Green sheet metal processing requires the following processes to achieve qualified production and emissions.
Passivation: Passivation treatment is required when electroplating sheet metal parts to obtain a finer oxide protective layer. The stainless steel plate itself has a certain corrosion resistance function and can be processed directly under normal circumstances, but it needs passivation treatment under special circumstances. If the boiler water tank uses SUS304 or SUS316, the parts still need to be passivated to ensure that they will not rust at high temperatures.
The passivation solution contains 5% nitric acid and 2% potassium dichromate, and the two-in-one pickling passivation solution contains 10% hydrofluoric acid. The hexavalent chromium Cr6+ in potassium dichromate will seriously pollute the environment and cause serious damage to the human body (such as the reproductive system). Hydrofluoric acid is highly corrosive, causing serious damage to teeth and bones, and it can also corrode glass. At present, my country has successfully replaced Cr6+ with Cr3+, thereby greatly reducing environmental pollution, and has replaced hydrofluoric acid with some additives.
Spray paint and powder spray: Spray paint is the construction of paint and solvent (or need hardener) mixed. The paint is atomized by compressed air or electrostatic force, sprayed onto the workpiece and attached to its surface. After the solvent evaporates (or reacts with each other), it solidifies into a film. The disadvantage of this process is the high content of VOC (volatile organic gas), which is harmful to the human body. The paint utilization rate is very low, only about 50%, which is a waste of resources. However, electrostatic spraying does not require a large amount of thinner, the powder does not contain harmful substances, and the additives are cured into a film after sweating, which does not pollute the environment, the coating is of good quality, high adhesion and mechanical strength, corrosion resistance, short curing time, no primer , The powder recycling rate is high.
With the popularization and application of epoxy resin and polyester powder spraying, the appearance of sheet metal parts is equivalent to that of spray paint, and the corrosion resistance is greatly improved. With the country’s increasing environmental protection requirements, many companies process the phosphated iron phosphate into other chemical raw materials after two precipitations in the sedimentation tank, thereby reducing the environmental pollution caused by the phosphating treatment.