Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
2000-04-26
2003-01-07
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S090000, C065S091000, C065S092000, C065S093000, C065S100000, C065S101000, C065S105000, C065S112000, C065S164000, C065S166000, C065S174000, C065S176000, C065S184000, C065S183000, C065S185000, C065S193000, C065S196000, C065S197000, C065S198000, C065S199000
Reexamination Certificate
active
06502423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making individual glass panes with a thickness between 0.03 mm and 2 mm, especially glass panes for electronic units, in which a glass band is drawn vertically downward from a hot forming tool and is subjected to a cutting operation, which includes an edge trimming process and/or cutting the panes to length from the glass band, and further processing steps, as needed. The invention also relates to an apparatus for making the individual glass panes and to an apparatus for monitoring the vertical alignment of the continuously produced vertical glass panes made from the glass band.
2. Prior Art
The individual glass panes for electronic units, such as laptops, which are also designated as display glass, are preferably each made with a thickness of from 0.4 to 2 mm. However glass panes with a thickness of down to 30 to 50 &mgr;m have been made in connection with the desire for special product properties for electronic units. On the one hand, it is a matter of a product that must have a high degree of planarity, on the other hand, a mass produced product which must be made as economically as possible. In order to arrive at reasonable manufacturing costs, the rejects, i.e. the panes with thickness variations, must be reduced and the waste minimized.
The glass panes are usually cut from a continuously produced glass band, which is drawn out vertically from a drawing orifice. For this purpose a drawing apparatus with several pairs of rollers is used, which engages on the border of the glass band. Although the drawing speed is identical on both sides, variations in the linearity of the glass band occur. Already variations of about 0.1 mm over a length of about 400 mm are too much for exactly cutting out individual rectangular glass panes, since the panes must be cut from the band without loss of intervening pieces and, not as in conventional processes, first approximately and then to length.
If an oblique course for the glass band is specified, the drawing roller pairs wander to the outside on one side and to the inside on another side relative to the glass. The trimming must thus have a safety margin or the position of the trimming or edging head must be adjusted to the position of the glass band.
Currently when the glass panes are cut from the vertical glass band, the cut is made transversely or across the width of the glass band. During the cutting away process the drawing force determined by the weight of the glass pane to be cut away changes continuously, which leads to feedback to the hot forming. In any case a tear or crack arising because of the cutting process easily continues into the hot forming region, which halts the entire hot forming apparatus. Disadvantageous thickness fluctuations in the resulting glass band are also caused by the feedback into the hot forming region, which increase the number of rejects. Similarly the variations caused by the cutting process continue until at the hot forming.
The drawing off of a glass band upward from the free surface of the melt and the guiding of the still plastic glass band horizontally over cooled bending rollers with a diameter of a few decimeters is described in Kitaigorodski, Technology of Glass (Technologie des Glases), 1957, pp. 227 to 228.
An apparatus for guiding horizontally is known from DE-OS 21 18 589 in which a gas cushion is provided between a guide roller and the glass band, so that the glass band does not rest on the roller. The glass band is drawn off upward or downward and is still plastic because of its high glass temperature, when it is guided. Edge rollers are used as parts of the guide rollers for guiding the glass band. Differences in the drawing forces acting in the longitudinal direction of the glass band in the bending region can be compensated for by maintaining the pressure differential in the gas cushion.
A photodetector device for observing the glass edge is known from the Derwent Abstract of SU 546 573A, in which the photosensor produces signals, which are used to control the drawing speed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method, with which individual rectangular glass panels can be cut from a vertical glass band drawn from a hot forming device in an in-line method with reduced rejects and waste.
According to the invention, this object is attained, by a method, in which, after drawing off, the vertical glass band is cooled to a temperature below the lower cooling point (strain point) of the glass, subsequently is deflected in a bending zone, while it is freely suspended, with a bending radius between 0.1 m and 4 m and then is conveyed into a horizontal zone in which at least one cutting process is performed on the horizontal glass band. The viscosity of the glass, &eegr;, is 10
14.5
dPas at the lower cooling point (strain point) of the glass.
The vertical alignment includes the linearity, the position and the angle of the glass edge. The linearity is a measure of the degree of bending of the edge of the glass band. The linearity is reduced or small, when the edge curvature is great or large. The position of the glass band relates to the lateral parallel displacement or shifting of the glass band, when the entire band is moved sideways. The oblique hanging of the glass band, i.e. the deviation from the vertical, is characterized by the angle. The vertical alignment of the glass band is preferably continuously monitored in order to minimize waste.
It has been shown that the cutting process for the glass band can be simplified and performed without feedback to the hot forming of the produced glass band, when the glass band is arranged in a horizontal position. Because of that feature the hot forming step is uncoupled from the subsequent production steps, so that a stabilization of the vertical glass band occurs and eventually occurring fluctuations or variations transmitted to the vertical band are in any event attenuated. The cutting to length of the glass panes has hardly any influence on the drawing forces acting on the vertical glass band. The process stability of the entire process chain is considerably improved because of those features. An additional advantage is that a crack or tear eventually occurring in the direction of the hot forming device during cutting continues only up to the guiding region and is halted there.
The cutting process for the horizontal glass band requires guiding of the vertical glass band, which up to now has not been considered to be possible with a glass band of a thickness from 0.4 mm to 2 mm. Since glass is a brittle material, it was believed that the flexural stiffness at lower temperatures at a glass thickness of about 0.4 mm is already so great that a deflection of about 90° could not be performed without breaking the glass. However it has been surprisingly found that, if a bending radius of between 1.5 m and 5 m is maintained, stable bending of the suspended glass band is possible. The bending radius is 3 to 4 m with a thickness of about 2 mm. Thus the bending radius can be, for example, 2 m for 1.1 mm thick glass and amounts to from 3 m to 4 m at a thickness of about 1.9 mm. So that no plastic deformation of the glass occurs, the temperature of the guided or deflected glass band must already be below the lower cooling point of the glass.
It has been shown that a deflection or bending of about 90° can be performed without glass breakage with thinner glasses of a thickness between 0.03 mm and 0.4 mm, even when the bending radius is selected so that it is between 0.1 m and 1.5 m.
In a preferred embodiment of the method for glasses having a thickness between 0.03 mm and 0.4 mm after the trimming the glass is rolled up or wound up instead of being cut to length. This simplifies the transport and it can be unrolled at a later time and cut. The glass can be more tightly wound, then prior to deflection or bending. The smallest winding radius amounts to about half the guiding radius.
In a preferred embodiment of
Berndt Andreas
Ostendarp Heinrich
Suennemann Rolf
Colaianni Michael
Schott Glas
Striker Michael J.
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