We need to balance pollution of sheet metal processing and environment. Green sheet metal processing requires qualified production and discharge in the following processes.
Passivation: The sheet metal part is electroplated with a passivation treatment to obtain a denser oxide protective layer. The stainless steel sheet itself has certain corrosion resistance, and it can be directly processed under normal conditions, but it needs to be passivated in certain occasions. If the water heater tank uses SUS304 or SUS316, the parts still need to be passivated to ensure that they do not rust at high temperatures. The passivation solution contains 5% nitric acid and 2% potassium dichromate, and 10% hydrofluoric acid in the pickling passivation liquid. Hexavalent chromium Cr6+ in potassium dichromate can seriously pollute the environment and cause serious harm to the human body (such as the reproductive system). Hydrofluoric acid is highly corrosive, causing serious damage to teeth and bones, and can also corrode glass. At present, China has successfully replaced Cr6+ with Cr3+, which greatly reduces environmental pollution, and has replaced hydrofluoric acid with an additive.
Spraying and dusting in sheet metal processing: Painting is a process in which the coating is dissolved with a solvent (or a hardener is added). The paint is atomized by compressed air or electrostatic force and sprayed onto the workpiece and attached to the surface. The solvent evaporates (or reacts with each other). After curing, it forms a film. The shortcoming of this process is that the VOC (volatile organic gas) content is high, which is harmful to the human body; the utilization rate of the paint is very low, only about 50%, wasting resources. The electrostatic powder does not require a large amount of thinner, the powder does not contain harmful substances, the auxiliary agent evaporates and solidifies into a film, does not pollute the environment, the coating quality is good, the adhesion and mechanical strength are high, the corrosion resistance, the curing time is short, and the bottom is not needed. Paint and powder recycling rate is high. With the popularization and application of epoxy resin and polyester powder coating, the appearance of sheet metal parts is comparable to that of spray paint, and the corrosion resistance is also greatly improved. With the increasing environmental protection requirements of the country, many companies have treated the phosphatized FePO4 into two other chemical raw materials through the sedimentation tank, thereby reducing the environmental pollution caused by phosphating.
Many spray lines have been robotic in sheet metal processing, which reduces the damage to workers and ensures the stability of quality. Nowadays, the powder recovery device in sheet metal processing industry has become the standard of the coating line. It can absorb most of the powder through the filter element, and by adding the solenoid valve and the sensor, it sprays water when the workpiece passes, and then closes after the filter, thereby saving energy and 50 % of water.