In order to make the metal surface better or for specific application, we always need to spray painting. According to the different properties of different metal pieces, the selection of surface coating and cleaning process is also different. Following we will explain the suggested pretreatment solutions for steel, galvanized steel , aluminum and other soft metals as well as alloy steel.
1- Steel
The most effective way to clean unpainted steel is by solvent cleaning or steam cleaning after blasting. Actually according to SSPC standards, it requires solvent cleaning priorior blasting. Sandblasting is recommended for cleaning damaged areas. Water type sandblasting is good option where dry blasting is not acceptable.
2 – Galvanized steel
Recommended cleaning methods for galvanized steel vary depending on surface conditions. Simple solvent cleaning of new clean galvanized sheet is sufficient to remove any protective grease. Other temporary protective measures such as chromate treatment, must be removed by recommended methods from manufacturer. Epoxy and latex coatings have no requirements of roughness and can be tightly bonded on smooth, clean galvanized sheet surfaces.
3 – Aluminum and other soft metals
New, clean aluminum and other soft metals can be cleaned easily by solvent. Dust and loose corrosion can be removed with cleaning agent; If it’s for repairing purpose, old paint can be removed with plastic pellets or other light blasting methods while abrasive blasting with coarse particles (steel balls or steel shot) will damage soft metal surfaces. These metal surfaces can be cleaned first to increase adhesion to solvent based or latex paints.
4 – Alloy steel
Low grade alloy steel generally does not need to be protected by painting, but relies on the formation of a natural oxide film. If it is necessary to remove inconspicuous rust spots for painting, high pressure or ultra-high pressure water blasting is required. In order to achieve surface roughness, it is also required to add sandblasting particles.
More about Sandblasting
- Sandblasting is to clean up the attachments, welding slag, grease and other contaminants on the metal surface;
- During the sandblasting process, the air temperature should be below 85 degrees;
- The compressed air used in the blasting process needs to be processed by a cooling device and an oil-water separator to ensure the compressed air is dry and oil-free;
- The best choice of abrasive is ceramic sand and iron sand. The abrasive is required to be angular, clean, dry and free of oil.
