What is the time compression factor of an accelerated weathering test?
Weatherometer testing is used across most industries for UV aging. Micom offers Weatherometer testing to different standards and exposure cycles. Weatherometer testing is based on ASTM G155 which uses a Xenon arc as a UV source. Experience demonstrates that the time compression factor concept, i.e. the rate of accelerated aging induced by the exposure, is often poorly understood. How does test chamber exposure time related to outdoor exposure time? What is the acceleration factor? How long do I have to test my product to simulate 5 years of outdoor exposure?
For decades, weathering experts have tried to find that magic number, but there is no such magic number. No matter how the question is formulated, the answer is always the same: “It depends!”
It depends for one simple reason: Mother Nature is not as reliable as lab equipment!
While doing Weatherometer testing we use calibrated lamps, specific filters, very accurately monitored irradiance, purified water, controlled atmosphere (humidity and temperature) and predefined light, dark and rain cycles durations. On the other hand, Outdoor exposure depends on when and where you are: latitude, altitude, cloudiness, humidity, smog, rain, temperature, orientation, season, time of day… all those parameters have a major influence on the “efficiency” of outdoor exposure.
In other words, if you were to spend 5 minutes in a weathering chamber, no matter when or where you do it, you would always get the same “tan”. On the other hand, can we say that 5 minutes of outdoor exposure in downtown London in December is equivalent to 5 minutes of outdoor exposure in Miami in June? Presented this way, the answer is obvious and that is exactly why it is impossible to have an ABSOLUTE acceleration factor for accelerated weathering testing.
So, why is accelerated weathering so popular and useful?
Accelerated weathering is actually a very powerful tool for comparative purposes. Testing simultaneous multiple formula can quickly give vital information. Instead of waiting years to get the data from outdoor exposure or feedback from customers, accelerated weathering gives you the data you need in days or weeks. Your market share declines? This is a fast and easy way to compare your product versus your competitors. You are the leader in your field but you want to take a leap forward? Test your current product versus improved formula.
Rule of Thumb
Even if the absolute acceleration factor cannot be determined for the reasons explained above, experience shows that using accelerated weathering, conclusions can usually be drawn after weeks (sometimes days) when outdoor exposures take months or years.
In a world where time is money and where technologies and trends are constantly moving, accelerated weathering has become a key asset for decision makers in many industries.