JP2000001320A - Method for forming glass gob as optical element or blank for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a glass gob capable of embodying high-accuracy shape transfer by making the pressure that the glass gob receives by the gases ejected from the forming surfaces of forming dies uniform at the time of contactless pressing of the glass gob. SOLUTION: The method for forming the glass gob as an optical element or a blank for its production consists in shaping the molten glass gob so as to profile its shape with the forming surfaces of the forming dies while maintaining the molten glass gob and the forming surfaces to each other in a contactless state by blowing out the gases from the forming surfaces at the time of press forming the molten glass gob in a softened state by using the porous forming dies 1, 2. In such a case, the blowout flow rate of the gases from the forming surfaces of the forming dies in the non-loading state of the molten glass gob is so set and controlled as to maintain a prescribed distribution within the forming surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an optical element or a material for producing the same by press-forming a softened molten glass block.

[0002]

2. Description of the Related Art In recent years, a glass block as a material for manufacturing an optical element is housed in a molding die having a predetermined surface accuracy, and is subjected to press molding under heating, followed by grinding and polishing. A method for manufacturing an optical element having a high-precision optical function surface that does not require processing has been developed. This method is roughly classified into two methods. One is a method in which a glass block called a preform is heated and molded at a temperature equal to or lower than a softening point to obtain an optical element, which is called a reheat press. The other is a method of directly molding a glass lump in a molten state to obtain an optical element, which is called a direct press.

[0003] The former is an advantageous method for improving the shape accuracy of a molded article. However, since a preform is formed from molten glass or the like and the preform is reheated to form an optical element, the overall method is as follows. The problem is that the manufacturing cost is high. In the latter case, although the manufacturing cost is low, since the glass mass is formed at an extremely high temperature, the glass is rapidly cooled when the molding surface of the molding die and the surface of the molten glass mass are in direct contact as in a reheat press. As a result, wrinkling occurs, fusion occurs to the mold, and the mold is worn out in a short time, which makes practical use difficult.

[0004] In addition to the purpose of obtaining a final optical element, direct pressing (the latter) is also performed for the purpose of molding a glass material for manufacturing an optical element having a shape very close to the final shape. In some cases, the glass material for an optical element is used as a material for a reheat press, or is processed into a final shape as an optical element by performing a small amount of grinding and polishing.

[0005] In the direct press, several non-contact molding techniques have been disclosed as measures against the problem of fusion of a molten glass lump to a molding die. JP-A-59-19554
No. 1 discloses that an optical element is obtained by supplying a pressurized gas to a molding die made of a porous member so that the molding surface of the molding die and the glass lump are not in contact with each other. A method is disclosed. Furthermore, Japanese Patent Publication No. 48-22977
In the publication, a gas is sent from the back using a porous mold, and at the same time, the molding die is ultrasonically vibrated so that the molding surface of the molding die and the glass lump are kept in a non-contact state. A method for performing molding is disclosed.

[0006]

As described above, in order to conform the shape of the molded article to the molding surface of the molding die while maintaining the non-contact state, the interface between the molding surface of the molding die and the glass block is required. The thickness of the gas film generated during
It must be kept uniform. However, the method disclosed in the former does not describe the thickness of the gas film along the molding surface of the mold. Further, the method disclosed in the latter describes that when the forming surface of the forming die is made to have a very small pore diameter and uniform air permeability, a thin gas film is uniformly formed on the forming surface. Have been.

However, in practice, when the interface of the glass lump is close to the molding surface of the mold, no matter how much the amount of gas injected into the mold, the amount of gas flowing into the mold does not affect the properties of the flowing gas. The pressure distribution of the generated gas differs between the molding surface of the molding die and the interface of the glass lump depending on the region. The uneven pressure distribution causes the gas to escape from the interface of the mold toward the outer periphery, so that the pressure is lowest at the outer periphery.

That is, when a glass block having an approximate shape is brought close to the molding surface of the molding die in which the gas is uniformly jetted, the gas flows outward along the interface. At this time, due to the flow resistance, the outer portion has the lowest gas pressure, and the center portion has the highest pressure. In particular, in an axially symmetric optical lens or the like, the center has the highest pressure and the outer peripheral portion has the lowest pressure.

Normally, in the case of press molding, the interface between adjacent glass blocks is in a softened state having a viscosity of about 10 ³ to 10 ⁸ dPaS, and easily deforms according to the pressure of gas at the interface. Therefore, according to the conventional method, the center of the molded product is most concave with respect to the shape of the molding surface of the molding die, and high-precision transfer is impossible.

