JPH0432772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a glass gob, and more particularly to a method and apparatus for obtaining a glass gob with high weight accuracy and no sink marks or scratches. This glass gob is particularly useful as a material for non-abrasive lenses.

(Prior Art) Lenses are manufactured from glass gobs or press-molded products called blanks.

Conventional gobs are manufactured by cutting round glass rods or cutting molten glass, and both have scratches, grains, shear marks, sink marks, etc. on their surfaces, which are then molded using lens molds. Even if there are scratches or sand marks,
Only lenses with surface defects due to shear marks, sink marks, etc. can be obtained. Therefore, conventional lenses require surface polishing to remove surface defects during the manufacturing process. This surface polishing is the most labor-intensive step in the lens manufacturing process, and a technique for producing lenses directly from gobs has been considered.

Conventional glass gobs are obtained by cutting the glass flowing from a melting crucible through a nozzle into an appropriate size with an opening/closing blade, or by pushing the molten glass in the crucible out of the nozzle with a plunger. The former is difficult to manufacture in a small size and has a complicated mechanism. Also, since the blade cuts hot glass, the glass may become burnt onto the blade. Furthermore, cut marks called shear marks left by the blade remain on the glass, and even if these marks are molded with a lens mold, they remain as surface defects on the molded lens. The latter is not suitable for optical glasses because it is used only for glasses with comparatively high drop viscosity, and the plunger prevents the glass from becoming uniform and makes stirring difficult.

There is also a method of stacking thin glass rods, cutting them, and then forming them into gob shapes, but there is a large loss due to the thickness of the blades, and the accuracy is not very good. Further, since the end face is a sanded surface, even if it is molded with a lens mold, the grain remains as a surface defect on the molded lens.

(Problems to be Solved by the Invention) The present invention provides a method for manufacturing glass gobs without shear marks, grains, scratches, sink marks, etc. that have conventionally been an obstacle in lens manufacturing, and an apparatus for manufacturing the glass gobs. The purpose is to provide.

(Means for Solving the Problems) The present invention first controls the temperature of the lower part of the nozzle to be 50 to 200°C higher than the temperature of the upper part of the nozzle, and at the same time, drops of glass melted in the melting crucible are dripped from the tip of the nozzle. The present invention also provides a method for manufacturing a glass gob, in which a glass gob is obtained by continuing to fall the molten glass droplets until the surface temperature thereof becomes lower than the softening temperature of the glass.

Second, the present invention includes a melting crucible for melting glass, a nozzle provided at the bottom of the melting crucible to drop the molten glass as glass droplets, and a temperature at the lower part of the nozzle that is 50°C higher than the temperature at the upper part of the nozzle.
Provided is a glass gob manufacturing apparatus characterized in that it is equipped with a temperature control means for controlling the temperature higher by ~200°C.

As shown in FIG. 1, the glass gob of the present invention allows glass 2 molten in a crucible 1 to fall naturally from the tip of a nozzle 3 until the surface temperature of the falling molten glass drops becomes lower than the softening temperature of the glass. , produced by dropping a drop of glass until the glass surface solidifies. When the glass surface cools below its softening temperature, it can be collected in a suitable receiver without causing shear marks or sink marks on the surface.

Therefore, when the glass gob thus obtained is placed in a mold and molded, a lens with no surface distortion can be obtained. This can be used as is as a non-polished lens.

The crucible and nozzle are preferably made of platinum in order to prevent coloring of the glass, as in the case of ordinary optical glass melting, but the crucible and nozzle are not limited thereto.

The crucible is equipped with a stirrer 4 and a heating heater 5a.

The temperatures of crucible 1 and nozzle 3 are maintained at desired temperatures by adjusting heaters 5a, 5b, 5c, and 5d. Crucible 1 and nozzle 3
The temperature can be set according to the properties of the glass, the size of the gob you are trying to obtain, etc., and is usually 500 to 1400℃.
is within the range of In particular, if the temperature of the lower and upper parts of the nozzle 3 is set high in the lower part and low in the upper part, the glass droplet 6 can be easily dropped. Preferably, the temperature of the lower part is about 50 to 200°C higher than that of the upper part.

