Glass manufacturing – Processes – Forming product or preform from molten glass
Patent
1998-08-31
2000-08-15
Silverman, Stanley S.
Glass manufacturing
Processes
Forming product or preform from molten glass
65 251, 65 252, 65 253, 65 66, 65 90, 65 991, 65100, 65169, 65170, 651821, 651822, 6537415, 1986261, 1986265, 1986881, 198691, C03B 1300
Patent
active
061018457
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel process for forming a glass sheet.
BACKGROUND ART
The presently most widely used process for producing glass sheets, is a so-called tin bath float process wherein prescribed materials are melted in a melting tank, then introduced onto a molten metal tin bath in a reducing atmosphere at a temperature at which the viscosity of glass becomes about 10,000 poise, permitted to spread and move in the longitudinal and transverse directions by means of a mechanical external force and gradually cooled to around the glass transition temperature, to obtain a flat plane glass having a smooth surface. By this process, the smoothness of the product is remarkably improved as compared with the previous roll out process or the like, whereby a polishing step which used to be required, is no longer necessary.
However, this process also has some drawbacks and problems, and improvements are still desired. Namely, in the tin bath float process, a large quantity of tin is used, whereby exhaustion of the tin resource which is not abundant, is feared, it is necessary to maintain the atmosphere to be reducing by means of hydrogen gas in order not to let the metal tin be oxidized, accordingly, applicable fining agent is rather limited, the installation is obliged to be of a large size in view of a problem such as heat balance, whereby the installation investment tends to be large, tin is likely to penetrate into the glass from the surface in contact with the tin, whereby the quality of the product tends to be affected, it is weak against vibration such as earth quake, and it takes time for recovery of the production after an earth quake, and a large quantity of energy is consumed by heating and warming the glass.
Whereas, a production method such as so-called fusion method, has also been proposed, but such a method has not been satisfactory with respect to the surface smoothness of the product or the constant productivity and quality. Further, there has been a proposal such that a gas such as air is supplied from pores on the surface of a support, and molten glass is spread thereon to form a glass sheet (JP-B-50-36445). However, in order to directly and continuously supply the gas as proposed, an enormous quantity of the gas is required. Further, in order to pass it through pores, an extremely high pressure is required, whereby a stabilized control is extremely difficult. Thus, this method is not practical.
The object of the present invention is to solve the various drawbacks in the above mentioned existing processes for forming glass sheets.
DISCLOSURE OF THE INVENTION
The present invention provides a process for forming a glass sheet, which is a process for continuously forming a glass sheet, and which comprises a step of introducing a vapor film-forming agent which is not vapor at least around room temperature and which is vapor at a temperature above the glass transition point of the glass, into a support having a structure or a material capable of internally containing a liquid, and a step of sliding the support and the glass of which temperature is above the glass transition point against each other via a thin layer of the vaporized vapor film-forming agent.
In the present invention, the vapor film-forming agent is vaporized, whereby the vapor is continuously supplied to the interface between the glass and the support. This vapor is present in the form of a thin layer at the interface between the glass and the support. The vapor layer at the interface is renewed by continuous supply of the vapor, whereby there will be no inclusion of impurities to the surface, and a glass sheet having good surface smoothness can be obtained. Further, the vapor film-forming agent is supplied to the support in the form of a liquid, whereby continuous supply is easy, and the amount of supply may be small. The vaporization of the vapor film-forming agent may occur at the forming plane of the support or in the vicinity of the forming plane in the support.
In a preferred embodiment of th
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Kojima Gen
Koyama Tsutomu
Matsumoto Kiyoshi
Takada Akira
Unoki Masao
Asahi Glass Company Ltd.
Colaianni Michael P.
Silverman Stanley S.
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