JPS62270423A - Forming of glass lens - Google Patents

Abstract

PURPOSE:To form a lens having uniform section and high accuracy, in high efficiency, using a liquid-drop method, by passing a glass droplet through a hollow conical guide having wide top opening and narrow bottom and dropping the droplet on a mold. CONSTITUTION:Molten glass 2 in a crucible 1 is spontaneously dropped on a mold 15 from the tip of a nozzle 4 in the form of a liquid droplet 6. In the above process, the droplet 6 is passed through a hollow conical guide 16 having wide top and narrow bottom openings. The guide 16 is made of iron, carbon, etc., and lined with SiC, Si3N4, etc. The bottom diameter of the guide 16 is about 1.02-2 times the diameter of the glass droplet 6, the top diameter of the guide 16 is about 1.5-10 times the diameter of the guide bottom and the height of the guide 16 is about 3-10 times the diameter of the glass droplet 6. The guide 16 is heated at about 300-500 deg.C. The tip diameter of the nozzle is about 0.5-15mm, the distance between the guide 16 and the mold is about 1.1-3 times the diameter of the glass droplet 6 and the distance from the nozzle tip to the guide 16 is about >=50cm.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. Detailed Description of the Invention Field 1 The present invention relates to a method for directly molding a non-polished glass lens with high precision.

Conventional methods for manufacturing non-polished glass include the 4-filtration droplet method, in which molten glass is dropped from the tip of a nozzle, the dropped glass droplets are received by a mold, and press molding is performed. No defects such as scratches, sand 1-1, jar marks, etc. on the surface of 1. A great way to get /ins and 1. The present invention was developed by On et al. and has already been filed (Japanese Patent Application No. 267058/1983).3 The droplet method is an excellent method for manufacturing non-abrasive glass, but there are some points that need to be improved. points have been discovered. In order to clarify the need for such improvements and the problems, the first
The droplet method will be explained in more detail using figures.

The droplet method uses melted glass (2) in a crucible (1).
At the tip of the nozzle (4), a liquid droplet of a certain size is applied. The area from the crucible (1) to the tip of the nozzle (4) is heated by heaters (5a) to (5(1)) so that the molten glass does not cool down and become solid. A glass droplet (6) controlled to fall naturally from the tip of the nozzle (4) (hereinafter such a glass droplet is referred to as a glass gob) is placed on a suitable metal plate placed at the point where the glass gob falls. It is collected in a mold, and immediately after collection, it is moved from the point where the glass droplets fall and is pressed with mold 1-4.

In the second half of the droplet method described above, the present invention involves collecting glass droplets on a mold after they fall from the tip of a nozzle.
This is an improvement over L from ~ro to ro.

Conventionally, the mold was installed so that the center point of the collecting mold was directly below the center point of the nozzle (4).

However, even with such a setting, the collection position of the glass gob will inevitably be shifted from the center point of the mold. Therefore, if press molding is carried out using the second mold in this state, the lens will have some thickness, which makes it difficult to achieve precision in the final molding process of the lens. Therefore, it has been difficult to obtain a lens with a good yield that has uniform thickness and is valuable as a commercial product, with the optical axis and physical center coincident.

Problems to be Solved by the Invention In the droplet method for manufacturing non-polished glass lenses, when glass gobs are collected, the collection position inevitably deviates from the center point. As a result, after the glass gob is molded, a piece of wall occurs in the glass lens, resulting in a misalignment between the optical axis and the physical center, resulting in a problem in which the precision of the lens is reduced.

Furthermore, the above causes poor yield in manufacturing glass lenses.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for molding a non-polished glass lens that can solve the above-mentioned problems in the droplet method and can be manufactured with high precision and efficiency.

Means for solving the problem, that is, the present invention, when forming a glass lens by the droplet method, drops a glass droplet onto a mold through a hollow conical guide that is wide at the top and narrow at the bottom. The present invention relates to a method for molding a glass lens, characterized in that:

According to the present invention, it is possible to efficiently obtain a highly accurate lens without any unevenness.

According to the present invention, when a glass droplet is dropped onto a mold through a hollow conical guide with a wide upper part and a narrow lower part, the glass gob falls within a diameter range of 0.2 mm from the center of the mold. When the guide of the present invention was not provided, the product would fall within a range of 3° to 6 mm in diameter from the center of the mold. Therefore, according to the present invention, the position of the drop of the glass gob onto the mold can be controlled very accurately. As a result, the production yield of glass lenses is 80% compared to when no guide is provided.
This has improved from 95% to 95%.

The guide used in the present invention has a hollow conical structure that is wide at the top and narrow at the bottom. In this specification, "two parts"
is relative to the point where the glass droplet begins to drip, along the line along which the glass droplet falls, and "bottom" is relative to the point where the glass droplet begins to drip, along the line along which the glass droplet falls. It refers to the one that is far away.

It is sufficient that the diameter of the lower part of the guide is large enough to allow the falling glass gob to pass through. The maximum value of the glass gob obtained by the droplet method 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 about 150 to 600 dyne/Qx, and the maximum weight of the gob obtained by the droplet method varies depending on the surface tension of the glass. Each number is about 1 to 59. For example, lanthanum-based glass with large surface tension horns can yield about 4 to 59 gobs, but heavy flint glass with low surface tension can yield gobs of about 2 to 3 grams.