Since the above-mentioned temperature affects the surface tension of the glass, that is, the size of the glass droplet, it is necessary to precisely control this temperature in order to obtain a glass gob with high weight accuracy. In order to precisely control the nozzle temperature and, if necessary, the glass temperature in the crucible, it is preferable to take measures to automatically control these temperatures. As a means for this, it is preferable to control the time from when a glass droplet is formed at the tip of the nozzle until it falls, that is, the dropping time of the glass droplet and the temperature of the glass droplet at the tip of the nozzle. Specifically, for example, a light emitter 8 emits light 9 passing through the nozzle tip,
A light receiver 10 that senses the light is placed at the tip of the nozzle, facing the light emitter, measures the time from the formation of the glass droplet to its fall, sends a signal corresponding to the measured value to the control unit 11, and sends a signal corresponding to the measured value to the control unit 11. A method may be adopted in which the amount of current applied to the nozzle and, if necessary, the heating heaters 5a, 5b, 5c, and 5d provided in the crucible is controlled according to the amount of change in the amount of change.

The nozzle tip diameter is a factor that affects the weight of the glass droplet. That is, the weight of a glass droplet is approximately expressed as mg=2πrγ (m: weight, r: nozzle tip diameter, γ: surface tension). Generally, the nozzle tip diameter is 0.5 to 15 mm.
Preferably it is 0.5 to 10 mm. If the nozzle tip diameter is too large, the glass flowing out will overcome the surface tension, resulting in a laminar flow, making it impossible to obtain glass droplets.

The glass that comes out of the nozzle tip falls one after another in the form of drops due to surface tension.

The glass droplet 6 is allowed to fall until its surface temperature becomes lower than the softening temperature of the glass. The falling distance varies depending on the ambient temperature, the size of the glass droplet, the temperature, the thermal conductivity of the glass, whether a forced cooling means is provided, etc. Normally, the temperature may be considerably lower than the softening temperature, and in some cases, the interior may be cooled to a temperature considerably lower than the softening temperature. Therefore, in the case of natural fall at room temperature, the falling distance is generally 150 cm or more, preferably 200 cm or more.

The falling distance may be adjusted by moving the support base 12 of the receiver 7 up and down. In this case, the same control means used for adjusting the nozzle temperature described above may be used, and the control section may be actuated based on signals from the light receiver and the radiation thermometer to raise and lower the support base and adjust the falling distance. .

Further, the glass droplets may be forcibly cooled, and in that case, a method may be adopted in which air is blown from below the nozzle to shorten the falling distance.

If the falling distance l is short and the temperature of the surface of the glass droplet does not become lower than the softening temperature of the glass, sinks or scratches will occur on the gob surface when it comes into contact with the receiver, making it unsuitable as a gob for molded lenses. If the falling distance is long enough, the glass droplet will be sufficiently cooled and a nearly spherical gob will be obtained.

The resulting glass gob does not necessarily have to be perfectly spherical, but may be an ellipsoid with a thickness sufficient to obtain the desired lens.

The glass droplet receptacle may be a metal plate receptacle with a recess inside, a mold for a lens, etc., but is not limited to this. In general, the specularity of the receiver is not a problem if it is completely solidified with a sufficient falling distance, but if it is cooled and solidified after hitting the receiver, it is preferable to use a well-polished receiver. In addition, the higher the thermal conductivity of the receiver, the less likely it is to cause sink marks on the glass gob. Therefore, if the falling distance is shortened and the glass droplets are collected into the receiver before they are sufficiently cooled,
It is preferable to use a receiver having high thermal conductivity such as copper or carbon.

When the falling distance is long and the glass droplets are sufficiently cooled, stainless steel or aluminum can also be used. These receivers may be transported to a predetermined location by moving the support stand as shown in Figure 2, or the glass droplets that have fallen into the receivers may be rolled along a sloped groove and brought to a predetermined location. May be collected. Alternatively, after allowing a sufficient fall distance and cooling the gob, it may be collected in a water or oil bath. In this case, the cooling distance is 2
If the temperature is around m, the gob will be too hot and will crack, so forced cooling such as air cooling is required. Alternatively, the lens 14 may be manufactured by collecting the fallen glass droplets into the lens molds 7 and 13 while their internal temperature is maintained at a temperature higher than the softening temperature, and press-molding them on the spot. With this method, there is no need to reheat the glass gob during lens molding, and since the glass droplet surface temperature is below its softening temperature, it does not stick to the mold, making it very effective. The resulting glass gob has no shear marks or sink marks,
A lens obtained by press-molding this has no surface distortion and can therefore be used as an optical lens.

That is, the polishing step can be omitted.

