JPH03137025A - Method and apparatus for producing glass lens - Google Patents

Abstract

PURPOSE:To prevent problems, such as sink mark, even if the falling distance of the glass drop formed at the tip of a nozzle is short by arranging nozzle temp. control means in such a manner as to heat only the tip of the nozzle without heating the glass drop. CONSTITUTION:Glass 2 is melted in a crucible 1 and is kept heated by heaters 5a to 5c so that the molten glass does not cool and solidify. The heating at the tip of the nozzle is executed by, for example, IR heating in such a manner that the IR rays radiated from an IR lamp 13 are reflected by a reflecting mirror 14 and are condensed to the tip of the nozzle 4, by which only the tip of the nozzle 4 is heated and the glass drop 6 is not heated. The glass drop 6 itself is not heated even in the event of falling of the IR rays onto the glass drop 6 as the wavelength is 1 to 2 mum in the case of the IR heating. The glass drop 6 falls by gravity from the tip of the nozzle 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved method and apparatus for manufacturing unpolished glass lenses.

Conventional technology The method for producing unpolished glass is the droplet method, in which molten glass is dropped from the tip of a nozzle, the falling glass droplets are received by a lower mold, and press-formed. An excellent method for obtaining lenses free of such defects has been developed by the present inventors and has already been filed (Japanese Patent Application No. 59-267058).

Although the droplet method is an excellent method for producing unpolished glass, several points that need improvement have been found. In order to clarify the issues requiring such improvements,
The droplet method will be explained in more detail with reference to FIG.

In the droplet method, first a glass (2) is melted in a crucible (1).
is made into liquid droplets of a certain size at the tip of the nozzle (4). The area from the crucible (1) to the tip of the nozzle (4) is heated by heaters (5a) to (5d) so that the molten glass does not cool down and become solid. Next, a glass droplet (6) controlled to a predetermined size and temperature is allowed to fall naturally from the tip of the nozzle (4), and is collected in an appropriate mold (12) installed at the point where the glass droplet falls. death,
After collection, move from the falling point of the glass droplet to the upper mold (13)
to obtain an unpolished glass lens. Alternatively, it is also possible to collect it in a water or oil bath without collecting it in the mold (12), and then press molding.

The heater (5d) heats not only the nozzle tip but also the area below the nozzle tip, and the entire glass droplet formed at the nozzle tip is heated in a uniform atmosphere to a uniform temperature. .

However, depending on the method of collecting with the mold (12), if the falling distance (C) from the nozzle tip to the lower mold is short, so-called "sink marks" may occur. Hike is the 6th
It can be thought of as a depression that occurs near the center of the lens, as shown in Figure d. This sink is shown in Figures 6-a to 6-
It is thought that this occurs due to the mechanism shown in Figure d. That is, FIG. 6a shows the state when the dropped glass droplets are collected on the mold. In the figure, the shaded area indicating the peripheral area where the glass droplet is in contact with the mold is where it solidifies faster than any other part, and after dropping the glass droplet, it solidifies along the shape of the mold. be done. However, the center part where the glass droplet is in contact with the mold (the part between the hatched parts) is not completely solidified and is in a softened state due to the heat from the high temperature part that remains inside the glass droplet. This is thought to be the case, and that portion is pulled upwards due to contraction as the entire glass droplet cools while moving through the mold. As a result, as shown in Figure 6-b, an air pocket is formed in the center of the glass droplet, and in this state, the
Since the molding is performed using the upper mold as shown in Figure 1-c, whiskers are formed on the resulting glass lens.

Another problem is that conventionally, the glass droplet (6) must be allowed to fall until it reaches a temperature lower than its surface temperature or the softening temperature of the glass, so the falling distance (12) of the glass droplet is Generally, 150 cm to 200 cm or more was required. If the falling distance is long like this, the mold (1
2) The position at which the lens falls is slightly different, and the quality of the resulting lens mold shape is also not the same (this failure to faithfully transfer the mold shape is referred to as "poor transferability").

