Why Hot-Dip Galvanizing?
Traditionally, hot-dip galvanized steel is specified for its superior corrosion protection, especially in harsh environments. Though corrosion resistance is inherent any time galvanizing is utilized, more and more specifiers select hot-dip galvanized steel for other reasons, including lowest initial cost, durability, longevity, availability, versatility, aesthetics, and sustainability.
Zinc: Natural, Abundant, Essential to Life
Zinc is the 24th most abundant element in the Earth’s curst and exists naturally in the air, water, and soil. Most rocks and many minerals contain zinc in varying amounts.
In fact, approximately 5.8 million tons of zinc are naturally cycled through the environment annually by plant and animal life, rainfall and other natural activity.
Not only is zinc abundant in nature, but it is quite common in our every-day life. Zinc oxides or other compound forms are used in numerous products we use regularly, such as:
•Personal care: sunscreens, sunburn treatments, lotions, chap sticks, diaper cream, treatment of acne, dandruff shampoos, cosmetics, cold medicines, wound ointments
•Household/Automotive products: tires, batteries, grease/lubricants, ceramics, cookware/tableware, paints, tv screens, fertilizers, animal feed
•Other: fireworks (incandescent shine), glow in the dark toys, dietary supplements, medical treatments, various foods (meat, fish, poultry, whole grains, dairy)
Zinc oxide blocks more UV rays than any other single ingredient – key to sunscreens and for sun treatment (healing).
ESSENTIAL TO LIFE
Zinc is essential to ALL life, from humans to the smallest microorganism. Zinc is vital to cell division, which is literally what leads to normal growth and development. In humans, zinc is crucial for growth of bones and organs, brain development (memory, sensory and cognition), and to strengthen our immune systems to prevent disease and fight infections.
Zinc deficiency is a serious global health risk as the World Health Organization (WHO) estimates 2 billion people worldwide are zinc deficient, leading to 800,000 deaths each year, 450,000 of which are children under the age of 5. Most people in developed countries consume enough zinc by eating zinc-rich foods such as meat, poultry, seafood, and nuts. However, people in developing countries often have plant-based diets that do not provide enough natural zinc for healthy development. Adding zinc fertilizers to crops in these areas not only helps to increase zinc intake in the diet, but also increases the yield and quality of the crops, which helps to feed growing populations.
Zinc deficiency leads to stunted growth and intellectual development, fertility problems, premature aging, and immune system dysfunction leaving people vulnerable to diarrhea and pneumonia (two of the biggest killers of children under 5) as well as a host of other infectious diseases and health issues. To help combat zinc deficiency around the world, the IZA and UNICEF partnered together to form the Zinc Saves Kids initiative to provide zinc tablets to children in developing countries. Donating even $5 can provide one child zinc tablets for an entire year.
Metallizing (Zinc Thermal Spray)
Zinc spraying, or metallizing, is accomplished by feeding zinc powder or wire into a heated gun, where it is melted and sprayed onto the part using combustion gases and/or auxiliary compressed air to provide the necessary velocity. Prior to metallizing, the steel must be abrasively cleaned.
The 100% zinc coating can be applied in the shop or field, but is more commonly done in the shop where heat for melting is more readily available. The heat is supplied by combustion of an oxygen-fuel gas flame or by electric arc. Processes have been developed for feeding molten zinc directly into the spray nozzle, but only for in shop applications. Following the zinc application, the coating is normally sealed with a low viscosity polyurethane, epoxy-phenolic, epoxy, or vinyl resin.
The metallized zinc coating is rough and slightly porous, with density about 85% that of batch hot-dip galvanizing. As the metallized coating is exposed to the atmosphere, zinc corrosion products tend to fill the pores providing consistent cathodic protection. Metallizing covers welds, seams, ends, and rivets well and can be applied in excess of 10 mils (254 µm). However, the mechanically-bonded pure zinc coating can be inconsistent and requires a skilled operator for best application. Coatings tend to be thinner on corners and edges, and no coating is applied to interior surfaces or difficult to access recesses and cavities.
Zinc spray metallizing can be applied to materials of any size, though complexity of the structure is important. Metallizing is commonly used as an alternative to batch hot-dip galvanizing when the part is too large for immersion in the galvanizing kettle. And though more often and easily applied in the shop, metallizing in the field is a great option for extending the life of already erected batch galvanized structures. The biggest limitations to metallizing applications are availability (skilled operator and equipment) and a significant cost premium.