On the other hand, the minimum size of the glass gob that can be manufactured is determined mainly by the diameter of the nozzle tip.The nozzle is made of precious metals such as platinum to prevent coloring of the glass, but it is difficult to process, so the diameter of the tip The practical lower limit is 0.5πm
Therefore, the minimum value of the gob is about 5 (Jtttg). Therefore, from this, the diameter of the lower part of the guide should be 1.02 to 2 times the diameter of the glass gob, preferably 1.
05 to 1.5 times, more preferably 1.05 to 1.2 times. If it is larger than 1.0 times, there is no effect of providing a guide, and if it is smaller than 1.02 times, the glass gob will not be able to pass through.

The size of the top part of the guide is 1.5 to 10 times the size of the bottom part.
Set to 2 times, preferably 2 to 5 times. If it is larger than 10 times, it will not come into contact with the glass gob and it is meaningless, and if it is smaller than l,5 times, the falling glass gob will not fall into the guide.

The height of the guide is 3 to IO times the diameter of the glass gob, preferably 5 to 7 times. If it is smaller than 3 times, the glass gob may get stuck in the guide, and if it is larger than 10 times, it is inconvenient to adjust it on the mold.

Materials that can be used for the guide of the present invention have good thermal conductivity. Carbon, tungsten carbide, iron, stainless steel, etc. can be used as such materials.

However, since stainless steel, iron, etc. have poor thermal conductivity compared to other materials, it is desirable to avoid using them as much as possible unless the glass droplets are sufficiently cooled. If the thermal conductivity is poor, when the glass gob comes into contact with the guide, sink marks are likely to occur on the surface of the glass gob, and the glass gob adheres to the surface of the guide and cannot pass through the guide.

The hollow conical surface provided in the guide preferably has a mirror finish. By doing so, the surface becomes smoother and even if the glass gob comes into contact with the guide, the surface of the glass gob will not become a scratched surface.

Furthermore, it is preferable that the hollow conical surface provided in the guide is resistant to oxidation. If oxides are formed on the surface, the oxides will adhere to the falling glass gob, resulting in poor quality glass lenses. In the present invention, since high-temperature glass droplets come into contact with each other, a material that does not oxidize at a temperature of at least 500° C. is used.

For this reason, when the guide is made of iron or carbon, the surface of the hollow cone is preferably coated with 5iXSiC, Si3N, Cr, or the like. In particular, it is preferable to coat iron with Cr or S I 3 N 4 and coat carbon with Sj or SiC.

The guide of the present invention is installed so that the center of the guide and the center of the mold coincide. Further, a distance of 1.1 to 3 times, preferably 1.1 to 2 times the diameter of the glass gob is provided between the guide and the mold. If I is larger than 3 times, the effect of providing the guide of the present invention cannot be obtained, and if I is smaller than 1 time, it becomes impossible to move the glass gob that has fallen onto the mold. However, if a means is provided to move the guide so as not to affect the glass gob after it falls into the mold, the lower limit does not need to be considered.

Although the guide of the present invention varies depending on the type of glass used, it is preferable to heat the guide to 300 to 5O-7=0°C using an appropriate heating means. By doing so, it is possible to reduce the length of the glass gob. If the temperature is set higher than the softening temperature of the glass, it will fuse.

The glass gob is preferably allowed to pass through the glass and fall onto the mold while the surface of the glass droplet is lower than the softening temperature of the glass. Otherwise, the problem of glass droplets adhering to the surface of the guide is likely to occur.

Therefore, temperature control of the glass gob is an important factor in the practice of this invention. The method for controlling the temperature of the glass gob will be explained below, taking the droplet method shown in FIG. 1 as an example.

As shown in FIG. 1, the glass gob is manufactured by allowing molten glass (2) in a crucible (1) to fall naturally from the tip of a nozzle (4).

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.

=8- The crucible is equipped with a stirrer (3) and a heating heater (5a).

The temperatures of the crucible (1) and nozzle (4) are maintained at desired temperatures by adjusting the heaters (5a, 5b, 5c, 5d). The temperature of the crucible (1) and nozzle (4) may be set depending on the properties of the glass, the size of the gob to be obtained, etc., and is usually 500 to 14
It is within the range of 00°C. In particular, if the temperature of the lower and upper parts of the nozzle (4) is set high in the lower part and low in the two sides, it becomes easier to drop the glass droplet (6). Preferably, the lower part is higher than the upper part by about 50 to 200°C.

Since the temperature of the two feet 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 provide means for automatically controlling these temperatures. As a means for this, it is preferable to control the temperature of the glass droplet at the tip of the nozzle by controlling the time it takes for the glass droplet to fall from the time it is formed at the tip of the nozzle. Specifically, for example, a light beam (9) that passes through the nozzle tip is emitted by a light emitter (8), and a light receiver (10) that senses the light.
is placed on the nozzle tip 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 (12), and controls the control unit (12) according to the amount of change in the time. A heating heater (5a) provided in the nozzle and, if necessary, in the crucible.