In order to eliminate poor transferability, if the falling distance is shortened,
The problem of sink marks mentioned above becomes more noticeable. Furthermore, in the method of collecting the glass droplets (6) in a water or oil bath instead of in a mold, care must be taken to prevent the glass droplets (6) from breaking due to the temperature difference between the glass droplets (6) and the water or oil. It was necessary to cool the glass droplet (6) by making the falling distance sufficiently long.

Problems to be Solved by the Invention The present invention solves the above-mentioned conventional problems and provides a method and apparatus for molding a glass lens in which problems such as sink marks are prevented even if the falling distance of glass droplets is short. The purpose is to

This purpose is not to uniformly heat the entire glass droplet formed from the tip of the nozzle to the tip of the nozzle as in the past, but the tip of the nozzle is heated to a predetermined temperature as in the past, but the glass droplet is This is achieved by cooling without heating.

Means for solving the problem, namely a glass melting crucible, provided at the bottom of the crucible,
In a glass lens manufacturing apparatus equipped with a nozzle temperature control means for dropping glass melted in the crucible as glass droplets, the nozzle temperature control means does not heat the glass droplets formed at the tip of the nozzle, The present invention relates to a glass lens manufacturing apparatus characterized in that the device heats only the tip of the nozzle. Furthermore, in a droplet method glass lens manufacturing method in which a glass lens is manufactured by dropping molten glass from the nozzle tip, only the nozzle tip is heated without heating the glass droplet formed at the nozzle tip.
The present invention relates to a method of manufacturing a glass lens in which the glass droplets are applied.

In order to heat only the nozzle tip and not the glass droplet as in the present invention, as shown in Fig. 1, conventional methods were used to heat the nozzle tip and its lower night part. This can be achieved by using means such as electrical heating, induction heating, infrared heating, etc., instead of using a heater (see 5dX Figure 5). Of course, the area under the nozzle from below the area heated by the heater (5c) to the tip is maintained at a uniform temperature by the above-mentioned means.

A configuration example in which the nozzle tip is heated by infrared heating is shown in Part 2-
It is shown in Figure a and Figure 2-b. Fig. 2-a shows an example of the approximate configuration as viewed from the side of the nozzle tip, and Fig. 2-b is a diagram showing the approximate configuration when looking up at the nozzle tip from the lower part of the nozzle tip. In each figure, (4) is the nozzle, (6
) shows a glass droplet formed at the tip of the nozzle, (13) shows an infrared lamp, and (14) shows a reflecting mirror. As shown in FIG. 2-b, this configuration example uses four infrared rungs.

The infrared rays emitted from the infrared lamp (13) are adjusted to be reflected by a reflecting mirror (14) and focused on the tip of the nozzle (4). Infrared rays have a wavelength of 1 to 2 μm, and even if such infrared rays hit the glass droplet (6), since the glass transmits light with a wavelength around this, the glass droplet itself has the advantage of not being heated.

An example of a configuration in which the nozzle tip is heated by electrical heating is shown in Part 4-
It is shown in Figure a and Figure 4-b. Fig. 4-a shows an example of the approximate configuration as viewed from the side of the nozzle tip, and Fig. 4-b is a diagram showing the approximate configuration when looking up at the nozzle tip from the lower part of the nozzle tip. In each figure, (4) is the nozzle, (6
) shows the glass droplet formed at the tip of the nozzle, and (15) shows the electrode.

The electrode (15) may be made of platinum and have various shapes, and is formed integrally with the nozzle (4) at its tip. During heating, an appropriate voltage is applied to both ends of the electrode to heat the center of the electrode, and the heat is used to heat the nozzle tip.

FIG. 3 shows an example of a configuration in which the nozzle tip is heated by induction heating. Figure 3 shows a schematic configuration example of the nozzle tip from the side. In the figure, (4) is the nozzle, (6) is the glass droplet formed at the nozzle tip, and (17) is the high-frequency induction heating coil. show. The base end of the nozzle is fitted with a high frequency induction heating coil.
It is heated by applying power of about 0 KHz. Heating by this high-frequency induction heating coil is also suitable because it does not heat the glass droplets.

