Analysis And Manufacture Of Hot-dipped Zinc Coatings Used On Ship Hull

Steel (or iron) will be coated with zinc and Zn-Fe alloy when it is put into the zinc liquid melt at about 450 ℃. The coatings separate steel (or iron) from its oxygenic environment, so they can protect the metal effectively. Now thanks to their special strongpoints, the coatings have gotten the widest use as anticorrosive material in industry.The Zn-Fe alloy is formed because Zn reacts to Fe after steel was put into the melted zinc, which make Zn adhere to Fe tightly. The co-existence of zinc and Zn-Fe alloy on the surface of steel enhances largely the thickness and improve greatly the ability of erosion protection. On the other hand, the use of Zn which is one of cheapest metals reduces the cost of production. Moreover, hot-dip method is easy to be realized in assemblely line and the process can be fast fulfilled. All of these give hot-dipped zinc wide- use in the whole world.With the development of industry, more and more requirements for improvements on hot-dipped zinc are brought forward. For example, it has been a hotpoint at present to change the ingredient of hot-dipped zinc for better properties. Some other elements which can react to Fe are put into melted zinc to change the phase of Zn-Fe , further the characteristic of the coatings, thickness, cohesion, appearance, corrosion resistance and so on. In Japanese, Zn-6%Al-3%Mg was researched whose corrosion resistance has as 18 times as that of pure zinc.The research is to obtain the best proportion of four elements with cooperation of Jiangnan shipyard (group) Co.,Ltd. Hard work to improve the corrosion resistance of ship hull has been done, the waste of material will reduce in seawater environment. On the basis of the achievements done by former researcher, three other elements were choosen to be added into the hot-dipped zinc. Al can help to improve the appearance and make it lighter. It also can protect the melted zinc from oxidized. The addition of Sn is to decrease the melting-point and to reduce the cost of production. Mg is regarded widely as effective element to enhance the corrosion resistance.The dissertation includes 4 chapters:Chapter 1: assay of concentration of Al,Mg,Sn. Because the elements react to Fe to form sedimentation, to oxygen to become floating dust, their concentration can not be calculated. It must be known by analysis. So three methods were established in my paper. In the presence of CTMAB, Al can form an colored complex compound with chrome azurol s(CAS), a satisfactory spectrophotometric method for the determination of Al in hot-dipped zinc alloy was established. Similarly Sn(II) can be determinated by spectrophotometric after its mixture with 2,4-dichlorophenyfluorone. And Mg is determinated by atomic absorption spectrometer .These methods have no interference with other coexisting ions. They are easy enough to meet the requirements of industrial analyse.Chapter 2: smelting of medial alloy. In this paper the three elements are not directly added into melted zinc . The medial alloy of Zn-Al, Zn-Sn and Zn-Mg were respectively produced and then mixed with zinc pro rate. In the process of preparation of medial alloy, the appropriate smelting temperature and time should be controlled.Chapter 3: study on the operation condition of galvanizing. The whole process is composed of seven operations. Each step is important. If they are not done appropriately, the final quality of hot-dipped zinc will become poor. Through great deal of experiments the optimum conditions have been affirmed.Chapter 4: effect of the three metals on property of zinc coating. In my test,the first step is to add different content of Al respectively into pure melted zinc. Steel plates were then dipped into these liquid-bath. Under the same conditions, the plates were coated and brought out. The next step is to analyse the quality index of these products, such as corrosion resistance, thickness, cohesion, appearance and so on.. Comparison with each other, the optimum content of Al can be obtained. In the same way, the effect of Mg and Sn were investigated. At last, the...