5b, 5c, 5d) may be adopted.

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 0.5~15 rtr
m, preferably 0.5 to IOx*. If the diameter of the nozzle tip is too large, the glass flowing out will overcome the surface tension and the flow will become laminar, making it impossible to obtain glass droplets.

The glass that comes out of the nozzle tip lies flat due to surface tension and falls one by one.

The falling distance varies depending on the ambient temperature, the size of the glass droplet, the temperature, the thermal conductivity of the glass, and whether a forced cooling means is installed. In the case of , generally 5 to guide (I6)
A falling distance of 0 cn or more, preferably 200 cβ or more is taken.

Although not shown in FIG. 1, the falling distance may be adjusted by moving the mold (15) downwards.

In this case, it is preferable that the guide is also configured to move downward in conjunction with the movement. If the configuration is not linked up and down, the distance between the guide and the mold should not be wider than 3 times the diameter of the J glass gob as described above. Also, the same control used for nozzle temperature adjustment as described above should be used. The control unit may be actuated based on signals from the light receiver and the radiation thermometer to lower the support base and adjust the falling distance.

Alternatively, the glass droplets may be forcibly cooled, in which case a method such as blowing air from below the nozzle to shorten the falling distance may be adopted.

If the falling distance is short and the temperature of the glass droplet surface does not become lower than the softening temperature of the glass, the gob surface will sink or be scratched when it comes into contact with the guide, and furthermore, the glass droplet will land on the guide surface. Problems are likely to occur.

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.

This method does not require reheating the glass gob during lens molding, and since the surface temperature of the glass droplet is below its softening temperature, it does not stick to the guide or mold, making it very effective.

Further, in the present invention, as shown in FIG. 1, a radiation thermometer (11) is provided to measure the temperature of the glass droplet, and a signal regarding the measured value is sent to the control unit (12) to form the glass droplet. Depending on the amount of change in time from drop to drop and the temperature of the glass droplet, the heater (5a).

5b, 5c, and 5d) may be controlled.

The glass gob is molded by pressing with the upper mold while the internal temperature of the glass gob collected in the mold (5) J2 is maintained at a temperature higher than the softening temperature. Mold to collect (1
5) may be convex or concave.

It is possible to manufacture lenses by press-molding the fallen glass droplet on the spot while its internal temperature remains below its softening temperature, and then moving the mold to a predetermined position and pressing it. You may.

The two-part mold may be concave or convex.

The lower mold (15) and the upper mold may be heated by a heater (14) through a heating plate (13) to control the temperature of the glass cob. The temperature of the lower mold (I5) is 10 to 150°C, preferably 30 to 100°C, higher than the softening temperature of the glass used.
It is preferable to keep it heated to a temperature as low as 0.degree.

By doing so, a lens with high surface precision can be molded and has the effect of preventing fusion between the mold and the glass. The upper mold is preferably heated to a temperature that is 10 to 150°C, preferably 30 to 100°C lower than the softening temperature of the glass used. By doing so, it has the same effect as the lower mold.

According to the present invention, various lenses such as double-sided convex, double-sided, single-sided convex, single-sided, single-sided convex and single-sided, etc. can be manufactured accurately and efficiently by roughly selecting the upper mold and the lower mold. can.

Example 1 Heavy flint glass (SP
II) Add 1.13Q and heat it at 1000°C (
The thermocouple (+9) was heated and melted. The glass was dropped by controlling (5b) to (5d) with the control device (12) so that the dropping glass (6) was at 900° C.±2° C. and the dropping interval was 5 seconds to 01 seconds. A mold (15) with a radius of curvature of 20 mm and a guide (+6) with a part diameter of 30 mm, a lower part diameter of 6 mm, and a height of 25 mm were set 2 m vertically below the nozzle to receive the falling glass droplet (7). . At this time, the guide (+6) was heated to 350° C. by the heater (18) to prevent the glass droplets from cooling down when they hit the guide (16).

The average deviation between the center of the glass droplet (17) and the mold (15) was 0.1 mm.

Similarly, when the guide (16) was not used and the glass droplet (17) was dropped 100 times, the average deviation between the mold (15) and the glass droplet (17) was 1.
It was 8 mm.

When the present invention is applied to the droplet method, it is possible to efficiently obtain a glass lens with high precision in which the optical axis and the physical center coincide.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the droplet method. (1) Platinum crucible, (2) Molten glass, (3)
Stirrer, (4) Platinum nozzle, (5a), (
5b), (5C), (5d) Heater, (6) Glass droplet (before dropping), (7) Glass droplet (during dropping), (8) Emitter, (9) Ray (10) Light receiver, (11) Radiation thermometer, (1
2) Control device, (13) Hot plate, (14) Heater, (15) Mold, =15- (16) Dripping guide, (17) Glass droplet, (
18) Heater, (19) to (23) thermocouple

Claims (1)

[Claims] 1. A method for forming a glass lens by dropping a glass droplet onto a mold through a hollow conical guide with a wide upper part and a narrow lower part.