Preparation Of New Phosphating Solution For Steel And Galvanized Steel

Phosphating technology aims to form a dense phosphate protective film on themetal surface by chemical reactions, was first founded by a British researcher Ross overone hundred years ago. Until now, it has been widely used in the area of automobile,steamship, military project, electrical equipment, machinery. et al. The main function ofphosphating technology includes antirust, wearproof, reducing friction, lubrication,paint on the bottom, and so on，especially for iron corrosion. Phosphating films can becombined with metal surface firmly and have ability of chemical resistance, for example,antioxidation. Furthermore, the pores of film can improve adhesion of coating and candecrease the corrosion current under paint films. It is worth to be mentioned that thefilms is so thin that the size of machinery parts almost cannot be changed. Sophosphating technology can also be used in precision instrument.Our works can be summarized into the following four parts:Firstly, we studied the discipline of formating phosphating films with highanticorrosion. Based on the theory of chemical reaction rate and our practices inphosphating, we summarized the relationship between reaction rate and temperature:Increasing temperature can speed up the phosphating, vice verse. When we want to getthe high corrosion resistance of phosphating film at low temperature and keeping thefree acidity unchanged, the total acidity must be increased. If we want to get thephosphating film with corrosion resistance highly at high temperature, the total aciditymust be reduced, while reducing the total acidity will slow down the phosphating rate,high temperature speed up the phosphating reaction, So if we want to get thephosphating films with highly corrosion resistance under intermediate temperate, totalacidity should be between high temperature and low temperature, and the phosphatingreaction rate caused by total acidity and intermediate temperate will also between hightemperature and low temperature. In one word, phosphating reaction rate must be in acertain value when forming perfect anticorrosion phosphating film, which means thatphosphating rate finally determines the anticorrosion of phosphate films.The aforementioned disciplines have been confirmed by experiments, and also canbe explained by structural chemical theory. When a large amount of separated particlesgathering to aggregate, the gathering speeds are different, and the internal structure ofthe aggregate are different, too. Only at a certain speed, the internal structure of theaggregate could be orderly and perhaps like a crystal structure. When deviated from the proper speed, the internal structure of the aggregate would be less orderly, even gotamorphous structure. The phosphating films formed at the best phosphating reactionspeed have the most minimum porosity, the best compactness, and the highestanticorrosion.Secondly, according to the disciplines mentioned above, comprehensiveexperiments with different material ratio were performed. Several phosphating solutionswere obtained for high, medium and low temperature when phosphating steels weresoaked in solutions. All phosphating films formed by the phosphating solutions haveexcellent properties of anticorrosion and adhesion.Thirdly, we studied the phosphating technology of galvanized steel in automobileenterprises. Because galvanized steel sheet is easier to be phosphated (phosphateprocess can be performed at room temperature), galvanized steel is widely used inautomobile factories at present. Zinc is more easily losing electronic than iron, thus thephosphating rate of zinc layer is more quickly and having higher adhesion than normalsteel. Furthermore, galvanized steel needs not to be washed by acid, so the formed filmshave high corrosion resistance.Fourthly, the phosphating process for automatic assembly line was carried out anda series of phosphating solution for pipeline phosphorization techonology at roomtemperature were developed. In the assembly line, some steel component can besprayed or soaked automatically, and then can be sent directly to the electrophoresistank for electricity paint. So, the phosphating solution has special requirements, forexample, less for corrosion resistance, but more for phosphating rate, adhesion of thephosphating film, no turbidity in the phosphating liquid, and without ash onphosphating film. Finally we synthesized the phosphating solution, with a little toxic,but having good properties.