MECHANICAL SCORING AND SEPARATION OF STRENGTHENED GLASS

• US 20110226832A1
• Filed: 03/17/2011
• Published: 09/22/2011
• Est. Priority Date: 03/19/2010
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Joseph, Michael Albert II, Brown, James William, Venkatachalam, Siva, Bayne, John Frederick, Widjaja, Sujanto
• Granted Patent: US 9,802,854 B2
• Time in Patent Office: Days
• US Class Current: 225/2
• CPC Class Codes: B26D 3/085 On sheet material
• CPC Class Codes: B28D 5/0011 with preliminary treatment, e.g. weakening by scoring
• CPC Class Codes: C03B 33/02 Cutting or splitting sheet glass or ribbons; Apparatus or machines therefor C03B33/09 takes precedence; glass-cutting tools C03B33/10
• CPC Class Codes: C03B 33/023 the sheet or ribbon being in a horizontal position
• CPC Class Codes: C03B 33/033 Apparatus for opening score lines in glass sheets
• CPC Class Codes: Y10T 225/12 With preliminary weakening
• CPC Class Codes: Y10T 225/371 Movable breaking tool
• CPC Class Codes: Y10T 83/0341 Processes

Abstract

A strengthened glass sheet is separated into undamaged sheet segments by mechanically scribing one or more vent lines of controlled depth into the sheet surface, the depths of the scribed lines being insufficient to effect sheet separation, and then applying a uniform bending moment across the vent lines to effect separation into multiple sheet segments, the vent lines being scribed from crack initiation sites comprising surface indentations formed proximate to the edges of the glass sheet.

Claims

1. A method for scribing a strengthened glass sheet comprising the steps of:

forming a crack initiation site in a first surface and proximate to a first edge of a glass sheet, the sheet comprising a surface compression layer of layer depth DOL and the crack initiation site comprising a surface indentation extending into the first surface; and

mechanically scoring the first surface from the crack initiation site a toward a second edge of the glass sheet to scribe a vent line extending into the first surface to a vent depth at least equal to DOL but less than a fracture depth causing separation of the glass sheet.

2. A method in accordance with claim 1 wherein the surface indentation extends into the first surface to a depth h that is greater than DOL but less than 3 times DOL.

3. A method in accordance with claim 1 wherein the strengthened glass sheet has a thickness not exceeding 1.5 mm.

4. A method in accordance with claim 3 wherein the surface compression layer exhibits a peak compressive stress in the range of 400-900 MPa, a peak central tension of less than 50 Mpa, and wherein layer depth DOL is in the range of 5-100 μ

m.

5. A method in accordance with claim 3 wherein the peak central tension does not exceed 40 MPa and the vent depth is the range of about 10-20% of the thickness.

6. A method in accordance with claim 3 wherein the surface indentation extends into the first surface to a depth that is less than 10% of the thickness.

7. A method in accordance with claim 1 wherein a plurality of vent lines extending from a plurality of crack initiation sites are scribed in the first surface of the glass sheet.

8. A method in accordance with claim 7 wherein at least one vent line crosses at least one other vent line.

9. A method in accordance with claim 1 wherein the glass sheet has a width W and a length L that is greater than the width W, and wherein mechanical scoring comprises scribing a plurality of spaced vent lines from a plurality of crack initiation sites along directions parallel to the length L.

10. A method in accordance with claim 9 wherein mechanical scoring further comprises cross-scribing at least one vent line from a crack initiation site proximate to a second edge of the glass sheet across the plurality of spaced vent lines in a direction parallel to the width W.

11. A method in accordance with claim 1 wherein mechanical scoring comprises scoring the first surface with a rotating abrasive scoring wheel.

12. A method in accordance with claim 11 wherein the scoring wheel comprises a tapered circumferential cutting edge.

13. A method in accordance with claim 12 wherein the circumferential cutting edge has a taper angle α

in the range of 90-140°

.

14. A method in accordance with claim 13 wherein mechanical scoring comprises moving the scoring wheel with respect to the first surface at a scoring speed in the range of 50-500 mm/s while applying a scribing load in the range of 10N to 30N to the first surface.

15. A method of separating a strengthened glass sheet incorporating surface compression layers into two or more sheet sections comprising the steps of:

scribing a vent line extending into the first surface to a vent depth at least equal to a depth DOL corresponding to the depth of a surface compression layer on the first surface, but less than a fracture depth causing separation of the glass sheet; and

applying a uniform bending moment across the vent line of a magnitude sufficient to separate the glass sheet along the vent line.

16. A method in accordance with claim 15 wherein the step of scribing a vent line in a first surface of the glass sheet comprises the steps of

forming a crack initiation site in a first surface and proximate to a first edge of the glass sheet, the sheet comprising a surface compression layer of layer depth DOL and the crack initiation site comprising a surface indentation extending into the first surface;

and

mechanically scoring the first surface from the crack initiation site a toward a second edge of the glass sheet to scribe a vent line extending into the first surface to a vent depth at least equal to DOL but less than a fracture depth causing separation of the glass sheet.

17. A method in accordance with claim 15 wherein the bending moment is applied by cantilever beam loading.

18. A method in accordance with claim 15 wherein the bending moment is applied by three-point bending.

19. A method in accordance with claim 15 wherein the bending moment generates a tensional stress a in the range of about 10-35 MPa across the vent line.

20. A method in accordance with claim 19 wherein the tensional stress is generated in three-point bending through the application of a mechanical force to a second surface of the glass sheet opposite the first surface.

21. A method in accordance with claim 20 wherein the mechanical force is applied to the second surface by a breaking bar aligned with the vent line.

22. A method in accordance with claim 21 wherein the glass sheet is supported on a compliant support surface as the mechanical force is applied.

23. A method in accordance with claim 22 wherein the vent line is positioned over a groove in the compliant support surface during application of the mechanical force.