JPH0672725A - Method for molding optical glass - Google Patents

Abstract

PURPOSE:To improve quality by arranging cylindrical heaters enclosing the outer peripheries of both molds and extrusion molding molten glass with a pair of the molds under heating by these heaters. CONSTITUTION:The molten glass 3 flowing out of a crucible 1 is cut by cutting member 4 and glass cob 5 is supplied to the lower mold 7. The lower mold 7 and the surface of the glass cob 5 are then heated by the cylindrical heater 6 to the temp. higher than the glass transition point so that the glass cob 5 maintains a sufficient flow property. The lower mold 7 carrying the glass cob 5 and the cylindrical heater 6 are integrally moved and are positioned coaxially with the upper mold 9. The upper mold 9 is slid and lowered within the cylindrical heater 8 and are fitted into the cylindrical heater 6. The temps. of the front and rear surfaces of the glass cob 5 and the upper mold 9 are then maintained uniformly at the temp. higher than the glass transition point and the glass cob is press molded. The glass molding 10 is clamped by the lower mold 7 and the upper mold 9 upon completion of the press flow and is then lowered and cooled, by which the optical glass molding having the good quality without having surface defects is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding optical glass.

[0002]

2. Description of the Related Art In recent years, a method of molding an optical glass does not require grinding and polishing and can manufacture a glass optical component having high shape accuracy and surface quality only by heating and pressing a glass material. Methods are being established. As such a manufacturing method, a manufacturing method to which a direct press method is applied has already been put into practical use. In this method, molten glass heated and melted in a crucible is made to flow down from an orifice, cut at a predetermined timing by a cutting member such as a shear, and a predetermined amount of molten glass lump is supplied to a mold, followed by press molding. Therefore, the processing steps are remarkably shortened as compared with the grinding and polishing method, and the manufacturing cost of the optical component can be significantly reduced.

However, in this direct press system, the molten glass gob is cooled during the conveying time from the feeding of the molten glass gob to the mold until the press molding, and the fluidity is lost and press molding becomes impossible. However, even if it can be molded, there is a problem that wrinkle-like defects are generated on the surface of the molten glass gob.

In order to solve such a problem, for example, the technique disclosed in Japanese Patent Laid-Open No. 2-258640 has been proposed. In the publication, in a non-oxidizing atmosphere, the molten glass is received by a first heat processing jig and then inverted, and the molten glass is inverted and replaced by a second heat processing jig.
There is disclosed a method of producing an optical glass molded body by using the heat processing jig and further press-molding this. According to this method, a molten glass gob (glass gob) having sufficient fluidity and good moldability can be obtained. Then, it becomes possible to remove the wrinkle-like surface defects that occur when the molten glass gob is supplied to the thermal processing jig, by thermally deforming it by surface reheating and then press molding.

[0005]

However, in the method described in the above publication, the number of processes such as preheating, supply, reversal, thermal deformation, pressing, cooling, and take-out is increased, and the size of the apparatus is increased, resulting in cost reduction. There was a problem that it became high. Further, since the surface reheating is performed in an open furnace, it is difficult to strictly control the temperature, and there is a problem that the heating temperature tends to vary. That is, the direct press method as described above is extremely effective in reducing the cost of the optical element, while obtaining a molten glass gob having good moldability, and easily wrinkle-like surface defects generated when the molten glass is cooled. There was no way to find a way to prevent it.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical glass molding method which has good moldability and can prevent the generation of wrinkle-like surface defects.

[0007]

In order to achieve the above object, in the optical glass molding method of the present invention, molten glass is supplied between a pair of molding dies whose molding surfaces are arranged to face each other,
In the optical glass molding method of pressing molten glass with the molding die, the step of arranging a cylindrical heater surrounding the outer periphery of both molding dies and pressing the molten glass with the pair of molding dies is performed. It was decided to perform it in a tubular heater.

[0008]

In the optical glass molding method of the present invention having the above-mentioned structure, when the glass gob cut by the cutting member is received by the lower mold, the cylindrical ring heater is arranged so as to surround the outer periphery of the lower mold tip. . This simultaneously heats the lower mold tip and the glass gob supplied on the lower mold surface. Then, the lower die and the cylindrical ring heater are integrally moved, and similarly to the lower die, the tip portion is heated by the cylindrical ring heater and positioned with the upper die maintained at substantially the same temperature as the lower die, and press molding is performed. .

Here, the cylindrical ring heater arranged at the tip of the lower die heats the tip of the lower die and the glass gob to the same temperature to prevent the glass gob from being cooled and solidified before being press-molded. Maintain good liquidity. Further, by heating both the upper surface and the lower surface of the glass gob to substantially the same temperature, it is possible to prevent the cooling of only one surface of the glass gob and the occurrence of wrinkle defects on the surface. Further, by press-molding the upper and lower molds and the glass gob at the same temperature, it is possible to prevent deterioration of the molding surface accuracy due to sink marks which are likely to occur in the cooling process.

Some embodiments of the optical glass molding method according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

[0011]

First Embodiment First, a first embodiment of the present invention will be described. Figure 1
[FIG. 3] is a process drawing showing an optical glass molding method. As shown, in this embodiment, the crucible 1 is heated by the crucible heater 2, and the molten glass 3 stored inside the crucible 1 is heated and melted. Here, the molten glass 3 uses SF11, and T
The g point is 503 ° C and the Sp point is 635 ° C. A pair of cutting members 4 is provided below the crucible 1.
The cutting member 4 is heated to about 520 ° C. by a heater (not shown), and is provided with a drive source (not shown) for performing forward / backward movement.