By configuring the nozzle tip as described above, the surface, especially the lower surface, of the glass droplet formed at the nozzle tip cools down simultaneously with the generation of the glass droplet. In the present invention, after the lowermost surface of the glass droplet has been cooled to a temperature below the glass softening temperature, the glass droplet is separated from the nozzle tip and dripped.

Temperature control is an important factor in dropping glass droplets under such conditions, and strict control is required not only at the nozzle tip but also at everything from the crucible (2) to the nozzle tip. is desired.

The temperatures of the crucible (1) and nozzle (4) are maintained at desired temperatures by adjusting the heaters (5a, 5b, 5c). The temperature of the crucible (1) and nozzle (4) may be set depending on the properties of the glass, the size of the glass droplet to be obtained, etc., and is usually within the range of 500 to 1400'c. In particular, if the temperature of the lower and upper parts of the nozzle (4) is set higher in the lower part and lower in the upper part, glass droplets (
6) Facilitate dripping. Preferably the lower part is 50-2
00℃, higher than the upper part.

The temperature of the glass droplet varies depending on the falling distance, 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., and furthermore, the temperature of the glass droplet is collected on the lower mold. Since the subsequent cooling rate of the glass droplet varies depending on the constituent material of the lower mold, the set temperature of the lower mold, etc., when implementing the present invention, the cooling rate is adjusted while taking these conditions into consideration.

Furthermore, in order to precisely control the glass temperature, it is preferable to take measures to automatically control these temperatures. As a means for this, it is preferable to control the temperature of the glass droplet at the nozzle tip by controlling the time it takes for the glass droplet to form at the nozzle tip and fall. Specifically, for example, a light beam passing through the nozzle tip is emitted by a light emitter (8), and a light receiver (9) for sensing the light is placed opposite to the light emitter with respect to the nozzle tip, and the formation of glass droplets is prevented. The time until the drop is measured, and a signal corresponding to the measured value is sent to a control unit (microcomputer, etc., not shown), which controls the nozzle tip heating means and, if necessary, a heating heater, depending on the amount of change in the time. (
5a, 5b, 5c) may be adopted. Alternatively, the temperature of the glass droplet may be directly measured using a radiation thermometer or the like instead of the light emitter (8) and the light receiver (9).

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=2π'γ (m: weight, r: nozzle tip diameter, 17 surface tension). Generally, the nozzle tip diameter is 0.5 to 15 mm, preferably 0.5 ~10 mm. If the diameter of the nozzle tip 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 forms a letter shape due to surface tension and falls one after another.

Although not shown in FIG. 1, the falling distance can be adjusted by moving the support base (2) of the lower mold (I5) up and down. At this time, using the same control means as used for adjusting the nozzle temperature described above, the control section is activated based on the signal from the light receiver or radiation thermometer to raise and lower the support base and adjust the falling distance. Good too. According to the present invention, when the glass droplet falls from the tip of the nozzle, the surface of the glass droplet part has already been cooled to below the softening point, so the falling distance can be 1 m or less. Therefore, glass lenses with good transferability can be manufactured with good reproducibility.

The lower mold (11) that collects glass droplets first has a nozzle (4).
), which receives the glass droplet dripping from the tip of the nozzle (4). After the glass droplet drips, it is moved to the molding position, and in cooperation with the upper mold (13), the glass lens is formed by compression molding. to form.

The upper mold (13) may be made of the same material as the lower mold (l l), or may be made of a different material.

Moreover, the lower mold (11) for collecting may be convex or concave. The present invention is particularly effective for manufacturing convex lenses using a concave lower mold.

The lower mold (15) has a temperature of 10% higher than the softening temperature of the glass used.
It is preferable to keep the temperature heated to a temperature lower than 150°C, preferably 30 to 100°C.

Normally, when using 5FII glass, the temperature is set at about 400°C. By doing so, lenses with high surface precision can be molded, and there is an effect of preventing fusion between the mold and the glass.

