PUMP DOWN OF EVACUATED GLAZING

Evacuated glazing consists of two sheets of glass separated by a small gap, hermetically sealed around the edges, and containing a thermally insulating vacuum. This article describes techniques to determine the time necessary to evacuate such a device through a small, pump out tube. The time constant for pressure reduction is determined by numerical modeling. An approximate analytic method is also developed which gives results in good agreement with the numerical data. The numerical results are validated by experimental measurements. It is shown that samples of area about 1 m(2) and internal gap similar to 0.2 mm can be evacuated in a few minutes through a small pump out tube. It is therefore likely that the evacuation time in the production process of evacuated glazing will be dominated by the heating and cooling cycles associated with outgassing of the internal surfaces, rather than by the pumping process itself.