Improvements to thermally insulating glass panels

Abstract: A thermally insulating glass panel (1), comprising two spaced apart sheets of glass (2,3) enclosing a low pressure space and interconnected by a peripheral joint (4) of fused solder glass an array of pillars, and a pump-out tube (8) to provide communication between the interior and the exterior of the panel during the creation of the low pressure space; wherein a pump-out tube (8) extends through a hole (25) extending from the bottom of a recess (26) in the exterior face of one sheet of glass to the interior face of that sheet of glass, and the tube (8) is joined to that sheet of glass by a solder glass joint (27) made between the outside surface of the pump-out tube (8) and the interior face of that sheet of glass.

Description: Technical field This invention concerns an improvement to thermally insulating evacuated glass panels; these panels may be used for windows. Background art In WO 91/02878 (The University of Sydney) a thermally insulating glass panel 1 is disclosed which comprises two spaced apart sheets of glass, 2 and 3, enclosing a low pressure space (see figures 1, 2 and 3). These sheets are interconnected by a peripheral joint of fused solder glass 4 and an array of pillars 5. The pillars 5 ensure sufficient structural strength to withstand the forces imposed by atmospheric pressure, and maintain the sheets of glass spaced-apart. The pillars 5 comprise a preform 6 made of glass, ceramic, metal or other materials completely coated with a layer of solder glass 7. The preform 6 is usually made from the same material as the glass sheets in order that the thermal expansion coefficients of the preforms, the sheets and the solder glass should match. The purpose of the preform is to maintain the separation of the glass sheets during the fusion operation when the solder glass has little mechanical strength. A pump-out tube 8 is incorporated into the panel and is used during the construction of the panel to evacuate the space between the glass sheets. The pump-out tube 8 is hermetically sealed by fused solder glass 9 to a hole 10 which passes from an interior face of glass sheet 2 to the bottom of a recess 11 in the exterior face of glass sheet 2. The recess 11 allows the pump-out tube 8 to be melted and sealed leaving a stub which does not protrude beyond the plane of the exterior face of the glass sheet 2. A chemical getter 12 is often included within a machined recess 13 in one of the sheets of glass in the panel of counteract any rise in pressure due to out-gassing from the glass. A low emittance coating may be provided on the interior surface of one or both sheets of glass. The emittance of the coatings is usually between 0.05 to 0.2 to ensure a thermal conductance due to radiation of approximately 0.15 to 0.6 Wm -2 K -1 or less. The internal pressure of the panel is usually below 10 -2 torr and sometimes below 10 -3 torr. The design of the pump-out tube imposes particularly challenges. Ideally, the tube should be very small, and located entirely within the nominal geometric dimensions of the evacuated window structure. However, small glass tubes can be extremely fragile and it is very difficult to seal mechanically to such tubes during evacuation without breaking them. Summary of the invention According to the present invention, as currently envisaged, there is provided a thermally insulating glass panel comprising two spaced apart sheets of glass enclosing a low pressure space interconnected by a peripheral joint of fused solder glass and an array of pillars, and a pump-out tube to provide communication between the interior and the exterior of the panel during the creation of the low pressure space; wherein the pump-out tube extends through a hole extending from the bottom of a recess in the exterior face of one sheet of glass to the interior face of that sheet of glass, and the tube is Joined to that sheet of glass by a solder glass joint made between the outside surface of the pump-out tube and the interior face of that sheet of glass. The solder glass seal between the pump-out tube and the polished internal surface of the sheet of glass, is more effective than a seal to an abraded surface such as in the bottom of the recess. This is because the abraded glass surface contains many microcracks which extend some distance into the body of the glass. The solder glass may not completely close all these microcracks and very slow leaks can occur due to lateral motion of gas through the poorly connected microcrack region. By fusing the solder glass onto the smooth interior surface of the glass plates, this problem does not arise. In addition the solder glass forms a smooth surface on the vacuum side, and is easily evacuated. It will be appreciated that if the fused seal between the solder glass and the glass sheet is made on the inside of the glass plate, then the end of the pump-out tube and the solder glass seal protrudes into the gap of the evacuated