The maximum value of the glass gob obtained in the present invention is mainly controlled by the surface tension of the glass. The surface tension of various optical glasses in the melting temperature range (700 to 1500°C) is approximately 150 to 600 dyne/cm, and the maximum weight of the gob obtained by the method of the present invention varies depending on the surface tension of the glass. Each amount is about 1 to 5 g. For example, gobs of about 4 to 5 g can be obtained with lanthanum glass, which has a high surface tension, but gobs of about 2 to 3 g can be obtained with heavy flint glass, which has a low surface tension. On the other hand, the minimum value of the glass gob that can be manufactured is mainly determined by the nozzle tip diameter. The nozzle is made of precious metals such as platinum to prevent the glass from discoloring, but since it is difficult to process, the practical lower limit of the tip diameter is
around 0.5mm, therefore the minimum value of the gob is 50mg
That's about it.

In addition, in the present invention, as shown in FIG. 2, a radiation thermometer 15 is provided to measure the temperature of the glass droplet, and a signal regarding the measured value is sent to the control unit 11. The heaters 5a,
The amount of current flowing through 5b, 5c, and 5d may be controlled.

Note that the present invention is applicable to almost all optical glasses.

The present invention will be explained below with reference to Examples.

Example: Heavy flint glass (1.8 mm) was placed in a platinum crucible with an inner volume of 2 and equipped with a platinum nozzle with an inner diameter of 10 mm, a tip diameter of 5 mm, and a length of 1000 mm at the bottom, and the glass was heated for 1000 minutes under stirring.
It was heated and melted at ℃. The upper part of the nozzle (400mm) is 800±
While heating the nozzle middle (400 mm) to 850 ± 2 °C and the nozzle lower part (200 mm) to 900 ± 2 °C, the molten glass was allowed to drip naturally.

A mirror-finished stainless steel mold for convex lenses with a diameter of 10 mm, depth of 0.36 mm, and radius of curvature of 34.9 mm was placed 3 m below the nozzle to catch the falling glass droplets, and press molded at 400°C to obtain 100 glass lenses. Ta. The weight of the glass lenses obtained was in the range of 277 to 283 mg, with an accuracy of ±1%. Further, when the glass surface was observed under a microscope, there were no scratches or distortions due to shear marks or sink marks on the surface, and it could be used as is as an optical lens without polishing.

(Effect of the invention) The gob obtained by the method of the present invention does not have scratches, grit, sink marks, shear marks, etc. that cause problems in optical lens molding, and the gob obtained under certain conditions has a very high weight. It had precision.

Further, according to the present invention, the gob can be obtained using a simple device and operation, and its weight accuracy can be controlled extremely easily. Moreover, it is economical with less glass loss.

The gob obtained by the method of the present invention has no scratches, grit, sink marks, etc.
Since it does not have shear marks or the like, by press-molding it, it can be used as it is as an optical lens, eliminating the need for conventional polishing work.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of the apparatus of the present invention. 1... Crucible, 2... Molten glass, 3... Nozzle, 4... Stirrer, 5a, 5b, 5c, 5d...
Heater, 6... Glass droplet, 7... Receiver, 8...
Emitter, 9... Light, 10... Light receiver, 11... Control unit, 12... Support stand, 13... Lens mold, 1
4... Lens, 15... Radiation thermometer.

Claims (1)

[Claims] 1. The temperature of the lower part of the nozzle is controlled to be 50°C to 200°C higher than the temperature of the upper part of the nozzle, and the glass droplets melted in the melting crucible are dropped from the nozzle tip, so that the surface temperature of the molten glass droplets is lowered. A method for manufacturing glass gobs, in which glass gobs are obtained by continuing to fall until the temperature drops below the softening temperature of glass. 2. The method for manufacturing a glass gob according to item 1, wherein the temperature of the lower part of the nozzle is controlled to be 600°C to 1400°C, and the temperature of the upper part of the nozzle is controlled to be 500°C to 1350°C. 3 A melting crucible for melting glass, a nozzle provided at the bottom of the melting crucible to drop the molten glass as glass droplets, and a temperature at the lower part of the nozzle that is controlled to be 50°C to 200°C higher than the temperature at the upper part of the nozzle. A glass gob manufacturing device characterized by comprising: a temperature control means for producing a glass gob. 4 The temperature control means controls the temperature of the lower part of the nozzle to 600℃.
Control the temperature between ℃~1400℃ and the temperature of the upper part of the nozzle to 500℃.
4. The glass gob manufacturing apparatus according to item 3, wherein the glass gob manufacturing apparatus is controlled at a temperature of 1350°C to 1350°C. 5. The glass gob manufacturing apparatus according to item 3, wherein the temperature control means performs temperature control based on the time from when the glass droplet is formed at the tip of the nozzle until it falls. 6. The glass gob manufacturing apparatus according to item 3, wherein the temperature control means performs temperature control based on the temperature of the glass droplet formed at the tip of the nozzle.