JPH0840726A - Apparatus for forming glass material for molding - Google Patents

Abstract

PURPOSE:To stably obtain a glass gob without causing a flash, the fusion in ridge line parts and an uneven wall thickness by providing the apparatus with a receiving mold having a mold surface tilted at a prescribed angle or above to the horizontal plane in the peripheral part of a cavity thereof and reduce the depth in the peripheral part of the cavity in the outside diametral direction. CONSTITUTION:This apparatus for forming a glass material for molding is obtained by providing the apparatus with a receiving mold different in shape between the central part and the peripheral part thereof so as to tilt the mold surface in the peripheral part of a cavity at >=45 deg. to the horizontal plane and reduce the depth in the outside diametral direction in the apparatus for receiving a molten glass discharged from an orifice in the cavity of the receiving mold and forming the glass material for molding an optical element. An example in the figure shows the receiving mold 1, a spherical surface in the central part of the receiving mold (curvature radius: R=15mm) 1A and a surface 1B in the peripheral part of the receiving mold (conical surface having a tilt thetafrom the horizontal plane) and a glass gob 2. The connecting part 1C of the spherical surface IA to the surface 1B is a smoothly connecting surface, e.g. a rounded surface of a suitable radius.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forming apparatus for preforming a glass material when an optical element is manufactured by precision press molding.
The present invention relates to an apparatus for forming a glass material for molding, which forms a glass material for press molding (hereinafter referred to as a glass gob) from a molten glass flow.

[0002]

2. Description of the Related Art In recent years, a glass material that has been ground and polished to a certain degree of shape and surface accuracy is housed in a molding die having a predetermined surface accuracy, and press molding is performed under heating to form lenses, prisms, etc. Has been developed for obtaining an optical element having a highly accurate optical function surface. This method
Through the glass outflow nozzle installed in the glass melting furnace,
Molten glass is allowed to flow down from the orifice, and the molten glass that has flowed down is cut with a shear (cutting blade) to separate a certain amount of molten glass mass, so-called, glass gob, and this glass gob is
An optical element is obtained by preforming with a molding die having a cavity close to the shape of the final molded product, and then grinding and polishing this preformed body.

However, this method has a problem that shear marks (cut marks) are generated when the molten glass is cut. The glass gob once marked with a shear mark does not lose its marks even after preforming, so that long-time grinding and polishing are required, which has been a cause of increasing the manufacturing cost.

On the other hand, a method for obtaining a glass gob by so-called shearless cutting without cutting with a shear has been already disclosed in, for example, Japanese Patent Laid-Open No. 2-354525. This method utilizes the fact that the glass having the proper viscosity is received by the receiving member, and when the predetermined weight is accumulated, the mold is lowered to cause the glass flow to be constricted in the process of stretching, and the glass is vertically separated by the surface tension. Is the way.

At this time, a concave receiving die is used to receive the glass gob, and the opposite side of the glass gob is
It was a free surface formed by the surface tension of glass. Then, when a concave glass gob is formed (preformed) after that, the free surface thereof is press-molded by a convex member.

[0006]

However, the above-mentioned conventional example has the following problems. That is, when the receiving die descends, or when it moves thereafter, the glass gob moves from the center of the receiving die, so that uneven thickness often occurs in the glass gob during preforming,
is happening. Especially when molding a concave lens from a glass gob having a concave surface, due to the uneven thickness of the glass gob,
The shape transfer property was remarkably lowered, and a number of defective molded products were generated.

As a method for preventing the uneven thickness of the glass gob, for example, a method described in Japanese Patent Laid-Open No. 62-270423 is known. This is a method in which molten glass is passed through a hollow conical guide when dropped onto a receiving mold, but when the glass flow comes into contact with the guide, local adhesion occurs, which causes It had a negative effect on the supply of glass to the mould.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an apparatus for forming a glass material for molding which can stably obtain a glass gob having no uneven thickness. It is in.

Further, in this case, without producing burrs and without causing fusion or cracking of the ridge portion,
It is necessary to obtain a glass gob without uneven thickness.

[0010]

In order to achieve the above object, the present invention provides a forming apparatus for forming a glass material for forming an optical element by receiving a molten glass flowing down from an orifice into a receiving mold cavity. , The shape of the receiving mold is such that the mold surface in the peripheral part of the cavity of the receiving mold has an inclination of 45 ° or more with respect to the horizontal plane, and the depth in the peripheral part of the cavity becomes shallower toward the outer diameter direction. The center part and the peripheral part are different.

In addition, it is preferable that the receiving die is formed of an integral body, and it is desirable that the shapes of the central portion and the peripheral portion of the cavity of the receiving die be smoothly continuous with each other.

