METHOD OF FORMING EVACUATED GLASS PANELS

Abstract: A method of forming an evacuated glass panel which facilitates the placement of a pump-out tube close to one edge of the finished panel. First and second glass sheets (12 and 13) are assembled in face-to-face spaced-apart relationship, with the first sheet (12) having an edge portion (33) that extends beyond the corresponding edge portion (34) of the second sheet. A pump-out tube (18) is provided in the first sheet at a location adjacent the corresponding edge portion (34) of the second sheet. The first and second sheets (12 and 13) are sealed around their edges to form a chamber (15) which is evacuated by way of an evacuating head (10). Following the evacuation process, the pump-out tube (18) is closed and the edge portion (33) of the first sheet is trimmed so as to lie adjacent the corresponding edge portion (34) of the second sheet.

Description: METHOD OF FORMING EVACUATED GLASS PANELS FIELD OF THE INVENTION This invention relates to a method of forming an evacuated glass panel having a chamber that is defined (ie, enclosed) by a glass wall that includes a port through which evacuation is effected. The invention has been developed in the context of evacuated door and/or window glazing ("vacuum glazing") and the invention is herein after described in that context. However, it will be understood that the invention does have broader application, for example in forming evacuated solar collector panels and panel-form display devices. BACKGROUND OF THE INVENTION In one form of vacuum glazing, two plane spaced-apart sheets of glass are positioned in face-to-face confronting relationship and are hermetically sealed around their edges with a low melting point glass that commonly is referred to a solder glass. The space (ie, chamber) between the sheets is evacuated and the face-to-face separation of the sheets is maintained by a network of small support pillars. In typical situations the glazing may comprise glass sheets that have a surface area in the order of 0.02 to 4.00 square metres, sheet thicknesses in the order of 2.0 to 5.0 millimetres and a face-to- face spacing in the order of 0.10 to 0.20 millimetres. The evacuation of glazing presents special problems (relative to the evacuation of many other glass objects), in that the region at which evacuation is effected should not be obtrusive in the final product and in that the evacuating procedure must be appropriate to panels having large surface areas or linear dimensions. The evacuating procedure involves heating the glazing to a high temperature in a so-called bake-out oven (whilst the chamber to be evacuated is connected to an evacuating system) in order to remove gases from surface regions of the sheets and the pillars. In one method of implementing the evacuating procedure, a small pump- out tube is connected (ie, sealed) to the external surface of one of the glass sheets in communication with an aperture that extends through the glass sheet. The connection between the tube and the glass sheet is made using solder glass, normally at the same time that the solder glass edge-seal is made between the sheets. The solder glass sealing is normally effected at a temperature around 450°C, that is at a temperature that is high enough to melt the solder glass and make a leak-free joint but below a temperature at which significant deformation might occur in the glass sheets. Following completion of the solder glass sealing, the structure is normally cooled to room temperature. Thereafter, a metal evacuating head is positioned over the pump-out tube and is connected to a remote vacuum pump. The evacuating head includes a central cavity that is dimensioned to receive the pump-out tube and to which the vacuum pump is connected. The glazing structure and the evacuating head are loaded into the bake- out oven where evacuation is effected whilst the complete structure is subjected to an out-gassing temperature. Thereafter, the outer end of the pump-out tube is closed by heating the tube to its melting temperature. A problem that is inherent in the above described procedure flows from the possibility that the evacuating head may be required to have a radial dimension that is larger than the desired distance of the pump-out tube from an edge of the glass sheet. This imposes a constraint on the location of the pump-out tube and, thus, may require that the pump-out tube be located further from the edge than might be required to meet aesthetic considerations. SUMMARY OF THE INVENTION The present invention is directed to a method of forming an evacuated glass panel and which facilitates the location of a pump-out tube close to an edge of the finished panel. Broadly defined, the invention provides a method of forming an evacuated glass panel and which comprises the steps of: (a) assembling first and second glass sheets in face-to-face spaced-apart relationship, with the first sheet having an edge portion extending beyond the corresponding edge portion of the second sheet, (b) providing a pump-out tube in the first sheet at a location adjacent the corresponding edge portion of the second sheet, (c) edge sealing the first and second sheets to form a chamber between the two sheets, (d) covering the pump-out tube and a portion of the first sheet that