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Electro galvanizing and hot dip galvanizing for iron castings

Electro galvanizing

Zinc plating includes electro galvanizing and hot dip galvanizing. Electro galvanizing is also called as cold galvanizing. It uses the principle of electrolysis, to form a even and dense zinc coating. Comparing with other metals, zinc is cheaper but good covering character, and not easy to become rusted. So, zinc plating has been widely used to protect iron castings. Especially to protect iron castings from air corrosion.

Characters of elector galvanizing

1. The thickness of coating is large, the surface of coating is even, dense and no porosity.
2. The zinc coating is pure and dense, so it has good anti-rust capability, can effectively protect iron castings from corrosion.
3. After the chromate treatment, the zinc coating can become white and colorful, so beautiful and has good decorative effect.
4. Because of the good ductile ability of zinc coating, so it can stand the cold punching, rolling and bending process without damage.

Hot dip galvanizing

Hot dip galvanizing is also shown as HDG, or also called as hot dipping galvanizing.

The hot liquid zinc can cover the surfaces of iron castings, and form a very complex zinc iron alloy coating. So, the coating includes a pour zinc layer and a alloy layer.

Therefore, it is not just anti-rust by zinc layer, but also by the alloy layer, which has very strong anti-rust capability. So, the iron castings with HDG coating can stand the environments of strong acid or alkali.

Characters of HDG

1. Very good protection from rust. The whole surfaces of iron castings could be protected, even at the depressed or inside positions.
2. Good reliability of anti-rust ability. The zinc layer stick on the surface of iron castings by the alloy of zinc and iron, so it has very good adhesiveness and endurance.
3. Good ductility. The alloy layer is a special alloy structure, so it can stand the mechanical damage during delivery.
4. Saving time and labors. The treatment is more simple and save the brushing time.

Comparing of electro galvanizing and hot dip galvanizing

Electro galvanizing is cheaper, has a certain anti-rust ability, has good appearance. The shortcoming is, this coating can not be used in the high-temperature situation. Normally can not be used at higher than 120 centigrade. Moreover, during plating, the tensile strength of iron castings will be reduced because of hydrogen evolution.

Electro galvanizing can emit polluted water with zinc, alkali and chromic acid, so cause high pollution to water. HDG can emit Zinc steam and hydrogen chloride, which is highly harmful to persons. So, most of HDG workshops are away from city and village.

Most of iron foundries in China can not do the zinc plating in-house, but normally there are some zinc plating workshops nearby.

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