[0012]

In the above structure, the shallowness in the peripheral portion of the cavity causes resistance when the molten glass received by the receiving mold spreads in the cavity, and should the molten glass be displaced from the center of the receiving mold. Even if dropped, uneven thickness does not occur in the glass gob. In addition, since the receiving die is integrated, unlike the one in which the central portion and the peripheral portion are configured separately, it is possible to prevent the flash of the glass gob that is likely to occur at the joint, and the cavity of the receiving die. Since the shape of the central part and the peripheral part of the is smoothly continuous, fusion or partial cracking of the ridge portion, which tends to occur when the connection part has a ridge line,
It is possible to avoid chipping.

[0013]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
It will be specifically described with reference to. In FIG. 1, reference numeral 1 is a receiving mold, 1A is a spherical surface at the center of the receiving mold (curvature radius: R = 15 mm, diameter: φ8 mm), 1B is a peripheral surface of the receiving mold (a cone having an inclination θ from the horizontal plane). Surface), 1
C indicates a connecting portion between the spherical surface 1A and the surface 1B, and is a smoothly continuous R surface having an appropriate radius. Further, reference numeral 2 indicates a glass gob.

FIG. 2 shows a cross section of a glass gob formed by the forming apparatus of the present invention, and FIG. 3 shows its plane. Here, reference numeral 2A denotes a point where the wall thickness of the glass gob is maximum, 2B and 2C are points on the outer peripheral edge where the radius from 2A is minimum and maximum, respectively, and x is 2A,
2B, and y represents the length between 2A and 2C.

In FIG. 4, reference numeral 3 is an upper mold member for molding an optical element from a glass gob, and 4 is a lower mold member therefor.

First, the receiving type θ shown in FIG.
Receiving dies of respective shapes of 5, 40, 45, 50, 55, and 60 degrees were prepared. Next, for example, optical glass SK12 (manufactured by OHARA) is started to flow out of an orifice of a glass melting furnace (not shown), and a plurality of receiving molds having the same shape are sequentially used. As described below, a plurality of glass gobs were continuously obtained. The temperature of this molten glass was 1180 ° C. (glass viscosity: 10 ^2.1 dPa · S), and the inner diameter of the orifice was set to 6 mm.

As the procedure, first, a receiving mold was placed at a position 8 mm immediately below the orifice, and the outflowing optical glass was received for 2 seconds to form a glass lump. In this case, the temperature of the receiving mold 1 was set to 500 ° C. Then, the receiving mold 2
The glass melt is lowered at a speed of 0 mm / sec to shear-cut the molten glass (the glass flow is elongated, constricted, and cut by surface tension) to form a glass gob 2 having a weight of 1.5 g. In this way, the same type of receiving type is continuously used.
I got a glass gob.

By the above method, the prepared receiving molds having the angle θ divided into seven stages from 30 to 60 degrees were sequentially changed, and 100 glass gobs were prepared for each of the receiving molds. . Further, for comparison with the present invention, as a conventional example, 100 glass gobs were also produced by a receiving die in which the entire receiving surface was made with a radius of curvature of R = 15 mm. In the conventional example, the glass gob formed without uneven thickness had an outer diameter of 12 mm and a wall thickness of 6 mm.

Next, the x and y of each glass gob is measured,
The difference y−x is calculated, and the results summarized in the frequency distribution table are shown in Table 1.

[0020]

[Table 1] As is apparent from Table 1, it was found that when the angle θ is 40 degrees or less, uneven thickness is likely to occur. Next, as shown in FIG. 4, a glass gob was put into a molding die to mold an optical element as a final product. In this case, the optical element has a radius of curvature: R1 = 16.3 mm, R2 = 16.8.
mm, outer diameter: φ15 mm, effective diameter: φ14 mm, central thickness: 4.5 mm.

In the method of charging the glass gob into the molding die,
With the auto hand, it sucks the outer diameter of the glass gob,
It is placed at the center of the molding surface of the lower mold member 4. Therefore, in the glass gob having uneven thickness, the glass transfer area is insufficient on one side, and the volume of the glass is too large on the opposite side, causing a problem of protruding from the molding die.

As a result of molding the glass gobs shown in Table 1, y
When −x was 0.4 mm or less, the transfer areas of diameter: φ15 mm or more were held on both surfaces of the optical element. However, when y−x exceeds 0.4 mm, the diameter: φ15 mm was used. A part of the transfer area of No. 1 was chipped and the surface was in a sagging state.

(Embodiment 2) FIGS. 5 to 7 show a second embodiment of the present invention.
5, reference numeral 11 denotes a receiving mold, 11A denotes a spherical surface (curvature radius: R = 30 mm, diameter: φ7 mm) at the center of the receiving mold, and 11B denotes a peripheral surface of the receiving mold. (A conical surface having an inclination angle θ from the horizontal plane), and 11C represents these surfaces 11A and 11B as desired R
It is a smoothly continuous connection part. Reference numeral 12 indicates a glass gob.