When such an uneven pressure distribution occurs, the glass block does not follow the molding surface of the mold in a non-uniform manner and is deformed, so that it is impossible to obtain a molded article having a desired shape. Becomes

The present invention has been made in view of the above circumstances,
At the time of non-contact pressing of the glass block, the pressure applied by the gas blown from the molding surface of the mold to the glass block is made uniform,
It is an object of the present invention to provide a method for forming a glass block capable of realizing highly accurate shape transfer.

[0012]

Therefore, in the present invention,
When pressure-molding the molten glass mass in the softened state using a porous mold, the molten glass mass and the molding surface are brought into non-contact with each other by ejecting gas from the molding surface of the molding die. While maintaining, shaping the shape of the molten glass lump so as to follow the molding surface, in a method of molding a glass lump as an optical element or a material for manufacturing the same, the method of molding the molten glass lump from the molding surface in the unloaded state. The injection flow rate of the gas is set and controlled so as to maintain a predetermined distribution in the molding surface.

That is, in the present invention, contrary to the prior art, the gas supply amount is controlled so that the pressure distribution of the gas film along the interface is uniform while the glass block is close to the molding surface of the mold. Specifically, by enabling the gas ejection pressure and flow rate from the molding surface of the mold to be individually controlled according to the position in the molding surface, the uniformity of the gas pressure at the time of pressing can be improved. To achieve.

For example, in the case of an axially symmetric lens, if the gas jet from the molding surface of the molding die is uniform, the gas pressure when molding the glass has a peak at the center of the molding surface and is directed toward the periphery. Resulting in a non-uniform distribution that decreases. Therefore, at the time of press molding, gas pressure adjustment and gas supply amount adjustment are performed in a reverse pressure distribution pattern in which the pressure becomes weaker at the center and becomes stronger at the periphery. Thereby, the gradient of the pressure distribution is canceled, and a gas film having a uniform pressure distribution can be obtained.

It is possible to measure the gas pressure at the interface of such a glass block. That is, instead of the glass block, a fine hole may be formed in a measuring tool having a shape following the forming surface of the forming die, and the gas pressure at the interface may be detected by the gas pressure sensor through the hole. Then, a gas pressure distribution is measured by making a hole at a desired position. It is also possible to calculate the gas pressure distribution as an approximate value. Furthermore, if there is a variation in the gas pressure distribution,
Since this is reflected in the shape of the molded article, it is also possible to infer the situation of the gas pressure distribution therefrom.

In the present invention, for example, the gas pressure distribution is inferred from the shape of the molded article, and conversely, by adjusting the pressure distribution, the gas pressure at the interface is made uniform, and the pressure is transferred from the molding surface with high precision. In addition, a molded glass block as an optical element or a material for an optical element having a desired interface can be obtained.

As a specific method, a desired gas pressure distribution can be obtained by injecting a gas whose flow rate is individually controlled from a plurality of inlets when injecting a gas into a molding die. . Further, as another example, the structure of the porous mold to be used is, for example, configured by a combination of a plurality of ring-shaped mold members, and between each mold member, a partition for blocking gas is separated, whereby The optimization of the gas pressure or gas flow rate of the mold member is performed. As still another example, it is effective to specify the composition of each mold member so that the porous mold has a concentric porosity distribution.

In the embodiment of the present invention described below, the control of the gas flow at the interface is performed by controlling the distribution of the gas flow to be injected into the molding die. However, the present invention is not limited to this. May be controlled.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic sectional view of a mold structure for showing a first embodiment of the present invention. Here, reference numeral 1 denotes an upper die, reference numeral 2 denotes a lower die, reference numeral 3 denotes an upper die holding member, reference numeral 4 denotes a lower die holding member, and reference numerals 5 to 8
Denotes a gas pipe, and reference numerals 9 to 12 denote flow meters. In the figure, the magnitude of the flow rate of the ejected gas per unit area is qualitatively indicated by the magnitude of the arrow (→).

FIG. 2 is a schematic sectional view showing a state in which a glass lump is formed by using the forming die shown in FIG. Here, code 1
Reference numeral 3 denotes a molded glass lump as a molded product.

In the embodiment of the molding method of the present invention, first, glass melted by a glass melting device (not shown) is supplied as a gob (molten glass lump) having a predetermined weight onto the molding surface of the lower mold 2. Start by doing. SK12 was used as the glass material for molding, and the final shape was 15 mm in diameter, 4 mm in center thickness, and the radius of curvature of the front and back sides: 1
A 6 mm biconvex lens is molded.

Here, for example, the upper mold 1 and the lower mold 2 are manufactured using porous carbon having a porosity of 15%. The mold is machined at one location around the hole for gas pipe insertion and eight locations at the periphery with the center being axially symmetric (only two of the eight locations are shown in FIG. 1), The center gas pipes 5 and 7 and the peripheral gas pipes 6 and 8 are inserted with the leading ends of the openings embedded therein.

