JPS61197429A - Production of molded glass article having high surface quality - Google Patents

Abstract

PURPOSE:To produce a molded glass article having high surface quality, by cooling the surface defect part of a glass block to a state having high ad controlled viscosity, taking only the glass of softened state out of the block and molding the glass. CONSTITUTION:A pair of molds 11' are placed opposite to each other on the lid mold 10, and a cavity 14 having a gap slightly larger than the thickness of the molded article is formed. A softened glass block 4 having highly viscous surface layer is supplied to the space formed by the body mold 5 and the lower mold 6 of the pressurized transfer mold, and is pressed by pushing up the lower mold 6. Only the glass in the glass block 4 and having softened state is transferred to the cavity 14. When the cavity 14 is filled with the transferred glass 12, the glass 12 is pressed with the forming mold 11'.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention is directed to the production of glass lumps in a softened state in which surface defects are unavoidably generated in the pre-production process.

The present invention relates to a method suitable for producing glass molded articles having high surface quality without surface defects, particularly optical element preforms such as lenses, or optical elements.

(B) Prior Art Conventionally, preforms for manufacturing optical elements have generally been manufactured by press-molding a glass gob obtained by cutting a molten glass flow with a shear.

However, in the preformed product manufactured by this method, traces (shear marks) from cutting with a shear remain on the glass surface, so when manufacturing optical elements, it is necessary to use the shear. Removal of the marks requires a series of complicated and expensive steps in which a considerable amount of the glass surface layer is ground and then polished. Also, depending on the type of glass, if the glass lump is kept within the molding temperature range,
There are glasses in which specific components volatilize, resulting in a surface-altered layer such as devitrification, but even in the case of such glasses, the above-mentioned processes such as polishing away surface defects are essential in order to obtain optical elements. .

On the other hand, a molding method is known in which optical elements are directly manufactured by pressure-molding a softened glass lump with a pair of molds with high-precision molding surfaces, but the softened glass lump used in this molding method is also complicated. It is common to reheat a glass gob that has been given a predetermined surface precision through a surface polishing process, and for glass that produces a surface-altered layer during this heating.

This molding method cannot be applied.

Furthermore, attempts have been made to apply the transfer molding method used for molding plastics to molding glass to obtain optical elements, but even with this type of molding method, softened glass with shear marks and surface deterioration layers cannot be produced. When using lumps, it is difficult to obtain optical elements with high surface quality with a high yield.

(c) Problems to be solved by the invention The present invention has been made in view of the above-mentioned situation, and its purpose is to eliminate the drawbacks of the above-mentioned prior art,
It is an object of the present invention to provide a method for manufacturing a glass molded article having no surface defects and having a high surface quality from a glass lump in a softened state having surface defects.

(d) Means for Solving the Problems The method of the present invention for achieving the above-mentioned object is suitable for obtaining a molded article having a high surface quality from a softened glass lump that inevitably has surface defects. This is based on the basic concept of cooling the surface defects of the glass gob to maintain a controlled high viscosity state, and then taking out only the softened glass inside the glass gob and molding it.

That is, the feature of the method of the present invention is that the softened glass gob, which is supplied into a pressurized transfer mold and whose only surface portion is in a high viscosity state, is pressurized, and the glass inside the glass gob is released from the opening of the mold. The process involves letting the glass escape, and then molding the escaped glass with a mold.

In carrying out the present invention, as the softened glass gob for molding, one obtained by directly cutting a molten glass flow or one obtained by reheating a glass gob that has been cooled can be used as appropriate, but the inside of the glass gob is pressurized. It is necessary that the material be in a sufficiently softened state to escape from the opening of the transfer mold, and that one surface be in a high viscosity state with poor fluidity.

In addition, as a method for molding the glass escaped from the opening of the pressurized transfer mold, it is possible to form the optical element by applying pressure with a mold or by press-fitting it into a pre-formed mold cavity. Although preforms can be obtained, optical elements can also be obtained directly by using molds with high precision molding surfaces in these methods.

(e) Examples Next, embodiments of the method of the present invention will be described with reference to the drawings.

Example 1 Figure 1 ((A) to (F)) is a process explanatory diagram for manufacturing a preformed product for a biconvex lens, and shows the state of the glass and the positional relationship of various molded members in the order of the molding operation. This is what is shown.

First, as shown in Figure (A), a glass flow (2) having a viscosity of about 1O3 poise flowing down from the conduit port (1) of the optical glass melting equipment is cut by a shear (3), and the obtained glass lump ( 4) is fed into the cavity formed by the old mold (5) and the lower mold (6) of the pressurized transfer mold. At this time, glass lump (4)
In this case, shear marks (A) due to cutting are inevitably formed on the upper and lower surfaces. The old model (5) and the lower model (6).

In order to cool the surface portion of the glass gob (4) and increase its viscosity, the temperature is kept below the glass transition point.

