Study On Process And Equipment Of Annealing And Pickling For Cold-Rolled Stainless Strip

With the development of our national economy, the demandment of stainless steel from national market has being raised at high speed during the recent years. From the requirement of the quality and cost of the stainless steel product, some product with high quality and other precisional productis still imported from oversea because our national technical drops behind some oversea plants such as, Shin Nippon Seitetsu of Japan,Mittal and Arcelor of Korea,AK of America,Thyssen Krupp Steel of Germany.Up to now, about 10 annealing and pickling lines for cold rolled stainless strip built in the several our national steel plants are imported from oversea. And there are only a little of equipment is manufactured in domestic factories l according to the drawings designed by foreigner. That is say, the ability of designing and manufacturing the whole process line by ourself is very poor.So, it is very important for us to improve the quality of the stainless strip product, low cost, decrease the consumption of energy, strengthen the power of produce stainless steel product, reduce the quantity of import product and meet the increasing demand of national markert through grasping the process technology of annealing and pickling for cold rolled stainless strip, improving the ability of designing and manufacturing the whole annealing and pickling line by ourself and optimizing the equipment.This thesis is based on one annealing and pickling line for cold-rolled stainless strip built in one great national plant. According to analyzing, comparing and studying the process and equipment choosed of the line and other several lines, offer some advantaged condition for designing and manufacturing the whole annealing and pickling line by ourself in the future.Heating the strip in the furnace via great temperature drop in order to reduce the heat time, to decrease the oxid created on the strip face, to unify the heating and the character of the strip and to increase the efficiency of the furnace and low the consumption of energy. In order to make all the heated exhaust gas go back to the pre-heating section to pre-heating the strip and to improve the efficiency of the furnace and reduce the consumption of the energy, each section of the furnace should be connected together to make the heat can used by each other. And in order to low the affect on the character of anti-erod of steel, within the temperature zone between 850~500℃, the austenitic stainless steel should be cooled quickly. According to the relationship between cooling rate and percent of carbon in the steel we can see greater percent of carbon in steel, higer speed of cooling required.The pickling process for austenitic stainless steel is as following:Na2SO4(electroanalysis) pickling→mixed acid(HNO3+HF) mechnical pickling, and the pickling process for ferrite stainless steel is as following:Na2SO4(electroanalysis) pickling→nitric acid (electroanalysis) pickling."V"type tank can make the acid liquid spray onto the above and under faces of the strip along the two sides of the tank and increase the touch- time between acid liquid and strip, reduce the pickling time and consumption of acid liquid, improve the efficiency of pickling.To protect environment, the relative exhaust gas treatment system should be equipped to each pickling tank and ensure all the waste gas exhausted into the circumstance has been controlled within the criterion. To low consumption of energy, rinsining section should apply the overflow and circulation using process to decrease the washing time and reduce the water consumption. Waste acid treatment system using the PYROMARS Process can collect both mixed acid and nitric acid together and treat and regenerat the acid for reusing. Regard to the bad NOx waste gas, the exhaust gas treatment system using the Oxidation-deoxidize process to meet the limits of exhausting before gas exhausted into environment.