surrounds the pump-out tube with an evacuating head, (e) evacuating the chamber by way of the evacuating head, (f) closing the pump-out tube upon completion of the evacuating process, and (g) trimming the edge portion of the first sheet that extends beyond the corresponding edge portion of the second sheet. PREFERRED FEATURES OF THE INVENTION The evacuating head may comprise one that has a first cavity that is arranged in use to communicate with the pump-out tube, and at least one further cavity that surrounds the first cavity and which is arranged in use to contact the wall portion of the first glass sheet that surrounds the pump-out tube. With this type of evacuating head, the chamber will be evacuated by way of the first cavity whilst a vacuum is maintained in the further cavity or, if more than one, in each of the further cavities. However, the evacuating head preferably comprises one having a first cavity that communicates with the pump-out tube and a second surrounding cavity that contains a polymer O-ring that contacts the wall portion of the first glass sheet that surrounds the pump-out tube. The invention will be more fully understood from the following description of embodiments of the invention. The description is provided with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS In the drawings: Figure 1 shows sequential steps A to E in a preferred method of fabricating glazing, Figure 2 shows sequential steps A to E in an alternative method of fabricating glazing, and Figure 3 shows a schematic representation of the glazing located within a bake-out oven and connected to one or more external vacuum pumps by way of an evacuating head. DETAILED DESCRIPTION OF THE INVENTION As illustrated in Figures 1 and 2, an evacuating head 10 is mounted to glazing 11 that is to be evacuated. The glazing comprises two plane glass sheets 12 and 13 that are maintained in spaced-apart face-to-face confronting relationship. The glass sheets would normally be composed of soda-lime glass and be interconnected along their edges by a bead 14 of edge-sealing solder glass. A chamber 15 is defined by the two glass sheets 12 and 13 and the sheets are maintained in spaced-apart relationship by a network or array of support pillars 16. The chamber 15 is evacuated to a level below 10 "3 Torr, this providing for gaseous heat conduction between the sheets that is negligible relative to other heat flow mechanisms. The glass sheet 12 is formed with an aperture 17, and a glass pump-out tube 18 is positioned to locate within and project outwardly from the aperture 17. The pump-out tube is sealed to the glass sheet by a bead 19 of solder glass. A metal filament 20 is shown to surround the pump-out tube 18 and this may be employed, following evacuation of the cavity 15, to melt and close the pump-out tube, although other techniques may be employed for this purpose. The evacuating head 10 as shown in Figure 1 comprises a metal body 21 which incorporates a central, first cavity 22. The first cavity is shaped and dimensioned to receive the pump-out tube 18 and to provide for unrestricted movement of gas during evacuation and out-gassing of the chamber 15. The first cavity 22 is connected by way of a port 23 and a conduit 24 to a vacuum pump 25 that is located outside a baking chamber 32, as shown schematically in Figure 3. A second, annular cavity 26 also is provided within the body 21 of the evacuating head. The second cavity 26 is positioned to surround the first cavity 22 and it contains a polymer O-ring 26A which contacts and, in use, seals against the surface of the glass sheet 12 that surrounds the pump-out tube 18. A first annular land is located between the first and second cavities 22 and 26, and a second annular land 28 surrounds the annular second cavity 26. Each of the two lands 27 and 28 makes contact with the surface of the glass sheet over a small area. The evacuating head 10 as shown in Figure 2 is in some respects similar to that shown in Figure 1 and like reference numerals are employed to identify like parts. As shown in Figure 2, the evacuating head 10 comprises a metal body 21 which incorporates a central, first cavity 22. The first cavity 22 is shaped and dimensioned to receive the pump-out tube 18 and to provide for unrestricted movement of gas during evacuation and out-gassing of the chamber 15. The first cavity 22 is connected by way of a port 23 and a conduit 24 to a vacuum pump 25 that is located outside of the baking chamber 32. A second, annular cavity 26 also is provided within the body 21 of the evacuating head. The second cavity 26 is positioned to surround the first cavity 22 and is arranged in use to be closed by the surface of the glass sheet 12 that surrounds the pump-out tube 18. A first annular land 27 is located between the first and second cavities 22 and 26, and a second annular land 28 surrounds the annular second cavity 26. Each of the two lands 27 and 28 makes contact with the surface of the glass sheet 12 over a small area and so limits gas flow into the second cavity 26 and between the two cavities 22-26. The second cavity 26 is connected by way of a port 29 and a conduit 30 to a further vacuum pump 31, as indicated in Figure 3. The evacuating heads 10 as shown in Figures 1 and 2 will typically have an outside