Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Reexamination Certificate
1999-06-07
2001-03-13
Loney, Donald (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
C428S156000, C428S213000, C428S218000, C428S219000, C428S220000, C428S410000, C296S146160
Reexamination Certificate
active
06200665
ABSTRACT:
The present invention relates to a glass sheet having a stepped portion (hereinbelow, referred to as a stepped glass sheet). In particular, the present invention relates to a tempered stepped glass sheet used for a side window glass for an automobile.
There has been known as a tepering method, a method for quenching by blowing a jet stream-like cooling medium to both surfaces of a glass sheet heated to a temperature near a glass softening point by means of an air blowing device in which cooing nozzles are arranged in a lattice or zigzag form. In such tempering method, a temperature difference is given between an inner portion and a surface of the glass sheet at the time of quenching whereby a layer having a residue compressive stress is formed in the surface of the glass sheet solidified.
When the glass sheet has infinite dimensions in longitudinal and lateral directions and a predetermined thickness, and if both surfaces of the glass sheet are uniformly quenched, a stress distribution in the direction of the thickness follows a so-called parabolic distribution. Then, a surface compressive stress value is equal to two times as much as a tensile stress value at the center of an inner portion in the direction of the thickness of the glass sheet, and the integrated value of stresses in the direction of the thickness becomes zero. In fact, however, a glass sheet has infinite dimensions. Generally, a chamfering treatment is conducted to the peripheral edge portion from the viewpoints of preventing cracking in a quenching time as well as design.
In quenching the glass sheet having an edge surface, quenching to the peripheral edge portion of the glass sheet affects the entire portion of the edge surface at (unlike a central region where there is scarcely influence of the peripheral edge portion), and it affects locally the entire thickness of the peripheral edge portion. Specifically, there are produced, in an extreme peripheral edge portion of the glass sheet, a region having a width twice to three times as much as the thickness of the glass sheet in which the averaged integrated value of stresses in the direction of the thickness exhibits compressibility, in an inner portion of the glass sheet, and an intermediate region in which the averaged integrated value of stresses in the direction of the thickness exhibits tension so as to balance the compressibility. This means that there is a region which is weak against an impact from the outside and which has a width in a portion slightly inside the peripheral edge portion of the glass sheet.
Here, description is made as to the averaged integrated value as well as the direction of a principal stress and a principal stress difference. First, a plane which is perpendicular to a glass sheet surface (a cross-sectional plane of the glass sheet) is selected. In the selected plane, any angle can be taken with respect to a linear line which is parallel to the glass sheet surface. Further, a point is selected in the selected plane. The values of stresses acting on this point, which are perpendicular to the selected plane, are different depending on angles in the selected plane, and accordingly, there are an angle at which a stress value is the maximum and an angle at which a stress value is minimum. The principal stress directions are a direction of a stress exhibiting the maximum value and a direction showing the minimum value which intersects at a right angle the direction of the stress exhibiting the maximum value. Hereinbelow, the direction of the stress exhibiting the maximum value is referred to as the principal stress direction.
Since the principal stress itself can not directly be measured, the principal stress in a tempered glass is evaluated by the principal stress difference obtained by a photoelasticity method. The principal stress difference obtained by the photoelasticity method corresponds to a value obtained by dividing the sum of values of the difference between the maximum value of stress and the minimum value of stress at each point aligned in the direction of the thickness of the glass sheet by the thickness of the glass sheet (an averaged value obtained by dividing an integrated value of the difference between the maximum value of stress and the minimum value of stress by the thickness). Accordingly, when a certain point is selected on a surface of the glass sheet, an averaged integrated value of the difference between the maximum value of stress and the minimum value of stress at each point which is aligned in the direction of the thickness from the selected point, is referred to as the principal stress difference at the selected point (the principal stress direction in this case is referred to as the principal stress direction at this point). In this specification, any principal stress direction exists in parallel to the glass sheet surface.
As a window glass disposed in a side window, especially a slidable door window, of an automobile, a stepped glass sheet as a kind of a window glass sheet, which eliminates any step between the glass sheet and a flange of automobile body, has been developed in response to needs for improving an aerodynamic performance and designing of automobiles.
FIG. 3
is a diagram showing an example of the shape of a peripheral edge portion of a glass sheet and a state of arrangement. In
FIG. 3
, reference numeral
1
designates a glass sheet having a stepped portion at its peripheral edge portion. Numeral
2
designates a sash having a recess
3
in which the peripheral edge portion of the glass sheet
1
is fitted. In this glass sheet, a chamfering operation is conducted to the peripheral edge portion to form a stepped portion whereby a thinner thickness portion is formed with a predetermined width, adjacent to a thicker thickness portion.
In particular, the stepped glass sheet to be disposed at a side of an automobile is adapted to frequently be slid in a vertical direction or an oblique vertical direction. Accordingly, the peripheral edge portion of the glass sheet suffers highly severe mechanical load, and a sufficient strength to endure such load is required to the glass sheet In the conventional method, however, the stepped glass sheet was tempered by equalizing a cooling rate over the entire surface of the glass sheet. Accordingly, it was difficult to apply a sufficient strength because stress values in a compressive stress layer in a surface portion of the intermediate region were relatively small
It is an object of the present invention to provide a stepped glass sheet having a peripheral edge portion which is durable to a highly severe mechanical load
In accordance with the present invention, there is provided a stepped glass sheet having a peripheral edge region A, a central region C and an intermediate region B provided between the peripheral edge region A and the central region C wherein a stepped portion is formed at the border between the peripheral edge region A and the intermediate region B, and the thickness of the peripheral edge region A is thinner than the thickness of the central region C, characterized in that the stepped glass sheet is tempered, and the averaged value of surface compressive stresses in the intermediate region B is 100-500 kg/cm
2
larger than the averaged value of surface compressive stresses in the central region C.
REFERENCES:
patent: 5380575 (1995-01-01), Kuster et al.
patent: 5397647 (1995-03-01), Kramling et al.
patent: 5570542 (1996-11-01), Cameron
patent: 0 884 286 (1998-12-01), None
patent: 62-32892 (1987-08-01), None
Asahi Glass Company Ltd.
Loney Donald
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Stepped glass sheet does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stepped glass sheet, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stepped glass sheet will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2534449