WO2001009471A1

WO2001009471A1 - A method and apparatus for evacuating glass panels

Info

Publication number: WO2001009471A1
Application number: PCT/AU2000/000738
Authority: WO
Inventors: Richard E. Collins
Original assignee: University of Sydney
Current assignee: University of Sydney
Priority date: 1999-07-30
Filing date: 2000-06-30
Publication date: 2001-02-08
Anticipated expiration: 2002-01-30
Also published as: JP2003506298A; AUPQ195599A0

Abstract

A method and apparatus for supporting glass pump-out tube (12) which extends out of an oven during outgassing and evacuation of air from chamber (28) between glass panes (16-17) of double-glazing unit (18). Vacuum cup (30), which is pumped out via tube (34), holds support bracket (20) firmly to glass sheet (16) so that it moves therewith during thermal expansion, thus eliminating lateral forces on tube (12). Any axial forces are accomodated by sliding of tube (12) within elastomeric O-ring seal (24) located outside the oven. Sealing of double-glazing unit (18) is achieved after evacuation, by radiative heater (42) which softens tube (12) which then collapses under atmospheric pressure.

Description

A METHOD AND APPARATUS FOR EVACUATING GLASS PANELS

Field of the Invention

The present invention relates broadly to a method and apparatus for evacuating glass panels, the glass panels comprising a chamber between two spaced-apart glass sheets. The invention will be described herein with reference to vacuum glazing, however, it will be appreciated that the invention does have broader applications, including for example to solar cell panels or glass panel displays. Background of the Invention

In permanently sealed evacuated devices such as vacuum glazing it is necessary to remove residual gases from internal surfaces of the volume that is being evacuated before the device is sealed. Unless removed prior to sealing, "outgassing" of the residual gases from the internal surfaces can degrade the internal vacuum, and adversely effect the operation of the vacuum glazing, for example its thermally insulating properties.

Most of the permanently sealed evacuated devices are evacuated through a small glass pump-out tube which is fused to a port of a pump-out channel formed in the device, and sealed to a vacuum fitting (connected to a pumping system) on the other end, using a flexible polymer or elastomer material. Following completion of the evacuation process, the glass pump-out tube is melted and thereby sealed, usually at a point very close to the port, i.e. close to for example one of the glass sheets of the vacuum glazing.

To achieve satisfactory removal of the unwanted gases from the internal surfaces, the most commonly used method is to heat the entire device to a high temperature, a process referred to as "bake-out" . The heating is usually performed within a suitably designed oven. During the bake-out, the glass pump-out tube projects out of the oven, so that the connection with the pumping system remains at a relatively low temperature during the bake-out process. This is important because the polymer or elastomer material used to seal the glass pump-out tube to the vacuum fitting typically cannot withstand the high temperatures necessary to achieve effective outgassing of the device. The high temperatures experienced by the device during the bake-out result in thermal expansion of the glass . For devices that include large substantially flat glass structures the resultant dimensional changes can be quite large.

Therefore, the small glass pump-out tube, which is typically fused to a glass component of the device, will not remain at a constant position relative to the external vacuum fitting for the connection to the vacuum system, which can cause excessive mechanical stresses in the glass pump-out tube, with the consequent risk of breakage. This evacuation technique has therefore been considered unsuitable for devices with large substantially flat evacuated glass structures.

The present invention addresses the problem associated with this dynamically fragile arrangement. Summary of the Invention

In accordance with the present invention, there is provided a method of evacuating a glass panel having a chamber located between two spaced-apart glass sheets and a glass pump-out tube connected to the chamber by way of at least one of the glass sheets; the method comprising the steps of a) removably securing a support structure to one of the glass sheets adjacent the pump-out tube; b) connecting an evacuating system to the pump-out tube; c) heating the glass panel to effect bake-out; and d) supporting the pump-out tube by way of the support structure whilst evacuating and heating the glass panel .

