Commonly used surface rust removal treatment technology

       1. Chemical rust removal



    Chemical rust removal is to use the acid (or alkaline) solution to chemically react with the rust layer on the metal surface to dissolve and peel off the surface rust layer, and then remove the surface rust. Chemical rust removal, also known as "etching" and "pickling", is often used for rust removal of small or complex-shaped workpieces.

    2. Electrochemical rust removal

    Electrochemical rust removal is divided into anode rust removal and cathode rust removal according to the polarity of the workpiece. In addition, there is also alternating current rust removal.

    Anode rust removal is to use the electrochemical dissolution, chemical dissolution and oxygen bubble precipitation of the anode to remove the rust by mechanical peeling of the oxide scale. Due to the large and scarce oxygen bubbles, the mechanical peeling effect is not strong. When removing rust from the anode, it should be noted that when the treatment time is too long, it is prone to over-corrosion. Anodic descaling is suitable for metal workpieces with high strength and good elasticity.

    Cathode rust removal is carried out by using the mechanical peeling effect of hydrogen gas bubble precipitation. Because the hydrogen bubbles are dense and small, the mechanical peeling effect on the oxide scale is strong, and the cathode rust removal hardly corrodes the substrate, which can ensure the geometric accuracy of the workpiece. The disadvantage of cathode rust removal is that the precipitation of hydrogen can easily cause metal hydrogen embrittlement, and other metal ions in the electrolyte will be reduced to form impurities on the surface of the cathode workpiece. Cathodic descaling is suitable for workpieces with dense oxide layers and high dimensional accuracy requirements.

    AC descaling has the characteristics of both anode descaling and cathode descaling. In actual production, alternating cathode and anode rust removal can not only shorten the etching time, but also ensure dimensional accuracy and reduce hydrogen embrittlement.

    3. Flame rust removal

    The workpiece is heated with an oxygen-acetylene flame, and the oxide skin is peeled off by using the different thermal expansion coefficients of steel and oxide skin. Mainly suitable for thick steel components and large castings, not suitable for thin-walled parts and small castings, because the quality of the workpiece will be affected by thermal deformation.

    4. Derusting by hand and power tools

    The rust layer is removed by mechanically cutting the surface of the workpiece with hand-held tools (shovel, emery cloth, steel brush, etc.) or motorized hand-held tools (electric or pneumatic grinding wheel, rust remover, etc.). This method has low production efficiency and high labor intensity, but is currently more commonly used due to its simple tools and convenient operation.

    5. Sandblasting (pellet) rust removal

    Sand blasting (pellet) derusting is the most commonly used derusting method at present. Sand blasting (pellet) derusting can also achieve the purpose of surface roughening and surface activation, and has the characteristics of one method and multiple purposes; In spraying application, rust removal sand and roughening sandblasting must be separated to avoid contamination of the coarsening sand. The process of sandblasting and rust removal cannot be used to replace the roughening treatment of the workpiece before spraying, which will affect the quality of the sprayed layer. For specific technical details of sandblasting (pellet) descaling, see the next section (Surface Roughening)

    6. Rust remover

    There are many kinds of rust removers currently on the market, as listed in Table 2-3. Generally, they are mainly based on special inorganic substances, supplemented by a variety of chemical corrosion inhibitors. It has the advantages of fast rust removal, obvious rust removal effect, convenient operation and use, and reduced emission pollution, but the cost is high.