Insulating glass assemblies for use in the manufacture of windows, doors and the like commonly have two substantially parallel, spaced-apart glass panes spaced apart by a peripheral spacer. Spacers commonly are of metal, usually of tubular configuration, that are formed so as to have two flat, substantially parallel sides facing the confronting surfaces of the panes and bent so as to conform to the periphery of the glass panes. Sealant materials such as polyisobutylene are employed between the flat sides of the spacer and the confronting glass surfaces to seal the glass surfaces to the spacer. To enhance the thermal resistance across the glass assemblies, the interpane space may be filled with an insulating gas such as argon having a thermal conductivity that is less than that of air.
In the manufacture of insulating glass units, uniform production line procedures enable glass assemblies of a single size to be made in large quantities. Custom insulating glass units, on the other hand, are generally manufactured in quantities as small as a single unit, and a single order may require the manufacture of units having varying sizes and shapes.
Various methods and apparatuses have been suggested to enable air within the interpane space to be replaced with an insulating gas such as argon. In one method, the glass panes are adhered to a spacer to form a substantially sealed interpane space, and then air within the space is gradually replaced with argon through an access port. In another method, the interpane space of a multipane glass assembly is filled with an insulating gas by first drawing a vacuum to remove air from the interpane space before both panes are sealed to the spacer, and then charging the evacuated interpane space with an insulating gas. After the interpane space is filled with the insulating gas, the panes are sealed to the spacer.
Various methods and apparatuses for replacing air with an insulating gas in insulating glass units are shown in U.S. Pat. Nos. 5,017,252, 4,780,164, 5,573,618 (Rueckheim) and U.S. Pat. No. 5,476,124 (Lisec). In the last mentioned patent, an apparatus is described in which an insulating glass unit having a pair of glass panes separated by a peripheral spacer is conveyed by a conveyor belt between parallel plates, the bottom edge of the outer glass pane being spaced slightly away from the spacer to provide generally vertical openings along the side edges of the unit. The leading edges of the glass panes are conveyed into contact with a vertical sealing device. Another vertical sealing device is then moved into contact with the trailing edge of the glass panes to seal, with the gas-tight conveyor belt, the space between the glass panes. An insulating gas is then flowed laterally from one vertical sealing device to the other under conditions avoiding turbulence. When the glass unit has been appropriately filled with insulating gas, one plate is advanced toward the other to compress the glass unit between the plates and thus completely adhere the glass panes to the peripheral spacer. This device replaces air with an insulating gas in one glass unit at a time, and due to its employment of non-turbulent gas flow, requires considerable time to replace the air with insulating gas. It would be advantageous to provide a method and apparatus for filling one or a plurality of the same or different size insulating glass units at a time with an insulating gas in a manner providing rapid and substantially complete replacement of air.
Applicant's U.S. Pat. No. 5,957,169 teaches an apparatus and method of filling insulating glass with insulating gas. In accordance with this method, a partially assembled glass unit is conveyed within an enclosure. This partially assembled glass unit has a pair of spaced panes of glass and a peripheral spacer, with the lower edge of one pane being spaced from the spacer to provide a bottom gap. An insulating gas is introduced under turbulent flow conditions upwardly through the gap in the partially assembled glass unit to turbulently mix with the air present therein. A mixture of insulating gas and air is exhausted from the enclosure until the concentration of insulating gas within the enclosure reaches a desired level. The lower edge of the glass pane of the partially assembled glass unit is then closed against the spacer to seal the interpane space.
One problem encountered in manufacturing insulating glass assemblies is that the seal between one or both of the glass panes and the spacer fails. While this can happen over time, this defect more commonly occurs at the time of manufacture due to an improper application of the sealant about the periphery of the frame. In most cases, the sealant is not applied uniformly and relatively small, pin-hole-sized pathways through the seal remain even after the glass panes are urged into contact with the spacer.
Seal failures can cause a variety of problems in insulating glass units. For example, a seal imperfection will cause a leak of the insulating gas from the interpane space, and the pressure in the glass unit may decrease to a point where the pressure is no longer sufficient to support the upper pane, and this in turn may cause the upper pane of glass of the unit to bow or sag under its own weight. Moreover, such a leak can allow the introduction of moisture and other unwanted environmental elements, leading to a faulty glass unit. A leak in the seal can thus lead to eventual failure of the entire glass unit, resulting in the most extreme cases in a blowout of the glass panes and/or the spacer and seal.
It has proven difficult to reliably detect imperfections or failures in the peripheral seal provided by the spacer. Applicant has found that the upper pane of glass in larger units with inadequate seals will tend to sag slightly if the unit is laid with the panes oriented horizontally. It has been found useful in commercial production for over a year to fill the insulating glass unit with an insulating gas at roughly atmospheric pressure and profile the shape of the upper sheet of glass. The upper sheet of glass will tend to sag slightly in the center under its own weight, but the insulating gas in the interpane space of a properly sealed unit will help support the glass and limit its deflection. If the seal has a significant leak, though, the outer surface of the glass unit will tend to be concave. Such a concave profile indicates that insulating gas is being forced out of the interpane space under the weight of the upper glass pane, thereby lowering the pressure of gas within the glass unit and allowing the upper glass pane to sag under its own weight.
Unfortunately, this process is not a reliable indicator of seal failure in smaller glass units. In larger glass units, the center of the glass is spaced sufficiently far away from the spacer to permit measurable deflection. In smaller units, however, the distance between the supported edge of the upper pane and its center of mass is smaller. As a consequence, the bending moment on the glass often falls short of that necessary to consistently induce a sagging of the glass pane significant enough to fall outside standard manufacturing tolerances.
Hence, monitoring thickness of larger panes can serve as a reasonably reliable means for detecting inadequate seals in insulating glass units. In smaller units, though, this measure is not a strong, statistically reliable indicator of seal failure. It would be advantageous to provide a method for reliably detecting seal imperfections or failures in insulating glass units of varying sizes and shapes, in a manner providing rapid detection of imperfection or failure regardless of the size of the glass unit.