The present invention may also be defined as providing an apparatus for evacuating a glass panel having a chamber located between two spaced-apart glass sheets and a glass pump-out tube connected to the chamber by way of at least one of the glass sheets; the apparatus comprising a support structure arranged to be removably secured to one of the glass sheets adjacent the pump-out tube; connecting means for connecting an evacuating system to the pump-out tube; heating means for heating the glass panel to effect bake- out; and wherein the support structure is arranged to, in use, support the pump-out tube whilst the glass panel is evacuated and heated.

In use of the invention, the heating of the glass panel may be effected in an oven, and in such an embodiment the pump-out tube is dimensioned to project outside the oven for connection to the evacuating system.

In one embodiment, the support structure is removably secured to one of the glass sheets by utilising a vacuum seal formed between the support structure and the glass sheet.

The glass pump-out tube may extend in substantially a perpendicular direction from a top surface of the at least one of the glass sheets. Alternatively, the glass pump-out tube may extend substantially in a perpendicular direction from a side surface of the at least one glass sheet.

The pump-out tube may be tapered in a manner such that it has a smaller diameter along a first portion at the end secured to the port .

The apparatus may further comprise a sealing means for effecting sealing of the pump-out tube at completion of the evacuating.

Preferably, the sealing means comprises a heating means for melting the glass pump-out tube to seal the same. The heating means may comprise resistive heating coils. Preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings .

Brief Description of the Drawings

Figure 1 is a cross-sectional side view of an apparatus, in use, embodying the present invention. Figures 2a to 2h are cross-sectional side views of an assembly illustrating a method embodying the present invention.

Figure 3 is a cross-sectional side view of another apparatus embodying the present invention.

Figure 4 is a cross-sectional side view of another apparatus, in use, embodying the present invention.

Figure 5 is a plan view of a vacuum glazing evacuated using an apparatus embodying the present invention. Figure 6 is a plan view of another vacuum glazing evacuated with an apparatus embodying the present invention. Detailed Description of the Preferred Embodiment

In Figure 1, a vacuum glazing 18 comprises a glass pump-out tube 12, which is connected to a cylindrical evacuating channel 14 formed in one of the glass sheets 16 of the vacuum glazing 18. A solder glass seal is formed between the glass pump-out tube 12 and the cylindrical evacuating channel 14, on the surface of the glass sheet 16 around the glass pump-out tube 12.

An apparatus 10 comprises a support bracket 20, to which a vacuum fitting 22 is mounted. The vacuum fitting 22 comprises an elastomer O-ring seal 24 to the glass pump- out tube 12. The vacuum fitting 22 provides connection to a pump-out hose 26, which is in turn connected to a pumping system (not shown) for evacuating an internal volume 28 between the glass sheets 16, 17.

The apparatus further comprises a vacuum cup 30 which is positioned with its open face abutting the surface 29 of glass sheet 16. The vacuum cup 30 comprises a pump-out port 32, to which a tube 34 is fitted, enabling evacuation of the recess 36 of the vacuum cup 30.

It has been found that the vacuum seal between the surface 38 of the vacuum cup 30 and the surface 29 of the glass sheet 16 is good enough to ensure that the recess 36 can be evacuated to a pressure which is negligible relative to atmospheric pressure. Therefore, the vacuum cup 30 is pushed onto the surface 29 of the glass sheet 16 with a force that is nearly equal to the area of the vacuum cup 30 multiplied by atmospheric pressure, thereby inhibiting any movement of the vacuum cup 30 relative to the glass sheet 16. As a result, the vacuum cup 30 will move substantially in the same manner as glass pump-out tube 12 during thermal expansion of the glass sheet 16. More particularly, very little non-axial movement of the glass pump-out tube 12 relative to the vacuum fitting 22 will occur, i.e. no excessive non axial stress will be placed on the glass pump-out tube 12 during evacuation and bake-out of the vacuum glazing 18. Any relative movement of glass pump-out tube 12 with respect to the vacuum fitting 22 is substantially limited to movement along the axis 40 of the tube 12, and can be accommodated by sliding of the glass pump-out tube 12 within the seal 24 of the vacuum fitting 22.

The apparatus 10 further comprises a tip-off heater 42, for melting the glass pump-out tube 12 to seal the internal volume 28 at the completion of the evacuation process. The heater 42 in this embodiment is a conventional radiative heating coil 44. The heater 42 may be conveniently mounted off the support bracket 20, close to the surface 29 of the glass sheet 16.

