Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Reexamination Certificate
1999-11-23
2002-02-05
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
C428S081000, C428S410000, C428S490000, C052S784110
Reexamination Certificate
active
06344259
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a method of finishing an edge of a sheet glass for use in e.g. fire-resistant construction material such as a fire-resistant door, a fire-resistant window or the like, a heat-tempered sheet glass using the method, and relates also to a fire-resistant construction material using this heat-tempered sheet glass.
2 Description of the Related Art
When a sheet glass is used in a fire-resistant construction material such as a fire-resistant door, it is necessary for the glass to have a high edge strength in order to avoid a heat cracking phenomenon of this sheet glass. Namely, when a sheet glass is subjected to a significant heat, heat expansion occurring at the center area of the sheet glass applies a tension to the edge of the sheet glass fixedly supported to a window sash, for example. Then, when this tension exceeds the edge strength of the sheet glass, a cracking occurs in the sheet glass. This is the heat cracking phenomenon.
As fire-resistant sheet glass, there are known a wired sheet glass and a laminated glass incorporating an intermediate layer made of silica hydrate alkaline. In the case of the former, its transparency may be a problem since the embedded wire hinders the the view. The latter also has the possibility of losing its transparency due to bubbling of the intermediate layer resulting from a thermal variation. As an alternative free from such drawbacks, there is known a sheet glass prepared by heat-tempering treatment of soda-lime glass material.
As such heat tempering treatment, the convention has provided a method comprising the steps of: heating a sheet glass at a temperature range (approximately, 760 deg. C.) significantly higher than a melting point of the glass (720 to 730 deg. C.); and then spraying a cooling air against the sheet glass at an extremely high pressure such as a back pressure of 950 mmAq, for instance. With such heat tempering treatment of the sheet glass as above, it is possible indeed to provide the sheet glass with a predetermined edge strength. However, since the air is sprayed at the very high pressure against the sheet glass which has been heated up to such high temperature range as exceeding the melting point of the glass, this spraying may result in surface irregularity or warping of the sheet glass which leads to distortion of the image reflected by the sheet glass.
According to a conventional method of finishing an edge of such sheet glass as described supra, in order to obtain a flat and even edge, as illustrated in FIGS.
6
(
a
) and (
b
), a cup abrading wheel
20
is rotated about an axis while causing a side face
20
a
of the wheel to contact an edge
21
a
or a ridge
21
b
of the sheet glass
21
. The cup abrading wheel includes diamond or abrading stone or the like affixed on the side face
20
a
thereof.
With such sheet glass edge abrading method as described supra, a very fine abrade streak, which is hardly recognizable with naked eyes, is formed at the ridge portion as a result from the abrading of the edge portion. For this reason, a thermal stress associated with a thermal expansion tends to be concentrated at the abrade streak. In particular, in the case of the soda-lime glass (without heat-tempering treatment), it is not possible to provide this glass with a high edge strength.
Accordingly, in order to allow its use as a fire-resistant sheet glass, the above-described heat tempering treatment is needed. But, this treatment involves the inconveniences described supra. Further, if the heat tempering treatment is effected at a lower heating temperature and/or lower back pressure of the spraying air than the conventional method in order to avoid the inconveniences (surface irregularity, warping) of the heat tempering treatment, then, this will result in an insufficient edge strength of the sheet glass obtained as a fire-resistant door.
In view of the above-described state of the art, the primary object of the invention is to solve the drawbacks of the conventional art by providing an improved method of finishing an edge of a sheet glass capable of increasing the edge strength of the glass, a heat-tempered glass with a predetermined edge strength made by using the method, and also a fire-resistant construction material using this heat-tempered sheet glass.
SUMMARY OF THE INVENTION
For fulfilling the above-noted object, a method of finishing an edge of a sheet glass, according to the present invention, comprises:
a first grinding step for abrading an edge of a sheet glass so as to provide the edge with an outwardly convex curved shape; and
a finishing step for finishing a bordering portion which has been formed by the first abrading step between the curved edge and each flat side face of the sheet glass, so as to provide this bordering portion with a greater smoothness than smoothness provided by the first abrading step.
In general, the stress occurring within a sheet glass is apt to be concentrated at the ridge portions of the sheet glass. Then, according to the sheet glass edge finishing method of the present invention, the method comprises the first abrading step for abrading an edge of a sheet glass so as to provide the edge with an outwardly convex curved shape; and a finishing step for finishing a bordering portion which has been formed by the first abrading step between the curved edge and each flat side face of the sheet glass, so as to provide this bordering portion with a greater smoothness than smoothness provided by the first abrading step. Hence, it is possible to restrict concentration of stress at the edge portion of the sheet glass. Especially, by effecting the finishing step for finishing a bordering portion which has been formed by the first grinding step between the curved edge and each flat side face of the sheet glass, so as to provide this bordering portion with a greater smoothness than smoothness provided by the first abrading step, the ridge portions are substantially eliminated to provide a smoother finished surface. Accordingly, it is possible to avoid the formation of the abrade streak which tends to invite the concentration of the stress at this portion. As a result, the method of the invention allows the sheet glass to obtain a higher edge strength than the convention.
With the increased edge strength, even if the heat tempering operation is effected at a lower temperature range and/or lower air-spraying pressure than the convention, the resulting sheet glass may retain a predetermined sufficient edge strength after the heat-tempering treatment. As a result, it becomes possible to avoid the inconveniences of the prior art such as the surface irregularity or warping which leads to a reflection image distortion. Moreover, the running costs of the heat-tempering system may be reduced as well.
In summary, according to the invention's method of finishing the edge of a sheet glass, it becomes possible to restrict concentration of thermal stress at the edge of the sheet glass and hence to increase the edge strength of the sheet glass. As the result, even if the heat-tempering treatment of the sheet glass is effected by a simpler method than the conventional method, the resulting glass may maintain sufficient performance as a fire-resistant sheet glass. Accordingly, the method achieves improvement of the quality of the sheet glass and also reduction of the running cost of the heat-tempering treatment system.
The finishing step may be carried out by a variety of manners such as buffing, heat melting, chemical melting or the like.
If the finishing step is carried out by buffing, it is possible to polish the surface with the irregularity in the order of a few um's.
Further, if the finishing step is carried out by heat melting, it is possible to provide the finished surface with the same finish as the sheet glass per se, so that the stress applied to the sheet glass may be born by the entire edge thereof. As a result, the edge strength of the sheet glass may be further increased.
If the finishing step is carrie
Obana Shigeki
Sugiura Kiminari
Tanaka Keisuke
Dixon Merrick
Fulbright & Jaworski L.L.P.
Nippon Sheet Glass Co. Ltd.
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