, it may be continuously flown out as a glass flow into a mold, and may be continuously molded into a plate-like or rod-like glass, etc., or the glass gob is separated by shear or surface tension, and on a porous mold. A glass gob may be formed by floating molding.

As the material of the flow path of the present invention, materials usually used in the glass melting process can be used, for example, platinum, reinforced platinum, gold, reinforced gold, rhodium, other noble metals and their alloys, or quartz. Can be used. Further, a material plated by a known method, for example, platinum having a gold-plated inner surface or a ceramic film such as SiC may be used.

Since the present invention defines the internal structure of the flow path, the atmosphere in the vicinity of the flow path outlet may be appropriately changed. For example, a nitrogen atmosphere or an inert gas atmosphere such as argon may be used. In some cases, the channel outlet may be covered with a heated atmosphere.

Specific examples of the present invention are shown below.

Example 1
In this example, the optical glass is melted in a platinum crucible, and the molten glass is discharged from the outlet at the end of the molten glass through a flow path connected to the crucible. The glass gob for use as a precision press-molding preform was obtained.

As the flow path, a reinforced platinum flow path having the same shape as that shown in FIG. 3 was used. Here, the inner diameter of the flow path is 3 mm (cross-sectional area 7.07 mm ² ), and the outlet is expanded to 6 mm. The total length of the channel, that is, the length from the outlet of the crucible to the outlet at the end of the channel was 2 m.

The partition plate in the flow path was attached to a point 50 mm from the outlet and the thickness was 1 mm. The area of the glass flow path at the part where the partition plate was attached was 3.23 mm ² . That is, the flow path cross-sectional area where the partition plate was installed was about 46% of the place where the partition plate was not installed.

The receiving mold was made of porous stainless steel, and received molten glass in a state where air was blown from the receiving surface thereof. Thus, the molten glass floated from the receiving mold to receive glass gob.

The glass used was melted optical glass mainly composed of boron oxide and lanthanum oxide. The crucible was kept at about 1200 ° C., and the outflow pipe was kept at about 1100 ° C. by electric heating. From the outlet, the molten glass was separated into droplets. The amount of molten glass flowing out at this time was 80 g per minute.

When this glass gob was visually observed for optical defects such as devitrification and striae, such a defect could not be found, and it was a high-quality glass gob that could be used as a preform for molding an optical element.

Overall flow diagram of the present invention

Explanation of symbols

1 partition plate 2 flow path 3 hole provided in the partition plate

Claims (4)

A flow path that is connected to a molten glass tank and allows molten glass to flow out, and is partitioned into a plurality of portions by one or more partition plates installed substantially perpendicular to the direction of flow of the molten glass. The said flow path characterized by providing a plurality of holes for passing. The flow path according to claim 1, wherein the plurality of holes provided in the partition plate have a smaller area as the distance from the center of gravity of the cross section of the flow path increases. At the partition plate installation position, the flow velocity at the center of the channel cross section when there is no partition plate is a, and the flow velocity at a position r away from the center of gravity of the channel cross section by r in the radial direction is b. When the cross-sectional area of the hole is c and the cross-sectional area of the hole at a position r away from the center of the partition plate in the radial direction is d, the glass flow is set so that the relationship b × c = a × d is satisfied. The flow path of Claim 2 provided with the hole to let it pass. A method for producing a glass molded body, comprising melting a glass raw material in a melting tank, and flowing a molten glass flow into a mold through a nozzle connected to the melting tank to form a glass molded body. The said manufacturing method including the process of averaging the temperature distribution in a flow path by allowing the flow path in any one of Claims 1-3 to pass through.