The apparatus 10 is made from metal except for the glass pump-out tube 12 and the seal 24. Therefor, all portions of the apparatus which, in use, are subject to the high temperatures inside a bake-out oven, can withstand those high temperatures.

In the following, a method for evacuating a vacuum using the apparatus 10 will be described with reference to Figure 2a to h.

In the first step, illustrated in Figure 2a, two glass sheets 50, 51 are arranged in a vacuum glazing configuration, i.e. a hole 52 is machined in the upper glass sheet 50, and solder glass 54 is deposited around the edges as a paste or slurry. The glass sheets 50,51 are kept in a placed apart relationship by an array of support pillars 56. As shown in Figure 2b, the vacuum cup 30 with its support bracket 20 is then placed on the upper glass sheet 50 and fixed in position by evacuating the recess 36. The glass pump-out tube 12 is then positioned with one end located in the hole 52 in the glass sheet 50, and the other end sealed to the vacuum fitting 22 which is attached to the support bracket 20, as shown in Figure 2c.

Solder glass 58 as a paste is then deposited around the join between the glass pump-out tube 12 and the glass sheet 50. Alternatively, a solder glass preform may be used in which case it would be placed in position before locating the tube 12 in the hole 52. The assembly at this point is illustrated in Figure 2d.

The assembly is then placed in an oven 60, with the end of the tube 12 connected to the vacuum fitting 22 with its elastomer seal 24 located outside the oven 60. The temperature in the oven 60 is then increased to about 450²C, and the solder glass 58 melts to form a seal between the tube 12 and the surface 62 of the glass sheet 60. The solder glass 54 around the edge of the glass sheets 50,51 also melts to form an edge seal, as shown in Figure 2e. The entire assembly is then cooled to a temperature at which the solder glass 54, 58 solidifies, but sufficiently high to effect bake-out of the assembly 68 for out-gassing. Typically, the temperature is 50 to 100^SC lower than the temperature at which the solder glass 58, 54 melts. At this point evacuation of the internal volume 64 between the glass sheets 50,51 can commence.

As shown in Figure 2f, the internal volume 64 is pumped through an evacuation line 66 connected to the vacuum fitting 22 which is attached to the support bracket 20. Very little force associated with the evacuation line 66 is therefore transmitted to the tube 12, rather, any force acts on the relatively rigid support bracket 20 and, through the vacuum cup 30, to the entire assembly 68 itself. Following completion of the out-gassing process, the temperature of the oven is further reduced and the tube 12 is locally melted to seal off the assembly 68, as shown in Figure 2g. This melting is accomplished with the surrounding heater 42, normally positioned as close as possible to the surface 62 of glass sheet 50. Finally, the tube 12 is cracked off in the fused region 70. The vacuum cup 30 can then be vented to atmospheric pressure for removal . The completed vacuum glazing 72 is shown in Figure 2h.

The diameter of the glass pump-out tube 12 would normally be designed to be as small as possible in order that the remaining stub 74 should protrude beyond the glazing by the least possible amount. However, initially the glass pump-out tube 12 may need to be 20 cm or more in length in order to reach to the outside of the oven. The pumping speed of such a tube 12 is relatively small, which can result in long evacuation times .

In Figure 3 , in an alternative embodiment a vacuum glazing 84 comprises a glass pump-out tube 82 which is tapered so that it has a very small diameter close to the glazing 84, and a larger diameter over most of its length. During the tip-off process, it is only necessary to melt the small diameter part of the tube 82, and a very small stub remains. Importantly, however, the tube 82 has a small diameter over only a short length, so that the overall pumping speed of the entire tube 82 can be designed to be much larger than for a tube of uniform diameter. This can enable a more effective evacuation.

Turning now to Figure 4, in another embodiment a vacuum glazing 96 comprises a tube 92 which is attached to the edge 94 of the glazing 96, rather than to one of the glass surfaces. In this embodiment, the tube 92 is entirely removed from the part of the glazing 96 that is visible in use, leading to improved appearance, and enhanced robustness .

