Here is a brief introduction to environmental factors affecting the performance of color coated sheets.
Color Coated Coils
1. Temperature. The coating is prone to soften under high temperatures, making corrosive medium ready to attach and penetrate into the substrates. Oxygen content in water increases under high temperature, which speeds up the corrosion of the sheets at certain temperatures.
2. Humidity. Substrate corrosion at the notch of the sheets and damaged parts in processing are classified as electro-chemical corrosion, and it’s hard to form corrosion cell (namely electro-chemistry circuit) in low-humidity conditions.
3. Diurnal temperature variation. Moisture condensation readily occurs under large temperature differences, as conditions for galvanic corrosion form on bare metal. Besides, the coating undergoes cold and thermal deformation frequently under large temperature differences, speeding up coating aging and loose, which make corrosion medium readily penetrate into the substrates.
4. Sunshine duration and sunlight intensity. Orientation and gradient affect sunshine duration, thus influencing the durability of the coating. Besides, gradient affects the settlement duration of corrosion medium or dust on the surface of the steel sheets. Sunlight is an electromagnetic wave, which can be classified as γ-ray, X-ray, ultraviolet ray, visible light, infrared ray, microwave and radio wave according to energy and frequency. Wave and radio wave has low energy and don’t interact on substances. Infrared ray is also a kind of low energy spectrum, which can only stretch or bend the chemical bond of a substance rather than generating a fracture. It’s obvious that light endows everything with abundant colors. UV spectrum is a variety of high frequency ray, which is more destructive than low energy spectrum. For instance, we know that dark spots on skin and skin cancer are caused by ultraviolet light from the sun. Similarly, UV can also disrupt and break chemical bonds, depending on the wave length of UV and the strength of chemical bonds of a substance. X-ray is penetrable, and γ-ray can break the chemical bonds of a substance and generate unbounded charged ions, which are deadly to organics. Fortunately, there are few such rays in the sunlight. Therefore, sunshine duration and sunlight intensity can affect the structure stability of the coating, especially in the dense ultraviolet-ray areas.
Color Coated Steel Coils
5. Rainfall and rainfall acidity. Rainfall acidity, beyond doubt, is unfavorable for anti-corrosion. The rainfall, however, could serve a dual function. For shingle and roof sheathing with heavy gradient, rainfall can clean the surface of the steel sheets, wash away corrosion products on the surface. For roof sheathing with low gradient and poorly drained parts, heavy rainfall could exacerbate corrosion.
6. Wind direction and speed. The role of wind direction and speed is similar to that of water, that is, they act together. It’s an ordeal for the joint parts of the materials, because wind will make the joint parts become flexible, and thus rainwater penetrates into the inside of buildings.
7. Corrosive fallout. Chloride ion, sulfur dioxide and other sorts of substances can accelerate corrosion, and the fallout is commonly seen in seaside and regions of serious industrial pollution (power stations, smelters, and so forth).
Copy Rights Reserved by SINOWELL METAL
Leave a Reply