Methods for measuring the asymmetry of a glass-sheet manufacturing process
Methods are provided for measuring the asymmetry of glass-sheet manufacturing processes. The methods include subjecting glass sheets or test samples taken from glass sheets to an ion-exchange process and measuring warp values. Metrics for the asymmetry of the glass-sheet manufacturing process are then obtained from the warp values. In one embodiment, the metric is independent of the geometry of the glass sheets or the test samples (the BM 1 metric); in another embodiment, the metric is independent of the geometry of the glass sheets or the test samples and substantially independent of the ion-exchange process used in the testing (the ASYM metric).
1. A method for producing low warp, ion-exchanged, glass sheets comprising:
(a) producing a population of glass sheets using a glass-sheet manufacturing process, each glass sheet in the population having an R value that is less than or equal to 2.5×10 −4 , where the R value is the ratio of the thickness of the glass sheet to the length of the glass sheet's diagonal; and
(b) ion exchange strengthening the population of glass sheets produced in step (a);
wherein the glass-sheet manufacturing process has an ASYM value that is less than or equal to 1,500 ppm and a BM 1 value that is less than or equal to 0.002 microns,
where the ASYM value is determined by:
(IA) producing a glass sheet using the glass-sheet manufacturing process;
(IIA) measuring the mass M 0 of the glass sheet or a test sample from the glass sheet;
(IIIA) subjecting the glass sheet or the test sample to an ion-exchange process;
(IVA) measuring the change in mass ΔM of the glass sheet or the test sample as a result of step (IIIA);
(VA) measuring a warp value W for the glass sheet or the test sample after step (IIIA); and
(VIA) computing an ASYM value for the glass sheet or the test sample using an equation of the form:
ASYM
=
2
R
2
3
(
2
L
x
+
2
L
y
+
2
L
z
)
W
Δ
M
2
M
0
(
W
i
n
-
W
out
)
W
Glass
where W Glass is the molecular weight in grams/mole of the glass making up the glass sheet or the test sample prior to step (IIIA), W in and W out are, respectively, the molecular weights in grams/mole of the ions being exchanged into and out of the glass in step (IIIA), taken singly and not as oxides, R is the glass sheet's or the test sample's thickness-to-diagonal ratio, and L x , L y , and L z are, respectively, the length, width, and thickness of the glass sheet or the test sample in the same units as the warp value W;
wherein the ASYM value computed in step (VIA) is an average value based on measurements made on multiple glass sheets or multiple test samples; and
where the BM 1 value is determined by:
(IB) producing a glass sheet using the glass-sheet manufacturing process;
(IIB) subjecting the glass sheet or a test sample from the glass sheet to an ion-exchange process;
(IIIB) measuring a warp value W for the glass sheet or the test sample after step (IIB); and
(IVB) computing a BM 1 value for the glass sheet or the test sample using an equation of the form:
BM 1 =K·W·R 2
where K is a constant and R is the glass sheet's or the test sample's thickness-to-diagonal ratio;
wherein the BM 1 value computed in step (IVB) is an average value based on measurements made on multiple glass sheets or multiple test samples and K=⅔.
2. The method of claim 1 wherein:
(a) the R value of the glass sheets is less than or equal 2.0×10 −4 , the ASYM value of the glass-sheet manufacturing process is less than or equal to 1,000 ppm, and the BM 1 value of the glass-sheet manufacturing process is less than or equal to 0.001 microns; or
(b) the R value of the glass sheets is less than or equal 1.5×10 −4 , the ASYM value of the glass-sheet manufacturing process is less than or equal to 500 ppm, and the BM 1 value of the glass-sheet manufacturing process is less than or equal to 0.0005 microns.
3. An ion-exchanged glass sheet having an R value that is less than or equal to 2.5×10 −4 and a W value that is less than or equal to 48 millimeters, where the R value is the ratio of the thickness of the glass sheet to the length of the glass sheet's diagonal and the W value is the glass sheet's gravity-free warp value,
wherein the glass sheet is produced by a process that comprises: (i) producing the glass sheet with a glass-sheet manufacturing process that has an ASYM value that is less than or equal to 1,500 ppm and (ii) ion exchange strengthening the glass sheet.
4. An ion-exchanged glass sheet having an R value that is less than or equal to 2.5×10 −4 and a W value that is less than or equal to 48 millimeters, where the R value is the ratio of the thickness of the glass sheet to the length of the glass sheet's diagonal and the W value is the glass sheet's gravity-free warp value,
wherein the glass sheet is produced by a process that comprises: (i) producing the glass sheet with a glass-sheet manufacturing process that has a BM 1 value that is less than or equal to 0.002 microns and (ii) ion exchange strengthening the glass sheet.
5. The ion-exchanged glass sheet of claim 3 wherein the R value is less than or equal to 2.0×10 −4 , the W value is less than or equal to 37.5 millimeters, and the ASYM value is less than or equal to 1,000 ppm.
6. The ion-exchanged glass sheet of claim 3 wherein the R value is less than or equal to 1.5×10 −4 , the W value is less than or equal to 33 millimeters, and the ASYM value is less than or equal to 500 ppm.
7. The ion-exchanged glass sheet of claim 3 wherein the glass-sheet manufacturing process has a BM 1 value that is less than or equal to 0.002 microns.
8. The ion-exchanged glass sheet of claim 7 wherein the R value is less than or equal to 2.0×10 −4 , the W value is less than or equal to 37.5 millimeters, the ASYM value is less than or equal to 1,000 ppm, and the BM 1 value is less than or equal to 0.001 microns.
9. The ion-exchanged glass sheet of claim 7 wherein the R value is less than or equal to 1.5×10 −4 , the W value is less than or equal to 33 millimeters, the ASYM value is less than or equal to 500 ppm, and the BM 1 value is less than or equal to 0.0005 microns.
10. The ion-exchanged glass sheet of claim 4 wherein the R value is less than or equal to 2.0×10 −4 , the W value is less than or equal to 37.5 millimeters, and the BM 1 value is less than or equal to 0.001 microns.
11. The ion-exchanged glass sheet of claim 4 wherein the R value is less than or equal to 1.5×10 −4 , the W value is less than or equal to 33 millimeters, and the BM 1 value is less than or equal to 0.0005 microns.