JPH06227828A - Production of glass preform for spherical molding - Google Patents

Abstract

PURPOSE:To produce a spherical molding glass preform to produce a glass optical element by press molding. CONSTITUTION:A volume controlled glass preliminary preform is processed to form a nearly spherical body by a high temperature processing by the use of extreme infrared radiation. The obtained nearly spherical glass body 4 is processed to form a spherical body by a low temperature processing.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, the method of manufacturing glass aspherical lenses has shifted from a cold working method by grinding and polishing to a hot working method of molding heat-softened glass using a precision-processed mold. I'm doing it. Many patent publications have been published so far regarding the molding method of the glass optical element, and the number of commercially available glass aspherical lenses has become very large in recent years.

However, the unit price of glass aspherical lenses is very high compared to spherical lenses and the like, and the use of aspherical lenses is useful for downsizing, but from the standpoint of cost reduction. The effect tends to be small.

There are various reasons why the market price of the glass aspherical lens is expensive, and one reason is that the cost of the material for molding the glass optical element is high. A glass material used for a biconvex lens shape or the like is often a spherical material shape, but the required quality is required to be almost the same as that of a ball lens. Therefore, it is necessary to provide a manufacturing method that is precisely processed by grinding and polishing.

In the conventional grinding and polishing, a glass is cut out from a glass block material into a cubic shape, polyhedral processing is performed as shown in FIG. 8, and then sphere processing is performed by grinding and polishing, and glass is press-formed. Then, after obtaining the material with the brim shown in FIG. 9, the grindstone 9 having the shape shown in FIG.
Generally, a method of grinding into a spherical shape is performed.

[0006]

However, in the step of processing a cube into a polyhedron or the step of processing a glass with a brim into a spherical shape as described above, the processing of glass is performed one by one, so that the processing time is shortened. However, it is very difficult to reduce the processing cost. Further, since the amount of glass to be processed and removed is large, the material before processing becomes large, which causes a cost increase. As a result, the unit price of the glass material for molding tends to be very high.

The present invention provides a method for mass-producing a glass material for molding at low cost with a simple manufacturing process in order to reduce the unit cost of the glass aspherical lens.

[0008]

In order to achieve the above object, the present invention arranges a plurality of volume-controlled glass preliminary materials in a saucer made of a material which is hard to get wet with glass and radiates far infrared rays, and is subjected to heat treatment. After obtaining a glass sphere having a substantially spherical shape, the plurality of glass lumps are simultaneously processed into a sphere by cold working.

That is, a large amount of roughly spherical glass is produced by a heat softening deformation method utilizing the thermal characteristics of glass,
It is characterized in that the glass material for molding is manufactured by subjecting them to mirror finishing by a conventional polishing method.

As a thermal property, glass has a temperature-specific singular point such as a specific transition point, yield point, softening point, etc. depending on the type of glass, and the state of the glass changes variously with the singular point as a boundary, and the glass transition point or Then, the glass exhibits a liquid phase property, and at a temperature above the softening point, the viscous flow phenomenon becomes remarkable and the glass deforms due to its own weight. From this fact, the glass is heated to the softening point or higher, and the deformation due to its own weight and the deformation due to the surface tension are combined to form a substantially spherical body. The roughly spherical glass thus obtained is subjected to mirror finishing by grinding and polishing, which are conventional techniques, to obtain a spherical glass material for molding.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. BSL7 (softening point 715 ° C.) was used as the glass material. As the shape of the glass preliminary material before heating, the cylindrical glass preliminary material 1 shown in FIG. 1 was used in this example. This is volume-controlled with an outer diameter φ ₁ and a height h ₁ by cutting a rod-shaped glass material. Since both end surfaces are cut surfaces, the processing unit price of the preliminary material is very low.

Next, the glass preliminary material 1 is set on the lower heating jig 2b shown in FIG.
The heat treatment is performed twice at the temperature and time shown in. The heating jigs 2a and 2b used here are made of a carbon material. Since carbon is hard to get wet with glass and is close to an ideal black body, far infrared rays of 2.5 μm or more, which is the absorption wavelength range of glass, are easily radiated as secondary radiation. Therefore, it is effective to use a carbon material for the heating jigs 2a and 2b because the glass is easily heated uniformly and the mold releasing property from the jig after the heat treatment is good.

