Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
2000-07-27
2002-08-13
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S033400, C065S060300, C065S114000, C116S207000, C116S216000
Reexamination Certificate
active
06430964
ABSTRACT:
The invention relates to a method of identifying glazing that has undergone a heat treatment. The term “glazing” encompasses single or multiple glass panes, these being bare or coated with thin films, such as pyrolytic films, or with thick films, such as enamels.
Although the invention is not limited to such applications, it will more particularly be described with reference to glazing that has undergone a treatment of the “Heat Soak Test” type. This type of treatment allows, in a destructive manner, the detection of nickel sulphides in glass substrates, such as toughened, semi-toughened or hardened sheets of glass.
The presence of nickel sulphides in such glass substrates is known in the literature, but their origins are not very clear. Many origins have already been envisaged; it could come from the reduction of sodium sulphates and from the reaction with nickel oxide, coming, for example, from the nozzles of burners. It turns out in fact that, at the present time, no specific origin has been able to be determined, but these nickel sulphides are present in glass in the form of inclusions. Although these inclusions do not impair the main properties desired of the glass substrates, they do nevertheless result in a major problem in the case in particular of toughened glass sheets. This is because the presence of these nickel sulphide inclusions results in so-called “spontaneous” breakages of toughened glass sheets well after their production. Certain catalogued cases have shown breakage of such a toughened glass sheet more than ten years after its manufacture. The consequences of this drawback are serious, since the glass sheets have, of course, already been sold and then used. Moreover, since this type of glazing is especially used for the external cladding of building facades, a breakage in the glazing after it has been installed may lead to serious accidents due to the said glazing falling from, for example, building facades or from glazed roofs covering pedestrian walkways.
The various nickel sulphide compositions causing these problems have already been demonstrated. These are especially stoichiometric nickel sulphide NiS, Ni
7
S
8
and nickel sulphides substoichiometric in nickel, NiS
(1+x)
with x varying from 0 to 0.08. These various compositions may be present in the glazing in the form of crystalline inclusions, the damaging diameters of which are essentially between 40 &mgr;m and 1 mm.
The abovementioned phenomenon of “spontaneous” breakage, but the breakage occurring over time, has also already been explained. Breakages associated with the presence of nickel sulphides in the glass are caused by the volume expansion which accompanies the transformation of the &agr; phase (hexagonal phase) to the &bgr; phase (rhombohedral phase). The &agr; phase is the “high temperature” phase of nickel sulphides, which is metastable at room temperature. The &bgr; phase is the “low temperature” phase, which is stable at room temperature. It is thus understandable that, if nickel sulphides exist in their &agr; phase within glass sheets ready to be used or already used, transformations to the &bgr; phase will occur over time.
The presence of nickel sulphides in their &agr; phase within glass sheets at room temperature may be explained, especially in the case of toughened glass sheets, by the heat treatment that they have undergone; this is because, in the case of thermal toughening, the rise in temperature of the glass sheet may lead to the appearance of the &agr; phase if nickel sulphides are present. The rapid cooling which follows does not allow, because of its speed, complete return to a &bgr; phase. The glass sheets thus treated may therefore include nickel sulphides in the &agr; phase, which will be transformed over time to a &bgr; phase, the said transformation being accompanied by a volume increase that causes the glass sheets to break.
For some uses of such glazing, especially those in which the breakage of the said glazing results in the risk of accidents, it is therefore necessary to detect glass sheets having nickel sulphide inclusions liable to cause breakage of the glass sheets over time.
One method, widely used, for detecting nickel sulphide, called the “Heat Soak Test”, consists in accelerating the transformation of the high-temperature &agr; phase to the low-temperature &bgr; phase, with respect to the rate of transformation at room temperature. Such a method therefore consists of a defined heat treatment resulting, as indicated previously, in destruction of any glazing comprising nickel sulphide inclusions.
In order to use such glass sheets, for example for the building industry, it is important to be able to identify the toughened glass sheets which have undergone a nickel sulphide detection treatment. This is because, although the building industry permits the use of toughened glass sheets which have not undergone this detection treatment, there are uses which require glass sheets free of nickel sulphide inclusions; these uses are, for example, the cladding of building facades which, above a certain height, make it dangerous to use glass sheets that may undergo spontaneous breakage over time.
The identification of glazing that has undergone a detection treatment therefore appears to be necessary in order to avoid any risk of confusion between glazing that has been treated and other glazing that has not been treated and which may, moreover, be identical. It is in fact preferable to prevent any confusion that may arise, for example when delivering or when storing the glazing.
One solution for the glassmaker consists in sticking a label on the glazing that has undergone a nickel sulphide detection treatment. However, such a solution has drawbacks; first of all, whatever the type of adhesion of the label, this may have deteriorated or even disappeared. Secondly, it requires vigilance and an infallible organization in order to prevent any error, and more particularly to prevent a label being stuck on untreated glazing. Although such an organization is achievable, it may be difficult to implement.
Thus, the objective of the invention is to provide a method of identifying treated glazing, especially treated using a technique of the “Heat Soak Test” type, by an indelible means under normal handling and storage conditions.
This objective is achieved according to the invention by a method of identifying glazing that has undergone a heat treatment, consisting in fixing a substance o its surface and/or onto an edge, an optical characteristic of the said substance being modified at a temperature reached during the heat treatment. In the case of glazing that includes thin or thick films, the substance may be fixed either on the glass or on he film.
According to a preferred way of implementing the invention, the optical characteristic modified is the colour. This choice makes it possible, in particular, for the modification to be very rapidly recognized usually. During manufacture or storage of the glazing, it is thus easy to avoid any risk of confusion be:ween treated glazing.
Other optical characteristics, such as light transmission or gloss, may be used.
According to the invention, a possibly coloured substance is therefore fixed to the glazing before the heat treatment, for example before the “Heat Soak Test” treatment in the case of nickel sulphide detection, and its optical characteristic changes during the said treatment. This method according to the invention thus permits, under the normal handling, and storage conditions, he glazing that has undergone the said heat treatment to be indelibly marked. Moreover, for the glassmaker this method simplifies the incorporation of this identification, the said identification being by its nature associated with the treatment; there is in fact no risk of marking untreated glazing.
The temperature leading to a change in the optical characteristic of the substance is, of course, above the temperatures to which the glazing may be subjected during their storage or handling at the glassmaker's premises and/or by the user.
Accordi
Beyrle Andre
Chaunac Michel
Dauba Henry
Saint-Gobain Glass France
Vincent Sean
LandOfFree
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