Wave beam guardrails, being a significant form of semirigid barriers, are made from corrugated steel panels that are interlocked and supported by posts. These guardrails are mainly designed to be used in exterior areas, where they are exposed to atmospheric conditions like sunlight, oxygen, ozone, temperature changes, water and humidity, and even microorganisms and insects; all these have a bearing on the lifespan of the protective coating.
The guardrails of wave beams have a service life of usually 5 to 10 years when the color does not change noticeably, without cracking and other surface phenomena. The decoration and integrity of its coating film are preserved effectively; thus, the weather resistance of the powder coating is particularly considerable.
Weather resistance is the ability of a powder coating to withstand atmospheric conditions when used in outdoor exposure. An important part is the temperature. The rate of photochemical reactions gets doubled for every ten °C temperature increase. Of all the wavelengths of solar radiation, wavelengths between 250-1400nm hit the earth. Of the infrared radiation (780-1400nm) that contributes 42-60% of the total solar radiation, mainly affected by the mode of heat to the objects. Visible light (380-780nm), that forms 39-53% of the total solar radiation, affects an object in both modes of heat and chemical reactions. Ultraviolet radiation (250-400nm) primarily affects materials via photochemical activity. It has been found through various studies that the most destructive ultraviolet radiation on polymer resins are of wavelengths between 290-400 nm and that most effective at about 300nm. This family of wavelengths is responsible for the degradation of polyolefin resins.
Weathering protection of powder coats can, therefore, be enhanced by isolating agents that lead to deterioration of the coatings and their remedial measures. Especially in recent years, raw material selections and additive formulations, mixing and extrusion, as well as grinding process and so forth, have been greatly advanced in China, resulting in the improvement of weather resistance.
However, one point to be mentioned is that quality varies greatly among powder manufacturers in China. Some of them even care about profits more than quality, to cut costs, recycle raw materials, and add cheap additives that are not adequately tested. The result is poor quality coatings that fade and crack prematurely. In contrast, good quality powder coatings can help to keep the wave beam guardrails in serviceable condition for 5-10 years and longer.
Meanwhile, rainwater may give rise to hydrolysis and water absorption, which deform the coating film. At the same time, it can also wash the dirt and aging products from the guardrail surface, decreasing the protection function and aging process.
Weather resistance might be evaluated using accelerated and natural weathering tests. From accelerated weathering tests, a prognosis about corresponding outside aging time can be gained about atmospheric influences. In comparison, natural exposure tests will achieve more realistic results; however, these tests will consume much time.
