Glass manufacturing – Processes – Utilizing parting or lubricating layer
Reexamination Certificate
2000-10-19
2003-09-30
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
Utilizing parting or lubricating layer
C065S025300, C065S084000, C065S085000, C065S127000, C065S182200, C065S182100, C065S303000, C065S304000, C065S066000, C065S081000, C065S083000, C065S068000, C065S037000
Reexamination Certificate
active
06626010
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of floating glass gobs, a method of manufacturing glass gobs, a method of manufacturing molded glass, and the devices employed in these methods.
BACKGROUND ART
In recent years, high-precision hot press molding techniques based on forming molds have been successfully developed as methods of manufacturing aspheric glass lenses and the like. The weight of the prepared member (referred to hereinafter as a “preform”) used in molding must be precise down to the milligram, and the presence of flaws such as striae, devitrification, scratches, and bubbles, as well as surface-adhering matter that cannot be washed away, is not permissible.
For example, a method of mass producing such preforms at low cost is described in Japanese Patent Application Publication No. Hei 2-14839. In that method, molten glass flowing out of a pipe is received in a depression in a forming mold. In this process, a gas such as air or an inert gas is injected through fine holes formed in the depression, creating a layer of gas between the molten glass gob and the inner surface of the depression in the forming mold. Until at least a portion of the outer surface of the molten glass gob reaches a temperature below the softening point, the molten glass gob is held within the depression in a state of substantial non-contact with the inner surface of the depression and cooled to manufacture glass gobs. Based on that method, since both the upper and lower surfaces are free surfaces, preforms of good surface quality can be obtained. Further, in that method, since the molten glass is allowed to drip naturally or is cut with a cutting blade to make it drop, a practical level of weight precision can also be achieved.
Japanese Patent Application Publication Nos. Hei 6-122526, Hei 6-144845, and Hei 6-206730 disclose methods in which a receiving mold comprised of a porous material is employed instead of the above-described forming mold with fine holes, molten glass is received with gas being injected through the receiving mold, and molten glass gobs are similarly held within a depression in a non-contact state and cooled to obtain glass gobs. Further, Japanese Patent Application Publication No. Hei 11-116252 discloses a method in which molten glass is received while gas is being injected through a receiving mold of a porous material having a hemispherical depression and the molten glass gob is rotated in a state of non-contact and cooled to obtain glass spheres. Additionally, Japanese Patent Application Publication No. Hei 10-139465 discloses a method in which molten glass is received in a receiving mold made of porous material that has been soaked in water, a liquid organic compound, or the like and the molten glass is floated by means of gas vaporization pressure and cooled to obtain glass gobs.
However, the above-cited prior art has the following drawbacks. In the method described in Japanese Patent Application Publication No. Hei 2-14839, gas is injected through fine holes in a mold with a depression to float molten glass. In this floating method, when the gas flow rate is increased to completely float the molten glass, pits similar to those on an orange-skin form in the molten glass surface. Since this pitting is formed in the glass by the pressure of gas injected through fine holes, it is necessary to decrease the gas flow rate to a degree where surface pits do not form. However, when the gas flow rate is lowered, it becomes impossible to completely prevent temporary contact between the forming mold and the glass, particularly at the initial stage of glass outflow. Accordingly, the depression surface in this method is machined to a mirror finish to prevent scratching of, and adhesion of dirt onto, the glass surface due to temporary contact.
There is also glass from which preforms of good quality cannot be manufactured by the above-described method. For example, when forming glass in which component volatility is high in the flow temperature range, vapor tends to condense and deposit on the forming mold, which is set to a low temperature. Volatile components that have deposited on the mold then re-adhere to the glass surface through contact between mold and glass. Glasses with high component volatility are glasses containing large amounts of components with high vapor pressures at high temperature, examples of which are alkali components such as Na
2
O, K
2
O, and Li
2
O, as well as B
2
O
3
; glasses with high liquidus temperatures; glasses with high viscosities at high temperature; and glasses with high outflow temperatures. Since common glasses contain alkali components, problems tend to occur with volatile matter in glasses with a liquidus temperature of 900° C. or above.
Further, even if contact with the mold is prevented, the small amount of floating above the mold increases the concentration of volatile components between the mold and the glass, and the volatile components tend to adhere to the glass. Further, when molding glasses that tend to crystallize (devitrify) near the outflow temperature, contact between the mold and the glass immediately after outflow triggers crystallization and the glass surface sometimes crystallizes. As set forth above, the forming of glass with a large amount of volatile matter in the outflow temperature range and glass tending to crystallize requires that there be absolutely no contact between mold and glass.
Further, the forming of glass with a large amount of volatile matter in the outflow temperature range requires that the gas flow rate be increased to lower the concentration of volatile matter in the gap between the mold and the molten glass and to expel volatile matter from the gap.
A more complete floating state can be achieved by employing a receiving mold comprised of a porous member and rendering uniform the flow of gas that is injected as described in Japanese Patent Application Publication No. Hei 6-122526. However, in practice, the following problems result from the porous member. For example, achieving uniform gas injection requires the selection of a porous member of small pore diameter. However, when a porous member with a small pore diameter is employed, an extremely high gas pressure is required to achieve a gas flow rate adequate for floating, which is a drawback in that the device becomes expensive. Further, when a porous member is employed, there is a drawback in that gas permeability differs substantially between individual molds and the gas flow rate must be substantially adjusted for each forming mold. Although there are various differences, there is a distribution in the gas permeability within a single porous member, making it difficult to achieve a stable floating state. The porous material can be a carbon or ceramic porous material, but these tend to present such problems as low material strength, damage to the porous member during mold assembly, falling off of the surface of the porous member during forming due to thermal shock, and adhesion of fragments to the molten glass surface. Porous members comprised of heat-resistant metals have few of the above-stated problems relating to material strength. However, due to the toughness of the material, the surface pores tend to be crushed during mold processing, often making it impossible to uniformly inject gas.
As set forth above, although a porous member is employed to achieve uniform gas for floating, it is difficult to achieve the intended ideal floating state. There is a further drawback in that mistakes such as forgetting to turn on the gas flow in the mold that result in contact between the mold and the glass tend to damage the mold.
There are additional drawbacks in that porous materials are expensive to buy and to process, and when volatile components have adhered to them, regeneration by washing and grinding is not effective.
The method of floating molten glass by means of the gas vaporization pressure of water or the like in a porous material described in Japanese Patent Application Publication No. Hei 10-139465 has the following problems. To
Colaianni Michael
Hoya Corporation
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