Weather testing for the real world.
Broader use of plastics in building products and a growing desire to minimize painting of automotive parts is increasing the need for reliable predictions of light stability and weathering performance. Accelerated weathering lab instruments and accelerated outdoor test methods are useful tools that give relatively quick answers for R&D, quality control, and material certification. But experts say nothing beats the reality check of natural outdoor testing--even though it takes much longer.
Exposure to heat, cold, UV, and moisture can lead to color changes, surface crazing craze
v. crazed, craz·ing, craz·es
1. To cause to become mentally deranged or obsessed; make insane.
2. To produce a network of fine cracks in the surface or glaze of.
v. , chalking, and embrittlement Embrittlement
A general set of phenomena whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties, such . Failure to test properly for these effects can result in product failures, warranty expenses, lawsuits, and damage to brand reputation.
Avoiding such situations requires two precautions, according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. experts at weather testing services such as Intertek Plastics Technology Laboratories and Bodycote Testing Group and at companies like Atlas Materials Testing Articles on Materials testing include:
REAL VS. SIMULATED
The three key approaches to weather testing are long-term natural outdoor exposures, laboratory accelerated weathering, and accelerated outdoor weathering. In many cases, a standard test is dictated by regulations or industry convention (i.e., ASTM ASTM
American Society for Testing and Materials , SAE sae abbr (BRIT) (= stamped addressed envelope) → sobre con las propias señas de uno y con sello , ISO (1) See ISO speed.
(2) (International Organization for Standardization, Geneva, Switzerland, www.iso.ch) An organization that sets international standards, founded in 1946. The U.S. member body is ANSI. ). Companies also have to consider the time they have available for testing before production decisions must be made, as well as the cost of testing.
Experts agree that the "ideal" approach is outdoor exposure in the intended service environment, but this is often impractical due to time and logistics. The next best thing is testing in "benchmark" climates (such as Arizona or Florida), choosing both the location and manner of exposure appropriate for the expected end use. This also requires lengthy test times--at least a year, and often two to five years.
The third best approach, according to Allen Zielnik, senior consultant in Weathering Science at Atlas Materials Testing Technology, is accelerated outdoor testing using real sunlight and weather plus mirrors and other devices to intensify the exposure. The fourth approach--one that is strongly advocated by experts and widely used in critical markets such as automotive and construction--is accelerated laboratory testing that is validated by real-time outdoor exposures.
The last choice is reliance solely on laboratory accelerated tests, which run the risk of inappropriately treating all environments and materials with a "one-size-fits-all" approach, according to Zielnik.
Most weathering damage is caused by light, heat, and moisture. They often work together synergistically syn·er·gis·tic
1. Of or relating to synergy: a synergistic effect.
2. Producing or capable of producing synergy: synergistic drugs.
3. to cause more damage than any one factor alone. The two most important climates worldwide identified as benchmarks for weathering testing are tropical/subtropical and desert environments because they are the most severe for plastics to withstand. Weather testing services of companies like Q-Lab, Atlas, and Bodycote have outdoor exposure sites near Miami, Fla., with its intense sunlight, high year-round temperatures, high annual rainfall, and high humidity; and/or near Phoenix, Ariz., with its hot, dry, high-UV environment and wide temperature fluctuations. "Natural" outdoor weathering in these especially stressful environments can be regarded as "accelerated" testing for a more temperate temperate /tem·per·ate/ (tem´per-at) restrained; characterized by moderation; as a temperate bacteriophage, which infects but does not lyse its host.
adj. environment. Auto companies, for example, may consider one year's weathering in Florida equal to two years' outdoor exposure in the northern U.S.
Accelerated weathering is conducted by exposing the plastic to controlled cycles of intense light, heat, and simulated rain spray. As a general rule, 12-months of outdoor exposure at the benchmark climate sites can be simulated in one-sixth the time with accelerated weathering tests, according to Zielnik. For example, simulation of five years outdoors in Miami requires about 7.5 to 10 months of laboratory weathering.
