Types And Trends Of Environmentally Friendly Metal Surface Pretreatment Technologies

- Jun 10, 2019-

Metal parts have always had high requirements for anti-corrosion. At present, the more common solution is to use a chemical and electrochemical reaction to form a phosphate chemical conversion film in the pre-metal coating process (this process is referred to as phosphating, The formed phosphate conversion film is called a phosphating film), and it protects the metal product together with the subsequent coating to ensure that rust wear does not occur in a period of 10 years or more.


Although the anti-corrosion properties of phosphating are excellent, it also causes many problems, such as high energy consumption, serious pollution, heavy metals, difficult wastewater treatment, and easy slagging in the pipe wall and pipeline. . With the continuous advancement of technology and the continuous improvement of environmental protection requirements, the more environmentally friendly metal surface pretreatment process is developing globally. At present, the research work in this area focuses on the new process of non-toxic environmental phosphating and completely eliminating the phosphorus-containing formula. Two aspects.


Phosphating and environmentally friendly non-toxic process development process


The phosphating process, an early and reliable record, was patented by Charles Ross in the United Kingdom in 1869 and has been in existence for more than a century. The development process of the phosphating process can be divided into the following stages:


Before the Second World War, the basic stage of the phosphating process, this period completed many basic findings, mainly in the UK.


Between the Second World War, a large-scale industrial application phase, when the development center of the phosphating process was transferred from the United Kingdom to the United States. During this period, T.W. Coslet in the United States dissolved zinc, zinc oxide or zinc phosphate in phosphoric acid to form a zinc phosphating solution. This research has greatly promoted the development of the phosphating process. ParcoPower, a Parker anti-rust company, developed a phosphating solution to reduce the phosphating time to 1 hour. In 1929, Bonderizing reduced the phosphating time to 10 minutes. In 1934, the phosphating technology was revolutionized. The development has been the use of a method of spraying a phosphating solution onto a workpiece.


During the Second World War, the new phase of the phosphating process, mainly in Germany.


After the end of World War II, the phosphating process was steadily developed and improved, and the phosphating process rarely made breakthroughs. Important improvements in phosphating treatment technology during this period include: low-temperature phosphating, various methods for controlling the weight of phosphating membranes, and high-speed phosphating of continuous steel strips (processing time is only 5 seconds).


In the 1990s, foreign environmentally friendly pre-treatment processes gradually became a hot topic in the industry. Due to the toxicity in the phosphating treatment process, the pollution is mainly nitrite, heavy metal Ni2+, Cr6+, Mn2+ plasma. Therefore, research in this field is mainly focused on finding alternatives for these substances, mainly divided into nitrite-free phosphating and nickel-free phosphating. This environmentally 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 cannot solve the problem fundamentally. The development direction of the metal surface pretreatment process should not only reduce the toxic and harmful substances, but should fundamentally solve the problem of phosphating pollution.


Development of phosphating alternative technology


Over the past 60 years, zinc and nickel have been the core of phosphating, and increasingly stringent environmental policies and rising prices of nickel and zinc raw materials have been the driving factors in developing suitable alternatives. People first evaluated the monomers and their composites of nanoparticles, zirconium, titanium, polymers and other metal ions, and decided to develop a new conversion film that replaced phosphating. This alternative should be phosphate-free and Other traditional heavy metal ions or metal ions limited by RoHS regulations, each treatment process contains less ion concentration than the current zinc phosphate process, thereby saving energy and water, meeting the performance requirements of today's pre-treatment industry.


Development prospects


As people pay more and more attention to environmental protection, environmental metal surface treatment technology has replaced traditional technology, which has become a trend and development direction, and this development speed is increasing with the maturity of metal surface treatment industry. fast. In the past one or two years, the environmental awareness of the domestic metal surface treatment industry has generally increased, and the acceptance of environmentally friendly pre-treatment processes has been greatly improved. It is expected that in the next 2-3 years, the phosphating alternative treatment process will replace the traditional process by 30%~40%. Share.


In the future, environmentally friendly metal surface pretreatment technology needs to rely on the cooperation of coating chemicals, equipment and three waste treatments, so the cooperation between relevant manufacturers and suppliers will become closer and closer.


The metal industry is constantly evolving, and the quality of the galvanized layer is also constantly improving. The process of better quality galvanized layer and subsequent conversion coating and corrosion-resistant protective coating will be continuously improved. In the future, metal products factories can directly use metal products with good corrosion resistance, and the production process will be more streamlined, more environmentally friendly, and the cost will be lower.