Next, as shown in Figure 1 (b), the glass gob (4) is pressurized with the upper mold (7) to cool the entire surface of the glass gob (4) and form a high viscosity glass layer (8). to form. In this case, since the top surface of the glass lump (4) was open before pressurization, the temperature is higher than other surfaces, so the desired high-viscosity glass layer (8) is formed on this part in a short time. The upper mold (7) is maintained at a temperature sufficiently lower than the glass transition point so that the temperature of the upper mold (7) is sufficiently lower than the glass transition point.

Next, as shown in FIG. 5) Attach to the top surface.

Next, as shown in Figure (d), a pair of molds (11)
are placed oppositely above the lid wall (10), and at the same time, the lower mold (6) of the pressurized transfer type is pushed up to pressurize the glass gob (4), and the high viscosity glass layer ( 8) The shell is broken and only the softened glass inside escapes from the opening (9) to the outside without contacting the molding surface (Ila). Next, as shown in Figure (E), a predetermined amount of Immediately after letting the glass escape, a pair of molds (1
After the escape glass (12) is clamped and pressurized in step 1) and solidified, the formed glass is taken out from the mold (11) and the pressurized transfer mold, and then slowly cooled in a slow cooling furnace (not shown). Unnecessary portions of the molded glass remaining in the pressurized transfer mold are cut and removed to obtain a desired molded product. The molded product thus obtained has no shear marks and has high surface quality, so it can be used as a preform for lenses.

In this example, the molding surface (lla
) can be mirror-finished and used to obtain a pre-molded product suitable for molding. Further, by using a molding surface (lla) that has been subjected to high-precision mirror polishing and further accurately controlling the relative spacing of the mold (11) by applying pressure, it is also possible to directly obtain an optical element.

Embodiment 2 FIG. 2 ((a) to (b)) is a process explanatory diagram in another embodiment for manufacturing a preformed product for a lens.

In this example, first, the above-mentioned Example 1 (Fig. 1 (
In the same manner as in (a) to (c)), glass lump (4)
is supplied into the cavity formed by the old mold (5) and lower mold (6) of the pressurized transfer type to form a high viscosity glass layer (8), and then the lid wall (io) is inserted into the old mold (5). Attach it to the top.

Next, as shown in FIG. 2 (a), on the lid wall (10),
A pair of molds (11') are arranged facing each other.

Cavity (14) with a spacing somewhat larger than the wall thickness of the molded product
is formed, and the lower mold (6) is pushed up to form a glass lump (4).
) to escape the softened glass inside the glass lump (4) into the cavity (14).Then, as shown in Figure (b), the cavity was filled with the escape glass (12). After that, the escape glass (12) is pressure-molded using a mold (11').

The molded product obtained in this example has a high surface quality free of shear marks and the like, so it is excellent as a preformed product for lenses.

Further, in this example, by using a mold (11') whose molding surface (11'a) is mirror-finished with high precision, an optical element can be directly obtained as in Example 1 above.

Although the embodiments have been described above, the specific implementation of the method of the present invention is not limited to the above embodiments.
The glass may be allowed to escape laterally or downwardly, and a set of pressurized transfer molds may be provided with a plurality of openings, and a plurality of molds may be arranged in correspondence with the openings to allow the glass to escape in the sideways or downward direction. Further, the operation of forming a high viscosity glass layer on the surface of the glass gob may be performed before the glass gob is fed into the pressurized transfer mold.

In addition, in the above example, the case where a molded article is manufactured from a glass ingot having a shear mark as a surface defect has been explained, but the case where a molded article is manufactured from a glass ingot having a surface defect such as surface devitrification etc. Needless to say, similar effects can be obtained.

(F) Effects of the Invention As mentioned above, the method of the present invention involves pressurizing a softened glass gob that is supplied into a pressurized transfer mold and whose surface portion is in a high viscosity state, and passing it through the opening of the mold. This method allows the softened glass inside the glass lump to escape and then molds the escaped glass with a mold, so surface defects existing on the surface of the raw glass can be completely separated and removed. Glass molded products with high surface quality can be manufactured without surface defects such as surface devitrification. Therefore, the method of the present invention is extremely suitable for manufacturing glass molded products that require a high level of surface quality, especially optical element preforms or optical elements that can significantly reduce the amount of work in post-processes such as grinding. suitable.

[Brief explanation of the drawing]

FIG. 1 ((a) to (f)) is a side sectional view showing the manufacturing process of an embodiment according to the method of the present invention, and FIG. FIG. 7 is a side cross-sectional view showing the latter half of the manufacturing process in such another embodiment. 4... Glass lump 5... Old model 6...
Lower mold 8... High viscosity glass layer 9... Opening 1
0...Lid wall 11, 11'...Mold 1
2... Escape glass A... Shermark patent applicant Ohara Optical Glass Manufacturing Co., Ltd.! lmu

Claims (1)

[Claims] The softened glass gob, which is supplied to the pressurized transfer mold and whose surface portion is in a high viscosity state, is pressurized to cause the glass inside the glass gob to escape from the opening of the pressurized transfer mold, and then the escaped glass is A method for producing a glass molded product having high surface quality, the method comprising: molding using a mold.