Raw materials inspection before galvanizing

For good galvanizing results, the incoming materials must have satisfied conditions.

1. • Steel quality and fabrication must be satisfactory.

2. Steel chemistry	• Carbon content should be less than 0.25% • Silicon content should be less than 0.04% and between (0.15% and 0.22%) • Manganese content should be less than 1.3% • Phosphorus content should be less than 0.04
   Steel surface condition and what kind of steel	• Excessively rusted surface • Pitted surface • Cast iron • Malleable iron • Hot-rolled and Cold-rolled steel
   Steel fabrication condition	• Superposition side and joint side are welding continuously or not • Welding slug are cleaning or not • Moving parts have enough radical clearance enough or not
   Distortion and warpage	• Use parts in the assembly of equal or near equal thickness at joint or not • Use temporary bracing or reinforcing on thin materials and asymmetrical design or not
   Vent hole, drain hole, hang hole and cropped corner	• These holes have made right place and diameter or not

Degreasing Process

1. • The most commonly used alkaline degreasing agent is sodium hydroxide (NaoH) solution at 80° C to remove paint, asphalt, grease and oil layers.
2. • Using stream heating method for heating the sodium hydroxide solution.

Water Rinsing after Degreasing

1. • After alkaline degreasing, the workpieces must be washed before pickling to ensure that the acid solution is not polluted. Purpose of the rinsing is to remove residual degreasing solution.
2. • Rinsing also ensures no grease/oil is carried across into the acid tank.

Acid Pickling Process

1. • The pickling process is a process to remove rust and scale from the surface of the steel which must be completely cleaned before fluxing.
2. • Hydrochloric acid (HCl) pickling process is the most commonly used in hot dip galvanizing.
3. • Pickling speed is proportional to the concentration of the acid, and therefore higher concentration leads leads to faster pickling speed.

Water Rinsing after Pickling

1. • Rinsing after pickling is very important, this can protect the fluxing solution from being polluted. It can avoid excessive acid and iron be brought into the fluxing solution.

Fluxing Process

1. • Fluxing is necessary before galvanizing. It can effectively improve galvanizing quality and save costs.
2. • The main chemicals in fluxing agent are zinc chloride and ammonium chloride and temperature is at (60-80° C).

Drying Process

1. • In order to avoid zinc splash and zinc-ash formation, the workpieces must dry before galvanizing.

Galvanizing Process

1. • The material is completely immersed in the kettle of molten zinc. While immersed in the kettle, the zinc reacts with the iron in the steel to form metallurgically bonded zinc-iron intermetallic alloy layers.
2. • The galvanizing quality is greatly determined by zinc ingot quality, molten zinc bath chemistry, temperature, dipping time, lifting speed and fixtures.

Water cooling and Passivation Process

1. • After galvanizing, the workpieces should immersed into the cooling water as soon as possible to prevent ash burning.
2. • White rust will form during long time storage and transportation so passivation is necessary after cooling.

Inspection and Repairing

1. • Coating film thickness and appearance inspection shall be performed according to requirements and standards. Drainage spikes, zinc skimming, chain mark and wire mark will be removed and polished by using proper tools (paper grinder, files).
2. • Repair process of galvanized material will be complied with ASTM A780/A780M standards.

3. Note: We comply ASTM A123/A123M (standard specification for zinc (hot-dip galvanize) coating on iron and steel articles), ASTM A780/A780M (standard practice for repair of damaged and uncoated area of hot dip galvanized coating) and ASTM E 376-96. (Standard Practice for Measuring Coating Thickness by Magnetic-Field or Eddy Current (Electromagnetic).

We can provide certificate for zinc coating and we can take responsibility for our product.

We comply ASTM A123/A123M (standard specification for zinc (hot-dip galvanize) coating on iron and steel articles)