(b) Adhesion after exposure to water.
(c) MVT as measured by dewpoint tempera-
ture rise after high humidity exposure.
(d) Seal fatigue due to flexing caused by
barometric pressure differentials.

The apparatus is pictured in figure 8. This equipment has been adapted from that used at National Research Council-Canada for several years. However, we have modified it by the addition of a series of black lights and uv sunlamps, to closely approximate that of natural uv. We have included a water pump which would give us an equivalent of an inch of rain per hour. In addition, we have also opened up the distance between lights of glass giving a greater air flow around the sealed units.

DEW POINT TEMPERATURE F

FIGURE 7. Correlation of measured dewpoint versus free water for a given volume of air space.

water. At the same time, we continued to take dewpoint readings and have been able to correlate measured dewpoint versus free water for a given volume air space. We are continuing to run this study on new improved sealant systems.

Figure 7 gives you some early values of these studies.

5. Accelerated Interior Weathering

In attempting to correlate the short-term field experience of most manufacturers, and a test for evaluating the hermetically sealed unit, an accelerated interior weathering test was developed to check a unit in a variety of environmental conditions. This test included freezing, thawing, rain exposure, ultraviolet radiation exposure and high humidity, all on a uniform programed cycle. We were looking for variations of performance based on the different formulations of sealants we developed.

What were we measuring?

(a) Adhesion after exposure to ultraviolet radiation (uv).

In addition to the accelerated interior weathering test, duplicate test units, unglazed, are placed outdoors at a 45 deg. angle facing south. Periodic dewpoint readings are taken in order to compare these with the readings on the accelerated interior weathering.

6. Fogging

Fogging tests in both architectural and refrigeration type units were developed to check the sealant against depositing a permanent layer of contaminate on the inside surface of the glass. These tests are for a 14-day duration at 150 °F. If no fogging occurs after that period, the units are considered to have passed the requirements of the test.

Many sealant manufacturers attempt to produce a more economical product by the addition of various low cost dilutes, etc. This type of test weeds out the poor sealant. Many times fogging will show up during the accelerated weathering cycle. Figures 9 and 10 illustrate the apparatus used in this test.

7. Glazing

Certain oil-based glazing compounds, used to install insulating glass units, have an effect on polysulfide sealants used in their manufacture. To check if a sealant is compatible, we have developed three specific tests.

1. The first we call static testing; it is done by taking the actual glazing compound and glazing a 6 x 6 in test unit into an aluminum sash and subjecting the unit for at least 30 days at 158 °F. The test sample is inspected for bleeding once a week. Bleed

ing shows up generally as a clear droplet of oil on the air space side of the glass. Sometimes the sealant is attacked causing reversion of the compound, or cracking, discoloration, etc.

2. The second method is of a dynamic nature, where a cross section of a sealed unit is fabricated. The sealed portion is exposed to both the glazing compound and ultraviolet radiation while being flexed at 60 cycles/minute. The flexing is equivalent to barometric pressure changes of 2,000 feet. As yet we have not been able to cor

relate the static versus versus the dynamic method, but these studies are continuing. 3. Method three is a direct immersion of a sealed unit in the respective oil vehicle at 158 °F. This test is the most dramatic and without a doubt the one which produces the quickest results.

A simple test on the sealant system alone is accomplished by means of weight loss. The sample of cured sealant is subjected to various glazing oil vehicles for a definite time period at an elevated temperature.

Figure 11 is a chart illustrating the weight loss of various sealant systems after exposure to oil at a 50 °C. temperature. Curve H is based on results of a new development on a sealant which is highly resistant to oil.

Those who do not wish to pay a premium for a highly resistant sealant can use a series of barrier coats. A barrier coat is used to prevent bleeding of these oils through the sealant. The coating is applied after the sealant has become tack-free. The system of sealant and barrier coat provides protection against defective installation techniques and materials. One sure way of eliminating

this problem at its source is to specify a compatible glazing compound.

8. Conclusion

The insulating glass industry is in a great growth period, and, from all indications, this growth will continue. This means that more manufacturers will be making more units than ever before. Now there are formal means at the disposal of all manufacturers to check the quality of their units a new specification with a certification program. Component parts have been improved over the years and more improvements will be forthcoming. All are aimed at product improvement so that extended warranties may be offered.

It looks as though the future of our industry is assured.

The author wishes to thank the PRC Laboratory staff for their assistance in furnishing and compiling the data.