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May-June 2009

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How to Fry Aluminum Siding: Will the Products You Buy Stand Up to What the Weather Has in Store?

It’s an eery sight—like some home improvement center run amok, with endless racks of paint chips in every conceivable color spread out over an open field and baking under the hot Arizona Sun. Why would anyone set up something like this and then leave it there for years?

The answer: to see how the Sun’s ultraviolet rays will eventually cause those paint chips to fade and discolor.

You read claims on labels and advertising for everything from house paint to car batteries: “Windproof & waterproof,” “Will not mildew or rust,” “Guaranteed to start down to -10°F.” But are these claims really true? And, if so, who has validated them? Moreover, how do we know how these products will stand up to nature’s onslaughts?

Welcome to the remarkable world of weatherability testing, where the products you use every day are drenched, frozen, scorched, and windblown to make certain they can stand up to everything that weather has in store.

Old advertisements were rife with claims such as, “We’ve strapped this wristwatch beneath a speeding motorboat, yet it’s still ticking!” But does anyone really perform such feats of derring-do to ensure a product’s durability?

“Mostly no,” chuckles Dr. David Dumbleton, a materials scientist and Senior Consultant at Chicago-based Atlas Material Testing Technology LLC.

Atlas, along with other leaders in the field—including Ohio-based Q-Lab Corporation and Arizona Weathering Material Testing Laboratory—taps a wide array of experts in different areas, each of whom brings a special focus to the business of weatherability testing. Staff at Atlas run the gamut from experts in radiometry and sensor technology to polymer and electrical engineers and thermodynamicists. It’s a range of expertise this field needs, given the wide variety of weather conditions and problems that can result from them. Hot Sun can fade paint or upholstery, humidity and rain can rust metal, and salt water can corrode many materials.

As such, weather testers must develop precise parameters for what a layman might simply call wind or rain. The American Society for Testing and Materials (ASTM) has set standards for such weather conditions, but exact definitions can vary even within an industry. For example, when measured to the wavelength, Toyota and Ford differ slightly on how they define sunshine.

 “Of course, most customers don’t think about this when considering a purchase,” Dumbleton notes. But “a great deal of work goes into qualifying even a very ordinary product.”

Why Test?
“A client may already know there’s a problem, or they may be expanding existing lines or entering new markets,” observes Jim Gauntner, the U.S. and Canadian Sales Manager of Q-Lab Corporation. “Change suppliers, introduce a new material or formulation, [and the question becomes]: will the product still stand up?”
New products especially require extensive testing before they can enter the market. “For example,” Dumbleton observes, “automakers will customarily take 5 or more years testing to approve new paints.” Without testing, a product might suffer failures ranging from cosmetic to what Gauntner calls “catastrophic” (significant loss of function), all of which can translate into lapsed warranties, recalls, and business losses.

And it’s not just auto parts, house siding, and survival gear that require testing against the elements; every year, scores of indoor products, from rugs and drapes to upholstered furniture, are tested for color change in the event that a consumer might place them too close to a sunny window. Even medicine vials “are often designed to provide some protection against sunlight,” Dumbleton notes, “in case you leave a prescription in the car.”

Watching Paint Dry
So did the manufacturer of that outdoor latex paint you bought at the hardware store really leave it out in the elements for 10 years, as its warranty claims?

“That’s best practice,” asserts Dumbleton. “Natural weathering is all about subjecting product samples to their characteristic environment. It’s a waiting game. I’ve seen samples of mastics and adhesives which have been exposed under test conditions for over 30 years.” In time, the Sun’s irradiance will turn that adhesive brittle, claim a paint’s original sheen, or turn a white vinyl window frame blotchy and yellowed.

To provide accurate results, such exposures must be performed precisely. “Everything is instrumented for testing,” Gauntner explains. “We’re tracking both the weather and the way it affects products.” Technicians erect mobile weather stations at the test site, charting precipitation, wind speed, temperature, and the Sun’s total radiant energy over time.

Metal racks, slightly raised to avoid ground moisture and angled to catch the Sun, carry the samples, which can vary from house paint to vinyl siding and fabric swatches.

“Paints and coatings are usually applied to substrate panels (highly uniform sheets of aluminum), while irregular samples, like a piece of auto upholstery, would first be attached to specially made mounts,” Gautner describes. Open-backed racks permit air circulation behind the samples (often the choice for testing outdoor signage).

Backed racks, usually made with plywood, cook samples a bit hotter (the choice for most building products). Even the angle the rack takes to the Sun is vital; many auto parts are exposed at 5° facing south (nearly looking into the sky), while siding products often stand vertically (the way they would hang on your house).

Using black metal boxes covered by sheets of glass, testers can also simulate the oppressive Sun inside a parked car in summer.

“Or we might just test the entire car,” Gauntner adds. Set on blocks and festooned with measuring instruments, what looks like a derelict auto lets test engineers study how seats, the dashboard, and other parts of its interior deteriorate with time. Placed on a “Sun tracking carousel,” the car turns like a giant clock, so its windows forever face the Sun.

Atlas also operates a piece of a house in Florida that is specifically designed to test products like casements for doors and windows.

Textbook Weather
When you think of sunny, rainy, or cold weather, locations that are known for these conditions probably spring to mind. In weather testing, “benchmark climates” are locales selected because of these textbook conditions. It’s a unique way to look at the weather map, like a series of natural environmental chambers.

Need high temperatures and high humidity to qualify the products you build?

“Southern Florida is the benchmark,” according to Gauntner. This classic subtropical environment is home to multi-acre test sites that evaluate scores of products.
Pat Carmody, owner of Arizona Weathering Material Testing Laboratory, notes that “Arizona, with its high ultraviolet, little rain, and low humidity, offers the reference environment for desert testing.”

