Electro galvanizing and hot dip galvanizing for iron castings
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
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
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
Comparing of electro galvanizing and hot dip
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.
iron foundries in China can not do the zinc plating
in-house, but normally there are some zinc plating workshops nearby.