BS EN ISO 877-3:2018 pdf download
BS EN ISO 877-3:2018 pdf download.Plastics – Methods of exposure to solar radiation Part 3: Intensified weathering using concentrated solar radiation.
7.2 Exposure site
Fresnel-reflecting solar concentrating devices operate most eflèctively at locations that receive at least 3 500 h of sunshine per year and where the average daytime relative humidity is less than 30%. ASTM G90 provides requirements for the exposure site’s average ratio ofdirect solar radiation to global normal solar radiation.
NOTh In regions that receIve 3 500 h of solar radiation and where the average daytime relative humidity is less than 30%, the average ratio or direct solar radiation to global normal solar radiation is at least 0,75. Areas that meet these criteria have a minimum diffuse component of solar radiation (sky radiation) The use of reflecting solar Concentrator devices in regions of moderate to high diffuse solar Irradiance will substantially reduce the amount of UV radiation at the specimen target board. Moderate to high levels of humidity and urban aerosols result in scattering of the direct component of solar radiation so that ultraviolet radiation is scattered into the hemispherical sky dome and Is not available to be focused by the mirrors on to the specimen target board. This is shown in Figure 3. In addition, the use of reflecting solar concentrator devices in regions of moderate to high diffuse solar irradlance can give different stability rankings for materials compared to exposures conducted In accordance with ISO 877-2 because of the differences in UV radiation.
7.3 Temperature control
Solar concentrating devices are equipped with a blower to cool the specimens. Specimen temperatures for most materials are typically 10 °C higher than the maximum temperature which would be reached if an identical specimen was exposed directly to solar radiation (without concentration) at normal incidence at the same time.
If more precise control or specimen temperature is required, the temperature of a black or white panel, the temperature of a black or white standard thermometer, the temperature of a particular specimen, the air temperature or the temperature indicated by a remote sensor may be monitored and used as an input to control the specimen temperature. If used, report the controlled temperature and any observed deviations In the test report.
Use of this method of temperature control may produce results that are not equivalent to typical solar concentrating exposures and may require longer radiant exposures to produce the same amount of degradation.
Unless otherwise specified, if measurement oIblack- or white-panel temperature is required, the panels shall be constructed, calibrated and maintained in accordance with ASTM G179. Unless otherwise specified, if measurement of black- or white-standard temperature Is required, the panels shall be constructed and maintained in accordance with ISO 4892-1.
NOTE If a black.standard tcmpcrature is used, the temperature indicated will be higher than that indicated by a black-panel thermometer under typical exposure conditions.
Temperatures during the night-time are typically not controlled. If agreed upon by the interested parties, heat sources placed behind the specimens may be used to control nightt1me temperatures. If so, the method used to control night-time temperatures shall be included in the test report.
8 Exposure stages
8.1 General
Since the amount of solar radiation is one of the most important lactors in the deterioration of plastics during weathering exposure, exposure stages shall, unless otherwise specified, he defined In terms of total solar radiant exposure, solar LJV radiant exposure or solar UV radiant exposure In a narrow passband,
8.2 Solar radiant exposure
8.2.1 Guidance for selection of the exposure stage
For guidance in selecting the exposure stage. Table I shows the average annual total solar radiation and solar ultraviolet radiation for sites in southern Florida and in the central Arizona desert. This data may be used as an equiva)ent standard year for setting desired exposure stages (e.g. an exposure stage of 305 MI/rn2 total solar UV from 295 nm to 385 nm could be used to simulate a one-year latitude-angle exposure in southern Florida conducted In accordance with ISO 8722:2O09, method A).
