The pretreatment of filter press before powder coating mainly includes degreasing, washing, surface adjustment, phosphating, etc. It is particularly important to purify the tank liquid in the spray production line of plate and frame. The purification of degreasing tank mainly takes into account the impurities in the raw materials of the tank liquid, the iron scraps, flocs and dust caused by the processing, transportation and storage of the workpiece, the rust and paint residue of the fixtures and hangers, and the particulate matter in the rework of the workpiece, etc. The purification of tank liquid does not directly affect the quality of workpiece treatment, but ensures the cleaning effect by guaranteeing the permeability of spray nozzles to ensure the phosphating effect. The degreasing tank can be filtered by using stainless steel wire mesh with a diameter of about 2 mm. Although filtered, the passage of small particles of insoluble matter is inevitable, and long-term accumulation in the inner wall of the pipeline will also block the pipeline. Therefore, regular inspection of spray system, replacement of blocked nozzles and cleaning of pipelines are also essential. Filtration of phosphating tanks requires finer pore sizes. The slag removal effect also ensures the phosphating effect by ensuring the permeability of the spraying system. After degreasing and washing, the impurities on the workpiece and hanger have been washed out. The particulate matter in the phosphating tank liquid is basically phosphating slag. Its particle diameter is less than tens of microns. Choosing a suitable filter device, plate-frame filter press, can continuously and uninterruptedly process the tank liquid to prevent the blockage of the nozzle. At the same time, the filter press produces dry slag, which can reduce the environmental pollution of slurry slag containing phosphating fluid. At present, it is necessary to stop production to precipitate phosphating slag by settling tower. Settlement method can not guarantee the blockage of sprinkler system, and the period of cleaning pipeline system is shorter.
According to the water quality characteristics of domestic wastewater at present, combined with the current sewage treatment process, the developed filter press wastewater treatment equipment adopts the oxidation-reduction and filtration process widely used in the world today, which is obviously superior to the conventional "ion exchange method", "air floatation method", "electrolysis method" and so on.