However, such instrumented testing cannot accelerate all the elements of weathering. While high-intensity UV radiation can simulate six months' outdoor sunlight exposure in one month, you cannot accelerate the effects of temperature or moisture by six times. A plastic's rate of weathering is substantially different above and below its glass-transition temperature (Tg). The temperature of many accelerated test methods, like those using xenon xenon (zē`nŏn) [Gr.,=strange], gaseous chemical element; symbol Xe; at. no. 54; at. wt. 131.29; m.p. −111.9°C;; b.p. −107.1°C;; density 5.86 grams per liter at STP; valence usually 0. arc illumination, are dangerously close to the Tg of many plastics, according to Zielnik. Industry experts allow that while no accelerated test can exactly predict plastics' performance in actual outdoor exposure, these controlled tests can offer meaningful relative comparisons of material formulations and function as pass/fail tests for screening and end-use certification.
The choice of testing approaches is also related to the expected lifetime of the product. Says Zielnik, "A roofing membrane meant to last 20 years would have to meet different expectations and require a different testing methodology than a disposable package or an ophthalmic ophthalmic /oph·thal·mic/ (of-thal´mik) ocular (1).
Of or relating to the eye; ocular.
Pertaining to the eye. lens."
When durable products are intended for outdoor service, the experts advise that accelerated weathering data should be validated with long-term outdoor testing. While the ideal "natural" weathering option may not always be realistic, experts advocate at least running two accelerated tests under different test conditions. This can involve using two different xenon arc test conditions, a xenon arc and a fluorescent UV tester, or a xenon arc and outdoor accelerated weathering device.
The auto industry uses short-term accelerated weathering as an interim benchmark to select materials while awaiting long-term (two- to five-year) final results from outdoor tests. For example, three to four months' accelerated tests are believed to approximate two-year Miami outdoor exposure for some materials. This approach has been validated by other industries, such as construction materials.
Accelerated weather testing typically required for packaging of consumer products, including pharmaceuticals, household cleaners, personal-care products, and soft drinks, can run 24 to 96 hr, or even up to five days. Building products like roofing shingles shingles: see herpes zoster.
or herpes zoster
Acute viral skin and nerve infection. Groups of small blisters appear along certain nerve segments, most often on the back, sometimes after a dull ache at the site; pain becomes , siding, and window profiles, are commonly subjected to three to six months or more of accelerated testing.
ACCELERATED LAB TESTS
Natural-light outdoor testing is realistic, easy to perform, and by far the least expensive. The cost of outdoor weathering tests at the benchmark sites is typically under $1/month per sample. But many companies cannot afford to wait several years to get answers. Accelerated laboratory weathering provides more than speed: Unlike the uncontrolled and variable phenomena of actual weather, lab instruments give the ability to manipulate weathering conditions on demand, as well as precision and repeatability.
The most common indoor accelerated weathering testers are fluorescent UV, pioneered by Q-Lab, and xenon arc instruments. Fluorescent UV devices such as Q-Lab's QUV QUV Relative Magnetic Bearing (radiotelegraphy) and Atlas's UV-2000, are based on the concept that short-wave UV radiation causes the most damage to plastics exposed outdoors. Specially designed fluorescent lamps fluorescent lamp
Type of electric discharge lamp consisting of a glass tube filled with a mixture of argon and mercury vapor. A current of electricity causes the vapor to produce ultraviolet radiation that, in turn, excites a phosphor coating on the inside of the tube, reproduce the damaging effects of sunlight in the short-wave range of 295 to 365 nm. Exposure of samples occurs inside closed boxes where moisture is provided by forced condensation and temperature is controlled by heaters.
