Accelerated weathering test apparatus with soaking cycle

Details Accelerated weathering test apparatus with soaking cycle Accelerated weathering test apparatus with soaking cycle

2001-10-30

2003-03-18

Gutierrez, Diego (Department: 2859)

Thermal measuring and testing

Thermal testing of a nonthermal quantity

Of susceptibility to thermally induced deteriouration, flaw,...

C374S005000, C073S865600

Reexamination Certificate

active

06533452

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a weathering test apparatus of the type used to expose test specimens to solar radiation and other weathering effects on an accelerated basis, and more particularly, to such an improved accelerated weathering test apparatus that provides an automated soaking cycle regardless of the time of day.
BACKGROUND OF THE INVENTION
Manufacturers of exterior coatings, such as paints and finishes, as well as plastics and other components which tend to degrade under exposure to solar radiation and other weathering effects, often want to know how such products will perform following years of exposure. However, such manufacturers typically require such information in a much shorter time than it would take to exposure such materials to weathering effects under normal conditions. Accordingly, accelerated weathering test apparatus have been developed which accelerate the effects of weathering due to outdoor exposure in a much shorter time so that manufacturers need not actually wait five or ten years in order to determine how their products will hold up after five or ten years of actual outdoor exposure.
One conventional outdoor accelerated weathering test apparatus is disclosed in U.S. Pat. No. 4,807,247 issued to Robins, III, and shown in FIG.
1
. The aforementioned test device includes a Fresnel-reflecting solar concentrator having a frame
32
with a series of ten flat mirrors
34
,
36
which focus natural sunlight onto a series of test specimens secured to a target board measuring approximately six (6) inches wide by fifty-five (55) inches long. The Fresnel-reflecting solar concentrator directs solar radiation onto the target board area with an intensity of approximately eight suns. Both the bed
32
which supports the mirrors
34
,
36
of the solar concentrator, and the target board, are supported by a frame which can be rotated to follow daily movements of the sun. A solar tracking mechanism responsive to the position of the sun, controls the operation of an electric motor used to rotate the test apparatus to follow movements of the sun.
The axis of rotation of the test machine is oriented in a north-south direction, with the north elevation having altitude adjustment capability to account for variation in the sun's altitude at various times during the year. Such known testing apparatus are also provided with an air tunnel
44
mounted above the target board. An air deflector causes air escaping from the air tunnel to be circulated across the test samples mounted to the target board to prevent the test samples from overheating due to the concentrated solar radiation to which they are exposed. A squirrel cage blower
48
communicates with the air tunnel
44
for blowing cooling ambient air there through. Devices and mechanisms have been adapted to control the blower in order to maintain the temperature of the target test samples substantially constant during daylight hours despite variations in the daytime ambient air temperature, and despite variations in the solar radiation intensity. In addition, water spray nozzles
60
are provided proximate to target board for wetting the test samples at periodic intervals to simulate the weathering effects of humidity, dew, rain, etc.
Standardized testing methods have been developed for operating outdoor accelerated weathering test apparatus of the type described above. The American Society for Testing and Materials (ASTM) has issued standards such as, but not limited to, standard G90, which is directed to testing procedures and operating parameters for conducting such outdoor accelerated weathering tests. Other standards have been developed by the Society of Automotive Engineers (SAE), Ford, International Standards Organization (ISO), American National Standards Institute (ANSI), Japan Industrial Standard (JIS) and other such standards organizations which are directed to accelerated weathering tests. However, no standard has been developed which incorporates a soaking cycle into an outdoor, natural light accelerated weathering test cycle. Standard D5722 was developed for accelerated finish failure involving loss of film integrity, such as cracking, peeling and flaking of factory-coated embossed hardboard. This Standard accelerates long-term weathering effects by subjecting the test specimens to concentrated natural sunlight (with optional periodic daytime surface water spray) plus a remote soak-freeze-thaw cycle. The Standard procedure requires removing the target board with attached test specimens from the testing apparatus and immersing the target board in a deionized water soak tank maintained at 21° C.+/−3° C. (70° F.+/−5° F.) for one hour. After soaking, the target board with attached test specimens is placed in a freezer maintained at −18° C.+/−3° C. (0° F.+/−5° F.) for 12 hours. The following morning, the test specimens are allowed to thaw for a minimum of one hour under laboratory ambient conditions. The target board with attached test specimens is then remounted on the exposure device in accordance with prior practice.
It has been recognized by independent study that a soaking cycle is a significant and important variable for evaluating degradation of materials in accelerated weathering tests. The inventor hereof has conducted numerous experiments in the field of accelerated weathering testing which verify and confirm that a soaking period is a significant and important variable in such testing. The results of these experiments were discussed in technical papers prepared, published and presented by the inventor titled “Fractional Factorial Approaches to Emmaqua Experiments” and “Applying Taguchi Designs to Emmaqua Weathering Experiments.”Both papers document the results of the background research related to different techniques for accelerated weathering tests which concludes that immersion plays a critical role in weathering degradations.
Apart from outdoor accelerated weathering test devices of the type described above, other test devices are also known which utilize an artificial source of radiation and immersion in water to exposure test samples. An example of such a test devices are disclosed in U.S. Pat. No. 3,116,977, issued to Grabowski, et al.; U.S. Pat. No. 3,224,266, issued to Klippert; U.S. Pat. No. 3,266,306, issued to Arnold, et al.; U.S. Pat. No. 3,685,969, issued to Young III; U.S. Pat. No. 3,936,273, issued to Powell; U.S. Pat. No. 4,012,954, issued to Klippert; U.S. Pat. No. 4,282,181, issued to Pierce; U.S. Pat. No. 4,698,507, issued to Tator, et al.; and other conventional testing methods.
U.S. Pat. No. 3,116,977 discloses an apparatus to screen corrosion inhibitors by immersing metallic test specimens into a heated bath of water having the inhibitor dissolved therein, withdrawing the metallic specimens and heating them and continuing the periodic immersion and withdrawal for a substantial period. There is no provision for exposure to solar radiation or other light source.
U.S. Pat. No. 3,224,266 claims an apparatus for testing samples under conditions such as humidity, rain, or complete immersion in liquid, heat and air circulation as well as light and dark periods with controlled changeover between light and dark. It provides for heating with a heater source of warm air in addition to heat from the illumination source. This prior apparatus does not provide for exposure to solar radiation or rapid sequencing of immersion followed by exposure to solar radiation.
U.S. Pat. No. 3,266,306 describes an apparatus to test resistance of materials to humidity by exposing them to steam pressure in a chamber. No solar radiance exposure or other light source exposure is practiced in this prior art patent.
U.S. Pat. No. 3,685,969 discloses an apparatus for testing the strength of specimens under corrosive conditions. Specimens under stress are subjected to intermittent immersion using gravity flow of a corrosive fluid to and from a fixed tank with the specimens. Solar radiation or other light source exposure

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