Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Patent
1994-06-15
1997-11-04
Griffin, Steven P.
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
65 64, 65 67, 65106, 65120, 65244, 65269, 65271, 65276, 65278, 65279, 65283, 65292, 65DIG8, 65DIG9, C03B 2302, C03B 2304
Patent
active
056834837
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to large quartz glass plate and the manufacturing method and equipment to produce it. In particular, the present invention relates to large quartz glass plate of high transparency and purity, in the form of flat plate and the manufacturing method and equipment to produce it.
BACKGROUND OF THE INVENTION
Large, flat quartz glass plate of high purity and transparency has typically been used as material for manufacturing square tanks for washing high-purity elements, such as wafers, large diameter quartz glass observation ports and lamp covers, where the adhesion of impurities must be avoided. Compared to other glass materials, the quartz glass used for these applications retains high viscosity even at high temperatures, which makes it difficult to form and cast it when it is melted and, therefore, difficult to form it into plate.
Generally, there are two existing methods by which such quartz glass plate is produced. One is by cutting a block of quartz glass into thin sheets. The other is a process in which a quartz glass tube is opened to form a quartz glass plate.
The prior art applied in the former method employs a technology in which plate is formed from pulverized powder by refining natural crystal or quartzite and then heating the powder electrically or with a gas burner to melt and fuse it into a block of quartz glass, which is then cut into plate using a diamond cutter or the like. However, as this method involves cutting blocks of quartz glass with a diamond cutter or the like, the surface of the plate thus obtained is rough, necessitating a surface smoothing treatment, such as a special separate polishing operation to make the surface transparent.
Quartz glass is a material with superior transparency and light transmission, and particularly in applications such as observation ports, lamp covers and the like, the material is usually required to have excellent optical transparency. Therefore, it is necessary to perform transparency finishing with some type of surface treatment, for example, surface fusing with fire or specular glossing with a granular abrasive after the coarse polishing on the plate material, which leaves a rough surface and reduced transparency as described in the previous paragraph. This transparency finishing treatment is extremely labor intensive and time consuming. Moreover, during the polishing with the granular abrasive, the material can be easily contaminated by impurities and metal elements which will have detrimental effects on semiconductors. In the surface fusing treatment using fire, thermal distortion tends to cause cracking, so this method is highly disadvantageous from an industrial point of view.
Also, because the aforementioned block forms are manufactured by melting and fusing a pulverized powder of natural crystal or quartzite in a special die, impurities or reactive gasses originating in the die body, as well as residual gasses within the melted substance tend to be retained in the form of bubbles in the melted, high viscosity quartz glass. Since this tendency becomes more pronounced as the size of the block body increases, inevitably there are foreign substances and bubbles in large plate cut from such blocks. This makes it difficult to use such plate for products that require a high degree of transparency such as quartz glass observation ports and lamp covers.
Also, because of the poor mechanical strength and heat resistance of the die used for melting and fusing the quartz powder, the prior art has substantial restrictions on the size of the block body that can be obtained. Furthermore, if large plate material is to be obtained from such large blocks, the thickness of the diamond cutter needs to be increased, resulting in a great deal of expensive quartz glass lost to the cutting margin. Thus, not only is it extremely disadvantageous from an industrial point of view, the resulting plate material is uneconomical. In summary, this method for the production of large quartz glass plate has a number of serious
REFERENCES:
patent: 1283333 (1918-10-01), Shaw
patent: 3740207 (1973-06-01), Bogerts et al.
patent: 4612023 (1986-09-01), Kreutzer et al.
Taro Moritani et al., "Glass Engineering Handbook", Apr. 20, 1964, Asakura Shoten, p. 611, Clause 2.1 Fabrication.
Hiroyuki Kimura
Kazuo Asajima
Shinichi Okosi
Yosiaki Ise
Griffin Steven P.
Shin-Etsu Quartz Products Co. Ltd.
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