In FIG. 6, the glass gob 12 is attached to the upper punch 13
A state is shown in which the glass gob 14 having a concave surface is formed by pressing (having a radius of curvature: R = 20 mm of a molding surface). Further, FIG. 7 shows the upper mold member 15 (radius of curvature: R = 1.
5.5 mm) and the lower die member 16 (curvature radius: R = 40 m
m) and the glass gob 14 is inserted between them and the optical element is press-molded.

Here, since the glass gob is molded, FIG.
The receiving angle θ is 30, 35, 40, 4 as shown in
A receiving die of each shape of 5, 50, 55, and 60 degrees is prepared, and for comparison with the present invention, as a conventional example, a receiving die having an entire receiving surface with a radius of curvature of R = 30 mm is prepared. did. Then, here, optical glass SK12 (manufactured by OHARA CORPORATION) is used as a raw material and melted in a glass melting furnace (not shown), and the temperature of the molten glass at the orifice is set to 11
80 ° C (glass viscosity: equivalent to 10 ^2.1 dPa · S),
Further, the inner diameter of the orifice was set to 6 mm.

Then, the receiving mold is first placed at a position 8 mm immediately below the orifice, and the molten glass flowing out is 1.5
After receiving for a second, a glass gob was formed on the receiving mold as described below. In this case, the temperature of the receiving mold 11 is set to 500 ° C. Next, the receiving mold 11 was lowered at a speed of 20 mm / sec, and the molten glass was shearless cut to form a glass gob 12 having a weight of 1.2 g. Immediately thereafter, the receiving die 11 was moved directly below the upper punch 13, and the free surface of the glass gob was press-molded by the upper punch 13 to obtain a glass gob 14 having a concave surface. In this procedure, a plurality of receiving molds of the same shape are used, and 10
0 glass gobs were obtained.

According to the above method, the angle θ is 30 to
100 concave glass gobs were prepared by dividing each into seven stages up to 60 degrees, using each receiving mold, and using the mold of the conventional example. In the conventional example, the glass gob formed without uneven thickness has an outer diameter of φ10 mm and a wall thickness of 4 mm.
Met.

Next, following Example 1, the distances from the point where the wall thickness of each glass gob is minimum to the points where the radius is minimum and maximum are x and y, respectively, and these are measured,
The difference y−x was calculated and summarized in the frequency distribution table. The results are shown in Table 2.

[0029]

[Table 2] As a result, as is clear from the table, it was found that when the angle θ is 40 degrees or less, uneven thickness is likely to occur. Next, as shown in FIG. 7, a glass gob was put into a molding die to finally mold an optical element. The radius of curvature of this optical element is R1 = 40 mm (convex), R2 = 15.5.
mm (concave), outer diameter: φ16 mm, effective diameter: φ14 mm,
Central concave thickness meniscus lens with a thickness of 1.8 mm.

However, in a glass gob having an uneven thickness,
There is a shortage of the glass transfer area on one side and too much glass capacity on the other side, causing a problem such as protrusion from the mold. As shown in Table 2, as a result of molding the glass gob, when y-x was 0.2 or less, the transfer area having a diameter of φ16 mm or more was held on both surfaces, but y-x was 0. More than 2, diameter: φ16mm
A part of the transfer area of No. 1 was chipped and the surface was in a sagging state.

(Third Embodiment) FIGS. 8 to 10 show a third embodiment. In FIG. 8, reference numeral 21 is a receiving type,
21A is a spherical surface (curvature radius: R
= 30 mm, diameter: φ20 mm), 21B is a receiving mold 21
Of the peripheral part of (the toric surface of the sagittal line: R = 10 mm,
In the connection portion with the spherical surface 21A, the inclination angle of the tangent line of the sagittal line from the horizontal plane: θ), 21C is an R connection portion that smoothly connects the surfaces 21A and 21B, and 22 is a glass gob.

FIG. 9 shows the upper punch 23 (radius of curvature: R =
20 mm) to press the glass gob 22 to create a biconcave glass gob 24. In addition, FIG.
A state in which a glass gob is inserted between the upper die member 15 (radius of curvature: R = 14.5 mm) and the lower die member (radius of curvature: R = 25 mm) to press-mold a required optical element is shown.

First, the angle θ of the receiving mold 21 shown in FIG. 8 is 3
The radius of curvature of each of the shapes of 0, 35, 40, 45, 50, 55, 60 degrees, and the conventional receiving surface as a conventional example: R
A receiving mold made with a thickness of 30 mm was prepared. Further, the glass material used here is optical glass SK12 (manufactured by OHARA CORPORATION), which is melted in a glass melting furnace (not shown), and the temperature of the molten glass at the orifice is 1180 ° C.
(Temperature corresponding to glass viscosity of 10 ^2.1 dPaS). In this case, the inner diameter of the orifice is 6m
set to m.

