materials feature | Weatherability Other important aspects of ASTM D7869 include
efforts to improve the light spectrum of test chambers. This has been done with specifications for daylight filters that closely match the spectrum of light in south Florida. Previous SAE test standards mandated daylight filters that often had slight variations in the shortwave portions of their spectra, which could create differences in data. The ASTM standard also sets performance param-
eters for the test chamber itself. Changes include calibrating the water-delivery system to assure that enough water is available to spray colour samples as necessary, and periodic repositioning of samples in rotating-rack or flat-array equipment. Fowler notes that uniform test results depend on a complex interaction of several factors, not just light. Repositioning samples is one way of promoting this interaction. The prospect of more accurate indoor test results
This Q-Lab facility in south Florida tests samples in ideal exposure conditions: high irradiance, heat and humidity
with OEMs Ford and Honda. Q-Lab and Atlas Material Testing Technology provided expertise in test equipment and outdoor testing.
Mimicking moisture uptake Sean Fowler, a technical marketing specialist at Q-Lab notes that research by the consortium found that moisture uptake and outdoor drying of coated panels in south Florida proved to be driving mechanisms that were previously unseen in indoor test standards, notably SAE J2527. Even though the SAE standard covered extensive use of water spray and high humidity in testing, it failed to result in sufficient water uptake to mimic the Florida exposures. Based on this information, ASTM D7869 specifies
Q-Lab’s Q-Fog
cyclic corrosion chamber
contributed to the
development of ASTM D7869
that test cycles begin with a four-hour “dark period” during which a water spray is applied to samples, along with requisite humidity levels. The dark period and spray duplicate dew formation at night, an important source of wetness in Florida. Since colour samples dry outdoors as the sun rises, the test standard mimics this in a test chamber by transitioning from the dark period to bright light with an intermediate step at relatively low irradiance and black panel temperature — in this case 50°C (122°F), Fowler explains. The test cycle replicates daytime exposure with high
temperature and irradiance, followed by a cycle of low irradiance that simulates dusk and dwindling sunlight. Night-time conditions are again introduced in a dark chamber with water spray. The standard includes sub-cycles of rapid thermal cycling to test for cracking and delamination, more darkness at relatively low temperatures, and dry conditions to relax samples and prevent “unnatural cracking or other unrealistic degradation,” he adds.
50 COMPOUNDING WORLD | June 2015
www.compoundingworld.com
with the standard improves the possibility of accurately correlating indoor test data with outdoor data. Fowler says this could, with the right analysis, permit the extrapolation of long-term colour performance after as little as two to three years of outdoor tests. By long- term he means 20 to 30 years, which would meet the warranty requirements of a number of products, notably building materials. “No one wants to wait five to 10 years to certify a material,” he adds.
Although ASTM D7869 is being phased in primarily
by automotive and transportation OEMs, other indus- tries and industry groups are looking at it. These include AAMA, the American Architectural Manufactur- ers Association, which Fowler says is considering adopting the indoor test standard as a way of speeding up its extensive outdoor tests of window profiles and other products, and thus the development and introduc- tion of colours.
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