Major automakers routinely test their products in both locales.

In today’s global markets, products might experience weather a world away from where they were made. So Southern France (with its high sunlight and long wet periods) provides a benchmark climate for the Mediterranean. For a tropical environment (with high sunlight, humidity, and temperature), the best place to test is Chennai, India.

“U.S. exports may need to test overseas, while products designed abroad for American markets might require a trip to say, Cleveland or Ottawa to test for North American freeze/thaw cycles,” says Dumbleton. His firm’s “Ever-summer” program tests in Miami, Florida, then ships samples to Townsend, Australia, so they can experience 2 summers each year.

Wherever they are located, test samples require periodic examination to chart the weather’s toll.

According to Carmody, such examinations “may take place in the field, or samples may be taken indoors. Paint samples might be subjected to a color analysis. This could be a visual inspection, against a standard, or using a computer to detect degradation unseen by the naked eye.”

Accelerated Seasons
Weather testers likewise use several means to help nature along. Sun tracking systems (like you’d use for solar cells) keep sample racks oriented toward the Sun throughout the day and year, creating a situation where it is always noon. Add a shiny box and glass cover (think of a solar oven), and years of natural solar exposure can be sustained in just months.

Such manipulation of weather conditions allows for accelerated testing, so that samples are subjected to concentrated doses of natural weather. Imagine focusing a magnifying glass on a pile of leaves (but far more carefully), and you’ve got the idea.

Among the most remarkable devices used by these companies to manipulate natural weather conditions are what weather testers call Fresnel Array Concentrators: literally, giant collectors of solar energy for “cooking” car parts and other products. Using their banks of angled mirrors, these arrays can focus the energy of 5 Suns on a sample. Motors reorient the machines’ mirror-like reflectors constantly, so they follow the Sun throughout the day and year. Meanwhile, air blowers cool the test samples, which are stationed at the machine’s focal point, since “the idea of accelerated testing is to put an amount of energy into the samples,” Dumbleton notes, “not melt them!”

Some accelerated testing even adds weather that isn’t there. For example, water spray from banks of nozzles can simulate the wetness and thermal shock of rain, even as samples bake in the desert. In “Scab Testing,” workers “water” samples on angled racks periodically with a salt solution to prompt corrosion.

Tempests in Teapots
Laboratory testing simulates nature’s effects inside specialized chambers. It’s convenient: technicians can conjure the heat of a New Delhi summer or create stratospheric cold to test parts from a fighter jet. And it’s fast: a few months inside the chamber and samples emerge brittle or faded as if they’d stood outside for years.

“Plus, because lab tests are more tightly controlled than natural weather, the results are highly repeatable,” Dumbleton adds.

The smallest of these chambers looks something like a toaster oven, while big, walk-in models offer enough room to refrigerate a snowmobile or humidify a Winnebego. Thermal shock chambers will switch temperature exposure from +200°C to -70°C in just seconds (a must for military electronics), while corrosion cabinets will assault a new line of boating gear with salt spray, humidity, and fog.

For reproducing the degrading effects of sunlight in the lab, weather testers use fluorescent, xenon, carbon arc, and metal halide lamps, which each provide somewhat different spectral distributions (something like the “cool,” “warm,” and “daylight” options you might find when shopping for light bulbs). The distribution is vital; beyond mere brightness, many products know (chemically) what wavelengths of light are striking them. Xenon test chambers virtually recreate sunlight because their lamps simulate the entire solar spectrum, from infrared and visible light through ultraviolet. Ultraviolet-based exposure delivers only shorter wavelengths of the spectrum, which can be particularly damaging to many products. (Think of these as tanning lamps you’d never want to sit under.) In many Sun stability chambers, periodic water sprays add the additonal damaging effects of rain and dew. Making sunshine in a box has its advantages: laboratory-based systems can deliver several natural Suns’ worth of intensity.

A Complex Problem
In addition to the obvious weather factors that testers must simulate, there are a number of subtler variables experts must keep an eye on.

“Most weather-related damage is caused by Sun, heat, and moisture,“ Dumbleton notes, “but these can also work together, yielding greater effects. On the material side, especially with modern plastics, even small changes in formulation can make a big difference in how a product stands up.”

Carmody adds, “Imagine you purchased a bright blue patio umbrella, but after a year outside, it’s turned dingy. What happened? Ultraviolet light breaks down textile pigments; if you live in the Southwest, maybe that’s the culprit. But what if that umbrella was sold in Brazil, where ocean salts could degrade it? Or in Rio de Janiero, where the Sun is even more intense?” Weather’s many factors can exert complex effects.

The complexity of products can add additional challenges. “Especially with modern plastics,” Dumbleton says, “even small changes in formulation can make a huge difference in how a product stands up outdoors.”

Like the effects it studies, weather testing is a long-term, interrelated process. Learning how best to combine results from natural, accelerated,
and laboratory testing demands experience and professionalism.

“If a simulation degrades a sample in ways that natural exposure would, then yes, that’s potentially a valid test,“ Gauntner advises. “In weather testing, real-time, natural exposure is always the benchmark; that’s what the product will experience.”

Sometimes testing can even require avoiding weather. The growth of cities, with their extra heat and invariable pollution, sends weather testers fleeing to more pristine test sites, the way astronomers move their telescopes to escape light pollution.

“We have almost 2 million paint samples in southern Florida,” Dumbleton muses, “which all need to be taken in and stored if a hurricane approaches.” After all, they aren’t testing for that kind of weather.                                              


NICK D'ALTO is a mechanical engineer who writes about technology, society, and adventure.

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