window. Since this gap is normally very small, there is a danger that the protrusion will contact onto the surface of the other glass sheet. In order to avoid this, a second recess may be machined onto the interior face of the other glass sheet in registration with the hole, to permit the extension of the pump-out tube to remain out of contact. Preferably there is a fused solder glass joint between the two glass sheets extending partly around the hole. This provides local structural reinforcement around the pump-out hole and the recess. Brief description of the drawings Figure 1 is a cross-sectional side view of a thermally insulating glass panel. Figure 2 is a plane view of the glass panel of Figure 1. Figure 3 is a cross-sectional side view of a detail of the glass panel of Figure 1. Figure 4 is a cross-sectional side view of a glass panel embodying the present invention. Figure 5 is a plane view of the glass panel of Figure 4, Figure 6 is a cross-sectional side view of another glass panel embodying the present invention. Detailed description of the preferred embodiments An embodiment of this aspect of the invention will now be described with reference to figures 4 and 5. Panel 1 comprises two spaced apart glass sheets 2 and 3. The sheets are interconnected by a peripheral joint 4 of fused solder glass, and by array of pillars 5. The pump-out tube 8 is positioned in a hole 25 drilled from the bottom of a machined recess 26 in the exterior face of one sheet of glass 2 to the interior face of that sheet of glass 2. The pump-out tube 108 is joined to that sheet of glass by an hermetic solder glass joint 27 made between the outside surface of the pump-out tube 108 and the interior face of sheet 2. A machined recess 28 in glass sheet 3, in registration with the pump-out tube hole, 25 provides clearance between the pump-out tube 8 and glass sheet 3. The hole for the pump-out tube and the recesses give rise to stress magnification. In particular, under temperature differentials, or due to the effects of atmospheric pressure, the tensile stresses that are inevitably present in the glass are larger in the immediate vicinity of these features. In order to reduce the effect of this stress concentration the solder glass deposited on the periphery of the glass sheets, which forms the fused solder glass joint 4, may be extended 29 to partly surround the pump-out tube 8 and the recess 28. A small gap 30 is left in the solder glass seal to permit the evacuation to take place. After fusion, solder glass 29 provides structural support around the pump-out tube 8. The existence of this solder glass around the pump-out tube results in almost complete elimination of mechanical tensile stresses due to bending or atmospheric pressure and has a highly advantageous effect in the reduction of the probability of failure due to stress magnification by the pump-out tube recess. After the space in the interior of the panel has been evacuated, the part of the tube 8 inside recess 26 is heated until it melts and is then sealed (tipped-off). It can be seen, in Figure 4, that the tube 8 when tipped off does not protrude beyond the surface of glass sheet 2. The reason for this is so that when the panel is framed tube 8 will not be damaged by the frame, and is protected by the frame. The stub of the pump-out tube may be encapsulated or otherwise protected prior to mounting in the frame, in order to facilitate handling without damage. A variant of the technique for sealing the pump-out tube, is to polish the inside of the recess in which the end of the pump-out tube is located. The polished surface 31 of the recess is suitable for the solder glass sealing operation, being smooth. In this case, a satisfactory seal can be made on the exterior surface of the glass, as shown in figure 6. It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims: A thermally insulating glass panel, comprising: two spaced apart sheets of glass enclosing a low pressure space and interconnected by a peripheral joint of fused solder glass an array of pillars, and a pump-out tube to provide communication between the interior and the exterior of the panel during the creation of the low pressure space; wherein a pump-out tube extends through a hole extending from the bottom of a recess in the exterior face of one sheet of glass to the interior face of that sheet of glass, and the tube is joined to that sheet of glass by a solder glass joint made between the outside surface of the pump-out tube and the interior face of that sheet of glass. A panel according to claim 1, wherein a recess is provided on the interior face of the other sheet of glass in registration with the hole. A panel according to claim 1, wherein the fused solder glass joint between the two glass sheets extends partly around the hole.

Inventors: COLLINS RICHARD EDWARD, COLLINS, RICHARD EDWARD
Applicants: UNIV SYDNEY, THE UNIVERSITY OF SYDNEY
Application year: 1993
Main classification: E06B3
IPC codes: E06B3