Xenon arc devices, such as Atlas's Weather Ometer Ci4000 and Ci5000 series and Q-Lab's Q-Sun Xe-1 or Xe-3 units, take a different approach. They use xenon arc lamps Xenon arc lamps are an artificial light source. Powered by electricity, they use ionized xenon gas to produce a bright white light that closely mimics natural daylight.
Xenon arc lamps can be roughly divided into three categories:
Regulation of the degree of saturation (relative humidity) or quantity (absolute humidity) of water vapor in a mixture of air and water vapor. Humidity is commonly mistaken as a quality of air. .
A recognized benefit of fluorescent UV testers is that their condensation mechanism is the most realistic simulation of outdoor moisture attack. The limitation of water spray used in xenon arc units is that when relatively cold water is sprayed onto a relatively hot test specimen, the specimen cools down, which may slow degradation. However, water spray is very useful for simulating thermal shock Thermal shock in mechanical models
Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high and mechanical erosion. However, fluorescent UV testers can be fitted with a water-spray system, and xenon arc testers, in some test conditions, can be programmed to provide the same condensation as fluorescent units.
Xenon arc testers like the Atlas Ci4000 and Ci5000 series expose samples on a rotating drum. Q-Sun xenon arc testers from Q-Lab and Atlas's small Suntest air-cooled units have a stationary, flat sample array.
The cost of accelerated weathering devices varies significantly. Fluorescent UV testers generally sell in the $10,000 to $14,000 range. Some lower-end xenon arc testers like Atlas' SunTest and Q-Lab's Q-Sun Xe-1 sell in the $12,000 to $15,000 range. But they are used primarily for testing indoor lightfastness, have limited moisture and temperature controls, and handle a small quantity of samples--typically under 50. These devices are used to test for photo-degradation and color change in packaging of pharmaceuticals, soft drinks, mouthwashes, and fabric fresheners.
The most widely used xenon arc testers, which have more elaborate controls for moisture and temperature exposure, range in price from $30,000 to $100,000. These bigger units also can test more samples or larger samples and typically have greater precision in their control systems and sensors for light, temperature, and moisture. Q-Lab's Q-Sun Xe-3 can run 50 to 100 samples measuring 2 x 4 in., while Atlas's Ci4000 and larger Ci5000 Weather Ometers can run 65 to 111 samples of 3 x 6 in. or 185 to 333 samples of 2 x 3 in.
Service costs for accelerated laboratory tests also vary. Fluorescent UV tests range from $800 to $2800/month, depending on the number of samples. Xenon-arc tests, depending on whether it's a standard or a customized test and on the number of samples, can range from $1200/month for five to 10 samples to as much as $25,000 for a typical three-month automotive test with a large number of samples.
When does it pay to buy your own accelerated weather tester rather than use a testing service? According to Zielnik, you reach the break-even point break-even point - In the process of implementing a new computer language, the point at which the language is sufficiently effective that one can implement the language in itself. if you have enough samples to keep an instrument filled and busy for a full year.
Accelerated outdoor weathering is conducted with Fresnel-array solar concentration systems, which are a series of giant motorized mo·tor·ize
tr.v. mo·tor·ized, mo·tor·iz·ing, mo·tor·iz·es
1. To equip with a motor.
2. To supply with motor-driven vehicles.
3. To provide with automobiles. mirrors that reflect sunlight onto the specimen board and track the sun's movement morning to night, season to season. This approach was pioneered in the 1960s by Atlas Weathering Services Group's DSET DSET Desert Sunshine Exposure Testing Inc. Laboratories with its EMMA EMMA
Engstrom Multigas Monitor for anesthesia. (Equatorial Mount equatorial mount
A mounting for astronomical telescopes having two axes, one of which revolves about an axis that is parallel to the axis of the Earth's rotation. with Mirrors for Acceleration) and EMMAQUA (Equatorial Mount with Mirrors for Acceleration with Water) devices. Atlas is now on its third-generation Emmaqua system and has added both temperature and moisture controls. Last year, Q-Lab introduced its QoTrac II, which has similar capabilities and twice the capacity of its predecessor.
