ABSRTACT: for a long time, the metal parts have higher requirements for anticorrosion. At present, the more common solution is that the metal parts have higher requirements for anticorrosion in the pre-treatment process of metal coating, at present, the common solution is to use a chemical and electrochemical reaction to form phosphate chemical conversion film (the process is called phosphating for short, and the phosphate conversion film is called phosphating film) in the pre-treatment process of metal coating, it and after the road coating together to protect metal products, to ensure that 10 years or more time do not rust wear and other problems. Although phosphating has excellent corrosion resistance and other properties, it also causes many problems, such as high energy consumption, serious pollution, containing harmful heavy metals, wastewater treatment is more difficult, easy in the pipe wall and pipe slagging and a series of problems. With the continuous progress of science and technology and the continuous improvement of environmental protection requirements, more environmentally friendly metal surface pretreatment processes are being developed on a global scale, at present, the research work in this area focuses on two aspects: non-toxic Environmental Protection phosphating and completely discarding the new technology of containing phosphorus formula. Development of phosphating and environment-friendly non-toxic process phosphating treatment process, the early reliable record is the United Kingdom Charles Ross in 1869 patents, has been more than a century. The development of the phosphating process can be divided into the following stages: before the Second World War, the basic stage of the phosphating process, during which many basic discoveries were made, mainly in the United Kingdom. World War II, a large-scale industrial application phase, at this time the development of phosphating process center from the United Kingdom to the United States. In the meantime, America’s T. W. Coslet dissolved zinc, zinc oxide or zinc phosphate in phosphoric acid to make zinc series phosphating solution. This research achievement has greatly promoted the development of phosphating technology. Parker anti-rust Research and development of PARCOPOWER (Parker powder) preparation of phosphating solution, the phosphating treatment time was shortened to 1 hour, in 1929 bondering will be shortened to 10 minutes, in 1934 phosphating treatment technology made a revolutionary development, that is, the phosphating solution is sprayed on the workpiece. During World War II, the new use of phosphating process stage, mainly in Germany. Since the end of World War II, the phosphating process has been steadily developed and perfected, and few breakthroughs have been made in phosphating. During this period, the important improvement of phosphating technology are: low temperature phosphating, various methods to control the weight of phosphating film, Continuous high-speed phosphating (the treatment time is only 5 seconds) . In the 1990s, the environmental-friendly coating pretreatment process abroad has gradually become a hot spot in the industry. Nitrite, heavy metals such as NI 2 + , CR 6 + , MN 2 + are the most toxic and polluted materials in phosphating process. Therefore, the field of research is also focused on the search for alternatives for these substances, mainly divided into non-nitrite phosphating and nickel-free phosphating. This environment-friendly non-toxic phosphating process is only a “Circle”in the original phosphating system. Although it reduces the toxic and harmful substances in the phosphating process, it can not solve the problem fundamentally. The Development Direction of metal surface pretreatment process should not only reduce toxic and harmful substances, but also solve the pollution problem of phosphating fundamentally. The development of alternative technologies for phosphatization over the past 60 years, two metal ions, zinc and nickel, have been at the heart of phosphatization, and increasingly stringent environmental policies and rising nickel and zinc raw material prices have been driving factors in the development of suitable alternatives. After the evaluation of Nanoparticles, zirconium, titanium, monomers of polymers and other metal ions, and their mutual compounds, it was decided to develop a new conversion membrane to replace phosphating, such alternatives should be free of phosphates and other traditional heavy metal ions or metal ions restricted by RoHS regulations, and each treatment process should contain less ion concentration than the current zinc phosphate process, thus saving energy and water, meet the performance requirements of today’s processing industry. Development Prospect with people paying more and more attention to environmental protection, it has become a trend and development direction that environmental metal surface pretreatment technology replaces traditional technology, and this development speed is along with the metal surface treatment industry mature day by day but more and more quickly. In the past two years, the environmental consciousness of the metal surface treatment industry has been strengthened, and the acceptance of the pretreatment process for the environmental protection coating has been greatly improved. The future environmental protection metal surface pretreatment technology needs to rely on coating chemicals, equipment and waste treatment of co-operation, so the relevant manufacturers, suppliers will be increasingly close cooperation. With the development of metal industry, the quality of zinc coating is also improving. The technology of better quality zinc coating and subsequent conversion coating and corrosion protection coating will also be improved correspondingly. In the future, the metal products factory can directly use the metal products with good corrosion resistance, the production process will be more streamlined, more environmentally friendly, and the cost will be lower. 

Source: The web

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