The peripheral gas pipes 6 and 8 are in communication with each other, and gas can be ejected from the peripheral portion under common conditions. Flow meters 9 to 12 are connected to the gas piping so that a desired gas flow distribution can be set. The temperature of the mold was 300 ° C.
At this temperature, even in the air, adverse effects such as oxidation on the molding surface of the mold are small. The temperature of the glass gob charged into the cavity of the mold is 700 to 720 ° C.

In this embodiment, nitrogen gas is used as the pressure gas. First, the flowmeters 9 to 12 are all 5 L /
The gas was adjusted so as to obtain the required time, the mold was closed, and press molding was performed. Cooling was performed while maintaining the predetermined thickness, and when the glass temperature became equal to the mold temperature, the mold was opened and a molded glass block as the optical element 13 was taken out.

When the shape of the optical element 13 was measured, the center was concave on both sides with respect to the desired radius of curvature of 16 mm, and the amount of depression was 50 μm. Then, in order to reduce the amount of gas corresponding to the center of the molding surface, the gas flow rate is adjusted so that the values of the flow meters 10 and 11 become 4.5 L / min, and molding is performed in the same manner. went. The dent amount at the center of the optical element molded at this time is 20 μm
Met. Similarly, the optimum set value of the gas flow rate was determined while measuring the dent amount. Finally, when the gas flow rate at the peripheral portion was 5 L / min and the gas flow rate at the central portion was 3.5 L / min, a molded optical element having a dent amount of 0 μm was obtained. Further, molding was performed 100 times under the same conditions, but an optical element without dents was stably obtained.

(Second Embodiment) FIG. 3 is a view of a mold structure for showing a second embodiment of the present invention. Here, reference numerals 14 to 16 denote mold members made of concentric porous materials, and these mold members are combined to form an upper mold. Reference numerals 20 and 21 are stainless steel foil partition plates for the purpose of blocking gas flow. Similarly,
Reference numerals 17 to 19 denote mold members made of concentric porous materials, and the mold members are combined to form a lower mold. Reference numerals 22 and 23 are the partition plates.

Reference numeral 24 denotes an upper mold holding member, reference numeral 25 denotes a lower mold holding member, and reference numerals 26 to 28 denote mold members 14 to 16, respectively.
And pipes for individually injecting gas into the mold members 17 to 19, respectively. Reference numerals 32 to 37 are gas flow meters.

As in the first embodiment, each mold member 14
For 19 to 19, porous carbon having a porosity of 15% is used and mounted on the mold holding members 24 and 25 via partition plates 20 to 23. In this state, the upper mold and the lower mold are assembled without any gap. The gas injection port is provided as a component of the upper mold.
For each of the eight axially symmetric locations (8 in FIG. 3).
Only two of them are shown), and
Gas piping. The lower die has the same configuration.

As a result of previously examining the relationship between the gas flow rate condition and the shape of the molded optical element under the same temperature condition in the first embodiment, the center mold member 1
The values of the flow meters 34 and 35 corresponding to 4, 17 are 3.2 L /
Minute, the flow meters 33, 3 corresponding to the middle mold members 15, 18
When the value of 6 was 4 L / min and the values of the flow meters 32 and 37 corresponding to the outer mold members 16 and 19 were 6.5 L / min, a dent-free optical element was obtained. Furthermore, under the same conditions, 100
The molding was performed a number of times, and an optical element having no dent was stably obtained.

(Third Embodiment) FIG. 4 is a diagram of a mold structure for showing a third embodiment. For the upper mold and the lower mold, materials having different porosity are used for mold constituent members (mold members) whose regions are concentrically partitioned in the molding surface. That is, reference numerals 38 to 40 denote regions having different porosity in one upper mold. Similarly, reference numerals 41 to 41
Reference numeral 43 denotes regions having different porosity in one lower mold. Reference numeral 44 denotes an upper mold holding member, reference numeral 45 denotes a lower mold holding member, reference numerals 46 and 47 denote gas pipes, and reference numerals 48 and 49 denote flow meters.

In the manufacture of the mold having such a configuration, a method of adjusting the porosity of the sintered stainless steel is adopted. As a method of manufacturing a sintered body, a raw material powder is pressed into a desired shape to form a green compact, the green compact is sintered at a predetermined sintering temperature, and then finished to a final shape by machining.

