Environmental weathering tests

The heated black box is a modification that produces significantly higher panel temperatures than those produced by the black box. It is equipped with heaters and blowers to heat the air inside to a specified temperature during daytime hours. 

Heating of the backside of the panels with warm air reduces the daily variability of specimen temperatures. The heater is turned off at night to allow specimens to cool down and thus allows for formation of condensation to simulate in-service conditions. It is most useM for exposures conducted in the late fall, winter, and early spring. 

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LABORATORY-ACCELERATED VERSUS ENVIRONMENTAL WEATHERING TESTS... 

Weathering is the ability of the colored system, i.e., the coating, paint, etc., not the pigment alone, to resist light and environmental conditions. Changes in color and gloss aie two main factors that are evaluated in weathering tests. 

In a study of nine commercially available acrylic adhesives, Wilkinson and Tyler found a considerable variation in the resistance to environmental exposure. The tests employed were 1,000-h water soak, 30 days at 125°F/100% RH, and 1,000-h 5% salt spray at 95°F aluminum adherends were used. The nature of the alloy was also a factor in determining joint durability. The authors concluded that excellent durability can be obtained with the proper selection of adhesive and alloy. A similar study by Zalucha using recently developed high-performance acrylic adhesives also indicates excellent performance for many acrylic-bonded assemblies. Minford has conducted weathering tests on both the early formulations and the more recently introduced second generation acrylics." He found that the durability of the earlier products was generally poor in both water soak and... 

Consequently, the errors of each kind of procedure are determined by the absence of simultaneously acting factors or supra estimation of applied conditions. The synergistic effects of environmental stressors determine correct results, which must be correlated with the chemistry of material. The repeatability of artificial weathering tests provides somewhat similar information, which is influenced by the material history. The outdoor exposure does not ever create identical intensities of degrading agents. The meaningful results are obtained by the simulation of natural... 

Further uncertainty arises from the environmental exposure. For accelerated tests, repeatability can be estimated from exposure of replicate test pieces and minimised by control of the exposure conditions. Particular points to consider are spatial variation in temperature as well as mean temperature and air flow in ovens. In accelerated weathering apparatus, spatial variation and variation with time of light sources can be very significant. 

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