| The phosphating technology has been widely used in modern iron and steel industries. The existing traditional phosphating technology is becoming more and more mature; however, there are some problems such as large consumption and serious environmental pollution, which have not been solved so far. With the rigid legislations of environmental protection, techniques with a low energy-consumption, little pollution, high efficiency of phosphating technology are required. Therefore, this present research focuses on an electrolytic phosphating process based on the traditional methods. The dissertation mainly investigated the effects of the chemical compositions of phosphating solution and electrolytic phosphating parameters on the morphologies, phase constituents and corrosion resistance of phosphating coating with the aim of optimizing the process for the commercial applications. Furthermore, the optimized phosphating process was applied in the real wire drawing and the real performance of the technology was also evaluated.The research was designed through orthogonal experiment design method to reveal the optimized electrolytic phosphating for the formation of phosphating coating on high carbon steel substrates. That is, the comprehensive performance of phosphating coating can be achieved when total acidity, phosphating time, temperature and electrolytic current of phosphating solution is 110 points,60 seconds,25℃ and 0.4 A, respectively. Based on the results and taking into account most of possible factors under the operational conditions in the study, a new type of electrolytic phosphating method is developed. This method is environmentally friendly and very efficient, especially for high carbon steels via the experimental observations. The constituents of phosphating solution are believed to be optimal when the concentration of phosphoric acid, zinc oxide, calcium nitrite, citric acid, tartaric acid, sodium nitrite, fluorosilicic acid and nickel nitrite in the phosphating solution is 147 g/L,75.5 g/L,320g/L,14 g/L,2 g/L,1 g/L,1 g/L and 2 g/L, respectively. It is also found that the phosphating coating prepared under the optimal condition exhibits moderate thickness, high uniformity and good corrosion resistance properties. Moreover, the micro structure and chemical components of the coating were analyzed with SEM, XRD and SEM techniques. The results showed that the coating is compact and uniform with the main composition of Zn3(PO4)2·4H2O phase.Subsequently, a series of experiments were performed in a factory for pilot production in order to reveal the practical feasibility of the electrolytic phosphating treatment technology. During the whole electrolytic phoaphating process of steel wire, some valuable parameters (i.e., total acid, free acid and acid ratio, etc) were tested and recorded. At the same time, the optimized technology was compared comprehensively with the conventional electrolytic phosphating technology which was currently applied in the factory in view of the consumption of phosphating liquid, energy consumption, energy cost, film appearance and film thickness. The results showed that the optimized electrolytic phosphating method developed in this work has a low solution-consumption even with mechanical descaling pre-treatment. Furthermore, the advantages of the technology also include high efficiency, pickling-free, no need to heat up the phosphating solution, less pollution, less discharges and cost savings. It can be found from the real observations that the coating thickness, the uniformity and corrosion resistance properties all meet the requirements of most current per-treatment processes. Furthermore, there was little iron dissolution and little deposition of ferric phosphate sludge in the bath, which also offered a lot of benefits in terms of energy savings and production costs. Consequently, the developed technique has a potential and promising application in the low-temperature drawing of steel wires and the pre-treatments before painting, etc. |
PDF Full Text Request