The upper mold (18) has a temperature of 10% higher than the softening temperature of the glass used.
It is preferable to keep it heated to a temperature lower than 150°C, preferably 30 to 100°C.

By doing so, it has the same effect as the lower mold.

According to the present invention, various types of lenses such as biconvex, biconcave, planoconvex, planoconcave, and meniscus lenses can be manufactured accurately and efficiently by selecting the upper mold and the lower mold.

Examples and Comparative Examples In the droplet method glass lens manufacturing apparatus having the configuration shown in Fig. 1, the nozzle tip heating section was heated by infrared heating means, and the other parts were heated by the same conventional method as shown in Table 1. As shown, a glass lens was manufactured by controlling the temperature of the crucible, the nozzle upper part, the nozzle middle part, and the nozzle tip part. Table 1 also shows the dropping interval and falling distance of the glass droplets at that time.

The type of glass used was 5FII, the lower mold was made of stainless steel, the upper mold was also made of stainless steel, and the temperature of the lower mold was set at about 400° C. and the upper mold was set at 400° C.

In the comparative example, the nozzle tip was heated using a heater (similar to those in 5a to 5C) as explained in the conventional example.
A glass lens was manufactured using the same apparatus as in Example except that the upper, lower, left and right atmospheres of the nozzle tip were maintained at the same temperature.

The condition of the lower surface of the obtained lens due to sink marks was examined, and the results are summarized in Table 1.

(Hereinafter, blank space) In Table 1, "○" indicates that no sink marks were observed, "△" indicates that slight whiskers were observed, and "×" indicates that sink marks were observed. .

As can be seen from Table 1, when the interval between drops is short, the lower surface of the glass is not sufficiently cooled and defects due to sink marks occur. In the comparative example in which the entire glass droplet is heated uniformly, the occurrence of sink marks depends only on the dropping distance, and therefore, if the dropping distance is 100 cm or less, the occurrence of sink marks is unavoidable.

From the above, it is understood that in the present invention, the longer the drop interval, the cooler the lower surface of the glass drop is, and that heating only the nozzle tip is effective.

Furthermore, instead of the infrared heating method, electrical heating and induction heating were also tried, and results similar to those obtained with infrared heating were obtained.

Effects of the Invention According to the present invention, by preventing the glass droplet formed at the tip of the nozzle from being heated, it is possible to manufacture a good lens without whiskers with a shorter droplet distance than before.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a schematic configuration of an apparatus for carrying out the droplet method of the present invention. Figure 2-a, Figure 2-b, Figure 3, Figure 4-a, Figure 4-
Figure b is a diagram schematically showing various embodiments of means for heating the nozzle tip. FIG. 5 is a diagram showing a schematic configuration example of an apparatus for explaining the conventional droplet method. Figures 6-a to 6-d are diagrams for explaining the mechanism by which whiskers occur.

Claims (1)

[Scope of Claims] 1. A glass lens manufacturing apparatus comprising a glass melting crucible, a nozzle provided at the bottom of the crucible for dropping glass melted in the crucible as glass droplets, and temperature control means for the nozzle, wherein the nozzle A glass lens manufacturing apparatus characterized in that the temperature control means is a means for heating only the nozzle tip without heating the glass droplet formed at the nozzle tip. 2. The glass lens manufacturing apparatus according to claim 1, wherein the nozzle temperature control means utilizes heating by infrared radiation. 3. The glass lens manufacturing apparatus according to claim 1, wherein the nozzle temperature control means utilizes energization heating by an electrode integrally formed with the nozzle at the tip of the nozzle. 4. The glass lens manufacturing apparatus according to claim 1, wherein the nozzle temperature control means utilizes induction heating using a high-frequency induction coil. 5. In the droplet method glass lens manufacturing method in which a glass lens is manufactured by dropping molten glass from the nozzle tip, the glass droplet formed at the nozzle tip is not heated, but only the nozzle tip is heated. A method of manufacturing a glass lens by dropping glass drops.