Stock material or miscellaneous articles – Composite – Of quartz or glass
Patent
1992-11-09
1995-03-14
Ryan, Patrick J.
Stock material or miscellaneous articles
Composite
Of quartz or glass
428 34, 428 38, 428192, 428212, 428215, 428218, 428410, 4284256, 428432, 296 9614, 296 977, 296 841, 219203, 219547, 65104, 65106, 65114, 65115, B32B 900
Patent
active
053976479
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a glazing pane, more especially intended for automobile vehicles, and notably for equipping the side regions with sliding panes. More specifically, the invention concerns a safety glass pane of the type known as laminated, of which the glass sheet or sheets have undergone a thermal treatment and are assembled to one another by a sheet of plastics material. The invention also has as its subject a method for the production of such a pane.
For improving the mechanical strength of a glass sheet, it is well known that it is advantageous to carry out a treatment known as thermal toughening enabling the surface of the glass to be brought into compression, the compressive strength of glass being much higher than its tensile strength.
Thermal toughening consists of cooling the surface of a glass sheet in such a way as to solidify it at the surface before the interior becomes fixed, with the result that, when cooling continues throughout the thickness, the interior cannot contract normally, since it is prevented by the solidification of the surface. The interior is then subject to tensile stresses, whereas at the surface compressive stresses form.
When the state of the stresses induced in a glass sheet by such a thermal treatment is considered, three principal regions should be distinguished. The first region is the central region, little influenced by the edge and where, to a first approximation, it may be assumed that the glass sheet behaves as a glass sheet of infinite dimensions. If this glass sheet is of constant thickness and is cooled uniformly on both its faces, the stresses are distributed through the thickness of the sheet in accordance with a parabolic distribution, characterized by a surface compressive stress and a tensile stress in the median plane of the sheet, also termed core tensile stress. This distribution, known as the thickness stress distribution, is isotropic, the integral of the stresses along the thickness being zero, as also is the integral of the moments.
In theory, the value of the surface compressive stress is exactly equal to twice the value of the core tensile stress, although in practice a higher value should be adopted.
Moreover, a glass sheet certainly has finite dimensions and at its arrises the cooling also affects the edge face and locally concerns the entire thickness of the glass sheet. In the region bordering on the edges thus affected, the integral of the stresses through the thickness is no longer zero but leads to a preponderance of compressive stresses. In this region, the thickness stresses are therefore anisotropic. The stress tangential to the surface, averaged over the entire thickness of the glass sheet, is termed the edge stress. This marginal region has a quite special importance, notably during installation and in the case of panes mounted with a free edge, such as for example the sliding lateral panes of an automobile vehicle. The width of this marginal region is generally of the order of 2 to 3 times the thickness of the glass sheet.
However, these edge stresses are balanced locally by tensile stresses. At the frontier between the marginal region of the edge stresses and the central region, there thus exists an intermediate region where the integral of the difference of the stresses is not zero and leads to a preponderance of tensile stresses. This intermediate region, therefore having anisotropic stresses, can reach a width of several centimeters and is a very brittle region because the glass there is locally prestressed in tension. The higher the edge stresses, the higher these tensile stresses will be.
It is important to emphasize that the foregoing analysis is true even in the case of non-toughened glass sheets which, in contrast, are annealed as are, in particular, the glass sheets more especially intended for the manufacture of laminated panes. In accordance with the technique most commonly used today these sheets of glass, after they have been cut to the desired shape, are superimposed in pairs on a c
REFERENCES:
patent: 2247118 (1938-06-01), Drake
patent: 3776709 (1973-12-01), Melling et al.
patent: 4075381 (1978-02-01), Furakawa et al.
patent: 4124733 (1978-11-01), Melling et al.
patent: 4913720 (1990-04-01), Gardon et al.
patent: 5270518 (1993-12-01), Naoumenko et al.
Charrue Herve
Didelot Claude
Kramling Franz
Letemps Bernard
Weber Frederic
Bahta Abraham
Ryan Patrick J.
Saint-Gobain Vitrage International
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