Metal Pickling Process and Common Defects

          We have introduced the advantages and functions of pickling boards above, and now we continue to pay attention to the metal pickling process and common defects.
         
1. Metal pickling process


Pickling principle:
          It is a surface process that uses acid solution to remove oxide scale and rust on the surface of steel, usually carried out together with pre-filming. Generally, the workpiece is immersed in a chemical solution such as sulfuric acid to remove oxides and other films on the metal surface, which is the pre-treatment or intermediate treatment of electroplating, enamel, rolling and other processes. Also known as wet cleaning.
          The pickling process mainly includes dipping pickling method, spray pickling method and acid paste rust removal method. The acids used are mostly sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid and mixed acids.

Process flow:
          Hanging on metal parts → chemical degreasing (conventional alkaline chemical degreasing or surfactant degreasing) → hot water washing → running water washing → one-step pickling → running water washing → second-step pickling → running water washing → transfer to the next process (Such as: chemical coloring→recycling→running water washing→hardening treatment→running water washing→sealing treatment→running water washing→drying→finished product)
Common defects:
          Iron oxide scale intrusion: Iron oxide scale intrusion is a surface defect formed during hot rolling. After pickling, it is often pressed in in the shape of black dots and strips, the surface is rough, generally has a hand feel, and appears sporadically or intensively. It is often caused by imperfect heating process, descaling process and rolling process of pickling.
Oxygen spot (surface landscape painting): refers to the dot-like, linear or pit-like appearance left after the iron oxide scale on the surface of the hot-rolled steel is washed off. The rolling is pressed into the matrix, which is highlighted after pickling. It has a certain effect on the appearance, but does not affect the performance.
          Macular: yellow spots appear on part or the whole board surface, which cannot be covered after oiling, which affects the quality and appearance of the product. The main reason is that the surface activity of the strip just out of the pickling tank is high, the rinsing water fails to wash the strip normally, the spray beam and nozzle of the rinse tank are blocked, and the angles are not equal.
          Under-pickling: The surface of the strip steel has local iron oxide scales that are not cleanly and insufficiently removed, and the plate surface is gray-black, with fish scales or horizontal water ripples. It has something to do with the acid process, mainly because the acid concentration is insufficient, the temperature is not high, the strip runs too fast, and the strip cannot be immersed in the acid.
          Over-pickling: The surface of the strip steel is often dark black or brownish black, showing block, flaky black spots or macular, and the surface of the plate is generally rough. The reason is the opposite of underpickling.

Gray and black spots produced by under-pickling

Environmental pollution:
          The main pollutants in the production process are the cleaning wastewater produced by the water washing process at all levels, the dust produced by the sandblasting process, the hydrogen chloride acid mist produced by the pickling process, and the waste produced by the pickling, rinsing, phosphating, neutralization and rust prevention processes. Tank liquid, waste residue, waste filter element, raw material empty barrels and packaging waste, etc. The main pollutants are hydrogen chloride, pH, SS, COD, BOD, ammonia nitrogen, petroleum, etc.
          The above is the relevant content introduced by the laser cutting machine manufacturer Ande Laser Intelligent Equipment. If you have any questions in the later stage, you are welcome to consult us. Laser cutting machine manufacturer Ande Laser Intelligent Equipment (Guangdong) Co., Ltd. is a laser equipment manufacturer integrating R&D, production and sales, mainly engaged in laser cutting machines, laser pipe cutting machines, laser welding machines, laser marking machines, etc. series equipment.
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