Main rules of galvanizing spray
Spray galvanizing is a reliable anti-corrosion technology, versatile and effective, applicable both in the workshop and on construction sites. The process allows you to protect steel with high-performance metallic coatings, improving durability, adhesion and possibility of subsequent painting.
Process overview
The spray galvanizing process consists of spraying molten zinc to the electric arc, nebulized and deposited on the previously cleaned support using a jet of compressed air at approximately 5,5 bar. This results in a protective coating that performs a dual function: passive, isolating the steel from the external environment, and active or sacrificial, since zinc is consumed instead of iron.
Lo zinco, aluminum and their alloys must comply with the standard EN ISO 14919:2001. During application, the average distance between gun and support must be between 15 and 25 cm, while the deposition of the metal occurs with crossed movements until the required thickness is reached.
Advantages of spray metallization
Maximum versatility
No limitation on the size of the items to be treated, with application possible both in the workshop and directly on site.
No deformation
Unlike hot dip galvanizing, the support does not undergo deformations due to high process temperatures.
Excellent paintability
The roughness of the coating favors the adhesion of paints and varnishes without the need for further chemical or mechanical pre-treatments.
- The thicknesses of the coating in zinc may vary from 50 µm a 300 µm, until 500 µm.
- The thicknesses of the coating in aluminum may vary from 100 µm a 300 µm.
- The different composition of steel does not represent an application problem for the metallization process.
Execution times after sandblasting
Depending on the environment
- 6 hours after sandblasting if the working environment is protected and ventilated.
- 3 hours after sandblasting if the work is carried out outdoors and in a dry atmosphere.
- 30 minutes after sandblasting if the work is carried out outdoors in humid weather.
Depending on humidity
- 6 hours if the maximum humidity is 60%.
- 4 hours if the maximum humidity is 75%.
- 2 hours if the maximum humidity is 85%.
It is essential to protect the steel from rain, wind and cold. The temperature of the substrate must be maintained at at least 3°C above the dew point.
Surface pretreatment
Surface pre-treatment must be carried out according to the standard EN ISO 13507:2001. Before sandblasting you must ensure that the surface is clean, rough and free from oils and greases.
The objective of sandblasting is to eliminate any surface impurities, like pre-existing paints, rust, mill scale and oxides, obtaining at the same time the degree of roughness essential for the adhesion of zinc, aluminum and related alloys.
Degree of purity
- Second EN ISO 8501-1:2001, the minimum degree required varies from Saddle 2,5 a Saddle 3.
- Saddle 2,5: near white metal, about 96%.
- Saddle 3: white metal, about 99%.
Roughness and abrasives
- Ra 7-8 µm for coverings less than 120 µm.
- Ra 11-12 µm for coatings higher than 120 µm.
- Rz 50–85 µm.
- The use of is preferable sharp steel shot, cast iron or corundum.
- The compressed air must be dry and free from impurities.
- After sandblasting is necessary dust carefully.
- The sandblasting profile must be approximately between < 50 µm and < 100 µm.
- The grit must be silicon-free and with grain size 0,5 – 1,5 mm.
Reference standards
Standards are used to determine the corrosiveness of the atmosphere EN ISO 12944-1 and EN ISO 12944-2, which allow the exposure environment to be classified and the minimum recommended thicknesses of the coatings to be defined.
Minimum thicknesses directive (µ) Recommended
| Environment | Classificazione ambienti ISO 12944-2 | Zinco Nudo | Zinc Coated | Aluminum Naked | Powder Coated Aluminium | Zn/Al 85/15 Naked | Zn/Al 85/15 Varnished | Al Mg 5 Naked | Al Mg 5 Varnished |
|---|---|---|---|---|---|---|---|---|---|
| Acqua salata | Im2 | NO | 100 | 200 | 150 | NRa | 100 | 250b | 200b |
| Soft water | Im3 | 200 | 100 | 200 | 150 | 150 | 100 | 150 | 100 |
| Urban environment | C2 e C3 | 100 | 50 | 150 | 100 | 100 | 50 | 150 | 100 |
| Industriale Environment | C4 is C5-I | NO | 100 | 200 | 100 | 150 | 100 | 200 | 100 |
| Marina atmosphere | C5-M | 150 | 100 | 200 | 100 | 150 | 100 | 250b | 200b |
| Dry atmosphere | C1 | 50 | 50 | 100 | 100 | 50 | 50 | 100 | 100 |
Technical checks
Check cleanliness
Check for the absence of rust or impurities according to the standard EN ISO 8501:2001.
Measure roughness
Measure the degree of surface roughness with the rugosimeter.
Dusting control
Check that the surface has been properly dusted according to EN ISO 8502-3:1995.