These units work properly only in desert environments, and thus are used at these companies' Arizona sites. They expose samples to the outdoor environment with the effects of wind and water. Atlas's Zielnik notes that laboratory testing allows greater control of exposure factors than is possible with outdoor accelerated devices.
Applications for accelerated outdoor weathering generally involve large-area samples, such as automotive taillight and headlamp housings, safety glazing Glazing
The application of finely ground glass, or glass-forming materials, or a mixture of both, to a ceramic body and heating (firing) to a temperature where the material or materials melt, forming a coating of glass on the surface of the ware. for armored vehicles, and aircraft, and coatings on fiberglass composites (see sidebar). Because these systems can expose plastics under glass, they are used to test interior automotive components. Cost of accelerated outdoor test services starts at about $55/month for one 3 x 6 in. test plaque.
Weathering test services use various exposure and mounting techniques to conduct outdoor exposure, and the choice depends on the material or product application. For maximum sunlight exposure, test specimens are typically mounted facing toward the Equator equator, imaginary great circle around the earth, everywhere equidistant from the two geographical poles and forming the base line from which latitude is reckoned. The equator, which measures c.24,902 mi (40,076 km), is designated as lat. 0°. . The amount of solar radiation solar radiation,
n the emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity. a test specimen receives depends on the angle at which is it exposed. A typical 5 x 12 ft exposure rack can mount flat, self-supporting panels or 3D products.
"Open unbacked exposures" are direct weathering tests whereby a specimen is fastened on the rack at its extremities ex·trem·i·ty
n. pl. ex·trem·i·ties
1. The outermost or farthest point or portion.
2. The greatest or utmost degree: the extremity of despair.
a. so that most of the material is exposed to ambient air on all sides. "Backed exposures" are also direct weathering tests, but specimens are mounted on a paper-faced plywood plywood, manufactured board composed of an odd number of thin sheets of wood glued together under pressure with grains of the successive layers at right angles. Laminated wood differs from plywood in that the grains of its sheets are parallel. substrate to simulate the end-use environment of materials that receive only one-sided exposure, such as siding, roofing membranes, and automotive moldings. "Under-glass exposures" are indirect weathering tests of materials not exposed directly to outdoor conditions, such as auto interiors, home carpeting, and upholstery upholstery, general term for household fittings, hangings, curtains, cushions, and covers. It refers to stuffed, padded, and spring-cushioned furniture, such as chairs and sofas, or to the usually decorative materials and fabrics that cover them. .
Exposure racks for the plastics industry are built by William Harrison William Harrison may refer to:
Since many companies have their own exposure sites outside or on the roofs of their buildings, Q-Lab has launched Q-Rack portable rack kit systems, which are said to be a close replica of the Harrison racks. These kits reportedly meet ISO, ASTM, and SAE requirements for outdoor testing.
Atlas has a new customizable, portable, "plug-and-play" weather-data collector, calked the Atlas Weather Station, for users that have their own test exposure sites or want to collect data on climate conditions in regions where there products might be used. At a starting price starting price n (COMM) → precio inicial
starting price n → prix initial
starting price start n (at auction of $25,000, the standard configuration includes a support mount, UV and full-spectrum radiometer radiometer (rā'dēŏm`ətər), instrument for detection or measurement of electromagnetic radiation; the term is applied in particular to devices used to measure infrared radiation. , data-collection capabilities, and solar power pack. Additional options include temperature and humidity probes, a rain gauge, and instruments to measure wind speed and direction.
USERS WEIGH IN ON TESTING
Roberts from Q-Lab says fluorescent UV and xenon arc testers are often used in R&D and QC to evaluate the performance of materials. Both UV and xenon arc testers meet a number of ASTM, ISO, or SAE standards. Generally, UV fluorescent devices are better for testing physical property changes, and xenon arc devices are better for testing color change.