As illustrated in Figures 5 and 6, the position of the evacuating channel (not shown) may be along the side of the glazing or in the corner, respectively. If the channel is located along a side 102, the stub 104 of the glass pump- out tube can be made so that it does not project out from the edge of the glazing by cutting a small piece of the glass sheet 106 away prior to assembly of the glazing 108 as illustrated in Figure 5. This enables the tip off heater coil (not shown) to be located closer to the glazing 108 than would otherwise be the case.

If the channel is located in a corner 112, the stub 114 of the tube can be made to project less if small triangular parts at the corner 112 of both glass sheets 116, 118 are removed prior to assembly as shown in Figure 6.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of evacuating a glass panel having a chamber located between two spaced-apart glass sheets and a glass pump-out tube connected to the chamber by way of at least one of the glass sheets; the method comprising the steps of: a) removably securing a support structure to one of the glass sheets adjacent the pump-out tube; b) connecting an evacuating system to the pump-out tube; c) heating the glass panel to effect bake-out; and e) supporting the pump-out tube by way of the support structure whilst evacuating and heating the glass panel.

2. A method as claimed in claim 1, wherein the heating of the glass panel is effected in an oven, and wherein the pump-out tube is dimensioned to project outside the oven for connection to the evacuating system.

3. A method as claimed in claims 1 or 2 , wherein the support structure is removably secured to one of the glass sheets by utilising a vacuum seal formed between the support structure and the glass sheet .

4. A method as claimed in any one of the preceding claims, wherein the glass pump-out tube extends in substantially a perpendicular direction from a top surface of the at least one of the glass sheets.

5. A method as claimed in any one of claims 1 to 3 , wherein the glass pump-out tube extends substantially in a perpendicular direction from a side surface of the at least one glass sheet.

6. A method as claimed in any one of the preceding claims, wherein the pump-out tube is tapered in a manner such that it has a smaller diameter along a first portion at the end secured to the at least one glass sheet.

7. A method as claimed in any one of the preceding claims, wherein a sealing means for effecting sealing of the pump-out tube at completion of the evacuating is provided.

8. A method as claimed in claim 7, wherein the sealing means comprises a heating means for melting the glass pump-out tube to seal the same.

9. A method as claimed in claim 8, wherein the heating means comprises resistive heating coils.

10. An apparatus for evacuating a glass panel having a chamber located between two spaced-apart glass sheets and a glass pump-out tube connected to the chamber by way of at least one of the glass sheets; the apparatus comprising:

- a support structure arranged to be removably secured to one of the glass sheets adjacent the pump-out tube;

- connecting means for connecting an evacuating system to the pump-out tube;

- heating means for heating the glass panel to effect bake-out; and

- wherein the support structure is arranged to, in use, support the pump-out tube whilst the glass panel is evacuated and heated.

11. An apparatus as claimed in claim 10, wherein, where the heating of the glass panel is effected in an oven, the pump-out tube is dimensioned to project outside the oven for connection to the evacuating system.

12. An apparatus as claimed in claims 10 or 11, wherein the support structure is removably secured to one of the glass sheets by way a vacuum sealing means for forming a vacuum seal between the support structure and the glass sheet.

13. An apparatus as claimed in any one of claims 10 to 12, wherein the glass pump-out tube is arranged, in use, to extend in substantially a perpendicular direction from a top surface of the at least one of the glass sheets.

14. An apparatus as claimed in any one of claims 10 to 12, wherein the glass pump-out tube is arranged, in use, to extend substantially in a perpendicular direction from a side surface of the at least one glass sheet.

15. An apparatus as claimed in any one of claims 10 to 14, wherein the pump-out tube is tapered in a manner such that, in use, it has a smaller diameter along a first portion at the end secured to the port.

16. An apparatus as claimed in any one of claims 10 to 15, wherein the apparatus further comprises a sealing means for, in use, effecting sealing of the pump-out tube at completion of the evacuating.

17. An apparatus as claimed in claim 16, wherein the sealing means comprises a heating means for melting the glass pump-out tube to seal the same.

18. An apparatus as claimed in claim 17, wherein the heating means comprises resistive heating coils.