Knowledge of surface treatment before painting

In the process of processing, transportation and storage, the surface of workpieces often contains oxide skin, residual molding sand, welding slag, dust, oil and other dirt In order to make the deep layer firmly attached to the surface of the workpiece, the surface of the workpiece must be cleaned before coating, otherwise, it will not only affect the adhesion and corrosion resistance of the coating and the base metal, but also make the base metal continue to corrode even with the protection of the coating, make the coating peel off, and affect the mechanical properties and service life of the workpiece Therefore, the surface treatment of workpiece before painting is an important guarantee and measure to obtain high quality protective layer and extend the service life of the product In order to provide a good workpiece surface, the treatment of the workpiece surface before painting has the following points: 1 No oil and moisture; 2 No rust and oxide; 3 No adhesive impurities; 4 No acid, alkali and other residues; 5 There is a certain roughness on the workpiece surface Common surface treatment methods are as follows: Manual treatment: such as scraper, wire brush or grinding wheel, etc The rust and oxide scale on the surface of the workpiece can be removed by hand, but the manual treatment has the advantages of high labor intensity, low production efficiency, poor quality and incomplete cleaning Chemical treatment: it mainly uses the acid or alkaline solution to react with the oxide and oil stain on the surface of the workpiece to dissolve them in the acid or alkaline solution, so as to remove the rust, scale and oil stain on the surface of the workpiece Chemical treatment is suitable for cleaning sheet metal, but the disadvantage is: if the time is not properly controlled, even if corrosion inhibitor is added, the steel can produce excessive corrosion For more complex structural parts and porous parts, it is difficult to completely remove the residual acid immersed in the gap or hole after acid pickling If not handled properly, it will become a hidden danger of future corrosion of the workpiece, and the chemicals are volatile, high cost, and the chemical emissions after treatment are difficult If not handled properly, it will cause serious pollution to the environment With the improvement of people's environmental awareness, this treatment method is being replaced by mechanical treatment Mechanical treatment: mainly including shot blasting and shot peening Shot blasting cleaning is a method of using centrifugal force to accelerate the shot, and shot to the workpiece for rust removal and cleaning However, due to the poor flexibility of shot blasting and the limitation of the site, there are some blindness in cleaning the workpiece, and it is easy to produce dead angles on the inner surface of the workpiece that cannot be cleaned The structure of the equipment is complex, there are many vulnerable parts, especially the blades and other parts wear fast, the maintenance time is much, the cost is high, and the one-time investment is large Shot peening is divided into shot peening and sand blasting The surface treatment with shot peening has great striking force and obvious cleaning effect However, the treatment of thin plate workpiece by shot peening is easy to deform the workpiece, and the steel shot strikes the workpiece surface (regardless of shot peening or shot peening) to deform the metal substrate Because Fe3O4 and Fe2O3 are not plastic, they are peeled after being broken, and the oil film and the substrate are deformed together, so for the workpiece with oil pollution, shot peening and shot peening cannot completely remove the oil pollution Among the existing surface treatment methods, blast cleaning is the best one Sandblasting is suitable for cleaning the workpiece surface with high requirements But at present, the general sand blasting equipment in our country is mainly composed of the original heavy sand conveying machinery such as hinge, scraper, bucket elevator, etc Users need to build a deep pit and make a waterproof layer to install machinery The construction cost is high, the maintenance workload and maintenance cost are huge A large number of silicon dust generated in the process of sand blasting cannot be removed, which seriously affects the health of operators and pollutes the environment With the continuous improvement of science and technology, with the continuous requirements of people for product quality, with the continuous application of high-tech equipment in enterprises, with the improvement of people's environmental awareness and strict requirements of environmental protection departments, it is imperative to control dust pollution and noise environment The competition of enterprises is more and more fierce, so how to gain the advantage in the fierce competition becomes the key to determine the development of enterprises Facts tell us that strict control of production links is the premise to ensure the quality of enterprise products, and the control of environmental pollution is the responsibility of each of us.