Then, the receiving mold 21 was placed at a position 8 mm immediately below the orifice, and the molten glass flowing out was received for 5 seconds to form a glass gob. The temperature of the receiving mold 21 at this time is set to 500 ° C. in advance. Thereafter, in the same manner as in Example 2, a concave glass gob 24 having a weight of 4 g was obtained. 100 concave glass gobs were prepared by using each of the molds and the mold of the conventional example which are different for seven stages with an angle θ of 30 to 60 °. However, as a result, the conventional type is
The molten glass slipped off the mold and could not form a glass gob. Here, as in Example 2, y-x was calculated, and the frequency distribution is shown in Table 3.

[0035]

[Table 3] As is clear from Table 3, it was found that uneven thickness is likely to occur when the angle θ is 40 ° or less. Next, as shown in FIG. 10, a glass gob was put into a molding die and a predetermined optical element was press-molded. Design values of the optical element at this time are as follows: radius of curvature: R1 = 14.5 mm, R2 = 25 m
m, outer diameter: φ26 mm, effective diameter: φ24 mm, central concave thickness 1.5 mm. As a result of press molding the glass gobs shown in Table 3, when y-x was 0.2 mm or less, a transfer area having a diameter of φ26 mm or more was secured on both surfaces. However, in the case where y−x exceeds 0.2 mm, a part of the transfer area having a diameter of φ26 mm was chipped and the surface was in a sagging state.

[0036]

As described above, the present invention can prevent uneven thickness of a glass gob when forming a glass gob as a glass material for forming an optical element, and has a high shape when the optical element is molded. The accuracy can be kept stable. Further, it is possible to obtain a glass gob that does not cause flash.
Further, since the glass gob has no ridge, it is possible to prevent fusion and cracking.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which a glass gob is received by a receiving mold according to a first embodiment of the present invention.

FIG. 2 is likewise a sectional view of the glass gob according to the first embodiment.

FIG. 3 is likewise a plan view of the glass gob according to the first embodiment.

FIG. 4 is a view showing a state in which an optical element is press-molded from the glass gob according to the first embodiment.

FIG. 5 is a diagram showing a state in which a glass gob is received by a receiving mold according to a second embodiment of the present invention.

FIG. 6 is a view showing a state where the glass gob according to Example 2 is press-molded with an upper punch.

FIG. 7 is a view showing a state in which an optical element is press-molded from the glass gob according to Example 2.

FIG. 8 is a diagram showing a state where a glass gob is received by a receiving mold according to a third embodiment of the present invention.

FIG. 9 is a view showing a state where the glass gob according to Example 3 is press-molded with an upper punch.

FIG. 10 is a diagram showing a state in which an optical element is press-molded from a glass gob according to a third embodiment.

[Explanation of symbols]

 1 Receiving die 1A Receiving die center spherical surface 1B Receiving die peripheral surface 1C Connection between 1A and 1B 2 Glass gob 2A Point with maximum wall thickness 2B Peripheral point with minimum radius 2C Perimeter with maximum radius Point x Length between 2A and 2B y Length between 2A and 2C 3 Upper mold member for optical element molding 4 Lower mold member for optical element molding 11 Receiving mold 11A Spherical center of receiving mold 11B Receiving Surface of mold peripheral part 11C Connection between 1A and 1B 12 Glass gob 13 Upper punch 14 Concave glass gob 15 Upper mold member for optical element molding 16 Lower mold member for optical element molding 21 Receiving mold 21A Receiving mold central spherical surface 21B Receiving mold periphery Surface of part 21C Connection part of 21A and 21B 22 Glass gob 23 Upper punch 24 Concave glass gob 25 Upper mold member for optical element molding 26 Lower mold member for optical element molding

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroyuki Kubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. In a forming apparatus for forming a glass material for forming an optical element by receiving a molten glass flowing down from an orifice into a cavity of a receiving die, the inclination of the die surface around the cavity of the receiving die is horizontal. On the other hand, it has an inclination of 45 ° or more, and the shape of the receiving mold is different between the central part and the peripheral part so that the depth in the peripheral part of the cavity becomes shallower toward the outer diameter direction. Equipment for forming glass material for molding. 2. The apparatus for forming a glass material for molding according to claim 1, wherein the receiving die is formed as an integral body. 3. The apparatus for forming a glass material for molding according to claim 1, wherein the shape of the center part and the peripheral part of the cavity of the receiving mold are smoothly continuous with each other.