(6) Welding fumes
The welding fumes held by electric welding products are usually alkaline. It is extremely unfavorable to coating adhesion and damage to anti-corrosion paint. It can be wiped with clean water.
(7) Various signs
Chalk notes are not good for adhesion and easily absorb moisture in the air; if the mark is different from the type to be constructed, it will often cause problems. The only way is to remove it by polishing.
(8) Old coating
The loose coating must be removed. The coating that affects the subsequent coating should be sealed or removed. Use high-pressure fresh water to remove the salt and dust contained in the middle, and remove the oil.
(9) Dust, abrasives and other debris
The large amount of dust, steel wire segments, pellets and other sundries after surface treatment must first be swept away with suction or blown with clean and oil-free compressed air. Vacuuming is the most ideal choice.
Surface treatment method
In order to obtain a good anti-corrosion effect, surface treatment is very important. According to statistics, about 70% of the problems are caused by improper surface treatment. Therefore, for the performance of a metal anticorrosive coating system, proper surface treatment is crucial. Usually we perform surface treatment in three steps:
a. Eliminate various loose substances;
b. Solvent cleaning to remove grease;
c. Use various manual or electric tools or sandblasting methods to process the surface to the paint standard.
Solvent cleaning
This is a treatment method that uses solvents or emulsions to remove grease and other similar contaminants on the surface. Since all kinds of manual or electric tools and even sandblasting can not remove the grease on the metal surface, the solvent cleaning must be processed before other processing methods.
Hand tool cleaning
This is a traditional cleaning method. It usually uses wire brushes, sandpaper sanding, scraping, chiseling or a combination of methods to remove loose oxide scale, old paint film and rust on steel and other surfaces. This processing method is generally slower, and will only be used when other processing methods cannot be used. Generally, the cleanliness of the metal surface treated by this method is not very high, and it is only suitable for light corrosion protection occasions.
Power tool cleaning
This method uses hand-held power tools such as rotating wire brushes, grinding wheels or sand mills, air hammers or needle guns. Using this method can remove the loose oxide scale on the surface, damage the old paint film and rust, etc. This method is more efficient than manual tool processing, but it is not suitable for heavy corrosion or immersion occasions.
Pickling cleaning
Pickling cleaning is an ancient workshop treatment method used to remove oxide scale on steel. There are still several steps in use, usually a dual system including acid etching and acid passivation. One disadvantage of pickling cleaning is that it cleans the steel surface but does not have a roughness, and the roughness helps to improve the adhesion of heavy-duty anticorrosive paint.
High pressure water jet
This method uses mortar and high-pressure water to remove old paint, oxide scale and rust. Using this method, the health hazard of dust in ordinary sandblasting is greatly overcome. Similarly, the surface roughness and cleaning efficiency depend on the water pressure and the concentration of abrasive in the mortar.
Sandblasting
Practice has proved that sandblasting is the most effective method to remove oxide scale, whether on the construction site or in the assembly workshop. This is a necessary treatment method for the successful use of various high-performance anticorrosive paint systems. The cleanliness of the sandblasting treatment must stipulate a general standard, preferably with standard pictures for reference, and stipulate and control the surface roughness during the operation. The primer must be applied immediately within 4 hours after the sandblasting is completed.