Roberts maintains that weathering effects on tensile tensile,
adj having a degree of elasticity; having the ability to be extended or stretched. and impact properties are assessed better with fluorescent UV. These devices are also used to test wood-plastic composites Wood-plastic composite is a composite material lumber or timber made of recycled plastic and wood wastes. There are also application in the market, which utilize only virgin raw materials. . Says Roberts, "The best test for plastic lumber is ASTM 6662, where you use a fluroescent device with UVA-340 lamps to achieve the best match to the short-wave portion of the solor spectrum. It includes a condensation step that is the best match for outdoor wetness caused by dew."
Technical manager Rocco Rizzo at Bodycote's Engineering & Technology Div. also likes the ability of fluorescent UV testers to handle whole planks of plastic lumber and also PVC PVC: see polyvinyl chloride.
in full polyvinyl chloride
Synthetic resin, an organic polymer made by treating vinyl chloride monomers with a peroxide. pipe and profiles. Rizzo is also seeing increasing requests for both UV exposure and thermal-shock testing of plastic lumber, for which he typically uses xenon arc.
Jim Galipeau, general manager at Intertek Plastics Technology Laboratories, says most customer demand is for testing with controlled irradiance ir·ra·di·ant
Sending forth radiant light.
[Latin irradi in a xenon arc apparatus, though his firm occasionally uses UV fluorescent testers to get a quick comparison between two materials.
Xenon arc is the preferred approach for determining color shifts in plastics, particularly where organic pigments and colorants are used, as they are very sensitive to the UV, visible, and IR spectra. Joe Fay, technical fellow at pigments and additives producer Ciba Corp., says xenon arc weather testers have been used quite heavily for screening new compounds and for improving existing additives. But he warns, "You have to be careful when you use accelerated weather testing and you have to use good judgment and experience to interpret the data, along with expertise in formulating products for outdoor exposure."
Phil Pickett, technical services manager at Ampacet Corp.'s color and additives laboratory, uses both fluorescent UV and xenon arc instruments, noting that xenon arc testing takes longer, but the data tends to correlate better with natural outdoor weathering. He finds all these tests most beneficial for comparing relative stability among a group of samples.
Capable of being chemically broken down by light. plastics is a big area of study for both Ciba and Ampacet. Says Fay, "We do weather testing on additive formulations with pro-degradants. We do preliminary testing for development using xenon arc, narrow down to a few formulation candidates, and then do field testing."
Ampacet's Picket tests photodegradable masterbatches both with accelerated weathering and outdoor exposure in different climates. "This has provided the baseline for performance, hut as always, there are still many variables that can and will affect the final performance. Some seasons are sunnier, rainier, dryer, hazier, etc."
For automotive testing, Edmond Lau, manager of laboratory services for exterior and interior automotive TPO (Twisted Pair Only) Refers to the use of twisted pair wire when other options are available. For example, a TPO suffix at the end of 3com Ethernet adapter model numbers indicates the card has only an RJ45 connector. components at LyondellBasell Industries (formerly Solvay Engineered Polymers), uses xenon arc instruments to evaluate materials during development and for comparative analyses of UV stabilizers and colorants. He also uses xenon arc for QC to ensure that products meet OEM (Original Equipment Manufacturer) The rebranding of equipment and selling it. The term initially referred to the company that made the products (the "original" manufacturer), but eventually became widely used to refer to the organization that buys the products and specifications for color and gloss. "In general, we find that data from xenon arc tests is a good indicator of how well a compound will perform under sun exposure." Lau also conducts outdoor testing for up to two years at weathering service facilities in Arizona and Florida.
Bodycote's Rizzo says automotive weather testing used to be performed mainly in Florida, but there is now a move to test also in Arizona. "We typically run tests for 24 months, with samples pulled out every six months." He also sees xenon arc tests for automotive moving toward ISO standards This is a list of ISO standards that are discussed in Wikipedia articles. For a list of all the more than 16,000 ISO standards (as of 2007), see the ISO Catalogue.
