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Phosphating process before paint
News Source: Suntory Xin   2013-1-18 10:12:57
The phosphating treatment before priming, will improve the adhesion of the metal film and the substrate, to improve the corrosion resistance of the coating system; provided step in order to avoid the formation of secondary rust protection. The most important issue of the paint before the phosphating phosphate coating and primer must have excellent supporting, phosphate coating rust is secondary, detailed and dense phosphate coating, thin film. When the phosphate coating is thick, the film's overall performance would produce a negative effect. Phosphate system and process selected by: workpiece material, the degree of oil rust, geometry; the phosphide painted interval; decision the primer varieties and construction as well as space and equipment conditions.
In general, low carbon steel and high carbon steel is easy to phosphate processing, better phosphate film-forming properties. Rust (oxide) workpiece must go through the pickling process, after pickling the workpiece will phosphide a lot of trouble, such as inter-process rust yellowing acid residues Clear, phosphate coating coarsening . The pickling workpiece during the zinc, zinc-manganese phosphate surface conditioning treatment generally.
In batch production due to the conditions imposed on the workpiece phosphide must be stored for a period of time to paint, thus requiring phosphate coating itself has good rust resistance. If the storage period of 10 days or more, the general should be used to the temperature phosphating, such as temperature and zinc-temperature zinc-manganese, temperature and zinc calcium-based phosphate coating thickness should preferably be between 2.0 to 4.5g/m2. The phosphating workpiece should immediately drying, should not dry naturally, in order to avoid cracks, welding the formation of rust. If the shelf life of only 3 to 5 days available low-temperature zinc the LRT phosphate, drying effect will be better in the natural air dry.   
  3.1 Single-chamber spray phosphating process
Throughout the pre-treatment process is only one spray chamber, below the spray chamber multiple sump body, different treatment liquid spray workpiece, then goes back to each tank. For example, first spray degreasing fluid flow to be skimmed back to the degreasing tank, close the valve; spray washing, washing valve is closed after the completion of the washing; Next spray phosphating solution, single-chamber approach can be implemented as follows kinds of process:
  Degreasing - phosphate "Combo" (Light Rail system) - water cleaning - (Chromium closed) - a piece
  Degreasing - water cleaning - phosphate - water cleaning - (Chromium closed) - the pieces
  Degreasing - water cleaning - Surface adjustment - phosphate - water cleaning - (Chromium closed) - the pieces
The phosphating process generally do not advocate arranged pickling process, so as to avoid corrosion of the equipment or the process in which it arises corrosion. Single-chamber process equipment less space occupied by small, simple, but the larger waste, only suitable quantities of small batch production situations. With another similar method, using the peripheral small-capacity tanks Sheng treatment liquid after mixing with the hot water spray, after pumping fluid through the pump and pipes achieved on the workpiece degreasing, phosphating effect, spray liquid not recycled this method is more simple, but the waste to be bigger.
  3.2 multi-room "standard" station phosphating process:
  ①Pre-degreasing 50~70℃ 1~2min
  ②Skimmed 50~70℃ 2~4min
  ③Water cleaning 1~2 Normal atmospheric temperature 0.5~1.0min
  ④Adjust the surface Normal atmospheric temperature 0.5~1.0min
  ⑤Phosphide 35~60℃ 2~6min
  ⑥Water cleaning<2Normal atmospheric temperature 0.5~1.0min
  ⑦Deionized water Normal atmospheric temperature 0.5~1.0min
  ⑧Chromate treatment 40~70℃ 0.5~1.0min
  ⑨Drying Less than 180℃
  The treatment can be spray, full immersion, spray - soaked combination of three ways. Full spray of the household appliances industry, it is efficient, the entire pre-treatment only takes ten minutes to complete, space-saving device. The popular cars IDM using a combination of spray - soaking.
  The surface conditioning step is not required, the table the toner add to skim tank can also achieve the same effect. The phosphating deionized water is essential. Chromate treatment after phosphating, can improve the corrosion resistance of the entire coating system), but due to the chromium pollution problems and should therefore be used with caution.
  Unless there is sufficient reason, pickling processes generally do not spray, spray a series of questions that will bring the corrosion of the equipment and work in process rust. Other processes can be used full spray or spray - dip a combination of construction methods.
  For mixed parts (no rust workpiece, rust, mixed oxide workpiece processing), degreasing rust "Combo" instead of the step-by-step degreasing rust method has been applied to several decades of history, the same to be satisfied with the results. "Combo" is generally more appropriate for non-volatile inorganic acid pickling and degreasing rust.


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