Next, a lower die 7 is provided below the cutting member 4 so as to be vertically movable by a vertical drive device (not shown).
Here, the vertical drive device is installed in a moving part of a horizontal movement device (not shown) and is movable in the left-right direction. On the other hand, the tip portion of the lower die 7 is inserted into the inner diameter portion of the cylindrical heater 6 installed by the left and right driving device (not shown). Since the heater 6 heats the lower mold 7 during molding and is used as a body mold for molding the side surface of the molded product, the heater 6 is made of the same material as the lower mold 7, and is provided with a heater in the inner diameter portion and the inner peripheral surface. It is mirror-finished. In this embodiment, the heating temperature is set to about 520 ° C. in order to mold the glass material as described above.

The molten glass 3 flowing out of the crucible 1 is cut into glass gobs 5 by a cutting member 4 and supplied onto a lower mold 7. Here, the cutting member 4 has a Tg point 50 of SF11.
Since it is heated to about 520 ° C, which is higher than 3 ° C, and the tip of the lower mold 7 and the surface of the glass gob 5 are also heated to about 520 ° C by the cylindrical heater 6,
The glass gob 5 can maintain sufficient fluidity on the lower mold 7. And the temperature of the upper and lower surfaces of the glass gob 5 can be kept uniform.

Next, as shown in FIG. 1B, the lower die 7 on which the glass gob 5 is placed and the cylindrical heater 6 are moved integrally and positioned coaxially with the upper die 9. Upper mold 9 is a cylindrical heater 8
Is heated to about 520 ° C. in advance. And FIG.
As shown in (c), the upper mold 9 slides down in the cylindrical heater 8 and fits into the cylindrical heater 6, and the glass gob 5 is press-molded. At this time, the upper and lower surfaces of the glass gob 5 and the lower mold 7
Since the upper mold 9 is maintained at a temperature higher than the Tg point and at a uniform temperature, it is possible to prevent deterioration of surface accuracy due to wrinkle-like surface defects, sink marks during shrinkage, etc., and to perform good press molding. Be seen. Then, when the press flow necessary for molding is completed, the lower mold 7 and the upper mold 9 are integrally lowered with the glass molded body 10 held therebetween, outside the cylindrical heater 6, as shown in FIG. The glass molded body 10 is cooled.

As described above, in this embodiment, the cylindrical heater is installed in the upper and lower molds to efficiently heat the upper and lower molds and the glass gob to the same temperature. Therefore, the glass gob has sufficient fluidity and temperature uniformity until the completion of press molding. Therefore, the optical glass lens having good appearance quality and surface accuracy can be molded.

The shape of the heater is not limited to the above-mentioned cylindrical shape, and may be variously set depending on the shape of the mold or the molding surface of the mold as long as it surrounds the circumference of the mold and the molding surface of the mold. Good. Further, in the present embodiment, the lower die and the cylindrical heater are moved, but conversely, the crucible and the upper die provided above may be moved to match the centers of the upper and lower dies. Further, in this embodiment, the cylindrical heater also functions as a barrel mold, but when the molten glass is molded by the pair of molding dies, the molten glass pressed from the outer periphery of the molding dies is not visible. If not, or if high accuracy is not required for the outer peripheral shape of the optical element to be molded, a normal heater that does not function as a barrel may be used.

[0017]

Second Embodiment Next, a second embodiment of the present invention will be described. Figure 2
[Fig. 4] is a process drawing showing the optical glass molding method of Example 2.
As shown in the figure, in this embodiment, the auxiliary cylindrical heater 1 is provided below the lower die 7 and the cylindrical heater 6 for heating the glass gob 5.
1 was placed. The auxiliary cylindrical heater 11 is set at a temperature slightly lower than the Tg point of the glass material to be molded.

2A and 2B show a process similar to that of the first embodiment. In this embodiment, when the press flow necessary for molding is completed, the glass molded body 10 is gradually cooled in the auxiliary cylindrical heater 11 set at a temperature slightly lower than the Tg point, as shown in FIG. 2 (c). To do. Then, after the temperature of the glass molded body 10 falls below the Tg point,
As shown in (d), cooling is performed outside the auxiliary cylindrical heater 11.

According to the present embodiment, the cooling after the completion of press flow is divided into two stages, and the glass molded body 10 and the upper and lower molds are cooled at the same temperature state up to the Tg point. It is effective for molding optical lenses that require strict surface accuracy.

[0020]

As described above, according to the optical glass molding method of the present invention, the step of press-molding the molten glass by the upper and lower molding dies is carried out in the cylindrical heater. Can maintain sufficient fluidity and temperature uniformity until the end of pressing, and an optical glass molded lens of good quality can be obtained. Further, since the temperature of the glass gob can be controlled without installing several heating furnaces in the molding machine, it is possible to achieve cost reduction and quality improvement with a small molding machine.

[Brief description of drawings]

FIG. 1 is a process drawing showing Example 1 of the optical glass molding method according to the present invention.

FIG. 2 is a process drawing showing Example 2 of the optical glass molding method according to the present invention.

[Explanation of symbols]

 1 crucible 2 crucible heater 3 molten glass 4 cutting member 5 glass gob 6,8 cylindrical heater 7 lower mold 9 upper mold 10 glass molded body 11 auxiliary cylindrical heater

Claims (1)

[Claims] 1. An optical glass molding method in which molten glass is supplied between a pair of molding dies whose molding surfaces are opposed to each other and the molten glass is pressed by the molding dies. An optical glass molding method, characterized in that a step of arranging a cylindrical heater surrounding the above is performed, and the step of press-molding the molten glass with the pair of molding dies is performed inside the cylindrical heater.