About 300 of the standards produced by ISO and IEC's Joint Technical Committee 1 (JTC1) have been made freely/publicly that test at longer wavelengths, which are closer to Arizona exposures.
Bill Briggs Bill Briggs is director of the Great American Ski School at Snow King (Wyoming) and the first to ski the Grand Teton (June 16 1971). His route required a free-hanging rappel down a 165-foot (50 m) cliff face, which he completed with his skis on. , staff engineer at John Deer Corp.'s Technology Innovation Center in Moline, Ill., says most of his firm's accelerated weather testing uses xenon arc based on the SAE J1960 standard for auto exterior components. Deere uses fluorescent UV testers more for relative comparisons. "We do not use accelerated tests as a direct correlation Noun 1. direct correlation - a correlation in which large values of one variable are associated with large values of the other and small with small; the correlation coefficient is between 0 and +1
positive correlation to outdoor testing. We use them as a quick screening tool whereby we can give preliminary approval to have a material tested outdoors and validate its performance.
Deere uses Atlas's outdoor services in Florida for two-year tests, but samples are pulled out every three months to evaluate color and gloss. "We have had excellent results with our Florida outdoor testing and decided to discontinue accelerated weathering testing in Arizona with the Emmaqua because we found that the intensity of the light generated and the high ambient temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. resulted in most of our samples distorting, unlike true weather exposure samples."
In response, Atlas notes that it introduced new variable-irradiance Emmaqua devices for samples that are very temperature sensitive.
For further information about these companies and their products, visit www.ptonline.com/ suppliers.
Ampacet Corp., Tarrytown, NY
(914) 631-6600 * www.ampacet.com
Atlas Material Testing Technology LLC (Logical Link Control) See "LANs" under data link protocol.
LLC - Logical Link Control , Chicago.
(773) 327-4520 * www.atlas-mts.com
Bodycote Testing Group., Warren, MI
(866) 263-9268 * www.bodycotetesting.com
Ciba Corporation, Tarrytown, NY
(914) 785-2000 * ciba.com/plastics
Intertek Plastics Technology Laboratories, Pittsfield, MA
(413) 499-0983 * www.ptli.com
Q-Lab Corp., Cleveland
(440) 835-8700 * www.q-panel.com
Accelerated Weathering For Large Parts
A relatively new weathering tester, developed by Atlas for the European automotive industry The automotive industry is the industry involved in the design, development, manufacture, marketing, and sale of motor vehicles. In 2006, more than 69 million motor vehicles, including cars and commercial vehicles were produced worldwide. , is now available here and gaining interest from automotive manufacturers and their suppliers who want to conduct accelerated weathering on entire components as large as instrument panels, door assemblies, and bumper fascia fascia (făsh`ēə), fibrous tissue network located between the skin and the underlying structure of muscle and bone. Fascia is composed of two layers, a superficial layer and a deep layer. systems. The SolarClimatic unit utilizes metal halide halide: see halogen. arc lamps that provide spectral distributions that closely match direct solar plus reflected sky radiation. These lamps are said to be efficient in illuminating a large area--2 x 6 ft for this device. The SolarClimatic can also perform freeze-thaw cycles freeze-thaw cycle
in cryosurgery, the process of rapid freeze and slow thaw that results in cell death. Often repeated a set number of times according to the size and nature of lesion being treated. .
Atlas is working with industry leaders to come up with weather standards for testing entire components, starting with instrument panels. SolarClimatic chambers are currently operating at Atlas' Florida and Germany test facilities. Testing service fees for this instrument are about $13,000/month. Purchase price starts around $250,000 for units that will hold an instrument panel and up to $1 million for larger customized systems.
By Lilli Manolis Sherman, Senior Editor