[0013]

[Table 1]

FIG. 2 to FIG. 5 show the deformed state of the glass by two successive heat treatments. Since the in-line type far-infrared belt furnace shown in FIG. 7 is used for the heat treatment of this glass, a large amount of heat treatment is possible. By using the far infrared heater 5 as the heating source and changing the feeding speed of the belt 7, it is possible to adjust the heating ultimate temperature of the glass arranged in the heating jig 2. Therefore, when the type of glass changes, the deformation of the glass can be controlled by changing the feed rate of the belt 7 without changing the setting of the temperature inside the furnace. From this, it is possible to meet the market demand for a wide variety of small quantities.

By performing the continuous heat treatment twice, the substantially spherical glass preform 4 shown in FIG. 6 is obtained. The preformed body 4 is then ground and finished into a spherical shape by a barrel processing machine. Since the barrel processing machine has a low equipment cost and requires a small number of processing personnel, the processing cost is very low. Since a substantially spherical shape is obtained, the amount of glass removed is extremely small, and the processing time of the barrel processing machine is about 8 hours, which is shorter than the barrel processing time of general glass. Further, since the number of glass preforms processed per barrel is about 2000 with a diameter of about 8 mm, there is an advantage that a large number of equipment is not required.

Next, a spherical glass material 10 is obtained by mirror finishing with a lapping machine such as a lapping machine. Since the final finish is a polishing finish by cold machining, there is little variation in shape, surface roughness, etc., and a high quality glass material for molding can be obtained. In the processing of a lapping machine or the like, a large amount of glass can be polished at one time, and since the processing step is one polishing step, the processing time per piece can be shortened and the processing cost can be reduced.

Table 2 shows the processing time of each step of the glass material for molding obtained by the above manufacturing steps, and Table 3 shows the measurement results of dimensions and weight.

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a volume-controlled cylindrical glass preliminary material is made into a substantially spherical shape by utilizing the thermal characteristics of glass, and then a spherical glass material with high precision is obtained by machining. It became possible to obtain. Further, unlike the conventional processing method, since grinding is not performed from a cube or the like, the amount of glass removed when grinding into a sphere is small, and the material can be effectively used economically.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a cylindrical glass preliminary material in an example of the present invention.

FIG. 2 is a cross-sectional view of a main part when a cylindrical glass preliminary material is placed on a heating jig.

FIG. 3 is a cross-sectional view showing a glass shape when the first heat treatment is completed.

FIG. 4 is a cross-sectional view showing a state in which the heating jig is turned upside down after the first heat treatment is completed.

FIG. 5 is a cross-sectional view showing a glass shape when the second heat treatment is completed.

FIG. 6 is a dimensional diagram showing the shape of a roughly spherical glass material for molding.

FIG. 7 is a schematic sectional view of an in-line far infrared belt furnace.

FIG. 8 is a diagram showing the shape of a glass material that has been subjected to polyhedral processing.

FIG. 9 is a view showing the shape of a glass material with a brim.

FIG. 10 is a schematic explanatory view of processing a glass material with a brim into a spherical shape by a grindstone.

FIG. 11 is a view showing the shape of a spherical glass material for molding.

[Explanation of symbols]

 1 cylindrical glass material 2 heating jig 2a upper heating jig 2b lower heating jig 3 glass shape after the first heat treatment 4 roughly spherical glass material 5 far infrared heater 7 heat resistant belt 8 glass material with brim 9 Sphere processing grindstone 10 Spherical glass material for forming

Claims (1)

[Claims] 1. A plurality of volume-controlled glass preliminary materials are placed in a saucer made of a material that is hard to get wet with glass and radiates far infrared rays, and a roughly spherical glass lump is obtained by heat treatment. A method for manufacturing a spherical glass material for forming, which comprises simultaneously processing a plurality of the glass into a spherical shape by cold working.