Experts talk about the phosphating process before applying primer

The phosphating treatment before the application of the primer will improve the adhesion between the paint film and the base metal, improve the corrosion resistance of the whole coating system, and provide inter process protection to avoid the formation of secondary rust Therefore, the primary problem of phosphating before painting is that the phosphating film must have excellent matching with the primer, while the rust resistance of the phosphating film itself is secondary, and the phosphating film is fine, dense and thin When the phosphating film is thick, it will have a negative effect on the overall performance of the film The selection of phosphating system and process is mainly determined by: workpiece material, oil rust degree, geometry; time interval between phosphating and painting; primer type and construction method as well as relevant site equipment conditions Generally speaking, the high carbon steel of low carbon steel is easy to carry out phosphating treatment, and the phosphating film forming performance is better For the rusty (oxide skin) workpiece, it must go through the pickling process, and the pickling workpiece will bring a lot of troubles to the phosphating, such as rust yellowing between processes, removal of residual acid, coarsening of phosphating film, etc After pickling, the surface of the workpiece should be adjusted before phosphating In the intermittent production situation, due to the limited conditions, the phosphating workpiece must be stored for a period of time before painting, so the phosphating film itself is required to have good rust resistance If the storage period is more than 10 days, medium temperature phosphating should be used generally, such as medium temperature zinc system, medium temperature zinc manganese system, medium temperature zinc calcium system, etc., and the thickness of phosphating film should preferably be between 2.0-4.5g/m2 After phosphating, the workpieces should be dried immediately, and should not be dried naturally, so as to avoid the formation of corrosion in the seam and welding If the storage period is only 3-5 days, low temperature zinc series and light iron series phosphating can be used, and the drying effect will be better than natural cool drying.