diameter of 50 mm to 100 mm and the first, central cavity 22 will typically have a diameter in the order of 10 mm to 20 mm. The lands 27 and 28 will each have a radial width in the order of 1 mm but may be in the range 0.10 mm to 10 mm. The sequential steps of fabricating the evacuated glazing unit in a situation where the pump-out tube 18 is required to be located very close to one edge of the unit are clearly shown in Figures 1 and 2. This is achieved by cutting the sheet 12 to provide a margin or edge portion 33 that extends beyond the corresponding margin or edge portion 34 of sheet 13, as shown in Figures A to D, and by trimming the margin of sheet 12 after fabrication of the complete glazing unit, as shown in Figure E. The sheets 12 and 13 are first assembled in spaced-apart relationship (as above described) and a bead 14 of unfused solder glass is deposited around the edge of sheet 13. Similarly, a bead 19 of unfused solder glass is deposited around the pump-out tube 18 that is located within aperture 17 in sheet 12. The further fabrication steps may then be performed by way of a single heating procedure or two heating procedures depending upon the levels of heat to be employed and/or on the type of evacuating head to be used. After assembling the two glass sheets and depositing the beads of solder glass, the glazing unit 11 is heated to around 450°C within the oven 32 and, during this process, the solder glass melts to form seals around the edges of the glazing and around the pump out tube. The glazing is then cooled to a temperature (around 380°C) at which the solder glass solidifies, and evacuation of the chamber 15 between the two glass sheets 12 and 13 is then effected by connecting the vacuum system 25 to the central cavity 22 of the evacuating head 10. Evacuation of the chamber is maintained as the glazing and evacuating head are cooled. The specific temperature/time schedule that is used during this cooling period will depend upon the time necessary to achieve adequate out-gassing of the internal surfaces of the glazing. When out-gassing and evacuation has been completed, the pump-out tube 18 is melted and fused closed, using the filament element 20. Thereafter, the margin of sheet 12 is trimmed as described above with reference to Figures IE and 2E.

Claims: CLALMS: 1. A method of forming an evacuated glass panel and which comprises the steps of: (a) assembling first and second glass sheets in face-to-face spaced-apart relationship, with the first sheet having an edge portion extending beyond the corresponding edge portion of the second sheet, (b) providing a pump-out tube in the first sheet at a location adjacent the corresponding edge portion of the second sheet, (c) edge sealing the first and second sheets to form a chamber between the two sheets, (d) covering the pump-out tube and a portion of the first sheet that surrounds the pump-out tube with an evacuating head, (e) evacuating the chamber by way of the evacuating head, (f) closing the pump-out tube upon completion of the evacuating process, and (g) trimming the edge portion of the first sheet that extends beyond the corresponding edge portion of the second sheet. 2. The method as claimed in claim 1 wherein the pump-out tube is positioned to locate immediately adjacent the inner margin of edge sealant that flows between the first and second sheets during the edge-sealing of the sheets and wherein the pump-out tube is located a distance from the edge portion of the first sheet which is slightly greater than the radial dimension of the evacuating head. 3. The method as claimed in claim 1 or claim 2 wherein the glass panel is exposed to heat-induced outgassing within an oven during evacuation of the chamber. 4. The method as claimed in any one of claims 1 to 3 wherein the evacuating head has a central first cavity which is shaped and dimensioned to receive the pump-out tube and has at least one further cavity that surrounds the first cavity whereby it lies adjacent the portion of the first sheet that surrounds the pump-out tube. 5. The method as claimed in claim 4 wherein one only further cavity surrounds the first cavity in the evacuating head and wherein a polymer O-ring is located within the further cavity for sealing engagement with the portion of the first sheet that surrounds the pump-out tube. 6. The method as claimed in claim 4 wherein the further cavity or, if more than one, each of the further cavities is closed by surface contact with the portion of the first sheet that surrounds the pump-out tube and wherein the or each further cavity is evacuated during the time that the chamber is evacuated by way of the first cavity in the evacuating head. 7. A method of forming an evacuated glass panel, substantially as hereinbefore described with reference to the accompanying drawings. 8. An evacuated glass panel when formed by the method as claimed in any one of the preceding claims. i 9. An evacuated glass panel substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: COLLINS RICHARD EDWARD, TANG JIAN-ZHENG, COLLINS, RICHARD, EDWARD, TANG, JIAN-ZHENG
Applicants: COLLINS RICHARD EDWARD, TANG JIAN ZHENG, UNIV SYDNEY, COLLINS, RICHARD, EDWARD, TANG, JIAN-ZHENG, THE UNIVERSITY OF SYDNEY
Application year: 1999
Main classification: E06B3
IPC codes: C03C27, E06B3