Since the porosity of the sintered body is also affected by the density of the green compact, the production of the upper mold in this embodiment requires the green compact corresponding to each of the mold components 38 to 40. After adjusting the density in three stages, a method is adopted in which the green compacts are combined concentrically, sintered, and integrated.
As a result, a sintered body having a porosity distribution that becomes concentric children is obtained. The upper die as shown in FIG. 4 is produced by machining the sintered body. Similarly, mold constituent members 41 to 43 having different porosity are created.

Then, under the condition of different porosity distribution,
Five types of samples were prepared, and crow lump was formed for each of the molds. The shaping was performed under the same temperature conditions as in the first embodiment, and the porosity distribution was compared with the amount of deviation of the formed glass block from the shape of the target optical element. Summarized.

[0034]

[Table 1] Further, NO. Molding was performed 100 times under the conditions shown in No. 5, and an optical element without displacement was stably obtained.

For comparison with the embodiment of the present invention, the results of a conventional molding die as shown in FIG. 5 were confirmed. Here, reference numeral 50 denotes an upper die, and 5
1 is a lower mold. Reference numeral 52 denotes an upper mold holding member, 53
Is a lower mold holding member, 54 and 55 are gas pipes, and 56 and 57 are flow meters. The porosity of the upper mold and the lower mold are 15%, the gas flow rate is 5 L / min, and the molding temperature conditions are the same as those in the first embodiment. As a result, in the molded optical element, the center of the molding transfer surface was depressed by about 50 μm with respect to the target shape.

In the above-described embodiment of the present invention,
Although the molding surface has been shown to be applied to molding of an axially symmetric lens, not only an axially symmetric lens, but also an asymmetric, complicated shape optical element, a molding die having a molding surface corresponding thereto, It goes without saying that by setting and controlling the distribution of the jet gas on the molding surface in the same manner as described above, it is possible to obtain a molded glass block with desired accuracy.

[0037]

According to the present invention, as described above, when a softened glass is press-formed using a porous mold, a gas is blown from the molding surface of the mold to melt the glass. A molding method for obtaining a molded crow lump as an optical element or a material for manufacturing an optical element by adjusting the shape of the molten glass lump so as to follow the molding surface while keeping the glass lump and the molding surface in a non-contact state with each other. In, when the glass block is not placed, the gas ejection flow rate from the molding surface of the mold,
By setting and controlling the distribution so as to have different distributions within the molding surface, a molded glass lump having no deviation from a target shape can be obtained.

Accordingly, depending on the desired accuracy, the final optical element can be directly obtained, and even when high precision is required, an optical element having a shape very similar to the final shape can be manufactured. It is possible to obtain a molded glass lump as a raw material, and it is possible to easily obtain an optical element by molding the lump by, for example, a reheat press or performing a minute grinding / polishing process.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a mold structure for explaining a first embodiment of the present invention.

FIG. 2 is also a view showing a state after molding of glass using the mold structure.

FIG. 3 is a schematic sectional view of a mold structure according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a mold structure according to a third embodiment.

FIG. 5 is a schematic cross-sectional view for explaining a conventional die structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper mold 2 Lower mold 3 Upper mold holding member 4 Lower mold holding member 5-8 Gas piping 9-12 Flow meter 13 Molded product (molded glass lump) 14-16 Upper mold member (component member) 17-19 Lower Mold member (constituent member) 20 to 23 Partition plate 24 Upper mold holding member 25 Lower mold holding member 26 to 31 Gas pipe 32 to 37 Flow meter 38 to 40 Upper mold member 41 to 43 Lower mold member 44 Upper die holding member 45 Lower die holding member 46, 47 Gas pipe 48, 49 Flow meter 50 Upper die 51 Lower die 52 Upper die holding member 53 Lower die holding member 54, 55 Gas pipe 56, 57 Flow meter

Claims (4)

[Claims] When a molten glass lump in a softened state is subjected to pressure molding using a porous molding die, a gas is blown from a molding surface of the molding die so that the molten glass lump and the molding surface are mutually bonded. While maintaining the non-contact state, in order to shape the molten glass lump to follow the molding surface, in the method of molding a glass lump as an optical element or a material for its production,
An optical element characterized by being set and controlled so that the flow rate of gas jetted from the molding surface of the molding die in the unloaded state of the molten glass lump maintains a predetermined distribution within the molding surface. A method for forming a glass block as a material for manufacturing. 2. The method according to claim 1, wherein the gas is injected into the molding die through a plurality of injection ports. 3. The molding die according to claim 1, wherein the molding die is formed by combining a plurality of mold members so as to partition an area of the molding surface and cut off gas flow between the areas. A method for forming a glass block as an optical element or a material for producing the same. 4. The method according to claim 3, wherein each of the mold members is configured to have a required porosity distribution in each region of the molding surface facing the molten glass block in a non-contact manner. A method for forming a glass lump as the optical element or the material for producing the same.